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NAME

       erlang - The Erlang BIFs.

DESCRIPTION

       By  convention,  most  Built-In  Functions (BIFs) are included in this module. Some of the
       BIFs are viewed more or less as part of the Erlang  programming  language  and  are  auto-
       imported.  Thus,  it  is  not necessary to specify the module name. For example, the calls
       atom_to_list(erlang) and erlang:atom_to_list(erlang) are identical.

       Auto-imported BIFs are listed without module prefix. BIFs listed with  module  prefix  are
       not auto-imported.

       BIFs  can  fail  for  various reasons. All BIFs fail with reason badarg if they are called
       with arguments of an incorrect type. The other reasons are described in the description of
       each individual BIF.

       Some BIFs can be used in guard tests and are marked with "Allowed in guard tests".

DATA TYPES

       ext_binary() = binary()

              A binary data object, structured according to the Erlang external term format.

       iovec() = [binary()]

              A   list   of   binaries.   This   datatype   is   useful   to  use  together  with
              enif_inspect_iovec.

       message_queue_data() = off_heap | on_heap

              See process_flag(message_queue_data, MQD).

       timestamp() =
           {MegaSecs :: integer() >= 0,
            Secs :: integer() >= 0,
            MicroSecs :: integer() >= 0}

              See erlang:timestamp/0.

       time_unit() =
           integer() >= 1 |
           second | millisecond | microsecond | nanosecond | native |
           perf_counter |
           deprecated_time_unit()

              Supported time unit representations:

                PartsPerSecond :: integer() >= 1:
                  Time unit expressed in  parts  per  second.  That  is,  the  time  unit  equals
                  1/PartsPerSecond second.

                second:
                  Symbolic representation of the time unit represented by the integer 1.

                millisecond:
                  Symbolic representation of the time unit represented by the integer 1000.

                microsecond:
                  Symbolic representation of the time unit represented by the integer 1000000.

                nanosecond:
                  Symbolic representation of the time unit represented by the integer 1000000000.

                native:
                  Symbolic  representation  of  the  native  time unit used by the Erlang runtime
                  system.

                  The native time unit is determined at runtime system  start,  and  remains  the
                  same  until  the  runtime system terminates. If a runtime system is stopped and
                  then started again (even on the same machine), the native time unit of the  new
                  runtime system instance can differ from the native time unit of the old runtime
                  system instance.

                  One  can  get  an  approximation  of  the   native   time   unit   by   calling
                  erlang:convert_time_unit(1,  second,  native).  The result equals the number of
                  whole native time units per second. If the number  of  native  time  units  per
                  second does not add up to a whole number, the result is rounded downwards.

            Note:
                The value of the native time unit gives you more or less no information about the
                quality of time values.  It  sets  a  limit  for  the   resolution  and  for  the
                precision of time values, but it gives no information about the  accuracy of time
                values. The resolution of the native time unit and the resolution of time  values
                can differ significantly.

                perf_counter:
                  Symbolic representation of the performance counter time unit used by the Erlang
                  runtime system.

                  The perf_counter time unit behaves much in the same  way  as  the  native  time
                  unit.  That  is,  it can differ between runtime restarts. To get values of this
                  type, call os:perf_counter/0.

                deprecated_time_unit():
                  Deprecated symbolic representations kept for backwards-compatibility.

              The time_unit/0 type can be extended. To convert time values  between  time  units,
              use erlang:convert_time_unit/3.

       deprecated_time_unit() =
           seconds | milli_seconds | micro_seconds | nano_seconds

              The time_unit() type also consist of the following deprecated symbolic time units:

                seconds:
                  Same as second.

                milli_seconds:
                  Same as millisecond.

                micro_seconds:
                  Same as microsecond.

                nano_seconds:
                  Same as nanosecond.

       dist_handle()

              An opaque handle identifing a distribution channel.

       nif_resource()

              An opaque handle identifing a NIF resource object .

EXPORTS

       abs(Float) -> float()

       abs(Int) -> integer() >= 0

              Types:

                 Int = integer()

              Returns  an  integer  or  float that is the arithmetical absolute value of Float or
              Int, for example:

              > abs(-3.33).
              3.33
              > abs(-3).
              3

              Allowed in guard tests.

       erlang:adler32(Data) -> integer() >= 0

              Types:

                 Data = iodata()

              Computes and returns the adler32 checksum for Data.

       erlang:adler32(OldAdler, Data) -> integer() >= 0

              Types:

                 OldAdler = integer() >= 0
                 Data = iodata()

              Continues computing the  adler32  checksum  by  combining  the  previous  checksum,
              OldAdler, with the checksum of Data.

              The following code:

              X = erlang:adler32(Data1),
              Y = erlang:adler32(X,Data2).

              assigns the same value to Y as this:

              Y = erlang:adler32([Data1,Data2]).

       erlang:adler32_combine(FirstAdler, SecondAdler, SecondSize) ->
                                 integer() >= 0

              Types:

                 FirstAdler = SecondAdler = SecondSize = integer() >= 0

              Combines  two  previously computed adler32 checksums. This computation requires the
              size of the data object for the second checksum to be known.

              The following code:

              Y = erlang:adler32(Data1),
              Z = erlang:adler32(Y,Data2).

              assigns the same value to Z as this:

              X = erlang:adler32(Data1),
              Y = erlang:adler32(Data2),
              Z = erlang:adler32_combine(X,Y,iolist_size(Data2)).

       erlang:append_element(Tuple1, Term) -> Tuple2

              Types:

                 Tuple1 = Tuple2 = tuple()
                 Term = term()

              Returns a new tuple that has  one  element  more  than  Tuple1,  and  contains  the
              elements in Tuple1 followed by Term as the last element. Semantically equivalent to
              list_to_tuple(tuple_to_list(Tuple1) ++ [Term]), but much faster. Example:

              > erlang:append_element({one, two}, three).
              {one,two,three}

       apply(Fun, Args) -> term()

              Types:

                 Fun = function()
                 Args = [term()]

              Calls a fun, passing the elements in Args as arguments.

              If the number of elements in the arguments are known at compile time, the  call  is
              better written as Fun(Arg1, Arg2, ... ArgN).

          Warning:
              Earlier,  Fun  could  also  be  specified  as  {Module,  Function},  equivalent  to
              apply(Module, Function, Args). This use is deprecated and will stop  working  in  a
              future release.

       apply(Module, Function, Args) -> term()

              Types:

                 Module = module()
                 Function = atom()
                 Args = [term()]

              Returns  the  result  of  applying Function in Module to Args. The applied function
              must be exported from Module. The arity of the function  is  the  length  of  Args.
              Example:

              > apply(lists, reverse, [[a, b, c]]).
              [c,b,a]
              > apply(erlang, atom_to_list, ['Erlang']).
              "Erlang"

              If the number of arguments are known at compile time, the call is better written as
              Module:Function(Arg1, Arg2, ..., ArgN).

              Failure: error_handler:undefined_function/3 is called if the  applied  function  is
              not  exported.  The  error  handler  can  be  redefined  (see  process_flag/2).  If
              error_handler is undefined, or if the user has redefined the default  error_handler
              so the replacement module is undefined, an error with reason undef is generated.

       atom_to_binary(Atom, Encoding) -> binary()

              Types:

                 Atom = atom()
                 Encoding = latin1 | unicode | utf8

              Returns  a  binary corresponding to the text representation of Atom. If Encoding is
              latin1, one byte exists for each character in the text representation. If  Encoding
              is  utf8  or  unicode,  the characters are encoded using UTF-8 where characters may
              require multiple bytes.

          Note:
              As  from  Erlang/OTP  20,   atoms   can   contain   any   Unicode   character   and
              atom_to_binary(Atom,  latin1) may fail if the text representation for Atom contains
              a Unicode character > 255.

              Example:

              > atom_to_binary('Erlang', latin1).
              <<"Erlang">>

       atom_to_list(Atom) -> string()

              Types:

                 Atom = atom()

              Returns a string corresponding to the text representation of Atom, for example:

              > atom_to_list('Erlang').
              "Erlang"

       binary_part(Subject, PosLen) -> binary()

              Types:

                 Subject = binary()
                 PosLen = {Start :: integer() >= 0, Length :: integer()}

              Extracts the part of the binary described by PosLen.

              Negative length can be used to extract bytes at the end of a binary, for example:

              1> Bin = <<1,2,3,4,5,6,7,8,9,10>>.
              2> binary_part(Bin,{byte_size(Bin), -5}).
              <<6,7,8,9,10>>

              Failure: badarg if PosLen in any way references outside the binary.

              Start is zero-based, that is:

              1> Bin = <<1,2,3>>
              2> binary_part(Bin,{0,2}).
              <<1,2>>

              For details about the PosLen semantics, see binary(3erl).

              Allowed in guard tests.

       binary_part(Subject, Start, Length) -> binary()

              Types:

                 Subject = binary()
                 Start = integer() >= 0
                 Length = integer()

              The same as binary_part(Subject, {Start, Length}).

              Allowed in guard tests.

       binary_to_atom(Binary, Encoding) -> atom()

              Types:

                 Binary = binary()
                 Encoding = latin1 | unicode | utf8

              Returns the atom whose text representation is Binary. If  Encoding  is  latin1,  no
              translation  of  bytes  in  the binary is done. If Encoding is utf8 or unicode, the
              binary must contain valid UTF-8 sequences.

          Note:
              As from Erlang/OTP 20, binary_to_atom(Binary, utf8)  is  capable  of  encoding  any
              Unicode  character.  Earlier  versions  would  fail if the binary contained Unicode
              characters > 255. For more information about Unicode support in atoms, see the note
              on UTF-8 encoded atoms in section "External Term Format" in the User's Guide.

              Examples:

              > binary_to_atom(<<"Erlang">>, latin1).
              'Erlang'
              > binary_to_atom(<<1024/utf8>>, utf8).

       binary_to_existing_atom(Binary, Encoding) -> atom()

              Types:

                 Binary = binary()
                 Encoding = latin1 | unicode | utf8

              As binary_to_atom/2, but the atom must exist.

              Failure: badarg if the atom does not exist.

          Note:
              Note  that  the  compiler  may  optimize away atoms. For example, the compiler will
              rewrite atom_to_list(some_atom) to "some_atom". If  that  expression  is  the  only
              mention  of  the  atom  some_atom  in  the  containing module, the atom will not be
              created   when   the   module   is   loaded,   and    a    subsequent    call    to
              binary_to_existing_atom(<<"some_atom">>, utf8) will fail.

       binary_to_float(Binary) -> float()

              Types:

                 Binary = binary()

              Returns the float whose text representation is Binary, for example:

              > binary_to_float(<<"2.2017764e+0">>).
              2.2017764

              Failure: badarg if Binary contains a bad representation of a float.

       binary_to_integer(Binary) -> integer()

              Types:

                 Binary = binary()

              Returns an integer whose text representation is Binary, for example:

              > binary_to_integer(<<"123">>).
              123

              Failure: badarg if Binary contains a bad representation of an integer.

       binary_to_integer(Binary, Base) -> integer()

              Types:

                 Binary = binary()
                 Base = 2..36

              Returns an integer whose text representation in base Base is Binary, for example:

              > binary_to_integer(<<"3FF">>, 16).
              1023

              Failure: badarg if Binary contains a bad representation of an integer.

       binary_to_list(Binary) -> [byte()]

              Types:

                 Binary = binary()

              Returns a list of integers corresponding to the bytes of Binary.

       binary_to_list(Binary, Start, Stop) -> [byte()]

              Types:

                 Binary = binary()
                 Start = Stop = integer() >= 1
                   1..byte_size(Binary)

              As binary_to_list/1, but returns a list of integers corresponding to the bytes from
              position Start to position Stop in Binary. The positions in the binary are numbered
              starting from 1.

          Note:
              The  one-based  indexing for binaries used by this function is deprecated. New code
              is to use binary:bin_to_list/3 in STDLIB instead. All functions  in  module  binary
              consistently use zero-based indexing.

       binary_to_term(Binary) -> term()

              Types:

                 Binary = ext_binary()

              Returns  an  Erlang term that is the result of decoding binary object Binary, which
              must be encoded according to the  Erlang external term format.

              > Bin = term_to_binary(hello).
              <<131,100,0,5,104,101,108,108,111>>
              > hello = binary_to_term(Bin).
              hello

          Warning:
              When decoding binaries from untrusted sources, consider using  binary_to_term/2  to
              prevent Denial of Service attacks.

              See also term_to_binary/1 and binary_to_term/2.

       binary_to_term(Binary, Opts) -> term() | {term(), Used}

              Types:

                 Binary = ext_binary()
                 Opt = safe | used
                 Opts = [Opt]
                 Used = integer() >= 1

              As binary_to_term/1, but takes these options:

                safe:
                  Use this option when receiving binaries from an untrusted source.

                  When  enabled,  it prevents decoding data that can be used to attack the Erlang
                  system. In the event of receiving unsafe data, decoding  fails  with  a  badarg
                  error.

                  This  prevents creation of new atoms directly, creation of new atoms indirectly
                  (as they are embedded in certain structures, such as process identifiers, refs,
                  and  funs),  and  creation  of  new external function references. None of those
                  resources are garbage collected, so unchecked  creation  of  them  can  exhaust
                  available memory.

                > binary_to_term(<<131,100,0,5,"hello">>, [safe]).
                ** exception error: bad argument
                > hello.
                hello
                > binary_to_term(<<131,100,0,5,"hello">>, [safe]).
                hello

                used:
                  Changes  the  return  value  to  {Term, Used} where Used is the number of bytes
                  actually read from Binary.

                > Input = <<131,100,0,5,"hello","world">>.
                <<131,100,0,5,104,101,108,108,111,119,111,114,108,100>>
                > {Term, Used} = binary_to_term(Input, [used]).
                {hello, 9}
                > split_binary(Input, Used).
                {<<131,100,0,5,104,101,108,108,111>>, <<"world">>}

              Failure: badarg if safe is specified and unsafe data is decoded.

              See also term_to_binary/1, binary_to_term/1, and list_to_existing_atom/1.

       bit_size(Bitstring) -> integer() >= 0

              Types:

                 Bitstring = bitstring()

              Returns an integer that is the size in bits of Bitstring, for example:

              > bit_size(<<433:16,3:3>>).
              19
              > bit_size(<<1,2,3>>).
              24

              Allowed in guard tests.

       bitstring_to_list(Bitstring) -> [byte() | bitstring()]

              Types:

                 Bitstring = bitstring()

              Returns a list of integers corresponding to the bytes of Bitstring. If  the  number
              of  bits  in  the  binary  is not divisible by 8, the last element of the list is a
              bitstring containing the remaining 1-7 bits.

       erlang:bump_reductions(Reductions) -> true

              Types:

                 Reductions = integer() >= 1

              This implementation-dependent function increments the  reduction  counter  for  the
              calling   process.  In  the  Beam  emulator,  the  reduction  counter  is  normally
              incremented by one for each function and BIF call. A context switch is forced  when
              the counter reaches the maximum number of reductions for a process (2000 reductions
              in Erlang/OTP R12B).

          Warning:
              This BIF can be removed in a future version  of  the  Beam  machine  without  prior
              warning. It is unlikely to be implemented in other Erlang implementations.

       byte_size(Bitstring) -> integer() >= 0

              Types:

                 Bitstring = bitstring()

              Returns  an  integer  that is the number of bytes needed to contain Bitstring. That
              is, if the number of bits in Bitstring is not divisible by 8, the resulting  number
              of bytes is rounded up. Examples:

              > byte_size(<<433:16,3:3>>).
              3
              > byte_size(<<1,2,3>>).
              3

              Allowed in guard tests.

       erlang:cancel_timer(TimerRef) -> Result

              Types:

                 TimerRef = reference()
                 Time = integer() >= 0
                 Result = Time | false

              Cancels a timer. The same as calling erlang:cancel_timer(TimerRef, []).

       erlang:cancel_timer(TimerRef, Options) -> Result | ok

              Types:

                 TimerRef = reference()
                 Async = Info = boolean()
                 Option = {async, Async} | {info, Info}
                 Options = [Option]
                 Time = integer() >= 0
                 Result = Time | false

              Cancels  a  timer that has been created by erlang:start_timer or erlang:send_after.
              TimerRef identifies the timer, and was returned by the BIF that created the timer.

              Options:

                {async, Async}:
                  Asynchronous request for cancellation. Async defaults to  false,  which  causes
                  the  cancellation to be performed synchronously. When Async is set to true, the
                  cancel operation is performed asynchronously. That is, cancel_timer() sends  an
                  asynchronous  request  for  cancellation  to the timer service that manages the
                  timer, and then returns ok.

                {info, Info}:
                  Requests information about the Result of the  cancellation.  Info  defaults  to
                  true,  which  means  the  Result  is  given.  When  Info  is  set  to false, no
                  information about the result of the cancellation is given.

                  * When  Async  is  false:  if  Info  is  true,  the  Result  is   returned   by
                    erlang:cancel_timer(). otherwise ok is returned.

                  * When  Async  is  true:  if Info is true, a message on the form {cancel_timer,
                    TimerRef, Result} is sent to the caller  of  erlang:cancel_timer()  when  the
                    cancellation operation has been performed, otherwise no message is sent.

              More Options may be added in the future.

              If  Result  is  an  integer,  it represents the time in milliseconds left until the
              canceled timer would have expired.

              If Result is false, a timer corresponding to TimerRef could not be found. This  can
              be  either  because  the  timer  had expired, already had been canceled, or because
              TimerRef never corresponded to a timer. Even if the timer had expired, it does  not
              tell you if the time-out message has arrived at its destination yet.

          Note:
              The  timer  service that manages the timer can be co-located with another scheduler
              than the scheduler that the calling process is executing on. If  so,  communication
              with the timer service takes much longer time than if it is located locally. If the
              calling process is in critical path, and can do other things while waiting for  the
              result  of this operation, or is not interested in the result of the operation, you
              want to use option {async, true}. If  using  option  {async,  false},  the  calling
              process blocks until the operation has been performed.

              See also erlang:send_after/4, erlang:start_timer/4, and erlang:read_timer/2.

       ceil(Number) -> integer()

              Types:

                 Number = number()

              Returns the smallest integer not less than Number. For example:

              > ceil(5.5).
              6

              Allowed in guard tests.

       check_old_code(Module) -> boolean()

              Types:

                 Module = module()

              Returns true if Module has old code, otherwise false.

              See also code(3erl).

       check_process_code(Pid, Module) -> CheckResult

              Types:

                 Pid = pid()
                 Module = module()
                 CheckResult = boolean()

              The same as check_process_code(Pid, Module, []).

       check_process_code(Pid, Module, OptionList) -> CheckResult | async

              Types:

                 Pid = pid()
                 Module = module()
                 RequestId = term()
                 Option = {async, RequestId} | {allow_gc, boolean()}
                 OptionList = [Option]
                 CheckResult = boolean() | aborted

              Checks if the node local process identified by Pid executes old code for Module.

              Options:

                {allow_gc, boolean()}:
                  Determines  if  garbage collection is allowed when performing the operation. If
                  {allow_gc, false} is passed, and a garbage collection is  needed  to  determine
                  the  result  of  the  operation,  the  operation is aborted (see information on
                  CheckResult below). The default  is  to  allow  garbage  collection,  that  is,
                  {allow_gc, true}.

                {async, RequestId}:
                  The function check_process_code/3 returns the value async immediately after the
                  request has been sent. When the request has been processed,  the  process  that
                  called  this  function  is  passed  a  message on the form {check_process_code,
                  RequestId, CheckResult}.

              If Pid equals self(), and no  async  option  has  been  passed,  the  operation  is
              performed  at  once.  Otherwise  a request for the operation is sent to the process
              identified by Pid, and is handled when appropriate. If no  async  option  has  been
              passed, the caller blocks until CheckResult is available and can be returned.

              CheckResult informs about the result of the request as follows:

                true:
                  The  process  identified  by  Pid  executes  old  code for Module. That is, the
                  current call of the process executes old code for this module, or  the  process
                  has  references  to old code for this module, or the process contains funs that
                  references old code for this module.

                false:
                  The process identified by Pid does not execute old code for Module.

                aborted:
                  The operation was aborted, as the process needed to  be  garbage  collected  to
                  determine  the  operation  result,  and  the operation was requested by passing
                  option {allow_gc, false}.

          Note:
              Up until ERTS version 8.*, the check process code operation checks for all types of
              references  to  the  old code. That is, direct references (e.g. return addresses on
              the process stack), indirect references (funs in process context),  and  references
              to literals in the code.

              As  of  ERTS  version  9.0, the check process code operation only checks for direct
              references to the code. Indirect references via funs will be ignored. If such  funs
              exist  and are used after a purge of the old code, an exception will be raised upon
              usage (same as the case when the fun is received by the process after  the  purge).
              Literals  will  be taken care of (copied) at a later stage. This behavior can as of
              ERTS version 8.1 be enabled when building OTP, and will automatically be enabled if
              dirty scheduler support is enabled.

              See also code(3erl).

              Failures:

                badarg:
                  If Pid is not a node local process identifier.

                badarg:
                  If Module is not an atom.

                badarg:
                  If OptionList is an invalid list of options.

       erlang:convert_time_unit(Time, FromUnit, ToUnit) -> ConvertedTime

              Types:

                 Time = ConvertedTime = integer()
                 FromUnit = ToUnit = time_unit()

              Converts  the  Time  value of time unit FromUnit to the corresponding ConvertedTime
              value of time unit ToUnit. The result is rounded using the floor function.

          Warning:
              You can lose accuracy and precision when converting between time units. To minimize
              such  loss,  collect  all data at native time unit and do the conversion on the end
              result.

       erlang:crc32(Data) -> integer() >= 0

              Types:

                 Data = iodata()

              Computes and returns the crc32 (IEEE 802.3 style) checksum for Data.

       erlang:crc32(OldCrc, Data) -> integer() >= 0

              Types:

                 OldCrc = integer() >= 0
                 Data = iodata()

              Continues computing the crc32 checksum by combining the previous checksum,  OldCrc,
              with the checksum of Data.

              The following code:

              X = erlang:crc32(Data1),
              Y = erlang:crc32(X,Data2).

              assigns the same value to Y as this:

              Y = erlang:crc32([Data1,Data2]).

       erlang:crc32_combine(FirstCrc, SecondCrc, SecondSize) ->
                               integer() >= 0

              Types:

                 FirstCrc = SecondCrc = SecondSize = integer() >= 0

              Combines  two  previously  computed  crc32 checksums. This computation requires the
              size of the data object for the second checksum to be known.

              The following code:

              Y = erlang:crc32(Data1),
              Z = erlang:crc32(Y,Data2).

              assigns the same value to Z as this:

              X = erlang:crc32(Data1),
              Y = erlang:crc32(Data2),
              Z = erlang:crc32_combine(X,Y,iolist_size(Data2)).

       date() -> Date

              Types:

                 Date = calendar:date()

              Returns the current date as {Year, Month, Day}.

              The time zone and Daylight Saving Time correction  depend  on  the  underlying  OS.
              Example:

              > date().
              {1995,2,19}

       erlang:decode_packet(Type, Bin, Options) ->
                               {ok, Packet, Rest} |
                               {more, Length} |
                               {error, Reason}

              Types:

                 Type =
                     raw | 0 | 1 | 2 | 4 | asn1 | cdr | sunrm | fcgi | tpkt |
                     line | http | http_bin | httph | httph_bin
                 Bin = binary()
                 Options = [Opt]
                 Opt =
                     {packet_size, integer() >= 0} |
                     {line_length, integer() >= 0}
                 Packet = binary() | HttpPacket
                 Rest = binary()
                 Length = integer() >= 0 | undefined
                 Reason = term()
                 HttpPacket =
                     HttpRequest | HttpResponse | HttpHeader | http_eoh | HttpError
                 HttpRequest = {http_request, HttpMethod, HttpUri, HttpVersion}
                 HttpResponse =
                     {http_response, HttpVersion, integer(), HttpString}
                 HttpHeader =
                     {http_header,
                      integer(),
                      HttpField,
                      Reserved :: term(),
                      Value :: HttpString}
                 HttpError = {http_error, HttpString}
                 HttpMethod =
                     'OPTIONS' | 'GET' | 'HEAD' | 'POST' | 'PUT' | 'DELETE' |
                     'TRACE' | HttpString
                 HttpUri =
                     '*' |
                     {absoluteURI,
                      http | https,
                      Host :: HttpString,
                      Port :: inet:port_number() | undefined,
                      Path :: HttpString} |
                     {scheme, Scheme :: HttpString, HttpString} |
                     {abs_path, HttpString} |
                     HttpString
                 HttpVersion =
                     {Major :: integer() >= 0, Minor :: integer() >= 0}
                 HttpField =
                     'Cache-Control' | 'Connection' | 'Date' | 'Pragma' |
                     'Transfer-Encoding' | 'Upgrade' | 'Via' | 'Accept' |
                     'Accept-Charset' | 'Accept-Encoding' | 'Accept-Language' |
                     'Authorization' | 'From' | 'Host' | 'If-Modified-Since' |
                     'If-Match' | 'If-None-Match' | 'If-Range' |
                     'If-Unmodified-Since' | 'Max-Forwards' |
                     'Proxy-Authorization' | 'Range' | 'Referer' | 'User-Agent' |
                     'Age' | 'Location' | 'Proxy-Authenticate' | 'Public' |
                     'Retry-After' | 'Server' | 'Vary' | 'Warning' |
                     'Www-Authenticate' | 'Allow' | 'Content-Base' |
                     'Content-Encoding' | 'Content-Language' | 'Content-Length' |
                     'Content-Location' | 'Content-Md5' | 'Content-Range' |
                     'Content-Type' | 'Etag' | 'Expires' | 'Last-Modified' |
                     'Accept-Ranges' | 'Set-Cookie' | 'Set-Cookie2' |
                     'X-Forwarded-For' | 'Cookie' | 'Keep-Alive' |
                     'Proxy-Connection' | HttpString
                 HttpString = string() | binary()

              Decodes  the binary Bin according to the packet protocol specified by Type. Similar
              to the packet handling done by sockets with option {packet,Type}.

              If an entire packet is contained in Bin, it is returned together with the remainder
              of the binary as {ok,Packet,Rest}.

              If  Bin  does  not  contain the entire packet, {more,Length} is returned. Length is
              either the expected total size of the packet, or undefined if the  expected  packet
              size is unknown. decode_packet can then be called again with more data added.

              If the packet does not conform to the protocol format, {error,Reason} is returned.

              Types:

                raw | 0:
                  No packet handling is done. The entire binary is returned unless it is empty.

                1 | 2 | 4:
                  Packets  consist  of  a  header  specifying  the number of bytes in the packet,
                  followed by that number of bytes. The length of the header can be one, two,  or
                  four  bytes;  the  order of the bytes is big-endian. The header is stripped off
                  when the packet is returned.

                line:
                  A packet is a line-terminated by a  delimiter  byte,  default  is  the  latin-1
                  newline character. The delimiter byte is included in the returned packet unless
                  the line was truncated according to option line_length.

                asn1 | cdr | sunrm | fcgi | tpkt:
                  The header is not stripped off.

                  The meanings of the packet types are as follows:

                  asn1 - ASN.1 BER:

                  sunrm - Sun's RPC encoding:

                  cdr - CORBA (GIOP 1.1):

                  fcgi - Fast CGI:

                  tpkt - TPKT format [RFC1006]:

                http | httph | http_bin | httph_bin:
                  The Hypertext Transfer Protocol. The  packets  are  returned  with  the  format
                  according  to  HttpPacket  described  earlier.  A packet is either a request, a
                  response, a header, or an end of header mark. Invalid  lines  are  returned  as
                  HttpError.

                  Recognized  request methods and header fields are returned as atoms. Others are
                  returned as strings. Strings of unrecognized header fields are  formatted  with
                  only  capital  letters  first  and  after hyphen characters, for example, "Sec-
                  Websocket-Key".

                  The protocol type http  is  only  to  be  used  for  the  first  line  when  an
                  HttpRequest  or  an  HttpResponse  is  expected. The following calls are to use
                  httph to get HttpHeaders until http_eoh is returned, which marks the end of the
                  headers and the beginning of any following message body.

                  The  variants  http_bin  and  httph_bin return strings (HttpString) as binaries
                  instead of lists.

              Options:

                {packet_size, integer() >= 0}:
                  Sets the maximum allowed  size  of  the  packet  body.  If  the  packet  header
                  indicates  that  the  length  of  the packet is longer than the maximum allowed
                  length, the packet is considered invalid. Defaults to 0, which  means  no  size
                  limit.

                {line_length, integer() >= 0}:
                  For packet type line, lines longer than the indicated length are truncated.

                  Option  line_length  also  applies to http* packet types as an alias for option
                  packet_size if packet_size itself is not set. This use  is  only  intended  for
                  backward compatibility.

                {line_delimiter, 0 =< byte() =< 255}:
                  For  packet  type  line,  sets  the  delimiting  byte.  Default  is the latin-1
                  character $\n.

              Examples:

              > erlang:decode_packet(1,<<3,"abcd">>,[]).
              {ok,<<"abc">>,<<"d">>}
              > erlang:decode_packet(1,<<5,"abcd">>,[]).
              {more,6}

       erlang:delete_element(Index, Tuple1) -> Tuple2

              Types:

                 Index = integer() >= 1
                   1..tuple_size(Tuple1)
                 Tuple1 = Tuple2 = tuple()

              Returns a new tuple with element at Index removed from tuple Tuple1, for example:

              > erlang:delete_element(2, {one, two, three}).
              {one,three}

       delete_module(Module) -> true | undefined

              Types:

                 Module = module()

              Makes the current code for Module become old code and deletes  all  references  for
              this  module from the export table. Returns undefined if the module does not exist,
              otherwise true.

          Warning:
              This BIF is intended for the code server (see code(3erl)) and is  not  to  be  used
              elsewhere.

              Failure: badarg if there already is an old version of Module.

       demonitor(MonitorRef) -> true

              Types:

                 MonitorRef = reference()

              If  MonitorRef  is  a  reference  that  the  calling  process  obtained  by calling
              monitor/2, this monitoring is turned off. If the monitoring is already turned  off,
              nothing happens.

              Once  demonitor(MonitorRef)  has  returned,  it  is  guaranteed  that  no  {'DOWN',
              MonitorRef, _, _, _} message, because of the monitor, will be placed in the  caller
              message  queue  in the future. However, a {'DOWN', MonitorRef, _, _, _} message can
              have been placed in the caller message queue  before  the  call.  It  is  therefore
              usually  advisable  to  remove  such  a 'DOWN' message from the message queue after
              monitoring has been stopped. demonitor(MonitorRef, [flush]) can be used instead  of
              demonitor(MonitorRef) if this cleanup is wanted.

          Note:
              Before  Erlang/OTP  R11B  (ERTS 5.5) demonitor/1 behaved completely asynchronously,
              that is, the monitor was active until the "demonitor signal" reached the  monitored
              entity.  This  had  one  undesirable  effect.  You  could  never know when you were
              guaranteed not to receive a DOWN message because of the monitor.

              The current behavior can be viewed as two combined operations: asynchronously  send
              a  "demonitor  signal" to the monitored entity and ignore any future results of the
              monitor.

              Failure: It is an error if MonitorRef refers to a  monitoring  started  by  another
              process.  Not  all  such  cases  are cheap to check. If checking is cheap, the call
              fails with badarg, for example if MonitorRef is a remote reference.

       demonitor(MonitorRef, OptionList) -> boolean()

              Types:

                 MonitorRef = reference()
                 OptionList = [Option]
                 Option = flush | info

              The returned value is true unless info is part of OptionList.

              demonitor(MonitorRef, []) is equivalent to demonitor(MonitorRef).

              Options:

                flush:
                  Removes (one) {_, MonitorRef, _, _, _} message,  if  there  is  one,  from  the
                  caller message queue after monitoring has been stopped.

                  Calling demonitor(MonitorRef, [flush]) is equivalent to the following, but more
                  efficient:

                demonitor(MonitorRef),
                receive
                    {_, MonitorRef, _, _, _} ->
                        true
                after 0 ->
                        true
                end

                info:
                  The returned value is one of the following:

                  true:
                    The  monitor  was  found  and  removed.  In  this  case,  no  'DOWN'  message
                    corresponding to this monitor has been delivered and will not be delivered.

                  false:
                    The  monitor  was  not  found and could not be removed. This probably because
                    someone already has placed a 'DOWN' message corresponding to this monitor  in
                    the caller message queue.

                  If  option info is combined with option flush, false is returned if a flush was
                  needed, otherwise true.

          Note:
              More options can be added in a future release.

              Failures:

                badarg:
                  If OptionList is not a list.

                badarg:
                  If Option is an invalid option.

                badarg:
                  The same failure as for demonitor/1.

       disconnect_node(Node) -> boolean() | ignored

              Types:

                 Node = node()

              Forces the disconnection of a node. This appears to the node Node as if  the  local
              node  has  crashed.  This  BIF  is mainly used in the Erlang network authentication
              protocols.

              Returns true if disconnection succeeds, otherwise false. If the local node  is  not
              alive, ignored is returned.

       erlang:display(Term) -> true

              Types:

                 Term = term()

              Prints a text representation of Term on the standard output.

          Warning:
              This BIF is intended for debugging only.

       erlang:dist_ctrl_get_data(DHandle) -> {Size, Data} | Data | none

              Types:

                 Size = integer() >= 0
                 DHandle = dist_handle()
                 Data = iodata()

              Get  distribution  channel  data  from  the  local node that is to be passed to the
              remote node. The distribution channel is identified  by  DHandle.  If  no  data  is
              available,  the  atom none is returned. One can request to be informed by a message
              when        more        data        is         available         by         calling
              erlang:dist_ctrl_get_data_notification(DHandle).

              The  returned  value  when  there  are  data  available depends on the value of the
              get_size option configured on the distribution channel identified by  DHandle.  For
              more   information   see   the   documentation  of  the  get_size  option  for  the
              erlang:dist_ctrl_set_opt/3 function.

          Note:
              Only the process registered as distribution controller for the distribution channel
              identified by DHandle is allowed to call this function.

              This  function  is used when implementing an alternative distribution carrier using
              processes as  distribution  controllers.  DHandle  is  retrived  via  the  callback
              f_handshake_complete.  More  information  can be found in the documentation of ERTS
              User's Guide  How to implement an Alternative Carrier for the Erlang  Distribution
               Distribution Module.

       erlang:dist_ctrl_get_opt(DHandle, Opt :: get_size) -> Value

              Types:

                 DHandle = dist_handle()
                 Value = boolean()

              Returns  the value of the get_size option on the distribution channel identified by
              DHandle. For more information see the documentation of the get_size option for  the
              erlang:dist_ctrl_set_opt/3 function.

          Note:
              Only the process registered as distribution controller for the distribution channel
              identified by DHandle is allowed to call this function.

              This function is used when implementing an alternative distribution  carrier  using
              processes  as  distribution  controllers.  DHandle  is  retrived  via  the callback
              f_handshake_complete. More information can be found in the  documentation  of  ERTS
              User's  Guide  How to implement an Alternative Carrier for the Erlang Distribution
               Distribution Module.

       erlang:dist_ctrl_get_data_notification(DHandle) -> ok

              Types:

                 DHandle = dist_handle()

              Request   notification   when   more   data   is   available   to    fetch    using
              erlang:dist_ctrl_get_data(DHandle)  for  the  distribution  channel  identified  by
              DHandle. When more data is present, the caller will be sent the message  dist_data.
              Once  a  dist_data  messages has been sent, no more dist_data messages will be sent
              until the dist_ctrl_get_data_notification/1 function has been called again.

          Note:
              Only the process registered as distribution controller for the distribution channel
              identified by DHandle is allowed to call this function.

              This  function  is used when implementing an alternative distribution carrier using
              processes as  distribution  controllers.  DHandle  is  retrived  via  the  callback
              f_handshake_complete.  More  information  can be found in the documentation of ERTS
              User's Guide  How to implement an Alternative Carrier for the Erlang  Distribution
               Distribution Module.

       erlang:dist_ctrl_input_handler(DHandle, InputHandler) -> ok

              Types:

                 DHandle = dist_handle()
                 InputHandler = pid()

              Register an alternate input handler process for the distribution channel identified
              by DHandle. Once this function has been called, InputHandler is  the  only  process
              allowed   to   call   erlang:dist_ctrl_put_data(DHandle,  Data)  with  the  DHandle
              identifing this distribution channel.

          Note:
              Only the process registered as distribution controller for the distribution channel
              identified by DHandle is allowed to call this function.

              This  function  is used when implementing an alternative distribution carrier using
              processes as  distribution  controllers.  DHandle  is  retrived  via  the  callback
              f_handshake_complete.  More  information  can be found in the documentation of ERTS
              User's Guide  How to implement an Alternative Carrier for the Erlang  Distribution
               Distribution Module.

       erlang:dist_ctrl_put_data(DHandle, Data) -> ok

              Types:

                 DHandle = dist_handle()
                 Data = iodata()

              Deliver distribution channel data from a remote node to the local node.

          Note:
              Only the process registered as distribution controller for the distribution channel
              identified by DHandle is allowed to call this function unless  an  alternate  input
              handler  process  has been registered using erlang:dist_ctrl_input_handler(DHandle,
              InputHandler). If  an  alternate  input  handler  has  been  registered,  only  the
              registered input handler process is allowed to call this function.

              This  function  is used when implementing an alternative distribution carrier using
              processes as  distribution  controllers.  DHandle  is  retrived  via  the  callback
              f_handshake_complete.  More  information  can be found in the documentation of ERTS
              User's Guide  How to implement an Alternative Carrier for the Erlang  Distribution
               Distribution Module.

       erlang:dist_ctrl_set_opt(DHandle, Opt :: get_size, Value) ->
                                   OldValue

              Types:

                 DHandle = dist_handle()
                 Value = OldValue = boolean()

              Sets  the  value  of  the get_size option on the distribution channel identified by
              DHandle.   This   option    controls    the    return    value    of    calls    to
              erlang:dist_ctrl_get_data(DHandle)  where  DHandle equals DHandle used when setting
              this option. When the get_size option is:

                false:
                   and    there    are    distribution    data    available,    a     call     to
                  erlang:dist_ctrl_get_data(DHandle)  will  just  return  Data  to  pass over the
                  channel. This is the default value of the get_size option.

                true:
                   and    there    are    distribution    data    available,    a     call     to
                  erlang:dist_ctrl_get_data(DHandle) will return Data to pass over the channel as
                  well as the Size of Data in bytes. This is returned as  a  tuple  on  the  form
                  {Size, Data}.

              All options are set to default when a channel is closed.

          Note:
              Only the process registered as distribution controller for the distribution channel
              identified by DHandle is allowed to call this function.

              This function is used when implementing an alternative distribution  carrier  using
              processes  as  distribution  controllers.  DHandle  is  retrived  via  the callback
              f_handshake_complete. More information can be found in the  documentation  of  ERTS
              User's  Guide  How to implement an Alternative Carrier for the Erlang Distribution
               Distribution Module.

       element(N, Tuple) -> term()

              Types:

                 N = integer() >= 1
                   1..tuple_size(Tuple)
                 Tuple = tuple()

              Returns the Nth element (numbering from 1) of Tuple, for example:

              > element(2, {a, b, c}).
              b

              Allowed in guard tests.

       erase() -> [{Key, Val}]

              Types:

                 Key = Val = term()

              Returns the process dictionary and deletes it, for example:

              > put(key1, {1, 2, 3}),
              put(key2, [a, b, c]),
              erase().
              [{key1,{1,2,3}},{key2,[a,b,c]}]

       erase(Key) -> Val | undefined

              Types:

                 Key = Val = term()

              Returns the value  Val  associated  with  Key  and  deletes  it  from  the  process
              dictionary. Returns undefined if no value is associated with Key. Example:

              > put(key1, {merry, lambs, are, playing}),
              X = erase(key1),
              {X, erase(key1)}.
              {{merry,lambs,are,playing},undefined}

       error(Reason) -> no_return()

              Types:

                 Reason = term()

              Stops  the execution of the calling process with the reason Reason, where Reason is
              any term. The exit reason is  {Reason,  Where},  where  Where  is  a  list  of  the
              functions  most  recently  called  (the current function first). As evaluating this
              function causes the process to terminate, it has no return value. Example:

              > catch error(foobar).
              {'EXIT',{foobar,[{shell,apply_fun,3,
                                      [{file,"shell.erl"},{line,906}]},
                               {erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,677}]},
                               {erl_eval,expr,5,[{file,"erl_eval.erl"},{line,430}]},
                               {shell,exprs,7,[{file,"shell.erl"},{line,687}]},
                               {shell,eval_exprs,7,[{file,"shell.erl"},{line,642}]},
                               {shell,eval_loop,3,[{file,"shell.erl"},{line,627}]}]}}

       error(Reason, Args) -> no_return()

              Types:

                 Reason = term()
                 Args = [term()]

              Stops the execution of the calling process with the reason Reason, where Reason  is
              any  term.  The  exit  reason  is  {Reason,  Where},  where  Where is a list of the
              functions most recently called (the current function first). Args is expected to be
              the  list  of arguments for the current function; in Beam it is used to provide the
              arguments for the current function in the term Where. As evaluating  this  function
              causes the process to terminate, it has no return value.

       exit(Reason) -> no_return()

              Types:

                 Reason = term()

              Stops the execution of the calling process with exit reason Reason, where Reason is
              any term. As evaluating this function causes the process to terminate,  it  has  no
              return value. Example:

              > exit(foobar).
              ** exception exit: foobar
              > catch exit(foobar).
              {'EXIT',foobar}

       exit(Pid, Reason) -> true

              Types:

                 Pid = pid() | port()
                 Reason = term()

              Sends  an  exit signal with exit reason Reason to the process or port identified by
              Pid.

              The following behavior applies if Reason is any term, except normal or kill:

                * If Pid is not trapping exits, Pid itself exits with exit reason Reason.

                * If Pid is trapping exits,  the  exit  signal  is  transformed  into  a  message
                  {'EXIT', From, Reason} and delivered to the message queue of Pid.

                * From  is  the  process identifier of the process that sent the exit signal. See
                  also process_flag/2.

              If Reason is the atom normal, Pid does not exit. If it is trapping exits, the  exit
              signal  is  transformed  into a message {'EXIT', From, normal} and delivered to its
              message queue.

              If Reason is the atom kill, that is, if exit(Pid, kill) is called,  an  untrappable
              exit signal is sent to Pid, which unconditionally exits with exit reason killed.

       erlang:external_size(Term) -> integer() >= 0

              Types:

                 Term = term()

              Calculates, without doing the encoding, the maximum byte size for a term encoded in
              the Erlang external term format. The following condition applies always:

              > Size1 = byte_size(term_to_binary(Term)),
              > Size2 = erlang:external_size(Term),
              > true = Size1 =< Size2.
              true

              This is equivalent to a call to:

              erlang:external_size(Term, [])

       erlang:external_size(Term, Options) -> integer() >= 0

              Types:

                 Term = term()
                 Options = [{minor_version, Version :: integer() >= 0}]

              Calculates, without doing the encoding, the maximum byte size for a term encoded in
              the Erlang external term format. The following condition applies always:

              > Size1 = byte_size(term_to_binary(Term, Options)),
              > Size2 = erlang:external_size(Term, Options),
              > true = Size1 =< Size2.
              true

              Option  {minor_version,  Version}  specifies how floats are encoded. For a detailed
              description, see term_to_binary/2.

       float(Number) -> float()

              Types:

                 Number = number()

              Returns a float by converting Number to a float, for example:

              > float(55).
              55.0

              Allowed in guard tests.

          Note:
              If used on the top level in a guard, it tests whether the argument  is  a  floating
              point number; for clarity, use is_float/1 instead.

              When  float/1  is  used  in an expression in a guard, such as 'float(A) == 4.0', it
              converts a number as described earlier.

       float_to_binary(Float) -> binary()

              Types:

                 Float = float()

              The same as float_to_binary(Float,[{scientific,20}]).

       float_to_binary(Float, Options) -> binary()

              Types:

                 Float = float()
                 Options = [Option]
                 Option =
                     {decimals, Decimals :: 0..253} |
                     {scientific, Decimals :: 0..249} |
                     compact

              Returns a binary corresponding to the text  representation  of  Float  using  fixed
              decimal  point  formatting.  Options  behaves  in  the same way as float_to_list/2.
              Examples:

              > float_to_binary(7.12, [{decimals, 4}]).
              <<"7.1200">>
              > float_to_binary(7.12, [{decimals, 4}, compact]).
              <<"7.12">>

       float_to_list(Float) -> string()

              Types:

                 Float = float()

              The same as float_to_list(Float,[{scientific,20}]).

       float_to_list(Float, Options) -> string()

              Types:

                 Float = float()
                 Options = [Option]
                 Option =
                     {decimals, Decimals :: 0..253} |
                     {scientific, Decimals :: 0..249} |
                     compact

              Returns a string corresponding to the text  representation  of  Float  using  fixed
              decimal point formatting.

              Available options:

                * If  option  decimals is specified, the returned value contains at most Decimals
                  number of digits past the decimal point. If the number  does  not  fit  in  the
                  internal static buffer of 256 bytes, the function throws badarg.

                * If  option  compact is specified, the trailing zeros at the end of the list are
                  truncated. This option is only meaningful together with option decimals.

                * If option scientific is specified, the  float  is  formatted  using  scientific
                  notation with Decimals digits of precision.

                * If Options is [], the function behaves as float_to_list/1.

              Examples:

              > float_to_list(7.12, [{decimals, 4}]).
              "7.1200"
              > float_to_list(7.12, [{decimals, 4}, compact]).
              "7.12"

       floor(Number) -> integer()

              Types:

                 Number = number()

              Returns the largest integer not greater than Number. For example:

              > floor(-10.5).
              -11

              Allowed in guard tests.

       erlang:fun_info(Fun) -> [{Item, Info}]

              Types:

                 Fun = function()
                 Item =
                     arity | env | index | name | module | new_index | new_uniq |
                     pid | type | uniq
                 Info = term()

              Returns  a  list  with information about the fun Fun. Each list element is a tuple.
              The order of the tuples is undefined, and more tuples can  be  added  in  a  future
              release.

          Warning:
              This  BIF  is  mainly  intended  for  debugging,  but it can sometimes be useful in
              library functions that need to verify, for example, the arity of a fun.

              Two types of funs have slightly different semantics:

                * A fun created by fun M:F/A is called an external fun. Calling  it  will  always
                  call  the  function F with arity A in the latest code for module M. Notice that
                  module M does not even need to be loaded when the fun fun M:F/A is created.

                * All other funs are called local. When a local fun is called, the  same  version
                  of  the  code  that  created  the fun is called (even if a newer version of the
                  module has been loaded).

              The following elements are always present in the list for both local  and  external
              funs:

                {type, Type}:
                  Type is local or external.

                {module, Module}:
                  Module (an atom) is the module name.

                  If Fun is a local fun, Module is the module in which the fun is defined.

                  If Fun is an external fun, Module is the module that the fun refers to.

                {name, Name}:
                  Name (an atom) is a function name.

                  If  Fun  is a local fun, Name is the name of the local function that implements
                  the fun. (This name was generated by the compiler, and is only of informational
                  use.  As  it  is a local function, it cannot be called directly.) If no code is
                  currently loaded for the fun, [] is returned instead of an atom.

                  If Fun is an external fun, Name is the name of the exported function  that  the
                  fun refers to.

                {arity, Arity}:
                  Arity is the number of arguments that the fun is to be called with.

                {env, Env}:
                  Env  (a  list)  is  the environment or free variables for the fun. For external
                  funs, the returned list is always empty.

              The following elements are only present in the list if Fun is local:

                {pid, Pid}:
                  Pid is the process identifier of the process that originally created the fun.

                  It might point to the init process if the Fun  was  statically  allocated  when
                  module  was  loaded (this optimisation is performed for local functions that do
                  not capture the enviornment).

                {index, Index}:
                  Index (an integer) is an index into the module fun table.

                {new_index, Index}:
                  Index (an integer) is an index into the module fun table.

                {new_uniq, Uniq}:
                  Uniq (a binary) is a unique value for this  fun.  It  is  calculated  from  the
                  compiled code for the entire module.

                {uniq, Uniq}:
                  Uniq  (an integer) is a unique value for this fun. As from Erlang/OTP R15, this
                  integer is calculated from the compiled code  for  the  entire  module.  Before
                  Erlang/OTP R15, this integer was based on only the body of the fun.

       erlang:fun_info(Fun, Item) -> {Item, Info}

              Types:

                 Fun = function()
                 Item = fun_info_item()
                 Info = term()
                 fun_info_item() =
                     arity | env | index | name | module | new_index | new_uniq |
                     pid | type | uniq

              Returns information about Fun as specified by Item, in the form {Item,Info}.

              For any fun, Item can be any of the atoms module, name, arity, env, or type.

              For  a  local  fun,  Item  can also be any of the atoms index, new_index, new_uniq,
              uniq, and pid. For an external fun, the value of any of these items is  always  the
              atom undefined.

              See erlang:fun_info/1.

       erlang:fun_to_list(Fun) -> string()

              Types:

                 Fun = function()

              Returns a string corresponding to the text representation of Fun.

       erlang:function_exported(Module, Function, Arity) -> boolean()

              Types:

                 Module = module()
                 Function = atom()
                 Arity = arity()

              Returns  true  if  the  module  Module  is loaded and contains an exported function
              Function/Arity, or if there is a BIF (a built-in function implemented  in  C)  with
              the specified name, otherwise returns false.

          Note:
              This function used to return false for BIFs before Erlang/OTP 18.0.

       garbage_collect() -> true

              Forces  an  immediate  garbage collection of the executing process. The function is
              not to be used unless it has been noticed (or there are good  reasons  to  suspect)
              that the spontaneous garbage collection will occur too late or not at all.

          Warning:
              Improper use can seriously degrade system performance.

       garbage_collect(Pid) -> GCResult

              Types:

                 Pid = pid()
                 GCResult = boolean()

              The same as garbage_collect(Pid, []).

       garbage_collect(Pid, OptionList) -> GCResult | async

              Types:

                 Pid = pid()
                 RequestId = term()
                 Option = {async, RequestId} | {type, major | minor}
                 OptionList = [Option]
                 GCResult = boolean()

              Garbage collects the node local process identified by Pid.

              Option:

                {async, RequestId}:
                  The  function  garbage_collect/2  returns the value async immediately after the
                  request has been sent. When the request has been processed,  the  process  that
                  called  this  function  is  passed  a  message  on  the  form {garbage_collect,
                  RequestId, GCResult}.

                {type, 'major' | 'minor'}:
                  Triggers garbage collection of requested type. Default value is 'major',  which
                  would  trigger  a fullsweep GC. The option 'minor' is considered a hint and may
                  lead to either minor or major GC run.

              If Pid equals self(), and no async option has been passed, the  garbage  collection
              is  performed  at once, that is, the same as calling garbage_collect/0. Otherwise a
              request for garbage collection is sent to the process identified by Pid,  and  will
              be  handled when appropriate. If no async option has been passed, the caller blocks
              until GCResult is available and can be returned.

              GCResult informs about the result of the garbage collection request as follows:

                true:
                   The process identified by Pid has been garbage collected.

                false:
                   No garbage  collection  was  performed,  as  the  process  identified  by  Pid
                  terminated before the request could be satisfied.

              Notice that the same caveats apply as for garbage_collect/0.

              Failures:

                badarg:
                   If Pid is not a node local process identifier.

                badarg:
                   If OptionList is an invalid list of options.

       get() -> [{Key, Val}]

              Types:

                 Key = Val = term()

              Returns the process dictionary as a list of {Key, Val} tuples, for example:

              > put(key1, merry),
              put(key2, lambs),
              put(key3, {are, playing}),
              get().
              [{key1,merry},{key2,lambs},{key3,{are,playing}}]

       get(Key) -> Val | undefined

              Types:

                 Key = Val = term()

              Returns  the  value Val associated with Key in the process dictionary, or undefined
              if Key does not exist. Example:

              > put(key1, merry),
              put(key2, lambs),
              put({any, [valid, term]}, {are, playing}),
              get({any, [valid, term]}).
              {are,playing}

       erlang:get_cookie() -> Cookie | nocookie

              Types:

                 Cookie = atom()

              Returns the magic cookie of the local node if the node is alive, otherwise the atom
              nocookie.

       get_keys() -> [Key]

              Types:

                 Key = term()

              Returns a list of all keys present in the process dictionary, for example:

              > put(dog, {animal,1}),
              put(cow, {animal,2}),
              put(lamb, {animal,3}),
              get_keys().
              [dog,cow,lamb]

       get_keys(Val) -> [Key]

              Types:

                 Val = Key = term()

              Returns  a  list  of  keys  that  are  associated with the value Val in the process
              dictionary, for example:

              > put(mary, {1, 2}),
              put(had, {1, 2}),
              put(a, {1, 2}),
              put(little, {1, 2}),
              put(dog, {1, 3}),
              put(lamb, {1, 2}),
              get_keys({1, 2}).
              [mary,had,a,little,lamb]

       erlang:get_stacktrace() -> [stack_item()]

              Types:

                 stack_item() =
                     {Module :: module(),
                      Function :: atom(),
                      Arity :: arity() | (Args :: [term()]),
                      Location ::
                          [{file, Filename :: string()} |
                           {line, Line :: integer() >= 1}]}

          Warning:
              erlang:get_stacktrace/0 is deprecated and will stop working in a future release.

              Instead of using erlang:get_stacktrace/0 to retrieve the call stack back-trace, use
              the following syntax:

              try Expr
              catch
                Class:Reason:Stacktrace ->
                 {Class,Reason,Stacktrace}
              end

              erlang:get_stacktrace/0  retrieves  the  call  stack back-trace (stacktrace) for an
              exception that  has  just  been  caught  in  the  calling  process  as  a  list  of
              {Module,Function,Arity,Location}  tuples. Field Arity in the first tuple can be the
              argument list of that function call instead of an arity integer, depending  on  the
              exception.

              If  there  has  not been any exceptions in a process, the stacktrace is []. After a
              code change for the process, the stacktrace can also be reset to [].

              The stacktrace is the same data as operator catch returns, for example:

              {'EXIT',{badarg,Stacktrace}} = catch abs(x)

              Location is a (possibly empty) list of two-tuples that can indicate the location in
              the  source  code of the function. The first element is an atom describing the type
              of information in the second element. The following items can occur:

                file:
                  The second element of the tuple is a string (list of  characters)  representing
                  the filename of the source file of the function.

                line:
                  The  second  element  of  the  tuple is the line number (an integer > 0) in the
                  source file where the exception occurred or the function was called.

          Warning:
              Developers should rely on stacktrace entries only for debugging purposes.

              The VM performs tail call optimization, which does  not  add  new  entries  to  the
              stacktrace,  and  also limits stacktraces to a certain depth. Furthermore, compiler
              options, optimizations and future changes may add  or  remove  stacktrace  entries,
              causing  any  code  that expects the stacktrace to be in a certain order or contain
              specific items to fail.

              The only exception to this rule is error:undef  which  guarantees  to  include  the
              Module, Function and Arity of the attempted function as the first stacktrace entry.

              See also error/1 and error/2.

       group_leader() -> pid()

              Returns  the  process identifier of the group leader for the process evaluating the
              function.

              Every process is a member of some process group and all groups have a group leader.
              All  I/O  from  the  group  is channeled to the group leader. When a new process is
              spawned, it gets the same group leader  as  the  spawning  process.  Initially,  at
              system  startup,  init  is  both  its  own group leader and the group leader of all
              processes.

       group_leader(GroupLeader, Pid) -> true

              Types:

                 GroupLeader = Pid = pid()

              Sets the group leader of Pid to GroupLeader. Typically, this is used when a process
              started from a certain shell is to have another group leader than init.

              The  group leader should be rarely changed in applications with a supervision tree,
              because OTP assumes the group  leader  of  their  processes  is  their  application
              master.

              See  also group_leader/0 and OTP design principles related to starting and stopping
              applications.

       halt() -> no_return()

              The same as halt(0, []). Example:

              > halt().
              os_prompt%

       halt(Status) -> no_return()

              Types:

                 Status = integer() >= 0 | abort | string()

              The same as halt(Status, []). Example:

              > halt(17).
              os_prompt% echo $?
              17
              os_prompt%

       halt(Status, Options) -> no_return()

              Types:

                 Status = integer() >= 0 | abort | string()
                 Options = [Option]
                 Option = {flush, boolean()}

              Status must be a non-negative integer, a string,  or  the  atom  abort.  Halts  the
              Erlang  runtime  system.  Has  no  return value. Depending on Status, the following
              occurs:

                integer():
                  The runtime system exits with integer  value  Status  as  status  code  to  the
                  calling environment (OS).

            Note:
                On  many  platforms,  the OS supports only status codes 0-255. A too large status
                code is truncated by clearing the high bits.

                string():
                  An Erlang crash dump is produced with Status as slogan. Then the runtime system
                  exits  with  status  code  1.  The  string will be truncated if longer than 200
                  characters.

            Note:
                Before ERTS 9.1 (OTP-20.1) only code points in the range 0-255  was  accepted  in
                the string. Now any unicode string is valid.

                abort:
                  The runtime system aborts producing a core dump, if that is enabled in the OS.

              For  integer  Status,  the  Erlang runtime system closes all ports and allows async
              threads to finish their operations before exiting. To exit without  such  flushing,
              use Option as {flush,false}.

              For statuses string() and abort, option flush is ignored and flushing is not done.

       hd(List) -> term()

              Types:

                 List = [term(), ...]

              Returns the head of List, that is, the first element, for example:

              > hd([1,2,3,4,5]).
              1

              Allowed in guard tests.

              Failure: badarg if List is the empty list [].

       erlang:hibernate(Module, Function, Args) -> no_return()

              Types:

                 Module = module()
                 Function = atom()
                 Args = [term()]

              Puts  the  calling  process  into a wait state where its memory allocation has been
              reduced as much as possible. This is useful if  the  process  does  not  expect  to
              receive any messages soon.

              The  process  is  awaken  when  a  message  is  sent  to it, and control resumes in
              Module:Function with the arguments specified by Args with the call  stack  emptied,
              meaning   that   the   process   terminates   when   that  function  returns.  Thus
              erlang:hibernate/3 never returns to its caller.

              If the process has any message in  its  message  queue,  the  process  is  awakened
              immediately in the same way as described earlier.

              In  more  technical  terms,  erlang:hibernate/3  discards  the  call  stack for the
              process, and then garbage collects the process. After this, all live data is in one
              continuous  heap. The heap is then shrunken to the exact same size as the live data
              that it holds (even if that size is  less  than  the  minimum  heap  size  for  the
              process).

              If the size of the live data in the process is less than the minimum heap size, the
              first garbage collection occurring after the process is awakened ensures  that  the
              heap size is changed to a size not smaller than the minimum heap size.

              Notice that emptying the call stack means that any surrounding catch is removed and
              must be re-inserted after hibernation. One effect of this is that processes started
              using  proc_lib  (also  indirectly,  such  as  gen_server  processes),  are  to use
              proc_lib:hibernate/3 instead, to ensure that the  exception  handler  continues  to
              work when the process wakes up.

       erlang:insert_element(Index, Tuple1, Term) -> Tuple2

              Types:

                 Index = integer() >= 1
                   1..tuple_size(Tuple1) + 1
                 Tuple1 = Tuple2 = tuple()
                 Term = term()

              Returns  a  new tuple with element Term inserted at position Index in tuple Tuple1.
              All elements from position Index and upwards are pushed one step higher in the  new
              tuple Tuple2. Example:

              > erlang:insert_element(2, {one, two, three}, new).
              {one,new,two,three}

       integer_to_binary(Integer) -> binary()

              Types:

                 Integer = integer()

              Returns a binary corresponding to the text representation of Integer, for example:

              > integer_to_binary(77).
              <<"77">>

       integer_to_binary(Integer, Base) -> binary()

              Types:

                 Integer = integer()
                 Base = 2..36

              Returns  a binary corresponding to the text representation of Integer in base Base,
              for example:

              > integer_to_binary(1023, 16).
              <<"3FF">>

       integer_to_list(Integer) -> string()

              Types:

                 Integer = integer()

              Returns a string corresponding to the text representation of Integer, for example:

              > integer_to_list(77).
              "77"

       integer_to_list(Integer, Base) -> string()

              Types:

                 Integer = integer()
                 Base = 2..36

              Returns a string corresponding to the text representation of Integer in base  Base,
              for example:

              > integer_to_list(1023, 16).
              "3FF"

       iolist_size(Item) -> integer() >= 0

              Types:

                 Item = iolist() | binary()

              Returns  an  integer,  that  is  the size in bytes, of the binary that would be the
              result of iolist_to_binary(Item), for example:

              > iolist_size([1,2|<<3,4>>]).
              4

       iolist_to_binary(IoListOrBinary) -> binary()

              Types:

                 IoListOrBinary = iolist() | binary()

              Returns a binary that is made from the integers and binaries in IoListOrBinary, for
              example:

              > Bin1 = <<1,2,3>>.
              <<1,2,3>>
              > Bin2 = <<4,5>>.
              <<4,5>>
              > Bin3 = <<6>>.
              <<6>>
              > iolist_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
              <<1,2,3,1,2,3,4,5,4,6>>

       erlang:iolist_to_iovec(IoListOrBinary) -> iovec()

              Types:

                 IoListOrBinary = iolist() | binary()

              Returns an iovec that is made from the integers and binaries in IoListOrBinary.

       is_alive() -> boolean()

              Returns  true  if  the  local  node is alive (that is, if the node can be part of a
              distributed system), otherwise false.

       is_atom(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is an atom, otherwise false.

              Allowed in guard tests.

       is_binary(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a binary, otherwise false.

              A binary always contains a complete number of bytes.

              Allowed in guard tests.

       is_bitstring(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a bitstring (including a binary), otherwise false.

              Allowed in guard tests.

       is_boolean(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is the atom true or the  atom  false  (that  is,  a  boolean).
              Otherwise returns false.

              Allowed in guard tests.

       erlang:is_builtin(Module, Function, Arity) -> boolean()

              Types:

                 Module = module()
                 Function = atom()
                 Arity = arity()

              This BIF is useful for builders of cross-reference tools.

              Returns true if Module:Function/Arity is a BIF implemented in C, otherwise false.

       is_float(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a floating point number, otherwise false.

              Allowed in guard tests.

       is_function(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a fun, otherwise false.

              Allowed in guard tests.

       is_function(Term, Arity) -> boolean()

              Types:

                 Term = term()
                 Arity = arity()

              Returns  true  if Term is a fun that can be applied with Arity number of arguments,
              otherwise false.

              Allowed in guard tests.

       is_integer(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is an integer, otherwise false.

              Allowed in guard tests.

       is_list(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a list with zero or more elements, otherwise false.

              Allowed in guard tests.

       is_map(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a map, otherwise false.

              Allowed in guard tests.

       is_map_key(Key, Map) -> boolean()

              Types:

                 Key = term()
                 Map = map()

              Returns true if map Map contains Key and returns false if it does not  contain  the
              Key.

              The call fails with a {badmap,Map} exception if Map is not a map.

              Example:

              > Map = #{"42" => value}.
              #{"42" => value}
              > is_map_key("42",Map).
              true
              > is_map_key(value,Map).
              false

       is_number(Term) -> boolean()

              Types:

                 Term = term()

              Returns  true  if  Term is an integer or a floating point number. Otherwise returns
              false.

              Allowed in guard tests.

       is_pid(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a process identifier, otherwise false.

              Allowed in guard tests.

       is_port(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a port identifier, otherwise false.

              Allowed in guard tests.

       is_process_alive(Pid) -> boolean()

              Types:

                 Pid = pid()

              Pid must refer to a process at the local node.

              Returns true if the process exists and is alive, that is, is not  exiting  and  has
              not exited. Otherwise returns false.

       is_record(Term, RecordTag) -> boolean()

              Types:

                 Term = term()
                 RecordTag = atom()

              Returns  true  if  Term  is  a  tuple and its first element is RecordTag. Otherwise
              returns false.

          Note:
              Normally the compiler treats calls to is_record/2  especially.  It  emits  code  to
              verify that Term is a tuple, that its first element is RecordTag, and that the size
              is correct. However, if RecordTag is not a literal atom,  the  BIF  is_record/2  is
              called instead and the size of the tuple is not verified.

              Allowed in guard tests, if RecordTag is a literal atom.

       is_record(Term, RecordTag, Size) -> boolean()

              Types:

                 Term = term()
                 RecordTag = atom()
                 Size = integer() >= 0

              RecordTag must be an atom.

              Returns  true  if  Term is a tuple, its first element is RecordTag, and its size is
              Size. Otherwise returns false.

              Allowed in guard tests if RecordTag is  a  literal  atom  and  Size  is  a  literal
              integer.

          Note:
              This BIF is documented for completeness. Usually is_record/2 is to be used.

       is_reference(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a reference, otherwise false.

              Allowed in guard tests.

       is_tuple(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a tuple, otherwise false.

              Allowed in guard tests.

       length(List) -> integer() >= 0

              Types:

                 List = [term()]

              Returns the length of List, for example:

              > length([1,2,3,4,5,6,7,8,9]).
              9

              Allowed in guard tests.

       link(PidOrPort) -> true

              Types:

                 PidOrPort = pid() | port()

              Creates a link between the calling process and another process (or port) PidOrPort,
              if there is not such a link already. If a process attempts  to  create  a  link  to
              itself, nothing is done. Returns true.

              If  PidOrPort  does  not  exist,  the behavior of the BIF depends on if the calling
              process is trapping exits or not (see process_flag/2):

                * If the calling process is not trapping exits, and checking PidOrPort  is  cheap
                  (that is, if PidOrPort is local), link/1 fails with reason noproc.

                * Otherwise,  if  the  calling  process  is  trapping  exits, and/or PidOrPort is
                  remote, link/1 returns true, but an exit signal with reason noproc is  sent  to
                  the calling process.

       list_to_atom(String) -> atom()

              Types:

                 String = string()

              Returns the atom whose text representation is String.

              As  from  Erlang/OTP 20, String may contain any Unicode character. Earlier versions
              allowed only ISO-latin-1 characters as the implementation  did  not  allow  Unicode
              characters above 255. For more information on Unicode support in atoms, see note on
              UTF-8 encoded atoms in section "External Term Format" in the User's Guide.

              Example:

              > list_to_atom("Erlang").
              'Erlang'

       list_to_binary(IoList) -> binary()

              Types:

                 IoList = iolist()

              Returns a binary that is made  from  the  integers  and  binaries  in  IoList,  for
              example:

              > Bin1 = <<1,2,3>>.
              <<1,2,3>>
              > Bin2 = <<4,5>>.
              <<4,5>>
              > Bin3 = <<6>>.
              <<6>>
              > list_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
              <<1,2,3,1,2,3,4,5,4,6>>

       list_to_bitstring(BitstringList) -> bitstring()

              Types:

                 BitstringList = bitstring_list()
                 bitstring_list() =
                     maybe_improper_list(byte() | bitstring() | bitstring_list(),
                                         bitstring() | [])

              Returns a bitstring that is made from the integers and bitstrings in BitstringList.
              (The last tail in BitstringList is allowed to be a bitstring.) Example:

              > Bin1 = <<1,2,3>>.
              <<1,2,3>>
              > Bin2 = <<4,5>>.
              <<4,5>>
              > Bin3 = <<6,7:4>>.
              <<6,7:4>>
              > list_to_bitstring([Bin1,1,[2,3,Bin2],4|Bin3]).
              <<1,2,3,1,2,3,4,5,4,6,7:4>>

       list_to_existing_atom(String) -> atom()

              Types:

                 String = string()

              Returns the atom whose text representation is String, but  only  if  there  already
              exists such atom.

              Failure:  badarg  if there does not already exist an atom whose text representation
              is String.

          Note:
              Note that the compiler may optimize away atoms.  For  example,  the  compiler  will
              rewrite  atom_to_list(some_atom)  to  "some_atom".  If  that expression is the only
              mention of the atom some_atom in the  containing  module,  the  atom  will  not  be
              created    when    the    module    is   loaded,   and   a   subsequent   call   to
              list_to_existing_atom("some_atom") will fail.

       list_to_float(String) -> float()

              Types:

                 String = string()

              Returns the float whose text representation is String, for example:

              > list_to_float("2.2017764e+0").
              2.2017764

              Failure: badarg if String contains a bad representation of a float.

       list_to_integer(String) -> integer()

              Types:

                 String = string()

              Returns an integer whose text representation is String, for example:

              > list_to_integer("123").
              123

              Failure: badarg if String contains a bad representation of an integer.

       list_to_integer(String, Base) -> integer()

              Types:

                 String = string()
                 Base = 2..36

              Returns an integer whose text representation in base Base is String, for example:

              > list_to_integer("3FF", 16).
              1023

              Failure: badarg if String contains a bad representation of an integer.

       list_to_pid(String) -> pid()

              Types:

                 String = string()

              Returns a process identifier whose text representation is a String, for example:

              > list_to_pid("<0.4.1>").
              <0.4.1>

              Failure: badarg if String contains a bad representation of a process identifier.

          Warning:
              This BIF is intended for debugging and is not to be used in application programs.

       list_to_port(String) -> port()

              Types:

                 String = string()

              Returns a port identifier whose text representation is a String, for example:

              > list_to_port("#Port<0.4>").
              #Port<0.4>

              Failure: badarg if String contains a bad representation of a port identifier.

          Warning:
              This BIF is intended for debugging and is not to be used in application programs.

       list_to_ref(String) -> reference()

              Types:

                 String = string()

              Returns a reference whose text representation is a String, for example:

              > list_to_ref("#Ref<0.4192537678.4073193475.71181>").
              #Ref<0.4192537678.4073193475.71181>

              Failure: badarg if String contains a bad representation of a reference.

          Warning:
              This BIF is intended for debugging and is not to be used in application programs.

       list_to_tuple(List) -> tuple()

              Types:

                 List = [term()]

              Returns a tuple corresponding to List, for example

              > list_to_tuple([share, ['Ericsson_B', 163]]).
              {share, ['Ericsson_B', 163]}

              List can contain any Erlang terms.

       load_module(Module, Binary) -> {module, Module} | {error, Reason}

              Types:

                 Module = module()
                 Binary = binary()
                 Reason = badfile | not_purged | on_load

              If Binary contains the object code for module Module, this BIF  loads  that  object
              code.  If  the  code  for  module  Module already exists, all export references are
              replaced so they point to the newly loaded code. The previously loaded code is kept
              in the system as old code, as there can still be processes executing that code.

              Returns either {module, Module}, or {error, Reason} if loading fails. Reason is one
              of the following:

                badfile:
                  The object code in Binary has an incorrect format or the object  code  contains
                  code for another module than Module.

                not_purged:
                  Binary contains a module that cannot be loaded because old code for this module
                  already exists.

          Warning:
              This BIF is intended for the code server (see code(3erl)) and is  not  to  be  used
              elsewhere.

       erlang:load_nif(Path, LoadInfo) -> ok | Error

              Types:

                 Path = string()
                 LoadInfo = term()
                 Error = {error, {Reason, Text :: string()}}
                 Reason =
                     load_failed | bad_lib | load | reload | upgrade | old_code

              Loads  and  links  a dynamic library containing native implemented functions (NIFs)
              for a module. Path is a file path to  the  shareable  object/dynamic  library  file
              minus  the  OS-dependent file extension (.so for Unix and .dll for Windows). Notice
              that on most OSs the library has to have a different name on disc when  an  upgrade
              of  the  nif  is  done.  If  the name is the same, but the contents differ, the old
              library may be loaded instead. For information on how to implement a  NIF  library,
              see erl_nif(3erl).

              LoadInfo  can  be  any  term.  It  is  passed  on  to  the  library  as part of the
              initialization. A good practice is to include a module version  number  to  support
              future code upgrade scenarios.

              The  call  to  load_nif/2  must be made directly from the Erlang code of the module
              that the NIF library belongs to. It returns either ok, or {error,{Reason,Text}}  if
              loading  fails. Reason is one of the following atoms while Text is a human readable
              string that can give more information about the failure:

                load_failed:
                  The OS failed to load the NIF library.

                bad_lib:
                  The library did not fulfill the requirements as a NIF library  of  the  calling
                  module.

                load | upgrade:
                  The corresponding library callback was unsuccessful.

                reload:
                  A  NIF  library  is  already  loaded  for  this module instance. The previously
                  deprecated reload feature was removed in OTP 20.

                old_code:
                  The call to load_nif/2 was made from the old code of a  module  that  has  been
                  upgraded; this is not allowed.

                notsup:
                  Lack of support. Such as loading NIF library for a HiPE compiled module.

       erlang:loaded() -> [Module]

              Types:

                 Module = module()

              Returns  a  list  of  all  loaded  Erlang modules (current and old code), including
              preloaded modules.

              See also code(3erl).

       erlang:localtime() -> DateTime

              Types:

                 DateTime = calendar:datetime()

              Returns the current local date  and  time,  {{Year,  Month,  Day},  {Hour,  Minute,
              Second}}, for example:

              > erlang:localtime().
              {{1996,11,6},{14,45,17}}

              The time zone and Daylight Saving Time correction depend on the underlying OS.

       erlang:localtime_to_universaltime(Localtime) -> Universaltime

              Types:

                 Localtime = Universaltime = calendar:datetime()

              Converts  local  date and time to Universal Time Coordinated (UTC), if supported by
              the underlying OS. Otherwise no conversion  is  done  and  Localtime  is  returned.
              Example:

              > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}).
              {{1996,11,6},{13,45,17}}

              Failure: badarg if Localtime denotes an invalid date and time.

       erlang:localtime_to_universaltime(Localtime, IsDst) ->
                                            Universaltime

              Types:

                 Localtime = Universaltime = calendar:datetime()
                 IsDst = true | false | undefined

              Converts   local   date   and   time   to   Universal  Time  Coordinated  (UTC)  as
              erlang:localtime_to_universaltime/1, but the caller decides if Daylight Saving Time
              is active.

              If IsDst == true, Localtime is during Daylight Saving Time, if IsDst == false it is
              not. If IsDst == undefined, the underlying OS can  guess,  which  is  the  same  as
              calling erlang:localtime_to_universaltime(Localtime).

              Examples:

              > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, true).
              {{1996,11,6},{12,45,17}}
              > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, false).
              {{1996,11,6},{13,45,17}}
              > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, undefined).
              {{1996,11,6},{13,45,17}}

              Failure: badarg if Localtime denotes an invalid date and time.

       make_ref() -> reference()

              Returns a  unique reference. The reference is unique among connected nodes.

          Warning:
              Known  issue:  When  a  node  is  restarted multiple times with the same node name,
              references created on a newer node can be mistaken for a reference  created  on  an
              older node with the same node name.

       erlang:make_tuple(Arity, InitialValue) -> tuple()

              Types:

                 Arity = arity()
                 InitialValue = term()

              Creates  a  new  tuple of the specified Arity, where all elements are InitialValue,
              for example:

              > erlang:make_tuple(4, []).
              {[],[],[],[]}

       erlang:make_tuple(Arity, DefaultValue, InitList) -> tuple()

              Types:

                 Arity = arity()
                 DefaultValue = term()
                 InitList = [{Position :: integer() >= 1, term()}]

              Creates a tuple of size Arity, where each element has value DefaultValue, and  then
              fills  in  values from InitList. Each list element in InitList must be a two-tuple,
              where the first element is a position in the newly created  tuple  and  the  second
              element  is  any  term.  If  a position occurs more than once in the list, the term
              corresponding to the last occurrence is used. Example:

              > erlang:make_tuple(5, [], [{2,ignored},{5,zz},{2,aa}]).
              {[],aa,[],[],zz}

       map_get(Key, Map) -> Value

              Types:

                 Map = map()
                 Key = Value = any()

              Returns value Value associated with Key if Map contains Key.

              The call fails with a {badmap,Map} exception if  Map  is  not  a  map,  or  with  a
              {badkey,Key} exception if no value is associated with Key.

              Example:

              > Key = 1337,
                Map = #{42 => value_two,1337 => "value one","a" => 1},
                map_get(Key,Map).
              "value one"

       map_size(Map) -> integer() >= 0

              Types:

                 Map = map()

              Returns an integer, which is the number of key-value pairs in Map, for example:

              > map_size(#{a=>1, b=>2, c=>3}).
              3

              Allowed in guard tests.

       erlang:match_spec_test(MatchAgainst, MatchSpec, Type) ->
                                 TestResult

              Types:

                 MatchAgainst = [term()] | tuple()
                 MatchSpec = term()
                 Type = table | trace
                 TestResult =
                     {ok, term(), [return_trace], [{error | warning, string()}]} |
                     {error, [{error | warning, string()}]}

              Tests    a    match    specification    used   in   calls   to   ets:select/2   and
              erlang:trace_pattern/3.  The  function  tests  both  a  match   specification   for
              "syntactic" correctness and runs the match specification against the object. If the
              match specification contains errors, the tuple {error, Errors} is  returned,  where
              Errors  is a list of natural language descriptions of what was wrong with the match
              specification.

              If Type is table, the object to match against is to be a tuple. The  function  then
              returns {ok,Result,[],Warnings}, where Result is what would have been the result in
              a real ets:select/2 call, or false if the match specification does  not  match  the
              object tuple.

              If Type is trace, the object to match against is to be a list. The function returns
              {ok, Result, Flags, Warnings}, where Result is one of the following:

                * true if a trace message is to be emitted

                * false if a trace message is not to be emitted

                * The message term to be appended to the trace message

              Flags is a list containing all the trace flags to be  enabled,  currently  this  is
              only return_trace.

              This is a useful debugging and test tool, especially when writing complicated match
              specifications.

              See also ets:test_ms/2.

       max(Term1, Term2) -> Maximum

              Types:

                 Term1 = Term2 = Maximum = term()

              Returns the largest of Term1 and Term2. If the terms are equal, Term1 is returned.

       erlang:md5(Data) -> Digest

              Types:

                 Data = iodata()
                 Digest = binary()

              Computes an MD5 message digest from Data, where the length of  the  digest  is  128
              bits (16 bytes). Data is a binary or a list of small integers and binaries.

              For more information about MD5, see  RFC 1321 - The MD5 Message-Digest Algorithm.

          Warning:
              The  MD5  Message-Digest  Algorithm  is  not  considered  safe  for code-signing or
              software-integrity purposes.

       erlang:md5_final(Context) -> Digest

              Types:

                 Context = Digest = binary()

              Finishes the update of an MD5 Context and returns the computed MD5 message digest.

       erlang:md5_init() -> Context

              Types:

                 Context = binary()

              Creates an MD5 context, to be used in the following calls to md5_update/2.

       erlang:md5_update(Context, Data) -> NewContext

              Types:

                 Context = binary()
                 Data = iodata()
                 NewContext = binary()

              Update an MD5 Context with Data and returns a NewContext.

       erlang:memory() -> [{Type, Size}]

              Types:

                 Type = memory_type()
                 Size = integer() >= 0
                 memory_type() =
                     total | processes | processes_used | system | atom |
                     atom_used | binary | code | ets

              Returns a list with information about memory dynamically allocated  by  the  Erlang
              emulator.  Each  list element is a tuple {Type, Size}. The first element Type is an
              atom describing memory type. The second element Size is the memory size in bytes.

              Memory types:

                total:
                  The total amount of memory currently allocated. This is the same as the sum  of
                  the memory size for processes and system.

                processes:
                  The total amount of memory currently allocated for the Erlang processes.

                processes_used:
                  The total amount of memory currently used by the Erlang processes. This is part
                  of the memory presented as processes memory.

                system:
                  The total amount of memory currently allocated for the  emulator  that  is  not
                  directly  related  to  any Erlang process. Memory presented as processes is not
                  included in this memory. instrument(3erl) can be used to get  a  more  detailed
                  breakdown of what memory is part of this type.

                atom:
                  The  total  amount of memory currently allocated for atoms. This memory is part
                  of the memory presented as system memory.

                atom_used:
                  The total amount of memory currently used for atoms. This memory is part of the
                  memory presented as atom memory.

                binary:
                  The  total  amount  of  memory currently allocated for binaries. This memory is
                  part of the memory presented as system memory.

                code:
                  The total amount of memory currently allocated for Erlang code. This memory  is
                  part of the memory presented as system memory.

                ets:
                  The  total  amount of memory currently allocated for ETS tables. This memory is
                  part of the memory presented as system memory.

                low:
                  Only on 64-bit halfword emulator. The total amount of memory allocated  in  low
                  memory  areas  that are restricted to < 4 GB, although the system can have more
                  memory.

                  Can be removed in a future release of the halfword emulator.

                maximum:
                  The maximum total amount of memory allocated since the  emulator  was  started.
                  This tuple is only present when the emulator is run with instrumentation.

                  For   information  on  how  to  run  the  emulator  with  instrumentation,  see
                  instrument(3erl) and/or erl(1).

          Note:
              The system value is not complete. Some allocated memory that is to be part of  this
              value is not.

              When  the  emulator is run with instrumentation, the system value is more accurate,
              but memory directly allocated for malloc (and friends) is still  not  part  of  the
              system  value.  Direct  calls  to  malloc  are  only  done from OS-specific runtime
              libraries and perhaps from user-implemented Erlang drivers  that  do  not  use  the
              memory allocation functions in the driver interface.

              As  the  total  value  is  the  sum  of  processes  and system, the error in system
              propagates to the total value.

              The different amounts of memory that are summed are not gathered atomically,  which
              introduces an error in the result.

              The  different  values  have the following relation to each other. Values beginning
              with an uppercase letter is not part of the result.

              total      = processes + system
              processes  = processes_used + ProcessesNotUsed
              system     = atom + binary + code + ets + OtherSystem
              atom       = atom_used + AtomNotUsed
              RealTotal  = processes + RealSystem
              RealSystem = system + MissedSystem

              More tuples in the returned list can be added in a future release.

          Note:
              The total value is supposed to be the total amount of memory dynamically  allocated
              by  the  emulator.  Shared  libraries,  the  code  of  the emulator itself, and the
              emulator stacks are not supposed to be included. That is, the total  value  is  not
              supposed to be equal to the total size of all pages mapped to the emulator.

              Also,  because of fragmentation and prereservation of memory areas, the size of the
              memory segments containing the dynamically allocated  memory  blocks  can  be  much
              larger than the total size of the dynamically allocated memory blocks.

          Note:
              As  from  ERTS 5.6.4, erlang:memory/0 requires that all erts_alloc(3erl) allocators
              are enabled (default behavior).

              Failure: notsup if an erts_alloc(3erl) allocator has been disabled.

       erlang:memory(Type :: memory_type()) -> integer() >= 0

       erlang:memory(TypeList :: [memory_type()]) ->
                        [{memory_type(), integer() >= 0}]

              Types:

                 memory_type() =
                     total | processes | processes_used | system | atom |
                     atom_used | binary | code | ets

              Returns the memory size in bytes allocated for memory of type  Type.  The  argument
              can  also  be  specified  as  a  list  of  memory_type()  atoms,  in  which  case a
              corresponding list of {memory_type(), Size :: integer >= 0} tuples is returned.

          Note:
              As from ERTS 5.6.4, erlang:memory/1 requires that all  erts_alloc(3erl)  allocators
              are enabled (default behavior).

              Failures:

                badarg:
                   If  Type  is  not  one  of  the  memory  types  listed  in  the description of
                  erlang:memory/0.

                badarg:
                   If maximum is passed as Type and the emulator is not run in instrumented mode.

                notsup:
                   If an erts_alloc(3erl) allocator has been disabled.

              See also erlang:memory/0.

       min(Term1, Term2) -> Minimum

              Types:

                 Term1 = Term2 = Minimum = term()

              Returns the smallest of Term1 and Term2. If the terms are equal, Term1 is returned.

       module_loaded(Module) -> boolean()

              Types:

                 Module = module()

              Returns true if the module Module is loaded, otherwise false. It does  not  attempt
              to load the module.

          Warning:
              This  BIF  is  intended  for the code server (see code(3erl)) and is not to be used
              elsewhere.

       monitor(Type :: process, Item :: monitor_process_identifier()) ->
                  MonitorRef

       monitor(Type :: port, Item :: monitor_port_identifier()) ->
                  MonitorRef

       monitor(Type :: time_offset, Item :: clock_service) -> MonitorRef

              Types:

                 MonitorRef = reference()
                 registered_name() = atom()
                 registered_process_identifier() =
                     registered_name() | {registered_name(), node()}
                 monitor_process_identifier() =
                     pid() | registered_process_identifier()
                 monitor_port_identifier() = port() | registered_name()

              Sends a monitor request of type Type to the  entity  identified  by  Item.  If  the
              monitored  entity  does  not  exist  or  it  changes monitored state, the caller of
              monitor/2 is notified by a message on the following format:

              {Tag, MonitorRef, Type, Object, Info}

          Note:
              The monitor request is an asynchronous signal. That is, it takes  time  before  the
              signal reaches its destination.

              Type can be one of the following atoms: process, port or time_offset.

              A  process  or  port  monitor is triggered only once, after that it is removed from
              both monitoring process and the monitored  entity.  Monitors  are  fired  when  the
              monitored  process or port terminates, does not exist at the moment of creation, or
              if the connection to it is lost. If the connection to it is lost, we do not know if
              it still exists. The monitoring is also turned off when demonitor/1 is called.

              A  process  or  port monitor by name resolves the RegisteredName to pid() or port()
              only once at the moment  of  monitor  instantiation,  later  changes  to  the  name
              registration will not affect the existing monitor.

              When  a process or port monitor is triggered, a 'DOWN' message is sent that has the
              following pattern:

              {'DOWN', MonitorRef, Type, Object, Info}

              In the monitor message MonitorRef and Type are the same as described earlier, and:

                Object:
                  The monitored entity, which  triggered  the  event.  When  monitoring  a  local
                  process  or  port,  Object  will be equal to the pid() or port() that was being
                  monitored. When monitoring process or port by name,  Object  will  have  format
                  {RegisteredName,  Node}  where  RegisteredName  is the name which has been used
                  with monitor/2 call and Node is local or remote node name (for ports  monitored
                  by name, Node is always local node name).

                Info:
                  Either the exit reason of the process, noproc (process or port did not exist at
                  the time of monitor creation), or noconnection (no connection to the node where
                  the monitored process resides).

                Monitoring a process:
                  Creates  monitor  between the current process and another process identified by
                  Item, which can be a pid() (local or remote), an atom RegisteredName or a tuple
                  {RegisteredName, Node} for a registered process, located elsewhere.

            Note:
                Before  ERTS  10.0 (OTP 21.0), monitoring a process could fail with badarg if the
                monitored  process  resided  on  a  primitive  node  (such  as  erl_interface  or
                jinterface), where remote process monitoring is not implemented.

                Now,  such  a  call to monitor will instead succeed and a monitor is created. But
                the monitor will only supervise the connection. That is, a {'DOWN',  _,  process,
                _,  noconnection} is the only message that may be received, as the primitive node
                have no way of reporting the status of the monitored process.

                Monitoring a port:
                  Creates monitor between the current process and  a  port  identified  by  Item,
                  which  can  be  a  port()  (only  local),  an  atom  RegisteredName  or a tuple
                  {RegisteredName, Node} for a registered port, located on this node. Note,  that
                  attempt to monitor a remote port will result in badarg.

                Monitoring a time_offset:
                  Monitors changes in time offset between Erlang monotonic time and Erlang system
                  time. One valid Item exists in combination with the  time_offset  Type,  namely
                  the  atom  clock_service.  Notice  that  the  atom  clock_service  is  not  the
                  registered name of a process. In this case it serves as an  identifier  of  the
                  runtime system internal clock service at current runtime system instance.

                  The  monitor  is  triggered when the time offset is changed. This either if the
                  time offset value is changed, or if the offset is changed from  preliminary  to
                  final  during finalization of the time offset when the single time warp mode is
                  used. When a change from preliminary to final time offset is made, the  monitor
                  is  triggered  once  regardless of whether the time offset value was changed or
                  not.

                  If the runtime system is in multi time warp mode, the time  offset  is  changed
                  when  the  runtime  system  detects  that  the  OS system time has changed. The
                  runtime system does, however, not detect this immediately  when  it  occurs.  A
                  task  checking  the time offset is scheduled to execute at least once a minute,
                  so under normal operation this is to be detected within a  minute,  but  during
                  heavy load it can take longer time.

                  The  monitor is not automatically removed after it has been triggered. That is,
                  repeated changes of the time offset trigger the monitor repeatedly.

                  When the monitor is triggered a 'CHANGE' message  is  sent  to  the  monitoring
                  process. A 'CHANGE' message has the following pattern:

                {'CHANGE', MonitorRef, Type, Item, NewTimeOffset}

                  where  MonitorRef,  Type,  and  Item  are  the  same  as  described  above, and
                  NewTimeOffset is the new time offset.

                  When the 'CHANGE' message has been received you are guaranteed not to  retrieve
                  the  old  time  offset  when  calling erlang:time_offset(). Notice that you can
                  observe the change of the time offset when calling erlang:time_offset()  before
                  you get the 'CHANGE' message.

              Making several calls to monitor/2 for the same Item and/or Type is not an error; it
              results in as many independent monitoring instances.

              The monitor functionality is expected to be extended.  That  is,  other  Types  and
              Items are expected to be supported in a future release.

          Note:
              If  or  when monitor/2 is extended, other possible values for Tag, Object, and Info
              in the monitor message will be introduced.

       monitor_node(Node, Flag) -> true

              Types:

                 Node = node()
                 Flag = boolean()

              Monitor the status of the node Node. If Flag is true, monitoring is turned  on.  If
              Flag is false, monitoring is turned off.

              Making several calls to monitor_node(Node, true) for the same Node is not an error;
              it results in as many independent monitoring instances.

              If Node fails or does not exist, the message {nodedown, Node} is delivered  to  the
              process.  If  a  process  has  made  two calls to monitor_node(Node, true) and Node
              terminates, two nodedown messages are delivered to the  process.  If  there  is  no
              connection  to  Node,  an  attempt is made to create one. If this fails, a nodedown
              message is delivered.

              Nodes connected through hidden connections can be monitored as any other nodes.

              Failure: badarg if the local node is not alive.

       erlang:monitor_node(Node, Flag, Options) -> true

              Types:

                 Node = node()
                 Flag = boolean()
                 Options = [Option]
                 Option = allow_passive_connect

              Behaves as monitor_node/2 except that it allows an extra option  to  be  specified,
              namely allow_passive_connect. This option allows the BIF to wait the normal network
              connection time-out for the monitored node to connect itself, even if it cannot  be
              actively  connected  from  this node (that is, it is blocked). The state where this
              can be useful can only be achieved by using  the  Kernel  option  dist_auto_connect
              once. If that option is not used, option allow_passive_connect has no effect.

          Note:
              Option   allow_passive_connect   is   used  internally  and  is  seldom  needed  in
              applications where the network topology and the Kernel options in effect are  known
              in advance.

              Failure: badarg if the local node is not alive or the option list is malformed.

       erlang:monotonic_time() -> integer()

              Returns  the  current  Erlang  monotonic  time  in  native  time  unit.  This  is a
              monotonically increasing time since some unspecified point in time.

          Note:
              This is a   monotonically  increasing  time,  but  not  a   strictly  monotonically
              increasing  time. That is, consecutive calls to erlang:monotonic_time/0 can produce
              the same result.

              Different runtime system instances will use different unspecified points in time as
              base  for  their  Erlang  monotonic  clocks.  That  is,  it  is pointless comparing
              monotonic times from different runtime system instances. Different  runtime  system
              instances  can also place this unspecified point in time different relative runtime
              system start. It can be placed in the future (time at start is a  negative  value),
              the  past (time at start is a positive value), or the runtime system start (time at
              start is zero). The monotonic time at runtime system  start  can  be  retrieved  by
              calling erlang:system_info(start_time).

       erlang:monotonic_time(Unit) -> integer()

              Types:

                 Unit = time_unit()

              Returns  the  current  Erlang  monotonic  time  converted  into  the Unit passed as
              argument.

              Same as calling  erlang:convert_time_unit(erlang:monotonic_time(),  native,  Unit),
              however optimized for commonly used Units.

       erlang:nif_error(Reason) -> no_return()

              Types:

                 Reason = term()

              Works  exactly  like  error/1,  but  Dialyzer  thinks  that this BIF will return an
              arbitrary term. When used in a stub function for a NIF  to  generate  an  exception
              when the NIF library is not loaded, Dialyzer does not generate false warnings.

       erlang:nif_error(Reason, Args) -> no_return()

              Types:

                 Reason = term()
                 Args = [term()]

              Works  exactly  like  error/2,  but  Dialyzer  thinks  that this BIF will return an
              arbitrary term. When used in a stub function for a NIF  to  generate  an  exception
              when the NIF library is not loaded, Dialyzer does not generate false warnings.

       node() -> Node

              Types:

                 Node = node()

              Returns  the  name  of  the  local node. If the node is not alive, nonode@nohost is
              returned instead.

              Allowed in guard tests.

       node(Arg) -> Node

              Types:

                 Arg = pid() | port() | reference()
                 Node = node()

              Returns the node  where  Arg  originates.  Arg  can  be  a  process  identifier,  a
              reference, or a port. If the local node is not alive, nonode@nohost is returned.

              Allowed in guard tests.

       nodes() -> Nodes

              Types:

                 Nodes = [node()]

              Returns  a  list of all visible nodes in the system, except the local node. Same as
              nodes(visible).

       nodes(Arg) -> Nodes

              Types:

                 Arg = NodeType | [NodeType]
                 NodeType = visible | hidden | connected | this | known
                 Nodes = [node()]

              Returns a list of nodes according to the argument specified. The  returned  result,
              when  the argument is a list, is the list of nodes satisfying the disjunction(s) of
              the list elements.

              NodeTypes:

                visible:
                  Nodes connected to this node through normal connections.

                hidden:
                  Nodes connected to this node through hidden connections.

                connected:
                  All nodes connected to this node.

                this:
                  This node.

                known:
                  Nodes that are known to this node. That is, connected nodes and nodes  referred
                  to  by  process  identifiers,  port identifiers, and references located on this
                  node. The set of known nodes is garbage collected.  Notice  that  this  garbage
                  collection     can     be     delayed.     For     more     information,    see
                  erlang:system_info(delayed_node_table_gc).

              Some  equalities:  [node()]  =  nodes(this),  nodes(connected)  =   nodes([visible,
              hidden]), and nodes() = nodes(visible).

       now() -> Timestamp

              Types:

                 Timestamp = timestamp()
                 timestamp() =
                     {MegaSecs :: integer() >= 0,
                      Secs :: integer() >= 0,
                      MicroSecs :: integer() >= 0}

          Warning:
              This function is deprecated. Do not use it.

              For  more  information,  see  section Time and Time Correction in the User's Guide.
              Specifically,  section   Dos  and  Dont's  describes  what  to   use   instead   of
              erlang:now/0.

              Returns  the  tuple  {MegaSecs,  Secs,  MicroSecs}, which is the elapsed time since
              00:00 GMT, January 1, 1970 (zero hour), if provided by the underlying OS. Otherwise
              some  other point in time is chosen. It is also guaranteed that the following calls
              to this BIF return continuously increasing values. Hence,  the  return  value  from
              erlang:now/0 can be used to generate unique time stamps. If it is called in a tight
              loop on a fast machine, the time of the node can become skewed.

              Can only be used to check the local time of day if the time-zone information of the
              underlying OS is properly configured.

       open_port(PortName, PortSettings) -> port()

              Types:

                 PortName =
                     {spawn, Command :: string() | binary()} |
                     {spawn_driver, Command :: string() | binary()} |
                     {spawn_executable, FileName :: file:name()} |
                     {fd, In :: integer() >= 0, Out :: integer() >= 0}
                 PortSettings = [Opt]
                 Opt =
                     {packet, N :: 1 | 2 | 4} |
                     stream |
                     {line, L :: integer() >= 0} |
                     {cd, Dir :: string() | binary()} |
                     {env,
                      Env ::
                          [{Name :: os:env_var_name(),
                            Val :: os:env_var_value() | false}]} |
                     {args, [string() | binary()]} |
                     {arg0, string() | binary()} |
                     exit_status | use_stdio | nouse_stdio | stderr_to_stdout |
                     in | out | binary | eof |
                     {parallelism, Boolean :: boolean()} |
                     hide

              Returns a port identifier as the result of opening a new Erlang port. A port can be
              seen as an external Erlang process.

              The name of the executable as well as the arguments specifed in cd, env, args,  and
              arg0  are  subject  to  Unicode  filename  translation  if the system is running in
              Unicode filename mode. To avoid translation or to force, for example UTF-8,  supply
              the  executable  and/or arguments as a binary in the correct encoding. For details,
              see the module file(3erl), the function file:native_name_encoding/0 in Kernel,  and
              the Using Unicode in Erlang User's Guide.

          Note:
              The characters in the name (if specified as a list) can only be > 255 if the Erlang
              virtual machine is started in Unicode filename translation mode. Otherwise the name
              of the executable is limited to the ISO Latin-1 character set.

              PortNames:

                {spawn, Command}:
                  Starts  an  external program. Command is the name of the external program to be
                  run. Command runs outside the Erlang work space unless an  Erlang  driver  with
                  the  name  Command is found. If found, that driver is started. A driver runs in
                  the Erlang work space, which means that it is linked with  the  Erlang  runtime
                  system.

                  For  external  programs,  PATH  is searched (or an equivalent method is used to
                  find programs, depending on the OS). This is done  by  invoking  the  shell  on
                  certain platforms. The first space-separated token of the command is considered
                  as the name of the executable (or driver). This (among other things) makes this
                  option  unsuitable  for  running programs with spaces in filenames or directory
                  names. If spaces in executable filenames are  desired,  use  {spawn_executable,
                  Command} instead.

                {spawn_driver, Command}:
                  Works  like  {spawn, Command}, but demands the first (space-separated) token of
                  the command to be the name of a loaded driver. If no driver with that  name  is
                  loaded, a badarg error is raised.

                {spawn_executable, FileName}:
                  Works  like  {spawn, FileName}, but only runs external executables. FileName in
                  its whole is used as the name of  the  executable,  including  any  spaces.  If
                  arguments are to be passed, the PortSettings args and arg0 can be used.

                  The shell is usually not invoked to start the program, it is executed directly.
                  PATH (or equivalent) is not searched. To find a program in PATH to execute, use
                  os:find_executable/1.

                  Only  if  a  shell  script  or  .bat  file is executed, the appropriate command
                  interpreter is invoked implicitly,  but  there  is  still  no  command-argument
                  expansion or implicit PATH search.

                  If  FileName  cannot be run, an error exception is raised, with the POSIX error
                  code as the reason. The error reason can  differ  between  OSs.  Typically  the
                  error  enoent  is  raised  when an attempt is made to run a program that is not
                  found and eacces is raised when the specified file is not executable.

                {fd, In, Out}:
                  Allows an Erlang process to access any currently opened file  descriptors  used
                  by  Erlang. The file descriptor In can be used for standard input, and the file
                  descriptor Out for standard output. It is only used for various servers in  the
                  Erlang OS (shell and user). Hence, its use is limited.

              PortSettings is a list of settings for the port. The valid settings are as follows:

                {packet, N}:
                  Messages  are  preceded  by  their  length,  sent  in  N  bytes,  with the most
                  significant byte first. The valid values for N are 1, 2, and 4.

                stream:
                  Output messages are sent without packet lengths. A user-defined  protocol  must
                  be used between the Erlang process and the external object.

                {line, L}:
                  Messages  are  delivered  on  a per line basis. Each line (delimited by the OS-
                  dependent newline sequence) is delivered in a single message. The message  data
                  format  is  {Flag,  Line},  where  Flag  is  eol or noeol, and Line is the data
                  delivered (without the newline sequence).

                  L specifies the maximum line length  in  bytes.  Lines  longer  than  this  are
                  delivered in more than one message, with Flag set to noeol for all but the last
                  message. If end of file is encountered anywhere else than immediately following
                  a  newline  sequence,  the  last line is also delivered with Flag set to noeol.
                  Otherwise lines are delivered with Flag set to eol.

                  The {packet, N} and {line, L} settings are mutually exclusive.

                {cd, Dir}:
                  Only valid for {spawn, Command} and {spawn_executable, FileName}. The  external
                  program starts using Dir as its working directory. Dir must be a string.

                {env, Env}:
                  Types:
                  Name = os:env_var_name()
                  Val = os:env_var_value() | false
                  Env = [{Name, Val}]

                  Only   valid  for  {spawn,  Command},  and  {spawn_executable,  FileName}.  The
                  environment  of  the  started  process  is  extended  using   the   environment
                  specifications in Env.

                  Env  is  to  be  a  list  of  tuples  {Name, Val}, where Name is the name of an
                  environment variable, and Val is the value it is to have in  the  spawned  port
                  process.  Both Name and Val must be strings. The one exception is Val being the
                  atom  false  (in  analogy  with  os:getenv/1,  which  removes  the  environment
                  variable.

                  For information about encoding requirements, see documentation of the types for
                  Name and Val.

                {args, [ string() | binary() ]}:
                  Only valid for {spawn_executable, FileName}  and  specifies  arguments  to  the
                  executable.  Each  argument  is  specified  as  a separate string and (on Unix)
                  eventually ends up as one  element  each  in  the  argument  vector.  On  other
                  platforms, a similar behavior is mimicked.

                  The  arguments  are  not  expanded by the shell before they are supplied to the
                  executable. Most notably this means  that  file  wildcard  expansion  does  not
                  occur.  To  expand  wildcards for the arguments, use filelib:wildcard/1. Notice
                  that even if the program is  a  Unix  shell  script,  meaning  that  the  shell
                  ultimately  is  invoked,  wildcard  expansion does not occur, and the script is
                  provided with the untouched arguments. On Windows, wildcard expansion is always
                  up to the program itself, therefore this is not an issue.

                  The  executable  name  (also  known  as argv[0]) is not to be specified in this
                  list. The proper executable  name  is  automatically  used  as  argv[0],  where
                  applicable.

                  If  you  explicitly want to set the program name in the argument vector, option
                  arg0 can be used.

                {arg0, string() | binary()}:
                  Only valid  for  {spawn_executable,  FileName}  and  explicitly  specifies  the
                  program   name   argument   when  running  an  executable.  This  can  in  some
                  circumstances, on some OSs, be desirable. How the program responds to  this  is
                  highly system-dependent and no specific effect is guaranteed.

                exit_status:
                  Only  valid  for {spawn, Command}, where Command refers to an external program,
                  and for {spawn_executable, FileName}.

                  When the external process connected to the port exits, a message  of  the  form
                  {Port,{exit_status,Status}}  is  sent to the connected process, where Status is
                  the exit status of the external process. If the program  aborts  on  Unix,  the
                  same convention is used as the shells do (that is, 128+signal).

                  If  option eof is specified also, the messages eof and exit_status appear in an
                  unspecified order.

                  If the port program closes its stdout without exiting, option exit_status  does
                  not work.

                use_stdio:
                  Only valid for {spawn, Command} and {spawn_executable, FileName}. It allows the
                  standard input and output (file descriptors 0 and  1)  of  the  spawned  (Unix)
                  process for communication with Erlang.

                nouse_stdio:
                  The  opposite  of use_stdio. It uses file descriptors 3 and 4 for communication
                  with Erlang.

                stderr_to_stdout:
                  Affects ports to external programs. The  executed  program  gets  its  standard
                  error  file  redirected  to  its  standard  output  file.  stderr_to_stdout and
                  nouse_stdio are mutually exclusive.

                overlapped_io:
                  Affects ports to external programs on Windows  only.  The  standard  input  and
                  standard  output  handles  of the port program are, if this option is supplied,
                  opened with flag FILE_FLAG_OVERLAPPED, so that the port program can (and  must)
                  do  overlapped  I/O  on its standard handles. This is not normally the case for
                  simple port programs, but an  option  of  value  for  the  experienced  Windows
                  programmer. On all other platforms, this option is silently discarded.

                in:
                  The port can only be used for input.

                out:
                  The port can only be used for output.

                binary:
                  All I/O from the port is binary data objects as opposed to lists of bytes.

                eof:
                  The  port  is  not  closed  at the end of the file and does not produce an exit
                  signal. Instead, it remains open and a {Port,  eof}  message  is  sent  to  the
                  process holding the port.

                hide:
                  When  running  on  Windows,  suppresses  creation  of a new console window when
                  spawning the port program. (This option has no effect on other platforms.)

                {parallelism, Boolean}:

                  Sets scheduler hint for port parallelism. If set to true, the  virtual  machine
                  schedules  port tasks; when doing so, it improves parallelism in the system. If
                  set to false, the virtual machine tries  to  perform  port  tasks  immediately,
                  improving  latency  at  the  expense  of parallelism. The default can be set at
                  system startup by passing command-line argument +spp to erl(1).

              Default is stream for all port types and use_stdio for spawned ports.

              Failure: if the port cannot be opened, the exit reason is badarg, system_limit,  or
              the  POSIX  error code that most closely describes the error, or einval if no POSIX
              code is appropriate:

                badarg:
                  Bad input arguments to open_port.

                system_limit:
                  All available ports in the Erlang emulator are in use.

                enomem:
                  Not enough memory to create the port.

                eagain:
                  No more available OS processes.

                enametoolong:
                  Too long external command.

                emfile:
                  No more available file descriptors (for the OS process that the Erlang emulator
                  runs in).

                enfile:
                  Full file table (for the entire OS).

                eacces:
                  Command  specified  in  {spawn_executable,  Command}  does  not  point  out  an
                  executable file.

                enoent:
                  FileName specified in  {spawn_executable,  FileName}  does  not  point  out  an
                  existing file.

              During  use  of  a  port  opened  using  {spawn,  Name},  {spawn_driver,  Name}, or
              {spawn_executable, Name}, errors arising when sending messages to it  are  reported
              to  the owning process using signals of the form {'EXIT', Port, PosixCode}. For the
              possible values of PosixCode, see file(3erl).

              The maximum number of ports that can be open at the same time can be configured  by
              passing command-line flag +Q to erl(1).

       erlang:phash(Term, Range) -> Hash

              Types:

                 Term = term()
                 Range = Hash = integer() >= 1
                   Range = 1..2^32, Hash = 1..Range

              Portable hash function that gives the same hash for the same Erlang term regardless
              of machine architecture and ERTS version (the BIF was introduced in ERTS  4.9.1.1).
              The  function  returns a hash value for Term within the range 1..Range. The maximum
              value for Range is 2^32.

       erlang:phash2(Term) -> Hash

       erlang:phash2(Term, Range) -> Hash

              Types:

                 Term = term()
                 Range = integer() >= 1
                   1..2^32
                 Hash = integer() >= 0
                   0..Range-1

              Portable hash function that gives the same hash for the same Erlang term regardless
              of  machine architecture and ERTS version (the BIF was introduced in ERTS 5.2). The
              function returns a hash value for Term within the  range  0..Range-1.  The  maximum
              value  for  Range  is  2^32.  When  without  argument  Range,  a value in the range
              0..2^27-1 is returned.

              This BIF is always to be used for hashing  terms.  It  distributes  small  integers
              better than phash/2, and it is faster for bignums and binaries.

              Notice  that  the range 0..Range-1 is different from the range of phash/2, which is
              1..Range.

       pid_to_list(Pid) -> string()

              Types:

                 Pid = pid()

              Returns a string corresponding to the text representation of Pid.

       erlang:port_call(Port, Operation, Data) -> term()

              Types:

                 Port = port() | atom()
                 Operation = integer()
                 Data = term()

              Performs a synchronous call to a port. The meaning of Operation and Data depends on
              the port, that is, on the port driver. Not all port drivers support this feature.

              Port is a port identifier, referring to a driver.

              Operation is an integer, which is passed on to the driver.

              Data  is  any Erlang term. This data is converted to binary term format and sent to
              the port.

              Returns a term from the driver. The meaning of the returned data  also  depends  on
              the port driver.

              Failures:

                badarg:
                   If  Port  is  not  an identifier of an open port, or the registered name of an
                  open port. If the calling process was previously linked  to  the  closed  port,
                  identified by Port, the exit signal from the port is guaranteed to be delivered
                  before this badarg exception occurs.

                badarg:
                   If Operation does not fit in a 32-bit integer.

                badarg:
                   If the port driver does not support synchronous control operations.

                badarg:
                  If the port driver so decides for any reason  (probably  something  wrong  with
                  Operation or Data).

            Warning:
                Do  not  call  port_call  with  an  unknown  Port  identifier  and  expect badarg
                exception. Any undefined behavior is possible (including node crash) depending on
                how the port driver interprets the supplied arguments.

       port_close(Port) -> true

              Types:

                 Port = port() | atom()

              Closes  an  open  port.  Roughly  the same as Port ! {self(), close} except for the
              error behavior (see below), being synchronous, and that the  port  does  not  reply
              with  {Port,  closed}. Any process can close a port with port_close/1, not only the
              port owner (the connected process). If the calling process is linked  to  the  port
              identified  by  Port,  the  exit signal from the port is guaranteed to be delivered
              before port_close/1 returns.

              For comparison: Port ! {self(), close} only fails with  badarg  if  Port  does  not
              refer to a port or a process. If Port is a closed port, nothing happens. If Port is
              an open port and the calling process is the  port  owner,  the  port  replies  with
              {Port,  closed}  when  all buffers have been flushed and the port really closes. If
              the calling process is not the port owner, the port owner fails with badsig.

              Notice that any process can close a port using Port ! {PortOwner, close} as  if  it
              itself was the port owner, but the reply always goes to the port owner.

              As  from  Erlang/OTP  R16,  Port ! {PortOwner, close} is truly asynchronous. Notice
              that this operation has always been documented as an asynchronous operation,  while
              the  underlying  implementation has been synchronous. port_close/1 is however still
              fully synchronous because of its error behavior.

              Failure: badarg if Port is not an identifier of an open  port,  or  the  registered
              name  of  an  open port. If the calling process was previously linked to the closed
              port, identified by Port, the exit  signal  from  the  port  is  guaranteed  to  be
              delivered before this badarg exception occurs.

       port_command(Port, Data) -> true

              Types:

                 Port = port() | atom()
                 Data = iodata()

              Sends  data  to  a port. Same as Port ! {PortOwner, {command, Data}} except for the
              error behavior and being synchronous (see below). Any process can send  data  to  a
              port with port_command/2, not only the port owner (the connected process).

              For  comparison: Port ! {PortOwner, {command, Data}} only fails with badarg if Port
              does not refer to a port or a process. If Port is a closed port, the  data  message
              disappears without a sound. If Port is open and the calling process is not the port
              owner, the port owner fails with badsig. The port owner fails with badsig  also  if
              Data is an invalid I/O list.

              Notice  that  any  process  can  send  to a port using Port ! {PortOwner, {command,
              Data}} as if it itself was the port owner.

              If the port is busy, the calling process is suspended until the port  is  not  busy
              any more.

              As  from Erlang/OTP R16, Port ! {PortOwner, {command, Data}} is truly asynchronous.
              Notice that this operation has always been documented as an asynchronous operation,
              while the underlying implementation has been synchronous. port_command/2 is however
              still fully synchronous because of its error behavior.

              Failures:

                badarg:
                  If Port is not an identifier of an open port, or the registered name of an open
                  port.  If  the  calling  process  was  previously  linked  to  the closed port,
                  identified by Port, the exit signal from the port is guaranteed to be delivered
                  before this badarg exception occurs.

                badarg:
                  If Data is an invalid I/O list.

          Warning:
              Do  not send data to an unknown port. Any undefined behavior is possible (including
              node crash) depending on how the port driver interprets the data.

       port_command(Port, Data, OptionList) -> boolean()

              Types:

                 Port = port() | atom()
                 Data = iodata()
                 Option = force | nosuspend
                 OptionList = [Option]

              Sends data to a port. port_command(Port, Data, []) equals port_command(Port, Data).

              If the port command is aborted, false is returned, otherwise true.

              If the port is busy, the calling process is suspended until the port  is  not  busy
              anymore.

              Options:

                force:
                  The  calling  process  is  not  suspended if the port is busy, instead the port
                  command is forced through. The call fails with a notsup exception if the driver
                  of  the  port  does  not  support  this.  For more information, see driver flag
                  ![CDATA[ERL_DRV_FLAG_SOFT_BUSY]].

                nosuspend:
                  The calling process is not suspended if the port  is  busy,  instead  the  port
                  command is aborted and false is returned.

          Note:
              More options can be added in a future release.

              Failures:

                badarg:
                   If  Port  is  not  an identifier of an open port, or the registered name of an
                  open port. If the calling process was previously linked  to  the  closed  port,
                  identified by Port, the exit signal from the port is guaranteed to be delivered
                  before this badarg exception occurs.

                badarg:
                   If Data is an invalid I/O list.

                badarg:
                   If OptionList is an invalid option list.

                notsup:
                   If option force has been passed, but the driver of the  port  does  not  allow
                  forcing through a busy port.

          Warning:
              Do  not send data to an unknown port. Any undefined behavior is possible (including
              node crash) depending on how the port driver interprets the data.

       port_connect(Port, Pid) -> true

              Types:

                 Port = port() | atom()
                 Pid = pid()

              Sets the port owner (the connected port) to Pid. Roughly the same as Port ! {Owner,
              {connect, Pid}} except for the following:

                * The error behavior differs, see below.

                * The port does not reply with {Port,connected}.

                * port_connect/1 is synchronous, see below.

                * The new port owner gets linked to the port.

              The  old  port owner stays linked to the port and must call unlink(Port) if this is
              not  desired.  Any  process  can  set  the  port  owner  to  be  any  process  with
              port_connect/2.

              For comparison: Port ! {self(), {connect, Pid}} only fails with badarg if Port does
              not refer to a port or a process. If Port is a closed  port,  nothing  happens.  If
              Port  is  an  open port and the calling process is the port owner, the port replies
              with {Port, connected} to the old port owner. Notice that the  old  port  owner  is
              still  linked  to  the  port, while the new is not. If Port is an open port and the
              calling process is not the port owner, the port owner fails with badsig.  The  port
              owner fails with badsig also if Pid is not an existing local process identifier.

              Notice  that  any process can set the port owner using Port ! {PortOwner, {connect,
              Pid}} as if it itself was the port owner, but the reply always  goes  to  the  port
              owner.

              As  from  Erlang/OTP R16, Port ! {PortOwner, {connect, Pid}} is truly asynchronous.
              Notice that this operation has always been documented as an asynchronous operation,
              while the underlying implementation has been synchronous. port_connect/2 is however
              still fully synchronous because of its error behavior.

              Failures:

                badarg:
                   If Port is not an identifier of an open port, or the  registered  name  of  an
                  open  port.  If  the  calling process was previously linked to the closed port,
                  identified by Port, the exit signal from the port is guaranteed to be delivered
                  before this badarg exception occurs.

                badarg:
                  If the process identified by Pid is not an existing local process.

       port_control(Port, Operation, Data) -> iodata() | binary()

              Types:

                 Port = port() | atom()
                 Operation = integer()
                 Data = iodata()

              Performs  a  synchronous  control operation on a port. The meaning of Operation and
              Data depends on the port, that is, on the port driver. Not all port drivers support
              this control feature.

              Returns  a list of integers in the range 0..255, or a binary, depending on the port
              driver. The meaning of the returned data also depends on the port driver.

              Failures:

                badarg:
                   If Port is not an open port or the registered name of an open port.

                badarg:
                   If Operation cannot fit in a 32-bit integer.

                badarg:
                   If the port driver does not support synchronous control operations.

                badarg:
                   If the port driver so decides for any reason (probably  something  wrong  with
                  Operation or Data).

            Warning:
                Do  not  call  port_control/3  with  an unknown Port identifier and expect badarg
                exception. Any undefined behavior is possible (including node crash) depending on
                how the port driver interprets the supplied arguments.

       erlang:port_info(Port) -> Result

              Types:

                 Port = port() | atom()
                 ResultItem =
                     {registered_name, RegisteredName :: atom()} |
                     {id, Index :: integer() >= 0} |
                     {connected, Pid :: pid()} |
                     {links, Pids :: [pid()]} |
                     {name, String :: string()} |
                     {input, Bytes :: integer() >= 0} |
                     {output, Bytes :: integer() >= 0} |
                     {os_pid, OsPid :: integer() >= 0 | undefined}
                 Result = [ResultItem] | undefined

              Returns  a  list containing tuples with information about Port, or undefined if the
              port is not open. The order of the tuples is undefined, and all the tuples are  not
              mandatory.  If  the port is closed and the calling process was previously linked to
              the port, the exit signal from the  port  is  guaranteed  to  be  delivered  before
              port_info/1 returns undefined.

              The result contains information about the following Items:

                * registered_name (if the port has a registered name)

                * id

                * connected

                * links

                * name

                * input

                * output

              For more information about the different Items, see port_info/2.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: connected) ->
                           {connected, Pid} | undefined

              Types:

                 Port = port() | atom()
                 Pid = pid()

              Pid is the process identifier of the process connected to the port.

              If  the  port identified by Port is not open, undefined is returned. If the port is
              closed and the calling process was previously linked to the port, the  exit  signal
              from the port is guaranteed to be delivered before port_info/2 returns undefined.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: id) -> {id, Index} | undefined

              Types:

                 Port = port() | atom()
                 Index = integer() >= 0

              Index is the internal index of the port. This index can be used to separate ports.

              If  the  port identified by Port is not open, undefined is returned. If the port is
              closed and the calling process was previously linked to the port, the  exit  signal
              from the port is guaranteed to be delivered before port_info/2 returns undefined.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: input) ->
                           {input, Bytes} | undefined

              Types:

                 Port = port() | atom()
                 Bytes = integer() >= 0

              Bytes is the total number of bytes read from the port.

              If  the  port identified by Port is not open, undefined is returned. If the port is
              closed and the calling process was previously linked to the port, the  exit  signal
              from the port is guaranteed to be delivered before port_info/2 returns undefined.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: links) -> {links, Pids} | undefined

              Types:

                 Port = port() | atom()
                 Pids = [pid()]

              Pids  is a list of the process identifiers of the processes that the port is linked
              to.

              If the port identified by Port is not open, undefined is returned. If the  port  is
              closed  and  the calling process was previously linked to the port, the exit signal
              from the port is guaranteed to be delivered before port_info/2 returns undefined.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: locking) ->
                           {locking, Locking} | undefined

              Types:

                 Port = port() | atom()
                 Locking = false | port_level | driver_level

              Locking is one of the following:

                * port_level (port-specific locking)

                * driver_level (driver-specific locking)

              Notice that these results are highly implementation-specific and can  change  in  a
              future release.

              If  the  port identified by Port is not open, undefined is returned. If the port is
              closed and the calling process was previously linked to the port, the  exit  signal
              from the port is guaranteed to be delivered before port_info/2 returns undefined.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: memory) ->
                           {memory, Bytes} | undefined

              Types:

                 Port = port() | atom()
                 Bytes = integer() >= 0

              Bytes  is  the total number of bytes allocated for this port by the runtime system.
              The port itself can have allocated memory that is not included in Bytes.

              If the port identified by Port is not open, undefined is returned. If the  port  is
              closed  and  the calling process was previously linked to the port, the exit signal
              from the port is guaranteed to be delivered before port_info/2 returns undefined.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: monitors) ->
                           {monitors, Monitors} | undefined

              Types:

                 Port = port() | atom()
                 Monitors = [{process, pid()}]

              Monitors represent processes monitored by this port.

              If the port identified by Port is not open, undefined is returned. If the  port  is
              closed  and  the calling process was previously linked to the port, the exit signal
              from the port is guaranteed to be delivered before port_info/2 returns undefined.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: monitored_by) ->
                           {monitored_by, MonitoredBy} | undefined

              Types:

                 Port = port() | atom()
                 MonitoredBy = [pid()]

              Returns list of pids that are monitoring given port at the moment.

              If the port identified by Port is not open, undefined is returned. If the  port  is
              closed  and  the calling process was previously linked to the port, the exit signal
              from the port is guaranteed to be delivered before port_info/2 returns undefined.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: name) -> {name, Name} | undefined

              Types:

                 Port = port() | atom()
                 Name = string()

              Name is the command name set by open_port/2.

              If the port identified by Port is not open, undefined is returned. If the  port  is
              closed  and  the calling process was previously linked to the port, the exit signal
              from the port is guaranteed to be delivered before port_info/2 returns undefined.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: os_pid) ->
                           {os_pid, OsPid} | undefined

              Types:

                 Port = port() | atom()
                 OsPid = integer() >= 0 | undefined

              OsPid is the process identifier (or equivalent)  of  an  OS  process  created  with
              open_port({spawn  |  spawn_executable,  Command},  Options). If the port is not the
              result of spawning an OS process, the value is undefined.

              If the port identified by Port is not open, undefined is returned. If the  port  is
              closed  and  the calling process was previously linked to the port, the exit signal
              from the port is guaranteed to be delivered before port_info/2 returns undefined.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: output) ->
                           {output, Bytes} | undefined

              Types:

                 Port = port() | atom()
                 Bytes = integer() >= 0

              Bytes is the total number of bytes written to the port from Erlang processes  using
              port_command/2, port_command/3, or Port ! {Owner, {command, Data}.

              If  the  port identified by Port is not open, undefined is returned. If the port is
              closed and the calling process was previously linked to the port, the  exit  signal
              from the port is guaranteed to be delivered before port_info/2 returns undefined.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: parallelism) ->
                           {parallelism, Boolean} | undefined

              Types:

                 Port = port() | atom()
                 Boolean = boolean()

              Boolean  corresponds  to  the  port  parallelism  hint  used by this port. For more
              information, see option parallelism of open_port/2.

       erlang:port_info(Port, Item :: queue_size) ->
                           {queue_size, Bytes} | undefined

              Types:

                 Port = port() | atom()
                 Bytes = integer() >= 0

              Bytes is the total number of bytes queued by the port using the ERTS  driver  queue
              implementation.

              If  the  port identified by Port is not open, undefined is returned. If the port is
              closed and the calling process was previously linked to the port, the  exit  signal
              from the port is guaranteed to be delivered before port_info/2 returns undefined.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: registered_name) ->
                           {registered_name, RegisteredName} |
                           [] | undefined

              Types:

                 Port = port() | atom()
                 RegisteredName = atom()

              RegisteredName  is  the  registered name of the port. If the port has no registered
              name, [] is returned.

              If the port identified by Port is not open, undefined is returned. If the  port  is
              closed  and  the calling process was previously linked to the port, the exit signal
              from the port is guaranteed to be delivered before port_info/2 returns undefined.

              Failure: badarg if Port is not a local port identifier, or an atom.

       port_to_list(Port) -> string()

              Types:

                 Port = port()

              Returns a string corresponding to the text representation of  the  port  identifier
              Port.

       erlang:ports() -> [port()]

              Returns  a  list of port identifiers corresponding to all the ports existing on the
              local node.

              Notice that an exiting port exists, but is not open.

       pre_loaded() -> [module()]

              Returns a list of Erlang modules that are preloaded in the system. As  all  loading
              of  code  is  done  through  the file system, the file system must have been loaded
              previously. Hence, at least the module init must be preloaded.

       erlang:process_display(Pid, Type) -> true

              Types:

                 Pid = pid()
                 Type = backtrace

              Writes information about the local process Pid on standard error. The only  allowed
              value  for  the atom Type is backtrace, which shows the contents of the call stack,
              including information about the call  chain,  with  the  current  function  printed
              first. The format of the output is not further defined.

       process_flag(Flag :: trap_exit, Boolean) -> OldBoolean

              Types:

                 Boolean = OldBoolean = boolean()

              When  trap_exit is set to true, exit signals arriving to a process are converted to
              {'EXIT', From, Reason} messages, which can be received  as  ordinary  messages.  If
              trap_exit  is  set  to false, the process exits if it receives an exit signal other
              than normal and the exit signal is propagated to its linked processes.  Application
              processes are normally not to trap exits.

              Returns the old value of the flag.

              See also exit/2.

       process_flag(Flag :: error_handler, Module) -> OldModule

              Types:

                 Module = OldModule = atom()

              Used  by  a  process to redefine the error handler for undefined function calls and
              undefined registered processes. Inexperienced users are not to use  this  flag,  as
              code auto-loading depends on the correct operation of the error handling module.

              Returns the old value of the flag.

       process_flag(Flag :: min_heap_size, MinHeapSize) -> OldMinHeapSize

              Types:

                 MinHeapSize = OldMinHeapSize = integer() >= 0

              Changes the minimum heap size for the calling process.

              Returns the old value of the flag.

       process_flag(Flag :: min_bin_vheap_size, MinBinVHeapSize) ->
                       OldMinBinVHeapSize

              Types:

                 MinBinVHeapSize = OldMinBinVHeapSize = integer() >= 0

              Changes the minimum binary virtual heap size for the calling process.

              Returns the old value of the flag.

       process_flag(Flag :: max_heap_size, MaxHeapSize) -> OldMaxHeapSize

              Types:

                 MaxHeapSize = OldMaxHeapSize = max_heap_size()
                 max_heap_size() =
                     integer() >= 0 |
                     #{size => integer() >= 0,
                       kill => boolean(),
                       error_logger => boolean()}

              This  flag sets the maximum heap size for the calling process. If MaxHeapSize is an
              integer, the system default values for kill and error_logger are used.

                size:
                  The maximum size in words of the process. If set to zero, the heap  size  limit
                  is  disabled.  badarg  is be thrown if the value is smaller than min_heap_size.
                  The size check is only done when a garbage collection is triggered.

                  size is the entire heap of the process when garbage  collection  is  triggered.
                  This includes all generational heaps, the process stack, any  messages that are
                  considered to be part of the heap,  and  any  extra  memory  that  the  garbage
                  collector needs during collection.

                  size   is   the   same  as  can  be  retrieved  using  erlang:process_info(Pid,
                  total_heap_size),  or  by  adding  heap_block_size,   old_heap_block_size   and
                  mbuf_size from erlang:process_info(Pid, garbage_collection_info).

                kill:
                  When  set  to  true,  the  runtime system sends an untrappable exit signal with
                  reason kill to the process if the maximum heap size  is  reached.  The  garbage
                  collection  that triggered the kill is not completed, instead the process exits
                  as soon as possible. When set to false, no exit signal is sent to the  process,
                  instead it continues executing.

                  If kill is not defined in the map, the system default will be used. The default
                  system default is true. It can be changed by either option +hmaxk in erl(1), or
                  erlang:system_flag(max_heap_size, MaxHeapSize).

                error_logger:
                  When set to true, the runtime system logs an error event via logger, containing
                  details about the process when the maximum heap size is reached. One log  event
                  is sent each time the limit is reached.

                  If  error_logger  is  not  defined  in the map, the system default is used. The
                  default system default is true. It can be changed by either the option  +hmaxel
                  int erl(1), or erlang:system_flag(max_heap_size, MaxHeapSize).

              The  heap  size  of  a  process  is quite hard to predict, especially the amount of
              memory that is used during the garbage collection. When  contemplating  using  this
              option,  it is recommended to first run it in production with kill set to false and
              inspect the log events to see what the normal peak sizes of the  processes  in  the
              system is and then tune the value accordingly.

       process_flag(Flag :: message_queue_data, MQD) -> OldMQD

              Types:

                 MQD = OldMQD = message_queue_data()
                 message_queue_data() = off_heap | on_heap

              This flag determines how messages in the message queue are stored, as follows:

                off_heap:
                  All  messages  in the message queue will be stored outside of the process heap.
                  This implies that no messages in the message queue will be part  of  a  garbage
                  collection of the process.

                on_heap:
                  All  messages  in the message queue will eventually be placed on heap. They can
                  however temporarily be stored off heap. This is how messages always  have  been
                  stored up until ERTS 8.0.

              The  default message_queue_data process flag is determined by command-line argument
              +hmqd in erl(1).

              If the process potentially can get many messages in its queue, you are  advised  to
              set  the  flag  to  off_heap.  This because a garbage collection with many messages
              placed on the heap can become extremely expensive and the process can consume large
              amounts  of  memory. Performance of the actual message passing is however generally
              better when not using flag off_heap.

              When changing this flag messages will be moved. This work has  been  initiated  but
              not completed when this function call returns.

              Returns the old value of the flag.

       process_flag(Flag :: priority, Level) -> OldLevel

              Types:

                 Level = OldLevel = priority_level()
                 priority_level() = low | normal | high | max

              Sets  the  process  priority.  Level  is  an atom. Four priority levels exist: low,
              normal, high, and max. Default is normal.

          Note:
              Priority level max is reserved for internal use in the Erlang runtime  system,  and
              is not to be used by others.

              Internally  in  each  priority  level,  processes  are  scheduled  in a round robin
              fashion.

              Execution of processes on priority normal and low  are  interleaved.  Processes  on
              priority  low are selected for execution less frequently than processes on priority
              normal.

              When runnable processes on priority high exist, no processes  on  priority  low  or
              normal  are  selected for execution. Notice however that this does not mean that no
              processes on priority low or normal can run when processes are running on  priority
              high.  When  using  multiple  schedulers, more processes can be running in parallel
              than processes on priority high. That is, a low and a  high  priority  process  can
              execute at the same time.

              When  runnable  processes  on  priority  max  exist,  no processes on priority low,
              normal, or high are selected for execution. As with  priority  high,  processes  on
              lower priorities can execute in parallel with processes on priority max.

              Scheduling  is pre-emptive. Regardless of priority, a process is pre-empted when it
              has consumed more than a certain number of reductions since the last  time  it  was
              selected for execution.

          Note:
              Do  not  depend  on  the scheduling to remain exactly as it is today. Scheduling is
              likely to be changed in a future release to use available processor cores better.

              There is no automatic mechanism for avoiding priority inversion, such  as  priority
              inheritance or priority ceilings. When using priorities, take this into account and
              handle such scenarios by yourself.

              Making calls from a high priority process into code that you has  no  control  over
              can cause the high priority process to wait for a process with lower priority. That
              is, effectively decreasing the priority of the high  priority  process  during  the
              call.  Even  if  this is not the case with one version of the code that you have no
              control over, it can be the case in a future version of it. This can, for  example,
              occur  if a high priority process triggers code loading, as the code server runs on
              priority normal.

              Other priorities than normal are normally not needed.  When  other  priorities  are
              used,  use  them with care, especially priority high. A process on priority high is
              only to perform work for short periods. Busy looping for long  periods  in  a  high
              priority  process  causes  most  likely  problems,  as important OTP servers run on
              priority normal.

              Returns the old value of the flag.

       process_flag(Flag :: save_calls, N) -> OldN

              Types:

                 N = OldN = 0..10000

              N must be an integer in the interval 0..10000. If N > 0, call saving is made active
              for  the  process.  This  means  that  information  about  the N most recent global
              function calls, BIF calls, sends, and receives made by the process are saved  in  a
              list,  which can be retrieved with process_info(Pid, last_calls). A global function
              call is one in which the module of the function is  explicitly  mentioned.  Only  a
              fixed amount of information is saved, as follows:

                * A tuple {Module, Function, Arity} for function calls

                * The atoms send, 'receive', and timeout for sends and receives ('receive' when a
                  message is received and timeout when a receive times out)

              If N = 0, call saving is disabled for the process, which is the  default.  Whenever
              the size of the call saving list is set, its contents are reset.

              Returns the old value of the flag.

       process_flag(Flag :: sensitive, Boolean) -> OldBoolean

              Types:

                 Boolean = OldBoolean = boolean()

              Sets  or  clears  flag  sensitive  for the current process. When a process has been
              marked as sensitive by  calling  process_flag(sensitive,  true),  features  in  the
              runtime  system  that  can  be  used for examining the data or inner working of the
              process are silently disabled.

              Features that are disabled include (but are not limited to) the following:

                * Tracing. Trace flags can still be set for the process, but no trace messages of
                  any  kind  are  generated. (If flag sensitive is turned off, trace messages are
                  again generated if any trace flags are set.)

                * Sequential tracing. The sequential trace token is propagated as usual,  but  no
                  sequential trace messages are generated.

              process_info/1,2  cannot  be  used  to  read  out  the message queue or the process
              dictionary (both are returned as empty lists).

              Stack back-traces cannot be displayed for the process.

              In crash dumps, the stack, messages, and the process dictionary are omitted.

              If {save_calls,N} has been set for the process, no function calls are saved to  the
              call  saving  list.  (The call saving list is not cleared. Also, send, receive, and
              time-out events are still added to the list.)

              Returns the old value of the flag.

       process_flag(Pid, Flag, Value) -> OldValue

              Types:

                 Pid = pid()
                 Flag = save_calls
                 Value = OldValue = integer() >= 0

              Sets certain flags for the process Pid,  in  the  same  manner  as  process_flag/2.
              Returns  the  old value of the flag. The valid values for Flag are only a subset of
              those allowed in process_flag/2, namely save_calls.

              Failure: badarg if Pid is not a local process.

       process_info(Pid) -> Info

              Types:

                 Pid = pid()
                 Info = [InfoTuple] | undefined
                 InfoTuple = process_info_result_item()
                 process_info_result_item() =
                     {backtrace, Bin :: binary()} |
                     {binary,
                      BinInfo ::
                          [{integer() >= 0,
                            integer() >= 0,
                            integer() >= 0}]} |
                     {catchlevel, CatchLevel :: integer() >= 0} |
                     {current_function,
                      {Module :: module(), Function :: atom(), Arity :: arity()} |
                      undefined} |
                     {current_location,
                      {Module :: module(),
                       Function :: atom(),
                       Arity :: arity(),
                       Location ::
                           [{file, Filename :: string()} |
                            {line, Line :: integer() >= 1}]}} |
                     {current_stacktrace, Stack :: [stack_item()]} |
                     {dictionary, Dictionary :: [{Key :: term(), Value :: term()}]} |
                     {error_handler, Module :: module()} |
                     {garbage_collection, GCInfo :: [{atom(), integer() >= 0}]} |
                     {garbage_collection_info,
                      GCInfo :: [{atom(), integer() >= 0}]} |
                     {group_leader, GroupLeader :: pid()} |
                     {heap_size, Size :: integer() >= 0} |
                     {initial_call, mfa()} |
                     {links, PidsAndPorts :: [pid() | port()]} |
                     {last_calls, false | (Calls :: [mfa()])} |
                     {memory, Size :: integer() >= 0} |
                     {message_queue_len, MessageQueueLen :: integer() >= 0} |
                     {messages, MessageQueue :: [term()]} |
                     {min_heap_size, MinHeapSize :: integer() >= 0} |
                     {min_bin_vheap_size, MinBinVHeapSize :: integer() >= 0} |
                     {max_heap_size, MaxHeapSize :: max_heap_size()} |
                     {monitored_by,
                      MonitoredBy :: [pid() | port() | nif_resource()]} |
                     {monitors,
                      Monitors ::
                          [{process | port,
                            Pid ::
                                pid() |
                                port() |
                                {RegName :: atom(), Node :: node()}}]} |
                     {message_queue_data, MQD :: message_queue_data()} |
                     {priority, Level :: priority_level()} |
                     {reductions, Number :: integer() >= 0} |
                     {registered_name, [] | (Atom :: atom())} |
                     {sequential_trace_token,
                      [] | (SequentialTraceToken :: term())} |
                     {stack_size, Size :: integer() >= 0} |
                     {status,
                      Status ::
                          exiting | garbage_collecting | waiting | running |
                          runnable | suspended} |
                     {suspending,
                      SuspendeeList ::
                          [{Suspendee :: pid(),
                            ActiveSuspendCount :: integer() >= 0,
                            OutstandingSuspendCount :: integer() >= 0}]} |
                     {total_heap_size, Size :: integer() >= 0} |
                     {trace, InternalTraceFlags :: integer() >= 0} |
                     {trap_exit, Boolean :: boolean()}
                 priority_level() = low | normal | high | max
                 stack_item() =
                     {Module :: module(),
                      Function :: atom(),
                      Arity :: arity() | (Args :: [term()]),
                      Location ::
                          [{file, Filename :: string()} |
                           {line, Line :: integer() >= 1}]}
                 max_heap_size() =
                     integer() >= 0 |
                     #{size => integer() >= 0,
                       kill => boolean(),
                       error_logger => boolean()}
                 message_queue_data() = off_heap | on_heap

              Returns a list containing  InfoTuples  with  miscellaneous  information  about  the
              process identified by Pid, or undefined if the process is not alive.

              The  order of the InfoTuples is undefined and all InfoTuples are not mandatory. The
              InfoTuples part of the result can be changed without prior notice.

              The InfoTuples with the following items are part of the result:

                * current_function

                * initial_call

                * status

                * message_queue_len

                * links

                * dictionary

                * trap_exit

                * error_handler

                * priority

                * group_leader

                * total_heap_size

                * heap_size

                * stack_size

                * reductions

                * garbage_collection

              If the process identified by Pid has a registered name, also an InfoTuple with item
              registered_name is included.

              For information about specific InfoTuples, see process_info/2.

          Warning:
              This   BIF   is   intended   for  debugging  only.  For  all  other  purposes,  use
              process_info/2.

              Failure: badarg if Pid is not a local process.

       process_info(Pid, Item) -> InfoTuple | [] | undefined

       process_info(Pid, ItemList) -> InfoTupleList | [] | undefined

              Types:

                 Pid = pid()
                 ItemList = [Item]
                 Item = process_info_item()
                 InfoTupleList = [InfoTuple]
                 InfoTuple = process_info_result_item()
                 process_info_item() =
                     backtrace | binary | catchlevel | current_function |
                     current_location | current_stacktrace | dictionary |
                     error_handler | garbage_collection | garbage_collection_info |
                     group_leader | heap_size | initial_call | links | last_calls |
                     memory | message_queue_len | messages | min_heap_size |
                     min_bin_vheap_size | monitored_by | monitors |
                     message_queue_data | priority | reductions | registered_name |
                     sequential_trace_token | stack_size | status | suspending |
                     total_heap_size | trace | trap_exit
                 process_info_result_item() =
                     {backtrace, Bin :: binary()} |
                     {binary,
                      BinInfo ::
                          [{integer() >= 0,
                            integer() >= 0,
                            integer() >= 0}]} |
                     {catchlevel, CatchLevel :: integer() >= 0} |
                     {current_function,
                      {Module :: module(), Function :: atom(), Arity :: arity()} |
                      undefined} |
                     {current_location,
                      {Module :: module(),
                       Function :: atom(),
                       Arity :: arity(),
                       Location ::
                           [{file, Filename :: string()} |
                            {line, Line :: integer() >= 1}]}} |
                     {current_stacktrace, Stack :: [stack_item()]} |
                     {dictionary, Dictionary :: [{Key :: term(), Value :: term()}]} |
                     {error_handler, Module :: module()} |
                     {garbage_collection, GCInfo :: [{atom(), integer() >= 0}]} |
                     {garbage_collection_info,
                      GCInfo :: [{atom(), integer() >= 0}]} |
                     {group_leader, GroupLeader :: pid()} |
                     {heap_size, Size :: integer() >= 0} |
                     {initial_call, mfa()} |
                     {links, PidsAndPorts :: [pid() | port()]} |
                     {last_calls, false | (Calls :: [mfa()])} |
                     {memory, Size :: integer() >= 0} |
                     {message_queue_len, MessageQueueLen :: integer() >= 0} |
                     {messages, MessageQueue :: [term()]} |
                     {min_heap_size, MinHeapSize :: integer() >= 0} |
                     {min_bin_vheap_size, MinBinVHeapSize :: integer() >= 0} |
                     {max_heap_size, MaxHeapSize :: max_heap_size()} |
                     {monitored_by,
                      MonitoredBy :: [pid() | port() | nif_resource()]} |
                     {monitors,
                      Monitors ::
                          [{process | port,
                            Pid ::
                                pid() |
                                port() |
                                {RegName :: atom(), Node :: node()}}]} |
                     {message_queue_data, MQD :: message_queue_data()} |
                     {priority, Level :: priority_level()} |
                     {reductions, Number :: integer() >= 0} |
                     {registered_name, [] | (Atom :: atom())} |
                     {sequential_trace_token,
                      [] | (SequentialTraceToken :: term())} |
                     {stack_size, Size :: integer() >= 0} |
                     {status,
                      Status ::
                          exiting | garbage_collecting | waiting | running |
                          runnable | suspended} |
                     {suspending,
                      SuspendeeList ::
                          [{Suspendee :: pid(),
                            ActiveSuspendCount :: integer() >= 0,
                            OutstandingSuspendCount :: integer() >= 0}]} |
                     {total_heap_size, Size :: integer() >= 0} |
                     {trace, InternalTraceFlags :: integer() >= 0} |
                     {trap_exit, Boolean :: boolean()}
                 stack_item() =
                     {Module :: module(),
                      Function :: atom(),
                      Arity :: arity() | (Args :: [term()]),
                      Location ::
                          [{file, Filename :: string()} |
                           {line, Line :: integer() >= 1}]}
                 priority_level() = low | normal | high | max
                 max_heap_size() =
                     integer() >= 0 |
                     #{size => integer() >= 0,
                       kill => boolean(),
                       error_logger => boolean()}
                 message_queue_data() = off_heap | on_heap

              Returns information about the process identified by Pid, as specified  by  Item  or
              ItemList. Returns undefined if the process is not alive.

              If  the  process is alive and a single Item is specified, the returned value is the
              corresponding InfoTuple, unless Item =:= registered_name and  the  process  has  no
              registered  name. In this case, [] is returned. This strange behavior is because of
              historical reasons, and is kept for backward compatibility.

              If  ItemList  is  specified,  the  result  is  InfoTupleList.  The  InfoTuples   in
              InfoTupleList  are  included  with the corresponding Items in the same order as the
              Items were included in ItemList. Valid Items can  be  included  multiple  times  in
              ItemList.

          Note:
              If  registered_name  is  part of ItemList and the process has no name registered, a
              {registered_name, []}, InfoTuple will be included in the  resulting  InfoTupleList.
              This behavior is different when a single Item =:= registered_name is specified, and
              when process_info/1 is used.

              Valid InfoTuples with corresponding Items:

                {backtrace, Bin}:
                  Binary   Bin   contains   the   same   information   as   the    output    from
                  erlang:process_display(Pid,  backtrace).  Use  binary_to_list/1  to  obtain the
                  string of characters from the binary.

                {binary, BinInfo}:
                  BinInfo is a list containing miscellaneous information about  binaries  on  the
                  heap  of  this  process. This InfoTuple can be changed or removed without prior
                  notice. In the current implementation BinInfo is a list of tuples.  The  tuples
                  contain; BinaryId, BinarySize, BinaryRefcCount.

                  The   message   queue   is   on   the   heap  depending  on  the  process  flag
                  message_queue_data.

                {catchlevel, CatchLevel}:
                  CatchLevel is the number of currently active  catches  in  this  process.  This
                  InfoTuple can be changed or removed without prior notice.

                {current_function, {Module, Function, Arity} | undefined}:
                  Module,  Function, Arity is the current function call of the process. The value
                  undefined can be returned if the process is currently executing native compiled
                  code.

                {current_location, {Module, Function, Arity, Location}}:
                  Module,  Function,  Arity is the current function call of the process. Location
                  is a list of two-tuples describing the location in the source code.

                {current_stacktrace, Stack}:
                  Returns the current call stack back-trace  (stacktrace)  of  the  process.  The
                  stack  has the same format as returned by erlang:get_stacktrace/0. The depth of
                  the stacktrace is  truncated  according  to  the  backtrace_depth  system  flag
                  setting.

                {dictionary, Dictionary}:
                  Dictionary is the process dictionary.

                {error_handler, Module}:
                  Module  is the error handler module used by the process (for undefined function
                  calls, for example).

                {garbage_collection, GCInfo}:
                  GCInfo is a list containing miscellaneous information about garbage  collection
                  for this process. The content of GCInfo can be changed without prior notice.

                {garbage_collection_info, GCInfo}:
                  GCInfo  is  a  list containing miscellaneous detailed information about garbage
                  collection for this process. The content of GCInfo can be changed without prior
                  notice.  For  details  about  the  meaning  of each item, see gc_minor_start in
                  erlang:trace/3.

                {group_leader, GroupLeader}:
                  GroupLeader is the group leader for the I/O of the process.

                {heap_size, Size}:
                  Size is the size in words of the youngest heap generation of the process.  This
                  generation   includes   the   process   stack.   This   information  is  highly
                  implementation-dependent, and can change if the implementation changes.

                {initial_call, {Module, Function, Arity}}:
                  Module, Function, Arity is the initial function call with which the process was
                  spawned.

                {links, PidsAndPorts}:
                  PidsAndPorts  is  a  list  of  process  identifiers  and port identifiers, with
                  processes or ports to which the process has a link.

                {last_calls, false|Calls}:
                  The value is  false  if  call  saving  is  not  active  for  the  process  (see
                  process_flag/3).  If  call  saving  is active, a list is returned, in which the
                  last element is the most recent called.

                {memory, Size}:

                  Size is the size in bytes of the process. This includes call stack,  heap,  and
                  internal structures.

                {message_queue_len, MessageQueueLen}:
                  MessageQueueLen is the number of messages currently in the message queue of the
                  process.  This  is  the  length  of  the  list  MessageQueue  returned  as  the
                  information item messages (see below).

                {messages, MessageQueue}:
                  MessageQueue  is a list of the messages to the process, which have not yet been
                  processed.

                {min_heap_size, MinHeapSize}:
                  MinHeapSize is the minimum heap size for the process.

                {min_bin_vheap_size, MinBinVHeapSize}:
                  MinBinVHeapSize is the minimum binary virtual heap size for the process.

                {monitored_by, MonitoredBy}:
                  A list of identifiers for all the processes, ports and NIF resources, that  are
                  monitoring the process.

                {monitors, Monitors}:
                  A  list of monitors (started by monitor/2) that are active for the process. For
                  a local process monitor or a remote process monitor by  a  process  identifier,
                  the list consists of:

                  {process, Pid}:
                    Process is monitored by pid.

                  {process, {RegName, Node}}:
                    Local or remote process is monitored by name.

                  {port, PortId}:
                    Local port is monitored by port id.

                  {port, {RegName, Node}}:
                    Local  port  is monitored by name. Please note, that remote port monitors are
                    not supported, so Node will always be the local node name.

                {message_queue_data, MQD}:
                  Returns the current state of process flag  message_queue_data.  MQD  is  either
                  off_heap   or   on_heap.   For  more  information,  see  the  documentation  of
                  process_flag(message_queue_data, MQD).

                {priority, Level}:
                  Level is the current priority level for the process. For  more  information  on
                  priorities, see process_flag(priority, Level).

                {reductions, Number}:
                  Number is the number of reductions executed by the process.

                {registered_name, Atom}:
                  Atom  is  the  registered  process name. If the process has no registered name,
                  this tuple is not present in the list.

                {sequential_trace_token, [] | SequentialTraceToken}:
                  SequentialTraceToken is the  sequential  trace  token  for  the  process.  This
                  InfoTuple can be changed or removed without prior notice.

                {stack_size, Size}:
                  Size is the stack size, in words, of the process.

                {status, Status}:
                  Status is the status of the process and is one of the following:

                  * exiting

                  * garbage_collecting

                  * waiting (for a message)

                  * running

                  * runnable (ready to run, but another process is running)

                  * suspended    (suspended    on    a    "busy"    port    or    by    the   BIF
                    erlang:suspend_process/1,2)

                {suspending, SuspendeeList}:
                  SuspendeeList    is    a    list     of     {Suspendee,     ActiveSuspendCount,
                  OutstandingSuspendCount}  tuples.  Suspendee  is  the  process  identifier of a
                  process that has been, or is to be, suspended by the process identified by  Pid
                  through the BIF erlang:suspend_process/2 or erlang:suspend_process/1.

                  ActiveSuspendCount  is the number of times Suspendee has been suspended by Pid.
                  OutstandingSuspendCount is the number of not  yet  completed  suspend  requests
                  sent by Pid, that is:

                  * If ActiveSuspendCount =/= 0, Suspendee is currently in the suspended state.

                  * If     OutstandingSuspendCount     =/=     0,    option    asynchronous    of
                    erlang:suspend_process/2 has been used and the suspendee  has  not  yet  been
                    suspended by Pid.

                  Notice  that  ActiveSuspendCount  and OutstandingSuspendCount are not the total
                  suspend count on Suspendee, only the parts contributed by Pid.

                {total_heap_size, Size}:
                  Size is the total size, in words, of all heap fragments of  the  process.  This
                  includes  the  process stack and any unreceived messages that are considered to
                  be part of the heap.

                {trace, InternalTraceFlags}:
                  InternalTraceFlags is an integer representing the internal trace flag for  this
                  process. This InfoTuple can be changed or removed without prior notice.

                {trap_exit, Boolean}:
                  Boolean is true if the process is trapping exits, otherwise false.

              Notice that not all implementations support all these Items.

              Failures:

                badarg:
                  If Pid is not a local process.

                badarg:
                  If Item is an invalid item.

       processes() -> [pid()]

              Returns  a list of process identifiers corresponding to all the processes currently
              existing on the local node.

              Notice  that  an  exiting  process   exists,   but   is   not   alive.   That   is,
              is_process_alive/1 returns false for an exiting process, but its process identifier
              is part of the result returned from processes/0.

              Example:

              > processes().
              [<0.0.0>,<0.2.0>,<0.4.0>,<0.5.0>,<0.7.0>,<0.8.0>]

       purge_module(Module) -> true

              Types:

                 Module = atom()

              Removes old code for Module. Before this BIF is used, check_process_code/2is to  be
              called to check that no processes execute old code in the module.

          Warning:
              This  BIF  is  intended  for the code server (see code(3erl)) and is not to be used
              elsewhere.

          Note:
              As from ERTS 8.0 (Erlang/OTP 19), any lingering processes that  still  execute  the
              old  code is killed by this function. In earlier versions, such incorrect use could
              cause much more fatal failures, like emulator crash.

              Failure: badarg if there is no old code for Module.

       put(Key, Val) -> term()

              Types:

                 Key = Val = term()

              Adds a new Key to the process  dictionary,  associated  with  the  value  Val,  and
              returns undefined. If Key exists, the old value is deleted and replaced by Val, and
              the function returns the old value. Example:

              > X = put(name, walrus), Y = put(name, carpenter),
              Z = get(name),
              {X, Y, Z}.
              {undefined,walrus,carpenter}

          Note:
              The values stored when put is evaluated  within  the  scope  of  a  catch  are  not
              retracted if a throw is evaluated, or if an error occurs.

       erlang:raise(Class, Reason, Stacktrace) -> no_return()

              Types:

                 Class = error | exit | throw
                 Reason = term()
                 Stacktrace = raise_stacktrace()
                 raise_stacktrace() =
                     [{module(), atom(), arity() | [term()]} |
                      {function(), [term()]}] |
                     [{module(), atom(), arity() | [term()], [{atom(), term()}]} |
                      {function(), [term()], [{atom(), term()}]}]

              Stops  the  execution  of  the  calling  process with an exception of the specified
              class, reason, and call stack backtrace (stacktrace).

              Class  is  error,  exit,  or  throw.  So,  if  it  were  not  for  the  stacktrace,
              erlang:raise(Class, Reason, Stacktrace) is equivalent to erlang:Class(Reason).

              Reason  is  any  term. Stacktrace is a list as returned from get_stacktrace(), that
              is, a list of four-tuples {Module, Function, Arity | Args, Location}, where  Module
              and  Function  are  atoms, and the third element is an integer arity or an argument
              list. The stacktrace can also contain {Fun, Args, Location} tuples, where Fun is  a
              local fun and Args is an argument list.

              Element Location at the end is optional. Omitting it is equivalent to specifying an
              empty list.

              The stacktrace is used as the exception stacktrace for the calling process;  it  is
              truncated to the current maximum stacktrace depth.

              As evaluating this function causes the process to terminate, it has no return value
              unless the arguments are invalid, in which case  the  function  returns  the  error
              reason   badarg.   If   you   want   to  be  sure  not  to  return,  you  can  call
              error(erlang:raise(Class, Reason, Stacktrace)) and hope to  distinguish  exceptions
              later.

       erlang:read_timer(TimerRef) -> Result

              Types:

                 TimerRef = reference()
                 Time = integer() >= 0
                 Result = Time | false

              Reads the state of a timer. The same as calling erlang:read_timer(TimerRef, []).

       erlang:read_timer(TimerRef, Options) -> Result | ok

              Types:

                 TimerRef = reference()
                 Async = boolean()
                 Option = {async, Async}
                 Options = [Option]
                 Time = integer() >= 0
                 Result = Time | false

              Reads  the  state  of a timer that has been created by either erlang:start_timer or
              erlang:send_after. TimerRef identifies the timer, and was returned by the BIF  that
              created the timer.

              Options:

                {async, Async}:
                  Asynchronous  request  for  state  information.  Async defaults to false, which
                  causes the operation to be performed synchronously. In this case, the Result is
                  returned  by  erlang:read_timer. When Async is true, erlang:read_timer sends an
                  asynchronous request for the  state  information  to  the  timer  service  that
                  manages  the  timer,  and then returns ok. A message on the format {read_timer,
                  TimerRef, Result} is sent to the caller of erlang:read_timer when the operation
                  has been processed.

              More Options can be added in the future.

              If  Result  is  an  integer,  it represents the time in milliseconds left until the
              timer expires.

              If Result is false, a timer corresponding to TimerRef  could  not  be  found.  This
              because  the  timer  had  expired,  or been canceled, or because TimerRef never has
              corresponded to a timer. Even if the timer  has  expired,  it  does  not  tell  you
              whether or not the time-out message has arrived at its destination yet.

          Note:
              The  timer  service that manages the timer can be co-located with another scheduler
              than the scheduler that the calling process is executing on. If  so,  communication
              with the timer service takes much longer time than if it is located locally. If the
              calling process is in a critical path, and can do other things  while  waiting  for
              the result of this operation, you want to use option {async, true}. If using option
              {async, false}, the calling  process  is  blocked  until  the  operation  has  been
              performed.

              See also erlang:send_after/4, erlang:start_timer/4, and erlang:cancel_timer/2.

       ref_to_list(Ref) -> string()

              Types:

                 Ref = reference()

              Returns a string corresponding to the text representation of Ref.

          Warning:
              This BIF is intended for debugging and is not to be used in application programs.

       register(RegName, PidOrPort) -> true

              Types:

                 RegName = atom()
                 PidOrPort = port() | pid()

              Associates  the  name RegName with a process identifier (pid) or a port identifier.
              RegName, which must be an atom, can be used instead of the pid or  port  identifier
              in send operator (RegName ! Message). Example:

              > register(db, Pid).
              true

              Failures:

                badarg:
                  If PidOrPort is not an existing local process or port.

                badarg:
                  If RegName is already in use.

                badarg:
                  If the process or port is already registered (already has a name).

                badarg:
                  If RegName is the atom undefined.

       registered() -> [RegName]

              Types:

                 RegName = atom()

              Returns a list of names that have been registered using register/2, for example:

              > registered().
              [code_server, file_server, init, user, my_db]

       erlang:resume_process(Suspendee) -> true

              Types:

                 Suspendee = pid()

              Decreases  the  suspend  count on the process identified by Suspendee. Suspendee is
              previously   to   have   been   suspended   through   erlang:suspend_process/2   or
              erlang:suspend_process/1  by  the process calling erlang:resume_process(Suspendee).
              When the suspend count on Suspendee reaches zero, Suspendee is  resumed,  that  is,
              its state is changed from suspended into the state it had before it was suspended.

          Warning:
              This BIF is intended for debugging only.

              Failures:

                badarg:
                   If Suspendee is not a process identifier.

                badarg:
                   If  the  process  calling erlang:resume_process/1 had not previously increased
                  the suspend count on the process identified by Suspendee.

                badarg:
                   If the process identified by Suspendee is not alive.

       round(Number) -> integer()

              Types:

                 Number = number()

              Returns an integer by rounding Number, for example:

              round(5.5).
              6

              Allowed in guard tests.

       self() -> pid()

              Returns the process identifier of the calling process, for example:

              > self().
              <0.26.0>

              Allowed in guard tests.

       erlang:send(Dest, Msg) -> Msg

              Types:

                 Dest = dst()
                 Msg = term()
                 dst() =
                     pid() |
                     port() |
                     (RegName :: atom()) |
                     {RegName :: atom(), Node :: node()}

              Sends a message and returns Msg. This is the same as using the  send operator: Dest
              ! Msg.

              Dest  can  be  a  remote  or  local  process  identifier, a (local) port, a locally
              registered name, or a tuple {RegName, Node} for a registered name at another node.

              The function fails with a badarg run-time error if Dest is an atom name,  but  this
              name  is  not  registered. This is the only case when send fails for an unreachable
              destination Dest (of correct type).

       erlang:send(Dest, Msg, Options) -> Res

              Types:

                 Dest = dst()
                 Msg = term()
                 Options = [nosuspend | noconnect]
                 Res = ok | nosuspend | noconnect
                 dst() =
                     pid() |
                     port() |
                     (RegName :: atom()) |
                     {RegName :: atom(), Node :: node()}

              Either sends a message and returns ok, or does not send  the  message  but  returns
              something  else (see below). Otherwise the same as erlang:send/2. For more detailed
              explanation and warnings, see erlang:send_nosuspend/2,3.

              Options:

                nosuspend:
                  If the sender would have to be suspended to do the send, nosuspend is  returned
                  instead.

                noconnect:
                   If  the  destination  node  would  have  to  be auto-connected to do the send,
                  noconnect is returned instead.

          Warning:
              As with erlang:send_nosuspend/2,3: use with extreme care.

       erlang:send_after(Time, Dest, Msg) -> TimerRef

              Types:

                 Time = integer() >= 0
                 Dest = pid() | atom()
                 Msg = term()
                 TimerRef = reference()

              Starts a timer. The same as calling erlang:send_after(Time, Dest, Msg, []).

       erlang:send_after(Time, Dest, Msg, Options) -> TimerRef

              Types:

                 Time = integer()
                 Dest = pid() | atom()
                 Msg = term()
                 Options = [Option]
                 Abs = boolean()
                 Option = {abs, Abs}
                 TimerRef = reference()

              Starts a timer. When the timer expires, the message Msg  is  sent  to  the  process
              identified  by  Dest.  Apart from the format of the time-out message, this function
              works exactly as erlang:start_timer/4.

       erlang:send_nosuspend(Dest, Msg) -> boolean()

              Types:

                 Dest = dst()
                 Msg = term()
                 dst() =
                     pid() |
                     port() |
                     (RegName :: atom()) |
                     {RegName :: atom(), Node :: node()}

              The same as erlang:send(Dest, Msg, [nosuspend]), but returns true  if  the  message
              was sent and false if the message was not sent because the sender would have had to
              be suspended.

              This function is intended for send operations to an unreliable remote node  without
              ever  blocking  the  sending (Erlang) process. If the connection to the remote node
              (usually not a real Erlang node, but a node written in C or  Java)  is  overloaded,
              this function does not send the message and returns false.

              The  same  occurs  if  Dest  refers  to  a  local  port that is busy. For all other
              destinations (allowed for the ordinary send operator '!'), this function sends  the
              message and returns true.

              This function is only to be used in rare circumstances where a process communicates
              with Erlang nodes that can disappear without any trace, causing the TCP buffers and
              the  drivers  queue  to  be over-full before the node is shut down (because of tick
              time-outs) by net_kernel. The normal reaction to take when this occurs is some kind
              of premature shutdown of the other node.

              Notice  that  ignoring  the  return  value  from  this  function would result in an
              unreliable message passing, which is contradictory to the Erlang programming model.
              The message is not sent if this function returns false.

              In  many  systems,  transient states of overloaded queues are normal. Although this
              function returns false does not mean that the other node is guaranteed to  be  non-
              responsive,  it  could  be  a temporary overload. Also, a return value of true does
              only mean that the message can be sent on the (TCP) channel without  blocking;  the
              message  is  not  guaranteed  to arrive at the remote node. For a disconnected non-
              responsive node, the return value is true (mimics the behavior of operator !).  The
              expected  behavior  and  the  actions  to  take when the function returns false are
              application- and hardware-specific.

          Warning:
              Use with extreme care.

       erlang:send_nosuspend(Dest, Msg, Options) -> boolean()

              Types:

                 Dest = dst()
                 Msg = term()
                 Options = [noconnect]
                 dst() =
                     pid() |
                     port() |
                     (RegName :: atom()) |
                     {RegName :: atom(), Node :: node()}

              The same as erlang:send(Dest, Msg, [nosuspend  |  Options]),  but  with  a  Boolean
              return value.

              This  function behaves like erlang:send_nosuspend/2, but takes a third parameter, a
              list of options. The only option is noconnect,  which  makes  the  function  return
              false  if  the remote node is not currently reachable by the local node. The normal
              behavior is to try to connect to the node, which can stall  the  process  during  a
              short  period.  The use of option noconnect makes it possible to be sure not to get
              the slightest delay when sending to a remote process.  This  is  especially  useful
              when  communicating  with  nodes that expect to always be the connecting part (that
              is, nodes written in C or Java).

              Whenever the function returns false (either when a  suspend  would  occur  or  when
              noconnect  was  specified  and  the node was not already connected), the message is
              guaranteed not to have been sent.

          Warning:
              Use with extreme care.

       erlang:set_cookie(Node, Cookie) -> true

              Types:

                 Node = node()
                 Cookie = atom()

              Sets the magic cookie of Node to the atom Cookie. If Node is the  local  node,  the
              function  also  sets  the  cookie of all other unknown nodes to Cookie (see section
              Distributed Erlang in the Erlang Reference Manual in System Documentation).

              Failure: function_clause if the local node is not alive.

       setelement(Index, Tuple1, Value) -> Tuple2

              Types:

                 Index = integer() >= 1
                   1..tuple_size(Tuple1
                 Tuple1 = Tuple2 = tuple()
                 Value = term()

              Returns a tuple that is a copy of argument Tuple1 with  the  element  specified  by
              integer  argument Index (the first element is the element with index 1) replaced by
              argument Value, for example:

              > setelement(2, {10, green, bottles}, red).
              {10,red,bottles}

       size(Item) -> integer() >= 0

              Types:

                 Item = tuple() | binary()

              Returns the number of elements in a tuple or the number of bytes  in  a  binary  or
              bitstring, for example:

              > size({morni, mulle, bwange}).
              3
              > size(<<11, 22, 33>>).
              3

              For  bitstrings,  the  number of whole bytes is returned. That is, if the number of
              bits in the bitstring is not divisible by 8,  the  resulting  number  of  bytes  is
              rounded down.

              Allowed in guard tests.

              See also tuple_size/1, byte_size/1, and bit_size/1.

       spawn(Fun) -> pid()

              Types:

                 Fun = function()

              Returns  the  process identifier of a new process started by the application of Fun
              to the empty list []. Otherwise works like spawn/3.

       spawn(Node, Fun) -> pid()

              Types:

                 Node = node()
                 Fun = function()

              Returns the process identifier of a new process started by the application  of  Fun
              to  the  empty  list [] on Node. If Node does not exist, a useless pid is returned.
              Otherwise works like spawn/3.

       spawn(Module, Function, Args) -> pid()

              Types:

                 Module = module()
                 Function = atom()
                 Args = [term()]

              Returns the process identifier of a new  process  started  by  the  application  of
              Module:Function to Args.

              error_handler:undefined_function(Module,  Function,  Args)  is evaluated by the new
              process if Module:Function/Arity does not exist  (where  Arity  is  the  length  of
              Args). The error handler can be redefined (see process_flag/2). If error_handler is
              undefined, or the user has redefined the default error_handler and its  replacement
              is undefined, a failure with reason undef occurs.

              Example:

              > spawn(speed, regulator, [high_speed, thin_cut]).
              <0.13.1>

       spawn(Node, Module, Function, Args) -> pid()

              Types:

                 Node = node()
                 Module = module()
                 Function = atom()
                 Args = [term()]

              Returns the process identifier (pid) of a new process started by the application of
              Module:Function to Args on Node. If Node does not exist, a useless pid is returned.
              Otherwise works like spawn/3.

       spawn_link(Fun) -> pid()

              Types:

                 Fun = function()

              Returns  the  process identifier of a new process started by the application of Fun
              to the empty list []. A link is created between the calling  process  and  the  new
              process, atomically. Otherwise works like spawn/3.

       spawn_link(Node, Fun) -> pid()

              Types:

                 Node = node()
                 Fun = function()

              Returns the process identifier (pid) of a new process started by the application of
              Fun to the empty list [] on Node. A link is created between the calling process and
              the  new process, atomically. If Node does not exist, a useless pid is returned and
              an exit signal with reason noconnection is sent to the calling  process.  Otherwise
              works like spawn/3.

       spawn_link(Module, Function, Args) -> pid()

              Types:

                 Module = module()
                 Function = atom()
                 Args = [term()]

              Returns  the  process  identifier  of  a  new process started by the application of
              Module:Function to Args. A link is created between the calling process and the  new
              process, atomically. Otherwise works like spawn/3.

       spawn_link(Node, Module, Function, Args) -> pid()

              Types:

                 Node = node()
                 Module = module()
                 Function = atom()
                 Args = [term()]

              Returns the process identifier (pid) of a new process started by the application of
              Module:Function to Args on Node. A link is created between the calling process  and
              the  new process, atomically. If Node does not exist, a useless pid is returned and
              an exit signal with reason noconnection is sent to the calling  process.  Otherwise
              works like spawn/3.

       spawn_monitor(Fun) -> {pid(), reference()}

              Types:

                 Fun = function()

              Returns  the process identifier of a new process, started by the application of Fun
              to the empty list [], and a reference for a monitor created  to  the  new  process.
              Otherwise works like spawn/3.

       spawn_monitor(Module, Function, Args) -> {pid(), reference()}

              Types:

                 Module = module()
                 Function = atom()
                 Args = [term()]

              A new process is started by the application of Module:Function to Args. The process
              is monitored at the same time. Returns the process identifier and a  reference  for
              the monitor. Otherwise works like spawn/3.

       spawn_opt(Fun, Options) -> pid() | {pid(), reference()}

              Types:

                 Fun = function()
                 Options = [spawn_opt_option()]
                 priority_level() = low | normal | high | max
                 max_heap_size() =
                     integer() >= 0 |
                     #{size => integer() >= 0,
                       kill => boolean(),
                       error_logger => boolean()}
                 message_queue_data() = off_heap | on_heap
                 spawn_opt_option() =
                     link | monitor |
                     {priority, Level :: priority_level()} |
                     {fullsweep_after, Number :: integer() >= 0} |
                     {min_heap_size, Size :: integer() >= 0} |
                     {min_bin_vheap_size, VSize :: integer() >= 0} |
                     {max_heap_size, Size :: max_heap_size()} |
                     {message_queue_data, MQD :: message_queue_data()}

              Returns the process identifier (pid) of a new process started by the application of
              Fun to the empty list []. Otherwise works like spawn_opt/4.

              If option monitor is specified, the newly created process is  monitored,  and  both
              the pid and reference for the monitor are returned.

       spawn_opt(Node, Fun, Options) -> pid() | {pid(), reference()}

              Types:

                 Node = node()
                 Fun = function()
                 Options = [spawn_opt_option()]
                 priority_level() = low | normal | high | max
                 max_heap_size() =
                     integer() >= 0 |
                     #{size => integer() >= 0,
                       kill => boolean(),
                       error_logger => boolean()}
                 message_queue_data() = off_heap | on_heap
                 spawn_opt_option() =
                     link | monitor |
                     {priority, Level :: priority_level()} |
                     {fullsweep_after, Number :: integer() >= 0} |
                     {min_heap_size, Size :: integer() >= 0} |
                     {min_bin_vheap_size, VSize :: integer() >= 0} |
                     {max_heap_size, Size :: max_heap_size()} |
                     {message_queue_data, MQD :: message_queue_data()}

              Returns the process identifier (pid) of a new process started by the application of
              Fun to the empty list [] on Node.  If  Node  does  not  exist,  a  useless  pid  is
              returned. Otherwise works like spawn_opt/4.

       spawn_opt(Module, Function, Args, Options) ->
                    pid() | {pid(), reference()}

              Types:

                 Module = module()
                 Function = atom()
                 Args = [term()]
                 Options = [spawn_opt_option()]
                 priority_level() = low | normal | high | max
                 max_heap_size() =
                     integer() >= 0 |
                     #{size => integer() >= 0,
                       kill => boolean(),
                       error_logger => boolean()}
                 message_queue_data() = off_heap | on_heap
                 spawn_opt_option() =
                     link | monitor |
                     {priority, Level :: priority_level()} |
                     {fullsweep_after, Number :: integer() >= 0} |
                     {min_heap_size, Size :: integer() >= 0} |
                     {min_bin_vheap_size, VSize :: integer() >= 0} |
                     {max_heap_size, Size :: max_heap_size()} |
                     {message_queue_data, MQD :: message_queue_data()}

              Works  as  spawn/3, except that an extra option list is specified when creating the
              process.

              If option monitor is specified, the newly created process is  monitored,  and  both
              the pid and reference for the monitor are returned.

              Options:

                link:
                  Sets a link to the parent process (like spawn_link/3 does).

                monitor:
                  Monitors the new process (like monitor/2 does).

                {priority, Level}:
                  Sets   the   priority   of   the   new   process.   Equivalent   to   executing
                  process_flag(priority, Level) in the start function of the new process,  except
                  that  the  priority is set before the process is selected for execution for the
                  first time. For more  information  on  priorities,  see  process_flag(priority,
                  Level).

                {fullsweep_after, Number}:
                  Useful only for performance tuning. Do not use this option unless you know that
                  there is problem with execution times or memory consumption,  and  ensure  that
                  the option improves matters.

                  The  Erlang runtime system uses a generational garbage collection scheme, using
                  an "old heap" for data that has survived at least one garbage collection.  When
                  there is no more room on the old heap, a fullsweep garbage collection is done.

                  Option  fullsweep_after  makes  it  possible  to  specify the maximum number of
                  generational collections before forcing a fullsweep, even if there is  room  on
                  the  old  heap.  Setting  the  number  to  zero disables the general collection
                  algorithm, that is, all live data is copied at every garbage collection.

                  A few cases when it can be useful to change fullsweep_after:

                  * If binaries that are no longer  used  are  to  be  thrown  away  as  soon  as
                    possible. (Set Number to zero.)

                  * A  process  that mostly have short-lived data is fullsweeped seldom or never,
                    that is, the  old  heap  contains  mostly  garbage.  To  ensure  a  fullsweep
                    occasionally, set Number to a suitable value, such as 10 or 20.

                  * In  embedded  systems with a limited amount of RAM and no virtual memory, you
                    might want to preserve memory by setting Number to zero. (The  value  can  be
                    set globally, see erlang:system_flag/2.)

                {min_heap_size, Size}:
                  Useful only for performance tuning. Do not use this option unless you know that
                  there is problem with execution times or memory consumption,  and  ensure  that
                  the option improves matters.

                  Gives  a minimum heap size, in words. Setting this value higher than the system
                  default can speed up some processes because less garbage  collection  is  done.
                  However,  setting  a  too  high value can waste memory and slow down the system
                  because of worse data locality. Therefore, use this option only for fine-tuning
                  an application and to measure the execution time with various Size values.

                {min_bin_vheap_size, VSize}:
                  Useful only for performance tuning. Do not use this option unless you know that
                  there is problem with execution times or memory consumption,  and  ensure  that
                  the option improves matters.

                  Gives  a  minimum binary virtual heap size, in words. Setting this value higher
                  than the system default can  speed  up  some  processes  because  less  garbage
                  collection  is  done.  However,  setting  a  too  high  value can waste memory.
                  Therefore, use this option only for fine-tuning an application and  to  measure
                  the execution time with various VSize values.

                {max_heap_size, Size}:
                  Sets the max_heap_size process flag. The default max_heap_size is determined by
                  command-line  argument  +hmax  in  erl(1).  For  more  information,   see   the
                  documentation of process_flag(max_heap_size, Size).

                {message_queue_data, MQD}:
                  Sets  the  state  of  the  message_queue_data process flag. MQD is to be either
                  off_heap or on_heap. The default message_queue_data process flag is  determined
                  by  command-line  argument  +hmqd  in  erl(1).  For  more  information, see the
                  documentation of process_flag(message_queue_data, MQD).

       spawn_opt(Node, Module, Function, Args, Options) ->
                    pid() | {pid(), reference()}

              Types:

                 Node = node()
                 Module = module()
                 Function = atom()
                 Args = [term()]
                 Options = [spawn_opt_option()]
                 priority_level() = low | normal | high | max
                 max_heap_size() =
                     integer() >= 0 |
                     #{size => integer() >= 0,
                       kill => boolean(),
                       error_logger => boolean()}
                 message_queue_data() = off_heap | on_heap
                 spawn_opt_option() =
                     link | monitor |
                     {priority, Level :: priority_level()} |
                     {fullsweep_after, Number :: integer() >= 0} |
                     {min_heap_size, Size :: integer() >= 0} |
                     {min_bin_vheap_size, VSize :: integer() >= 0} |
                     {max_heap_size, Size :: max_heap_size()} |
                     {message_queue_data, MQD :: message_queue_data()}

              Returns the process identifier (pid) of a new process started by the application of
              Module:Function to Args on Node. If Node does not exist, a useless pid is returned.
              Otherwise works like spawn_opt/4.

          Note:
              Option monitor is not supported by spawn_opt/5.

       split_binary(Bin, Pos) -> {binary(), binary()}

              Types:

                 Bin = binary()
                 Pos = integer() >= 0
                   0..byte_size(Bin)

              Returns a tuple containing the binaries that are the result of splitting  Bin  into
              two  parts  at  position  Pos.  This  is  not  a  destructive  operation. After the
              operation, there are three binaries altogether. Example:

              > B = list_to_binary("0123456789").
              <<"0123456789">>
              > byte_size(B).
              10
              > {B1, B2} = split_binary(B,3).
              {<<"012">>,<<"3456789">>}
              > byte_size(B1).
              3
              > byte_size(B2).
              7

       erlang:start_timer(Time, Dest, Msg) -> TimerRef

              Types:

                 Time = integer() >= 0
                 Dest = pid() | atom()
                 Msg = term()
                 TimerRef = reference()

              Starts a timer. The same as calling erlang:start_timer(Time, Dest, Msg, []).

       erlang:start_timer(Time, Dest, Msg, Options) -> TimerRef

              Types:

                 Time = integer()
                 Dest = pid() | atom()
                 Msg = term()
                 Options = [Option]
                 Abs = boolean()
                 Option = {abs, Abs}
                 TimerRef = reference()

              Starts a timer. When the timer expires, the message  {timeout,  TimerRef,  Msg}  is
              sent to the process identified by Dest.

              Options:

                {abs, false}:
                  This  is  the  default.  It  means  the  Time value is interpreted as a time in
                  milliseconds relative current Erlang monotonic time.

                {abs, true}:
                  Absolute Time value. The Time  value  is  interpreted  as  an  absolute  Erlang
                  monotonic time in milliseconds.

              More Options can be added in the future.

              The  absolute point in time, the timer is set to expire on, must be in the interval
              [erlang:system_info(start_time), erlang:system_info(end_time)]. If a relative  time
              is specified, the Time value is not allowed to be negative.

              If  Dest is a pid(), it must be a pid() of a process created on the current runtime
              system instance. This process has either terminated or not. If Dest is  an  atom(),
              it is interpreted as the name of a locally registered process. The process referred
              to by the name is looked up at the time of timer expiration. No error  is  returned
              if the name does not refer to a process.

              If  Dest is a pid(), the timer is automatically canceled if the process referred to
              by the pid() is not alive, or if the process exits. This feature was introduced  in
              ERTS  5.4.11.  Notice  that  timers  are not automatically canceled when Dest is an
              atom().

              See also erlang:send_after/4, erlang:cancel_timer/2, and erlang:read_timer/2.

              Failure: badarg if the arguments do not satisfy the requirements specified here.

       statistics(Item :: active_tasks) -> [ActiveTasks]

              Types:

                 ActiveTasks = integer() >= 0

              Returns the  same  as  statistics(active_tasks_all)  with  the  exception  that  no
              information  about  the dirty IO run queue and its associated schedulers is part of
              the result. That is, only tasks that are expected to be CPU bound are part  of  the
              result.

       statistics(Item :: active_tasks_all) -> [ActiveTasks]

              Types:

                 ActiveTasks = integer() >= 0

              Returns  a  list  where  each element represents the amount of active processes and
              ports on each run queue and its associated  schedulers.  That  is,  the  number  of
              processes  and  ports  that  are ready to run, or are currently running. Values for
              normal run queues  and  their  associated  schedulers  are  located  first  in  the
              resulting  list.  The first element corresponds to scheduler number 1 and so on. If
              support for dirty schedulers exist, an element with the value for the dirty CPU run
              queue  and  its associated dirty CPU schedulers follow and then as last element the
              value for the the dirty IO run queue and its associated dirty IO schedulers follow.
              The  information is not gathered atomically. That is, the result is not necessarily
              a consistent snapshot of the state, but instead quite efficiently gathered.

          Note:
              Each normal scheduler has one run  queue  that  it  manages.  If  dirty  schedulers
              schedulers  are  supported,  all  dirty CPU schedulers share one run queue, and all
              dirty IO schedulers share one run queue. That  is,  we  have  multiple  normal  run
              queues,  one  dirty  CPU run queue and one dirty IO run queue. Work can not migrate
              between the different types of run queues. Only  work  in  normal  run  queues  can
              migrate  to  other  normal  run  queues.  This  has  to  be taken into account when
              evaluating the result.

              See     also     statistics(total_active_tasks),     statistics(run_queue_lengths),
              statistics(run_queue_lengths_all),     statistics(total_run_queue_lengths),     and
              statistics(total_run_queue_lengths_all).

       statistics(Item :: context_switches) -> {ContextSwitches, 0}

              Types:

                 ContextSwitches = integer() >= 0

              Returns the total number of context switches since the system started.

       statistics(Item :: exact_reductions) ->
                     {Total_Exact_Reductions,
                      Exact_Reductions_Since_Last_Call}

              Types:

                 Total_Exact_Reductions = Exact_Reductions_Since_Last_Call = integer() >= 0

              Returns the number of exact reductions.

          Note:
              statistics(exact_reductions)    is    a    more    expensive     operation     than
              statistics(reductions).

       statistics(Item :: garbage_collection) ->
                     {Number_of_GCs, Words_Reclaimed, 0}

              Types:

                 Number_of_GCs = Words_Reclaimed = integer() >= 0

              Returns information about garbage collection, for example:

              > statistics(garbage_collection).
              {85,23961,0}

              This information can be invalid for some implementations.

       statistics(Item :: io) -> {{input, Input}, {output, Output}}

              Types:

                 Input = Output = integer() >= 0

              Returns  Input,  which  is  the  total  number of bytes received through ports, and
              Output, which is the total number of bytes output to ports.

       statistics(Item :: microstate_accounting) ->
                     [MSAcc_Thread] | undefined

              Types:

                 MSAcc_Thread =
                     #{type := MSAcc_Thread_Type,
                       id := MSAcc_Thread_Id,
                       counters := MSAcc_Counters}
                 MSAcc_Thread_Type =
                     async | aux | dirty_io_scheduler | dirty_cpu_scheduler |
                     poll | scheduler
                 MSAcc_Thread_Id = integer() >= 0
                 MSAcc_Counters = #{MSAcc_Thread_State => integer() >= 0}
                 MSAcc_Thread_State =
                     alloc | aux | bif | busy_wait | check_io | emulator | ets |
                     gc | gc_fullsweep | nif | other | port | send | sleep | timers

              Microstate accounting can be used to measure  how  much  time  the  Erlang  runtime
              system spends doing various tasks. It is designed to be as lightweight as possible,
              but some overhead exists when this is enabled. Microstate accounting is meant to be
              a  profiling  tool  to  help  finding  performance bottlenecks. To start/stop/reset
              microstate accounting, use system flag microstate_accounting.

              statistics(microstate_accounting) returns a list of maps representing some  of  the
              OS  threads  within  ERTS. Each map contains type and id fields that can be used to
              identify what thread it is, and also a counters field that contains data about  how
              much time has been spent in the various states.

              Example:

              > erlang:statistics(microstate_accounting).
              [#{counters => #{aux => 1899182914,
                               check_io => 2605863602,
                               emulator => 45731880463,
                               gc => 1512206910,
                               other => 5421338456,
                               port => 221631,
                               sleep => 5150294100},
                 id => 1,
                 type => scheduler}|...]

              The  time  unit  is the same as returned by os:perf_counter/0. So, to convert it to
              milliseconds, you can do something like this:

              lists:map(
                fun(#{ counters := Cnt } = M) ->
                        MsCnt = maps:map(fun(_K, PerfCount) ->
                                                 erlang:convert_time_unit(PerfCount, perf_counter, 1000)
                                         end, Cnt),
                       M#{ counters := MsCnt }
                end, erlang:statistics(microstate_accounting)).

              Notice that these values are not guaranteed to be the  exact  time  spent  in  each
              state.  This  is because of various optimisation done to keep the overhead as small
              as possible.

              MSAcc_Thread_Types:

                scheduler:
                  The main execution threads that do most of  the  work.  See  erl  +S  for  more
                  details.

                dirty_cpu_scheduler:
                  The  threads  for  long  running  cpu  intensive  work. See erl +SDcpu for more
                  details.

                dirty_io_scheduler:
                  The threads for long running I/O work. See erl +SDio for more details.

                async:
                  Async threads are used by various linked-in drivers (mainly the  file  drivers)
                  do offload non-CPU intensive work. See erl +A for more details.

                aux:
                  Takes care of any work that is not specifically assigned to a scheduler.

                poll:
                  Does the IO polling for the emulator. See erl +IOt for more details.

              The  following MSAcc_Thread_States are available. All states are exclusive, meaning
              that a thread cannot be in two states at once. So, if you add the  numbers  of  all
              counters in a thread, you get the total runtime for that thread.

                aux:
                  Time spent handling auxiliary jobs.

                check_io:
                  Time spent checking for new I/O events.

                emulator:
                  Time spent executing Erlang processes.

                gc:
                  Time  spent doing garbage collection. When extra states are enabled this is the
                  time spent doing non-fullsweep garbage collections.

                other:
                  Time spent doing unaccounted things.

                port:
                  Time spent executing ports.

                sleep:
                  Time spent sleeping.

              More fine-grained MSAcc_Thread_States can  be  added  through  configure  (such  as
              ./configure   --with-microstate-accounting=extra).  Enabling  these  states  causes
              performance degradation when microstate accounting is turned off and increases  the
              overhead when it is turned on.

                alloc:
                  Time  spent  managing memory. Without extra states this time is spread out over
                  all other states.

                bif:
                  Time spent in BIFs. Without extra states this time  is  part  of  the  emulator
                  state.

                busy_wait:
                  Time  spent  busy  waiting.  This is also the state where a scheduler no longer
                  reports that it is active when using  statistics(scheduler_wall_time).  So,  if
                  you  add  all other states but this and sleep, and then divide that by all time
                  in the thread, you should get something very similar to the scheduler_wall_time
                  fraction. Without extra states this time is part of the other state.

                ets:
                  Time  spent  executing  ETS BIFs. Without extra states this time is part of the
                  emulator state.

                gc_full:
                  Time spent doing fullsweep garbage collection. Without extra states  this  time
                  is part of the gc state.

                nif:
                  Time  spent  in  NIFs.  Without  extra states this time is part of the emulator
                  state.

                send:
                  Time spent sending messages (processes only). Without extra states this time is
                  part of the emulator state.

                timers:
                  Time spent managing timers. Without extra states this time is part of the other
                  state.

              The utility module msacc(3erl) can be used to more easily analyse these statistics.

              Returns undefined if system flag microstate_accounting is turned off.

              The list of thread information is  unsorted  and  can  appear  in  different  order
              between calls.

          Note:
              The threads and states are subject to change without any prior notice.

       statistics(Item :: reductions) ->
                     {Total_Reductions, Reductions_Since_Last_Call}

              Types:

                 Total_Reductions = Reductions_Since_Last_Call = integer() >= 0

              Returns information about reductions, for example:

              > statistics(reductions).
              {2046,11}

          Note:
              As  from  ERTS  5.5  (Erlang/OTP  R11B),  this  value  does  not include reductions
              performed in current time slices of currently  scheduled  processes.  If  an  exact
              value is wanted, use statistics(exact_reductions).

       statistics(Item :: run_queue) -> integer() >= 0

              Returns the total length of all normal run-queues. That is, the number of processes
              and ports that are ready to run on  all  available  normal  run-queues.  Dirty  run
              queues are not part of the result. The information is gathered atomically. That is,
              the result is a consistent snapshot of the state, but this operation is  much  more
              expensive  compared to statistics(total_run_queue_lengths), especially when a large
              amount of schedulers is used.

       statistics(Item :: run_queue_lengths) -> [RunQueueLength]

              Types:

                 RunQueueLength = integer() >= 0

              Returns the same as statistics(run_queue_lengths_all) with the  exception  that  no
              information  about  the dirty IO run queue is part of the result. That is, only run
              queues with work that is expected to be CPU bound is part of the result.

       statistics(Item :: run_queue_lengths_all) -> [RunQueueLength]

              Types:

                 RunQueueLength = integer() >= 0

              Returns a list where each element represents the  amount  of  processes  and  ports
              ready  to run for each run queue. Values for normal run queues are located first in
              the resulting list. The first element  corresponds  to  the  normal  run  queue  of
              scheduler number 1 and so on. If support for dirty schedulers exist, values for the
              dirty CPU run queue and the dirty IO run queue follow (in that order) at  the  end.
              The  information is not gathered atomically. That is, the result is not necessarily
              a consistent snapshot of the state, but instead quite efficiently gathered.

          Note:
              Each normal scheduler has one run  queue  that  it  manages.  If  dirty  schedulers
              schedulers  are  supported,  all  dirty CPU schedulers share one run queue, and all
              dirty IO schedulers share one run queue. That  is,  we  have  multiple  normal  run
              queues,  one  dirty  CPU run queue and one dirty IO run queue. Work can not migrate
              between the different types of run queues. Only  work  in  normal  run  queues  can
              migrate  to  other  normal  run  queues.  This  has  to  be taken into account when
              evaluating the result.

              See  also  statistics(run_queue_lengths),  statistics(total_run_queue_lengths_all),
              statistics(total_run_queue_lengths),                      statistics(active_tasks),
              statistics(active_tasks_all),          and          statistics(total_active_tasks),
              statistics(total_active_tasks_all).

       statistics(Item :: runtime) ->
                     {Total_Run_Time, Time_Since_Last_Call}

              Types:

                 Total_Run_Time = Time_Since_Last_Call = integer() >= 0

              Returns information about runtime, in milliseconds.

              This is the sum of the runtime for all threads in the Erlang runtime system and can
              therefore be greater than the wall clock time.

          Warning:
              This value might wrap due to limitations in the underlying  functionality  provided
              by the operating system that is used.

              Example:

              > statistics(runtime).
              {1690,1620}

       statistics(Item :: scheduler_wall_time) ->
                     [{SchedulerId, ActiveTime, TotalTime}] | undefined

              Types:

                 SchedulerId = integer() >= 1
                 ActiveTime = TotalTime = integer() >= 0

              Returns   a  list  of  tuples  with  {SchedulerId,  ActiveTime,  TotalTime},  where
              SchedulerId is an integer ID of the  scheduler,  ActiveTime  is  the  duration  the
              scheduler   has  been  busy,  and  TotalTime  is  the  total  time  duration  since
              scheduler_wall_time activation for the specific  scheduler.  Note  that  activation
              time  can  differ  significantly between schedulers. Currently dirty schedulers are
              activated at system start while normal schedulers are activated some time after the
              scheduler_wall_time functionality is enabled. The time unit is undefined and can be
              subject to change between releases, OSs, and system  restarts.  scheduler_wall_time
              is  only  to  be  used  to  calculate  relative  values  for scheduler utilization.
              ActiveTime can never exceed TotalTime.

              The definition of a busy scheduler is when it is not idle  and  is  not  scheduling
              (selecting) a process or port, that is:

                * Executing process code

                * Executing linked-in driver or NIF code

                * Executing BIFs, or any other runtime handling

                * Garbage collecting

                * Handling any other memory management

              Notice  that  a  scheduler  can  also  be busy even if the OS has scheduled out the
              scheduler thread.

              Returns undefined if system flag scheduler_wall_time is turned off.

              The list of scheduler information is unsorted and can  appear  in  different  order
              between calls.

              As  of  ERTS version 9.0, also dirty CPU schedulers will be included in the result.
              That is, all scheduler threads that are expected to handle CPU bound work.  If  you
              also      want      information     about     dirty     I/O     schedulers,     use
              statistics(scheduler_wall_time_all) instead.

              Normal schedulers will have scheduler identifiers in the range 1 =< SchedulerId  =<
              erlang:system_info(schedulers).   Dirty   CPU   schedulers   will   have  scheduler
              identifiers  in  the  range   erlang:system_info(schedulers)   <   SchedulerId   =<
              erlang:system_info(schedulers) + erlang:system_info(dirty_cpu_schedulers).

          Note:
              The  different  types  of  schedulers  handle  specific types of jobs. Every job is
              assigned  to  a  specific  scheduler  type.  Jobs  can  migrate  between  different
              schedulers  of the same type, but never between schedulers of different types. This
              fact has to be taken under consideration when evaluating the result returned.

              Using scheduler_wall_time to calculate scheduler utilization:

              > erlang:system_flag(scheduler_wall_time, true).
              false
              > Ts0 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.
              ok

              Some  time  later  the  user  takes  another  snapshot  and  calculates   scheduler
              utilization per scheduler, for example:

              > Ts1 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.
              ok
              > lists:map(fun({{I, A0, T0}, {I, A1, T1}}) -> {I, (A1 - A0)/(T1 - T0)} end, lists:zip(Ts0,Ts1)).
              [{1,0.9743474730177548},
               {2,0.9744843782751444},
               {3,0.9995902361669045},
               {4,0.9738012596572161},
               {5,0.9717956667018103},
               {6,0.9739235846420741},
               {7,0.973237033077876},
               {8,0.9741297293248656}]

              Using the same snapshots to calculate a total scheduler utilization:

              > {A, T} = lists:foldl(fun({{_, A0, T0}, {_, A1, T1}}, {Ai,Ti}) -> {Ai + (A1 - A0), Ti + (T1 - T0)} end, {0, 0}, lists:zip(Ts0,Ts1)), TotalSchedulerUtilization = A/T.
              0.9769136803764825

              Total scheduler utilization will equal 1.0 when all schedulers have been active all
              the time between the two measurements.

              Another (probably more) useful value is to calculate  total  scheduler  utilization
              weighted against maximum amount of available CPU time:

              > WeightedSchedulerUtilization = (TotalSchedulerUtilization * (erlang:system_info(schedulers) + erlang:system_info(dirty_cpu_schedulers))) / erlang:system_info(logical_processors_available).
              0.9769136803764825

              This  weighted  scheduler utilization will reach 1.0 when schedulers are active the
              same amount of time as maximum available CPU time. If more  schedulers  exist  than
              available logical processors, this value may be greater than 1.0.

              As  of  ERTS  version  9.0,  the  Erlang  runtime  system will as default have more
              schedulers than logical processors. This due to the dirty schedulers.

          Note:
              scheduler_wall_time   is   by    default    disabled.    To    enable    it,    use
              erlang:system_flag(scheduler_wall_time, true).

       statistics(Item :: scheduler_wall_time_all) ->
                     [{SchedulerId, ActiveTime, TotalTime}] | undefined

              Types:

                 SchedulerId = integer() >= 1
                 ActiveTime = TotalTime = integer() >= 0

              The   same   as   statistics(scheduler_wall_time),  except  that  it  also  include
              information about all dirty I/O schedulers.

              Dirty   IO   schedulers   will   have   scheduler   identifiers   in   the    range
              erlang:system_info(schedulers)    +    erlang:system_info(dirty_cpu_schedulers)   <
              SchedulerId             =<             erlang:system_info(schedulers)             +
              erlang:system_info(dirty_cpu_schedulers) + erlang:system_info(dirty_io_schedulers).

          Note:
              Note  that  work  executing on dirty I/O schedulers are expected to mainly wait for
              I/O. That is, when you get high scheduler utilization on dirty I/O schedulers,  CPU
              utilization is not expected to be high due to this work.

       statistics(Item :: total_active_tasks) -> ActiveTasks

              Types:

                 ActiveTasks = integer() >= 0

              The same as calling lists:sum(statistics(active_tasks)), but more efficient.

       statistics(Item :: total_active_tasks_all) -> ActiveTasks

              Types:

                 ActiveTasks = integer() >= 0

              The same as calling lists:sum(statistics(active_tasks_all)), but more efficient.

       statistics(Item :: total_run_queue_lengths) ->
                     TotalRunQueueLengths

              Types:

                 TotalRunQueueLengths = integer() >= 0

              The same as calling lists:sum(statistics(run_queue_lengths)), but more efficient.

       statistics(Item :: total_run_queue_lengths_all) ->
                     TotalRunQueueLengths

              Types:

                 TotalRunQueueLengths = integer() >= 0

              The   same   as   calling  lists:sum(statistics(run_queue_lengths_all)),  but  more
              efficient.

       statistics(Item :: wall_clock) ->
                     {Total_Wallclock_Time,
                      Wallclock_Time_Since_Last_Call}

              Types:

                 Total_Wallclock_Time = Wallclock_Time_Since_Last_Call = integer() >= 0

              Returns information about wall clock. wall_clock can be used in the same manner  as
              runtime, except that real time is measured as opposed to runtime or CPU time.

       erlang:suspend_process(Suspendee) -> true

              Types:

                 Suspendee = pid()

              Suspends   the   process   identified   by   Suspendee.   The   same   as   calling
              erlang:suspend_process(Suspendee, []).

          Warning:
              This BIF is intended for debugging only.

       erlang:suspend_process(Suspendee, OptList) -> boolean()

              Types:

                 Suspendee = pid()
                 OptList = [Opt]
                 Opt = unless_suspending | asynchronous | {asynchronous, term()}

              Increases the suspend count on the process identified by Suspendee and puts  it  in
              the  suspended state if it is not already in that state. A suspended process is not
              scheduled for execution until the process has been resumed.

              A process can be suspended by multiple processes  and  can  be  suspended  multiple
              times  by  a single process. A suspended process does not leave the suspended state
              until its suspend count reaches zero. The suspend count of Suspendee  is  decreased
              when  erlang:resume_process(Suspendee)  is  called  by the same process that called
              erlang:suspend_process(Suspendee). All increased suspend counts on other  processes
              acquired by a process are automatically decreased when the process terminates.

              Options (Opts):

                asynchronous:
                  A  suspend  request  is  sent to the process identified by Suspendee. Suspendee
                  eventually suspends unless it is resumed before it could suspend. The caller of
                  erlang:suspend_process/2  returns  immediately, regardless of whether Suspendee
                  has suspended yet or not. The point in time when Suspendee suspends  cannot  be
                  deduced  from  other events in the system. It is only guaranteed that Suspendee
                  eventually suspends (unless it is resumed). If no asynchronous options has been
                  passed,  the  caller of erlang:suspend_process/2 is blocked until Suspendee has
                  suspended.

                {asynchronous, ReplyTag}:
                  A suspend request is sent to the process  identified  by  Suspendee.  When  the
                  suspend  request  has  been processed, a reply message is sent to the caller of
                  this function. The reply is on  the  form  {ReplyTag,  State}  where  State  is
                  either:

                  exited:
                    Suspendee has exited.

                  suspended:
                    Suspendee is now suspended.

                  not_suspended:
                    Suspendee is not suspended. This can only happen when the process that issued
                    this request, have called resume_process(Suspendee) before getting the reply.

                  Appart from the reply message,  the  {asynchronous,  ReplyTag}  option  behaves
                  exactly the same as the asynchronous option without reply tag.

                unless_suspending:
                  The  process  identified  by  Suspendee is suspended unless the calling process
                  already is suspending Suspendee. If unless_suspending is combined  with  option
                  asynchronous,  a  suspend request is sent unless the calling process already is
                  suspending Suspendee or if a suspend request already has been sent  and  is  in
                  transit. If the calling process already is suspending Suspendee, or if combined
                  with option asynchronous and a send request already is  in  transit,  false  is
                  returned and the suspend count on Suspendee remains unchanged.

              If  the  suspend count on the process identified by Suspendee is increased, true is
              returned, otherwise false.

          Warning:
              This BIF is intended for debugging only.

          Warning:
              You can easily create deadlocks if processes suspends each other  (directly  or  in
              circles). In ERTS versions prior to ERTS version 10.0, the runtime system prevented
              such deadlocks, but this  prevention  has  now  been  removed  due  to  performance
              reasons.

              Failures:

                badarg:
                   If Suspendee is not a process identifier.

                badarg:
                   If  the  process  identified  by  Suspendee is the same process as the process
                  calling erlang:suspend_process/2.

                badarg:
                   If the process identified by Suspendee is not alive.

                badarg:
                   If the process identified by Suspendee resides on another node.

                badarg:
                   If OptList is not a proper list of valid Opts.

                system_limit:
                   If the process identified by Suspendee has been suspended more  times  by  the
                  calling  process  than  can  be represented by the currently used internal data
                  structures. The system limit is > 2,000,000,000  suspends  and  will  never  be
                  lower.

       erlang:system_flag(Flag :: backtrace_depth, Depth) -> OldDepth

              Types:

                 Depth = OldDepth = integer() >= 0

              Sets  the  maximum  depth  of  call stack back-traces in the exit reason element of
              'EXIT' tuples. The flag also limits the stacktrace depth returned  by  process_info
              item current_stacktrace.

              Returns the old value of the flag.

       erlang:system_flag(Flag :: cpu_topology, CpuTopology) ->
                             OldCpuTopology

              Types:

                 CpuTopology = OldCpuTopology = cpu_topology()
                 cpu_topology() = [LevelEntry :: level_entry()] | undefined
                 level_entry() =
                     {LevelTag :: level_tag(), SubLevel :: sub_level()} |
                     {LevelTag :: level_tag(),
                      InfoList :: info_list(),
                      SubLevel :: sub_level()}
                 level_tag() = core | node | processor | thread
                 sub_level() =
                     [LevelEntry :: level_entry()] |
                     (LogicalCpuId :: {logical, integer() >= 0})
                 info_list() = []

          Warning:
              This  argument  is  deprecated.  Instead  of  using this argument, use command-line
              argument +sct in erl(1).

              When this argument is removed, a  final  CPU  topology  to  use  is  determined  at
              emulator boot time.

              Sets  the  user-defined  CpuTopology.  The  user-defined CPU topology overrides any
              automatically detected CPU topology.  By  passing  undefined  as  CpuTopology,  the
              system  reverts  to  the  CPU  topology  automatically detected. The returned value
              equals the value returned from erlang:system_info(cpu_topology) before  the  change
              was made.

              Returns the old value of the flag.

              The  CPU  topology  is  used  when  binding  schedulers  to  logical processors. If
              schedulers are already bound when the CPU topology is changed, the  schedulers  are
              sent a request to rebind according to the new CPU topology.

              The user-defined CPU topology can also be set by passing command-line argument +sct
              to erl(1).

              For information on type CpuTopology and more, see  erlang:system_info(cpu_topology)
              as well as command-line flags +sct and +sbt in erl(1).

       erlang:system_flag(Flag :: dirty_cpu_schedulers_online,
                          DirtyCPUSchedulersOnline) ->
                             OldDirtyCPUSchedulersOnline

              Types:

                 DirtyCPUSchedulersOnline = OldDirtyCPUSchedulersOnline = integer() >= 1

              Sets   the   number   of   dirty   CPU   schedulers   online.   Range   is   1   <=
              DirtyCPUSchedulersOnline <= N, where N is the smallest  of  the  return  values  of
              erlang:system_info(dirty_cpu_schedulers) and erlang:system_info(schedulers_online).

              Returns the old value of the flag.

              The  number  of  dirty CPU schedulers online can change if the number of schedulers
              online changes. For example, if 12  schedulers  and  6  dirty  CPU  schedulers  are
              online, and system_flag/2 is used to set the number of schedulers online to 6, then
              the number of dirty CPU schedulers online is automatically  decreased  by  half  as
              well,  down  to  3.  Similarly, the number of dirty CPU schedulers online increases
              proportionally to increases in the number of schedulers online.

              For   more   information,    see    erlang:system_info(dirty_cpu_schedulers)    and
              erlang:system_info(dirty_cpu_schedulers_online).

       erlang:system_flag(Flag :: erts_alloc, Value :: {Alloc, F, V}) ->
                             ok | notsup

              Types:

                 Alloc = F = atom()
                 V = integer()

              Sets  system  flags  for  erts_alloc(3erl).  Alloc  is the allocator to affect, for
              example binary_alloc. F is the flag to change and V is the new value.

              Only a subset of all erts_alloc flags can be changed at run time.  This  subset  is
              currently only the flag sbct.

              Returns ok if the flag was set or notsup if not supported by erts_alloc.

       erlang:system_flag(Flag :: fullsweep_after, Number) -> OldNumber

              Types:

                 Number = OldNumber = integer() >= 0

              Sets  system  flag fullsweep_after. Number is a non-negative integer indicating how
              many times generational garbage collections can be done without forcing a fullsweep
              collection. The value applies to new processes, while processes already running are
              not affected.

              Returns the old value of the flag.

              In low-memory systems (especially without virtual memory), setting the value  to  0
              can help to conserve memory.

              This value can also be set through (OS) environment variable ERL_FULLSWEEP_AFTER.

       erlang:system_flag(Flag :: microstate_accounting, Action) ->
                             OldState

              Types:

                 Action = true | false | reset
                 OldState = true | false

              Turns  on/off  microstate accounting measurements. When passing reset, all counters
              are reset to 0.

              For more information see statistics(microstate_accounting).

       erlang:system_flag(Flag :: min_heap_size, MinHeapSize) ->
                             OldMinHeapSize

              Types:

                 MinHeapSize = OldMinHeapSize = integer() >= 0

              Sets the default minimum heap size for processes. The size is specified  in  words.
              The   new  min_heap_size  effects  only  processes  spawned  after  the  change  of
              min_heap_size has been made. min_heap_size can be set for individual  processes  by
              using spawn_opt/4 or process_flag/2.

              Returns the old value of the flag.

       erlang:system_flag(Flag :: min_bin_vheap_size, MinBinVHeapSize) ->
                             OldMinBinVHeapSize

              Types:

                 MinBinVHeapSize = OldMinBinVHeapSize = integer() >= 0

              Sets  the  default  minimum  binary  virtual  heap  size for processes. The size is
              specified in words. The new  min_bin_vhheap_size  effects  only  processes  spawned
              after the change of min_bin_vheap_size has been made. min_bin_vheap_size can be set
              for individual processes by using spawn_opt/2,3,4 or process_flag/2.

              Returns the old value of the flag.

       erlang:system_flag(Flag :: max_heap_size, MaxHeapSize) ->
                             OldMaxHeapSize

              Types:

                 MaxHeapSize = OldMaxHeapSize = max_heap_size()
                 max_heap_size() =
                     integer() >= 0 |
                     #{size => integer() >= 0,
                       kill => boolean(),
                       error_logger => boolean()}

              Sets the default maximum heap size settings for processes. The size is specified in
              words.  The  new  max_heap_size effects only processes spawned efter the change has
              been made. max_heap_size can be set for individual processes using  spawn_opt/2,3,4
              or process_flag/2.

              Returns the old value of the flag.

       erlang:system_flag(Flag :: multi_scheduling, BlockState) ->
                             OldBlockState

              Types:

                 BlockState = block | unblock | block_normal | unblock_normal
                 OldBlockState = blocked | disabled | enabled

              If  multi-scheduling  is  enabled,  more  than  one scheduler thread is used by the
              emulator. Multi-scheduling can  be  blocked  in  two  different  ways.  Either  all
              schedulers  but  one  is blocked, or all normal schedulers but one is blocked. When
              only normal schedulers are blocked,  dirty  schedulers  are  free  to  continue  to
              schedule processes.

              If  BlockState  =:=  block,  multi-scheduling is blocked. That is, one and only one
              scheduler thread will execute. If BlockState =:= unblock and  no  one  else  blocks
              multi-scheduling,  and  this  process  has  blocked  only once, multi-scheduling is
              unblocked.

              If BlockState =:= block_normal, normal multi-scheduling is blocked. That  is,  only
              one  normal  scheduler  thread  will  execute,  but  multiple  dirty schedulers can
              execute. If BlockState =:= unblock_normal and no  one  else  blocks  normal  multi-
              scheduling,  and  this  process  has  blocked only once, normal multi-scheduling is
              unblocked.

              One process can block multi-scheduling and normal multi-scheduling multiple  times.
              If  a  process has blocked multiple times, it must unblock exactly as many times as
              it has blocked before it has released its multi-scheduling block. If a process that
              has  blocked  multi-scheduling  or  normal multi-scheduling exits, it automatically
              releases its blocking of multi-scheduling and normal multi-scheduling.

              The return values are disabled, blocked, blocked_normal, or enabled.  The  returned
              value      describes      the      state     just     after     the     call     to
              erlang:system_flag(multi_scheduling, BlockState) has  been  made.  For  information
              about the return values, see erlang:system_info(multi_scheduling).

          Note:
              Blocking of multi-scheduling and normal multi-scheduling is normally not needed. If
              you feel that you need to use these features, consider it a few more  times  again.
              Blocking multi-scheduling is only to be used as a last resort, as it is most likely
              a very inefficient way to solve the problem.

              See                   also                    erlang:system_info(multi_scheduling),
              erlang:system_info(normal_multi_scheduling_blockers),
              erlang:system_info(multi_scheduling_blockers), and erlang:system_info(schedulers).

       erlang:system_flag(Flag :: scheduler_bind_type, How) ->
                             OldBindType

              Types:

                 How = scheduler_bind_type() | default_bind
                 OldBindType = scheduler_bind_type()
                 scheduler_bind_type() =
                     no_node_processor_spread | no_node_thread_spread | no_spread |
                     processor_spread | spread | thread_spread |
                     thread_no_node_processor_spread | unbound

          Warning:
              This argument is deprecated. Instead  of  using  this  argument,  use  command-line
              argument +sbt in erl(1). When this argument is removed, a final scheduler bind type
              to use is determined at emulator boot time.

              Controls if and how schedulers are bound to logical processors.

              When erlang:system_flag(scheduler_bind_type, How) is called, an asynchronous signal
              is  sent  to  all  schedulers  online,  causing  them  to  try to bind or unbind as
              requested.

          Note:
              If a scheduler fails to bind, this is often silently ignored, as it is  not  always
              possible to verify valid logical processor identifiers. If an error is reported, an
              error event is logged. To verify that the schedulers have bound as requested,  call
              erlang:system_info(scheduler_bindings).

              Schedulers  can be bound on newer Linux, Solaris, FreeBSD, and Windows systems, but
              more systems will be supported in future releases.

              In order for the runtime system to be able to bind  schedulers,  the  CPU  topology
              must   be   known.  If  the  runtime  system  fails  to  detect  the  CPU  topology
              automatically, it can be defined. For more information on how  to  define  the  CPU
              topology, see command-line flag +sct in erl(1).

              The runtime system does by default not bind schedulers to logical processors.

          Note:
              If  the  Erlang  runtime  system  is the only OS process binding threads to logical
              processors, this improves the performance of the runtime system. However, if  other
              OS  processes  (for  example,  another  Erlang runtime system) also bind threads to
              logical processors, there can be a  performance  penalty  instead.  Sometimes  this
              performance  penalty  can  be  severe.  If  so,  it  is recommended to not bind the
              schedulers.

              Schedulers can be bound in different ways. Argument How determines  how  schedulers
              are bound and can be any of the following:

                unbound:
                  Same as command-line argument +sbt u in erl(1).

                no_spread:
                  Same as command-line argument +sbt ns in erl(1).

                thread_spread:
                  Same as command-line argument +sbt ts in erl(1).

                processor_spread:
                  Same as command-line argument +sbt ps in erl(1).

                spread:
                  Same as command-line argument +sbt s in erl(1).

                no_node_thread_spread:
                  Same as command-line argument +sbt nnts in erl(1).

                no_node_processor_spread:
                  Same as command-line argument +sbt nnps in erl(1).

                thread_no_node_processor_spread:
                  Same as command-line argument +sbt tnnps in erl(1).

                default_bind:
                  Same as command-line argument +sbt db in erl(1).

              The returned value equals How before flag scheduler_bind_type was changed.

              Failures:

                notsup:
                  If binding of schedulers is not supported.

                badarg:
                  If How is not one of the documented alternatives.

                badarg:
                  If CPU topology information is unavailable.

              The  scheduler  bind  type can also be set by passing command-line argument +sbt to
              erl(1).

              For     more     information,     see      erlang:system_info(scheduler_bind_type),
              erlang:system_info(scheduler_bindings), as well as command-line flags +sbt and +sct
              in erl(1).

       erlang:system_flag(Flag :: scheduler_wall_time, Boolean) ->
                             OldBoolean

              Types:

                 Boolean = OldBoolean = boolean()

              Turns on or off scheduler wall time measurements.

              For more information, see statistics(scheduler_wall_time).

       erlang:system_flag(Flag :: schedulers_online, SchedulersOnline) ->
                             OldSchedulersOnline

              Types:

                 SchedulersOnline = OldSchedulersOnline = integer() >= 1

              Sets  the  number  of  schedulers  online.  Range  is  1  <=  SchedulersOnline   <=
              erlang:system_info(schedulers).

              Returns the old value of the flag.

              If  the  emulator was built with support for  dirty schedulers, changing the number
              of schedulers online can also change the number of dirty CPU schedulers online. For
              example,  if 12 schedulers and 6 dirty CPU schedulers are online, and system_flag/2
              is used to set the number of schedulers online to 6, then the number of  dirty  CPU
              schedulers online is automatically decreased by half as well, down to 3. Similarly,
              the number of dirty CPU schedulers online increases proportionally to increases  in
              the number of schedulers online.

              For      more      information,      see     erlang:system_info(schedulers)     and
              erlang:system_info(schedulers_online).

       erlang:system_flag(Flag :: system_logger, Logger) -> PrevLogger

              Types:

                 Logger = PrevLogger = logger | undefined | pid()

              Sets the process that will receive the logging messages generated by ERTS.  If  set
              to  undefined, all logging messages generated by ERTS will be dropped. The messages
              will be in the format:

              {log,Level,Format,ArgList,Metadata} where

              Level = atom(),
              Format = string(),
              ArgList = list(term()),
              Metadata = #{ pid => pid(),
                 group_leader => pid(),
                 time := logger:timestamp(),
                 error_logger := #{ emulator := true, tag := atom() }

              If the system_logger process dies, this flag will be reset to logger.

              The default is the process named logger.

              Returns the old value of the flag.

          Note:
              This function is designed to be used by the KERNEL logger. Be careful if you change
              it to something else as log messages may be lost. If you want to intercept emulator
              log messages, do it by adding a specialized handler to the KERNEL logger.

       erlang:system_flag(Flag :: trace_control_word, TCW) -> OldTCW

              Types:

                 TCW = OldTCW = integer() >= 0

              Sets the value of the node trace control word to TCW, which is to  be  an  unsigned
              integer.   For   more   information,   see   function  set_tcw  in  section  "Match
              Specifications in Erlang" in the User's Guide.

              Returns the old value of the flag.

       erlang:system_flag(Flag :: time_offset, Value :: finalize) ->
                             OldState

              Types:

                 OldState = preliminary | final | volatile

              Finalizes the time offset when single time warp mode is used. If another time  warp
              mode is used, the time offset state is left unchanged.

              Returns the old state identifier, that is:

                * If  preliminary  is returned, finalization was performed and the time offset is
                  now final.

                * If final is returned, the time offset was already  in  the  final  state.  This
                  either   because  another  erlang:system_flag(time_offset,  finalize)  call  or
                  because no time warp mode is used.

                * If volatile is returned, the time offset cannot be finalized because multi-time
                  warp mode is used.

       erlang:system_info(Item ::
                              wordsize |
                              {wordsize, internal} |
                              {wordsize, external}) ->
                             4 | 8

              Returns information about the current system. The documentation of this function is
              broken into the following sections in order to make it easier to navigate.

                Memory Allocation:
                  allocated_areas, allocator, alloc_util_allocators, allocator_sizes, elib_malloc

                CPU Topology:
                  cpu_topology, logical_processors, update_cpu_info

                Process Information:
                  fullsweep_after,  garbage_collection,  heap_sizes,  heap_type,   max_heap_size,
                  message_queue_data, min_heap_size, min_bin_vheap_size, procs

                System Limits:
                  atom_count,   atom_limit,   ets_count,   ets_limit,   port_count,   port_limit,
                  process_count, process_limit

                System Time:
                  end_time,    os_monotonic_time_source,    os_system_time_source,    start_time,
                  time_correction, time_offset, time_warp_mode, tolerant_timeofday

                Scheduler Information:
                  dirty_cpu_schedulers,     dirty_cpu_schedulers_online,     dirty_io_schedulers,
                  multi_scheduling, multi_scheduling_blockers,  normal_multi_scheduling_blockers,
                  scheduler_bind_type, scheduler_bindings, scheduler_id, schedulers, smp_support,
                  threads, thread_pool_size

                Distribution Information:
                  creation, delayed_node_table_gc, dist, dist_buf_busy_limit, dist_ctrl

                System Information:
                  build_type,    c_compiler_used,    check_io,    compat_rel,     debug_compiled,
                  driver_version, dynamic_trace, dynamic_trace_probes, info, kernel_poll, loaded,
                  machine,  modified_timing_level,  nif_version,  otp_release,  port_parallelism,
                  system_architecture,    system_logger,    system_version,   trace_control_word,
                  version, wordsize

       erlang:system_info(Item :: allocated_areas) -> [tuple()]

       erlang:system_info(Item :: allocator) ->
                             {Allocator, Version, Features, Settings}

       erlang:system_info(Item :: {allocator, Alloc}) -> [term()]

       erlang:system_info(Item :: alloc_util_allocators) -> [Alloc]

       erlang:system_info(Item :: {allocator_sizes, Alloc}) -> [term()]

       erlang:system_info(Item :: elib_malloc) -> false

              Types:

                 Allocator = undefined | glibc
                 Version = [integer() >= 0]
                 Features = [atom()]
                 Settings =
                     [{Subsystem :: atom(),
                       [{Parameter :: atom(), Value :: term()}]}]
                 Alloc = atom()

              Returns various information about the  memory  allocators  of  the  current  system
              (emulator) as specified by Item:

                allocated_areas:
                  Returns  a list of tuples with information about miscellaneous allocated memory
                  areas.

                  Each tuple contains an atom describing the type of memory as first element  and
                  the  amount  of  allocated  memory in bytes as second element. When information
                  about allocated and used memory is present, also a third  element  is  present,
                  containing the amount of used memory in bytes.

                  erlang:system_info(allocated_areas)  is intended for debugging, and the content
                  is highly  implementation-dependent.  The  content  of  the  results  therefore
                  changes when needed without prior notice.

                  Notice that the sum of these values is not the total amount of memory allocated
                  by the emulator. Some values are part of other values, and  some  memory  areas
                  are  not  part  of the result. For information about the total amount of memory
                  allocated by the emulator, see erlang:memory/0,1.

                allocator:
                  Returns {Allocator, Version, Features, Settings, where:

                  * Allocator corresponds to  the  malloc()  implementation  used.  If  Allocator
                    equals  undefined,  the  malloc()  implementation  used cannot be identified.
                    glibc can be identified.

                  * Version is a list of integers (but not a string) representing the version  of
                    the malloc() implementation used.

                  * Features is a list of atoms representing the allocation features used.

                  * Settings  is  a  list  of subsystems, their configurable parameters, and used
                    values. Settings can differ  between  different  combinations  of  platforms,
                    allocators, and allocation features. Memory sizes are given in bytes.

                  See also "System Flags Effecting erts_alloc" in erts_alloc(3erl).

                {allocator, Alloc}:
                  Returns  information  about  the  specified  allocator. As from ERTS 5.6.1, the
                  return value is a list of {instance, InstanceNo,  InstanceInfo}  tuples,  where
                  InstanceInfo  contains  information about a specific instance of the allocator.
                  If Alloc is not a recognized allocator, undefined  is  returned.  If  Alloc  is
                  disabled, false is returned.

                  Notice that the information returned is highly implementation-dependent and can
                  be changed or removed at any  time  without  prior  notice.  It  was  initially
                  intended as a tool when developing new allocators, but as it can be of interest
                  for others it has been briefly documented.

                  The recognized allocators are listed  in  erts_alloc(3erl).  Information  about
                  super  carriers  can  be  obtained from ERTS 8.0 with {allocator, erts_mmap} or
                  from ERTS 5.10.4; the returned list when calling with  {allocator,  mseg_alloc}
                  also includes an {erts_mmap, _} tuple as one element in the list.

                  After reading the erts_alloc(3erl) documentation, the returned information more
                  or less speaks for itself, but it can be worth  explaining  some  things.  Call
                  counts  are  presented  by  two  values, the first value is giga calls, and the
                  second value is calls. mbcs and sbcs denote multi-block carriers,  and  single-
                  block  carriers, respectively. Sizes are presented in bytes. When a size is not
                  presented, it is the amount of something. Sizes and amounts are often presented
                  by three values:

                  * The first is the current value.

                  * The    second    is    the   maximum   value   since   the   last   call   to
                    erlang:system_info({allocator, Alloc}).

                  * The third is the maximum value since the emulator was started.

                  If only one value is present, it is the current value. fix_alloc  memory  block
                  types  are presented by two values. The first value is the memory pool size and
                  the second value is the used memory size.

                alloc_util_allocators:
                  Returns a list  of  the  names  of  all  allocators  using  the  ERTS  internal
                  alloc_util framework as atoms. For more information, see section The alloc_util
                  framework in erts_alloc(3erl).

                {allocator_sizes, Alloc}:
                  Returns various size information for the specified allocator.  The  information
                  returned     is     a     subset     of    the    information    returned    by
                  erlang:system_info({allocator, Alloc}).

                elib_malloc:
                  This option will be removed in a future release. The return value  will  always
                  be false, as the elib_malloc allocator has been removed.

       erlang:system_info(Item :: cpu_topology) -> CpuTopology

       erlang:system_info(Item ::
                              {cpu_topology, defined | detected | used}) ->
                             CpuTopology

       erlang:system_info(Item ::
                              logical_processors |
                              logical_processors_available |
                              logical_processors_online) ->
                             unknown | integer() >= 1

       erlang:system_info(Item :: update_cpu_info) -> changed | unchanged

              Types:

                 cpu_topology() = [LevelEntry :: level_entry()] | undefined
                    All  LevelEntrys  of a list must contain the same LevelTag, except on the top
                   level where both node and processorLevelTags can coexist.
                 level_entry() =
                     {LevelTag :: level_tag(), SubLevel :: sub_level()} |
                     {LevelTag :: level_tag(),
                      InfoList :: info_list(),
                      SubLevel :: sub_level()}
                   {LevelTag, SubLevel} == {LevelTag, [], SubLevel}
                 level_tag() = core | node | processor | thread
                    More LevelTags can be introduced in a future release.
                 sub_level() =
                     [LevelEntry :: level_entry()] |
                     (LogicalCpuId :: {logical, integer() >= 0})
                 info_list() = []
                    The info_list() can be extended in a future release.

              Returns various information about the CPU topology of the current system (emulator)
              as specified by Item:

                cpu_topology:
                  Returns  the  CpuTopology  currently  used by the emulator. The CPU topology is
                  used when binding schedulers to logical processors. The CPU  topology  used  is
                  the   user-defined  CPU  topology, if such exists, otherwise the  automatically
                  detected CPU topology, if such exists. If no CPU topology exists, undefined  is
                  returned.

                  node  refers  to  Non-Uniform  Memory  Access  (NUMA)  nodes.  thread refers to
                  hardware threads (for example, Intel hyper-threads).

                  A level in term CpuTopology can  be  omitted  if  only  one  entry  exists  and
                  InfoList is empty.

                  thread  can  only be a sublevel to core. core can be a sublevel to processor or
                  node. processor can be on the top level or a sublevel to node. node can  be  on
                  the  top level or a sublevel to processor. That is, NUMA nodes can be processor
                  internal or processor external.  A  CPU  topology  can  consist  of  a  mix  of
                  processor internal and external NUMA nodes, as long as each logical CPU belongs
                  to one NUMA node. Cache hierarchy is not part of the CpuTopology type, but will
                  be  in a future release. Other things can also make it into the CPU topology in
                  a future release. So, expect the CpuTopology type to change.

                {cpu_topology, defined}:

                  Returns the user-defined CpuTopology. For more  information,  see  command-line
                  flag +sct in erl(1) and argument cpu_topology.

                {cpu_topology, detected}:

                  Returns  the  automatically detected CpuTopologyy. The emulator detects the CPU
                  topology on some newer Linux, Solaris, FreeBSD, and Windows systems. On Windows
                  system with more than 32 logical processors, the CPU topology is not detected.

                  For more information, see argument cpu_topology.

                {cpu_topology, used}:
                  Returns  CpuTopology  used  by the emulator. For more information, see argument
                  cpu_topology.

                logical_processors:
                  Returns the detected number of logical processors configured in the system. The
                  return  value  is either an integer, or the atom unknown if the emulator cannot
                  detect the configured logical processors.

                logical_processors_available:
                  Returns the detected number of  logical  processors  available  to  the  Erlang
                  runtime  system.  The return value is either an integer, or the atom unknown if
                  the emulator cannot detect the available  logical  processors.  The  number  of
                  available  logical  processors  is less than or equal to the number of  logical
                  processors online.

                logical_processors_online:
                  Returns the detected number of logical processors online  on  the  system.  The
                  return  value  is either an integer, or the atom unknown if the emulator cannot
                  detect logical processors online. The number of logical  processors  online  is
                  less than or equal to the number of logical processors configured.

                update_cpu_info:
                  The  runtime  system  rereads  the  CPU  information  available and updates its
                  internally stored information about the detected CPU topology and the number of
                  logical processors configured, online, and  available.

                  If  the  CPU  information has changed since the last time it was read, the atom
                  changed is returned, otherwise the atom unchanged. If the CPU  information  has
                  changed,  you  probably  want  to  adjust  the number of schedulers online. You
                  typically want  to  have  as  many  schedulers  online  as  logical  processors
                  available.

       erlang:system_info(Item :: fullsweep_after) ->
                             {fullsweep_after, integer() >= 0}

       erlang:system_info(Item :: garbage_collection) ->
                             [{atom(), integer()}]

       erlang:system_info(Item :: heap_sizes) -> [integer() >= 0]

       erlang:system_info(Item :: heap_type) -> private

       erlang:system_info(Item :: max_heap_size) ->
                             {max_heap_size,
                              MaxHeapSize :: max_heap_size()}

       erlang:system_info(Item :: message_queue_data) ->
                             message_queue_data()

       erlang:system_info(Item :: min_heap_size) ->
                             {min_heap_size,
                              MinHeapSize :: integer() >= 1}

       erlang:system_info(Item :: min_bin_vheap_size) ->
                             {min_bin_vheap_size,
                              MinBinVHeapSize :: integer() >= 1}

       erlang:system_info(Item :: procs) -> binary()

              Types:

                 message_queue_data() = off_heap | on_heap
                 max_heap_size() =
                     integer() >= 0 |
                     #{size => integer() >= 0,
                       kill => boolean(),
                       error_logger => boolean()}

              Returns information about the default process heap settings:

                fullsweep_after:
                  Returns {fullsweep_after, integer() >= 0}, which is the fullsweep_after garbage
                  collection   setting   used   by   default.   For   more    information,    see
                  garbage_collection described below.

                garbage_collection:
                  Returns  a  list  describing the default garbage collection settings. A process
                  spawned on the  local  node  by  a  spawn  or  spawn_link  uses  these  garbage
                  collection   settings.   The   default   settings   can  be  changed  by  using
                  erlang:system_flag/2. spawn_opt/2,3,4 can spawn a process that does not use the
                  default settings.

                heap_sizes:
                  Returns  a  list of integers representing valid heap sizes in words. All Erlang
                  heaps are sized from sizes in this list.

                heap_type:
                  Returns the heap type used by the current emulator. One heap type exists:

                  private:
                     Each process has a heap reserved for its use and no references between heaps
                    of  different  processes  are  allowed. Messages passed between processes are
                    copied between heaps.

                max_heap_size:
                  Returns {max_heap_size, MaxHeapSize}, where MaxHeapSize is the current  system-
                  wide  maximum heap size settings for spawned processes. This setting can be set
                  using the command-line flags +hmax, +hmaxk and +hmaxel in erl(1). It  can  also
                  be changed at runtime using erlang:system_flag(max_heap_size, MaxHeapSize). For
                  more    details    about    the     max_heap_size     process     flag,     see
                  process_flag(max_heap_size, MaxHeapSize).

                message_queue_data:
                  Returns  the  default  value  of  the message_queue_data process flag, which is
                  either off_heap or on_heap. This default is set by command-line argument  +hmqd
                  in  erl(1).  For  more  information on the message_queue_data process flag, see
                  documentation of process_flag(message_queue_data, MQD).

                min_heap_size:
                  Returns {min_heap_size, MinHeapSize}, where MinHeapSize is the current  system-
                  wide minimum heap size for spawned processes.

                min_bin_vheap_size:
                  Returns  {min_bin_vheap_size,  MinBinVHeapSize},  where  MinBinVHeapSize is the
                  current system-wide minimum binary virtual heap size for spawned processes.

                procs:
                  Returns a binary containing a string of process and port information  formatted
                  as  in  Erlang crash dumps. For more information, see section  How to interpret
                  the Erlang crash dumps in the User's Guide.

       erlang:system_info(Item :: atom_count) -> integer() >= 1

       erlang:system_info(Item :: atom_limit) -> integer() >= 1

       erlang:system_info(Item :: ets_count) -> integer() >= 1

       erlang:system_info(Item :: ets_limit) -> integer() >= 1

       erlang:system_info(Item :: port_count) -> integer() >= 0

       erlang:system_info(Item :: port_limit) -> integer() >= 1

       erlang:system_info(Item :: process_count) -> integer() >= 1

       erlang:system_info(Item :: process_limit) -> integer() >= 1

              Returns information about the current system  (emulator)  limits  as  specified  by
              Item:

                atom_count:
                  Returns  the number of atoms currently existing at the local node. The value is
                  given as an integer.

                atom_limit:
                  Returns the maximum number of atoms allowed. This limit  can  be  increased  at
                  startup by passing command-line flag +t to erl(1).

                ets_count:
                  Returns the number of ETS tables currently existing at the local node.

                ets_limit:
                  Returns  the  limit  for number of ETS tables. This limit is partially obsolete
                  and number of tables are only limited by available memory.

                port_count:
                  Returns the number of ports currently existing at the local node. The value  is
                  given   as   an   integer.   This   is   the   same   value   as   returned  by
                  length(erlang:ports()), but more efficient.

                port_limit:
                  Returns the maximum number of simultaneously existing ports at the  local  node
                  as  an  integer.  This limit can be configured at startup by using command-line
                  flag +Q in erl(1).

                process_count:
                  Returns the number of processes currently existing at the local node. The value
                  is   given   as   an   integer.   This   is  the  same  value  as  returned  by
                  length(processes()), but more efficient.

                process_limit:
                  Returns the maximum number of simultaneously existing processes  at  the  local
                  node. The value is given as an integer. This limit can be configured at startup
                  by using command-line flag +P in erl(1).

       erlang:system_info(Item :: end_time) -> integer() >= 0

       erlang:system_info(Item :: os_monotonic_time_source) ->
                             [{atom(), term()}]

       erlang:system_info(Item :: os_system_time_source) ->
                             [{atom(), term()}]

       erlang:system_info(Item :: start_time) -> integer()

       erlang:system_info(Item :: time_correction) -> true | false

       erlang:system_info(Item :: time_offset) ->
                             preliminary | final | volatile

       erlang:system_info(Item :: time_warp_mode) ->
                             no_time_warp | single_time_warp |
                             multi_time_warp

       erlang:system_info(Item :: tolerant_timeofday) ->
                             enabled | disabled

              Returns information about the current system (emulator) time as specified by Item:

                end_time:
                  The last Erlang monotonic time in native time  unit  that  can  be  represented
                  internally  in the current Erlang runtime system instance. The time between the
                  start time and the end time is at least a quarter of a millennium.

                os_monotonic_time_source:
                  Returns a list containing information about the source  of  OS  monotonic  time
                  that is used by the runtime system.

                  If  []  is  returned, no OS monotonic time is available. The list contains two-
                  tuples with Keys as first element, and Values as second element. The  order  of
                  these  tuples  is  undefined. The following tuples can be part of the list, but
                  more tuples can be introduced in the future:

                  {function, Function}:
                    Function is the name of the function used. This tuple  always  exists  if  OS
                    monotonic time is available to the runtime system.

                  {clock_id, ClockId}:
                    This tuple only exists if Function can be used with different clocks. ClockId
                    corresponds to the clock identifier used when calling Function.

                  {resolution, OsMonotonicTimeResolution}:
                    Highest possible  resolution of current OS monotonic time source as parts per
                    second.   If  no  resolution  information  can  be  retrieved  from  the  OS,
                    OsMonotonicTimeResolution is set to  the  resolution  of  the  time  unit  of
                    Functions  return  value.  That  is,  the actual resolution can be lower than
                    OsMonotonicTimeResolution. Notice that the resolution does not  say  anything
                    about the  accuracy or whether the  precision aligns with the resolution. You
                    do,   however,   know   that   the   precision    is    not    better    than
                    OsMonotonicTimeResolution.

                  {extended, Extended}:
                    Extended  equals yes if the range of time values has been extended; otherwise
                    Extended equals no. The range must be extended  if  Function  returns  values
                    that  wrap fast. This typically is the case when the return value is a 32-bit
                    value.

                  {parallel, Parallel}:
                    Parallel equals yes if Function is called in parallel from multiple  threads.
                    If  it  is not called in parallel, because calls must be serialized, Parallel
                    equals no.

                  {time, OsMonotonicTime}:
                    OsMonotonicTime equals current OS monotonic time in native time unit.

                os_system_time_source:
                  Returns a list containing information about the source of OS system  time  that
                  is used by the runtime system.

                  The  list  contains two-tuples with Keys as first element, and Values as second
                  element. The order of these tuples is undefined. The following  tuples  can  be
                  part of the list, but more tuples can be introduced in the future:

                  {function, Function}:
                    Function is the name of the funcion used.

                  {clock_id, ClockId}:
                    Exists   only  if  Function  can  be  used  with  different  clocks.  ClockId
                    corresponds to the clock identifier used when calling Function.

                  {resolution, OsSystemTimeResolution}:
                    Highest possible  resolution of current OS system time source  as  parts  per
                    second.   If  no  resolution  information  can  be  retrieved  from  the  OS,
                    OsSystemTimeResolution is set to the resolution of the time unit of Functions
                    return   value.   That   is,   the   actual  resolution  can  be  lower  than
                    OsSystemTimeResolution. Notice that the  resolution  does  not  say  anything
                    about  the   accuracy or whether the  precision do align with the resolution.
                    You  do,  however,   know   that   the   precision   is   not   better   than
                    OsSystemTimeResolution.

                  {parallel, Parallel}:
                    Parallel  equals yes if Function is called in parallel from multiple threads.
                    If it is not called in  parallel,  because  calls  needs  to  be  serialized,
                    Parallel equals no.

                  {time, OsSystemTime}:
                    OsSystemTime equals current OS system time in native time unit.

                start_time:
                  The  Erlang  monotonic time in native time unit at the time when current Erlang
                  runtime system instance started.

                  See also erlang:system_info(end_time).

                time_correction:
                  Returns a boolean value indicating whether  time correction is enabled or not.

                time_offset:
                  Returns the state of the time offset:

                  preliminary:
                    The time offset is preliminary, and will be changed and finalized later.  The
                    preliminary  time  offset is used during the preliminary phase of the  single
                    time warp mode.

                  final:
                    The time offset is final. This either because  no time warp mode is used,  or
                    because  the  time  offset have been finalized when  single time warp mode is
                    used.

                  volatile:
                    The time offset is volatile. That is, it can change  at  any  time.  This  is
                    because  multi-time warp mode is used.

                time_warp_mode:
                  Returns a value identifying the  time warp mode that is used:

                  no_time_warp:
                    The  no time warp mode is used.

                  single_time_warp:
                    The  single time warp mode is used.

                  multi_time_warp:
                    The  multi-time warp mode is used.

                tolerant_timeofday:
                  Returns  whether  a  pre  ERTS 7.0 backwards compatible compensation for sudden
                  changes of system time is enabled or disabled.  Such  compensation  is  enabled
                  when the time offset is final, and  time correction is enabled.

       erlang:system_info(Item :: dirty_cpu_schedulers) ->
                             integer() >= 0

       erlang:system_info(Item :: dirty_cpu_schedulers_online) ->
                             integer() >= 0

       erlang:system_info(Item :: dirty_io_schedulers) ->
                             integer() >= 0

       erlang:system_info(Item :: multi_scheduling) ->
                             disabled | blocked | blocked_normal |
                             enabled

       erlang:system_info(Item :: multi_scheduling_blockers) ->
                             [Pid :: pid()]

       erlang:system_info(Item :: otp_release) -> string()

       erlang:system_info(Item :: scheduler_bind_type) ->
                             spread | processor_spread | thread_spread |
                             thread_no_node_processor_spread |
                             no_node_processor_spread |
                             no_node_thread_spread | no_spread | unbound

       erlang:system_info(Item :: scheduler_bindings) -> tuple()

       erlang:system_info(Item :: scheduler_id) ->
                             SchedulerId :: integer() >= 1

       erlang:system_info(Item :: schedulers | schedulers_online) ->
                             integer() >= 1

       erlang:system_info(Item :: smp_support) -> boolean()

       erlang:system_info(Item :: threads) -> boolean()

       erlang:system_info(Item :: thread_pool_size) -> integer() >= 0

              Returns  information about schedulers, scheduling and threads in the current system
              as specified by Item:

                dirty_cpu_schedulers:
                  Returns the number of dirty CPU scheduler threads used by the  emulator.  Dirty
                  CPU  schedulers  execute  CPU-bound  native  functions, such as NIFs, linked-in
                  driver code, and BIFs that cannot be managed cleanly  by  the  normal  emulator
                  schedulers.

                  The  number  of dirty CPU scheduler threads is determined at emulator boot time
                  and cannot be changed after that. However, the number of  dirty  CPU  scheduler
                  threads  online  can be changed at any time. The number of dirty CPU schedulers
                  can be set at startup by passing command-line flag +SDcpu or +SDPcpu in erl(1).

                  See            also             erlang:system_flag(dirty_cpu_schedulers_online,
                  DirtyCPUSchedulersOnline),     erlang:system_info(dirty_cpu_schedulers_online),
                  erlang:system_info(dirty_io_schedulers),        erlang:system_info(schedulers),
                  erlang:system_info(schedulers_online),                                      and
                  erlang:system_flag(schedulers_online, SchedulersOnline).

                dirty_cpu_schedulers_online:
                  Returns the number of dirty CPU schedulers online. The return value satisfies 1
                  <=  DirtyCPUSchedulersOnline <= N, where N is the smallest of the return values
                  of                 erlang:system_info(dirty_cpu_schedulers)                 and
                  erlang:system_info(schedulers_online).

                  The  number  of  dirty  CPU  schedulers online can be set at startup by passing
                  command-line flag +SDcpu in erl(1).

                  For    more    information,    see    erlang:system_info(dirty_cpu_schedulers),
                  erlang:system_info(dirty_io_schedulers), erlang:system_info(schedulers_online),
                  and erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline).

                dirty_io_schedulers:
                  Returns the number of dirty I/O schedulers as an integer. Dirty I/O  schedulers
                  execute  I/O-bound  native  functions,  such as NIFs and linked-in driver code,
                  which cannot be managed cleanly by the normal emulator schedulers.

                  This value can be set at startup by  passing  command-line  argument  +SDio  in
                  erl(1).

                  For    more    information,    see    erlang:system_info(dirty_cpu_schedulers),
                  erlang:system_info(dirty_cpu_schedulers_online),                            and
                  erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline).

                multi_scheduling:
                  Returns one of the following:

                  disabled:
                    The emulator has been started with only one scheduler thread.

                  blocked:
                    The  emulator  has  more than one scheduler thread, but all scheduler threads
                    except one are blocked. That is, only one scheduler thread  schedules  Erlang
                    processes and executes Erlang code.

                  blocked_normal:
                    The  emulator  has  more  than one scheduler thread, but all normal scheduler
                    threads except one are blocked. Notice that dirty schedulers are not blocked,
                    and can schedule Erlang processes and execute native code.

                  enabled:
                    The emulator has more than one scheduler thread, and no scheduler threads are
                    blocked. That is, all available scheduler threads schedule  Erlang  processes
                    and execute Erlang code.

                  See        also        erlang:system_flag(multi_scheduling,        BlockState),
                  erlang:system_info(multi_scheduling_blockers),
                  erlang:system_info(normal_multi_scheduling_blockers),                       and
                  erlang:system_info(schedulers).

                multi_scheduling_blockers:
                  Returns a list of Pids when multi-scheduling is blocked,  otherwise  the  empty
                  list  is  returned.  The Pids in the list represent all the processes currently
                  blocking multi-scheduling. A Pid occurs only once in  the  list,  even  if  the
                  corresponding process has blocked multiple times.

                  See        also        erlang:system_flag(multi_scheduling,        BlockState),
                  erlang:system_info(multi_scheduling),
                  erlang:system_info(normal_multi_scheduling_blockers),                       and
                  erlang:system_info(schedulers).

                normal_multi_scheduling_blockers:
                  Returns a list of Pids when normal multi-scheduling is blocked  (that  is,  all
                  normal  schedulers  but  one is blocked), otherwise the empty list is returned.
                  The Pids in the list represent all  the  processes  currently  blocking  normal
                  multi-scheduling. A Pid occurs only once in the list, even if the corresponding
                  process has blocked multiple times.

                  See        also        erlang:system_flag(multi_scheduling,        BlockState),
                  erlang:system_info(multi_scheduling),
                  erlang:system_info(multi_scheduling_blockers),                              and
                  erlang:system_info(schedulers).

                scheduler_bind_type:
                  Returns  information about how the user has requested schedulers to be bound or
                  not bound.

                  Notice that although a user has requested schedulers  to  be  bound,  they  can
                  silently  have  failed  to  bind.  To  inspect  the  scheduler  bindings,  call
                  erlang:system_info(scheduler_bindings).

                  For  more  information,  see  command-line  argument   +sbt   in   erl(1)   and
                  erlang:system_info(scheduler_bindings).

                scheduler_bindings:
                  Returns information about the currently used scheduler bindings.

                  A  tuple  of  a  size  equal to erlang:system_info(schedulers) is returned. The
                  tuple elements are integers or the atom unbound. Logical processor  identifiers
                  are  represented  as  integers. The Nth element of the tuple equals the current
                  binding for the scheduler  with  the  scheduler  identifier  equal  to  N.  For
                  example, if the schedulers are bound, element(erlang:system_info(scheduler_id),
                  erlang:system_info(scheduler_bindings)) returns the identifier of  the  logical
                  processor that the calling process is executing on.

                  Notice that only schedulers online can be bound to logical processors.

                  For   more   information,   see   command-line  argument  +sbt  in  erl(1)  and
                  erlang:system_info(schedulers_online).

                scheduler_id:
                  Returns the scheduler ID (SchedulerId) of the scheduler thread that the calling
                  process  is  executing  on.  SchedulerId  is  a  positive  integer,  where 1 <=
                  SchedulerId <= erlang:system_info(schedulers).

                  See also erlang:system_info(schedulers).

                schedulers:
                  Returns the number of scheduler threads used by the emulator. Scheduler threads
                  online schedules Erlang processes and Erlang ports, and execute Erlang code and
                  Erlang linked-in driver code.

                  The number of scheduler threads is determined at emulator boot time and  cannot
                  be  changed  later.  However, the number of schedulers online can be changed at
                  any time.

                  See     also      erlang:system_flag(schedulers_online,      SchedulersOnline),
                  erlang:system_info(schedulers_online),        erlang:system_info(scheduler_id),
                  erlang:system_flag(multi_scheduling,                               BlockState),
                  erlang:system_info(multi_scheduling),
                  erlang:system_info(normal_multi_scheduling_blockers)                        and
                  erlang:system_info(multi_scheduling_blockers).

                schedulers_online:
                  Returns   the  number  of  schedulers  online.  The  scheduler  identifiers  of
                  schedulers   online   satisfy   the   relationship   1   <=   SchedulerId    <=
                  erlang:system_info(schedulers_online).

                  For     more     information,     see     erlang:system_info(schedulers)    and
                  erlang:system_flag(schedulers_online, SchedulersOnline).

                smp_support:
                  Returns true.

                threads:
                  Returns true.

                thread_pool_size:

                  Returns the number  of  async  threads  in  the  async  thread  pool  used  for
                  asynchronous driver calls (erl_driver:driver_async()). The value is given as an
                  integer.

       erlang:system_info(Item :: creation) -> integer()

       erlang:system_info(Item :: delayed_node_table_gc) ->
                             infinity | integer() >= 0

       erlang:system_info(Item :: dist) -> binary()

       erlang:system_info(Item :: dist_buf_busy_limit) ->
                             integer() >= 0

       erlang:system_info(Item :: dist_ctrl) ->
                             {Node :: node(),
                              ControllingEntity :: port() | pid()}

              Returns information about Erlang Distribution in the current system as specified by
              Item:

                creation:
                  Returns  the  creation of the local node as an integer. The creation is changed
                  when a node is  restarted.  The  creation  of  a  node  is  stored  in  process
                  identifiers,  port  identifiers, and references. This makes it (to some extent)
                  possible to distinguish between identifiers from different  incarnations  of  a
                  node.  The  valid  creations  are  integers  in  the  range 1..3, but this will
                  probably change in a future release. If the node is not alive, 0 is returned.

                delayed_node_table_gc:
                  Returns the amount of time in seconds garbage collection of an entry in a  node
                  table is delayed. This limit can be set on startup by passing command-line flag
                  +zdntgc to erl(1). For more information, see the documentation of the  command-
                  line flag.

                dist:
                  Returns  a  binary containing a string of distribution information formatted as
                  in Erlang crash dumps. For more information, see section  How to interpret  the
                  Erlang crash dumps in the User's Guide.

                dist_buf_busy_limit:
                  Returns  the  value  of the distribution buffer busy limit in bytes. This limit
                  can be set at startup by passing command-line flag +zdbbl to erl(1).

                dist_ctrl:
                  Returns a  list  of  tuples  {Node,  ControllingEntity},  one  entry  for  each
                  connected  remote node. Node is the node name and ControllingEntity is the port
                  or process identifier responsible for the  communication  to  that  node.  More
                  specifically,  ControllingEntity for nodes connected through TCP/IP (the normal
                  case) is the socket used in communication with the specific node.

       erlang:system_info(Item :: build_type) ->
                             opt | debug | purify | quantify | purecov |
                             gcov | valgrind | gprof | lcnt | frmptr

       erlang:system_info(Item :: c_compiler_used) -> {atom(), term()}

       erlang:system_info(Item :: check_io) -> [term()]

       erlang:system_info(Item :: compat_rel) -> integer()

       erlang:system_info(Item :: debug_compiled) -> boolean()

       erlang:system_info(Item :: driver_version) -> string()

       erlang:system_info(Item :: dynamic_trace) ->
                             none | dtrace | systemtap

       erlang:system_info(Item :: dynamic_trace_probes) -> boolean()

       erlang:system_info(Item :: info) -> binary()

       erlang:system_info(Item :: kernel_poll) -> boolean()

       erlang:system_info(Item :: loaded) -> binary()

       erlang:system_info(Item :: machine) -> string()

       erlang:system_info(Item :: modified_timing_level) ->
                             integer() | undefined

       erlang:system_info(Item :: nif_version) -> string()

       erlang:system_info(Item :: otp_release) -> string()

       erlang:system_info(Item :: port_parallelism) -> boolean()

       erlang:system_info(Item :: system_architecture) -> string()

       erlang:system_info(Item :: system_logger) ->
                             logger | undefined | pid()

       erlang:system_info(Item :: system_version) -> string()

       erlang:system_info(Item :: trace_control_word) ->
                             integer() >= 0

       erlang:system_info(Item :: version) -> string()

       erlang:system_info(Item ::
                              wordsize |
                              {wordsize, internal} |
                              {wordsize, external}) ->
                             4 | 8

              Returns various information about the current system  (emulator)  as  specified  by
              Item:

                build_type:
                  Returns  an  atom  describing  the  build  type  of the runtime system. This is
                  normally the atom opt for optimized. Other possible return  values  are  debug,
                  purify,  quantify,  purecov,  gcov,  valgrind, gprof, and lcnt. Possible return
                  values can be added or removed at any time without prior notice.

                c_compiler_used:
                  Returns a two-tuple describing the C compiler used when compiling  the  runtime
                  system.  The  first  element is an atom describing the name of the compiler, or
                  undefined if unknown. The second element is a term describing  the  version  of
                  the compiler, or undefined if unknown.

                check_io:
                  Returns  a  list  containing  miscellaneous  information  about  the  emulators
                  internal I/O checking. Notice that the content of the returned  list  can  vary
                  between platforms and over time. It is only guaranteed that a list is returned.

                compat_rel:
                  Returns  the  compatibility  mode  of the local node as an integer. The integer
                  returned represents the Erlang/OTP release that the current emulator  has  been
                  set to be backward compatible with. The compatibility mode can be configured at
                  startup by using command-line flag +R in erl(1).

                debug_compiled:
                  Returns true if the emulator has been debug-compiled, otherwise false.

                driver_version:
                  Returns a string containing the Erlang  driver  version  used  by  the  runtime
                  system. It has the form  "<major ver>.<minor ver>".

                dynamic_trace:
                  Returns  an  atom  describing  the  dynamic  trace  framework compiled into the
                  virtual machine. It can be dtrace, systemtap, or  none.  For  a  commercial  or
                  standard  build,  it  is always none. The other return values indicate a custom
                  configuration (for example, ./configure --with-dynamic-trace=dtrace). For  more
                  information  about  dynamic  tracing,  see  dyntrace(3erl)  manual page and the
                  README.dtrace/README.systemtap files in the Erlang source code top directory.

                dynamic_trace_probes:
                  Returns a boolean() indicating if dynamic trace probes  (dtrace  or  systemtap)
                  are  built  into the emulator. This can only be true if the virtual machine was
                  built for dynamic tracing (that is, system_info(dynamic_trace)  returns  dtrace
                  or systemtap).

                info:
                  Returns  a  binary  containing  a  string  of  miscellaneous system information
                  formatted as in Erlang crash dumps. For more information, see section   How  to
                  interpret the Erlang crash dumps in the User's Guide.

                kernel_poll:
                  Returns  true  if  the  emulator  uses some kind of kernel-poll implementation,
                  otherwise false.

                loaded:
                  Returns a binary containing a string of loaded module information formatted  as
                  in  Erlang  crash dumps. For more information, see section How to interpret the
                  Erlang crash dumps in the User's Guide.

                machine:
                  Returns a string containing the Erlang machine name.

                modified_timing_level:
                  Returns the modified timing-level (an integer) if modified timing  is  enabled,
                  otherwise  undefined.  For more information about modified timing, see command-
                  line flag +T in erl(1)

                nif_version:
                  Returns a string containing the version of the Erlang NIF interface used by the
                  runtime system. It is on the form "<major ver>.<minor ver>".

                otp_release:

                  Returns  a string containing the OTP release number of the OTP release that the
                  currently executing ERTS application is part of.

                  As from Erlang/OTP 17, the OTP release number  corresponds  to  the  major  OTP
                  version  number.  No erlang:system_info() argument gives the exact OTP version.
                  This is because the exact OTP version in  the  general  case  is  difficult  to
                  determine.  For  more  information,  see the description of versions in  System
                  principles in System Documentation.

                port_parallelism:
                  Returns  the  default  port  parallelism  scheduling  hint   used.   For   more
                  information, see command-line argument +spp in erl(1).

                system_architecture:
                  Returns  a  string containing the processor and OS architecture the emulator is
                  built for.

                system_logger:
                  Returns the current system_logger as set  by  erlang:system_flag(system_logger,
                  _).

                system_version:
                  Returns  a string containing version number and some important properties, such
                  as the number of schedulers.

                trace_control_word:
                  Returns the value of the node trace control word.  For  more  information,  see
                  function  get_tcw  in  section   Match  Specifications  in Erlang in the User's
                  Guide.

                version:
                  Returns a string containing the version number of the emulator.

                wordsize:
                  Same as {wordsize, internal}.

                {wordsize, internal}:
                  Returns the size of Erlang term words in bytes as an integer,  that  is,  4  is
                  returned  on  a  32-bit  architecture,  and  8  is  returned  on  a pure 64-bit
                  architecture. On a halfword 64-bit emulator, 4 is returned, as the Erlang terms
                  are stored using a virtual word size of half the system word size.

                {wordsize, external}:
                  Returns the true word size of the emulator, that is, the size of a pointer. The
                  value is given in bytes as an integer. On a  pure  32-bit  architecture,  4  is
                  returned. On both a half word and on a pure 64-bit architecture, 8 is returned.

       erlang:system_monitor() -> MonSettings

              Types:

                 MonSettings = undefined | {MonitorPid, Options}
                 MonitorPid = pid()
                 Options = [system_monitor_option()]
                 system_monitor_option() =
                     busy_port | busy_dist_port |
                     {long_gc, integer() >= 0} |
                     {long_schedule, integer() >= 0} |
                     {large_heap, integer() >= 0}

              Returns  the  current  system monitoring settings set by erlang:system_monitor/2 as
              {MonitorPid, Options}, or undefined if no settings exist. The order of the  options
              can be different from the one that was set.

       erlang:system_monitor(Arg) -> MonSettings

              Types:

                 Arg = MonSettings = undefined | {MonitorPid, Options}
                 MonitorPid = pid()
                 Options = [system_monitor_option()]
                 system_monitor_option() =
                     busy_port | busy_dist_port |
                     {long_gc, integer() >= 0} |
                     {long_schedule, integer() >= 0} |
                     {large_heap, integer() >= 0}

              When called with argument undefined, all system performance monitoring settings are
              cleared.

              Calling the function with {MonitorPid, Options} as argument is the same as  calling
              erlang:system_monitor(MonitorPid, Options).

              Returns the previous system monitor settings just like erlang:system_monitor/0.

       erlang:system_monitor(MonitorPid, Options) -> MonSettings

              Types:

                 MonitorPid = pid()
                 Options = [system_monitor_option()]
                 MonSettings = undefined | {OldMonitorPid, OldOptions}
                 OldMonitorPid = pid()
                 OldOptions = [system_monitor_option()]
                 system_monitor_option() =
                     busy_port | busy_dist_port |
                     {long_gc, integer() >= 0} |
                     {long_schedule, integer() >= 0} |
                     {large_heap, integer() >= 0}

              Sets  the  system  performance  monitoring  options.  MonitorPid is a local process
              identifier (pid) receiving system monitor messages. The second argument is  a  list
              of monitoring options:

                {long_gc, Time}:
                  If  a  garbage  collection  in  the  system  takes  at  least  Time  wall clock
                  milliseconds, a message {monitor, GcPid, long_gc, Info} is sent to  MonitorPid.
                  GcPid  is  the  pid  that  was garbage collected. Info is a list of two-element
                  tuples describing the result of the garbage collection.

                  One of the tuples is {timeout, GcTime},  where  GcTime  is  the  time  for  the
                  garbage collection in milliseconds. The other tuples are tagged with heap_size,
                  heap_block_size, stack_size, mbuf_size, old_heap_size, and old_heap_block_size.
                  These  tuples  are explained in the description of trace message gc_minor_start
                  (see erlang:trace/3). New tuples can be added, and the order of the  tuples  in
                  the Info list can be changed at any time without prior notice.

                {long_schedule, Time}:
                  If  a  process  or port in the system runs uninterrupted for at least Time wall
                  clock milliseconds, a message {monitor, PidOrPort, long_schedule, Info} is sent
                  to  MonitorPid.  PidOrPort  is  the process or port that was running. Info is a
                  list of two-element tuples describing the event.

                  If a pid(), the tuples {timeout, Millis}, {in, Location}, and  {out,  Location}
                  are  present,  where  Location  is  either  an  MFA ({Module, Function, Arity})
                  describing the function where the process was scheduled  in/out,  or  the  atom
                  undefined.

                  If  a  port(), the tuples {timeout, Millis} and {port_op,Op} are present. Op is
                  one of proc_sig, timeout, input, output, event, or dist_cmd, depending on which
                  driver callback was executing.

                  proc_sig  is  an  internal  operation  and is never to appear, while the others
                  represent   the   corresponding   driver   callbacks   timeout,    ready_input,
                  ready_output, event, and outputv (when the port is used by distribution). Value
                  Millis in tuple timeout informs about the uninterrupted execution time  of  the
                  process  or  port,  which  always  is  equal  to  or higher than the Time value
                  supplied when starting the trace. New tuples can be added to the Info list in a
                  future  release. The order of the tuples in the list can be changed at any time
                  without prior notice.

                  This can be used to detect problems with NIFs or drivers that take too long  to
                  execute. 1 ms is considered a good maximum time for a driver callback or a NIF.
                  However, a time-sharing system is usually to consider everything <  100  ms  as
                  "possible"  and  fairly  "normal".  However, longer schedule times can indicate
                  swapping or a misbehaving NIF/driver. Misbehaving NIFs and  drivers  can  cause
                  bad resource utilization and bad overall system performance.

                {large_heap, Size}:
                  If  a  garbage collection in the system results in the allocated size of a heap
                  being at least Size words, a message {monitor, GcPid, large_heap, Info} is sent
                  to  MonitorPid. GcPid and Info are the same as for long_gc earlier, except that
                  the tuple tagged with timeout is not present.

                  The monitor message is sent if the sum  of  the  sizes  of  all  memory  blocks
                  allocated  for  all  heap generations after a garbage collection is equal to or
                  higher than Size.

                  When a process is killed by max_heap_size, it  is  killed  before  the  garbage
                  collection is complete and thus no large heap message is sent.

                busy_port:
                  If  a  process  in the system gets suspended because it sends to a busy port, a
                  message {monitor, SusPid, busy_port, Port} is sent to MonitorPid. SusPid is the
                  pid that got suspended when sending to Port.

                busy_dist_port:
                  If  a  process  in the system gets suspended because it sends to a process on a
                  remote node whose inter-node communication  was  handled  by  a  busy  port,  a
                  message  {monitor,  SusPid, busy_dist_port, Port} is sent to MonitorPid. SusPid
                  is the pid that got suspended when sending through the inter-node communication
                  port Port.

              Returns the previous system monitor settings just like erlang:system_monitor/0.

          Note:
              If a monitoring process gets so large that it itself starts to cause system monitor
              messages when garbage collecting, the messages enlarge the  process  message  queue
              and probably make the problem worse.

              Keep  the  monitoring  process  neat  and  do not set the system monitor limits too
              tight.

              Failures:

                badarg:
                  If MonitorPid does not exist.

                badarg:
                  If MonitorPid is not a local process.

       erlang:system_profile() -> ProfilerSettings

              Types:

                 ProfilerSettings = undefined | {ProfilerPid, Options}
                 ProfilerPid = pid() | port()
                 Options = [system_profile_option()]
                 system_profile_option() =
                     exclusive | runnable_ports | runnable_procs | scheduler |
                     timestamp | monotonic_timestamp | strict_monotonic_timestamp

              Returns the current system profiling settings  set  by  erlang:system_profile/2  as
              {ProfilerPid,  Options},  or  undefined  if there are no settings. The order of the
              options can be different from the one that was set.

       erlang:system_profile(ProfilerPid, Options) -> ProfilerSettings

              Types:

                 ProfilerPid = pid() | port() | undefined
                 Options = [system_profile_option()]
                 ProfilerSettings =
                     undefined | {pid() | port(), [system_profile_option()]}
                 system_profile_option() =
                     exclusive | runnable_ports | runnable_procs | scheduler |
                     timestamp | monotonic_timestamp | strict_monotonic_timestamp

              Sets system profiler options. ProfilerPid is a local process  identifier  (pid)  or
              port receiving profiling messages. The receiver is excluded from all profiling. The
              second argument is a list of profiling options:

                exclusive:
                  If a synchronous call to a port from a process is done, the calling process  is
                  considered  not  runnable  during  the  call  runtime  to the port. The calling
                  process is notified as inactive,  and  later  active  when  the  port  callback
                  returns.

                monotonic_timestamp:
                  Time  stamps in profile messages use Erlang monotonic time. The time stamp (Ts)
                  has the same format and value as produced by erlang:monotonic_time(nanosecond).

                runnable_procs:
                  If a process is put into or removed from the run queue,  a  message,  {profile,
                  Pid,  State,  Mfa,  Ts},  is  sent  to  ProfilerPid. Running processes that are
                  reinserted into the run queue after having been pre-empted do not trigger  this
                  message.

                runnable_ports:
                  If a port is put into or removed from the run queue, a message, {profile, Port,
                  State, 0, Ts}, is sent to ProfilerPid.

                scheduler:
                  If a scheduler is put to sleep or awoken, a message, {profile,  scheduler,  Id,
                  State, NoScheds, Ts}, is sent to ProfilerPid.

                strict_monotonic_timestamp:
                  Time  stamps  in  profile  messages  consist  of  Erlang  monotonic  time and a
                  monotonically increasing integer. The time stamp (Ts) has the same  format  and
                  value       as       produced       by      {erlang:monotonic_time(nanosecond),
                  erlang:unique_integer([monotonic])}.

                timestamp:
                  Time stamps in profile messages include a time stamp (Ts)  that  has  the  same
                  form  as  returned  by  erlang:now(). This is also the default if no time stamp
                  flag is specified. If cpu_timestamp has been  enabled  through  erlang:trace/3,
                  this  also  effects  the  time  stamp  produced in profiling messages when flag
                  timestamp is enabled.

          Note:
              erlang:system_profile behavior can change in a future release.

       erlang:system_time() -> integer()

              Returns current  Erlang system time in native time unit.

              Calling   erlang:system_time()   is   equivalent   to   erlang:monotonic_time()   +
              erlang:time_offset().

          Note:
              This  time  is  not  a  monotonically increasing time in the general case. For more
              information, see the documentation of  time warp modes in the User's Guide.

       erlang:system_time(Unit) -> integer()

              Types:

                 Unit = time_unit()

              Returns current  Erlang system time converted into the Unit passed as argument.

              Calling         erlang:system_time(Unit)         is          equivalent          to
              erlang:convert_time_unit(erlang:system_time(), native, Unit).

          Note:
              This  time  is  not  a  monotonically increasing time in the general case. For more
              information, see the documentation of  time warp modes in the User's Guide.

       term_to_binary(Term) -> ext_binary()

              Types:

                 Term = term()

              Returns a binary data object that is the result of encoding Term according  to  the
              Erlang external term format.

              This  can be used for various purposes, for example, writing a term to a file in an
              efficient way, or sending an Erlang term to some type of communications channel not
              supported by distributed Erlang.

              > Bin = term_to_binary(hello).
              <<131,100,0,5,104,101,108,108,111>>
              > hello = binary_to_term(Bin).
              hello

              See also binary_to_term/1.

          Note:
              There   is   no   guarantee  that  this  function  will  return  the  same  encoded
              representation for the same term.

       term_to_binary(Term, Options) -> ext_binary()

              Types:

                 Term = term()
                 Options =
                     [compressed |
                      {compressed, Level :: 0..9} |
                      {minor_version, Version :: 0..2}]

              Returns a binary data object that is the result of encoding Term according  to  the
              Erlang external term format.

              If  option  compressed  is  provided,  the  external term format is compressed. The
              compressed  format  is  automatically  recognized  by  binary_to_term/1   as   from
              Erlang/OTP R7B.

              A compression level can be specified by giving option {compressed, Level}. Level is
              an integer with range 0..9, where:

                * 0 - No compression is done (it is the same as giving no compressed option).

                * 1 - Takes least time but may not compress as well as the higher levels.

                * 6 - Default level when option compressed is provided.

                * 9 - Takes most time and tries to produce a smaller result.  Notice  "tries"  in
                  the preceding sentence; depending on the input term, level 9 compression either
                  does or does not produce a smaller result than level 1 compression.

              Option {minor_version, Version} can be used to control some encoding details.  This
              option was introduced in Erlang/OTP R11B-4. The valid values for Version are:

                0:
                  Floats  are  encoded  using  a textual representation. This option is useful to
                  ensure that releases before Erlang/OTP R11B-4 can decode resulting binary.

                  This version encode atoms that can be represented  by  a  latin1  string  using
                  latin1  encoding  while  only  atoms  that  cannot be represented by latin1 are
                  encoded using utf8.

                1:
                  This is as of Erlang/OTP 17.0 the default. It forces any floats in the term  to
                  be  encoded  in a more space-efficient and exact way (namely in the 64-bit IEEE
                  format, rather than converted to a textual representation). As from  Erlang/OTP
                  R11B-4, binary_to_term/1 can decode this representation.

                  This  version  encode  atoms  that  can be represented by a latin1 string using
                  latin1 encoding while only atoms that  cannot  be  represented  by  latin1  are
                  encoded using utf8.

                2:
                  Drops  usage  of the latin1 atom encoding and unconditionally use utf8 encoding
                  for all atoms. This will be changed to the default in a future major release of
                  Erlang/OTP. Erlang/OTP systems as of R16B can decode this representation.

              See also binary_to_term/1.

       throw(Any) -> no_return()

              Types:

                 Any = term()

              A  non-local  return  from  a  function. If evaluated within a catch, catch returns
              value Any. Example:

              > catch throw({hello, there}).
              {hello,there}

              Failure: nocatch if not evaluated within a catch.

       time() -> Time

              Types:

                 Time = calendar:time()

              Returns the current time as {Hour, Minute, Second}.

              The time zone and Daylight Saving Time correction  depend  on  the  underlying  OS.
              Example:

              > time().
              {9,42,44}

       erlang:time_offset() -> integer()

              Returns  the  current time offset between  Erlang monotonic time and  Erlang system
              time in native time unit. Current time offset added to  an  Erlang  monotonic  time
              gives corresponding Erlang system time.

              The  time  offset may or may not change during operation depending on the time warp
              mode used.

          Note:
              A change in time offset can be observed at slightly different  points  in  time  by
              different processes.

              If  the  runtime system is in multi-time warp mode, the time offset is changed when
              the runtime system detects that the OS system time has changed. The runtime  system
              will, however, not detect this immediately when it occurs. A task checking the time
              offset is scheduled to execute at least once a minute; so, under  normal  operation
              this  is  to  be detected within a minute, but during heavy load it can take longer
              time.

       erlang:time_offset(Unit) -> integer()

              Types:

                 Unit = time_unit()

              Returns the current time offset between  Erlang monotonic time and   Erlang  system
              time converted into the Unit passed as argument.

              Same   as   calling  erlang:convert_time_unit(erlang:time_offset(),  native,  Unit)
              however optimized for commonly used Units.

       erlang:timestamp() -> Timestamp

              Types:

                 Timestamp = timestamp()
                 timestamp() =
                     {MegaSecs :: integer() >= 0,
                      Secs :: integer() >= 0,
                      MicroSecs :: integer() >= 0}

              Returns current  Erlang system time on the format {MegaSecs, Secs, MicroSecs}. This
              format  is  the  same  as  os:timestamp/0  and the deprecated erlang:now/0 use. The
              reason for the existence of  erlang:timestamp()  is  purely  to  simplify  use  for
              existing  code  that assumes this time stamp format. Current Erlang system time can
              more  efficiently  be  retrieved  in  the  time   unit   of   your   choice   using
              erlang:system_time/1.

              The erlang:timestamp() BIF is equivalent to:

              timestamp() ->
                  ErlangSystemTime = erlang:system_time(microsecond),
                  MegaSecs = ErlangSystemTime div 1000000000000,
                  Secs = ErlangSystemTime div 1000000 - MegaSecs*1000000,
                  MicroSecs = ErlangSystemTime rem 1000000,
                  {MegaSecs, Secs, MicroSecs}.

              It,  however,  uses a native implementation that does not build garbage on the heap
              and with slightly better performance.

          Note:
              This time is not a monotonically increasing time in  the  general  case.  For  more
              information, see the documentation of  time warp modes in the User's Guide.

       tl(List) -> term()

              Types:

                 List = [term(), ...]

              Returns the tail of List, that is, the list minus the first element, for example:

              > tl([geesties, guilies, beasties]).
              [guilies, beasties]

              Allowed in guard tests.

              Failure: badarg if List is the empty list [].

       erlang:trace(PidPortSpec, How, FlagList) -> integer()

              Types:

                 PidPortSpec =
                     pid() |
                     port() |
                     all | processes | ports | existing | existing_processes |
                     existing_ports | new | new_processes | new_ports
                 How = boolean()
                 FlagList = [trace_flag()]
                 trace_flag() =
                     all | send | 'receive' | procs | ports | call | arity |
                     return_to | silent | running | exiting | running_procs |
                     running_ports | garbage_collection | timestamp |
                     cpu_timestamp | monotonic_timestamp |
                     strict_monotonic_timestamp | set_on_spawn |
                     set_on_first_spawn | set_on_link | set_on_first_link |
                     {tracer, pid() | port()} |
                     {tracer, module(), term()}

              Turns  on (if How == true) or off (if How == false) the trace flags in FlagList for
              the process or processes represented by PidPortSpec.

              PidPortSpec is either a process identifier  (pid)  for  a  local  process,  a  port
              identifier, or one of the following atoms:

                all:
                  All  currently existing processes and ports and all that will be created in the
                  future.

                processes:
                  All currently existing processes and all that will be created in the future.

                ports:
                  All currently existing ports and all that will be created in the future.

                existing:
                  All currently existing processes and ports.

                existing_processes:
                  All currently existing processes.

                existing_ports:
                  All currently existing ports.

                new:
                  All processes and ports that will be created in the future.

                new_processes:
                  All processes that will be created in the future.

                new_ports:
                  All ports that will be created in the future.

              FlagList can contain any number of the following flags (the "message  tags"  refers
              to the list of trace messages):

                all:
                  Sets all trace flags except tracer and cpu_timestamp, which are in their nature
                  different than the others.

                send:
                  Traces sending of messages.

                  Message tags: send and send_to_non_existing_process.

                'receive':
                  Traces receiving of messages.

                  Message tags: 'receive'.

                call:
                  Traces certain function calls. Specify which function calls to trace by calling
                  erlang:trace_pattern/3.

                  Message tags: call and return_from.

                silent:
                  Used  with  the  call  trace  flag.  The call, return_from, and return_to trace
                  messages are inhibited if this flag is set, but they are executed as normal  if
                  there are match specifications.

                  Silent mode is inhibited by executing erlang:trace(_, false, [silent|_]), or by
                  a match specification executing the function {silent, false}.

                  The silent trace flag facilitates setting up  a  trace  on  many  or  even  all
                  processes  in the system. The trace can then be activated and deactivated using
                  the match specification function {silent,Bool}, giving a high degree of control
                  of which functions with which arguments that trigger the trace.

                  Message tags: call, return_from, and return_to. Or rather, the absence of.

                return_to:
                  Used with the call trace flag. Traces the return from a traced function back to
                  its  caller.  Only  works  for  functions   traced   with   option   local   to
                  erlang:trace_pattern/3.

                  The  semantics  is  that  a  trace  message is sent when a call traced function
                  returns, that is, when a chain of tail recursive calls  ends.  Only  one  trace
                  message  is  sent  per chain of tail recursive calls, so the properties of tail
                  recursiveness for function calls are kept while tracing with this  flag.  Using
                  call  and  return_to  trace together makes it possible to know exactly in which
                  function a process executes at any time.

                  To get  trace  messages  containing  return  values  from  functions,  use  the
                  {return_trace} match specification action instead.

                  Message tags: return_to.

                procs:
                  Traces process-related events.

                  Message  tags:  spawn,  spawned,  exit,  register,  unregister,  link,  unlink,
                  getting_linked, and getting_unlinked.

                ports:
                  Traces port-related events.

                  Message  tags:  open,  closed,  register,   unregister,   getting_linked,   and
                  getting_unlinked.

                running:
                  Traces scheduling of processes.

                  Message tags: in and out.

                exiting:
                  Traces scheduling of exiting processes.

                  Message tags: in_exiting, out_exiting, and out_exited.

                running_procs:
                  Traces  scheduling  of  processes  just like running. However, this option also
                  includes schedule events when the process executes within the context of a port
                  without being scheduled out itself.

                  Message tags: in and out.

                running_ports:
                  Traces scheduling of ports.

                  Message tags: in and out.

                garbage_collection:
                  Traces garbage collections of processes.

                  Message tags: gc_minor_start, gc_max_heap_size, and gc_minor_end.

                timestamp:
                  Includes  a  time stamp in all trace messages. The time stamp (Ts) has the same
                  form as returned by erlang:now().

                cpu_timestamp:
                  A global trace flag for the Erlang node that makes all trace time stamps  using
                  flag  timestamp  to be in CPU time, not wall clock time. That is, cpu_timestamp
                  is not be used if monotonic_timestamp or strict_monotonic_timestamp is enabled.
                  Only  allowed  with  PidPortSpec==all.  If the host machine OS does not support
                  high-resolution CPU time measurements, trace/3 exits with badarg.  Notice  that
                  most  OS  do  not synchronize this value across cores, so be prepared that time
                  can seem to go backwards when using this option.

                monotonic_timestamp:
                  Includes an Erlang monotonic time time stamp in all trace  messages.  The  time
                  stamp    (Ts)    has    the    same   format   and   value   as   produced   by
                  erlang:monotonic_time(nanosecond). This flag overrides flag cpu_timestamp.

                strict_monotonic_timestamp:
                  Includes an time stamp consisting of Erlang monotonic time and a  monotonically
                  increasing  integer  in  all  trace  messages. The time stamp (Ts) has the same
                  format  and  value  as   produced   by   {   erlang:monotonic_time(nanosecond),
                  erlang:unique_integer([monotonic])}. This flag overrides flag cpu_timestamp.

                arity:
                  Used  with  the  call  trace flag. {M, F, Arity} is specified instead of {M, F,
                  Args} in call trace messages.

                set_on_spawn:
                  Makes any process  created  by  a  traced  process  inherit  its  trace  flags,
                  including flag set_on_spawn.

                set_on_first_spawn:
                  Makes  the  first  process created by a traced process inherit its trace flags,
                  excluding flag set_on_first_spawn.

                set_on_link:
                  Makes any process linked by a traced process inherit its trace flags, including
                  flag set_on_link.

                set_on_first_link:
                  Makes  the first process linked to by a traced process inherit its trace flags,
                  excluding flag set_on_first_link.

                {tracer, Tracer}:
                  Specifies where to  send  the  trace  messages.  Tracer  must  be  the  process
                  identifier of a local process or the port identifier of a local port.

                {tracer, TracerModule, TracerState}:
                  Specifies  that  a  tracer  module  is  to be called instead of sending a trace
                  message. The tracer module can then ignore or change  the  trace  message.  For
                  more details on how to write a tracer module, see erl_tracer(3erl).

              If no tracer is specified, the calling process receives all the trace messages.

              The  effect  of  combining  set_on_first_link  with  set_on_link  is  the  same  as
              set_on_first_link alone. Likewise for set_on_spawn and set_on_first_spawn.

              The tracing process receives the trace messages described in  the  following  list.
              Pid  is  the process identifier of the traced process in which the traced event has
              occurred. The third tuple element is the message tag.

              If flag timestamp, strict_monotonic_timestamp, or monotonic_timestamp is specified,
              the  first  tuple  element  is  trace_ts instead, and the time stamp is added as an
              extra element last in the message tuple. If multiple time stamp flags  are  passed,
              timestamp  has  precedence  over  strict_monotonic_timestamp,  which  in  turn  has
              precedence over monotonic_timestamp. All time stamp flags are remembered, so if two
              are  passed  and  the  one with highest precedence later is disabled, the other one
              becomes active.

              Trace messages:

                {trace, PidPort, send, Msg, To}:
                  When PidPort sends message Msg to process To.

                {trace, PidPort, send_to_non_existing_process, Msg, To}:
                  When PidPort sends message Msg to the non-existing process To.

                {trace, PidPort, 'receive', Msg}:
                  When PidPort receives message Msg.  If  Msg  is  set  to  time-out,  a  receive
                  statement  can  have  timed  out,  or  the  process received a message with the
                  payload timeout.

                {trace, Pid, call, {M, F, Args}}:
                  When Pid calls a  traced  function.  The  return  values  of  calls  are  never
                  supplied, only the call and its arguments.

                  Trace  flag  arity  can be used to change the contents of this message, so that
                  Arity is specified instead of Args.

                {trace, Pid, return_to, {M, F, Arity}}:
                  When Pid returns to the specified function. This trace message is sent if  both
                  the  flags  call and return_to are set, and the function is set to be traced on
                  local function calls. The message is only sent when returning from a  chain  of
                  tail  recursive  function calls, where at least one call generated a call trace
                  message (that is, the functions  match  specification  matched,  and  {message,
                  false} was not an action).

                {trace, Pid, return_from, {M, F, Arity}, ReturnValue}:
                  When  Pid  returns  from  the specified function. This trace message is sent if
                  flag  call  is  set,  and  the  function  has  a  match  specification  with  a
                  return_trace or exception_trace action.

                {trace, Pid, exception_from, {M, F, Arity}, {Class, Value}}:
                  When  Pid exits from the specified function because of an exception. This trace
                  message is sent if flag call is set, and the function has a match specification
                  with an exception_trace action.

                {trace, Pid, spawn, Pid2, {M, F, Args}}:
                  When  Pid  spawns  a new process Pid2 with the specified function call as entry
                  point.

                  Args is supposed to be the argument list, but can be any term if the  spawn  is
                  erroneous.

                {trace, Pid, spawned, Pid2, {M, F, Args}}:
                  When  Pid  is spawned by process Pid2 with the specified function call as entry
                  point.

                  Args is supposed to be the argument list, but can be any term if the  spawn  is
                  erroneous.

                {trace, Pid, exit, Reason}:
                  When Pid exits with reason Reason.

                {trace, PidPort, register, RegName}:
                  When PidPort gets the name RegName registered.

                {trace, PidPort, unregister, RegName}:
                  When  PidPort  gets  the  name RegName unregistered. This is done automatically
                  when a registered process or port exits.

                {trace, Pid, link, Pid2}:
                  When Pid links to a process Pid2.

                {trace, Pid, unlink, Pid2}:
                  When Pid removes the link from a process Pid2.

                {trace, PidPort, getting_linked, Pid2}:
                  When PidPort gets linked to a process Pid2.

                {trace, PidPort, getting_unlinked, Pid2}:
                  When PidPort gets unlinked from a process Pid2.

                {trace, Pid, exit, Reason}:
                  When Pid exits with reason Reason.

                {trace, Port, open, Pid, Driver}:
                  When Pid opens a new port Port with the running Driver.

                  Driver is the name of the driver as an atom.

                {trace, Port, closed, Reason}:
                  When Port closes with Reason.

                {trace, Pid, in | in_exiting, {M, F, Arity} | 0}:
                  When Pid is scheduled to run. The process runs in function {M,  F,  Arity}.  On
                  some  rare  occasions, the current function cannot be determined, then the last
                  element is 0.

                {trace, Pid, out | out_exiting | out_exited, {M, F, Arity} | 0}:
                  When Pid is scheduled out. The process was running in function {M,  F,  Arity}.
                  On  some  rare  occasions,  the current function cannot be determined, then the
                  last element is 0.

                {trace, Port, in, Command | 0}:
                  When Port is scheduled to run.  Command  is  the  first  thing  the  port  will
                  execute,  it  can  however  run several commands before being scheduled out. On
                  some rare occasions, the current function cannot be determined, then  the  last
                  element is 0.

                  The  possible commands are call, close, command, connect, control, flush, info,
                  link, open, and unlink.

                {trace, Port, out, Command | 0}:
                  When Port is scheduled out. The last command run  was  Command.  On  some  rare
                  occasions,  the current function cannot be determined, then the last element is
                  0. Command can contain the same commands as in

                {trace, Pid, gc_minor_start, Info}:

                  Sent when a young garbage collection is about to be started. Info is a list  of
                  two-element  tuples,  where  the  first element is a key, and the second is the
                  value. Do not depend on any  order  of  the  tuples.  The  following  keys  are
                  defined:

                  heap_size:
                    The size of the used part of the heap.

                  heap_block_size:
                    The size of the memory block used for storing the heap and the stack.

                  old_heap_size:
                    The size of the used part of the old heap.

                  old_heap_block_size:
                    The size of the memory block used for storing the old heap.

                  stack_size:
                    The size of the stack.

                  recent_size:
                    The size of the data that survived the previous garbage collection.

                  mbuf_size:
                    The combined size of message buffers associated with the process.

                  bin_vheap_size:
                    The total size of unique off-heap binaries referenced from the process heap.

                  bin_vheap_block_size:
                    The  total size of binaries allowed in the virtual heap in the process before
                    doing a garbage collection.

                  bin_old_vheap_size:
                    The total size of unique off-heap binaries referenced from  the  process  old
                    heap.

                  bin_old_vheap_block_size:
                    The  total  size  of  binaries allowed in the virtual old heap in the process
                    before doing a garbage collection.

                  All sizes are in words.

                {trace, Pid, gc_max_heap_size, Info}:
                  Sent when the max_heap_size is reached during garbage collection. Info contains
                  the  same  kind of list as in message gc_start, but the sizes reflect the sizes
                  that triggered max_heap_size to be reached.

                {trace, Pid, gc_minor_end, Info}:
                  Sent when young garbage collection is finished. Info contains the same kind  of
                  list  as  in  message gc_minor_start, but the sizes reflect the new sizes after
                  garbage collection.

                {trace, Pid, gc_major_start, Info}:
                  Sent when fullsweep garbage collection is about to be  started.  Info  contains
                  the same kind of list as in message gc_minor_start.

                {trace, Pid, gc_major_end, Info}:
                  Sent when fullsweep garbage collection is finished. Info contains the same kind
                  of list as in message gc_minor_start, but the sizes reflect the new sizes after
                  a fullsweep garbage collection.

              If the tracing process/port dies or the tracer module returns remove, the flags are
              silently removed.

              Each process can only be traced by one tracer.  Therefore,  attempts  to  trace  an
              already traced process fail.

              Returns  a  number  indicating the number of processes that matched PidPortSpec. If
              PidPortSpec is a process identifier, the return value is 1. If PidPortSpec  is  all
              or existing, the return value is the number of processes running. If PidPortSpec is
              new, the return value is 0.

              Failure: badarg  if  the  specified  arguments  are  not  supported.  For  example,
              cpu_timestamp is not supported on all platforms.

       erlang:trace_delivered(Tracee) -> Ref

              Types:

                 Tracee = pid() | all
                 Ref = reference()

              The  delivery  of  trace messages (generated by erlang:trace/3, seq_trace(3erl), or
              erlang:system_profile/2) is dislocated on the time-line compared to other events in
              the  system.  If  you  know  that  Tracee  has  passed  some  specific point in its
              execution, and you want to know when at least all trace messages  corresponding  to
              events     up     to     this     point    have    reached    the    tracer,    use
              erlang:trace_delivered(Tracee).

              When it is guaranteed that all trace messages are delivered to the tracer up to the
              point     that    Tracee    reached    at    the    time    of    the    call    to
              erlang:trace_delivered(Tracee), then a {trace_delivered, Tracee,  Ref}  message  is
              sent to the caller of erlang:trace_delivered(Tracee) .

              Notice  that  message  trace_delivered does not imply that trace messages have been
              delivered. Instead it implies that all trace messages that are to be delivered have
              been  delivered.  It  is  not an error if Tracee is not, and has not been traced by
              someone, but if this is the case, no trace messages have been  delivered  when  the
              trace_delivered message arrives.

              Notice  that Tracee must refer to a process currently or previously existing on the
              same node as the caller of erlang:trace_delivered(Tracee) resides on.  The  special
              Tracee atom all denotes all processes that currently are traced in the node.

              When used together with a  Tracer Module, any message sent in the trace callback is
              guaranteed to have reached its recipient  before  the  trace_delivered  message  is
              sent.

              Example:  Process A is Tracee, port B is tracer, and process C is the port owner of
              B. C wants to close B when A exits. To ensure that the trace is  not  truncated,  C
              can   call   erlang:trace_delivered(A)   when   A   exits,  and  wait  for  message
              {trace_delivered, A, Ref} before closing B.

              Failure: badarg if Tracee does not refer to a process (dead or alive) on  the  same
              node as the caller of erlang:trace_delivered(Tracee) resides on.

       erlang:trace_info(PidPortFuncEvent, Item) -> Res

              Types:

                 PidPortFuncEvent =
                     pid() |
                     port() |
                     new | new_processes | new_ports |
                     {Module, Function, Arity} |
                     on_load | send | 'receive'
                 Module = module()
                 Function = atom()
                 Arity = arity()
                 Item =
                     flags | tracer | traced | match_spec | meta |
                     meta_match_spec | call_count | call_time | all
                 Res = trace_info_return()
                 trace_info_return() =
                     undefined |
                     {flags, [trace_info_flag()]} |
                     {tracer, pid() | port() | []} |
                     {tracer, module(), term()} |
                     trace_info_item_result() |
                     {all, [trace_info_item_result()] | false | undefined}
                 trace_info_item_result() =
                     {traced, global | local | false | undefined} |
                     {match_spec, trace_match_spec() | false | undefined} |
                     {meta, pid() | port() | false | undefined | []} |
                     {meta, module(), term()} |
                     {meta_match_spec, trace_match_spec() | false | undefined} |
                     {call_count, integer() >= 0 | boolean() | undefined} |
                     {call_time,
                      [{pid(),
                        integer() >= 0,
                        integer() >= 0,
                        integer() >= 0}] |
                      boolean() |
                      undefined}
                 trace_info_flag() =
                     send | 'receive' | set_on_spawn | call | return_to | procs |
                     set_on_first_spawn | set_on_link | running |
                     garbage_collection | timestamp | monotonic_timestamp |
                     strict_monotonic_timestamp | arity
                 trace_match_spec() =
                     [{[term()] | '_' | match_variable(), [term()], [term()]}]
                 match_variable() = atom()
                    Approximation of '$1' | '$2' | '$3' | ...

              Returns trace information about a port, process, function, or event.

              To  get  information  about  a port or process, PidPortFuncEvent is to be a process
              identifier (pid), port identifier, or one  of  the  atoms  new,  new_processes,  or
              new_ports.  The  atom  new  or new_processes means that the default trace state for
              processes to be created is returned. The atom  new_ports  means  that  the  default
              trace state for ports to be created is returned.

              Valid Items for ports and processes:

                flags:
                  Returns  a  list  of  atoms  indicating  what kind of traces is enabled for the
                  process. The list is empty if no traces are enabled, and one  or  more  of  the
                  followings  atoms  if  traces are enabled: send, 'receive', set_on_spawn, call,
                  return_to,   procs,   ports,    set_on_first_spawn,    set_on_link,    running,
                  running_procs,    running_ports,    silent,    exiting,    monotonic_timestamp,
                  strict_monotonic_timestamp, garbage_collection, timestamp, and arity. The order
                  is arbitrary.

                tracer:
                  Returns  the  identifier  for  process,  port, or a tuple containing the tracer
                  module and tracer state tracing this process. If this process  is  not  traced,
                  the return value is [].

              To  get  information  about a function, PidPortFuncEvent is to be the three-element
              tuple {Module, Function, Arity} or the atom  on_load.  No  wildcards  are  allowed.
              Returns  undefined  if the function does not exist, or false if the function is not
              traced. If PidPortFuncEvent is on_load, the  information  returned  refers  to  the
              default value for code that will be loaded.

              Valid Items for functions:

                traced:
                  Returns  global  if  this function is traced on global function calls, local if
                  this function is traced on local function calls  (that  is,  local  and  global
                  function calls), and false if local or global function calls are not traced.

                match_spec:
                  Returns  the  match  specification  for  this  function,  if it has one. If the
                  function is locally or globally traced but has no match specification  defined,
                  the returned value is [].

                meta:
                  Returns the meta-trace tracer process, port, or trace module for this function,
                  if it has one. If the function is not meta-traced, the returned value is false.
                  If the function is meta-traced but has once detected that the tracer process is
                  invalid, the returned value is [].

                meta_match_spec:
                  Returns the meta-trace match specification for this function, if it has one. If
                  the  function  is  meta-traced  but  has  no  match  specification defined, the
                  returned value is [].

                call_count:
                  Returns the call count value for this function or true for the pseudo  function
                  on_load if call count tracing is active. Otherwise false is returned.

                  See also erlang:trace_pattern/3.

                call_time:
                  Returns  the call time values for this function or true for the pseudo function
                  on_load if call time tracing is active. Otherwise false is returned.  The  call
                  time  values  returned,  [{Pid,  Count, S, Us}], is a list of each process that
                  executed the function and its specific counters.

                  See also erlang:trace_pattern/3.

                all:
                  Returns a list containing the {Item, Value} tuples  for  all  other  items,  or
                  returns false if no tracing is active for this function.

              To  get information about an event, PidPortFuncEvent is to be one of the atoms send
              or 'receive'.

              One valid Item for events exists:

                match_spec:
                  Returns the match specification for this event, if it has one, or  true  if  no
                  match specification has been set.

              The  return  value  is  {Item,  Value}, where Value is the requested information as
              described earlier. If a pid for a dead process was specified, or the name of a non-
              existing function, Value is undefined.

       erlang:trace_pattern(MFA, MatchSpec) -> integer() >= 0

              Types:

                 MFA = trace_pattern_mfa() | send | 'receive'
                 MatchSpec =
                     (MatchSpecList :: trace_match_spec()) |
                     boolean() |
                     restart | pause
                 trace_pattern_mfa() = {atom(), atom(), arity() | '_'} | on_load
                 trace_match_spec() =
                     [{[term()] | '_' | match_variable(), [term()], [term()]}]
                 match_variable() = atom()
                    Approximation of '$1' | '$2' | '$3' | ...

              The  same  as  erlang:trace_pattern(Event,  MatchSpec,  []),  retained for backward
              compatibility.

       erlang:trace_pattern(MFA :: send, MatchSpec, FlagList :: []) ->
                               integer() >= 0

              Types:

                 MatchSpec = (MatchSpecList :: trace_match_spec()) | boolean()
                 trace_match_spec() =
                     [{[term()] | '_' | match_variable(), [term()], [term()]}]
                 match_variable() = atom()
                    Approximation of '$1' | '$2' | '$3' | ...

              Sets trace pattern for message sending. Must be combined with erlang:trace/3 to set
              the  send  trace  flag for one or more processes. By default all messages sent from
              send traced processes are traced. To limit traced send events based on the  message
              content, the sender and/or the receiver, use erlang:trace_pattern/3.

              Argument MatchSpec can take the following forms:

                MatchSpecList:
                  A  list  of  match  specifications. The matching is done on the list [Receiver,
                  Msg]. Receiver is the process or port identity of the receiver and Msg  is  the
                  message  term.  The  pid  of the sending process can be accessed with the guard
                  function self/0. An empty list is the same as true. For more  information,  see
                  section  Match Specifications in Erlang in the User's Guide.

                true:
                  Enables  tracing  for all sent messages (from send traced processes). Any match
                  specification is removed. This is the default.

                false:
                  Disables tracing for all sent messages. Any match specification is removed.

              Argument FlagList must be [] for send tracing.

              The return value is always 1.

              Examples:

              Only trace messages to a specific process Pid:

              > erlang:trace_pattern(send, [{[Pid, '_'],[],[]}], []).
              1

              Only trace messages matching {reply, _}:

              > erlang:trace_pattern(send, [{['_', {reply,'_'}],[],[]}], []).
              1

              Only trace messages sent to the sender itself:

              > erlang:trace_pattern(send, [{['$1', '_'],[{'=:=','$1',{self}}],[]}], []).
              1

              Only trace messages sent to other nodes:

              > erlang:trace_pattern(send, [{['$1', '_'],[{'=/=',{node,'$1'},{node}}],[]}], []).
              1

          Note:
              A match specification for send trace can use all guard and  body  functions  except
              caller.

       erlang:trace_pattern(MFA :: 'receive', MatchSpec, FlagList :: []) ->
                               integer() >= 0

              Types:

                 MatchSpec = (MatchSpecList :: trace_match_spec()) | boolean()
                 trace_match_spec() =
                     [{[term()] | '_' | match_variable(), [term()], [term()]}]
                 match_variable() = atom()
                    Approximation of '$1' | '$2' | '$3' | ...

              Sets  trace  pattern for message receiving. Must be combined with erlang:trace/3 to
              set the 'receive' trace flag for one or more processes.  By  default  all  messages
              received  by  'receive' traced processes are traced. To limit traced receive events
              based  on  the   message   content,   the   sender   and/or   the   receiver,   use
              erlang:trace_pattern/3.

              Argument MatchSpec can take the following forms:

                MatchSpecList:
                  A list of match specifications. The matching is done on the list [Node, Sender,
                  Msg]. Node is the node name of the  sender.  Sender  is  the  process  or  port
                  identity of the sender, or the atom undefined if the sender is not known (which
                  can be the case for remote senders). Msg is the message term. The  pid  of  the
                  receiving process can be accessed with the guard function self/0. An empty list
                  is the same as true. For more information, see section  Match Specifications in
                  Erlang in the User's Guide.

                true:
                  Enables  tracing for all received messages (to 'receive' traced processes). Any
                  match specification is removed. This is the default.

                false:
                  Disables tracing for all received messages. Any match specification is removed.

              Argument FlagList must be [] for receive tracing.

              The return value is always 1.

              Examples:

              Only trace messages from a specific process Pid:

              > erlang:trace_pattern('receive', [{['_',Pid, '_'],[],[]}], []).
              1

              Only trace messages matching {reply, _}:

              > erlang:trace_pattern('receive', [{['_','_', {reply,'_'}],[],[]}], []).
              1

              Only trace messages from other nodes:

              > erlang:trace_pattern('receive', [{['$1', '_', '_'],[{'=/=','$1',{node}}],[]}], []).
              1

          Note:
              A match specification for 'receive' trace can use  all  guard  and  body  functions
              except    caller,   is_seq_trace,   get_seq_token,   set_seq_token,   enable_trace,
              disable_trace, trace, silent, and process_dump.

       erlang:trace_pattern(MFA, MatchSpec, FlagList) ->
                               integer() >= 0

              Types:

                 MFA = trace_pattern_mfa()
                 MatchSpec =
                     (MatchSpecList :: trace_match_spec()) |
                     boolean() |
                     restart | pause
                 FlagList = [trace_pattern_flag()]
                 trace_pattern_mfa() = {atom(), atom(), arity() | '_'} | on_load
                 trace_match_spec() =
                     [{[term()] | '_' | match_variable(), [term()], [term()]}]
                 trace_pattern_flag() =
                     global | local | meta |
                     {meta, Pid :: pid()} |
                     {meta, TracerModule :: module(), TracerState :: term()} |
                     call_count | call_time
                 match_variable() = atom()
                    Approximation of '$1' | '$2' | '$3' | ...

              Enables or disables call tracing for one or more functions. Must be  combined  with
              erlang:trace/3 to set the call trace flag for one or more processes.

              Conceptually,  call  tracing works as follows. Inside the Erlang virtual machine, a
              set of processes and a set of functions are to be traced. If a traced process calls
              a traced function, the trace action is taken. Otherwise, nothing happens.

              To  add  or  remove  one  or  more  processes  to  the set of traced processes, use
              erlang:trace/3.

              To  add   or   remove   functions   to   the   set   of   traced   functions,   use
              erlang:trace_pattern/3.

              The  BIF  erlang:trace_pattern/3 can also add match specifications to a function. A
              match specification comprises a pattern that the function arguments must  match,  a
              guard  expression  that  must  evaluate to true, and an action to be performed. The
              default action is to send a trace message. If the pattern does  not  match  or  the
              guard fails, the action is not executed.

              Argument  MFA  is  to  be  a  tuple, such as {Module, Function, Arity}, or the atom
              on_load (described below). It can be the module, function, and arity for a function
              (or  a  BIF  in  any  module). The atom '_' can be used as a wildcard in any of the
              following ways:

                {Module,Function,'_'}:
                  All functions of any arity named Function in module Module.

                {Module,'_','_'}:
                  All functions in module Module.

                {'_','_','_'}:
                  All functions in all loaded modules.

              Other combinations, such as {Module,'_',Arity}, are not  allowed.  Local  functions
              match wildcards only if option local is in FlagList.

              If argument MFA is the atom on_load, the match specification and flag list are used
              on all modules that are newly loaded.

              Argument MatchSpec can take the following forms:

                false:
                  Disables tracing  for  the  matching  functions.  Any  match  specification  is
                  removed.

                true:
                  Enables tracing for the matching functions. Any match specification is removed.

                MatchSpecList:
                  A  list  of  match  specifications.  An empty list is equivalent to true. For a
                  description of match  specifications,  see  section   Match  Specifications  in
                  Erlang in the User's Guide.

                restart:
                  For  the  FlagList  options  call_count  and  call_time:  restarts the existing
                  counters. The behavior is undefined for other FlagList options.

                pause:
                  For  the  FlagList  options  call_count  and  call_time:  pauses  the  existing
                  counters. The behavior is undefined for other FlagList options.

              Parameter FlagList is a list of options. The following are the valid options:

                global:
                  Turns  on  or  off  call  tracing  for  global  function  calls (that is, calls
                  specifying the module explicitly).  Only  exported  functions  match  and  only
                  global calls generate trace messages. This is the default.

                local:
                  Turns  on  or  off call tracing for all types of function calls. Trace messages
                  are sent whenever any of the specified functions are called, regardless of  how
                  they  are called. If flag return_to is set for the process, a return_to message
                  is also sent when this function returns to its caller.

                meta | {meta, Pid} | {meta, TracerModule, TracerState}:
                  Turns on or off meta-tracing for all types of function  calls.  Trace  messages
                  are  sent  to the tracer whenever any of the specified functions are called. If
                  no tracer is specified, self() is used as a default tracer process.

                  Meta-tracing traces all processes and does not care  about  the  process  trace
                  flags  set  by  erlang:trace/3,  the  trace  flags  are instead fixed to [call,
                  timestamp].

                  The match specification function {return_trace} works with meta-trace and sends
                  its trace message to the same tracer.

                call_count:
                  Starts (MatchSpec == true) or stops (MatchSpec == false) call count tracing for
                  all types of function calls. For every function, a counter is incremented  when
                  the  function  is  called,  in  any  process. No process trace flags need to be
                  activated.

                  If call count tracing is started while already running, the count is  restarted
                  from  zero.  To  pause  running  counters,  use  MatchSpec == pause. Paused and
                  running counters can be restarted from zero with MatchSpec == restart.

                  To read the counter value, use erlang:trace_info/2.

                call_time:
                  Starts (MatchSpec == true) or stops (MatchSpec == false) call time tracing  for
                  all  types of function calls. For every function, a counter is incremented when
                  the function is called. Time spent in the function is accumulated in two  other
                  counters,  seconds  and  microseconds.  The  counters  are stored for each call
                  traced process.

                  If call time tracing is started while  already  running,  the  count  and  time
                  restart  from  zero.  To pause running counters, use MatchSpec == pause. Paused
                  and running counters can be restarted from zero with MatchSpec == restart.

                  To read the counter value, use erlang:trace_info/2.

              The options global and local are mutually exclusive, and global is the default  (if
              no  options are specified). The options call_count and meta perform a kind of local
              tracing, and cannot be combined with global. A function can be globally or  locally
              traced.  If  global  tracing is specified for a set of functions, then local, meta,
              call time, and call count tracing for  the  matching  set  of  local  functions  is
              disabled, and conversely.

              When  disabling trace, the option must match the type of trace set on the function.
              That is, local tracing must be disabled with option local and global  tracing  with
              option global (or no option), and so on.

              Part  of a match specification list cannot be changed directly. If a function has a
              match specification, it can be replaced with a new one. To change an existing match
              specification,  use  the  BIF  erlang:trace_info/2  to  retrieve the existing match
              specification.

              Returns the number of functions  matching  argument  MFA.  This  is  zero  if  none
              matched.

       trunc(Number) -> integer()

              Types:

                 Number = number()

              Returns an integer by truncating Number, for example:

              > trunc(5.5).
              5

              Allowed in guard tests.

       tuple_size(Tuple) -> integer() >= 0

              Types:

                 Tuple = tuple()

              Returns an integer that is the number of elements in Tuple, for example:

              > tuple_size({morni, mulle, bwange}).
              3

              Allowed in guard tests.

       tuple_to_list(Tuple) -> [term()]

              Types:

                 Tuple = tuple()

              Returns a list corresponding to Tuple. Tuple can contain any Erlang terms. Example:

              > tuple_to_list({share, {'Ericsson_B', 163}}).
              [share,{'Ericsson_B',163}]

       erlang:unique_integer() -> integer()

              Generates  and  returns  an  integer unique on current runtime system instance. The
              same as calling erlang:unique_integer([]).

       erlang:unique_integer(ModifierList) -> integer()

              Types:

                 ModifierList = [Modifier]
                 Modifier = positive | monotonic

              Generates and returns an  integer unique on current runtime  system  instance.  The
              integer is unique in the sense that this BIF, using the same set of modifiers, does
              not return the same integer more than once on the current runtime system  instance.
              Each integer value can of course be constructed by other means.

              By  default, when [] is passed as ModifierList, both negative and positive integers
              can be returned. This to use the range of integers that do  not  need  heap  memory
              allocation  as  much  as  possible.  By default the returned integers are also only
              guaranteed to be unique, that is, any returned integer can  be  smaller  or  larger
              than previously returned integers.

              Modifiers:

                positive:
                  Returns only positive integers.

                  Notice  that  by  passing  the  positive  modifier  you will get heap allocated
                  integers (bignums) quicker.

                monotonic:
                  Returns  strictly monotonically increasing integers corresponding  to  creation
                  time.  That  is, the integer returned is always larger than previously returned
                  integers on the current runtime system instance.

                  These values can be used to determine  order  between  events  on  the  runtime
                  system  instance. That is, if both X = erlang:unique_integer([monotonic]) and Y
                  = erlang:unique_integer([monotonic]) are executed by  different  processes  (or
                  the same process) on the same runtime system instance and X < Y, we know that X
                  was created before Y.

            Warning:
                Strictly monotonically  increasing  values  are  inherently  quite  expensive  to
                generate  and  scales  poorly. This is because the values need to be synchronized
                between CPU cores. That is, do not pass the monotonic modifier unless you  really
                need strictly monotonically increasing values.

              All valid Modifiers can be combined. Repeated (valid) Modifiers in the ModifierList
              are ignored.

          Note:
              The set of integers returned by erlang:unique_integer/1  using  different  sets  of
              Modifiers  will  overlap.  For example, by calling unique_integer([monotonic]), and
              unique_integer([positive, monotonic]) repeatedly,  you  will  eventually  see  some
              integers that are returned by both calls.

              Failures:

                badarg:
                  if ModifierList is not a proper list.

                badarg:
                  if Modifier is not a valid modifier.

       erlang:universaltime() -> DateTime

              Types:

                 DateTime = calendar:datetime()

              Returns  the current date and time according to Universal Time Coordinated (UTC) in
              the form  {{Year,  Month,  Day},  {Hour,  Minute,  Second}}  if  supported  by  the
              underlying     OS.    Otherwise    erlang:universaltime()    is    equivalent    to
              erlang:localtime(). Example:

              > erlang:universaltime().
              {{1996,11,6},{14,18,43}}

       erlang:universaltime_to_localtime(Universaltime) -> Localtime

              Types:

                 Localtime = Universaltime = calendar:datetime()

              Converts Universal Time Coordinated (UTC) date and time to local date and  time  in
              the  form  {{Year,  Month,  Day},  {Hour,  Minute,  Second}}  if  supported  by the
              underlying OS. Otherwise no conversion is  done,  and  Universaltime  is  returned.
              Example:

              > erlang:universaltime_to_localtime({{1996,11,6},{14,18,43}}).
              {{1996,11,7},{15,18,43}}

              Failure: badarg if Universaltime denotes an invalid date and time.

       unlink(Id) -> true

              Types:

                 Id = pid() | port()

              Removes  the  link, if there is one, between the calling process and the process or
              port referred to by Id.

              Returns true and does not fail, even if there is no link to Id, or if Id  does  not
              exist.

              Once unlink(Id) has returned, it is guaranteed that the link between the caller and
              the entity referred to by Id has no effect on the caller in the future (unless  the
              link  is  setup again). If the caller is trapping exits, an {'EXIT', Id, _} message
              from the link can have been placed in the caller's message queue before the call.

              Notice that the {'EXIT', Id, _} message can be the result of the link, but can also
              be  the  result  of Id calling exit/2. Therefore, it can be appropriate to clean up
              the message queue when trapping exits after the call to unlink(Id), as follows:

              unlink(Id),
              receive
                  {'EXIT', Id, _} ->
                      true
              after 0 ->
                      true
              end

          Note:
              Before Erlang/OTP R11B (ERTS 5.5) unlink/1 behaved completely asynchronously,  that
              is,  the  link was active until the "unlink signal" reached the linked entity. This
              had an undesirable effect, as you could never know when you were guaranteed not  to
              be effected by the link.

              The  current behavior can be viewed as two combined operations: asynchronously send
              an "unlink signal" to the linked entity and ignore any future results of the link.

       unregister(RegName) -> true

              Types:

                 RegName = atom()

              Removes the registered name RegName associated with a process identifier or a  port
              identifier, for example:

              > unregister(db).
              true

              Users are advised not to unregister system processes.

              Failure: badarg if RegName is not a registered name.

       whereis(RegName) -> pid() | port() | undefined

              Types:

                 RegName = atom()

              Returns the process identifier or port identifier with the registered name RegName.
              Returns undefined if the name is not registered. Example:

              > whereis(db).
              <0.43.0>

       erlang:yield() -> true

              Voluntarily lets other processes (if any) get  a  chance  to  execute.  Using  this
              function is similar to receive after 1 -> ok end, except that yield() is faster.

          Warning:
              There  is seldom or never any need to use this BIF as other processes have a chance
              to run in another scheduler thread anyway. Using this BIF without a thorough  grasp
              of how the scheduler works can cause performance degradation.