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NAME
erlang - The Erlang BIFs.
DESCRIPTION
By convention, most Built-In Functions (BIFs) are seen as being 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()
A binary data object, structured according to the Erlang external term format.
timestamp() =
{MegaSecs :: integer() >= 0,
Secs :: integer() >= 0,
MicroSecs :: integer() >= 0}
See erlang:timestamp/0.
time_unit() =
integer() >= 1 |
seconds |
milli_seconds |
micro_seconds |
nano_seconds |
native
Supported time unit representations:
PartsPerSecond :: integer() >= 1:
Time unit expressed in parts per second. That is, the time unit equals
1/PartsPerSecond second.
seconds:
Symbolic representation of the time unit represented by the integer 1.
milli_seconds:
Symbolic representation of the time unit represented by the integer 1000.
micro_seconds:
Symbolic representation of the time unit represented by the integer 1000000.
nano_seconds:
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, seconds, native). The result equals the number of
whole native time units per second. In case 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 at all
about the quality of time values. It sets a limit for the resolution as well as
for the precision of time values, but it gives absolutely no information at all
about the accuracy of time values. The resolution of the native time unit and the
resolution of time values can differ significantly.
The time_unit/0 type may be extended. Use erlang:convert_time_unit/3 in order to
convert time values between time units.
EXPORTS
abs(Float) -> float()
abs(Int) -> integer() >= 0
Types:
Int = integer()
Types:
Float = float()
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 given 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 the 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, there is one byte for each character in the text representation. If
Encoding is utf8 or unicode, the characters are encoded using UTF-8 (that is,
characters from 128 through 255 are encoded in two bytes).
Note:
atom_to_binary(Atom, latin1) never fails because the text representation of an atom
can only contain characters from 0 through 255. In a future release, the text
representation of atoms can be allowed to contain any Unicode character and
atom_to_binary(Atom, latin1) will then fail if the text representation for Atom
contains a Unicode character greater than 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 the binary manual page in STDLIB.
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. Only Unicode characters up to 255 are
allowed.
Note:
binary_to_atom(Binary, utf8) fails if the binary contains Unicode characters
greater than 255. In a future release, such Unicode characters can be allowed and
binary_to_atom(Binary, utf8) does then not fail. For more information on 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).
** exception error: bad argument
in function binary_to_atom/2
called as binary_to_atom(<<208,128>>,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.
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.
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.
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.
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()
Types:
Binary = ext_binary()
Opts = [safe]
As binary_to_term/1, but takes options that affect decoding of the binary.
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.
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.
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 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, 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.
Available Options:
{async, Async}:
Asynchronous request for cancellation. Async defaults to false which will cause
the cancellation to be performed synchronously. When Async is set to true, the
cancel operation is performed asynchronously. That is, erlang:cancel_timer()
will send an asynchronous request for cancellation to the timer service that
manages the timer, and then return ok.
{info, Info}:
Request 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 the operation is performed
synchronously:
If Info is true, the Result is returned by erlang:cancel_timer(); otherwise,
ok is returned.
asynchronously:
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 milli-seconds 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 whether or not the timeout message has arrived at its destination yet.
Note:
The timer service that manages the timer may be co-located with another scheduler
than the scheduler that the calling process is executing on. If this is the case,
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.
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, []).
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 erlang: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.
The available Options are as follows:
{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 in the following). 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}.
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 may lose accuracy and precision when converting between time units. In order 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.
The following Types are valid:
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 latin1
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.
The following options are available:
{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. Default is 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 latin1 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. A {'DOWN', MonitorRef, _, _, _} message can have been
placed in the caller message queue before the call, though. 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:
Prior to OTP release R11B (ERTS version 5.5) demonitor/1 behaved completely
asynchronously, i.e., 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 due to the monitor.
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).
The available Options are as follows:
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. On OSE, the term is
printed to the ramlog.
Warning:
This BIF is intended for debugging only.
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). Since evaluating this
function causes the process to terminate, it has no return value.
Example:
> catch error(foobar).
{'EXIT',{foobar,[{erl_eval,do_apply,5},
{erl_eval,expr,5},
{shell,exprs,6},
{shell,eval_exprs,6},
{shell,eval_loop,3}]}}
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. Since 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. Since 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. The options are as follows:
* 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 provided, the trailing zeros at the end of the list are
truncated. This option is only meaningful together with option decimals.
* If option scientific is provided, 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"
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.
{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 OTP R15, this integer
is calculated from the compiled code for the entire module. Before 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 given name, otherwise returns false.
Note:
This function used to return false for built-in functions before the 18.0 release.
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}
OptionList = [Option]
GCResult = boolean()
Garbage collects the node local process identified by Pid.
The available Options are as follows:
{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}.
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 keys all keys present in the process dictionary.
> 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}]}
Gets the call stack back-trace (stacktrace) of the last exception 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 the catch operator 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 file name of the source file of the function.
line:
The second element of the tuple is the line number (an integer greater than
zero) in the source file where the exception occurred or the function was
called.
See also erlang:error/1 and erlang: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 start-up, 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.
See also group_leader/0.
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).
string():
An Erlang crash dump is produced with Status as slogan. Then the runtime system
exits with status code 1.
abort:
The runtime system aborts producing a core dump, if that is enabled in the OS.
Note:
On many platforms, the OS supports only status codes 0-255. A too large status code
will be truncated by clearing the high bits.
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.
erlang:hash(Term, Range) -> integer() >= 1
Types:
Term = term()
Range = integer() >= 1
Returns a hash value for Term within the range 1..Range. The maximum range is
1..2^27-1.
Warning:
This BIF is deprecated, as the hash value can differ on different architectures.
The hash values for integer terms higher than 2^27 and large binaries are poor. The
BIF is retained for backward compatibility reasons (it can have been used to hash
records into a file), but all new code is to use one of the BIFs erlang:phash/2 or
erlang:phash2/1,2 instead.
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 given 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, what erlang:hibernate/3 does is the following. It 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 reinserted 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_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>>
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
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_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 specially. 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.
String can only contain ISO-latin-1 characters (that is, numbers less than 256) as
the implementation does not allow unicode characters equal to or above 256 in
atoms. 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.
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_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 any
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
Note:
Before OTP R14B, NIFs were an experimental feature. Versions before OTP R14B can
have different and possibly incompatible NIF semantics and interfaces. For example,
in OTP R13B03 the return value on failure was {error,Reason,Text}.
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. For
information on how to implement a NIF library, see erl_nif.
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 | reload | upgrade:
The corresponding library callback was unsuccessful.
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.
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 given 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_size(Map) -> integer() >= 0
Types:
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.
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 subsequent calls to md5_update/2.
erlang:md5_update(Context, Data) -> NewContext
Types:
Context = binary()
Data = iodata()
NewContext = binary()
Updates 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 |
low |
maximum
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.
The memory types are as follows:
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.
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 less than 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.
Furthermore, 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 |
low |
maximum
Returns the memory size in bytes allocated for memory of type Type. The argument
can also be given 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 version 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 :: 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()
Send a monitor request of type Type to the entity identified by Item. The caller of
monitor/2 will later be notified by a monitor message on the following format if
the monitored state is changed:
{Tag, MonitorRef, Type, Object, Info}
Note:
The monitor request is an asynchronous signal. That is, it takes time before the
signal reaches its destination.
Valid Types:
process:
Monitor the existence of the process identified by Item. Valid Items in
combination with the process Type can be any of the following:
pid():
The process identifier of the process to monitor.
{RegisteredName, Node}:
A tuple consisting of a registered name of a process and a node name. The
process residing on the node Node with the registered name {RegisteredName,
Node} will be monitored.
RegisteredName:
The process locally registered as RegisteredName will become monitored.
Note:
When a registered name is used, the process that has the registered name when the
monitor request reach its destination will be monitored. The monitor is not
effected if the registered name is unregistered, or unregistered and later
registered on another process.
The monitor is triggered either when the monitored process terminates, is non
existing, or if the connection to it is lost. In the case the connection to it
is lost, we do not know if it still exist or not. After this type of monitor
has been triggered, the monitor is automatically removed.
When the monitor is triggered a 'DOWN' message is sent to the monitoring
process. A 'DOWN' message has the following pattern:
{'DOWN', MonitorRef, Type, Object, Info}
Here MonitorRef and Type are the same as described earlier, and:
Object:
equals:
Item:
If Item is specified by a process identifier.
{RegisteredName, Node}:
If Item is specified as RegisteredName, or {RegisteredName, Node} where
Node corresponds to the node that the monitored process resides on.
Info:
Either the exit reason of the process, noproc (non-existing process), or
noconnection (no connection to the node where the monitored process resides).
The monitoring is turned off when the 'DOWN' message is sent or when
demonitor/1 is called.
If an attempt is made to monitor a process on an older node (where remote
process monitoring is not implemented or where remote process monitoring by
registered name is not implemented), the call fails with badarg.
Note:
The format of the 'DOWN' message changed in ERTS version 5.2 (OTP R9B) for
monitoring by registered name. Element Object of the 'DOWN' message could in
earlier versions sometimes be the process identifier of the monitored process and
sometimes be the registered name. Now element Object is always a tuple consisting
of the registered name and the node name. Processes on new nodes (ERTS version
5.2 or higher) always get 'DOWN' messages on the new format even if they are
monitoring processes on old nodes. Processes on old nodes always get 'DOWN'
messages on the old format.
time_offset:
Monitor changes in time offset between Erlang monotonic time and Erlang system
time. There is only one valid Item in combination with the time_offset Type,
namely the atom clock_service. Note that the atom clock_service is not the
registered name of a process. In this specific 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
will be triggered once regardless of whether the time offset value was actually
changed or not.
If the runtime system is in multi time warp mode, the time offset will be
changed when the runtime system detects that the OS system time has changed.
The runtime system will, however, not detect this immediately when it happens.
A task checking the time offset is scheduled to execute at least once a minute,
so under normal operation this should be detected within a minute, but during
heavy load it might take longer time.
The monitor will not be automatically removed after it has been triggered. That
is, repeated changes of the time offset will trigger the monitor repeatedly.
When the monitor is triggered a 'CHANGE' message will be 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(). Note 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()
Monitors 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 given, 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 may also place this unspecified point in time different relative runtime
system start. It may 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 erlang: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 erlang: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 given. The returned result when
the argument is a list, is the list of nodes satisfying the disjunction(s) of the
list elements.
NodeType can be any of the following:
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 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! See the users guide chapter Time and
Time Correction for more information. Specifically the Dos and Dont's section for
information on 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), on the assumption that the underlying OS supports
this. Otherwise some other point in time is chosen. It is also guaranteed that
subsequent calls to this BIF return continuously increasing values. Hence, the
return value from now() 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 :: string(), Val :: string() | 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 given in cd, env, args, and
arg0 are subject to Unicode file name translation if the system is running in
Unicode file name 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, the function file:native_name_encoding/0, and the STDLIB
User's Guide.
Note:
The characters in the name (if given as a list) can only be higher than 255 if the
Erlang Virtual Machine is started in Unicode file name translation mode. Otherwise
the name of the executable is limited to the ISO-latin-1 character set.
PortName can be any of the following:
{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.
When starting external programs on Solaris, the system call vfork is used in
preference to fork for performance reasons, although it has a history of being
less robust. If there are problems using vfork, setting environment variable
ERL_NO_VFORK to any value causes fork to be used instead.
For external programs, PATH is searched (or an equivalent method is used to
find programs, depending on 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 having spaces in file names or directory names.
If spaces in executable file names 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 given 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 new line 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 new line 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 new line 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}:
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.
{args, [ string() | binary() ]}:
Only valid for {spawn_executable, FileName} and specifies arguments to the
executable. Each argument is given 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 being supplied to the
executable. Most notably this means that file wild card expansion does not
happen. To expand wild cards 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, wild card expansion does not happen, and the script is
provided with the untouched arguments. On Windows, wild card expansion is
always up to the program itself, therefore this is not an issue issue.
The executable name (also known as argv[0]) is not to be given 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 also given, 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 given in {spawn_executable, Command} does not point out an executable
file.
enoent:
FileName given 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 the file(3erl) manual page in Kernel.
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.
This BIF can be used instead of the old deprecated BIF erlang:hash/2, as it
calculates better hashes for all data types, but consider using phash2/1,2 instead.
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.
Warning:
This BIF is intended for debugging and is not to be used in application programs.
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 the following), 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 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. This 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 the following). 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 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. This 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.
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
any more.
The following Options are valid:
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
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.
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 the following.
* The port does not reply with {Port,connected}.
* port_connect/1 is synchronous, see the following.
* 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 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. This 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 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).
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).
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:
* false (emulator without SMP support)
* 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 that this port monitors.
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 being 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.
erlang:port_to_list(Port) -> string()
Types:
Port = port()
Returns a string corresponding to the text representation of the port identifier
Port.
Warning:
This BIF is intended for debugging. It is not to be used in application programs.
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 :: priority, Level) -> OldLevel
Types:
Level = OldLevel = priority_level()
priority_level() = low | normal | high | max
Sets the process priority. Level is an atom. There are four priority levels: 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 there are runnable processes on priority high, 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 there are processes running on
priority high. On the runtime system with SMP support, 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 there are runnable processes on priority max, 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 preemptive. Regardless of priority, a process is preempted 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, at
least on the runtime system with SMP support, 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 have 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 does most likely cause 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 is greater than 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. Furthermore, send, receive,
and timeout 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()}} |
{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}]} |
{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} |
{monitored_by, Pids :: [pid()]} |
{monitors,
Monitors ::
[{process,
Pid :: pid() | {RegName :: atom(), Node :: node()}}]} |
{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}]}
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
* messages
* 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 appears.
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 |
group_leader |
heap_size |
initial_call |
links |
last_calls |
memory |
message_queue_len |
messages |
min_heap_size |
min_bin_vheap_size |
monitored_by |
monitors |
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()}} |
{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}]} |
{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} |
{monitored_by, Pids :: [pid()]} |
{monitors,
Monitors ::
[{process,
Pid :: pid() | {RegName :: atom(), Node :: node()}}]} |
{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
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 given, 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 given, the result is InfoTupleList. The InfoTuples in InfoTupleList
appear with the corresponding Items in the same order as the Items appeared in
ItemList. Valid Items can appear multiple times in ItemList.
Note:
If registered_name is part of ItemList and the process has no name registered a
{registered_name, []}, InfoTuple will appear in the resulting InfoTupleList. This
behavior is different when a single Item =:= registered_name is given, and when
process_info/1 is used.
The following InfoTuples with corresponding Items are valid:
{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 currently
being referred to by this process. This InfoTuple can be changed or removed
without prior notice.
{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}}:
Module, Function, Arity is the current function call of the process.
{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.
{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.
{group_leader, GroupLeader}:
GroupLeader is 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 the following).
{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, Pids}:
A list of process identifiers monitoring the process (with monitor/2).
{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 item is {process, Pid}. For a remote process monitor by name, the list
item is {process, {RegName, Node}}.
{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 name of the process. 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 one of the following BIFs:
* erlang:suspend_process/2
* 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.
{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, erlang:check_process_code/2
is 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.
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 given class,
reason, and call stack backtrace (stacktrace).
Warning:
This BIF is intended for debugging. Avoid to use it in applications, unless you
really know what you are doing.
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.
Since 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, Options) -> Result | ok
Types:
TimerRef = reference()
Async = boolean()
Option = {async, Async}
Options = [Option]
Time = integer() >= 0
Result = Time | false
Read 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.
Available Options:
{async, Async}:
Asynchronous request for state information. Async defaults to false which will
cause 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 may be added in the future.
If Result is an integer, it represents the time in milli-seconds left until the
timer expires.
If Result is false, a timer corresponding to TimerRef could not be found. This can
be because the timer had expired, it had 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 timeout message has arrived at its destination yet.
Note:
The timer service that manages the timer may be co-located with another scheduler
than the scheduler that the calling process is executing on. If this is the case,
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, you want to use option {async, true}. If
using option {async, false}, the calling process will be blocked until the
operation has been performed.
See also erlang:send_after/4, erlang:start_timer/4, and erlang:cancel_timer/2.
erlang:read_timer(TimerRef) -> Result
Types:
TimerRef = reference()
Time = integer() >= 0
Result = Time | false
Read the state of a timer. The same as calling erlang:read_timer(TimerRef, []).
erlang: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 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.
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 the following). Otherwise the same as erlang:send/2. For more
detailed explanation and warnings, see erlang:send_nosuspend/2,3.
The options are as follows:
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, 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 timeout message,
erlang:send_after/4 works exactly as erlang:start_timer/4.
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_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. The fact that
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 given 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 = [Option]
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}
priority_level() = low | normal | high | max
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 given, the newly created process is monitored, and both the
pid and reference for the monitor is returned.
spawn_opt(Node, Fun, Options) -> pid() | {pid(), reference()}
Types:
Node = node()
Fun = function()
Options = [Option]
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}
priority_level() = low | normal | high | max
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 = [Option]
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}
priority_level() = low | normal | high | max
Works as spawn/3, except that an extra option list is given when creating the
process.
If option monitor is given, the newly created process is monitored, and both the
pid and reference for the monitor is returned.
The options are as follows:
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.
spawn_opt(Node, Module, Function, Args, Options) ->
pid() | {pid(), reference()}
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Options = [Option]
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}
priority_level() = low | normal | high | max
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, 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.
Available Options:
{abs, false}:
This is the default. It means the Time value is interpreted as a time in milli-
seconds relative current Erlang monotonic time.
{abs, true}:
Absolute Time value. The Time value is interpreted as an absolute Erlang
monotonic time in milli-seconds.
More Options may be added in the future.
The absolute point in time, the timer is set to expire on, has to be in the
interval [erlang:system_info(start_time), erlang:system_info(end_time)]. Further,
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 may or may not have terminated. 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 given 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 version 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.
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, []).
statistics(Item :: active_tasks) -> [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 scheduler. That is, the number of
processes and ports that are ready to run, or are currently running. The element
location in the list corresponds to the scheduler and its run queue. The first
element corresponds to scheduler number 1 and so on. The information is not
gathered atomically. That is, the result is not necessarily a consistent snapshot
of the state, but instead quite efficiently gathered. See also,
statistics(total_active_tasks), statistics(run_queue_lengths), and
statistics(total_run_queue_lengths).
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), especially on an Erlang machine with SMP support.
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 :: 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 (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 the run-queues. That is, the number of processes and
ports that are ready to run on all available run-queues. 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). This especially when a large amount of
schedulers is used.
statistics(Item :: run_queue_lengths) -> [RunQueueLenght]
Types:
RunQueueLenght = integer() >= 0
Returns a list where each element represents the amount of processes and ports
ready to run for each run queue. The element location in the list corresponds to
the run queue of a scheduler. The first element corresponds to the run queue of
scheduler number 1 and so on. The information is not gathered atomically. That is,
the result is not necessarily a consistent snapshot of the state, but instead quite
efficiently gathered. See also, statistics(total_run_queue_lengths),
statistics(active_tasks), and statistics(total_active_tasks).
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.
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. 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 built-in-functions, 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.
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)), A/T.
0.9769136803764825
Note:
scheduler_wall_time is by default disabled. To enable it, use
erlang:system_flag(scheduler_wall_time, true).
statistics(Item :: total_active_tasks) -> ActiveTasks
Types:
ActiveTasks = integer() >= 0
Returns the total amount of active processes and ports in the system. That is, the
number of processes and ports that are ready to run, or are currently running. The
information is not gathered atomically. That is, the result is not necessarily a
consistent snapshot of the state, but instead quite efficiently gathered. See also,
statistics(active_tasks), statistics(run_queue_lengths), and
statistics(total_run_queue_lengths).
statistics(Item :: total_run_queue_lengths) ->
TotalRunQueueLenghts
Types:
TotalRunQueueLenghts = integer() >= 0
Returns the total length of the run-queues. That is, the number of processes and
ports that are ready to run on all available run-queues. The information is not
gathered atomically. That is, the result is not necessarily a consistent snapshot
of the state, but much more efficiently gathered compared to statistics(run_queue).
See also, statistics(run_queue_lengths), statistics(total_active_tasks), and
statistics(active_tasks).
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, OptList) -> boolean()
Types:
Suspendee = pid()
OptList = [Opt]
Opt = unless_suspending | asynchronous
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 will
not be 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.
The options (Opts) are as follows:
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
Suspendeeeventually suspends (unless it is resumed). If option asynchronous has
not been passed, the caller of erlang:suspend_process/2 is blocked until
Suspendee has suspended.
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.
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 higher than 2,000,000,000 suspends and will
never be lower.
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: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.
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 and scheduled for removal in ERTS 5.10/OTP R16. 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 the 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.
Note:
The dirty schedulers functionality is experimental. Enable support for dirty
schedulers when building OTP to try out the functionality.
For more information, see erlang:system_info(dirty_cpu_schedulers) and
erlang:system_info(dirty_cpu_schedulers_online).
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 :: min_heap_size, MinHeapSize) ->
OldMinHeapSize
Types:
MinHeapSize = OldMinHeapSize = integer() >= 0
Sets the default minimum heap size for processes. The size is given 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/N 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 given
in words. The new min_bin_vhheap_size effects only processes spawned after the
change of min_bin_vhheap_size has been made. min_bin_vheap_size can be set for
individual processes by using spawn_opt/N or process_flag/2.
Returns the old value of the flag.
erlang:system_flag(Flag :: multi_scheduling, BlockState) ->
OldBlockState
Types:
BlockState = block | unblock
OldBlockState = block | unblock | enabled
If multi-scheduling is enabled, more than one scheduler thread is used by the
emulator. Multi-scheduling can be blocked. When multi-scheduling is blocked, only
one scheduler thread schedules Erlang processes.
If BlockState =:= block, multi-scheduling is blocked. If BlockState =:= unblock and
no one else blocks multi-scheduling, and this process has blocked only once, multi-
scheduling is unblocked.
One process can block 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 exits, it releases its blocking of multi-scheduling.
The return values are disabled, blocked, 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 is normally not needed. If you feel that you need to
block multi-scheduling, 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(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 and scheduled for removal in ERTS 5.10/OTP R16. 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, it
is reported to error_logger. 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 erlang: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 :: 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 the 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 :: allocated_areas) -> [tuple()]
erlang:system_info(Item :: allocator) ->
{Allocator, Version, Features, Settings}
erlang:system_info(Item :: alloc_util_allocators) -> [Alloc]
erlang:system_info(Item :: {allocator, Alloc}) -> [term()]
erlang:system_info(Item :: {allocator_sizes, Alloc}) -> [term()]
Types:
Allocator = undefined | glibc
Version = [integer() >= 0]
Features = [atom()]
Settings =
[{Subsystem :: atom(),
[{Parameter :: atom(), Value :: term()}]}]
Alloc = atom()
Returns various information about the 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).
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, 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.
As from ERTS 5.10.4, the returned list when calling
erlang:system_info({allocator, mseg_alloc}) also includes an {erts_mmap, _}
tuple as one element in the list. 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). 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.
{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}).
erlang:system_info(Item :: cpu_topology) -> CpuTopology
erlang:system_info(Item ::
{cpu_topology, defined | detected | used}) ->
CpuTopology
Types:
CpuTopology = cpu_topology()
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 sub level to core. core can be a sub level to processor or
node. processor can be on the top level or a sub level to node. node can be on
the top level or a sub level 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. In other words, 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.
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 :: creation) -> integer()
erlang:system_info(Item :: debug_compiled) -> boolean()
erlang:system_info(Item :: delayed_node_table_gc) ->
infinity | integer() >= 0
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 :: dist) -> binary()
erlang:system_info(Item :: dist_buf_busy_limit) ->
integer() >= 0
erlang:system_info(Item :: dist_ctrl) ->
{Node :: node(),
ControllingEntity :: port() | pid()}
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 :: elib_malloc) -> false
erlang:system_info(Item :: eager_check_io) -> boolean()
erlang:system_info(Item :: ets_limit) -> integer() >= 1
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 :: info) -> binary()
erlang:system_info(Item :: kernel_poll) -> boolean()
erlang:system_info(Item :: loaded) -> binary()
erlang:system_info(Item ::
logical_processors |
logical_processors_available |
logical_processors_online) ->
unknown | integer() >= 1
erlang:system_info(Item :: machine) -> string()
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 :: modified_timing_level) ->
integer() | undefined
erlang:system_info(Item :: multi_scheduling) ->
disabled | blocked | enabled
erlang:system_info(Item :: multi_scheduling_blockers) ->
[Pid :: pid()]
erlang:system_info(Item :: nif_version) -> string()
erlang:system_info(Item :: otp_release) -> string()
erlang:system_info(Item :: os_monotonic_time_source) ->
[{atom(), term()}]
erlang:system_info(Item :: os_system_time_source) ->
[{atom(), term()}]
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
erlang:system_info(Item :: procs) -> binary()
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 :: start_time) -> integer()
erlang:system_info(Item :: system_version) -> string()
erlang:system_info(Item :: system_architecture) -> string()
erlang:system_info(Item :: threads) -> boolean()
erlang:system_info(Item :: thread_pool_size) -> integer() >= 0
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
erlang:system_info(Item :: trace_control_word) ->
integer() >= 0
erlang:system_info(Item :: update_cpu_info) -> changed | unchanged
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:
allocated_areas, allocator, alloc_util_allocators, allocator_sizes:
See above.
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).
cpu_topology:
See above.
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.
debug_compiled:
Returns true if the emulator has been debug compiled, otherwise false.
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 the command line
flag +zdntgc to erl. For more information see the documentation of the command
line flag.
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).
Notice that the dirty schedulers functionality is experimental. Enable support
for dirty schedulers when building OTP to try out the functionality.
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).
Notice that the dirty schedulers functionality is experimental. Enable support
for dirty schedulers when building OTP to try out the functionality.
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).
Notice that the dirty schedulers functionality is experimental. Enable support
for dirty schedulers when building OTP to try out the functionality.
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).
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.
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.
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 the dyntrace 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).
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.
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.
eager_check_io:
Returns the value of the erl command line flag +secio which is either true or
false. See the documentation of the command line flag for information about the
different values.
ets_limit:
Returns the maximum number of ETS tables allowed. This limit can be increased
at startup by passing command-line flag +e to erl(1) or by setting environment
variable ERL_MAX_ETS_TABLES before starting the Erlang runtime system.
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 in the following.
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
system_flag/2. spawn_opt/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.
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.
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.
machine:
Returns a string containing the Erlang machine name.
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.
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)
multi_scheduling:
Returns disabled, blocked, or enabled:
disabled:
The emulator has only one scheduler thread. The emulator does not have SMP
support, or have 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.
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), 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), and erlang:system_info(schedulers).
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 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.
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 exist if OS
monotonic time is available to the runtime system.
{clock_id, ClockId}:
This tuple only exist 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. Also note that the resolution does not say
anything about the accuracy, and whether the precision do align 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 needs to 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 needs to 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 if 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}:
This tuple only exist 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 may be lower than
OsSystemTimeResolution. Also note that the resolution does not say anything
about the accuracy, and 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.
port_parallelism:
Returns the default port parallelism scheduling hint used. For more
information, see command-line argument +spp in erl(1).
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).
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.
scheduler_bind_type:
Returns information about how the user has requested schedulers to be bound or
not bound.
Notice that even though 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), 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 if the emulator has been compiled with SMP support, otherwise
false is returned.
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).
system_version:
Returns a string containing version number and some important properties, such
as the number of schedulers.
system_architecture:
Returns a string containing the processor and OS architecture the emulator is
built for.
threads:
Returns true if the emulator has been compiled with thread support, otherwise
false is returned.
thread_pool_size:
Returns the number of async threads in the async thread pool used for
asynchronous driver calls (driver_async()). The value is given as an integer.
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 at a later time when
being finalized. 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 being 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.
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.
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.
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.
Note:
Argument scheduler has changed name to scheduler_id to avoid mix up with argument
schedulers. Argument scheduler was introduced in ERTS 5.5 and renamed in ERTS
5.5.1.
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 there are no settings. 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_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 the timeout tuple 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 below 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.
As of ERTS 5.6, the monitor message is sent if the sum of the sizes of all
memory blocks allocated for all heap generations is equal to or higher than
Size. Previously the monitor message was sent if the memory block allocated for
the youngest generation was equal to or higher than Size.
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:
Timestamps in profile messages will use Erlang monotonic time. The time-stamp
(Ts) has the same format and value as produced by
erlang:monotonic_time(nano_seconds).
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 preempted 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:
Timestamps in profile messages will consisting 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(nano_seconds),
erlang:unique_integer([monotonic])}.
timestamp:
Timestamps in profile messages will include a time-stamp (Ts) that has the same
form as returned by erlang:now(). This is also the default if no timestamp flag
is given. If cpu_timestamp has been enabled via erlang:trace/3, this will also
effect the timestamp produced in profiling messages when timestamp flag is
enabled.
Note:
erlang:system_profile is considered experimental and its 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 ERTS 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 ERTS 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.
See also binary_to_term/1.
term_to_binary(Term, Options) -> ext_binary()
Types:
Term = term()
Options =
[compressed |
{compressed, Level :: 0..9} |
{minor_version, Version :: 0..1}]
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
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 OTP R11B-4. The valid values for Version are 0 and 1.
As from OTP 17.0, {minor_version, 1} is 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 OTP R11B-4, binary_to_term/1 can decode this representation.
{minor_version, 0} means that floats are encoded using a textual representation.
This option is useful to ensure that releases before OTP R11B-4 can decode
resulting binary.
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 may be observed at slightly different points in time by
different processes.
If the runtime system is in multi time warp mode, the time offset will be changed
when the runtime system detects that the OS system time has changed. The runtime
system will, however, not detect this immediately when it happens. A task checking
the time offset is scheduled to execute at least once a minute, so under normal
operation this should be detected within a minute, but during heavy load it might
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 uses. The
reason for the existence of erlang:timestamp() is purely to simplify usage for
existing code that assumes this timestamp 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(micro_seconds),
MegaSecs = ErlangSystemTime div 1000000000000,
Secs = ErlangSystemTime div 1000000 - MegaSecs*1000000,
MicroSecs = ErlangSystemTime rem 1000000,
{MegaSecs, Secs, MicroSecs}.
It, however, uses a native implementation which 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 ERTS 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(PidSpec, How, FlagList) -> integer()
Types:
PidSpec = pid() | existing | new | all
How = boolean()
FlagList = [trace_flag()]
trace_flag() =
all |
send |
'receive' |
procs |
call |
silent |
return_to |
running |
exiting |
garbage_collection |
timestamp |
cpu_timestamp |
monotonic_timestamp |
strict_monotonic_timestamp |
arity |
set_on_spawn |
set_on_first_spawn |
set_on_link |
set_on_first_link |
{tracer, pid() | port()}
Turns on (if How == true) or off (if How == false) the trace flags in FlagList for
the process or processes represented by PidSpec.
PidSpec is either a process identifier (pid) for a local process, or one of the
following atoms:
existing:
All currently existing processes.
new:
All processes that are created in the future.
all:
All currently existing processes and all processes that are 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, 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'.
procs:
Traces process-related events.
Message tags: spawn, exit, register, unregister, link, unlink, getting_linked,
and getting_unlinked.
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.
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.
garbage_collection:
Traces garbage collections of processes.
Message tags: gc_start and gc_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
the timestamp flag to be in CPU time, not wall clock time. That is,
cpu_timestamp will not be used if monotonic_timestamp, or
strict_monotonic_timestamp is enabled. Only allowed with PidSpec==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 might 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(nano_seconds). This flag overrides the cpu_timestamp
flag.
strict_monotonic_timestamp:
Includes an timestamp 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(nano_seconds),
erlang:unique_integer([monotonic])}. This flag overrides the cpu_timestamp
flag.
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. If this
flag is not given, trace messages are sent to the process that called
erlang:trace/3.
The effect of combining set_on_first_link with set_on_link is the same as having
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 given, 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 timestamp flags are passed,
timestamp has precedence over strict_monotonic_timestamp which in turn has
precedence over monotonic_timestamp. All timestamp flags are remembered, so if two
are passed and the one with highest precedence later is disabled the other one will
become active.
{trace, Pid, 'receive', Msg}:
When Pid receives message Msg.
{trace, Pid, send, Msg, To}:
When Pid sends message Msg to process To.
{trace, Pid, send_to_non_existing_process, Msg, To}:
When Pid sends message Msg to the non-existing process To.
{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, exit, Reason}:
When Pid exits with reason Reason.
{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, Pid, getting_linked, Pid2}:
When Pid gets linked to a process Pid2.
{trace, Pid, getting_unlinked, Pid2}:
When Pid gets unlinked from a process Pid2.
{trace, Pid, register, RegName}:
When Pid gets the name RegName registered.
{trace, Pid, unregister, RegName}:
When Pid gets the name RegName unregistered. This is done automatically when a
registered process exits.
{trace, Pid, in, {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, {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, Pid, gc_start, Info}:
Sent when 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_end, Info}:
Sent when garbage collection is finished. Info contains the same kind of list
as in message gc_start, but the sizes reflect the new sizes after garbage
collection.
If the tracing process dies, the flags are silently removed.
Only one process can trace a particular process. Therefore, attempts to trace an
already traced process fail.
Returns: A number indicating the number of processes that matched PidSpec. If
PidSpec is a process identifier, the return value is 1. If PidSpec is all or
existing, the return value is the number of processes running, excluding tracer
processes. If PidSpec 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 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). A {trace_delivered, Tracee, Ref} message is sent to
the caller of 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).
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 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.
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(PidOrFunc, Item) -> Res
Types:
PidOrFunc = pid() | new | {Module, Function, Arity} | on_load
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() | []} |
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_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()] | '_', [term()], [term()]}]
Returns trace information about a process or function.
To get information about a process, PidOrFunc is to be a process identifier (pid)
or the atom new. The atom new means that the default trace state for processes to
be created is returned.
The following Items are valid:
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, set_on_first_spawn, set_on_link, running, garbage_collection,
timestamp, and arity. The order is arbitrary.
tracer:
Returns the identifier for process or port tracing this process. If this
process is not being traced, the return value is [].
To get information about a function, PidOrFunc is to be the three-element tuple
{Module, Function, Arity} or the atom on_load. No wild cards are allowed. Returns
undefined if the function does not exist, or false if the function is not traced.
The following Items are valid::
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 or port 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.
The return value is {Item, Value}, where Value is the requested information as
described earlier. If a pid for a dead process was given, or the name of a non-
existing function, Value is undefined.
If PidOrFunc is on_load, the information returned refers to the default value for
code that will be loaded.
erlang:trace_pattern(MFA, MatchSpec) -> integer() >= 0
Types:
MFA = trace_pattern_mfa()
MatchSpec =
(MatchSpecList :: trace_match_spec()) |
boolean() |
restart |
pause
trace_pattern_mfa() = {atom(), atom(), arity() | '_'} | on_load
trace_match_spec() = [{[term()] | '_', [term()], [term()]}]
The same as erlang:trace_pattern(MFA, MatchSpec, []), retained for backward
compatibility.
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()] | '_', [term()], [term()]}]
trace_pattern_flag() =
global |
local |
meta |
{meta, Pid :: pid()} |
call_count |
call_time
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 in the following). It can be the module, function, and arity for
a function (or a BIF in any module). The atom '_' can be used as a wild card 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 wild cards 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.
MatchSpecList:
A list of match specifications. An empty list is equivalent to true. For a
description of match specifications, see 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}:
Turns on or off meta-tracing for all types of function calls. Trace messages
are sent to the tracer process or port Pid whenever any of the specified
functions are called, regardless of how they are called. If no Pid 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 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 process.
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 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.
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 forth.
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: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.
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, will
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 in order to utilize 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.
Valid Modifiers:
positive:
Return only positive integers.
Note that by passing the positive modifier you will get heap allocated integers
(bignums) quicker.
monotonic:
Return strictly monotonically increasing integers corresponding to creation
time. That is, the integer returned will always be 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:
Note that the set of integers returned by 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 being returned by both calls.
Failures:
badarg:
if ModifierList is not a proper list.
badarg:
if Modifier is not a valid modifier.
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:
Prior to OTP release R11B (ERTS version 5.5) unlink/1 behaved completely
asynchronously, i.e., 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
erlang:yield() 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, especially in the SMP emulator,
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.