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NAME
erlang - The Erlang BIFs
DESCRIPTION
By convention, most built-in functions (BIFs) are seen as being in the module erlang. A
number 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 and both the calls
atom_to_list(Erlang) and erlang:atom_to_list(Erlang) are identical.
In the text, auto-imported BIFs are listed without module prefix. BIFs listed with module
prefix are not auto-imported.
BIFs may fail for a variety of reasons. All BIFs fail with reason badarg if they are
called with arguments of an incorrect type. The other reasons that may make BIFs fail are
described in connection with the description of each individual BIF.
Some BIFs may be used in guard tests, these 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 now/0.
EXPORTS
abs(Float) -> float()
abs(Int) -> integer() >= 0
Types:
Float = float()
Int = integer()
Returns an integer or float which is the arithmetical absolute value of Float or
Int.
> 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()
Continue 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).
- would assign the same value to Y as this would:
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).
- would assign the same value to Z as this would:
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 which 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.
> erlang:append_element({one, two}, three).
{one,two,three}
apply(Fun, Args) -> term()
Types:
Fun = function()
Args = [term()]
Call a fun, passing the elements in Args as arguments.
Note: 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 usage is deprecated and will stop working in a future release
of Erlang/OTP.
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.
> apply(lists, reverse, [[a, b, c]]).
[c,b,a]
apply can be used to evaluate BIFs by using the module name erlang.
> apply(erlang, atom_to_list, ['Erlang']).
"Erlang"
Note: 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 the
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 which corresponds to the text representation of Atom. If Encoding
is latin1, there will be one byte for each character in the text representation. If
Encoding is utf8 or unicode, the characters will be encoded using UTF-8 (meaning
that characters from 16#80 up to 0xFF will be encoded in two bytes).
Note:
Currently, atom_to_binary(Atom, latin1) can never fail because the text
representation of an atom can only contain characters from 0 to 16#FF. In a future
release, the text representation of atoms might be allowed to contain any Unicode
character and atom_to_binary(Atom, latin1) will fail if the text representation for
the Atom contains a Unicode character greater than 16#FF.
> atom_to_binary('Erlang', latin1).
<<"Erlang">>
atom_to_list(Atom) -> string()
Types:
Atom = atom()
Returns a string which corresponds to the text representation of Atom.
> 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:
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>>
If PosLen in any way references outside the binary, a badarg exception is raised.
Start is zero-based, i.e.:
1> Bin = <<1,2,3>>
2> binary_part(Bin,{0,2}).
<<1,2>>
See the STDLIB module binary for details about the PosLen semantics.
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; furthermore, only Unicode characters up
to 0xFF are allowed.
Note:
binary_to_atom(Binary, utf8) will fail if the binary contains Unicode characters
greater than 16#FF. In a future release, such Unicode characters might be allowed
and binary_to_atom(Binary, utf8) will not fail in that case. For more information
on Unicode support in atoms see note on UTF-8 encoded atoms in the chapter about
the external term format in the ERTS User's Guide.
> 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
Works like binary_to_atom/2, but the atom must already exist.
Failure: badarg if the atom does not already exist.
binary_to_float(Binary) -> float()
Types:
Binary = binary()
Returns the float whose text representation is Binary.
> 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.
> 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.
> 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 which correspond 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. Positions in the binary are numbered
starting from 1.
Note:
This function's indexing style of using one-based indices for binaries is
deprecated. New code should use the functions in the STDLIB module binary instead.
They consequently use the same (zero-based) style of indexing.
bitstring_to_list(Bitstring) -> [byte() | bitstring()]
Types:
Bitstring = bitstring()
Returns a list of integers which correspond to the bytes of Bitstring. If the
number of bits in the binary is not divisible by 8, the last element of the list
will be a bitstring containing the remaining bits (1 up to 7 bits).
binary_to_term(Binary) -> term()
Types:
Binary = ext_binary()
Returns an Erlang term which is the result of decoding the 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 may be used to attack the Erlang
system. In the event of receiving unsafe data, decoding fails with a badarg
error.
Currently, this prevents creation of new atoms directly, creation of new atoms
indirectly (as they are embedded in certain structures like pids, refs, funs,
etc.), and creation of new external function references. None of those
resources are currently 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 which is the size in bits of Bitstring.
> 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, and a context switch is forced
when the counter reaches the maximum number of reductions for a process (2000
reductions in R12B).
Warning:
This BIF might 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 which 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 will be rounded up.)
> byte_size(<<433:16,3:3>>).
3
> byte_size(<<1,2,3>>).
3
Allowed in guard tests.
erlang:cancel_timer(TimerRef) -> Time | false
Types:
TimerRef = reference()
Time = integer() >= 0
Cancels a timer, where TimerRef was returned by either erlang:send_after/3 or
erlang:start_timer/3. If the timer is there to be removed, the function returns the
time in milliseconds left until the timer would have expired, otherwise false
(which means that TimerRef was never a timer, that it has already been cancelled,
or that it has already delivered its message).
See also erlang:send_after/3, erlang:start_timer/3, and erlang:read_timer/1.
Note: Cancelling a timer does not guarantee that the message has not already been
delivered to the message queue.
check_old_code(Module) -> boolean()
Types:
Module = module()
Returns true if the Module has old code, and false otherwise.
See also code(3erl).
check_process_code(Pid, Module) -> boolean()
Types:
Pid = pid()
Module = module()
Returns true if the process Pid is executing old code for Module. That is, if the
current call of the process executes old code for this module, or if the process
has references to old code for this module, or if the process contains funs that
references old code for this module. Otherwise, it returns false.
> check_process_code(Pid, lists).
false
See also code(3erl).
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()
Continue 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).
- would assign the same value to Y as this would:
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).
- would assign the same value to Z as this would:
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.
> 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. Very
similar to the packet handling done by sockets with the 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 not known. 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 values of Type are valid:
raw | 0:
No packet handling is done. 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 header can be one, two, or four
bytes; the order of the bytes is big-endian. The header will be stripped off
when the packet is returned.
line:
A packet is a line terminated with newline. The newline character is included
in the returned packet unless the line was truncated according to the 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 above. 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 (like "Sec-Websocket-
Key").
The protocol type http should only be used for the first line when a
HttpRequest or a HttpResponse is expected. The following calls should use httph
to get HttpHeader's until http_eoh is returned that marks the end of the
headers and the beginning of any following message body.
The variants http_bin and httph_bin will return strings (HttpString) as
binaries instead of lists.
The following options are available:
{packet_size, integer() >= 0}:
Sets the max allowed size of the packet body. If the packet header indicates
that the length of the packet is longer than the max allowed length, the packet
is considered invalid. Default is 0 which means no size limit.
{line_length, integer() >= 0}:
For packet type line, truncate lines longer than the indicated length.
Option line_length also applies to http* packet types as an alias for option
packet_size in the case when packet_size itself is not set. This usage is only
intended for backward compatibility.
> 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.
> 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 should not be used
elsewhere.
Failure: badarg if there is already an old version of Module.
demonitor(MonitorRef) -> true
Types:
MonitorRef = reference()
If MonitorRef is a reference which 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 due to the monitor will be placed in the caller's
message queue in the future. A {'DOWN', MonitorRef, _, _, _} message might have
been placed in the caller's message queue prior to the call, though. Therefore, in
most cases, it is 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
asynchronous, i.e., the monitor was active until the "demonitor signal" reached the
monitored entity. This had one undesirable effect, though. 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).
Currently the following Options are valid:
flush:
Remove (one) {_, MonitorRef, _, _, _} message, if there is one, from the
caller's 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 due to this
monitor have been nor will be placed in the message queue of the caller.
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's message queue.
If the info option is combined with the flush option, false will be returned if
a flush was needed; otherwise, true.
Note:
More options may be added in the future.
Failure: badarg if OptionList is not a list, or if Option is not a valid option, or
the same failure as for demonitor/1
disconnect_node(Node) -> boolean() | ignored
Types:
Node = node()
Forces the disconnection of a node. This will appear 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, the function returns ignored.
erlang:display(Term) -> true
Types:
Term = term()
Prints a text representation of Term on the standard output.
Warning:
This BIF is intended for debugging only.
element(N, Tuple) -> term()
Types:
N = integer() >= 1
1..tuple_size(Tuple)
Tuple = tuple()
Returns the Nth element (numbering from 1) of Tuple.
> element(2, {a, b, c}).
b
Allowed in guard tests.
erase() -> [{Key, Val}]
Types:
Key = Val = term()
Returns the process dictionary and deletes it.
> 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.
> 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 actual exit reason will be {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.
> 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 actual exit reason will be {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 will be used to
provide the actual arguments for the current function in the Where term. 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 the exit reason Reason, where
Reason is any term. Since evaluating this function causes the process to terminate,
it has no return value.
> 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 apply if Reason is any term except normal or kill:
If Pid is not trapping exits, Pid itself will exit 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 pid of the process
which sent the exit signal. See also process_flag/2.
If Reason is the atom normal, Pid will 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 will unconditionally exit 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
The option {minor_version, Version} specifies how floats are encoded. See
term_to_binary/2 for a more detailed description.
float(Number) -> float()
Types:
Number = number()
Returns a float by converting Number to a float.
> float(55).
55.0
Allowed in guard tests.
Note:
Note that if used on the top-level in a guard, it will test 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 above.
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 which corresponds to the text representation of Float using fixed
decimal point formatting. The Options behave in the same way as float_to_list/2.
> 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 which corresponds to the text representation of Float using fixed
decimal point formatting. When decimals option is specified the returned value will
contain at most Decimals number of digits past the decimal point. If the number
doesn't fit in the internal static buffer of 256 bytes, the function throws badarg.
When compact option is provided the trailing zeros at the end of the list are
truncated (this option is only meaningful together with the decimals option). When
scientific option is provided, the float will be formatted using scientific
notation with Decimals digits of precision. If Options is [] the function behaves
like float_to_list/1.
> 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 containing information about the fun Fun. Each element of the list
is a tuple. The order of the tuples is not defined, and more tuples may be added in
a future release.
Warning:
This BIF is mainly intended for debugging, but it can occasionally be useful in
library functions that might need to verify, for instance, the arity of a fun.
There are two types of funs with 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. Note 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 will be called (even if newer version of the module
has been loaded).
The following elements will always be present in the list for both local and
external funs:
{type, Type}:
Type is either 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 generally only of
informational use. As it is a local function, it is not possible to call it
directly.) If no code is currently loaded for the fun, [] will be 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 should 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 will only be present in the list if Fun is local:
{pid, Pid}:
Pid is the pid of the process that originally created the fun.
{index, Index}:
Index (an integer) is an index into the module's fun table.
{new_index, Index}:
Index (an integer) is an index into the module's 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. Starting in the R15 release,
this integer is calculated from the compiled code for the entire module. Before
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 which corresponds 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; otherwise false.
Returns false for any BIF (functions implemented in C rather than in Erlang).
garbage_collect() -> true
Forces an immediate garbage collection of the currently executing process. The
function should not 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. Improper use may seriously degrade system performance.
Compatibility note: In versions of OTP prior to R7, the garbage collection took
place at the next context switch, not immediately. To force a context switch after
a call to erlang:garbage_collect(), it was sufficient to make any function call.
garbage_collect(Pid) -> boolean()
Types:
Pid = pid()
Works like erlang:garbage_collect() but on any process. The same caveats apply.
Returns false if Pid refers to a dead process; true otherwise.
get() -> [{Key, Val}]
Types:
Key = Val = term()
Returns the process dictionary as a list of {Key, Val} tuples.
> 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 Valassociated with Key in the process dictionary, or undefined if
Key does not exist.
> 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(Val) -> [Key]
Types:
Val = Key = term()
Returns a list of keys which are associated with the value Val in the process
dictionary.
> 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}]}
Get the call stack back-trace (stacktrace) of the last exception in the calling
process as a list of {Module,Function,Arity,Location} tuples. The Arity field in
the first tuple may 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 may 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 may indicate the location in
the source code of the function. The first element is an atom that describes the
type of information in the second element. Currently the following items may occur:
file:
The second element of the tuple is a string (list of characters) representing
the filename of the source file of the function.
line:
The second element of the tuple is the line number (an integer 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 pid of the group leader for the process which evaluates the function.
Every process is a member of some process group and all groups have a group leader.
All IO 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
processes started from a certain shell should have another group leader than init.
See also group_leader/0.
halt() -> no_return()
The same as halt(0, []).
> halt().
os_prompt%
halt(Status) -> no_return()
Types:
Status = integer() >= 0 | abort | string()
The same as halt(Status, []).
> 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:
integer():
The runtime system exits with the integer value Status as status code to the
calling environment (operating system).
string():
An erlang crash dump is produced with Status as slogan, and then the runtime
system exits with status code 1.
abort:
The runtime system aborts producing a core dump, if that is enabled in the
operating system.
Note that on many platforms, only the status codes 0-255 are supported by the
operating system.
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 the flush option 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 allowed range is
1..2^27-1.
Warning:
This BIF is deprecated as the hash value may differ on different architectures.
Also the hash values for integer terms larger than 2^27 as well as large binaries
are very poor. The BIF is retained for backward compatibility reasons (it may have
been used to hash records into a file), but all new code should 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.
> 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, which is useful if the process does not expect to
receive any messages in the near future.
The process will be awaken when a message is sent to it, and control will resume in
Module:Function with the arguments given by Args with the call stack emptied,
meaning that the process will terminate when that function returns. Thus
erlang:hibernate/3 will never return to its caller.
If the process has any message in its message queue, the process will be awaken
immediately in the same way as described above.
In more technical terms, what erlang:hibernate/3 does is the following. It discards
the call stack for the process. Then it garbage collects the process. After the
garbage collection, all live data is in one continuous heap. The heap is then
shrunken to the exact same size as the live data which 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 has been awaken will ensure
that the heap size is changed to a size not smaller than the minimum heap size.
Note that emptying the call stack means that any surrounding catch is removed and
has to be re-inserted after hibernation. One effect of this is that processes
started using proc_lib (also indirectly, such as gen_server processes), should 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 insert at position Index in tuple Tuple1. All
elements from position Index and upwards are subsequently pushed one step higher in
the new tuple Tuple2.
> erlang:insert_element(2, {one, two, three}, new).
{one,new,two,three}
integer_to_binary(Integer) -> binary()
Types:
Integer = integer()
Returns a binary which corresponds to the text representation of Integer.
> integer_to_binary(77).
<<"77">>
integer_to_binary(Integer, Base) -> binary()
Types:
Integer = integer()
Base = 2..36
Returns a binary which corresponds to the text representation of Integer in base
Base.
> integer_to_binary(1023, 16).
<<"3FF">>
integer_to_list(Integer) -> string()
Types:
Integer = integer()
Returns a string which corresponds to the text representation of Integer.
> integer_to_list(77).
"77"
integer_to_list(Integer, Base) -> string()
Types:
Integer = integer()
Base = 2..36
Returns a string which corresponds to the text representation of Integer in base
Base.
> integer_to_list(1023, 16).
"3FF"
iolist_to_binary(IoListOrBinary) -> binary()
Types:
IoListOrBinary = iolist() | binary()
Returns a binary which is made from the integers and binaries in IoListOrBinary.
> 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 which is the size in bytes of the binary that would be the
result of iolist_to_binary(Item).
> 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, it returns false.
is_atom(Term) -> boolean()
Types:
Term = term()
Returns true if Term is an atom; otherwise returns false.
Allowed in guard tests.
is_binary(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a binary; otherwise returns 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 returns false.
Allowed in guard tests.
is_boolean(Term) -> boolean()
Types:
Term = term()
Returns true if Term is either the atom true or the atom false (i.e. a boolean);
otherwise returns false.
Allowed in guard tests.
erlang:is_builtin(Module, Function, Arity) -> boolean()
Types:
Module = module()
Function = atom()
Arity = arity()
Returns true if Module:Function/Arity is a BIF implemented in C; otherwise returns
false. This BIF is useful for builders of cross reference tools.
is_float(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a floating point number; otherwise returns false.
Allowed in guard tests.
is_function(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a fun; otherwise returns 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 returns false.
Allowed in guard tests.
is_integer(Term) -> boolean()
Types:
Term = term()
Returns true if Term is an integer; otherwise returns 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 returns false.
Allowed in guard tests.
is_number(Term) -> boolean()
Types:
Term = term()
Returns true if Term is either 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 pid (process identifier); otherwise returns false.
Allowed in guard tests.
is_port(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a port identifier; otherwise returns 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 the RecordTag is not a literal atom, the is_record/2 BIF
will be called instead and the size of the tuple will not be 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, provided that RecordTag is a literal atom and Size is a
literal integer.
Note:
This BIF is documented for completeness. In most cases is_record/2 should be used.
is_reference(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a reference; otherwise returns false.
Allowed in guard tests.
is_tuple(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a tuple; otherwise returns false.
Allowed in guard tests.
length(List) -> integer() >= 0
Types:
List = [term()]
Returns the length of List.
> 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 may only contain ISO-latin-1 characters (i.e. numbers below 256) as the
current implementation does not allow unicode characters >= 256 in atoms. For more
information on Unicode support in atoms see note on UTF-8 encoded atoms in the
chapter about the external term format in the ERTS User's Guide.
> list_to_atom("Erlang").
'Erlang'
list_to_binary(IoList) -> binary()
Types:
IoList = iolist()
Returns a binary which is made from the integers and binaries in IoList.
> 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 which is made from the integers and bitstrings in
BitstringList. (The last tail in BitstringList is allowed to be a bitstring.)
> Bin1 = <<1,2,3>>.
<<1,2,3>>
> Bin2 = <<4,5>>.
<<4,5>>
> Bin3 = <<6,7:4,>>.
<<6>>
> list_to_bitstring([Bin1,1,[2,3,Bin2],4|Bin3]).
<<1,2,3,1,2,3,4,5,4,6,7:46>>
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.
> 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.
> 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.
> 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 pid whose text representation is String.
Warning:
This BIF is intended for debugging and for use in the Erlang operating system. It
should not be used in application programs.
> list_to_pid("<0.4.1>").
<0.4.1>
Failure: badarg if String contains a bad representation of a pid.
list_to_tuple(List) -> tuple()
Types:
List = [term()]
Returns a tuple which corresponds to List. List can contain any Erlang terms.
> list_to_tuple([share, ['Ericsson_B', 163]]).
{share, ['Ericsson_B', 163]}
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 the module Module, this BIF loads that
object code. Also, if the code for the 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 may still be processes
which are executing that code. It returns either {module, Module}, or {error,
Reason} if loading fails. Reason is one of the following:
badfile:
The object code in Binary has an incorrect format or the object code contains
code for another module than Module.
not_purged:
Binary contains a module which cannot be loaded because old code for this
module already exists.
Warning:
This BIF is intended for the code server (see code(3erl)) and should not 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:
In releases older than OTP R14B, NIFs were an experimental feature. Versions of OTP
older than R14B might have different and possibly incompatible NIF semantics and
interfaces. For example, in 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 sharable object/dynamic library file minus
the OS-dependent file extension (.so for Unix and .dll for Windows). See erl_nif on
how to implement a NIF library.
LoadInfo can be any term. It will be 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 atoms below, while Text is a human readable string that may give some more
information about the failure.
load_failed:
The OS failed to load the NIF library.
bad_lib:
The library did not fulfil the requirements as a NIF library of the calling
module.
load | reload | upgrade:
The corresponding library callback was not successful.
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/or 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}}.
The time zone and daylight saving time correction depend on the underlying OS.
> erlang:localtime().
{{1996,11,6},{14,45,17}}
erlang:localtime_to_universaltime(Localtime) -> Universaltime
Types:
Localtime = Universaltime = calendar:datetime()
Converts local date and time to Universal Time Coordinated (UTC), if this is
supported by the underlying OS. Otherwise, no conversion is done and Localtime is
returned.
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}).
{{1996,11,6},{13,45,17}}
Failure: badarg if Localtime does not denote a valid 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) just like
erlang:localtime_to_universaltime/1, but the caller decides if daylight saving time
is active or not.
If IsDst == true the Localtime is during daylight saving time, if IsDst == false it
is not, and if IsDst == undefined the underlying OS may guess, which is the same as
calling erlang:localtime_to_universaltime(Localtime).
> 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 does not denote a valid date and time.
make_ref() -> reference()
Returns an almost unique reference.
The returned reference will re-occur after approximately 2^82 calls; therefore it
is unique enough for practical purposes.
> make_ref().
#Ref<0.0.0.135>
erlang:make_tuple(Arity, InitialValue) -> tuple()
Types:
Arity = arity()
InitialValue = term()
Returns a new tuple of the given Arity, where all elements are InitialValue.
> erlang:make_tuple(4, []).
{[],[],[],[]}
erlang:make_tuple(Arity, DefaultValue, InitList) -> tuple()
Types:
Arity = arity()
DefaultValue = term()
InitList = [{Position :: integer() >= 1, term()}]
erlang:make_tuple first creates a tuple of size Arity where each element has the
value DefaultValue. It 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 last occurrence will be used.
> erlang:make_tuple(5, [], [{2,ignored},{5,zz},{2,aa}]).
{{[],aa,[],[],zz}
max(Term1, Term2) -> Maximum
Types:
Term1 = Term2 = Maximum = term()
Return the largest of Term1 and Term2; if the terms compare equal, Term1 will be
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.
See The MD5 Message Digest Algorithm (RFC 1321) for more information about MD5.
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 containing information about memory dynamically allocated by the
Erlang emulator. Each element of the list is a tuple {Type, Size}. The first
element Typeis an atom describing memory type. The second element Sizeis memory
size in bytes. A description of each memory type follows:
total:
The total amount of memory currently allocated, which is the same as the sum of
memory size for processes and system.
processes:
The total amount of memory currently allocated by the Erlang processes.
processes_used:
The total amount of memory currently used by the Erlang processes.
This memory is part of the memory presented as processes memory.
system:
The total amount of memory currently allocated by 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 even though the system may have more physical memory.
May be removed in future releases of 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 should be part of the
system value are not.
When the emulator is run with instrumentation, the system value is more accurate,
but memory directly allocated by malloc (and friends) are 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.
Since the total value is the sum of processes and system the error in system will
propagate to the total value.
The different amounts of memory that are summed are not gathered atomically which
also introduce an error in the result.
The different values has 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 may be added in the future.
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 stack(s) 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, due to fragmentation and pre-reservation of memory areas, the size of
the memory segments which contain the dynamically allocated memory blocks can be
substantially larger than the total size of the dynamically allocated memory
blocks.
Note:
Since erts version 5.6.4 erlang:memory/0 requires that all erts_alloc(3erl)
allocators are enabled (default behaviour).
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:
Since erts version 5.6.4 erlang:memory/1 requires that all erts_alloc(3erl)
allocators are enabled (default behaviour).
Failures:
badarg:
If Type is not one of the memory types listed in the documentation 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()
Return the smallest of Term1 and Term2; if the terms compare equal, Term1 will be
returned.
module_loaded(Module) -> boolean()
Types:
Module = module()
Returns true if the module Module is loaded, otherwise returns false. It does not
attempt to load the module.
Warning:
This BIF is intended for the code server (see code(3erl)) and should not be used
elsewhere.
monitor(Type, Item) -> MonitorRef
Types:
Type = process
Item = pid() | RegName | {RegName, Node}
RegName = module()
Node = node()
MonitorRef = reference()
The calling process starts monitoring Item which is an object of type Type.
Currently only processes can be monitored, i.e. the only allowed Type is process,
but other types may be allowed in the future.
Item can be:
pid():
The pid of the process to monitor.
{RegName, 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 RegName will be
monitored.
RegName:
The process locally registered as RegName will be monitored.
Note:
When a process is monitored by registered name, the process that has the registered
name at the time when monitor/2 is called will be monitored. The monitor will not
be effected, if the registered name is unregistered.
A 'DOWN' message will be sent to the monitoring process if Item dies, if Item does
not exist, or if the connection is lost to the node which Item resides on. A 'DOWN'
message has the following pattern:
{'DOWN', MonitorRef, Type, Object, Info}
where MonitorRef and Type are the same as described above, and:
Object:
A reference to the monitored object:
* the pid of the monitored process, if Item was specified as a pid.
* {RegName, Node}, if Item was specified as {RegName, Node}.
* {RegName, Node}, if Item was specified as RegName. Node will in this case be
the name of the local node (node()).
Info:
Either the exit reason of the process, noproc (non-existing process), or
noconnection (no connection to Node).
Note:
If/when monitor/2 is extended (e.g. to handle other item types than process), other
possible values for Object, and Info in the 'DOWN' message will be introduced.
The monitoring is turned off either 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 one where remote process monitoring by registered
name is not implemented), the call fails with badarg.
Making several calls to monitor/2 for the same Item is not an error; it results in
as many, completely independent, monitorings.
Note:
The format of the 'DOWN' message changed in the 5.2 version of the emulator (OTP
release R9B) for monitor by registered name. The Object element of the 'DOWN'
message could in earlier versions sometimes be the pid of the monitored process and
sometimes be the registered name. Now the Object element is always a tuple
consisting of the registered name and the node name. Processes on new nodes
(emulator version 5.2 or greater) will always get 'DOWN' messages on the new format
even if they are monitoring processes on old nodes. Processes on old nodes will
always get 'DOWN' messages on the old format.
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, completely independent, monitorings.
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, there will be an attempt to create one. If this fails, a
nodedown message is delivered.
Nodes connected through hidden connections can be monitored as any other node.
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. The option allows the BIF to wait the normal net connection
timeout for the monitored node to connect itself, even if it cannot be actively
connected from this node (i.e. it is blocked). The state where this might be useful
can only be achieved by using the kernel option dist_auto_connect once. If that
kernel option is not used, the allow_passive_connect option has no effect.
Note:
The allow_passive_connect option is used internally and is seldom needed in
applications where the network topology and the kernel options in effect is known
in advance.
Failure: badarg if the local node is not alive or the option list is malformed.
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 will 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 will 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 is located. Arg can be a pid, 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, excluding 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 argument given. The result returned 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 which are known to this node, i.e., connected, previously connected, etc.
Some equalities: [node()] = nodes(this), nodes(connected) = nodes([visible,
hidden]), and nodes() = nodes(visible).
If the local node is not alive, nodes(this) == nodes(known) == [nonode@nohost], for
any other Arg the empty list [] is returned.
now() -> Timestamp
Types:
Timestamp = timestamp()
timestamp() =
{MegaSecs :: integer() >= 0,
Secs :: integer() >= 0,
MicroSecs :: integer() >= 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 returns continuously increasing values. Hence, the
return value from now() can be used to generate unique time-stamps, and if it is
called in a tight loop on a fast machine the time of the node can become skewed.
It can only be used to check the local time of day if the time-zone info of the
underlying operating system is properly configured.
If you do not need the return value to be unique and monotonically increasing, use
os:timestamp/0 instead to avoid some overhead.
open_port(PortName, PortSettings) -> port()
Types:
PortName = {spawn, Command :: string()}
| {spawn_driver, Command :: [byte()]}
| {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()}
| {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. PortName is one of the following:
{spawn, Command}:
Starts an external program. Command is the name of the external program which
will be run. Command runs outside the Erlang work space unless an Erlang driver
with the name Command is found. If found, that driver will be started. A driver
runs in the Erlang workspace, 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 with using vfork, setting the environment
variable ERL_NO_VFORK to any value will cause fork to be used instead.
For external programs, the PATH is searched (or an equivalent method is used to
find programs, depending on operating system). This is done by invoking the
shell on certain platforms. The first space separated token of the command will
be considered as the name of the executable (or driver). This (among other
things) makes this option unsuitable for running programs having spaces in file
or directory names. Use {spawn_executable, Command} instead if spaces in
executable file names is desired.
{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. The FileName
in its whole is used as the name of the executable, including any spaces. If
arguments are to be passed, the args and arg0 PortSettings can be used.
The shell is not usually invoked to start the program, it's executed directly.
Neither is the PATH (or equivalent) searched. To find a program in the PATH to
execute, use os:find_executable/1.
Only if a shell script or .bat file is executed, the appropriate command
interpreter will implicitly be invoked, but there will still be no command
argument expansion or implicit PATH search.
The name of the executable as well as the arguments given in args and arg0 is
subject to Unicode file name translation if the system is running in Unicode
file name mode. To avoid translation or force i.e. UTF-8, supply the executable
and/or arguments as a binary in the correct encoding. See the file module, the
file:native_name_encoding/0 function and the stdlib users guide for details.
Note:
The characters in the name (if given as a list) can only be > 255 if the Erlang
VM is started in Unicode file name translation mode, otherwise the name of the
executable is limited to the ISO-latin-1 character set.
If the FileName cannot be run, an error exception, with the posix error code as
the reason, is raised. The error reason may differ between operating systems.
Typically the error enoent is raised when one tries to run a program that is
not found and eaccess 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 operating system (shell and user). Hence, its use is very limited.
PortSettings is a list of settings for the port. Valid settings are:
{packet, N}:
Messages are preceded by their length, sent in N bytes, with the most
significant byte first. Valid values for N are 1, 2, or 4.
stream:
Output messages are sent without packet lengths. A user-defined protocol must
be used between the Erlang process and the external object.
{line, L}:
Messages are delivered on a per line basis. Each line (delimited by the OS-
dependent newline sequence) is delivered in one single message. The message
data format is {Flag, Line}, where Flag is either eol or noeol and Line is the
actual data delivered (without the newline sequence).
L specifies the maximum line length in bytes. Lines longer than this will be
delivered in more than one message, with the Flag set to noeol for all but the
last message. If end of file is encountered anywhere else than immediately
following a newline sequence, the last line will also be delivered with the
Flag set to noeol. In all other cases, lines are delivered with Flag set to
eol.
The {packet, N} and {line, L} settings are mutually exclusive.
{cd, Dir}:
This is 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}:
This is only valid for {spawn, Command} and {spawn_executable, FileName}. The
environment of the started process is extended using the environment
specifications in Env.
Env should 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.
If Unicode filename encoding is in effect (see the erl manual page), the
strings (both Name and Value) may contain characters with codepoints > 255.
{args, [ string() | binary() ]}:
This option is 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, similar behavior is mimicked.
The arguments are not expanded by the shell prior to being supplied to the
executable, most notably this means that file wildcard expansion will not
happen. Use filelib:wildcard/1 to expand wildcards for the arguments. Note that
even if the program is a Unix shell script, meaning that the shell will
ultimately be invoked, wildcard expansion will not happen and the script will
be provided with the untouched arguments. On Windows(R), wildcard expansion is
always up to the program itself, why this isn't an issue.
Note also that the actual executable name (a.k.a. argv[0]) should not be given
in this list. The proper executable name will automatically be used as argv[0]
where applicable.
When the Erlang VM is running in Unicode file name mode, the arguments can
contain any Unicode characters and will be translated into whatever is
appropriate on the underlying OS, which means UTF-8 for all platforms except
Windows, which has other (more transparent) ways of dealing with Unicode
arguments to programs. To avoid Unicode translation of arguments, they can be
supplied as binaries in whatever encoding is deemed appropriate.
Note:
The characters in the arguments (if given as a list of characters) can only be >
255 if the Erlang VM is started in Unicode file name mode, otherwise the
arguments are limited to the ISO-latin-1 character set.
If one, for any reason, wants to explicitly set the program name in the
argument vector, the arg0 option can be used.
{arg0, string() | binary()}:
This option is only valid for {spawn_executable, FileName} and explicitly
specifies the program name argument when running an executable. This might in
some circumstances, on some operating systems, be desirable. How the program
responds to this is highly system dependent and no specific effect is
guaranteed.
The unicode file name translation rules of the args option apply to this option
as well.
exit_status:
This is 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 (i.e., 128+signal).
If the eof option has been given as well, the eof message and the exit_status
message appear in an unspecified order.
If the port program closes its stdout without exiting, the exit_status option
will not work.
use_stdio:
This is 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. 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(R) only. The standard input and
standard output handles of the port program will, if this option is supplied,
be opened with the flag FILE_FLAG_OVERLAPPED, so that the port program can (and
has to) 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 IO from the port are binary data objects as opposed to lists of bytes.
eof:
The port will not be closed at the end of the file and produce an exit signal.
Instead, it will remain open and a {Port, eof} message will be sent to the
process holding the port.
hide:
When running on Windows, suppress creation of a new console window when
spawning the port program. (This option has no effect on other platforms.)
{parallelism, Boolean}:
Set scheduler hint for port parallelism. If set to true, the VM will schedule
port tasks when it by this can improve the parallelism in the system. If set to
false, the VM will try to perform port tasks immediately and by this improving
the latency at the expense of parallelism. The default can be set on system
startup by passing the +spp command line argument to erl(1).
The default is stream for all types of port 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 which 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:
There was not enough memory to create the port.
eagain:
There are no more available operating system processes.
enametoolong:
The external command given was too long.
emfile:
There are no more available file descriptors (for the operating system process
that the Erlang emulator runs in).
enfile:
The file table is full (for the entire operating system).
eacces:
The Command given in {spawn_executable, Command} does not point out an
executable file.
enoent:
The 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}. See
file(3erl) for possible values of PosixCode.
The maximum number of ports that can be open at the same time can be configured by
passing the +Q command line flag 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 will give 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). Range can be between 1 and 2^32, the function returns a hash value for
Term within the range 1..Range.
This BIF could be used instead of the old deprecated erlang:hash/2 BIF, 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 will give the same hash for the same Erlang term
regardless of machine architecture and ERTS version (the BIF was introduced in ERTS
5.2). Range can be between 1 and 2^32, the function returns a hash value for Term
within the range 0..Range-1. When called without the Range argument, a value in the
range 0..2^27-1 is returned.
This BIF should always be used for hashing terms. It distributes small integers
better than phash/2, and it is faster for bignums and binaries.
Note that the range 0..Range-1 is different from the range of phash/2 (1..Range).
pid_to_list(Pid) -> string()
Types:
Pid = pid()
Returns a string which corresponds to the text representation of Pid.
Warning:
This BIF is intended for debugging and for use in the Erlang operating system. It
should not 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 behaviour (see below), being synchronous, and that the port does not reply
with {Port, closed}. Any process may close a port with port_close/1, not only the
port owner (the connected process). If the calling process is linked to port
identified by Port, an exit signal due to that link will be received by the process
prior to the return from port_close/1.
For comparison: Port ! {self(), close} fails with badarg if Port cannot be sent to
(i.e., Port refers neither to a port nor to 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, but if the calling process is not the port owner the port owner
fails with badsig.
Note that any process can close a port using Port ! {PortOwner, close} just as if
it itself was the port owner, but the reply always goes to the port owner.
As of OTP-R16 Port ! {PortOwner, close} is truly asynchronous. Note 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 due to 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 linked to the previously open port
identified by Port, an exit signal due to this link was received by the process
prior to this exception.
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 behaviour and being synchronous (see below). Any process may send data to a
port with port_command/2, not only the port owner (the connected process).
For comparison: Port ! {PortOwner, {command, Data}} fails with badarg if Port
cannot be sent to (i.e., Port refers neither to a port nor to 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 not a valid IO list.
Note that any process can send to a port using Port ! {PortOwner, {command, Data}}
just as if it itself was the port owner.
If the port is busy, the calling process will be suspended until the port is not
busy anymore.
As of OTP-R16 Port ! {PortOwner, {command, Data}} is truly asynchronous. Note 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 due to 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 linked to the previously open port
identified by Port, an exit signal due to this link was received by the process
prior to this exception.
badarg:
If Data is not a valid io 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 is returned.
If the port is busy, the calling process will be suspended until the port is not
busy anymore.
Currently the following Options are valid:
force:
The calling process will not be suspended if the port is busy; instead, the
port command is forced through. The call will fail with a notsup exception if
the driver of the port does not support this. For more information see the
ERL_DRV_FLAG_SOFT_BUSY driver flag.
nosuspend:
The calling process will not be suspended if the port is busy; instead, the
port command is aborted and false is returned.
Note:
More options may be added in the future.
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 linked to the previously open port
identified by Port, an exit signal due to this link was received by the process
prior to this exception.
badarg:
If Data is not a valid io list.
badarg:
If OptionList is not a valid option list.
notsup:
If the force option 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 below.
* The port does not reply with {Port,connected}.
* port_connect/1 is synchronous, see below.
* The new port owner gets linked to the port.
The old port owner stays linked to the port and have to call unlink(Port) if this
is not desired. Any process may set the port owner to be any process with
port_connect/2.
For comparison: Port ! {self(), {connect, Pid}} fails with badarg if Port cannot be
sent to (i.e., Port refers neither to a port nor to 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. Note that the
old port owner is still linked to the port, and that 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 pid.
Note that any process can set the port owner using Port ! {PortOwner, {connect,
Pid}} just as if it itself was the port owner, but the reply always goes to the
port owner.
As of OTP-R16 Port ! {PortOwner, {connect, Pid}} is truly asynchronous. Note 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 due to 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 linked to the previously open port
identified by Port, an exit signal due to this link was received by the process
prior to this exception.
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, i.e., on the port driver. Not all port drivers support
this control feature.
Returns: a list of integers in the range 0 through 255, or a binary, depending on
the port driver. The meaning of the returned data also depends on the port driver.
Failure: badarg if Port is not an open port or the registered name of an open port,
if Operation cannot fit in a 32-bit integer, if the port driver does not support
synchronous control operations, or 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, i.e., 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 linked to the previously open port
identified by Port, an exit signal due to this link was received by the process
prior to this exception.
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 the Port, or undefined if
the port is not open. The order of the tuples is not defined, nor are all the
tuples mandatory. If undefined is returned and the calling process was linked to a
previously open port identified by Port, an exit signal due to this link was
received by the process prior to the return from port_info/1.
Currently the result will containt information about the following Items:
registered_name (if the port has a registered name), id, connected, links, name,
input, and 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 undefined is
returned and the calling process was linked to a previously open port identified by
Port, an exit signal due to this link was received by the process prior to the
return from port_info/2.
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 may be used to separate ports.
If the port identified by Port is not open, undefined is returned. If undefined is
returned and the calling process was linked to a previously open port identified by
Port, an exit signal due to this link was received by the process prior to the
return from port_info/2.
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 undefined is
returned and the calling process was linked to a previously open port identified by
Port, an exit signal due to this link was received by the process prior to the
return from port_info/2.
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 undefined is
returned and the calling process was linked to a previously open port identified by
Port, an exit signal due to this link was received by the process prior to the
return from port_info/2.
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 currently either false (emulator without SMP support), port_level (port
specific locking), or driver_level (driver specific locking). Note that these
results are highly implementation specific and might change in the future.
If the port identified by Port is not open, undefined is returned. If undefined is
returned and the calling process was linked to a previously open port identified by
Port, an exit signal due to this link was received by the process prior to the
return from port_info/2.
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 amount of memory, in bytes, allocated for this port by the
runtime system. Note that the port itself might have allocated memory which is not
included in Bytes.
If the port identified by Port is not open, undefined is returned. If undefined is
returned and the calling process was linked to a previously open port identified by
Port, an exit signal due to this link was received by the process prior to the
return from port_info/2.
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 is monitoring.
If the port identified by Port is not open, undefined is returned. If undefined is
returned and the calling process was linked to a previously open port identified by
Port, an exit signal due to this link was received by the process prior to the
return from port_info/2.
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 undefined is
returned and the calling process was linked to a previously open port identified by
Port, an exit signal due to this link was received by the process prior to the
return from port_info/2.
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 undefined is
returned and the calling process was linked to a previously open port identified by
Port, an exit signal due to this link was received by the process prior to the
return from port_info/2.
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
either port_command/2, port_command/3, or Port ! {Owner, {command, Data}.
If the port identified by Port is not open, undefined is returned. If undefined is
returned and the calling process was linked to a previously open port identified by
Port, an exit signal due to this link was received by the process prior to the
return from port_info/2.
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 the parallelism option 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 amount of data, in bytes, queued by the port using the ERTS
driver queue implementation.
If the port identified by Port is not open, undefined is returned. If undefined is
returned and the calling process was linked to a previously open port identified by
Port, an exit signal due to this link was received by the process prior to the
return from port_info/2.
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 undefined is
returned and the calling process was linked to a previously open port identified by
Port, an exit signal due to this link was received by the process prior to the
return from port_info/2.
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 which corresponds to the text representation of the port
identifier Port.
Warning:
This BIF is intended for debugging and for use in the Erlang operating system. It
should not be used in application programs.
erlang:ports() -> [port()]
Returns a list of port identifiers corresponding to all the ports currently
existing on the local node.
Note that a port that is exiting, exists but is not open.
pre_loaded() -> [module()]
Returns a list of Erlang modules which are pre-loaded 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 pre-loaded.
erlang:process_display(Pid, Type) -> true
Types:
Pid = pid()
Type = backtrace
Writes information about the local process Pid on standard error. The currently
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 should normally not trap exits.
Returns the old value of the flag.
See also exit/2.
process_flag(Flag :: error_handler, Module) -> OldModule
Types:
Module = OldModule = atom()
This is used by a process to redefine the error handler for undefined function
calls and undefined registered processes. Inexperienced users should not use this
flag since code auto-loading is dependent 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
This 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
This 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
This sets the process priority. Level is an atom. There are currently four priority
levels: low, normal, high, and max. The default priority level is normal. NOTE: The
max priority level is reserved for internal use in the Erlang runtime system, and
should not be used by others.
Internally in each priority level processes are scheduled in a round robin fashion.
Execution of processes on priority normal and priority low will be interleaved.
Processes on priority low will be 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 will be selected for execution. Note, however, that this does not mean that
no processes on priority low, or normal will be able to run when there are
processes on priority high running. On the runtime system with SMP support there
might be more processes running in parallel than processes on priority high, i.e.,
a low, and a high priority process might execute at the same time.
When there are runnable processes on priority max no processes on priority low,
normal, or high will be selected for execution. As with the high priority,
processes on lower priorities might 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 amount of reductions since the last time it was
selected for execution.
NOTE: You should not depend on the scheduling to remain exactly as it is today.
Scheduling, at least on the runtime system with SMP support, is very likely to be
modified in the future in order to better utilize available processor cores.
There is currently no automatic mechanism for avoiding priority inversion, such as
priority inheritance, or priority ceilings. When using priorities you have to take
this into account and handle such scenarios by yourself.
Making calls from a high priority process into code that you don't have control
over may cause the high priority process to wait for a processes with lower
priority, i.e., effectively decreasing the priority of the high priority process
during the call. Even if this isn't the case with one version of the code that you
don't have under your control, it might be the case in a future version of it. This
might, for example, happen if a high priority process triggers code loading, since
the code server runs on priority normal.
Other priorities than normal are normally not needed. When other priorities are
used, they need to be used with care, especially the high priority must be used
with care. A process on high priority should only perform work for short periods of
time. Busy looping for long periods of time in a high priority process will most
likely cause problems, since there are important servers in OTP running on priority
normal.
Returns the old value of the flag.
process_flag(Flag :: save_calls, N) -> OldN
Types:
N = OldN = 0..10000
N must be an integer in the interval 0..10000. If N > 0, call saving is made active
for the process, which 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: a tuple {Module, Function, Arity} for
function calls, and the mere 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()
Set or clear the sensitive flag for the current process. When a process has been
marked as sensitive by calling process_flag(sensitive, true), features in the run-
time system that can be used for examining the data and/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 will be generated. (If the sensitive flag is turned off, trace messages will
again be generated if there are any trace flags set.)
Sequential tracing: The sequential trace token will be propagated as usual, but no
sequential trace messages will be generated.
process_info/1,2 cannot be used to read out the message queue or the process
dictionary (both will be returned as empty lists).
Stack back-traces cannot be displayed for the process.
In crash dumps, the stack, messages, and the process dictionary will be omitted.
If {save_calls,N} has been set for the process, no function calls will be saved to
the call saving list. (The call saving list will not be cleared; furthermore, send,
receive, and timeout events will still be 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 allowed 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 not defined, nor are all the InfoTuples mandatory.
The InfoTuples part of the result may be changed without prior notice. Currently
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, and garbage_collection. If the process identified by Pid has a
registered name also an InfoTuple with the item registered_name will appear.
See process_info/2 for information about specific InfoTuples.
Warning:
This BIF is intended for debugging only, use process_info/2 for all other purposes.
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 the Item or
the ItemList, or 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 due to
historical reasons, and is kept for backward compatibility.
If an ItemList is given, the result is an InfoTupleList. The InfoTuples in the
InfoTupleList will appear with the corresponding Items in the same order as the
Items appeared in the ItemList. Valid Items may appear multiple times in the
ItemList.
Note:
If registered_name is part of an ItemList and the process has no name registered a
{registered_name, []} InfoTuple will appear in the resulting InfoTupleList. This
behavior is different than when a single Item =:= registered_name is given, and
than when process_info/1 is used.
Currently the following InfoTuples with corresponding Items are valid:
{backtrace, Bin}:
The 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 may be changed or removed
without prior notice.
{catchlevel, CatchLevel}:
CatchLevel is the number of currently active catches in this process. This
InfoTuple may 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 that describes the location in the source code.
{current_stacktrace, Stack}:
Return 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 dictionary of the process.
{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 which contains miscellaneous information about garbage
collection for this process. The content of GCInfo may be changed without prior
notice.
{group_leader, GroupLeader}:
GroupLeader is group leader for the IO of the process.
{heap_size, Size}:
Size is the size in words of youngest heap generation of the process. This
generation currently include the stack of the process. This information is
highly implementation dependent, and may change if the implementation change.
{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 pids 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 info item
messages (see below).
{messages, MessageQueue}:
MessageQueue is a list of the messages to the process, which have not yet been
processed.
{min_heap_size, MinHeapSize}:
MinHeapSize is the minimum heap size for the process.
{min_bin_vheap_size, MinBinVHeapSize}:
MinBinVHeapSize is the minimum binary virtual heap size for the process.
{monitored_by, Pids}:
A list of pids that are 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 pid, the list item is
{process, Pid}, and 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 the sequential trace token for the process. This InfoTuple
may be changed or removed without prior notice.
{stack_size, Size}:
Size is the stack size of the process in words.
{status, Status}:
Status is the status of the process. Status is exiting, garbage_collecting,
waiting (for a message), running, runnable (ready to run, but another process
is running), or suspended (suspended on a "busy" port or by the
erlang:suspend_process/[1,2] BIF).
{suspending, SuspendeeList}:
SuspendeeList is a list of {Suspendee, ActiveSuspendCount,
OutstandingSuspendCount} tuples. Suspendee is the pid of a process that have
been or is to be suspended by the process identified by Pid via the
erlang:suspend_process/2 BIF, or the erlang:suspend_process/1 BIF.
ActiveSuspendCount is the number of times the 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, and if OutstandingSuspendCount =/= 0 the
asynchronous option of erlang:suspend_process/2 has been used and the suspendee
has not yet been suspended by Pid. Note that the 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
currently include the stack of the process.
{trace, InternalTraceFlags}:
InternalTraceFlags is an integer representing internal trace flag for this
process. This InfoTuple may be changed or removed without prior notice.
{trap_exit, Boolean}:
Boolean is true if the process is trapping exits, otherwise it is false.
Note however, that not all implementations support every one of the above Items.
Failure: badarg if Pid is not a local process, or if Item is not a valid Item.
processes() -> [pid()]
Returns a list of process identifiers corresponding to all the processes currently
existing on the local node.
Note that a process that is exiting, exists but is not alive, i.e.,
is_process_alive/1 will return false for a process that is exiting, but its process
identifier will be part of the result returned from processes/0.
> 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
should be called to check that no processes are executing old code in the module.
Warning:
This BIF is intended for the code server (see code(3erl)) and should not 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 already exists, the old value is deleted and replaced by
Val and the function returns the old value.
Note:
The values stored when put is evaluated within the scope of a catch will not be
retracted if a throw is evaluated, or if an error occurs.
> X = put(name, walrus), Y = put(name, carpenter),
Z = get(name),
{X, Y, Z}.
{undefined,walrus,carpenter}
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 and for use in the Erlang operating system. In
general, it should be avoided in applications, unless you know very well what you
are doing.
Class is one of 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 and Stacktrace is a list as returned from get_stacktrace(), that
is a list of 4-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 may also contain {Fun, Args, Location} tuples where Fun is a local
fun and Args is an argument list.
The Location element 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 will
be truncated to the current maximum stacktrace depth.
Because 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, that is badarg. If you want to be really sure not to return you can
call error(erlang:raise(Class, Reason, Stacktrace)) and hope to distinguish
exceptions later.
erlang:read_timer(TimerRef) -> integer() >= 0 | false
Types:
TimerRef = reference()
TimerRef is a timer reference returned by erlang:send_after/3 or
erlang:start_timer/3. If the timer is active, the function returns the time in
milliseconds left until the timer will expire, otherwise false (which means that
TimerRef was never a timer, that it has been cancelled, or that it has already
delivered its message).
See also erlang:send_after/3, erlang:start_timer/3, and erlang:cancel_timer/1.
erlang:ref_to_list(Ref) -> string()
Types:
Ref = reference()
Returns a string which corresponds to the text representation of Ref.
Warning:
This BIF is intended for debugging and for use in the Erlang operating system. It
should not be used in application programs.
register(RegName, PidOrPort) -> true
Types:
RegName = atom()
PidOrPort = port() | pid()
Associates the name RegName with a pid or a port identifier. RegName, which must be
an atom, can be used instead of the pid / port identifier in the send operator
(RegName ! Message).
> register(db, Pid).
true
Failure: badarg if PidOrPort is not an existing, local process or port, if RegName
is already in use, if the process or port is already registered (already has a
name), or if RegName is the atom undefined.
registered() -> [RegName]
Types:
RegName = atom()
Returns a list of names which have been registered using register/2.
> 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
should previously have been suspended via erlang:suspend_process/2, or
erlang:suspend_process/1 by the process calling erlang:resume_process(Suspendee).
When the suspend count on Suspendee reach zero, Suspendee will be resumed, i.e.,
the state of the Suspendee is changed from suspended into the state Suspendee was
in before it was suspended.
Warning:
This BIF is intended for debugging only.
Failures:
badarg:
If Suspendee isn't 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.
> round(5.5).
6
Allowed in guard tests.
self() -> pid()
Returns the pid (process identifier) of the calling process.
> 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 may be a remote or local pid, 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()}
Sends a message and returns ok, or does not send the message but returns something
else (see below). Otherwise the same as erlang:send/2. See also
erlang:send_nosuspend/2,3. for more detailed explanation and warnings.
The possible options are:
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 before doing the send,
noconnect is returned instead.
Warning:
As with erlang:send_nosuspend/2,3: Use with extreme care!
erlang:send_after(Time, Dest, Msg) -> TimerRef
Types:
Time = integer() >= 0
0 <= Time <= 4294967295
Dest = pid() | atom()
Msg = term()
TimerRef = reference()
Starts a timer which will send the message Msg to Dest after Time milliseconds.
If Dest is a pid() it has to be a pid() of a local process, dead or alive.
The Time value can, in the current implementation, not be greater than 4294967295.
If Dest is an atom(), it is supposed to be the name of a registered process. The
process referred to by the name is looked up at the time of delivery. No error is
given if the name does not refer to a process.
If Dest is a pid(), the timer will be automatically canceled if the process
referred to by the pid() is not alive, or when the process exits. This feature was
introduced in erts version 5.4.11. Note that timers will not be automatically
canceled when Dest is an atom.
See also erlang:start_timer/3, erlang:cancel_timer/1, and erlang:read_timer/1.
Failure: badarg if the arguments does not satisfy the requirements specified above.
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 towards 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 will not send the message but return false instead.
The same happens, 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 very 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 will actually be shut
down (due to tick timeouts) by net_kernel. The normal reaction to take when this
happens is some kind of premature shutdown of the other node.
Note that ignoring the return value from this function would result in unreliable
message passing, which is contradictory to the Erlang programming model. The
message is not sent if this function returns false.
Note also that in many systems, transient states of overloaded queues are normal.
The fact that this function returns false does not in any way 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 could be sent on the (TCP)
channel without blocking, the message is not guaranteed to have arrived at the
remote node. Also in the case of a disconnected non-responsive node, the return
value is true (mimics the behaviour of the ! operator). The expected behaviour as
well as 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 boolean return
value.
This function behaves like erlang:send_nosuspend/2), but takes a third parameter, a
list of options. The only currently implemented option is noconnect. The option
noconnect makes the function return false if the remote node is not currently
reachable by the local node. The normal behaviour is to try to connect to the node,
which may stall the process for a shorter period. The use of the noconnect option
makes it possible to be absolutely sure not to get even the slightest delay when
sending to a remote process. This is especially useful when communicating with
nodes who expect to always be the connecting part (i.e. 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 Distributed
Erlang in the Erlang Reference Manual).
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 which is a copy of the argument Tuple1 with the element given by
the integer argument Index (the first element is the element with index 1) replaced
by the argument Value.
> setelement(2, {10, green, bottles}, red).
{10,red,bottles}
size(Item) -> integer() >= 0
Types:
Item = tuple() | binary()
Returns an integer which is the size of the argument Item, which must be either a
tuple or a binary.
> size({morni, mulle, bwange}).
3
Allowed in guard tests.
spawn(Fun) -> pid()
Types:
Fun = function()
Returns the pid 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 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/3.
spawn(Module, Function, Args) -> pid()
Types:
Module = module()
Function = atom()
Args = [term()]
Returns the pid of a new process started by the application of Module:Function to
Args. The new process created will be placed in the system scheduler queue and be
run some time later.
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 its replacement is
undefined, a failure with the reason undef will occur.
> 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 pid of a new process started by the application of Module:Function to
Args on Node. If Node does not exists, a useless pid is returned. Otherwise works
like spawn/3.
spawn_link(Fun) -> pid()
Types:
Fun = function()
Returns the pid 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 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 due to the link,
an exit signal with exit reason noconnection will be received). Otherwise works
like spawn/3.
spawn_link(Module, Function, Args) -> pid()
Types:
Module = module()
Function = atom()
Args = [term()]
Returns the pid 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 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 due to the link,
an exit signal with exit reason noconnection will be received). Otherwise works
like spawn/3.
spawn_monitor(Fun) -> {pid(), reference()}
Types:
Fun = function()
Returns the pid of a new process started by the application of Fun to the empty
list [] and 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, and the
process is monitored at the same time. Returns the pid 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 pid of a new process started by the application of Fun to the empty
list []. Otherwise works like spawn_opt/4.
If the option monitor is given, the newly created process will be monitored and
both the pid and reference for the monitor will be 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 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 exactly like spawn/3, except that an extra option list is given when creating
the process.
If the option monitor is given, the newly created process will be monitored and
both the pid and reference for the monitor will be returned.
link:
Sets a link to the parent process (like spawn_link/3 does).
monitor:
Monitor the new process (just 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 will be 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}:
This option is only useful for performance tuning. In general, you should not
use this option unless you know that there is problem with execution times
and/or memory consumption, and you should measure to make sure that the option
improved 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 will be
done.
The fullsweep_after option makes it possible to specify the maximum number of
generational collections before forcing a fullsweep even if there is still room
on the old heap. Setting the number to zero effectively disables the general
collection algorithm, meaning that all live data is copied at every garbage
collection.
Here are a few cases when it could be useful to change fullsweep_after.
Firstly, if binaries that are no longer used should be thrown away as soon as
possible. (Set Number to zero.) Secondly, a process that mostly have short-
lived data will be fullsweeped seldom or never, meaning that the old heap will
contain mostly garbage. To ensure a fullsweep once in a while, set Number to a
suitable value such as 10 or 20. Thirdly, in embedded systems with limited
amount of RAM and no virtual memory, one might want to preserve memory by
setting Number to zero. (The value may be set globally, see
erlang:system_flag/2.)
{min_heap_size, Size}:
This option is only useful for performance tuning. In general, you should not
use this option unless you know that there is problem with execution times
and/or memory consumption, and you should measure to make sure that the option
improved matters.
Gives a minimum heap size in words. Setting this value higher than the system
default might speed up some processes because less garbage collection is done.
Setting too high value, however, might waste memory and slow down the system
due to worse data locality. Therefore, it is recommended to use this option
only for fine-tuning an application and to measure the execution time with
various Size values.
{min_bin_vheap_size, VSize}:
This option is only useful for performance tuning. In general, you should not
use this option unless you know that there is problem with execution times
and/or memory consumption, and you should measure to make sure that the option
improved matters.
Gives a minimum binary virtual heap size in words. Setting this value higher
than the system default might speed up some processes because less garbage
collection is done. Setting too high value, however, might waste memory.
Therefore, it is recommended to 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 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.
split_binary(Bin, Pos) -> {binary(), binary()}
Types:
Bin = binary()
Pos = integer() >= 0
0..byte_size(Bin)
Returns a tuple containing the binaries which are the result of splitting Bin into
two parts at position Pos. This is not a destructive operation. After the
operation, there will be three binaries altogether.
> B = list_to_binary("0123456789").
<<"0123456789">>
> byte_size(B).
10
> {B1, B2} = split_binary(B,3).
{<<"012">>,<<"3456789">>}
> byte_size(B1).
3
> byte_size(B2).
7
erlang:start_timer(Time, Dest, Msg) -> TimerRef
Types:
Time = integer() >= 0
0 <= Time <= 4294967295
Dest = pid() | atom()
Msg = term()
TimerRef = reference()
Starts a timer which will send the message {timeout, TimerRef, Msg} to Dest after
Time milliseconds.
If Dest is a pid() it has to be a pid() of a local process, dead or alive.
The Time value can, in the current implementation, not be greater than 4294967295.
If Dest is an atom(), it is supposed to be the name of a registered process. The
process referred to by the name is looked up at the time of delivery. No error is
given if the name does not refer to a process.
If Dest is a pid(), the timer will be automatically canceled if the process
referred to by the pid() is not alive, or when the process exits. This feature was
introduced in erts version 5.4.11. Note that timers will not be automatically
canceled when Dest is an atom().
See also erlang:send_after/3, erlang:cancel_timer/1, and erlang:read_timer/1.
Failure: badarg if the arguments does not satisfy the requirements specified above.
statistics(Item :: context_switches) -> {ContextSwitches, 0}
Types:
ContextSwitches = integer() >= 0
ContextSwitches is 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
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
This information may not be valid for all implementations.
> statistics(garbage_collection).
{85,23961,0}
statistics(Item :: io) -> {{input, Input}, {output, Output}}
Types:
Input = Output = integer() >= 0
Input is the total number of bytes received through ports, and Output 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
Note:
Since erts-5.5 (OTP release 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(reductions).
{2046,11}
statistics(Item :: run_queue) -> integer() >= 0
Returns the total length of the run queues, that is, the number of processes that
are ready to run on all available run queues.
statistics(Item :: runtime) ->
{Total_Run_Time, Time_Since_Last_Call}
Types:
Total_Run_Time = Time_Since_Last_Call = integer() >= 0
Note that the run-time is the sum of the run-time for all threads in the Erlang
run-time system and may therefore be greater than the wall-clock time.
> 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, TotalTime is the total time duration since
scheduler_wall_time activation. The time unit is not defined and may be subject to
change between releases, operating systems and system restarts. scheduler_wall_time
should only 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 or not scheduling
(selecting) a process or port, meaning; executing process code, executing linked-
in-driver or NIF code, executing built-in-functions or any other runtime handling,
garbage collecting or handling any other memory management. Note, a scheduler may
also be busy even if the operating system has scheduled out the scheduler thread.
Returns undefined if the system flag scheduler_wall_time is turned off.
The list of scheduler information is unsorted and may 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 we will take another snapshot and calculate scheduler-utilization
per scheduler.
> 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. Use
erlang:system_flag(scheduler_wall_time, true) to enable it.
statistics(Item :: wall_clock) ->
{Total_Wallclock_Time,
Wallclock_Time_Since_Last_Call}
Types:
Total_Wallclock_Time = Wallclock_Time_Since_Last_Call = integer() >= 0
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 isn't already in the suspended 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 will not leave the suspended state
until its suspend count reach 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 will automatically be decreased when the process terminates.
Currently the following options (Opts) are available:
asynchronous:
A suspend request is sent to the process identified by Suspendee. Suspendee
will eventually suspend unless it is resumed before it was able to suspend. The
caller of erlang:suspend_process/2 will return immediately, regardless of
whether the Suspendee has suspended yet or not. Note that the point in time
when the Suspendee will actually suspend cannot be deduced from other events in
the system. The only guarantee given is that the Suspendee will eventually
suspend (unless it is resumed). If the asynchronous option has not been passed,
the caller of erlang:suspend_process/2 will be blocked until the Suspendee has
actually suspended.
unless_suspending:
The process identified by Suspendee will be suspended unless the calling
process already is suspending the Suspendee. If unless_suspending is combined
with the asynchronous option, a suspend request will be sent unless the calling
process already is suspending the Suspendee or if a suspend request already has
been sent and is in transit. If the calling process already is suspending the
Suspendee, or if combined with the asynchronous option and a send request
already is in transit, false is returned and the suspend count on Suspendee
will remain unchanged.
If the suspend count on the process identified by Suspendee was increased, true is
returned; otherwise, false is returned.
Warning:
This BIF is intended for debugging only.
Failures:
badarg:
If Suspendee isn't a process identifier.
badarg:
If the process identified by Suspendee is same the 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 isn't 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 current system limit is larger than 2 000 000 000 suspends, and
it will never be less than that.
erlang:suspend_process(Suspendee) -> true
Types:
Suspendee = pid()
Suspends the process identified by Suspendee. The same as calling
erlang:suspend_process(Suspendee, []). For more information see the documentation
of erlang:suspend_process/2.
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 you are advised to use the erl command line argument +sct.
When this argument has been removed a final CPU topology to use will be determined
at emulator boot time.
Sets the user defined CpuTopology. The user defined CPU topology will override any
automatically detected CPU topology. By passing undefined as CpuTopology the system
will revert back 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 will
be sent a request to rebind according to the new CPU topology.
The user defined CPU topology can also be set by passing the +sct command line
argument to erl.
For information on the CpuTopology type and more, see the documentation of
erlang:system_info(cpu_topology), and the erl +sct and +sbt command line flags.
erlang:system_flag(Flag :: fullsweep_after, Number) -> OldNumber
Types:
Number = OldNumber = integer() >= 0
Number is a non-negative integer which indicates how many times generational
garbage collections can be done without forcing a fullsweep collection. The value
applies to new processes; 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.
An alternative way to set this value is through the (operating system) 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 only effects processes spawned after the change of min_heap_size
has been made. The min_heap_size can be set for individual processes by use of
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 only effects processes spawned after the
change of min_bin_vhheap_size has been made. The min_bin_vheap_size can be set for
individual processes by use of 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 has been blocked,
only one scheduler thread will schedule Erlang processes.
If BlockState =:= block, multi-scheduling will be blocked. If BlockState =:=
unblock and no-one else is blocking multi-scheduling and this process has only
blocked one time, multi-scheduling will be unblocked. One process can block multi-
scheduling multiple times. If a process has blocked multiple times, it has to
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 will
release 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. The return values are described in the documentation of
erlang:system_info(multi_scheduling).
NOTE: Blocking of multi-scheduling should normally not be needed. If you feel that
you need to block multi-scheduling, think through the problem at least a couple of
times again. Blocking multi-scheduling should only be used as a last resort since
it will most likely be 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 you are advised to use the erl command line argument +sbt.
When this argument has been removed a final scheduler bind type to use will be
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 which causes them to try to bind or unbind as
requested. NOTE: If a scheduler fails to bind, this will often be silently ignored.
This since it isn't always possible to verify valid logical processor identifiers.
If an error is reported, it will be reported to the error_logger. If you want to
verify that the schedulers actually have bound as requested, call
erlang:system_info(scheduler_bindings).
Schedulers can currently only be bound on newer Linux, Solaris, FreeBSD, and
Windows systems, but more systems will be supported in the future.
In order for the runtime system to be able to bind schedulers, the CPU topology
needs to be known. If the runtime system fails to automatically detect the CPU
topology, it can be defined. For more information on how to define the CPU
topology, see the erl +sct command line flag.
The runtime system will by default not bind schedulers to logical processors.
NOTE: If the Erlang runtime system is the only operating system process that binds
threads to logical processors, this improves the performance of the runtime system.
However, if other operating system processes (as for example another Erlang runtime
system) also bind threads to logical processors, there might be a performance
penalty instead. In some cases this performance penalty might be severe. If this is
the case, you are advised to not bind the schedulers.
Schedulers can be bound in different ways. The How argument determines how
schedulers are bound. How can currently be one of:
unbound:
Same as the erl command line argument +sbt u.
no_spread:
Same as the erl command line argument +sbt ns.
thread_spread:
Same as the erl command line argument +sbt ts.
processor_spread:
Same as the erl command line argument +sbt ps.
spread:
Same as the erl command line argument +sbt s.
no_node_thread_spread:
Same as the erl command line argument +sbt nnts.
no_node_processor_spread:
Same as the erl command line argument +sbt nnps.
thread_no_node_processor_spread:
Same as the erl command line argument +sbt tnnps.
default_bind:
Same as the erl command line argument +sbt db.
The value returned equals How before the scheduler_bind_type flag was changed.
Failure:
notsup:
If binding of schedulers is not supported.
badarg:
If How isn't one of the documented alternatives.
badarg:
If no CPU topology information is available.
The scheduler bind type can also be set by passing the +sbt command line argument
to erl.
For more information, see erlang:system_info(scheduler_bind_type),
erlang:system_info(scheduler_bindings), the erl +sbt and +sct command line flags.
erlang:system_flag(Flag :: scheduler_wall_time, Boolean) ->
OldBoolean
Types:
Boolean = OldBoolean = boolean()
Turns on/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 amount of schedulers online. Valid range is 1 <= SchedulersOnline <=
erlang:system_info(schedulers).
Returns the old value of the flag.
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's trace control word to TCW. TCW should be an unsigned
integer. For more information see documentation of the set_tcw function in the
match specification documentation in the ERTS User's Guide.
Returns the old value of the flag.
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 type of memory as first element and
amount of allocated memory in bytes as second element. In those cases when
there is information present about allocated and used memory, a third element
is present. This third element contains 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 will therefore
change when needed without prior notice.
Note: 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. If you are interested in the total amount of memory
allocated by the emulator see erlang:memory/0,1.
allocator:
Returns {Allocator, Version, Features, Settings}.
Explanation:
* Allocator corresponds to the malloc() implementation used. If Allocator
equals undefined, the malloc() implementation used could not be identified.
Currently 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 allocation features used.
* Settings is a list of subsystems, their configurable parameters, and used
values. Settings may 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 the "the alloc_util
framework" section in the erts_alloc(3erl) documentation.
{allocator, Alloc}:
Returns information about the specified allocator. As of erts version 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 of erts version 5.10.4 the returned list when calling
erlang:system_info({allocator, mseg_alloc}) also include 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.
Note: The information returned is highly implementation dependent and may be
changed, or removed at any time without prior notice. It was initially intended
as a tool when developing new allocators, but since it might 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 should more or less
speak 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 are abbreviations for, respectively, multi-block
carriers, and single-block carriers. Sizes are presented in bytes. When it is
not a size that is presented, it is the amount of something. Sizes and amounts
are often presented by three values, the first is current value, the second is
maximum value since the last call to erlang:system_info({allocator, Alloc}),
and the third is 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 memory pool size and the second
value 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 may co-exist.
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 may be introduced in the future.
sub_level() = [LevelEntry :: level_entry()]
| (LogicalCpuId :: {logical, integer() >= 0})
info_list() = []
The info_list() may be extended in the future.
Returns various information about the CPU topology of the current system (emulator)
as specified by Item:
cpu_topology:
Returns the CpuTopology which currently is 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 NUMA (non-uniform memory access) nodes, and thread refers to
hardware threads (e.g. Intels hyper-threads).
A level in the CpuTopology term can be omitted if only one entry exists and the
InfoList is empty.
thread can only be a sub level to core. core can be a sub level to either
processor or node. processor can either be on the top level or a sub level to
node. node can either 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 and only one NUMA node. Cache hierarchy is not part
of the CpuTopology type yet, but will be in the future. Other things may also
make it into the CPU topology in the future. In other words, expect the
CpuTopology type to change.
{cpu_topology, defined}:
Returns the user defined CpuTopology. For more information see the
documentation of the erl +sct command line flag, and the documentation of the
cpu_topology argument.
{cpu_topology, detected}:
Returns the automatically detected CpuTopology. The emulator currently only
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 the documentation of the cpu_topology argument.
{cpu_topology, used}:
Returns the CpuTopology which is used by the emulator. For more information see
the documentation of the cpu_topology argument.
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 :: 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 :: 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 :: otp_release) -> string()
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 :: 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 :: 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 may be added and/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 regarding the emulators
internal I/O checking. Note, the content of the returned list may vary between
platforms and over time. The only thing guaranteed is 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 which the current emulator has been
set to be backward compatible with. The compatibility mode can be configured at
startup by using the command line flag +R, see 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. Currently valid creations are integers in the range 1..3, but this may
(probably will) change in the future. If the node is not alive, 0 is returned.
debug_compiled:
Returns true if the emulator has been debug compiled; otherwise, false.
dist:
Returns a binary containing a string of distribution information formatted as
in Erlang crash dumps. For more information see the "How to interpret the
Erlang crash dumps" chapter in the ERTS User's Guide.
dist_buf_busy_limit:
Returns the value of the distribution buffer busy limit in bytes. This limit
can be set on startup by passing the +zdbbl command line flag to erl.
dist_ctrl:
Returns a list of tuples {Node, ControllingEntity}, one entry for each
connected remote node. The Node is the name of the node and the
ControllingEntity is the port or pid responsible for the communication to that
node. More specifically, the ControllingEntity for nodes connected via TCP/IP
(the normal case) is the socket actually used in communication with the
specific node.
driver_version:
Returns a string containing the erlang driver version used by the runtime
system. It will be on the form "<major ver>.<minor ver>".
dynamic_trace:
Returns an atom describing the dynamic trace framework compiled into the
virtual machine. It can currently be either dtrace, systemtap or none. For a
commercial or standard build, this is always none, the other return values
indicate a custom configuration (e.g. ./configure --with-dynamic-trace=dtrace).
See the dyntrace manual page and the README.dtrace/README.systemtap files in
the Erlang source code top directory for more information about dynamic
tracing.
dynamic_trace_probes:
Returns a boolean() indicating if dynamic trace probes (either dtrace or
systemtap) are built into the emulator. This can only be true if the virtual
machine was built for dynamic tracing (i.e. system_info(dynamic_trace) returns
dtrace or systemtap).
elib_malloc:
This option will be removed in a future release. The return value will always
be false since the elib_malloc allocator has been removed.
ets_limit:
Returns the maximum number of ETS tables allowed. This limit can be increased
on startup by passing the +e command line flag to erl or by setting the
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 below.
garbage_collection:
Returns a list describing the default garbage collection settings. A process
spawned on the local node by a spawn or spawn_link will use these garbage
collection settings. The default settings can be changed by use of
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. Currently only the
following 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 the "How to
interpret the Erlang crash dumps" chapter in the ERTS 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 the "How to interpret the
Erlang crash dumps" chapter in the ERTS User's Guide.
logical_processors:
Returns the detected number of logical processors configured on the system. The
return value is either an integer, or the atom unknown if the emulator wasn't
able to detect logical processors configured.
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 wasn't able to detect logical processors available. The number of
logical processors available 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 wasn't
able to 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 has been
enabled; otherwise, undefined. See the +T command line flag in the
documentation of the erl(1) command for more information on modified timing.
multi_scheduling:
Returns disabled, blocked, or enabled. A description of the return values:
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
but one have been blocked, i.e., only one scheduler thread will schedule
Erlang processes and execute Erlang code.
enabled:
The emulator has more than one scheduler thread, and no scheduler threads
have been blocked, i.e., all available scheduler threads will 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. The PIDs in the list is PIDs of the processes currently blocking multi-
scheduling. A PID will only be present 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).
otp_release:
Returns a string containing the OTP release number.
port_parallelism:
Returns the default port parallelism scheduling hint used. For more information
see the +spp command line argument of erl(1).
port_count:
Returns the number of ports currently existing at the local node as an integer.
The same value as length(erlang:ports()) returns, 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 the +Q command
line flag of erl(1).
process_count:
Returns the number of processes currently existing at the local node as an
integer. The same value as length(processes()) returns, but more efficient.
process_limit:
Returns the maximum number of simultaneously existing processes at the local
node as an integer. This limit can be configured at startup by using the +P
command line flag of erl(1).
procs:
Returns a binary containing a string of process and port information formatted
as in Erlang crash dumps. For more information see the "How to interpret the
Erlang crash dumps" chapter in the ERTS User's Guide.
scheduler_bind_type:
Returns information on how user has requested schedulers to be bound or not
bound.
NOTE: Even though user has requested schedulers to be bound, they might have
silently failed to bind. In order to inspect actual scheduler bindings call
erlang:system_info(scheduler_bindings).
For more information, see the erl +sbt command line argument, and
erlang:system_info(scheduler_bindings).
scheduler_bindings:
Returns information on currently used scheduler bindings.
A tuple of a size equal to erlang:system_info(schedulers) is returned. The
elements of the tuple 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.
E.g., if the schedulers have been bound,
element(erlang:system_info(scheduler_id),
erlang:system_info(scheduler_bindings)) will return the identifier of the
logical processor that the calling process is executing on.
Note that only schedulers online can be bound to logical processors.
For more information, see the erl +sbt command line argument,
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 after that. The amount of schedulers online can however 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 and
erlang:system_info(multi_scheduling_blockers).
schedulers_online:
Returns the amount of schedulers online. The scheduler identifiers of
schedulers online satisfy the following relationship: 1 <= SchedulerId <=
erlang:system_info(schedulers_online).
For more information, see erlang:system_info(schedulers), and
erlang:system_flag(schedulers_online, SchedulersOnline).
erlang:system_info(Item :: threads) -> boolean()
smp_support:
Returns true if the emulator has been compiled with smp support; otherwise,
false.
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()) as an integer.
trace_control_word:
Returns the value of the node's trace control word. For more information see
documentation of the function get_tcw in "Match Specifications in Erlang", ERTS
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 amount 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 is returned. If the CPU information has changed
you probably want to adjust the amount 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, i.e. on a 32-bit
architecture 4 is returned, and on a pure 64-bit architecture 8 is returned. On
a halfword 64-bit emulator, 4 is returned, as the Erlang terms are stored using
a virtual wordsize of half the system's wordsize.
{wordsize, external}:
Returns the true wordsize of the emulator, i.e. the size of a pointer, in bytes
as an integer. On a pure 32-bit architecture 4 is returned, on both a halfword
and pure 64-bit architecture, 8 is returned.
Note:
The scheduler argument has changed name to scheduler_id. This in order to avoid
mixup with the schedulers argument. The scheduler argument was introduced in ERTS
version 5.5 and renamed in ERTS version 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 may 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 the 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 system performance monitoring options. MonitorPid is a local pid that will
receive system monitor messages, and the second argument is a list of monitoring
options:
{long_gc, Time}:
If a garbage collection in the system takes at least Time wallclock
milliseconds, a message {monitor, GcPid, long_gc, Info} is sent to MonitorPid.
GcPid is the pid that was garbage collected and 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 actual 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 documentation of the gc_start trace message (see
erlang:trace/3). New tuples may be added, and the order of the tuples in the
Info list may 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 and Info is a
list of two-element tuples describing the event. In case of a pid(), the tuples
{timeout, Millis}, {in, Location} and {out, Location} will be present, where
Location is either an MFA ({Module, Function, Arity}) describing the function
where the process was scheduled in/out, or the atom undefined. In case of a
port(), the tuples {timeout, Millis} and {port_op,Op} will be present. Op will
be 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
should never appear, while the others represent the corresponding driver
callbacks timeout, ready_input, ready_output, event and finally outputv (when
the port is used by distribution). The Millis value in the timeout tuple will
tell you the actual uninterrupted execution time of the process or port, which
will always be >= the Time value supplied when starting the trace. New tuples
may be added to the Info list in the future, and the order of the tuples in the
list may be changed at any time without prior notice.
This can be used to detect problems with NIF's or drivers that take too long to
execute. Generally, 1 ms is considered a good maximum time for a driver
callback or a NIF. However, a time sharing system should usually consider
everything below 100 ms as "possible" and fairly "normal". Schedule times above
that might however indicate swapping or a NIF/driver that is misbehaving.
Misbehaving NIF's and drivers could cause bad resource utilization and bad
overall performance of the system.
{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 above, except that
the tuple tagged with timeout is not present. Note: As of erts version 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 larger than Size. Previously the
monitor message was sent if the memory block allocated for the youngest
generation was equal to or larger 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 will enlarge the process's message
queue and probably make the problem worse.
Keep the monitoring process neat and do not set the system monitor limits too
tight.
Failure: badarg if MonitorPid does not exist or 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
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 may 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
Sets system profiler options. ProfilerPid is a local pid or port that will receive
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 subsequently active when the port callback
returns.
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 is
reinserted into the run queue after having been preemptively scheduled out will
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.
Note:
erlang:system_profile is considered experimental and its behaviour may change in
the future.
term_to_binary(Term) -> ext_binary()
Types:
Term = term()
Returns a binary data object which is the result of encoding Term according to the
Erlang external term format.
This can be used for a variety of 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 which is the result of encoding Term according to the
Erlang external term format.
If the option compressed is provided, the external term format will be compressed.
The compressed format is automatically recognized by binary_to_term/1 in R7B and
later.
It is also possible to specify a compression level by giving the option
{compressed, Level}, where Level is an integer from 0 through 9. 0 means that no
compression will be done (it is the same as not giving any compressed option); 1
will take the least time but may not compress as well as the higher levels; 9 will
take the most time and may produce a smaller result. Note the "mays" in the
preceding sentence; depending on the input term, level 9 compression may or may not
produce a smaller result than level 1 compression.
Currently, compressed gives the same result as {compressed, 6}.
The option {minor_version, Version} can be use to control some details of the
encoding. This option was introduced in R11B-4. Currently, the allowed values for
Version are 0 and 1.
{minor_version, 1} 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). binary_to_term/1 in R11B-4 and later is able decode the
new representation.
{minor_version, 0} is currently the default, meaning that floats will be encoded
using a textual representation; this option is useful if you want to ensure that
releases prior to 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 will return
the value Any.
> 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.
> time().
{9,42,44}
tl(List) -> term()
Types:
List = [term(), ...]
Returns the tail of List, that is, the list minus the first element.
> 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
| 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 pid for a local process, or one of the following atoms:
existing:
All processes currently existing.
new:
All processes that will be created in the future.
all:
All currently existing processes and all processes that will be created in the
future.
FlagList can contain any number of the following flags (the "message tags" refers
to the list of messages following below):
all:
Set all trace flags except {tracer, Tracer} and cpu_timestamp that are in their
nature different than the others.
send:
Trace sending of messages.
Message tags: send, send_to_non_existing_process.
'receive':
Trace receiving of messages.
Message tags: 'receive'.
procs:
Trace process related events.
Message tags: spawn, exit, register, unregister, link, unlink, getting_linked,
getting_unlinked.
call:
Trace certain function calls. Specify which function calls to trace by calling
erlang:trace_pattern/3.
Message tags: call, return_from.
silent:
Used in conjunction with the call trace flag. The call, return_from and
return_to trace messages are inhibited if this flag is set, but if there are
match specs they are executed as normal.
Silent mode is inhibited by executing erlang:trace(_, false, [silent|_]), or by
a match spec executing the {silent, false} function.
The silent trace flag facilitates setting up a trace on many or even all
processes in the system. Then the interesting trace can be activated and
deactivated using the {silent,Bool} match spec function, giving a high degree
of control of which functions with which arguments that triggers the trace.
Message tags: call, return_from, return_to. Or rather, the absence of.
return_to:
Used in conjunction with the call trace flag. Trace the actual return from a
traced function back to its caller. Only works for functions traced with the
local option to erlang:trace_pattern/3.
The semantics is that a trace message is sent when a call traced function
actually returns, that is, when a chain of tail recursive calls is ended. There
will be only one trace message sent per chain of tail recursive calls, why 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_spec action instead.
Message tags: return_to.
running:
Trace scheduling of processes.
Message tags: in, and out.
exiting:
Trace scheduling of an exiting processes.
Message tags: in_exiting, out_exiting, and out_exited.
garbage_collection:
Trace garbage collections of processes.
Message tags: gc_start, gc_end.
timestamp:
Include a time stamp in all trace messages. The time stamp (Ts) is of the same
form as returned by erlang:now().
cpu_timestamp:
A global trace flag for the Erlang node that makes all trace timestamps be in
CPU time, not wallclock. It is only allowed with PidSpec==all. If the host
machine operating system does not support high resolution CPU time
measurements, trace/3 exits with badarg.
arity:
Used in conjunction with the call trace flag. {M, F, Arity} will be 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 the set_on_spawn flag.
set_on_first_spawn:
Makes the first process created by a traced process inherit its trace flags,
excluding the set_on_first_spawn flag.
set_on_link:
Makes any process linked by a traced process inherit its trace flags, including
the set_on_link flag.
set_on_first_link:
Makes the first process linked to by a traced process inherit its trace flags,
excluding the set_on_first_link flag.
{tracer, Tracer}:
Specify where to send the trace messages. Tracer must be the pid of a local
process or the port identifier of a local port. If this flag is not given,
trace messages will be 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.
If the timestamp flag is not given, the tracing process will receive the trace
messages described below. Pid is the pid of the traced process in which the traced
event has occurred. The third element of the tuple is the message tag.
If the timestamp flag is given, the first element of the tuple will be trace_ts
instead and the timestamp is added last in the tuple.
{trace, Pid, 'receive', Msg}:
When Pid receives the message Msg.
{trace, Pid, send, Msg, To}:
When Pid sends the message Msg to the process To.
{trace, Pid, send_to_non_existing_process, Msg, To}:
When Pid sends the 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.
Note that the 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 call and the return_to flags 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 the
call flag 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 due to an exception. This trace
message is sent if the call flag 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.
Note that Args is supposed to be the argument list, but may be any term in the
case of an erroneous spawn.
{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. Note that this is done
automatically when a registered process exits.
{trace, Pid, in, {M, F, Arity} | 0}:
When Pid is scheduled to run. The process will run in function {M, F, Arity}.
On some rare occasions the current function cannot be determined, then the last
element Arity 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 Arity 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.
You should not depend on the tuples have any defined order. Currently, 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 actual 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, in words, 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_vheap_block_size:
The total size of binaries, in words, 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 the gc_start message, but the sizes reflect the new sizes after garbage
collection.
If the tracing process dies, the flags will be silently removed.
Only one process can trace a particular process. For this reason, attempts to trace
an already traced process will fail.
Returns: A number indicating the number of processes that matched PidSpec. If
PidSpec is a pid, the return value will be 1. If PidSpec is all or existing the
return value will be the number of processes running, excluding tracer processes.
If PidSpec is new, the return value will be 0.
Failure: If 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 the 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 you can 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 have been delivered to the tracer up to the point that the Tracee had
reached at the time of the call to erlang:trace_delivered(Tracee).
Note that the trace_delivered message does not imply that trace messages have been
delivered; instead, it implies that all trace messages that should be delivered
have been delivered. It is not an error if Tracee isn't, and hasn't been traced by
someone, but if this is the case, no trace messages will have been delivered when
the trace_delivered message arrives.
Note that Tracee has to 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.
An 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. C can ensure that the trace isn't truncated
by calling erlang:trace_delivered(A) when A exits and wait for the
{trace_delivered, A, Ref} message 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
| arity
trace_match_spec() = [{[term()] | '_', [term()], [term()]}]
Returns trace information about a process or function.
To get information about a process, PidOrFunc should be a pid or the atom new. The
atom new means that the default trace state for processes to be created will be
returned. Item must have one of the following values:
flags:
Return a list of atoms indicating what kind of traces is enabled for the
process. The list will be 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:
Return the identifier for process or port tracing this process. If this process
is not being traced, the return value will be [].
To get information about a function, PidOrFunc should be a three-element tuple:
{Module, Function, Arity} or the atom on_load. No wildcards are allowed. Returns
undefined if the function does not exist or false if the function is not traced at
all. Item must have one of the following values:
traced:
Return global if this function is traced on global function calls, local if
this function is traced on local function calls (i.e local and global function
calls), and false if neither local nor global function calls are traced.
match_spec:
Return 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:
Return 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, and if the
function is meta traced but has once detected that the tracer proc is invalid,
the returned value is [].
meta_match_spec:
Return 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:
Return the call count value for this function or true for the pseudo function
on_load if call count tracing is active. Return false otherwise. See also
erlang:trace_pattern/3.
call_time:
Return the call time values for this function or true for the pseudo function
on_load if call time tracing is active. Returns false otherwise. The call time
values returned, [{Pid, Count, S, Us}], is a list of each process that has
executed the function and its specific counters. See also
erlang:trace_pattern/3.
all:
Return a list containing the {Item, Value} tuples for all other items, or
return false if no tracing is active for this function.
The actual return value will be {Item, Value}, where Value is the requested
information as described above. If a pid for a dead process was given, or the name
of a non-existing function, Value will be undefined.
If PidOrFunc is the 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
This BIF is used to enable or disable call tracing for exported functions. It must
be combined with erlang:trace/3 to set the call trace flag for one or more
processes.
Conceptually, call tracing works like this: Inside the Erlang virtual machine there
is a set of processes to be traced and a set of functions to be traced. Tracing
will be enabled on the intersection of the set. That is, if a process included in
the traced process set calls a function included in the traced function set, the
trace action will be taken. Otherwise, nothing will happen.
Use erlang:trace/3 to add or remove one or more processes to the set of traced
processes. Use erlang:trace_pattern/2 to add or remove exported functions to the
set of traced functions.
The erlang:trace_pattern/3 BIF can also add match specifications to an exported
function. A match specification comprises a pattern that the arguments to the
function must match, a guard expression which 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 will not be executed.
The MFA argument should be a tuple like {Module, Function, Arity} or the atom
on_load (described below). It can be the module, function, and arity for an
exported function (or a BIF in any module). The '_' atom can be used to mean any of
that kind. Wildcards can be used in any of the following ways:
{Module,Function,'_'}:
All exported functions of any arity named Function in module Module.
{Module,'_','_'}:
All exported functions in module Module.
{'_','_','_'}:
All exported functions in all loaded modules.
Other combinations, such as {Module,'_',Arity}, are not allowed. Local functions
will match wildcards only if the local option is in the FlagList.
If the MFA argument is the atom on_load, the match specification and flag list will
be used on all modules that are newly loaded.
The MatchSpec argument can take any of the following forms:
false:
Disable tracing for the matching function(s). Any match specification will be
removed.
true:
Enable tracing for the matching function(s).
MatchSpecList:
A list of match specifications. An empty list is equivalent to true. See the
ERTS User's Guide for a description of match specifications.
restart:
For the FlagList option call_count and call_time: restart the existing
counters. The behaviour is undefined for other FlagList options.
pause:
For the FlagList option call_count and call_time: pause the existing counters.
The behaviour is undefined for other FlagList options.
The FlagList parameter is a list of options. The following options are allowed:
global:
Turn on or off call tracing for global function calls (that is, calls
specifying the module explicitly). Only exported functions will match and only
global calls will generate trace messages. This is the default.
local:
Turn on or off call tracing for all types of function calls. Trace messages
will be sent whenever any of the specified functions are called, regardless of
how they are called. If the return_to flag is set for the process, a return_to
message will also be sent when this function returns to its caller.
meta | {meta, Pid}:
Turn on or off meta tracing for all types of function calls. Trace messages
will be 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 spec function {return_trace} works with meta trace and send 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. Running counters can be paused with MatchSpec == pause. Paused and
running counters can be restarted from zero with MatchSpec == restart.
The counter value can be read with 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 micro-seconds. 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. Running counters can be paused with MatchSpec == pause.
Paused and running counters can be restarted from zero with MatchSpec ==
restart.
The counter value can be read with erlang:trace_info/2.
The global and local options are mutually exclusive and global is the default (if
no options are specified). The call_count and meta options perform a kind of local
tracing, and can also not be combined with global. A function can be either
globally or locally traced. If global tracing is specified for a specified set of
functions; local, meta, call time and call count tracing for the matching set of
local functions will be disabled, and vice versa.
When disabling trace, the option must match the type of trace that is set on the
function, so that local tracing must be disabled with the local option and global
tracing with the global option (or no option at all), and so forth.
There is no way to directly change part of a match specification list. If a
function has a match specification, you can replace it with a completely new one.
If you need to change an existing match specification, use the erlang:trace_info/2
BIF to retrieve the existing match specification.
Returns the number of exported functions that matched the MFA argument. This will
be zero if none matched at all.
trunc(Number) -> integer()
Types:
Number = number()
Returns an integer by the truncating Number.
> trunc(5.5).
5
Allowed in guard tests.
tuple_size(Tuple) -> integer() >= 0
Types:
Tuple = tuple()
Returns an integer which is the number of elements in Tuple.
> tuple_size({morni, mulle, bwange}).
3
Allowed in guard tests.
tuple_to_list(Tuple) -> [term()]
Types:
Tuple = tuple()
Returns a list which corresponds to Tuple. Tuple may contain any Erlang terms.
> 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),
also called GMT, in the form {{Year, Month, Day}, {Hour, Minute, Second}} if
supported by the underlying operating system. If not, erlang:universaltime() is
equivalent to erlang:localtime().
> 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, if
this is supported by the underlying OS. Otherwise, no conversion is done, and
Universaltime is returned.
> erlang:universaltime_to_localtime({{1996,11,6},{14,18,43}}).
{{1996,11,7},{15,18,43}}
Failure: badarg if Universaltime does not denote a valid date and time.
unlink(Id) -> true
Types:
Id = pid() | port()
Removes the link, if there is one, between the calling process and the process or
port referred to by Id.
Returns true and does not fail, even if there is no link to Id, or if Id does not
exist.
Once unlink(Id) has returned it is guaranteed that the link between the caller and
the entity referred to by Id has no effect on the caller in the future (unless the
link is setup again). If caller is trapping exits, an {'EXIT', Id, _} message due
to the link might have been placed in the caller's message queue prior to the call,
though. Note, the {'EXIT', Id, _} message can be the result of the link, but can
also be the result of Id calling exit/2. Therefore, it may be appropriate to
cleanup the message queue when trapping exits after the call to unlink(Id), as
follow:
unlink(Id),
receive
{'EXIT', Id, _} ->
true
after 0 ->
true
end
Note:
Prior to OTP release R11B (erts version 5.5) unlink/1 behaved completely
asynchronous, i.e., the link was active until the "unlink signal" reached the
linked entity. This had one undesirable effect, though. You could never know when
you were guaranteed not to be effected by the link.
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 pid or a port identifier.
> 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 pid or port identifier with the registered name RegName. Returns
undefined if the name is not registered.
> whereis(db).
<0.43.0>
erlang:yield() -> true
Voluntarily let 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 will have a chance to run in another scheduler thread anyway.
Using this BIF without a thorough grasp of how the scheduler works may cause
performance degradation.