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Man Pages


Manual Reference Pages  -  ERLANG (3)

NAME

erlang - The Erlang BIFs.

CONTENTS

Description
Data Types
Exports

DESCRIPTION

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

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

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

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

DATA TYPES

ext_binary()

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

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

See erlang:timestamp/0.

time_unit() =
integer() >= 1 |
seconds |
milli_seconds |
micro_seconds |
nano_seconds |
native

Supported time unit representations:

PartsPerSecond :: integer() >= 1: Time unit expressed in parts per second. That is, the time unit equals 1/PartsPerSecond second.
seconds: Symbolic representation of the time unit represented by the integer 1.
milli_seconds: Symbolic representation of the time unit represented by the integer 1000.
micro_seconds: Symbolic representation of the time unit represented by the integer 1000000.
nano_seconds: Symbolic representation of the time unit represented by the integer 1000000000.
native: Symbolic representation of the native time unit used by the Erlang runtime system.

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

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

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

The time_unit/0 type may be extended. Use erlang:convert_time_unit/3 in order to convert time values between time units.

EXPORTS

abs(Float) -> float()

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

Types:

Int = integer()

Types:

Float = float()
Int = integer()

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

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

Allowed in guard tests.

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

Types:

Data = iodata()

Computes and returns the adler32 checksum for Data.

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

Types:

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

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

The following code:

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

assigns the same value to Y as this:

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

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

Types:

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

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

The following code:

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

assigns the same value to Z as this:

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

erlang:append_element(Tuple1, Term) -> Tuple2

Types:

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

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

Example:

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

apply(Fun, Args) -> term()

Types:

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

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

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

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

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

Types:

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

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

Example:

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

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

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

atom_to_binary(Atom, Encoding) -> binary()

Types:

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

Returns a binary corresponding to the text representation of Atom. If Encoding is latin1, there is one byte for each character in the text representation. If Encoding is utf8 or unicode, the characters are encoded using UTF-8 (that is, characters from 128 through 255 are encoded in two bytes).

Note:
atom_to_binary(Atom, latin1) never fails because the text representation of an atom can only contain characters from 0 through 255. In a future release, the text representation of atoms can be allowed to contain any Unicode character and atom_to_binary(Atom, latin1) will then fail if the text representation for Atom contains a Unicode character greater than 255.

Example:

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

atom_to_list(Atom) -> string()

Types:

Atom = atom()

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

> atom_to_list(’Erlang’). "Erlang"

binary_part(Subject, PosLen) -> binary()

Types:

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

Extracts the part of the binary described by PosLen.

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

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

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

Start is zero-based, that is:

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

For details about the PosLen semantics, see the binary manual page in STDLIB.

Allowed in guard tests.

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

Types:

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

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

Allowed in guard tests.

binary_to_atom(Binary, Encoding) -> atom()

Types:

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

Returns the atom whose text representation is Binary. If Encoding is latin1, no translation of bytes in the binary is done. If Encoding is utf8 or unicode, the binary must contain valid UTF-8 sequences. Only Unicode characters up to 255 are allowed.

Note:
binary_to_atom(Binary, utf8) fails if the binary contains Unicode characters greater than 255. In a future release, such Unicode characters can be allowed and binary_to_atom(Binary, utf8) does then not fail. For more information on Unicode support in atoms, see the note on UTF-8 encoded atoms in Section "External Term Format" in the User’s Guide.

Examples:

> binary_to_atom(<<"Erlang">>, latin1).
.Erlang’ > binary_to_atom(<<1024/utf8>>, utf8). ** exception error: bad argument in function binary_to_atom/2 called as binary_to_atom(<<208,128>>,utf8)

binary_to_existing_atom(Binary, Encoding) -> atom()

Types:

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

As binary_to_atom/2, but the atom must exist.

Failure: badarg if the atom does not exist.

binary_to_float(Binary) -> float()

Types:

Binary = binary()

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

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

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

binary_to_integer(Binary) -> integer()

Types:

Binary = binary()

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

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

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

binary_to_integer(Binary, Base) -> integer()

Types:

Binary = binary()
Base = 2..36

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

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

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

binary_to_list(Binary) -> [byte()]

Types:

Binary = binary()

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

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

Types:

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

1..byte_size(Binary)

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

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

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

Types:

Bitstring = bitstring()

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

binary_to_term(Binary) -> term()

Types:

Binary = ext_binary()

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

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

See also term_to_binary/1 and binary_to_term/2.

binary_to_term(Binary, Opts) -> term()

Types:

Binary = ext_binary()
Opts = [safe]

As binary_to_term/1, but takes options that affect decoding of the binary.

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

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

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

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

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

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

Types:

Bitstring = bitstring()

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

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

Allowed in guard tests.

erlang:bump_reductions(Reductions) -> true

Types:

Reductions = integer() >= 1

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

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

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

Types:

Bitstring = bitstring()

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

Examples:

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

Allowed in guard tests.

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

Types:

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

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

Available Options:

{async, Async}: Asynchronous request for cancellation. Async defaults to false which will cause the cancellation to be performed synchronously. When Async is set to true, the cancel operation is performed asynchronously. That is, erlang:cancel_timer() will send an asynchronous request for cancellation to the timer service that manages the timer, and then return ok.
{info, Info}: Request information about the Result of the cancellation. Info defaults to true which means the Result is given. When Info is set to false, no information about the result of the cancellation is given. When the operation is performed
synchronously: If Info is true, the Result is returned by erlang:cancel_timer(); otherwise, ok is returned.
asynchronously: If Info is true, a message on the form {cancel_timer, TimerRef, Result} is sent to the caller of erlang:cancel_timer() when the cancellation operation has been performed; otherwise, no message is sent.

More Options may be added in the future.

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

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

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

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

erlang:cancel_timer(TimerRef) -> Result

Types:

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

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

check_old_code(Module) -> boolean()

Types:

Module = module()

Returns true if Module has old code, otherwise false.

See also code(3).

check_process_code(Pid, Module) -> CheckResult

Types:

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

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

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

Types:

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

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

The available Options are as follows:

{allow_gc, boolean()}: Determines if garbage collection is allowed when performing the operation. If {allow_gc, false} is passed, and a garbage collection is needed to determine the result of the operation, the operation is aborted (see information on CheckResult in the following). The default is to allow garbage collection, that is, {allow_gc, true}.
{async, RequestId}: The function check_process_code/3 returns the value async immediately after the request has been sent. When the request has been processed, the process that called this function is passed a message on the form {check_process_code, RequestId, CheckResult}.

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

CheckResult informs about the result of the request as follows:

true: The process identified by Pid executes old code for Module. That is, the current call of the process executes old code for this module, or the process has references to old code for this module, or the process contains funs that references old code for this module.
false: The process identified by Pid does not execute old code for Module.
aborted: The operation was aborted, as the process needed to be garbage collected to determine the operation result, and the operation was requested by passing option {allow_gc, false}.

See also code(3).

Failures:

badarg: If Pid is not a node local process identifier.
badarg: If Module is not an atom.
badarg: If OptionList is an invalid list of options.

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

Types:

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

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

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

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

Types:

Data = iodata()

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

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

Types:

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

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

The following code:

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

assigns the same value to Y as this:

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

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

Types:

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

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

The following code:

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

assigns the same value to Z as this:

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

date() -> Date

Types:

Date = calendar:date()

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

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

Example:

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

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

Types:

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

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

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

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

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

The following Types are valid:

raw | 0: No packet handling is done. The entire binary is returned unless it is empty.
1 | 2 | 4: Packets consist of a header specifying the number of bytes in the packet, followed by that number of bytes. The length of the header can be one, two, or four bytes; the order of the bytes is big-endian. The header is stripped off when the packet is returned.
line: A packet is a line terminated by a delimiter byte, default is the latin1 newline character. The delimiter byte is included in the returned packet unless the line was truncated according to option line_length.
asn1 | cdr | sunrm | fcgi | tpkt: The header is not stripped off.

The meanings of the packet types are as follows:
asn1 - ASN.1 BER:

sunrm - Sun’s RPC encoding:

cdr - CORBA (GIOP 1.1):

fcgi - Fast CGI:

tpkt - TPKT format [RFC1006]:

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

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

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

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

The following options are available:

{packet_size, integer() >= 0}: Sets the maximum allowed size of the packet body. If the packet header indicates that the length of the packet is longer than the maximum allowed length, the packet is considered invalid. Default is 0, which means no size limit.
{line_length, integer() >= 0}: For packet type line, lines longer than the indicated length are truncated.

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

{line_delimiter, 0 =< byte() =< 255}: For packet type line, sets the delimiting byte. Default is the latin1 character $\n.

Examples:

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

erlang:delete_element(Index, Tuple1) -> Tuple2

Types:

Index = integer() >= 1

1..tuple_size(Tuple1)
Tuple1 = Tuple2 = tuple()

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

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

delete_module(Module) -> true | undefined

Types:

Module = module()

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

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

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

demonitor(MonitorRef) -> true

Types:

MonitorRef = reference()

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

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

Note:
Prior to OTP release R11B (ERTS version 5.5) demonitor/1 behaved completely asynchronously, i.e., the monitor was active until the "demonitor signal" reached the monitored entity. This had one undesirable effect. You could never know when you were guaranteed not to receive a DOWN message due to the monitor.

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

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

demonitor(MonitorRef, OptionList) -> boolean()

Types:

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

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

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

The available Options are as follows:

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

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

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

info: The returned value is one of the following:
true: The monitor was found and removed. In this case, no ’DOWN’ message corresponding to this monitor has been delivered and will not be delivered.
false: The monitor was not found and could not be removed. This probably because someone already has placed a ’DOWN’ message corresponding to this monitor in the caller message queue.

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

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

Failures:

badarg: If OptionList is not a list.
badarg: If Option is an invalid option.
badarg: The same failure as for demonitor/1.

disconnect_node(Node) -> boolean() | ignored

Types:

Node = node()

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

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

erlang:display(Term) -> true

Types:

Term = term()

Prints a text representation of Term on the standard output. On OSE, the term is printed to the ramlog.

Warning:
This BIF is intended for debugging only.

element(N, Tuple) -> term()

Types:

N = integer() >= 1

1..tuple_size(Tuple)
Tuple = tuple()

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

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

Allowed in guard tests.

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

Types:

Key = Val = term()

Returns the process dictionary and deletes it, for example:

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

erase(Key) -> Val | undefined

Types:

Key = Val = term()

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

Example:

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

error(Reason) -> no_return()

Types:

Reason = term()

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

Example:

> catch error(foobar). {’EXIT’,{foobar,[{erl_eval,do_apply,5}, {erl_eval,expr,5}, {shell,exprs,6}, {shell,eval_exprs,6}, {shell,eval_loop,3}]}}

error(Reason, Args) -> no_return()

Types:

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

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

exit(Reason) -> no_return()

Types:

Reason = term()

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

Example:

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

exit(Pid, Reason) -> true

Types:

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

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

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

* If Pid is not trapping exits, Pid itself exits with exit reason Reason.
* If Pid is trapping exits, the exit signal is transformed into a message {’EXIT’, From, Reason} and delivered to the message queue of Pid.
* From is the process identifier of the process that sent the exit signal. See also process_flag/2.

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

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

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

Types:

Term = term()

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

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

This is equivalent to a call to:

erlang:external_size(Term, [])

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

Types:

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

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

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

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

float(Number) -> float()

Types:

Number = number()

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

> float(55). 55.0

Allowed in guard tests.

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

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

float_to_binary(Float) -> binary()

Types:

Float = float()

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

float_to_binary(Float, Options) -> binary()

Types:

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

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

Examples:

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

float_to_list(Float) -> string()

Types:

Float = float()

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

float_to_list(Float, Options) -> string()

Types:

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

Returns a string corresponding to the text representation of Float using fixed decimal point formatting. The options are as follows:

* If option decimals is specified, the returned value contains at most Decimals number of digits past the decimal point. If the number does not fit in the internal static buffer of 256 bytes, the function throws badarg.
* If option compact is provided, the trailing zeros at the end of the list are truncated. This option is only meaningful together with option decimals.
* If option scientific is provided, the float is formatted using scientific notation with Decimals digits of precision.
* If Options is [], the function behaves as float_to_list/1.

Examples:

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

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

Types:

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

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

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

Two types of funs have slightly different semantics:

* A fun created by fun M:F/A is called an external fun. Calling it will always call the function F with arity A in the latest code for module M. Notice that module M does not even need to be loaded when the fun fun M:F/A is created.
* All other funs are called local. When a local fun is called, the same version of the code that created the fun is called (even if a newer version of the module has been loaded).

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

{type, Type}: Type is local or external.
{module, Module}: Module (an atom) is the module name.

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

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

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

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

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

{arity, Arity}: Arity is the number of arguments that the fun is to be called with.
{env, Env}: Env (a list) is the environment or free variables for the fun. For external funs, the returned list is always empty.

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

{pid, Pid}: Pid is the process identifier of the process that originally created the fun.
{index, Index}: Index (an integer) is an index into the module fun table.
{new_index, Index}: Index (an integer) is an index into the module fun table.
{new_uniq, Uniq}: Uniq (a binary) is a unique value for this fun. It is calculated from the compiled code for the entire module.
{uniq, Uniq}: Uniq (an integer) is a unique value for this fun. As from OTP R15, this integer is calculated from the compiled code for the entire module. Before OTP R15, this integer was based on only the body of the fun.

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

Types:

Fun = function()
Item = fun_info_item()
Info = term()

fun_info_item() =
arity |
env |
index |
name |
module |
new_index |
new_uniq |
pid |
type |
uniq

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

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

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

See erlang:fun_info/1.

erlang:fun_to_list(Fun) -> string()

Types:

Fun = function()

Returns a string corresponding to the text representation of Fun.

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

Types:

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

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

Note:
This function used to return false for built-in functions before the 18.0 release.

garbage_collect() -> true

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

Warning:
Improper use can seriously degrade system performance.

garbage_collect(Pid) -> GCResult

Types:

Pid = pid()
GCResult = boolean()

The same as garbage_collect(Pid, []).

garbage_collect(Pid, OptionList) -> GCResult | async

Types:

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

Garbage collects the node local process identified by Pid.

The available Options are as follows:

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

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

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

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

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

Failures:

badarg:
If Pid is not a node local process identifier.
badarg:
If OptionList is an invalid list of options.

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

Types:

Key = Val = term()

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

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

get(Key) -> Val | undefined

Types:

Key = Val = term()

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

Example:

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

erlang:get_cookie() -> Cookie | nocookie

Types:

Cookie = atom()

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

get_keys() -> [Key]

Types:

Key = term()

Returns a list of keys all keys present in the process dictionary.

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

get_keys(Val) -> [Key]

Types:

Val = Key = term()

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

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

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

Types:

stack_item() =


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

Gets the call stack back-trace (stacktrace) of the last exception in the calling process as a list of {Module,Function,Arity,Location} tuples. Field Arity in the first tuple can be the argument list of that function call instead of an arity integer, depending on the exception.

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

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

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

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

file: The second element of the tuple is a string (list of characters) representing the file name of the source file of the function.
line: The second element of the tuple is the line number (an integer greater than zero) in the source file where the exception occurred or the function was called.

See also erlang:error/1 and erlang:error/2.

group_leader() -> pid()

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

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

group_leader(GroupLeader, Pid) -> true

Types:

GroupLeader = Pid = pid()

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

See also group_leader/0.

halt() -> no_return()

The same as halt(0, []).

Example:

> halt(). os_prompt%

halt(Status) -> no_return()

Types:

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

The same as halt(Status, []).

Example:

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

halt(Status, Options) -> no_return()

Types:

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

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

integer(): The runtime system exits with integer value Status as status code to the calling environment (OS).
string(): An Erlang crash dump is produced with Status as slogan. Then the runtime system exits with status code 1.
abort:
The runtime system aborts producing a core dump, if that is enabled in the OS.

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

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

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

erlang:hash(Term, Range) -> integer() >= 1

Types:

Term = term()
Range = integer() >= 1

Returns a hash value for Term within the range 1..Range. The maximum range is 1..2^27-1.

Warning:
This BIF is deprecated, as the hash value can differ on different architectures. The hash values for integer terms higher than 2^27 and large binaries are poor. The BIF is retained for backward compatibility reasons (it can have been used to hash records into a file), but all new code is to use one of the BIFs erlang:phash/2 or erlang:phash2/1,2 instead.

hd(List) -> term()

Types:

List = [term(), ...]

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

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

Allowed in guard tests.

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

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

Types:

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

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

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

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

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

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

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

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

Types:

Index = integer() >= 1

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

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

Example:

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

integer_to_binary(Integer) -> binary()

Types:

Integer = integer()

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

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

integer_to_binary(Integer, Base) -> binary()

Types:

Integer = integer()
Base = 2..36

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

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

integer_to_list(Integer) -> string()

Types:

Integer = integer()

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

> integer_to_list(77). "77"

integer_to_list(Integer, Base) -> string()

Types:

Integer = integer()
Base = 2..36

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

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

iolist_to_binary(IoListOrBinary) -> binary()

Types:

IoListOrBinary = iolist() | binary()

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

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

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

Types:

Item = iolist() | binary()

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

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

is_alive() -> boolean()

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

is_atom(Term) -> boolean()

Types:

Term = term()

Returns true if Term is an atom, otherwise false.

Allowed in guard tests.

is_binary(Term) -> boolean()

Types:

Term = term()

Returns true if Term is a binary, otherwise false.

A binary always contains a complete number of bytes.

Allowed in guard tests.

is_bitstring(Term) -> boolean()

Types:

Term = term()

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

Allowed in guard tests.

is_boolean(Term) -> boolean()

Types:

Term = term()

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

Allowed in guard tests.

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

Types:

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

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

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

is_float(Term) -> boolean()

Types:

Term = term()

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

Allowed in guard tests.

is_function(Term) -> boolean()

Types:

Term = term()

Returns true if Term is a fun, otherwise false.

Allowed in guard tests.

is_function(Term, Arity) -> boolean()

Types:

Term = term()
Arity = arity()

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

Allowed in guard tests.

is_integer(Term) -> boolean()

Types:

Term = term()

Returns true if Term is an integer, otherwise false.

Allowed in guard tests.

is_list(Term) -> boolean()

Types:

Term = term()

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

Allowed in guard tests.

is_map(Term) -> boolean()

Types:

Term = term()

Returns true if Term is a map, otherwise false.

Allowed in guard tests.

is_number(Term) -> boolean()

Types:

Term = term()

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

Allowed in guard tests.

is_pid(Term) -> boolean()

Types:

Term = term()

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

Allowed in guard tests.

is_port(Term) -> boolean()

Types:

Term = term()

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

Allowed in guard tests.

is_process_alive(Pid) -> boolean()

Types:

Pid = pid()

Pid must refer to a process at the local node.

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

is_record(Term, RecordTag) -> boolean()

Types:

Term = term()
RecordTag = atom()

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

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

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

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

Types:

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

RecordTag must be an atom.

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

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

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

is_reference(Term) -> boolean()

Types:

Term = term()

Returns true if Term is a reference, otherwise false.

Allowed in guard tests.

is_tuple(Term) -> boolean()

Types:

Term = term()

Returns true if Term is a tuple, otherwise false.

Allowed in guard tests.

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

Types:

List = [term()]

Returns the length of List, for example:

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

Allowed in guard tests.

link(PidOrPort) -> true

Types:

PidOrPort = pid() | port()

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

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

* If the calling process is not trapping exits, and checking PidOrPort is cheap (that is, if PidOrPort is local), link/1 fails with reason noproc.
* Otherwise, if the calling process is trapping exits, and/or PidOrPort is remote, link/1 returns true, but an exit signal with reason noproc is sent to the calling process.

list_to_atom(String) -> atom()

Types:

String = string()

Returns the atom whose text representation is String.

String can only contain ISO-latin-1 characters (that is, numbers less than 256) as the implementation does not allow unicode characters equal to or above 256 in atoms. For more information on Unicode support in atoms, see note on UTF-8 encoded atoms in Section "External Term Format" in the User’s Guide.

Example:

> list_to_atom("Erlang").
.Erlang’

list_to_binary(IoList) -> binary()

Types:

IoList = iolist()

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

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

list_to_bitstring(BitstringList) -> bitstring()

Types:

BitstringList = bitstring_list()

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

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

Example:

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

list_to_existing_atom(String) -> atom()

Types:

String = string()

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

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

list_to_float(String) -> float()

Types:

String = string()

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

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

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

list_to_integer(String) -> integer()

Types:

String = string()

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

> list_to_integer("123"). 123

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

list_to_integer(String, Base) -> integer()

Types:

String = string()
Base = 2..36

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

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

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

list_to_pid(String) -> pid()

Types:

String = string()

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

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

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

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

list_to_tuple(List) -> tuple()

Types:

List = [term()]

Returns a tuple corresponding to List, for example

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

List can contain any Erlang terms.

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

Types:

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

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

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

badfile: The object code in Binary has an incorrect format or the object code contains code for another module than Module.
not_purged: Binary contains a module that cannot be loaded because old code for this module already exists.

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

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

Types:

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

Note:
Before OTP R14B, NIFs were an experimental feature. Versions before OTP R14B can have different and possibly incompatible NIF semantics and interfaces. For example, in OTP R13B03 the return value on failure was {error,Reason,Text}.

Loads and links a dynamic library containing native implemented functions (NIFs) for a module. Path is a file path to the shareable object/dynamic library file minus the OS-dependent file extension (.so for Unix and .dll for Windows. For information on how to implement a NIF library, see erl_nif.

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

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

load_failed: The OS failed to load the NIF library.
bad_lib: The library did not fulfill the requirements as a NIF library of the calling module.
load | reload | upgrade: The corresponding library callback was unsuccessful.
old_code: The call to load_nif/2 was made from the old code of a module that has been upgraded; this is not allowed.

erlang:loaded() -> [Module]

Types:

Module = module()

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

See also code(3).

erlang:localtime() -> DateTime

Types:

DateTime = calendar:datetime()

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

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

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

erlang:localtime_to_universaltime(Localtime) -> Universaltime

Types:

Localtime = Universaltime = calendar:datetime()

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

Example:

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

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

erlang:localtime_to_universaltime(Localtime, IsDst) -> Universaltime

Types:

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

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

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

Examples:

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

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

make_ref() -> reference()

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

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

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

Types:

Arity = arity()
InitialValue = term()

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

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

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

Types:

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

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

Example:

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

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

Types:

Map = #{}

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

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

Allowed in guard tests.

max(Term1, Term2) -> Maximum

Types:

Term1 = Term2 = Maximum = term()

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

erlang:md5(Data) -> Digest

Types:

Data = iodata()
Digest = binary()

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

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

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

erlang:md5_final(Context) -> Digest

Types:

Context = Digest = binary()

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

erlang:md5_init() -> Context

Types:

Context = binary()

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

erlang:md5_update(Context, Data) -> NewContext

Types:

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

Updates an MD5 Context with Data and returns a NewContext.

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

Types:

Type = memory_type()
Size = integer() >= 0

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

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

The memory types are as follows:

total: The total amount of memory currently allocated. This is the same as the sum of the memory size for processes and system.
processes: The total amount of memory currently allocated for the Erlang processes.
processes_used: The total amount of memory currently used by the Erlang processes. This is part of the memory presented as processes memory.
system: The total amount of memory currently allocated for the emulator that is not directly related to any Erlang process. Memory presented as processes is not included in this memory.
atom: The total amount of memory currently allocated for atoms. This memory is part of the memory presented as system memory.
atom_used: The total amount of memory currently used for atoms. This memory is part of the memory presented as atom memory.
binary: The total amount of memory currently allocated for binaries. This memory is part of the memory presented as system memory.
code: The total amount of memory currently allocated for Erlang code. This memory is part of the memory presented as system memory.
ets: The total amount of memory currently allocated for ets tables. This memory is part of the memory presented as system memory.
low: Only on 64-bit halfword emulator. The total amount of memory allocated in low memory areas that are restricted to less than 4 GB, although the system can have more memory.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Types:

memory_type() =


total |
processes |
processes_used |
system |
atom |
atom_used |
binary |
code |
ets |
low |
maximum

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

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

Failures:

badarg:
If Type is not one of the memory types listed in the description of erlang:memory/0.
badarg:
If maximum is passed as Type and the emulator is not run in instrumented mode.
notsup:
If an erts_alloc(3) allocator has been disabled.

See also erlang:memory/0.

min(Term1, Term2) -> Minimum

Types:

Term1 = Term2 = Minimum = term()

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

module_loaded(Module) -> boolean()

Types:

Module = module()

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

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

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

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

Types:

MonitorRef = reference()

registered_name() = atom()

registered_process_identifier() =
registered_name() | {registered_name(), node()}

monitor_process_identifier() =
pid() | registered_process_identifier()

Send a monitor request of type Type to the entity identified by Item. The caller of monitor/2 will later be notified by a monitor message on the following format if the monitored state is changed:

{Tag, MonitorRef, Type, Object, Info}

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

Valid Types:

process: Monitor the existence of the process identified by Item. Valid Items in combination with the process Type can be any of the following:
pid(): The process identifier of the process to monitor.
{RegisteredName, Node}: A tuple consisting of a registered name of a process and a node name. The process residing on the node Node with the registered name {RegisteredName, Node} will be monitored.
RegisteredName: The process locally registered as RegisteredName will become monitored.

Note:
When a registered name is used, the process that has the registered name when the monitor request reach its destination will be monitored. The monitor is not effected if the registered name is unregistered, or unregistered and later registered on another process.

The monitor is triggered either when the monitored process terminates, is non existing, or if the connection to it is lost. In the case the connection to it is lost, we do not know if it still exist or not. After this type of monitor has been triggered, the monitor is automatically removed.

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

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

Here MonitorRef and Type are the same as described earlier, and:

Object: equals:
Item: If Item is specified by a process identifier.
{RegisteredName, Node}: If Item is specified as RegisteredName, or {RegisteredName, Node} where Node corresponds to the node that the monitored process resides on.
Info: Either the exit reason of the process, noproc (non-existing process), or noconnection (no connection to the node where the monitored process resides).

The monitoring is turned off when the ’DOWN’ message is sent or when demonitor/1 is called.

If an attempt is made to monitor a process on an older node (where remote process monitoring is not implemented or where remote process monitoring by registered name is not implemented), the call fails with badarg.

Note:
The format of the ’DOWN’ message changed in ERTS version 5.2 (OTP R9B) for monitoring by registered name. Element Object of the ’DOWN’ message could in earlier versions sometimes be the process identifier of the monitored process and sometimes be the registered name. Now element Object is always a tuple consisting of the registered name and the node name. Processes on new nodes (ERTS version 5.2 or higher) always get ’DOWN’ messages on the new format even if they are monitoring processes on old nodes. Processes on old nodes always get ’DOWN’ messages on the old format.

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

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

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

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

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

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

 

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

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

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

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

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

monitor_node(Node, Flag) -> true

Types:

Node = node()
Flag = boolean()

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

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

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

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

Failure: badarg if the local node is not alive.

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

Types:

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

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

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

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

erlang:monotonic_time() -> integer()

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

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

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

erlang:monotonic_time(Unit) -> integer()

Types:

Unit = time_unit()

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

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

erlang:nif_error(Reason) -> no_return()

Types:

Reason = term()

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

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

Types:

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

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

node() -> Node

Types:

Node = node()

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

Allowed in guard tests.

node(Arg) -> Node

Types:

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

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

Allowed in guard tests.

nodes() -> Nodes

Types:

Nodes = [node()]

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

nodes(Arg) -> Nodes

Types:

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

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

NodeType can be any of the following:

visible: Nodes connected to this node through normal connections.
hidden: Nodes connected to this node through hidden connections.
connected: All nodes connected to this node.
this: This node.
known: Nodes that are known to this node. That is, connected nodes and nodes referred to by process identifiers, port identifiers and references located on this node. The set of known nodes is garbage collected. Notice that this garbage collection can be delayed. For more information, see delayed_node_table_gc.

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

now() -> Timestamp

Types:

Timestamp = timestamp()

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

Warning:
This function is deprecated! Do not use it! See the users guide chapter Time and Time Correction for more information. Specifically the Dos and Dont’s section for information on what to use instead of erlang:now/0.

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

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

open_port(PortName, PortSettings) -> port()

Types:

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

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

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

Note:
The characters in the name (if given as a list) can only be higher than 255 if the Erlang Virtual Machine is started in Unicode file name translation mode. Otherwise the name of the executable is limited to the ISO-latin-1 character set.

PortName can be any of the following:

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

When starting external programs on Solaris, the system call vfork is used in preference to fork for performance reasons, although it has a history of being less robust. If there are problems using vfork, setting environment variable ERL_NO_VFORK to any value causes fork to be used instead.

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

{spawn_driver, Command}: Works like {spawn, Command}, but demands the first (space-separated) token of the command to be the name of a loaded driver. If no driver with that name is loaded, a badarg error is raised.
{spawn_executable, FileName}: Works like {spawn, FileName}, but only runs external executables. FileName in its whole is used as the name of the executable, including any spaces. If arguments are to be passed, the PortSettings args and arg0 can be used.

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

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

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

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

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

{packet, N}: Messages are preceded by their length, sent in N bytes, with the most significant byte first. The valid values for N are 1, 2, and 4.
stream: Output messages are sent without packet lengths. A user-defined protocol must be used between the Erlang process and the external object.
{line, L}: Messages are delivered on a per line basis. Each line (delimited by the OS-dependent new line sequence) is delivered in a single message. The message data format is {Flag, Line}, where Flag is eol or noeol, and Line is the data delivered (without the new line sequence).

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

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

{cd, Dir}: Only valid for {spawn, Command} and {spawn_executable, FileName}. The external program starts using Dir as its working directory. Dir must be a string.
{env, Env}: Only valid for {spawn, Command} and {spawn_executable, FileName}. The environment of the started process is extended using the environment specifications in Env.

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

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

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

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

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

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

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

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

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

use_stdio: Only valid for {spawn, Command} and {spawn_executable, FileName}. It allows the standard input and output (file descriptors 0 and 1) of the spawned (Unix) process for communication with Erlang.
nouse_stdio: The opposite of use_stdio. It uses file descriptors 3 and 4 for communication with Erlang.
stderr_to_stdout: Affects ports to external programs. The executed program gets its standard error file redirected to its standard output file. stderr_to_stdout and nouse_stdio are mutually exclusive.
overlapped_io: Affects ports to external programs on Windows only. The standard input and standard output handles of the port program are, if this option is supplied, opened with flag FILE_FLAG_OVERLAPPED, so that the port program can (and must) do overlapped I/O on its standard handles. This is not normally the case for simple port programs, but an option of value for the experienced Windows programmer. On all other platforms, this option is silently discarded.
in: The port can only be used for input.
out: The port can only be used for output.
binary: All I/O from the port is binary data objects as opposed to lists of bytes.
eof: The port is not closed at the end of the file and does not produce an exit signal. Instead, it remains open and a {Port, eof} message is sent to the process holding the port.
hide: When running on Windows, suppresses creation of a new console window when spawning the port program. (This option has no effect on other platforms.)
{parallelism, Boolean}:

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

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

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

badarg: Bad input arguments to open_port.
system_limit: All available ports in the Erlang emulator are in use.
enomem: Not enough memory to create the port.
eagain: No more available OS processes.
enametoolong: Too long external command.
emfile: No more available file descriptors (for the OS process that the Erlang emulator runs in).
enfile: Full file table (for the entire OS).
eacces: Command given in {spawn_executable, Command} does not point out an executable file.
enoent: FileName given in {spawn_executable, FileName} does not point out an existing file.

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

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

erlang:phash(Term, Range) -> Hash

Types:

Term = term()
Range = Hash = integer() >= 1

Range = 1..2^32, Hash = 1..Range

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

This BIF can be used instead of the old deprecated BIF erlang:hash/2, as it calculates better hashes for all data types, but consider using phash2/1,2 instead.

erlang:phash2(Term) -> Hash

erlang:phash2(Term, Range) -> Hash

Types:

Term = term()
Range = integer() >= 1

1..2^32
Hash = integer() >= 0

0..Range-1

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

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

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

pid_to_list(Pid) -> string()

Types:

Pid = pid()

Returns a string corresponding to the text representation of Pid.

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

port_close(Port) -> true

Types:

Port = port() | atom()

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

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

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

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

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

port_command(Port, Data) -> true

Types:

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

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

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

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

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

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

Failures:

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

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

Types:

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

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

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

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

The following Options are valid:

force: The calling process is not suspended if the port is busy, instead the port command is forced through. The call fails with a notsup exception if the driver of the port does not support this. For more information, see driver flag ERL_DRV_FLAG_SOFT_BUSY.
nosuspend: The calling process is not suspended if the port is busy, instead the port command is aborted and false is returned.

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

Failures:

badarg:
If Port is not an identifier of an open port, or the registered name of an open port. If the calling process was previously linked to the closed port, identified by Port, the exit signal from the port is guaranteed to be delivered before this badarg exception occurs.
badarg:
If Data is an invalid I/O list.
badarg:
If OptionList is an invalid option list.
notsup:
If option force has been passed, but the driver of the port does not allow forcing through a busy port.

port_connect(Port, Pid) -> true

Types:

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

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

* The error behavior differs, see the following.
* The port does not reply with {Port,connected}.
* port_connect/1 is synchronous, see the following.
* The new port owner gets linked to the port.

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

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

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

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

Failures:

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

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

Types:

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

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

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

Failures:

badarg:
If Port is not an open port or the registered name of an open port.
badarg:
If Operation cannot fit in a 32-bit integer.
badarg:
If the port driver does not support synchronous control operations.
badarg:
If the port driver so decides for any reason (probably something wrong with Operation or Data).

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

Types:

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

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

Port is a port identifier, referring to a driver.

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

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

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

Failures:

badarg:
If Port is not an identifier of an open port, or the registered name of an open port. If the calling process was previously linked to the closed port, identified by Port, the exit signal from the port is guaranteed to be delivered before this badarg exception occurs.
badarg:
If Operation does not fit in a 32-bit integer.
badarg:
If the port driver does not support synchronous control operations.
badarg:
If the port driver so decides for any reason (probably something wrong with Operation or Data).

erlang:port_info(Port) -> Result

Types:

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

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

The result contains information about the following Items:

* registered_name (if the port has a registered name)
* id
* connected
* links
* name
* input
* output

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

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

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

Types:

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

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

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

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

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

Types:

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

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

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

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

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

Types:

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

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

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

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

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

Types:

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

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

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

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

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

Types:

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

Locking is one of the following:

* false (emulator without SMP support)
* port_level (port-specific locking)
* driver_level (driver-specific locking)

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

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

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

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

Types:

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

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

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

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

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

Types:

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

Monitors represent processes that this port monitors.

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

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

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

Types:

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

Name is the command name set by open_port/2.

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

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

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

Types:

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

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

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

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

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

Types:

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

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

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

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

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

Types:

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

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

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

Types:

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

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

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

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

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

Types:

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

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

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

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

erlang:port_to_list(Port) -> string()

Types:

Port = port()

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

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

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

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

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

pre_loaded() -> [module()]

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

erlang:process_display(Pid, Type) -> true

Types:

Pid = pid()
Type = backtrace

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

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

Types:

Boolean = OldBoolean = boolean()

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

Returns the old value of the flag.

See also exit/2.

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

Types:

Module = OldModule = atom()

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

Returns the old value of the flag.

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

Types:

MinHeapSize = OldMinHeapSize = integer() >= 0

Changes the minimum heap size for the calling process.

Returns the old value of the flag.

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

Types:

MinBinVHeapSize = OldMinBinVHeapSize = integer() >= 0

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

Returns the old value of the flag.

process_flag(Flag :: priority, Level) -> OldLevel

Types:

Level = OldLevel = priority_level()

priority_level() = low | normal | high | max

Sets the process priority. Level is an atom. There are four priority levels: low, normal, high, and max. Default is normal.

Note:
Priority level max is reserved for internal use in the Erlang runtime system, and is not to be used by others.

Internally in each priority level, processes are scheduled in a round robin fashion.

Execution of processes on priority normal and low are interleaved. Processes on priority low are selected for execution less frequently than processes on priority normal.

When there are runnable processes on priority high, no processes on priority low or normal are selected for execution. Notice however, that this does not mean that no processes on priority low or normal can run when there are processes running on priority high. On the runtime system with SMP support, more processes can be running in parallel than processes on priority high, that is, a low and a high priority process can execute at the same time.

When there are runnable processes on priority max, no processes on priority low, normal, or high are selected for execution. As with priority high, processes on lower priorities can execute in parallel with processes on priority max.

Scheduling is preemptive. Regardless of priority, a process is preempted when it has consumed more than a certain number of reductions since the last time it was selected for execution.

Note:
Do not depend on the scheduling to remain exactly as it is today. Scheduling, at least on the runtime system with SMP support, is likely to be changed in a future release to use available processor cores better.

There is no automatic mechanism for avoiding priority inversion, such as priority inheritance or priority ceilings. When using priorities, take this into account and handle such scenarios by yourself.

Making calls from a high priority process into code that you have no control over can cause the high priority process to wait for a process with lower priority. That is, effectively decreasing the priority of the high priority process during the call. Even if this is not the case with one version of the code that you have no control over, it can be the case in a future version of it. This can, for example, occur if a high priority process triggers code loading, as the code server runs on priority normal.

Other priorities than normal are normally not needed. When other priorities are used, use them with care, especially priority high. A process on priority high is only to perform work for short periods. Busy looping for long periods in a high priority process does most likely cause problems, as important OTP servers run on priority normal.

Returns the old value of the flag.

process_flag(Flag :: save_calls, N) -> OldN

Types:

N = OldN = 0..10000

N must be an integer in the interval 0..10000. If N is greater than 0, call saving is made active for the process. This means that information about the N most recent global function calls, BIF calls, sends, and receives made by the process are saved in a list, which can be retrieved with process_info(Pid, last_calls). A global function call is one in which the module of the function is explicitly mentioned. Only a fixed amount of information is saved, as follows:

* A tuple {Module, Function, Arity} for function calls
* The atoms send, ’receive’, and timeout for sends and receives (’receive’ when a message is received and timeout when a receive times out)

If N = 0, call saving is disabled for the process, which is the default. Whenever the size of the call saving list is set, its contents are reset.

Returns the old value of the flag.

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

Types:

Boolean = OldBoolean = boolean()

Sets or clears flag sensitive for the current process. When a process has been marked as sensitive by calling process_flag(sensitive, true), features in the runtime system that can be used for examining the data or inner working of the process are silently disabled.

Features that are disabled include (but are not limited to) the following:

* Tracing: Trace flags can still be set for the process, but no trace messages of any kind are generated. (If flag sensitive is turned off, trace messages are again generated if any trace flags are set.)
* Sequential tracing: The sequential trace token is propagated as usual, but no sequential trace messages are generated.

process_info/1,2 cannot be used to read out the message queue or the process dictionary (both are returned as empty lists).

Stack back-traces cannot be displayed for the process.

In crash dumps, the stack, messages, and the process dictionary are omitted.

If {save_calls,N} has been set for the process, no function calls are saved to the call saving list. (The call saving list is not cleared. Furthermore, send, receive, and timeout events are still added to the list.)

Returns the old value of the flag.

process_flag(Pid, Flag, Value) -> OldValue

Types:

Pid = pid()
Flag = save_calls
Value = OldValue = integer() >= 0

Sets certain flags for the process Pid, in the same manner as process_flag/2. Returns the old value of the flag. The valid values for Flag are only a subset of those allowed in process_flag/2, namely save_calls.

Failure: badarg if Pid is not a local process.

process_info(Pid) -> Info

Types:

Pid = pid()
Info = [InfoTuple] | undefined
InfoTuple = process_info_result_item()

process_info_result_item() =
{backtrace, Bin :: binary()} |
{binary,
BinInfo ::
[{integer() >= 0,
integer() >= 0,
integer() >= 0}]} |
{catchlevel, CatchLevel :: integer() >= 0} |
{current_function,
{Module :: module(), Function :: atom(), Arity :: arity()}} |
{current_location,
{Module :: module(),
Function :: atom(),
Arity :: arity(),
Location ::
[{file, Filename :: string()} |
{line, Line :: integer() >= 1}]}} |
{current_stacktrace, Stack :: [stack_item()]} |
{dictionary, Dictionary :: [{Key :: term(), Value :: term()}]} |
{error_handler, Module :: module()} |
{garbage_collection, GCInfo :: [{atom(), integer() >= 0}]} |
{group_leader, GroupLeader :: pid()} |
{heap_size, Size :: integer() >= 0} |
{initial_call, mfa()} |
{links, PidsAndPorts :: [pid() | port()]} |
{last_calls, false | (Calls :: [mfa()])} |
{memory, Size :: integer() >= 0} |
{message_queue_len, MessageQueueLen :: integer() >= 0} |
{messages, MessageQueue :: [term()]} |
{min_heap_size, MinHeapSize :: integer() >= 0} |
{min_bin_vheap_size, MinBinVHeapSize :: integer() >= 0} |
{monitored_by, Pids :: [pid()]} |
{monitors,
Monitors ::
[{process,
Pid :: pid() | {RegName :: atom(), Node :: node()}}]} |
{priority, Level :: priority_level()} |
{reductions, Number :: integer() >= 0} |
{registered_name, Atom :: atom()} |
{sequential_trace_token,
[] | (SequentialTraceToken :: term())} |
{stack_size, Size :: integer() >= 0} |
{status,
Status ::
exiting |
garbage_collecting |
waiting |
running |
runnable |
suspended} |
{suspending,
SuspendeeList ::
[{Suspendee :: pid(),
ActiveSuspendCount :: integer() >= 0,
OutstandingSuspendCount :: integer() >= 0}]} |
{total_heap_size, Size :: integer() >= 0} |
{trace, InternalTraceFlags :: integer() >= 0} |
{trap_exit, Boolean :: boolean()}

priority_level() = low | normal | high | max

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

Returns a list containing InfoTuples with miscellaneous information about the process identified by Pid, or undefined if the process is not alive.

The order of the InfoTuples is undefined and all InfoTuples are not mandatory. The InfoTuples part of the result can be changed without prior notice.

The InfoTuples with the following items are part of the result:

* current_function
* initial_call
* status
* message_queue_len
* messages
* links
* dictionary
* trap_exit
* error_handler
* priority
* group_leader
* total_heap_size
* heap_size
* stack_size
* reductions
* garbage_collection

If the process identified by Pid has a registered name, also an InfoTuple with item registered_name appears.

For information about specific InfoTuples, see process_info/2.

Warning:
This BIF is intended for debugging only. For all other purposes, use process_info/2.

Failure: badarg if Pid is not a local process.

process_info(Pid, Item) -> InfoTuple | [] | undefined

process_info(Pid, ItemList) -> InfoTupleList | [] | undefined

Types:

Pid = pid()
ItemList = [Item]
Item = process_info_item()
InfoTupleList = [InfoTuple]
InfoTuple = process_info_result_item()

process_info_item() =
backtrace |
binary |
catchlevel |
current_function |
current_location |
current_stacktrace |
dictionary |
error_handler |
garbage_collection |
group_leader |
heap_size |
initial_call |
links |
last_calls |
memory |
message_queue_len |
messages |
min_heap_size |
min_bin_vheap_size |
monitored_by |
monitors |
priority |
reductions |
registered_name |
sequential_trace_token |
stack_size |
status |
suspending |
total_heap_size |
trace |
trap_exit

process_info_result_item() =
{backtrace, Bin :: binary()} |
{binary,
BinInfo ::
[{integer() >= 0,
integer() >= 0,
integer() >= 0}]} |
{catchlevel, CatchLevel :: integer() >= 0} |
{current_function,
{Module :: module(), Function :: atom(), Arity :: arity()}} |
{current_location,
{Module :: module(),
Function :: atom(),
Arity :: arity(),
Location ::
[{file, Filename :: string()} |
{line, Line :: integer() >= 1}]}} |
{current_stacktrace, Stack :: [stack_item()]} |
{dictionary, Dictionary :: [{Key :: term(), Value :: term()}]} |
{error_handler, Module :: module()} |
{garbage_collection, GCInfo :: [{atom(), integer() >= 0}]} |
{group_leader, GroupLeader :: pid()} |
{heap_size, Size :: integer() >= 0} |
{initial_call, mfa()} |
{links, PidsAndPorts :: [pid() | port()]} |
{last_calls, false | (Calls :: [mfa()])} |
{memory, Size :: integer() >= 0} |
{message_queue_len, MessageQueueLen :: integer() >= 0} |
{messages, MessageQueue :: [term()]} |
{min_heap_size, MinHeapSize :: integer() >= 0} |
{min_bin_vheap_size, MinBinVHeapSize :: integer() >= 0} |
{monitored_by, Pids :: [pid()]} |
{monitors,
Monitors ::
[{process,
Pid :: pid() | {RegName :: atom(), Node :: node()}}]} |
{priority, Level :: priority_level()} |
{reductions, Number :: integer() >= 0} |
{registered_name, Atom :: atom()} |
{sequential_trace_token,
[] | (SequentialTraceToken :: term())} |
{stack_size, Size :: integer() >= 0} |
{status,
Status ::
exiting |
garbage_collecting |
waiting |
running |
runnable |
suspended} |
{suspending,
SuspendeeList ::
[{Suspendee :: pid(),
ActiveSuspendCount :: integer() >= 0,
OutstandingSuspendCount :: integer() >= 0}]} |
{total_heap_size, Size :: integer() >= 0} |
{trace, InternalTraceFlags :: integer() >= 0} |
{trap_exit, Boolean :: boolean()}

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

priority_level() = low | normal | high | max

Returns information about the process identified by Pid, as specified by Item or ItemList. Returns undefined if the process is not alive.

If the process is alive and a single Item is given, the returned value is the corresponding InfoTuple, unless Item =:= registered_name and the process has no registered name. In this case, [] is returned. This strange behavior is because of historical reasons, and is kept for backward compatibility.

If ItemList is given, the result is InfoTupleList. The InfoTuples in InfoTupleList appear with the corresponding Items in the same order as the Items appeared in ItemList. Valid Items can appear multiple times in ItemList.

Note:
If registered_name is part of ItemList and the process has no name registered a {registered_name, []}, InfoTuple will appear in the resulting InfoTupleList. This behavior is different when a single Item =:= registered_name is given, and when process_info/1 is used.

The following InfoTuples with corresponding Items are valid:

{backtrace, Bin}: Binary Bin contains the same information as the output from erlang:process_display(Pid, backtrace). Use binary_to_list/1 to obtain the string of characters from the binary.
{binary, BinInfo}: BinInfo is a list containing miscellaneous information about binaries currently being referred to by this process. This InfoTuple can be changed or removed without prior notice.
{catchlevel, CatchLevel}: CatchLevel is the number of currently active catches in this process. This InfoTuple can be changed or removed without prior notice.
{current_function, {Module, Function, Arity}}: Module, Function, Arity is the current function call of the process.
{current_location, {Module, Function, Arity, Location}}: Module, Function, Arity is the current function call of the process. Location is a list of two-tuples describing the location in the source code.
{current_stacktrace, Stack}: Returns the current call stack back-trace (stacktrace) of the process. The stack has the same format as returned by erlang:get_stacktrace/0.
{dictionary, Dictionary}: Dictionary is the process dictionary.
{error_handler, Module}: Module is the error handler module used by the process (for undefined function calls, for example).
{garbage_collection, GCInfo}: GCInfo is a list containing miscellaneous information about garbage collection for this process. The content of GCInfo can be changed without prior notice.
{group_leader, GroupLeader}: GroupLeader is group leader for the I/O of the process.
{heap_size, Size}: Size is the size in words of the youngest heap generation of the process. This generation includes the process stack. This information is highly implementation-dependent, and can change if the implementation changes.
{initial_call, {Module, Function, Arity}}: Module, Function, Arity is the initial function call with which the process was spawned.
{links, PidsAndPorts}: PidsAndPorts is a list of process identifiers and port identifiers, with processes or ports to which the process has a link.
{last_calls, false|Calls}: The value is false if call saving is not active for the process (see process_flag/3). If call saving is active, a list is returned, in which the last element is the most recent called.
{memory, Size}: Size is the size in bytes of the process. This includes call stack, heap, and internal structures.
{message_queue_len, MessageQueueLen}: MessageQueueLen is the number of messages currently in the message queue of the process. This is the length of the list MessageQueue returned as the information item messages (see the following).
{messages, MessageQueue}: MessageQueue is a list of the messages to the process, which have not yet been processed.
{min_heap_size, MinHeapSize}: MinHeapSize is the minimum heap size for the process.
{min_bin_vheap_size, MinBinVHeapSize}: MinBinVHeapSize is the minimum binary virtual heap size for the process.
{monitored_by, Pids}: A list of process identifiers monitoring the process (with monitor/2).
{monitors, Monitors}: A list of monitors (started by monitor/2) that are active for the process. For a local process monitor or a remote process monitor by a process identifier, the list item is {process, Pid}. For a remote process monitor by name, the list item is {process, {RegName, Node}}.
{priority, Level}: Level is the current priority level for the process. For more information on priorities, see process_flag(priority, Level).
{reductions, Number}: Number is the number of reductions executed by the process.
{registered_name, Atom}: Atom is the registered name of the process. If the process has no registered name, this tuple is not present in the list.
{sequential_trace_token, [] | SequentialTraceToken}: SequentialTraceToken is the sequential trace token for the process. This InfoTuple can be changed or removed without prior notice.
{stack_size, Size}: Size is the stack size, in words, of the process.
{status, Status}: Status is the status of the process and is one of the following:
* exiting
* garbage_collecting
* waiting (for a message)
* running
* runnable (ready to run, but another process is running)
* suspended (suspended on a "busy" port or by the BIF erlang:suspend_process/[1,2])

{suspending, SuspendeeList}: SuspendeeList is a list of {Suspendee, ActiveSuspendCount, OutstandingSuspendCount} tuples. Suspendee is the process identifier of a process that has been, or is to be, suspended by the process identified by Pid through one of the following BIFs:
* erlang:suspend_process/2
* erlang:suspend_process/1

ActiveSuspendCount is the number of times Suspendee has been suspended by Pid. OutstandingSuspendCount is the number of not yet completed suspend requests sent by Pid, that is:
* If ActiveSuspendCount =/= 0, Suspendee is currently in the suspended state.
* If OutstandingSuspendCount =/= 0, option asynchronous of erlang:suspend_process/2 has been used and the suspendee has not yet been suspended by Pid.

Notice that ActiveSuspendCount and OutstandingSuspendCount are not the total suspend count on Suspendee, only the parts contributed by Pid.

{total_heap_size, Size}: Size is the total size, in words, of all heap fragments of the process. This includes the process stack.
{trace, InternalTraceFlags}: InternalTraceFlags is an integer representing the internal trace flag for this process. This InfoTuple can be changed or removed without prior notice.
{trap_exit, Boolean}: Boolean is true if the process is trapping exits, otherwise false.

Notice that not all implementations support all these Items.

Failures:

badarg: If Pid is not a local process.
badarg: If Item is an invalid item.

processes() -> [pid()]

Returns a list of process identifiers corresponding to all the processes currently existing on the local node.

Notice that an exiting process exists, but is not alive. That is, is_process_alive/1 returns false for an exiting process, but its process identifier is part of the result returned from processes/0.

Example:

> processes(). [<0.0.0>,<0.2.0>,<0.4.0>,<0.5.0>,<0.7.0>,<0.8.0>]

purge_module(Module) -> true

Types:

Module = atom()

Removes old code for Module. Before this BIF is used, erlang:check_process_code/2 is to be called to check that no processes execute old code in the module.

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

Failure: badarg if there is no old code for Module.

put(Key, Val) -> term()

Types:

Key = Val = term()

Adds a new Key to the process dictionary, associated with the value Val, and returns undefined. If Key exists, the old value is deleted and replaced by Val, and the function returns the old value.

Example:

> X = put(name, walrus), Y = put(name, carpenter), Z = get(name), {X, Y, Z}. {undefined,walrus,carpenter}

Note:
The values stored when put is evaluated within the scope of a catch are not retracted if a throw is evaluated, or if an error occurs.

erlang:raise(Class, Reason, Stacktrace) -> no_return()

Types:

Class = error | exit | throw
Reason = term()
Stacktrace = raise_stacktrace()

raise_stacktrace() =
[{module(), atom(), arity() | [term()]} |
{function(), [term()]}] |
[{module(), atom(), arity() | [term()], [{atom(), term()}]} |
{function(), [term()], [{atom(), term()}]}]

Stops the execution of the calling process with an exception of given class, reason, and call stack backtrace (stacktrace).

Warning:
This BIF is intended for debugging. Avoid to use it in applications, unless you really know what you are doing.

Class is error, exit, or throw. So, if it were not for the stacktrace, erlang:raise(Class, Reason, Stacktrace) is equivalent to erlang:Class(Reason).

Reason is any term. Stacktrace is a list as returned from get_stacktrace(), that is, a list of four-tuples {Module, Function, Arity | Args, Location}, where Module and Function are atoms, and the third element is an integer arity or an argument list. The stacktrace can also contain {Fun, Args, Location} tuples, where Fun is a local fun and Args is an argument list.

Element Location at the end is optional. Omitting it is equivalent to specifying an empty list.

The stacktrace is used as the exception stacktrace for the calling process; it is truncated to the current maximum stacktrace depth.

Since evaluating this function causes the process to terminate, it has no return value unless the arguments are invalid, in which case the function returns the error reason badarg. If you want to be sure not to return, you can call error(erlang:raise(Class, Reason, Stacktrace)) and hope to distinguish exceptions later.

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

Types:

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

Read the state of a timer that has been created by either erlang:start_timer(), or erlang:send_after(). TimerRef identifies the timer, and was returned by the BIF that created the timer.

Available Options:

{async, Async}: Asynchronous request for state information. Async defaults to false which will cause the operation to be performed synchronously. In this case, the Result is returned by erlang:read_timer(). When Async is true, erlang:read_timer() sends an asynchronous request for the state information to the timer service that manages the timer, and then returns ok. A message on the format {read_timer, TimerRef, Result} is sent to the caller of erlang:read_timer() when the operation has been processed.

More Options may be added in the future.

If Result is an integer, it represents the time in milli-seconds left until the timer expires.

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

Note:
The timer service that manages the timer may be co-located with another scheduler than the scheduler that the calling process is executing on. If this is the case, communication with the timer service takes much longer time than if it is located locally. If the calling process is in critical path, and can do other things while waiting for the result of this operation, you want to use option {async, true}. If using option {async, false}, the calling process will be blocked until the operation has been performed.

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

erlang:read_timer(TimerRef) -> Result

Types:

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

Read the state of a timer. The same as calling erlang:read_timer(TimerRef, []).

erlang:ref_to_list(Ref) -> string()

Types:

Ref = reference()

Returns a string corresponding to the text representation of Ref.

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

register(RegName, PidOrPort) -> true

Types:

RegName = atom()
PidOrPort = port() | pid()

Associates the name RegName with a process identifier (pid) or a port identifier. RegName, which must be an atom, can be used instead of the pid or port identifier in send operator (RegName ! Message).

Example:

> register(db, Pid). true

Failures:

badarg: If PidOrPort is not an existing local process or port.
badarg: If RegName is already in use.
badarg: If the process or port is already registered (already has a name).
badarg: If RegName is the atom undefined.

registered() -> [RegName]

Types:

RegName = atom()

Returns a list of names that have been registered using register/2, for example:

> registered(). [code_server, file_server, init, user, my_db]

erlang:resume_process(Suspendee) -> true

Types:

Suspendee = pid()

Decreases the suspend count on the process identified by Suspendee. Suspendee is previously to have been suspended through erlang:suspend_process/2 or erlang:suspend_process/1 by the process calling erlang:resume_process(Suspendee). When the suspend count on Suspendee reaches zero, Suspendee is resumed, that is, its state is changed from suspended into the state it had before it was suspended.

Warning:
This BIF is intended for debugging only.

Failures:

badarg:
If Suspendee is not a process identifier.
badarg:
If the process calling erlang:resume_process/1 had not previously increased the suspend count on the process identified by Suspendee.
badarg:
If the process identified by Suspendee is not alive.

round(Number) -> integer()

Types:

Number = number()

Returns an integer by rounding Number, for example:

round(5.5). 6

Allowed in guard tests.

self() -> pid()

Returns the process identifier of the calling process, for example:

> self(). <0.26.0>

Allowed in guard tests.

erlang:send(Dest, Msg) -> Msg

Types:

Dest = dst()
Msg = term()

dst() =
pid() |
port() |
(RegName :: atom()) |
{RegName :: atom(), Node :: node()}

Sends a message and returns Msg. This is the same as Dest ! Msg.

Dest can be a remote or local process identifier, a (local) port, a locally registered name, or a tuple {RegName, Node} for a registered name at another node.

erlang:send(Dest, Msg, Options) -> Res

Types:

Dest = dst()
Msg = term()
Options = [nosuspend | noconnect]
Res = ok | nosuspend | noconnect

dst() =
pid() |
port() |
(RegName :: atom()) |
{RegName :: atom(), Node :: node()}

Either sends a message and returns ok, or does not send the message but returns something else (see the following). Otherwise the same as erlang:send/2. For more detailed explanation and warnings, see erlang:send_nosuspend/2,3.

The options are as follows:

nosuspend: If the sender would have to be suspended to do the send, nosuspend is returned instead.
noconnect: If the destination node would have to be auto-connected to do the send, noconnect is returned instead.

Warning:
As with erlang:send_nosuspend/2,3: use with extreme care.

erlang:send_after(Time, Dest, Msg, Options) -> TimerRef

Types:

Time = integer()
Dest = pid() | atom()
Msg = term()
Options = [Option]
Abs = boolean()
Option = {abs, Abs}
TimerRef = reference()

Starts a timer. When the timer expires, the message Msg is sent to the process identified by Dest. Apart from the format of the timeout message, erlang:send_after/4 works exactly as erlang:start_timer/4.

erlang:send_after(Time, Dest, Msg) -> TimerRef

Types:

Time = integer() >= 0
Dest = pid() | atom()
Msg = term()
TimerRef = reference()

Starts a timer. The same as calling erlang:send_after(Time, Dest, Msg, []).

erlang:send_nosuspend(Dest, Msg) -> boolean()

Types:

Dest = dst()
Msg = term()

dst() =
pid() |
port() |
(RegName :: atom()) |
{RegName :: atom(), Node :: node()}

The same as erlang:send(Dest, Msg, [nosuspend]), but returns true if the message was sent and false if the message was not sent because the sender would have had to be suspended.

This function is intended for send operations to an unreliable remote node without ever blocking the sending (Erlang) process. If the connection to the remote node (usually not a real Erlang node, but a node written in C or Java) is overloaded, this function does not send the message and returns false.

The same occurs if Dest refers to a local port that is busy. For all other destinations (allowed for the ordinary send operator ’!’), this function sends the message and returns true.

This function is only to be used in rare circumstances where a process communicates with Erlang nodes that can disappear without any trace, causing the TCP buffers and the drivers queue to be over-full before the node is shut down (because of tick time-outs) by net_kernel. The normal reaction to take when this occurs is some kind of premature shutdown of the other node.

Notice that ignoring the return value from this function would result in an unreliable message passing, which is contradictory to the Erlang programming model. The message is not sent if this function returns false.

In many systems, transient states of overloaded queues are normal. The fact that this function returns false does not mean that the other node is guaranteed to be non-responsive, it could be a temporary overload. Also, a return value of true does only mean that the message can be sent on the (TCP) channel without blocking, the message is not guaranteed to arrive at the remote node. For a disconnected non-responsive node, the return value is true (mimics the behavior of operator !). The expected behavior and the actions to take when the function returns false are application- and hardware-specific.

Warning:
Use with extreme care.

erlang:send_nosuspend(Dest, Msg, Options) -> boolean()

Types:

Dest = dst()
Msg = term()
Options = [noconnect]

dst() =
pid() |
port() |
(RegName :: atom()) |
{RegName :: atom(), Node :: node()}

The same as erlang:send(Dest, Msg, [nosuspend | Options]), but with a Boolean return value.

This function behaves like erlang:send_nosuspend/2, but takes a third parameter, a list of options. The only option is noconnect, which makes the function return false if the remote node is not currently reachable by the local node. The normal behavior is to try to connect to the node, which can stall the process during a short period. The use of option noconnect makes it possible to be sure not to get the slightest delay when sending to a remote process. This is especially useful when communicating with nodes that expect to always be the connecting part (that is, nodes written in C or Java).

Whenever the function returns false (either when a suspend would occur or when noconnect was specified and the node was not already connected), the message is guaranteed not to have been sent.

Warning:
Use with extreme care.

erlang:set_cookie(Node, Cookie) -> true

Types:

Node = node()
Cookie = atom()

Sets the magic cookie of Node to the atom Cookie. If Node is the local node, the function also sets the cookie of all other unknown nodes to Cookie (see Section Distributed Erlang in the Erlang Reference Manual in System Documentation).

Failure: function_clause if the local node is not alive.

setelement(Index, Tuple1, Value) -> Tuple2

Types:

Index = integer() >= 1

1..tuple_size(Tuple1
Tuple1 = Tuple2 = tuple()
Value = term()

Returns a tuple that is a copy of argument Tuple1 with the element given by integer argument Index (the first element is the element with index 1) replaced by argument Value, for example:

> setelement(2, {10, green, bottles}, red). {10,red,bottles}

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

Types:

Item = tuple() | binary()

Returns the number of elements in a tuple or the number of bytes in a binary or bitstring, for example:

> size({morni, mulle, bwange}). 3 > size(<<11, 22, 33>>). 3

For bitstrings the number of whole bytes is returned. That is, if the number of bits in the bitstring is not divisible by 8, the resulting number of bytes is rounded down.

Allowed in guard tests.

See also tuple_size/1, byte_size/1 and bit_size/1.

spawn(Fun) -> pid()

Types:

Fun = function()

Returns the process identifier of a new process started by the application of Fun to the empty list []. Otherwise works like spawn/3.

spawn(Node, Fun) -> pid()

Types:

Node = node()
Fun = function()

Returns the process identifier of a new process started by the application of Fun to the empty list [] on Node. If Node does not exist, a useless pid is returned. Otherwise works like spawn/3.

spawn(Module, Function, Args) -> pid()

Types:

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

Returns the process identifier of a new process started by the application of Module:Function to Args.

error_handler:undefined_function(Module, Function, Args) is evaluated by the new process if Module:Function/Arity does not exist (where Arity is the length of Args). The error handler can be redefined (see process_flag/2). If error_handler is undefined, or the user has redefined the default error_handler and its replacement is undefined, a failure with reason undef occurs.

Example:

> spawn(speed, regulator, [high_speed, thin_cut]). <0.13.1>

spawn(Node, Module, Function, Args) -> pid()

Types:

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

Returns the process identifier (pid) of a new process started by the application of Module:Function to Args on Node. If Node does not exist, a useless pid is returned. Otherwise works like spawn/3.

spawn_link(Fun) -> pid()

Types:

Fun = function()

Returns the process identifier of a new process started by the application of Fun to the empty list []. A link is created between the calling process and the new process, atomically. Otherwise works like spawn/3.

spawn_link(Node, Fun) -> pid()

Types:

Node = node()
Fun = function()

Returns the process identifier (pid) of a new process started by the application of Fun to the empty list [] on Node. A link is created between the calling process and the new process, atomically. If Node does not exist, a useless pid is returned and an exit signal with reason noconnection is sent to the calling process. Otherwise works like spawn/3.

spawn_link(Module, Function, Args) -> pid()

Types:

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

Returns the process identifier of a new process started by the application of Module:Function to Args. A link is created between the calling process and the new process, atomically. Otherwise works like spawn/3.

spawn_link(Node, Module, Function, Args) -> pid()

Types:

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

Returns the process identifier (pid) of a new process started by the application of Module:Function to Args on Node. A link is created between the calling process and the new process, atomically. If Node does not exist, a useless pid is returned and an exit signal with reason noconnection is sent to the calling process. Otherwise works like spawn/3.

spawn_monitor(Fun) -> {pid(), reference()}

Types:

Fun = function()

Returns the process identifier of a new process, started by the application of Fun to the empty list [], and a reference for a monitor created to the new process. Otherwise works like spawn/3.

spawn_monitor(Module, Function, Args) -> {pid(), reference()}

Types:

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

A new process is started by the application of Module:Function to Args. The process is monitored at the same time. Returns the process identifier and a reference for the monitor. Otherwise works like spawn/3.

spawn_opt(Fun, Options) -> pid() | {pid(), reference()}

Types:

Fun = function()
Options = [Option]
Option =
link |
monitor |
{priority, Level :: priority_level()} |
{fullsweep_after, Number :: integer() >= 0} |
{min_heap_size, Size :: integer() >= 0} |
{min_bin_vheap_size, VSize :: integer() >= 0}

priority_level() = low | normal | high | max

Returns the process identifier (pid) of a new process started by the application of Fun to the empty list []. Otherwise works like spawn_opt/4.

If option monitor is given, the newly created process is monitored, and both the pid and reference for the monitor is returned.

spawn_opt(Node, Fun, Options) -> pid() | {pid(), reference()}

Types:

Node = node()
Fun = function()
Options = [Option]
Option =
link |
monitor |
{priority, Level :: priority_level()} |
{fullsweep_after, Number :: integer() >= 0} |
{min_heap_size, Size :: integer() >= 0} |
{min_bin_vheap_size, VSize :: integer() >= 0}

priority_level() = low | normal | high | max

Returns the process identifier (pid) of a new process started by the application of Fun to the empty list [] on Node. If Node does not exist, a useless pid is returned. Otherwise works like spawn_opt/4.

spawn_opt(Module, Function, Args, Options) -> pid() | {pid(), reference()}

Types:

Module = module()
Function = atom()
Args = [term()]
Options = [Option]
Option =
link |
monitor |
{priority, Level :: priority_level()} |
{fullsweep_after, Number :: integer() >= 0} |
{min_heap_size, Size :: integer() >= 0} |
{min_bin_vheap_size, VSize :: integer() >= 0}

priority_level() = low | normal | high | max

Works as spawn/3, except that an extra option list is given when creating the process.

If option monitor is given, the newly created process is monitored, and both the pid and reference for the monitor is returned.

The options are as follows:

link: Sets a link to the parent process (like spawn_link/3 does).
monitor: Monitors the new process (like monitor/2 does).
{priority, Level: Sets the priority of the new process. Equivalent to executing process_flag(priority, Level) in the start function of the new process, except that the priority is set before the process is selected for execution for the first time. For more information on priorities, see process_flag(priority, Level).
{fullsweep_after, Number}: Useful only for performance tuning. Do not use this option unless you know that there is problem with execution times or memory consumption, and ensure that the option improves matters.

The Erlang runtime system uses a generational garbage collection scheme, using an "old heap" for data that has survived at least one garbage collection. When there is no more room on the old heap, a fullsweep garbage collection is done.

Option fullsweep_after makes it possible to specify the maximum number of generational collections before forcing a fullsweep, even if there is room on the old heap. Setting the number to zero disables the general collection algorithm, that is, all live data is copied at every garbage collection.

A few cases when it can be useful to change fullsweep_after:
* If binaries that are no longer used are to be thrown away as soon as possible. (Set Number to zero.)
* A process that mostly have short-lived data is fullsweeped seldom or never, that is, the old heap contains mostly garbage. To ensure a fullsweep occasionally, set Number to a suitable value, such as 10 or 20.
* In embedded systems with a limited amount of RAM and no virtual memory, you might want to preserve memory by setting Number to zero. (The value can be set globally, see erlang:system_flag/2.)

{min_heap_size, Size}: Useful only for performance tuning. Do not use this option unless you know that there is problem with execution times or memory consumption, and ensure that the option improves matters.

Gives a minimum heap size, in words. Setting this value higher than the system default can speed up some processes because less garbage collection is done. However, setting a too high value can waste memory and slow down the system because of worse data locality. Therefore, use this option only for fine-tuning an application and to measure the execution time with various Size values.

{min_bin_vheap_size, VSize}: Useful only for performance tuning. Do not use this option unless you know that there is problem with execution times or memory consumption, and ensure that the option improves matters.

Gives a minimum binary virtual heap size, in words. Setting this value higher than the system default can speed up some processes because less garbage collection is done. However, setting a too high value can waste memory. Therefore, use this option only for fine-tuning an application and to measure the execution time with various VSize values.

spawn_opt(Node, Module, Function, Args, Options) -> pid() | {pid(), reference()}

Types:

Node = node()
Module = module()
Function = atom()
Args = [term()]
Options = [Option]
Option =
link |
monitor |
{priority, Level :: priority_level()} |
{fullsweep_after, Number :: integer() >= 0} |
{min_heap_size, Size :: integer() >= 0} |
{min_bin_vheap_size, VSize :: integer() >= 0}

priority_level() = low | normal | high | max

Returns the process identifier (pid) of a new process started by the application of Module:Function to Args on Node. If Node does not exist, a useless pid is returned. Otherwise works like spawn_opt/4.

Note:
Option monitor is not supported by spawn_opt/5.

split_binary(Bin, Pos) -> {binary(), binary()}

Types:

Bin = binary()
Pos = integer() >= 0

0..byte_size(Bin)

Returns a tuple containing the binaries that are the result of splitting Bin into two parts at position Pos. This is not a destructive operation. After the operation, there are three binaries altogether.

Example:

> B = list_to_binary("0123456789"). <<"0123456789">> > byte_size(B). 10 > {B1, B2} = split_binary(B,3). {<<"012">>,<<"3456789">>} > byte_size(B1). 3 > byte_size(B2). 7

erlang:start_timer(Time, Dest, Msg, Options) -> TimerRef

Types:

Time = integer()
Dest = pid() | atom()
Msg = term()
Options = [Option]
Abs = boolean()
Option = {abs, Abs}
TimerRef = reference()

Starts a timer. When the timer expires, the message {timeout, TimerRef, Msg} is sent to the process identified by Dest.

Available Options:

{abs, false}: This is the default. It means the Time value is interpreted as a time in milli-seconds relative current Erlang monotonic time.
{abs, true}: Absolute Time value. The Time value is interpreted as an absolute Erlang monotonic time in milli-seconds.

More Options may be added in the future.

The absolute point in time, the timer is set to expire on, has to be in the interval [erlang:system_info(start_time), erlang:system_info(end_time)]. Further, if a relative time is specified, the Time value is not allowed to be negative.

If Dest is a pid(), it must be a pid() of a process created on the current runtime system instance. This process may or may not have terminated. If Dest is an atom(), it is interpreted as the name of a locally registered process. The process referred to by the name is looked up at the time of timer expiration. No error is given if the name does not refer to a process.

If Dest is a pid(), the timer is automatically canceled if the process referred to by the pid() is not alive, or if the process exits. This feature was introduced in ERTS version 5.4.11. Notice that timers are not automatically canceled when Dest is an atom().

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

Failure: badarg if the arguments do not satisfy the requirements specified here.

erlang:start_timer(Time, Dest, Msg) -> TimerRef

Types:

Time = integer() >= 0
Dest = pid() | atom()
Msg = term()
TimerRef = reference()

Starts a timer. The same as calling erlang:start_timer(Time, Dest, Msg, []).

statistics(Item :: active_tasks) -> [ActiveTasks]

Types:

ActiveTasks = integer() >= 0

Returns a list where each element represents the amount of active processes and ports on each run queue and its associated scheduler. That is, the number of processes and ports that are ready to run, or are currently running. The element location in the list corresponds to the scheduler and its run queue. The first element corresponds to scheduler number 1 and so on. The information is not gathered atomically. That is, the result is not necessarily a consistent snapshot of the state, but instead quite efficiently gathered. See also, statistics(total_active_tasks), statistics(run_queue_lengths), and statistics(total_run_queue_lengths).

statistics(Item :: context_switches) -> {ContextSwitches, 0}

Types:

ContextSwitches = integer() >= 0

Returns the total number of context switches since the system started.

statistics(Item :: exact_reductions) -> {Total_Exact_Reductions, Exact_Reductions_Since_Last_Call}

Types:

Total_Exact_Reductions = Exact_Reductions_Since_Last_Call = integer() >= 0

Returns the number of exact reductions.

Note:
statistics(exact_reductions) is a more expensive operation than statistics(reductions), especially on an Erlang machine with SMP support.

statistics(Item :: garbage_collection) -> {Number_of_GCs, Words_Reclaimed, 0}

Types:

Number_of_GCs = Words_Reclaimed = integer() >= 0

Returns information about garbage collection, for example:

> statistics(garbage_collection). {85,23961,0}

This information can be invalid for some implementations.

statistics(Item :: io) -> {{input, Input}, {output, Output}}

Types:

Input = Output = integer() >= 0

Returns Input, which is the total number of bytes received through ports, and Output, which is the total number of bytes output to ports.

statistics(Item :: reductions) -> {Total_Reductions, Reductions_Since_Last_Call}

Types:

Total_Reductions = Reductions_Since_Last_Call = integer() >= 0

Returns information about reductions, for example:

> statistics(reductions). {2046,11}

Note:
As from ERTS 5.5 (OTP R11B), this value does not include reductions performed in current time slices of currently scheduled processes. If an exact value is wanted, use statistics(exact_reductions).

statistics(Item :: run_queue) -> integer() >= 0

Returns the total length of the run-queues. That is, the number of processes and ports that are ready to run on all available run-queues. The information is gathered atomically. That is, the result is a consistent snapshot of the state, but this operation is much more expensive compared to statistics(total_run_queue_lengths). This especially when a large amount of schedulers is used.

statistics(Item :: run_queue_lengths) -> [RunQueueLenght]

Types:

RunQueueLenght = integer() >= 0

Returns a list where each element represents the amount of processes and ports ready to run for each run queue. The element location in the list corresponds to the run queue of a scheduler. The first element corresponds to the run queue of scheduler number 1 and so on. The information is not gathered atomically. That is, the result is not necessarily a consistent snapshot of the state, but instead quite efficiently gathered. See also, statistics(total_run_queue_lengths), statistics(active_tasks), and statistics(total_active_tasks).

statistics(Item :: runtime) -> {Total_Run_Time, Time_Since_Last_Call}

Types:

Total_Run_Time = Time_Since_Last_Call = integer() >= 0

Returns information about runtime, in milliseconds.

This is the sum of the runtime for all threads in the Erlang runtime system and can therefore be greater than the wall clock time.

Example:

> statistics(runtime). {1690,1620}

statistics(Item :: scheduler_wall_time) -> [{SchedulerId, ActiveTime, TotalTime}] | undefined

Types:

SchedulerId = integer() >= 1
ActiveTime = TotalTime = integer() >= 0

Returns a list of tuples with {SchedulerId, ActiveTime, TotalTime}, where SchedulerId is an integer ID of the scheduler, ActiveTime is the duration the scheduler has been busy, and TotalTime is the total time duration since scheduler_wall_time activation. The time unit is undefined and can be subject to change between releases, OSs, and system restarts. scheduler_wall_time is only to be used to calculate relative values for scheduler-utilization. ActiveTime can never exceed TotalTime.

The definition of a busy scheduler is when it is not idle and is not scheduling (selecting) a process or port, that is:

* Executing process code
* Executing linked-in-driver or NIF code
* Executing built-in-functions, or any other runtime handling
* Garbage collecting
* Handling any other memory management

Notice that a scheduler can also be busy even if the OS has scheduled out the scheduler thread.

Returns undefined if system flag scheduler_wall_time is turned off.

The list of scheduler information is unsorted and can appear in different order between calls.

Using scheduler_wall_time to calculate scheduler-utilization:

> erlang:system_flag(scheduler_wall_time, true). false > Ts0 = lists:sort(erlang:statistics(scheduler_wall_time)), ok. ok

Some time later the user takes another snapshot and calculates scheduler-utilization per scheduler, for example:

> Ts1 = lists:sort(erlang:statistics(scheduler_wall_time)), ok. ok > lists:map(fun({{I, A0, T0}, {I, A1, T1}}) -> {I, (A1 - A0)/(T1 - T0)} end, lists:zip(Ts0,Ts1)). [{1,0.9743474730177548}, {2,0.9744843782751444}, {3,0.9995902361669045}, {4,0.9738012596572161}, {5,0.9717956667018103}, {6,0.9739235846420741}, {7,0.973237033077876}, {8,0.9741297293248656}]

Using the same snapshots to calculate a total scheduler-utilization:

> {A, T} = lists:foldl(fun({{_, A0, T0}, {_, A1, T1}}, {Ai,Ti}) -> {Ai + (A1 - A0), Ti + (T1 - T0)} end, {0, 0}, lists:zip(Ts0,Ts1)), A/T. 0.9769136803764825

Note:
scheduler_wall_time is by default disabled. To enable it, use erlang:system_flag(scheduler_wall_time, true).

statistics(Item :: total_active_tasks) -> ActiveTasks

Types:

ActiveTasks = integer() >= 0

Returns the total amount of active processes and ports in the system. That is, the number of processes and ports that are ready to run, or are currently running. The information is not gathered atomically. That is, the result is not necessarily a consistent snapshot of the state, but instead quite efficiently gathered. See also, statistics(active_tasks), statistics(run_queue_lengths), and statistics(total_run_queue_lengths).

statistics(Item :: total_run_queue_lengths) -> TotalRunQueueLenghts

Types:

TotalRunQueueLenghts = integer() >= 0

Returns the total length of the run-queues. That is, the number of processes and ports that are ready to run on all available run-queues. The information is not gathered atomically. That is, the result is not necessarily a consistent snapshot of the state, but much more efficiently gathered compared to statistics(run_queue). See also, statistics(run_queue_lengths), statistics(total_active_tasks), and statistics(active_tasks).

statistics(Item :: wall_clock) -> {Total_Wallclock_Time, Wallclock_Time_Since_Last_Call}

Types:

Total_Wallclock_Time = Wallclock_Time_Since_Last_Call = integer() >= 0

Returns information about wall clock. wall_clock can be used in the same manner as runtime, except that real time is measured as opposed to runtime or CPU time.

erlang:suspend_process(Suspendee, OptList) -> boolean()

Types:

Suspendee = pid()
OptList = [Opt]
Opt = unless_suspending | asynchronous

Increases the suspend count on the process identified by Suspendee and puts it in the suspended state if it is not already in that state. A suspended process will not be scheduled for execution until the process has been resumed.

A process can be suspended by multiple processes and can be suspended multiple times by a single process. A suspended process does not leave the suspended state until its suspend count reaches zero. The suspend count of Suspendee is decreased when erlang:resume_process(Suspendee) is called by the same process that called erlang:suspend_process(Suspendee). All increased suspend counts on other processes acquired by a process are automatically decreased when the process terminates.

The options (Opts) are as follows:

asynchronous:
A suspend request is sent to the process identified by Suspendee. Suspendee eventually suspends unless it is resumed before it could suspend. The caller of erlang:suspend_process/2 returns immediately, regardless of whether Suspendee has suspended yet or not. The point in time when Suspendee suspends cannot be deduced from other events in the system. It is only guaranteed that Suspendeeeventually suspends (unless it is resumed). If option asynchronous has not been passed, the caller of erlang:suspend_process/2 is blocked until Suspendee has suspended.
unless_suspending:
The process identified by Suspendee is suspended unless the calling process already is suspending Suspendee. If unless_suspending is combined with option asynchronous, a suspend request is sent unless the calling process already is suspending Suspendee or if a suspend request already has been sent and is in transit. If the calling process already is suspending Suspendee, or if combined with option asynchronous and a send request already is in transit, false is returned and the suspend count on Suspendee remains unchanged.

If the suspend count on the process identified by Suspendee is increased, true is returned, otherwise false.

Warning:
This BIF is intended for debugging only.

Failures:

badarg:
If Suspendee is not a process identifier.
badarg:
If the process identified by Suspendee is the same process as the process calling erlang:suspend_process/2.
badarg:
If the process identified by Suspendee is not alive.
badarg:
If the process identified by Suspendee resides on another node.
badarg:
If OptList is not a proper list of valid Opts.
system_limit:
If the process identified by Suspendee has been suspended more times by the calling process than can be represented by the currently used internal data structures. The system limit is higher than 2,000,000,000 suspends and will never be lower.

erlang:suspend_process(Suspendee) -> true

Types:

Suspendee = pid()

Suspends the process identified by Suspendee. The same as calling erlang:suspend_process(Suspendee, []).

Warning:
This BIF is intended for debugging only.

erlang:system_flag(Flag :: backtrace_depth, Depth) -> OldDepth

Types:

Depth = OldDepth = integer() >= 0

Sets the maximum depth of call stack back-traces in the exit reason element of ’EXIT’ tuples.

Returns the old value of the flag.

erlang:system_flag(Flag :: cpu_topology, CpuTopology) -> OldCpuTopology

Types:

CpuTopology = OldCpuTopology = cpu_topology()

cpu_topology() = [LevelEntry :: level_entry()] | undefined

level_entry() =
{LevelTag :: level_tag(), SubLevel :: sub_level()} |
{LevelTag :: level_tag(),
InfoList :: info_list(),
SubLevel :: sub_level()}

level_tag() = core | node | processor | thread

sub_level() =
[LevelEntry :: level_entry()] |
(LogicalCpuId :: {logical, integer() >= 0})

info_list() = []

Warning:
This argument is deprecated and scheduled for removal in ERTS 5.10/OTP R16. Instead of using this argument, use command-line argument +sct in erl(1).

When this argument is removed, a final CPU topology to use is determined at emulator boot time.

Sets the user-defined CpuTopology. The user-defined CPU topology overrides any automatically detected CPU topology. By passing undefined as CpuTopology, the system reverts to the CPU topology automatically detected. The returned value equals the value returned from erlang:system_info(cpu_topology) before the change was made.

Returns the old value of the flag.

The CPU topology is used when binding schedulers to logical processors. If schedulers are already bound when the CPU topology is changed, the schedulers are sent a request to rebind according to the new CPU topology.

The user-defined CPU topology can also be set by passing command-line argument +sct to erl(1).

For information on type CpuTopology and more, see erlang:system_info(cpu_topology) as well as the command-line flags +sct and +sbt in erl(1).

erlang:system_flag(Flag :: dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline) -> OldDirtyCPUSchedulersOnline

Types:

DirtyCPUSchedulersOnline = OldDirtyCPUSchedulersOnline = integer() >= 1

Sets the number of dirty CPU schedulers online. Range is 1 <= DirtyCPUSchedulersOnline <= N, where N is the smallest of the return values of erlang:system_info(dirty_cpu_schedulers) and erlang:system_info(schedulers_online).

Returns the old value of the flag.

The number of dirty CPU schedulers online can change if the number of schedulers online changes. For example, if 12 schedulers and 6 dirty CPU schedulers are online, and system_flag/2 is used to set the number of schedulers online to 6, then the number of dirty CPU schedulers online is automatically decreased by half as well, down to 3. Similarly, the number of dirty CPU schedulers online increases proportionally to increases in the number of schedulers online.

Note:
The dirty schedulers functionality is experimental. Enable support for dirty schedulers when building OTP to try out the functionality.

For more information, see erlang:system_info(dirty_cpu_schedulers) and erlang:system_info(dirty_cpu_schedulers_online).

erlang:system_flag(Flag :: fullsweep_after, Number) -> OldNumber

Types:

Number = OldNumber = integer() >= 0

Sets system flag fullsweep_after. Number is a non-negative integer indicating how many times generational garbage collections can be done without forcing a fullsweep collection. The value applies to new processes, while processes already running are not affected.

Returns the old value of the flag.

In low-memory systems (especially without virtual memory), setting the value to 0 can help to conserve memory.

This value can also be set through (OS) environment variable ERL_FULLSWEEP_AFTER.

erlang:system_flag(Flag :: min_heap_size, MinHeapSize) -> OldMinHeapSize

Types:

MinHeapSize = OldMinHeapSize = integer() >= 0

Sets the default minimum heap size for processes. The size is given in words. The new min_heap_size effects only processes spawned after the change of min_heap_size has been made. min_heap_size can be set for individual processes by using spawn_opt/N or process_flag/2.

Returns the old value of the flag.

erlang:system_flag(Flag :: min_bin_vheap_size, MinBinVHeapSize) -> OldMinBinVHeapSize

Types:

MinBinVHeapSize = OldMinBinVHeapSize = integer() >= 0

Sets the default minimum binary virtual heap size for processes. The size is given in words. The new min_bin_vhheap_size effects only processes spawned after the change of min_bin_vhheap_size has been made. min_bin_vheap_size can be set for individual processes by using spawn_opt/N or process_flag/2.

Returns the old value of the flag.

erlang:system_flag(Flag :: multi_scheduling, BlockState) -> OldBlockState

Types:

BlockState = block | unblock
OldBlockState = block | unblock | enabled

If multi-scheduling is enabled, more than one scheduler thread is used by the emulator. Multi-scheduling can be blocked. When multi-scheduling is blocked, only one scheduler thread schedules Erlang processes.

If BlockState =:= block, multi-scheduling is blocked. If BlockState =:= unblock and no one else blocks multi-scheduling, and this process has blocked only once, multi-scheduling is unblocked.

One process can block multi-scheduling multiple times. If a process has blocked multiple times, it must unblock exactly as many times as it has blocked before it has released its multi-scheduling block. If a process that has blocked multi-scheduling exits, it releases its blocking of multi-scheduling.

The return values are disabled, blocked, or enabled. The returned value describes the state just after the call to erlang:system_flag(multi_scheduling, BlockState) has been made. For information about the return values, see erlang:system_info(multi_scheduling).

Note:
Blocking of multi-scheduling is normally not needed. If you feel that you need to block multi-scheduling, consider it a few more times again. Blocking multi-scheduling is only to be used as a last resort, as it is most likely a very inefficient way to solve the problem.

See also erlang:system_info(multi_scheduling), erlang:system_info(multi_scheduling_blockers), and erlang:system_info(schedulers).

erlang:system_flag(Flag :: scheduler_bind_type, How) -> OldBindType

Types:

How = scheduler_bind_type() | default_bind
OldBindType = scheduler_bind_type()

scheduler_bind_type() =
no_node_processor_spread |
no_node_thread_spread |
no_spread |
processor_spread |
spread |
thread_spread |
thread_no_node_processor_spread |
unbound

Warning:
This argument is deprecated and scheduled for removal in ERTS 5.10/OTP R16. Instead of using this argument, use command-line argument +sbt in erl(1). When this argument is removed, a final scheduler bind type to use is determined at emulator boot time.

Controls if and how schedulers are bound to logical processors.

When erlang:system_flag(scheduler_bind_type, How) is called, an asynchronous signal is sent to all schedulers online, causing them to try to bind or unbind as requested.

Note:
If a scheduler fails to bind, this is often silently ignored, as it is not always possible to verify valid logical processor identifiers. If an error is reported, it is reported to error_logger. To verify that the schedulers have bound as requested, call erlang:system_info(scheduler_bindings).

Schedulers can be bound on newer Linux, Solaris, FreeBSD, and Windows systems, but more systems will be supported in future releases.

In order for the runtime system to be able to bind schedulers, the CPU topology must be known. If the runtime system fails to detect the CPU topology automatically, it can be defined. For more information on how to define the CPU topology, see command-line flag +sct in erl(1).

The runtime system does by default not bind schedulers to logical processors.

Note:
If the Erlang runtime system is the only OS process binding threads to logical processors, this improves the performance of the runtime system. However, if other OS processes (for example, another Erlang runtime system) also bind threads to logical processors, there can be a performance penalty instead. Sometimes this performance penalty can be severe. If so, it is recommended to not bind the schedulers.

Schedulers can be bound in different ways. Argument How determines how schedulers are bound and can be any of the following:

unbound: Same as command-line argument +sbt u in erl(1).
no_spread: Same as command-line argument +sbt ns in erl(1).
thread_spread: Same as command-line argument +sbt ts in erl(1).
processor_spread: Same as command-line argument +sbt ps in erl(1).
spread: Same as command-line argument +sbt s in erl(1).
no_node_thread_spread: Same as command-line argument +sbt nnts in erl(1).
no_node_processor_spread: Same as command-line argument +sbt nnps in erl(1).
thread_no_node_processor_spread: Same as command-line argument +sbt tnnps in erl(1).
default_bind: Same as command-line argument +sbt db in erl(1).

The returned value equals How before flag scheduler_bind_type was changed.

Failures:

notsup: If binding of schedulers is not supported.
badarg: If How is not one of the documented alternatives.
badarg: If CPU topology information is unavailable.

The scheduler bind type can also be set by passing command-line argument +sbt to erl(1).

For more information, see erlang:system_info(scheduler_bind_type), erlang:system_info(scheduler_bindings), as well as command-line flags +sbt and +sct in erl(1).

erlang:system_flag(Flag :: scheduler_wall_time, Boolean) -> OldBoolean

Types:

Boolean = OldBoolean = boolean()

Turns on or off scheduler wall time measurements.

For more information, see erlang:statistics(scheduler_wall_time).

erlang:system_flag(Flag :: schedulers_online, SchedulersOnline) -> OldSchedulersOnline

Types:

SchedulersOnline = OldSchedulersOnline = integer() >= 1

Sets the number of schedulers online. Range is 1 <= SchedulersOnline <= erlang:system_info(schedulers).

Returns the old value of the flag.

If the emulator was built with support for dirty schedulers, changing the number of schedulers online can also change the number of dirty CPU schedulers online. For example, if 12 schedulers and 6 dirty CPU schedulers are online, and system_flag/2 is used to set the number of schedulers online to 6, then the number of dirty CPU schedulers online is automatically decreased by half as well, down to 3. Similarly, the number of dirty CPU schedulers online increases proportionally to increases in the number of schedulers online.

For more information, see erlang:system_info(schedulers) and erlang:system_info(schedulers_online).

erlang:system_flag(Flag :: trace_control_word, TCW) -> OldTCW

Types:

TCW = OldTCW = integer() >= 0

Sets the value of the node trace control word to TCW, which is to be an unsigned integer. For more information, see the function set_tcw in Section "Match Specifications in Erlang" in the User’s Guide.

Returns the old value of the flag.

erlang:system_flag(Flag :: time_offset, Value :: finalize) -> OldState

Types:

OldState = preliminary | final | volatile

Finalizes the time offset when single time warp mode is used. If another time warp mode is used, the time offset state is left unchanged.

Returns the old state identifier. That is:

* If preliminary is returned, finalization was performed and the time offset is now final.
* If final is returned, the time offset was already in the final state. This either because another erlang:system_flag(time_offset, finalize) call, or because no time warp mode is used.
* If volatile is returned, the time offset cannot be finalized because multi time warp mode is used.

erlang:system_info(Item :: allocated_areas) -> [tuple()]

erlang:system_info(Item :: allocator) -> {Allocator, Version, Features, Settings}

erlang:system_info(Item :: alloc_util_allocators) -> [Alloc]

erlang:system_info(Item :: {allocator, Alloc}) -> [term()]

erlang:system_info(Item :: {allocator_sizes, Alloc}) -> [term()]

Types:

Allocator = undefined | glibc
Version = [integer() >= 0]
Features = [atom()]
Settings =
[{Subsystem :: atom(),
[{Parameter :: atom(), Value :: term()}]}]
Alloc = atom()

Returns various information about the allocators of the current system (emulator) as specified by Item:

allocated_areas: Returns a list of tuples with information about miscellaneous allocated memory areas.

Each tuple contains an atom describing the type of memory as first element and the amount of allocated memory in bytes as second element. When information about allocated and used memory is present, also a third element is present, containing the amount of used memory in bytes.

erlang:system_info(allocated_areas) is intended for debugging, and the content is highly implementation-dependent. The content of the results therefore changes when needed without prior notice.

Notice that the sum of these values is not the total amount of memory allocated by the emulator. Some values are part of other values, and some memory areas are not part of the result. For information about the total amount of memory allocated by the emulator, see erlang:memory/0,1.

allocator:

Returns {Allocator, Version, Features, Settings, where:
* Allocator corresponds to the malloc() implementation used. If Allocator equals undefined, the malloc() implementation used cannot be identified. glibc can be identified.
* Version is a list of integers (but not a string) representing the version of the malloc() implementation used.
* Features is a list of atoms representing the allocation features used.
* Settings is a list of subsystems, their configurable parameters, and used values. Settings can differ between different combinations of platforms, allocators, and allocation features. Memory sizes are given in bytes.

See also "System Flags Effecting erts_alloc" in erts_alloc(3).

alloc_util_allocators:

Returns a list of the names of all allocators using the ERTS internal alloc_util framework as atoms. For more information, see Section "The alloc_util framework" in erts_alloc(3).

{allocator, Alloc}:

Returns information about the specified allocator. As from ERTS 5.6.1, the return value is a list of {instance, InstanceNo, InstanceInfo} tuples, where InstanceInfo contains information about a specific instance of the allocator. As from ERTS 5.10.4, the returned list when calling erlang:system_info({allocator, mseg_alloc}) also includes an {erts_mmap, _} tuple as one element in the list. If Alloc is not a recognized allocator, undefined is returned. If Alloc is disabled, false is returned.

Notice that the information returned is highly implementation-dependent and can be changed or removed at any time without prior notice. It was initially intended as a tool when developing new allocators, but as it can be of interest for others it has been briefly documented.

The recognized allocators are listed in erts_alloc(3). After reading the erts_alloc(3) documentation, the returned information more or less speaks for itself, but it can be worth explaining some things. Call counts are presented by two values, the first value is giga calls, and the second value is calls. mbcs and sbcs denote multi-block carriers, and single-block carriers, respectively. Sizes are presented in bytes. When a size is not presented, it is the amount of something. Sizes and amounts are often presented by three values:
* The first is the current value.
* The second is the maximum value since the last call to erlang:system_info({allocator, Alloc}).
* The third is the maximum value since the emulator was started.

If only one value is present, it is the current value. fix_alloc memory block types are presented by two values. The first value is the memory pool size and the second value is the used memory size.

{allocator_sizes, Alloc}:

Returns various size information for the specified allocator. The information returned is a subset of the information returned by erlang:system_info({allocator, Alloc}).

erlang:system_info(Item :: cpu_topology) -> CpuTopology

erlang:system_info(Item :: {cpu_topology, defined | detected | used}) -> CpuTopology

Types:

CpuTopology = cpu_topology()

cpu_topology() = [LevelEntry :: level_entry()] | undefined

All LevelEntrys of a list must contain the same LevelTag, except on the top level where both node and processorLevelTags can coexist.
level_entry() =


{LevelTag :: level_tag(), SubLevel :: sub_level()} |
{LevelTag :: level_tag(),
InfoList :: info_list(),
SubLevel :: sub_level()}

{LevelTag, SubLevel} == {LevelTag, [], SubLevel}
level_tag() = core | node | processor | thread


More LevelTags can be introduced in a future release.
sub_level() =


[LevelEntry :: level_entry()] |
(LogicalCpuId :: {logical, integer() >= 0})

info_list() = []

The info_list() can be extended in a future release.

Returns various information about the CPU topology of the current system (emulator) as specified by Item:

cpu_topology: Returns the CpuTopology currently used by the emulator. The CPU topology is used when binding schedulers to logical processors. The CPU topology used is the user-defined CPU topology, if such exists, otherwise the automatically detected CPU topology, if such exists. If no CPU topology exists, undefined is returned.

node refers to Non-Uniform Memory Access (NUMA) nodes. thread refers to hardware threads (for example, Intel hyper-threads).

A level in term CpuTopology can be omitted if only one entry exists and InfoList is empty.

thread can only be a sub level to core. core can be a sub level to processor or node. processor can be on the top level or a sub level to node. node can be on the top level or a sub level to processor. That is, NUMA nodes can be processor internal or processor external. A CPU topology can consist of a mix of processor internal and external NUMA nodes, as long as each logical CPU belongs to one NUMA node. Cache hierarchy is not part of the CpuTopology type, but will be in a future release. Other things can also make it into the CPU topology in a future release. In other words, expect the CpuTopology type to change.

{cpu_topology, defined}:

Returns the user-defined CpuTopology. For more information, see command-line flag +sct in erl(1) and argument cpu_topology.

{cpu_topology, detected}:

Returns the automatically detected CpuTopologyy. The emulator detects the CPU topology on some newer Linux, Solaris, FreeBSD, and Windows systems. On Windows system with more than 32 logical processors, the CPU topology is not detected.

For more information, see argument cpu_topology.

{cpu_topology, used}: Returns CpuTopology used by the emulator. For more information, see argument cpu_topology.

erlang:system_info(Item :: build_type) -> opt | debug | purify | quantify | purecov | gcov | valgrind | gprof | lcnt | frmptr

erlang:system_info(Item :: c_compiler_used) -> {atom(), term()}

erlang:system_info(Item :: check_io) -> [term()]

erlang:system_info(Item :: compat_rel) -> integer()

erlang:system_info(Item :: creation) -> integer()

erlang:system_info(Item :: debug_compiled) -> boolean()

erlang:system_info(Item :: delayed_node_table_gc) -> infinity | integer() >= 0

erlang:system_info(Item :: dirty_cpu_schedulers) -> integer() >= 0

erlang:system_info(Item :: dirty_cpu_schedulers_online) -> integer() >= 0

erlang:system_info(Item :: dirty_io_schedulers) -> integer() >= 0

erlang:system_info(Item :: dist) -> binary()

erlang:system_info(Item :: dist_buf_busy_limit) -> integer() >= 0

erlang:system_info(Item :: dist_ctrl) -> {Node :: node(), ControllingEntity :: port() | pid()}

erlang:system_info(Item :: driver_version) -> string()

erlang:system_info(Item :: dynamic_trace) -> none | dtrace | systemtap

erlang:system_info(Item :: dynamic_trace_probes) -> boolean()

erlang:system_info(Item :: elib_malloc) -> false

erlang:system_info(Item :: eager_check_io) -> boolean()

erlang:system_info(Item :: ets_limit) -> integer() >= 1

erlang:system_info(Item :: fullsweep_after) -> {fullsweep_after, integer() >= 0}

erlang:system_info(Item :: garbage_collection) -> [{atom(), integer()}]

erlang:system_info(Item :: heap_sizes) -> [integer() >= 0]

erlang:system_info(Item :: heap_type) -> private

erlang:system_info(Item :: info) -> binary()

erlang:system_info(Item :: kernel_poll) -> boolean()

erlang:system_info(Item :: loaded) -> binary()

erlang:system_info(Item :: logical_processors | logical_processors_available | logical_processors_online) -> unknown | integer() >= 1

erlang:system_info(Item :: machine) -> string()

erlang:system_info(Item :: min_heap_size) -> {min_heap_size, MinHeapSize :: integer() >= 1}

erlang:system_info(Item :: min_bin_vheap_size) -> {min_bin_vheap_size, MinBinVHeapSize :: integer() >= 1}

erlang:system_info(Item :: modified_timing_level) -> integer() | undefined

erlang:system_info(Item :: multi_scheduling) -> disabled | blocked | enabled

erlang:system_info(Item :: multi_scheduling_blockers) -> [Pid :: pid()]

erlang:system_info(Item :: nif_version) -> string()

erlang:system_info(Item :: otp_release) -> string()

erlang:system_info(Item :: os_monotonic_time_source) -> [{atom(), term()}]

erlang:system_info(Item :: os_system_time_source) -> [{atom(), term()}]

erlang:system_info(Item :: port_count) -> integer() >= 0

erlang:system_info(Item :: port_limit) -> integer() >= 1

erlang:system_info(Item :: process_count) -> integer() >= 1

erlang:system_info(Item :: process_limit) -> integer() >= 1

erlang:system_info(Item :: procs) -> binary()

erlang:system_info(Item :: scheduler_bind_type) -> spread | processor_spread | thread_spread | thread_no_node_processor_spread | no_node_processor_spread | no_node_thread_spread | no_spread | unbound

erlang:system_info(Item :: scheduler_bindings) -> tuple()

erlang:system_info(Item :: scheduler_id) -> SchedulerId :: integer() >= 1

erlang:system_info(Item :: schedulers | schedulers_online) -> integer() >= 1

erlang:system_info(Item :: smp_support) -> boolean()

erlang:system_info(Item :: start_time) -> integer()

erlang:system_info(Item :: system_version) -> string()

erlang:system_info(Item :: system_architecture) -> string()

erlang:system_info(Item :: threads) -> boolean()

erlang:system_info(Item :: thread_pool_size) -> integer() >= 0

erlang:system_info(Item :: time_correction) -> true | false

erlang:system_info(Item :: time_offset) -> preliminary | final | volatile

erlang:system_info(Item :: time_warp_mode) -> no_time_warp | single_time_warp | multi_time_warp

erlang:system_info(Item :: tolerant_timeofday) -> enabled | disabled

erlang:system_info(Item :: trace_control_word) -> integer() >= 0

erlang:system_info(Item :: update_cpu_info) -> changed | unchanged

erlang:system_info(Item :: version) -> string()

erlang:system_info(Item :: wordsize | {wordsize, internal} | {wordsize, external}) -> 4 | 8

Returns various information about the current system (emulator) as specified by Item:

allocated_areas, allocator, alloc_util_allocators, allocator_sizes: See above.
build_type: Returns an atom describing the build type of the runtime system. This is normally the atom opt for optimized. Other possible return values are debug, purify, quantify, purecov, gcov, valgrind, gprof, and lcnt. Possible return values can be added or removed at any time without prior notice.
c_compiler_used: Returns a two-tuple describing the C compiler used when compiling the runtime system. The first element is an atom describing the name of the compiler, or undefined if unknown. The second element is a term describing the version of the compiler, or undefined if unknown.
check_io: Returns a list containing miscellaneous information about the emulators internal I/O checking. Notice that the content of the returned list can vary between platforms and over time. It is only guaranteed that a list is returned.
compat_rel: Returns the compatibility mode of the local node as an integer. The integer returned represents the Erlang/OTP release that the current emulator has been set to be backward compatible with. The compatibility mode can be configured at startup by using command-line flag +R in erl(1).
cpu_topology: See above.
creation: Returns the creation of the local node as an integer. The creation is changed when a node is restarted. The creation of a node is stored in process identifiers, port identifiers, and references. This makes it (to some extent) possible to distinguish between identifiers from different incarnations of a node. The valid creations are integers in the range 1..3, but this will probably change in a future release. If the node is not alive, 0 is returned.
debug_compiled: Returns true if the emulator has been debug compiled, otherwise false.
delayed_node_table_gc:

Returns the amount of time in seconds garbage collection of an entry in a node table is delayed. This limit can be set on startup by passing the command line flag +zdntgc to erl. For more information see the documentation of the command line flag.

dirty_cpu_schedulers:

Returns the number of dirty CPU scheduler threads used by the emulator. Dirty CPU schedulers execute CPU-bound native functions, such as NIFs, linked-in driver code, and BIFs that cannot be managed cleanly by the normal emulator schedulers.

The number of dirty CPU scheduler threads is determined at emulator boot time and cannot be changed after that. However, the number of dirty CPU scheduler threads online can be changed at any time. The number of dirty CPU schedulers can be set at startup by passing command-line flag +SDcpu or +SDPcpu in erl(1).

Notice that the dirty schedulers functionality is experimental. Enable support for dirty schedulers when building OTP to try out the functionality.

See also erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline), erlang:system_info(dirty_cpu_schedulers_online), erlang:system_info(dirty_io_schedulers), erlang:system_info(schedulers), erlang:system_info(schedulers_online), and erlang:system_flag(schedulers_online, SchedulersOnline).

dirty_cpu_schedulers_online:

Returns the number of dirty CPU schedulers online. The return value satisfies 1 <= DirtyCPUSchedulersOnline <= N, where N is the smallest of the return values of erlang:system_info(dirty_cpu_schedulers) and erlang:system_info(schedulers_online).

The number of dirty CPU schedulers online can be set at startup by passing command-line flag +SDcpu in erl(1).

Notice that the dirty schedulers functionality is experimental. Enable support for dirty schedulers when building OTP to try out the functionality.

For more information, see erlang:system_info(dirty_cpu_schedulers), erlang:system_info(dirty_io_schedulers), erlang:system_info(schedulers_online), and erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline).

dirty_io_schedulers:

Returns the number of dirty I/O schedulers as an integer. Dirty I/O schedulers execute I/O-bound native functions, such as NIFs and linked-in driver code, which cannot be managed cleanly by the normal emulator schedulers.

This value can be set at startup by passing command-line argument +SDio in erl(1).

Notice that the dirty schedulers functionality is experimental. Enable support for dirty schedulers when building OTP to try out the functionality.

For more information, see erlang:system_info(dirty_cpu_schedulers), erlang:system_info(dirty_cpu_schedulers_online), and erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline).

dist: Returns a binary containing a string of distribution information formatted as in Erlang crash dumps. For more information, see Section "How to interpret the Erlang crash dumps" in the User’s Guide.
dist_buf_busy_limit:

Returns the value of the distribution buffer busy limit in bytes. This limit can be set at startup by passing command-line flag +zdbbl to erl.

dist_ctrl: Returns a list of tuples {Node, ControllingEntity}, one entry for each connected remote node. Node is the node name and ControllingEntity is the port or process identifier responsible for the communication to that node. More specifically, ControllingEntity for nodes connected through TCP/IP (the normal case) is the socket used in communication with the specific node.
driver_version: Returns a string containing the Erlang driver version used by the runtime system. It has the form "<major ver>.<minor ver>".
dynamic_trace: Returns an atom describing the dynamic trace framework compiled into the virtual machine. It can be dtrace, systemtap, or none. For a commercial or standard build, it is always none. The other return values indicate a custom configuration (for example, ./configure --with-dynamic-trace=dtrace). For more information about dynamic tracing, see the dyntrace manual page and the README.dtrace/README.systemtap files in the Erlang source code top directory.
dynamic_trace_probes: Returns a boolean() indicating if dynamic trace probes (dtrace or systemtap) are built into the emulator. This can only be true if the Virtual Machine was built for dynamic tracing (that is, system_info(dynamic_trace) returns dtrace or systemtap).
end_time: The last Erlang monotonic time in native time unit that can be represented internally in the current Erlang runtime system instance. The time between the start time and the end time is at least a quarter of a millennium.
elib_malloc: This option will be removed in a future release. The return value will always be false, as the elib_malloc allocator has been removed.
eager_check_io: Returns the value of the erl command line flag +secio which is either true or false. See the documentation of the command line flag for information about the different values.
ets_limit: Returns the maximum number of ETS tables allowed. This limit can be increased at startup by passing command-line flag +e to erl(1) or by setting environment variable ERL_MAX_ETS_TABLES before starting the Erlang runtime system.
fullsweep_after: Returns {fullsweep_after, integer() >= 0}, which is the fullsweep_after garbage collection setting used by default. For more information, see garbage_collection described in the following.
garbage_collection: Returns a list describing the default garbage collection settings. A process spawned on the local node by a spawn or spawn_link uses these garbage collection settings. The default settings can be changed by using system_flag/2. spawn_opt/4 can spawn a process that does not use the default settings.
heap_sizes: Returns a list of integers representing valid heap sizes in words. All Erlang heaps are sized from sizes in this list.
heap_type: Returns the heap type used by the current emulator. One heap type exists:
private: Each process has a heap reserved for its use and no references between heaps of different processes are allowed. Messages passed between processes are copied between heaps.
info: Returns a binary containing a string of miscellaneous system information formatted as in Erlang crash dumps. For more information, see Section "How to interpret the Erlang crash dumps" in the User’s Guide.
kernel_poll: Returns true if the emulator uses some kind of kernel-poll implementation, otherwise false.
loaded: Returns a binary containing a string of loaded module information formatted as in Erlang crash dumps. For more information, see Section "How to interpret the Erlang crash dumps" in the User’s Guide.
logical_processors:

Returns the detected number of logical processors configured in the system. The return value is either an integer, or the atom unknown if the emulator cannot detect the configured logical processors.

logical_processors_available:

Returns the detected number of logical processors available to the Erlang runtime system. The return value is either an integer, or the atom unknown if the emulator cannot detect the available logical processors. The number of available logical processors is less than or equal to the number of logical processors online.

logical_processors_online:

Returns the detected number of logical processors online on the system. The return value is either an integer, or the atom unknown if the emulator cannot detect logical processors online. The number of logical processors online is less than or equal to the number of logical processors configured.

machine: Returns a string containing the Erlang machine name.
min_heap_size: Returns {min_heap_size, MinHeapSize}, where MinHeapSize is the current system-wide minimum heap size for spawned processes.
min_bin_vheap_size: Returns {min_bin_vheap_size, MinBinVHeapSize}, where MinBinVHeapSize is the current system-wide minimum binary virtual heap size for spawned processes.
modified_timing_level: Returns the modified timing-level (an integer) if modified timing is enabled, otherwise, undefined. For more information about modified timing, see command-line flag +T in erl(1)
multi_scheduling:

Returns disabled, blocked, or enabled:
disabled: The emulator has only one scheduler thread. The emulator does not have SMP support, or have been started with only one scheduler thread.
blocked: The emulator has more than one scheduler thread, but all scheduler threads except one are blocked, that is, only one scheduler thread schedules Erlang processes and executes Erlang code.
enabled: The emulator has more than one scheduler thread, and no scheduler threads are blocked, that is, all available scheduler threads schedule Erlang processes and execute Erlang code.

See also erlang:system_flag(multi_scheduling, BlockState), erlang:system_info(multi_scheduling_blockers), and erlang:system_info(schedulers).

multi_scheduling_blockers:

Returns a list of Pids when multi-scheduling is blocked, otherwise the empty list is returned. The Pids in the list represent all the processes currently blocking multi-scheduling. A Pid occurs only once in the list, even if the corresponding process has blocked multiple times.

See also erlang:system_flag(multi_scheduling, BlockState), erlang:system_info(multi_scheduling), and erlang:system_info(schedulers).

nif_version: Returns a string containing the version of the Erlang NIF interface used by the runtime system. It is on the form "<major ver>.<minor ver>".
otp_release:

Returns a string containing the OTP release number of the OTP release that the currently executing ERTS application is part of.

As from OTP 17, the OTP release number corresponds to the major OTP version number. No erlang:system_info() argument gives the exact OTP version. This is because the exact OTP version in the general case is difficult to determine. For more information, see the description of versions in System principles in System Documentation.

os_monotonic_time_source: Returns a list containing information about the source of OS monotonic time that is used by the runtime system.

If [] is returned, no OS monotonic time is available. The list contains two-tuples with Keys as first element, and Values as second element. The order of these tuples is undefined. The following tuples can be part of the list, but more tuples can be introduced in the future:
{function, Function}: Function is the name of the function used. This tuple always exist if OS monotonic time is available to the runtime system.
{clock_id, ClockId}: This tuple only exist if Function can be used with different clocks. ClockId corresponds to the clock identifier used when calling Function.
{resolution, OsMonotonicTimeResolution}: Highest possible resolution of current OS monotonic time source as parts per second. If no resolution information can be retrieved from the OS, OsMonotonicTimeResolution is set to the resolution of the time unit of Functions return value. That is, the actual resolution can be lower than OsMonotonicTimeResolution. Also note that the resolution does not say anything about the accuracy, and whether the precision do align with the resolution. You do, however, know that the precision is not better than OsMonotonicTimeResolution.
{extended, Extended}: Extended equals yes if the range of time values has been extended; otherwise, Extended equals no. The range needs to be extended if Function returns values that wrap fast. This typically is the case when the return value is a 32-bit value.
{parallel, Parallel}: Parallel equals yes if Function is called in parallel from multiple threads. If it is not called in parallel, because calls needs to be serialized, Parallel equals no.
{time, OsMonotonicTime}: OsMonotonicTime equals current OS monotonic time in native time unit.

os_system_time_source: Returns a list containing information about the source of OS system time that is used by the runtime system.

The list contains two-tuples with Keys as first element, and Values as second element. The order if these tuples is undefined. The following tuples can be part of the list, but more tuples can be introduced in the future:
{function, Function}: Function is the name of the funcion used.
{clock_id, ClockId}: This tuple only exist if Function can be used with different clocks. ClockId corresponds to the clock identifier used when calling Function.
{resolution, OsSystemTimeResolution}: Highest possible resolution of current OS system time source as parts per second. If no resolution information can be retrieved from the OS, OsSystemTimeResolution is set to the resolution of the time unit of Functions return value. That is, the actual resolution may be lower than OsSystemTimeResolution. Also note that the resolution does not say anything about the accuracy, and whether the precision do align with the resolution. You do, however, know that the precision is not better than OsSystemTimeResolution.
{parallel, Parallel}: Parallel equals yes if Function is called in parallel from multiple threads. If it is not called in parallel, because calls needs to be serialized, Parallel equals no.
{time, OsSystemTime}: OsSystemTime equals current OS system time in native time unit.

port_parallelism:

Returns the default port parallelism scheduling hint used. For more information, see command-line argument +spp in erl(1).

port_count: Returns the number of ports currently existing at the local node. The value is given as an integer. This is the same value as returned by length(erlang:ports()), but more efficient.
port_limit:

Returns the maximum number of simultaneously existing ports at the local node as an integer. This limit can be configured at startup by using command-line flag +Q in erl(1).

process_count: Returns the number of processes currently existing at the local node. The value is given as an integer. This is the same value as returned by length(processes()), but more efficient.
process_limit:

Returns the maximum number of simultaneously existing processes at the local node. The value is given as an integer. This limit can be configured at startup by using command-line flag +P in erl(1).

procs: Returns a binary containing a string of process and port information formatted as in Erlang crash dumps. For more information, see Section "How to interpret the Erlang crash dumps" in the User’s Guide.
scheduler_bind_type:

Returns information about how the user has requested schedulers to be bound or not bound.

Notice that even though a user has requested schedulers to be bound, they can silently have failed to bind. To inspect the scheduler bindings, call erlang:system_info(scheduler_bindings).

For more information, see command-line argument +sbt in erl(1) and erlang:system_info(scheduler_bindings).

scheduler_bindings:

Returns information about the currently used scheduler bindings.

A tuple of a size equal to erlang:system_info(schedulers) is returned. The tuple elements are integers or the atom unbound. Logical processor identifiers are represented as integers. The Nth element of the tuple equals the current binding for the scheduler with the scheduler identifier equal to N. For example, if the schedulers are bound, element(erlang:system_info(scheduler_id), erlang:system_info(scheduler_bindings)) returns the identifier of the logical processor that the calling process is executing on.

Notice that only schedulers online can be bound to logical processors.

For more information, see command-line argument +sbt in erl(1) and erlang:system_info(schedulers_online).

scheduler_id:

Returns the scheduler ID (SchedulerId) of the scheduler thread that the calling process is executing on. SchedulerId is a positive integer, where 1 <= SchedulerId <= erlang:system_info(schedulers). See also erlang:system_info(schedulers).

schedulers:

Returns the number of scheduler threads used by the emulator. Scheduler threads online schedules Erlang processes and Erlang ports, and execute Erlang code and Erlang linked-in driver code.

The number of scheduler threads is determined at emulator boot time and cannot be changed later. However, the number of schedulers online can be changed at any time.

See also erlang:system_flag(schedulers_online, SchedulersOnline), erlang:system_info(schedulers_online), erlang:system_info(scheduler_id), erlang:system_flag(multi_scheduling, BlockState), erlang:system_info(multi_scheduling), and erlang:system_info(multi_scheduling_blockers).

schedulers_online:

Returns the number of schedulers online. The scheduler identifiers of schedulers online satisfy the relationship 1 <= SchedulerId <= erlang:system_info(schedulers_online).

For more information, see erlang:system_info(schedulers) and erlang:system_flag(schedulers_online, SchedulersOnline).

smp_support: Returns true if the emulator has been compiled with SMP support, otherwise false is returned.
start_time: The Erlang monotonic time in native time unit at the time when current Erlang runtime system instance started. See also erlang:system_info(end_time).
system_version: Returns a string containing version number and some important properties, such as the number of schedulers.
system_architecture: Returns a string containing the processor and OS architecture the emulator is built for.
threads: Returns true if the emulator has been compiled with thread support, otherwise false is returned.
thread_pool_size:

Returns the number of async threads in the async thread pool used for asynchronous driver calls (driver_async()). The value is given as an integer.

time_correction:

Returns a boolean value indicating whether time correction is enabled or not.

time_offset:

Returns the state of the time offset:
preliminary: The time offset is preliminary, and will be changed at a later time when being finalized. The preliminary time offset is used during the preliminary phase of the single time warp mode.
final: The time offset is final. This either because no time warp mode is used, or because the time offset have been finalized when single time warp mode is used.
volatile: The time offset is volatile. That is, it can change at any time. This is because multi time warp mode is used.

time_warp_mode: Returns a value identifying the time warp mode being used:
no_time_warp: The no time warp mode is used.
single_time_warp: The single time warp mode is used.
multi_time_warp: The multi time warp mode is used.
tolerant_timeofday:

Returns whether a pre erts-7.0 backwards compatible compensation for sudden changes of system time is enabled or disabled. Such compensation is enabled when the time offset is final, and time correction is enabled.

trace_control_word: Returns the value of the node trace control word. For more information, see function get_tcw in Section Match Specifications in Erlang in the User’s Guide.
update_cpu_info:

The runtime system rereads the CPU information available and updates its internally stored information about the detected CPU topology and the number of logical processors configured, online, and available.

If the CPU information has changed since the last time it was read, the atom changed is returned, otherwise the atom unchanged. If the CPU information has changed, you probably want to adjust the number of schedulers online. You typically want to have as many schedulers online as logical processors available.

version:

Returns a string containing the version number of the emulator.

wordsize: Same as {wordsize, internal}.
{wordsize, internal}: Returns the size of Erlang term words in bytes as an integer, that is, 4 is returned on a 32-bit architecture, and 8 is returned on a pure 64-bit architecture. On a halfword 64-bit emulator, 4 is returned, as the Erlang terms are stored using a virtual word size of half the system word size.
{wordsize, external}: Returns the true word size of the emulator, that is, the size of a pointer. The value is given in bytes as an integer. On a pure 32-bit architecture, 4 is returned. On both a half word and on a pure 64-bit architecture, 8 is returned.

Note:
Argument scheduler has changed name to scheduler_id to avoid mix up with argument schedulers. Argument scheduler was introduced in ERTS 5.5 and renamed in ERTS 5.5.1.

erlang:system_monitor() -> MonSettings

Types:

MonSettings = undefined | {MonitorPid, Options}
MonitorPid = pid()
Options = [system_monitor_option()]

system_monitor_option() =
busy_port |
busy_dist_port |
{long_gc, integer() >= 0} |
{long_schedule, integer() >= 0} |
{large_heap, integer() >= 0}

Returns the current system monitoring settings set by erlang:system_monitor/2 as {MonitorPid, Options}, or undefined if there are no settings. The order of the options can be different from the one that was set.

erlang:system_monitor(Arg) -> MonSettings

Types:

Arg = MonSettings = undefined | {MonitorPid, Options}
MonitorPid = pid()
Options = [system_monitor_option()]

system_monitor_option() =
busy_port |
busy_dist_port |
{long_gc, integer() >= 0} |
{long_schedule, integer() >= 0} |
{large_heap, integer() >= 0}

When called with argument undefined, all system performance monitoring settings are cleared.

Calling the function with {MonitorPid, Options} as argument is the same as calling erlang:system_monitor(MonitorPid, Options).

Returns the previous system monitor settings just like erlang:system_monitor/0.

erlang:system_monitor(MonitorPid, Options) -> MonSettings

Types:

MonitorPid = pid()
Options = [system_monitor_option()]
MonSettings = undefined | {OldMonitorPid, OldOptions}
OldMonitorPid = pid()
OldOptions = [system_monitor_option()]

system_monitor_option() =
busy_port |
busy_dist_port |
{long_gc, integer() >= 0} |
{long_schedule, integer() >= 0} |
{large_heap, integer() >= 0}

Sets the system performance monitoring options. MonitorPid is a local process identifier (pid) receiving system monitor messages. The second argument is a list of monitoring options:

{long_gc, Time}: If a garbage collection in the system takes at least Time wall clock milliseconds, a message {monitor, GcPid, long_gc, Info} is sent to MonitorPid. GcPid is the pid that was garbage collected. Info is a list of two-element tuples describing the result of the garbage collection.

One of the tuples is {timeout, GcTime}, where GcTime is the time for the garbage collection in milliseconds. The other tuples are tagged with heap_size, heap_block_size stack_size, mbuf_size, old_heap_size, and old_heap_block_size. These tuples are explained in the description of trace message gc_start (see erlang:trace/3). New tuples can be added, and the order of the tuples in the Info list can be changed at any time without prior notice.

{long_schedule, Time}: If a process or port in the system runs uninterrupted for at least Time wall clock milliseconds, a message {monitor, PidOrPort, long_schedule, Info} is sent to MonitorPid. PidOrPort is the process or port that was running. Info is a list of two-element tuples describing the event.

If a pid(), the tuples {timeout, Millis}, {in, Location}, and {out, Location} are present, where Location is either an MFA ({Module, Function, Arity}) describing the function where the process was scheduled in/out, or the atom undefined.

If a port(), the tuples {timeout, Millis} and {port_op,Op} are present. Op is one of proc_sig, timeout, input, output, event, or dist_cmd, depending on which driver callback was executing.

proc_sig is an internal operation and is never to appear, while the others represent the corresponding driver callbacks timeout, ready_input, ready_output, event, and outputv (when the port is used by distribution). Value Millis in the timeout tuple informs about the uninterrupted execution time of the process or port, which always is equal to or higher than the Time value supplied when starting the trace. New tuples can be added to the Info list in a future release. The order of the tuples in the list can be changed at any time without prior notice.

This can be used to detect problems with NIFs or drivers that take too long to execute. 1 ms is considered a good maximum time for a driver callback or a NIF. However, a time-sharing system is usually to consider everything below 100 ms as "possible" and fairly "normal". However, longer schedule times can indicate swapping or a misbehaving NIF/driver. Misbehaving NIFs and drivers can cause bad resource utilization and bad overall system performance.

{large_heap, Size}: If a garbage collection in the system results in the allocated size of a heap being at least Size words, a message {monitor, GcPid, large_heap, Info} is sent to MonitorPid. GcPid and Info are the same as for long_gc earlier, except that the tuple tagged with timeout is not present.

As of ERTS 5.6, the monitor message is sent if the sum of the sizes of all memory blocks allocated for all heap generations is equal to or higher than Size. Previously the monitor message was sent if the memory block allocated for the youngest generation was equal to or higher than Size.

busy_port: If a process in the system gets suspended because it sends to a busy port, a message {monitor, SusPid, busy_port, Port} is sent to MonitorPid. SusPid is the pid that got suspended when sending to Port.
busy_dist_port: If a process in the system gets suspended because it sends to a process on a remote node whose inter-node communication was handled by a busy port, a message {monitor, SusPid, busy_dist_port, Port} is sent to MonitorPid. SusPid is the pid that got suspended when sending through the inter-node communication port Port.

Returns the previous system monitor settings just like erlang:system_monitor/0.

Note:
If a monitoring process gets so large that it itself starts to cause system monitor messages when garbage collecting, the messages enlarge the process message queue and probably make the problem worse.

Keep the monitoring process neat and do not set the system monitor limits too tight.

Failures:

badarg: If MonitorPid does not exist.
badarg: If MonitorPid is not a local process.

erlang:system_profile() -> ProfilerSettings

Types:

ProfilerSettings = undefined | {ProfilerPid, Options}
ProfilerPid = pid() | port()
Options = [system_profile_option()]

system_profile_option() =
exclusive |
runnable_ports |
runnable_procs |
scheduler |
timestamp |
monotonic_timestamp |
strict_monotonic_timestamp

Returns the current system profiling settings set by erlang:system_profile/2 as {ProfilerPid, Options}, or undefined if there are no settings. The order of the options can be different from the one that was set.

erlang:system_profile(ProfilerPid, Options) -> ProfilerSettings

Types:

ProfilerPid = pid() | port() | undefined
Options = [system_profile_option()]
ProfilerSettings =
undefined | {pid() | port(), [system_profile_option()]}

system_profile_option() =
exclusive |
runnable_ports |
runnable_procs |
scheduler |
timestamp |
monotonic_timestamp |
strict_monotonic_timestamp

Sets system profiler options. ProfilerPid is a local process identifier (pid) or port receiving profiling messages. The receiver is excluded from all profiling. The second argument is a list of profiling options:

exclusive: If a synchronous call to a port from a process is done, the calling process is considered not runnable during the call runtime to the port. The calling process is notified as inactive, and later active when the port callback returns.
monotonic_timestamp: Timestamps in profile messages will use Erlang monotonic time. The time-stamp (Ts) has the same format and value as produced by erlang:monotonic_time(nano_seconds).
runnable_procs: If a process is put into or removed from the run queue, a message, {profile, Pid, State, Mfa, Ts}, is sent to ProfilerPid. Running processes that are reinserted into the run queue after having been preempted do not trigger this message.
runnable_ports: If a port is put into or removed from the run queue, a message, {profile, Port, State, 0, Ts}, is sent to ProfilerPid.
scheduler: If a scheduler is put to sleep or awoken, a message, {profile, scheduler, Id, State, NoScheds, Ts}, is sent to ProfilerPid.
strict_monotonic_timestamp: Timestamps in profile messages will consisting of Erlang monotonic time and a monotonically increasing integer. The time-stamp (Ts) has the same format and value as produced by {erlang:monotonic_time(nano_seconds), erlang:unique_integer([monotonic])}.
timestamp: Timestamps in profile messages will include a time-stamp (Ts) that has the same form as returned by erlang:now(). This is also the default if no timestamp flag is given. If cpu_timestamp has been enabled via erlang:trace/3, this will also effect the timestamp produced in profiling messages when timestamp flag is enabled.

Note:
erlang:system_profile is considered experimental and its behavior can change in a future release.

erlang:system_time() -> integer()

Returns current Erlang system time in native time unit.

Calling erlang:system_time() is equivalent to: erlang:monotonic_time() + erlang:time_offset().

Note:
This time is not a monotonically increasing time in the general case. For more information, see the documentation of time warp modes in the ERTS User’s Guide.

erlang:system_time(Unit) -> integer()

Types:

Unit = time_unit()

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

Calling erlang:system_time(Unit) is equivalent to: erlang:convert_time_unit(erlang:system_time(), native, Unit).

Note:
This time is not a monotonically increasing time in the general case. For more information, see the documentation of time warp modes in the ERTS User’s Guide.

term_to_binary(Term) -> ext_binary()

Types:

Term = term()

Returns a binary data object that is the result of encoding Term according to the Erlang external term format.

This can be used for various purposes, for example, writing a term to a file in an efficient way, or sending an Erlang term to some type of communications channel not supported by distributed Erlang.

See also binary_to_term/1.

term_to_binary(Term, Options) -> ext_binary()

Types:

Term = term()
Options =
[compressed |
{compressed, Level :: 0..9} |
{minor_version, Version :: 0..1}]

Returns a binary data object that is the result of encoding Term according to the Erlang external term format.

If option compressed is provided, the external term format is compressed. The compressed format is automatically recognized by binary_to_term/1 as from Erlang R7B.

A compression level can be specified by giving option {compressed, Level}. Level is an integer with range 0..9, where:

* 0 - No compression is done (it is the same as giving no compressed option).
* 1 - Takes least time but may not compress as well as the higher levels.
* 6 - Default level when option compressed is provided.
* 9 - Takes most time and tries to produce a smaller result. Notice "tries" in the preceding sentence; depending on the input term, level 9 compression either does or does not produce a smaller result than level 1 compression.

Option {minor_version, Version} can be used to control some encoding details. This option was introduced in OTP R11B-4. The valid values for Version are 0 and 1.

As from OTP 17.0, {minor_version, 1} is the default. It forces any floats in the term to be encoded in a more space-efficient and exact way (namely in the 64-bit IEEE format, rather than converted to a textual representation).

As from OTP R11B-4, binary_to_term/1 can decode this representation.

{minor_version, 0} means that floats are encoded using a textual representation. This option is useful to ensure that releases before OTP R11B-4 can decode resulting binary.

See also binary_to_term/1.

throw(Any) -> no_return()

Types:

Any = term()

A non-local return from a function. If evaluated within a catch, catch returns value Any.

Example:

> catch throw({hello, there}). {hello,there}

Failure: nocatch if not evaluated within a catch.

time() -> Time

Types:

Time = calendar:time()

Returns the current time as {Hour, Minute, Second}.

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

Example:

> time(). {9,42,44}

erlang:time_offset() -> integer()

Returns the current time offset between Erlang monotonic time and Erlang system time in native time unit. Current time offset added to an Erlang monotonic time gives corresponding Erlang system time.

The time offset may or may not change during operation depending on the time warp mode used.

Note:
A change in time offset may be observed at slightly different points in time by different processes.

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

erlang:time_offset(Unit) -> integer()

Types:

Unit = time_unit()

Returns the current time offset between Erlang monotonic time and Erlang system time converted into the Unit passed as argument.

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

erlang:timestamp() -> Timestamp

Types:

Timestamp = timestamp()

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

Returns current Erlang system time on the format {MegaSecs, Secs, MicroSecs}. This format is the same as os:timestamp/0 and the deprecated erlang:now/0 uses. The reason for the existence of erlang:timestamp() is purely to simplify usage for existing code that assumes this timestamp format. Current Erlang system time can more efficiently be retrieved in the time unit of your choice using erlang:system_time/1.

The erlang:timestamp() BIF is equivalent to:

timestamp() -> ErlangSystemTime = erlang:system_time(micro_seconds), MegaSecs = ErlangSystemTime div 1000000000000, Secs = ErlangSystemTime div 1000000 - MegaSecs*1000000, MicroSecs = ErlangSystemTime rem 1000000, {MegaSecs, Secs, MicroSecs}.

It, however, uses a native implementation which does not build garbage on the heap and with slightly better performance.

Note:
This time is not a monotonically increasing time in the general case. For more information, see the documentation of time warp modes in the ERTS User’s Guide.

tl(List) -> term()

Types:

List = [term(), ...]

Returns the tail of List, that is, the list minus the first element, for example:

> tl([geesties, guilies, beasties]). [guilies, beasties]

Allowed in guard tests.

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

erlang:trace(PidSpec, How, FlagList) -> integer()

Types:

PidSpec = pid() | existing | new | all
How = boolean()
FlagList = [trace_flag()]

trace_flag() =
all |
send |
’receive’ |
procs |
call |
silent |
return_to |
running |
exiting |
garbage_collection |
timestamp |
cpu_timestamp |
monotonic_timestamp |
strict_monotonic_timestamp |
arity |
set_on_spawn |
set_on_first_spawn |
set_on_link |
set_on_first_link |
{tracer, pid() | port()}

Turns on (if How == true) or off (if How == false) the trace flags in FlagList for the process or processes represented by PidSpec.

PidSpec is either a process identifier (pid) for a local process, or one of the following atoms:

existing: All currently existing processes.
new: All processes that are created in the future.
all: All currently existing processes and all processes that are created in the future.

FlagList can contain any number of the following flags (the "message tags" refers to the list of trace messages):

all: Sets all trace flags except {tracer, Tracer} and cpu_timestamp, which are in their nature different than the others.
send: Traces sending of messages.

Message tags: send and send_to_non_existing_process.

’receive’: Traces receiving of messages.

Message tags: ’receive’.

procs: Traces process-related events.

Message tags: spawn, exit, register, unregister, link, unlink, getting_linked, and getting_unlinked.

call: Traces certain function calls. Specify which function calls to trace by calling erlang:trace_pattern/3.

Message tags: call and return_from.

silent: Used with the call trace flag. The call, return_from, and return_to trace messages are inhibited if this flag is set, but they are executed as normal if there are match specifications.

Silent mode is inhibited by executing erlang:trace(_, false, [silent|_]), or by a match specification executing the function {silent, false}.

The silent trace flag facilitates setting up a trace on many or even all processes in the system. The trace can then be activated and deactivated using the match specification function {silent,Bool}, giving a high degree of control of which functions with which arguments that trigger the trace.

Message tags: call, return_from, and return_to. Or rather, the absence of.

return_to: Used with the call trace flag. Traces the return from a traced function back to its caller. Only works for functions traced with option local to erlang:trace_pattern/3.

The semantics is that a trace message is sent when a call traced function returns, that is, when a chain of tail recursive calls ends. Only one trace message is sent per chain of tail recursive calls, so the properties of tail recursiveness for function calls are kept while tracing with this flag. Using call and return_to trace together makes it possible to know exactly in which function a process executes at any time.

To get trace messages containing return values from functions, use the {return_trace} match specification action instead.

Message tags: return_to.

running: Traces scheduling of processes.

Message tags: in and out.

exiting: Traces scheduling of exiting processes.

Message tags: in_exiting, out_exiting, and out_exited.

garbage_collection: Traces garbage collections of processes.

Message tags: gc_start and gc_end.

timestamp: Includes a time-stamp in all trace messages. The time-stamp (Ts) has the same form as returned by erlang:now().
cpu_timestamp: A global trace flag for the Erlang node that makes all trace time-stamps using the timestamp flag to be in CPU time, not wall clock time. That is, cpu_timestamp will not be used if monotonic_timestamp, or strict_monotonic_timestamp is enabled. Only allowed with PidSpec==all. If the host machine OS does not support high-resolution CPU time measurements, trace/3 exits with badarg. Notice that most OS do not synchronize this value across cores, so be prepared that time might seem to go backwards when using this option.
monotonic_timestamp: Includes an Erlang monotonic time time-stamp in all trace messages. The time-stamp (Ts) has the same format and value as produced by erlang:monotonic_time(nano_seconds). This flag overrides the cpu_timestamp flag.
strict_monotonic_timestamp: Includes an timestamp consisting of Erlang monotonic time and a monotonically increasing integer in all trace messages. The time-stamp (Ts) has the same format and value as produced by {erlang:monotonic_time(nano_seconds), erlang:unique_integer([monotonic])}. This flag overrides the cpu_timestamp flag.
arity: Used with the call trace flag. {M, F, Arity} is specified instead of {M, F, Args} in call trace messages.
set_on_spawn: Makes any process created by a traced process inherit its trace flags, including flag set_on_spawn.
set_on_first_spawn: Makes the first process created by a traced process inherit its trace flags, excluding flag set_on_first_spawn.
set_on_link: Makes any process linked by a traced process inherit its trace flags, including flag set_on_link.
set_on_first_link: Makes the first process linked to by a traced process inherit its trace flags, excluding flag set_on_first_link.
{tracer, Tracer}: Specifies where to send the trace messages. Tracer must be the process identifier of a local process or the port identifier of a local port. If this flag is not given, trace messages are sent to the process that called erlang:trace/3.

The effect of combining set_on_first_link with set_on_link is the same as having set_on_first_link alone. Likewise for set_on_spawn and set_on_first_spawn.

The tracing process receives the trace messages described in the following list. Pid is the process identifier of the traced process in which the traced event has occurred. The third tuple element is the message tag.

If flag timestamp, strict_monotonic_timestamp, or monotonic_timestamp is given, the first tuple element is trace_ts instead, and the time-stamp is added as an extra element last in the message tuple. If multiple timestamp flags are passed, timestamp has precedence over strict_monotonic_timestamp which in turn has precedence over monotonic_timestamp. All timestamp flags are remembered, so if two are passed and the one with highest precedence later is disabled the other one will become active.

{trace, Pid, ’receive’, Msg}: When Pid receives message Msg.
{trace, Pid, send, Msg, To}: When Pid sends message Msg to process To.
{trace, Pid, send_to_non_existing_process, Msg, To}: When Pid sends message Msg to the non-existing process To.
{trace, Pid, call, {M, F, Args}}: When Pid calls a traced function. The return values of calls are never supplied, only the call and its arguments.

Trace flag arity can be used to change the contents of this message, so that Arity is specified instead of Args.

{trace, Pid, return_to, {M, F, Arity}}: When Pid returns to the specified function. This trace message is sent if both the flags call and return_to are set, and the function is set to be traced on local function calls. The message is only sent when returning from a chain of tail recursive function calls, where at least one call generated a call trace message (that is, the functions match specification matched, and {message, false} was not an action).
{trace, Pid, return_from, {M, F, Arity}, ReturnValue}: When Pid returns from the specified function. This trace message is sent if flag call is set, and the function has a match specification with a return_trace or exception_trace action.
{trace, Pid, exception_from, {M, F, Arity}, {Class, Value}}: When Pid exits from the specified function because of an exception. This trace message is sent if flag call is set, and the function has a match specification with an exception_trace action.
{trace, Pid, spawn, Pid2, {M, F, Args}}: When Pid spawns a new process Pid2 with the specified function call as entry point.

Args is supposed to be the argument list, but can be any term if the spawn is erroneous.

{trace, Pid, exit, Reason}: When Pid exits with reason Reason.
{trace, Pid, link, Pid2}: When Pid links to a process Pid2.
{trace, Pid, unlink, Pid2}: When Pid removes the link from a process Pid2.
{trace, Pid, getting_linked, Pid2}: When Pid gets linked to a process Pid2.
{trace, Pid, getting_unlinked, Pid2}: When Pid gets unlinked from a process Pid2.
{trace, Pid, register, RegName}: When Pid gets the name RegName registered.
{trace, Pid, unregister, RegName}: When Pid gets the name RegName unregistered. This is done automatically when a registered process exits.
{trace, Pid, in, {M, F, Arity} | 0}: When Pid is scheduled to run. The process runs in function {M, F, Arity}. On some rare occasions, the current function cannot be determined, then the last element is 0.
{trace, Pid, out, {M, F, Arity} | 0}: When Pid is scheduled out. The process was running in function {M, F, Arity}. On some rare occasions, the current function cannot be determined, then the last element is 0.
{trace, Pid, gc_start, Info}:

Sent when garbage collection is about to be started. Info is a list of two-element tuples, where the first element is a key, and the second is the value. Do not depend on any order of the tuples. The following keys are defined:
heap_size: The size of the used part of the heap.
heap_block_size: The size of the memory block used for storing the heap and the stack.
old_heap_size: The size of the used part of the old heap.
old_heap_block_size: The size of the memory block used for storing the old heap.
stack_size: The size of the stack.
recent_size: The size of the data that survived the previous garbage collection.
mbuf_size: The combined size of message buffers associated with the process.
bin_vheap_size: The total size of unique off-heap binaries referenced from the process heap.
bin_vheap_block_size: The total size of binaries allowed in the virtual heap in the process before doing a garbage collection.
bin_old_vheap_size: The total size of unique off-heap binaries referenced from the process old heap.
bin_old_vheap_block_size: The total size of binaries allowed in the virtual old heap in the process before doing a garbage collection.

All sizes are in words.

{trace, Pid, gc_end, Info}: Sent when garbage collection is finished. Info contains the same kind of list as in message gc_start, but the sizes reflect the new sizes after garbage collection.

If the tracing process dies, the flags are silently removed.

Only one process can trace a particular process. Therefore, attempts to trace an already traced process fail.

Returns: A number indicating the number of processes that matched PidSpec. If PidSpec is a process identifier, the return value is 1. If PidSpec is all or existing, the return value is the number of processes running, excluding tracer processes. If PidSpec is new, the return value is 0.

Failure: badarg if the specified arguments are not supported. For example, cpu_timestamp is not supported on all platforms.

erlang:trace_delivered(Tracee) -> Ref

Types:

Tracee = pid() | all
Ref = reference()

The delivery of trace messages is dislocated on the time-line compared to other events in the system. If you know that Tracee has passed some specific point in its execution, and you want to know when at least all trace messages corresponding to events up to this point have reached the tracer, use erlang:trace_delivered(Tracee). A {trace_delivered, Tracee, Ref} message is sent to the caller of erlang:trace_delivered(Tracee) when it is guaranteed that all trace messages are delivered to the tracer up to the point that Tracee reached at the time of the call to erlang:trace_delivered(Tracee).

Notice that message trace_delivered does not imply that trace messages have been delivered. Instead it implies that all trace messages that are to be delivered have been delivered. It is not an error if Tracee is not, and has not been traced by someone, but if this is the case, no trace messages have been delivered when the trace_delivered message arrives.

Notice that that Tracee must refer to a process currently, or previously existing on the same node as the caller of erlang:trace_delivered(Tracee) resides on. The special Tracee atom all denotes all processes that currently are traced in the node.

Example: Process A is Tracee, port B is tracer, and process C is the port owner of B. C wants to close B when A exits. To ensure that the trace is not truncated, C can call erlang:trace_delivered(A), when A exits, and wait for message {trace_delivered, A, Ref} before closing B.

Failure: badarg if Tracee does not refer to a process (dead or alive) on the same node as the caller of erlang:trace_delivered(Tracee) resides on.

erlang:trace_info(PidOrFunc, Item) -> Res

Types:

PidOrFunc = pid() | new | {Module, Function, Arity} | on_load
Module = module()
Function = atom()
Arity = arity()
Item =
flags |
tracer |
traced |
match_spec |
meta |
meta_match_spec |
call_count |
call_time |
all
Res = trace_info_return()

trace_info_return() =
undefined |
{flags, [trace_info_flag()]} |
{tracer, pid() | port() | []} |
trace_info_item_result() |
{all, [trace_info_item_result()] | false | undefined}

trace_info_item_result() =
{traced, global | local | false | undefined} |
{match_spec, trace_match_spec() | false | undefined} |
{meta, pid() | port() | false | undefined | []} |
{meta_match_spec, trace_match_spec() | false | undefined} |
{call_count, integer() >= 0 | boolean() | undefined} |
{call_time,
[{pid(),
integer() >= 0,
integer() >= 0,
integer() >= 0}] |
boolean() |
undefined}

trace_info_flag() =
send |
’receive’ |
set_on_spawn |
call |
return_to |
procs |
set_on_first_spawn |
set_on_link |
running |
garbage_collection |
timestamp |
monotonic_timestamp |
strict_monotonic_timestamp |
arity

trace_match_spec() = [{[term()] | ’_’, [term()], [term()]}]

Returns trace information about a process or function.

To get information about a process, PidOrFunc is to be a process identifier (pid) or the atom new. The atom new means that the default trace state for processes to be created is returned.

The following Items are valid:

flags: Returns a list of atoms indicating what kind of traces is enabled for the process. The list is empty if no traces are enabled, and one or more of the followings atoms if traces are enabled: send, ’receive’, set_on_spawn, call, return_to, procs, set_on_first_spawn, set_on_link, running, garbage_collection, timestamp, and arity. The order is arbitrary.
tracer: Returns the identifier for process or port tracing this process. If this process is not being traced, the return value is [].

To get information about a function, PidOrFunc is to be the three-element tuple {Module, Function, Arity} or the atom on_load. No wild cards are allowed. Returns undefined if the function does not exist, or false if the function is not traced.

The following Items are valid::

traced: Returns global if this function is traced on global function calls, local if this function is traced on local function calls (that is, local and global function calls), and false if local or global function calls are not traced.
match_spec: Returns the match specification for this function, if it has one. If the function is locally or globally traced but has no match specification defined, the returned value is [].
meta: Returns the meta-trace tracer process or port for this function, if it has one. If the function is not meta-traced, the returned value is false. If the function is meta-traced but has once detected that the tracer process is invalid, the returned value is [].
meta_match_spec: Returns the meta-trace match specification for this function, if it has one. If the function is meta-traced but has no match specification defined, the returned value is [].
call_count: Returns the call count value for this function or true for the pseudo function on_load if call count tracing is active. Otherwise false is returned. See also erlang:trace_pattern/3.
call_time: Returns the call time values for this function or true for the pseudo function on_load if call time tracing is active. Otherwise false is returned. The call time values returned, [{Pid, Count, S, Us}], is a list of each process that executed the function and its specific counters. See also erlang:trace_pattern/3.
all: Returns a list containing the {Item, Value} tuples for all other items, or returns false if no tracing is active for this function.

The return value is {Item, Value}, where Value is the requested information as described earlier. If a pid for a dead process was given, or the name of a non-existing function, Value is undefined.

If PidOrFunc is on_load, the information returned refers to the default value for code that will be loaded.

erlang:trace_pattern(MFA, MatchSpec) -> integer() >= 0

Types:

MFA = trace_pattern_mfa()
MatchSpec =
(MatchSpecList :: trace_match_spec()) |
boolean() |
restart |
pause

trace_pattern_mfa() = {atom(), atom(), arity() | ’_’} | on_load

trace_match_spec() = [{[term()] | ’_’, [term()], [term()]}]

The same as erlang:trace_pattern(MFA, MatchSpec, []), retained for backward compatibility.

erlang:trace_pattern(MFA, MatchSpec, FlagList) -> integer() >= 0

Types:

MFA = trace_pattern_mfa()
MatchSpec =
(MatchSpecList :: trace_match_spec()) |
boolean() |
restart |
pause
FlagList = [trace_pattern_flag()]

trace_pattern_mfa() = {atom(), atom(), arity() | ’_’} | on_load

trace_match_spec() = [{[term()] | ’_’, [term()], [term()]}]

trace_pattern_flag() =
global |
local |
meta |
{meta, Pid :: pid()} |
call_count |
call_time

Enables or disables call tracing for one or more functions. Must be combined with erlang:trace/3 to set the call trace flag for one or more processes.

Conceptually, call tracing works as follows. Inside the Erlang Virtual Machine, a set of processes and a set of functions are to be traced. If a traced process calls a traced function, the trace action is taken. Otherwise, nothing happens.

To add or remove one or more processes to the set of traced processes, use erlang:trace/3.

To add or remove functions to the set of traced functions, use erlang:trace_pattern/3.

The BIF erlang:trace_pattern/3 can also add match specifications to a function. A match specification comprises a pattern that the function arguments must match, a guard expression that must evaluate to true, and an action to be performed. The default action is to send a trace message. If the pattern does not match or the guard fails, the action is not executed.

Argument MFA is to be a tuple, such as {Module, Function, Arity}, or the atom on_load (described in the following). It can be the module, function, and arity for a function (or a BIF in any module). The atom ’_’ can be used as a wild card in any of the following ways:

{Module,Function,’_’}: All functions of any arity named Function in module Module.
{Module,’_’,’_’}: All functions in module Module.
{’_’,’_’,’_’}: All functions in all loaded modules.

Other combinations, such as {Module,’_’,Arity}, are not allowed. Local functions match wild cards only if option local is in FlagList.

If argument MFA is the atom on_load, the match specification and flag list are used on all modules that are newly loaded.

Argument MatchSpec can take the following forms:

false: Disables tracing for the matching functions. Any match specification is removed.
true: Enables tracing for the matching functions.
MatchSpecList: A list of match specifications. An empty list is equivalent to true. For a description of match specifications, see the User’s Guide.
restart: For the FlagList options call_count and call_time: restarts the existing counters. The behavior is undefined for other FlagList options.
pause: For the FlagList options call_count and call_time: pauses the existing counters. The behavior is undefined for other FlagList options.

Parameter FlagList is a list of options. The following are the valid options:

global: Turns on or off call tracing for global function calls (that is, calls specifying the module explicitly). Only exported functions match and only global calls generate trace messages. This is the default.
local: Turns on or off call tracing for all types of function calls. Trace messages are sent whenever any of the specified functions are called, regardless of how they are called. If flag return_to is set for the process, a return_to message is also sent when this function returns to its caller.
meta | {meta, Pid}: Turns on or off meta-tracing for all types of function calls. Trace messages are sent to the tracer process or port Pid whenever any of the specified functions are called, regardless of how they are called. If no Pid is specified, self() is used as a default tracer process.

Meta-tracing traces all processes and does not care about the process trace flags set by trace/3, the trace flags are instead fixed to [call, timestamp].

The match specification function {return_trace} works with meta-trace and sends its trace message to the same tracer process.

call_count: Starts (MatchSpec == true) or stops (MatchSpec == false) call count tracing for all types of function calls. For every function, a counter is incremented when the function is called, in any process. No process trace flags need to be activated.

If call count tracing is started while already running, the count is restarted from zero. To pause running counters, use MatchSpec == pause. Paused and running counters can be restarted from zero with MatchSpec == restart.

To read the counter value, use erlang:trace_info/2.

call_time: Starts (MatchSpec == true) or stops (MatchSpec == false) call time tracing for all types of function calls. For every function, a counter is incremented when the function is called. Time spent in the function is accumulated in two other counters, seconds and microseconds. The counters are stored for each call traced process.

If call time tracing is started while already running, the count and time is restarted from zero. To pause running counters, use MatchSpec == pause. Paused and running counters can be restarted from zero with MatchSpec == restart.

To read the counter value, use erlang:trace_info/2.

The options global and local are mutually exclusive, and global is the default (if no options are specified). The options call_count and meta perform a kind of local tracing, and cannot be combined with global. A function can be globally or locally traced. If global tracing is specified for a set of functions, then local, meta, call time, and call count tracing for the matching set of local functions is disabled, and conversely.

When disabling trace, the option must match the type of trace set on the function. That is, local tracing must be disabled with option local and global tracing with option global (or no option), and so forth.

Part of a match specification list cannot be changed directly. If a function has a match specification, it can be replaced with a new one. To change an existing match specification, use the BIF erlang:trace_info/2 to retrieve the existing match specification.

Returns the number of functions matching argument MFA. This is zero if none matched.

trunc(Number) -> integer()

Types:

Number = number()

Returns an integer by truncating Number, for example:

> trunc(5.5). 5

Allowed in guard tests.

tuple_size(Tuple) -> integer() >= 0

Types:

Tuple = tuple()

Returns an integer that is the number of elements in Tuple, for example:

> tuple_size({morni, mulle, bwange}). 3

Allowed in guard tests.

tuple_to_list(Tuple) -> [term()]

Types:

Tuple = tuple()

Returns a list corresponding to Tuple. Tuple can contain any Erlang terms.

Example:

> tuple_to_list({share, {’Ericsson_B’, 163}}). [share,{’Ericsson_B’,163}]

erlang:universaltime() -> DateTime

Types:

DateTime = calendar:datetime()

Returns the current date and time according to Universal Time Coordinated (UTC) in the form {{Year, Month, Day}, {Hour, Minute, Second}} if supported by the underlying OS. Otherwise erlang:universaltime() is equivalent to erlang:localtime().

Example:

> erlang:universaltime(). {{1996,11,6},{14,18,43}}

erlang:universaltime_to_localtime(Universaltime) -> Localtime

Types:

Localtime = Universaltime = calendar:datetime()

Converts Universal Time Coordinated (UTC) date and time to local date and time in the form {{Year, Month, Day}, {Hour, Minute, Second}} if supported by the underlying OS. Otherwise no conversion is done, and Universaltime is returned.

Example:

> erlang:universaltime_to_localtime({{1996,11,6},{14,18,43}}). {{1996,11,7},{15,18,43}}

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

erlang:unique_integer() -> integer()

Generates and returns an integer unique on current runtime system instance. The same as calling erlang:unique_integer([]).

erlang:unique_integer(ModifierList) -> integer()

Types:

ModifierList = [Modifier]
Modifier = positive | monotonic

Generates and returns an integer unique on current runtime system instance. The integer is unique in the sense that this BIF, using the same set of modifiers, will not return the same integer more than once on the current runtime system instance. Each integer value can of course be constructed by other means.

By default, when [] is passed as ModifierList, both negative and positive integers can be returned. This in order to utilize the range of integers that do not need heap memory allocation as much as possible. By default the returned integers are also only guaranteed to be unique, that is, any returned integer can be smaller or larger than previously returned integers.

Valid Modifiers:

positive: Return only positive integers.

Note that by passing the positive modifier you will get heap allocated integers (bignums) quicker.

monotonic: Return strictly monotonically increasing integers corresponding to creation time. That is, the integer returned will always be larger than previously returned integers on the current runtime system instance.

These values can be used to determine order between events on the runtime system instance. That is, if both X = erlang:unique_integer([monotonic]) and Y = erlang:unique_integer([monotonic]) are executed by different processes (or the same process) on the same runtime system instance and X < Y we know that X was created before Y.

Warning:
Strictly monotonically increasing values are inherently quite expensive to generate and scales poorly. This is because the values need to be synchronized between cpu cores. That is, do not pass the monotonic modifier unless you really need strictly monotonically increasing values.

All valid Modifiers can be combined. Repeated (valid) Modifiers in the ModifierList are ignored.

Note:
Note that the set of integers returned by unique_integer/1 using different sets of Modifiers will overlap. For example, by calling unique_integer([monotonic]), and unique_integer([positive, monotonic]) repeatedly, you will eventually see some integers being returned by both calls.

Failures:

badarg: if ModifierList is not a proper list.
badarg: if Modifier is not a valid modifier.

unlink(Id) -> true

Types:

Id = pid() | port()

Removes the link, if there is one, between the calling process and the process or port referred to by Id.

Returns true and does not fail, even if there is no link to Id, or if Id does not exist.

Once unlink(Id) has returned, it is guaranteed that the link between the caller and the entity referred to by Id has no effect on the caller in the future (unless the link is setup again). If the caller is trapping exits, an {’EXIT’, Id, _} message from the link can have been placed in the caller’s message queue before the call.

Notice that the {’EXIT’, Id, _} message can be the result of the link, but can also be the result of Id calling exit/2. Therefore, it can be appropriate to clean up the message queue when trapping exits after the call to unlink(Id), as follows:

unlink(Id), receive {’EXIT’, Id, _} -> true after 0 -> true end

Note:
Prior to OTP release R11B (ERTS version 5.5) unlink/1 behaved completely asynchronously, i.e., the link was active until the "unlink signal" reached the linked entity. This had an undesirable effect, as you could never know when you were guaranteed not to be effected by the link.

The current behavior can be viewed as two combined operations: asynchronously send an "unlink signal" to the linked entity and ignore any future results of the link.

unregister(RegName) -> true

Types:

RegName = atom()

Removes the registered name RegName associated with a process identifier or a port identifier, for example:

> unregister(db). true

Users are advised not to unregister system processes.

Failure: badarg if RegName is not a registered name.

whereis(RegName) -> pid() | port() | undefined

Types:

RegName = atom()

Returns the process identifier or port identifier with the registered name RegName. Returns undefined if the name is not registered.

Example:

> whereis(db). <0.43.0>

erlang:yield() -> true

Voluntarily lets other processes (if any) get a chance to execute. Using erlang:yield() is similar to receive after 1 -> ok end, except that yield() is faster.

Warning:
There is seldom or never any need to use this BIF, especially in the SMP emulator, as other processes have a chance to run in another scheduler thread anyway. Using this BIF without a thorough grasp of how the scheduler works can cause performance degradation.

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