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erlang(3erl) | Erlang Module Definition | erlang(3erl) |
NAME¶
erlang - The Erlang BIFs.DESCRIPTION¶
By convention, most Built-In Functions (BIFs) are included in this module. Some of the BIFs are viewed more or less as part of the Erlang programming language and are auto-imported. Thus, it is not necessary to specify the module name. For example, the calls atom_to_list(Erlang) and erlang:atom_to_list(Erlang) are identical. Auto-imported BIFs are listed without module prefix. BIFs listed with module prefix are not auto-imported. BIFs can fail for various reasons. All BIFs fail with reason badarg if they are called with arguments of an incorrect type. The other reasons are described in the description of each individual BIF. Some BIFs can be used in guard tests and are marked with "Allowed in guard tests".DATA TYPES¶
ext_binary()
A binary data object, structured according to the Erlang external term
format.
message_queue_data() = off_heap | on_heap
See process_flag(message_queue_data, MQD).
timestamp() ={MegaSecs :: integer() >= 0,Secs :: integer() >= 0,MicroSecs :: integer() >= 0}
See erlang:timestamp/0.
time_unit() =integer() >= 1 |second |millisecond |microsecond |nanosecond |native |perf_counter |deprecated_time_unit()
Supported time unit representations:
The time_unit/0 type can be extended. To convert time values between time
units, use erlang:convert_time_unit/3.
- PartsPerSecond :: integer() >= 1:
- Time unit expressed in parts per second. That is, the time unit equals 1/PartsPerSecond second.
- second:
- Symbolic representation of the time unit represented by the integer 1.
- millisecond:
- Symbolic representation of the time unit represented by the integer 1000.
- microsecond:
- Symbolic representation of the time unit represented by the integer 1000000.
- nanosecond:
- Symbolic representation of the time unit represented by the integer 1000000000.
- native:
- Symbolic representation of the native time unit used by the Erlang runtime system.
The native time unit is determined at runtime system start, and remains
the same until the runtime system terminates. If a runtime system is stopped
and then started again (even on the same machine), the native time unit
of the new runtime system instance can differ from the native time unit
of the old runtime system instance.
One can get an approximation of the native time unit by calling
erlang:convert_time_unit(1, second, native). The result equals
the number of whole native time units per second. If the number of
native time units per second does not add up to a whole number, the
result is rounded downwards.
Note:
The value of the native time unit gives you more or less no information
about the quality of time values. It sets a limit for the resolution
and for the precision of time values, but it gives no information
about the accuracy of time values. The resolution of the native
time unit and the resolution of time values can differ significantly.
- perf_counter:
- Symbolic representation of the performance counter time unit used by the Erlang runtime system.
The perf_counter time unit behaves much in the same way as the
native time unit. That is, it can differ between runtime restarts. To
get values of this type, call os:perf_counter/0.
- deprecated_time_unit():
- Deprecated symbolic representations kept for backwards-compatibility.
deprecated_time_unit() =seconds | milli_seconds | micro_seconds | nano_seconds
The time_unit() type also consist of the following
deprecated symbolic time units:
- seconds:
- Same as second.
- milli_seconds:
- Same as millisecond.
- micro_seconds:
- Same as microsecond.
- nano_seconds:
- Same as nanosecond.
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). 3Allowed in guard tests.
erlang:adler32(Data) -> integer() >= 0
Types:
Data = iodata()
Computes and returns the adler32 checksum for Data.
erlang:adler32(OldAdler, Data) -> integer() >= 0
Types:
OldAdler = integer() >= 0
Data = iodata()
Continues computing the adler32 checksum by combining the previous checksum,
OldAdler, with the checksum of Data.
The following code:
X = erlang:adler32(Data1), Y = erlang:adler32(X,Data2).assigns the same value to Y as this:
Y = erlang:adler32([Data1,Data2]).
erlang:adler32_combine(FirstAdler, SecondAdler, SecondSize) -> integer() >= 0
Types:
FirstAdler = SecondAdler = SecondSize = integer() >= 0
Combines two previously computed adler32 checksums. This computation requires
the size of the data object for the second checksum to be known.
The following code:
Y = erlang:adler32(Data1), Z = erlang:adler32(Y,Data2).assigns the same value to Z as this:
X = erlang:adler32(Data1), Y = erlang:adler32(Data2), Z = erlang:adler32_combine(X,Y,iolist_size(Data2)).
erlang:append_element(Tuple1, Term) -> Tuple2
Types:
Tuple1 = Tuple2 = tuple()
Term = term()
Returns a new tuple that has one element more than Tuple1, and contains
the elements in Tuple1 followed by Term as the last element.
Semantically equivalent to list_to_tuple(tuple_to_list(Tuple1) ++
[Term]), but much faster. Example:
> erlang:append_element({one, two}, three). {one,two,three}
apply(Fun, Args) -> term()
Types:
Fun = function()
Args = [term()]
Calls a fun, passing the elements in Args as arguments.
If the number of elements in the arguments are known at compile time, the call
is better written as Fun(Arg1, Arg2, ... ArgN).
Warning:
Earlier, Fun could also be specified as {Module, Function},
equivalent to apply(Module, Function, Args). This use is deprecated
and will stop working in a future release.
apply(Module, Function, Args) -> term()
Types:
Module = module()
Function = atom()
Args = [term()]
Returns the result of applying Function in Module to Args.
The applied function must be exported from Module. The arity of the
function is the length of Args. Example:
> apply(lists, reverse, [[a, b, c]]). [c,b,a] > apply(erlang, atom_to_list, ['Erlang']). "Erlang"If the number of arguments are known at compile time, the call is better written as Module:Function(Arg1, Arg2, ..., ArgN). Failure: error_handler:undefined_function/3 is called if the applied function is not exported. The error handler can be redefined (see process_flag/2). If error_handler is undefined, or if the user has redefined the default error_handler so the replacement module is undefined, an error with reason undef is generated.
atom_to_binary(Atom, Encoding) -> binary()
Types:
Atom = atom()
Encoding = latin1 | unicode | utf8
Returns a binary corresponding to the text representation of Atom. If
Encoding is latin1, one byte exists for each character in the
text representation. If Encoding is utf8 or unicode, the
characters are encoded using UTF-8 (that is, characters from 128 through 255
are encoded in two bytes).
Note:
atom_to_binary(Atom, latin1) never fails, as 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) then fails if the text
representation for Atom contains a Unicode character > 255.
Example:
> atom_to_binary('Erlang', latin1). <<"Erlang">>
atom_to_list(Atom) -> string()
Types:
Atom = atom()
Returns a string corresponding to the text representation of Atom, for
example:
> atom_to_list('Erlang'). "Erlang"
binary_part(Subject, PosLen) -> binary()
Types:
Subject = binary()
PosLen = {Start :: integer() >= 0, Length :: integer()}
Extracts the part of the binary described by PosLen.
Negative length can be used to extract bytes at the end of a binary, for
example:
1> Bin = <<1,2,3,4,5,6,7,8,9,10>>. 2> binary_part(Bin,{byte_size(Bin), -5}). <<6,7,8,9,10>>Failure: badarg if PosLen in any way references outside the binary. Start is zero-based, that is:
1> Bin = <<1,2,3>> 2> binary_part(Bin,{0,2}). <<1,2>>For details about the PosLen semantics, see binary(3erl). Allowed in guard tests.
binary_part(Subject, Start, Length) -> binary()
Types:
Subject = binary()
Start = integer() >= 0
Length = integer()
The same as binary_part(Subject, {Start, Length}).
Allowed in guard tests.
binary_to_atom(Binary, Encoding) -> atom()
Types:
Binary = binary()
Encoding = latin1 | unicode | utf8
Returns the atom whose text representation is Binary. If Encoding
is latin1, no translation of bytes in the binary is done. If
Encoding is utf8 or unicode, the binary must contain
valid UTF-8 sequences. Only Unicode characters up to 255 are allowed.
Note:
binary_to_atom(Binary, utf8) fails if the binary contains Unicode
characters > 255. In a future release, such Unicode characters can be
allowed and binary_to_atom(Binary, utf8) does then not fail. For more
information about Unicode support in atoms, see the note on UTF-8 encoded
atoms in section "External Term Format" in the User's Guide.
Examples:
> binary_to_atom(<<"Erlang">>, latin1). 'Erlang' > binary_to_atom(<<1024/utf8>>, utf8). ** 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">>). 2.2017764Failure: 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">>). 123Failure: 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). 1023Failure: badarg if Binary contains a bad representation of an integer.
binary_to_list(Binary) -> [byte()]
Types:
Binary = binary()
Returns a list of integers corresponding to the bytes of Binary.
binary_to_list(Binary, Start, Stop) -> [byte()]
Types:
Binary = binary()
Start = Stop = integer() >= 1
1..byte_size(Binary)
As binary_to_list/1, but returns a list of integers corresponding to the
bytes from position Start to position Stop in Binary. The
positions in the binary are numbered starting from 1.
Note:
The one-based indexing for binaries used by this function is deprecated.
New code is to use binary:bin_to_list/3 in STDLIB instead. All
functions in module binary consistently use zero-based indexing.
binary_to_term(Binary) -> term()
Types:
Binary = ext_binary()
Returns an Erlang term that is the result of decoding binary object
Binary, which must be encoded according to the Erlang external term
format.
> Bin = term_to_binary(hello). <<131,100,0,5,104,101,108,108,111>> > hello = binary_to_term(Bin). hello
Warning:
When decoding binaries from untrusted sources, consider using
binary_to_term/2 to prevent Denial of Service attacks.
See also term_to_binary/1 and
binary_to_term/2.binary_to_term(Binary, Opts) -> term()
Types:
Binary = ext_binary()
Opts = [safe]
As binary_to_term/1, but takes options that affect decoding of the
binary.
Option:
Failure: badarg if safe is specified and unsafe data is decoded.
- safe:
- Use this option when receiving binaries from an untrusted source.
When enabled, it prevents decoding data that can be used to attack the Erlang
system. In the event of receiving unsafe data, decoding fails with a
badarg error.
This prevents creation of new atoms directly, creation of new atoms indirectly
(as they are embedded in certain structures, such as process identifiers,
refs, and funs), and creation of new external function references. None of
those resources are garbage collected, so unchecked creation of them can
exhaust available memory.
> binary_to_term(<<131,100,0,5,104,101,108,108,111>>, [safe]). ** exception error: bad argument > hello. hello > binary_to_term(<<131,100,0,5,104,101,108,108,111>>, [safe]). helloSee 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>>). 24Allowed in guard tests.
bitstring_to_list(Bitstring) -> [byte() | bitstring()]
Types:
Bitstring = bitstring()
Returns a list of integers corresponding to the bytes of Bitstring. If
the number of bits in the binary is not divisible by 8, the last element of
the list is a bitstring containing the remaining 1-7 bits.
erlang:bump_reductions(Reductions) -> true
Types:
Reductions = integer() >= 1
This implementation-dependent function increments the reduction counter for the
calling process. In the Beam emulator, the reduction counter is normally
incremented by one for each function and BIF call. A context switch is forced
when the counter reaches the maximum number of reductions for a process (2000
reductions in Erlang/OTP R12B).
Warning:
This BIF can be removed in a future version of the Beam machine without prior
warning. It is unlikely to be implemented in other Erlang implementations.
byte_size(Bitstring) -> integer() >= 0
Types:
Bitstring = bitstring()
Returns an integer that is the number of bytes needed to contain
Bitstring. That is, if the number of bits in Bitstring is not
divisible by 8, the resulting number of bytes is rounded up. Examples:
> byte_size(<<433:16,3:3>>). 3 > byte_size(<<1,2,3>>). 3Allowed in guard tests.
erlang:cancel_timer(TimerRef) -> Result
Types:
TimerRef = reference()
Time = integer() >= 0
Result = Time | false
Cancels a timer. The same as calling erlang:cancel_timer(TimerRef,
[]).
erlang:cancel_timer(TimerRef, Options) -> Result | ok
Types:
TimerRef = reference()
Async = Info = boolean()
Option = {async, Async} | {info, Info}
Options = [Option]
Time = integer() >= 0
Result = Time | false
Cancels a timer that has been created by erlang:start_timer or
erlang:send_after. TimerRef identifies the timer, and
was returned by the BIF that created the timer.
Options:
More Options may be added in the future.
If Result is an integer, it represents the time in milliseconds left
until the canceled timer would have expired.
If Result is false, a timer corresponding to TimerRef could
not be found. This can be either because the timer had expired, already had
been canceled, or because TimerRef never corresponded to a timer. Even
if the timer had expired, it does not tell you if the time-out message has
arrived at its destination yet.
- {async, Async}:
- Asynchronous request for cancellation. Async defaults to false, which causes the cancellation to be performed synchronously. When Async is set to true, the cancel operation is performed asynchronously. That is, cancel_timer() sends an asynchronous request for cancellation to the timer service that manages the timer, and then returns ok.
- {info, Info}:
- Requests information about the Result of the cancellation. Info defaults to true, which means the Result is given. When Info is set to false, no information about the result of the cancellation is given.
- *
- When Async is false: if Info is true, the Result is returned by erlang:cancel_timer(). otherwise ok is returned.
- *
- When Async is true: if Info is true, a message on the form {cancel_timer, TimerRef, Result} is sent to the caller of erlang:cancel_timer() when the cancellation operation has been performed, otherwise no message is sent.
Note:
The timer service that manages the timer can be co-located with another
scheduler than the scheduler that the calling process is executing on. If so,
communication with the timer service takes much longer time than if it is
located locally. If the calling process is in critical path, and can do other
things while waiting for the result of this operation, or is not interested in
the result of the operation, you want to use option {async, true}. If
using option {async, false}, the calling process blocks until the
operation has been performed.
See also erlang:send_after/4, erlang:start_timer/4,
and erlang:read_timer/2.check_old_code(Module) -> boolean()
Types:
Module = module()
Returns true if Module has old code, otherwise false.
See also code(3erl).
check_process_code(Pid, Module) -> CheckResult
Types:
Pid = pid()
Module = module()
CheckResult = boolean()
The same as check_process_code(Pid, Module, []).
check_process_code(Pid, Module, OptionList) -> CheckResult | async
Types:
Pid = pid()
Module = module()
RequestId = term()
Option = {async, RequestId} | {allow_gc, boolean()}
OptionList = [Option]
CheckResult = boolean() | aborted
Checks if the node local process identified by Pid executes old code for
Module.
Options:
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:
- {allow_gc, boolean()}:
- Determines if garbage collection is allowed when performing the operation. If {allow_gc, false} is passed, and a garbage collection is needed to determine the result of the operation, the operation is aborted (see information on CheckResult below). The default is to allow garbage collection, that is, {allow_gc, true}.
- {async, RequestId}:
- The function check_process_code/3 returns the value async immediately after the request has been sent. When the request has been processed, the process that called this function is passed a message on the form {check_process_code, RequestId, CheckResult}.
- true:
- The process identified by Pid executes old code for Module. That is, the current call of the process executes old code for this module, or the process has references to old code for this module, or the process contains funs that references old code for this module.
- false:
- The process identified by Pid does not execute old code for Module.
- aborted:
- The operation was aborted, as the process needed to be garbage collected to determine the operation result, and the operation was requested by passing option {allow_gc, false}.
Note:
Up until ERTS version 8.*, the check process code operation checks for all types
of references to the old code. That is, direct references (e.g. return
addresses on the process stack), indirect references ( funs in process
context), and references to literals in the code.
As of ERTS version 9.0, the check process code operation only checks for direct
references to the code. Indirect references via funs will be ignored.
If such funs exist and are used after a purge of the old code, an
exception will be raised upon usage (same as the case when the fun is
received by the process after the purge). Literals will be taken care of
(copied) at a later stage. This behavior can as of ERTS version 8.1 be enabled
when building OTP, and will automatically be enabled if dirty scheduler
support is enabled.
See also code(3erl).
Failures:
- badarg:
- If Pid is not a node local process identifier.
- badarg:
- If Module is not an atom.
- badarg:
- If OptionList is an invalid list of options.
erlang:convert_time_unit(Time, FromUnit, ToUnit) -> ConvertedTime
Types:
Time = ConvertedTime = integer()
FromUnit = ToUnit = time_unit()
Converts the Time value of time unit FromUnit to the corresponding
ConvertedTime value of time unit ToUnit. The result is rounded
using the floor function.
Warning:
You can lose accuracy and precision when converting between time units. To
minimize such loss, collect all data at native time unit and do the
conversion on the end result.
erlang:crc32(Data) -> integer() >= 0
Types:
Data = iodata()
Computes and returns the crc32 (IEEE 802.3 style) checksum for
Data.
erlang:crc32(OldCrc, Data) -> integer() >= 0
Types:
OldCrc = integer() >= 0
Data = iodata()
Continues computing the crc32 checksum by combining the previous checksum,
OldCrc, with the checksum of Data.
The following code:
X = erlang:crc32(Data1), Y = erlang:crc32(X,Data2).assigns the same value to Y as this:
Y = erlang:crc32([Data1,Data2]).
erlang:crc32_combine(FirstCrc, SecondCrc, SecondSize) -> integer() >= 0
Types:
FirstCrc = SecondCrc = SecondSize = integer() >= 0
Combines two previously computed crc32 checksums. This computation requires the
size of the data object for the second checksum to be known.
The following code:
Y = erlang:crc32(Data1), Z = erlang:crc32(Y,Data2).assigns the same value to Z as this:
X = erlang:crc32(Data1), Y = erlang:crc32(Data2), Z = erlang:crc32_combine(X,Y,iolist_size(Data2)).
date() -> Date
Types:
Date = calendar:date()
Returns the current date as {Year, Month, Day}.
The time zone and Daylight Saving Time correction depend on the underlying OS.
Example:
> date(). {1995,2,19}
erlang:decode_packet(Type, Bin, Options) -> {ok, Packet, Rest} | {more, Length} | {error, Reason}
Types:
Type =
raw |
0 |
1 |
2 |
4 |
asn1 |
cdr |
sunrm |
fcgi |
tpkt |
line |
http |
http_bin |
httph |
httph_bin
Bin = binary()
Options = [Opt]
Opt =
{packet_size, integer() >= 0} |
{line_length, integer() >= 0}
Packet = binary() | HttpPacket
Rest = binary()
Length = integer() >= 0 | undefined
Reason = term()
HttpPacket =
HttpRequest | HttpResponse | HttpHeader | http_eoh | HttpError
HttpRequest = {http_request, HttpMethod, HttpUri, HttpVersion}
HttpResponse =
{http_response, HttpVersion, integer(), HttpString}
HttpHeader =
{http_header,
integer(),
HttpField,
Reserved :: term(),
Value :: HttpString}
HttpError = {http_error, HttpString}
HttpMethod =
'OPTIONS' |
'GET' |
'HEAD' |
'POST' |
'PUT' |
'DELETE' |
'TRACE' |
HttpString
HttpUri =
'*' |
{absoluteURI,
http | https,
Host :: HttpString,
Port :: inet:port_number() | undefined,
Path :: HttpString} |
{scheme, Scheme :: HttpString, HttpString} |
{abs_path, HttpString} |
HttpString
HttpVersion =
{Major :: integer() >= 0, Minor :: integer() >= 0}
HttpField =
'Cache-Control' |
'Connection' |
'Date' |
'Pragma' |
'Transfer-Encoding' |
'Upgrade' |
'Via' |
'Accept' |
'Accept-Charset' |
'Accept-Encoding' |
'Accept-Language' |
'Authorization' |
'From' |
'Host' |
'If-Modified-Since' |
'If-Match' |
'If-None-Match' |
'If-Range' |
'If-Unmodified-Since' |
'Max-Forwards' |
'Proxy-Authorization' |
'Range' |
'Referer' |
'User-Agent' |
'Age' |
'Location' |
'Proxy-Authenticate' |
'Public' |
'Retry-After' |
'Server' |
'Vary' |
'Warning' |
'Www-Authenticate' |
'Allow' |
'Content-Base' |
'Content-Encoding' |
'Content-Language' |
'Content-Length' |
'Content-Location' |
'Content-Md5' |
'Content-Range' |
'Content-Type' |
'Etag' |
'Expires' |
'Last-Modified' |
'Accept-Ranges' |
'Set-Cookie' |
'Set-Cookie2' |
'X-Forwarded-For' |
'Cookie' |
'Keep-Alive' |
'Proxy-Connection' |
HttpString
HttpString = string() | binary()
raw |
0 |
1 |
2 |
4 |
asn1 |
cdr |
sunrm |
fcgi |
tpkt |
line |
http |
http_bin |
httph |
httph_bin
{packet_size, integer() >= 0} |
{line_length, integer() >= 0}
HttpRequest | HttpResponse | HttpHeader | http_eoh | HttpError
{http_response, HttpVersion, integer(), HttpString}
{http_header,
integer(),
HttpField,
Reserved :: term(),
Value :: HttpString}
'OPTIONS' |
'GET' |
'HEAD' |
'POST' |
'PUT' |
'DELETE' |
'TRACE' |
HttpString
'*' |
{absoluteURI,
http | https,
Host :: HttpString,
Port :: inet:port_number() | undefined,
Path :: HttpString} |
{scheme, Scheme :: HttpString, HttpString} |
{abs_path, HttpString} |
HttpString
{Major :: integer() >= 0, Minor :: integer() >= 0}
'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
Decodes the binary Bin according to the packet protocol specified by
Type. Similar to the packet handling done by sockets with option
{packet,Type}.
If an entire packet is contained in Bin, it is returned together with the
remainder of the binary as {ok,Packet,Rest}.
If Bin does not contain the entire packet, {more,Length} is
returned. Length is either the expected total size of the
packet, or undefined if the expected packet size is unknown.
decode_packet can then be called again with more data added.
If the packet does not conform to the protocol format, {error,Reason} is
returned.
Types:
Options:
Examples:
- raw | 0:
- No packet handling is done. The entire binary is returned unless it is empty.
- 1 | 2 | 4:
- Packets consist of a header specifying the number of bytes in the packet, followed by that number of bytes. The length of the header can be one, two, or four bytes; the order of the bytes is big-endian. The header is stripped off when the packet is returned.
- line:
- A packet is a line-terminated by a delimiter byte, default is the latin-1 newline character. The delimiter byte is included in the returned packet unless the line was truncated according to option line_length.
- asn1 | cdr | sunrm | fcgi | tpkt:
- The header is not stripped off.
The meanings of the packet types are as follows:
- asn1 - ASN.1 BER:
- sunrm - Sun's RPC encoding:
- cdr - CORBA (GIOP 1.1):
- fcgi - Fast CGI:
- tpkt - TPKT format [RFC1006]:
- http | httph | http_bin | httph_bin:
- The Hypertext Transfer Protocol. The packets are returned with the format according to HttpPacket described earlier. A packet is either a request, a response, a header, or an end of header mark. Invalid lines are returned as HttpError.
Recognized request methods and header fields are returned as atoms. Others are
returned as strings. Strings of unrecognized header fields are formatted with
only capital letters first and after hyphen characters, for example,
"Sec-Websocket-Key".
The protocol type http is only to be used for the first line when an
HttpRequest or an HttpResponse is expected. The following calls
are to use httph to get HttpHeaders until http_eoh is
returned, which marks the end of the headers and the beginning of any
following message body.
The variants http_bin and httph_bin return strings
(HttpString) as binaries instead of lists.
- {packet_size, integer() >= 0}:
- Sets the maximum allowed size of the packet body. If the packet header indicates that the length of the packet is longer than the maximum allowed length, the packet is considered invalid. Defaults to 0, which means no size limit.
- {line_length, integer() >= 0}:
- For packet type line, lines longer than the indicated length are truncated.
Option line_length also applies to http* packet types as an alias
for option packet_size if packet_size itself is not set. This
use is only intended for backward compatibility.
- {line_delimiter, 0 =< byte() =< 255}:
- For packet type line, sets the delimiting byte. Default is the latin-1 character $\n.
> erlang:decode_packet(1,<<3,"abcd">>,[]). {ok,<<"abc">>,<<"d">>} > erlang:decode_packet(1,<<5,"abcd">>,[]). {more,6}
erlang:delete_element(Index, Tuple1) -> Tuple2
Types:
Index = integer() >= 1
1..tuple_size(Tuple1)
Tuple1 = Tuple2 = tuple()
Returns a new tuple with element at Index removed from tuple
Tuple1, for example:
> erlang:delete_element(2, {one, two, three}). {one,three}
delete_module(Module) -> true | undefined
Types:
Module = module()
Makes the current code for Module become old code and deletes all
references for this module from the export table. Returns undefined if
the module does not exist, otherwise true.
Warning:
This BIF is intended for the code server (see code(3erl)) and is
not to be used elsewhere.
Failure: badarg if there already is an old version of
Module.demonitor(MonitorRef) -> true
Types:
MonitorRef = reference()
If MonitorRef is a reference that the calling process obtained by calling
monitor/2, this monitoring is turned off. If the monitoring is
already turned off, nothing happens.
Once demonitor(MonitorRef) has returned, it is guaranteed that no
{'DOWN', MonitorRef, _, _, _} message, because of the monitor, will be
placed in the caller message queue in the future. However, a {'DOWN',
MonitorRef, _, _, _} message can have been placed in the caller message
queue before the call. It is therefore usually advisable to remove such a
'DOWN' message from the message queue after monitoring has been
stopped. demonitor(MonitorRef, [flush]) can be used instead of
demonitor(MonitorRef) if this cleanup is wanted.
Note:
Before Erlang/OTP R11B (ERTS 5.5) demonitor/1 behaved completely
asynchronously, that is, the monitor was active until the "demonitor
signal" reached the monitored entity. This had one undesirable effect.
You could never know when you were guaranteed not to receive a
DOWN message because of the monitor.
The current behavior can be viewed as two combined operations: asynchronously
send a "demonitor signal" to the monitored entity and ignore any
future results of the monitor.
Failure: It is an error if MonitorRef refers to a monitoring started by
another process. Not all such cases are cheap to check. If checking is cheap,
the call fails with badarg, for example if MonitorRef is a
remote reference.demonitor(MonitorRef, OptionList) -> boolean()
Types:
MonitorRef = reference()
OptionList = [Option]
Option = flush | info
The returned value is true unless info is part of
OptionList.
demonitor(MonitorRef, []) is equivalent to
demonitor(MonitorRef).
Options:
- flush:
- Removes (one) {_, MonitorRef, _, _, _} message, if there is one, from the caller message queue after monitoring has been stopped.
Calling demonitor(MonitorRef, [flush]) is equivalent to the following,
but more efficient:
demonitor(MonitorRef), receive {_, MonitorRef, _, _, _} -> true after 0 -> true end
- info:
- The returned value is one of the following:
- true:
- The monitor was found and removed. In this case, no 'DOWN' message corresponding to this monitor has been delivered and will not be delivered.
- false:
- The monitor was not found and could not be removed. This probably because someone already has placed a 'DOWN' message corresponding to this monitor in the caller message queue.
If option info is combined with option flush, false is
returned if a flush was needed, otherwise true.
Note:
More options can be added in a future release.
Failures:
- badarg:
- If OptionList is not a list.
- badarg:
- If Option is an invalid option.
- badarg:
- The same failure as for demonitor/1.
disconnect_node(Node) -> boolean() | ignored
Types:
Node = node()
Forces the disconnection of a node. This appears to the node Node as if
the local node has crashed. This BIF is mainly used in the Erlang network
authentication protocols.
Returns true if disconnection succeeds, otherwise false. If the
local node is not alive, ignored is returned.
erlang:display(Term) -> true
Types:
Term = term()
Prints a text representation of Term on the standard output.
Warning:
This BIF is intended for debugging only.
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}). bAllowed in guard tests.
erase() -> [{Key, Val}]
Types:
Key = Val = term()
Returns the process dictionary and deletes it, for example:
> put(key1, {1, 2, 3}), put(key2, [a, b, c]), erase(). [{key1,{1,2,3}},{key2,[a,b,c]}]
erase(Key) -> Val | undefined
Types:
Key = Val = term()
Returns the value Val associated with Key and deletes it from the
process dictionary. Returns undefined if no value is associated with
Key. Example:
> put(key1, {merry, lambs, are, playing}), X = erase(key1), {X, erase(key1)}. {{merry,lambs,are,playing},undefined}
error(Reason) -> no_return()
Types:
Reason = term()
Stops the execution of the calling process with the reason Reason, where
Reason is any term. The exit reason is {Reason, Where}, where
Where is a list of the functions most recently called (the current
function first). As evaluating this function causes the process to terminate,
it has no return value. Example:
> catch error(foobar). {'EXIT',{foobar,[{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. As evaluating this function causes the
process to terminate, it has no return value.
exit(Reason) -> no_return()
Types:
Reason = term()
Stops the execution of the calling process with exit reason Reason, where
Reason is any term. As evaluating this function causes the process to
terminate, it has no return value. Example:
> exit(foobar). ** exception exit: foobar > catch exit(foobar). {'EXIT',foobar}
exit(Pid, Reason) -> true
Types:
Pid = pid() | port()
Reason = term()
Sends an exit signal with exit reason Reason to the process or port
identified by Pid.
The following behavior applies if Reason is any term, except
normal or kill:
If 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.
- *
- 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.
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. trueThis 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. trueOption {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). 55.0Allowed 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
{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
{decimals, Decimals :: 0..253} |
{scientific, Decimals :: 0..249} |
compact
Returns a string corresponding to the text representation of Float using
fixed decimal point formatting.
Available options:
Examples:
- *
- If option decimals is specified, the returned value contains at most Decimals number of digits past the decimal point. If the number does not fit in the internal static buffer of 256 bytes, the function throws badarg.
- *
- If option compact is specified, the trailing zeros at the end of the list are truncated. This option is only meaningful together with option decimals.
- *
- If option scientific is specified, the float is formatted using scientific notation with Decimals digits of precision.
- *
- If Options is [], the function behaves as float_to_list/1.
> 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()
arity |
env |
index |
name |
module |
new_index |
new_uniq |
pid |
type |
uniq
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.
The following elements are always present in the list for both local and
external funs:
The following elements are only present in the list if Fun is local:
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).
- {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.
- {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 Erlang/OTP R15, this integer is calculated from the compiled code for the entire module. Before Erlang/OTP R15, this integer was based on only the body of the fun.
erlang:fun_info(Fun, Item) -> {Item, Info}
Types:
Fun = function()
Item = fun_info_item()
Info = term()
fun_info_item() =arity |env |index |name |module |new_index |new_uniq |pid |type |uniq
Returns information about Fun as specified by Item, in the form
{Item,Info}.
For any fun, Item can be any of the atoms module, name,
arity, env, or type.
For a local fun, Item can also be any of the atoms index,
new_index, new_uniq, uniq, and pid. For an
external fun, the value of any of these items is always the atom
undefined.
See erlang:fun_info/1.
erlang:fun_to_list(Fun) -> string()
Types:
Fun = function()
Returns a string corresponding to the text representation of Fun.
erlang:function_exported(Module, Function, Arity) -> boolean()
Types:
Module = module()
Function = atom()
Arity = arity()
Returns true if the module Module is loaded and contains an
exported function Function/Arity, or if there is a BIF (a built-in
function implemented in C) with the specified name, otherwise returns
false.
Note:
This function used to return false for BIFs before Erlang/OTP 18.0.
garbage_collect() -> true
Forces an immediate garbage collection of the executing process. The function is
not to be used unless it has been noticed (or there are good reasons to
suspect) that the spontaneous garbage collection will occur too late or not at
all.
Warning:
Improper use can seriously degrade system performance.
garbage_collect(Pid) -> GCResult
Types:
Pid = pid()
GCResult = boolean()
The same as garbage_collect(Pid, []).
garbage_collect(Pid, OptionList) -> GCResult | async
Types:
Pid = pid()
RequestId = term()
Option = {async, RequestId}
OptionList = [Option]
GCResult = boolean()
Garbage collects the node local process identified by Pid.
Option:
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:
Notice that the same caveats apply as for garbage_collect/0.
Failures:
- {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}.
- 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.
- badarg:
-
If Pid is not a node local process identifier.
- badarg:
-
If OptionList is an invalid list of options.
get() -> [{Key, Val}]
Types:
Key = Val = term()
Returns the process dictionary as a list of {Key, Val} tuples, for
example:
> put(key1, merry), put(key2, lambs), put(key3, {are, playing}), get(). [{key1,merry},{key2,lambs},{key3,{are,playing}}]
get(Key) -> Val | undefined
Types:
Key = Val = term()
Returns the value Val associated with Key in the process
dictionary, or undefined if Key does not exist. Example:
> put(key1, merry), put(key2, lambs), put({any, [valid, term]}, {are, playing}), get({any, [valid, term]}). {are,playing}
erlang:get_cookie() -> Cookie | nocookie
Types:
Cookie = atom()
Returns the magic cookie of the local node if the node is alive, otherwise the
atom nocookie.
get_keys() -> [Key]
Types:
Key = term()
Returns a list of all keys present in the process dictionary, for example:
> put(dog, {animal,1}), put(cow, {animal,2}), put(lamb, {animal,3}), get_keys(). [dog,cow,lamb]
get_keys(Val) -> [Key]
Types:
Val = Key = term()
Returns a list of keys that are associated with the value Val in the
process dictionary, for example:
> put(mary, {1, 2}), put(had, {1, 2}), put(a, {1, 2}), put(little, {1, 2}), put(dog, {1, 3}), put(lamb, {1, 2}), get_keys({1, 2}). [mary,had,a,little,lamb]
erlang:get_stacktrace() -> [stack_item()]
Types:
stack_item() ={Module :: module(),Function :: atom(),Arity :: arity() | (Args :: [term()]),Location ::[{file, Filename :: string()} |{line, Line :: integer() >= 1}]}
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 operator catch returns, for example:
See also error/1 and error/2.
{'EXIT',{badarg,Stacktrace}} = catch abs(x)Location is a (possibly empty) list of two-tuples that can indicate the location in the source code of the function. The first element is an atom describing the type of information in the second element. The following items can occur:
- file:
- The second element of the tuple is a string (list of characters) representing the filename of the source file of the function.
- line:
- The second element of the tuple is the line number (an integer > 0) in the source file where the exception occurred or the function was called.
group_leader() -> pid()
Returns the process identifier of the group leader for the process evaluating
the function.
Every process is a member of some process group and all groups have a group
leader. All I/O from the group is channeled to the group leader. When a
new process is spawned, it gets the same group leader as the spawning process.
Initially, at system startup, init is both its own group leader and the
group leader of all processes.
group_leader(GroupLeader, Pid) -> true
Types:
GroupLeader = Pid = pid()
Sets the group leader of Pid to GroupLeader. Typically, this is
used when a process started from a certain shell is to have another group
leader than init.
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. Note that only code points in the range 0-255 may be used and the string will be truncated if longer than 200 characters.
- 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 is 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 > 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]). 1Allowed in guard tests. Failure: badarg if List is the empty list [].
erlang:hibernate(Module, Function, Args) -> no_return()
Types:
Module = module()
Function = atom()
Args = [term()]
Puts the calling process into a wait state where its memory allocation has been
reduced as much as possible. This is useful if the process does not expect to
receive any messages soon.
The process is awaken when a message is sent to it, and control resumes in
Module:Function with the arguments specified by Args with the
call stack emptied, meaning that the process terminates when that function
returns. Thus erlang:hibernate/3 never returns to its caller.
If the process has any message in its message queue, the process is awakened
immediately in the same way as described earlier.
In more technical terms, erlang:hibernate/3 discards the call stack for
the process, and then garbage collects the process. After this, all live data
is in one continuous heap. The heap is then shrunken to the exact same size as
the live data that it holds (even if that size is less than the minimum heap
size for the process).
If the size of the live data in the process is less than the minimum heap size,
the first garbage collection occurring after the process is awakened ensures
that the heap size is changed to a size not smaller than the minimum heap
size.
Notice that emptying the call stack means that any surrounding catch is
removed and must be re-inserted after hibernation. One effect of this is that
processes started using proc_lib (also indirectly, such as
gen_server processes), are to use proc_lib:hibernate/3
instead, to ensure that the exception handler continues to work when the
process wakes up.
erlang:insert_element(Index, Tuple1, Term) -> Tuple2
Types:
Index = integer() >= 1
Term = term()
1..tuple_size(Tuple1) + 1
Tuple1 = Tuple2 = tuple()
Returns a new tuple with element Term inserted at position Index
in tuple Tuple1. All elements from position Index and upwards
are pushed one step higher in the new tuple Tuple2. Example:
> erlang:insert_element(2, {one, two, three}, new). {one,new,two,three}
integer_to_binary(Integer) -> binary()
Types:
Integer = integer()
Returns a binary corresponding to the text representation of Integer, for
example:
> integer_to_binary(77). <<"77">>
integer_to_binary(Integer, Base) -> binary()
Types:
Integer = integer()
Base = 2..36
Returns a binary corresponding to the text representation of Integer in
base Base, for example:
> integer_to_binary(1023, 16). <<"3FF">>
integer_to_list(Integer) -> string()
Types:
Integer = integer()
Returns a string corresponding to the text representation of Integer, for
example:
> integer_to_list(77). "77"
integer_to_list(Integer, Base) -> string()
Types:
Integer = integer()
Base = 2..36
Returns a string corresponding to the text representation of Integer in
base Base, for example:
> integer_to_list(1023, 16). "3FF"
iolist_size(Item) -> integer() >= 0
Types:
Item = iolist() | binary()
Returns an integer, that is the size in bytes, of the binary that would be the
result of iolist_to_binary(Item), for example:
> iolist_size([1,2|<<3,4>>]). 4
iolist_to_binary(IoListOrBinary) -> binary()
Types:
IoListOrBinary = iolist() | binary()
Returns a binary that is made from the integers and binaries in
IoListOrBinary, for example:
> Bin1 = <<1,2,3>>. <<1,2,3>> > Bin2 = <<4,5>>. <<4,5>> > Bin3 = <<6>>. <<6>> > iolist_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]). <<1,2,3,1,2,3,4,5,4,6>>
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 especially. It emits
code to verify that Term is a tuple, that its first element is
RecordTag, and that the size is correct. However, if RecordTag
is not a literal atom, the BIF is_record/2 is called instead and the
size of the tuple is not verified.
Allowed in guard tests, if RecordTag is a literal atom.is_record(Term, RecordTag, Size) -> boolean()
Types:
Term = term()
RecordTag = atom()
Size = integer() >= 0
RecordTag must be an atom.
Returns true if Term is a tuple, its first element is
RecordTag, and its size is Size. Otherwise returns false.
Allowed in guard tests if RecordTag is a literal atom and Size is
a literal integer.
Note:
This BIF is documented for completeness. Usually is_record/2 is to be
used.
is_reference(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a reference, otherwise false.
Allowed in guard tests.
is_tuple(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a tuple, otherwise false.
Allowed in guard tests.
length(List) -> integer() >= 0
Types:
List = [term()]
Returns the length of List, for example:
> length([1,2,3,4,5,6,7,8,9]). 9Allowed 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 <
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"). 2.2017764Failure: 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"). 123Failure: 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). 1023Failure: 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 one of the following:
- badfile:
- The object code in Binary has an incorrect format or the object code contains code for another module than Module.
- not_purged:
- Binary contains a module that cannot be loaded because old code for this module already exists.
Warning:
This BIF is intended for the code server (see code(3erl)) and is
not to be used elsewhere.
erlang:load_nif(Path, LoadInfo) -> ok | Error
Types:
Path = string()
LoadInfo = term()
Error = {error, {Reason, Text :: string()}}
Reason =
load_failed | bad_lib | load | reload | upgrade | old_code
load_failed | bad_lib | load | reload | upgrade | old_code
Note:
Before Erlang/OTP R14B, NIFs were an experimental feature. Versions before
Erlang/OTP R14B can have different and possibly incompatible NIF semantics and
interfaces. For example, in Erlang/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). Notice that on most OSs the library has to have a
different name on disc when an upgrade of the nif is done. If the name is the
same, but the contents differ, the old library may be loaded instead. For
information on how to implement a NIF library, see
erl_nif(3erl).
LoadInfo can be any term. It is passed on to the library as part of the
initialization. A good practice is to include a module version number to
support future code upgrade scenarios.
The call to load_nif/2 must be made directly from the Erlang code
of the module that the NIF library belongs to. It returns either ok, or
{error,{Reason,Text}} if loading fails. Reason is one of the
following atoms while Text is a human readable string that can give
more information about the failure:
- load_failed:
- The OS failed to load the NIF library.
- bad_lib:
- The library did not fulfill the requirements as a NIF library of the calling module.
- load | reload | upgrade:
- The corresponding library callback was unsuccessful.
- old_code:
- The call to load_nif/2 was made from the old code of a module that has been upgraded; this is not allowed.
erlang:loaded() -> [Module]
Types:
Module = module()
Returns a list of all loaded Erlang modules (current and old code), including
preloaded modules.
See also code(3erl).
erlang:localtime() -> DateTime
Types:
DateTime = calendar:datetime()
Returns the current local date and time, {{Year, Month, Day}, {Hour, Minute,
Second}}, for example:
> erlang:localtime(). {{1996,11,6},{14,45,17}}The time zone and Daylight Saving Time correction depend on the underlying OS.
erlang:localtime_to_universaltime(Localtime) -> Universaltime
Types:
Localtime = Universaltime = calendar:datetime()
Converts local date and time to Universal Time Coordinated (UTC), if supported
by the underlying OS. Otherwise no conversion is done and Localtime is
returned. Example:
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}). {{1996,11,6},{13,45,17}}Failure: badarg if Localtime denotes an invalid date and time.
erlang:localtime_to_universaltime(Localtime, IsDst) -> Universaltime
Types:
Localtime = Universaltime = calendar:datetime()
IsDst = true | false | undefined
Converts local date and time to Universal Time Coordinated (UTC) as
erlang:localtime_to_universaltime/1, but the caller decides if Daylight
Saving Time is active.
If IsDst == true, Localtime is during Daylight Saving Time, if
IsDst == false it is not. If IsDst == undefined, the underlying
OS can guess, which is the same as calling
erlang:localtime_to_universaltime(Localtime).
Examples:
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, true). {{1996,11,6},{12,45,17}} > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, false). {{1996,11,6},{13,45,17}} > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, undefined). {{1996,11,6},{13,45,17}}Failure: badarg if Localtime denotes an invalid date and time.
make_ref() -> reference()
Returns a unique reference. The reference is unique among connected
nodes.
Warning:
Known issue: When a node is restarted multiple times with the same node name,
references created on a newer node can be mistaken for a reference created on
an older node with the same node name.
erlang:make_tuple(Arity, InitialValue) -> tuple()
Types:
Arity = arity()
InitialValue = term()
Creates a new tuple of the specified Arity, where all elements are
InitialValue, for example:
> erlang:make_tuple(4, []). {[],[],[],[]}
erlang:make_tuple(Arity, DefaultValue, InitList) -> tuple()
Types:
Arity = arity()
DefaultValue = term()
InitList = [{Position :: integer() >= 1, term()}]
Creates a tuple of size Arity, where each element has value
DefaultValue, and then fills in values from InitList. Each list
element in InitList must be a two-tuple, where the first element is a
position in the newly created tuple and the second element is any term. If a
position occurs more than once in the list, the term corresponding to the last
occurrence is used. Example:
> erlang:make_tuple(5, [], [{2,ignored},{5,zz},{2,aa}]). {[],aa,[],[],zz}
map_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}). 3Allowed in guard tests.
erlang:match_spec_test(MatchAgainst, MatchSpec, Type) -> TestResult
Types:
MatchAgainst = [term()] | tuple()
MatchSpec = term()
Type = table | trace
TestResult =
{ok, term(), [return_trace], [{error | warning, string()}]} |
{error, [{error | warning, string()}]}
{ok, term(), [return_trace], [{error | warning, string()}]} |
{error, [{error | warning, string()}]}
Tests a match specification used in calls to ets:select/2 and
erlang:trace_pattern/3. The function tests both a match
specification for "syntactic" correctness and runs the match
specification against the object. If the match specification contains errors,
the tuple {error, Errors} is returned, where Errors is a list of
natural language descriptions of what was wrong with the match specification.
If Type is table, the object to match against is to be a tuple.
The function then returns {ok,Result,[],Warnings}, where Result
is what would have been the result in a real ets:select/2 call, or
false if the match specification does not match the object tuple.
If Type is trace, the object to match against is to be a list. The
function returns {ok, Result, Flags, Warnings}, where Result is
one of the following:
Flags is a list containing all the trace flags to be enabled, currently
this is only return_trace.
This is a useful debugging and test tool, especially when writing complicated
match specifications.
See also ets:test_ms/2.
- *
- true if a trace message is to be emitted
- *
- false if a trace message is not to be emitted
- *
- The message term to be appended to the trace message
max(Term1, Term2) -> Maximum
Types:
Term1 = Term2 = Maximum = term()
Returns the largest of Term1 and Term2. If the terms are equal,
Term1 is returned.
erlang:md5(Data) -> Digest
Types:
Data = iodata()
Digest = binary()
Computes an MD5 message digest from Data, where the length of the digest
is 128 bits (16 bytes). Data is a binary or a list of small integers
and binaries.
For more information about MD5, see RFC 1321 - The MD5 Message-Digest Algorithm.
Warning:
The MD5 Message-Digest Algorithm is not considered safe for code-signing
or software-integrity purposes.
erlang:md5_final(Context) -> Digest
Types:
Context = Digest = binary()
Finishes the update of an MD5 Context and returns the computed MD5
message digest.
erlang:md5_init() -> Context
Types:
Context = binary()
Creates an MD5 context, to be used in the following calls to
md5_update/2.
erlang:md5_update(Context, Data) -> NewContext
Types:
Context = binary()
Data = iodata()
NewContext = binary()
Update an MD5 Context with Data and returns a
NewContext.
erlang:memory() -> [{Type, Size}]
Types:
Type = memory_type()
Size = integer() >= 0
memory_type() =total |processes |processes_used |system |atom |atom_used |binary |code |ets |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.
Memory types:
- total:
- The total amount of memory currently allocated. This is the same as the sum of the memory size for processes and system.
- processes:
- The total amount of memory currently allocated for the Erlang processes.
- processes_used:
- The total amount of memory currently used by the Erlang processes. This is part of the memory presented as processes memory.
- system:
- The total amount of memory currently allocated for the emulator that is not directly related to any Erlang process. Memory presented as processes is not included in this memory.
- atom:
- The total amount of memory currently allocated for atoms. This memory is part of the memory presented as system memory.
- atom_used:
- The total amount of memory currently used for atoms. This memory is part of the memory presented as atom memory.
- binary:
- The total amount of memory currently allocated for binaries. This memory is part of the memory presented as system memory.
- code:
- The total amount of memory currently allocated for Erlang code. This memory is part of the memory presented as system memory.
- ets:
- The total amount of memory currently allocated for ETS tables. This memory is part of the memory presented as system memory.
- low:
- Only on 64-bit halfword emulator. The total amount of memory allocated in low memory areas that are restricted to < 4 GB, although the system can have more memory.
Can be removed in a future release of the halfword emulator.
- maximum:
- The maximum total amount of memory allocated since the emulator was started. This tuple is only present when the emulator is run with instrumentation.
For information on how to run the emulator with instrumentation, see
instrument(3erl) and/or erl(1).
Note:
The system value is not complete. Some allocated memory that is to be
part of this value is not.
When the emulator is run with instrumentation, the system value is more
accurate, but memory directly allocated for malloc (and friends) is
still not part of the system value. Direct calls to malloc are
only done from OS-specific runtime libraries and perhaps from user-implemented
Erlang drivers that do not use the memory allocation functions in the driver
interface.
As the total value is the sum of processes and system, the
error in system propagates to the total value.
The different amounts of memory that are summed are not gathered
atomically, which introduces an error in the result.
The different values have the following relation to each other. Values beginning
with an uppercase letter is not part of the result.
total = processes + system processes = processes_used + ProcessesNotUsed system = atom + binary + code + ets + OtherSystem atom = atom_used + AtomNotUsed RealTotal = processes + RealSystem RealSystem = system + MissedSystemMore tuples in the returned list can be added in a future release.
Note:
The total value is supposed to be the total amount of memory dynamically
allocated by the emulator. Shared libraries, the code of the emulator itself,
and the emulator stacks are not supposed to be included. That is, the
total value is not supposed to be equal to the total size of all
pages mapped to the emulator.
Also, because of fragmentation and prereservation of memory areas, the size of
the memory segments containing the dynamically allocated memory blocks can be
much larger than the total size of the dynamically allocated memory blocks.
Note:
As from ERTS 5.6.4, erlang:memory/0 requires that all
erts_alloc(3erl) allocators are enabled (default behavior).
Failure: notsup if an erts_alloc(3erl) allocator has been
disabled.erlang:memory(Type :: memory_type()) -> integer() >= 0
erlang:memory(TypeList :: [memory_type()]) -> [{memory_type(), integer() >= 0}]
Types:
memory_type() =total |processes |processes_used |system |atom |atom_used |binary |code |ets |low |maximum
Returns the memory size in bytes allocated for memory of type Type. The
argument can also be specified as a list of memory_type() atoms, in
which case a corresponding list of {memory_type(), Size :: integer >=
0} tuples is returned.
See also erlang:memory/0.
Note:
As from ERTS 5.6.4, erlang:memory/1 requires that all
erts_alloc(3erl) allocators are enabled (default behavior).
Failures:
- badarg:
-
If Type is not one of the memory types listed in the description of erlang:memory/0.
- badarg:
-
If maximum is passed as Type and the emulator is not run in instrumented mode.
- notsup:
-
If an erts_alloc(3erl) allocator has been disabled.
min(Term1, Term2) -> Minimum
Types:
Term1 = Term2 = Minimum = term()
Returns the smallest of Term1 and Term2. If the terms are equal,
Term1 is returned.
module_loaded(Module) -> boolean()
Types:
Module = module()
Returns true if the module Module is loaded, otherwise
false. It does not attempt to load the module.
Warning:
This BIF is intended for the code server (see code(3erl)) and is
not to be used elsewhere.
monitor(Type :: process, Item :: monitor_process_identifier()) -> MonitorRef
monitor(Type :: port, Item :: monitor_port_identifier()) -> MonitorRef
monitor(Type :: time_offset, Item :: clock_service) -> MonitorRef
Types:
MonitorRef = reference()
registered_name() = atom()
registered_process_identifier() =registered_name() | {registered_name(), node()}
monitor_process_identifier() =pid() | registered_process_identifier()
monitor_port_identifier() = port() | registered_name()
Sends a monitor request of type Type to the entity identified by
Item. If the monitored entity does not exist or it changes monitored
state, the caller of monitor/2 is notified by a message on the
following format:
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.
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.
{Tag, MonitorRef, Type, Object, Info}
Note:
The monitor request is an asynchronous signal. That is, it takes time before the
signal reaches its destination.
Type can be one of the following atoms: process, port or
time_offset.
A process or port monitor is triggered only once, after that it is
removed from both monitoring process and the monitored entity. Monitors are
fired when the monitored process or port terminates, does not exist at the
moment of creation, or if the connection to it is lost. If the connection to
it is lost, we do not know if it still exists. The monitoring is also turned
off when demonitor/1 is called.
A process or port monitor by name resolves the
RegisteredName to pid() or port() only once at the moment
of monitor instantiation, later changes to the name registration will not
affect the existing monitor.
When a process or port monitor is triggered, a 'DOWN'
message is sent that has the following pattern:
{'DOWN', MonitorRef, Type, Object, Info}In the monitor message MonitorRef and Type are the same as described earlier, and:
- Object:
- The monitored entity, which triggered the event. When monitoring a local process or port, Object will be equal to the pid() or port() that was being monitored. When monitoring process or port by name, Object will have format {RegisteredName, Node} where RegisteredName is the name which has been used with monitor/2 call and Node is local or remote node name (for ports monitored by name, Node is always local node name).
- Info:
- Either the exit reason of the process, noproc (process or port did not exist at the time of monitor creation), or noconnection (no connection to the node where the monitored process resides).
Note:
The format of the 'DOWN' message changed in ERTS 5.2 (Erlang/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 5.2 or higher versions) 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.
- Monitoring a process:
- Creates monitor between the current process and another process identified by Item, which can be a pid() (local or remote), an atom RegisteredName or a tuple {RegisteredName, Node} for a registered process, located elsewhere.
- Monitoring a port:
- Creates monitor between the current process and a port identified by Item, which can be a port() (only local), an atom RegisteredName or a tuple {RegisteredName, Node} for a registered port, located on this node. Note, that attempt to monitor a remote port will result in badarg.
- Monitoring a time_offset:
- Monitors changes in time offset between Erlang monotonic time and Erlang system time. One valid Item exists in combination with the time_offset Type, namely the atom clock_service. Notice that the atom clock_service is not the registered name of a process. In this case it serves as an identifier of the runtime system internal clock service at current runtime system instance.
The monitor is triggered when the time offset is changed. This either if the
time offset value is changed, or if the offset is changed from preliminary to
final during finalization of the time offset when the single time
warp mode is used. When a change from preliminary to final time offset is
made, the monitor is triggered once regardless of whether the time offset
value was changed or not.
If the runtime system is in multi time warp mode, the time offset is
changed when the runtime system detects that the OS system time has
changed. The runtime system does, however, not detect this immediately when it
occurs. A task checking the time offset is scheduled to execute at least once
a minute, so under normal operation this is to be detected within a minute,
but during heavy load it can take longer time.
The monitor is not automatically removed after it has been triggered.
That is, repeated changes of the time offset trigger the monitor
repeatedly.
When the monitor is triggered a 'CHANGE' message is sent to the
monitoring process. A 'CHANGE' message has the following pattern:
{'CHANGE', MonitorRef, Type, Item, NewTimeOffset}
where MonitorRef, Type, and Item are the same as described
above, and NewTimeOffset is the new time offset.
When the 'CHANGE' message has been received you are guaranteed not to
retrieve the old time offset when calling erlang:time_offset().
Notice that you can observe the change of the time offset when calling
erlang:time_offset() before you get the 'CHANGE' message.
Note:
If or when monitor/2 is extended, other possible values for Tag,
Object, and Info in the monitor message will be introduced.
monitor_node(Node, Flag) -> true
Types:
Node = node()
Flag = boolean()
Monitor the status of the node Node. If Flag is true,
monitoring is turned on. If Flag is false, monitoring is turned
off.
Making several calls to monitor_node(Node, true) for the same Node
is not an error; it results in as many independent monitoring instances.
If Node fails or does not exist, the message {nodedown, Node} is
delivered to the process. If a process has made two calls to
monitor_node(Node, true) and Node terminates, two
nodedown messages are delivered to the process. If there is no
connection to Node, an attempt is made to create one. If this fails, a
nodedown message is delivered.
Nodes connected through hidden connections can be monitored as any other nodes.
Failure: badarg if the local node is not alive.
erlang:monitor_node(Node, Flag, Options) -> true
Types:
Node = node()
Flag = boolean()
Options = [Option]
Option = allow_passive_connect
Behaves as monitor_node/2 except that it allows an extra option to
be specified, namely allow_passive_connect. This option allows the BIF
to wait the normal network connection time-out for the monitored node
to connect itself, even if it cannot be actively connected from this node
(that is, it is blocked). The state where this can be useful can only be
achieved by using the Kernel option dist_auto_connect once. If that
option is not used, option allow_passive_connect has no effect.
Note:
Option allow_passive_connect is used internally and is seldom needed in
applications where the network topology and the Kernel options in effect are
known in advance.
Failure: badarg if the local node is not alive or the option list is
malformed.erlang:monotonic_time() -> integer()
Returns the current Erlang monotonic time in native time
unit. This is a monotonically increasing time since some unspecified point
in time.
Note:
This is a monotonically increasing time, but not a strictly
monotonically increasing time. That is, consecutive calls to
erlang:monotonic_time/0 can produce the same result.
Different runtime system instances will use different unspecified points in time
as base for their Erlang monotonic clocks. That is, it is pointless
comparing monotonic times from different runtime system instances. Different
runtime system instances can also place this unspecified point in time
different relative runtime system start. It can be placed in the future (time
at start is a negative value), the past (time at start is a positive value),
or the runtime system start (time at start is zero). The monotonic time at
runtime system start can be retrieved by calling
erlang:system_info(start_time).
erlang:monotonic_time(Unit) -> integer()
Types:
Unit = time_unit()
Returns the current Erlang monotonic time converted into the Unit
passed as argument.
Same as calling
erlang:convert_time_unit(erlang:monotonic_time()
, native, Unit), however optimized for commonly used
Units.
erlang:nif_error(Reason) -> no_return()
Types:
Reason = term()
Works exactly like error/1, but Dialyzer thinks that this BIF will
return an arbitrary term. When used in a stub function for a NIF to generate
an exception when the NIF library is not loaded, Dialyzer does not generate
false warnings.
erlang:nif_error(Reason, Args) -> no_return()
Types:
Reason = term()
Args = [term()]
Works exactly like error/2, but Dialyzer thinks that this BIF will
return an arbitrary term. When used in a stub function for a NIF to generate
an exception when the NIF library is not loaded, Dialyzer does not generate
false warnings.
node() -> Node
Types:
Node = node()
Returns the name of the local node. If the node is not alive,
nonode@nohost is returned instead.
Allowed in guard tests.
node(Arg) -> Node
Types:
Arg = pid() | port() | reference()
Node = node()
Returns the node where Arg originates. Arg can be a process
identifier, a reference, or a port. If the local node is not alive,
nonode@nohost is returned.
Allowed in guard tests.
nodes() -> Nodes
Types:
Nodes = [node()]
Returns a list of all visible nodes in the system, except the local node. Same
as nodes(visible).
nodes(Arg) -> Nodes
Types:
Arg = NodeType | [NodeType]
NodeType = visible | hidden | connected | this | known
Nodes = [node()]
Returns a list of nodes according to the argument specified. The returned
result, when the argument is a list, is the list of nodes satisfying the
disjunction(s) of the list elements.
NodeTypes:
Some equalities: [node()] = nodes(this), nodes(connected) =
nodes([visible, hidden]), and nodes() = nodes(visible).
- visible:
- Nodes connected to this node through normal connections.
- hidden:
- Nodes connected to this node through hidden connections.
- connected:
- All nodes connected to this node.
- this:
- This node.
- known:
- Nodes that are known to this node. That is, connected nodes and nodes referred to by process identifiers, port identifiers, and references located on this node. The set of known nodes is garbage collected. Notice that this garbage collection can be delayed. For more information, see erlang:system_info(delayed_node_table_gc).
now() -> Timestamp
Types:
Timestamp = timestamp()
timestamp() ={MegaSecs :: integer() >= 0,Secs :: integer() >= 0,MicroSecs :: integer() >= 0}
Warning:
This function is deprecated. Do not use it.
For more information, see section Time and Time Correction in the User's
Guide. Specifically, section Dos and Dont's describes what to use
instead of erlang:now/0.
Returns the tuple {MegaSecs, Secs, MicroSecs}, which is the elapsed time
since 00:00 GMT, January 1, 1970 (zero hour), if provided by the underlying
OS. Otherwise some other point in time is chosen. It is also guaranteed that
the following calls to this BIF return continuously increasing values. Hence,
the return value from erlang:now/0 can be used to generate unique time
stamps. If it is called in a tight loop on a fast machine, the time of the
node can become skewed.
Can only be used to check the local time of day if the time-zone information of
the underlying OS is properly configured.open_port(PortName, PortSettings) -> port()
Types:
PortName =
{spawn, Command :: string() | binary()} |
{spawn_driver, Command :: string() | binary()} |
{spawn_executable, FileName :: file:name()} |
{fd, In :: integer() >= 0, Out :: integer() >= 0}
PortSettings = [Opt]
Opt =
{packet, N :: 1 | 2 | 4} |
stream |
{line, L :: integer() >= 0} |
{cd, Dir :: string() | binary()} |
{env, Env :: [{Name :: 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
{spawn, Command :: string() | binary()} |
{spawn_driver, Command :: string() | binary()} |
{spawn_executable, FileName :: file:name()} |
{fd, In :: integer() >= 0, Out :: integer() >= 0}
{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 specifed in cd,
env, args, and arg0 are subject to Unicode filename
translation if the system is running in Unicode filename mode. To avoid
translation or to force, for example UTF-8, supply the executable and/or
arguments as a binary in the correct encoding. For details, see the module
file(3erl), the function
file:native_name_encoding/0 in Kernel, and the Using
Unicode in Erlang User's Guide.
PortSettings is a list of settings for the port. The valid settings are
as follows:
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:
During use of a port opened using {spawn, Name}, {spawn_driver,
Name}, or {spawn_executable, Name}, errors arising when sending
messages to it are reported to the owning process using signals of the form
{'EXIT', Port, PosixCode}. For the possible values of PosixCode,
see file(3erl).
The maximum number of ports that can be open at the same time can be configured
by passing command-line flag +Q to erl(1).
Note:
The characters in the name (if specified as a list) can only be > 255 if the
Erlang virtual machine is started in Unicode filename translation mode.
Otherwise the name of the executable is limited to the ISO Latin-1 character
set.
PortNames:
- {spawn, Command}:
- Starts an external program. Command is the name of the external program to be run. Command runs outside the Erlang work space unless an Erlang driver with the name Command is found. If found, that driver is started. A driver runs in the Erlang work space, which means that it is linked with the Erlang runtime system.
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 the OS). This is done by invoking the shell on
certain platforms. The first space-separated token of the command is
considered as the name of the executable (or driver). This (among other
things) makes this option unsuitable for running programs with spaces in
filenames or directory names. If spaces in executable filenames are desired,
use {spawn_executable, Command} instead.
- {spawn_driver, Command}:
- Works like {spawn, Command}, but demands the first (space-separated) token of the command to be the name of a loaded driver. If no driver with that name is loaded, a badarg error is raised.
- {spawn_executable, FileName}:
- Works like {spawn, FileName}, but only runs external executables. FileName in its whole is used as the name of the executable, including any spaces. If arguments are to be passed, the PortSettings args and arg0 can be used.
The shell is usually not invoked to start the program, it is executed directly.
PATH (or equivalent) is not searched. To find a program in PATH
to execute, use os:find_executable/1.
Only if a shell script or .bat file is executed, the appropriate command
interpreter is invoked implicitly, but there is still no command-argument
expansion or implicit PATH search.
If FileName cannot be run, an error exception is raised, with the POSIX
error code as the reason. The error reason can differ between OSs. Typically
the error enoent is raised when an attempt is made to run a program
that is not found and eacces is raised when the specified file is not
executable.
- {fd, In, Out}:
- Allows an Erlang process to access any currently opened file descriptors used by Erlang. The file descriptor In can be used for standard input, and the file descriptor Out for standard output. It is only used for various servers in the Erlang OS ( shell and user). Hence, its use is limited.
- {packet, N}:
- Messages are preceded by their length, sent in N bytes, with the most significant byte first. The valid values for N are 1, 2, and 4.
- stream:
- Output messages are sent without packet lengths. A user-defined protocol must be used between the Erlang process and the external object.
- {line, L}:
- Messages are delivered on a per line basis. Each line (delimited by the OS-dependent newline sequence) is delivered in a single message. The message data format is {Flag, Line}, where Flag is eol or noeol, and Line is the data delivered (without the newline sequence).
L specifies the maximum line length in bytes. Lines longer than this are
delivered in more than one message, with Flag set to noeol for
all but the last message. If end of file is encountered anywhere else than
immediately following a newline sequence, the last line is also delivered with
Flag set to noeol. Otherwise lines are delivered with
Flag set to eol.
The {packet, N} and {line, L} settings are mutually
exclusive.
- {cd, Dir}:
- Only valid for {spawn, Command} and {spawn_executable, FileName}. The external program starts using Dir as its working directory. Dir must be a string.
- {env, Env}:
- 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 specified as a separate string and (on Unix) eventually ends up as one element each in the argument vector. On other platforms, a similar behavior is mimicked.
The arguments are not expanded by the shell before they are supplied to the
executable. Most notably this means that file wildcard expansion does not
occur. To expand wildcards for the arguments, use
filelib:wildcard/1. Notice that even if the program is a Unix
shell script, meaning that the shell ultimately is invoked, wildcard expansion
does not occur, and the script is provided with the untouched arguments. On
Windows, wildcard expansion is always up to the program itself, therefore this
is not an issue.
The executable name (also known as argv[0]) is not to be specified in
this list. The proper executable name is automatically used as argv[0],
where applicable.
If you explicitly want to set the program name in the argument vector, option
arg0 can be used.
- {arg0, string() | binary()}:
- Only valid for {spawn_executable, FileName} and explicitly specifies the program name argument when running an executable. This can in some circumstances, on some OSs, be desirable. How the program responds to this is highly system-dependent and no specific effect is guaranteed.
- exit_status:
- Only valid for {spawn, Command}, where Command refers to an external program, and for {spawn_executable, FileName}.
When the external process connected to the port exits, a message of the form
{Port,{exit_status,Status}} is sent to the connected process, where
Status is the exit status of the external process. If the program
aborts on Unix, the same convention is used as the shells do (that is,
128+signal).
If option eof is specified also, the messages eof and
exit_status appear in an unspecified order.
If the port program closes its stdout without exiting, option
exit_status does not work.
- use_stdio:
- Only valid for {spawn, Command} and {spawn_executable, FileName}. It allows the standard input and output (file descriptors 0 and 1) of the spawned (Unix) process for communication with Erlang.
- nouse_stdio:
- The opposite of use_stdio. It uses file descriptors 3 and 4 for communication with Erlang.
- stderr_to_stdout:
- Affects ports to external programs. The executed program gets its standard error file redirected to its standard output file. stderr_to_stdout and nouse_stdio are mutually exclusive.
- overlapped_io:
- Affects ports to external programs on Windows only. The standard input and standard output handles of the port program are, if this option is supplied, opened with flag FILE_FLAG_OVERLAPPED, so that the port program can (and must) do overlapped I/O on its standard handles. This is not normally the case for simple port programs, but an option of value for the experienced Windows programmer. On all other platforms, this option is silently discarded.
- in:
- The port can only be used for input.
- out:
- The port can only be used for output.
- binary:
- All I/O from the port is binary data objects as opposed to lists of bytes.
- eof:
- The port is not closed at the end of the file and does not produce an exit signal. Instead, it remains open and a {Port, eof} message is sent to the process holding the port.
- hide:
- When running on Windows, suppresses creation of a new console window when spawning the port program. (This option has no effect on other platforms.)
- {parallelism, Boolean}:
Sets scheduler hint for port parallelism. If set to true, the virtual
machine schedules port tasks; when doing so, it improves parallelism in the
system. If set to false, the virtual machine tries to perform port
tasks immediately, improving latency at the expense of parallelism. The
default can be set at system startup by passing command-line argument
+spp to erl(1).
- badarg:
- Bad input arguments to open_port.
- system_limit:
- All available ports in the Erlang emulator are in use.
- enomem:
- Not enough memory to create the port.
- eagain:
- No more available OS processes.
- enametoolong:
- Too long external command.
- emfile:
- No more available file descriptors (for the OS process that the Erlang emulator runs in).
- enfile:
- Full file table (for the entire OS).
- eacces:
- Command specified in {spawn_executable, Command} does not point out an executable file.
- enoent:
- FileName specified in {spawn_executable, FileName} does not point out an existing file.
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.
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).
port_close(Port) -> true
Types:
Port = port() | atom()
Closes an open port. Roughly the same as Port ! {self(), close} except
for the error behavior (see below), being synchronous, and that the port does
not reply with {Port, closed}. Any process can close a port with
port_close/1, not only the port owner (the connected process). If the
calling process is linked to the port identified by Port, the exit
signal from the port is guaranteed to be delivered before port_close/1
returns.
For comparison: Port ! {self(), close} only fails with badarg if
Port does not refer to a port or a process. If Port is a closed
port, nothing happens. If Port is an open port and the calling process
is the port owner, the port replies with {Port, closed} when all
buffers have been flushed and the port really closes. If the calling process
is not the port owner, the port owner fails with badsig.
Notice that any process can close a port using Port ! {PortOwner, close}
as if it itself was the port owner, but the reply always goes to the port
owner.
As from Erlang/OTP R16, Port ! {PortOwner, close} is truly asynchronous.
Notice that this operation has always been documented as an asynchronous
operation, while the underlying implementation has been synchronous.
port_close/1 is however still fully synchronous because of its error
behavior.
Failure: badarg if Port is not an identifier of an open port, or
the registered name of an open port. If the calling process was previously
linked to the closed port, identified by Port, the exit signal from the
port is guaranteed to be delivered before this badarg exception
occurs.
port_command(Port, Data) -> true
Types:
Port = port() | atom()
Data = iodata()
Sends data to a port. Same as Port ! {PortOwner, {command, Data}} except
for the error behavior and being synchronous (see below). Any process can send
data to a port with port_command/2, not only the port owner (the
connected process).
For comparison: Port ! {PortOwner, {command, Data}} only fails with
badarg if Port does not refer to a port or a process. If
Port is a closed port, the data message disappears without a sound. If
Port is open and the calling process is not the port owner, the port
owner fails with badsig. The port owner fails with badsig
also if Data is an invalid I/O list.
Notice that any process can send to a port using Port ! {PortOwner, {command,
Data}} as if it itself was the port owner.
If the port is busy, the calling process is suspended until the port is not busy
any more.
As from Erlang/OTP R16, Port ! {PortOwner, {command, Data}} is truly
asynchronous. Notice that this operation has always been documented as an
asynchronous operation, while the underlying implementation has been
synchronous. port_command/2 is however still fully synchronous because
of its error behavior.
Failures:
- badarg:
- If Port is not an identifier of an open port, or the registered name of an open port. If the calling process was previously linked to the closed port, identified by Port, the exit signal from the port is guaranteed to be delivered before this badarg exception occurs.
- badarg:
- If Data is an invalid I/O list.
port_command(Port, Data, OptionList) -> boolean()
Types:
Port = port() | atom()
Data = iodata()
Option = force | nosuspend
OptionList = [Option]
Sends data to a port. port_command(Port, Data, []) equals
port_command(Port, Data).
If the port command is aborted, false is returned, otherwise true.
If the port is busy, the calling process is suspended until the port is not busy
anymore.
Options:
- force:
- The calling process is not suspended if the port is busy, instead the port command is forced through. The call fails with a notsup exception if the driver of the port does not support this. For more information, see driver flag ![CDATA[ERL_DRV_FLAG_SOFT_BUSY]].
- nosuspend:
- The calling process is not suspended if the port is busy, instead the port command is aborted and false is returned.
Note:
More options can be added in a future release.
Failures:
- badarg:
-
If Port is not an identifier of an open port, or the registered name of an open port. If the calling process was previously linked to the closed port, identified by Port, the exit signal from the port is guaranteed to be delivered before this badarg exception occurs.
- badarg:
-
If Data is an invalid I/O list.
- badarg:
-
If OptionList is an invalid option list.
- notsup:
-
If option force has been passed, but the driver of the port does not allow forcing through a busy port.
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 old port owner stays linked to the port and must call unlink(Port) if
this is not desired. Any process can set the port owner to be any process with
port_connect/2.
For comparison: Port ! {self(), {connect, Pid}} only fails with
badarg if Port does not refer to a port or a process. If
Port is a closed port, nothing happens. If Port is an open port
and the calling process is the port owner, the port replies with {Port,
connected} to the old port owner. Notice that the old port owner is still
linked to the port, while the new is not. If Port is an open port and
the calling process is not the port owner, the port owner fails with
badsig. The port owner fails with badsig also if Pid is
not an existing local process identifier.
Notice that any process can set the port owner using Port ! {PortOwner,
{connect, Pid}} as if it itself was the port owner, but the reply always
goes to the port owner.
As from Erlang/OTP R16, Port ! {PortOwner, {connect, Pid}} is truly
asynchronous. Notice that this operation has always been documented as an
asynchronous operation, while the underlying implementation has been
synchronous. port_connect/2 is however still fully synchronous because
of its error behavior.
Failures:
- *
- The error behavior differs, see below.
- *
- The port does not reply with {Port,connected}.
- *
- port_connect/1 is synchronous, see below.
- *
- The new port owner gets linked to the port.
- badarg:
-
If Port is not an identifier of an open port, or the registered name of an open port. If the calling process was previously linked to the closed port, identified by Port, the exit signal from the port is guaranteed to be delivered before this badarg exception occurs.
- badarg:
- If the process identified by Pid is not an existing local process.
port_control(Port, Operation, Data) -> iodata() | binary()
Types:
Port = port() | atom()
Operation = integer()
Data = iodata()
Performs a synchronous control operation on a port. The meaning of
Operation and Data depends on the port, that is, on the port
driver. Not all port drivers support this control feature.
Returns a list of integers in the range 0..255, or a binary, depending on the
port driver. The meaning of the returned data also depends on the port driver.
Failures:
- badarg:
-
If Port is not an open port or the registered name of an open port.
- badarg:
-
If Operation cannot fit in a 32-bit integer.
- badarg:
-
If the port driver does not support synchronous control operations.
- badarg:
-
If the port driver so decides for any reason (probably something wrong with Operation or Data).
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
{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}
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:
For more information about the different Items, see
port_info/2.
Failure: badarg if Port is not a local port identifier, or an
atom.
- *
- registered_name (if the port has a registered name)
- *
- id
- *
- connected
- *
- links
- *
- name
- *
- input
- *
- output
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:
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.
- *
- false (emulator without SMP support)
- *
- port_level (port-specific locking)
- *
- driver_level (driver-specific locking)
erlang:port_info(Port, Item :: memory) -> {memory, Bytes} | undefined
Types:
Port = port() | atom()
Bytes = integer() >= 0
Bytes is the total number of bytes allocated for this port by the runtime
system. The port itself can have allocated memory that is not included in
Bytes.
If the port identified by Port is not open, undefined is returned.
If the port is closed and the calling process was previously linked to the
port, the exit signal from the port is guaranteed to be delivered before
port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: monitors) -> {monitors, Monitors} | undefined
Types:
Port = port() | atom()
Monitors = [{process, pid()}]
Monitors represent processes monitored by this port.
If the port identified by Port is not open, undefined is returned.
If the port is closed and the calling process was previously linked to the
port, the exit signal from the port is guaranteed to be delivered before
port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: monitored_by) -> {monitored_by, MonitoredBy} | undefined
Types:
Port = port() | atom()
MonitoredBy = [pid()]
Returns list of pids that are monitoring given port at the moment.
If the port identified by Port is not open, undefined is returned.
If the port is closed and the calling process was previously linked to the
port, the exit signal from the port is guaranteed to be delivered before
port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: name) -> {name, Name} | undefined
Types:
Port = port() | atom()
Name = string()
Name is the command name set by open_port/2.
If the port identified by Port is not open, undefined is returned.
If the port is closed and the calling process was previously linked to the
port, the exit signal from the port is guaranteed to be delivered before
port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: os_pid) -> {os_pid, OsPid} | undefined
Types:
Port = port() | atom()
OsPid = integer() >= 0 | undefined
OsPid is the process identifier (or equivalent) of an OS process created
with open_port({spawn | spawn_executable, Command}, Options). If
the port is not the result of spawning an OS process, the value is
undefined.
If the port identified by Port is not open, undefined is returned.
If the port is closed and the calling process was previously linked to the
port, the exit signal from the port is guaranteed to be delivered before
port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: output) -> {output, Bytes} | undefined
Types:
Port = port() | atom()
Bytes = integer() >= 0
Bytes is the total number of bytes written to the port from Erlang
processes using port_command/2, port_command/3, or
Port ! {Owner, {command, Data}.
If the port identified by Port is not open, undefined is returned.
If the port is closed and the calling process was previously linked to the
port, the exit signal from the port is guaranteed to be delivered before
port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: parallelism) -> {parallelism, Boolean} | undefined
Types:
Port = port() | atom()
Boolean = boolean()
Boolean corresponds to the port parallelism hint used by this port. For
more information, see option parallelism of
open_port/2.
erlang:port_info(Port, Item :: queue_size) -> {queue_size, Bytes} | undefined
Types:
Port = port() | atom()
Bytes = integer() >= 0
Bytes is the total number of bytes queued by the port using the ERTS
driver queue implementation.
If the port identified by Port is not open, undefined is returned.
If the port is closed and the calling process was previously linked to the
port, the exit signal from the port is guaranteed to be delivered before
port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: registered_name) -> {registered_name, RegisteredName} | [] | undefined
Types:
Port = port() | atom()
RegisteredName = atom()
RegisteredName is the registered name of the port. If the port has no
registered name, [] is returned.
If the port identified by Port is not open, undefined is returned.
If the port is closed and the calling process was previously linked to the
port, the exit signal from the port is guaranteed to be delivered before
port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
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 :: max_heap_size, MaxHeapSize) -> OldMaxHeapSize
Types:
MaxHeapSize = OldMaxHeapSize = max_heap_size()
max_heap_size() =integer() >= 0 |#{size => integer() >= 0,kill => boolean(),error_logger => boolean()}
This flag sets the maximum heap size for the calling process. If
MaxHeapSize is an integer, the system default values for kill
and error_logger are used.
The heap size of a process is quite hard to predict, especially the amount of
memory that is used during the garbage collection. When contemplating using
this option, it is recommended to first run it in production with kill
set to false and inspect the error_logger reports to see what
the normal peak sizes of the processes in the system is and then tune the
value accordingly.
- size:
- The maximum size in words of the process. If set to zero, the heap size limit is disabled. badarg is be thrown if the value is smaller than min_heap_size. The size check is only done when a garbage collection is triggered.
size is the entire heap of the process when garbage collection is
triggered. This includes all generational heaps, the process stack, any
messages that are considered to be part of the heap, and any extra memory
that the garbage collector needs during collection.
size is the same as can be retrieved using
erlang:process_info(Pid, total_heap_size), or by adding
heap_block_size, old_heap_block_size and mbuf_size from
erlang:process_info(Pid, garbage_collection_info).
- kill:
- When set to true, the runtime system sends an untrappable exit signal with reason kill to the process if the maximum heap size is reached. The garbage collection that triggered the kill is not completed, instead the process exits as soon as possible. When set to false, no exit signal is sent to the process, instead it continues executing.
If kill is not defined in the map, the system default will be used. The
default system default is true. It can be changed by either option
+hmaxk in erl(1), or erlang:system_flag(max_heap_size,
MaxHeapSize).
- error_logger:
- When set to true, the runtime system sends a message to the current error_logger containing details about the process when the maximum heap size is reached. One error_logger report is sent each time the limit is reached.
If error_logger is not defined in the map, the system default is used.
The default system default is true. It can be changed by either the
option +hmaxel int erl(1), or
erlang:system_flag(max_heap_size, MaxHeapSize).
process_flag(Flag :: message_queue_data, MQD) -> OldMQD
Types:
MQD = OldMQD = message_queue_data()
message_queue_data() = off_heap | on_heap
This flag determines how messages in the message queue are stored, as follows:
The default message_queue_data process flag is determined by command-line
argument +hmqd in erl(1).
If the process potentially can get many messages, you are advised to set the
flag to off_heap. This because a garbage collection with many messages
placed on the heap can become extremly expensive and the process can consume
large amounts of memory. Performance of the actual message passing is however
generally better when not using flag off_heap.
When changing this flag messages will be moved. This work has been initiated but
not completed when this function call returns.
Returns the old value of the flag.
- off_heap:
- All messages in the message queue will be stored outside of the process heap. This implies that no messages in the message queue will be part of a garbage collection of the process.
- on_heap:
- All messages in the message queue will eventually be placed on heap. They can however temporarily be stored off heap. This is how messages always have been stored up until ERTS 8.0.
process_flag(Flag :: priority, Level) -> OldLevel
Types:
Level = OldLevel = priority_level()
priority_level() = low | normal | high | max
Sets the process priority. Level is an atom. Four priority levels exist:
low, normal, high, and max. Default is
normal.
Note:
Priority level max is reserved for internal use in the Erlang runtime
system, and is not to be used by others.
Internally in each priority level, processes are scheduled in a round robin
fashion.
Execution of processes on priority normal and low are interleaved.
Processes on priority low are selected for execution less frequently
than processes on priority normal.
When runnable processes on priority high exist, no processes on priority
low or normal are selected for execution. Notice however that
this does not mean that no processes on priority low or
normal can run when processes are running on priority high. 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 runnable processes on priority max exist, no processes on priority
low, normal, or high are selected for execution. As with
priority high, processes on lower priorities can execute in parallel
with processes on priority max.
Scheduling is pre-emptive. Regardless of priority, a process is pre-empted when
it has consumed more than a certain number of reductions since the last time
it was selected for execution.
Note:
Do not depend on the scheduling to remain exactly as it is today. Scheduling, 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 has no
control over can cause the high priority process to wait for a process
with lower priority. That is, effectively decreasing the priority of the
high priority process during the call. Even if this is not the case
with one version of the code that you have no control over, it can be the case
in a future version of it. This can, for example, occur if a high
priority process triggers code loading, as the code server runs on priority
normal.
Other priorities than normal are normally not needed. When other
priorities are used, use them with care, especially priority
high. A process on priority high is only to perform work for
short periods. Busy looping for long periods in a high priority process
causes most likely problems, as important OTP servers run on priority
normal.
Returns the old value of the flag.process_flag(Flag :: save_calls, N) -> OldN
Types:
N = OldN = 0..10000
N must be an integer in the interval 0..10000. If N > 0, call
saving is made active for the process. This means that information about the
N most recent global function calls, BIF calls, sends, and receives
made by the process are saved in a list, which can be retrieved with
process_info(Pid, last_calls). A global function call is one in which
the module of the function is explicitly mentioned. Only a fixed amount of
information is saved, as follows:
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.
- *
- 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)
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:
process_info/1,2 cannot be used to read out the message queue or the
process dictionary (both are returned as empty lists).
Stack back-traces cannot be displayed for the process.
In crash dumps, the stack, messages, and the process dictionary are omitted.
If {save_calls,N} has been set for the process, no function calls are
saved to the call saving list. (The call saving list is not cleared. Also,
send, receive, and time-out events are still added to the list.)
Returns the old value of the flag.
- *
- 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_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}]} |{garbage_collection_info,GCInfo :: [{atom(), integer() >= 0}]} |{group_leader, GroupLeader :: pid()} |{heap_size, Size :: integer() >= 0} |{initial_call, mfa()} |{links, PidsAndPorts :: [pid() | port()]} |{last_calls, false | (Calls :: [mfa()])} |{memory, Size :: integer() >= 0} |{message_queue_len, MessageQueueLen :: integer() >= 0} |{messages, MessageQueue :: [term()]} |{min_heap_size, MinHeapSize :: integer() >= 0} |{min_bin_vheap_size, MinBinVHeapSize :: integer() >= 0} |{max_heap_size, MaxHeapSize :: max_heap_size()} |{monitored_by, Pids :: [pid()]} |{monitors,Monitors ::[{process | port,Pid ::pid() |port() |{RegName :: atom(), Node :: node()}}]} |{message_queue_data, MQD :: message_queue_data()} |{priority, Level :: priority_level()} |{reductions, Number :: integer() >= 0} |{registered_name, [] | (Atom :: atom())} |{sequential_trace_token,[] | (SequentialTraceToken :: term())} |{stack_size, Size :: integer() >= 0} |{status,Status ::exiting |garbage_collecting |waiting |running |runnable |suspended} |{suspending,SuspendeeList ::[{Suspendee :: pid(),ActiveSuspendCount :: integer() >= 0,OutstandingSuspendCount :: integer() >= 0}]} |{total_heap_size, Size :: integer() >= 0} |{trace, InternalTraceFlags :: integer() >= 0} |{trap_exit, Boolean :: boolean()}
priority_level() = low | normal | high | max
stack_item() ={Module :: module(),Function :: atom(),Arity :: arity() | (Args :: [term()]),Location ::[{file, Filename :: string()} |{line, Line :: integer() >= 1}]}
max_heap_size() =integer() >= 0 |#{size => integer() >= 0,kill => boolean(),error_logger => boolean()}
message_queue_data() = off_heap | on_heap
Returns a list containing InfoTuples with miscellaneous information about
the process identified by Pid, or undefined if the process is
not alive.
The order of the InfoTuples is undefined and all InfoTuples are
not mandatory. The InfoTuples part of the result can be changed without
prior notice.
The InfoTuples with the following items are part of the result:
If the process identified by Pid has a registered name, also an
InfoTuple with item registered_name is included.
For information about specific InfoTuples, see
process_info/2.
- *
- 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
Warning:
This BIF is intended for debugging only. For all other purposes, use
process_info/2.
Failure: badarg if Pid is not a local process.process_info(Pid, Item) -> InfoTuple | [] | undefined
process_info(Pid, ItemList) -> InfoTupleList | [] | undefined
Types:
Pid = pid()
ItemList = [Item]
Item = process_info_item()
InfoTupleList = [InfoTuple]
InfoTuple = process_info_result_item()
process_info_item() =backtrace |binary |catchlevel |current_function |current_location |current_stacktrace |dictionary |error_handler |garbage_collection |garbage_collection_info |group_leader |heap_size |initial_call |links |last_calls |memory |message_queue_len |messages |min_heap_size |min_bin_vheap_size |monitored_by |monitors |message_queue_data |priority |reductions |registered_name |sequential_trace_token |stack_size |status |suspending |total_heap_size |trace |trap_exit
process_info_result_item() ={backtrace, Bin :: binary()} |{binary,BinInfo ::[{integer() >= 0,integer() >= 0,integer() >= 0}]} |{catchlevel, CatchLevel :: integer() >= 0} |{current_function,{Module :: module(), Function :: atom(), Arity :: arity()}} |{current_location,{Module :: module(),Function :: atom(),Arity :: arity(),Location ::[{file, Filename :: string()} |{line, Line :: integer() >= 1}]}} |{current_stacktrace, Stack :: [ stack_item()]} |{dictionary, Dictionary :: [{Key :: term(), Value :: term()}]} |{error_handler, Module :: module()} |{garbage_collection, GCInfo :: [{atom(), integer() >= 0}]} |{garbage_collection_info,GCInfo :: [{atom(), integer() >= 0}]} |{group_leader, GroupLeader :: pid()} |{heap_size, Size :: integer() >= 0} |{initial_call, mfa()} |{links, PidsAndPorts :: [pid() | port()]} |{last_calls, false | (Calls :: [mfa()])} |{memory, Size :: integer() >= 0} |{message_queue_len, MessageQueueLen :: integer() >= 0} |{messages, MessageQueue :: [term()]} |{min_heap_size, MinHeapSize :: integer() >= 0} |{min_bin_vheap_size, MinBinVHeapSize :: integer() >= 0} |{max_heap_size, MaxHeapSize :: max_heap_size()} |{monitored_by, Pids :: [pid()]} |{monitors,Monitors ::[{process | port,Pid ::pid() |port() |{RegName :: atom(), Node :: node()}}]} |{message_queue_data, MQD :: message_queue_data()} |{priority, Level :: priority_level()} |{reductions, Number :: integer() >= 0} |{registered_name, [] | (Atom :: atom())} |{sequential_trace_token,[] | (SequentialTraceToken :: term())} |{stack_size, Size :: integer() >= 0} |{status,Status ::exiting |garbage_collecting |waiting |running |runnable |suspended} |{suspending,SuspendeeList ::[{Suspendee :: pid(),ActiveSuspendCount :: integer() >= 0,OutstandingSuspendCount :: integer() >= 0}]} |{total_heap_size, Size :: integer() >= 0} |{trace, InternalTraceFlags :: integer() >= 0} |{trap_exit, Boolean :: boolean()}
stack_item() ={Module :: module(),Function :: atom(),Arity :: arity() | (Args :: [term()]),Location ::[{file, Filename :: string()} |{line, Line :: integer() >= 1}]}
priority_level() = low | normal | high | max
max_heap_size() =integer() >= 0 |#{size => integer() >= 0,kill => boolean(),error_logger => boolean()}
message_queue_data() = off_heap | on_heap
Returns information about the process identified by Pid, as specified by
Item or ItemList. Returns undefined if the process is not
alive.
If the process is alive and a single Item is specified, the returned
value is the corresponding InfoTuple, unless Item =:=
registered_name and the process has no registered name. In this case,
[] is returned. This strange behavior is because of historical reasons,
and is kept for backward compatibility.
If ItemList is specified, the result is InfoTupleList. The
InfoTuples in InfoTupleList are included with the corresponding
Items in the same order as the Items were included in
ItemList. Valid Items can be included multiple times in
ItemList.
Notice that not all implementations support all these Items.
Failures:
Note:
If registered_name is part of ItemList and the process has no name
registered, a {registered_name, []}, InfoTuple will be
included in the resulting InfoTupleList. This behavior is different
when a single Item =:= registered_name is specified, and when
process_info/1 is used.
Valid InfoTuples with corresponding Items:
- {backtrace, Bin}:
- Binary Bin contains the same information as the output from erlang:process_display(Pid, backtrace). Use binary_to_list/1 to obtain the string of characters from the binary.
- {binary, BinInfo}:
- BinInfo is a list containing miscellaneous information about binaries currently 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.
- {garbage_collection_info, GCInfo}:
- GCInfo is a list containing miscellaneous detailed information about garbage collection for this process. The content of GCInfo can be changed without prior notice. For details about the meaning of each item, see gc_minor_start in erlang:trace/3.
- {group_leader, GroupLeader}:
- GroupLeader is the group leader for the I/O of the process.
- {heap_size, Size}:
- Size is the size in words of the youngest heap generation of the process. This generation includes the process stack. This information is highly implementation-dependent, and can change if the implementation changes.
- {initial_call, {Module, Function, Arity}}:
- Module, Function, Arity is the initial function call with which the process was spawned.
- {links, PidsAndPorts}:
- PidsAndPorts is a list of process identifiers and port identifiers, with processes or ports to which the process has a link.
- {last_calls, false|Calls}:
- The value is false if call saving is not active for the process (see process_flag/3). If call saving is active, a list is returned, in which the last element is the most recent called.
- {memory, Size}:
- Size is the size in bytes of the process. This includes call stack, heap, and internal structures.
- {message_queue_len, MessageQueueLen}:
- MessageQueueLen is the number of messages currently in the message queue of the process. This is the length of the list MessageQueue returned as the information item messages (see below).
- {messages, MessageQueue}:
- MessageQueue is a list of the messages to the process, which have not yet been processed.
- {min_heap_size, MinHeapSize}:
- MinHeapSize is the minimum heap size for the process.
- {min_bin_vheap_size, MinBinVHeapSize}:
- MinBinVHeapSize is the minimum binary virtual heap size for the process.
- {monitored_by, 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 consists of:
- {process, Pid}:
- Process is monitored by pid.
- {process, {RegName, Node}}:
- Local or remote process is monitored by name.
- {port, PortId}:
- Local port is monitored by port id.
- {port, {RegName, Node}}:
- Local port is monitored by name. Please note, that remote port monitors are not supported, so Node will always be the local node name.
- {message_queue_data, MQD}:
- Returns the current state of process flag message_queue_data. MQD is either off_heap or on_heap. For more information, see the documentation of process_flag(message_queue_data, MQD).
- {priority, Level}:
- Level is the current priority level for the process. For more information on priorities, see process_flag(priority, Level).
- {reductions, Number}:
- Number is the number of reductions executed by the process.
- {registered_name, Atom}:
- Atom is the registered process name. If the process has no registered name, this tuple is not present in the list.
- {sequential_trace_token, [] | SequentialTraceToken}:
- SequentialTraceToken is the sequential trace token for the process. This InfoTuple can be changed or removed without prior notice.
- {stack_size, Size}:
- Size is the stack size, in words, of the process.
- {status, Status}:
- Status is the status of the process and is one of the following:
- *
- exiting
- *
- garbage_collecting
- *
- waiting (for a message)
- *
- running
- *
- runnable (ready to run, but another process is running)
- *
- suspended (suspended on a "busy" port or by the BIF erlang:suspend_process/1,2)
- {suspending, SuspendeeList}:
- SuspendeeList is a list of {Suspendee, ActiveSuspendCount, OutstandingSuspendCount} tuples. Suspendee is the process identifier of a process that has been, or is to be, suspended by the process identified by Pid through the BIF erlang:suspend_process/2 or erlang:suspend_process/1.
ActiveSuspendCount is the number of times Suspendee has been
suspended by Pid. OutstandingSuspendCount is the number of not
yet completed suspend requests sent by Pid, that is:
- *
- If ActiveSuspendCount =/= 0, Suspendee is currently in the suspended state.
- *
- If OutstandingSuspendCount =/= 0, option asynchronous of erlang:suspend_process/2 has been used and the suspendee has not yet been suspended by Pid.
Notice that ActiveSuspendCount and OutstandingSuspendCount are not
the total suspend count on Suspendee, only the parts contributed by
Pid.
- {total_heap_size, Size}:
- Size is the total size, in words, of all heap fragments of the process. This includes the process stack and any unreceived messages that are considered to be part of the heap.
- {trace, InternalTraceFlags}:
- InternalTraceFlags is an integer representing the internal trace flag for this process. This InfoTuple can be changed or removed without prior notice.
- {trap_exit, Boolean}:
- Boolean is true if the process is trapping exits, otherwise false.
- badarg:
- If Pid is not a local process.
- badarg:
- If Item is an invalid item.
processes() -> [pid()]
Returns a list of process identifiers corresponding to all the processes
currently existing on the local node.
Notice that an exiting process exists, but is not alive. That is,
is_process_alive/1 returns false for an exiting process, but its
process identifier is part of the result returned from processes/0.
Example:
> processes(). [<0.0.0>,<0.2.0>,<0.4.0>,<0.5.0>,<0.7.0>,<0.8.0>]
purge_module(Module) -> true
Types:
Module = atom()
Removes old code for Module. Before this BIF is used,
check_process_code/2is to be called to check that no processes
execute old code in the module.
Warning:
This BIF is intended for the code server (see code(3erl)) and is
not to be used elsewhere.
Note:
As from ERTS 8.0 (Erlang/OTP 19), any lingering processes that still execute the
old code is killed by this function. In earlier versions, such incorrect use
could cause much more fatal failures, like emulator crash.
Failure: badarg if there is no old code for Module.put(Key, Val) -> term()
Types:
Key = Val = term()
Adds a new Key to the process dictionary, associated with the value
Val, and returns undefined. If Key exists, the old value
is deleted and replaced by Val, and the function returns the old value.
Example:
> X = put(name, walrus), Y = put(name, carpenter), Z = get(name), {X, Y, Z}. {undefined,walrus,carpenter}
Note:
The values stored when put is evaluated within the scope of a
catch are not retracted if a throw is evaluated, or if an error
occurs.
erlang:raise(Class, Reason, Stacktrace) -> no_return()
Types:
Class = error | exit | throw
Reason = term()
Stacktrace = raise_stacktrace()
raise_stacktrace() =[{module(), atom(), arity() | [term()]} |{function(), [term()]}] |[{module(), atom(), arity() | [term()], [{atom(), term()}]} |{function(), [term()], [{atom(), term()}]}]
Stops the execution of the calling process with an exception of the specified
class, reason, and call stack backtrace ( stacktrace).
Class is error, exit, or throw. So, if it were not
for the stacktrace, erlang:raise(Class, Reason, Stacktrace) is
equivalent to erlang:Class(Reason).
Reason is any term. Stacktrace is a list as returned from
get_stacktrace(), that is, a list of four-tuples {Module, Function,
Arity | Args, Location}, where Module and Function are
atoms, and the third element is an integer arity or an argument list. The
stacktrace can also contain {Fun, Args, Location} tuples, where
Fun is a local fun and Args is an argument list.
Element Location at the end is optional. Omitting it is equivalent to
specifying an empty list.
The stacktrace is used as the exception stacktrace for the calling process; it
is truncated to the current maximum stacktrace depth.
As evaluating this function causes the process to terminate, it has no return
value unless the arguments are invalid, in which case the function returns
the error reason badarg. If you want to be sure not to return, you
can call error(erlang:raise(Class, Reason, Stacktrace)) and hope to
distinguish exceptions later.
erlang:read_timer(TimerRef) -> Result
Types:
TimerRef = reference()
Time = integer() >= 0
Result = Time | false
Reads the state of a timer. The same as calling
erlang:read_timer(TimerRef, []).
erlang:read_timer(TimerRef, Options) -> Result | ok
Types:
TimerRef = reference()
Async = boolean()
Option = {async, Async}
Options = [Option]
Time = integer() >= 0
Result = Time | false
Reads the state of a timer that has been created by either
erlang:start_timer or erlang:send_after.
TimerRef identifies the timer, and was returned by the BIF that created
the timer.
Options:
More Options can be added in the future.
If Result is an integer, it represents the time in milliseconds left
until the timer expires.
If Result is false, a timer corresponding to TimerRef could
not be found. This because the timer had expired, or been canceled, or because
TimerRef never has corresponded to a timer. Even if the timer has
expired, it does not tell you whether or not the time-out message has arrived
at its destination yet.
- {async, Async}:
- Asynchronous request for state information. Async defaults to false, which causes the operation to be performed synchronously. In this case, the Result is returned by erlang:read_timer. When Async is true, erlang:read_timer sends an asynchronous request for the state information to the timer service that manages the timer, and then returns ok. A message on the format {read_timer, TimerRef, Result} is sent to the caller of erlang:read_timer when the operation has been processed.
Note:
The timer service that manages the timer can be co-located with another
scheduler than the scheduler that the calling process is executing on. If so,
communication with the timer service takes much longer time than if it is
located locally. If the calling process is in a critical path, and can do
other things while waiting for the result of this operation, you want to use
option {async, true}. If using option {async, false}, the
calling process is blocked until the operation has been performed.
See also erlang:send_after/4, erlang:start_timer/4,
and erlang:cancel_timer/2.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). trueFailures:
- 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). 6Allowed 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 below). Otherwise the same as
erlang:send/2. For more detailed explanation and warnings, see
erlang:send_nosuspend/2,3.
Options:
- nosuspend:
- If the sender would have to be suspended to do the send, nosuspend is returned instead.
- noconnect:
-
If the destination node would have to be auto-connected to do the send, noconnect is returned instead.
Warning:
As with erlang:send_nosuspend/2,3: use with extreme care.
erlang:send_after(Time, Dest, Msg) -> TimerRef
Types:
Time = integer() >= 0
Dest = pid() | atom()
Msg = term()
TimerRef = reference()
Starts a timer. The same as calling erlang:send_after(Time, Dest, Msg,
[]).
erlang:send_after(Time, Dest, Msg, Options) -> TimerRef
Types:
Time = integer()
Dest = pid() | atom()
Msg = term()
Options = [Option]
Abs = boolean()
Option = {abs, Abs}
TimerRef = reference()
Starts a timer. When the timer expires, the message Msg is sent to the
process identified by Dest. Apart from the format of the time-out
message, this function works exactly as
erlang:start_timer/4.
erlang:send_nosuspend(Dest, Msg) -> boolean()
Types:
Dest = dst()
Msg = term()
dst() =pid() |port() |(RegName :: atom()) |{RegName :: atom(), Node :: node()}
The same as erlang:send(Dest, Msg, [nosuspend]), but returns
true if the message was sent and false if the message was not
sent because the sender would have had to be suspended.
This function is intended for send operations to an unreliable remote node
without ever blocking the sending (Erlang) process. If the connection to the
remote node (usually not a real Erlang node, but a node written in C or Java)
is overloaded, this function does not send the message and returns
false.
The same occurs if Dest refers to a local port that is busy. For all
other destinations (allowed for the ordinary send operator '!'), this
function sends the message and returns true.
This function is only to be used in rare circumstances where a process
communicates with Erlang nodes that can disappear without any trace, causing
the TCP buffers and the drivers queue to be over-full before the node is shut
down (because of tick time-outs) by net_kernel. The normal reaction to
take when this occurs is some kind of premature shutdown of the other node.
Notice that ignoring the return value from this function would result in an
unreliable message passing, which is contradictory to the Erlang
programming model. The message is not sent if this function returns
false.
In many systems, transient states of overloaded queues are normal. Although this
function returns false does not mean that the other node is guaranteed
to be non-responsive, it could be a temporary overload. Also, a return value
of true does only mean that the message can be sent on the (TCP)
channel without blocking; the message is not guaranteed to arrive at the
remote node. For a disconnected non-responsive node, the return value is
true (mimics the behavior of operator !). The expected behavior
and the actions to take when the function returns false are
application- and hardware-specific.
Warning:
Use with extreme care.
erlang:send_nosuspend(Dest, Msg, Options) -> boolean()
Types:
Dest = dst()
Msg = term()
Options = [noconnect]
dst() =pid() |port() |(RegName :: atom()) |{RegName :: atom(), Node :: node()}
The same as erlang:send(Dest, Msg, [nosuspend | Options]), but
with a Boolean return value.
This function behaves like erlang:send_nosuspend/2, but takes a
third parameter, a list of options. The only option is noconnect, which
makes the function return false if the remote node is not currently
reachable by the local node. The normal behavior is to try to connect to the
node, which can stall the process during a short period. The use of option
noconnect makes it possible to be sure not to get the slightest delay
when sending to a remote process. This is especially useful when communicating
with nodes that expect to always be the connecting part (that is, nodes
written in C or Java).
Whenever the function returns false (either when a suspend would occur or
when noconnect was specified and the node was not already connected),
the message is guaranteed not to have been sent.
Warning:
Use with extreme care.
erlang:set_cookie(Node, Cookie) -> true
Types:
Node = node()
Cookie = atom()
Sets the magic cookie of Node to the atom Cookie. If Node
is the local node, the function also sets the cookie of all other unknown
nodes to Cookie (see section Distributed Erlang in the Erlang
Reference Manual in System Documentation).
Failure: function_clause if the local node is not alive.
setelement(Index, Tuple1, Value) -> Tuple2
Types:
Index = integer() >= 1
Value = term()
1..tuple_size(Tuple1
Tuple1 = Tuple2 = tuple()
Returns a tuple that is a copy of argument Tuple1 with the element
specified by integer argument Index (the first element is the element
with index 1) replaced by argument Value, for example:
> setelement(2, {10, green, bottles}, red). {10,red,bottles}
size(Item) -> integer() >= 0
Types:
Item = tuple() | binary()
Returns the number of elements in a tuple or the number of bytes in a binary or
bitstring, for example:
> size({morni, mulle, bwange}). 3 > size(<<11, 22, 33>>). 3For bitstrings, the number of whole bytes is returned. That is, if the number of bits in the bitstring is not divisible by 8, the resulting number of bytes is rounded down. Allowed in guard tests. See also tuple_size/1, byte_size/1, and bit_size/1.
spawn(Fun) -> pid()
Types:
Fun = function()
Returns the process identifier of a new process started by the application of
Fun to the empty list []. Otherwise works like
spawn/3.
spawn(Node, Fun) -> pid()
Types:
Node = node()
Fun = function()
Returns the process identifier of a new process started by the application of
Fun to the empty list [] on Node. If Node does not
exist, a useless pid is returned. Otherwise works like
spawn/3.
spawn(Module, Function, Args) -> pid()
Types:
Module = module()
Function = atom()
Args = [term()]
Returns the process identifier of a new process started by the application of
Module:Function to Args.
error_handler:undefined_function(Module, Function, Args) is evaluated by
the new process if Module:Function/Arity does not exist (where
Arity is the length of Args). The error handler can be redefined
(see process_flag/2). If error_handler is undefined, or
the user has redefined the default error_handler and its replacement is
undefined, a failure with reason undef occurs.
Example:
> spawn(speed, regulator, [high_speed, thin_cut]). <0.13.1>
spawn(Node, Module, Function, Args) -> pid()
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Returns the process identifier (pid) of a new process started by the application
of Module:Function to Args on Node. If Node does
not exist, a useless pid is returned. Otherwise works like
spawn/3.
spawn_link(Fun) -> pid()
Types:
Fun = function()
Returns the process identifier of a new process started by the application of
Fun to the empty list []. A link is created between the calling
process and the new process, atomically. Otherwise works like
spawn/3.
spawn_link(Node, Fun) -> pid()
Types:
Node = node()
Fun = function()
Returns the process identifier (pid) of a new process started by the application
of Fun to the empty list [] on Node. A link is created
between the calling process and the new process, atomically. If Node
does not exist, a useless pid is returned and an exit signal with reason
noconnection is sent to the calling process. Otherwise works like
spawn/3.
spawn_link(Module, Function, Args) -> pid()
Types:
Module = module()
Function = atom()
Args = [term()]
Returns the process identifier of a new process started by the application of
Module:Function to Args. A link is created between the calling
process and the new process, atomically. Otherwise works like
spawn/3.
spawn_link(Node, Module, Function, Args) -> pid()
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Returns the process identifier (pid) of a new process started by the application
of Module:Function to Args on Node. A link is created
between the calling process and the new process, atomically. If Node
does not exist, a useless pid is returned and an exit signal with reason
noconnection is sent to the calling process. Otherwise works like
spawn/3.
spawn_monitor(Fun) -> {pid(), reference()}
Types:
Fun = function()
Returns the process identifier of a new process, started by the application of
Fun to the empty list [], and a reference for a monitor created
to the new process. Otherwise works like spawn/3.
spawn_monitor(Module, Function, Args) -> {pid(), reference()}
Types:
Module = module()
Function = atom()
Args = [term()]
A new process is started by the application of Module:Function to
Args. The process is monitored at the same time. Returns the process
identifier and a reference for the monitor. Otherwise works like
spawn/3.
spawn_opt(Fun, Options) -> pid() | {pid(), reference()}
Types:
Fun = function()
Options = [ spawn_opt_option()]
priority_level() = low | normal | high | max
max_heap_size() =integer() >= 0 |#{size => integer() >= 0,kill => boolean(),error_logger => boolean()}
message_queue_data() = off_heap | on_heap
spawn_opt_option() =link |monitor |{priority, Level :: priority_level()} |{fullsweep_after, Number :: integer() >= 0} |{min_heap_size, Size :: integer() >= 0} |{min_bin_vheap_size, VSize :: integer() >= 0} |{max_heap_size, Size :: max_heap_size()} |{message_queue_data, MQD :: message_queue_data()}
Returns the process identifier (pid) of a new process started by the application
of Fun to the empty list []. Otherwise works like
spawn_opt/4.
If option monitor is specified, the newly created process is monitored,
and both the pid and reference for the monitor are returned.
spawn_opt(Node, Fun, Options) -> pid() | {pid(), reference()}
Types:
Node = node()
Fun = function()
Options = [ spawn_opt_option()]
priority_level() = low | normal | high | max
max_heap_size() =integer() >= 0 |#{size => integer() >= 0,kill => boolean(),error_logger => boolean()}
message_queue_data() = off_heap | on_heap
spawn_opt_option() =link |monitor |{priority, Level :: priority_level()} |{fullsweep_after, Number :: integer() >= 0} |{min_heap_size, Size :: integer() >= 0} |{min_bin_vheap_size, VSize :: integer() >= 0} |{max_heap_size, Size :: max_heap_size()} |{message_queue_data, MQD :: message_queue_data()}
Returns the process identifier (pid) of a new process started by the application
of Fun to the empty list [] on Node. If Node does
not exist, a useless pid is returned. Otherwise works like
spawn_opt/4.
spawn_opt(Module, Function, Args, Options) -> pid() | {pid(), reference()}
Types:
Module = module()
Function = atom()
Args = [term()]
Options = [ spawn_opt_option()]
priority_level() = low | normal | high | max
max_heap_size() =integer() >= 0 |#{size => integer() >= 0,kill => boolean(),error_logger => boolean()}
message_queue_data() = off_heap | on_heap
spawn_opt_option() =link |monitor |{priority, Level :: priority_level()} |{fullsweep_after, Number :: integer() >= 0} |{min_heap_size, Size :: integer() >= 0} |{min_bin_vheap_size, VSize :: integer() >= 0} |{max_heap_size, Size :: max_heap_size()} |{message_queue_data, MQD :: message_queue_data()}
Works as spawn/3, except that an extra option list is specified
when creating the process.
If option monitor is specified, the newly created process is monitored,
and both the pid and reference for the monitor are returned.
Options:
- link:
- Sets a link to the parent process (like spawn_link/3 does).
- monitor:
- Monitors the new process (like monitor/2 does).
- {priority, Level:
- Sets the priority of the new process. Equivalent to executing process_flag(priority, Level) in the start function of the new process, except that the priority is set before the process is selected for execution for the first time. For more information on priorities, see process_flag(priority, Level).
- {fullsweep_after, Number}:
- Useful only for performance tuning. Do not use this option unless you know that there is problem with execution times or memory consumption, and ensure that the option improves matters.
The Erlang runtime system uses a generational garbage collection scheme, using
an "old heap" for data that has survived at least one garbage
collection. When there is no more room on the old heap, a fullsweep garbage
collection is done.
Option fullsweep_after makes it possible to specify the maximum number of
generational collections before forcing a fullsweep, even if there is room on
the old heap. Setting the number to zero disables the general collection
algorithm, that is, all live data is copied at every garbage collection.
A few cases when it can be useful to change fullsweep_after:
- *
- If binaries that are no longer used are to be thrown away as soon as possible. (Set Number to zero.)
- *
- A process that mostly have short-lived data is fullsweeped seldom or never, that is, the old heap contains mostly garbage. To ensure a fullsweep occasionally, set Number to a suitable value, such as 10 or 20.
- *
- In embedded systems with a limited amount of RAM and no virtual memory, you might want to preserve memory by setting Number to zero. (The value can be set globally, see erlang:system_flag/2.)
- {min_heap_size, Size}:
- Useful only for performance tuning. Do not use this option unless you know that there is problem with execution times or memory consumption, and ensure that the option improves matters.
Gives a minimum heap size, in words. Setting this value higher than the system
default can speed up some processes because less garbage collection is done.
However, setting a too high value can waste memory and slow down the system
because of worse data locality. Therefore, use this option only for
fine-tuning an application and to measure the execution time with various
Size values.
- {min_bin_vheap_size, VSize}:
- Useful only for performance tuning. Do not use this option unless you know that there is problem with execution times or memory consumption, and ensure that the option improves matters.
Gives a minimum binary virtual heap size, in words. Setting this value higher
than the system default can speed up some processes because less garbage
collection is done. However, setting a too high value can waste memory.
Therefore, use this option only for fine-tuning an application and to measure
the execution time with various VSize values.
- {max_heap_size, Size}:
- Sets the max_heap_size process flag. The default max_heap_size is determined by command-line argument +hmax in erl(1). For more information, see the documentation of process_flag(max_heap_size, Size).
- {message_queue_data, MQD}:
- Sets the state of the message_queue_data process flag. MQD is to be either off_heap or on_heap. The default message_queue_data process flag is determined by command-line argument +hmqd in erl(1). For more information, see the documentation of process_flag(message_queue_data, MQD).
spawn_opt(Node, Module, Function, Args, Options) -> pid() | {pid(), reference()}
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Options = [ spawn_opt_option()]
priority_level() = low | normal | high | max
max_heap_size() =integer() >= 0 |#{size => integer() >= 0,kill => boolean(),error_logger => boolean()}
message_queue_data() = off_heap | on_heap
spawn_opt_option() =link |monitor |{priority, Level :: priority_level()} |{fullsweep_after, Number :: integer() >= 0} |{min_heap_size, Size :: integer() >= 0} |{min_bin_vheap_size, VSize :: integer() >= 0} |{max_heap_size, Size :: max_heap_size()} |{message_queue_data, MQD :: message_queue_data()}
Returns the process identifier (pid) of a new process started by the application
of Module:Function to Args on Node. If Node does
not exist, a useless pid is returned. Otherwise works like
spawn_opt/4.
Note:
Option monitor is not supported by spawn_opt/5.
split_binary(Bin, Pos) -> {binary(), binary()}
Types:
Bin = binary()
Pos = integer() >= 0
0..byte_size(Bin)
Returns a tuple containing the binaries that are the result of splitting
Bin into two parts at position Pos. This is not a destructive
operation. After the operation, there are three binaries altogether. Example:
> B = list_to_binary("0123456789"). <<"0123456789">> > byte_size(B). 10 > {B1, B2} = split_binary(B,3). {<<"012">>,<<"3456789">>} > byte_size(B1). 3 > byte_size(B2). 7
erlang:start_timer(Time, Dest, Msg) -> TimerRef
Types:
Time = integer() >= 0
Dest = pid() | atom()
Msg = term()
TimerRef = reference()
Starts a timer. The same as calling erlang:start_timer(Time, Dest,
Msg, []).
erlang:start_timer(Time, Dest, Msg, Options) -> TimerRef
Types:
Time = integer()
Dest = pid() | atom()
Msg = term()
Options = [Option]
Abs = boolean()
Option = {abs, Abs}
TimerRef = reference()
Starts a timer. When the timer expires, the message {timeout, TimerRef,
Msg} is sent to the process identified by Dest.
Options:
More Options can be added in the future.
The absolute point in time, the timer is set to expire on, must be in the
interval [erlang:system_info(start_time),
erlang:system_info(end_time)]. If a relative time is
specified, the Time value is not allowed to be negative.
If Dest is a pid(), it must be a pid() of a process created
on the current runtime system instance. This process has either terminated or
not. If Dest is an atom(), it is interpreted as the name of a
locally registered process. The process referred to by the name is looked up
at the time of timer expiration. No error is returned if the name does not
refer to a process.
If Dest is a pid(), the timer is automatically canceled if the
process referred to by the pid() is not alive, or if the process exits.
This feature was introduced in ERTS 5.4.11. Notice that timers are not
automatically canceled when Dest is an atom().
See also erlang:send_after/4, erlang:cancel_timer/2,
and erlang:read_timer/2.
Failure: badarg if the arguments do not satisfy the requirements
specified here.
- {abs, false}:
- This is the default. It means the Time value is interpreted as a time in milliseconds relative current Erlang monotonic time.
- {abs, true}:
- Absolute Time value. The Time value is interpreted as an absolute Erlang monotonic time in milliseconds.
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 :: microstate_accounting) -> [MSAcc_Thread] | undefined
Types:
MSAcc_Thread =
#{type := MSAcc_Thread_Type,
id := MSAcc_Thread_Id,
counters := MSAcc_Counters}
MSAcc_Thread_Type = scheduler | async | aux
MSAcc_Thread_Id = integer() >= 0
MSAcc_Counters = #{MSAcc_Thread_State => integer() >= 0}
MSAcc_Thread_State =
alloc |
aux |
bif |
busy_wait |
check_io |
emulator |
ets |
gc |
gc_fullsweep |
nif |
other |
port |
send |
sleep |
timers
#{type := MSAcc_Thread_Type,
id := MSAcc_Thread_Id,
counters := MSAcc_Counters}
alloc |
aux |
bif |
busy_wait |
check_io |
emulator |
ets |
gc |
gc_fullsweep |
nif |
other |
port |
send |
sleep |
timers
Microstate accounting can be used to measure how much time the Erlang runtime
system spends doing various tasks. It is designed to be as lightweight as
possible, but some overhead exists when this is enabled. Microstate accounting
is meant to be a profiling tool to help finding performance bottlenecks. To
start/stop/reset microstate accounting, use system flag
microstate_accounting.
statistics(microstate_accounting) returns a list of maps representing
some of the OS threads within ERTS. Each map contains type and
id fields that can be used to identify what thread it is, and also a
counters field that contains data about how much time has been spent in the
various states.
Example:
The following MSAcc_Thread_States are available. All states are
exclusive, meaning that a thread cannot be in two states at once. So, if you
add the numbers of all counters in a thread, you get the total runtime for
that thread.
More fine-grained MSAcc_Thread_States can be added through configure
(such as ./configure --with-microstate-accounting=extra). Enabling
these states causes performance degradation when microstate accounting is
turned off and increases the overhead when it is turned on.
The utility module msacc(3erl) can be used to more easily analyse
these statistics.
Returns undefined if system flag microstate_accounting is
turned off.
The list of thread information is unsorted and can appear in different order
between calls.
> erlang:statistics(microstate_accounting). [#{counters => #{aux => 1899182914, check_io => 2605863602, emulator => 45731880463, gc => 1512206910, other => 5421338456, port => 221631, sleep => 5150294100}, id => 1, type => scheduler}|...]The time unit is the same as returned by os:perf_counter/0. So, to convert it to milliseconds, you can do something like this:
lists:map( fun(#{ counters := Cnt } = M) -> MsCnt = maps:map(fun(_K, PerfCount) -> erlang:convert_time_unit(PerfCount, perf_counter, 1000) end, Cnt), M#{ counters := MsCnt } end, erlang:statistics(microstate_accounting)).Notice that these values are not guaranteed to be the exact time spent in each state. This is because of various optimisation done to keep the overhead as small as possible. MSAcc_Thread_Types:
- scheduler:
- The main execution threads that do most of the work.
- dirty_cpu_scheduler:
- The threads for long running cpu intensive work.
- dirty_io_scheduler:
- The threads for long running I/O work.
- async:
- Async threads are used by various linked-in drivers (mainly the file drivers) do offload non-CPU intensive work.
- aux:
- Takes care of any work that is not specifically assigned to a scheduler.
- aux:
- Time spent handling auxiliary jobs.
- check_io:
- Time spent checking for new I/O events.
- emulator:
- Time spent executing Erlang processes.
- gc:
- Time spent doing garbage collection. When extra states are enabled this is the time spent doing non-fullsweep garbage collections.
- other:
- Time spent doing unaccounted things.
- port:
- Time spent executing ports.
- sleep:
- Time spent sleeping.
- alloc:
- Time spent managing memory. Without extra states this time is spread out over all other states.
- bif:
- Time spent in BIFs. Without extra states this time is part of the emulator state.
- busy_wait:
- Time spent busy waiting. This is also the state where a scheduler no longer reports that it is active when using statistics(scheduler_wall_time). So, if you add all other states but this and sleep, and then divide that by all time in the thread, you should get something very similar to the scheduler_wall_time fraction. Without extra states this time is part of the other state.
- ets:
- Time spent executing ETS BIFs. Without extra states this time is part of the emulator state.
- gc_full:
- Time spent doing fullsweep garbage collection. Without extra states this time is part of the gc state.
- nif:
- Time spent in NIFs. Without extra states this time is part of the emulator state.
- send:
- Time spent sending messages (processes only). Without extra states this time is part of the emulator state.
- timers:
- Time spent managing timers. Without extra states this time is part of the other state.
Note:
The threads and states are subject to change without any prior notice.
statistics(Item :: reductions) -> {Total_Reductions, Reductions_Since_Last_Call}
Types:
Total_Reductions = Reductions_Since_Last_Call = integer()
>= 0
Returns information about reductions, for example:
> statistics(reductions). {2046,11}
Note:
As from ERTS 5.5 (Erlang/OTP R11B), this value does not include reductions
performed in current time slices of currently scheduled processes. If an exact
value is wanted, use statistics(exact_reductions).
statistics(Item :: run_queue) -> integer() >= 0
Returns the total length of 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), 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:
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:
- *
- Executing process code
- *
- Executing linked-in driver or NIF code
- *
- Executing BIFs, or any other runtime handling
- *
- Garbage collecting
- *
- Handling any other memory management
> erlang:system_flag(scheduler_wall_time, true). false > Ts0 = lists:sort(erlang:statistics(scheduler_wall_time)), ok. okSome 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) -> true
Types:
Suspendee = pid()
Suspends the process identified by Suspendee. The same as calling
erlang:suspend_process(Suspendee, []).
Warning:
This BIF is intended for debugging only.
erlang:suspend_process(Suspendee, OptList) -> boolean()
Types:
Suspendee = pid()
OptList = [Opt]
Opt = unless_suspending | asynchronous
Increases the suspend count on the process identified by Suspendee and
puts it in the suspended state if it is not already in that state. A suspended
process is not scheduled for execution until the process has been resumed.
A process can be suspended by multiple processes and can be suspended multiple
times by a single process. A suspended process does not leave the suspended
state until its suspend count reaches zero. The suspend count of
Suspendee is decreased when
erlang:resume_process(Suspendee) is called by the same process
that called erlang:suspend_process(Suspendee). All increased suspend
counts on other processes acquired by a process are automatically decreased
when the process terminates.
Options ( Opts):
If the suspend count on the process identified by Suspendee is increased,
true is returned, otherwise false.
- asynchronous:
- A suspend request is sent to the process identified by Suspendee. Suspendee eventually suspends unless it is resumed before it could suspend. The caller of erlang:suspend_process/2 returns immediately, regardless of whether Suspendee has suspended yet or not. The point in time when Suspendee suspends cannot be deduced from other events in the system. It is only guaranteed that Suspendee eventually suspends (unless it is resumed). If 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.
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 > 2,000,000,000 suspends and will never be lower.
erlang:system_flag(Flag :: backtrace_depth, Depth) -> OldDepth
Types:
Depth = OldDepth = integer() >= 0
Sets the maximum depth of call stack back-traces in the exit reason element of
'EXIT' tuples.
Returns the old value of the flag.
erlang:system_flag(Flag :: cpu_topology, CpuTopology) -> OldCpuTopology
Types:
CpuTopology = OldCpuTopology = cpu_topology()
cpu_topology() = [LevelEntry :: level_entry()] | undefined
level_entry() ={LevelTag :: level_tag(), SubLevel :: sub_level()} |{LevelTag :: level_tag(),InfoList :: info_list(),SubLevel :: sub_level()}
level_tag() = core | node | processor | thread
sub_level() =[LevelEntry :: level_entry()] |(LogicalCpuId :: {logical, integer() >= 0})
info_list() = []
Warning:
This argument is deprecated. Instead of using this argument, use
command-line argument +sct in erl(1).
When this argument is removed, a final CPU topology to use is determined at
emulator boot time.
Sets the user-defined CpuTopology. The user-defined CPU topology
overrides any automatically detected CPU topology. By passing undefined
as CpuTopology, the system reverts to the CPU topology automatically
detected. The returned value equals the value returned from
erlang:system_info(cpu_topology) before the change was made.
Returns the old value of the flag.
The CPU topology is used when binding schedulers to logical processors. If
schedulers are already bound when the CPU topology is changed, the schedulers
are sent a request to rebind according to the new CPU topology.
The user-defined CPU topology can also be set by passing command-line argument
+sct to erl(1).
For information on type CpuTopology and more, see
erlang:system_info(cpu_topology) as well as command-line flags
+sct and +sbt in erl(1).erlang:system_flag(Flag :: dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline) -> OldDirtyCPUSchedulersOnline
Types:
DirtyCPUSchedulersOnline = OldDirtyCPUSchedulersOnline =
integer() >= 1
Sets the number of dirty CPU schedulers online. Range is 1 <=
DirtyCPUSchedulersOnline <= N, where N is the smallest of the
return values of erlang:system_info(dirty_cpu_schedulers) and
erlang:system_info(schedulers_online).
Returns the old value of the flag.
The number of dirty CPU schedulers online can change if the number of schedulers
online changes. For example, if 12 schedulers and 6 dirty CPU schedulers are
online, and system_flag/2 is used to set the number of schedulers
online to 6, then the number of dirty CPU schedulers online is automatically
decreased by half as well, down to 3. Similarly, the number of dirty CPU
schedulers online increases proportionally to increases in the number of
schedulers online.
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 :: microstate_accounting, Action) -> OldState
Types:
Action = true | false | reset
OldState = true | false
Turns on/off microstate accounting measurements. When passing reset, all
counters are reset to 0.
For more information see statistics(microstate_accounting).
erlang:system_flag(Flag :: min_heap_size, MinHeapSize) -> OldMinHeapSize
Types:
MinHeapSize = OldMinHeapSize = integer() >= 0
Sets the default minimum heap size for processes. The size is specified in
words. The new min_heap_size effects only processes spawned after the
change of min_heap_size has been made. min_heap_size can be set
for individual processes by using spawn_opt/4 or
process_flag/2.
Returns the old value of the flag.
erlang:system_flag(Flag :: min_bin_vheap_size, MinBinVHeapSize) -> OldMinBinVHeapSize
Types:
MinBinVHeapSize = OldMinBinVHeapSize = integer() >= 0
Sets the default minimum binary virtual heap size for processes. The size is
specified in words. The new min_bin_vhheap_size effects only processes
spawned after the change of min_bin_vheap_size has been made.
min_bin_vheap_size can be set for individual processes by using
spawn_opt/2,3,4 or process_flag/2.
Returns the old value of the flag.
erlang:system_flag(Flag :: max_heap_size, MaxHeapSize) -> OldMaxHeapSize
Types:
MaxHeapSize = OldMaxHeapSize = max_heap_size()
max_heap_size() =integer() >= 0 |#{size => integer() >= 0,kill => boolean(),error_logger => boolean()}
Sets the default maximum heap size settings for processes. The size is specified
in words. The new max_heap_size effects only processes spawned efter
the change has been made. max_heap_size can be set for individual
processes using spawn_opt/2,3,4 or process_flag/2.
Returns the old value of the flag.
erlang:system_flag(Flag :: multi_scheduling, BlockState) -> OldBlockState
Types:
BlockState = block | unblock | block_normal |
unblock_normal
OldBlockState = blocked | disabled | enabled
If multi-scheduling is enabled, more than one scheduler thread is used by the
emulator. Multi-scheduling can be blocked in two different ways. Either all
schedulers but one is blocked, or all normal schedulers but one is
blocked. When only normal schedulers are blocked, dirty schedulers are free to
continue to schedule processes.
If BlockState =:= block, multi-scheduling is blocked. That is, one and
only one scheduler thread will execute. If BlockState =:= unblock and
no one else blocks multi-scheduling, and this process has blocked only once,
multi-scheduling is unblocked.
If BlockState =:= block_normal, normal multi-scheduling is blocked. That
is, only one normal scheduler thread will execute, but multiple dirty
schedulers can execute. If BlockState =:= unblock_normal and no one
else blocks normal multi-scheduling, and this process has blocked only once,
normal multi-scheduling is unblocked.
One process can block multi-scheduling and normal multi-scheduling multiple
times. If a process has blocked multiple times, it must unblock exactly as
many times as it has blocked before it has released its multi-scheduling
block. If a process that has blocked multi-scheduling or normal
multi-scheduling exits, it automatically releases its blocking of
multi-scheduling and normal multi-scheduling.
The return values are disabled, blocked, blocked_normal, or
enabled. The returned value describes the state just after the call to
erlang:system_flag(multi_scheduling, BlockState) has been made. For
information about the return values, see
erlang:system_info(multi_scheduling).
Note:
Blocking of multi-scheduling and normal multi-scheduling is normally not needed.
If you feel that you need to use these features, consider it a few more times
again. Blocking multi-scheduling is only to be used as a last resort, as it is
most likely a very inefficient way to solve the problem.
See also erlang:system_info(multi_scheduling),
erlang:system_info(normal_multi_scheduling_blockers),
erlang:system_info(multi_scheduling_blockers), and
erlang:system_info(schedulers).erlang:system_flag(Flag :: scheduler_bind_type, How) -> OldBindType
Types:
How = scheduler_bind_type() | default_bind
OldBindType = scheduler_bind_type()
scheduler_bind_type() =no_node_processor_spread |no_node_thread_spread |no_spread |processor_spread |spread |thread_spread |thread_no_node_processor_spread |unbound
Warning:
This argument is deprecated. Instead of using this argument, use
command-line argument +sbt in erl(1). When this argument
is removed, a final scheduler bind type to use is determined at emulator boot
time.
Controls if and how schedulers are bound to logical processors.
When erlang:system_flag(scheduler_bind_type, How) is called, an
asynchronous signal is sent to all schedulers online, causing them to try to
bind or unbind as requested.
Note:
If a scheduler fails to bind, this is often silently ignored, as it is not
always possible to verify valid logical processor identifiers. If an error is
reported, 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).
- 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.
erlang:system_flag(Flag :: scheduler_wall_time, Boolean) -> OldBoolean
Types:
Boolean = OldBoolean = boolean()
Turns on or off scheduler wall time measurements.
For more information, see statistics(scheduler_wall_time).
erlang:system_flag(Flag :: schedulers_online, SchedulersOnline) -> OldSchedulersOnline
Types:
SchedulersOnline = OldSchedulersOnline = integer() >=
1
Sets the number of schedulers online. Range is 1 <= SchedulersOnline <=
erlang:system_info(schedulers).
Returns the old value of the flag.
If the emulator was built with support for dirty schedulers, changing
the number of schedulers online can also change the number of dirty CPU
schedulers online. For example, if 12 schedulers and 6 dirty CPU schedulers
are online, and system_flag/2 is used to set the number of schedulers
online to 6, then the number of dirty CPU schedulers online is automatically
decreased by half as well, down to 3. Similarly, the number of dirty CPU
schedulers online increases proportionally to increases in the number of
schedulers online.
For more information, see erlang:system_info(schedulers) and
erlang:system_info(schedulers_online).
erlang:system_flag(Flag :: trace_control_word, TCW) -> OldTCW
Types:
TCW = OldTCW = integer() >= 0
Sets the value of the node trace control word to TCW, which is to be an
unsigned integer. For more information, see function set_tcw in
section "Match Specifications in Erlang" in the User's Guide.
Returns the old value of the flag.
erlang:system_flag(Flag :: time_offset, Value :: finalize) -> OldState
Types:
OldState = preliminary | final | volatile
Finalizes the time offset when single time warp mode is used. If
another time warp mode is used, the time offset state is left unchanged.
Returns the old state identifier, that is:
- *
- If preliminary is returned, finalization was performed and the time offset is now final.
- *
- If final is returned, the time offset was already in the final state. This either because another erlang:system_flag(time_offset, finalize) call or because no time warp mode is used.
- *
- If volatile is returned, the time offset cannot be finalized because multi-time warp mode is used.
erlang:system_info(Item :: 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()
[{Subsystem :: atom(),
[{Parameter :: atom(), Value :: term()}]}]
Returns various information about the allocators of the current system
(emulator) as specified by Item:
- allocated_areas:
- Returns a list of tuples with information about miscellaneous allocated memory areas.
Each tuple contains an atom describing the type of memory as first element and
the amount of allocated memory in bytes as second element. When information
about allocated and used memory is present, also a third element is present,
containing the amount of used memory in bytes.
erlang:system_info(allocated_areas) is intended for debugging, and the
content is highly implementation-dependent. The content of the results
therefore changes when needed without prior notice.
Notice that the sum of these values is not the total amount of memory
allocated by the emulator. Some values are part of other values, and some
memory areas are not part of the result. For information about the total
amount of memory allocated by the emulator, see
erlang:memory/0,1.
- allocator:
Returns {Allocator, Version, Features, Settings, where:
- *
- Allocator corresponds to the malloc() implementation used. If Allocator equals undefined, the malloc() implementation used cannot be identified. glibc can be identified.
- *
- Version is a list of integers (but not a string) representing the version of the malloc() implementation used.
- *
- Features is a list of atoms representing the allocation features used.
- *
- Settings is a list of subsystems, their configurable parameters, and used values. Settings can differ between different combinations of platforms, allocators, and allocation features. Memory sizes are given in bytes.
See also "System Flags Effecting erts_alloc" in
erts_alloc(3erl).
- alloc_util_allocators:
Returns a list of the names of all allocators using the ERTS internal
alloc_util framework as atoms. For more information, see section The
alloc_util framework in erts_alloc(3erl).
- {allocator, Alloc}:
Returns information about the specified allocator. As from ERTS 5.6.1, the
return value is a list of {instance, InstanceNo, InstanceInfo} tuples,
where InstanceInfo contains information about a specific instance of
the allocator. If Alloc is not a recognized allocator, undefined
is returned. If Alloc is disabled, false is returned.
Notice that the information returned is highly implementation-dependent and can
be changed or removed at any time without prior notice. It was initially
intended as a tool when developing new allocators, but as it can be of
interest for others it has been briefly documented.
The recognized allocators are listed in erts_alloc(3erl).
Information about super carriers can be obtained from ERTS 8.0 with
{allocator, erts_mmap} or from ERTS 5.10.4; the returned list when
calling with {allocator, mseg_alloc} also includes an {erts_mmap,
_} tuple as one element in the list.
After reading the erts_alloc(3erl) documentation, the returned
information more or less speaks for itself, but it can be worth explaining
some things. Call counts are presented by two values, the first value is giga
calls, and the second value is calls. mbcs and sbcs denote
multi-block carriers, and single-block carriers, respectively. Sizes are
presented in bytes. When a size is not presented, it is the amount of
something. Sizes and amounts are often presented by three values:
- *
- The first is the current value.
- *
- The second is the maximum value since the last call to erlang:system_info({allocator, Alloc}).
- *
- The third is the maximum value since the emulator was started.
If only one value is present, it is the current value. fix_alloc memory
block types are presented by two values. The first value is the memory pool
size and the second value is the used memory size.
- {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()
All LevelEntrys of a list must contain the same LevelTag, except on the top level where both node and processorLevelTags can coexist.
More LevelTags can be introduced in a future release.
The info_list() can be extended in a future release.
cpu_topology() = [LevelEntry :: level_entry()] | undefined
All LevelEntrys of a list must contain the same LevelTag, except on the top level where both node and processorLevelTags can coexist.
level_entry() ={LevelTag :: level_tag(), SubLevel :: sub_level()} |{LevelTag :: level_tag(),InfoList :: info_list(),SubLevel :: sub_level()}
{LevelTag, SubLevel} == {LevelTag, [],
SubLevel}
level_tag() = core | node | processor | thread
More LevelTags can be introduced in a future release.
sub_level() =[LevelEntry :: level_entry()] |(LogicalCpuId :: {logical, integer() >= 0})
info_list() = []
The info_list() can be extended in a future release.
Returns various information about the CPU topology of the current system
(emulator) as specified by Item:
- cpu_topology:
- Returns the CpuTopology currently used by the emulator. The CPU topology is used when binding schedulers to logical processors. The CPU topology used is the user-defined CPU topology, if such exists, otherwise the automatically detected CPU topology, if such exists. If no CPU topology exists, undefined is returned.
node refers to Non-Uniform Memory Access (NUMA) nodes. thread
refers to hardware threads (for example, Intel hyper-threads).
A level in term CpuTopology can be omitted if only one entry exists and
InfoList is empty.
thread can only be a sublevel to core. core can be a
sublevel to processor or node. processor can be on the
top level or a sublevel to node. node can be on the top level or
a sublevel to processor. That is, NUMA nodes can be processor internal
or processor external. A CPU topology can consist of a mix of processor
internal and external NUMA nodes, as long as each logical CPU belongs to
one NUMA node. Cache hierarchy is not part of the CpuTopology
type, but will be in a future release. Other things can also make it into the
CPU topology in a future release. So, expect the CpuTopology type to
change.
- {cpu_topology, defined}:
Returns the user-defined CpuTopology. For more information, see
command-line flag +sct in erl(1) and argument
cpu_topology.
- {cpu_topology, detected}:
Returns the automatically detected CpuTopologyy. The emulator detects the
CPU topology on some newer Linux, Solaris, FreeBSD, and Windows systems. On
Windows system with more than 32 logical processors, the CPU topology is not
detected.
For more information, see argument cpu_topology.
- {cpu_topology, used}:
- Returns CpuTopology used by the emulator. For more information, see argument cpu_topology.
erlang:system_info(Item :: fullsweep_after) -> {fullsweep_after, integer() >= 0}
erlang:system_info(Item :: garbage_collection) -> [{atom(), integer()}]
erlang:system_info(Item :: max_heap_size) -> {max_heap_size, MaxHeapSize :: max_heap_size()}
erlang:system_info(Item :: message_queue_data) -> message_queue_data()
erlang:system_info(Item :: min_heap_size) -> {min_heap_size, MinHeapSize :: integer() >= 1}
erlang:system_info(Item :: min_bin_vheap_size) -> {min_bin_vheap_size, MinBinVHeapSize :: integer() >= 1}
Types:
message_queue_data() = off_heap | on_heap
max_heap_size() =integer() >= 0 |#{size => integer() >= 0,kill => boolean(),error_logger => boolean()}
Returns information about the default process heap settings:
- fullsweep_after:
- Returns {fullsweep_after, integer() >= 0}, which is the fullsweep_after garbage collection setting used by default. For more information, see garbage_collection described below.
- garbage_collection:
- Returns a list describing the default garbage collection settings. A process spawned on the local node by a spawn or spawn_link uses these garbage collection settings. The default settings can be changed by using erlang:system_flag/2. spawn_opt/2,3,4 can spawn a process that does not use the default settings.
- max_heap_size:
- Returns {max_heap_size, MaxHeapSize}, where MaxHeapSize is the current system-wide maximum heap size settings for spawned processes. This setting can be set using the command-line flags +hmax, +hmaxk and +hmaxel in erl(1). It can also be changed at runtime using erlang:system_flag(max_heap_size, MaxHeapSize). For more details about the max_heap_size process flag, see process_flag(max_heap_size, MaxHeapSize).
- min_heap_size:
- Returns {min_heap_size, MinHeapSize}, where MinHeapSize is the current system-wide minimum heap size for spawned processes.
- message_queue_data:
- Returns the default value of the message_queue_data process flag, which is either off_heap or on_heap. This default is set by command-line argument +hmqd in erl(1). For more information on the message_queue_data process flag, see documentation of process_flag(message_queue_data, MQD).
- min_bin_vheap_size:
- Returns {min_bin_vheap_size, MinBinVHeapSize}, where MinBinVHeapSize is the current system-wide minimum binary virtual heap size for spawned processes.
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 :: 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 :: modified_timing_level) -> integer() | undefined
erlang:system_info(Item :: multi_scheduling) -> disabled | blocked | blocked_normal | enabled
erlang:system_info(Item :: multi_scheduling_blockers) -> [Pid :: pid()]
erlang:system_info(Item :: nif_version) -> string()
erlang:system_info(Item :: normal_multi_scheduling_blockers) -> [Pid :: pid()]
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()
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 command-line
flag +zdntgc to erl(1). 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(1).
- dist_ctrl:
- Returns a list of tuples {Node, ControllingEntity}, one entry for each connected remote node. Node is the node name and ControllingEntity is the port or process identifier responsible for the communication to that node. More specifically, ControllingEntity for nodes connected through TCP/IP (the normal case) is the socket used in communication with the specific node.
- driver_version:
- Returns a string containing the Erlang driver version used by the runtime system. It has the form "<major ver>.<minor ver>".
- dynamic_trace:
- Returns an atom describing the dynamic trace framework compiled into the virtual machine. It can be dtrace, systemtap, or none. For a commercial or standard build, it is always none. The other return values indicate a custom configuration (for example, ./configure --with-dynamic-trace=dtrace). For more information about dynamic tracing, see dyntrace(3erl) manual page and the README.dtrace/README.systemtap files in the Erlang source code top directory.
- dynamic_trace_probes:
- Returns a boolean() indicating if dynamic trace probes (dtrace or systemtap) are built into the emulator. This can only be true if the virtual machine was built for dynamic tracing (that is, system_info(dynamic_trace) returns dtrace or systemtap).
- 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 command-line flag +secio in erl(1), which is either true or false. For information about the different values, see the documentation of the command-line flag.
- 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.
- 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.
- 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 one of the following:
- 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.
- blocked_normal:
- The emulator has more than one scheduler thread, but all normal scheduler threads except one are blocked. Notice that dirty schedulers are not blocked, and can schedule Erlang processes and execute native code.
- enabled:
- The emulator has more than one scheduler thread, and no scheduler threads are blocked. That is, all available scheduler threads schedule Erlang processes and execute Erlang code.
See also erlang:system_flag(multi_scheduling, BlockState),
erlang:system_info(multi_scheduling_blockers),
erlang:system_info(normal_multi_scheduling_blockers), and
erlang:system_info(schedulers).
- multi_scheduling_blockers:
Returns a list of Pids when multi-scheduling is blocked, otherwise the
empty list is returned. The Pids in the list represent all the
processes currently blocking multi-scheduling. A Pid occurs only once
in the list, even if the corresponding process has blocked multiple
times.
See also erlang:system_flag(multi_scheduling, BlockState),
erlang:system_info(multi_scheduling),
erlang:system_info(normal_multi_scheduling_blockers), and
erlang:system_info(schedulers).
- 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>".
- normal_multi_scheduling_blockers:
Returns a list of Pids when normal multi-scheduling is blocked (that is,
all normal schedulers but one is blocked), otherwise the empty list is
returned. The Pids in the list represent all the processes currently
blocking normal multi-scheduling. A Pid occurs only once in the list,
even if the corresponding process has blocked multiple times.
See also erlang:system_flag(multi_scheduling, BlockState),
erlang:system_info(multi_scheduling),
erlang:system_info(multi_scheduling_blockers), and
erlang:system_info(schedulers).
- otp_release:
Returns a string containing the OTP release number of the OTP release that the
currently executing ERTS application is part of.
As from Erlang/OTP 17, the OTP release number corresponds to the major OTP
version number. No erlang:system_info() argument gives the exact OTP
version. This is because the exact OTP version in the general case is
difficult to determine. For more information, see the description of versions
in System principles in System Documentation.
- os_monotonic_time_source:
- Returns a list containing information about the source of OS monotonic time that is used by the runtime system.
If [] is returned, no OS monotonic time is available. The list contains
two-tuples with Keys as first element, and Values as second
element. The order of these tuples is undefined. The following tuples can be
part of the list, but more tuples can be introduced in the future:
- {function, Function}:
- Function is the name of the function used. This tuple always exists if OS monotonic time is available to the runtime system.
- {clock_id, ClockId}:
- This tuple only exists if Function can be used with different clocks. ClockId corresponds to the clock identifier used when calling Function.
- {resolution, OsMonotonicTimeResolution}:
- Highest possible resolution of current OS monotonic time source as parts per second. If no resolution information can be retrieved from the OS, OsMonotonicTimeResolution is set to the resolution of the time unit of Functions return value. That is, the actual resolution can be lower than OsMonotonicTimeResolution. Notice that the resolution does not say anything about the accuracy or whether the precision aligns with the resolution. You do, however, know that the precision is not better than OsMonotonicTimeResolution.
- {extended, Extended}:
- Extended equals yes if the range of time values has been extended; otherwise Extended equals no. The range must be extended if Function returns values that wrap fast. This typically is the case when the return value is a 32-bit value.
- {parallel, Parallel}:
- Parallel equals yes if Function is called in parallel from multiple threads. If it is not called in parallel, because calls must be serialized, Parallel equals no.
- {time, OsMonotonicTime}:
- OsMonotonicTime equals current OS monotonic time in native time unit.
- os_system_time_source:
- Returns a list containing information about the source of OS system time that is used by the runtime system.
The list contains two-tuples with Keys as first element, and
Values as second element. The order 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}:
- Exists only if Function can be used with different clocks. ClockId corresponds to the clock identifier used when calling Function.
- {resolution, OsSystemTimeResolution}:
- Highest possible resolution of current OS system time source as parts per second. If no resolution information can be retrieved from the OS, OsSystemTimeResolution is set to the resolution of the time unit of Functions return value. That is, the actual resolution can be lower than OsSystemTimeResolution. Notice that the resolution does not say anything about the accuracy or whether the precision do align with the resolution. You do, however, know that the precision is not better than OsSystemTimeResolution.
- {parallel, Parallel}:
- Parallel equals yes if Function is called in parallel from multiple threads. If it is not called in parallel, because calls needs to be serialized, Parallel equals no.
- {time, OsSystemTime}:
- OsSystemTime equals current OS system time in native time unit.
- 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 although a user has requested schedulers to be bound, they can
silently have failed to bind. To inspect the scheduler bindings, call
erlang:system_info(scheduler_bindings).
For more information, see command-line argument +sbt in
erl(1) and erlang:system_info(scheduler_bindings).
- scheduler_bindings:
Returns information about the currently used scheduler bindings.
A tuple of a size equal to erlang:system_info(schedulers) is
returned. The tuple elements are integers or the atom unbound. Logical
processor identifiers are represented as integers. The Nth element of
the tuple equals the current binding for the scheduler with the scheduler
identifier equal to N. For example, if the schedulers are bound,
element(erlang:system_info(scheduler_id),
erlang:system_info(scheduler_bindings)) returns the identifier of the
logical processor that the calling process is executing on.
Notice that only schedulers online can be bound to logical processors.
For more information, see command-line argument +sbt in
erl(1) and erlang:system_info(schedulers_online).
- scheduler_id:
Returns the scheduler ID ( SchedulerId) of the scheduler thread that the
calling process is executing on. SchedulerId is a positive integer,
where 1 <= SchedulerId <= erlang:system_info(schedulers).
See also erlang:system_info(schedulers).
- schedulers:
Returns the number of scheduler threads used by the emulator. Scheduler threads
online schedules Erlang processes and Erlang ports, and execute Erlang code
and Erlang linked-in driver code.
The number of scheduler threads is determined at emulator boot time and cannot
be changed later. However, the number of schedulers online can be changed at
any time.
See also erlang:system_flag(schedulers_online, SchedulersOnline),
erlang:system_info(schedulers_online),
erlang:system_info(scheduler_id),
erlang:system_flag(multi_scheduling, BlockState),
erlang:system_info(multi_scheduling),
erlang:system_info(normal_multi_scheduling_blockers) and
erlang:system_info(multi_scheduling_blockers).
- schedulers_online:
Returns the number of schedulers online. The scheduler identifiers of schedulers
online satisfy the relationship 1 <= SchedulerId <=
erlang:system_info(schedulers_online).
For more information, see erlang:system_info(schedulers) and
erlang:system_flag(schedulers_online, SchedulersOnline).
- smp_support:
- Returns true 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 ( erl_driver: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 and finalized later. The preliminary time offset is used during the preliminary phase of the single time warp mode.
- final:
- The time offset is final. This either because no time warp mode is used, or because the time offset have been finalized when single time warp mode is used.
- volatile:
- The time offset is volatile. That is, it can change at any time. This is because multi-time warp mode is used.
- time_warp_mode:
- Returns a value identifying the time warp mode that is used:
- no_time_warp:
- The no time warp mode is used.
- single_time_warp:
- The single time warp mode is used.
- multi_time_warp:
- The multi-time warp mode is used.
- tolerant_timeofday:
Returns whether a pre ERTS 7.0 backwards compatible compensation for sudden
changes of system time is enabled or disabled. Such compensation
is enabled when the time offset is final, and time
correction is enabled.
- 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 no settings exist. The order of the options can be
different from the one that was set.
erlang:system_monitor(Arg) -> MonSettings
Types:
Arg = MonSettings = undefined | {MonitorPid, Options}
MonitorPid = pid()
Options = [ system_monitor_option()]
system_monitor_option() =busy_port |busy_dist_port |{long_gc, integer() >= 0} |{long_schedule, integer() >= 0} |{large_heap, integer() >= 0}
When called with argument undefined, all system performance monitoring
settings are cleared.
Calling the function with {MonitorPid, Options} as argument is the same
as calling erlang:system_monitor(MonitorPid, Options).
Returns the previous system monitor settings just like
erlang:system_monitor/0.
erlang:system_monitor(MonitorPid, Options) -> MonSettings
Types:
MonitorPid = pid()
Options = [ system_monitor_option()]
MonSettings = undefined | {OldMonitorPid, OldOptions}
OldMonitorPid = pid()
OldOptions = [ system_monitor_option()]
system_monitor_option() =busy_port |busy_dist_port |{long_gc, integer() >= 0} |{long_schedule, integer() >= 0} |{large_heap, integer() >= 0}
Sets the system performance monitoring options. MonitorPid is a local
process identifier (pid) receiving system monitor messages. The second
argument is a list of monitoring options:
Returns the previous system monitor settings just like
erlang:system_monitor/0.
- {long_gc, Time}:
- If a garbage collection in the system takes at least Time wall clock milliseconds, a message {monitor, GcPid, long_gc, Info} is sent to MonitorPid. GcPid is the pid that was garbage collected. Info is a list of two-element tuples describing the result of the garbage collection.
One of the tuples is {timeout, GcTime}, where GcTime is the time
for the garbage collection in milliseconds. The other tuples are tagged with
heap_size, heap_block_size, stack_size, mbuf_size,
old_heap_size, and old_heap_block_size. These tuples are
explained in the description of trace message gc_minor_start
(see erlang:trace/3). New tuples can be added, and the order of
the tuples in the Info list can be changed at any time without prior
notice.
- {long_schedule, Time}:
- If a process or port in the system runs uninterrupted for at least Time wall clock milliseconds, a message {monitor, PidOrPort, long_schedule, Info} is sent to MonitorPid. PidOrPort is the process or port that was running. Info is a list of two-element tuples describing the event.
If a pid(), the tuples {timeout, Millis}, {in, Location},
and {out, Location} are present, where Location is either an MFA
( {Module, Function, Arity}) describing the function where the process
was scheduled in/out, or the atom undefined.
If a port(), the tuples {timeout, Millis} and {port_op,Op}
are present. Op is one of proc_sig, timeout,
input, output, event, or dist_cmd, depending on
which driver callback was executing.
proc_sig is an internal operation and is never to appear, while the
others represent the corresponding driver callbacks timeout,
ready_input, ready_output, event, and outputv
(when the port is used by distribution). Value Millis in tuple
timeout informs about the uninterrupted execution time of the process
or port, which always is equal to or higher than the Time value
supplied when starting the trace. New tuples can be added to the Info
list in a future release. The order of the tuples in the list can be changed
at any time without prior notice.
This can be used to detect problems with NIFs or drivers that take too long to
execute. 1 ms is considered a good maximum time for a driver callback or a
NIF. However, a time-sharing system is usually to consider everything < 100
ms as "possible" and fairly "normal". However, longer
schedule times can indicate swapping or a misbehaving NIF/driver. Misbehaving
NIFs and drivers can cause bad resource utilization and bad overall system
performance.
- {large_heap, Size}:
- If a garbage collection in the system results in the allocated size of a heap being at least Size words, a message {monitor, GcPid, large_heap, Info} is sent to MonitorPid. GcPid and Info are the same as for long_gc earlier, except that the tuple tagged with timeout is not present.
The monitor message is sent if the sum of the sizes of all memory blocks
allocated for all heap generations after a garbage collection is equal to or
higher than Size.
When a process is killed by max_heap_size, it is killed before the
garbage collection is complete and thus no large heap message is sent.
- busy_port:
- If a process in the system gets suspended because it sends to a busy port, a message {monitor, SusPid, busy_port, Port} is sent to MonitorPid. SusPid is the pid that got suspended when sending to Port.
- busy_dist_port:
- If a process in the system gets suspended because it sends to a process on a remote node whose inter-node communication was handled by a busy port, a message {monitor, SusPid, busy_dist_port, Port} is sent to MonitorPid. SusPid is the pid that got suspended when sending through the inter-node communication port Port.
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()]}
undefined | {pid() | port(), [ system_profile_option()]}
system_profile_option() =exclusive |runnable_ports |runnable_procs |scheduler |timestamp |monotonic_timestamp |strict_monotonic_timestamp
Sets system profiler options. ProfilerPid is a local process identifier
(pid) or port receiving profiling messages. The receiver is excluded from all
profiling. The second argument is a list of profiling options:
- exclusive:
- If a synchronous call to a port from a process is done, the calling process is considered not runnable during the call runtime to the port. The calling process is notified as inactive, and later active when the port callback returns.
- monotonic_timestamp:
- Time stamps in profile messages use Erlang monotonic time. The time stamp (Ts) has the same format and value as produced by erlang:monotonic_time(nanosecond).
- runnable_procs:
- If a process is put into or removed from the run queue, a message, {profile, Pid, State, Mfa, Ts}, is sent to ProfilerPid. Running processes that are reinserted into the run queue after having been pre-empted do not trigger this message.
- runnable_ports:
- If a port is put into or removed from the run queue, a message, {profile, Port, State, 0, Ts}, is sent to ProfilerPid.
- scheduler:
- If a scheduler is put to sleep or awoken, a message, {profile, scheduler, Id, State, NoScheds, Ts}, is sent to ProfilerPid.
- strict_monotonic_timestamp:
- Time stamps in profile messages consist of Erlang monotonic time and a monotonically increasing integer. The time stamp (Ts) has the same format and value as produced by {erlang:monotonic_time(nanosecond), erlang:unique_integer([monotonic])}.
- timestamp:
- Time stamps in profile messages include a time stamp (Ts) that has the same form as returned by erlang:now(). This is also the default if no time stamp flag is specified. If cpu_timestamp has been enabled through erlang:trace/3, this also effects the time stamp produced in profiling messages when flag timestamp is enabled.
Note:
erlang:system_profile behavior can change in a future release.
erlang:system_time() -> integer()
Returns current Erlang system time in native time unit.
Calling erlang:system_time() is equivalent to
erlang:monotonic_time() +
erlang:time_offset().
Note:
This time is not a monotonically increasing time in the general case. For
more information, see the documentation of time warp modes in the
User's Guide.
erlang:system_time(Unit) -> integer()
Types:
Unit = time_unit()
Returns current Erlang system time converted into the Unit passed
as argument.
Calling erlang:system_time(Unit) is equivalent to
erlang:convert_time_unit
(erlang:system_time() , native, Unit).
Note:
This time is not a monotonically increasing time in the general case. For
more information, see the documentation of time warp modes in the
User's Guide.
term_to_binary(Term) -> ext_binary()
Types:
Term = term()
Returns a binary data object that is the result of encoding Term
according to the Erlang external term format.
This can be used for various purposes, for example, writing a term to a file in
an efficient way, or sending an Erlang term to some type of communications
channel not supported by distributed Erlang.
> Bin = term_to_binary(hello). <<131,100,0,5,104,101,108,108,111>> > hello = binary_to_term(Bin). helloSee 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}]
[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/OTP R7B.
A compression level can be specified by giving option {compressed,
Level}. Level is an integer with range 0..9, where:
Option {minor_version, Version} can be used to control some encoding
details. This option was introduced in Erlang/OTP R11B-4. The valid values for
Version are 0 and 1.
As from Erlang/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 Erlang/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
Erlang/OTP R11B-4 can decode resulting binary.
See also binary_to_term/1.
- *
- 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.
throw(Any) -> no_return()
Types:
Any = term()
A non-local return from a function. If evaluated within a catch,
catch returns value Any. Example:
> catch throw({hello, there}). {hello,there}Failure: nocatch if not evaluated within a catch.
time() -> Time
Types:
Time = calendar:time()
Returns the current time as {Hour, Minute, Second}.
The time zone and Daylight Saving Time correction depend on the underlying OS.
Example:
> time(). {9,42,44}
erlang:time_offset() -> integer()
Returns the current time offset between Erlang monotonic time and
Erlang system time in native time unit. Current time offset
added to an Erlang monotonic time gives corresponding Erlang system time.
The time offset may or may not change during operation depending on the time
warp mode used.
Note:
A change in time offset can be observed at slightly different points in time by
different processes.
If the runtime system is in multi-time warp mode, the time offset is
changed when the runtime system detects that the OS system time has
changed. The runtime system will, however, not detect this immediately when it
occurs. A task checking the time offset is scheduled to execute at least once
a minute; so, under normal operation this is to be detected within a minute,
but during heavy load it can take longer time.
erlang:time_offset(Unit) -> integer()
Types:
Unit = time_unit()
Returns the current time offset between Erlang monotonic time and
Erlang system time converted into the Unit passed as argument.
Same as calling
erlang:convert_time_unit(erlang:time_offset()
, native, Unit) however optimized for commonly used Units.
erlang:timestamp() -> Timestamp
Types:
Timestamp = timestamp()
timestamp() ={MegaSecs :: integer() >= 0,Secs :: integer() >= 0,MicroSecs :: integer() >= 0}
Returns current Erlang system time on the format {MegaSecs, Secs,
MicroSecs}. This format is the same as os:timestamp/0 and
the deprecated erlang:now/0 use. The reason for the existence of
erlang:timestamp() is purely to simplify use for existing code that
assumes this time stamp format. Current Erlang system time can more
efficiently be retrieved in the time unit of your choice using
erlang:system_time/1.
The erlang:timestamp() BIF is equivalent to:
timestamp() -> ErlangSystemTime = erlang:system_time(microsecond), MegaSecs = ErlangSystemTime div 1000000000000, Secs = ErlangSystemTime div 1000000 - MegaSecs*1000000, MicroSecs = ErlangSystemTime rem 1000000, {MegaSecs, Secs, MicroSecs}.It, however, uses a native implementation that does not build garbage on the heap and with slightly better performance.
Note:
This time is not a monotonically increasing time in the general case. For
more information, see the documentation of time warp modes in the
User's Guide.
tl(List) -> term()
Types:
List = [term(), ...]
Returns the tail of List, that is, the list minus the first element, for
example:
> tl([geesties, guilies, beasties]). [guilies, beasties]Allowed in guard tests. Failure: badarg if List is the empty list [].
erlang:trace(PidPortSpec, How, FlagList) -> integer()
Types:
PidPortSpec =
pid() |
port() |
all |
processes |
ports |
existing |
existing_processes |
existing_ports |
new |
new_processes |
new_ports
How = boolean()
FlagList = [ trace_flag()]
pid() |
port() |
all |
processes |
ports |
existing |
existing_processes |
existing_ports |
new |
new_processes |
new_ports
trace_flag() =all |send |'receive' |procs |ports |call |arity |return_to |silent |running |exiting |running_procs |running_ports |garbage_collection |timestamp |cpu_timestamp |monotonic_timestamp |strict_monotonic_timestamp |set_on_spawn |set_on_first_spawn |set_on_link |set_on_first_link |{tracer, pid() | port()} |{tracer, module(), term()}
Turns on (if How == true) or off (if How == false) the trace flags
in FlagList for the process or processes represented by
PidPortSpec.
PidPortSpec is either a process identifier (pid) for a local process, a
port identifier, or one of the following atoms:
FlagList can contain any number of the following flags (the "message
tags" refers to the list of trace messages):
If no tracer is specified, the calling process receives all the trace
messages.
The effect of combining set_on_first_link with set_on_link is the
same as set_on_first_link alone. Likewise for set_on_spawn and
set_on_first_spawn.
The tracing process receives the trace messages described in the
following list. Pid is the process identifier of the traced process in
which the traced event has occurred. The third tuple element is the message
tag.
If flag timestamp, strict_monotonic_timestamp, or
monotonic_timestamp is specified, the first tuple element is
trace_ts instead, and the time stamp is added as an extra element last
in the message tuple. If multiple time stamp flags are passed,
timestamp has precedence over strict_monotonic_timestamp, which
in turn has precedence over monotonic_timestamp. All time stamp flags
are remembered, so if two are passed and the one with highest precedence later
is disabled, the other one becomes active.
Trace messages:
If the tracing process/port dies or the tracer module returns remove, the
flags are silently removed.
Each process can only be traced by one tracer. Therefore, attempts to trace an
already traced process fail.
Returns a number indicating the number of processes that matched
PidPortSpec. If PidPortSpec is a process identifier, the return
value is 1. If PidPortSpec is all or existing, the
return value is the number of processes running. If PidPortSpec is
new, the return value is 0.
Failure: badarg if the specified arguments are not supported. For
example, cpu_timestamp is not supported on all platforms.
- all:
- All currently existing processes and ports and all that will be created in the future.
- processes:
- All currently existing processes and all that will be created in the future.
- ports:
- All currently existing ports and all that will be created in the future.
- existing:
- All currently existing processes and ports.
- existing_processes:
- All currently existing processes.
- existing_ports:
- All currently existing ports.
- new:
- All processes and ports that will be created in the future.
- new_processes:
- All processes that will be created in the future.
- new_ports:
- All ports that will be created in the future.
- all:
- Sets all trace flags except tracer and cpu_timestamp, which are in their nature different than the others.
- send:
- Traces sending of messages.
Message tags: send and
send_to_non_existing_process.
- 'receive':
- Traces receiving of messages.
Message tags: 'receive'.
- call:
- Traces certain function calls. Specify which function calls to trace by calling erlang:trace_pattern/3.
Message tags: call and return_from.
- silent:
- Used with the call trace flag. The call, return_from, and return_to trace messages are inhibited if this flag is set, but they are executed as normal if there are match specifications.
Silent mode is inhibited by executing erlang:trace(_, false, [silent|_]),
or by a match specification executing the function {silent,
false}.
The silent trace flag facilitates setting up a trace on many or even all
processes in the system. The trace can then be activated and deactivated using
the match specification function {silent,Bool}, giving a high degree of
control of which functions with which arguments that trigger the trace.
Message tags: call, return_from, and
return_to. Or rather, the absence of.
- return_to:
- Used with the call trace flag. Traces the return from a traced function back to its caller. Only works for functions traced with option local to erlang:trace_pattern/3.
The semantics is that a trace message is sent when a call traced function
returns, that is, when a chain of tail recursive calls ends. Only one trace
message is sent per chain of tail recursive calls, so the properties of tail
recursiveness for function calls are kept while tracing with this flag. Using
call and return_to trace together makes it possible to know
exactly in which function a process executes at any time.
To get trace messages containing return values from functions, use the
{return_trace} match specification action instead.
Message tags: return_to.
- procs:
- Traces process-related events.
Message tags: spawn, spawned, exit,
register, unregister, link,
unlink, getting_linked, and
getting_unlinked.
- ports:
- Traces port-related events.
Message tags: open, closed, register,
unregister, getting_linked, and
getting_unlinked.
- running:
- Traces scheduling of processes.
Message tags: in and out.
- exiting:
- Traces scheduling of exiting processes.
Message tags: in_exiting, out_exiting, and
out_exited.
- running_procs:
- Traces scheduling of processes just like running. However, this option also includes schedule events when the process executes within the context of a port without being scheduled out itself.
Message tags: in and out.
- running_ports:
- Traces scheduling of ports.
Message tags: in and out.
- garbage_collection:
- Traces garbage collections of processes.
Message tags: gc_minor_start, gc_max_heap_size, and
gc_minor_end.
- timestamp:
- Includes a time stamp in all trace messages. The time stamp (Ts) has the same form as returned by erlang:now().
- cpu_timestamp:
- A global trace flag for the Erlang node that makes all trace time stamps using flag timestamp to be in CPU time, not wall clock time. That is, cpu_timestamp is not be used if monotonic_timestamp or strict_monotonic_timestamp is enabled. Only allowed with PidPortSpec==all. If the host machine OS does not support high-resolution CPU time measurements, trace/3 exits with badarg. Notice that most OS do not synchronize this value across cores, so be prepared that time can seem to go backwards when using this option.
- monotonic_timestamp:
- Includes an Erlang monotonic time time stamp in all trace messages. The time stamp (Ts) has the same format and value as produced by erlang:monotonic_time(nanosecond). This flag overrides flag cpu_timestamp.
- strict_monotonic_timestamp:
- Includes an time stamp consisting of Erlang monotonic time and a monotonically increasing integer in all trace messages. The time stamp (Ts) has the same format and value as produced by { erlang:monotonic_time(nanosecond) , erlang:unique_integer([monotonic]) }. This flag overrides flag cpu_timestamp.
- arity:
- Used with the call trace flag. {M, F, Arity} is specified instead of {M, F, Args} in call trace messages.
- set_on_spawn:
- Makes any process created by a traced process inherit its trace flags, including flag set_on_spawn.
- set_on_first_spawn:
- Makes the first process created by a traced process inherit its trace flags, excluding flag set_on_first_spawn.
- set_on_link:
- Makes any process linked by a traced process inherit its trace flags, including flag set_on_link.
- set_on_first_link:
- Makes the first process linked to by a traced process inherit its trace flags, excluding flag set_on_first_link.
- {tracer, Tracer}:
- Specifies where to send the trace messages. Tracer must be the process identifier of a local process or the port identifier of a local port.
- {tracer, TracerModule, TracerState}:
- Specifies that a tracer module is to be called instead of sending a trace message. The tracer module can then ignore or change the trace message. For more details on how to write a tracer module, see erl_tracer(3erl).
- {trace, PidPort, send, Msg, To}:
- When PidPort sends message Msg to process To.
- {trace, PidPort, send_to_non_existing_process, Msg, To}:
- When PidPort sends message Msg to the non-existing process To.
- {trace, PidPort, 'receive', Msg}:
- When PidPort receives message Msg. If Msg is set to time-out, a receive statement can have timed out, or the process received a message with the payload timeout.
- {trace, Pid, call, {M, F, Args}}:
- When Pid calls a traced function. The return values of calls are never supplied, only the call and its arguments.
Trace flag arity can be used to change the contents of this message, so
that Arity is specified instead of Args.
- {trace, Pid, return_to, {M, F, Arity}}:
- When Pid returns to the specified function. This trace message is sent if both the flags call and return_to are set, and the function is set to be traced on local function calls. The message is only sent when returning from a chain of tail recursive function calls, where at least one call generated a call trace message (that is, the functions match specification matched, and {message, false} was not an action).
- {trace, Pid, return_from, {M, F, Arity}, ReturnValue}:
- When Pid returns from the specified function. This trace message is sent if flag call is set, and the function has a match specification with a return_trace or exception_trace action.
- {trace, Pid, exception_from, {M, F, Arity}, {Class, Value}}:
- When Pid exits from the specified function because of an exception. This trace message is sent if flag call is set, and the function has a match specification with an exception_trace action.
- {trace, Pid, spawn, Pid2, {M, F, Args}}:
- When Pid spawns a new process Pid2 with the specified function call as entry point.
Args is supposed to be the argument list, but can be any term if the
spawn is erroneous.
- {trace, Pid, spawned, Pid2, {M, F, Args}}:
- When Pid is spawned by process Pid2 with the specified function call as entry point.
Args is supposed to be the argument list, but can be any term if the
spawn is erroneous.
- {trace, Pid, exit, Reason}:
- When Pid exits with reason Reason.
- {trace, PidPort, register, RegName}:
- When PidPort gets the name RegName registered.
- {trace, PidPort, unregister, RegName}:
- When PidPort gets the name RegName unregistered. This is done automatically when a registered process or port exits.
- {trace, Pid, link, Pid2}:
- When Pid links to a process Pid2.
- {trace, Pid, unlink, Pid2}:
- When Pid removes the link from a process Pid2.
- {trace, PidPort, getting_linked, Pid2}:
- When PidPort gets linked to a process Pid2.
- {trace, PidPort, getting_unlinked, Pid2}:
- When PidPort gets unlinked from a process Pid2.
- {trace, Pid, exit, Reason}:
- When Pid exits with reason Reason.
- {trace, Port, open, Pid, Driver}:
- When Pid opens a new port Port with the running Driver.
Driver is the name of the driver as an atom.
- {trace, Port, closed, Reason}:
- When Port closes with Reason.
- {trace, Pid, in | in_exiting, {M, F, Arity} | 0}:
- When Pid is scheduled to run. The process runs in function {M, F, Arity}. On some rare occasions, the current function cannot be determined, then the last element is 0.
- {trace, Pid, out | out_exiting | out_exited, {M, F, Arity} | 0}:
- When Pid is scheduled out. The process was running in function {M, F, Arity}. On some rare occasions, the current function cannot be determined, then the last element is 0.
- {trace, Port, in, Command | 0}:
- When Port is scheduled to run. Command is the first thing the port will execute, it can however run several commands before being scheduled out. On some rare occasions, the current function cannot be determined, then the last element is 0.
The possible commands are call, close, command,
connect, control, flush, info, link,
open, and unlink.
- {trace, Port, out, Command | 0}:
- When Port is scheduled out. The last command run was Command. On some rare occasions, the current function cannot be determined, then the last element is 0. Command can contain the same commands as in
- {trace, Pid, gc_minor_start, Info}:
Sent when a young garbage collection is about to be started. Info is a
list of two-element tuples, where the first element is a key, and the second
is the value. Do not depend on any order of the tuples. The following keys are
defined:
- heap_size:
- The size of the used part of the heap.
- heap_block_size:
- The size of the memory block used for storing the heap and the stack.
- old_heap_size:
- The size of the used part of the old heap.
- old_heap_block_size:
- The size of the memory block used for storing the old heap.
- stack_size:
- The size of the stack.
- recent_size:
- The size of the data that survived the previous garbage collection.
- mbuf_size:
- The combined size of message buffers associated with the process.
- bin_vheap_size:
- The total size of unique off-heap binaries referenced from the process heap.
- bin_vheap_block_size:
- The total size of binaries allowed in the virtual heap in the process before doing a garbage collection.
- bin_old_vheap_size:
- The total size of unique off-heap binaries referenced from the process old heap.
- bin_old_vheap_block_size:
- The total size of binaries allowed in the virtual old heap in the process before doing a garbage collection.
All sizes are in words.
- {trace, Pid, gc_max_heap_size, Info}:
- Sent when the max_heap_size is reached during garbage collection. Info contains the same kind of list as in message gc_start, but the sizes reflect the sizes that triggered max_heap_size to be reached.
- {trace, Pid, gc_minor_end, Info}:
- Sent when young garbage collection is finished. Info contains the same kind of list as in message gc_minor_start, but the sizes reflect the new sizes after garbage collection.
- {trace, Pid, gc_major_start, Info}:
- Sent when fullsweep garbage collection is about to be started. Info contains the same kind of list as in message gc_minor_start.
- {trace, Pid, gc_major_end, Info}:
- Sent when fullsweep garbage collection is finished. Info contains the same kind of list as in message gc_minor_start, but the sizes reflect the new sizes after a fullsweep garbage collection.
erlang:trace_delivered(Tracee) -> Ref
Types:
Tracee = pid() | all
Ref = reference()
The delivery of trace messages (generated by erlang:trace/3,
seq_trace(3erl), or erlang:system_profile/2) is
dislocated on the time-line compared to other events in the system. If you
know that Tracee has passed some specific point in its execution, and
you want to know when at least all trace messages corresponding to events up
to this point have reached the tracer, use
erlang:trace_delivered(Tracee).
When it is guaranteed that all trace messages are delivered to the tracer up to
the point that Tracee reached at the time of the call to
erlang:trace_delivered(Tracee), then a {trace_delivered, Tracee,
Ref} message is sent to the caller of
erlang:trace_delivered(Tracee) .
Notice that message trace_delivered does not imply that trace
messages have been delivered. Instead it implies that all trace messages that
are to be delivered have been delivered. It is not an error if
Tracee is not, and has not been traced by someone, but if this is the
case, no trace messages have been delivered when the
trace_delivered message arrives.
Notice that Tracee must refer to a process currently or previously
existing on the same node as the caller of
erlang:trace_delivered(Tracee) resides on. The special Tracee
atom all denotes all processes that currently are traced in the node.
When used together with a Tracer Module, any message sent in the trace
callback is guaranteed to have reached its recipient before the
trace_delivered message is sent.
Example: Process A is Tracee, port B is tracer, and process
C is the port owner of B. C wants to close B when
A exits. To ensure that the trace is not truncated, C can call
erlang:trace_delivered(A) when A exits, and wait for message
{trace_delivered, A, Ref} before closing B.
Failure: badarg if Tracee does not refer to a process (dead or
alive) on the same node as the caller of erlang:trace_delivered(Tracee)
resides on.
erlang:trace_info(PidPortFuncEvent, Item) -> Res
Types:
PidPortFuncEvent =
pid() |
port() |
new |
new_processes |
new_ports |
{Module, Function, Arity} |
on_load |
send |
'receive'
Module = module()
Function = atom()
Arity = arity()
Item =
flags |
tracer |
traced |
match_spec |
meta |
meta_match_spec |
call_count |
call_time |
all
Res = trace_info_return()
Approximation of '$1' | '$2' | '$3' | ...
pid() |
port() |
new |
new_processes |
new_ports |
{Module, Function, Arity} |
on_load |
send |
'receive'
flags |
tracer |
traced |
match_spec |
meta |
meta_match_spec |
call_count |
call_time |
all
trace_info_return() =undefined |{flags, [ trace_info_flag()]} |{tracer, pid() | port() | []} |{tracer, module(), term()} |trace_info_item_result() |{all, [ trace_info_item_result()] | false | undefined}
trace_info_item_result() ={traced, global | local | false | undefined} |{match_spec, trace_match_spec() | false | undefined} |{meta, pid() | port() | false | undefined | []} |{meta, module(), term()} |{meta_match_spec, trace_match_spec() | false | undefined} |{call_count, integer() >= 0 | boolean() | undefined} |{call_time,[{pid(),integer() >= 0,integer() >= 0,integer() >= 0}] |boolean() |undefined}
trace_info_flag() =send |'receive' |set_on_spawn |call |return_to |procs |set_on_first_spawn |set_on_link |running |garbage_collection |timestamp |monotonic_timestamp |strict_monotonic_timestamp |arity
trace_match_spec() =[{[term()] | '_' | match_variable(), [term()], [term()]}]
match_variable() = atom()
Approximation of '$1' | '$2' | '$3' | ...
Returns trace information about a port, process, function, or event.
To get information about a port or process, PidPortFuncEvent is to
be a process identifier (pid), port identifier, or one of the atoms
new, new_processes, or new_ports. The atom new or
new_processes means that the default trace state for processes to be
created is returned. The atom new_ports means that the default trace
state for ports to be created is returned.
Valid Items for ports and processes:
To get information about a function, PidPortFuncEvent is to be the
three-element tuple {Module, Function, Arity} or the atom
on_load. No wildcards are allowed. Returns undefined if the
function does not exist, or false if the function is not traced. If
PidPortFuncEvent is on_load, the information returned refers to
the default value for code that will be loaded.
Valid Items for functions:
To get information about an event, PidPortFuncEvent is to be one
of the atoms send or 'receive'.
One valid Item for events exists:
The return value is {Item, Value}, where Value is the requested
information as described earlier. If a pid for a dead process was specified,
or the name of a non-existing function, Value is
undefined.
- flags:
- Returns a list of atoms indicating what kind of traces is enabled for the process. The list is empty if no traces are enabled, and one or more of the followings atoms if traces are enabled: send, 'receive', set_on_spawn, call, return_to, procs, ports, set_on_first_spawn, set_on_link, running, running_procs, running_ports, silent, exiting, monotonic_timestamp, strict_monotonic_timestamp, garbage_collection, timestamp, and arity. The order is arbitrary.
- tracer:
- Returns the identifier for process, port, or a tuple containing the tracer module and tracer state tracing this process. If this process is not traced, the return value is [].
- traced:
- Returns global if this function is traced on global function calls, local if this function is traced on local function calls (that is, local and global function calls), and false if local or global function calls are not traced.
- match_spec:
- Returns the match specification for this function, if it has one. If the function is locally or globally traced but has no match specification defined, the returned value is [].
- meta:
- Returns the meta-trace tracer process, port, or trace module for this function, if it has one. If the function is not meta-traced, the returned value is false. If the function is meta-traced but has once detected that the tracer process is invalid, the returned value is [].
- meta_match_spec:
- Returns the meta-trace match specification for this function, if it has one. If the function is meta-traced but has no match specification defined, the returned value is [].
- call_count:
- Returns the call count value for this function or true for the pseudo function on_load if call count tracing is active. Otherwise false is returned.
See also erlang:trace_pattern/3.
- call_time:
- Returns the call time values for this function or true for the pseudo function on_load if call time tracing is active. Otherwise false is returned. The call time values returned, [{Pid, Count, S, Us}], is a list of each process that executed the function and its specific counters.
See also erlang:trace_pattern/3.
- all:
- Returns a list containing the {Item, Value} tuples for all other items, or returns false if no tracing is active for this function.
- match_spec:
- Returns the match specification for this event, if it has one, or true if no match specification has been set.
erlang:trace_pattern(MFA, MatchSpec) -> integer() >= 0
Types:
MFA = trace_pattern_mfa() | send | 'receive'
MatchSpec =
(MatchSpecList :: trace_match_spec()) |
boolean() |
restart |
pause
Approximation of '$1' | '$2' | '$3' | ...
(MatchSpecList :: trace_match_spec()) |
boolean() |
restart |
pause
trace_pattern_mfa() = {atom(), atom(), arity() | '_'} | on_load
trace_match_spec() =[{[term()] | '_' | match_variable(), [term()], [term()]}]
match_variable() = atom()
Approximation of '$1' | '$2' | '$3' | ...
The same as erlang:trace_pattern(Event, MatchSpec, []), retained
for backward compatibility.
erlang:trace_pattern(MFA :: send, MatchSpec, FlagList :: []) -> integer() >= 0
Types:
MatchSpec = (MatchSpecList :: trace_match_spec())
| boolean()
Approximation of '$1' | '$2' | '$3' | ...
trace_match_spec() =[{[term()] | '_' | match_variable(), [term()], [term()]}]
match_variable() = atom()
Approximation of '$1' | '$2' | '$3' | ...
Sets trace pattern for message sending. Must be combined with
erlang:trace/3 to set the send trace flag for one or more
processes. By default all messages sent from send traced processes are
traced. To limit traced send events based on the message content, the sender
and/or the receiver, use erlang:trace_pattern/3.
Argument MatchSpec can take the following forms:
Argument FlagList must be [] for send tracing.
The return value is always 1.
Examples:
Only trace messages to a specific process Pid:
- MatchSpecList:
- A list of match specifications. The matching is done on the list [Receiver, Msg]. Receiver is the process or port identity of the receiver and Msg is the message term. The pid of the sending process can be accessed with the guard function self/0. An empty list is the same as true. For more information, see section Match Specifications in Erlang in the User's Guide.
- true:
- Enables tracing for all sent messages (from send traced processes). Any match specification is removed. This is the default.
- false:
- Disables tracing for all sent messages. Any match specification is removed.
> erlang:trace_pattern(send, [{[Pid, '_'],[],[]}], []). 1Only trace messages matching {reply, _}:
> erlang:trace_pattern(send, [{['_', {reply,'_'}],[],[]}], []). 1Only trace messages sent to the sender itself:
> erlang:trace_pattern(send, [{['$1', '_'],[{'=:=','$1',{self}}],[]}], []). 1Only trace messages sent to other nodes:
> erlang:trace_pattern(send, [{['$1', '_'],[{'=/=',{node,'$1'},{node}}],[]}], []). 1
Note:
A match specification for send trace can use all guard and body functions
except caller.
erlang:trace_pattern(MFA :: 'receive', MatchSpec, FlagList :: []) -> integer() >= 0
Types:
MatchSpec = (MatchSpecList :: trace_match_spec())
| boolean()
Approximation of '$1' | '$2' | '$3' | ...
trace_match_spec() =[{[term()] | '_' | match_variable(), [term()], [term()]}]
match_variable() = atom()
Approximation of '$1' | '$2' | '$3' | ...
Sets trace pattern for message receiving. Must be combined with
erlang:trace/3 to set the 'receive' trace flag for one or
more processes. By default all messages received by 'receive' traced
processes are traced. To limit traced receive events based on the message
content, the sender and/or the receiver, use erlang:trace_pattern/3.
Argument MatchSpec can take the following forms:
Argument FlagList must be [] for receive tracing.
The return value is always 1.
Examples:
Only trace messages from a specific process Pid:
- MatchSpecList:
- A list of match specifications. The matching is done on the list [Node, Sender, Msg]. Node is the node name of the sender. Sender is the process or port identity of the sender, or the atom undefined if the sender is not known (which can be the case for remote senders). Msg is the message term. The pid of the receiving process can be accessed with the guard function self/0. An empty list is the same as true. For more information, see section Match Specifications in Erlang in the User's Guide.
- true:
- Enables tracing for all received messages (to 'receive' traced processes). Any match specification is removed. This is the default.
- false:
- Disables tracing for all received messages. Any match specification is removed.
> erlang:trace_pattern('receive', [{['_',Pid, '_'],[],[]}], []). 1Only trace messages matching {reply, _}:
> erlang:trace_pattern('receive', [{['_','_', {reply,'_'}],[],[]}], []). 1Only trace messages from other nodes:
> erlang:trace_pattern('receive', [{['$1', '_', '_'],[{'=/=','$1',{node}}],[]}], []). 1
Note:
A match specification for 'receive' trace can use all guard and body
functions except caller, is_seq_trace, get_seq_token,
set_seq_token, enable_trace, disable_trace, trace,
silent, and process_dump.
erlang:trace_pattern(MFA, MatchSpec, FlagList) -> integer() >= 0
Types:
MFA = trace_pattern_mfa()
MatchSpec =
(MatchSpecList :: trace_match_spec()) |
boolean() |
restart |
pause
FlagList = [ trace_pattern_flag()]
Approximation of '$1' | '$2' | '$3' | ...
(MatchSpecList :: trace_match_spec()) |
boolean() |
restart |
pause
trace_pattern_mfa() = {atom(), atom(), arity() | '_'} | on_load
trace_match_spec() =[{[term()] | '_' | match_variable(), [term()], [term()]}]
trace_pattern_flag() =global |local |meta |{meta, Pid :: pid()} |{meta, TracerModule :: module(), TracerState :: term()} |call_count |call_time
match_variable() = atom()
Approximation of '$1' | '$2' | '$3' | ...
Enables or disables call tracing for one or more functions. Must be
combined with erlang:trace/3 to set the call trace flag
for one or more processes.
Conceptually, call tracing works as follows. Inside the Erlang virtual machine,
a set of processes and a set of functions are to be traced. If a traced
process calls a traced function, the trace action is taken. Otherwise, nothing
happens.
To add or remove one or more processes to the set of traced processes, use
erlang:trace/3.
To add or remove functions to the set of traced functions, use
erlang:trace_pattern/3.
The BIF erlang:trace_pattern/3 can also add match specifications to a
function. A match specification comprises a pattern that the function
arguments must match, a guard expression that must evaluate to true,
and an action to be performed. The default action is to send a trace message.
If the pattern does not match or the guard fails, the action is not executed.
Argument MFA is to be a tuple, such as {Module, Function, Arity},
or the atom on_load (described below). It can be the module, function,
and arity for a function (or a BIF in any module). The atom '_' can be
used as a wildcard in any of the following ways:
Other combinations, such as {Module,'_',Arity}, are not allowed. Local
functions match wildcards only if option local is in FlagList.
If argument MFA is the atom on_load, the match specification and
flag list are used on all modules that are newly loaded.
Argument MatchSpec can take the following forms:
Parameter FlagList is a list of options. The following are the valid
options:
The options global and local are mutually exclusive, and
global is the default (if no options are specified). The options
call_count and meta perform a kind of local tracing, and cannot
be combined with global. A function can be globally or locally traced.
If global tracing is specified for a set of functions, then local, meta, call
time, and call count tracing for the matching set of local functions is
disabled, and conversely.
When disabling trace, the option must match the type of trace set on the
function. That is, local tracing must be disabled with option local and
global tracing with option global (or no option), and so on.
Part of a match specification list cannot be changed directly. If a function has
a match specification, it can be replaced with a new one. To change an
existing match specification, use the BIF erlang:trace_info/2 to
retrieve the existing match specification.
Returns the number of functions matching argument MFA. This is zero if
none matched.
- {Module,Function,'_'}:
- All functions of any arity named Function in module Module.
- {Module,'_','_'}:
- All functions in module Module.
- {'_','_','_'}:
- All functions in all loaded modules.
- false:
- Disables tracing for the matching functions. Any match specification is removed.
- true:
- Enables tracing for the matching functions. Any match specification is removed.
- MatchSpecList:
- A list of match specifications. An empty list is equivalent to true. For a description of match specifications, see section Match Specifications in Erlang in the User's Guide.
- restart:
- For the FlagList options call_count and call_time: restarts the existing counters. The behavior is undefined for other FlagList options.
- pause:
- For the FlagList options call_count and call_time: pauses the existing counters. The behavior is undefined for other FlagList options.
- global:
- Turns on or off call tracing for global function calls (that is, calls specifying the module explicitly). Only exported functions match and only global calls generate trace messages. This is the default.
- local:
- Turns on or off call tracing for all types of function calls. Trace messages are sent whenever any of the specified functions are called, regardless of how they are called. If flag return_to is set for the process, a return_to message is also sent when this function returns to its caller.
- meta | {meta, Pid} | {meta, TracerModule, TracerState}:
- Turns on or off meta-tracing for all types of function calls. Trace messages are sent to the tracer whenever any of the specified functions are called. If no tracer is specified, self() is used as a default tracer process.
Meta-tracing traces all processes and does not care about the process trace
flags set by erlang:trace/3, the trace flags are instead fixed to
[call, timestamp].
The match specification function {return_trace} works with meta-trace and
sends its trace message to the same tracer.
- call_count:
- Starts (MatchSpec == true) or stops (MatchSpec == false) call count tracing for all types of function calls. For every function, a counter is incremented when the function is called, in any process. No process trace flags need to be activated.
If call count tracing is started while already running, the count is restarted
from zero. To pause running counters, use MatchSpec == pause. Paused
and running counters can be restarted from zero with MatchSpec ==
restart.
To read the counter value, use erlang:trace_info/2.
- call_time:
- Starts (MatchSpec == true) or stops (MatchSpec == false) call time tracing for all types of function calls. For every function, a counter is incremented when the function is called. Time spent in the function is accumulated in two other counters, seconds and microseconds. The counters are stored for each call traced process.
If call time tracing is started while already running, the count and time
restart from zero. To pause running counters, use MatchSpec == pause.
Paused and running counters can be restarted from zero with MatchSpec ==
restart.
To read the counter value, use erlang:trace_info/2.
trunc(Number) -> integer()
Types:
Number = number()
Returns an integer by truncating Number, for example:
> trunc(5.5). 5Allowed 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}). 3Allowed in guard tests.
tuple_to_list(Tuple) -> [term()]
Types:
Tuple = tuple()
Returns a list corresponding to Tuple. Tuple can contain any
Erlang terms. Example:
> tuple_to_list({share, {'Ericsson_B', 163}}). [share,{'Ericsson_B',163}]
erlang:unique_integer() -> integer()
Generates and returns an integer unique on current runtime system
instance. The same as calling
erlang:unique_integer([]).
erlang:unique_integer(ModifierList) -> integer()
Types:
ModifierList = [Modifier]
Modifier = positive | monotonic
Generates and returns an integer unique on current runtime system
instance. The integer is unique in the sense that this BIF, using the same
set of modifiers, does not return the same integer more than once on the
current runtime system instance. Each integer value can of course be
constructed by other means.
By default, when [] is passed as ModifierList, both negative and
positive integers can be returned. This to use the range of integers that do
not need heap memory allocation as much as possible. By default the returned
integers are also only guaranteed to be unique, that is, any returned integer
can be smaller or larger than previously returned integers.
Modifiers:
All valid Modifiers can be combined. Repeated (valid) Modifiers in
the ModifierList are ignored.
- positive:
- Returns only positive integers.
Notice that by passing the positive modifier you will get heap allocated
integers (bignums) quicker.
- monotonic:
- Returns strictly monotonically increasing integers corresponding to creation time. That is, the integer returned is always larger than previously returned integers on the current runtime system instance.
These values can be used to determine order between events on the runtime system
instance. That is, if both X = erlang:unique_integer([monotonic]) and
Y = erlang:unique_integer([monotonic]) are executed by different
processes (or the same process) on the same runtime system instance and X
< Y, we know that X was created before Y.
Warning:
Strictly monotonically increasing values are inherently quite expensive to
generate and scales poorly. This is because the values need to be synchronized
between CPU cores. That is, do not pass the monotonic modifier unless
you really need strictly monotonically increasing values.
Note:
The set of integers returned by erlang:unique_integer/1 using different
sets of Modifiers will overlap. For example, by calling
unique_integer([monotonic]), and unique_integer([positive,
monotonic]) repeatedly, you will eventually see some integers that are
returned by both calls.
Failures:
- badarg:
- if ModifierList is not a proper list.
- badarg:
- if Modifier is not a valid modifier.
erlang:universaltime() -> DateTime
Types:
DateTime = calendar:datetime()
Returns the current date and time according to Universal Time Coordinated (UTC)
in the form {{Year, Month, Day}, {Hour, Minute, Second}} if supported
by the underlying OS. Otherwise erlang:universaltime() is equivalent to
erlang:localtime(). Example:
> erlang:universaltime(). {{1996,11,6},{14,18,43}}
erlang:universaltime_to_localtime(Universaltime) -> Localtime
Types:
Localtime = Universaltime = calendar:datetime()
Converts Universal Time Coordinated (UTC) date and time to local date and time
in the form {{Year, Month, Day}, {Hour, Minute, Second}} if supported
by the underlying OS. Otherwise no conversion is done, and
Universaltime is returned. Example:
> erlang:universaltime_to_localtime({{1996,11,6},{14,18,43}}). {{1996,11,7},{15,18,43}}Failure: badarg if Universaltime denotes an invalid date and time.
unlink(Id) -> true
Types:
Id = pid() | port()
Removes the link, if there is one, between the calling process and the process
or port referred to by Id.
Returns true and does not fail, even if there is no link to Id, or
if Id does not exist.
Once unlink(Id) has returned, it is guaranteed that the link between the
caller and the entity referred to by Id has no effect on the caller in
the future (unless the link is setup again). If the caller is trapping exits,
an {'EXIT', Id, _} message from the link can have been placed in the
caller's message queue before the call.
Notice that the {'EXIT', Id, _} message can be the result of the link,
but can also be the result of Id calling exit/2. Therefore, it
can be appropriate to clean up the message queue when trapping exits
after the call to unlink(Id), as follows:
unlink(Id), receive {'EXIT', Id, _} -> true after 0 -> true end
Note:
Before Erlang/OTP R11B (ERTS 5.5) unlink/1 behaved completely
asynchronously, that is, the link was active until the "unlink
signal" reached the linked entity. This had an undesirable effect, as you
could never know when you were guaranteed not to be effected by the
link.
The current behavior can be viewed as two combined operations: asynchronously
send an "unlink signal" to the linked entity and ignore any future
results of the link.
unregister(RegName) -> true
Types:
RegName = atom()
Removes the registered name RegName associated with a process identifier
or a port identifier, for example:
> unregister(db). trueUsers are advised not to unregister system processes. Failure: badarg if RegName is not a registered name.
whereis(RegName) -> pid() | port() | undefined
Types:
RegName = atom()
Returns the process identifier or port identifier with the registered name
RegName. Returns undefined if the name is not registered.
Example:
> whereis(db). <0.43.0>
erlang:yield() -> true
Voluntarily lets other processes (if any) get a chance to execute. Using this
function is similar to receive after 1 -> ok end, except that
yield() is faster.
Warning:
There is seldom or never any need to use this BIF, 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.
erts 8.2.1 | Ericsson AB |