erlang

Types

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

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

Allowed in guard tests.

Computes and returns the adler32 checksum for Data.

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]).

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)).

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}

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).

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.

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

Example:

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

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

> atom_to_list('Erlang').
"Erlang"

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(3).

Allowed in guard tests.

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

Allowed in guard tests.

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.

Examples:

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

As binary_to_atom/2, but the atom must exist.

Failure: badarg if the atom does not exist.

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

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

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

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

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

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

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

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

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

Returns a list of integers corresponding to the bytes of 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.

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

See also term_to_binary/1 and binary_to_term/2.

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

Option:

safe

Use this option when receiving binaries from an untrusted source.

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

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

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

> 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]).
hello

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

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

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

Allowed in guard tests.

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.

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).

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

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

Allowed in guard tests.

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

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

Options:

{async, Async}

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

{info, Info}

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

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

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

More Options may be added in the future.

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

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

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

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

> ceil(5.5).
6

Allowed in guard tests.

Returns true if Module has old code, otherwise false.

See also code(3).

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

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

Options:

{allow_gc, boolean()}

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

{async, RequestId}

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

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

CheckResult informs about the result of the request as follows:

true

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

false

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

aborted

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

See also code(3).

Failures:

badarg

If Pid is not a node local process identifier.

badarg

If Module is not an atom.

badarg

If OptionList is an invalid list of options.

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.

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

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]).

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)).

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}

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

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

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

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

Types:

raw | 0

No packet handling is done. The entire binary is returned unless it is empty.

1 | 2 | 4

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

line

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

asn1 | cdr | sunrm | fcgi | tpkt

The header is not stripped off.

The meanings of the packet types are as follows:

asn1 - ASN.1 BER

sunrm - Sun's RPC encoding

cdr - CORBA (GIOP 1.1)

fcgi - Fast CGI

tpkt - TPKT format [RFC1006]

http | httph | http_bin | httph_bin

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

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

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

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

Options:

{packet_size, integer() >= 0}

Sets the maximum allowed size of the packet body. If the packet header indicates that the length of the packet is longer than the maximum allowed length, the packet is considered invalid. Defaults to 0, which means no size limit.

{line_length, integer() >= 0}

For packet type line, lines longer than the indicated length are truncated.

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

{line_delimiter, 0 =< byte() =< 255}

For packet type line, sets the delimiting byte. Default is the latin-1 character $\n.

Examples:

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

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

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

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.

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

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.

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.

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.

Failures:

badarg

If OptionList is not a list.

badarg

If Option is an invalid option.

badarg

The same failure as for demonitor/1.

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.

Prints a text representation of Term on the standard output.

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

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

Allowed in guard tests.

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]}]

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}

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}]}}

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.

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}

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

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

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

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

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

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

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

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

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

This is equivalent to a call to:

erlang:external_size(Term, [])

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

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

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

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

> float(55).
55.0

Allowed in guard tests.

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

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">>

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

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

Available options:

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

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

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

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

Examples:

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

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

> floor(-10.5).
-11

Allowed in guard tests.

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.

Two types of funs have slightly different semantics:

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

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

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

{type, Type}

Type is local or external.

{module, Module}

Module (an atom) is the module name.

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

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

{name, Name}

Name (an atom) is a function name.

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

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

{arity, Arity}

Arity is the number of arguments that the fun is to be called with.

{env, Env}

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

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

{pid, Pid}

Pid is the process identifier of the process that originally created the fun.

{index, Index}

Index (an integer) is an index into the module fun table.

{new_index, Index}

Index (an integer) is an index into the module fun table.

{new_uniq, Uniq}

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

{uniq, Uniq}

Uniq (an integer) is a unique value for this fun. As from 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.

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.

Returns a string corresponding to the text representation of Fun.

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.

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.

The same as garbage_collect(Pid, []).

Garbage collects the node local process identified by Pid.

Option:

{async, RequestId}

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

{type, 'major' | 'minor'}

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

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

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

true

The process identified by Pid has been garbage collected.

false

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

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

Failures:

badarg

If Pid is not a node local process identifier.

badarg

If OptionList is an invalid list of options.

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}}]

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}

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

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]

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]

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

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

erlang:get_stacktrace/0 is only guaranteed to return a stacktrace if called (directly or indirectly) from within the scope of a try expression. That is, the following call works:

try Expr
catch
  C:R ->
   {C,R,erlang:get_stacktrace()}
end

As does this call:

try Expr
catch
  C:R ->
   {C,R,helper()}
end

helper() ->
  erlang:get_stacktrace().

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

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

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

file

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

line

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

See also error/1 and error/2.

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.

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.

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

> halt().
os_prompt%

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

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

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.

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.

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

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

Allowed in guard tests.

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

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.

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}

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

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

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

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

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

> integer_to_list(77).
"77"

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

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

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

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>>

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

Returns true if Term is an atom, otherwise false.

Allowed in guard tests.

Returns true if Term is a binary, otherwise false.

A binary always contains a complete number of bytes.

Allowed in guard tests.

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

Allowed in guard tests.

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

Allowed in guard tests.

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

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

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

Allowed in guard tests.

Returns true if Term is a fun, otherwise false.

Allowed in guard tests.

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

Allowed in guard tests.

Returns true if Term is an integer, otherwise false.

Allowed in guard tests.

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

Allowed in guard tests.

Returns true if Term is a map, otherwise false.

Allowed in guard tests.

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

Allowed in guard tests.

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

Allowed in guard tests.

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

Allowed in guard tests.

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.

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

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

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.

Returns true if Term is a reference, otherwise false.

Allowed in guard tests.

Returns true if Term is a tuple, otherwise false.

Allowed in guard tests.

Returns the length of List, for example:

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

Allowed in guard tests.

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.

Returns the atom whose text representation is String.

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

Example:

> list_to_atom("Erlang").
'Erlang'

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>>

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>>

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.

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

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

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

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

> list_to_integer("123").
123

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

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

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

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

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.

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

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

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

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

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

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

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.

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.

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(3).

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

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

load_failed

The OS failed to load the NIF library.

bad_lib

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

load | upgrade

The corresponding library callback was unsuccessful.

reload

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

old_code

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

notsup

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

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

See also code(3).

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.

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.

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.

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

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

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

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}

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

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

Allowed in guard tests.

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

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

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

• true if a trace message is to be emitted
• false if a trace message is not to be emitted
• The message term to be appended to the trace message

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

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

See also ets:test_ms/2.

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

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.

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

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

Update an MD5 Context with Data and returns a NewContext.

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(3) and/or erl(1).

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

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

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

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

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.

Failures:

badarg

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

badarg

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

notsup

If an erts_alloc(3) allocator has been disabled.

See also erlang:memory/0.

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

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

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

{Tag, MonitorRef, Type, Object, Info}

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).

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.

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.

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.

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.

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.

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

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

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.

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.

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.

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

Allowed in guard tests.

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.

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

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

NodeTypes:

visible

Nodes connected to this node through normal connections.

hidden

Nodes connected to this node through hidden connections.

connected

All nodes connected to this node.

this

This node.

known

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

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

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.

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(3), the function file:native_name_encoding/0 in Kernel, and the Using Unicode in Erlang User's Guide.

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.

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

{packet, N}

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

stream

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

{line, L}

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

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

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

{cd, Dir}

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

{env, Env}

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).

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

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

badarg

Bad input arguments to open_port.

system_limit

All available ports in the Erlang emulator are in use.

enomem

Not enough memory to create the port.

eagain

No more available OS processes.

enametoolong

Too long external command.

emfile

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

enfile

Full file table (for the entire OS).

eacces

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

enoent

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

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

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).

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.

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.

Returns a string corresponding to the text representation of Pid.

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).

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.

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.

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.

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.

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

• The error behavior differs, see below.

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

• port_connect/1 is synchronous, see below.

• The new port owner gets linked to the port.

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

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

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

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

Failures:

badarg

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

badarg

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

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).

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

The result contains information about the following Items:

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

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

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

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.

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.

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.

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.

Locking is one of the following:

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

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

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

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

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.

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.

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.

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.

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.

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.

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

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.

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.

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

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.

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.

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.

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.

Changes the minimum heap size for the calling process.

Returns the old value of the flag.

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

Returns the old value of the flag.

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

size

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

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

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

kill

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

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

error_logger

When set to true, the runtime system 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).

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.

This flag determines how messages in the message queue are stored, as follows:

off_heap

All messages in the message queue will be stored outside of the process heap. This implies that no messages in the message queue will be part of a garbage collection of the process.

on_heap

All messages in the message queue will eventually be placed on heap. They can however temporarily be stored off heap. This is how messages always have been stored up until ERTS 8.0.

The default message_queue_data process flag is determined by command-line argument +hmqd in erl(1).

If the process potentially can get many messages, you are advised to set the flag to off_heap. This because a garbage collection with many messages placed on the heap can become extremely expensive and the process can consume large amounts of memory. Performance of the actual message passing is however generally better when not using flag off_heap.

When changing this flag messages will be moved. This work has been initiated but not completed when this function call returns.

Returns the old value of the flag.

Sets the process priority. Level is an atom. Four priority levels exist: low, normal, high, and max. Default is normal.

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.

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.

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

• A tuple {Module, Function, Arity} for function calls

• The atoms send, 'receive', and timeout for sends and receives ('receive' when a message is received and timeout when a receive times out)

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

Returns the old value of the flag.

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

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

• Tracing. Trace flags can still be set for the process, but no trace messages of any kind are generated. (If flag sensitive is turned off, trace messages are again generated if any trace flags are set.)

• Sequential tracing. The sequential trace token is propagated as usual, but no sequential trace messages are generated.

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

Stack back-traces cannot be displayed for the process.

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

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

Returns the old value of the flag.

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.

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

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

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

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

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

For information about specific InfoTuples, see process_info/2.

Failure: badarg if Pid is not a local process.

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.

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. In the current implementation BinInfo is a list of tuples. The tuples contain; BinaryId, BinarySize, BinaryRefcCount.

{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. The depth of the stacktrace is truncated according to the backtrace_depth system flag setting.

{dictionary, Dictionary}

Dictionary is the process dictionary.

{error_handler, Module}

Module is the error handler module used by the process (for undefined function calls, for example).

{garbage_collection, GCInfo}

GCInfo is a list containing miscellaneous information about garbage collection for this process. The content of GCInfo can be changed without prior notice.

{garbage_collection_info, GCInfo}

GCInfo is a list containing miscellaneous detailed information about garbage collection for this process. The content of GCInfo can be changed without prior notice. For details about the meaning of each item, see gc_minor_start in erlang:trace/3.

{group_leader, GroupLeader}

GroupLeader is the group leader for the I/O of the process.

{heap_size, Size}

Size is the size in words of the youngest heap generation of the process. This generation includes the process stack. This information is highly implementation-dependent, and can change if the implementation changes.

{initial_call, {Module, Function, Arity}}

Module, Function, Arity is the initial function call with which the process was spawned.

{links, PidsAndPorts}

PidsAndPorts is a list of process identifiers and port identifiers, with processes or ports to which the process has a link.

{last_calls, false|Calls}

The value is false if call saving is not active for the process (see process_flag/3). If call saving is active, a list is returned, in which the last element is the most recent called.

{memory, Size}

Size is the size in bytes of the process. This includes call stack, heap, and internal structures.

{message_queue_len, MessageQueueLen}

MessageQueueLen is the number of messages currently in the message queue of the process. This is the length of the list MessageQueue returned as the information item messages (see below).

{messages, MessageQueue}

MessageQueue is a list of the messages to the process, which have not yet been processed.

{min_heap_size, MinHeapSize}

MinHeapSize is the minimum heap size for the process.

{min_bin_vheap_size, MinBinVHeapSize}

MinBinVHeapSize is the minimum binary virtual heap size for the process.

{monitored_by, 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.