erlang

The Erlang BIFs

By convention, most built-in functions (BIFs) are seen as being in the module erlang. A number of the BIFs are viewed more or less as part of the Erlang programming language and are auto-imported. Thus, it is not necessary to specify the module name and both the calls atom_to_list(Erlang) and erlang:atom_to_list(Erlang) are identical.

In the text, auto-imported BIFs are listed without module prefix. BIFs listed with module prefix are not auto-imported.

BIFs may fail for a variety of reasons. All BIFs fail with reason badarg if they are called with arguments of an incorrect type. The other reasons that may make BIFs fail are described in connection with the description of each individual BIF.

Some BIFs may be used in guard tests, these are marked with "Allowed in guard tests".

Types


ext_binary()

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

timestamp/0

See now/0.

Functions


abs/1

Returns an integer or float which is the arithmetical absolute value of Float or Int.

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

Allowed in guard tests.

adler32/1

Computes and returns the adler32 checksum for Data.

adler32/2

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

The following code:

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

- would assign the same value to Y as this would:

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

adler32_combine/3

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

The following code:

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

- would assign the same value to Z as this would:

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

append_element/2

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

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

apply/2

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

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

Warning!

Earlier, Fun could also be given as {Module, Function}, equivalent to apply(Module, Function, Args). This usage is deprecated and will stop working in a future release of Erlang/OTP.

apply/3

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

> apply(lists, reverse, [[a, b, c]]).
[c,b,a]

apply can be used to evaluate BIFs by using the module name erlang.

> apply(erlang, atom_to_list, ['Erlang']).
"Erlang"

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

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

atom_to_binary/2

Returns a binary which corresponds to the text representation of Atom. If Encoding is latin1, there will be one byte for each character in the text representation. If Encoding is utf8 or unicode, the characters will be encoded using UTF-8 (meaning that characters from 16#80 up to 0xFF will be encoded in two bytes).

Note!

Currently, atom_to_binary(Atom, latin1) can never fail because the text representation of an atom can only contain characters from 0 to 16#FF. In a future release, the text representation of atoms might be allowed to contain any Unicode character and atom_to_binary(Atom, latin1) will fail if the text representation for the Atom contains a Unicode character greater than 16#FF.

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

atom_to_list/1

Returns a string which corresponds to the text representation of Atom.

> atom_to_list('Erlang').
"Erlang"

binary_part/2

Extracts the part of the binary described by PosLen.

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

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

If PosLen in any way references outside the binary, a badarg exception is raised.

Start is zero-based, i.e.:

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

See the STDLIB module binary for details about the PosLen semantics.

Allowed in guard tests.

binary_part/3

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

Allowed in guard tests.

binary_to_atom/2

Returns the atom whose text representation is Binary. If Encoding is latin1, no translation of bytes in the binary is done. If Encoding is utf8 or unicode, the binary must contain valid UTF-8 sequences; furthermore, only Unicode characters up to 0xFF are allowed.

Note!

binary_to_atom(Binary, utf8) will fail if the binary contains Unicode characters greater than 16#FF. In a future release, such Unicode characters might be allowed and binary_to_atom(Binary, utf8) will not fail in that case. For more information on Unicode support in atoms see note on UTF-8 encoded atoms in the chapter about the external term format in the ERTS User's Guide.

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

binary_to_existing_atom/2

Works like binary_to_atom/2, but the atom must already exist.

Failure: badarg if the atom does not already exist.

binary_to_float/1

Returns the float whose text representation is Binary.

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

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

binary_to_integer/1

Returns an integer whose text representation is Binary.

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

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

binary_to_integer/2

Returns an integer whose text representation in base Base is Binary.

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

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

binary_to_list/1

Returns a list of integers which correspond to the bytes of Binary.

binary_to_list/3

1..byte_size(Binary)

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

Note!

This function's indexing style of using one-based indices for binaries is deprecated. New code should use the functions in the STDLIB module binary instead. They consequently use the same (zero-based) style of indexing.

bitstring_to_list/1

Returns a list of integers which correspond to the bytes of Bitstring. If the number of bits in the binary is not divisible by 8, the last element of the list will be a bitstring containing the remaining bits (1 up to 7 bits).

binary_to_term/1

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

Warning!

When decoding binaries from untrusted sources, consider using binary_to_term/2 to prevent denial of service attacks.

See also term_to_binary/1 and binary_to_term/2.

binary_to_term/2

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

safe

Use this option when receiving binaries from an untrusted source.

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

Currently, this prevents creation of new atoms directly, creation of new atoms indirectly (as they are embedded in certain structures like pids, refs, funs, etc.), and creation of new external function references. None of those resources are currently garbage collected, so unchecked creation of them can exhaust available memory.

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

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

bit_size/1

Returns an integer which is the size in bits of Bitstring.

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

Allowed in guard tests.

bump_reductions/1

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

Warning!

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

byte_size/1

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

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

Allowed in guard tests.

cancel_timer/1

Cancels a timer, where TimerRef was returned by either erlang:send_after/3 or erlang:start_timer/3. If the timer is there to be removed, the function returns the time in milliseconds left until the timer would have expired, otherwise false (which means that TimerRef was never a timer, that it has already been cancelled, or that it has already delivered its message).

See also erlang:send_after/3, erlang:start_timer/3, and erlang:read_timer/1.

Note: Cancelling a timer does not guarantee that the message has not already been delivered to the message queue.

check_old_code/1

Returns true if the Module has old code, and false otherwise.

See also code(3).

check_process_code/2

check_process_code/3

Check if the node local process identified by Pid is executing old code for Module.

Currently available 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 in order to determine the result of the operation, the operation will be aborted (see information on CheckResult below). The default is to allow garbage collection, i.e., {allow_gc, true}.
{async, RequestId}
The check_process_code/3 function will return the value async immediately after the request has been sent. When the request has been processed, the process that called this function will be passed a message on the form:
{check_process_code, RequestId, CheckResult}.

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

CheckResult informs about the result of the request:

true
The process identified by Pid is executing 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 is not executing old code for Module.
aborted
The operation was aborted since the process needed to be garbage collected in order to determine the result of the operation, and the operation was requested by passing the {allow_gc, false} option.

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 not a valid list of options.

crc32/1

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

crc32/2

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

The following code:

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

- would assign the same value to Y as this would:

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

crc32_combine/3

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

The following code:

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

- would assign the same value to Z as this would:

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

date/0

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

The time zone and daylight saving time correction depend on the underlying OS.

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

decode_packet/3

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

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

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

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

The following values of Type are valid:

raw | 0

No packet handling is done. Entire binary is returned unless it is empty.

1 | 2 | 4

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

line

A packet is a line terminated with newline. The newline character is included in the returned packet unless the line was truncated according to the option line_length.

asn1 | cdr | sunrm | fcgi | tpkt

The header is not stripped off.

The meanings of the packet types are as follows:

asn1 - ASN.1 BER
sunrm - Sun's RPC encoding
cdr - CORBA (GIOP 1.1)
fcgi - Fast CGI
tpkt - TPKT format [RFC1006]
http | httph | http_bin | httph_bin

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

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

The protocol type http should only be used for the first line when a HttpRequest or a HttpResponse is expected. The following calls should use httph to get HttpHeader's until http_eoh is returned that marks the end of the headers and the beginning of any following message body.

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

The following options are available:

{packet_size, integer() >= 0}

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

{line_length, integer() >= 0}

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

Option line_length also applies to http* packet types as an alias for option packet_size in the case when packet_size itself is not set. This usage is only intended for backward compatibility.

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

delete_element/2

1..tuple_size(Tuple1)

Returns a new tuple with element at Index removed from tuple Tuple1.

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

delete_module/1

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

Warning!

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

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

demonitor/1

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

Once demonitor(MonitorRef) has returned it is guaranteed that no {'DOWN', MonitorRef, _, _, _} message due to the monitor will be placed in the caller's message queue in the future. A {'DOWN', MonitorRef, _, _, _} message might have been placed in the caller's message queue prior to the call, though. Therefore, in most cases, it is advisable to remove such a 'DOWN' message from the message queue after monitoring has been stopped. demonitor(MonitorRef, [flush]) can be used instead of demonitor(MonitorRef) if this cleanup is wanted.

Note!

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

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

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

demonitor/2

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

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

Currently the following Options are valid:

flush

Remove (one) {_, MonitorRef, _, _, _} message, if there is one, from the caller's message queue after monitoring has been stopped.

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


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

The returned value is one of the following:

true

The monitor was found and removed. In this case no 'DOWN' message due to this monitor have been nor will be placed in the message queue of the caller.

false

The monitor was not found and could not be removed. This probably because someone already has placed a 'DOWN' message corresponding to this monitor in the caller's message queue.

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

Note!

More options may be added in the future.

Failure: badarg if OptionList is not a list, or if Option is not a valid option, or the same failure as for demonitor/1

disconnect_node/1

Forces the disconnection of a node. This will appear to the node Node as if the local node has crashed. This BIF is mainly used in the Erlang network authentication protocols. Returns true if disconnection succeeds, otherwise false. If the local node is not alive, the function returns ignored.

display/1

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

Warning!

This BIF is intended for debugging only.

element/2

1..tuple_size(Tuple)

Returns the Nth element (numbering from 1) of Tuple.

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

Allowed in guard tests.

erase/0

Returns the process dictionary and deletes it.

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

erase/1

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

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

error/1

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

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

error/2

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

exit/1

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

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

exit/2

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

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

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

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

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

external_size/1

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, [])

external_size/2

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

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

The option {minor_version, Version} specifies how floats are encoded. See term_to_binary/2 for a more detailed description.

float/1

Returns a float by converting Number to a float.

> float(55).
55.0

Allowed in guard tests.

Note!

Note that if used on the top-level in a guard, it will test whether the argument is a floating point number; for clarity, use is_float/1 instead.

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

float_to_binary/1

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

float_to_binary/2

Returns a binary which corresponds to the text representation of Float using fixed decimal point formatting. The Options behave in the same way as float_to_list/2.

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

float_to_list/1

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

float_to_list/2

Returns a string which corresponds to the text representation of Float using fixed decimal point formatting. When decimals option is specified the returned value will contain at most Decimals number of digits past the decimal point. If the number doesn't fit in the internal static buffer of 256 bytes, the function throws badarg. When compact option is provided the trailing zeros at the end of the list are truncated (this option is only meaningful together with the decimals option). When scientific option is provided, the float will be formatted using scientific notation with Decimals digits of precision. If Options is [] the function behaves like float_to_list/1.

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

fun_info/1

Returns a list containing information about the fun Fun. Each element of the list is a tuple. The order of the tuples is not defined, and more tuples may be added in a future release.

Warning!

This BIF is mainly intended for debugging, but it can occasionally be useful in library functions that might need to verify, for instance, the arity of a fun.

There are two types of funs with slightly different semantics:

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

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

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

{type, Type}

Type is either local or external.

{module, Module}

Module (an atom) is the module name.

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

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

{name, Name}

Name (an atom) is a function name.

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

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

{arity, Arity}

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

{env, Env}

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

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

{pid, Pid}

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

{index, Index}

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

{new_index, Index}

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

{new_uniq, Uniq}

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

{uniq, Uniq}

Uniq (an integer) is a unique value for this fun. Starting in the R15 release, this integer is calculated from the compiled code for the entire module. Before R15, this integer was based on only the body of the fun.

fun_info/2

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.

fun_to_list/1

Returns a string which corresponds to the text representation of Fun.

function_exported/3

Returns true if the module Module is loaded and contains an exported function Function/Arity; otherwise false.

Returns false for any BIF (functions implemented in C rather than in Erlang).

garbage_collect/0

Forces an immediate garbage collection of the currently executing process. The function should not be used, unless it has been noticed -- or there are good reasons to suspect -- that the spontaneous garbage collection will occur too late or not at all. Improper use may seriously degrade system performance.

garbage_collect/1

garbage_collect/2

Garbage collect the node local process identified by Pid.

Currently available Options:

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

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

GCResult informs about the result of the garbage collection request:

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

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

Failures:

badarg
If Pid is not a node local process identifier.
badarg
If OptionList is not a valid list of options.

get/0

Returns the process dictionary as a list of {Key, Val} tuples.

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

get/1

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

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

get_cookie/0

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

get_keys/1

Returns a list of keys which are associated with the value Val in the process dictionary.

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

get_stacktrace/0

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

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

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

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

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

file

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

line

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

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

group_leader/0

Returns the pid of the group leader for the process which evaluates the function.

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

group_leader/2

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

See also group_leader/0.

halt/0

The same as halt(0, []).

> halt().
os_prompt% 

halt/1

The same as halt(Status, []).

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

halt/2

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

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

Note that on many platforms, only the status codes 0-255 are supported by the operating system.

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

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

hash/2

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

Warning!

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

hd/1

Returns the head of List, that is, the first element.

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

Allowed in guard tests.

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

hibernate/3

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

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

If the process has any message in its message queue, the process will be awaken immediately in the same way as described above.

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

If the size of the live data in the process is less than the minimum heap size, the first garbage collection occurring after the process has been awaken will ensure that the heap size is changed to a size not smaller than the minimum heap size.

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

insert_element/3

1..tuple_size(Tuple1) + 1

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

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

integer_to_binary/1

Returns a binary which corresponds to the text representation of Integer.

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

integer_to_binary/2

Returns a binary which corresponds to the text representation of Integer in base Base.

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

integer_to_list/1

Returns a string which corresponds to the text representation of Integer.

> integer_to_list(77).
"77"

integer_to_list/2

Returns a string which corresponds to the text representation of Integer in base Base.

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

iolist_to_binary/1

Returns a binary which is made from the integers and binaries in IoListOrBinary.

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

iolist_size/1

Returns an integer which is the size in bytes of the binary that would be the result of iolist_to_binary(Item).

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

is_alive/0

Returns true if the local node is alive; that is, if the node can be part of a distributed system. Otherwise, it returns false.

is_atom/1

Returns true if Term is an atom; otherwise returns false.

Allowed in guard tests.

is_binary/1

Returns true if Term is a binary; otherwise returns false.

A binary always contains a complete number of bytes.

Allowed in guard tests.

is_bitstring/1

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

Allowed in guard tests.

is_boolean/1

Returns true if Term is either the atom true or the atom false (i.e. a boolean); otherwise returns false.

Allowed in guard tests.

is_builtin/3

Returns true if Module:Function/Arity is a BIF implemented in C; otherwise returns false. This BIF is useful for builders of cross reference tools.

is_float/1

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

Allowed in guard tests.

is_function/1

Returns true if Term is a fun; otherwise returns false.

Allowed in guard tests.

is_function/2

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

Allowed in guard tests.

is_integer/1

Returns true if Term is an integer; otherwise returns false.

Allowed in guard tests.

is_list/1

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

Allowed in guard tests.

is_map/1

Returns true if Term is a map; otherwise returns false.

Allowed in guard tests.

is_number/1

Returns true if Term is either an integer or a floating point number; otherwise returns false.

Allowed in guard tests.

is_pid/1

Returns true if Term is a pid (process identifier); otherwise returns false.

Allowed in guard tests.

is_port/1

Returns true if Term is a port identifier; otherwise returns false.

Allowed in guard tests.

is_process_alive/1

Pid must refer to a process at the local node. Returns true if the process exists and is alive, that is, is not exiting and has not exited. Otherwise, returns false.

is_record/2

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

Note!

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

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

is_record/3

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

Allowed in guard tests, provided that RecordTag is a literal atom and Size is a literal integer.

Note!

This BIF is documented for completeness. In most cases is_record/2 should be used.

is_reference/1

Returns true if Term is a reference; otherwise returns false.

Allowed in guard tests.

is_tuple/1

Returns true if Term is a tuple; otherwise returns false.

Allowed in guard tests.

length/1

Returns the length of List.

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

Allowed in guard tests.

link/1

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

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

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

list_to_atom/1

Returns the atom whose text representation is String.

String may only contain ISO-latin-1 characters (i.e. numbers below 256) as the current implementation does not allow unicode characters >= 256 in atoms. For more information on Unicode support in atoms see note on UTF-8 encoded atoms in the chapter about the external term format in the ERTS User's Guide.

> list_to_atom("Erlang").
'Erlang'

list_to_binary/1

Returns a binary which is made from the integers and binaries in IoList.

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

list_to_bitstring/1

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

> Bin1 = <<1,2,3>>.
<<1,2,3>>
> Bin2 = <<4,5>>.
<<4,5>>
> Bin3 = <<6,7:4,>>.
<<6>>
> list_to_bitstring([Bin1,1,[2,3,Bin2],4|Bin3]).
<<1,2,3,1,2,3,4,5,4,6,7:46>>

list_to_existing_atom/1

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

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

list_to_float/1

Returns the float whose text representation is String.

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

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

list_to_integer/1

Returns an integer whose text representation is String.

> list_to_integer("123").
123

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

list_to_integer/2

Returns an integer whose text representation in base Base is String.

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

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

list_to_pid/1

Returns a pid whose text representation is String.

Warning!

This BIF is intended for debugging and for use in the Erlang operating system. It should not be used in application programs.

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

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

list_to_tuple/1

Returns a tuple which corresponds to List. List can contain any Erlang terms.

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

load_module/2

If Binary contains the object code for the module Module, this BIF loads that object code. Also, if the code for the module Module already exists, all export references are replaced so they point to the newly loaded code. The previously loaded code is kept in the system as old code, as there may still be processes which are executing that code. It returns either {module, Module}, or {error, Reason} if loading fails. Reason is one of the following:

badfile

The object code in Binary has an incorrect format or the object code contains code for another module than Module.

not_purged

Binary contains a module which cannot be loaded because old code for this module already exists.

Warning!

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

load_nif/2

Note!

In releases older than OTP R14B, NIFs were an experimental feature. Versions of OTP older than R14B might have different and possibly incompatible NIF semantics and interfaces. For example, in R13B03 the return value on failure was {error,Reason,Text}.

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

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

The call to load_nif/2 must be made directly from the Erlang code of the module that the NIF library belongs to.

It returns either ok, or {error,{Reason,Text}} if loading fails. Reason is one of the atoms below, while Text is a human readable string that may give some more information about the failure.

load_failed

The OS failed to load the NIF library.

bad_lib

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

load | reload | upgrade

The corresponding library callback was not successful.

old_code

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

loaded/0

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

See also code(3).

localtime/0

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

The time zone and daylight saving time correction depend on the underlying OS.

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

localtime_to_universaltime/1

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

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

Failure: badarg if Localtime does not denote a valid date and time.

localtime_to_universaltime/2

Converts local date and time to Universal Time Coordinated (UTC) just like erlang:localtime_to_universaltime/1, but the caller decides if daylight saving time is active or not.

If IsDst == true the Localtime is during daylight saving time, if IsDst == false it is not, and if IsDst == undefined the underlying OS may guess, which is the same as calling erlang:localtime_to_universaltime(Localtime).

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

Failure: badarg if Localtime does not denote a valid date and time.

make_ref/0

Returns an almost unique reference.

The returned reference will re-occur after approximately 2^82 calls; therefore it is unique enough for practical purposes.

> make_ref().
#Ref<0.0.0.135>

make_tuple/2

Returns a new tuple of the given Arity, where all elements are InitialValue.

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

make_tuple/3

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

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

map_size/1

Returns an integer which is the number of key-value pairs in Map.

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

Allowed in guard tests.

max/2

Return the largest of Term1 and Term2; if the terms compare equal, Term1 will be returned.

md5/1

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

See The MD5 Message Digest Algorithm (RFC 1321) for more information about MD5.

Warning!

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

md5_final/1

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

md5_init/0

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

md5_update/2

Updates an MD5 Context with Data, and returns a NewContext.

memory/0

Returns a list containing information about memory dynamically allocated by the Erlang emulator. Each element of the list is a tuple {Type, Size}. The first element Typeis an atom describing memory type. The second element Sizeis memory size in bytes. A description of each memory type follows:

total

The total amount of memory currently allocated, which is the same as the sum of memory size for processes and system.

processes

The total amount of memory currently allocated by the Erlang processes.

processes_used

The total amount of memory currently used by the Erlang processes.

This memory is part of the memory presented as processes memory.

system

The total amount of memory currently allocated by the emulator that is not directly related to any Erlang process.

Memory presented as processes is not included in this memory.

atom

The total amount of memory currently allocated for atoms.

This memory is part of the memory presented as system memory.

atom_used

The total amount of memory currently used for atoms.

This memory is part of the memory presented as atom memory.

binary

The total amount of memory currently allocated for binaries.

This memory is part of the memory presented as system memory.

code

The total amount of memory currently allocated for Erlang code.

This memory is part of the memory presented as system memory.

ets

The total amount of memory currently allocated for ets tables.

This memory is part of the memory presented as system memory.

low

Only on 64-bit halfword emulator.

The total amount of memory allocated in low memory areas that are restricted to less than 4 Gb even though the system may have more physical memory.

May be removed in future releases of halfword emulator.

maximum

The maximum total amount of memory allocated since the emulator was started.

This tuple is only present when the emulator is run with instrumentation.

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

Note!

The system value is not complete. Some allocated memory that should be part of the system value are not.

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

Since the total value is the sum of processes and system the error in system will propagate to the total value.

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

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

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

        RealTotal = processes + RealSystem
        RealSystem = system + MissedSystem

More tuples in the returned list may be added in the future.

Note!

The total value is supposed to be the total amount of memory dynamically allocated by the emulator. Shared libraries, the code of the emulator itself, and the emulator stack(s) are not supposed to be included. That is, the total value is not supposed to be equal to the total size of all pages mapped to the emulator. Furthermore, due to fragmentation and pre-reservation of memory areas, the size of the memory segments which contain the dynamically allocated memory blocks can be substantially larger than the total size of the dynamically allocated memory blocks.

Note!

Since erts version 5.6.4 erlang:memory/0 requires that all erts_alloc(3) allocators are enabled (default behaviour).

Failure:

notsup
If an erts_alloc(3) allocator has been disabled.

memory/1

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

Note!

Since erts version 5.6.4 erlang:memory/1 requires that all erts_alloc(3) allocators are enabled (default behaviour).

Failures:

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

See also erlang:memory/0.

min/2

Return the smallest of Term1 and Term2; if the terms compare equal, Term1 will be returned.

module_loaded/1

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

Warning!

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

monitor/2

The calling process starts monitoring Item which is an object of type Type.

Currently only processes can be monitored, i.e. the only allowed Type is process, but other types may be allowed in the future.

Item can be:

pid()

The pid of the process to monitor.

{RegName, Node}

A tuple consisting of a registered name of a process and a node name. The process residing on the node Node with the registered name RegName will be monitored.

RegName

The process locally registered as RegName will be monitored.

Note!

When a process is monitored by registered name, the process that has the registered name at the time when monitor/2 is called will be monitored. The monitor will not be effected, if the registered name is unregistered.

A 'DOWN' message will be sent to the monitoring process if Item dies, if Item does not exist, or if the connection is lost to the node which Item resides on. A 'DOWN' message has the following pattern:

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

where MonitorRef and Type are the same as described above, and:

Object

A reference to the monitored object:

the pid of the monitored process, if Item was specified as a pid. {RegName, Node}, if Item was specified as {RegName, Node}. {RegName, Node}, if Item was specified as RegName. Node will in this case be the name of the local node (node()).
Info

Either the exit reason of the process, noproc (non-existing process), or noconnection (no connection to Node).

Note!

If/when monitor/2 is extended (e.g. to handle other item types than process), other possible values for Object, and Info in the 'DOWN' message will be introduced.

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

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

Making several calls to monitor/2 for the same Item is not an error; it results in as many, completely independent, monitorings.

Note!

The format of the 'DOWN' message changed in the 5.2 version of the emulator (OTP release R9B) for monitor by registered name. The Object element of the 'DOWN' message could in earlier versions sometimes be the pid of the monitored process and sometimes be the registered name. Now the Object element is always a tuple consisting of the registered name and the node name. Processes on new nodes (emulator version 5.2 or greater) will always get 'DOWN' messages on the new format even if they are monitoring processes on old nodes. Processes on old nodes will always get 'DOWN' messages on the old format.

monitor_node/2

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

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

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

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

Failure: badarg if the local node is not alive.

monitor_node/3

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

Note!

The allow_passive_connect option is used internally and is seldom needed in applications where the network topology and the kernel options in effect is known in advance.

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

nif_error/1

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

nif_error/2

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

node/0

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

Allowed in guard tests.

node/1

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

Allowed in guard tests.

nodes/0

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

nodes/1

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

NodeType can be any of the following:

visible

Nodes connected to this node through normal connections.

hidden

Nodes connected to this node through hidden connections.

connected

All nodes connected to this node.

this

This node.

known

Nodes which are known to this node, i.e., connected, previously connected, etc.

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

If the local node is not alive, nodes(this) == nodes(known) == [nonode@nohost], for any other Arg the empty list [] is returned.

now/0

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

It can only be used to check the local time of day if the time-zone info of the underlying operating system is properly configured.

If you do not need the return value to be unique and monotonically increasing, use os:timestamp/0 instead to avoid some overhead.

open_port/2

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

The name of the executable as well as the arguments given in cd, env, args and arg0 is subject to Unicode file name translation if the system is running in Unicode file name mode. To avoid translation or force i.e. UTF-8, supply the executable and/or arguments as a binary in the correct encoding. See the file module, the file:native_name_encoding/0 function and the stdlib users guide for details.

Note!

The characters in the name (if given as a list) can only be > 255 if the Erlang VM is started in Unicode file name translation mode, otherwise the name of the executable is limited to the ISO-latin-1 character set.

PortName is one of the following:

{spawn, Command}

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

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

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

{spawn_driver, Command}

Works like {spawn, Command}, but demands the first (space separated) token of the command to be the name of a loaded driver. If no driver with that name is loaded, a badarg error is raised.

{spawn_executable, FileName}

Works like {spawn, FileName}, but only runs external executables. The FileName in its whole is used as the name of the executable, including any spaces. If arguments are to be passed, the args and arg0 PortSettings can be used.

The shell is not usually invoked to start the program, it's executed directly. Neither is the PATH (or equivalent) searched. To find a program in the PATH to execute, use os:find_executable/1.

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

If the FileName cannot be run, an error exception, with the posix error code as the reason, is raised. The error reason may differ between operating systems. Typically the error enoent is raised when one tries to run a program that is not found and eaccess is raised when the given file is not executable.

{fd, In, Out}

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

PortSettings is a list of settings for the port. Valid settings are:

{packet, N}

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

stream

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

{line, L}

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

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

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

{cd, Dir}

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

{env, Env}

This is only valid for {spawn, Command} and {spawn_executable, FileName}. The environment of the started process is extended using the environment specifications in Env.

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

{args, [ string() | binary() ]}

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

The arguments are not expanded by the shell prior to being supplied to the executable, most notably this means that file wildcard expansion will not happen. Use filelib:wildcard/1 to expand wildcards for the arguments. Note that even if the program is a Unix shell script, meaning that the shell will ultimately be invoked, wildcard expansion will not happen and the script will be provided with the untouched arguments. On Windows®, wildcard expansion is always up to the program itself, why this isn't an issue.

Note also that the actual executable name (a.k.a. argv[0]) should not be given in this list. The proper executable name will automatically be used as argv[0] where applicable.

If one, for any reason, wants to explicitly set the program name in the argument vector, the arg0 option can be used.

{arg0, string() | binary()}

This option is only valid for {spawn_executable, FileName} and explicitly specifies the program name argument when running an executable. This might in some circumstances, on some operating systems, be desirable. How the program responds to this is highly system dependent and no specific effect is guaranteed.

exit_status

This is only valid for {spawn, Command} where Command refers to an external program, and for {spawn_executable, FileName}.

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

If the eof option has been given as well, the eof message and the exit_status message appear in an unspecified order.

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

use_stdio

This is only valid for {spawn, Command} and {spawn_executable, FileName}. It allows the standard input and output (file descriptors 0 and 1) of the spawned (UNIX) process for communication with Erlang.

nouse_stdio

The opposite of use_stdio. Uses file descriptors 3 and 4 for communication with Erlang.

stderr_to_stdout

Affects ports to external programs. The executed program gets its standard error file redirected to its standard output file. stderr_to_stdout and nouse_stdio are mutually exclusive.

overlapped_io

Affects ports to external programs on Windows® only. The standard input and standard output handles of the port program will, if this option is supplied, be opened with the flag FILE_FLAG_OVERLAPPED, so that the port program can (and has to) do overlapped I/O on its standard handles. This is not normally the case for simple port programs, but an option of value for the experienced Windows programmer. On all other platforms, this option is silently discarded.

in

The port can only be used for input.

out

The port can only be used for output.

binary

All IO from the port are binary data objects as opposed to lists of bytes.

eof

The port will not be closed at the end of the file and produce an exit signal. Instead, it will remain open and a {Port, eof} message will be sent to the process holding the port.

hide

When running on Windows, suppress creation of a new console window when spawning the port program. (This option has no effect on other platforms.)

{parallelism, Boolean}

Set scheduler hint for port parallelism. If set to true, the VM will schedule port tasks when doing so will improve parallelism in the system. If set to false, the VM will try to perform port tasks immediately, improving latency at the expense of parallelism. The default can be set on system startup by passing the +spp command line argument to erl(1).

The default is stream for all types of port and use_stdio for spawned ports.

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

badarg

Bad input arguments to open_port.

system_limit

All available ports in the Erlang emulator are in use.

enomem

There was not enough memory to create the port.

eagain

There are no more available operating system processes.

enametoolong

The external command given was too long.

emfile

There are no more available file descriptors (for the operating system process that the Erlang emulator runs in).

enfile

The file table is full (for the entire operating system).

eacces

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

enoent

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

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

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

phash/2

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

Portable hash function that will give the same hash for the same Erlang term regardless of machine architecture and ERTS version (the BIF was introduced in ERTS 4.9.1.1). Range can be between 1 and 2^32, the function returns a hash value for Term within the range 1..Range.

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

phash2/1

phash2/2

Range = 1..2^32
Hash = 0..Range-1

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

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

Note that the range 0..Range-1 is different from the range of phash/2 (1..Range).

pid_to_list/1

Returns a string which corresponds to the text representation of Pid.

Warning!

This BIF is intended for debugging and for use in the Erlang operating system. It should not be used in application programs.

port_close/1

Closes an open port. Roughly the same as Port ! {self(), close} except for the error behaviour (see below), being synchronous, and that the port does not reply with {Port, closed}. Any process may close a port with port_close/1, not only the port owner (the connected process). If the calling process is linked to port identified by Port, an exit signal due to that link will be received by the process prior to the return from port_close/1.

For comparison: Port ! {self(), close} fails with badarg if Port cannot be sent to (i.e., Port refers neither to a port nor to a process). If Port is a closed port nothing happens. If Port is an open port and the calling process is the port owner, the port replies with {Port, closed} when all buffers have been flushed and the port really closes, but if the calling process is not the port owner the port owner fails with badsig.

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

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

Failure:

badarg
If Port is not an identifier of an open port, or the registered name of an open port. If the calling process was linked to the previously open port identified by Port, an exit signal due to this link was received by the process prior to this exception.

port_command/2

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

For comparison: Port ! {PortOwner, {command, Data}} fails with badarg if Port cannot be sent to (i.e., Port refers neither to a port nor to a process). If Port is a closed port the data message disappears without a sound. If Port is open and the calling process is not the port owner, the port owner fails with badsig. The port owner fails with badsig also if Data is not a valid IO list.

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

If the port is busy, the calling process will be suspended until the port is not busy anymore.

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

Failures:

badarg
If Port is not an identifier of an open port, or the registered name of an open port. If the calling process was linked to the previously open port identified by Port, an exit signal due to this link was received by the process prior to this exception.
badarg
If Data is not a valid io list.

port_command/3

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

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

If the port is busy, the calling process will be suspended until the port is not busy anymore.

Currently the following Options are valid:

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

Note!

More options may be added in the future.

Failures:

badarg
If Port is not an identifier of an open port, or the registered name of an open port. If the calling process was linked to the previously open port identified by Port, an exit signal due to this link was received by the process prior to this exception.
badarg
If Data is not a valid io list.
badarg
If OptionList is not a valid option list.
notsup
If the force option has been passed, but the driver of the port does not allow forcing through a busy port.

port_connect/2

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

The error behavior differs, see below.

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

port_connect/1 is synchronous, see below.

The new port owner gets linked to the port.

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

For comparison: Port ! {self(), {connect, Pid}} fails with badarg if Port cannot be sent to (i.e., Port refers neither to a port nor to a process). If Port is a closed port nothing happens. If Port is an open port and the calling process is the port owner, the port replies with {Port, connected} to the old port owner. Note that the old port owner is still linked to the port, and that the new is not. If Port is an open port and the calling process is not the port owner, the port owner fails with badsig. The port owner fails with badsig also if Pid is not an existing local pid.

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

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

Failures:

badarg
If Port is not an identifier of an open port, or the registered name of an open port. If the calling process was linked to the previously open port identified by Port, an exit signal due to this link was received by the process prior to this exception.
badarg
If process identified by Pid is not an existing local process.

port_control/3

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

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

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

port_call/3

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

Port is a port identifier, referring to a driver.

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

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

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

Failures:

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

port_info/1

Returns a list containing tuples with information about the Port, or undefined if the port is not open. The order of the tuples is not defined, nor are all the tuples mandatory. If undefined is returned and the calling process was linked to a previously open port identified by Port, an exit signal due to this link was received by the process prior to the return from port_info/1.

Currently the result will containt information about the following Items: registered_name (if the port has a registered name), id, connected, links, name, input, and output. For more information about the different Items, see port_info/2.

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

port_info/2

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

If the port identified by Port is not open, undefined is returned. If undefined is returned and the calling process was linked to a previously open port identified by Port, an exit signal due to this link was received by the process prior to the return from port_info/2.

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

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

If the port identified by Port is not open, undefined is returned. If undefined is returned and the calling process was linked to a previously open port identified by Port, an exit signal due to this link was received by the process prior to the return from port_info/2.

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

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

If the port identified by Port is not open, undefined is returned. If undefined is returned and the calling process was linked to a previously open port identified by Port, an exit signal due to this link was received by the process prior to the return from port_info/2.

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

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

If the port identified by Port is not open, undefined is returned. If undefined is returned and the calling process was linked to a previously open port identified by Port, an exit signal due to this link was received by the process prior to the return from port_info/2.

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

Locking is currently either false (emulator without SMP support), port_level (port specific locking), or driver_level (driver specific locking). Note that these results are highly implementation specific and might change in the future.

If the port identified by Port is not open, undefined is returned. If undefined is returned and the calling process was linked to a previously open port identified by Port, an exit signal due to this link was received by the process prior to the return from port_info/2.

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

Bytes is the total amount of memory, in bytes, allocated for this port by the runtime system. Note that the port itself might have allocated memory which is not included in Bytes.

If the port identified by Port is not open, undefined is returned. If undefined is returned and the calling process was linked to a previously open port identified by Port, an exit signal due to this link was received by the process prior to the return from port_info/2.

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

Monitors represent processes that this port is monitoring.

If the port identified by Port is not open, undefined is returned. If undefined is returned and the calling process was linked to a previously open port identified by Port, an exit signal due to this link was received by the process prior to the return from port_info/2.

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

Name is the command name set by open_port/2.

If the port identified by Port is not open, undefined is returned. If undefined is returned and the calling process was linked to a previously open port identified by Port, an exit signal due to this link was received by the process prior to the return from port_info/2.

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

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

If the port identified by Port is not open, undefined is returned. If undefined is returned and the calling process was linked to a previously open port identified by Port, an exit signal due to this link was received by the process prior to the return from port_info/2.

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

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

If the port identified by Port is not open, undefined is returned. If undefined is returned and the calling process was linked to a previously open port identified by Port, an exit signal due to this link was received by the process prior to the return from port_info/2.

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

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

Bytes is the total amount of data, in bytes, queued by the port using the ERTS driver queue implementation.

If the port identified by Port is not open, undefined is returned. If undefined is returned and the calling process was linked to a previously open port identified by Port, an exit signal due to this link was received by the process prior to the return from port_info/2.

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

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

If the port identified by Port is not open, undefined is returned. If undefined is returned and the calling process was linked to a previously open port identified by Port, an exit signal due to this link was received by the process prior to the return from port_info/2.

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

port_to_list/1

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

Warning!

This BIF is intended for debugging and for use in the Erlang operating system. It should not be used in application programs.

ports/0

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

Note that a port that is exiting, exists but is not open.

pre_loaded/0

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

process_display/2

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

process_flag/2

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

Returns the old value of the flag.

See also exit/2.

This is used by a process to redefine the error handler for undefined function calls and undefined registered processes. Inexperienced users should not use this flag since code auto-loading is dependent on the correct operation of the error handling module.

Returns the old value of the flag.

This changes the minimum heap size for the calling process.

Returns the old value of the flag.

This changes the minimum binary virtual heap size for the calling process.

Returns the old value of the flag.

This sets the process priority. Level is an atom. There are currently four priority levels: low, normal, high, and max. The default priority level is normal. NOTE: The max priority level is reserved for internal use in the Erlang runtime system, and should not be used by others.

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

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

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

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

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

NOTE: You should not depend on the scheduling to remain exactly as it is today. Scheduling, at least on the runtime system with SMP support, is very likely to be modified in the future in order to better utilize available processor cores.

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

Making calls from a high priority process into code that you don't have control over may cause the high priority process to wait for a processes with lower priority, i.e., effectively decreasing the priority of the high priority process during the call. Even if this isn't the case with one version of the code that you don't have under your control, it might be the case in a future version of it. This might, for example, happen if a high priority process triggers code loading, since the code server runs on priority normal.

Other priorities than normal are normally not needed. When other priorities are used, they need to be used with care, especially the high priority must be used with care. A process on high priority should only perform work for short periods of time. Busy looping for long periods of time in a high priority process will most likely cause problems, since there are important servers in OTP running on priority normal.

Returns the old value of the flag.

N must be an integer in the interval 0..10000. If N > 0, call saving is made active for the process, which means that information about the N most recent global function calls, BIF calls, sends and receives made by the process are saved in a list, which can be retrieved with process_info(Pid, last_calls). A global function call is one in which the module of the function is explicitly mentioned. Only a fixed amount of information is saved: a tuple {Module, Function, Arity} for function calls, and the mere atoms send, 'receive' and timeout for sends and receives ('receive' when a message is received and timeout when a receive times out). If N = 0, call saving is disabled for the process, which is the default. Whenever the size of the call saving list is set, its contents are reset.

Returns the old value of the flag.

Set or clear the sensitive flag for the current process. When a process has been marked as sensitive by calling process_flag(sensitive, true), features in the run-time system that can be used for examining the data and/or inner working of the process are silently disabled.

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

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

Sequential tracing: The sequential trace token will be propagated as usual, but no sequential trace messages will be generated.

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

Stack back-traces cannot be displayed for the process.

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

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

Returns the old value of the flag.

process_flag/3

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

Failure: badarg if Pid is not a local process.

process_info/1

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

The order of the InfoTuples is not defined, nor are all the InfoTuples mandatory. The InfoTuples part of the result may be changed without prior notice. Currently InfoTuples with the following items are part of the result: current_function, initial_call, status, message_queue_len, messages, links, dictionary, trap_exit, error_handler, priority, group_leader, total_heap_size, heap_size, stack_size, reductions, and garbage_collection. If the process identified by Pid has a registered name also an InfoTuple with the item registered_name will appear.

See process_info/2 for information about specific InfoTuples.

Warning!

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

Failure: badarg if Pid is not a local process.

process_info/2

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

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

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

Note!

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

Currently the following InfoTuples with corresponding Items are valid:

{backtrace, Bin}

The binary Bin contains the same information as the output from erlang:process_display(Pid, backtrace). Use binary_to_list/1 to obtain the string of characters from the binary.

{binary, BinInfo}

BinInfo is a list containing miscellaneous information about binaries currently being referred to by this process. This InfoTuple may be changed or removed without prior notice.

{catchlevel, CatchLevel}

CatchLevel is the number of currently active catches in this process. This InfoTuple may be changed or removed without prior notice.

{current_function, {Module, Function, Arity}}

Module, Function, Arity is the current function call of the process.

{current_location, {Module, Function, Arity, Location}}

Module, Function, Arity is the current function call of the process. Location is a list of two-tuples that describes the location in the source code.

{current_stacktrace, Stack}

Return the current call stack back-trace (stacktrace) of the process. The stack has the same format as returned by erlang:get_stacktrace/0.

{dictionary, Dictionary}

Dictionary is the dictionary of the process.

{error_handler, Module}

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

{garbage_collection, GCInfo}

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

{group_leader, GroupLeader}

GroupLeader is group leader for the IO of the process.

{heap_size, Size}

Size is the size in words of youngest heap generation of the process. This generation currently include the stack of the process. This information is highly implementation dependent, and may change if the implementation change.

{initial_call, {Module, Function, Arity}}

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

{links, PidsAndPorts}

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

{last_calls, false|Calls}

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

{memory, Size}

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

{message_queue_len, MessageQueueLen}

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

{messages, MessageQueue}

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

{min_heap_size, MinHeapSize}

MinHeapSize is the minimum heap size for the process.

{min_bin_vheap_size, MinBinVHeapSize}

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

{monitored_by, Pids}

A list of pids that are monitoring the process (with monitor/2).

{monitors, Monitors}

A list of monitors (started by monitor/2) that are active for the process. For a local process monitor or a remote process monitor by pid, the list item is {process, Pid}, and for a remote process monitor by name, the list item is {process, {RegName, Node}}.

{priority, Level}

Level is the current priority level for the process. For more information on priorities see process_flag(priority, Level).

{reductions, Number}

Number is the number of reductions executed by the process.

{registered_name, Atom}

Atom is the registered name of the process. If the process has no registered name, this tuple is not present in the list.

{sequential_trace_token, [] | SequentialTraceToken}

SequentialTraceToken the sequential trace token for the process. This InfoTuple may be changed or removed without prior notice.

{stack_size, Size}

Size is the stack size of the process in words.

{status, Status}

Status is the status of the process. Status is exiting, garbage_collecting, waiting (for a message), running, runnable (ready to run, but another process is running), or suspended (suspended on a "busy" port or by the erlang:suspend_process/[1,2] BIF).

{suspending, SuspendeeList}

SuspendeeList is a list of {Suspendee, ActiveSuspendCount, OutstandingSuspendCount} tuples. Suspendee is the pid of a process that have been or is to be suspended by the process identified by Pid via the erlang:suspend_process/2 BIF, or the erlang:suspend_process/1 BIF. ActiveSuspendCount is the number of times the Suspendee has been suspended by Pid. OutstandingSuspendCount is the number of not yet completed suspend requests sent by Pid. That is, if ActiveSuspendCount =/= 0, Suspendee is currently in the suspended state, and if OutstandingSuspendCount =/= 0 the asynchronous option of erlang:suspend_process/2 has been used and the suspendee has not yet been suspended by Pid. Note that the ActiveSuspendCount and OutstandingSuspendCount are not the total suspend count on Suspendee, only the parts contributed by Pid.

{total_heap_size, Size}

Size is the total size in words of all heap fragments of the process. This currently include the stack of the process.

{trace, InternalTraceFlags}

InternalTraceFlags is an integer representing internal trace flag for this process. This InfoTuple may be changed or removed without prior notice.

{trap_exit, Boolean}

Boolean is true if the process is trapping exits, otherwise it is false.

Note however, that not all implementations support every one of the above Items.

Failure: badarg if Pid is not a local process, or if Item is not a valid Item.

processes/0

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

Note that a process that is exiting, exists but is not alive, i.e., is_process_alive/1 will return false for a process that is exiting, but its process identifier will be part of the result returned from processes/0.

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

purge_module/1

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

Warning!

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

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

put/2

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

Note!

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

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

raise/3

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

Warning!

This BIF is intended for debugging and for use in the Erlang operating system. In general, it should be avoided in applications, unless you know very well what you are doing.

Class is one of error, exit or throw, so if it were not for the stacktrace erlang:raise(Class, Reason, Stacktrace) is equivalent to erlang:Class(Reason). Reason is any term and Stacktrace is a list as returned from get_stacktrace(), that is a list of 4-tuples {Module, Function, Arity | Args, Location} where Module and Function are atoms and the third element is an integer arity or an argument list. The stacktrace may also contain {Fun, Args, Location} tuples where Fun is a local fun and Args is an argument list.

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

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

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

read_timer/1

TimerRef is a timer reference returned by erlang:send_after/3 or erlang:start_timer/3. If the timer is active, the function returns the time in milliseconds left until the timer will expire, otherwise false (which means that TimerRef was never a timer, that it has been cancelled, or that it has already delivered its message).

See also erlang:send_after/3, erlang:start_timer/3, and erlang:cancel_timer/1.

ref_to_list/1

Returns a string which corresponds to the text representation of Ref.

Warning!

This BIF is intended for debugging and for use in the Erlang operating system. It should not be used in application programs.

register/2

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

> register(db, Pid).
true

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

registered/0

Returns a list of names which have been registered using register/2.

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

resume_process/1

Decreases the suspend count on the process identified by Suspendee. Suspendee should previously have been suspended via erlang:suspend_process/2, or erlang:suspend_process/1 by the process calling erlang:resume_process(Suspendee). When the suspend count on Suspendee reach zero, Suspendee will be resumed, i.e., the state of the Suspendee is changed from suspended into the state Suspendee was in before it was suspended.

Warning!

This BIF is intended for debugging only.

Failures:

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

round/1

Returns an integer by rounding Number.

> round(5.5).
6

Allowed in guard tests.

self/0

Returns the pid (process identifier) of the calling process.

> self().
<0.26.0>

Allowed in guard tests.

send/2

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

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

send/3

Sends a message and returns ok, or does not send the message but returns something else (see below). Otherwise the same as erlang:send/2. See also erlang:send_nosuspend/2,3. for more detailed explanation and warnings.

The possible options are:

nosuspend

If the sender would have to be suspended to do the send, nosuspend is returned instead.

noconnect

If the destination node would have to be auto-connected before doing the send, noconnect is returned instead.

Warning!

As with erlang:send_nosuspend/2,3: Use with extreme care!

send_after/3

0 <= Time <= 4294967295

Starts a timer which will send the message Msg to Dest after Time milliseconds.

If Dest is a pid() it has to be a pid() of a local process, dead or alive.

The Time value can, in the current implementation, not be greater than 4294967295.

If Dest is an atom(), it is supposed to be the name of a registered process. The process referred to by the name is looked up at the time of delivery. No error is given if the name does not refer to a process.

If Dest is a pid(), the timer will be automatically canceled if the process referred to by the pid() is not alive, or when the process exits. This feature was introduced in erts version 5.4.11. Note that timers will not be automatically canceled when Dest is an atom.

See also erlang:start_timer/3, erlang:cancel_timer/1, and erlang:read_timer/1.

Failure: badarg if the arguments does not satisfy the requirements specified above.

send_nosuspend/2