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erlang(3erl) | Erlang Module Definition | erlang(3erl) |
NAME¶
erlang - The Erlang BIFsDESCRIPTION¶
By convention, most built-in functions (BIFs) are seen as being in the module erlang. A number of the BIFs are viewed more or less as part of the Erlang programming language and are auto-imported. Thus, it is not necessary to specify the module name and both the calls atom_to_list(Erlang) and erlang:atom_to_list(Erlang) are identical. In the text, auto-imported BIFs are listed without module prefix. BIFs listed with module prefix are not auto-imported. BIFs may fail for a variety of reasons. All BIFs fail with reason badarg if they are called with arguments of an incorrect type. The other reasons that may make BIFs fail are described in connection with the description of each individual BIF. Some BIFs may be used in guard tests, these are marked with "Allowed in guard tests".DATA TYPES¶
ext_binary()
A binary data object, structured according to the Erlang external term
format.
timestamp() ={MegaSecs :: integer() >= 0,Secs :: integer() >= 0,MicroSecs :: integer() >= 0}
See now/0.
EXPORTS¶
abs(Number) -> integer() | float()
Types:
Number = number()
Returns an integer or float which is the arithmetical absolute value of
Number.
> abs(-3.33). 3.33 > abs(-3). 3Allowed in guard tests.
Types:
Data = iodata()
Computes and returns the adler32 checksum for Data.
Types:
OldAdler = integer()
Data = iodata()
Continue computing the adler32 checksum by combining the previous checksum,
OldAdler, with the checksum of Data.
The following code:
X = erlang:adler32(Data1), Y = erlang:adler32(X,Data2).- would assign the same value to Y as this would:
Y = erlang:adler32([Data1,Data2]).
Types:
FirstAdler = SecondAdler = integer()
SecondSize = integer()
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)).
Types:
Tuple1 = Tuple2 = tuple()
Term = term()
Returns a new tuple which has one element more than Tuple1, and contains
the elements in Tuple1 followed by Term as the last element.
Semantically equivalent to list_to_tuple(tuple_to_list(Tuple) ++
[Term]), but much faster.
> erlang:append_element({one, two}, three). {one,two,three}
apply(Fun, Args) -> term()
Types:
Fun = function()
Args = [term()]
Call a fun, passing the elements in Args as arguments.
Note: If the number of elements in the arguments are known at compile-time, the
call is better written as Fun(Arg1, Arg2, ... ArgN).
Warning:
Earlier, Fun could also be given as {Module, Function}, equivalent
to apply(Module, Function, Args). This usage is deprecated and will
stop working in a future release of Erlang/OTP.
apply(Module, Function, Args) -> term()
Types:
Module = module()
Function = atom()
Args = [term()]
Returns the result of applying Function in Module to Args.
The applied function must be exported from Module. The arity of the
function is the length of Args.
> apply(lists, reverse, [[a, b, c]]). [c,b,a]apply can be used to evaluate BIFs by using the module name erlang.
> apply(erlang, atom_to_list, ['Erlang']). "Erlang"Note: If the number of arguments are known at compile-time, the call is better written as Module:Function(Arg1, Arg2, ..., ArgN). Failure: error_handler:undefined_function/3 is called if the applied function is not exported. The error handler can be redefined (see process_flag/2). If the error_handler is undefined, or if the user has redefined the default error_handler so the replacement module is undefined, an error with the reason undef is generated.
Types:
Atom = atom()
Encoding = latin1 | utf8 | unicode
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">>
Types:
Atom = atom()
Returns a string which corresponds to the text representation of Atom.
> atom_to_list('Erlang'). "Erlang"
Types:
Subject = binary()
PosLen = {Start,Length}
Start = integer() >= 0
Length = integer() >= 0
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.
Types:
Subject = binary()
Start = integer() >= 0
Length = integer() >= 0
The same as binary_part(Subject, {Pos, Len}).
Allowed in guard tests.
Types:
Binary = binary()
Encoding = latin1 | utf8 | unicode
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.
> 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)
Types:
Binary = binary()
Encoding = latin1 | utf8 | unicode
Works like binary_to_atom/2, but the atom must already exist.
Failure: badarg if the atom does not already exist.
Types:
Binary = binary()
Returns a list of integers which correspond to the bytes of Binary.
Types:
Binary = binary()
Start = Stop = 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.
Types:
Bitstring = bitstring()
Returns a list of integers which correspond to the bytes of Bitstring. If
the number of bits in the binary is not divisible by 8, the last element of
the list will be a bitstring containing the remaining bits (1 up to 7
bits).
Types:
Binary = ext_binary()
Returns an Erlang term which is the result of decoding the binary object
Binary, which must be encoded according to the Erlang external term
format.
See also term_to_binary/1 and binary_to_term/2.
Warning:
When decoding binaries from untrusted sources, consider using
binary_to_term/2 to prevent denial of service attacks.
Types:
Opts = [safe]
Binary = ext_binary()
As binary_to_term/1, but takes options that affect decoding of the
binary.
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.
- 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.
Types:
Bitstring = bitstring()
Returns an integer which is the size in bits of Bitstring.
> bit_size(<<433:16,3:3>>). 19 > bit_size(<<1,2,3>>). 24Allowed in guard tests.
Types:
Reductions = integer() >= 0
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.
Types:
Bitstring = bitstring()
Returns an integer which is the number of bytes needed to contain
Bitstring. (That is, if the number of bits in Bitstring is not
divisible by 8, the resulting number of bytes will be rounded up.)
> byte_size(<<433:16,3:3>>). 3 > byte_size(<<1,2,3>>). 3Allowed in guard tests.
Types:
TimerRef = reference()
Time = integer() >= 0
Cancels a timer, where TimerRef was returned by either
erlang:send_after/3 or erlang:start_timer/3. If the timer is
there to be removed, the function returns the time in milliseconds left until
the timer would have expired, otherwise false (which means that
TimerRef was never a timer, that it has already been cancelled, or that
it has already delivered its message).
See also erlang:send_after/3, erlang:start_timer/3, and
erlang:read_timer/1.
Note: Cancelling a timer does not guarantee that the message has not already
been delivered to the message queue.
Types:
Module = atom()
Returns true if the Module has old code, and false
otherwise.
See also code(3erl).
Types:
Pid = pid()
Module = atom()
Returns true if the process Pid is executing old code for
Module. That is, if the current call of the process executes old code
for this module, or if the process has references to old code for this module,
or if the process contains funs that references old code for this module.
Otherwise, it returns false.
> check_process_code(Pid, lists). falseSee also code(3erl).
Types:
Data = iodata()
Computes and returns the crc32 (IEEE 802.3 style) checksum for
Data.
Types:
OldCrc = integer() >= 0
Data = iodata()
Continue computing the crc32 checksum by combining the previous checksum,
OldCrc, with the checksum of Data.
The following code:
X = erlang:crc32(Data1), Y = erlang:crc32(X,Data2).- would assign the same value to Y as this would:
Y = erlang:crc32([Data1,Data2]).
Types:
FirstCrc = SecondCrc = integer() >= 0
SecondSize = integer() >= 0
Combines two previously computed crc32 checksums. This computation requires the
size of the data object for the second checksum to be known.
The following code:
Y = erlang:crc32(Data1), Z = erlang:crc32(Y,Data2).- would assign the same value to Z as this would:
X = erlang:crc32(Data1), Y = erlang:crc32(Data2), Z = erlang:crc32_combine(X,Y,iolist_size(Data2)).
Types:
Date = calendar:date()
Returns the current date as {Year, Month, Day}.
The time zone and daylight saving time correction depend on the underlying OS.
> date(). {1995,2,19}
Types:
Bin = binary()
Options = [Opt]
Packet = binary() | HttpPacket
Rest = binary()
Length = integer() > 0 | undefined
Reason = term()
Type, Opt -- see below
HttpPacket = HttpRequest | HttpResponse | HttpHeader | http_eoh | HttpError
HttpRequest = {http_request, HttpMethod, HttpUri, HttpVersion}
HttpResponse = {http_response, HttpVersion, integer(), HttpString}
HttpHeader = {http_header, integer(), HttpField, Reserved=term(),
Value=HttpString}
HttpError = {http_error, HttpString}
HttpMethod = HttpMethodAtom | HttpString
HttpMethodAtom = 'OPTIONS' | 'GET' | 'HEAD' | 'POST' | 'PUT' | 'DELETE' |
'TRACE'
HttpUri = '*' | {absoluteURI, http|https, Host=HttpString,
Port=integer()|undefined, Path=HttpString} | {scheme, Scheme=HttpString,
HttpString} | {abs_path, HttpString} | HttpString
HttpVersion = {Major=integer(), Minor=integer()}
HttpString = string() | binary()
HttpField = HttpFieldAtom | HttpString
HttpFieldAtom = 'Cache-Control' | 'Connection' | 'Date' | 'Pragma' |
'Transfer-Encoding' | 'Upgrade' | 'Via' | 'Accept' | 'Accept-Charset' |
'Accept-Encoding' | 'Accept-Language' | 'Authorization' | 'From' | 'Host' |
'If-Modified-Since' | 'If-Match' | 'If-None-Match' | 'If-Range' |
'If-Unmodified-Since' | 'Max-Forwards' | 'Proxy-Authorization' | 'Range' |
'Referer' | 'User-Agent' | 'Age' | 'Location' | 'Proxy-Authenticate' |
'Public' | 'Retry-After' | 'Server' | 'Vary' | 'Warning' | 'Www-Authenticate'
| 'Allow' | 'Content-Base' | 'Content-Encoding' | 'Content-Language' |
'Content-Length' | 'Content-Location' | 'Content-Md5' | 'Content-Range' |
'Content-Type' | 'Etag' | 'Expires' | 'Last-Modified' | 'Accept-Ranges' |
'Set-Cookie' | 'Set-Cookie2' | 'X-Forwarded-For' | 'Cookie' | 'Keep-Alive' |
'Proxy-Connection'
Type, Opt -- see below
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:
The following options are available:
- 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.
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.
- {packet_size, integer()}:
- 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()}:
- 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}
Types:
Module = atom()
Makes the current code for Module become old code, and deletes all
references for this module from the export table. Returns undefined if
the module does not exist, otherwise true.
Failure: badarg if there is already an old version of
Module.
Warning:
This BIF is intended for the code server (see code(3erl)) and should not
be used elsewhere.
Types:
MonitorRef = reference()
If MonitorRef is a reference which the calling process obtained by
calling monitor/2, this monitoring is turned off. If the monitoring is
already turned off, nothing happens.
Once demonitor(MonitorRef) has returned it is guaranteed that no
{'DOWN', MonitorRef, _, _, _} message due to the monitor will be placed
in the caller's message queue in the future. A {'DOWN', MonitorRef, _, _,
_} message might have been placed in the caller's message queue prior to
the call, though. Therefore, in most cases, it is advisable to remove such a
'DOWN' message from the message queue after monitoring has been
stopped. demonitor(MonitorRef, [flush]) can be used instead of
demonitor(MonitorRef) if this cleanup is wanted.
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).
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.
Types:
MonitorRef = reference()
OptionList = [Option]
Option = flush | info
Option = flush | info
The returned value is true unless info is part of
OptionList.
demonitor(MonitorRef, []) is equivalent to demonitor(MonitorRef).
Currently the following Options are valid:
Failure: badarg if OptionList is not a list, or if Option
is not a valid option, or the same failure as for demonitor/1
- 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.
disconnect_node(Node) -> boolean() | ignored
Types:
Node = node()
Forces the disconnection of a node. This will appear to the node Node as
if the local node has crashed. This BIF is mainly used in the Erlang network
authentication protocols. Returns true if disconnection succeeds,
otherwise false. If the local node is not alive, the function returns
ignored.
Types:
Term = term()
Prints a text representation of Term on the standard output.
Warning:
This BIF is intended for debugging only.
Types:
N = 1..tuple_size(Tuple)
Tuple = tuple()
Returns the Nth element (numbering from 1) of Tuple.
> element(2, {a, b, c}). bAllowed in guard tests.
Types:
Key = Val = term()
Returns the process dictionary and deletes it.
> put(key1, {1, 2, 3}), put(key2, [a, b, c]), erase(). [{key1,{1,2,3}},{key2,[a,b,c]}]
Types:
Key = Val = term()
Returns the value Val associated with Key and deletes it from the
process dictionary. Returns undefined if no value is associated with
Key.
> put(key1, {merry, lambs, are, playing}), X = erase(key1), {X, erase(key1)}. {{merry,lambs,are,playing},undefined}
Types:
Reason = term()
Stops the execution of the calling process with the reason Reason, where
Reason is any term. The actual exit reason will be {Reason,
Where}, where Where is a list of the functions most recently called
(the current function first). Since evaluating this function causes the
process to terminate, it has no return value.
> catch error(foobar). {'EXIT',{foobar,[{erl_eval,do_apply,5}, {erl_eval,expr,5}, {shell,exprs,6}, {shell,eval_exprs,6}, {shell,eval_loop,3}]}}
Types:
Reason = term()
Args = [term()]
Stops the execution of the calling process with the reason Reason, where
Reason is any term. The actual exit reason will be {Reason,
Where}, where Where is a list of the functions most recently called
(the current function first). Args is expected to be the list of
arguments for the current function; in Beam it will be used to provide the
actual arguments for the current function in the Where term. Since
evaluating this function causes the process to terminate, it has no return
value.
Types:
Reason = term()
Stops the execution of the calling process with the exit reason Reason,
where Reason is any term. Since evaluating this function causes the
process to terminate, it has no return value.
> exit(foobar). ** exception exit: foobar > catch exit(foobar). {'EXIT',foobar}
Types:
Pid = pid()
Reason = term()
Sends an exit signal with exit reason Reason to the process 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.
Types:
Term = term()
Calculates, without doing the encoding, the maximum byte size for a term encoded
in the Erlang external term format. The following condition applies always:
> Size1 = byte_size(term_to_binary(Term)), > Size2 = erlang:external_size(Term), > true = Size1 =< Size2. trueThis is equivalent to a call to:
erlang:external_size(Term, [])
Types:
Term = term()
Option = {minor_version, Version}
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. trueThe option {minor_version, Version} specifies how floats are encoded. See term_to_binary/2 for a more detailed description.
Types:
Number = number()
Returns a float by converting Number to a float.
> float(55). 55.0Allowed 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.
Types:
Float = float()
Returns a string which corresponds to the text representation of Float.
> float_to_list(7.0). "7.00000000000000000000e+00"
erlang:fun_info(Fun) -> [{Item, Info}]
Types:
Fun = function()
Item = arity
| env
| index
| name
| module
| new_index
| new_uniq
| pid
| type
| uniq
Info = term()
| env
| index
| name
| module
| new_index
| new_uniq
| pid
| type
| uniq
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.
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:
The following elements will only be present in the list if Fun is local:
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.
- {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.)
- {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.
Types:
Fun = fun()
Item, Info -- see below
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.
Types:
Fun = fun()
Returns a string which corresponds to the text representation of
Fun.
Types:
Module = Function = atom()
Arity = arity()
Returns true if the module Module is loaded and contains an
exported function Function/Arity; otherwise false.
Returns false for any BIF (functions implemented in C rather than in
Erlang).
Forces an immediate garbage collection of the currently executing process. The
function should not be used, unless it has been noticed -- or there are good
reasons to suspect -- that the spontaneous garbage collection will occur too
late or not at all. Improper use may seriously degrade system performance.
Compatibility note: In versions of OTP prior to R7, the garbage collection took
place at the next context switch, not immediately. To force a context switch
after a call to erlang:garbage_collect(), it was sufficient to make any
function call.
Types:
Pid = pid()
Works like erlang:garbage_collect() but on any process. The same caveats
apply. Returns false if Pid refers to a dead process;
true otherwise.
Types:
Key = Val = term()
Returns the process dictionary as a list of {Key, Val} tuples.
> put(key1, merry), put(key2, lambs), put(key3, {are, playing}), get(). [{key1,merry},{key2,lambs},{key3,{are,playing}}]
Types:
Key = Val = term()
Returns the value Valassociated with Key in the process
dictionary, or undefined if Key does not exist.
> put(key1, merry), put(key2, lambs), put({any, [valid, term]}, {are, playing}), get({any, [valid, term]}). {are,playing}
erlang:get_cookie() -> Cookie | nocookie
Types:
Cookie = atom()
Returns the magic cookie of the local node, if the node is alive; otherwise the
atom nocookie.
Types:
Val = Key = term()
Returns a list of keys which are associated with the value Val in the
process dictionary.
> put(mary, {1, 2}), put(had, {1, 2}), put(a, {1, 2}), put(little, {1, 2}), put(dog, {1, 3}), put(lamb, {1, 2}), get_keys({1, 2}). [mary,had,a,little,lamb]
Types:
Module = Function = atom()
Arity = arity()
Args = [term()]
Location = [{atom(),term()}]
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:
See also erlang:error/1 and erlang:error/2.
- 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.
Types:
GroupLeader = pid()
Returns the pid of the group leader for the process which evaluates the
function.
Every process is a member of some process group and all groups have a group
leader. All IO from the group is channeled to the group leader. When a new
process is spawned, it gets the same group leader as the spawning process.
Initially, at system start-up, init is both its own group leader and
the group leader of all processes.
Types:
GroupLeader = Pid = pid()
Sets the group leader of Pid to GroupLeader. Typically, this is
used when a processes started from a certain shell should have another group
leader than init.
See also group_leader/0.
The same as halt(0, []).
> halt(). os_prompt%
Types:
Status = integer() >= 0 | string() | abort
The same as halt(Status, []).
> halt(17). os_prompt% echo $? 17 os_prompt%
Types:
Status = integer() >= 0 | string() | abort
Options = [Option]
Option = {flush,boolean()} | term()
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:
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.
- 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.
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.
Types:
List = [term()]
Returns the head of List, that is, the first element.
> hd([1,2,3,4,5]). 1Allowed in guard tests. Failure: badarg if List is the empty list [].
Types:
Module = Function = atom()
Args = [term()]
Puts the calling process into a wait state where its memory allocation has been
reduced as much as possible, which is useful if the process does not expect to
receive any messages in the near future.
The process will be awaken when a message is sent to it, and control will resume
in Module:Function with the arguments given by Args with the
call stack emptied, meaning that the process will terminate when that function
returns. Thus erlang:hibernate/3 will never return to its caller.
If the process has any message in its message queue, the process will be awaken
immediately in the same way as described above.
In more technical terms, what erlang:hibernate/3 does is the following.
It discards the call stack for the process. Then it garbage collects the
process. After the garbage collection, all live data is in one continuous
heap. The heap is then shrunken to the exact same size as the live data which
it holds (even if that size is less than the minimum heap size for the
process).
If the size of the live data in the process is less than the minimum heap size,
the first garbage collection occurring after the process has been awaken will
ensure that the heap size is changed to a size not smaller than the minimum
heap size.
Note that emptying the call stack means that any surrounding catch is
removed and has to be re-inserted after hibernation. One effect of this is
that processes started using proc_lib (also indirectly, such as
gen_server processes), should use proc_lib:hibernate/3 instead
to ensure that the exception handler continues to work when the process wakes
up.
Types:
Integer = integer()
Returns a string which corresponds to the text representation of Integer.
> integer_to_list(77). "77"
integer_to_list(Integer, Base) -> string()
Types:
Integer = integer()
Base = 2..36
Returns a string which corresponds to the text representation of Integer
in base Base.
> integer_to_list(1023, 16). "3FF"
Types:
IoListOrBinary = iolist() | binary()
Returns a binary which is made from the integers and binaries in
IoListOrBinary.
> Bin1 = <<1,2,3>>. <<1,2,3>> > Bin2 = <<4,5>>. <<4,5>> > Bin3 = <<6>>. <<6>> > iolist_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]). <<1,2,3,1,2,3,4,5,4,6>>
Types:
Item = iolist() | binary()
Returns an integer which is the size in bytes of the binary that would be the
result of iolist_to_binary(Item).
> iolist_size([1,2|<<3,4>>]). 4
Returns true if the local node is alive; that is, if the node can be part
of a distributed system. Otherwise, it returns false.
Types:
Term = term()
Returns true if Term is an atom; otherwise returns false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is a binary; otherwise returns false.
A binary always contains a complete number of bytes.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is a bitstring (including a binary);
otherwise returns false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is either the atom true or the atom
false (i.e. a boolean); otherwise returns false.
Allowed in guard tests.
Types:
Module = Function = atom()
Arity = arity()
Returns true if Module:Function/Arity is a BIF implemented in C;
otherwise returns false. This BIF is useful for builders of cross
reference tools.
Types:
Term = term()
Returns true if Term is a floating point number; otherwise returns
false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is a fun; otherwise returns false.
Allowed in guard tests.
Types:
Term = term()
Arity = arity()
Returns true if Term is a fun that can be applied with
Arity number of arguments; otherwise returns false.
Allowed in guard tests.
Warning:
Currently, is_function/2 will also return true if the first
argument is a tuple fun (a tuple containing two atoms). In a future release,
tuple funs will no longer be supported and is_function/2 will return
false if given a tuple fun.
Types:
Term = term()
Returns true if Term is an integer; otherwise returns
false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is a list with zero or more elements;
otherwise returns false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is either an integer or a floating point
number; otherwise returns false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is a pid (process identifier); otherwise
returns false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is a port identifier; otherwise returns
false.
Allowed in guard tests.
Types:
Pid = pid()
Pid must refer to a process at the local node. Returns true if the
process exists and is alive, that is, is not exiting and has not exited.
Otherwise, returns false.
Types:
Term = term()
RecordTag = atom()
Returns true if Term is a tuple and its first element is
RecordTag. Otherwise, returns false.
Allowed in guard tests, if RecordTag is a literal atom.
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.
Types:
Term = term()
RecordTag = atom()
Size = integer()
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.
Types:
Term = term()
Returns true if Term is a reference; otherwise returns
false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is a tuple; otherwise returns false.
Allowed in guard tests.
Types:
List = [term()]
Returns the length of List.
> length([1,2,3,4,5,6,7,8,9]). 9Allowed in guard tests.
Types:
Pid = pid() | port()
Creates a link between the calling process and another process (or port)
Pid, if there is not such a link already. If a process attempts to
create a link to itself, nothing is done. Returns true.
If Pid 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 Pid is cheap -- that is, if Pid is local -- link/1 fails with reason noproc.
- *
- Otherwise, if the calling process is trapping exits, and/or Pid is remote, link/1 returns true, but an exit signal with reason noproc is sent to the calling process.
Types:
String = string()
Returns the atom whose text representation is String.
> list_to_atom("Erlang"). 'Erlang'
Types:
IoList = iolist()
Returns a binary which is made from the integers and binaries in IoList.
> Bin1 = <<1,2,3>>. <<1,2,3>> > Bin2 = <<4,5>>. <<4,5>> > Bin3 = <<6>>. <<6>> > list_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]). <<1,2,3,1,2,3,4,5,4,6>>
Types:
BitstringList = [BitstringList | bitstring() |
char()]
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_binary([Bin1,1,[2,3,Bin2],4|Bin3]). <<1,2,3,1,2,3,4,5,4,6,7:46>>
Types:
String = string()
Returns the atom whose text representation is String, but only if there
already exists such atom.
Failure: badarg if there does not already exist an atom whose text
representation is String.
Types:
String = string()
Returns the float whose text representation is String.
> list_to_float("2.2017764e+0"). 2.2017764Failure: badarg if String contains a bad representation of a float.
Types:
String = string()
Returns an integer whose text representation is String.
> list_to_integer("123"). 123Failure: badarg if String contains a bad representation of an integer.
list_to_integer(String, Base) -> integer()
Types:
String = string()
Base = 2..36
Returns an integer whose text representation in base Base is
String.
> list_to_integer("3FF", 16). 1023Failure: badarg if String contains a bad representation of an integer.
Types:
String = string()
Returns a pid whose text representation is String.
Warning:
This BIF is intended for debugging and for use in the Erlang operating system.
It should not be used in application programs.
> list_to_pid("<0.4.1>"). <0.4.1>Failure: badarg if String contains a bad representation of a pid.
Types:
List = [term()]
Returns a tuple which corresponds to List. List can contain any
Erlang terms.
> list_to_tuple([share, ['Ericsson_B', 163]]). {share, ['Ericsson_B', 163]}
Types:
Module = atom()
Binary = binary()
Reason = badfile | not_purged | badfile
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.
- not_purged:
- Binary contains a module which cannot be loaded because old code for this module already exists.
- badfile:
- The object code contains code for another module than Module
Warning:
This BIF is intended for the code server (see code(3erl)) and should not
be used elsewhere.
Types:
Path = string()
LoadInfo = term()
Reason = load_failed | bad_lib | load | reload | upgrade | old_code
Text = string()
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}.
- 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.
Types:
Module = atom()
Returns a list of all loaded Erlang modules (current and/or old code), including
preloaded modules.
See also code(3erl).
Types:
DateTime = calendar:datetime()
Returns the current local date and time {{Year, Month, Day}, {Hour, Minute,
Second}}.
The time zone and daylight saving time correction depend on the underlying OS.
> erlang:localtime(). {{1996,11,6},{14,45,17}}
erlang:localtime_to_universaltime(Localtime :: {Date1, Time1}) -> {Date2, Time2}
Types:
Date1 = Date2 = calendar:date()
Time1 = Time2 = calendar:time()
Converts local date and time to Universal Time Coordinated (UTC), if this is
supported by the underlying OS. Otherwise, no conversion is done and
{Date1, Time1} is returned.
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}). {{1996,11,6},{13,45,17}}Failure: badarg if Date1 or Time1 do not denote a valid date or time.
Types:
Date1 = Date2 = calendar:date()
Time1 = Time2 = calendar:time()
IsDst = true | false | undefined
Converts local date and time to Universal Time Coordinated (UTC) just like
erlang:localtime_to_universaltime/1, but the caller decides if daylight
saving time is active or not.
If IsDst == true the {Date1, Time1} 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({Date1, Time1}).
> 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 Date1 or Time1 do not denote a valid date or time.
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>
Types:
Arity = arity()
InitialValue = term()
Returns a new tuple of the given Arity, where all elements are
InitialValue.
> erlang:make_tuple(4, []). {[],[],[],[]}
Types:
Arity = arity()
Default = term()
InitList = [{Position,term()}]
Position = integer()
erlang:make_tuple first creates a tuple of size Arity where each
element has the value Default. It then fills in values from
InitList. Each list element in InitList must be a two-tuple
where the first element is a position in the newly created tuple and the
second element is any term. If a position occurs more than once in the list,
the term corresponding to last occurrence will be used.
> erlang:make_tuple(5, [], [{2,ignored},{5,zz},{2,aa}]). {{[],aa,[],[],zz}
max(Term1, Term2) -> Maximum
Types:
Term1 = Term2 = Maximum = term()
Return the largest of Term1 and Term2; if the terms compare equal,
Term1 will be returned.
Types:
Data = iodata()
Digest = binary()
Computes an MD5 message digest from Data, where the length of the
digest is 128 bits (16 bytes). Data is a binary or a list of small
integers and binaries.
See The MD5 Message Digest Algorithm (RFC 1321) for more information about MD5.
Warning:
The MD5 Message Digest Algorithm is not considered safe for code-signing
or software integrity purposes.
Types:
Context = Digest = binary()
Finishes the update of an MD5 Context and returns the computed MD5
message digest.
Types:
Context = binary()
Creates an MD5 context, to be used in subsequent calls to
md5_update/2.
Types:
Data = iodata()
Context = NewContext = binary()
Updates an MD5 Context with Data, and returns a
NewContext.
Types:
Type, Size -- see below
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:
The different values has the following relation to each other. Values beginning
with an uppercase letter is not part of the result.
Failure:
- 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.
- maximum:
- The maximum total amount of memory allocated since the emulator was started.
This tuple is only present when the emulator is run with instrumentation.
For information on how to run the emulator with instrumentation see
instrument(3erl) and/or erl(1).
- 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.
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.
total = processes + system processes = processes_used + ProcessesNotUsed system = atom + binary + code + ets + OtherSystem atom = atom_used + AtomNotUsed RealTotal = processes + RealSystem RealSystem = system + MissedSystemMore tuples in the returned list may be added in the future.
Note:
The total value is supposed to be the total amount of memory dynamically
allocated by the emulator. Shared libraries, the code of the emulator itself,
and the emulator stack(s) are not supposed to be included. That is, the
total value is not supposed to be equal to the total size of all
pages mapped to the emulator. Furthermore, due to fragmentation and
pre-reservation of memory areas, the size of the memory segments which contain
the dynamically allocated memory blocks can be substantially larger than the
total size of the dynamically allocated memory blocks.
Note:
Since erts version 5.6.4 erlang:memory/0 requires that all
erts_alloc(3erl) allocators are enabled (default behaviour).
- notsup:
-
If an erts_alloc(3erl) allocator has been disabled.
Types:
Type, Size -- see below
Returns the memory size in bytes allocated for memory of type Type. The
argument can also be given as a list of Type atoms, in which case a
corresponding list of {Type, Size} tuples is returned.
Failures:
See also erlang:memory/0.
Note:
Since erts version 5.6.4 erlang:memory/1 requires that all
erts_alloc(3erl) allocators are enabled (default behaviour).
- badarg:
-
If Type is not one of the memory types listed in the documentation of erlang:memory/0.
- badarg:
-
If maximum is passed as Type and the emulator is not run in instrumented mode.
- notsup:
-
If an erts_alloc(3erl) allocator has been disabled.
min(Term1, Term2) -> Minimum
Types:
Term1 = Term2 = Minimum = term()
Return the smallest of Term1 and Term2; if the terms compare
equal, Term1 will be returned.
Types:
Module = atom()
Returns true if the module Module is loaded, otherwise returns
false. It does not attempt to load the module.
Warning:
This BIF is intended for the code server (see code(3erl)) and should not
be used elsewhere.
Types:
Type = process
Item = pid() | {RegName, Node} | RegName
RegName = atom()
Node = node()
MonitorRef = reference()
RegName = atom()
Node = node()
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:
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:
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.
- 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.
{'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.
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.
Types:
Node = node()
Flag = boolean()
Monitors the status of the node Node. If Flag is true,
monitoring is turned on; if Flag is false, monitoring is turned
off.
Making several calls to monitor_node(Node, true) for the same Node
is not an error; it results in as many, completely independent, monitorings.
If Node fails or does not exist, the message {nodedown, Node} is
delivered to the process. If a process has made two calls to
monitor_node(Node, true) and Node terminates, two
nodedown messages are delivered to the process. If there is no
connection to Node, there will be an attempt to create one. If this
fails, a nodedown message is delivered.
Nodes connected through hidden connections can be monitored as any other node.
Failure: badargif the local node is not alive.
Types:
Node = node()
Flag = boolean()
Options = [Option]
Option = allow_passive_connect
Behaves as monitor_node/2 except that it allows an extra option to be
given, namely allow_passive_connect. The option allows the BIF to wait
the normal net connection timeout for the monitored node to connect
itself, even if it cannot be actively connected from this node (i.e. it is
blocked). The state where this might be useful can only be achieved by using
the kernel option dist_auto_connect once. If that kernel option is not
used, the allow_passive_connect option has no effect.
Failure: badarg if the local node is not alive or the option list is
malformed.
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.
Types:
Reason = term()
Works exactly like erlang:error/1, but Dialyzer thinks that this BIF will
return an arbitrary term. When used in a stub function for a NIF to generate
an exception when the NIF library is not loaded, Dialyzer will not generate
false warnings.
Types:
Reason = term()
Args = [term()]
Works exactly like erlang:error/2, but Dialyzer thinks that this BIF will
return an arbitrary term. When used in a stub function for a NIF to generate
an exception when the NIF library is not loaded, Dialyzer will not generate
false warnings.
Types:
Node = node()
Returns the name of the local node. If the node is not alive,
nonode@nohost is returned instead.
Allowed in guard tests.
Types:
Arg = pid() | port() | reference()
Node = node()
Returns the node where Arg is located. Arg can be a pid, a
reference, or a port. If the local node is not alive, nonode@nohost is
returned.
Allowed in guard tests.
nodes() -> Nodes
Types:
Nodes = [node()]
Returns a list of all visible nodes in the system, excluding the local node.
Same as nodes(visible).
Types:
Arg = visible | hidden | connected | this |
known
Nodes = [node()]
Returns a list of nodes according to argument given. The result returned when
the argument is a list, is the list of nodes satisfying the disjunction(s) of
the list elements.
Arg can be any of the following:
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.
- 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.
Types:
timestamp() = {MegaSecs, Secs, MicroSecs}
MegaSecs = Secs = MicroSecs = integer() >= 0
Returns the tuple {MegaSecs, Secs, MicroSecs} which is the elapsed time
since 00:00 GMT, January 1, 1970 (zero hour) on the assumption that the
underlying OS supports this. Otherwise, some other point in time is chosen. It
is also guaranteed that subsequent calls to this BIF returns continuously
increasing values. Hence, the return value from now() can be used to
generate unique time-stamps, and if it is called in a tight loop on a fast
machine the time of the node can become skewed.
It can only be used to check the local time of day if the time-zone info of the
underlying operating system is properly configured.
Types:
PortName = {spawn, Command} | {spawn_driver,
Command} | {spawn_executable, FileName} | {fd, In, Out}
Command = string()
FileName = [ FileNameChar ] | binary()
FileNameChar = integer() (1..255 or any Unicode codepoint, see description)
In = Out = integer()
PortSettings = [Opt]
Opt = {packet, N} | stream | {line, L} | {cd, Dir} | {env, Env} | {args, [ ArgString ]} | {arg0, ArgString} | exit_status | use_stdio | nouse_stdio | stderr_to_stdout | in | out | binary | eof
N = 1 | 2 | 4
L = integer()
Dir = string()
ArgString = [ FileNameChar ] | binary()
Env = [{Name, Val}]
Name = string()
Val = string() | false
Command = string()
FileName = [ FileNameChar ] | binary()
FileNameChar = integer() (1..255 or any Unicode codepoint, see description)
In = Out = integer()
Opt = {packet, N} | stream | {line, L} | {cd, Dir} | {env, Env} | {args, [ ArgString ]} | {arg0, ArgString} | exit_status | use_stdio | nouse_stdio | stderr_to_stdout | in | out | binary | eof
N = 1 | 2 | 4
L = integer()
Dir = string()
ArgString = [ FileNameChar ] | binary()
Env = [{Name, Val}]
Name = string()
Val = string() | false
Returns a port identifier as the result of opening a new Erlang port. A port can
be seen as an external Erlang process. PortName is one of the
following:
PortSettings is a list of settings for the port. Valid settings are:
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:
During use of a port opened using {spawn, Name}, {spawn_driver,
Name} or {spawn_executable, Name}, errors arising when sending
messages to it are reported to the owning process using signals of the form
{'EXIT', Port, PosixCode}. See file(3erl) for possible values of
PosixCode.
The maximum number of ports that can be open at the same time is 1024 by
default, but can be configured by the environment variable
ERL_MAX_PORTS.
- {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, Command}:
- Works like {spawn, Command}, but only runs external executables. The Command in its whole is used as the name of the executable, including any spaces. If arguments are to be passed, the args and arg0 PortSettings can be used.
The shell is not usually invoked to start the program, it's executed directly.
Neither is the PATH (or equivalent) searched. To find a program in the
PATH to execute, use os:find_executable/1.
Only if a shell script or .bat file is executed, the appropriate command
interpreter will implicitly be invoked, but there will still be no command
argument expansion or implicit PATH search.
The name of the executable as well as the arguments given in args and
arg0 is subject to Unicode file name translation if the system is
running in Unicode file name mode. To avoid translation or force i.e. UTF-8,
supply the executable and/or arguments as a binary in the correct encoding.
See the file module, the file:native_name_encoding/0 function
and the stdlib users guide for details.
Note:
The characters in the name (if given as a list) can only be > 255 if the
Erlang VM is started in Unicode file name translation mode, otherwise the name
of the executable is limited to the ISO-latin-1 character set.
If the Command 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.
- {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, Command}. The external program starts using Dir as its working directory. Dir must be a string. Not available on VxWorks.
- {env, Env}:
- This is only valid for {spawn, Command} and {spawn_executable, Command}. 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. Not available on
VxWorks.
- {args, [ string() ]}:
- This option is only valid for {spawn_executable, Command} and specifies arguments to the executable. Each argument is given as a separate string and (on Unix) eventually ends up as one element each in the argument vector. On other platforms, similar behavior is mimicked.
The arguments are not expanded by the shell prior to being supplied to the
executable, most notably this means that file wildcard expansion will not
happen. Use filelib:wildcard/1 to expand wildcards for the arguments.
Note that even if the program is a Unix shell script, meaning that the shell
will ultimately be invoked, wildcard expansion will not happen and the script
will be provided with the untouched arguments. On Windows(R), wildcard
expansion is always up to the program itself, why this isn't an issue.
Note also that the actual executable name (a.k.a. argv[0]) should not be
given in this list. The proper executable name will automatically be used as
argv[0] where applicable.
When the Erlang VM is running in Unicode file name mode, the arguments can
contain any Unicode characters and will be translated into whatever is
appropriate on the underlying OS, which means UTF-8 for all platforms except
Windows, which has other (more transparent) ways of dealing with Unicode
arguments to programs. To avoid Unicode translation of arguments, they can be
supplied as binaries in whatever encoding is deemed appropriate.
Note:
The characters in the arguments (if given as a list of characters) can only be
> 255 if the Erlang VM is started in Unicode file name mode, otherwise the
arguments are limited to the ISO-latin-1 character set.
If one, for any reason, wants to explicitly set the program name in the argument
vector, the arg0 option can be used.
- {arg0, string()}:
- This option is only valid for {spawn_executable, Command} and explicitly specifies the program name argument when running an executable. This might in some circumstances, on some operating systems, be desirable. How the program responds to this is highly system dependent and no specific effect is guaranteed.
The unicode file name translation rules of the args option apply to this
option as well.
- exit_status:
- This is only valid for {spawn, Command} where Command refers to an external program, and for {spawn_executable, Command}.
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, Command}. It allows the standard input and output (file descriptors 0 and 1) of the spawned (UNIX) process for communication with Erlang.
- nouse_stdio:
- The opposite of use_stdio. Uses file descriptors 3 and 4 for communication with Erlang.
- stderr_to_stdout:
- Affects ports to external programs. The executed program gets its standard error file redirected to its standard output file. stderr_to_stdout and nouse_stdio are mutually exclusive.
- overlapped_io:
- Affects ports to external programs on Windows(R) only. The standard input and standard output handles of the port program will, if this option is supplied, be opened with the flag FILE_FLAG_OVERLAPPED, so that the port program can (and has to) do overlapped I/O on its standard handles. This is not normally the case for simple port programs, but an option of value for the experienced Windows programmer. On all other platforms, this option is silently discarded.
- in:
- The port can only be used for input.
- out:
- The port can only be used for output.
- binary:
- All IO from the port are binary data objects as opposed to lists of bytes.
- eof:
- The port will not be closed at the end of the file and produce an exit signal. Instead, it will remain open and a {Port, eof} message will be sent to the process holding the port.
- hide:
- When running on Windows, suppress creation of a new console window when spawning the port program. (This option has no effect on other platforms.)
- 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 Command given in {spawn_executable, Command} does not point out an existing file.
Types:
Term = term()
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.
Types:
Term = term()
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).
Types:
Pid = pid()
Returns a string which corresponds to the text representation of Pid.
Warning:
This BIF is intended for debugging and for use in the Erlang operating system.
It should not be used in application programs.
Types:
Port = port() | atom()
Closes an open port. Roughly the same as Port ! {self(), close} except
for the error behaviour (see below), 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).
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.
In short: port_close(Port) has a cleaner and more logical behaviour than
Port ! {self(), close}.
Failure: badarg if Port is not an open port or the registered name
of an open port.
Types:
Port = port() | atom()
Data = iodata()
Sends data to a port. Same as Port ! {self(), {command, Data}} except for
the error behaviour (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 ! {self(), {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.
In short: port_command(Port, Data) has a cleaner and more logical
behaviour than Port ! {self(), {command, Data}}.
If the port is busy, the calling process will be suspended until the port is not
busy anymore.
Failures:
- badarg:
-
If Port is not an open port or the registered name of an open port.
- badarg:
-
If Data is not a valid io list.
Types:
Port = port() | atom()
Data = iodata()
OptionList = [Option]
Option = force
Option = nosuspend
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:
Failures:
- 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.
- badarg:
-
If Port is not an open port or the registered name of an open port.
- 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.
Types:
Port = port() | atom()
Pid = pid()
Sets the port owner (the connected port) to Pid. Roughly the same as
Port ! {self(), {connect, Pid}} except for the following:
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.
In short: port_connect(Port, Pid) has a cleaner and more logical
behaviour than Port ! {self(),{connect,Pid}}.
Failure: badarg if Port is not an open port or the registered name
of an open port, or if Pid is not an existing local pid.
- *
- The error behavior differs, see below.
- *
- The port does not reply with {Port,connected}.
- *
- The new port owner gets linked to the port.
Types:
Port = port() | atom()
Operation = integer()
Data = Res = iodata()
Performs a synchronous control operation on a port. The meaning of
Operation and Data depends on the port, i.e., on the port
driver. Not all port drivers support this control feature.
Returns: a list of integers in the range 0 through 255, or a binary, depending
on the port driver. The meaning of the returned data also depends on the port
driver.
Failure: badarg if Port is not an open port or the registered name
of an open port, if Operation cannot fit in a 32-bit integer, if the
port driver does not support synchronous control operations, or if the port
driver so decides for any reason (probably something wrong with
Operation or Data).
Types:
Port = port() | atom()
Operation = integer()
Data = term()
Performs a synchronous call to a port. The meaning of Operation and
Data depends on the port, i.e., on the port driver. Not all port
drivers support this feature.
Port is a port identifier, referring to a driver.
Operation is an integer, which is passed on to the driver.
Data is any Erlang term. This data is converted to binary term format and
sent to the port.
Returns: a term from the driver. The meaning of the returned data also depends
on the port driver.
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).
Types:
Port = port() | atom()
Item, Info -- see below
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.
Failure: badarg if Port is not a local port.
- {registered_name, RegName}:
- RegName (an atom) is the registered name of the port. If the port has no registered name, this tuple is not present in the list.
- {id, Index}:
- Index (an integer) is the internal index of the port. This index may be used to separate ports.
- {connected, Pid}:
- Pid is the process connected to the port.
- {links, Pids}:
- Pids is a list of pids to which processes the port is linked.
- {name, String}:
- String is the command name set by open_port.
- {input, Bytes}:
- Bytes is the total number of bytes read from the port.
- {output, Bytes}:
- Bytes is the total number of bytes written to the port.
Types:
Port = port() | atom()
Item, Info -- see below
Returns information about Port as specified by Item, or
undefined if the port is not open. Also, if Item ==
registered_name and the port has no registered name, [] is returned.
For valid values of Item, and corresponding values of Info, see
erlang:port_info/1.
Failure: badarg if Port is not a local port.
Types:
Port = port()
Returns a string which corresponds to the text representation of the port
identifier Port.
Warning:
This BIF is intended for debugging and for use in the Erlang operating system.
It should not be used in application programs.
Returns a list of all ports on the local node.
Types:
Module = atom()
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.
Types:
Pid = pid()
Type = backtrace
Writes information about the local process Pid on standard error. The
currently allowed value for the atom Type is backtrace, which
shows the contents of the call stack, including information about the call
chain, with the current function printed first. The format of the output is
not further defined.
Types:
Flag, Value, OldValue -- see below
Sets certain flags for the process which calls this function. Returns the old
value of the flag.
- process_flag(trap_exit, Boolean):
- When trap_exit is set to true, exit signals arriving to a process are converted to {'EXIT', From, Reason} messages, which can be received as ordinary messages. If trap_exit is set to false, the process exits if it receives an exit signal other than normal and the exit signal is propagated to its linked processes. Application processes should normally not trap exits.
See also exit/2.
- process_flag(error_handler, Module):
- 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.
- process_flag(min_heap_size, MinHeapSize):
- This changes the minimum heap size for the calling process.
- process_flag(min_bin_vheap_size, MinBinVHeapSize):
- This changes the minimum binary virtual heap size for the calling process.
- process_flag(priority, Level):
- 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.
- process_flag(save_calls, N):
- 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.
- process_flag(sensitive, Boolean):
- Set or clear the sensitive flag for the current process. When a process has been marked as sensitive by calling process_flag(sensitive, true), features in the run-time system that can be used for examining the data and/or inner working of the process are silently disabled.
Features that are disabled include (but are not limited to) the following:
Tracing: Trace flags can still be set for the process, but no trace messages of
any kind will be generated. (If the sensitive flag is turned off, trace
messages will again be generated if there are any trace flags set.)
Sequential tracing: The sequential trace token will be propagated as usual, but
no sequential trace messages will be generated.
process_info/1,2 cannot be used to read out the message queue or the
process dictionary (both will be returned as empty lists).
Stack back-traces cannot be displayed for the process.
In crash dumps, the stack, messages, and the process dictionary will be
omitted.
If {save_calls,N} has been set for the process, no function calls will be
saved to the call saving list. (The call saving list will not be cleared;
furthermore, send, receive, and timeout events will still be added to the
list.)
Types:
Pid = pid()
Flag, Value, OldValue -- see below
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.
Types:
Pid = pid()
Item = atom()
Info = term()
InfoTuple = {Item, Info}
InfoTupleList = [InfoTuple]
InfoResult = InfoTupleList | undefined
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 Item == registered_name
will appear.
See process_info/2 for information about specific InfoTuples.
Failure: badarg if Pid is not a local process.
Warning:
This BIF is intended for debugging only, use process_info/2 for
all other purposes.
Types:
Pid = pid()
Item = atom()
Info = term()
ItemList = [Item]
ItemSpec = Item | ItemList
InfoTuple = {Item, Info}
InfoTupleList = [InfoTuple]
InfoResult = InfoTuple | InfoTupleList | undefined | []
Returns information about the process identified by Pid as specified by
the ItemSpec, or undefined if the process is not alive.
If the process is alive and ItemSpec is a single Item, the
returned value is the corresponding InfoTuple unless ItemSpec ==
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 ItemSpec is an ItemList, 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.
Currently the following InfoTuples with corresponding Items are
valid:
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.
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 ItemSpec == registered_name, and than when process_info/1
is used.
- {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, Pids}:
- Pids is a list of pids, with processes 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_binary, BinInfo}:
- BinInfo is a list containing miscellaneous information about binaries currently being referred to by the message area. This InfoTuple is only valid on an emulator using the hybrid heap type. This InfoTuple may be changed or removed without prior notice.
- {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.
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>]
Types:
Module = atom()
Removes old code for Module. Before this BIF is used,
erlang:check_process_code/2 should be called to check that no processes
are executing old code in the module.
Failure: badarg if there is no old code for Module.
Warning:
This BIF is intended for the code server (see code(3erl)) and should not
be used elsewhere.
Types:
Key = Val = OldVal = term()
Adds a new Key to the process dictionary, associated with the value
Val, and returns undefined. If Key already exists, the
old value is deleted and replaced by Val and the function returns the
old value.
Note:
The values stored when put is evaluated within the scope of a
catch will not be retracted if a throw is evaluated, or if an
error occurs.
> X = put(name, walrus), Y = put(name, carpenter), Z = get(name), {X, Y, Z}. {undefined,walrus,carpenter}
Types:
Class = error | exit | throw
Reason = term()
Stacktrace = [{Module, Function, Arity | Args} | {Fun, Args}]
Module = Function = atom()
Arity = arity()
Args = [term()]
Fun = [fun()]
Module = Function = atom()
Arity = arity()
Args = [term()]
Fun = [fun()]
Stops the execution of the calling process with an exception of given class,
reason and call stack backtrace ( stacktrace).
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.
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.
Types:
TimerRef = reference()
TimerRef is a timer reference returned by erlang:send_after/3 or
erlang:start_timer/3. If the timer is active, the function returns the
time in milliseconds left until the timer will expire, otherwise false
(which means that TimerRef was never a timer, that it has been
cancelled, or that it has already delivered its message).
See also erlang:send_after/3, erlang:start_timer/3, and
erlang:cancel_timer/1.
Types:
Ref = reference()
Returns a string which corresponds to the text representation of Ref.
Warning:
This BIF is intended for debugging and for use in the Erlang operating system.
It should not be used in application programs.
Types:
RegName = atom()
Pid = pid()
Port = port()
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). trueFailure: badarg if Pid 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.
Types:
RegName = atom()
Returns a list of names which have been registered using register/2.
> registered(). [code_server, file_server, init, user, my_db]
Types:
Suspendee = pid()
Decreases the suspend count on the process identified by Suspendee.
Suspendee should previously have been suspended via
erlang:suspend_process/2, or erlang:suspend_process/1 by the
process calling erlang:resume_process(Suspendee). When the suspend
count on Suspendee reach zero, Suspendee will be resumed, i.e.,
the state of the Suspendee is changed from suspended into the state
Suspendee was in before it was suspended.
Failures:
Warning:
This BIF is intended for debugging only.
- 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.
Types:
Number = number()
Returns an integer by rounding Number.
> round(5.5). 6Allowed in guard tests.
Returns the pid (process identifier) of the calling process.
> self(). <0.26.0>Allowed in guard tests.
Types:
Dest = pid() | port() | RegName | {RegName,
Node}
Msg = term()
RegName = atom()
Node = node()
RegName = atom()
Node = node()
Sends a message and returns Msg. This is the same as Dest ! Msg.
Dest may be a remote or local pid, a (local) port, a locally registered
name, or a tuple {RegName, Node} for a registered name at another
node.
Types:
Dest = pid() | port() | RegName | {RegName,
Node}
RegName = atom()
Node = node()
Msg = term()
Option = nosuspend | noconnect
Res = ok | nosuspend | noconnect
RegName = atom()
Node = node()
Sends a message and returns ok, or does not send the message but returns
something else (see below). Otherwise the same as erlang:send/2. See
also erlang:send_nosuspend/2,3. for more detailed explanation and
warnings.
The possible options are:
- nosuspend:
- If the sender would have to be suspended to do the send, nosuspend is returned instead.
- noconnect:
- If the destination node would have to be auto-connected before doing the send, noconnect is returned instead.
Warning:
As with erlang:send_nosuspend/2,3: Use with extreme care!
Types:
Time = integer() >= 0
0 <= Time <= 4294967295
Dest = pid() | RegName
LocalPid = pid() (of a process, alive or dead, on the local node)
Msg = term()
TimerRef = reference()
0 <= Time <= 4294967295
LocalPid = pid() (of a process, alive or dead, on the local node)
Starts a timer which will send the message Msg to Dest after
Time milliseconds.
If Dest is an atom, it is supposed to be the name of a registered
process. The process referred to by the name is looked up at the time of
delivery. No error is given if the name does not refer to a process.
If Dest is a pid, the timer will be automatically canceled if the process
referred to by the pid is not alive, or when the process exits. This feature
was introduced in erts version 5.4.11. Note that timers will not be
automatically canceled when Dest is an atom.
See also erlang:start_timer/3, erlang:cancel_timer/1, and
erlang:read_timer/1.
Failure: badarg if the arguments does not satisfy the requirements
specified above.
erlang:send_nosuspend(Dest, Msg) -> boolean()
Types:
Dest = dst()
Msg = term()
dst() = pid()| port()| (RegName :: atom())| {RegName :: atom(), Node :: node()}
The same as erlang:send(Dest, Msg, [nosuspend]), but returns true
if the message was sent and false if the message was not sent because
the sender would have had to be suspended.
This function is intended for send operations towards an unreliable remote node
without ever blocking the sending (Erlang) process. If the connection to the
remote node (usually not a real Erlang node, but a node written in C or Java)
is overloaded, this function will not send the message but return
false instead.
The same happens, if Dest refers to a local port that is busy. For all
other destinations (allowed for the ordinary send operator '!') this
function sends the message and returns true.
This function is only to be used in very rare circumstances where a process
communicates with Erlang nodes that can disappear without any trace causing
the TCP buffers and the drivers queue to be over-full before the node will
actually be shut down (due to tick timeouts) by net_kernel. The normal
reaction to take when this happens is some kind of premature shutdown of the
other node.
Note that ignoring the return value from this function would result in
unreliable message passing, which is contradictory to the Erlang
programming model. The message is not sent if this function returns
false.
Note also that in many systems, transient states of overloaded queues are
normal. The fact that this function returns false does not in any way
mean that the other node is guaranteed to be non-responsive, it could be a
temporary overload. Also a return value of true does only mean that the
message could be sent on the (TCP) channel without blocking, the message is
not guaranteed to have arrived at the remote node. Also in the case of a
disconnected non-responsive node, the return value is true (mimics the
behaviour of the ! operator). The expected behaviour as well as the
actions to take when the function returns false are application and
hardware specific.
Warning:
Use with extreme care!
erlang:send_nosuspend(Dest, Msg, Options) -> boolean()
Types:
Dest = dst()
Msg = term()
Options = [noconnect]
dst() = pid()| port()| (RegName :: atom())| {RegName :: atom(), Node :: node()}
The same as erlang:send(Dest, Msg, [nosuspend | Options]), but with
boolean return value.
This function behaves like erlang:send_nosuspend/2), but takes a third
parameter, a list of options. The only currently implemented option is
noconnect. The option noconnect makes the function return
false if the remote node is not currently reachable by the local node.
The normal behaviour is to try to connect to the node, which may stall the
process for a shorter period. The use of the noconnect option makes it
possible to be absolutely sure not to get even the slightest delay when
sending to a remote process. This is especially useful when communicating with
nodes who expect to always be the connecting part (i.e. nodes written in C or
Java).
Whenever the function returns false (either when a suspend would occur or
when noconnect was specified and the node was not already connected),
the message is guaranteed not to have been sent.
Warning:
Use with extreme care!
erlang:set_cookie(Node, Cookie) -> true
Types:
Node = node()
Cookie = atom()
Sets the magic cookie of Node to the atom Cookie. If Node
is the local node, the function also sets the cookie of all other unknown
nodes to Cookie (see Distributed Erlang in the Erlang Reference
Manual).
Failure: function_clause if the local node is not alive.
Types:
Index = 1..tuple_size(Tuple1)
Tuple1 = Tuple2 = tuple()
Value = term()
Returns a tuple which is a copy of the argument Tuple1 with the element
given by the integer argument Index (the first element is the element
with index 1) replaced by the argument Value.
> setelement(2, {10, green, bottles}, red). {10,red,bottles}
Types:
Item = tuple() | binary()
Returns an integer which is the size of the argument Item, which must be
either a tuple or a binary.
> size({morni, mulle, bwange}). 3Allowed in guard tests.
spawn(Fun) -> pid()
Types:
Fun = function()
Returns the pid of a new process started by the application of Fun to the
empty list []. Otherwise works like spawn/3.
spawn(Node, Fun) -> pid()
Types:
Node = node()
Fun = function()
Returns the pid of a new process started by the application of Fun to the
empty list [] on Node. If Node does not exist, a useless
pid is returned. Otherwise works like spawn/3.
Types:
Module = Function = atom()
Args = [term()]
Returns the pid of a new process started by the application of
Module:Function to Args. The new process created will be placed
in the system scheduler queue and be run some time later.
error_handler:undefined_function(Module, Function, Args) is evaluated by
the new process if Module:Function/Arity does not exist (where
Arity is the length of Args). The error handler can be redefined
(see process_flag/2). If error_handler is undefined, or the user
has redefined the default error_handler its replacement is undefined, a
failure with the reason undef will occur.
> spawn(speed, regulator, [high_speed, thin_cut]). <0.13.1>
spawn(Node, Module, Function, Args) -> pid()
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Returns the pid of a new process started by the application of
Module:Function to Args on Node. If Node does not
exists, a useless pid is returned. Otherwise works like spawn/3.
spawn_link(Fun) -> pid()
Types:
Fun = function()
Returns the pid of a new process started by the application of Fun to the
empty list []. A link is created between the calling process and the new
process, atomically. Otherwise works like spawn/3.
spawn_link(Node, Fun) -> pid()
Types:
Node = node()
Fun = function()
Returns the pid of a new process started by the application of Fun to the
empty list [] on Node. A link is created between the calling process
and the new process, atomically. If Node does not exist, a useless pid
is returned (and due to the link, an exit signal with exit reason
noconnection will be received). Otherwise works like
spawn/3.
Types:
Module = Function = atom()
Args = [term()]
Returns the pid of a new process started by the application of
Module:Function to Args. A link is created between the calling
process and the new process, atomically. Otherwise works like
spawn/3.
spawn_link(Node, Module, Function, Args) -> pid()
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Returns the pid of a new process started by the application of
Module:Function to Args on Node. A link is created
between the calling process and the new process, atomically. If Node
does not exist, a useless pid is returned (and due to the link, an exit signal
with exit reason noconnection will be received). Otherwise works like
spawn/3.
spawn_monitor(Fun) -> {pid(), reference()}
Types:
Fun = function()
Returns the pid of a new process started by the application of Fun to the
empty list [] and reference for a monitor created to the new process.
Otherwise works like spawn/3.
spawn_monitor(Module, Function, Args) -> {pid(), reference()}
Types:
Module = module()
Function = atom()
Args = [term()]
A new process is started by the application of Module:Function to
Args, and the process is monitored at the same time. Returns the pid
and a reference for the monitor. Otherwise works like spawn/3.
spawn_opt(Fun, Options) -> pid() | {pid(), reference()}
Types:
Fun = function()
Options = [Option]
Option = link
| monitor
| {priority, Level}
| {fullsweep_after, Number :: integer() >= 0}
| {min_heap_size, Size :: integer() >= 0}
| {min_bin_vheap_size, VSize :: integer() >= 0}
Level = low | normal | high
| monitor
| {priority, Level}
| {fullsweep_after, Number :: integer() >= 0}
| {min_heap_size, Size :: integer() >= 0}
| {min_bin_vheap_size, VSize :: integer() >= 0}
Returns the pid of a new process started by the application of Fun to the
empty list []. Otherwise works like spawn_opt/4.
If the option monitor is given, the newly created process will be
monitored and both the pid and reference for the monitor will be
returned.
spawn_opt(Node, Fun, Options) -> pid() | {pid(), reference()}
Types:
Node = node()
Fun = function()
Options = [Option]
Option = link
| monitor
| {priority, Level}
| {fullsweep_after, Number :: integer() >= 0}
| {min_heap_size, Size :: integer() >= 0}
| {min_bin_vheap_size, VSize :: integer() >= 0}
Level = low | normal | high
| monitor
| {priority, Level}
| {fullsweep_after, Number :: integer() >= 0}
| {min_heap_size, Size :: integer() >= 0}
| {min_bin_vheap_size, VSize :: integer() >= 0}
Returns the pid of a new process started by the application of Fun to the
empty list [] on Node. If Node does not exist, a useless
pid is returned. Otherwise works like spawn_opt/4.
spawn_opt(Module, Function, Args, Options) -> pid() | {pid(), reference()}
Types:
Module = module()
Function = atom()
Args = [term()]
Options = [Option]
Option = link
| monitor
| {priority, Level}
| {fullsweep_after, Number :: integer() >= 0}
| {min_heap_size, Size :: integer() >= 0}
| {min_bin_vheap_size, VSize :: integer() >= 0}
Level = low | normal | high
| monitor
| {priority, Level}
| {fullsweep_after, Number :: integer() >= 0}
| {min_heap_size, Size :: integer() >= 0}
| {min_bin_vheap_size, VSize :: integer() >= 0}
Works exactly like spawn/3, except that an extra option list is given
when creating the process.
If the option monitor is given, the newly created process will be
monitored and both the pid and reference for the monitor will be returned.
- link:
- Sets a link to the parent process (like spawn_link/3 does).
- monitor:
- Monitor the new process (just like monitor/2 does).
- {priority, Level}:
- Sets the priority of the new process. Equivalent to executing process_flag(priority, Level) in the start function of the new process, except that the priority will be set before the process is selected for execution for the first time. For more information on priorities see process_flag(priority, Level).
- {fullsweep_after, Number}:
- This option is only useful for performance tuning. In general, you should not use this option unless you know that there is problem with execution times and/or memory consumption, and you should measure to make sure that the option improved matters.
The Erlang runtime system uses a generational garbage collection scheme, using
an "old heap" for data that has survived at least one garbage
collection. When there is no more room on the old heap, a fullsweep garbage
collection will be done.
The fullsweep_after option makes it possible to specify the maximum
number of generational collections before forcing a fullsweep even if there is
still room on the old heap. Setting the number to zero effectively disables
the general collection algorithm, meaning that all live data is copied at
every garbage collection.
Here are a few cases when it could be useful to change fullsweep_after.
Firstly, if binaries that are no longer used should be thrown away as soon as
possible. (Set Number to zero.) Secondly, a process that mostly have
short-lived data will be fullsweeped seldom or never, meaning that the old
heap will contain mostly garbage. To ensure a fullsweep once in a while, set
Number to a suitable value such as 10 or 20. Thirdly, in embedded
systems with limited amount of RAM and no virtual memory, one might want to
preserve memory by setting Number to zero. (The value may be set
globally, see erlang:system_flag/2.)
- {min_heap_size, Size}:
- This option is only useful for performance tuning. In general, you should not use this option unless you know that there is problem with execution times and/or memory consumption, and you should measure to make sure that the option improved matters.
Gives a minimum heap size in words. Setting this value higher than the system
default might speed up some processes because less garbage collection is done.
Setting too high value, however, might waste memory and slow down the system
due to worse data locality. Therefore, it is recommended to use this option
only for fine-tuning an application and to measure the execution time with
various Size values.
- {min_bin_vheap_size, VSize}:
- This option is only useful for performance tuning. In general, you should not use this option unless you know that there is problem with execution times and/or memory consumption, and you should measure to make sure that the option improved matters.
Gives a minimum binary virtual heap size in words. Setting this value higher
than the system default might speed up some processes because less garbage
collection is done. Setting too high value, however, might waste memory.
Therefore, it is recommended to use this option only for fine-tuning an
application and to measure the execution time with various VSize
values.
spawn_opt(Node, Module, Function, Args, Options) -> pid() | {pid(), reference()}
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Options = [Option]
Option = link
| monitor
| {priority, Level}
| {fullsweep_after, Number :: integer() >= 0}
| {min_heap_size, Size :: integer() >= 0}
| {min_bin_vheap_size, VSize :: integer() >= 0}
Level = low | normal | high
| monitor
| {priority, Level}
| {fullsweep_after, Number :: integer() >= 0}
| {min_heap_size, Size :: integer() >= 0}
| {min_bin_vheap_size, VSize :: integer() >= 0}
Returns the pid of a new process started by the application of
Module:Function to Args on Node. If Node does not
exist, a useless pid is returned. Otherwise works like
spawn_opt/4.
Types:
Bin = Bin1 = Bin2 = binary()
Pos = 0..byte_size(Bin)
Returns a tuple containing the binaries which are the result of splitting
Bin into two parts at position Pos. This is not a destructive
operation. After the operation, there will be three binaries altogether.
> B = list_to_binary("0123456789"). <<"0123456789">> > byte_size(B). 10 > {B1, B2} = split_binary(B,3). {<<"012">>,<<"3456789">>} > byte_size(B1). 3 > byte_size(B2). 7
Types:
Time = integer() >= 0
0 <= Time <= 4294967295
Dest = LocalPid | RegName
LocalPid = pid() (of a process, alive or dead, on the local node)
RegName = atom()
Msg = term()
TimerRef = reference()
0 <= Time <= 4294967295
LocalPid = pid() (of a process, alive or dead, on the local node)
RegName = atom()
Starts a timer which will send the message {timeout, TimerRef, Msg} to
Dest after Time milliseconds.
If Dest is an atom, it is supposed to be the name of a registered
process. The process referred to by the name is looked up at the time of
delivery. No error is given if the name does not refer to a process.
If Dest is a pid, the timer will be automatically canceled if the process
referred to by the pid is not alive, or when the process exits. This feature
was introduced in erts version 5.4.11. Note that timers will not be
automatically canceled when Dest is an atom.
See also erlang:send_after/3, erlang:cancel_timer/1, and
erlang:read_timer/1.
Failure: badarg if the arguments does not satisfy the requirements
specified above.
Types:
Type, Res -- see below
All times are in milliseconds unless otherwise specified.
Returns information about the system as specified by Type:
- context_switches:
- Returns {ContextSwitches, 0}, where ContextSwitches is the total number of context switches since the system started.
- exact_reductions:
- Returns {Total_Exact_Reductions, Exact_Reductions_Since_Last_Call}.
Note:
statistics(exact_reductions) is a more expensive operation than
statistics(reductions) especially on an Erlang machine with SMP
support.
- garbage_collection:
- Returns {Number_of_GCs, Words_Reclaimed, 0}. This information may not be valid for all implementations.
> statistics(garbage_collection). {85,23961,0}
- io:
- Returns {{input, Input}, {output, Output}}, where Input is the total number of bytes received through ports, and Output is the total number of bytes output to ports.
- reductions:
- Returns {Total_Reductions, Reductions_Since_Last_Call}.
Note:
From erts version 5.5 (OTP release R11B) this value does not include reductions
performed in current time slices of currently scheduled processes. If an exact
value is wanted, use statistics(exact_reductions).
> statistics(reductions). {2046,11}
- run_queue:
- Returns the length of the run queue, that is, the number of processes that are ready to run.
- runtime:
- Returns {Total_Run_Time, Time_Since_Last_Call}. Note that the run-time is the sum of the run-time for all threads in the Erlang run-time system and may therefore be greater than the wall-clock time.
> statistics(runtime). {1690,1620}
- scheduler_wall_time:
- Returns a list of tuples with {SchedulerId, ActiveTime, TotalTime}, where SchedulerId is an integer id of the scheduler, ActiveTime is the duration the scheduler has been busy, TotalTime is the total time duration since scheduler_wall_time activation. The time unit is not defined and may be subject to change between releases, operating systems and system restarts. scheduler_wall_time should only be used to calculate relative values for scheduler-utilization. ActiveTime can never exceed TotalTime.
The definition of a busy scheduler is when it is not idle or not scheduling
(selecting) a process or port, meaning; executing process code, executing
linked-in-driver or NIF code, executing built-in-functions or any other
runtime handling, garbage collecting or handling any other memory management.
Note, a scheduler may also be busy even if the operating system has scheduled
out the scheduler thread.
Returns undefined if the system flag scheduler_wall_time is
turned off.
The list of scheduler information is unsorted and may appear in different order
between calls.
Using scheduler_wall_time to calculate scheduler utilization.
> erlang:system_flag(scheduler_wall_time, true). false > Ts0 = lists:sort(erlang:statistics(scheduler_wall_time)), ok. ok
Some time later we will take another snapshot and calculate
scheduler-utilization per scheduler.
> Ts1 = lists:sort(erlang:statistics(scheduler_wall_time)), ok. ok > lists:map(fun({{I, A0, T0}, {I, A1, T1}}) -> {I, (A1 - A0)/(T1 - T0)} end, lists:zip(Ts0,Ts1)). [{1,0.9743474730177548}, {2,0.9744843782751444}, {3,0.9995902361669045}, {4,0.9738012596572161}, {5,0.9717956667018103}, {6,0.9739235846420741}, {7,0.973237033077876}, {8,0.9741297293248656}]
Using the same snapshots to calculate a total scheduler-utilization.
> {A, T} = lists:foldl(fun({{_, A0, T0}, {_, A1, T1}}, {Ai,Ti}) -> {Ai + (A1 - A0), Ti + (T1 - T0)} end, {0, 0}, lists:zip(Ts0,Ts1)), A/T. 0.9769136803764825
Note:
scheduler_wall_time is by default disabled. Use
erlang:system_flag(scheduler_wall_time, true) to enable it.
- wall_clock:
- Returns {Total_Wallclock_Time, Wallclock_Time_Since_Last_Call}. wall_clock can be used in the same manner as runtime, except that real time is measured as opposed to runtime or CPU time.
Types:
Suspendee = pid()
OptList = [Opt]
Opt = atom()
Increases the suspend count on the process identified by Suspendee and
puts it in the suspended state if it isn't already in the suspended state. A
suspended process will not be scheduled for execution until the process has
been resumed.
A process can be suspended by multiple processes and can be suspended multiple
times by a single process. A suspended process will not leave the suspended
state until its suspend count reach zero. The suspend count of
Suspendee is decreased when erlang:resume_process(Suspendee) is
called by the same process that called
erlang:suspend_process(Suspendee). All increased suspend counts on
other processes acquired by a process will automatically be decreased when the
process terminates.
Currently the following options ( Opts) are available:
If the suspend count on the process identified by Suspendee was
increased, true is returned; otherwise, false is returned.
Failures:
- asynchronous:
-
A suspend request is sent to the process identified by Suspendee. Suspendee will eventually suspend unless it is resumed before it was able to suspend. The caller of erlang:suspend_process/2 will return immediately, regardless of whether the Suspendee has suspended yet or not. Note that the point in time when the Suspendee will actually suspend cannot be deduced from other events in the system. The only guarantee given is that the Suspendee will eventually suspend (unless it is resumed). If the asynchronous option has not been passed, the caller of erlang:suspend_process/2 will be blocked until the Suspendee has actually suspended.
- unless_suspending:
-
The process identified by Suspendee will be suspended unless the calling process already is suspending the Suspendee. If unless_suspending is combined with the asynchronous option, a suspend request will be sent unless the calling process already is suspending the Suspendee or if a suspend request already has been sent and is in transit. If the calling process already is suspending the Suspendee, or if combined with the asynchronous option and a send request already is in transit, false is returned and the suspend count on Suspendee will remain unchanged.
Warning:
This BIF is intended for debugging only.
- badarg:
-
If Suspendee isn't a process identifier.
- badarg:
-
If the process identified by Suspendee is same the process as the process calling erlang:suspend_process/2.
- badarg:
-
If the process identified by Suspendee is not alive.
- badarg:
-
If the process identified by Suspendee resides on another node.
- badarg:
-
If OptList isn't a proper list of valid Opts.
- system_limit:
-
If the process identified by Suspendee has been suspended more times by the calling process than can be represented by the currently used internal data structures. The current system limit is larger than 2 000 000 000 suspends, and it will never be less than that.
erlang:suspend_process(Suspendee) -> true
Types:
Suspendee = pid()
Suspends the process identified by Suspendee. The same as calling
erlang:suspend_process(Suspendee, []). For more information see the
documentation of erlang:suspend_process/2.
Warning:
This BIF is intended for debugging only.
Types:
Flag, Value, OldValue -- see below
Warning:
The cpu_topology, and scheduler_bind_type Flags are
deprecated and have been scheduled for removal in erts-5.10/OTP-R16.
- erlang:system_flag(backtrace_depth, Depth):
- Sets the maximum depth of call stack back-traces in the exit reason element of 'EXIT' tuples.
- erlang:system_flag(cpu_topology, CpuTopology):
- NOTE: This argument is deprecated and scheduled for removal in erts-5.10/OTP-R16. Instead of using this argument you are advised to use the erl command line argument +sct. When this argument has been removed a final CPU topology to use will be determined at emulator boot time.
Sets the user defined CpuTopology. The user defined CPU topology will
override any automatically detected CPU topology. By passing undefined
as CpuTopology the system will revert back to the CPU topology
automatically detected. The returned value equals the value returned from
erlang:system_info(cpu_topology) before the change was made.
The CPU topology is used when binding schedulers to logical processors. If
schedulers are already bound when the CPU topology is changed, the schedulers
will be sent a request to rebind according to the new CPU topology.
The user defined CPU topology can also be set by passing the +sct command
line argument to erl.
For information on the CpuTopology type and more, see the documentation
of erlang:system_info(cpu_topology), and the erl +sct and
+sbt command line flags.
- erlang:system_flag(fullsweep_after, Number):
- Number is a non-negative integer which indicates how many times generational garbage collections can be done without forcing a fullsweep collection. The value applies to new processes; processes already running are not affected.
In low-memory systems (especially without virtual memory), setting the value to
0 can help to conserve memory.
An alternative way to set this value is through the (operating system)
environment variable ERL_FULLSWEEP_AFTER.
- erlang:system_flag(min_heap_size, MinHeapSize):
- Sets the default minimum heap size for processes. The size is given in words. The new min_heap_size only effects processes spawned after the change of min_heap_size has been made. The min_heap_size can be set for individual processes by use of spawn_opt/N or process_flag/2.
- erlang:system_flag(min_bin_vheap_size, MinBinVHeapSize):
- Sets the default minimum binary virtual heap size for processes. The size is given in words. The new min_bin_vhheap_size only effects processes spawned after the change of min_bin_vhheap_size has been made. The min_bin_vheap_size can be set for individual processes by use of spawn_opt/N or process_flag/2.
- erlang:system_flag(multi_scheduling, BlockState):
- BlockState = block | unblock
If multi-scheduling is enabled, more than one scheduler thread is used by the
emulator. Multi-scheduling can be blocked. When multi-scheduling has been
blocked, only one scheduler thread will schedule Erlang processes.
If BlockState =:= block, multi-scheduling will be blocked. If
BlockState =:= unblock and no-one else is blocking multi-scheduling and
this process has only blocked one time, multi-scheduling will be unblocked.
One process can block multi-scheduling multiple times. If a process has
blocked multiple times, it has to unblock exactly as many times as it has
blocked before it has released its multi-scheduling block. If a process that
has blocked multi-scheduling exits, it will release its blocking of
multi-scheduling.
The return values are disabled, blocked, or enabled. The
returned value describes the state just after the call to
erlang:system_flag(multi_scheduling, BlockState) has been made. The
return values are described in the documentation of
erlang:system_info(multi_scheduling).
NOTE: Blocking of multi-scheduling should normally not be needed. If you
feel that you need to block multi-scheduling, think through the problem at
least a couple of times again. Blocking multi-scheduling should only be used
as a last resort since it will most likely be a very inefficient way to
solve the problem.
See also erlang:system_info(multi_scheduling),
erlang:system_info(multi_scheduling_blockers), and
erlang:system_info(schedulers).
- erlang:system_flag(scheduler_bind_type, How):
- NOTE: This argument is deprecated and scheduled for removal in erts-5.10/OTP-R16. Instead of using this argument you are advised to use the erl command line argument +sbt. When this argument has been removed a final scheduler bind type to use will be determined at emulator boot time.
Controls if and how schedulers are bound to logical processors.
When erlang:system_flag(scheduler_bind_type, How) is called, an
asynchronous signal is sent to all schedulers online which causes them to try
to bind or unbind as requested. NOTE: If a scheduler fails to bind,
this will often be silently ignored. This since it isn't always possible to
verify valid logical processor identifiers. If an error is reported, it will
be reported to the error_logger. If you want to verify that the
schedulers actually have bound as requested, call
erlang:system_info(scheduler_bindings).
Schedulers can currently only be bound on newer Linux, Solaris, FreeBSD, and
Windows systems, but more systems will be supported in the future.
In order for the runtime system to be able to bind schedulers, the CPU topology
needs to be known. If the runtime system fails to automatically detect the CPU
topology, it can be defined. For more information on how to define the CPU
topology, see the erl +sct command line flag.
The runtime system will by default not bind schedulers to logical
processors.
NOTE: If the Erlang runtime system is the only operating system process
that binds threads to logical processors, this improves the performance of the
runtime system. However, if other operating system processes (as for example
another Erlang runtime system) also bind threads to logical processors, there
might be a performance penalty instead. In some cases this performance penalty
might be severe. If this is the case, you are advised to not bind the
schedulers.
Schedulers can be bound in different ways. The How argument determines
how schedulers are bound. How can currently be one of:
- unbound:
- Same as the erl command line argument +sbt u.
- no_spread:
- Same as the erl command line argument +sbt ns.
- thread_spread:
- Same as the erl command line argument +sbt ts.
- processor_spread:
- Same as the erl command line argument +sbt ps.
- spread:
- Same as the erl command line argument +sbt s.
- no_node_thread_spread:
- Same as the erl command line argument +sbt nnts.
- no_node_processor_spread:
- Same as the erl command line argument +sbt nnps.
- thread_no_node_processor_spread:
- Same as the erl command line argument +sbt tnnps.
- default_bind:
- Same as the erl command line argument +sbt db.
The value returned equals How before the scheduler_bind_type flag
was changed.
Failure:
- notsup:
- If binding of schedulers is not supported.
- badarg:
- If How isn't one of the documented alternatives.
- badarg:
- If no CPU topology information is available.
The scheduler bind type can also be set by passing the +sbt command line
argument to erl.
For more information, see erlang:system_info(scheduler_bind_type),
erlang:system_info(scheduler_bindings), the erl +sbt and
+sct command line flags.
- erlang:system_flag(scheduler_wall_time, Boolean):
- Turns on/off scheduler wall time measurements.
For more information see, erlang:statistics(scheduler_wall_time).
- erlang:system_flag(schedulers_online, SchedulersOnline):
- Sets the amount of schedulers online. Valid range is 1 <= SchedulerId <= erlang:system_info(schedulers).
For more information see, erlang:system_info(schedulers), and
erlang:system_info(schedulers_online).
- erlang:system_flag(trace_control_word, TCW):
- Sets the value of the node's trace control word to TCW. TCW should be an unsigned integer. For more information see documentation of the set_tcw function in the match specification documentation in the ERTS User's Guide.
Note:
The schedulers option has been removed as of erts version 5.5.3. The
number of scheduler threads is determined at emulator boot time, and cannot be
changed after that.
Types:
Type, Res -- see below
Returns various information about the current system (emulator) as specified by
Type:
- allocated_areas:
- Returns a list of tuples with information about miscellaneous allocated memory areas.
Each tuple contains an atom describing type of memory as first element and
amount of allocated memory in bytes as second element. In those cases when
there is information present about allocated and used memory, a third element
is present. This third element contains the amount of used memory in
bytes.
erlang:system_info(allocated_areas) is intended for debugging, and the
content is highly implementation dependent. The content of the results will
therefore change when needed without prior notice.
Note: The sum of these values is not the total amount of memory
allocated by the emulator. Some values are part of other values, and some
memory areas are not part of the result. If you are interested in the total
amount of memory allocated by the emulator see erlang:memory/0,1.
- allocator:
- Returns {Allocator, Version, Features, Settings}.
Types:
- *
- Allocator = undefined | glibc
- *
- Version = [integer()]
- *
- Features = [atom()]
- *
- Settings = [{Subsystem, [{Parameter, Value}]}]
- *
- Subsystem = atom()
- *
- Parameter = atom()
- *
- Value = term()
Explanation:
- *
- Allocator corresponds to the malloc() implementation used. If Allocator equals undefined, the malloc() implementation used could not be identified. Currently glibc can be identified.
- *
- Version is a list of integers (but not a string) representing the version of the malloc() implementation used.
- *
- Features is a list of atoms representing allocation features used.
- *
- Settings is a list of subsystems, their configurable parameters, and used values. Settings may differ between different combinations of platforms, allocators, and allocation features. Memory sizes are given in bytes.
See also "System Flags Effecting erts_alloc" in
erts_alloc(3erl).
- alloc_util_allocators:
- Returns a list of the names of all allocators using the ERTS internal alloc_util framework as atoms. For more information see the "the alloc_util framework" section in the erts_alloc(3erl) documentation.
- {allocator, Alloc}:
- Returns information about the specified allocator. As of erts version 5.6.1 the return value is a list of {instance, InstanceNo, InstanceInfo} tuples where InstanceInfo contains information about a specific instance of the allocator. If Alloc is not a recognized allocator, undefined is returned. If Alloc is disabled, false is returned.
Note: The information returned is highly implementation dependent and may
be changed, or removed at any time without prior notice. It was initially
intended as a tool when developing new allocators, but since it might be of
interest for others it has been briefly documented.
The recognized allocators are listed in erts_alloc(3erl). After reading
the erts_alloc(3erl) documentation, the returned information should
more or less speak for itself. But it can be worth explaining some things.
Call counts are presented by two values. The first value is giga calls, and
the second value is calls. mbcs, and sbcs are abbreviations for,
respectively, multi-block carriers, and single-block carriers. Sizes are
presented in bytes. When it is not a size that is presented, it is the amount
of something. Sizes and amounts are often presented by three values, the first
is current value, the second is maximum value since the last call to
erlang:system_info({allocator, Alloc}), and the third is maximum value
since the emulator was started. If only one value is present, it is the
current value. fix_alloc memory block types are presented by two
values. The first value is memory pool size and the second value used memory
size.
- {allocator_sizes, Alloc}:
- Returns various size information for the specified allocator. The information returned is a subset of the information returned by erlang:system_info({allocator, Alloc}).
- build_type:
- Returns an atom describing the build type of the runtime system. This is normally the atom opt for optimized. Other possible return values are debug, purify, quantify, purecov, gcov, valgrind, gprof, and lcnt. Possible return values may be added and/or removed at any time without prior notice.
- c_compiler_used:
- Returns a two-tuple describing the C compiler used when compiling the runtime system. The first element is an atom describing the name of the compiler, or undefined if unknown. The second element is a term describing the version of the compiler, or undefined if unknown.
- check_io:
- Returns a list containing miscellaneous information regarding the emulators internal I/O checking. Note, the content of the returned list may vary between platforms and over time. The only thing guaranteed is that a list is returned.
- compat_rel:
- Returns the compatibility mode of the local node as an integer. The integer returned represents the Erlang/OTP release which the current emulator has been set to be backward compatible with. The compatibility mode can be configured at startup by using the command line flag +R, see erl(1).
- cpu_topology:
- Returns the CpuTopology which currently is used by the emulator. The CPU topology is used when binding schedulers to logical processors. The CPU topology used is the user defined CPU topology if such exists; otherwise, the automatically detected CPU topology if such exists. If no CPU topology exists, undefined is returned.
Types:
- *
- CpuTopology = LevelEntryList | undefined
- *
- LevelEntryList = [LevelEntry] (all LevelEntrys of a LevelEntryList must contain the same LevelTag, except on the top level where both node and processor LevelTags may co-exist)
- *
- LevelEntry = {LevelTag, SubLevel} | {LevelTag, InfoList, SubLevel} ( {LevelTag, SubLevel} == {LevelTag, [], SubLevel})
- *
- LevelTag = node|processor|core|thread (more LevelTags may be introduced in the future)
- *
- SubLevel = [LevelEntry] | LogicalCpuId
- *
- LogicalCpuId = {logical, integer()}
- *
- InfoList = [] (the InfoList may be extended in the future)
node refers to NUMA (non-uniform memory access) nodes, and thread
refers to hardware threads (e.g. Intels hyper-threads).
A level in the CpuTopology term can be omitted if only one entry exists
and the InfoList is empty.
thread can only be a sub level to core. core can be a sub
level to either processor or node. processor can either
be on the top level or a sub level to node. node can either be
on the top level or a sub level to processor. That is, NUMA nodes can
be processor internal or processor external. A CPU topology can consist of a
mix of processor internal and external NUMA nodes, as long as each logical CPU
belongs to one and only one NUMA node. Cache hierarchy is not part of the
CpuTopology type yet, but will be in the future. Other things may also
make it into the CPU topology in the future. In other words, expect the
CpuTopology type to change.
- {cpu_topology, defined}:
- Returns the user defined CpuTopology. For more information see the documentation of the erl +sct command line flag, and the documentation of the cpu_topology argument.
- {cpu_topology, detected}:
- Returns the automatically detected CpuTopology. The emulator currently only detects the CPU topology on some newer Linux, Solaris, FreeBSD, and Windows systems. On Windows system with more than 32 logical processors the CPU topology is not detected.
For more information see the documentation of the cpu_topology
argument.
- {cpu_topology, used}:
- Returns the CpuTopology which is used by the emulator. For more information see the documentation of the cpu_topology argument.
- creation:
- Returns the creation of the local node as an integer. The creation is changed when a node is restarted. The creation of a node is stored in process identifiers, port identifiers, and references. This makes it (to some extent) possible to distinguish between identifiers from different incarnations of a node. Currently valid creations are integers in the range 1..3, but this may (probably will) change in the future. If the node is not alive, 0 is returned.
- debug_compiled:
- Returns true if the emulator has been debug compiled; otherwise, false.
- dist:
- Returns a binary containing a string of distribution information formatted as in Erlang crash dumps. For more information see the "How to interpret the Erlang crash dumps" chapter in the ERTS User's Guide.
- dist_ctrl:
- Returns a list of tuples {Node, ControllingEntity}, one entry for each connected remote node. The Node is the name of the node and the ControllingEntity is the port or pid responsible for the communication to that node. More specifically, the ControllingEntity for nodes connected via TCP/IP (the normal case) is the socket actually used in communication with the specific node.
- driver_version:
- Returns a string containing the erlang driver version used by the runtime system. It will be on the form "<major ver>.<minor ver>".
- dynamic_trace:
- Returns an atom describing the dynamic trace framework compiled into the virtual machine. It can currently be either dtrace, systemtap or none. For a commercial or standard build, this is always none, the other return values indicate a custom configuration (e.g. ./configure --with-dynamic-trace=dtrace). See the dyntrace manual page and the README.dtrace/README.systemtap files in the Erlang source code top directory for more information about dynamic tracing.
- dynamic_trace_probes:
- Returns a boolean() indicating if dynamic trace probes (either dtrace or systemtap) are built into the emulator. This can only be true if the virtual machine was built for dynamic tracing (i.e. system_info(dynamic_trace) returns dtrace or systemtap).
- elib_malloc:
- This option will be removed in a future release. The return value will always be false since the elib_malloc allocator has been removed.
- dist_buf_busy_limit:
- Returns the value of the distribution buffer busy limit in bytes. This limit can be set on startup by passing the +zdbbl command line flag to erl.
- fullsweep_after:
- Returns {fullsweep_after, integer()} which is the fullsweep_after garbage collection setting used by default. For more information see garbage_collection described below.
- garbage_collection:
- Returns a list describing the default garbage collection settings. A process spawned on the local node by a spawn or spawn_link will use these garbage collection settings. The default settings can be changed by use of system_flag/2. spawn_opt/4 can spawn a process that does not use the default settings.
- global_heaps_size:
- Returns the current size of the shared (global) heap.
- heap_sizes:
- Returns a list of integers representing valid heap sizes in words. All Erlang heaps are sized from sizes in this list.
- heap_type:
- Returns the heap type used by the current emulator. Currently the following heap types exist:
- private:
- Each process has a heap reserved for its use and no references between heaps of different processes are allowed. Messages passed between processes are copied between heaps.
- shared:
- One heap for use by all processes. Messages passed between processes are passed by reference.
- hybrid:
- A hybrid of the private and shared heap types. A shared heap as well as private heaps are used.
- info:
- Returns a binary containing a string of miscellaneous system information formatted as in Erlang crash dumps. For more information see the "How to interpret the Erlang crash dumps" chapter in the ERTS User's Guide.
- kernel_poll:
- Returns true if the emulator uses some kind of kernel-poll implementation; otherwise, false.
- loaded:
- Returns a binary containing a string of loaded module information formatted as in Erlang crash dumps. For more information see the "How to interpret the Erlang crash dumps" chapter in the ERTS User's Guide.
- logical_processors:
- Returns the detected number of logical processors configured on the system. The return value is either an integer, or the atom unknown if the emulator wasn't able to detect logical processors configured.
- logical_processors_available:
- Returns the detected number of logical processors available to the Erlang runtime system. The return value is either an integer, or the atom unknown if the emulator wasn't able to detect logical processors available. The number of logical processors available is less than or equal to the number of logical processors online.
- logical_processors_online:
- Returns the detected number of logical processors online on the system. The return value is either an integer, or the atom unknown if the emulator wasn't able to detect logical processors online. The number of logical processors online is less than or equal to the number of logical processors configured.
- machine:
- Returns a string containing the Erlang machine name.
- min_heap_size:
- Returns {min_heap_size, MinHeapSize} where MinHeapSize is the current system wide minimum heap size for spawned processes.
- min_bin_vheap_size:
- Returns {min_bin_vheap_size, MinBinVHeapSize} where MinBinVHeapSize is the current system wide minimum binary virtual heap size for spawned processes.
- modified_timing_level:
- Returns the modified timing level (an integer) if modified timing has been enabled; otherwise, undefined. See the +T command line flag in the documentation of the erl(1) command for more information on modified timing.
- multi_scheduling:
- Returns disabled, blocked, or enabled. A description of the return values:
- disabled:
- The emulator has only one scheduler thread. The emulator does not have SMP support, or have been started with only one scheduler thread.
- blocked:
- The emulator has more than one scheduler thread, but all scheduler threads but one have been blocked, i.e., only one scheduler thread will schedule Erlang processes and execute Erlang code.
- enabled:
- The emulator has more than one scheduler thread, and no scheduler threads have been blocked, i.e., all available scheduler threads will schedule Erlang processes and execute Erlang code.
See also erlang:system_flag(multi_scheduling, BlockState),
erlang:system_info(multi_scheduling_blockers), and
erlang:system_info(schedulers).
- multi_scheduling_blockers:
- Returns a list of PIDs when multi-scheduling is blocked; otherwise, the empty list. The PIDs in the list is PIDs of the processes currently blocking multi-scheduling. A PID will only be present once in the list, even if the corresponding process has blocked multiple times.
See also erlang:system_flag(multi_scheduling, BlockState),
erlang:system_info(multi_scheduling), and
erlang:system_info(schedulers).
- otp_release:
- Returns a string containing the OTP release number.
- process_count:
- Returns the number of processes currently existing at the local node as an integer. The same value as length(processes()) returns.
- process_limit:
- Returns the maximum number of concurrently existing processes at the local node as an integer. This limit can be configured at startup by using the command line flag +P, see erl(1).
- procs:
- Returns a binary containing a string of process and port information formatted as in Erlang crash dumps. For more information see the "How to interpret the Erlang crash dumps" chapter in the ERTS User's Guide.
- scheduler_bind_type:
- Returns information on how user has requested schedulers to be bound or not bound.
NOTE: Even though user has requested schedulers to be bound, they might
have silently failed to bind. In order to inspect actual scheduler bindings
call erlang:system_info(scheduler_bindings).
For more information, see the erl +sbt command line argument, and
erlang:system_info(scheduler_bindings).
- scheduler_bindings:
- Returns information on currently used scheduler bindings.
A tuple of a size equal to erlang:system_info(schedulers) is returned.
The elements of the tuple are integers or the atom unbound. Logical
processor identifiers are represented as integers. The Nth element of
the tuple equals the current binding for the scheduler with the scheduler
identifier equal to N. E.g., if the schedulers have been bound,
element(erlang:system_info(scheduler_id),
erlang:system_info(scheduler_bindings)) will return the identifier of the
logical processor that the calling process is executing on.
Note that only schedulers online can be bound to logical processors.
For more information, see the erl +sbt command line argument,
erlang:system_info(schedulers_online).
- scheduler_id:
- Returns the scheduler id (SchedulerId) of the scheduler thread that the calling process is executing on. SchedulerId is a positive integer; where 1 <= SchedulerId <= erlang:system_info(schedulers). See also erlang:system_info(schedulers).
- schedulers:
- Returns the number of scheduler threads used by the emulator. Scheduler threads online schedules Erlang processes and Erlang ports, and execute Erlang code and Erlang linked in driver code.
The number of scheduler threads is determined at emulator boot time and cannot
be changed after that. The amount of schedulers online can however be changed
at any time.
See also erlang:system_flag(schedulers_online, SchedulersOnline),
erlang:system_info(schedulers_online),
erlang:system_info(scheduler_id),
erlang:system_flag(multi_scheduling, BlockState),
erlang:system_info(multi_scheduling), and and
erlang:system_info(multi_scheduling_blockers).
- schedulers_online:
- Returns the amount of schedulers online. The scheduler identifiers of schedulers online satisfy the following relationship: 1 <= SchedulerId <= erlang:system_info(schedulers_online).
For more information, see erlang:system_info(schedulers), and
erlang:system_flag(schedulers_online, SchedulersOnline).
- smp_support:
- Returns true if the emulator has been compiled with smp support; otherwise, false.
- system_version:
- Returns a string containing version number and some important properties such as the number of schedulers.
- system_architecture:
- Returns a string containing the processor and OS architecture the emulator is built for.
- threads:
- Returns true if the emulator has been compiled with thread support; otherwise, false is returned.
- thread_pool_size:
- Returns the number of async threads in the async thread pool used for asynchronous driver calls ( driver_async()) as an integer.
- trace_control_word:
- Returns the value of the node's trace control word. For more information see documentation of the function get_tcw in "Match Specifications in Erlang", ERTS User's Guide.
- update_cpu_info:
- The runtime system rereads the CPU information available and updates its internally stored information about the detected CPU topology and the amount of logical processors configured, online, and available. If the CPU information has changed since the last time it was read, the atom changed is returned; otherwise, the atom unchanged is returned. If the CPU information has changed you probably want to adjust the amount of schedulers online. You typically want to have as many schedulers online as logical processors available.
- version:
- Returns a string containing the version number of the emulator.
- wordsize:
- Same as {wordsize, internal}.
- {wordsize, internal}:
- Returns the size of Erlang term words in bytes as an integer, i.e. on a 32-bit architecture 4 is returned, and on a pure 64-bit architecture 8 is returned. On a halfword 64-bit emulator, 4 is returned, as the Erlang terms are stored using a virtual wordsize of half the system's wordsize.
- {wordsize, external}:
- Returns the true wordsize of the emulator, i.e. the size of a pointer, in bytes as an integer. On a pure 32-bit architecture 4 is returned, on both a halfword and pure 64-bit architecture, 8 is returned.
Note:
The scheduler argument has changed name to scheduler_id. This in
order to avoid mixup with the schedulers argument. The scheduler
argument was introduced in ERTS version 5.5 and renamed in ERTS version 5.5.1.
Types:
MonSettings -> {MonitorPid, Options} |
undefined
MonitorPid = pid()
Options = [Option]
Option = {long_gc, Time} | {large_heap, Size} | busy_port | busy_dist_port
Time = Size = integer()
MonitorPid = pid()
Options = [Option]
Option = {long_gc, Time} | {large_heap, Size} | busy_port | busy_dist_port
Time = Size = integer()
Returns the current system monitoring settings set by
erlang:system_monitor/2 as {MonitorPid, Options}, or
undefined if there are no settings. The order of the options may be
different from the one that was set.
Types:
MonitorPid, Options, MonSettings -- see below
When called with the argument undefined, all system performance
monitoring settings are cleared.
Calling the function with {MonitorPid, Options} as argument, is the same
as calling erlang:system_monitor(MonitorPid, Options).
Returns the previous system monitor settings just like
erlang:system_monitor/0.
Types:
MonitorPid = pid()
Option = {long_gc, Time} | {large_heap, Size} | busy_port | busy_dist_port
Time = Size = integer()
MonSettings = {OldMonitorPid, [Option]}
OldMonitorPid = pid()
Time = Size = integer()
OldMonitorPid = pid()
Sets system performance monitoring options. MonitorPid is a local pid
that will receive system monitor messages, and the second argument is a list
of monitoring options:
Returns the previous system monitor settings just like
erlang:system_monitor/0.
Failure: badarg if MonitorPid does not exist.
- {long_gc, Time}:
- If a garbage collection in the system takes at least Time wallclock milliseconds, a message {monitor, GcPid, long_gc, Info} is sent to MonitorPid. GcPid is the pid that was garbage collected and Info is a list of two-element tuples describing the result of the garbage collection. One of the tuples is {timeout, GcTime} where GcTime is the actual time for the garbage collection in milliseconds. The other tuples are tagged with heap_size, heap_block_size, stack_size, mbuf_size, old_heap_size, and old_heap_block_size. These tuples are explained in the documentation of the gc_start trace message (see erlang:trace/3). New tuples may be added, and the order of the tuples in the Info list may be changed at any time without prior notice.
- {large_heap, Size}:
- If a garbage collection in the system results in the allocated size of a heap being at least Size words, a message {monitor, GcPid, large_heap, Info} is sent to MonitorPid. GcPid and Info are the same as for long_gc above, except that the tuple tagged with timeout is not present. Note: As of erts version 5.6 the monitor message is sent if the sum of the sizes of all memory blocks allocated for all heap generations is equal to or larger than Size. Previously the monitor message was sent if the memory block allocated for the youngest generation was equal to or larger than Size.
- busy_port:
- If a process in the system gets suspended because it sends to a busy port, a message {monitor, SusPid, busy_port, Port} is sent to MonitorPid. SusPid is the pid that got suspended when sending to Port.
- busy_dist_port:
- If a process in the system gets suspended because it sends to a process on a remote node whose inter-node communication was handled by a busy port, a message {monitor, SusPid, busy_dist_port, Port} is sent to MonitorPid. SusPid is the pid that got suspended when sending through the inter-node communication port Port.
Note:
If a monitoring process gets so large that it itself starts to cause system
monitor messages when garbage collecting, the messages will enlarge the
process's message queue and probably make the problem worse.
Keep the monitoring process neat and do not set the system monitor limits too
tight.
Types:
ProfilerSettings -> {ProfilerPid, Options}
| undefined
ProfilerPid = pid() | port()
Options = [Option]
Option = runnable_procs | runnable_ports | scheduler | exclusive
ProfilerPid = pid() | port()
Options = [Option]
Option = runnable_procs | runnable_ports | scheduler | exclusive
Returns the current system profiling settings set by
erlang:system_profile/2 as {ProfilerPid, Options}, or
undefined if there are no settings. The order of the options may be
different from the one that was set.
Types:
ProfilerSettings -> {ProfilerPid, Options}
| undefined
ProfilerPid = pid() | port()
Options = [Option]
Option = runnable_procs | runnable_ports | scheduler | exclusive
ProfilerPid = pid() | port()
Options = [Option]
Option = runnable_procs | runnable_ports | scheduler | exclusive
Sets system profiler options. ProfilerPid is a local pid or port that
will receive profiling messages. The receiver is excluded from all profiling.
The second argument is a list of profiling options:
- runnable_procs:
- If a process is put into or removed from the run queue a message, {profile, Pid, State, Mfa, Ts}, is sent to ProfilerPid. Running processes that is reinserted into the run queue after having been preemptively scheduled out will not trigger this message.
- runnable_ports:
- If a port is put into or removed from the run queue a message, {profile, Port, State, 0, Ts}, is sent to ProfilerPid.
- scheduler:
- If a scheduler is put to sleep or awoken a message, {profile, scheduler, Id, State, NoScheds, Ts}, is sent to ProfilerPid.
- exclusive:
- If a synchronous call to a port from a process is done, the calling process is considered not runnable during the call runtime to the port. The calling process is notified as inactive and subsequently active when the port callback returns.
Note:
erlang:system_profile is considered experimental and its behaviour may
change in the future.
Types:
Term = term()
Returns a binary data object which is the result of encoding Term
according to the Erlang external term format.
This can be used for a variety of purposes, for example writing a term to a file
in an efficient way, or sending an Erlang term to some type of communications
channel not supported by distributed Erlang.
See also binary_to_term/1.
Types:
Term = term()
Option = compressed | {compressed,Level} | {minor_version,Version}
Returns a binary data object which is the result of encoding Term
according to the Erlang external term format.
If the option compressed is provided, the external term format will be
compressed. The compressed format is automatically recognized by
binary_to_term/1 in R7B and later.
It is also possible to specify a compression level by giving the option
{compressed,Level}, where Level is an integer from 0 through 9.
0 means that no compression will be done (it is the same as not giving
any compressed option); 1 will take the least time but may not
compress as well as the higher levels; 9 will take the most time and
may produce a smaller result. Note the "mays" in the preceding
sentence; depending on the input term, level 9 compression may or may not
produce a smaller result than level 1 compression.
Currently, compressed gives the same result as {compressed,6}.
The option {minor_version,Version} can be use to control some details of
the encoding. This option was introduced in R11B-4. Currently, the allowed
values for Version are 0 and 1.
{minor_version,1} forces any floats in the term to be encoded in a more
space-efficient and exact way (namely in the 64-bit IEEE format, rather than
converted to a textual representation). binary_to_term/1 in R11B-4 and
later is able decode the new representation.
{minor_version,0} is currently the default, meaning that floats will be
encoded using a textual representation; this option is useful if you want to
ensure that releases prior to R11B-4 can decode resulting binary.
See also binary_to_term/1.
Types:
Any = term()
A non-local return from a function. If evaluated within a catch,
catch will return the value Any.
> catch throw({hello, there}). {hello,there}Failure: nocatch if not evaluated within a catch.
Types:
Hour = Minute = Second = integer() >= 0
Returns the current time as {Hour, Minute, Second}.
The time zone and daylight saving time correction depend on the underlying OS.
> time(). {9,42,44}
Types:
List1 = List2 = [term()]
Returns the tail of List1, that is, the list minus the first element.
> tl([geesties, guilies, beasties]). [guilies, beasties]Allowed in guard tests. Failure: badarg if List is the empty list [].
Types:
PidSpec = pid() | existing | new | all
How = boolean()
FlagList = [Flag]
Flag -- see below
Flag -- see below
Turns on (if How == true) or off (if How == false) the trace flags
in FlagList for the process or processes represented by PidSpec.
PidSpec is either a pid for a local process, or one of the following
atoms:
FlagList can contain any number of the following flags (the "message
tags" refers to the list of messages following below):
The effect of combining set_on_first_link with set_on_link is the
same as having set_on_first_link alone. Likewise for
set_on_spawn and set_on_first_spawn.
If the timestamp flag is not given, the tracing process will receive the
trace messages described below. Pid is the pid of the traced process in
which the traced event has occurred. The third element of the tuple is the
message tag.
If the timestamp flag is given, the first element of the tuple will be
trace_ts instead and the timestamp is added last in the tuple.
If the tracing process dies, the flags will be silently removed.
Only one process can trace a particular process. For this reason, attempts to
trace an already traced process will fail.
Returns: A number indicating the number of processes that matched
PidSpec. If PidSpec is a pid, the return value will be 1.
If PidSpec is all or existing the return value will be
the number of processes running, excluding tracer processes. If PidSpec
is new, the return value will be 0.
Failure: If specified arguments are not supported. For example
cpu_timestamp is not supported on all platforms.
- existing:
- All processes currently existing.
- new:
- All processes that will be created in the future.
- all:
- All currently existing processes and all processes that will be created in the future.
- all:
- Set all trace flags except {tracer, Tracer} and cpu_timestamp that are in their nature different than the others.
- send:
- Trace sending of messages.
Message tags: send, send_to_non_existing_process.
- 'receive':
- Trace receiving of messages.
Message tags: 'receive'.
- procs:
- Trace process related events.
Message tags: spawn, exit, register, unregister,
link, unlink, getting_linked,
getting_unlinked.
- call:
- Trace certain function calls. Specify which function calls to trace by calling erlang:trace_pattern/3.
Message tags: call, return_from.
- silent:
- Used in conjunction with the call trace flag. The call, return_from and return_to trace messages are inhibited if this flag is set, but if there are match specs they are executed as normal.
Silent mode is inhibited by executing erlang:trace(_, false, [silent|_]),
or by a match spec executing the {silent, false} function.
The silent trace flag facilitates setting up a trace on many or even all
processes in the system. Then the interesting trace can be activated and
deactivated using the {silent,Bool} match spec function, giving a high
degree of control of which functions with which arguments that triggers the
trace.
Message tags: call, return_from, return_to. Or rather, the
absence of.
- return_to:
- Used in conjunction with the call trace flag. Trace the actual return from a traced function back to its caller. Only works for functions traced with the local option to erlang:trace_pattern/3.
The semantics is that a trace message is sent when a call traced function
actually returns, that is, when a chain of tail recursive calls is ended.
There will be only one trace message sent per chain of tail recursive calls,
why the properties of tail recursiveness for function calls are kept while
tracing with this flag. Using call and return_to trace together
makes it possible to know exactly in which function a process executes at any
time.
To get trace messages containing return values from functions, use the
{return_trace} match_spec action instead.
Message tags: return_to.
- running:
- Trace scheduling of processes.
Message tags: in, and out.
- exiting:
- Trace scheduling of an exiting processes.
Message tags: in_exiting, out_exiting, and
out_exited.
- garbage_collection:
- Trace garbage collections of processes.
Message tags: gc_start, gc_end.
- timestamp:
- Include a time stamp in all trace messages. The time stamp (Ts) is of the same form as returned by erlang:now().
- cpu_timestamp:
- A global trace flag for the Erlang node that makes all trace timestamps be in CPU time, not wallclock. It is only allowed with PidSpec==all. If the host machine operating system does not support high resolution CPU time measurements, trace/3 exits with badarg.
- arity:
- Used in conjunction with the call trace flag. {M, F, Arity} will be specified instead of {M, F, Args} in call trace messages.
- set_on_spawn:
- Makes any process created by a traced process inherit its trace flags, including the set_on_spawn flag.
- set_on_first_spawn:
- Makes the first process created by a traced process inherit its trace flags, excluding the set_on_first_spawn flag.
- set_on_link:
- Makes any process linked by a traced process inherit its trace flags, including the set_on_link flag.
- set_on_first_link:
- Makes the first process linked to by a traced process inherit its trace flags, excluding the set_on_first_link flag.
- {tracer, Tracer}:
- Specify where to send the trace messages. Tracer must be the pid of a local process or the port identifier of a local port. If this flag is not given, trace messages will be sent to the process that called erlang:trace/3.
- {trace, Pid, 'receive', Msg}:
- When Pid receives the message Msg.
- {trace, Pid, send, Msg, To}:
- When Pid sends the message Msg to the process To.
- {trace, Pid, send_to_non_existing_process, Msg, To}:
- When Pid sends the message Msg to the non-existing process To.
- {trace, Pid, call, {M, F, Args}}:
- When Pid calls a traced function. The return values of calls are never supplied, only the call and its arguments.
Note that the trace flag arity can be used to change the contents of this
message, so that Arity is specified instead of Args.
- {trace, Pid, return_to, {M, F, Arity}}:
- When Pid returns to the specified function. This trace message is sent if both the call and the return_to flags are set, and the function is set to be traced on local function calls. The message is only sent when returning from a chain of tail recursive function calls where at least one call generated a call trace message (that is, the functions match specification matched and {message, false} was not an action).
- {trace, Pid, return_from, {M, F, Arity}, ReturnValue}:
- When Pid returns from the specified function. This trace message is sent if the call flag is set, and the function has a match specification with a return_trace or exception_trace action.
- {trace, Pid, exception_from, {M, F, Arity}, {Class, Value}}:
- When Pid exits from the specified function due to an exception. This trace message is sent if the call flag is set, and the function has a match specification with an exception_trace action.
- {trace, Pid, spawn, Pid2, {M, F, Args}}:
- When Pid spawns a new process Pid2 with the specified function call as entry point.
Note that Args is supposed to be the argument list, but may be any term
in the case of an erroneous spawn.
- {trace, Pid, exit, Reason}:
- When Pid exits with reason Reason.
- {trace, Pid, link, Pid2}:
- When Pid links to a process Pid2.
- {trace, Pid, unlink, Pid2}:
- When Pid removes the link from a process Pid2.
- {trace, Pid, getting_linked, Pid2}:
- When Pid gets linked to a process Pid2.
- {trace, Pid, getting_unlinked, Pid2}:
- When Pid gets unlinked from a process Pid2.
- {trace, Pid, register, RegName}:
- When Pid gets the name RegName registered.
- {trace, Pid, unregister, RegName}:
- When Pid gets the name RegName unregistered. Note that this is done automatically when a registered process exits.
- {trace, Pid, in, {M, F, Arity} | 0}:
- When Pid is scheduled to run. The process will run in function {M, F, Arity}. On some rare occasions the current function cannot be determined, then the last element Arity is 0.
- {trace, Pid, out, {M, F, Arity} | 0}:
- When Pid is scheduled out. The process was running in function {M, F, Arity}. On some rare occasions the current function cannot be determined, then the last element Arity is 0.
- {trace, Pid, gc_start, Info}:
- Sent when garbage collection is about to be started. Info is a list of two-element tuples, where the first element is a key, and the second is the value. You should not depend on the tuples have any defined order. Currently, the following keys are defined:
- heap_size:
- The size of the used part of the heap.
- heap_block_size:
- The size of the memory block used for storing the heap and the stack.
- old_heap_size:
- The size of the used part of the old heap.
- old_heap_block_size:
- The size of the memory block used for storing the old heap.
- stack_size:
- The actual size of the stack.
- recent_size:
- The size of the data that survived the previous garbage collection.
- mbuf_size:
- The combined size of message buffers associated with the process.
- bin_vheap_size:
- The total size of unique off-heap binaries referenced from the process heap.
- bin_vheap_block_size:
- The total size of binaries, in words, allowed in the virtual heap in the process before doing a garbage collection.
- bin_old_vheap_size:
- The total size of unique off-heap binaries referenced from the process old heap.
- bin_vheap_block_size:
- The total size of binaries, in words, allowed in the virtual old heap in the process before doing a garbage collection.
All sizes are in words.
- {trace, Pid, gc_end, Info}:
- Sent when garbage collection is finished. Info contains the same kind of list as in the gc_start message, but the sizes reflect the new sizes after garbage collection.
Types:
Tracee = pid() | all
Ref = reference()
The delivery of trace messages is dislocated on the time-line compared to other
events in the system. If you know that the Tracee has passed some
specific point in its execution, and you want to know when at least all trace
messages corresponding to events up to this point have reached the tracer you
can use erlang:trace_delivered(Tracee). A {trace_delivered, Tracee,
Ref} message is sent to the caller of
erlang:trace_delivered(Tracee) when it is guaranteed that all trace
messages have been delivered to the tracer up to the point that the
Tracee had reached at the time of the call to
erlang:trace_delivered(Tracee).
Note that the trace_delivered message does not imply that trace
messages have been delivered; instead, it implies that all trace messages that
should be delivered have been delivered. It is not an error if
Tracee isn't, and hasn't been traced by someone, but if this is the
case, no trace messages will have been delivered when the
trace_delivered message arrives.
Note that Tracee has to refer to a process currently, or previously
existing on the same node as the caller of
erlang:trace_delivered(Tracee) resides on. The special Tracee
atom all denotes all processes that currently are traced in the node.
An example: Process A is tracee, port B is tracer, and process
C is the port owner of B. C wants to close B when
A exits. C can ensure that the trace isn't truncated by calling
erlang:trace_delivered(A) when A exits and wait for the
{trace_delivered, A, Ref} message before closing B.
Failure: badarg if Tracee does not refer to a process (dead or
alive) on the same node as the caller of erlang:trace_delivered(Tracee)
resides on.
Types:
PidOrFunc = pid() | new | {Module, Function,
Arity} | on_load
Module = Function = atom()
Arity = arity()
Item, Res -- see below
Module = Function = atom()
Arity = arity()
Returns trace information about a process or function.
To get information about a process, PidOrFunc should be a pid or the atom
new. The atom new means that the default trace state for
processes to be created will be returned. Item must have one of the
following values:
To get information about a function, PidOrFunc should be a three-element
tuple: {Module, Function, Arity} or the atom on_load. No
wildcards are allowed. Returns undefined if the function does not exist
or false if the function is not traced at all. Item must have
one of the following values:
The actual return value will be {Item, Value}, where Value is the
requested information as described above. If a pid for a dead process was
given, or the name of a non-existing function, Value will be
undefined.
If PidOrFunc is the on_load, the information returned refers to
the default value for code that will be loaded.
- flags:
- Return a list of atoms indicating what kind of traces is enabled for the process. The list will be empty if no traces are enabled, and one or more of the followings atoms if traces are enabled: send, 'receive', set_on_spawn, call, return_to, procs, set_on_first_spawn, set_on_link, running, garbage_collection, timestamp, and arity. The order is arbitrary.
- tracer:
- Return the identifier for process or port tracing this process. If this process is not being traced, the return value will be [].
- traced:
- Return global if this function is traced on global function calls, local if this function is traced on local function calls (i.e local and global function calls), and false if neither local nor global function calls are traced.
- match_spec:
- Return the match specification for this function, if it has one. If the function is locally or globally traced but has no match specification defined, the returned value is [].
- meta:
- Return the meta trace tracer process or port for this function, if it has one. If the function is not meta traced the returned value is false, and if the function is meta traced but has once detected that the tracer proc is invalid, the returned value is [].
- meta_match_spec:
- Return the meta trace match specification for this function, if it has one. If the function is meta traced but has no match specification defined, the returned value is [].
- call_count:
- Return the call count value for this function or true for the pseudo function on_load if call count tracing is active. Return false otherwise. See also erlang:trace_pattern/3.
- call_time:
- Return the call time values for this function or true for the pseudo function on_load if call time tracing is active. Returns false otherwise. The call time values returned, [{Pid, Count, S, Us}], is a list of each process that has executed the function and its specific counters. See also erlang:trace_pattern/3.
- all:
- Return a list containing the {Item, Value} tuples for all other items, or return false if no tracing is active for this function.
The same as erlang:trace_pattern(MFA, MatchSpec, []), retained for
backward compatibility.
Types:
MFA, MatchSpec, FlagList -- see below
This BIF is used to enable or disable call tracing for exported functions. It
must be combined with erlang:trace/3 to set the call trace flag
for one or more processes.
Conceptually, call tracing works like this: Inside the Erlang virtual machine
there is a set of processes to be traced and a set of functions to be traced.
Tracing will be enabled on the intersection of the set. That is, if a process
included in the traced process set calls a function included in the traced
function set, the trace action will be taken. Otherwise, nothing will happen.
Use erlang:trace/3 to add or remove one or more processes to the set of
traced processes. Use erlang:trace_pattern/2 to add or remove exported
functions to the set of traced functions.
The erlang:trace_pattern/3 BIF can also add match specifications to an
exported function. A match specification comprises a pattern that the
arguments to the function must match, a guard expression which must evaluate
to true and an action to be performed. The default action is to send a
trace message. If the pattern does not match or the guard fails, the action
will not be executed.
The MFA argument should be a tuple like {Module, Function, Arity}
or the atom on_load (described below). It can be the module, function,
and arity for an exported function (or a BIF in any module). The '_'
atom can be used to mean any of that kind. Wildcards can be used in any of the
following ways:
Other combinations, such as {Module,'_',Arity}, are not allowed. Local
functions will match wildcards only if the local option is in the
FlagList.
If the MFA argument is the atom on_load, the match specification
and flag list will be used on all modules that are newly loaded.
The MatchSpec argument can take any of the following forms:
The FlagList parameter is a list of options. The following options are
allowed:
The global and local options are mutually exclusive and
global is the default (if no options are specified). The
call_count and meta options perform a kind of local tracing, and
can also not be combined with global. A function can be either globally
or locally traced. If global tracing is specified for a specified set of
functions; local, meta, call time and call count tracing for the matching set
of local functions will be disabled, and vice versa.
When disabling trace, the option must match the type of trace that is set on the
function, so that local tracing must be disabled with the local option
and global tracing with the global option (or no option at all), and so
forth.
There is no way to directly change part of a match specification list. If a
function has a match specification, you can replace it with a completely new
one. If you need to change an existing match specification, use the
erlang:trace_info/2 BIF to retrieve the existing match specification.
Returns the number of exported functions that matched the MFA argument.
This will be zero if none matched at all.
- {Module,Function,'_'}:
- All exported functions of any arity named Function in module Module.
- {Module,'_','_'}:
- All exported functions in module Module.
- {'_','_','_'}:
- All exported functions in all loaded modules.
- false:
- Disable tracing for the matching function(s). Any match specification will be removed.
- true:
- Enable tracing for the matching function(s).
- MatchSpecList:
- A list of match specifications. An empty list is equivalent to true. See the ERTS User's Guide for a description of match specifications.
- restart:
- For the FlagList option call_count and call_time: restart the existing counters. The behaviour is undefined for other FlagList options.
- pause:
- For the FlagList option call_count and call_time: pause the existing counters. The behaviour is undefined for other FlagList options.
- global:
- Turn on or off call tracing for global function calls (that is, calls specifying the module explicitly). Only exported functions will match and only global calls will generate trace messages. This is the default.
- local:
- Turn on or off call tracing for all types of function calls. Trace messages will be sent whenever any of the specified functions are called, regardless of how they are called. If the return_to flag is set for the process, a return_to message will also be sent when this function returns to its caller.
- meta | {meta, Pid}:
- Turn on or off meta tracing for all types of function calls. Trace messages will be sent to the tracer process or port Pid whenever any of the specified functions are called, regardless of how they are called. If no Pid is specified, self() is used as a default tracer process.
Meta tracing traces all processes and does not care about the process trace
flags set by trace/3, the trace flags are instead fixed to [call,
timestamp].
The match spec function {return_trace} works with meta trace and send its
trace message to the same tracer process.
- call_count:
- Starts (MatchSpec == true) or stops (MatchSpec == false) call count tracing for all types of function calls. For every function a counter is incremented when the function is called, in any process. No process trace flags need to be activated.
If call count tracing is started while already running, the count is restarted
from zero. Running counters can be paused with MatchSpec == pause.
Paused and running counters can be restarted from zero with MatchSpec ==
restart.
The counter value can be read with erlang:trace_info/2.
- call_time:
- Starts (MatchSpec == true) or stops (MatchSpec == false) call time tracing for all types of function calls. For every function a counter is incremented when the function is called. Time spent in the function is accumulated in two other counters, seconds and micro-seconds. The counters are stored for each call traced process.
If call time tracing is started while already running, the count and time is
restarted from zero. Running counters can be paused with MatchSpec ==
pause. Paused and running counters can be restarted from zero with
MatchSpec == restart.
The counter value can be read with erlang:trace_info/2.
Types:
Number = number()
Returns an integer by the truncating Number.
> trunc(5.5). 5Allowed in guard tests.
Types:
Tuple = tuple()
Returns an integer which is the number of elements in Tuple.
> tuple_size({morni, mulle, bwange}). 3Allowed in guard tests.
Types:
Tuple = tuple()
Returns a list which corresponds to Tuple. Tuple may contain any
Erlang terms.
> tuple_to_list({share, {'Ericsson_B', 163}}). [share,{'Ericsson_B',163}]
Types:
DateTime = calendar:datetime()
Returns the current date and time according to Universal Time Coordinated (UTC),
also called GMT, in the form {{Year, Month, Day}, {Hour, Minute,
Second}} if supported by the underlying operating system. If not,
erlang:universaltime() is equivalent to erlang:localtime().
> erlang:universaltime(). {{1996,11,6},{14,18,43}}
Types:
Date1 = Date2 = calendar:date()
Time1 = Time2 = calendar:time()
Converts Universal Time Coordinated (UTC) date and time to local date and time,
if this is supported by the underlying OS. Otherwise, no conversion is done,
and {Date1, Time1} is returned.
> erlang:universaltime_to_localtime({{1996,11,6},{14,18,43}}). {{1996,11,7},{15,18,43}}Failure: badarg if Date1 or Time1 do not denote a valid date or time.
Types:
Id = pid() | port()
Removes the link, if there is one, between the calling process and the process
or port referred to by Id.
Returns true and does not fail, even if there is no link to Id, or
if Id does not exist.
Once unlink(Id) has returned it is guaranteed that the link between the
caller and the entity referred to by Id has no effect on the caller in
the future (unless the link is setup again). If caller is trapping exits, an
{'EXIT', Id, _} message due to the link might have been placed in the
caller's message queue prior to the call, though. Note, the {'EXIT', Id,
_} message can be the result of the link, but can also be the result of
Id calling exit/2. Therefore, it may be appropriate to
cleanup the message queue when trapping exits after the call to
unlink(Id), as follow:
unlink(Id), receive {'EXIT', Id, _} -> true after 0 -> true end
Note:
Prior to OTP release R11B (erts version 5.5) unlink/1 behaved completely
asynchronous, i.e., the link was active until the "unlink signal"
reached the linked entity. This had one undesirable effect, though. You could
never know when you were guaranteed not to be effected by the link.
Current behavior can be viewed as two combined operations: asynchronously send
an "unlink signal" to the linked entity and ignore any future
results of the link.
Types:
RegName = atom()
Removes the registered name RegName, associated with a pid or a port
identifier.
> unregister(db). trueUsers are advised not to unregister system processes. Failure: badarg if RegName is not a registered name.
Returns the pid or port identifier with the registered name RegName.
Returns undefined if the name is not registered.
> whereis(db). <0.43.0>
erlang:yield() -> true
Voluntarily let other processes (if any) get a chance to execute. Using
erlang:yield() is similar to receive after 1 -> ok end,
except that yield() is faster.
Warning:
There is seldom or never any need to use this BIF, especially in the
SMP-emulator as other processes will have a chance to run in another scheduler
thread anyway. Using this BIF without a thorough grasp of how the scheduler
works may cause performance degradation.
erts 5.9.1 | Ericsson AB |