The Erlang BIFs.
By convention, most Built-In Functions (BIFs) are included
in this module. Some of the BIFs are viewed more
or less as part of the Erlang programming language and are
auto-imported. Thus, it is not necessary to specify the
module name. For example, the calls atom_to_list(erlang)
and erlang:atom_to_list(erlang)
are identical.
Auto-imported BIFs are listed without module prefix. BIFs listed with module prefix are not auto-imported.
BIFs can fail for various reasons. All BIFs fail with
reason badarg
if they are called with arguments of an
incorrect type. The other reasons are described in the
description of each individual BIF.
Some BIFs can be used in guard tests and are marked with "Allowed in guard tests".
Types
ext_binary() = binary()
A binary data object, structured according to the Erlang external term format.
iovec() = [binary()]
A list of binaries. This datatype is useful to use
together with
enif_inspect_iovec
.
message_queue_data() = off_heap | on_heap
timestamp() =
{MegaSecs :: integer() >= 0,
Secs :: integer() >= 0,
MicroSecs :: integer() >= 0}
See
erlang:timestamp/0
.
time_unit() =
integer() >= 1 |
second | millisecond | microsecond | nanosecond | native |
perf_counter |
deprecated_time_unit()
Supported time unit representations:
PartsPerSecond :: integer() >= 1
Time unit expressed in parts per second. That is,
the time unit equals 1/PartsPerSecond
second.
second
Symbolic representation of the time unit
represented by the integer 1
.
millisecond
Symbolic representation of the time unit
represented by the integer 1000
.
microsecond
Symbolic representation of the time unit
represented by the integer 1000000
.
nanosecond
Symbolic representation of the time unit
represented by the integer 1000000000
.
native
Symbolic representation of the native time unit used by the Erlang runtime system.
The native
time unit is determined at
runtime system start, and remains the same until
the runtime system terminates. If a runtime system
is stopped and then started again (even on the same
machine), the native
time unit of the new
runtime system instance can differ from the
native
time unit of the old runtime system
instance.
One can get an approximation of the native
time unit by calling
erlang:convert_time_unit(1, second, native)
.
The result equals the number
of whole native
time units per second. If
the number of native
time units per second does not
add up to a whole number, the result is rounded downwards.
Note!
The value of the native
time unit gives
you more or less no information about the
quality of time values. It sets a limit for the
resolution and for the
precision of time values,
but it gives no information about the
accuracy of time values. The resolution of
the native
time unit and the resolution of time
values can differ significantly.
perf_counter
Symbolic representation of the performance counter time unit used by the Erlang runtime system.
The perf_counter
time unit behaves much in the same way
as the native
time unit. That is, it can differ between
runtime restarts. To get values of this type, call
os:perf_counter/0
.
deprecated_time_unit()
Deprecated symbolic representations kept for backwards-compatibility.
The time_unit/0
type can be extended.
To convert time values between time units, use
erlang:convert_time_unit/3
.
deprecated_time_unit() =
seconds | milli_seconds | micro_seconds | nano_seconds
The time_unit()
type also consist of the following deprecated symbolic
time units:
seconds
Same as second
.
milli_seconds
Same as millisecond
.
micro_seconds
Same as microsecond
.
nano_seconds
Same as nanosecond
.
dist_handle()
An opaque handle identifing a distribution channel.
nif_resource()
An opaque handle identifing a NIF resource object .
Functions
Returns an integer or float that is the arithmetical
absolute value of
or
, for example:
>abs(-3.33).
3.33 >abs(-3).
3
Allowed in guard tests.
erlang:adler32(Data) -> integer() >= 0
Data = iodata()
Computes and returns the adler32 checksum for
.
erlang:adler32(OldAdler, Data) -> integer() >= 0
OldAdler = integer() >= 0
Data = iodata()
Continues computing the adler32 checksum by combining
the previous checksum,
, with
the checksum of
.
The following code:
X = erlang:adler32(Data1),
Y = erlang:adler32(X,Data2).
assigns the same value to Y
as this:
Y = erlang:adler32([Data1,Data2]).
erlang:adler32_combine(FirstAdler, SecondAdler, SecondSize) ->
integer() >= 0
FirstAdler = SecondAdler = SecondSize = integer() >= 0
Combines two previously computed adler32 checksums. This computation requires the size of the data object for the second checksum to be known.
The following code:
Y = erlang:adler32(Data1),
Z = erlang:adler32(Y,Data2).
assigns the same value to Z
as this:
X = erlang:adler32(Data1),
Y = erlang:adler32(Data2),
Z = erlang:adler32_combine(X,Y,iolist_size(Data2)).
erlang:append_element(Tuple1, Term) -> Tuple2
Tuple1 = Tuple2 = tuple()
Term = term()
Returns a new tuple that has one element more than
, and contains the elements in
followed by
as the last element.
Semantically equivalent to
list_to_tuple(tuple_to_list(
, but much faster. Example:
> erlang:append_element({one, two}, three).
{one,two,three}
apply(Fun, Args) -> term()
Fun = function()
Args = [term()]
Calls a fun, passing the elements in
as arguments.
If the number of elements in the arguments are known at
compile time, the call is better written as
.
Warning!
Earlier,
could also be specified as
{Module, Function}
, equivalent to
apply(Module, Function, Args)
. This use is
deprecated and will stop working in a future release.
apply(Module, Function, Args) -> term()
Module = module()
Function = atom()
Args = [term()]
Returns the result of applying Function
in
to
.
The applied function must
be exported from Module
. The arity of the function is
the length of Args
. Example:
>apply(lists, reverse, [[a, b, c]]).
[c,b,a] >apply(erlang, atom_to_list, ['Erlang']).
"Erlang"
If the number of arguments are known at compile time,
the call is better written as
.
Failure:
error_handler:undefined_function/3
is called
if the applied function is not exported. The error handler
can be redefined (see
process_flag/2
).
If error_handler
is undefined, or if the user has
redefined the default error_handler
so the replacement
module is undefined, an error with reason undef
is generated.
atom_to_binary(Atom, Encoding) -> binary()
Atom = atom()
Encoding = latin1 | unicode | utf8
Returns a binary corresponding to the text
representation of
.
If
is latin1
, one byte exists for each character
in the text representation. If
is
utf8
or
unicode
, the characters are encoded using UTF-8 where
characters may require multiple bytes.
Note!
As from Erlang/OTP 20, atoms can contain any Unicode character
and atom_to_binary(
may fail if the
text representation for
contains a Unicode
character > 255.
Example:
> atom_to_binary('Erlang', latin1).
<<"Erlang">>
atom_to_list(Atom) -> string()
Atom = atom()
Returns a string corresponding to the text
representation of
, for example:
> atom_to_list('Erlang').
"Erlang"
binary_part(Subject, PosLen) -> binary()
Subject = binary()
PosLen = {Start :: integer() >= 0, Length :: integer()}
Extracts the part of the binary described by
.
Negative length can be used to extract bytes at the end of a binary, for example:
1> Bin = <<1,2,3,4,5,6,7,8,9,10>>.
2> binary_part(Bin,{byte_size(Bin), -5}).
<<6,7,8,9,10>>
Failure: badarg
if
in any way
references outside the binary.
is zero-based, that is:
1> Bin = <<1,2,3>>
2> binary_part(Bin,{0,2}).
<<1,2>>
For details about the
semantics, see
binary(3)
.
Allowed in guard tests.
binary_part(Subject, Start, Length) -> binary()
Subject = binary()
Start = integer() >= 0
Length = integer()
The same as binary_part(
.
Allowed in guard tests.
binary_to_atom(Binary, Encoding) -> atom()
Binary = binary()
Encoding = latin1 | unicode | utf8
Returns the atom whose text representation is
.
If
is latin1
, no
translation of bytes in the binary is done.
If
is utf8
or unicode
, the binary must contain
valid UTF-8 sequences.
Note!
As from Erlang/OTP 20, binary_to_atom(
is capable of encoding any Unicode character. Earlier versions would
fail if the binary contained Unicode characters > 255.
For more information about Unicode support in atoms, see the
note on UTF-8
encoded atoms
in section "External Term Format" in the User's Guide.
Examples:
>binary_to_atom(<<"Erlang">>, latin1).
'Erlang' >binary_to_atom(<<1024/utf8>>, utf8).
'Ѐ'
binary_to_existing_atom(Binary, Encoding) -> atom()
Binary = binary()
Encoding = latin1 | unicode | utf8
As
binary_to_atom/2
,
but the atom must exist.
Failure: badarg
if the atom does not exist.
Note!
Note that the compiler may optimize away atoms. For
example, the compiler will rewrite
atom_to_list(some_atom)
to "some_atom"
. If
that expression is the only mention of the atom
some_atom
in the containing module, the atom will not
be created when the module is loaded, and a subsequent call
to binary_to_existing_atom(<<"some_atom">>, utf8)
will fail.
binary_to_float(Binary) -> float()
Binary = binary()
Returns the float whose text representation is
, for example:
> binary_to_float(<<"2.2017764e+0">>).
2.2017764
Failure: badarg
if
contains a bad
representation of a float.
binary_to_integer(Binary) -> integer()
Binary = binary()
Returns an integer whose text representation is
, for example:
> binary_to_integer(<<"123">>).
123
Failure: badarg
if
contains a bad
representation of an integer.
binary_to_integer(Binary, Base) -> integer()
Binary = binary()
Base = 2..36
Returns an integer whose text representation in base
is
, for
example:
> binary_to_integer(<<"3FF">>, 16).
1023
Failure: badarg
if
contains a bad
representation of an integer.
binary_to_list(Binary) -> [byte()]
Binary = binary()
Returns a list of integers corresponding to the bytes of
.
binary_to_list(Binary, Start, Stop) -> [byte()]
Binary = binary()
Start = Stop = integer() >= 1
Binary
)
As binary_to_list/1
, but returns a list of integers
corresponding to the bytes from position
to
position
in
.
The positions in the
binary are numbered starting from 1.
Note!
The one-based indexing for binaries used by
this function is deprecated. New code is to use
binary:bin_to_list/3
in STDLIB instead. All functions in module
binary
consistently use zero-based indexing.
binary_to_term(Binary) -> term()
Binary = ext_binary()
Returns an Erlang term that is the result of decoding
binary object
, which must be encoded
according to the
Erlang external term format.
>Bin = term_to_binary(hello).
<<131,100,0,5,104,101,108,108,111>> >hello = binary_to_term(Bin).
hello
Warning!
When decoding binaries from untrusted sources,
consider using binary_to_term/2
to prevent Denial
of Service attacks.
See also
term_to_binary/1
and
binary_to_term/2
.
binary_to_term(Binary, Opts) -> term() | {term(), Used}
Binary = ext_binary()
Opt = safe | used
Opts = [Opt]
Used = integer() >= 1
As binary_to_term/1
, but takes these options:
safe
Use this option when receiving binaries from an untrusted source.
When enabled, it prevents decoding data that can be used to
attack the Erlang system. In the event of receiving unsafe
data, decoding fails with a badarg
error.
This prevents creation of new atoms directly, creation of new atoms indirectly (as they are embedded in certain structures, such as process identifiers, refs, and funs), and creation of new external function references. None of those resources are garbage collected, so unchecked creation of them can exhaust available memory.
>binary_to_term(<<131,100,0,5,"hello">>, [safe]).
** exception error: bad argument >hello.
hello >binary_to_term(<<131,100,0,5,"hello">>, [safe]).
hello
used
Changes the return value to {Term, Used}
where Used
is the number of bytes actually read from Binary
.
>Input = <<131,100,0,5,"hello","world">>.
<<131,100,0,5,104,101,108,108,111,119,111,114,108,100>> >{Term, Used} = binary_to_term(Input, [used]).
{hello, 9} >split_binary(Input, Used).
{<<131,100,0,5,104,101,108,108,111>>, <<"world">>}
Failure: badarg
if safe
is specified and unsafe
data is decoded.
See also
term_to_binary/1
,
binary_to_term/1
, and
list_to_existing_atom/1
.
bit_size(Bitstring) -> integer() >= 0
Bitstring = bitstring()
Returns an integer that is the size in bits of
, for example:
>bit_size(<<433:16,3:3>>).
19 >bit_size(<<1,2,3>>).
24
Allowed in guard tests.
bitstring_to_list(Bitstring) -> [byte() | bitstring()]
Bitstring = bitstring()
Returns a list of integers corresponding to the bytes of
. If the number of bits in the binary
is not divisible by 8, the last element of the list is a bitstring
containing the remaining 1-7 bits.
erlang:bump_reductions(Reductions) -> true
Reductions = integer() >= 1
This implementation-dependent function increments the reduction counter for the calling process. In the Beam emulator, the reduction counter is normally incremented by one for each function and BIF call. A context switch is forced when the counter reaches the maximum number of reductions for a process (2000 reductions in Erlang/OTP R12B).
Warning!
This BIF can be removed in a future version of the Beam machine without prior warning. It is unlikely to be implemented in other Erlang implementations.
byte_size(Bitstring) -> integer() >= 0
Bitstring = bitstring()
Returns an integer that is the number of bytes needed to
contain
. That is, if the number of bits
in
is not divisible by 8, the resulting
number of bytes is rounded up. Examples:
>byte_size(<<433:16,3:3>>).
3 >byte_size(<<1,2,3>>).
3
Allowed in guard tests.
erlang:cancel_timer(TimerRef) -> Result
TimerRef = reference()
Time = integer() >= 0
Result = Time | false
Cancels a timer. The same as calling
erlang:cancel_timer(TimerRef, [])
.
erlang:cancel_timer(TimerRef, Options) -> Result | ok
TimerRef = reference()
Async = Info = boolean()
Option = {async, Async} | {info, Info}
Options = [Option]
Time = integer() >= 0
Result = Time | false
Cancels a timer that has been created by
erlang:start_timer
or
erlang:send_after
.
identifies the timer, and
was returned by the BIF that created the timer.
s:
{async, Async}
Asynchronous request for cancellation. Async
defaults to false
, which causes the
cancellation to be performed synchronously. When
Async
is set to true
, the cancel
operation is performed asynchronously. That is,
cancel_timer()
sends an asynchronous
request for cancellation to the timer service that
manages the timer, and then returns ok
.
{info, Info}
Requests information about the
of the cancellation. Info
defaults to true
,
which means the
is
given. When Info
is set to false
, no
information about the result of the cancellation
is given.
-
When
Async
isfalse
: ifInfo
istrue
, theResult
is returned byerlang:cancel_timer()
. otherwiseok
is returned. -
When
Async
istrue
: ifInfo
istrue
, a message on the form{cancel_timer,
is sent to the caller ofTimerRef ,Result }erlang:cancel_timer()
when the cancellation operation has been performed, otherwise no message is sent.
More
s may be added in the future.
If
is an integer, it represents
the time in milliseconds left until the canceled timer would
have expired.
If
is false
, a
timer corresponding to
could not
be found. This can be either because the timer had expired,
already had been canceled, or because
never corresponded to a timer. Even if the timer had expired,
it does not tell you if the time-out message has
arrived at its destination yet.
Note!
The timer service that manages the timer can be co-located
with another scheduler than the scheduler that the calling
process is executing on. If so, communication
with the timer service takes much longer time than if it
is located locally. If the calling process is in critical
path, and can do other things while waiting for the result
of this operation, or is not interested in the result of
the operation, you want to use option {async, true}
.
If using option {async, false}
, the calling
process blocks until the operation has been performed.
See also
erlang:send_after/4
,
erlang:start_timer/4
, and
erlang:read_timer/2
.
ceil(Number) -> integer()
Number = number()
Returns the smallest integer not less than
.
For example:
> ceil(5.5).
6
Allowed in guard tests.
check_old_code(Module) -> boolean()
Module = module()
Returns true
if
has old code,
otherwise false
.
See also
code(3)
.
check_process_code(Pid, Module) -> CheckResult
Pid = pid()
Module = module()
CheckResult = boolean()
The same as
check_process_code(
.
check_process_code(Pid, Module, OptionList) -> CheckResult | async
Pid = pid()
Module = module()
RequestId = term()
Option = {async, RequestId} | {allow_gc, boolean()}
OptionList = [Option]
CheckResult = boolean() | aborted
Checks if the node local process identified by
executes old code for
.
s:
{allow_gc, boolean()}
Determines if garbage collection is allowed when performing
the operation. If {allow_gc, false}
is passed, and
a garbage collection is needed to determine the
result of the operation, the operation is aborted (see
information on
below).
The default is to allow garbage collection, that is,
{allow_gc, true}
.
{async, RequestId}
The function check_process_code/3
returns
the value async
immediately after the request
has been sent. When the request has been processed, the
process that called this function is passed a
message on the form {check_process_code,
.
If
equals self()
, and
no async
option has been passed, the operation
is performed at once. Otherwise a request for
the operation is sent to the process identified by
, and is handled when
appropriate. If no async
option has been passed,
the caller blocks until
is available and can be returned.
informs about the result of
the request as follows:
true
The process identified by
executes old code for
.
That is, the current call of the process executes old
code for this module, or the process has references
to old code for this module, or the process contains
funs that references old code for this module.
false
The process identified by
does
not execute old code for
.
aborted
The operation was aborted, as the process needed to
be garbage collected to determine the operation result,
and the operation was requested
by passing option {allow_gc, false}
.
Note!
Up until ERTS version 8.*, the check process code operation
checks for all types of references to the old code. That is,
direct references (e.g. return addresses on the process
stack), indirect references (fun
s in process
context), and references to literals in the code.
As of ERTS version 9.0, the check process code operation
only checks for direct references to the code. Indirect
references via fun
s will be ignored. If such
fun
s exist and are used after a purge of the old
code, an exception will be raised upon usage (same as
the case when the fun
is received by the process
after the purge). Literals will be taken care of (copied)
at a later stage. This behavior can as of ERTS version
8.1 be enabled when
building OTP,
and will automatically be enabled if dirty scheduler
support is enabled.
See also
code(3)
.
Failures:
badarg
Pid
is not a node local process
identifier.
badarg
Module
is not an atom.
badarg
OptionList
is an invalid list of options.
erlang:convert_time_unit(Time, FromUnit, ToUnit) -> ConvertedTime
Time = ConvertedTime = integer()
FromUnit = ToUnit = time_unit()
Converts the
value of time unit
to the corresponding
value of time unit
. The result is rounded
using the floor function.
Warning!
You can lose accuracy and precision when converting
between time units. To minimize such loss, collect all
data at native
time unit and do the conversion on the end
result.
erlang:crc32(Data) -> integer() >= 0
Data = iodata()
Computes and returns the crc32 (IEEE 802.3 style) checksum
for
.
erlang:crc32(OldCrc, Data) -> integer() >= 0
OldCrc = integer() >= 0
Data = iodata()
Continues computing the crc32 checksum by combining
the previous checksum,
, with the checksum
of
.
The following code:
X = erlang:crc32(Data1),
Y = erlang:crc32(X,Data2).
assigns the same value to Y
as this:
Y = erlang:crc32([Data1,Data2]).
erlang:crc32_combine(FirstCrc, SecondCrc, SecondSize) ->
integer() >= 0
FirstCrc = SecondCrc = SecondSize = integer() >= 0
Combines two previously computed crc32 checksums. This computation requires the size of the data object for the second checksum to be known.
The following code:
Y = erlang:crc32(Data1),
Z = erlang:crc32(Y,Data2).
assigns the same value to Z
as this:
X = erlang:crc32(Data1),
Y = erlang:crc32(Data2),
Z = erlang:crc32_combine(X,Y,iolist_size(Data2)).
date() -> Date
Date = calendar:date()
Returns the current date as {Year, Month, Day}
.
The time zone and Daylight Saving Time correction depend on the underlying OS. Example:
> date().
{1995,2,19}
erlang:decode_packet(Type, Bin, Options) ->
{ok, Packet, Rest} |
{more, Length} |
{error, Reason}
Type =
raw | 0 | 1 | 2 | 4 | asn1 | cdr | sunrm | fcgi | tpkt |
line | http | http_bin | httph | httph_binBin = binary()
Options = [Opt]
Opt =
{packet_size, integer() >= 0} |
{line_length, integer() >= 0}Packet = binary() | HttpPacket
Rest = binary()
Length = integer() >= 0 | undefined
Reason = term()
HttpPacket =
HttpRequest | HttpResponse | HttpHeader | http_eoh | HttpErrorHttpRequest = {http_request, HttpMethod, HttpUri, HttpVersion}
HttpResponse =
{http_response, HttpVersion, integer(), HttpString}HttpHeader =
{http_header,
integer(),
HttpField,
Reserved :: term(),
Value :: HttpString}HttpError = {http_error, HttpString}
HttpMethod =
'OPTIONS' | 'GET' | 'HEAD' | 'POST' | 'PUT' | 'DELETE' |
'TRACE' | HttpStringHttpUri =
'*' |
{absoluteURI,
http | https,
Host :: HttpString,
Port :: inet:port_number() | undefined,
Path :: HttpString} |
{scheme, Scheme :: HttpString, HttpString} |
{abs_path, HttpString} |
HttpStringHttpVersion =
{Major :: integer() >= 0, Minor :: integer() >= 0}HttpField =
'Cache-Control' | 'Connection' | 'Date' | 'Pragma' |
'Transfer-Encoding' | 'Upgrade' | 'Via' | 'Accept' |
'Accept-Charset' | 'Accept-Encoding' | 'Accept-Language' |
'Authorization' | 'From' | 'Host' | 'If-Modified-Since' |
'If-Match' | 'If-None-Match' | 'If-Range' |
'If-Unmodified-Since' | 'Max-Forwards' |
'Proxy-Authorization' | 'Range' | 'Referer' | 'User-Agent' |
'Age' | 'Location' | 'Proxy-Authenticate' | 'Public' |
'Retry-After' | 'Server' | 'Vary' | 'Warning' |
'Www-Authenticate' | 'Allow' | 'Content-Base' |
'Content-Encoding' | 'Content-Language' | 'Content-Length' |
'Content-Location' | 'Content-Md5' | 'Content-Range' |
'Content-Type' | 'Etag' | 'Expires' | 'Last-Modified' |
'Accept-Ranges' | 'Set-Cookie' | 'Set-Cookie2' |
'X-Forwarded-For' | 'Cookie' | 'Keep-Alive' |
'Proxy-Connection' | HttpStringHttpString = string() | binary()
Decodes the binary
according to the packet
protocol specified by
. Similar to the packet
handling done by sockets with option
{packet,
If an entire packet is contained in
, it is
returned together with the remainder of the binary as
{ok,
.
If
does not contain the entire packet,
{more,
is returned.
is either the
expected total size of the packet, or undefined
if the expected packet size is unknown. decode_packet
can then be called again with more data added.
If the packet does not conform to the protocol format,
{error,
is returned.
Type
s:
raw | 0
No packet handling is done. The entire binary is returned unless it is empty.
1 | 2 | 4
Packets consist of a header specifying the number of bytes in the packet, followed by that number of bytes. The length of the header can be one, two, or four bytes; the order of the bytes is big-endian. The header is stripped off when the packet is returned.
line
A packet is a line-terminated by a delimiter byte,
default is the latin-1 newline character. The delimiter
byte is included in the returned packet unless the line
was truncated according to option line_length
.
asn1 | cdr | sunrm | fcgi | tpkt
The header is not stripped off.
The meanings of the packet types are as follows:
asn1
- ASN.1 BERsunrm
- Sun's RPC encodingcdr
- CORBA (GIOP 1.1)fcgi
- Fast CGItpkt
- TPKT format [RFC1006]http | httph | http_bin | httph_bin
The Hypertext Transfer Protocol. The packets
are returned with the format according to
described earlier.
A packet is either a
request, a response, a header, or an end of header
mark. Invalid lines are returned as
.
Recognized request methods and header fields are returned
as atoms. Others are returned as strings. Strings of
unrecognized header fields are formatted with only
capital letters first and after hyphen characters, for
example, "Sec-Websocket-Key"
.
The protocol type http
is only to be used for
the first line when an
or an
is expected.
The following calls are to use httph
to get
s until
http_eoh
is returned, which marks the end of the
headers and the beginning of any following message body.
The variants http_bin
and httph_bin
return
strings (HttpString
) as binaries instead of lists.
Options:
{packet_size, integer() >= 0}
Sets the maximum allowed size of the packet body. If the packet header indicates that the length of the packet is longer than the maximum allowed length, the packet is considered invalid. Defaults to 0, which means no size limit.
{line_length, integer() >= 0}
For packet type line
, lines longer than
the indicated length are truncated.
Option line_length
also applies to http*
packet types as an alias for option packet_size
if packet_size
itself is not set. This use is
only intended for backward compatibility.
{line_delimiter, 0 =< byte() =< 255}
For packet type line
, sets the delimiting byte.
Default is the latin-1 character $\n
.
Examples:
>erlang:decode_packet(1,<<3,"abcd">>,[]).
{ok,<<"abc">>,<<"d">>} >erlang:decode_packet(1,<<5,"abcd">>,[]).
{more,6}
erlang:delete_element(Index, Tuple1) -> Tuple2
Index = integer() >= 1
Tuple1 = Tuple2 = tuple()
Returns a new tuple with element at
removed from tuple
, for example:
> erlang:delete_element(2, {one, two, three}).
{one,three}
delete_module(Module) -> true | undefined
Module = module()
Makes the current code for
become old
code and deletes all references for this module from the export table.
Returns undefined
if the module does not exist,
otherwise true
.
Warning!
This BIF is intended for the code server (see
code(3)
)
and is not to be used elsewhere.
Failure: badarg
if there already is an old version of
Module
.
demonitor(MonitorRef) -> true
MonitorRef = reference()
If
is a reference that the
calling process obtained by calling
monitor/2
,
this monitoring is turned off. If the monitoring is already
turned off, nothing happens.
Once demonitor(
has returned, it is
guaranteed that no {'DOWN',
message,
because of the monitor, will be placed in the caller message queue
in the future. However, a {'DOWN',
message
can have been placed in the caller message queue before
the call. It is therefore usually advisable
to remove such a 'DOWN'
message from the message queue
after monitoring has been stopped.
demonitor(
can be used instead of demonitor(
if this cleanup is wanted.
Note!
Before Erlang/OTP R11B (ERTS 5.5) demonitor/1
behaved completely asynchronously, that is, the monitor was active
until the "demonitor signal" reached the monitored entity. This
had one undesirable effect. You could never know when
you were guaranteed not to receive a DOWN
message
because of the monitor.
The current behavior can be viewed as two combined operations: asynchronously send a "demonitor signal" to the monitored entity and ignore any future results of the monitor.
Failure: It is an error if
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
is a
remote reference.
demonitor(MonitorRef, OptionList) -> boolean()
MonitorRef = reference()
OptionList = [Option]
Option = flush | info
The returned value is true
unless info
is part
of
.
demonitor(
is equivalent to
demonitor(
.
s:
flush
Removes (one) {_,
message,
if there is one, from the caller message queue after
monitoring has been stopped.
Calling demonitor(
is equivalent to the following, but more efficient:
demonitor(MonitorRef), receive {_, MonitorRef, _, _, _} -> true after 0 -> true end
info
The returned value is one of the following:
true
The monitor was found and removed. In this case,
no 'DOWN'
message corresponding to this
monitor has been delivered and will not be delivered.
false
The monitor was not found and could not be removed.
This probably because someone already has placed a
'DOWN'
message corresponding to this monitor
in the caller message queue.
If option info
is combined with option flush
,
false
is returned if a flush was needed,
otherwise true
.
Note!
More options can be added in a future release.
Failures:
badarg
OptionList
is not a list.
badarg
Option
is an invalid option.
badarg
demonitor/1
.
disconnect_node(Node) -> boolean() | ignored
Node = node()
Forces the disconnection of a node. This appears to
the node
as if the local node has crashed.
This BIF is mainly used in the Erlang network authentication
protocols.
Returns true
if disconnection succeeds,
otherwise false
. If the local node is not alive,
ignored
is returned.
erlang:display(Term) -> true
Term = term()
Prints a text representation of
on the
standard output.
Warning!
This BIF is intended for debugging only.
erlang:dist_ctrl_get_data(DHandle) -> {Size, Data} | Data | none
Size = integer() >= 0
DHandle = dist_handle()
Data = iodata()
Get distribution channel data from the local node that is
to be passed to the remote node. The distribution channel
is identified by
. If no data
is available, the atom none
is returned. One
can request to be informed by a message when more
data is available by calling
erlang:dist_ctrl_get_data_notification(DHandle)
.
The returned value when there are data available depends
on the value of the get_size
option configured on the
distribution channel identified by
.
For more information see the documentation of the get_size
option for the
erlang:dist_ctrl_set_opt/3
function.
Note!
Only the process registered as distribution
controller for the distribution channel identified by
is allowed to call this
function.
This function is used when implementing an alternative
distribution carrier using processes as distribution
controllers.
is retrived
via the callback
f_handshake_complete
.
More information can be found in the documentation of
ERTS
User's Guide ➜ How to implement an Alternative Carrier
for the Erlang Distribution ➜ Distribution Module.
Returns the value of the get_size
option on the distribution channel
identified by
. For more information see the
documentation of the get_size
option for the
erlang:dist_ctrl_set_opt/3
function.
Note!
Only the process registered as distribution
controller for the distribution channel identified by
is allowed to call this
function.
This function is used when implementing an alternative
distribution carrier using processes as distribution
controllers.
is retrived
via the callback
f_handshake_complete
.
More information can be found in the documentation of
ERTS
User's Guide ➜ How to implement an Alternative Carrier
for the Erlang Distribution ➜ Distribution Module.
erlang:dist_ctrl_get_data_notification(DHandle) -> ok
DHandle = dist_handle()
Request notification when more data is available to
fetch using
erlang:dist_ctrl_get_data(DHandle)
for the distribution channel identified by
. When more data is present,
the caller will be sent the message dist_data
.
Once a dist_data
messages has been sent, no
more dist_data
messages will be sent until
the dist_ctrl_get_data_notification/1
function has been called
again.
Note!
Only the process registered as distribution
controller for the distribution channel identified by
is allowed to call this
function.
This function is used when implementing an alternative
distribution carrier using processes as distribution
controllers.
is retrived
via the callback
f_handshake_complete
.
More information can be found in the documentation of
ERTS
User's Guide ➜ How to implement an Alternative Carrier
for the Erlang Distribution ➜ Distribution Module.
erlang:dist_ctrl_input_handler(DHandle, InputHandler) -> ok
DHandle = dist_handle()
InputHandler = pid()
Register an alternate input handler process for the
distribution channel identified by
.
Once this function has been called,
is the only process allowed to call
erlang:dist_ctrl_put_data(DHandle, Data)
with the
identifing this distribution
channel.
Note!
Only the process registered as distribution
controller for the distribution channel identified by
is allowed to call this
function.
This function is used when implementing an alternative
distribution carrier using processes as distribution
controllers.
is retrived
via the callback
f_handshake_complete
.
More information can be found in the documentation of
ERTS
User's Guide ➜ How to implement an Alternative Carrier
for the Erlang Distribution ➜ Distribution Module.
erlang:dist_ctrl_put_data(DHandle, Data) -> ok
DHandle = dist_handle()
Data = iodata()
Deliver distribution channel data from a remote node to the local node.
Note!
Only the process registered as distribution
controller for the distribution channel identified by
is allowed to call this
function unless an alternate input handler process
has been registered using
erlang:dist_ctrl_input_handler(DHandle, InputHandler)
.
If an alternate input handler has been registered, only
the registered input handler process is allowed to call
this function.
This function is used when implementing an alternative
distribution carrier using processes as distribution
controllers.
is retrived
via the callback
f_handshake_complete
.
More information can be found in the documentation of
ERTS
User's Guide ➜ How to implement an Alternative Carrier
for the Erlang Distribution ➜ Distribution Module.
Sets the value of the get_size
option on the distribution channel
identified by
. This option controls the return
value of calls to
erlang:dist_ctrl_get_data(
equals
used
when setting this option.
When the get_size
option is:
false
erlang:dist_ctrl_get_data(DHandle )
will just return Data
to pass over the channel.
This is the default value of the get_size
option.
true
erlang:dist_ctrl_get_data(DHandle )
will return Data
to pass over the channel as well as
the Size
of Data
in bytes. This is returned as
a tuple on the form {Size, Data}
.
All options are set to default when a channel is closed.
Note!
Only the process registered as distribution
controller for the distribution channel identified by
is allowed to call this
function.
This function is used when implementing an alternative
distribution carrier using processes as distribution
controllers.
is retrived
via the callback
f_handshake_complete
.
More information can be found in the documentation of
ERTS
User's Guide ➜ How to implement an Alternative Carrier
for the Erlang Distribution ➜ Distribution Module.
element(N, Tuple) -> term()
N = integer() >= 1
Tuple = tuple()
Returns the
th element (numbering from 1) of
, for example:
> element(2, {a, b, c}).
b
Allowed in guard tests.
erase() -> [{Key, Val}]
Key = Val = term()
Returns the process dictionary and deletes it, for example:
>put(key1, {1, 2, 3}),
put(key2, [a, b, c]),
erase().
[{key1,{1,2,3}},{key2,[a,b,c]}]
erase(Key) -> Val | undefined
Key = Val = term()
Returns the value
associated with
and deletes it from the process dictionary.
Returns undefined
if no value is associated with
. Example:
>put(key1, {merry, lambs, are, playing}),
X = erase(key1),
{X, erase(key1)}.
{{merry,lambs,are,playing},undefined}
error(Reason) -> no_return()
Reason = term()
Stops the execution of the calling process with the reason
, where
is any term. The exit reason is
{
, where Where
is a list of the functions most recently called (the current
function first). As evaluating this function causes
the process to terminate, it has no return value. Example:
> catch error(foobar).
{'EXIT',{foobar,[{shell,apply_fun,3,
[{file,"shell.erl"},{line,906}]},
{erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,677}]},
{erl_eval,expr,5,[{file,"erl_eval.erl"},{line,430}]},
{shell,exprs,7,[{file,"shell.erl"},{line,687}]},
{shell,eval_exprs,7,[{file,"shell.erl"},{line,642}]},
{shell,eval_loop,3,[{file,"shell.erl"},{line,627}]}]}}
error(Reason, Args) -> no_return()
Reason = term()
Args = [term()]
Stops the execution of the calling process with the reason
, where
is any term. The exit reason is
{
, where Where
is a list of the functions most recently called (the current
function first).
is expected to be the
list of arguments for the current function; in Beam it is used
to provide the arguments for the current function in
the term Where
. As evaluating this function causes
the process to terminate, it has no return value.
exit(Reason) -> no_return()
Reason = term()
Stops the execution of the calling process with exit reason
, where
is any term. As
evaluating this function causes the process to terminate, it
has no return value. Example:
>exit(foobar).
** exception exit: foobar >catch exit(foobar).
{'EXIT',foobar}
exit(Pid, Reason) -> true
Pid = pid() | port()
Reason = term()
Sends an exit signal with exit reason
to
the process or port identified by
.
The following behavior applies if
is any term, except normal
or kill
:
If
is not trapping exits,Pid
itself exits with exit reasonPid
.Reason If
is trapping exits, the exit signal is transformed into a messagePid {'EXIT', From,
and delivered to the message queue ofReason }
.Pid From
is the process identifier of the process that sent the exit signal. See alsoprocess_flag/2
.
If
is the atom normal
,
does not exit. If it is trapping exits, the exit signal is
transformed into a message {'EXIT', From, normal}
and delivered to its message queue.
If
is the atom kill
,
that is, if exit(
is called,
an untrappable exit signal is sent to
,
which unconditionally exits with exit reason killed
.
erlang:external_size(Term) -> integer() >= 0
Term = term()
Calculates, without doing the encoding, the maximum byte size for a term encoded in the Erlang external term format. The following condition applies always:
>Size1 = byte_size(term_to_binary(
>Term )),Size2 = erlang:external_size(
>Term ),true = Size1 =< Size2.
true
This is equivalent to a call to:
erlang:external_size(Term , [])
erlang:external_size(Term, Options) -> integer() >= 0
Term = term()
Options = [{minor_version, Version :: integer() >= 0}]
Calculates, without doing the encoding, the maximum byte size for a term encoded in the Erlang external term format. The following condition applies always:
>Size1 = byte_size(term_to_binary(
>Term ,Options )),Size2 = erlang:external_size(
>Term ,Options ),true = Size1 =< Size2.
true
Option {minor_version,
specifies how
floats are encoded. For a detailed description, see
term_to_binary/2
.
float(Number) -> float()
Number = number()
Returns a float by converting
to a float,
for example:
> float(55).
55.0
Allowed in guard tests.
Note!
If used on the top level in a guard, it tests whether the
argument is a floating point number; for clarity, use
is_float/1
instead.
When float/1
is used in an expression in a guard,
such as 'float(A) == 4.0
', it converts a number as
described earlier.
float_to_binary(Float) -> binary()
Float = float()
The same as
float_to_binary(
.
float_to_binary(Float, Options) -> binary()
Float = float()
Options = [Option]
Option =
{decimals, Decimals :: 0..253} |
{scientific, Decimals :: 0..249} |
compact
Returns a binary corresponding to the text
representation of
using fixed decimal
point formatting.
behaves in the same
way as
float_to_list/2
. Examples:
>float_to_binary(7.12, [{decimals, 4}]).
<<"7.1200">> >float_to_binary(7.12, [{decimals, 4}, compact]).
<<"7.12">>
float_to_list(Float) -> string()
Float = float()
The same as
float_to_list(
.
float_to_list(Float, Options) -> string()
Float = float()
Options = [Option]
Option =
{decimals, Decimals :: 0..253} |
{scientific, Decimals :: 0..249} |
compact
Returns a string corresponding to the text representation
of Float
using fixed decimal point formatting.
Available options:
If option
decimals
is specified, the returned value contains at mostDecimals
number of digits past the decimal point. If the number does not fit in the internal static buffer of 256 bytes, the function throwsbadarg
.If option
compact
is specified, the trailing zeros at the end of the list are truncated. This option is only meaningful together with optiondecimals
.If option
scientific
is specified, the float is formatted using scientific notation withDecimals
digits of precision.If
Options
is[]
, the function behaves asfloat_to_list/1
.
Examples:
>float_to_list(7.12, [{decimals, 4}]).
"7.1200" >float_to_list(7.12, [{decimals, 4}, compact]).
"7.12"
floor(Number) -> integer()
Number = number()
Returns the largest integer not greater than
.
For example:
> floor(-10.5).
-11
Allowed in guard tests.
erlang:fun_info(Fun) -> [{Item, Info}]
Fun = function()
Item =
arity | env | index | name | module | new_index | new_uniq |
pid | type | uniqInfo = term()
Returns a list with information about the fun
. Each list element is a tuple. The order
of the tuples is undefined, and more tuples can be added in a
future release.
Warning!
This BIF is mainly intended for debugging, but it can sometimes be useful in library functions that need to verify, for example, the arity of a fun.
Two types of funs have slightly different semantics:
A fun created by
fun M:F/A
is called an external fun. Calling it will always call the functionF
with arityA
in the latest code for moduleM
. Notice that moduleM
does not even need to be loaded when the funfun M:F/A
is created.All other funs are called local. When a local fun is called, the same version of the code that created the fun is called (even if a newer version of the module has been loaded).
The following elements are always present in the list for both local and external funs:
{type, Type}
Type
is local
or external
.
{module, Module}
Module
(an atom) is the module name.
If Fun
is a local fun, Module
is the module
in which the fun is defined.
If Fun
is an external fun, Module
is the
module that the fun refers to.
{name, Name}
Name
(an atom) is a function name.
If Fun
is a local fun, Name
is the name
of the local function that implements the fun.
(This name was generated by the compiler, and is
only of informational use. As it is a local function, it
cannot be called directly.)
If no code is currently loaded for the fun, []
is returned instead of an atom.
If Fun
is an external fun, Name
is the name
of the exported function that the fun refers to.
{arity, Arity}
Arity
is the number of arguments that the fun
is to be called with.
{env, Env}
Env
(a list) is the environment or free variables
for the fun. For external funs, the returned list is
always empty.
The following elements are only present in the list if
Fun
is local:
{pid, Pid}
Pid
is the process identifier of the process
that originally created the fun.
It might point to the init
process if the
Fun
was statically allocated when module was
loaded (this optimisation is performed for local
functions that do not capture the enviornment).
{index, Index}
Index
(an integer) is an index into the module
fun table.
{new_index, Index}
Index
(an integer) is an index into the module
fun table.
{new_uniq, Uniq}
Uniq
(a binary) is a unique value for this fun. It
is calculated from the compiled code for the entire module.
{uniq, Uniq}
Uniq
(an integer) is a unique value for this fun.
As from Erlang/OTP R15, this integer is calculated from the
compiled code for the entire module. Before Erlang/OTP R15, this
integer was based on only the body of the fun.
erlang:fun_info(Fun, Item) -> {Item, Info}
Fun = function()
Item = fun_info_item()
Info = term()
fun_info_item() =
arity | env | index | name | module | new_index | new_uniq |
pid | type | uniq
Returns information about
as specified by
, in the form
{
.
For any fun,
can be any of the atoms
module
, name
, arity
, env
, or
type
.
For a local fun,
can also be any of the
atoms index
, new_index
, new_uniq
,
uniq
, and pid
. For an external fun, the value
of any of these items is always the atom undefined
.
See
erlang:fun_info/1
.
erlang:fun_to_list(Fun) -> string()
Fun = function()
Returns a string corresponding to the text
representation of
.
erlang:function_exported(Module, Function, Arity) -> boolean()
Module = module()
Function = atom()
Arity = arity()
Returns true
if the module
is
loaded and contains an exported function
,
or if there is a BIF (a built-in function implemented in C)
with the specified name, otherwise returns false
.
Note!
This function used to return false
for BIFs
before Erlang/OTP 18.0.
garbage_collect() -> true
Forces an immediate garbage collection of the executing process. The function is not to be used unless it has been noticed (or there are good reasons to suspect) that the spontaneous garbage collection will occur too late or not at all.
Warning!
Improper use can seriously degrade system performance.
garbage_collect(Pid) -> GCResult
Pid = pid()
GCResult = boolean()
The same as
garbage_collect(
.
garbage_collect(Pid, OptionList) -> GCResult | async
Pid = pid()
RequestId = term()
Option = {async, RequestId} | {type, major | minor}
OptionList = [Option]
GCResult = boolean()
Garbage collects the node local process identified by
.
:
{async, RequestId}
garbage_collect/2
returns
the value async
immediately after the request
has been sent. When the request has been processed, the
process that called this function is passed a message on
the form {garbage_collect,
RequestId , GCResult }
.
{type, 'major' | 'minor'}
'major'
, which would trigger a fullsweep GC.
The option 'minor'
is considered a hint and may lead to
either minor or major GC run.If
equals self()
, and
no async
option has been passed, the garbage
collection is performed at once, that is, the same as calling
garbage_collect/0
.
Otherwise a request for garbage collection
is sent to the process identified by
,
and will be handled when appropriate. If no async
option has been passed, the caller blocks until
is available and can be returned.
informs about the result of
the garbage collection request as follows:
true
Pid
has
been garbage collected.
false
Pid
terminated before the request could be satisfied.
Notice that the same caveats apply as for
garbage_collect/0
.
Failures:
badarg
Pid
is not a node local process identifier.
badarg
OptionList
is an invalid list of options.
get() -> [{Key, Val}]
Key = Val = term()
Returns the process dictionary as a list of
{
tuples, for example:
>put(key1, merry),
put(key2, lambs),
put(key3, {are, playing}),
get().
[{key1,merry},{key2,lambs},{key3,{are,playing}}]
get(Key) -> Val | undefined
Key = Val = term()
Returns the value
associated with
in the process dictionary, or undefined
if
does not exist. Example:
>put(key1, merry),
put(key2, lambs),
put({any, [valid, term]}, {are, playing}),
get({any, [valid, term]}).
{are,playing}
erlang:get_cookie() -> Cookie | nocookie
Cookie = atom()
Returns the magic cookie of the local node if the node is
alive, otherwise the atom nocookie
.
get_keys() -> [Key]
Key = term()
Returns a list of all keys present in the process dictionary, for example:
>put(dog, {animal,1}),
put(cow, {animal,2}),
put(lamb, {animal,3}),
get_keys().
[dog,cow,lamb]
get_keys(Val) -> [Key]
Val = Key = term()
Returns a list of keys that are associated with the value
in the process dictionary, for example:
>put(mary, {1, 2}),
put(had, {1, 2}),
put(a, {1, 2}),
put(little, {1, 2}),
put(dog, {1, 3}),
put(lamb, {1, 2}),
get_keys({1, 2}).
[mary,had,a,little,lamb]
erlang:get_stacktrace() -> [stack_item()]
stack_item() =
{Module :: module(),
Function :: atom(),
Arity :: arity() | (Args :: [term()]),
Location ::
[{file, Filename :: string()} |
{line, Line :: integer() >= 1}]}
Warning!
erlang:get_stacktrace/0
is deprecated and will stop working
in a future release.
Instead of using erlang:get_stacktrace/0
to retrieve
the call stack back-trace, use the following syntax:
try Expr catch Class:Reason:Stacktrace -> {Class,Reason,Stacktrace} end
erlang:get_stacktrace/0
retrieves the call stack back-trace
(stacktrace) for an exception that has just been
caught in the calling process as a list of
{
tuples. Field
in the first tuple can
be the argument list of that function call instead of an arity
integer, depending on the exception.
If there has not been any exceptions in a process, the
stacktrace is []
. After a code change for the process,
the stacktrace can also be reset to []
.
The stacktrace is the same data as operator catch
returns, for example:
{'EXIT',{badarg,Stacktrace}} = catch abs(x)
is a (possibly empty) list
of two-tuples that
can indicate the location in the source code of the function.
The first element is an atom describing the type of
information in the second element. The following
items can occur:
file
line
Warning!
Developers should rely on stacktrace entries only for debugging purposes.
The VM performs tail call optimization, which does not add new entries to the stacktrace, and also limits stacktraces to a certain depth. Furthermore, compiler options, optimizations and future changes may add or remove stacktrace entries, causing any code that expects the stacktrace to be in a certain order or contain specific items to fail.
The only exception to this rule is error:undef
which
guarantees to include the
group_leader() -> pid()
Returns the process identifier of the group leader for the process evaluating the function.
Every process is a member of some process group and all
groups have a group leader. All I/O from the group
is channeled to the group leader. When a new process is
spawned, it gets the same group leader as the spawning
process. Initially, at system startup, init
is both
its own group leader and the group leader of all processes.
group_leader(GroupLeader, Pid) -> true
GroupLeader = Pid = pid()
Sets the group leader of
to
.
Typically, this is used when a process started from a
certain shell is to have another group leader than
init
.
The group leader should be rarely changed in applications with a supervision tree, because OTP assumes the group leader of their processes is their application master.
See also
group_leader/0
and OTP
design principles related to starting and stopping
applications.
halt() -> no_return()
The same as
halt(0, [])
. Example:
> halt().
os_prompt%
halt(Status) -> no_return()
Status = integer() >= 0 | abort | string()
The same as
halt(
. Example:
>halt(17).
os_prompt%echo $?
17 os_prompt%
halt(Status, Options) -> no_return()
Status = integer() >= 0 | abort | string()
Options = [Option]
Option = {flush, boolean()}
must be a non-negative integer, a string,
or the atom abort
.
Halts the Erlang runtime system. Has no return value.
Depending on
, the following occurs:
Status
as status code to the calling environment (OS).
Note!
On many platforms, the OS supports only status codes 0-255. A too large status code is truncated by clearing the high bits.
Status
as slogan. Then the runtime system exits with status code 1
.
The string will be truncated if longer than 200 characters.
Note!
Before ERTS 9.1 (OTP-20.1) only code points in the range 0-255 was accepted in the string. Now any unicode string is valid.
abort
For integer
, the Erlang runtime system
closes all ports and allows async threads to finish their
operations before exiting. To exit without such flushing, use
as {flush,false}
.
For statuses string()
and abort
, option
flush
is ignored and flushing is not done.
hd(List) -> term()
List = [term(), ...]
Returns the head of
, that is,
the first element, for example:
> hd([1,2,3,4,5]).
1
Allowed in guard tests.
Failure: badarg
if
is the empty
list []
.
erlang:hibernate(Module, Function, Args) -> no_return()
Module = module()
Function = atom()
Args = [term()]
Puts the calling process into a wait state where its memory allocation has been reduced as much as possible. This is useful if the process does not expect to receive any messages soon.
The process is awaken when a message is sent to it, and control
resumes in
with
the arguments specified by
with the call
stack emptied, meaning that the process terminates when that
function returns. Thus erlang:hibernate/3
never
returns to its caller.
If the process has any message in its message queue, the process is awakened immediately in the same way as described earlier.
In more technical terms, erlang:hibernate/3
discards the call stack for the process,
and then garbage collects the process. After this,
all live data is in one continuous heap. The heap
is then shrunken to the exact same size as the live data
that it holds (even if that size is less than the minimum
heap size for the process).
If the size of the live data in the process is less than the minimum heap size, the first garbage collection occurring after the process is awakened ensures that the heap size is changed to a size not smaller than the minimum heap size.
Notice that emptying the call stack means that any surrounding
catch
is removed and must be re-inserted after
hibernation. One effect of this is that processes started
using proc_lib
(also indirectly, such as
gen_server
processes), are to use
proc_lib:hibernate/3
instead, to ensure that the exception handler continues to work
when the process wakes up.
erlang:insert_element(Index, Tuple1, Term) -> Tuple2
Index = integer() >= 1
Tuple1 = Tuple2 = tuple()
Term = term()
Returns a new tuple with element
inserted at position
in tuple
.
All elements from position
and upwards are
pushed one step higher in the new tuple
.
Example:
> erlang:insert_element(2, {one, two, three}, new).
{one,new,two,three}
integer_to_binary(Integer) -> binary()
Integer = integer()
Returns a binary corresponding to the text
representation of
, for example:
> integer_to_binary(77).
<<"77">>
integer_to_binary(Integer, Base) -> binary()
Integer = integer()
Base = 2..36
Returns a binary corresponding to the text
representation of
in base
, for example:
> integer_to_binary(1023, 16).
<<"3FF">>
integer_to_list(Integer) -> string()
Integer = integer()
Returns a string corresponding to the text
representation of
, for example:
> integer_to_list(77).
"77"
integer_to_list(Integer, Base) -> string()
Integer = integer()
Base = 2..36
Returns a string corresponding to the text
representation of
in base
, for example:
> integer_to_list(1023, 16).
"3FF"
iolist_size(Item) -> integer() >= 0
Item = iolist() | binary()
Returns an integer, that is the size in bytes,
of the binary that would be the result of
iolist_to_binary(
, for example:
> iolist_size([1,2|<<3,4>>]).
4
iolist_to_binary(IoListOrBinary) -> binary()
IoListOrBinary = iolist() | binary()
Returns a binary that is made from the integers and
binaries in
, for example:
>Bin1 = <<1,2,3>>.
<<1,2,3>> >Bin2 = <<4,5>>.
<<4,5>> >Bin3 = <<6>>.
<<6>> >iolist_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
<<1,2,3,1,2,3,4,5,4,6>>
erlang:iolist_to_iovec(IoListOrBinary) -> iovec()
IoListOrBinary = iolist() | binary()
Returns an iovec that is made from the integers and binaries in
.
is_alive() -> boolean()
Returns true
if the local node is alive (that is, if
the node can be part of a distributed system), otherwise
false
.
is_atom(Term) -> boolean()
Term = term()
Returns true
if
is an atom,
otherwise false
.
Allowed in guard tests.
is_binary(Term) -> boolean()
Term = term()
Returns true
if
is a binary,
otherwise false
.
A binary always contains a complete number of bytes.
Allowed in guard tests.
is_bitstring(Term) -> boolean()
Term = term()
Returns true
if
is a
bitstring (including a binary), otherwise false
.
Allowed in guard tests.
is_boolean(Term) -> boolean()
Term = term()
Returns true
if
is the
atom true
or the atom false
(that is, a boolean).
Otherwise returns false
.
Allowed in guard tests.
erlang:is_builtin(Module, Function, Arity) -> boolean()
Module = module()
Function = atom()
Arity = arity()
This BIF is useful for builders of cross-reference tools.
Returns true
if
is a BIF implemented in C, otherwise false
.
is_float(Term) -> boolean()
Term = term()
Returns true
if
is a floating point
number, otherwise false
.
Allowed in guard tests.
is_function(Term) -> boolean()
Term = term()
Returns true
if
is a fun, otherwise
false
.
Allowed in guard tests.
is_function(Term, Arity) -> boolean()
Term = term()
Arity = arity()
Returns true
if
is a fun that can be
applied with
number of arguments, otherwise
false
.
Allowed in guard tests.
is_integer(Term) -> boolean()
Term = term()
Returns true
if
is an integer,
otherwise false
.
Allowed in guard tests.
is_list(Term) -> boolean()
Term = term()
Returns true
if
is a list with
zero or more elements, otherwise false
.
Allowed in guard tests.
is_map(Term) -> boolean()
Term = term()
Returns true
if
is a map,
otherwise false
.
Allowed in guard tests.
is_map_key(Key, Map) -> boolean()
Key = term()
Map = map()
Returns true
if map
contains
and returns false
if it does not
contain the
.
The call fails with a {badmap,Map}
exception if
is not a map.
Example:
> Map = #{"42" => value}. #{"42" => value} > is_map_key("42",Map). true > is_map_key(value,Map). false
is_number(Term) -> boolean()
Term = term()
Returns true
if
is an integer or a
floating point number. Otherwise returns false
.
Allowed in guard tests.
is_pid(Term) -> boolean()
Term = term()
Returns true
if
is a process
identifier, otherwise false
.
Allowed in guard tests.
is_port(Term) -> boolean()
Term = term()
Returns true
if
is a port identifier,
otherwise false
.
Allowed in guard tests.
is_process_alive(Pid) -> boolean()
Pid = pid()
must refer to a process at the local
node.
Returns true
if the process exists and is alive, that
is, is not exiting and has not exited. Otherwise returns
false
.
is_record(Term, RecordTag) -> boolean()
Term = term()
RecordTag = atom()
Returns true
if
is a tuple and its
first element is
.
Otherwise returns false
.
Note!
Normally the compiler treats calls to is_record/2
especially. It emits code to verify that
is a tuple, that its first element is
, and that the
size is correct. However, if
is
not a literal atom, the BIF is_record/2
is called
instead and the size of the tuple is not verified.
Allowed in guard tests, if
is
a literal atom.
is_record(Term, RecordTag, Size) -> boolean()
Term = term()
RecordTag = atom()
Size = integer() >= 0
must be an atom.
Returns true
if
is a tuple,
its first element is
,
and its size is
.
Otherwise returns false
.
Allowed in guard tests if
is
a literal atom and Size
is a literal integer.
Note!
This BIF is documented for completeness. Usually
is_record/2
is to be used.
is_reference(Term) -> boolean()
Term = term()
Returns true
if
is a reference,
otherwise false
.
Allowed in guard tests.
is_tuple(Term) -> boolean()
Term = term()
Returns true
if
is a tuple,
otherwise false
.
Allowed in guard tests.
length(List) -> integer() >= 0
List = [term()]
Returns the length of
, for example:
> length([1,2,3,4,5,6,7,8,9]).
9
Allowed in guard tests.
link(PidOrPort) -> true
PidOrPort = pid() | port()
Creates a link between the calling process and another
process (or port)
, if there is
not such a link
already. If a process attempts to create a link to itself,
nothing is done. Returns true
.
If
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
is cheap (that is, ifPidOrPort
is local),PidOrPort link/1
fails with reasonnoproc
.Otherwise, if the calling process is trapping exits, and/or
is remote,PidOrPort link/1
returnstrue
, but an exit signal with reasonnoproc
is sent to the calling process.
list_to_atom(String) -> atom()
String = string()
Returns the atom whose text representation is
.
As from Erlang/OTP 20,
may contain
any Unicode character. Earlier versions allowed only ISO-latin-1
characters as the implementation did not allow Unicode characters
above 255. For more information on Unicode support in atoms, see
note on UTF-8
encoded atoms
in section "External Term Format" in the User's Guide.
Example:
> list_to_atom("Erlang").
'Erlang'
list_to_binary(IoList) -> binary()
IoList = iolist()
Returns a binary that is made from the integers and
binaries in
, for example:
>Bin1 = <<1,2,3>>.
<<1,2,3>> >Bin2 = <<4,5>>.
<<4,5>> >Bin3 = <<6>>.
<<6>> >list_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
<<1,2,3,1,2,3,4,5,4,6>>
list_to_bitstring(BitstringList) -> bitstring()
BitstringList = bitstring_list()
bitstring_list() =
maybe_improper_list(byte() | bitstring() | bitstring_list(),
bitstring() | [])
Returns a bitstring that is made from the integers and
bitstrings in
. (The last tail in
is allowed to be a bitstring.)
Example:
>Bin1 = <<1,2,3>>.
<<1,2,3>> >Bin2 = <<4,5>>.
<<4,5>> >Bin3 = <<6,7:4>>.
<<6,7:4>> >list_to_bitstring([Bin1,1,[2,3,Bin2],4|Bin3]).
<<1,2,3,1,2,3,4,5,4,6,7:4>>
list_to_existing_atom(String) -> atom()
String = string()
Returns the atom whose text representation is
,
but only if there already exists such atom.
Failure: badarg
if there does not already exist an atom
whose text representation is
.
Note!
Note that the compiler may optimize away atoms. For
example, the compiler will rewrite
atom_to_list(some_atom)
to "some_atom"
. If
that expression is the only mention of the atom
some_atom
in the containing module, the atom will not
be created when the module is loaded, and a subsequent call
to list_to_existing_atom("some_atom")
will fail.
list_to_float(String) -> float()
String = string()
Returns the float whose text representation is
, for example:
> list_to_float("2.2017764e+0").
2.2017764
Failure: badarg
if
contains a bad
representation of a float.
list_to_integer(String) -> integer()
String = string()
Returns an integer whose text representation is
, for example:
> list_to_integer("123").
123
Failure: badarg
if
contains a bad
representation of an integer.
list_to_integer(String, Base) -> integer()
String = string()
Base = 2..36
Returns an integer whose text representation in base
is
,
for example:
> list_to_integer("3FF", 16).
1023
Failure: badarg
if
contains a bad
representation of an integer.
list_to_pid(String) -> pid()
String = string()
Returns a process identifier whose text representation is a
, for example:
> list_to_pid("<0.4.1>").
<0.4.1>
Failure: badarg
if
contains a bad
representation of a process identifier.
Warning!
This BIF is intended for debugging and is not to be used in application programs.
list_to_port(String) -> port()
String = string()
Returns a port identifier whose text representation is a
, for example:
> list_to_port("#Port<0.4>").
#Port<0.4>
Failure: badarg
if
contains a bad
representation of a port identifier.
Warning!
This BIF is intended for debugging and is not to be used in application programs.
list_to_ref(String) -> reference()
String = string()
Returns a reference whose text representation is a
, for example:
> list_to_ref("#Ref<0.4192537678.4073193475.71181>").
#Ref<0.4192537678.4073193475.71181>
Failure: badarg
if
contains a bad
representation of a reference.
Warning!
This BIF is intended for debugging and is not to be used in application programs.
list_to_tuple(List) -> tuple()
List = [term()]
Returns a tuple corresponding to
,
for example
> list_to_tuple([share, ['Ericsson_B', 163]]).
{share, ['Ericsson_B', 163]}
can contain any Erlang terms.
load_module(Module, Binary) -> {module, Module} | {error, Reason}
Module = module()
Binary = binary()
Reason = badfile | not_purged | on_load
If
contains the object code for module
, this BIF loads that object code. If
the code for module
already exists, all
export references are replaced so they point to the newly
loaded code. The previously loaded code is kept in the system
as old code, as there can still be processes executing
that code.
Returns either {module,
, or
{error,
if loading fails.
is one of the following:
badfile
Binary
has an
incorrect format or the object code contains code
for another module than Module
.
not_purged
Binary
contains a module that cannot be
loaded because old code for this module already exists.
Warning!
This BIF is intended for the code server (see
code(3)
)
and is not to be used elsewhere.
erlang:load_nif(Path, LoadInfo) -> ok | Error
Path = string()
LoadInfo = term()
Error = {error, {Reason, Text :: string()}}
Reason =
load_failed | bad_lib | load | reload | upgrade | old_code
Loads and links a dynamic library containing native
implemented functions (NIFs) for a module.
is a file path to the shareable object/dynamic library file minus
the OS-dependent file extension (.so
for Unix and
.dll
for Windows). Notice that on most OSs the library has
to have a different name on disc when an upgrade of the nif is
done. If the name is the same, but the contents differ, the
old library may be loaded instead. For information on how to
implement a NIF library, see
erl_nif(3)
.
can be any term. It is passed on to
the library as part of the initialization. A good practice is
to include a module version number to support future code
upgrade scenarios.
The call to load_nif/2
must be made
directly from the Erlang code of the module that the
NIF library belongs to. It returns either ok
, or
{error,{
if loading fails.
is one of the following atoms
while
is a human readable string that
can give more information about the failure:
load_failed
bad_lib
load | upgrade
reload
reload
feature was removed in OTP 20.
old_code
load_nif/2
was made from the old
code of a module that has been upgraded; this is not
allowed.
notsup
erlang:loaded() -> [Module]
Module = module()
Returns a list of all loaded Erlang modules (current and old code), including preloaded modules.
See also
code(3)
.
erlang:localtime() -> DateTime
DateTime = calendar:datetime()
Returns the current local date and time,
{{Year, Month, Day}, {Hour, Minute, Second}}
,
for example:
> erlang:localtime().
{{1996,11,6},{14,45,17}}
The time zone and Daylight Saving Time correction depend on the underlying OS.
erlang:localtime_to_universaltime(Localtime) -> Universaltime
Localtime = Universaltime = calendar:datetime()
Converts local date and time to Universal Time Coordinated
(UTC), if supported by the underlying OS. Otherwise
no conversion is done and
is returned. Example:
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}).
{{1996,11,6},{13,45,17}}
Failure: badarg
if
denotes an
invalid date and time.
erlang:localtime_to_universaltime(Localtime, IsDst) ->
Universaltime
Localtime = Universaltime = calendar:datetime()
IsDst = true | false | undefined
Converts local date and time to Universal Time Coordinated
(UTC) as erlang:localtime_to_universaltime/1
,
but the caller decides if Daylight Saving Time is active.
If
,
is during Daylight Saving Time, if
it is not. If
, the underlying
OS can guess, which is the same as calling
erlang:localtime_to_universaltime(
.
Examples:
>erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, true).
{{1996,11,6},{12,45,17}} >erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, false).
{{1996,11,6},{13,45,17}} >erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, undefined).
{{1996,11,6},{13,45,17}}
Failure: badarg
if
denotes an
invalid date and time.
make_ref() -> reference()
Returns a unique reference. The reference is unique among connected nodes.
Warning!
Known issue: When a node is restarted multiple times with the same node name, references created on a newer node can be mistaken for a reference created on an older node with the same node name.
erlang:make_tuple(Arity, InitialValue) -> tuple()
Arity = arity()
InitialValue = term()
Creates a new tuple of the specified
, where
all elements are
, for example:
> erlang:make_tuple(4, []).
{[],[],[],[]}
erlang:make_tuple(Arity, DefaultValue, InitList) -> tuple()
Arity = arity()
DefaultValue = term()
InitList = [{Position :: integer() >= 1, term()}]
Creates a tuple of size
, where each element
has value
, and then fills in
values from
.
Each list element in
must be a two-tuple, where the first element is a position in the
newly created tuple and the second element is any term. If a
position occurs more than once in the list, the term corresponding
to the last occurrence is used. Example:
> erlang:make_tuple(5, [], [{2,ignored},{5,zz},{2,aa}]).
{[],aa,[],[],zz}
map_get(Key, Map) -> Value
Map = map()
Key = Value = any()
Returns value
associated with
if
contains
.
The call fails with a {badmap,Map}
exception if
is not a map, or with a {badkey,Key}
exception if no value is associated with
.
Example:
> Key = 1337, Map = #{42 => value_two,1337 => "value one","a" => 1}, map_get(Key,Map). "value one"
map_size(Map) -> integer() >= 0
Map = map()
Returns an integer, which is the number of key-value pairs
in
, for example:
> map_size(#{a=>1, b=>2, c=>3}).
3
Allowed in guard tests.
erlang:match_spec_test(MatchAgainst, MatchSpec, Type) ->
TestResult
MatchAgainst = [term()] | tuple()
MatchSpec = term()
Type = table | trace
TestResult =
{ok, term(), [return_trace], [{error | warning, string()}]} |
{error, [{error | warning, string()}]}
Tests a match specification used in calls to
ets:select/2
and
erlang:trace_pattern/3
.
The function tests both a match specification for "syntactic"
correctness and runs the match specification against the object. If
the match specification contains errors, the tuple {error,
Errors}
is returned, where Errors
is a list of natural
language descriptions of what was wrong with the match
specification.
If
is table
, the object to match
against is to be a tuple. The function then returns
{ok,Result,[],Warnings}
, where Result
is what would
have been the result in a real ets:select/2
call, or
false
if the match specification does not match the object
tuple.
If
is trace
, the object to match
against is to be a list. The function returns
{ok, Result, Flags, Warnings}
, where Result
is one of
the following:
true
if a trace message is to be emittedfalse
if a trace message is not to be emitted- The message term to be appended to the trace message
Flags
is a list containing all the trace flags to be enabled,
currently this is only return_trace
.
This is a useful debugging and test tool, especially when writing complicated match specifications.
See also
ets:test_ms/2
.
max(Term1, Term2) -> Maximum
Term1 = Term2 = Maximum = term()
Returns the largest of
and
.
If the terms are equal,
is returned.
erlang:md5(Data) -> Digest
Data = iodata()
Digest = binary()
Computes an MD5 message digest from
, where
the length of the digest is 128 bits (16 bytes).
is a binary or a list of small integers and binaries.
For more information about MD5, see
Warning!
The MD5 Message-Digest Algorithm is not considered safe for code-signing or software-integrity purposes.
erlang:md5_final(Context) -> Digest
Context = Digest = binary()
Finishes the update of an MD5
and returns
the computed MD5
message digest.
erlang:md5_init() -> Context
Context = binary()
Creates an MD5 context, to be used in the following calls to
md5_update/2
.
erlang:md5_update(Context, Data) -> NewContext
Context = binary()
Data = iodata()
NewContext = binary()
Update an MD5
with
and returns a
.
erlang:memory() -> [{Type, Size}]
Type = memory_type()
Size = integer() >= 0
memory_type() =
total | processes | processes_used | system | atom |
atom_used | binary | code | ets
Returns a list with information about memory
dynamically allocated by the Erlang emulator. Each list
element is a tuple {Type, Size}
. The first element
is an atom describing memory type. The second
element
is the memory size in bytes.
Memory types:
total
The total amount of memory currently allocated. This is
the same as the sum of the memory size for processes
and system
.
processes
The total amount of memory currently allocated for the Erlang processes.
processes_used
The total amount of memory currently used by the Erlang
processes. This is part of the memory presented as
processes
memory.
system
The total amount of memory currently allocated for
the emulator that is not directly related to any Erlang
process. Memory presented as processes
is not
included in this memory.
instrument(3)
can be used to
get a more detailed breakdown of what memory is part
of this type.
atom
The total amount of memory currently allocated for atoms.
This memory is part of the memory presented as
system
memory.
atom_used
The total amount of memory currently used for atoms.
This memory is part of the memory presented as
atom
memory.
binary
The total amount of memory currently allocated for
binaries. This memory is part of the memory presented
as system
memory.
code
The total amount of memory currently allocated for
Erlang code. This memory is part of the memory presented
as system
memory.
ets
The total amount of memory currently allocated for ETS
tables. This memory is part of the memory presented as
system
memory.
low
Only on 64-bit halfword emulator. The total amount of memory allocated in low memory areas that are restricted to < 4 GB, although the system can have more memory.
Can be removed in a future release of the halfword emulator.
maximum
The maximum total amount of memory allocated since the emulator was started. This tuple is only present when the emulator is run with instrumentation.
For information on how to run the emulator with
instrumentation, see
instrument(3)
and/or erl(1)
.
Note!
The system
value is not complete. Some allocated
memory that is to be part of this value is not.
When the emulator is run with instrumentation,
the system
value is more accurate, but memory
directly allocated for malloc
(and friends) is still
not part of the system
value. Direct calls to
malloc
are only done from OS-specific runtime
libraries and perhaps from user-implemented Erlang drivers
that do not use the memory allocation functions in
the driver interface.
As the total
value is the sum of processes
and system
, the error in system
propagates
to the total
value.
The different amounts of memory that are summed are not gathered atomically, which introduces an error in the result.
The different values have the following relation to each other. Values beginning with an uppercase letter is not part of the result.
total = processes + system processes = processes_used + ProcessesNotUsed system = atom + binary + code + ets + OtherSystem atom = atom_used + AtomNotUsed RealTotal = processes + RealSystem RealSystem = system + MissedSystem
More tuples in the returned list can be added in a future release.
Note!
The total
value is supposed to be the total amount
of memory dynamically allocated by the emulator. Shared
libraries, the code of the emulator itself, and
the emulator stacks are not supposed to be included. That
is, the total
value is not supposed to be
equal to the total size of all pages mapped to the emulator.
Also, because of fragmentation and prereservation of memory areas, the size of the memory segments containing the dynamically allocated memory blocks can be much larger than the total size of the dynamically allocated memory blocks.
Note!
As from ERTS 5.6.4, erlang:memory/0
requires that
all erts_alloc(3)
allocators are enabled (default behavior).
Failure: notsup
if an
erts_alloc(3)
allocator has been disabled.
memory_type() =
total | processes | processes_used | system | atom |
atom_used | binary | code | ets
Returns the memory size in bytes allocated for memory of type
. The argument can also be specified as a list
of memory_type()
atoms, in which case a corresponding list of
{memory_type(), Size :: integer >= 0}
tuples is returned.
Note!
As from ERTS 5.6.4,
erlang:memory/1
requires that
all erts_alloc(3)
allocators are enabled (default behavior).
Failures:
badarg
Type
is not one of the memory types
listed in the description of
erlang:memory/0
.
badarg
maximum
is passed as Type
and
the emulator is not run in instrumented mode.
notsup
erts_alloc(3)
allocator has been disabled.
See also
erlang:memory/0
.
min(Term1, Term2) -> Minimum
Term1 = Term2 = Minimum = term()
Returns the smallest of
and
.
If the terms are equal,
is returned.
module_loaded(Module) -> boolean()
Module = module()
Returns true
if the module
is loaded, otherwise false
. It does not attempt to load
the module.
Warning!
This BIF is intended for the code server (see
code(3)
)
and is not to be used elsewhere.
registered_name() = atom()
registered_process_identifier() =
registered_name() | {registered_name(), node()}
monitor_process_identifier() =
pid() | registered_process_identifier()
monitor_port_identifier() = port() | registered_name()
Sends a monitor request of type
to the
entity identified by
. If the monitored entity
does not exist or it changes monitored state, the caller of
monitor/2
is notified by a message on the following format:
{Tag,MonitorRef ,Type , Object, Info}
Note!
The monitor request is an asynchronous signal. That is, it takes time before the signal reaches its destination.
can be one of the following atoms:
process
, port
or time_offset
.
A process
or port
monitor is triggered only once,
after that it is removed from both monitoring process and
the monitored entity. Monitors are fired when the monitored process
or port terminates, does not exist at the moment of creation,
or if the connection to it is lost. If the connection to it is lost,
we do not know if it still exists. The monitoring is also turned off
when demonitor/1 is
called.
A process
or port
monitor by name
resolves the RegisteredName
to pid()
or port()
only once at the moment of monitor instantiation, later changes to
the name registration will not affect the existing monitor.
When a process
or port
monitor is triggered,
a 'DOWN'
message is sent that has the following pattern:
{'DOWN', MonitorRef, Type, Object, Info}
In the monitor message MonitorRef
and Type
are the
same as described earlier, and:
Object
The monitored entity, which triggered the event. When monitoring
a local process or port, Object
will be equal to the
pid()
or port()
that was being monitored. When
monitoring process or port by name, Object
will have format
{RegisteredName, Node}
where RegisteredName
is the
name which has been used with monitor/2
call and
Node
is local or remote node name (for ports monitored by
name, Node
is always local node name).
Info
Either the exit reason of the process, noproc
(process or port did not exist at the time of monitor creation),
or noconnection
(no connection to the node where the
monitored process resides).
process
Creates monitor between the current process and another
process identified by
, which can be a
pid()
(local or remote), an atom RegisteredName
or
a tuple {RegisteredName, Node}
for a registered process,
located elsewhere.
Note!
Before ERTS 10.0 (OTP 21.0), monitoring a process could fail with
badarg
if the monitored process resided on a primitive node
(such as erl_interface or jinterface), where remote process monitoring
is not implemented.
Now, such a call to monitor
will instead succeed and a
monitor is created. But the monitor will only supervise the
connection. That is, a {'DOWN', _, process, _, noconnection}
is
the only message that may be received, as the primitive node have no
way of reporting the status of the monitored process.
port
Creates monitor between the current process and a port
identified by
, which can be a
port()
(only local), an atom RegisteredName
or
a tuple {RegisteredName, Node}
for a registered port,
located on this node. Note, that attempt to monitor a remote port
will result in badarg
.
time_offset
Monitors changes in
time offset
between
Erlang
monotonic time and
Erlang
system time. One valid
exists in combination with the
time_offset
, namely the atom
clock_service
. Notice that the atom clock_service
is
not the registered name of a process. In this
case it serves as an identifier of the runtime system internal
clock service at current runtime system instance.
The monitor is triggered when the time offset is changed. This either if the time offset value is changed, or if the offset is changed from preliminary to final during finalization of the time offset when the single time warp mode is used. When a change from preliminary to final time offset is made, the monitor is triggered once regardless of whether the time offset value was changed or not.
If the runtime system is in multi time warp mode, the time offset is changed when the runtime system detects that the OS system time has changed. The runtime system does, however, not detect this immediately when it occurs. A task checking the time offset is scheduled to execute at least once a minute, so under normal operation this is to be detected within a minute, but during heavy load it can take longer time.
The monitor is not automatically removed after it has been triggered. That is, repeated changes of the time offset trigger the monitor repeatedly.
When the monitor is triggered a 'CHANGE'
message is
sent to the monitoring process. A 'CHANGE'
message has
the following pattern:
{'CHANGE', MonitorRef, Type, Item, NewTimeOffset}
where MonitorRef
,
, and
are the same as described above, and
NewTimeOffset
is the new time offset.
When the 'CHANGE'
message has been received you are
guaranteed not to retrieve the old time offset when calling
erlang:time_offset()
.
Notice that you can observe the change of the time offset
when calling erlang:time_offset()
before you
get the 'CHANGE'
message.
Making several calls to monitor/2
for the same
and/or
is not
an error; it results in as many independent monitoring instances.
The monitor functionality is expected to be extended. That is,
other
s and
s
are expected to be supported in a future release.
Note!
If or when monitor/2
is extended, other
possible values for Tag
, Object
, and
Info
in the monitor message will be introduced.
monitor_node(Node, Flag) -> true
Node = node()
Flag = boolean()
Monitor the status of the node
.
If
is true
, monitoring is turned on. If
is false
, monitoring is turned off.
Making several calls to monitor_node(Node, true)
for
the same
is not an error; it results
in as many independent monitoring instances.
If
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
terminates, two nodedown
messages
are delivered to the process. If there is no connection to
, an attempt is made to create one.
If this fails, a nodedown
message is delivered.
Nodes connected through hidden connections can be monitored as any other nodes.
Failure: badarg
if the local node is not alive.
erlang:monitor_node(Node, Flag, Options) -> true
Node = node()
Flag = boolean()
Options = [Option]
Option = allow_passive_connect
Behaves as
monitor_node/2
except that it allows an
extra option to be specified, namely allow_passive_connect
.
This option allows the BIF to wait the normal network connection
time-out for the monitored node to connect itself,
even if it cannot be actively connected from this node
(that is, it is blocked). The state where this can be useful
can only be achieved by using the Kernel option
dist_auto_connect once
. If that option is not
used, option allow_passive_connect
has no effect.
Note!
Option allow_passive_connect
is used
internally and is seldom needed in applications where the
network topology and the Kernel options in effect
are known in advance.
Failure: badarg
if the local node is not alive or the
option list is malformed.
erlang:monotonic_time() -> integer()
Returns the current
Erlang
monotonic time in native
time unit. This
is a monotonically increasing time since some unspecified point in
time.
Note!
This is a
monotonically increasing time, but not a
strictly monotonically increasing
time. That is, consecutive calls to
erlang:monotonic_time/0
can produce the same result.
Different runtime system instances will use different unspecified
points in time as base for their Erlang monotonic clocks.
That is, it is pointless comparing monotonic times from
different runtime system instances. Different runtime system
instances can also place this unspecified point in time different
relative runtime system start. It can be placed in the future (time
at start is a negative value), the past (time at start is a
positive value), or the runtime system start (time at start is
zero). The monotonic time at runtime system start can be
retrieved by calling
erlang:system_info(start_time)
.
erlang:monotonic_time(Unit) -> integer()
Unit = time_unit()
Returns the current
Erlang
monotonic time converted
into the
passed as argument.
Same as calling
erlang:convert_time_unit
(
erlang:monotonic_time()
,
native,
,
however optimized for commonly used
s.
erlang:nif_error(Reason) -> no_return()
Reason = term()
Works exactly like
error/1
, but
Dialyzer thinks that this BIF will return an arbitrary
term. When used in a stub function for a NIF to generate an
exception when the NIF library is not loaded, Dialyzer
does not generate false warnings.
erlang:nif_error(Reason, Args) -> no_return()
Reason = term()
Args = [term()]
Works exactly like
error/2
, but
Dialyzer thinks that this BIF will return an arbitrary
term. When used in a stub function for a NIF to generate an
exception when the NIF library is not loaded, Dialyzer
does not generate false warnings.
node() -> Node
Node = node()
Returns the name of the local node. If the node is not alive,
nonode@nohost
is returned instead.
Allowed in guard tests.
node(Arg) -> Node
Arg = pid() | port() | reference()
Node = node()
Returns the node where
originates.
can
be a process identifier, a reference, or a port.
If the local node is not
alive, nonode@nohost
is returned.
Allowed in guard tests.
nodes() -> Nodes
Nodes = [node()]
Returns a list of all visible nodes in the system, except
the local node. Same as nodes(visible)
.
nodes(Arg) -> Nodes
Arg = NodeType | [NodeType]
NodeType = visible | hidden | connected | this | known
Nodes = [node()]
Returns a list of nodes according to the argument specified. The returned result, when the argument is a list, is the list of nodes satisfying the disjunction(s) of the list elements.
s:
visible
Nodes connected to this node through normal connections.
hidden
Nodes connected to this node through hidden connections.
connected
All nodes connected to this node.
this
This node.
known
Nodes that are known to this node. That is, connected
nodes and nodes referred to by process identifiers, port
identifiers, and references located on this node.
The set of known nodes is garbage collected. Notice that
this garbage collection can be delayed. For more
information, see
erlang:system_info(delayed_node_table_gc)
.
Some equalities: [node()] = nodes(this)
,
nodes(connected) = nodes([visible, hidden])
, and
nodes() = nodes(visible)
.
now() -> Timestamp
Timestamp = timestamp()
timestamp() =
{MegaSecs :: integer() >= 0,
Secs :: integer() >= 0,
MicroSecs :: integer() >= 0}
Warning!
This function is deprecated. Do not use it.
For more information, see section
Time and Time Correction
in the User's Guide. Specifically, section
Dos and Dont's describes what to use instead of
erlang:now/0
.
Returns the tuple {MegaSecs, Secs, MicroSecs}
, which is
the elapsed time since 00:00 GMT, January 1, 1970 (zero hour),
if provided by the underlying OS.
Otherwise some other point in time is chosen. It is also
guaranteed that the following calls to this BIF return
continuously increasing values. Hence, the return value from
erlang:now/0
can be used to generate unique time stamps.
If it is called in a tight loop on a fast machine,
the time of the node can become skewed.
Can only be used to check the local time of day if the time-zone information of the underlying OS is properly configured.
open_port(PortName, PortSettings) -> port()
PortName =
{spawn, Command :: string() | binary()} |
{spawn_driver, Command :: string() | binary()} |
{spawn_executable, FileName :: file:name()} |
{fd, In :: integer() >= 0, Out :: integer() >= 0}PortSettings = [Opt]
Opt =
{packet, N :: 1 | 2 | 4} |
stream |
{line, L :: integer() >= 0} |
{cd, Dir :: string() | binary()} |
{env,
Env ::
[{Name :: os:env_var_name(),
Val :: os:env_var_value() | false}]} |
{args, [string() | binary()]} |
{arg0, string() | binary()} |
exit_status | use_stdio | nouse_stdio | stderr_to_stdout |
in | out | binary | eof |
{parallelism, Boolean :: boolean()} |
hide
Returns a port identifier as the result of opening a new Erlang port. A port can be seen as an external Erlang process.
The name of the executable as well as the arguments
specifed in cd
, env
, args
, and arg0
are
subject to Unicode filename translation if the system is running
in Unicode filename mode. To avoid
translation or to force, for example UTF-8, supply the executable
and/or arguments as a binary in the correct
encoding. For details, see the module
file(3)
, the
function
file:native_name_encoding/0
in Kernel, and
the
Using Unicode in Erlang
User's Guide.
Note!
The characters in the name (if specified as a list) can only be > 255 if the Erlang virtual machine is started in Unicode filename translation mode. Otherwise the name of the executable is limited to the ISO Latin-1 character set.
s:
{spawn, Command }
Starts an external program.
is the name of the external program to be run.
runs outside the Erlang work space unless an Erlang
driver with the name
is found.
If found, that driver is started. A driver runs in the Erlang
work space, which means that it is linked with the Erlang
runtime system.
For external programs, PATH
is searched
(or an equivalent method is used to find programs,
depending on the OS). This is done by invoking
the shell on certain platforms. The first space-separated
token of the command is considered as the
name of the executable (or driver). This (among other
things) makes this option unsuitable for running
programs with spaces in filenames or directory names.
If spaces in executable filenames are desired, use
{spawn_executable,
instead.
{spawn_driver, Command }
Works like {spawn,
, but demands
the first (space-separated) token of the command to be the name
of a loaded driver. If no driver with that name is loaded, a
badarg
error is raised.
{spawn_executable, FileName }
Works like {spawn,
, but only runs
external executables.
in its whole
is used as the name of the executable, including any spaces.
If arguments are to be passed, the
args
and arg0
can be used.
The shell is usually not invoked to start the
program, it is executed directly. PATH
(or
equivalent) is not searched. To find a program
in PATH
to execute, use
os:find_executable/1
.
Only if a shell script or .bat
file is
executed, the appropriate command interpreter is
invoked implicitly, but there is still no
command-argument expansion or implicit PATH
search.
If
cannot be run, an error
exception is raised, with the POSIX error code as the reason.
The error reason can differ between OSs.
Typically the error enoent
is raised when an
attempt is made to run a program that is not found and
eacces
is raised when the specified file is not
executable.
{fd, In , Out }
Allows an Erlang process to access any currently opened
file descriptors used by Erlang. The file descriptor
can be used for standard input, and the
file descriptor
for standard output.
It is only used for various servers in the Erlang OS (shell
and user
). Hence, its use is limited.
is a list of settings for the port.
The valid settings are as follows:
{packet, N }
Messages are preceded by their length, sent in
bytes, with the most significant byte first. The valid values
for N
are 1, 2, and 4.
stream
Output messages are sent without packet lengths. A user-defined protocol must be used between the Erlang process and the external object.
{line, L }
Messages are delivered on a per line basis. Each line
(delimited by the OS-dependent newline sequence) is
delivered in a single message. The message data format
is {Flag, Line}
, where Flag
is
eol
or noeol
, and Line
is the
data delivered (without the newline sequence).
specifies the maximum line length in bytes.
Lines longer than this are delivered in more than one
message, with Flag
set to noeol
for all
but the last message. If end of file is encountered
anywhere else than immediately following a newline
sequence, the last line is also delivered with
Flag
set to noeol
. Otherwise
lines are delivered with Flag
set to eol
.
The {packet,
and {line,
settings are mutually exclusive.
{cd, Dir }
Only valid for {spawn,
and
{spawn_executable,
.
The external program starts using
as its
working directory.
must be a string.
{env, Env }
Types:
��os:env_var_name()
��os:env_var_value()
| false
��Env = [{
Only valid for {spawn,
, and
{spawn_executable,
.
The environment of the started process is extended using
the environment specifications in
.
is to be a list of tuples
{
,
where
is the name of an
environment variable, and
is the
value it is to have in the spawned
port process. Both
and
must be strings. The one
exception is
being the atom
false
(in analogy with
os:getenv/1
,
which removes the environment variable.
For information about encoding requirements, see documentation
of the types for
and
.
{args, [ string() | binary() ]}
Only valid for {spawn_executable,
and specifies arguments to the executable. Each argument
is specified as a separate string and (on Unix) eventually
ends up as one element each in the argument vector. On
other platforms, a similar behavior is mimicked.
The arguments are not expanded by the shell before
they are supplied to the executable. Most notably this
means that file wildcard expansion does not occur.
To expand wildcards for the arguments, use
filelib:wildcard/1
.
Notice that even if
the program is a Unix shell script, meaning that the
shell ultimately is invoked, wildcard expansion
does not occur, and the script is provided with the
untouched arguments. On Windows, wildcard expansion
is always up to the program itself, therefore this is
not an issue.
The executable name (also known as argv[0]
)
is not to be specified in this list. The proper executable name
is automatically used as argv[0]
, where applicable.
If you explicitly want to set the
program name in the argument vector, option arg0
can be used.
{arg0, string() | binary()}
Only valid for {spawn_executable,
and explicitly specifies the program name argument when
running an executable. This can in some circumstances,
on some OSs, be desirable. How the program
responds to this is highly system-dependent and no specific
effect is guaranteed.
exit_status
Only valid for {spawn,
, where
refers to an external program, and
for {spawn_executable,
.
When the external process connected to the port exits, a
message of the form {Port,{exit_status,Status}}
is
sent to the connected process, where Status
is the
exit status of the external process. If the program
aborts on Unix, the same convention is used as the shells
do (that is, 128+signal).
If option eof
is specified also, the messages eof
and exit_status
appear in an unspecified order.
If the port program closes its stdout
without exiting,
option exit_status
does not work.
use_stdio
Only valid for {spawn,
and
{spawn_executable,
. It
allows the standard input and output (file descriptors 0
and 1) of the spawned (Unix) process for communication
with Erlang.
nouse_stdio
The opposite of use_stdio
. It uses file descriptors
3 and 4 for communication with Erlang.
stderr_to_stdout
Affects ports to external programs. The executed program
gets its standard error file redirected to its standard
output file. stderr_to_stdout
and
nouse_stdio
are mutually exclusive.
overlapped_io
Affects ports to external programs on Windows only. The
standard input and standard output handles of the port program
are, if this option is supplied, opened with flag
FILE_FLAG_OVERLAPPED
, so that the port program can
(and must) do
overlapped I/O on its standard handles. This is not normally
the case for simple port programs, but an option of value for the
experienced Windows programmer. On all other platforms, this
option is silently discarded.
in
The port can only be used for input.
out
The port can only be used for output.
binary
All I/O from the port is binary data objects as opposed to lists of bytes.
eof
The port is not closed at the end of the file and does not
produce an exit signal. Instead, it remains open and
a {Port, eof}
message is sent to the process
holding the port.
hide
When running on Windows, suppresses creation of a new console window when spawning the port program. (This option has no effect on other platforms.)
{parallelism, Boolean}
Sets scheduler hint for port parallelism. If set to
true
, the virtual machine schedules port tasks;
when doing so, it improves parallelism in the system. If set
to false
, the virtual machine tries to
perform port tasks immediately, improving latency at the
expense of parallelism. The default can be set at system startup
by passing command-line argument
+spp
to
erl(1)
.
Default is stream
for all port types and
use_stdio
for spawned ports.
Failure: if the port cannot be opened, the exit reason is
badarg
, system_limit
, or the POSIX error code that
most closely describes the error, or einval
if no POSIX
code is appropriate:
badarg
open_port
.
system_limit
enomem
eagain
enametoolong
emfile
enfile
eacces
Command
specified in {spawn_executable, Command}
does not point out an executable file.
enoent
FileName
specified in
{spawn_executable, FileName }
does not point out an existing file.
During use of a port opened using {spawn, Name}
,
{spawn_driver, Name}
, or {spawn_executable, Name}
,
errors arising when sending messages to it are reported to
the owning process using signals of the form
{'EXIT', Port, PosixCode}
. For the possible values of
PosixCode
, see
file(3)
.
The maximum number of ports that can be open at the same
time can be configured by passing command-line flag
+Q
to
erl(1)
.
erlang:phash(Term, Range) -> Hash
Term = term()
Range = Hash = integer() >= 1
Range = Range = 1..2^32, Hash = 1..Range
Portable hash function that gives the same hash for
the same Erlang term regardless of machine architecture and
ERTS version (the BIF was introduced in ERTS 4.9.1.1).
The function returns a hash value for
within the range
1..
. The maximum value for
is 2^32.
erlang:phash2(Term) -> Hash
Term = term()
Hash = integer() >= 0
erlang:phash2(Term, Range) -> Hash
Term = term()
Range = integer() >= 1
Hash = integer() >= 0
Range = 1..2^32
Hash = 0..Range-1
Portable hash function that gives the same hash for
the same Erlang term regardless of machine architecture and
ERTS version (the BIF was introduced in ERTS 5.2).
The function returns a hash value for
within the range
0..
. The maximum value for
is 2^32. When without argument
, a value in the range
0..2^27-1 is returned.
This BIF is always to be used for hashing terms. It
distributes small integers better than phash/2
, and
it is faster for bignums and binaries.
Notice that the range 0..
is
different from the range of phash/2
, which is
1..
.
pid_to_list(Pid) -> string()
Pid = pid()
Returns a string corresponding to the text
representation of
.
erlang:port_call(Port, Operation, Data) -> term()
Port = port() | atom()
Operation = integer()
Data = term()
Performs a synchronous call to a port. The meaning of
and
depends on the port, that is,
on the port driver. Not all port drivers support this feature.
is a port identifier,
referring to a driver.
is an integer, which is passed on to
the driver.
is any Erlang term. This data is converted
to binary term format and sent to the port.
Returns a term from the driver. The meaning of the returned data also depends on the port driver.
Failures:
badarg
Port
is not an identifier of an open port,
or the registered name of an open port. If the calling
process was previously linked to the closed port,
identified by Port
, the exit signal
from the port is guaranteed to be delivered before this
badarg
exception occurs.
badarg
Operation
does not fit in a 32-bit integer.
badarg
badarg
If the port driver so decides for any reason (probably
something wrong with
or
).
Warning!
Do not call port_call
with an unknown
identifier and expect badarg
exception. Any undefined behavior is possible (including node
crash) depending on how the port driver interprets the supplied
arguments.
port_close(Port) -> true
Port = port() | atom()
Closes an open port. Roughly the same as
except for the error behavior
(see below), being synchronous, and that the port does
not reply with {Port, closed}
. Any process can
close a port with port_close/1
, not only the port owner
(the connected process). If the calling process is linked to
the port identified by
, the exit
signal from the port is guaranteed to be delivered before
port_close/1
returns.
For comparison:
only fails with badarg
if
does
not refer to a port or a process. If
is a closed port, nothing happens. If
is an open port and the calling process is the port owner,
the port replies with {Port, closed}
when all buffers
have been flushed and the port really closes. If the calling
process is not the port owner, the port owner fails
with badsig
.
Notice that any process can close a port using
as if it itself was
the port owner, but the reply always goes to the port owner.
As from Erlang/OTP R16,
is truly
asynchronous. Notice that this operation has always been
documented as an asynchronous operation, while the underlying
implementation has been synchronous. port_close/1
is
however still fully synchronous because of its error behavior.
Failure: badarg
if
is not an
identifier of an open port, or the registered name of an open port.
If the calling process was previously linked to the closed
port, identified by
, the exit
signal from the port is guaranteed to be delivered before
this badarg
exception occurs.
port_command(Port, Data) -> true
Port = port() | atom()
Data = iodata()
Sends data to a port. Same as
except for
the error behavior and being synchronous (see below). Any process
can send data to a port with port_command/2
, not only the
port owner (the connected process).
For comparison:
only fails with badarg
if
does not refer to a port or a process. If
is
a closed port, the data message disappears
without a sound. If
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
is an invalid I/O list.
Notice that any process can send to a port using
as if it itself was the port owner.
If the port is busy, the calling process is suspended until the port is not busy any more.
As from Erlang/OTP R16,
is truly asynchronous. Notice that this operation has always been
documented as an asynchronous operation, while the underlying
implementation has been synchronous. port_command/2
is
however still fully synchronous because of its error behavior.
Failures:
badarg
If
is not an identifier of an open
port, or the registered name of an open port. If the
calling process was previously linked to the closed port,
identified by
, the exit signal
from the port is guaranteed to be delivered before this
badarg
exception occurs.
badarg
If
is an invalid I/O list.
Warning!
Do not send data to an unknown port. Any undefined behavior is possible (including node crash) depending on how the port driver interprets the data.
port_command(Port, Data, OptionList) -> boolean()
Port = port() | atom()
Data = iodata()
Option = force | nosuspend
OptionList = [Option]
Sends data to a port. port_command(Port, Data, [])
equals port_command(Port, Data)
.
If the port command is aborted, false
is returned,
otherwise true
.
If the port is busy, the calling process is suspended until the port is not busy anymore.
s:
force
notsup
exception if the
driver of the port does not support this. For more
information, see driver flag
![CDATA[ERL_DRV_FLAG_SOFT_BUSY]]
.
nosuspend
false
is returned.
Note!
More options can be added in a future release.
Failures:
badarg
Port
is not an identifier of an open
port, or the registered name of an open port. If the
calling process was previously linked to the closed port,
identified by Port
, the exit signal
from the port is guaranteed to be delivered before this
badarg
exception occurs.
badarg
Data
is an invalid I/O list.
badarg
OptionList
is an invalid option list.
notsup
force
has been passed, but the
driver of the port does not allow forcing through
a busy port.
Warning!
Do not send data to an unknown port. Any undefined behavior is possible (including node crash) depending on how the port driver interprets the data.
port_connect(Port, Pid) -> true
Port = port() | atom()
Pid = pid()
Sets the port owner (the connected port) to
.
Roughly the same as
except for the following:
-
The error behavior differs, see below.
-
The port does not reply with
{Port,connected}
. -
port_connect/1
is synchronous, see below. -
The new port owner gets linked to the port.
The old port owner stays linked to the port and must call
unlink(Port)
if this is not desired. Any process can
set the port owner to be any process with
port_connect/2
.
For comparison:
only fails with badarg
if
does not refer to a port or a process. If
is a closed port, nothing happens.
If
is an open port and the calling process is the port owner,
the port replies with {Port, connected}
to the old
port owner. Notice that the old port owner is still linked to
the port, while the new is not. If
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
is not
an existing local process identifier.
Notice that any process can set the port owner using
as if it itself was the port owner, but the reply always goes to
the port owner.
As from Erlang/OTP R16,
is truly asynchronous. Notice that this operation has always been
documented as an asynchronous operation, while the underlying
implementation has been synchronous. port_connect/2
is
however still fully synchronous because of its error behavior.
Failures:
badarg
Port
is not an identifier of an open port,
or the registered name of an open port. If the calling
process was previously linked to the closed port,
identified by Port
, the exit signal
from the port is guaranteed to be delivered before this
badarg
exception occurs.
badarg
Pid
is not an existing
local process.port_control(Port, Operation, Data) -> iodata() | binary()
Port = port() | atom()
Operation = integer()
Data = iodata()
Performs a synchronous control operation on a port.
The meaning of
and
depends on
the port, that is, on the port driver. Not all port drivers
support this control feature.
Returns a list of integers in the range 0..255, or a binary, depending on the port driver. The meaning of the returned data also depends on the port driver.
Failures:
badarg
Port
is not an open port or the registered
name of an open port.
badarg
Operation
cannot fit in a 32-bit integer.
badarg
badarg
Operation
or
Data
).
Warning!
Do not call port_control/3
with an unknown
identifier and expect badarg
exception. Any undefined behavior is possible (including node
crash) depending on how the port driver interprets the supplied
arguments.
erlang:port_info(Port) -> Result
Port = port() | atom()
ResultItem =
{registered_name, RegisteredName :: atom()} |
{id, Index :: integer() >= 0} |
{connected, Pid :: pid()} |
{links, Pids :: [pid()]} |
{name, String :: string()} |
{input, Bytes :: integer() >= 0} |
{output, Bytes :: integer() >= 0} |
{os_pid, OsPid :: integer() >= 0 | undefined}Result = [ResultItem] | undefined
Returns a list containing tuples with information about
, or undefined
if the port is not open.
The order of the tuples is undefined, and all the
tuples are not mandatory.
If the port is closed and the calling process
was previously linked to the port, the exit signal from the
port is guaranteed to be delivered before port_info/1
returns undefined
.
The result contains information about the following
Item
s:
registered_name
(if the port has a registered name)id
connected
links
name
input
output
For more information about the different Item
s, see
port_info/2
.
Failure: badarg
if Port
is not a local port
identifier, or an atom.
is the process identifier of the process
connected to the port.
If the port identified by
is not open,
undefined
is returned. If the port is closed and the
calling process was previously linked to the port, the exit
signal from the port is guaranteed to be delivered before
port_info/2
returns undefined
.
Failure: badarg
if
is not a local
port identifier, or an atom.
is the internal index of the port. This
index can be used to separate ports.
If the port identified by
is not open,
undefined
is returned. If the port is closed and the
calling process was previously linked to the port, the exit
signal from the port is guaranteed to be delivered before
port_info/2
returns undefined
.
Failure: badarg
if
is not a local
port identifier, or an atom.
is the total number of bytes
read from the port.
If the port identified by
is not open,
undefined
is returned. If the port is closed and the
calling process was previously linked to the port, the exit
signal from the port is guaranteed to be delivered before
port_info/2
returns undefined
.
Failure: badarg
if
is not a local
port identifier, or an atom.
is a list of the process identifiers
of the processes that the port is linked to.
If the port identified by
is not open,
undefined
is returned. If the port is closed and the
calling process was previously linked to the port, the exit
signal from the port is guaranteed to be delivered before
port_info/2
returns undefined
.
Failure: badarg
if
is not a local
port identifier, or an atom.
is one of the following:
port_level
(port-specific locking)driver_level
(driver-specific locking)
Notice that these results are highly implementation-specific and can change in a future release.
If the port identified by
is not open,
undefined
is returned. If the port is closed and the
calling process was previously linked to the port, the exit
signal from the port is guaranteed to be delivered before
port_info/2
returns undefined
.
Failure: badarg
if
is not a local
port identifier, or an atom.
is the total number of
bytes allocated for this port by the runtime system. The
port itself can have allocated memory that is not
included in
.
If the port identified by
is not open,
undefined
is returned. If the port is closed and the
calling process was previously linked to the port, the exit
signal from the port is guaranteed to be delivered before
port_info/2
returns undefined
.
Failure: badarg
if
is not a local
port identifier, or an atom.
represent processes monitored by
this port.
If the port identified by
is not open,
undefined
is returned. If the port is closed and the
calling process was previously linked to the port, the exit
signal from the port is guaranteed to be delivered before
port_info/2
returns undefined
.
Failure: badarg
if
is not a local
port identifier, or an atom.
Returns list of pids that are monitoring given port at the moment.
If the port identified by
is not open,
undefined
is returned. If the port is closed and the
calling process was previously linked to the port, the exit
signal from the port is guaranteed to be delivered before
port_info/2
returns undefined
.
Failure: badarg
if
is not a local
port identifier, or an atom.
is the command name set by
open_port/2
.
If the port identified by
is not open,
undefined
is returned. If the port is closed and the
calling process was previously linked to the port, the exit
signal from the port is guaranteed to be delivered before
port_info/2
returns undefined
.
Failure: badarg
if
is not a local
port identifier, or an atom.
is the process identifier (or equivalent)
of an OS process created with
open_port({spawn | spawn_executable,
Command}, Options)
. If the port is not the result of
spawning an OS process, the value is undefined
.
If the port identified by
is not open,
undefined
is returned. If the port is closed and the
calling process was previously linked to the port, the exit
signal from the port is guaranteed to be delivered before
port_info/2
returns undefined
.
Failure: badarg
if
is not a local
port identifier, or an atom.
is the total number of bytes written
to the port from Erlang processes using
port_command/2
,
port_command/3
,
or
.
If the port identified by
is not open,
undefined
is returned. If the port is closed and the
calling process was previously linked to the port, the exit
signal from the port is guaranteed to be delivered before
port_info/2
returns undefined
.
Failure: badarg
if
is not a local
port identifier, or an atom.
corresponds to the port parallelism
hint used by this port. For more information, see option
parallelism
of open_port/2
.
is the total number
of bytes queued by the port using the ERTS driver queue
implementation.
If the port identified by
is not open,
undefined
is returned. If the port is closed and the
calling process was previously linked to the port, the exit
signal from the port is guaranteed to be delivered before
port_info/2
returns undefined
.
Failure: badarg
if
is not a local
port identifier, or an atom.
is the registered name of
the port. If the port has no registered name, []
is
returned.
If the port identified by
is not open,
undefined
is returned. If the port is closed and the
calling process was previously linked to the port, the exit
signal from the port is guaranteed to be delivered before
port_info/2
returns undefined
.
Failure: badarg
if
is not a local
port identifier, or an atom.
port_to_list(Port) -> string()
Port = port()
Returns a string corresponding to the text
representation of the port identifier
.
erlang:ports() -> [port()]
Returns a list of port identifiers corresponding to all the ports existing on the local node.
Notice that an exiting port exists, but is not open.
pre_loaded() -> [module()]
Returns a list of Erlang modules that are preloaded in
the system. As all loading of code is done through the file
system, the file system must have been loaded previously.
Hence, at least the module init
must be preloaded.
erlang:process_display(Pid, Type) -> true
Pid = pid()
Type = backtrace
Writes information about the local process
on
standard error. The only allowed value for the atom
is backtrace
, which shows the contents
of the call stack, including information about the call chain, with
the current function printed first. The format of the output
is not further defined.
When trap_exit
is set to true
, exit signals
arriving to a process are converted to {'EXIT', From, Reason}
messages, which can be received as ordinary
messages. If trap_exit
is set to false
, the
process exits if it receives an exit signal other than
normal
and the exit signal is propagated to its
linked processes. Application processes are normally
not to trap exits.
Returns the old value of the flag.
See also exit/2
.
Used by a process to redefine the error handler for undefined function calls and undefined registered processes. Inexperienced users are not to use this flag, as code auto-loading depends on the correct operation of the error handling module.
Returns the old value of the flag.
Changes the minimum heap size for the calling process.
Returns the old value of the flag.
Changes the minimum binary virtual heap size for the calling process.
Returns the old value of the flag.
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
This flag sets the maximum heap size for the calling process.
If
is an integer, the system default
values for kill
and error_logger
are used.
size
The maximum size in words of the process. If set to zero, the
heap size limit is disabled. badarg
is be thrown if the
value is smaller than
min_heap_size
. The size check is only done when
a garbage collection is triggered.
size
is the entire heap of the process when garbage collection
is triggered. This includes all generational heaps, the process stack,
any
messages that are considered to be part of the heap, and any
extra memory that the garbage collector needs during collection.
size
is the same as can be retrieved using
erlang:process_info(Pid, total_heap_size)
,
or by adding heap_block_size
, old_heap_block_size
and mbuf_size
from
erlang:process_info(Pid, garbage_collection_info)
.
kill
When set to true
, the runtime system sends an
untrappable exit signal with reason kill
to the process
if the maximum heap size is reached. The garbage collection
that triggered the kill
is not completed, instead the
process exits as soon as possible. When set to false
,
no exit signal is sent to the process, instead it continues
executing.
If kill
is not defined in the map,
the system default will be used. The default system default
is true
. It can be changed by either option
+hmaxk in erl(1)
,
or
erlang:system_flag(max_heap_size, MaxHeapSize)
.
error_logger
When set to true
, the runtime system logs an
error event via
logger
,
containing details about the process when the maximum
heap size is reached. One log event is sent
each time the limit is reached.
If error_logger
is not defined in the map, the system
default is used. The default system default is true
.
It can be changed by either the option
+hmaxel int erl(1)
,
or
erlang:system_flag(max_heap_size, MaxHeapSize)
.
The heap size of a process is quite hard to predict, especially the
amount of memory that is used during the garbage collection. When
contemplating using this option, it is recommended to first run
it in production with kill
set to false
and inspect
the log events to see what the normal peak sizes
of the processes in the system is and then tune the value
accordingly.
message_queue_data() = off_heap | on_heap
This flag determines how messages in the message queue are stored, as follows:
off_heap
All messages in the message queue will be stored outside of the process heap. This implies that no messages in the message queue will be part of a garbage collection of the process.
on_heap
All messages in the message queue will eventually be placed on heap. They can however temporarily be stored off heap. This is how messages always have been stored up until ERTS 8.0.
The default message_queue_data
process flag is determined
by command-line argument
+hmqd
in erl(1)
.
If the process potentially can get many messages in its queue,
you are advised to set the flag to off_heap
. This
because a garbage collection with many messages placed on
the heap can become extremely expensive and the process can
consume large amounts of memory. Performance of the
actual message passing is however generally better when not
using flag off_heap
.
When changing this flag messages will be moved. This work has been initiated but not completed when this function call returns.
Returns the old value of the flag.
priority_level() = low | normal | high | max
Sets the process priority.
is an atom.
Four priority levels exist: low
,
normal
, high
, and max
. Default
is normal
.
Note!
Priority level max
is reserved for internal use in
the Erlang runtime system, and is not to be used
by others.
Internally in each priority level, processes are scheduled in a round robin fashion.
Execution of processes on priority normal
and
low
are interleaved. Processes on priority
low
are selected for execution less
frequently than processes on priority normal
.
When runnable processes on priority high
exist,
no processes on priority low
or normal
are
selected for execution. Notice however that this does
not mean that no processes on priority low
or normal
can run when processes
are running on priority high
. When using multiple
schedulers, more processes can be running
in parallel than processes on priority high
. That is,
a low
and a high
priority process can
execute at the same time.
When runnable processes on priority max
exist,
no processes on priority low
, normal
, or
high
are selected for execution. As with priority
high
, processes on lower priorities can
execute in parallel with processes on priority max
.
Scheduling is pre-emptive. Regardless of priority, a process is pre-empted when it has consumed more than a certain number of reductions since the last time it was selected for execution.
Note!
Do not depend on the scheduling to remain exactly as it is today. Scheduling is likely to be changed in a future release to use available processor cores better.
There is no automatic mechanism for avoiding priority inversion, such as priority inheritance or priority ceilings. When using priorities, take this into account and handle such scenarios by yourself.
Making calls from a high
priority process into code
that you has no control over can cause the high
priority process to wait for a process with lower
priority. That is, effectively decreasing the priority of the
high
priority process during the call. Even if this
is not the case with one version of the code that you have no
control over, it can be the case in a future
version of it. This can, for example, occur if a
high
priority process triggers code loading, as
the code server runs on priority normal
.
Other priorities than normal
are normally not needed.
When other priorities are used, use them with care,
especially priority high
. A
process on priority high
is only
to perform work for short periods. Busy looping for
long periods in a high
priority process causes
most likely problems, as important OTP servers
run on priority normal
.
Returns the old value of the flag.
must be an integer in the interval 0..10000.
If
> 0, call saving is made
active for the
process. This means that information about the
most recent global function calls, BIF calls, sends, and
receives made by the process are saved in a list, which
can be retrieved with
process_info(Pid, last_calls)
. A global function
call is one in which the module of the function is
explicitly mentioned. Only a fixed amount of information
is saved, as follows:
A tuple
{Module, Function, Arity}
for function callsThe atoms
send
,'receive'
, andtimeout
for sends and receives ('receive'
when a message is received andtimeout
when a receive times out)
If N
= 0,
call saving is disabled for the process, which is the
default. Whenever the size of the call saving list is set,
its contents are reset.
Returns the old value of the flag.
Sets or clears flag sensitive
for the current process.
When a process has been marked as sensitive by calling
process_flag(sensitive, true)
, features in the runtime
system that can be used for examining the data or inner working
of the process are silently disabled.
Features that are disabled include (but are not limited to) the following:
Tracing. Trace flags can still be set for the process, but no trace messages of any kind are generated. (If flag
sensitive
is turned off, trace messages are again generated if any trace flags are set.)Sequential tracing. The sequential trace token is propagated as usual, but no sequential trace messages are generated.
process_info/1,2
cannot be used to read out the
message queue or the process dictionary (both are returned
as empty lists).
Stack back-traces cannot be displayed for the process.
In crash dumps, the stack, messages, and the process dictionary are omitted.
If {save_calls,N}
has been set for the process, no
function calls are saved to the call saving list.
(The call saving list is not cleared. Also, send, receive,
and time-out events are still added to the list.)
Returns the old value of the flag.
process_flag(Pid, Flag, Value) -> OldValue
Pid = pid()
Flag = save_calls
Value = OldValue = integer() >= 0
Sets certain flags for the process
,
in the same manner as
process_flag/2
.
Returns the old value of the flag. The valid values for
are only a subset of those allowed in
process_flag/2
, namely save_calls
.
Failure: badarg
if
is not a local process.
process_info(Pid) -> Info
Pid = pid()
Info = [InfoTuple] | undefined
InfoTuple = process_info_result_item()
process_info_result_item() =
{backtrace, Bin :: binary()} |
{binary,
BinInfo ::
[{integer() >= 0,
integer() >= 0,
integer() >= 0}]} |
{catchlevel, CatchLevel :: integer() >= 0} |
{current_function,
{Module :: module(), Function :: atom(), Arity :: arity()} |
undefined} |
{current_location,
{Module :: module(),
Function :: atom(),
Arity :: arity(),
Location ::
[{file, Filename :: string()} |
{line, Line :: integer() >= 1}]}} |
{current_stacktrace, Stack :: [stack_item()]} |
{dictionary, Dictionary :: [{Key :: term(), Value :: term()}]} |
{error_handler, Module :: module()} |
{garbage_collection, GCInfo :: [{atom(), integer() >= 0}]} |
{garbage_collection_info,
GCInfo :: [{atom(), integer() >= 0}]} |
{group_leader, GroupLeader :: pid()} |
{heap_size, Size :: integer() >= 0} |
{initial_call, mfa()} |
{links, PidsAndPorts :: [pid() | port()]} |
{last_calls, false | (Calls :: [mfa()])} |
{memory, Size :: integer() >= 0} |
{message_queue_len, MessageQueueLen :: integer() >= 0} |
{messages, MessageQueue :: [term()]} |
{min_heap_size, MinHeapSize :: integer() >= 0} |
{min_bin_vheap_size, MinBinVHeapSize :: integer() >= 0} |
{max_heap_size, MaxHeapSize :: max_heap_size()} |
{monitored_by,
MonitoredBy :: [pid() | port() | nif_resource()]} |
{monitors,
Monitors ::
[{process | port,
Pid ::
pid() |
port() |
{RegName :: atom(), Node :: node()}}]} |
{message_queue_data, MQD :: message_queue_data()} |
{priority, Level :: priority_level()} |
{reductions, Number :: integer() >= 0} |
{registered_name, [] | (Atom :: atom())} |
{sequential_trace_token,
[] | (SequentialTraceToken :: term())} |
{stack_size, Size :: integer() >= 0} |
{status,
Status ::
exiting | garbage_collecting | waiting | running |
runnable | suspended} |
{suspending,
SuspendeeList ::
[{Suspendee :: pid(),
ActiveSuspendCount :: integer() >= 0,
OutstandingSuspendCount :: integer() >= 0}]} |
{total_heap_size, Size :: integer() >= 0} |
{trace, InternalTraceFlags :: integer() >= 0} |
{trap_exit, Boolean :: boolean()}
priority_level() = low | normal | high | max
stack_item() =
{Module :: module(),
Function :: atom(),
Arity :: arity() | (Args :: [term()]),
Location ::
[{file, Filename :: string()} |
{line, Line :: integer() >= 1}]}
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
message_queue_data() = off_heap | on_heap
Returns a list containing
s with
miscellaneous information about the process identified by
Pid
, or undefined
if the process is not alive.
The order of the
s is undefined and
all
s are not mandatory.
The
s
part of the result can be changed without prior notice.
The
s with the following items
are part of the result:
current_function
initial_call
status
message_queue_len
links
dictionary
trap_exit
error_handler
priority
group_leader
total_heap_size
heap_size
stack_size
reductions
garbage_collection
If the process identified by
has a
registered name,
also an
with item registered_name
is included.
For information about specific
s, see
process_info/2
.
Warning!
This BIF is intended for debugging only. For
all other purposes, use
process_info/2
.
Failure: badarg
if
is not a
local process.
process_info_item() =
backtrace | binary | catchlevel | current_function |
current_location | current_stacktrace | dictionary |
error_handler | garbage_collection | garbage_collection_info |
group_leader | heap_size | initial_call | links | last_calls |
memory | message_queue_len | messages | min_heap_size |
min_bin_vheap_size | monitored_by | monitors |
message_queue_data | priority | reductions | registered_name |
sequential_trace_token | stack_size | status | suspending |
total_heap_size | trace | trap_exit
process_info_result_item() =
{backtrace, Bin :: binary()} |
{binary,
BinInfo ::
[{integer() >= 0,
integer() >= 0,
integer() >= 0}]} |
{catchlevel, CatchLevel :: integer() >= 0} |
{current_function,
{Module :: module(), Function :: atom(), Arity :: arity()} |
undefined} |
{current_location,
{Module :: module(),
Function :: atom(),
Arity :: arity(),
Location ::
[{file, Filename :: string()} |
{line, Line :: integer() >= 1}]}} |
{current_stacktrace, Stack :: [stack_item()]} |
{dictionary, Dictionary :: [{Key :: term(), Value :: term()}]} |
{error_handler, Module :: module()} |
{garbage_collection, GCInfo :: [{atom(), integer() >= 0}]} |
{garbage_collection_info,
GCInfo :: [{atom(), integer() >= 0}]} |
{group_leader, GroupLeader :: pid()} |
{heap_size, Size :: integer() >= 0} |
{initial_call, mfa()} |
{links, PidsAndPorts :: [pid() | port()]} |
{last_calls, false | (Calls :: [mfa()])} |
{memory, Size :: integer() >= 0} |
{message_queue_len, MessageQueueLen :: integer() >= 0} |
{messages, MessageQueue :: [term()]} |
{min_heap_size, MinHeapSize :: integer() >= 0} |
{min_bin_vheap_size, MinBinVHeapSize :: integer() >= 0} |
{max_heap_size, MaxHeapSize :: max_heap_size()} |
{monitored_by,
MonitoredBy :: [pid() | port() | nif_resource()]} |
{monitors,
Monitors ::
[{process | port,
Pid ::
pid() |
port() |
{RegName :: atom(), Node :: node()}}]} |
{message_queue_data, MQD :: message_queue_data()} |
{priority, Level :: priority_level()} |
{reductions, Number :: integer() >= 0} |
{registered_name, [] | (Atom :: atom())} |
{sequential_trace_token,
[] | (SequentialTraceToken :: term())} |
{stack_size, Size :: integer() >= 0} |
{status,
Status ::
exiting | garbage_collecting | waiting | running |
runnable | suspended} |
{suspending,
SuspendeeList ::
[{Suspendee :: pid(),
ActiveSuspendCount :: integer() >= 0,
OutstandingSuspendCount :: integer() >= 0}]} |
{total_heap_size, Size :: integer() >= 0} |
{trace, InternalTraceFlags :: integer() >= 0} |
{trap_exit, Boolean :: boolean()}
stack_item() =
{Module :: module(),
Function :: atom(),
Arity :: arity() | (Args :: [term()]),
Location ::
[{file, Filename :: string()} |
{line, Line :: integer() >= 1}]}
priority_level() = low | normal | high | max
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
message_queue_data() = off_heap | on_heap
Returns information about the process identified by
, as specified by
or
.
Returns undefined
if the process is not alive.
If the process is alive and a single
is specified, the returned value is the corresponding
, unless Item =:= registered_name
and the process has no registered name. In this case,
[]
is returned. This strange behavior is because of
historical reasons, and is kept for backward compatibility.
If
is specified, the result is
.
The
s in
are included with the corresponding
s in the same order as the
s were included
in
. Valid
s can
be included multiple times in
.
Note!
If registered_name
is part of
and the process has no name registered, a
{registered_name, []}
,
will be included in the resulting
. This
behavior is different when a single
Item =:= registered_name
is specified, and when
process_info/1
is used.
Valid
s with corresponding
s:
{backtrace, Bin }
Binary
contains the same information
as the output from
erlang:process_display(
. Use
binary_to_list/1
to obtain the string of characters
from the binary.
{binary, BinInfo }
is a list containing miscellaneous
information about binaries on the heap of this
process.
This
can be changed or
removed without prior notice. In the current implementation
is a list of tuples. The tuples
contain; BinaryId
, BinarySize
, BinaryRefcCount
.
The message queue is on the heap depending on the
process flag
message_queue_data
.
{catchlevel, CatchLevel }
is the number of currently active
catches in this process. This
can be
changed or removed without prior notice.
{current_function, {Module ,
Function , Arity} | undefined}
,
,
is
the current function call of the process. The value
undefined
can be returned if the process is
currently executing native compiled code.
{current_location, {Module ,
Function , Arity ,
Location }}
,
,
is
the current function call of the process.
is a list of two-tuples describing
the location in the source code.
{current_stacktrace, Stack }
Returns the current call stack back-trace (stacktrace)
of the process. The stack has the same format as returned by
erlang:get_stacktrace/0
. The depth of the
stacktrace is truncated according to the backtrace_depth
system flag setting.
{dictionary, Dictionary }
is the process dictionary.
{error_handler, Module }
is the error handler module used by
the process (for undefined function calls, for example).
{garbage_collection, GCInfo }
is a list containing miscellaneous
information about garbage collection for this process.
The content of
can be changed without
prior notice.
{garbage_collection_info, GCInfo }
is a list containing miscellaneous
detailed information about garbage collection for this process.
The content of
can be changed without
prior notice. For details about the meaning of each item, see
gc_minor_start
in erlang:trace/3
.
{group_leader, GroupLeader }
is the group leader for the I/O
of the process.
{heap_size, Size }
is the size in words of the youngest
heap generation of the process. This generation includes
the process stack. This information is highly
implementation-dependent, and can change if the
implementation changes.
{initial_call, {Module , Function ,
Arity }}
,
,
is
the initial function call with which the process was
spawned.
{links, PidsAndPorts }
is a list of process identifiers
and port identifiers, with processes or ports to which the process
has a link.
{last_calls, false|Calls}
The value is false
if call saving is not active
for the process (see
process_flag/3
).
If call saving is active, a list is returned, in which
the last element is the most recent called.
{memory, Size }
is the size in bytes of the process.
This includes call stack, heap, and internal structures.
{message_queue_len, MessageQueueLen }
is the number of messages
currently in the message queue of the process. This is the
length of the list
returned as
the information item messages
(see below).
{messages, MessageQueue }
is a list of the messages to
the process, which have not yet been processed.
{min_heap_size, MinHeapSize }
is the minimum heap size
for the process.
{min_bin_vheap_size, MinBinVHeapSize }
is the minimum binary virtual
heap size for the process.
{monitored_by, MonitoredBy }
A list of identifiers for all the processes, ports and NIF resources, that are monitoring the process.
{monitors, Monitors }
A list of monitors (started by monitor/2
)
that are active for the process. For a local process
monitor or a remote process monitor by a process
identifier, the list consists of:
{process, Pid }
{process, {RegName , Node }}
{port, PortId}
{port, {RegName , Node }}
Node
will
always be the local node name.{message_queue_data, MQD }
Returns the current state of process flag
message_queue_data
.
is either
off_heap
or on_heap
. For more
information, see the documentation of
process_flag(message_queue_data, MQD)
.
{priority, Level }
is the current priority level for
the process. For more information on priorities, see
process_flag(priority, Level)
.
{reductions, Number }
is the number of reductions executed
by the process.
{registered_name, Atom }
is the registered process name.
If the process has no registered name, this tuple is not
present in the list.
{sequential_trace_token, [] |
SequentialTraceToken }
is the sequential trace
token for the process. This
can be
changed or removed without prior notice.
{stack_size, Size }
is the stack size, in words,
of the process.
{status, Status }
is the status of the process and is
one of the following:
exiting
garbage_collecting
waiting
(for a message)running
runnable
(ready to run, but another process is running)suspended
(suspended on a "busy" port or by the BIFerlang:suspend_process/1,2
)
{suspending, SuspendeeList }
is a list of
{
tuples.
is the process identifier of a
process that has been, or is to be,
suspended by the process identified by
through the BIF
erlang:suspend_process/2
or
erlang:suspend_process/1
.
is the number of
times
has been suspended by
.
is the number of not
yet completed suspend requests sent by
,
that is:
-
If
,ActiveSuspendCount =/= 0
is currently in the suspended state.Suspendee -
If
, optionOutstandingSuspendCount =/= 0asynchronous
oferlang:suspend_process/2
has been used and the suspendee has not yet been suspended by
.Pid
Notice that
and
are not the
total suspend count on
,
only the parts contributed by
.
{total_heap_size, Size }
is the total size, in words, of all heap
fragments of the process. This includes the process stack and
any unreceived messages that are considered to be part of the
heap.
{trace, InternalTraceFlags }
is an integer
representing the internal trace flag for this process.
This
can be changed or removed without prior notice.
{trap_exit, Boolean }
is true
if the process
is trapping exits, otherwise false
.
Notice that not all implementations support all
these
s.
Failures:
badarg
Pid
is not a local process.badarg
Item
is an invalid item.processes() -> [pid()]
Returns a list of process identifiers corresponding to all the processes currently existing on the local node.
Notice that an exiting process exists, but is not alive.
That is, is_process_alive/1
returns false
for an exiting process, but its process identifier is part
of the result returned from processes/0
.
Example:
> processes().
[<0.0.0>,<0.2.0>,<0.4.0>,<0.5.0>,<0.7.0>,<0.8.0>]
purge_module(Module) -> true
Module = atom()
Removes old code for
.
Before this BIF is used,
check_process_code/2
is to be called to check
that no processes execute old code in the module.
Warning!
This BIF is intended for the code server (see
code(3)
)
and is not to be used elsewhere.
Note!
As from ERTS 8.0 (Erlang/OTP 19), any lingering processes that still execute the old code is killed by this function. In earlier versions, such incorrect use could cause much more fatal failures, like emulator crash.
Failure: badarg
if there is no old code for
.
put(Key, Val) -> term()
Key = Val = term()
Adds a new
to the process dictionary,
associated with the value
, and returns
undefined
. If
exists, the old
value is deleted and replaced by
, and
the function returns the old value. Example:
>X = put(name, walrus), Y = put(name, carpenter),
Z = get(name),
{X, Y, Z}.
{undefined,walrus,carpenter}
Note!
The values stored when put
is evaluated within
the scope of a catch
are not retracted if a
throw
is evaluated, or if an error occurs.
erlang:raise(Class, Reason, Stacktrace) -> no_return()
Class = error | exit | throw
Reason = term()
Stacktrace = raise_stacktrace()
raise_stacktrace() =
[{module(), atom(), arity() | [term()]} |
{function(), [term()]}] |
[{module(), atom(), arity() | [term()], [{atom(), term()}]} |
{function(), [term()], [{atom(), term()}]}]
Stops the execution of the calling process with an exception of the specified class, reason, and call stack backtrace (stacktrace).
is error
, exit
, or
throw
. So, if it were not for the stacktrace,
erlang:raise(
is equivalent to
erlang:
.
is any term.
is a list as
returned from get_stacktrace()
, that is, a list of
four-tuples {Module, Function, Arity | Args,
Location}
, where Module
and Function
are atoms, and the third element is an integer arity or an
argument list. The stacktrace can also contain {Fun,
Args, Location}
tuples, where Fun
is a local
fun and Args
is an argument list.
Element Location
at the end is optional.
Omitting it is equivalent to specifying an empty list.
The stacktrace is used as the exception stacktrace for the calling process; it is truncated to the current maximum stacktrace depth.
As evaluating this function causes the process to
terminate, it has no return value unless the arguments are
invalid, in which case the function returns the error
reason badarg
. If you want to be
sure not to return, you can call
error(erlang:raise(
and hope to distinguish exceptions later.
erlang:read_timer(TimerRef) -> Result
TimerRef = reference()
Time = integer() >= 0
Result = Time | false
Reads the state of a timer. The same as calling
erlang:read_timer(TimerRef,
[])
.
erlang:read_timer(TimerRef, Options) -> Result | ok
TimerRef = reference()
Async = boolean()
Option = {async, Async}
Options = [Option]
Time = integer() >= 0
Result = Time | false
Reads the state of a timer that has been created by either
erlang:start_timer
or erlang:send_after
.
identifies the timer, and
was returned by the BIF that created the timer.
:
{async, Async}
Asynchronous request for state information. Async
defaults to false
, which causes the operation
to be performed synchronously. In this case, the Result
is returned by erlang:read_timer
. When
Async
is true
, erlang:read_timer
sends an asynchronous request for the state information
to the timer service that manages the timer, and then returns
ok
. A message on the format {read_timer,
is
sent to the caller of erlang:read_timer
when the
operation has been processed.
More
s can be added in the future.
If
is an integer, it represents the
time in milliseconds left until the timer expires.
If
is false
, a
timer corresponding to
could not
be found. This because the timer had expired,
or been canceled, or because
never has corresponded to a timer. Even if the timer has expired,
it does not tell you whether or not the time-out message has
arrived at its destination yet.
Note!
The timer service that manages the timer can be co-located
with another scheduler than the scheduler that the calling
process is executing on. If so, communication
with the timer service takes much longer time than if it
is located locally. If the calling process is in a critical
path, and can do other things while waiting for the result
of this operation, you want to use option {async, true}
.
If using option {async, false}
, the calling
process is blocked until the operation has been performed.
See also
erlang:send_after/4
,
erlang:start_timer/4
, and
erlang:cancel_timer/2
.
ref_to_list(Ref) -> string()
Ref = reference()
Returns a string corresponding to the text
representation of
.
Warning!
This BIF is intended for debugging and is not to be used in application programs.
register(RegName, PidOrPort) -> true
RegName = atom()
PidOrPort = port() | pid()
Associates the name
with a process
identifier (pid) or a port identifier.
, which must be an atom, can be used
instead of the pid or port identifier in send operator
(
). Example:
> register(db, Pid).
true
Failures:
badarg
PidOrPort
is not an existing local
process or port.badarg
RegName
is already in use.badarg
badarg
RegName
is the atom
undefined
.registered() -> [RegName]
RegName = atom()
Returns a list of names that have been registered using
register/2
, for
example:
> registered().
[code_server, file_server, init, user, my_db]
erlang:resume_process(Suspendee) -> true
Suspendee = pid()
Decreases the suspend count on the process identified by
.
is previously to have been suspended through
erlang:suspend_process/2
or
erlang:suspend_process/1
by the process calling
erlang:resume_process(
. When the
suspend count on
reaches zero,
is resumed, that is, its state
is changed from suspended into the state it had before it was
suspended.
Warning!
This BIF is intended for debugging only.
Failures:
badarg
Suspendee
is not a process identifier.
badarg
erlang:resume_process/1
had
not previously increased the suspend count on the process
identified by Suspendee
.
badarg
Suspendee
is not alive.
round(Number) -> integer()
Number = number()
Returns an integer by rounding
,
for example:
round(5.5).
6
Allowed in guard tests.
self() -> pid()
Returns the process identifier of the calling process, for example:
> self().
<0.26.0>
Allowed in guard tests.
erlang:send(Dest, Msg) -> Msg
Dest = dst()
Msg = term()
dst() =
pid() |
port() |
(RegName :: atom()) |
{RegName :: atom(), Node :: node()}
Sends a message and returns
. This
is the same as using the
send operator:
.
can be a remote or local process identifier,
a (local) port, a locally registered name, or a tuple
{
for a registered name at another node.
The function fails with a badarg
run-time error if
is an atom name, but this name is not
registered. This is the only case when send
fails for an
unreachable destination
(of correct type).
erlang:send(Dest, Msg, Options) -> Res
Dest = dst()
Msg = term()
Options = [nosuspend | noconnect]
Res = ok | nosuspend | noconnect
dst() =
pid() |
port() |
(RegName :: atom()) |
{RegName :: atom(), Node :: node()}
Either sends a message and returns ok
, or does not send
the message but returns something else (see below).
Otherwise the same as
erlang:send/2
.
For more detailed explanation and warnings, see
erlang:send_nosuspend/2,3
.
Options:
nosuspend
nosuspend
is returned instead.
noconnect
noconnect
is returned
instead.
Warning!
As with erlang:send_nosuspend/2,3
: use with extreme
care.
erlang:send_after(Time, Dest, Msg) -> TimerRef
Time = integer() >= 0
Dest = pid() | atom()
Msg = term()
TimerRef = reference()
Starts a timer. The same as calling
erlang:send_after(
.
erlang:send_after(Time, Dest, Msg, Options) -> TimerRef
Time = integer()
Dest = pid() | atom()
Msg = term()
Options = [Option]
Abs = boolean()
Option = {abs, Abs}
TimerRef = reference()
Starts a timer. When the timer expires, the message
is sent to the process
identified by
. Apart from
the format of the time-out message, this function works exactly as
erlang:start_timer/4
.
erlang:send_nosuspend(Dest, Msg) -> boolean()
Dest = dst()
Msg = term()
dst() =
pid() |
port() |
(RegName :: atom()) |
{RegName :: atom(), Node :: node()}
The same as
erlang:send(
,
but returns true
if
the message was sent and false
if the message was not
sent because the sender would have had to be suspended.
This function is intended for send operations to an
unreliable remote node without ever blocking the sending
(Erlang) process. If the connection to the remote node
(usually not a real Erlang node, but a node written in C or
Java) is overloaded, this function does not send the message
and returns false
.
The same occurs if
refers to a local port
that is busy. For all other destinations (allowed for the ordinary
send operator '!'
), this function sends the message and
returns true
.
This function is only to be used in rare circumstances
where a process communicates with Erlang nodes that can
disappear without any trace, causing the TCP buffers and
the drivers queue to be over-full before the node is
shut down (because of tick time-outs) by net_kernel
.
The normal reaction to take when this occurs is some kind of
premature shutdown of the other node.
Notice that ignoring the return value from this function would
result in an unreliable message passing, which is
contradictory to the Erlang programming model. The message is
not sent if this function returns false
.
In many systems, transient states of
overloaded queues are normal. Although this function
returns false
does not mean that the other
node is guaranteed to be non-responsive, it could be a
temporary overload. Also, a return value of true
does
only mean that the message can be sent on the (TCP) channel
without blocking; the message is not guaranteed to
arrive at the remote node. For a disconnected
non-responsive node, the return value is true
(mimics
the behavior of operator !
). The expected
behavior and the actions to take when the function
returns false
are application- and hardware-specific.
Warning!
Use with extreme care.
erlang:send_nosuspend(Dest, Msg, Options) -> boolean()
Dest = dst()
Msg = term()
Options = [noconnect]
dst() =
pid() |
port() |
(RegName :: atom()) |
{RegName :: atom(), Node :: node()}
The same as
erlang:send(
,
but with a Boolean return value.
This function behaves like
erlang:send_nosuspend/2
,
but takes a third parameter, a list of options.
The only option is noconnect
, which
makes the function return false
if
the remote node is not currently reachable by the local
node. The normal behavior is to try to connect to the node,
which can stall the process during a short period. The use of
option noconnect
makes it possible to be
sure not to get the slightest delay when
sending to a remote process. This is especially useful when
communicating with nodes that expect to always be
the connecting part (that is, nodes written in C or Java).
Whenever the function returns false
(either when a
suspend would occur or when noconnect
was specified and
the node was not already connected), the message is guaranteed
not to have been sent.
Warning!
Use with extreme care.
erlang:set_cookie(Node, Cookie) -> true
Node = node()
Cookie = atom()
Sets the magic cookie of
to the atom
. If
is the
local node, the function
also sets the cookie of all other unknown nodes to
(see section
Distributed Erlang
in the Erlang Reference Manual in System Documentation).
Failure: function_clause
if the local node is not
alive.
setelement(Index, Tuple1, Value) -> Tuple2
Index = integer() >= 1
Tuple1 = Tuple2 = tuple()
Value = term()
Returns a tuple that is a copy of argument
with the element specified by integer argument
(the first element is the element with index 1) replaced by
argument
, for example:
> setelement(2, {10, green, bottles}, red).
{10,red,bottles}
size(Item) -> integer() >= 0
Item = tuple() | binary()
Returns the number of elements in a tuple or the number of bytes in a binary or bitstring, for example:
>size({morni, mulle, bwange}).
3 >size(<<11, 22, 33>>).
3
For bitstrings, the number of whole bytes is returned. That is, if the number of bits in the bitstring is not divisible by 8, the resulting number of bytes is rounded down.
Allowed in guard tests.
See also
tuple_size/1
,
byte_size/1
, and
bit_size/1
.
spawn(Fun) -> pid()
Fun = function()
Returns the process identifier of a new process started by the
application of
to the empty list
[]
. Otherwise
works like spawn/3
.
spawn(Node, Fun) -> pid()
Node = node()
Fun = function()
Returns the process identifier of a new process started
by the application of
to the
empty list []
on
. If
does not exist, a useless pid is
returned. Otherwise works like
spawn/3
.
spawn(Module, Function, Args) -> pid()
Module = module()
Function = atom()
Args = [term()]
Returns the process identifier of a new process started by
the application of
to
.
error_handler:undefined_function(
is evaluated by the new process if
does not exist (where Arity
is the length of
). The error handler
can be redefined (see
process_flag/2
).
If error_handler
is undefined, or the user has
redefined the default error_handler
and its replacement is
undefined, a failure with reason undef
occurs.
Example:
> spawn(speed, regulator, [high_speed, thin_cut]).
<0.13.1>
spawn(Node, Module, Function, Args) -> pid()
Node = node()
Module = module()
Function = atom()
Args = [term()]
Returns the process identifier (pid) of a new process started
by the application
of
to
on
. If
does not exist, a useless pid is returned.
Otherwise works like
spawn/3
.
spawn_link(Fun) -> pid()
Fun = function()
Returns the process identifier of a new process started by
the application of
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()
Node = node()
Fun = function()
Returns the process identifier (pid) of a new process started
by the application of
to the empty
list []
on
. A link is
created between the calling process and the new process,
atomically. If
does not exist,
a useless pid is returned and an exit signal with
reason noconnection
is sent to the calling
process. Otherwise works like
spawn/3
.
spawn_link(Module, Function, Args) -> pid()
Module = module()
Function = atom()
Args = [term()]
Returns the process identifier of a new process started by
the application of
to
. 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()
Node = node()
Module = module()
Function = atom()
Args = [term()]
Returns the process identifier (pid) of a new process
started by the application
of
to
on
. A
link is created between the calling process and the new
process, atomically. If
does
not exist, a useless pid is returned and an exit signal with
reason noconnection
is sent to the calling
process. Otherwise works like
spawn/3
.
spawn_monitor(Fun) -> {pid(), reference()}
Fun = function()
Returns the process identifier of a new process, started by
the application of
to the empty list
[]
,
and a reference for a monitor created to the new process.
Otherwise works like
spawn/3
.
spawn_monitor(Module, Function, Args) -> {pid(), reference()}
Module = module()
Function = atom()
Args = [term()]
A new process is started by the application
of
to
. The process is
monitored at the same time. Returns the process identifier
and a reference for the monitor. Otherwise works like
spawn/3
.
spawn_opt(Fun, Options) -> pid() | {pid(), reference()}
Fun = function()
Options = [spawn_opt_option()]
priority_level() = low | normal | high | max
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
message_queue_data() = off_heap | on_heap
spawn_opt_option() =
link | monitor |
{priority, Level :: priority_level()} |
{fullsweep_after, Number :: integer() >= 0} |
{min_heap_size, Size :: integer() >= 0} |
{min_bin_vheap_size, VSize :: integer() >= 0} |
{max_heap_size, Size :: max_heap_size()} |
{message_queue_data, MQD :: message_queue_data()}
Returns the process identifier (pid) of a new process
started by the application of
to the empty list []
. Otherwise works like
spawn_opt/4
.
If option monitor
is specified, the newly created
process is monitored, and both the pid and reference for
the monitor are returned.
spawn_opt(Node, Fun, Options) -> pid() | {pid(), reference()}
Node = node()
Fun = function()
Options = [spawn_opt_option()]
priority_level() = low | normal | high | max
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
message_queue_data() = off_heap | on_heap
spawn_opt_option() =
link | monitor |
{priority, Level :: priority_level()} |
{fullsweep_after, Number :: integer() >= 0} |
{min_heap_size, Size :: integer() >= 0} |
{min_bin_vheap_size, VSize :: integer() >= 0} |
{max_heap_size, Size :: max_heap_size()} |
{message_queue_data, MQD :: message_queue_data()}
Returns the process identifier (pid) of a new process started
by the application of
to the
empty list []
on
. If
does not exist, a useless pid is
returned. Otherwise works like
spawn_opt/4
.
spawn_opt(Module, Function, Args, Options) ->
pid() | {pid(), reference()}
Module = module()
Function = atom()
Args = [term()]
Options = [spawn_opt_option()]
priority_level() = low | normal | high | max
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
message_queue_data() = off_heap | on_heap
spawn_opt_option() =
link | monitor |
{priority, Level :: priority_level()} |
{fullsweep_after, Number :: integer() >= 0} |
{min_heap_size, Size :: integer() >= 0} |
{min_bin_vheap_size, VSize :: integer() >= 0} |
{max_heap_size, Size :: max_heap_size()} |
{message_queue_data, MQD :: message_queue_data()}
Works as
spawn/3
, except that an
extra option list is specified when creating the process.
If option monitor
is specified, the newly created
process is monitored, and both the pid and reference for
the monitor are returned.
Options:
link
Sets a link to the parent process (like
spawn_link/3
does).
monitor
Monitors the new process (like
monitor/2
does).
{priority, Level }
Sets the priority of the new process. Equivalent to
executing
process_flag(priority,
in the start function of the new process,
except that the priority is set before the process is
selected for execution for the first time. For more
information on priorities, see
process_flag(priority,
.
{fullsweep_after, Number }
Useful only for performance tuning. Do not use this option unless you know that there is problem with execution times or memory consumption, and ensure that the option improves matters.
The Erlang runtime system uses a generational garbage collection scheme, using an "old heap" for data that has survived at least one garbage collection. When there is no more room on the old heap, a fullsweep garbage collection is done.
Option fullsweep_after
makes it possible to
specify the maximum number of generational collections
before forcing a fullsweep, even if there is room on
the old heap. Setting the number to zero
disables the general collection algorithm, that is,
all live data is copied at every garbage collection.
A few cases when it can be useful to change
fullsweep_after
:
If binaries that are no longer used are to be thrown away as soon as possible. (Set
to zero.)Number A process that mostly have short-lived data is fullsweeped seldom or never, that is, the old heap contains mostly garbage. To ensure a fullsweep occasionally, set
to a suitable value, such as 10 or 20.Number - In embedded systems with a limited amount of RAM
and no virtual memory, you might want to preserve memory
by setting
to zero. (The value can be set globally, seeNumber erlang:system_flag/2
.)
{min_heap_size, Size }
Useful only for performance tuning. Do not use this option unless you know that there is problem with execution times or memory consumption, and ensure that the option improves matters.
Gives a minimum heap size, in words. Setting this value
higher than the system default can speed up some
processes because less garbage collection is done.
However, setting a too high value can waste memory and
slow down the system because of worse data locality.
Therefore, use this option only for
fine-tuning an application and to measure the execution
time with various
values.
{min_bin_vheap_size, VSize }
Useful only for performance tuning. Do not use this option unless you know that there is problem with execution times or memory consumption, and ensure that the option improves matters.
Gives a minimum binary virtual heap size, in words.
Setting this value
higher than the system default can speed up some
processes because less garbage collection is done.
However, setting a too high value can waste memory.
Therefore, use this option only for
fine-tuning an application and to measure the execution
time with various
values.
{max_heap_size, Size }
Sets the max_heap_size
process flag. The default
max_heap_size
is determined by command-line argument
+hmax
in erl(1)
. For more information, see the
documentation of
process_flag(max_heap_size,
.
{message_queue_data, MQD }
Sets the state of the message_queue_data
process
flag.
is to be either off_heap
or on_heap
. The default
message_queue_data
process flag is determined by
command-line argument
+hmqd
in erl(1)
.
For more information, see the documentation of
process_flag(message_queue_data,
.
spawn_opt(Node, Module, Function, Args, Options) ->
pid() | {pid(), reference()}
Node = node()
Module = module()
Function = atom()
Args = [term()]
Options = [spawn_opt_option()]
priority_level() = low | normal | high | max
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
message_queue_data() = off_heap | on_heap
spawn_opt_option() =
link | monitor |
{priority, Level :: priority_level()} |
{fullsweep_after, Number :: integer() >= 0} |
{min_heap_size, Size :: integer() >= 0} |
{min_bin_vheap_size, VSize :: integer() >= 0} |
{max_heap_size, Size :: max_heap_size()} |
{message_queue_data, MQD :: message_queue_data()}
Returns the process identifier (pid) of a new process started
by the application
of
to
on
. If
does not exist, a useless pid is returned.
Otherwise works like
spawn_opt/4
.
Note!
Option monitor
is not supported by
spawn_opt/5
.
split_binary(Bin, Pos) -> {binary(), binary()}
Bin = binary()
Pos = integer() >= 0
Pos = 0..byte_size(Bin)
Returns a tuple containing the binaries that are the result
of splitting
into two parts at
position
.
This is not a destructive operation. After the operation,
there are three binaries altogether. Example:
>B = list_to_binary("0123456789").
<<"0123456789">> >byte_size(B).
10 >{B1, B2} = split_binary(B,3).
{<<"012">>,<<"3456789">>} >byte_size(B1).
3 >byte_size(B2).
7
erlang:start_timer(Time, Dest, Msg) -> TimerRef
Time = integer() >= 0
Dest = pid() | atom()
Msg = term()
TimerRef = reference()
Starts a timer. The same as calling
erlang:start_timer(
.
erlang:start_timer(Time, Dest, Msg, Options) -> TimerRef
Time = integer()
Dest = pid() | atom()
Msg = term()
Options = [Option]
Abs = boolean()
Option = {abs, Abs}
TimerRef = reference()
Starts a timer. When the timer expires, the message
{timeout,
is sent to the process identified by
.
s:
{abs, false}
This is the default. It means the
value is interpreted
as a time in milliseconds relative current
Erlang
monotonic time.
{abs, true}
Absolute
value. The
value is interpreted as an
absolute Erlang monotonic time in milliseconds.
More
s can be added in the future.
The absolute point in time, the timer is set to expire on,
must be in the interval
[
erlang:system_info(start_time)
,
erlang:system_info(end_time)
]
.
If a relative time is specified, the
value is not allowed to be negative.
If
is a pid()
, it must
be a pid()
of a process created on the current
runtime system instance. This process has either terminated
or not. If
is an
atom()
, it is interpreted as the name of a
locally registered process. The process referred to by the
name is looked up at the time of timer expiration. No error
is returned if the name does not refer to a process.
If
is a pid()
, the timer is
automatically canceled if the process referred to by the
pid()
is not alive, or if the process exits. This
feature was introduced in ERTS 5.4.11. Notice that
timers are not automatically canceled when
is an atom()
.
See also
erlang:send_after/4
,
erlang:cancel_timer/2
, and
erlang:read_timer/2
.
Failure: badarg
if the arguments do not satisfy
the requirements specified here.
Returns the same as
statistics(active_tasks_all)
with the exception that no information about the dirty
IO run queue and its associated schedulers is part of
the result. That is, only tasks that are expected to be
CPU bound are part of the result.
Returns a list where each element represents the amount of active processes and ports on each run queue and its associated schedulers. That is, the number of processes and ports that are ready to run, or are currently running. Values for normal run queues and their associated schedulers are located first in the resulting list. The first element corresponds to scheduler number 1 and so on. If support for dirty schedulers exist, an element with the value for the dirty CPU run queue and its associated dirty CPU schedulers follow and then as last element the value for the the dirty IO run queue and its associated dirty IO schedulers follow. The information is not gathered atomically. That is, the result is not necessarily a consistent snapshot of the state, but instead quite efficiently gathered.
Note!
Each normal scheduler has one run queue that it manages. If dirty schedulers schedulers are supported, all dirty CPU schedulers share one run queue, and all dirty IO schedulers share one run queue. That is, we have multiple normal run queues, one dirty CPU run queue and one dirty IO run queue. Work can not migrate between the different types of run queues. Only work in normal run queues can migrate to other normal run queues. This has to be taken into account when evaluating the result.
See also
statistics(total_active_tasks)
,
statistics(run_queue_lengths)
,
statistics(run_queue_lengths_all)
,
statistics(total_run_queue_lengths)
, and
statistics(total_run_queue_lengths_all)
.
Returns the total number of context switches since the system started.
Returns the number of exact reductions.
Note!
statistics(exact_reductions)
is
a more expensive operation than
statistics(reductions).
Returns information about garbage collection, for example:
> statistics(garbage_collection).
{85,23961,0}
This information can be invalid for some implementations.
Returns
,
which is the total number of bytes
received through ports, and
,
which is the total number of bytes output to ports.
Microstate accounting can be used to measure how much time the Erlang
runtime system spends doing various tasks. It is designed to be as
lightweight as possible, but some overhead exists when this
is enabled. Microstate accounting is meant to be a profiling tool
to help finding performance bottlenecks.
To start
/stop
/reset
microstate accounting, use
system flag
microstate_accounting
.
statistics(microstate_accounting)
returns a list of maps
representing some of the OS threads within ERTS. Each map
contains type
and id
fields that can be used to
identify what
thread it is, and also a counters field that contains data about how
much time has been spent in the various states.
Example:
> erlang:statistics(microstate_accounting).
[#{counters => #{aux => 1899182914,
check_io => 2605863602,
emulator => 45731880463,
gc => 1512206910,
other => 5421338456,
port => 221631,
sleep => 5150294100},
id => 1,
type => scheduler}|...]
The time unit is the same as returned by
os:perf_counter/0
.
So, to convert it to milliseconds, you can do something like this:
lists:map( fun(#{ counters := Cnt } = M) -> MsCnt = maps:map(fun(_K, PerfCount) -> erlang:convert_time_unit(PerfCount, perf_counter, 1000) end, Cnt), M#{ counters := MsCnt } end, erlang:statistics(microstate_accounting)).
Notice that these values are not guaranteed to be the exact time spent in each state. This is because of various optimisation done to keep the overhead as small as possible.
s:
scheduler
dirty_cpu_scheduler
dirty_io_scheduler
async
aux
poll
The following
s are available.
All states are exclusive, meaning that a thread cannot be in two
states at once. So, if you add the numbers of all counters in a
thread, you get the total runtime for that thread.
aux
check_io
emulator
gc
other
port
sleep
More fine-grained
s can
be added through configure (such as
./configure --with-microstate-accounting=extra
).
Enabling these states causes performance degradation when
microstate accounting is turned off and increases the overhead when
it is turned on.
alloc
bif
emulator
state.busy_wait
statistics(scheduler_wall_time)
. So, if you add
all other states but this and sleep, and then divide that by all
time in the thread, you should get something very similar to the
scheduler_wall_time
fraction. Without extra states this
time is part of the other
state.ets
emulator
state.gc_full
gc
state.nif
emulator
state.send
emulator
state.timers
other
state.The utility module
msacc(3)
can be used to more easily analyse these statistics.
Returns undefined
if system flag
microstate_accounting
is turned off.
The list of thread information is unsorted and can appear in different order between calls.
Note!
The threads and states are subject to change without any prior notice.
Returns information about reductions, for example:
> statistics(reductions).
{2046,11}
Note!
As from ERTS 5.5 (Erlang/OTP R11B),
this value does not include reductions performed in current
time slices of currently scheduled processes. If an
exact value is wanted, use
statistics(exact_reductions)
.
Returns the total length of all normal run-queues. That is, the number
of processes and ports that are ready to run on all available
normal run-queues. Dirty run queues are not part of the
result. The information is gathered atomically. That
is, the result is a consistent snapshot of the state, but
this operation is much more expensive compared to
statistics(total_run_queue_lengths)
,
especially when a large amount of schedulers is used.
Returns the same as
statistics(run_queue_lengths_all)
with the exception that no information about the dirty
IO run queue is part of the result. That is, only
run queues with work that is expected to be CPU bound
is part of the result.
Returns a list where each element represents the amount of processes and ports ready to run for each run queue. Values for normal run queues are located first in the resulting list. The first element corresponds to the normal run queue of scheduler number 1 and so on. If support for dirty schedulers exist, values for the dirty CPU run queue and the dirty IO run queue follow (in that order) at the end. The information is not gathered atomically. That is, the result is not necessarily a consistent snapshot of the state, but instead quite efficiently gathered.
Note!
Each normal scheduler has one run queue that it manages. If dirty schedulers schedulers are supported, all dirty CPU schedulers share one run queue, and all dirty IO schedulers share one run queue. That is, we have multiple normal run queues, one dirty CPU run queue and one dirty IO run queue. Work can not migrate between the different types of run queues. Only work in normal run queues can migrate to other normal run queues. This has to be taken into account when evaluating the result.
See also
statistics(run_queue_lengths)
,
statistics(total_run_queue_lengths_all)
,
statistics(total_run_queue_lengths)
,
statistics(active_tasks)
,
statistics(active_tasks_all)
, and
statistics(total_active_tasks)
,
statistics(total_active_tasks_all)
.
Returns information about runtime, in milliseconds.
This is the sum of the runtime for all threads in the Erlang runtime system and can therefore be greater than the wall clock time.
Warning!
This value might wrap due to limitations in the underlying functionality provided by the operating system that is used.
Example:
> statistics(runtime).
{1690,1620}
Returns a list of tuples with
{
, where
is an integer ID of the scheduler,
is
the duration the scheduler has been busy, and
is the total time duration since
scheduler_wall_time
activation for the specific scheduler. Note that
activation time can differ significantly between
schedulers. Currently dirty schedulers are activated
at system start while normal schedulers are activated
some time after the scheduler_wall_time
functionality is enabled. The time unit is undefined
and can be subject to change between releases, OSs,
and system restarts. scheduler_wall_time
is only
to be used to calculate relative values for scheduler
utilization.
can never
exceed
.
The definition of a busy scheduler is when it is not idle and is not scheduling (selecting) a process or port, that is:
- Executing process code
- Executing linked-in driver or NIF code
- Executing BIFs, or any other runtime handling
- Garbage collecting
- Handling any other memory management
Notice that a scheduler can also be busy even if the OS has scheduled out the scheduler thread.
Returns undefined
if system flag
scheduler_wall_time
is turned off.
The list of scheduler information is unsorted and can appear in different order between calls.
As of ERTS version 9.0, also dirty CPU schedulers will
be included in the result. That is, all scheduler threads
that are expected to handle CPU bound work. If you also
want information about dirty I/O schedulers, use
statistics(scheduler_wall_time_all)
instead.
Normal schedulers will have scheduler identifiers in
the range 1 =<
erlang:system_info(schedulers)
.
Dirty CPU schedulers will have scheduler identifiers in
the range erlang:system_info(schedulers) <
erlang:system_info(dirty_cpu_schedulers)
.
Note!
The different types of schedulers handle specific types of jobs. Every job is assigned to a specific scheduler type. Jobs can migrate between different schedulers of the same type, but never between schedulers of different types. This fact has to be taken under consideration when evaluating the result returned.
Using scheduler_wall_time
to calculate
scheduler utilization:
>erlang:system_flag(scheduler_wall_time, true).
false >Ts0 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.
ok
Some time later the user takes another snapshot and calculates scheduler utilization per scheduler, for example:
>Ts1 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.
ok >lists:map(fun({{I, A0, T0}, {I, A1, T1}}) -> {I, (A1 - A0)/(T1 - T0)} end, lists:zip(Ts0,Ts1)).
[{1,0.9743474730177548}, {2,0.9744843782751444}, {3,0.9995902361669045}, {4,0.9738012596572161}, {5,0.9717956667018103}, {6,0.9739235846420741}, {7,0.973237033077876}, {8,0.9741297293248656}]
Using the same snapshots to calculate a total scheduler utilization:
> {A, T} = lists:foldl(fun({{_, A0, T0}, {_, A1, T1}}, {Ai,Ti}) ->
{Ai + (A1 - A0), Ti + (T1 - T0)} end, {0, 0}, lists:zip(Ts0,Ts1)),
TotalSchedulerUtilization = A/T.
0.9769136803764825
Total scheduler utilization will equal 1.0
when
all schedulers have been active all the time between the
two measurements.
Another (probably more) useful value is to calculate total scheduler utilization weighted against maximum amount of available CPU time:
> WeightedSchedulerUtilization = (TotalSchedulerUtilization
* (erlang:system_info(schedulers)
+ erlang:system_info(dirty_cpu_schedulers)))
/ erlang:system_info(logical_processors_available).
0.9769136803764825
This weighted scheduler utilization will reach 1.0
when schedulers are active the same amount of time as
maximum available CPU time. If more schedulers exist
than available logical processors, this value may
be greater than 1.0
.
As of ERTS version 9.0, the Erlang runtime system will as default have more schedulers than logical processors. This due to the dirty schedulers.
Note!
scheduler_wall_time
is by default disabled. To
enable it, use
erlang:system_flag(scheduler_wall_time, true)
.
The same as
statistics(scheduler_wall_time)
,
except that it also include information about all dirty I/O
schedulers.
Dirty IO schedulers will have scheduler identifiers in
the range
erlang:system_info(schedulers)
+
erlang:system_info(dirty_cpu_schedulers)
<
erlang:system_info(dirty_io_schedulers)
.
Note!
Note that work executing on dirty I/O schedulers are expected to mainly wait for I/O. That is, when you get high scheduler utilization on dirty I/O schedulers, CPU utilization is not expected to be high due to this work.
The same as calling
lists:sum(
statistics(active_tasks)
)
,
but more efficient.
The same as calling
lists:sum(
statistics(active_tasks_all)
)
,
but more efficient.
The same as calling
lists:sum(
statistics(run_queue_lengths)
)
,
but more efficient.
The same as calling
lists:sum(
statistics(run_queue_lengths_all)
)
,
but more efficient.
Returns information about wall clock. wall_clock
can
be used in the same manner as
runtime
, except that real time is measured as
opposed to runtime or CPU time.
erlang:suspend_process(Suspendee) -> true
Suspendee = pid()
Suspends the process identified by
. The same as calling
erlang:suspend_process(
.
Warning!
This BIF is intended for debugging only.
erlang:suspend_process(Suspendee, OptList) -> boolean()
Suspendee = pid()
OptList = [Opt]
Opt = unless_suspending | asynchronous | {asynchronous, term()}
Increases the suspend count on the process identified by
and puts it in the suspended
state if it is not
already in that state. A suspended process is not
scheduled for execution until the process has been resumed.
A process can be suspended by multiple processes and can
be suspended multiple times by a single process. A suspended
process does not leave the suspended state until its suspend
count reaches zero. The suspend count of
is decreased when
erlang:resume_process(
is called by the same process that called
erlang:suspend_process(
.
All increased suspend
counts on other processes acquired by a process are automatically
decreased when the process terminates.
Options (
s):
asynchronous
A suspend request is sent to the process identified by
.
eventually suspends
unless it is resumed before it could suspend. The caller
of erlang:suspend_process/2
returns immediately,
regardless of whether
has
suspended yet or not. The point in time when
suspends cannot be deduced
from other events in the system. It is only guaranteed that
eventually suspends
(unless it
is resumed). If no asynchronous
options has
been passed, the caller of erlang:suspend_process/2
is
blocked until
has suspended.
{asynchronous, ReplyTag}
A suspend request is sent to the process identified by
. When the suspend request
has been processed, a reply message is sent to the caller
of this function. The reply is on the form {ReplyTag,
State}
where State
is either:
exited
has exited.
suspended
is now suspended.
not_suspended
is not suspended.
This can only happen when the process that
issued this request, have called
resume_process(
before getting the reply.
Appart from the reply message, the {asynchronous,
ReplyTag}
option behaves exactly the same as the
asynchronous
option without reply tag.
unless_suspending
The process identified by
is
suspended unless the calling process already is suspending
.
If unless_suspending
is combined
with option asynchronous
, a suspend request is
sent unless the calling process already is suspending
or if a suspend request
already has been sent and is in transit. If the calling
process already is suspending
,
or if combined with option asynchronous
and a send request already is in transit,
false
is returned and the suspend count on
remains unchanged.
If the suspend count on the process identified by
is increased, true
is returned, otherwise false
.
Warning!
This BIF is intended for debugging only.
Warning!
You can easily create deadlocks if processes suspends each other (directly or in circles). In ERTS versions prior to ERTS version 10.0, the runtime system prevented such deadlocks, but this prevention has now been removed due to performance reasons.
Failures:
badarg
Suspendee
is not a process identifier.
badarg
Suspendee
is the same process
as the process calling erlang:suspend_process/2
.
badarg
Suspendee
is not alive.
badarg
Suspendee
resides on another node.
badarg
OptList
is not a proper list of valid
Opt
s.
system_limit
Suspendee
has been suspended
more times by the calling process than can be represented by the
currently used internal data structures. The system limit is
> 2,000,000,000 suspends and will never be lower.
Sets the maximum depth of call stack back-traces in the
exit reason element of 'EXIT'
tuples. The flag
also limits the stacktrace depth returned by process_info
item current_stacktrace.
Returns the old value of the flag.
cpu_topology() = [LevelEntry :: level_entry()] | undefined
level_entry() =
{LevelTag :: level_tag(), SubLevel :: sub_level()} |
{LevelTag :: level_tag(),
InfoList :: info_list(),
SubLevel :: sub_level()}
level_tag() = core | node | processor | thread
sub_level() =
[LevelEntry :: level_entry()] |
(LogicalCpuId :: {logical, integer() >= 0})
info_list() = []
Warning!
This argument is deprecated.
Instead of using this argument, use command-line argument
+sct
in
erl(1)
.
When this argument is removed, a final CPU topology to use is determined at emulator boot time.
Sets the user-defined
.
The user-defined
CPU topology overrides any automatically detected
CPU topology. By passing undefined
as
,
the system reverts to the CPU topology automatically
detected. The returned value equals the value returned
from erlang:system_info(cpu_topology)
before the
change was made.
Returns the old value of the flag.
The CPU topology is used when binding schedulers to logical processors. If schedulers are already bound when the CPU topology is changed, the schedulers are sent a request to rebind according to the new CPU topology.
The user-defined CPU topology can also be set by passing
command-line argument
+sct
to
erl(1)
.
For information on type
and more, see
erlang:system_info(cpu_topology)
as well as command-line flags
+sct
and
+sbt
in
erl(1)
.
Sets the number of dirty CPU schedulers online. Range is
1 <= DirtyCPUSchedulersOnline <= N
, where N
is the smallest of the return values of
erlang:system_info(dirty_cpu_schedulers)
and
erlang:system_info(schedulers_online)
.
Returns the old value of the flag.
The number of dirty CPU schedulers online can change if the
number of schedulers online changes. For example, if 12
schedulers and 6 dirty CPU schedulers are online, and
system_flag/2
is used to set the number of
schedulers online to 6, then the number of dirty CPU
schedulers online is automatically decreased by half as well,
down to 3. Similarly, the number of dirty CPU schedulers
online increases proportionally to increases in the number of
schedulers online.
For more information, see
erlang:system_info(dirty_cpu_schedulers)
and
erlang:system_info(dirty_cpu_schedulers_online)
.
Sets system flags for
erts_alloc(3)
.
is the allocator to affect, for example
binary_alloc
.
is the flag to change and
is the new value.
Only a subset of all erts_alloc
flags can be changed
at run time. This subset is currently only the flag
sbct
.
Returns ok
if the flag was set or notsup
if not
supported by erts_alloc
.
Sets system flag fullsweep_after
.
is a non-negative integer indicating
how many times generational garbage collections can be
done without forcing a fullsweep collection. The value
applies to new processes, while processes already running are
not affected.
Returns the old value of the flag.
In low-memory systems (especially without virtual
memory), setting the value to 0
can help to conserve
memory.
This value can also be set through (OS)
environment variable ERL_FULLSWEEP_AFTER
.
Turns on/off microstate accounting measurements. When passing reset, all counters are reset to 0.
For more information see
statistics(microstate_accounting)
.
Sets the default minimum heap size for processes. The size
is specified in words. The new min_heap_size
effects
only processes spawned after the change of
min_heap_size
has been made. min_heap_size
can be set for individual processes by using
spawn_opt/4
or
process_flag/2
.
Returns the old value of the flag.
Sets the default minimum binary virtual heap size for
processes. The size is specified in words.
The new min_bin_vhheap_size
effects only
processes spawned after the change of
min_bin_vheap_size
has been made.
min_bin_vheap_size
can be set for individual
processes by using
spawn_opt/2,3,4
or
process_flag/2
.
Returns the old value of the flag.
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
Sets the default maximum heap size settings for processes.
The size is specified in words. The new max_heap_size
effects only processes spawned efter the change has been made.
max_heap_size
can be set for individual processes using
spawn_opt/2,3,4
or
process_flag/2
.
Returns the old value of the flag.
If multi-scheduling is enabled, more than one scheduler thread is used by the emulator. Multi-scheduling can be blocked in two different ways. Either all schedulers but one is blocked, or all normal schedulers but one is blocked. When only normal schedulers are blocked, dirty schedulers are free to continue to schedule processes.
If
, multi-scheduling is
blocked. That is, one and only one scheduler thread will
execute. If
and no one
else blocks multi-scheduling, and this process has
blocked only once, multi-scheduling is unblocked.
If
, normal
multi-scheduling is blocked. That is, only one normal scheduler
thread will execute, but multiple dirty schedulers can execute.
If
and no one
else blocks normal multi-scheduling, and this process has
blocked only once, normal multi-scheduling is unblocked.
One process can block multi-scheduling and normal multi-scheduling multiple times. If a process has blocked multiple times, it must unblock exactly as many times as it has blocked before it has released its multi-scheduling block. If a process that has blocked multi-scheduling or normal multi-scheduling exits, it automatically releases its blocking of multi-scheduling and normal multi-scheduling.
The return values are disabled
, blocked
,
blocked_normal
, or enabled
. The returned value
describes the state just after the call to
erlang:system_flag(multi_scheduling,
has been made. For information about the return values, see
erlang:system_info(multi_scheduling)
.
Note!
Blocking of multi-scheduling and normal multi-scheduling is normally not needed. If you feel that you need to use these features, consider it a few more times again. Blocking multi-scheduling is only to be used as a last resort, as it is most likely a very inefficient way to solve the problem.
See also
erlang:system_info(multi_scheduling)
,
erlang:system_info(normal_multi_scheduling_blockers)
,
erlang:system_info(multi_scheduling_blockers)
, and
erlang:system_info(schedulers)
.
scheduler_bind_type() =
no_node_processor_spread | no_node_thread_spread | no_spread |
processor_spread | spread | thread_spread |
thread_no_node_processor_spread | unbound
Warning!
This argument is deprecated.
Instead of using this argument, use command-line argument
+sbt
in
erl(1)
. When this argument is removed, a final scheduler bind
type to use is determined at emulator boot time.
Controls if and how schedulers are bound to logical processors.
When erlang:system_flag(scheduler_bind_type,
is called, an asynchronous signal is sent to all schedulers
online, causing them to try to bind or unbind as requested.
Note!
If a scheduler fails to bind, this is often silently
ignored, as it is not always possible to verify valid
logical processor identifiers. If an error is reported,
an error event is logged. To verify that the
schedulers have bound as requested, call
erlang:system_info(scheduler_bindings)
.
Schedulers can be bound on newer Linux, Solaris, FreeBSD, and Windows systems, but more systems will be supported in future releases.
In order for the runtime system to be able to bind schedulers,
the CPU topology must be known. If the runtime system fails
to detect the CPU topology automatically, it can be defined.
For more information on how to define the CPU topology, see
command-line flag
+sct
in erl(1)
.
The runtime system does by default not bind schedulers to logical processors.
Note!
If the Erlang runtime system is the only OS process binding threads to logical processors, this improves the performance of the runtime system. However, if other OS processes (for example, another Erlang runtime system) also bind threads to logical processors, there can be a performance penalty instead. Sometimes this performance penalty can be severe. If so, it is recommended to not bind the schedulers.
Schedulers can be bound in different ways. Argument
determines how schedulers are
bound and can be any of the following:
unbound
+sbt u
in
erl(1)
.
no_spread
+sbt ns
in erl(1)
.
thread_spread
+sbt ts
in erl(1)
.
processor_spread
+sbt ps
in erl(1)
.
spread
+sbt s
in erl(1)
.
no_node_thread_spread
+sbt nnts
in erl(1)
.
no_node_processor_spread
+sbt nnps
in erl(1)
.
thread_no_node_processor_spread
+sbt tnnps
in erl(1)
.
default_bind
+sbt db
in erl(1)
.
The returned value equals
before flag
scheduler_bind_type
was changed.
Failures:
notsup
badarg
How
is not one of the documented
alternatives.
badarg
The scheduler bind type can also be set by passing command-line
argument
+sbt
to erl(1)
.
For more information, see
erlang:system_info(scheduler_bind_type)
,
erlang:system_info(scheduler_bindings)
,
as well as command-line flags
+sbt
and +sct
in erl(1)
.
Turns on or off scheduler wall time measurements.
For more information, see
statistics(scheduler_wall_time)
.
Sets the number of schedulers online. Range is
1 <= SchedulersOnline <=
erlang:system_info(schedulers)
.
Returns the old value of the flag.
If the emulator was built with support for
dirty schedulers,
changing the number of schedulers online can also change the
number of dirty CPU schedulers online. For example, if 12
schedulers and 6 dirty CPU schedulers are online, and
system_flag/2
is used to set the number of schedulers
online to 6, then the number of dirty CPU schedulers online
is automatically decreased by half as well, down to 3.
Similarly, the number of dirty CPU schedulers online increases
proportionally to increases in the number of schedulers online.
For more information, see
erlang:system_info(schedulers)
and
erlang:system_info(schedulers_online)
.
Sets the process that will receive the logging
messages generated by ERTS. If set to undefined
,
all logging messages generated by ERTS will be dropped.
The messages will be in the format:
{log,Level,Format,ArgList,Metadata} where
Level = atom(),
Format = string(),
ArgList = list(term()),
Metadata = #{ pid => pid(),
group_leader => pid(),
time := logger:timestamp(),
error_logger := #{ emulator := true, tag := atom() }
If the system_logger
process dies,
this flag will be reset to logger
.
The default is the process named logger
.
Returns the old value of the flag.
Note!
This function is designed to be used by the
KERNEL logger
.
Be careful if you change it to something else as
log messages may be lost. If you want to intercept
emulator log messages, do it by adding a specialized handler
to the KERNEL logger.
Sets the value of the node trace control word to
, which is to be an unsigned integer.
For more information, see function
set_tcw
in section "Match Specifications in Erlang" in the
User's Guide.
Returns the old value of the flag.
Finalizes the time offset when single time warp mode is used. If another time warp mode is used, the time offset state is left unchanged.
Returns the old state identifier, that is:
If
preliminary
is returned, finalization was performed and the time offset is now final.If
final
is returned, the time offset was already in the final state. This either because anothererlang:system_flag(time_offset, finalize)
call or because no time warp mode is used.If
volatile
is returned, the time offset cannot be finalized because multi-time warp mode is used.
Returns information about the current system. The documentation of this function is broken into the following sections in order to make it easier to navigate.
Memory Allocation
allocated_areas
,
allocator
,
alloc_util_allocators
,
allocator_sizes
,
elib_malloc
CPU Topology
Process Information
fullsweep_after
,
garbage_collection
,
heap_sizes
,
heap_type
,
max_heap_size
,
message_queue_data
,
min_heap_size
,
min_bin_vheap_size
,
procs
System Limits
atom_count
,
atom_limit
,
ets_count
,
ets_limit
,
port_count
,
port_limit
,
process_count
,
process_limit
System Time
end_time
,
os_monotonic_time_source
,
os_system_time_source
,
start_time
,
time_correction
,
time_offset
,
time_warp_mode
,
tolerant_timeofday
Scheduler Information
dirty_cpu_schedulers
,
dirty_cpu_schedulers_online
,
dirty_io_schedulers
,
multi_scheduling
,
multi_scheduling_blockers
,
normal_multi_scheduling_blockers
,
scheduler_bind_type
,
scheduler_bindings
,
scheduler_id
,
schedulers
,
smp_support
,
threads
,
thread_pool_size
Distribution Information
creation
,
delayed_node_table_gc
,
dist
,
dist_buf_busy_limit
,
dist_ctrl
System Information
build_type
,
c_compiler_used
,
check_io
,
compat_rel
,
debug_compiled
,
driver_version
,
dynamic_trace
,
dynamic_trace_probes
,
info
,
kernel_poll
,
loaded
,
machine
,
modified_timing_level
,
nif_version
,
otp_release
,
port_parallelism
,
system_architecture
,
system_logger
,
system_version
,
trace_control_word
,
version
,
wordsize
Returns various information about the memory allocators
of the current system (emulator) as specified by
:
allocated_areas
Returns a list of tuples with information about miscellaneous allocated memory areas.
Each tuple contains an atom describing the type of memory as first element and the amount of allocated memory in bytes as second element. When information about allocated and used memory is present, also a third element is present, containing the amount of used memory in bytes.
erlang:system_info(allocated_areas)
is intended
for debugging, and the content is highly
implementation-dependent. The content of the results
therefore changes when needed without prior notice.
Notice that the sum of these values is not
the total amount of memory allocated by the emulator.
Some values are part of other values, and some memory
areas are not part of the result. For information about
the total amount of memory allocated by the emulator, see
erlang:memory/0,1
.
allocator
Returns {
, where:
-
corresponds to theAllocator malloc()
implementation used. If
equalsAllocator undefined
, themalloc()
implementation used cannot be identified.glibc
can be identified. -
is a list of integers (but not a string) representing the version of theVersion malloc()
implementation used. -
is a list of atoms representing the allocation features used.Features -
is a list of subsystems, their configurable parameters, and used values. Settings can differ between different combinations of platforms, allocators, and allocation features. Memory sizes are given in bytes.Settings
See also "System Flags Effecting erts_alloc" in
erts_alloc(3)
.
{allocator, Alloc }
Returns information about the specified allocator.
As from ERTS 5.6.1, the return value is a list
of {instance, InstanceNo, InstanceInfo}
tuples,
where InstanceInfo
contains information about
a specific instance of the allocator.
If
is not a
recognized allocator, undefined
is returned.
If
is disabled,
false
is returned.
Notice that the information returned is highly implementation-dependent and can be changed or removed at any time without prior notice. It was initially intended as a tool when developing new allocators, but as it can be of interest for others it has been briefly documented.
The recognized allocators are listed in
erts_alloc(3)
.
Information about super carriers can be obtained from
ERTS 8.0 with {allocator, erts_mmap}
or from
ERTS 5.10.4; the returned list when calling with
{allocator, mseg_alloc}
also includes an
{erts_mmap, _}
tuple as one element in the list.
After reading the erts_alloc(3)
documentation,
the returned information
more or less speaks for itself, but it can be worth
explaining some things. Call counts are presented by two
values, the first value is giga calls, and the second
value is calls. mbcs
and sbcs
denote
multi-block carriers, and single-block carriers,
respectively. Sizes are presented in bytes. When a
size is not presented, it is the amount of something.
Sizes and amounts are often presented by three values:
- The first is the current value.
- The second is the maximum value since the last call
to
erlang:system_info({allocator, Alloc})
. - The third is the maximum value since the emulator was started.
If only one value is present, it is the current value.
fix_alloc
memory block types are presented by two
values. The first value is the memory pool size and
the second value is the used memory size.
alloc_util_allocators
Returns a list of the names of all allocators using
the ERTS internal alloc_util
framework
as atoms. For more information, see section
The
alloc_util framework
in erts_alloc(3)
.
{allocator_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,
.
elib_malloc
This option will be removed in a future release.
The return value will always be false
, as the
elib_malloc
allocator has been removed.
cpu_topology() = [LevelEntry :: level_entry()] | undefined
level_entry() =
{LevelTag :: level_tag(), SubLevel :: sub_level()} |
{LevelTag :: level_tag(),
InfoList :: info_list(),
SubLevel :: sub_level()}
LevelEntry
s of a list
must contain the same LevelTag
, except
on the top level where both node
and
processor
LevelTag
s can coexist.
{LevelTag ,
SubLevel } == {LevelTag , [],
SubLevel }
level_tag() = core | node | processor | thread
LevelTag
s can be introduced in a
future release.
sub_level() =
[LevelEntry :: level_entry()] |
(LogicalCpuId :: {logical, integer() >= 0})
info_list() = []
info_list()
can be extended in a future release.
Returns various information about the CPU topology of
the current system (emulator) as specified by
:
cpu_topology
Returns the
currently used by
the emulator. The CPU topology is used when binding schedulers
to logical processors. The CPU topology used is the
user-defined CPU topology,
if such exists, otherwise the
automatically detected CPU topology,
if such exists. If no CPU topology
exists, undefined
is returned.
node
refers to Non-Uniform Memory Access (NUMA)
nodes. thread
refers to hardware threads
(for example, Intel hyper-threads).
A level in term
can be
omitted if only one entry exists and
is empty.
thread
can only be a sublevel to core
.
core
can be a sublevel to processor
or node
. processor
can be on the
top level or a sublevel to node
. node
can be on the top level or a sublevel to
processor
. That is, NUMA nodes can be processor
internal or processor external. A CPU topology can
consist of a mix of processor internal and external
NUMA nodes, as long as each logical CPU belongs to
one NUMA node. Cache hierarchy is not part of
the
type, but will be in a
future release. Other things can also make it into the CPU
topology in a future release. So, expect the
type to change.
{cpu_topology, defined}
Returns the user-defined
.
For more information, see command-line flag
+sct
in
erl(1)
and argument
cpu_topology
.
{cpu_topology, detected}
Returns the automatically detected
. The
emulator detects the CPU topology on some newer
Linux, Solaris, FreeBSD, and Windows systems.
On Windows system with more than 32 logical processors,
the CPU topology is not detected.
For more information, see argument
cpu_topology
.
{cpu_topology, used}
Returns
used by the emulator.
For more information, see argument
cpu_topology
.
logical_processors
Returns the detected number of logical processors configured
in the system. The return value is either an integer, or
the atom unknown
if the emulator cannot
detect the configured logical processors.
logical_processors_available
Returns the detected number of logical processors available
to the Erlang runtime system. The return value is either an
integer, or the atom unknown
if the emulator
cannot detect the available logical processors. The number
of available logical processors is less than or equal to
the number of
logical processors online.
logical_processors_online
Returns the detected number of logical processors online on
the system. The return value is either an integer,
or the atom unknown
if the emulator cannot
detect logical processors online. The number of logical
processors online is less than or equal to the number of
logical processors
configured.
update_cpu_info
The runtime system rereads the CPU information available and updates its internally stored information about the detected CPU topology and the number of logical processors configured, online, and available.
If the CPU information has changed since the last time
it was read, the atom changed
is returned, otherwise
the atom unchanged
. If the CPU information has changed,
you probably want to
adjust the
number of schedulers online. You typically want
to have as many schedulers online as
logical
processors available.
message_queue_data() = off_heap | on_heap
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
Returns information about the default process heap settings:
fullsweep_after
Returns {fullsweep_after, integer() >= 0}
, which is
the fullsweep_after
garbage collection setting used
by default. For more information, see
garbage_collection
described below.
garbage_collection
Returns a list describing the default garbage collection
settings. A process spawned on the local node by a
spawn
or spawn_link
uses these
garbage collection settings. The default settings can be
changed by using
erlang:system_flag/2
.
spawn_opt/2,3,4
can spawn a process that does not use the default
settings.
heap_sizes
Returns a list of integers representing valid heap sizes in words. All Erlang heaps are sized from sizes in this list.
heap_type
Returns the heap type used by the current emulator. One heap type exists:
private
max_heap_size
Returns {max_heap_size,
,
where
is the current
system-wide maximum heap size settings for spawned processes.
This setting can be set using the command-line flags
+hmax
,
+hmaxk
and
+hmaxel
in
erl(1)
. It can also be changed at runtime using
erlang:system_flag(max_heap_size, MaxHeapSize)
.
For more details about the max_heap_size
process flag,
see
process_flag(max_heap_size, MaxHeapSize)
.
message_queue_data
Returns the default value of the message_queue_data
process flag, which is either off_heap
or on_heap
.
This default is set by command-line argument
+hmqd
in
erl(1)
. For more information on the
message_queue_data
process flag, see documentation of
process_flag(message_queue_data, MQD)
.
min_heap_size
Returns {min_heap_size,
,
where
is the current
system-wide minimum heap size for spawned processes.
min_bin_vheap_size
Returns {min_bin_vheap_size,
, where
is the current system-wide
minimum binary virtual heap size for spawned processes.
procs
Returns a binary containing a string of process and port information formatted as in Erlang crash dumps. For more information, see section How to interpret the Erlang crash dumps in the User's Guide.
Returns information about the current system
(emulator) limits as specified by
:
atom_count
Returns the number of atoms currently existing at the local node. The value is given as an integer.
atom_limit
Returns the maximum number of atoms allowed.
This limit can be increased at startup by passing
command-line flag
+t
to
erl(1)
.
ets_count
Returns the number of ETS tables currently existing at the local node.
ets_limit
Returns the limit for number of ETS tables. This limit is partially obsolete and number of tables are only limited by available memory.
port_count
Returns the number of ports currently existing at the
local node. The value is given as an integer. This is
the same value as returned by
length(erlang:ports())
, but more efficient.
port_limit
Returns the maximum number of simultaneously existing
ports at the local node as an integer. This limit can be
configured at startup by using command-line flag
+Q
in erl(1)
.
process_count
Returns the number of processes currently existing at the
local node. The value is given as an integer. This is
the same value as returned by
length(processes())
, but more efficient.
process_limit
Returns the maximum number of simultaneously existing
processes at the local node. The value is given as an
integer. This limit can be configured at startup by using
command-line flag +P
in erl(1)
.
Returns information about the current system
(emulator) time as specified by
:
end_time
The last Erlang monotonic
time in native
time unit that
can be represented internally in the current Erlang runtime system
instance. The time between the
start time and
the end time is at least a quarter of a millennium.
os_monotonic_time_source
Returns a list containing information about the source of OS monotonic time that is used by the runtime system.
If []
is returned, no OS monotonic time is
available. The list contains two-tuples with Key
s
as first element, and Value
s as second element. The
order of these tuples is undefined. The following
tuples can be part of the list, but more tuples can be
introduced in the future:
{function, Function}
Function
is the name of the function
used. This tuple always exists if OS monotonic time is
available to the runtime system.
{clock_id, ClockId}
This tuple only exists if Function
can be used with different clocks. ClockId
corresponds to the clock identifier used when calling
Function
.
{resolution, OsMonotonicTimeResolution}
Highest possible
resolution
of current OS monotonic time source as parts per
second. If no resolution information can be retrieved
from the OS, OsMonotonicTimeResolution
is
set to the resolution of the time unit of
Function
s return value. That is, the actual
resolution can be lower than
OsMonotonicTimeResolution
. Notice that
the resolution does not say anything about the
accuracy or whether the
precision aligns with the resolution. You do,
however, know that the precision is not better than
OsMonotonicTimeResolution
.
{extended, Extended}
Extended
equals yes
if
the range of time values has been extended;
otherwise Extended
equals no
. The
range must be extended if Function
returns values that wrap fast. This typically
is the case when the return value is a 32-bit value.
{parallel, Parallel}
Parallel
equals yes
if
Function
is called in parallel from multiple
threads. If it is not called in parallel, because
calls must be serialized, Parallel
equals
no
.
{time, OsMonotonicTime}
OsMonotonicTime
equals current OS
monotonic time in native
time unit.
os_system_time_source
Returns a list containing information about the source of OS system time that is used by the runtime system.
The list contains two-tuples with Key
s
as first element, and Value
s as second element. The
order of these tuples is undefined. The following
tuples can be part of the list, but more tuples can be
introduced in the future:
{function, Function}
Function
is the name of the funcion used.
{clock_id, ClockId}
Exists only if Function
can be used with different clocks. ClockId
corresponds to the clock identifier used when calling
Function
.
{resolution, OsSystemTimeResolution}
Highest possible
resolution
of current OS system time source as parts per
second. If no resolution information can be retrieved
from the OS, OsSystemTimeResolution
is
set to the resolution of the time unit of
Function
s return value. That is, the actual
resolution can be lower than
OsSystemTimeResolution
. Notice that
the resolution does not say anything about the
accuracy or whether the
precision do align with the resolution. You do,
however, know that the precision is not better than
OsSystemTimeResolution
.
{parallel, Parallel}
Parallel
equals yes
if
Function
is called in parallel from multiple
threads. If it is not called in parallel, because
calls needs to be serialized, Parallel
equals
no
.
{time, OsSystemTime}
OsSystemTime
equals current OS
system time in native
time unit.
start_time
The Erlang monotonic
time in native
time unit at the
time when current Erlang runtime system instance started.
See also
erlang:system_info(end_time)
.
time_correction
Returns a boolean value indicating whether time correction is enabled or not.
time_offset
Returns the state of the time offset:
preliminary
The time offset is preliminary, and will be changed and finalized later. The preliminary time offset is used during the preliminary phase of the single time warp mode.
final
The time offset is final. This either because no time warp mode is used, or because the time offset have been finalized when single time warp mode is used.
volatile
The time offset is volatile. That is, it can change at any time. This is because multi-time warp mode is used.
time_warp_mode
Returns a value identifying the time warp mode that is used:
no_time_warp
single_time_warp
multi_time_warp
tolerant_timeofday
Returns whether a pre ERTS 7.0 backwards compatible
compensation for sudden changes of system time is enabled
or disabled
. Such compensation is enabled
when the
time offset
is final
, and
time correction is enabled.
Returns information about schedulers, scheduling and threads in the
current system as specified by
:
dirty_cpu_schedulers
Returns the number of dirty CPU scheduler threads used by the emulator. Dirty CPU schedulers execute CPU-bound native functions, such as NIFs, linked-in driver code, and BIFs that cannot be managed cleanly by the normal emulator schedulers.
The number of dirty CPU scheduler threads is determined
at emulator boot time and cannot be changed after that.
However, the number of dirty CPU scheduler threads online
can be changed at any time. The number of dirty CPU
schedulers can be set at startup by passing
command-line flag
+SDcpu
or
+SDPcpu
in
erl(1)
.
See also
erlang:system_flag(dirty_cpu_schedulers_online,
DirtyCPUSchedulersOnline)
,
erlang:system_info(dirty_cpu_schedulers_online)
,
erlang:system_info(dirty_io_schedulers)
,
erlang:system_info(schedulers)
,
erlang:system_info(schedulers_online)
, and
erlang:system_flag(schedulers_online,
SchedulersOnline)
.
dirty_cpu_schedulers_online
Returns the number of dirty CPU schedulers online.
The return value satisfies
1 <= DirtyCPUSchedulersOnline <= N
,
where N
is the smallest of the return values of
erlang:system_info(dirty_cpu_schedulers)
and
erlang:system_info(schedulers_online)
.
The number of dirty CPU schedulers online can be set at
startup by passing command-line flag
+SDcpu
in
erl(1)
.
For more information, see
erlang:system_info(dirty_cpu_schedulers)
,
erlang:system_info(dirty_io_schedulers)
,
erlang:system_info(schedulers_online)
, and
erlang:system_flag(dirty_cpu_schedulers_online,
DirtyCPUSchedulersOnline)
.
dirty_io_schedulers
Returns the number of dirty I/O schedulers as an integer. Dirty I/O schedulers execute I/O-bound native functions, such as NIFs and linked-in driver code, which cannot be managed cleanly by the normal emulator schedulers.
This value can be set at startup by passing command-line
argument +SDio
in erl(1)
.
For more information, see
erlang:system_info(dirty_cpu_schedulers)
,
erlang:system_info(dirty_cpu_schedulers_online)
,
and
erlang:system_flag(dirty_cpu_schedulers_online,
DirtyCPUSchedulersOnline)
.
multi_scheduling
Returns one of the following:
disabled
The emulator has been started with only one scheduler thread.
blocked
The emulator has more than one scheduler thread, but all scheduler threads except one are blocked. That is, only one scheduler thread schedules Erlang processes and executes Erlang code.
blocked_normal
The emulator has more than one scheduler thread, but all normal scheduler threads except one are blocked. Notice that dirty schedulers are not blocked, and can schedule Erlang processes and execute native code.
enabled
The emulator has more than one scheduler thread, and no scheduler threads are blocked. That is, all available scheduler threads schedule Erlang processes and execute Erlang code.
See also
erlang:system_flag(multi_scheduling, BlockState)
,
erlang:system_info(multi_scheduling_blockers)
,
erlang:system_info(normal_multi_scheduling_blockers)
,
and
erlang:system_info(schedulers)
.
multi_scheduling_blockers
Returns a list of
s when
multi-scheduling is blocked, otherwise the empty list is
returned. The
s in the list
represent all the processes currently
blocking multi-scheduling. A
occurs
only once in the list, even if the corresponding
process has blocked multiple times.
See also
erlang:system_flag(multi_scheduling, BlockState)
,
erlang:system_info(multi_scheduling)
,
erlang:system_info(normal_multi_scheduling_blockers)
,
and
erlang:system_info(schedulers)
.
normal_multi_scheduling_blockers
Returns a list of
s when
normal multi-scheduling is blocked (that is, all normal schedulers
but one is blocked), otherwise the empty list is returned.
The
s in the list represent all the
processes currently blocking normal multi-scheduling.
A
occurs only once in the list, even if
the corresponding process has blocked multiple times.
See also
erlang:system_flag(multi_scheduling, BlockState)
,
erlang:system_info(multi_scheduling)
,
erlang:system_info(multi_scheduling_blockers)
,
and
erlang:system_info(schedulers)
.
scheduler_bind_type
Returns information about how the user has requested schedulers to be bound or not bound.
Notice that although a user has requested
schedulers to be bound, they can silently have failed
to bind. To inspect the scheduler bindings, call
erlang:system_info(scheduler_bindings)
.
For more information, see command-line argument
+sbt
in erl(1)
and
erlang:system_info(scheduler_bindings)
.
scheduler_bindings
Returns information about the currently used scheduler bindings.
A tuple of a size equal to
erlang:system_info(schedulers)
is returned. The tuple elements are integers
or the atom unbound
. Logical processor identifiers
are represented as integers. The N
th
element of the tuple equals the current binding for
the scheduler with the scheduler identifier equal to
N
. For example, if the schedulers are bound,
element(erlang:system_info(scheduler_id),
erlang:system_info(scheduler_bindings))
returns
the identifier of the logical processor that the calling
process is executing on.
Notice that only schedulers online can be bound to logical processors.
For more information, see command-line argument
+sbt
in erl(1)
and
erlang:system_info(schedulers_online)
.
scheduler_id
Returns the scheduler ID (SchedulerId
) of the
scheduler thread that the calling process is executing
on.
is a positive integer,
where 1 <= SchedulerId <=
erlang:system_info(schedulers)
.
See also
erlang:system_info(schedulers)
.
schedulers
Returns the number of scheduler threads used by the emulator. Scheduler threads online schedules Erlang processes and Erlang ports, and execute Erlang code and Erlang linked-in driver code.
The number of scheduler threads is determined at emulator boot time and cannot be changed later. However, the number of schedulers online can be changed at any time.
See also
erlang:system_flag(schedulers_online,
SchedulersOnline)
,
erlang:system_info(schedulers_online)
,
erlang:system_info(scheduler_id)
,
erlang:system_flag(multi_scheduling, BlockState)
,
erlang:system_info(multi_scheduling)
,
erlang:system_info(normal_multi_scheduling_blockers)
and
erlang:system_info(multi_scheduling_blockers)
.
schedulers_online
Returns the number of schedulers online. The scheduler
identifiers of schedulers online satisfy the relationship
1 <= SchedulerId <=
erlang:system_info(schedulers_online)
.
For more information, see
erlang:system_info(schedulers)
and
erlang:system_flag(schedulers_online,
SchedulersOnline)
.
smp_support
Returns true
.
threads
Returns true
.
thread_pool_size
Returns the number of async threads in the async thread
pool used for asynchronous driver calls
(
erl_driver:driver_async()
).
The value is given as an integer.
Returns information about Erlang Distribution in the
current system as specified by
:
creation
Returns the creation of the local node as an integer.
The creation is changed when a node is restarted. The
creation of a node is stored in process identifiers, port
identifiers, and references. This makes it (to some
extent) possible to distinguish between identifiers from
different incarnations of a node. The valid
creations are integers in the range 1..3, but this will
probably change in a future release. If the node is not
alive, 0
is returned.
delayed_node_table_gc
Returns the amount of time in seconds garbage collection
of an entry in a node table is delayed. This limit can be set
on startup by passing command-line flag
+zdntgc
to erl(1)
. For more information, see the documentation of
the command-line flag.
dist
Returns a binary containing a string of distribution information formatted as in Erlang crash dumps. For more information, see section How to interpret the Erlang crash dumps in the User's Guide.
dist_buf_busy_limit
Returns the value of the distribution buffer busy limit
in bytes. This limit can be set at startup by passing
command-line flag
+zdbbl
to erl(1)
.
dist_ctrl
Returns a list of tuples
{
,
one entry for each connected remote node.
is the node name
and
is the port or process
identifier responsible for the communication to that node.
More specifically,
for
nodes connected through TCP/IP (the normal case) is the socket
used in communication with the specific node.
Returns various information about the current system
(emulator) as specified by
:
build_type
Returns an atom describing the build type of the runtime
system. This is normally the atom opt
for optimized.
Other possible return values are debug
, purify
,
quantify
, purecov
, gcov
, valgrind
,
gprof
, and lcnt
. Possible return values
can be added or removed at any time without prior notice.
c_compiler_used
Returns a two-tuple describing the C compiler used when
compiling the runtime system. The first element is an
atom describing the name of the compiler, or undefined
if unknown. The second element is a term describing the
version of the compiler, or undefined
if unknown.
check_io
Returns a list containing miscellaneous information about the emulators internal I/O checking. Notice that the content of the returned list can vary between platforms and over time. It is only guaranteed that a list is returned.
compat_rel
Returns the compatibility mode of the local node as
an integer. The integer returned represents the
Erlang/OTP release that the current emulator has been
set to be backward compatible with. The compatibility
mode can be configured at startup by using command-line flag
+R
in
erl(1)
.
debug_compiled
Returns true
if the emulator has been
debug-compiled, otherwise false
.
driver_version
Returns a string containing the Erlang driver version used by the runtime system. It has the form "<major ver>.<minor ver>".
dynamic_trace
Returns an atom describing the dynamic trace framework
compiled into the virtual machine. It can be
dtrace
, systemtap
, or none
. For a
commercial or standard build, it is always none
.
The other return values indicate a custom configuration
(for example, ./configure --with-dynamic-trace=dtrace
).
For more information about dynamic tracing, see
dyntrace(3)
manual page and the
README.dtrace
/README.systemtap
files in the
Erlang source code top directory.
dynamic_trace_probes
Returns a boolean()
indicating if dynamic trace
probes (dtrace
or systemtap
) are built into
the emulator. This can only be true
if the virtual
machine was built for dynamic tracing (that is,
system_info(dynamic_trace)
returns
dtrace
or systemtap
).
info
Returns a binary containing a string of miscellaneous system information formatted as in Erlang crash dumps. For more information, see section How to interpret the Erlang crash dumps in the User's Guide.
kernel_poll
Returns true
if the emulator uses some kind of
kernel-poll implementation, otherwise false
.
loaded
Returns a binary containing a string of loaded module information formatted as in Erlang crash dumps. For more information, see section How to interpret the Erlang crash dumps in the User's Guide.
machine
Returns a string containing the Erlang machine name.
modified_timing_level
Returns the modified timing-level (an integer) if
modified timing is enabled, otherwise undefined
.
For more information about modified timing, see
command-line flag
+T
in erl(1)
nif_version
Returns a string containing the version of the Erlang NIF interface used by the runtime system. It is on the form "<major ver>.<minor ver>".
otp_release
Returns a string containing the OTP release number of the OTP release that the currently executing ERTS application is part of.
As from Erlang/OTP 17, the OTP release number corresponds to
the major OTP version number. No
erlang:system_info()
argument gives the exact OTP
version. This is because the exact OTP version in the general case
is difficult to determine. For more information, see the
description of versions in
System principles in System Documentation.
port_parallelism
Returns the default port parallelism scheduling hint used.
For more information, see command-line argument
+spp
in erl(1)
.
system_architecture
Returns a string containing the processor and OS architecture the emulator is built for.
system_logger
Returns the current system_logger
as set by
erlang:system_flag(system_logger, _)
.
system_version
Returns a string containing version number and some important properties, such as the number of schedulers.
trace_control_word
Returns the value of the node trace control word. For
more information, see function get_tcw
in section
Match Specifications in Erlang in the User's Guide.
version
Returns a string containing the version number of the emulator.
wordsize
Same as {wordsize, internal}
.
{wordsize, internal}
Returns the size of Erlang term words in bytes as an integer, that is, 4 is returned on a 32-bit architecture, and 8 is returned on a pure 64-bit architecture. On a halfword 64-bit emulator, 4 is returned, as the Erlang terms are stored using a virtual word size of half the system word size.
{wordsize, external}
Returns the true word size of the emulator, that is, the size of a pointer. The value is given in bytes as an integer. On a pure 32-bit architecture, 4 is returned. On both a half word and on a pure 64-bit architecture, 8 is returned.
erlang:system_monitor() -> MonSettings
MonSettings = undefined | {MonitorPid, Options}
MonitorPid = pid()
Options = [system_monitor_option()]
system_monitor_option() =
busy_port | busy_dist_port |
{long_gc, integer() >= 0} |
{long_schedule, integer() >= 0} |
{large_heap, integer() >= 0}
Returns the current system monitoring settings set by
erlang:system_monitor/2
as {
,
or undefined
if no settings exist. The order of the
options can be different from the one that was set.
erlang:system_monitor(Arg) -> MonSettings
Arg = MonSettings = undefined | {MonitorPid, Options}
MonitorPid = pid()
Options = [system_monitor_option()]
system_monitor_option() =
busy_port | busy_dist_port |
{long_gc, integer() >= 0} |
{long_schedule, integer() >= 0} |
{large_heap, integer() >= 0}
When called with argument undefined
, all
system performance monitoring settings are cleared.
Calling the function with {
as argument is the same as calling
erlang:system_monitor(
.
Returns the previous system monitor settings just like
erlang:system_monitor/0
.
erlang:system_monitor(MonitorPid, Options) -> MonSettings
MonitorPid = pid()
Options = [system_monitor_option()]
MonSettings = undefined | {OldMonitorPid, OldOptions}
OldMonitorPid = pid()
OldOptions = [system_monitor_option()]
system_monitor_option() =
busy_port | busy_dist_port |
{long_gc, integer() >= 0} |
{long_schedule, integer() >= 0} |
{large_heap, integer() >= 0}
Sets the system performance monitoring options.
is a local process identifier (pid)
receiving system monitor messages. The
second argument is a list of monitoring options:
{long_gc, Time}
If a garbage collection in the system takes at least
Time
wall clock milliseconds, a message
{monitor, GcPid, long_gc, Info}
is sent to
. GcPid
is the pid that
was garbage collected. Info
is a list of two-element
tuples describing the result of the garbage collection.
One of the tuples is {timeout, GcTime}
, where
GcTime
is the time for the garbage
collection in milliseconds. The other tuples are
tagged with heap_size
, heap_block_size
,
stack_size
, mbuf_size
, old_heap_size
,
and old_heap_block_size
. These tuples are
explained in the description of trace message
gc_minor_start
(see erlang:trace/3
).
New tuples can be added, and the order of the tuples in
the Info
list can be changed at any time without
prior notice.
{long_schedule, Time}
If a process or port in the system runs uninterrupted
for at least Time
wall clock milliseconds, a
message {monitor, PidOrPort, long_schedule, Info}
is sent to MonitorPid
. PidOrPort
is the
process or port that was running. Info
is a
list of two-element tuples describing the event.
If a pid()
, the tuples {timeout, Millis}
,
{in, Location}
, and {out, Location}
are
present, where Location
is either an MFA
({Module, Function, Arity}
) describing the
function where the process was scheduled in/out, or the
atom undefined
.
If a port()
, the
tuples {timeout, Millis}
and {port_op,Op}
are present. Op
is one of proc_sig
,
timeout
, input
, output
,
event
, or dist_cmd
, depending on which
driver callback was executing.
proc_sig
is an
internal operation and is never to appear, while the
others represent the corresponding driver callbacks
timeout
, ready_input
, ready_output
,
event
, and outputv
(when the port
is used by distribution). Value Millis
in
tuple timeout
informs about the
uninterrupted execution time of the process or port, which
always is equal to or higher than the Time
value
supplied when starting the trace. New tuples can be
added to the Info
list in a future release. The
order of the tuples in the list can be changed at any
time without prior notice.
This can be used to detect problems with NIFs or drivers that take too long to execute. 1 ms is considered a good maximum time for a driver callback or a NIF. However, a time-sharing system is usually to consider everything < 100 ms as "possible" and fairly "normal". However, longer schedule times can indicate swapping or a misbehaving NIF/driver. Misbehaving NIFs and drivers can cause bad resource utilization and bad overall system performance.
{large_heap, Size}
If a garbage collection in the system results in
the allocated size of a heap being at least Size
words, a message {monitor, GcPid, large_heap, Info}
is sent to
.
GcPid
and Info
are the same as for long_gc
earlier, except that
the tuple tagged with timeout
is not present.
The monitor message is sent if the sum of the sizes of
all memory blocks allocated for all heap generations after
a garbage collection is equal to or higher than Size
.
When a process is killed by
max_heap_size
, it is killed before the
garbage collection is complete and thus no large heap message
is sent.
busy_port
If a process in the system gets suspended because it
sends to a busy port, a message
{monitor, SusPid, busy_port, Port}
is sent to
. 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
. SusPid
is the pid
that got suspended when sending through the inter-node
communication port Port
.
Returns the previous system monitor settings just like
erlang:system_monitor/0
.
Note!
If a monitoring process gets so large that it itself starts to cause system monitor messages when garbage collecting, the messages enlarge the process message queue and probably make the problem worse.
Keep the monitoring process neat and do not set the system monitor limits too tight.
Failures:
badarg
MonitorPid
does not exist.badarg
MonitorPid
is not a local process.erlang:system_profile() -> ProfilerSettings
ProfilerSettings = undefined | {ProfilerPid, Options}
ProfilerPid = pid() | port()
Options = [system_profile_option()]
system_profile_option() =
exclusive | runnable_ports | runnable_procs | scheduler |
timestamp | monotonic_timestamp | strict_monotonic_timestamp
Returns the current system profiling settings set by
erlang:system_profile/2
as {
,
or undefined
if there
are no settings. The order of the options can be different
from the one that was set.
erlang:system_profile(ProfilerPid, Options) -> ProfilerSettings
ProfilerPid = pid() | port() | undefined
Options = [system_profile_option()]
ProfilerSettings =
undefined | {pid() | port(), [system_profile_option()]}
system_profile_option() =
exclusive | runnable_ports | runnable_procs | scheduler |
timestamp | monotonic_timestamp | strict_monotonic_timestamp
Sets system profiler options.
is a local process identifier (pid) or port receiving profiling
messages. The receiver is excluded from all profiling.
The second argument is a list of profiling options:
exclusive
If a synchronous call to a port from a process is done, the
calling process is considered not runnable during the call
runtime to the port. The calling process is notified as
inactive
, and later active
when the port
callback returns.
monotonic_timestamp
Time stamps in profile messages use
Erlang
monotonic time. The time stamp (Ts) has the same
format and value as produced by
erlang:monotonic_time(nanosecond)
.
runnable_procs
If a process is put into or removed from the run queue, a
message, {profile, Pid, State, Mfa, Ts}
, is sent to
. Running processes that
are reinserted into the run queue after having been
pre-empted do not trigger this message.
runnable_ports
If a port is put into or removed from the run queue, a
message, {profile, Port, State, 0, Ts}
, is sent to
.
scheduler
If a scheduler is put to sleep or awoken, a message,
{profile, scheduler, Id, State, NoScheds, Ts}
, is
sent to
.
strict_monotonic_timestamp
Time stamps in profile messages consist of
Erlang
monotonic time and a monotonically increasing
integer. The time stamp (Ts) has the same format and value
as produced by {erlang:monotonic_time(nanosecond),
erlang:unique_integer([monotonic])}
.
timestamp
Time stamps in profile messages include a
time stamp (Ts) that has the same form as returned by
erlang:now()
. This is also the default if no
time stamp flag is specified. If cpu_timestamp
has
been enabled through
erlang:trace/3
,
this also effects the time stamp produced in profiling messages
when flag timestamp
is enabled.
Note!
erlang:system_profile
behavior can change
in a future release.
erlang:system_time() -> integer()
Returns current
Erlang system time in native
time unit.
Calling erlang:system_time()
is equivalent to
erlang:monotonic_time()
+
erlang:time_offset()
.
Note!
This time is not a monotonically increasing time in the general case. For more information, see the documentation of time warp modes in the User's Guide.
erlang:system_time(Unit) -> integer()
Unit = time_unit()
Returns current
Erlang system time
converted into the
passed as argument.
Calling erlang:system_time(
is equivalent
to
erlang:convert_time_unit
(
erlang:system_time()
,
native,
.
Note!
This time is not a monotonically increasing time in the general case. For more information, see the documentation of time warp modes in the User's Guide.
term_to_binary(Term) -> ext_binary()
Term = term()
Returns a binary data object that is the result of encoding
according to the
Erlang external
term format.
This can be used for various purposes, for example, writing a term to a file in an efficient way, or sending an Erlang term to some type of communications channel not supported by distributed Erlang.
>Bin = term_to_binary(hello).
<<131,100,0,5,104,101,108,108,111>> >hello = binary_to_term(Bin).
hello
See also
binary_to_term/1
.
Note!
There is no guarantee that this function will return the same encoded representation for the same term.
term_to_binary(Term, Options) -> ext_binary()
Term = term()
Options =
[compressed |
{compressed, Level :: 0..9} |
{minor_version, Version :: 0..2}]
Returns a binary data object that is the result of encoding
according to the Erlang external
term format.
If option compressed
is provided, the external term
format is compressed. The compressed format is automatically
recognized by binary_to_term/1
as from Erlang/OTP R7B.
A compression level can be specified by giving option
{compressed,
.
is an integer
with range 0..9, where:
0
- No compression is done (it is the same as giving nocompressed
option).1
- Takes least time but may not compress as well as the higher levels.6
- Default level when optioncompressed
is provided.9
- Takes most time and tries to produce a smaller result. Notice "tries" in the preceding sentence; depending on the input term, level 9 compression either does or does not produce a smaller result than level 1 compression.
Option {minor_version,
can be used to control some
encoding details. This option was introduced in Erlang/OTP R11B-4.
The valid values for
are:
0
Floats are encoded using a textual representation. This option is useful to ensure that releases before Erlang/OTP R11B-4 can decode resulting binary.
This version encode atoms that can be represented by a latin1 string using latin1 encoding while only atoms that cannot be represented by latin1 are encoded using utf8.
1
This is as of Erlang/OTP 17.0 the default. It forces any floats
in the term to be encoded in a more space-efficient and exact way
(namely in the 64-bit IEEE format, rather than converted to a
textual representation). As from Erlang/OTP R11B-4,
binary_to_term/1
can decode this representation.
This version encode atoms that can be represented by a latin1 string using latin1 encoding while only atoms that cannot be represented by latin1 are encoded using utf8.
2
Drops usage of the latin1 atom encoding and unconditionally use utf8 encoding for all atoms. This will be changed to the default in a future major release of Erlang/OTP. Erlang/OTP systems as of R16B can decode this representation.
See also
binary_to_term/1
.
throw(Any) -> no_return()
Any = term()
A non-local return from a function. If evaluated within a
catch
, catch
returns value
.
Example:
> catch throw({hello, there}).
{hello,there}
Failure: nocatch
if not evaluated within a catch.
time() -> Time
Time = calendar:time()
Returns the current time as {Hour, Minute, Second}
.
The time zone and Daylight Saving Time correction depend on the underlying OS. Example:
> time().
{9,42,44}
erlang:time_offset() -> integer()
Returns the current time offset between
Erlang monotonic time and
Erlang system time in
native
time unit.
Current time offset added to an Erlang monotonic time gives
corresponding Erlang system time.
The time offset may or may not change during operation depending on the time warp mode used.
Note!
A change in time offset can be observed at slightly different points in time by different processes.
If the runtime system is in multi-time warp mode, the time offset is changed when the runtime system detects that the OS system time has changed. The runtime system will, however, not detect this immediately when it occurs. A task checking the time offset is scheduled to execute at least once a minute; so, under normal operation this is to be detected within a minute, but during heavy load it can take longer time.
erlang:time_offset(Unit) -> integer()
Unit = time_unit()
Returns the current time offset between
Erlang monotonic time and
Erlang system time
converted into the
passed as argument.
Same as calling
erlang:convert_time_unit
(
erlang:time_offset()
, native,
however optimized for commonly used
s.
erlang:timestamp() -> Timestamp
Timestamp = timestamp()
timestamp() =
{MegaSecs :: integer() >= 0,
Secs :: integer() >= 0,
MicroSecs :: integer() >= 0}
Returns current
Erlang system time
on the format {MegaSecs, Secs, MicroSecs}
. This format is
the same as
os:timestamp/0
and the deprecated
erlang:now/0
use. The reason for the existence of erlang:timestamp()
is
purely to simplify use for existing code that assumes this time stamp
format. Current Erlang system time can more efficiently be retrieved
in the time unit of your choice using
erlang:system_time/1
.
The erlang:timestamp()
BIF is equivalent to:
timestamp() -> ErlangSystemTime = erlang:system_time(microsecond), MegaSecs = ErlangSystemTime div 1000000000000, Secs = ErlangSystemTime div 1000000 - MegaSecs*1000000, MicroSecs = ErlangSystemTime rem 1000000, {MegaSecs, Secs, MicroSecs}.
It, however, uses a native implementation that does not build garbage on the heap and with slightly better performance.
Note!
This time is not a monotonically increasing time in the general case. For more information, see the documentation of time warp modes in the User's Guide.
tl(List) -> term()
List = [term(), ...]
Returns the tail of
, that is,
the list minus the first element, for example:
> tl([geesties, guilies, beasties]).
[guilies, beasties]
Allowed in guard tests.
Failure: badarg
if
is the empty list []
.
erlang:trace(PidPortSpec, How, FlagList) -> integer()
PidPortSpec =
pid() |
port() |
all | processes | ports | existing | existing_processes |
existing_ports | new | new_processes | new_portsHow = boolean()
FlagList = [trace_flag()]
trace_flag() =
all | send | 'receive' | procs | ports | call | arity |
return_to | silent | running | exiting | running_procs |
running_ports | garbage_collection | timestamp |
cpu_timestamp | monotonic_timestamp |
strict_monotonic_timestamp | set_on_spawn |
set_on_first_spawn | set_on_link | set_on_first_link |
{tracer, pid() | port()} |
{tracer, module(), term()}
Turns on (if
) or off (if
) the trace flags in
for
the process or processes represented by
.
is either a process identifier
(pid) for a local process, a port identifier,
or one of the following atoms:
all
processes
ports
existing
existing_processes
existing_ports
new
new_processes
new_ports
can contain any number of the
following flags (the "message tags" refers to the list of
trace messages
):
all
Sets all trace flags except tracer
and
cpu_timestamp
, which are in their nature different
than the others.
send
Traces sending of messages.
Message tags:
send
and
send_to_non_existing_process
.
'receive'
Traces receiving of messages.
Message tags:
'receive'
.
call
Traces certain function calls. Specify which function
calls to trace by calling
erlang:trace_pattern/3
.
Message tags:
call
and
return_from
.
silent
Used with the call
trace flag.
The call
, return_from
, and return_to
trace messages are inhibited if this flag is set, but they
are executed as normal if there are match specifications.
Silent mode is inhibited by executing
erlang:trace(_, false, [silent|_])
,
or by a match specification executing the function
{silent, false}
.
The silent
trace flag facilitates setting up
a trace on many or even all processes in the system.
The trace can then be activated and deactivated using the match
specification function {silent,Bool}
, giving
a high degree of control of which functions with which
arguments that trigger the trace.
Message tags:
call
,
return_from
, and
return_to
. Or rather, the absence of.
return_to
Used with the call
trace flag.
Traces the return from a traced function back to
its caller. Only works for functions traced with
option local
to
erlang:trace_pattern/3
.
The semantics is that a trace message is sent when a
call traced function returns, that is, when a
chain of tail recursive calls ends. Only one trace
message is sent per chain of tail recursive calls,
so the properties of tail recursiveness for
function calls are kept while tracing with this flag.
Using call
and return_to
trace together
makes it possible to know exactly in which function a
process executes at any time.
To get trace messages containing return values from
functions, use the {return_trace}
match
specification action instead.
Message tags:
return_to
.
procs
Traces process-related events.
Message tags:
spawn
,
spawned
,
exit
,
register
,
unregister
,
link
,
unlink
,
getting_linked
, and
getting_unlinked
.
ports
Traces port-related events.
Message tags:
open
,
closed
,
register
,
unregister
,
getting_linked
, and
getting_unlinked
.
running
Traces scheduling of processes.
exiting
Traces scheduling of exiting processes.
Message tags:
in_exiting
,
out_exiting
, and
out_exited
.
running_procs
Traces scheduling of processes just like running
.
However, this option also includes schedule events when the
process executes within the context of a port without
being scheduled out itself.
running_ports
Traces scheduling of ports.
garbage_collection
Traces garbage collections of processes.
Message tags:
gc_minor_start
,
gc_max_heap_size
, and
gc_minor_end
.
timestamp
Includes a time stamp in all trace messages. The
time stamp (Ts) has the same form as returned by
erlang:now()
.
cpu_timestamp
A global trace flag for the Erlang node that makes all
trace time stamps using flag timestamp
to be
in CPU time, not wall clock time. That is, cpu_timestamp
is not be used if monotonic_timestamp
or
strict_monotonic_timestamp
is enabled.
Only allowed with
. If the
host machine OS does not support high-resolution
CPU time measurements, trace/3
exits with
badarg
. Notice that most OS do
not synchronize this value across cores, so be prepared
that time can seem to go backwards when using this option.
monotonic_timestamp
Includes an
Erlang
monotonic time time stamp in all trace messages. The
time stamp (Ts) has the same format and value as produced by
erlang:monotonic_time(nanosecond)
.
This flag overrides flag cpu_timestamp
.
strict_monotonic_timestamp
Includes an time stamp consisting of
Erlang
monotonic time and a monotonically increasing
integer in all trace messages. The time stamp (Ts) has the
same format and value as produced by {
erlang:monotonic_time(nanosecond)
,
erlang:unique_integer([monotonic])
}
.
This flag overrides flag cpu_timestamp
.
arity
Used with the call
trace flag.
{M, F, Arity}
is specified instead of
{M, F, Args}
in call trace messages.
set_on_spawn
Makes any process created by a traced process inherit
its trace flags, including flag set_on_spawn
.
set_on_first_spawn
Makes the first process created by a traced process
inherit its trace flags, excluding flag
set_on_first_spawn
.
set_on_link
Makes any process linked by a traced process inherit its
trace flags, including flag set_on_link
.
set_on_first_link
Makes the first process linked to by a traced process
inherit its trace flags, excluding flag
set_on_first_link
.
{tracer, Tracer}
Specifies where to send the trace messages. Tracer
must be the process identifier of a local process
or the port identifier of a local port.
{tracer, TracerModule, TracerState}
Specifies that a tracer module is to be called
instead of sending a trace message. The tracer module
can then ignore or change the trace message. For more details
on how to write a tracer module, see
erl_tracer(3)
.
If no tracer
is specified, the calling process
receives all the trace messages.
The effect of combining set_on_first_link
with
set_on_link
is the same as
set_on_first_link
alone. Likewise for
set_on_spawn
and set_on_first_spawn
.
The tracing process receives the trace messages described
in the following list. Pid
is the process identifier of the
traced process in which the traced event has occurred. The
third tuple element is the message tag.
If flag timestamp
, strict_monotonic_timestamp
, or
monotonic_timestamp
is specified, the first tuple
element is trace_ts
instead, and the time stamp
is added as an extra element last in the message tuple. If
multiple time stamp flags are passed, timestamp
has
precedence over strict_monotonic_timestamp
, which
in turn has precedence over monotonic_timestamp
. All
time stamp flags are remembered, so if two are passed
and the one with highest precedence later is disabled,
the other one becomes active.
Trace messages:
{trace, PidPort, send, Msg, To}
When PidPort
sends message Msg
to
process To
.
{trace, PidPort, send_to_non_existing_process, Msg, To}
When PidPort
sends message Msg
to
the non-existing process To
.
{trace, PidPort, 'receive', Msg}
When PidPort
receives message Msg
.
If Msg
is set to time-out, a receive
statement can have timed out, or the process received
a message with the payload timeout
.
{trace, Pid, call, {M, F, Args}}
When Pid
calls a traced function. The return
values of calls are never supplied, only the call and its
arguments.
Trace flag arity
can be used to
change the contents of this message, so that Arity
is specified instead of Args
.
{trace, Pid, return_to, {M, F, Arity}}
When Pid
returns to the specified
function. This trace message is sent if both
the flags call
and return_to
are set,
and the function is set to be traced on local
function calls. The message is only sent when returning
from a chain of tail recursive function calls, where at
least one call generated a call
trace message
(that is, the functions match specification matched, and
{message, false}
was not an action).
{trace, Pid, return_from, {M, F, Arity}, ReturnValue}
When Pid
returns from the specified
function. This trace message is sent if flag call
is set, and the function has a match specification
with a return_trace
or exception_trace
action.
{trace, Pid, exception_from, {M, F, Arity}, {Class, Value}}
When Pid
exits from the specified
function because of an exception. This trace message is
sent if flag call
is set, and the function has
a match specification with an exception_trace
action.
{trace, Pid, spawn, Pid2, {M, F, Args}}
When Pid
spawns a new process Pid2
with
the specified function call as entry point.
Args
is supposed to be the argument list,
but can be any term if the spawn is erroneous.
{trace, Pid, spawned, Pid2, {M, F, Args}}
When Pid
is spawned by process Pid2
with
the specified function call as entry point.
Args
is supposed to be the argument list,
but can be any term if the spawn is erroneous.
{trace, Pid, exit, Reason}
When Pid
exits with reason Reason
.
{trace, PidPort, register, RegName}
When PidPort
gets the name RegName
registered.
{trace, PidPort, unregister, RegName}
When PidPort
gets the name RegName
unregistered.
This is done automatically when a registered
process or port exits.
{trace, Pid, link, Pid2}
When Pid
links to a process Pid2
.
{trace, Pid, unlink, Pid2}
When Pid
removes the link from a process
Pid2
.
{trace, PidPort, getting_linked, Pid2}
When PidPort
gets linked to a process Pid2
.
{trace, PidPort, getting_unlinked, Pid2}
When PidPort
gets unlinked from a process Pid2
.
{trace, Pid, exit, Reason}
When Pid
exits with reason Reason
.
{trace, Port, open, Pid, Driver}
When Pid
opens a new port Port
with
the running Driver
.
Driver
is the name of the driver as an atom.
{trace, Port, closed, Reason}
When Port
closes with Reason
.
{trace, Pid, in | in_exiting, {M, F, Arity} | 0}
When Pid
is scheduled to run. The process
runs in function {M, F, Arity}
. On some rare
occasions, the current function cannot be determined,
then the last element is 0
.
{trace, Pid, out | out_exiting | out_exited, {M, F, Arity}
| 0}
When Pid
is scheduled out. The process was
running in function {M, F, Arity}. On some rare occasions,
the current function cannot be determined, then the last
element is 0
.
{trace, Port, in, Command | 0}
When Port
is scheduled to run. Command
is the
first thing the port will execute, it can however run several
commands before being scheduled out. On some rare
occasions, the current function cannot be determined,
then the last element is 0
.
The possible commands are call
, close
,
command
, connect
, control
, flush
,
info
, link
, open
, and unlink
.
{trace, Port, out, Command | 0}
When Port
is scheduled out. The last command run
was Command
. On some rare occasions,
the current function cannot be determined, then the last
element is 0
. Command
can contain the same
commands as in
{trace, Pid, gc_minor_start, Info}
Sent when a young garbage collection is about to be started.
Info
is a list of two-element tuples, where
the first element is a key, and the second is the value.
Do not depend on any order of the tuples.
The following keys are defined:
heap_size
heap_block_size
old_heap_size
old_heap_block_size
stack_size
recent_size
mbuf_size
bin_vheap_size
bin_vheap_block_size
bin_old_vheap_size
bin_old_vheap_block_size
All sizes are in words.
{trace, Pid, gc_max_heap_size, Info}
Sent when the
max_heap_size
is reached during garbage collection. Info
contains the
same kind of list as in message gc_start
,
but the sizes reflect the sizes that triggered
max_heap_size
to be reached.
{trace, Pid, gc_minor_end, Info}
Sent when young garbage collection is finished. Info
contains the same kind of list as in message
gc_minor_start
,
but the sizes reflect the new sizes after
garbage collection.
{trace, Pid, gc_major_start, Info}
Sent when fullsweep garbage collection is about to be started.
Info
contains the same kind of list as in message
gc_minor_start
.
{trace, Pid, gc_major_end, Info}
Sent when fullsweep garbage collection is finished. Info
contains the same kind of list as in message
gc_minor_start
, but the sizes reflect the new sizes after
a fullsweep garbage collection.
If the tracing process/port dies or the tracer module returns
remove
, the flags are silently removed.
Each process can only be traced by one tracer. Therefore, attempts to trace an already traced process fail.
Returns a number indicating the number of processes that
matched
.
If
is a process
identifier, the return value is 1
.
If
is all
or existing
, the return value is
the number of processes running.
If
is new
, the return value is
0
.
Failure: badarg
if the specified arguments are
not supported. For example, cpu_timestamp
is not
supported on all platforms.
erlang:trace_delivered(Tracee) -> Ref
Tracee = pid() | all
Ref = reference()
The delivery of trace messages (generated by
erlang:trace/3
,
seq_trace(3)
,
or
erlang:system_profile/2
)
is dislocated on the time-line
compared to other events in the system. If you know that
has passed some specific point
in its execution,
and you want to know when at least all trace messages
corresponding to events up to this point have reached the
tracer, use erlang:trace_delivered(
.
When it is guaranteed that all trace messages are delivered to
the tracer up to the point that
reached
at the time of the call to
erlang:trace_delivered(
, then a
{trace_delivered,
message is sent to the caller of
erlang:trace_delivered(
.
Notice that message trace_delivered
does not
imply that trace messages have been delivered.
Instead it implies that all trace messages that
are to be delivered have been delivered.
It is not an error if
is not, and
has not been traced by someone, but if this is the case,
no trace messages have been delivered when the
trace_delivered
message arrives.
Notice that
must refer
to a process currently
or previously existing on the same node as the caller of
erlang:trace_delivered(
resides on.
The special
atom all
denotes all processes that currently are traced in the node.
When used together with a
Tracer Module, any message sent in the trace callback
is guaranteed to have reached its recipient before the
trace_delivered
message is sent.
Example: Process A
is
,
port B
is tracer, and process C
is the port
owner of B
. C
wants to close B
when
A
exits. To ensure that the trace is not truncated,
C
can call erlang:trace_delivered(A)
when
A
exits, and wait for message {trace_delivered, A,
before closing B
.
Failure: badarg
if
does not refer to a
process (dead or alive) on the same node as the caller of
erlang:trace_delivered(
resides on.
erlang:trace_info(PidPortFuncEvent, Item) -> Res
PidPortFuncEvent =
pid() |
port() |
new | new_processes | new_ports |
{Module, Function, Arity} |
on_load | send | 'receive'Module = module()
Function = atom()
Arity = arity()
Item =
flags | tracer | traced | match_spec | meta |
meta_match_spec | call_count | call_time | allRes = trace_info_return()
trace_info_return() =
undefined |
{flags, [trace_info_flag()]} |
{tracer, pid() | port() | []} |
{tracer, module(), term()} |
trace_info_item_result() |
{all, [trace_info_item_result()] | false | undefined}
trace_info_item_result() =
{traced, global | local | false | undefined} |
{match_spec, trace_match_spec() | false | undefined} |
{meta, pid() | port() | false | undefined | []} |
{meta, module(), term()} |
{meta_match_spec, trace_match_spec() | false | undefined} |
{call_count, integer() >= 0 | boolean() | undefined} |
{call_time,
[{pid(),
integer() >= 0,
integer() >= 0,
integer() >= 0}] |
boolean() |
undefined}
trace_info_flag() =
send | 'receive' | set_on_spawn | call | return_to | procs |
set_on_first_spawn | set_on_link | running |
garbage_collection | timestamp | monotonic_timestamp |
strict_monotonic_timestamp | arity
trace_match_spec() =
[{[term()] | '_' | match_variable(), [term()], [term()]}]
match_variable() = atom()
Returns trace information about a port, process, function, or event.
To get information about a port or process,
is to
be a process identifier (pid), port identifier, or one of
the atoms new
, new_processes
, or new_ports
. The
atom new
or new_processes
means that the default trace
state for processes to be created is returned. The atom
new_ports
means that the default trace state for ports to be
created is returned.
Valid Item
s for ports and processes:
flags
Returns a list of atoms indicating what kind of traces is
enabled for the process. The list is empty if no
traces are enabled, and one or more of the followings
atoms if traces are enabled: send
,
'receive'
, set_on_spawn
, call
,
return_to
, procs
, ports
,
set_on_first_spawn
,
set_on_link
, running
, running_procs
,
running_ports
, silent
, exiting
,
monotonic_timestamp
, strict_monotonic_timestamp
,
garbage_collection
, timestamp
, and
arity
. The order is arbitrary.
tracer
Returns the identifier for process, port, or a tuple containing
the tracer module and tracer state tracing this
process. If this process is not traced, the return
value is []
.
To get information about a function,
is to
be the three-element tuple {Module, Function, Arity}
or
the atom on_load
. No wildcards are allowed. Returns
undefined
if the function does not exist, or
false
if the function is not traced.
If
is on_load
, the information returned refers to
the default value for code that will be loaded.
Valid Item
s for functions:
traced
Returns global
if this function is traced on
global function calls, local
if this function is
traced on local function calls (that is, local and global
function calls), and false
if local or
global function calls are not traced.
match_spec
Returns the match specification for this function, if it
has one. If the function is locally or globally traced but
has no match specification defined, the returned value
is []
.
meta
Returns the meta-trace tracer process, port, or trace module
for this function, if it has one. If the function is not
meta-traced, the returned value is false
. If
the function is meta-traced but has once detected that
the tracer process is invalid, the returned value is
[]
.
meta_match_spec
Returns the meta-trace match specification for this
function, if it has one. If the function is meta-traced
but has no match specification defined, the returned
value is []
.
call_count
Returns the call count value for this function or
true
for the pseudo function on_load
if call
count tracing is active. Otherwise false
is returned.
See also
erlang:trace_pattern/3
.
call_time
Returns the call time values for this function or
true
for the pseudo function on_load
if call
time tracing is active. Otherwise false
is returned.
The call time values returned, [{Pid, Count, S, Us}]
,
is a list of each process that executed the function
and its specific counters.
See also
erlang:trace_pattern/3
.
all
Returns a list containing the
{
tuples
for all other items, or returns false
if no tracing
is active for this function.
To get information about an event,
is to
be one of the atoms send
or 'receive'
.
One valid Item
for events exists:
match_spec
Returns the match specification for this event, if it
has one, or true
if no match specification has been
set.
The return value is {
, where
Value
is the requested information as described earlier.
If a pid for a dead process was specified, or the name of a
non-existing function, Value
is undefined
.
trace_pattern_mfa() = {atom(), atom(), arity() | '_'} | on_load
trace_match_spec() =
[{[term()] | '_' | match_variable(), [term()], [term()]}]
match_variable() = atom()
The same as
erlang:trace_pattern(Event, MatchSpec, [])
,
retained for backward compatibility.
trace_match_spec() =
[{[term()] | '_' | match_variable(), [term()], [term()]}]
match_variable() = atom()
Sets trace pattern for message sending.
Must be combined with
erlang:trace/3
to set the send
trace flag for one or more processes.
By default all messages sent from send
traced processes
are traced. To limit
traced send events based on the message content, the sender
and/or the receiver, use erlang:trace_pattern/3
.
Argument
can take the
following forms:
MatchSpecList
A list of match specifications. The matching is done
on the list [Receiver, Msg]
. Receiver
is the process or port identity of the receiver and
Msg
is the message term. The pid of the sending
process can be accessed with the guard function
self/0
. An empty list is the same as true
.
For more information, see section
Match Specifications in Erlang in the User's Guide.
true
Enables tracing for all sent messages (from send
traced processes). Any match specification is
removed. This is the default.
false
Disables tracing for all sent messages. Any match specification is removed.
Argument
must be []
for send tracing.
The return value is always 1
.
Examples:
Only trace messages to a specific process Pid
:
> erlang:trace_pattern(send, [{[Pid, '_'],[],[]}], []).
1
Only trace messages matching {reply, _}
:
> erlang:trace_pattern(send, [{['_', {reply,'_'}],[],[]}], []).
1
Only trace messages sent to the sender itself:
> erlang:trace_pattern(send, [{['$1', '_'],[{'=:=','$1',{self}}],[]}], []).
1
Only trace messages sent to other nodes:
> erlang:trace_pattern(send, [{['$1', '_'],[{'=/=',{node,'$1'},{node}}],[]}], []).
1
Note!
A match specification for send
trace can use
all guard and body functions except caller
.
trace_match_spec() =
[{[term()] | '_' | match_variable(), [term()], [term()]}]
match_variable() = atom()
Sets trace pattern for message receiving.
Must be combined with
erlang:trace/3
to set the 'receive'
trace flag for one or more processes.
By default all messages received by 'receive'
traced
processes are traced. To limit
traced receive events based on the message content, the sender
and/or the receiver, use erlang:trace_pattern/3
.
Argument
can take the
following forms:
MatchSpecList
A list of match specifications. The matching is done
on the list [Node, Sender, Msg]
. Node
is the node name of the sender. Sender
is the
process or port identity of the sender, or the atom
undefined
if the sender is not known (which can
be the case for remote senders). Msg
is the
message term. The pid of the receiving process can be
accessed with the guard function self/0
. An empty
list is the same as true
. For more information, see
section
Match Specifications in Erlang in the User's Guide.
true
Enables tracing for all received messages (to 'receive'
traced processes). Any match specification is
removed. This is the default.
false
Disables tracing for all received messages. Any match specification is removed.
Argument
must be []
for receive tracing.
The return value is always 1
.
Examples:
Only trace messages from a specific process Pid
:
> erlang:trace_pattern('receive', [{['_',Pid, '_'],[],[]}], []).
1
Only trace messages matching {reply, _}
:
> erlang:trace_pattern('receive', [{['_','_', {reply,'_'}],[],[]}], []).
1
Only trace messages from other nodes:
> erlang:trace_pattern('receive', [{['$1', '_', '_'],[{'=/=','$1',{node}}],[]}], []).
1
Note!
A match specification for 'receive'
trace can
use all guard and body functions except caller
,
is_seq_trace
, get_seq_token
, set_seq_token
,
enable_trace
, disable_trace
, trace
,
silent
, and process_dump
.
trace_pattern_mfa() = {atom(), atom(), arity() | '_'} | on_load
trace_match_spec() =
[{[term()] | '_' | match_variable(), [term()], [term()]}]
trace_pattern_flag() =
global | local | meta |
{meta, Pid :: pid()} |
{meta, TracerModule :: module(), TracerState :: term()} |
call_count | call_time
match_variable() = atom()
Enables or disables call tracing for one or more functions.
Must be combined with
erlang:trace/3
to set the call
trace flag
for one or more processes.
Conceptually, call tracing works as follows. Inside the Erlang virtual machine, a set of processes and a set of functions are to be traced. If a traced process calls a traced function, the trace action is taken. Otherwise, nothing happens.
To add or remove one or more processes to the set of traced
processes, use
erlang:trace/3
.
To add or remove functions to the set of traced
functions, use erlang:trace_pattern/3
.
The BIF erlang:trace_pattern/3
can also add match
specifications to a function. A match specification
comprises a pattern that the function arguments must
match, a guard expression that must evaluate to true
,
and an action to be performed. The default action is to send a
trace message. If the pattern does not match or the guard
fails, the action is not executed.
Argument
is to be a tuple, such as
{Module, Function, Arity}
, or the atom on_load
(described below). It can be the module, function,
and arity for a function (or a BIF in any module).
The atom '_'
can be used as a wildcard in any of the
following ways:
{Module,Function,'_'}
All functions of any arity named Function
in module Module
.
{Module,'_','_'}
All functions in module Module
.
{'_','_','_'}
All functions in all loaded modules.
Other combinations, such as {Module,'_',Arity}
, are
not allowed. Local functions match wildcards only if
option local
is in
.
If argument
is the atom on_load
,
the match specification and flag list are used on all
modules that are newly loaded.
Argument
can take the
following forms:
false
Disables tracing for the matching functions. Any match specification is removed.
true
Enables tracing for the matching functions. Any match specification is removed.
MatchSpecList
A list of match specifications. An empty list is
equivalent to true
. For a description of match
specifications, see section
Match Specifications in Erlang in the User's Guide.
restart
For the
options call_count
and call_time
: restarts
the existing counters. The behavior is undefined
for other
options.
pause
For the
options
call_count
and call_time
: pauses
the existing counters. The behavior is undefined for
other
options.
Parameter
is a list of options.
The following are the valid options:
global
Turns on or off call tracing for global function calls (that is, calls specifying the module explicitly). Only exported functions match and only global calls generate trace messages. This is the default.
local
Turns on or off call tracing for all types of function
calls. Trace messages are sent whenever any of
the specified functions are called, regardless of how they
are called. If flag return_to
is set for
the process, a return_to
message is also sent
when this function returns to its caller.
meta | {meta, Pid } |
{meta, TracerModule , TracerState }
Turns on or off meta-tracing for all types of function
calls. Trace messages are sent to the tracer whenever any of
the specified functions are called. If no tracer is specified,
self()
is used as a default tracer process.
Meta-tracing traces all processes and does not care
about the process trace flags set by erlang:trace/3
,
the trace flags are instead fixed to
[call, timestamp]
.
The match specification function {return_trace}
works with meta-trace and sends its trace message to the
same tracer.
call_count
Starts (
) or stops
(
)
call count tracing for all
types of function calls. For every function, a counter is
incremented when the function is called, in any process.
No process trace flags need to be activated.
If call count tracing is started while already running,
the count is restarted from zero. To pause running
counters, use
.
Paused and running counters can be restarted from zero with
.
To read the counter value, use
erlang:trace_info/2
.
call_time
Starts (
) or stops
(
) call time
tracing for all
types of function calls. For every function, a counter is
incremented when the function is called.
Time spent in the function is accumulated in
two other counters, seconds and microseconds.
The counters are stored for each call traced process.
If call time tracing is started while already running,
the count and time restart from zero. To pause
running counters, use
.
Paused and running counters can be restarted from zero with
.
To read the counter value, use
erlang:trace_info/2
.
The options global
and local
are mutually
exclusive, and global
is the default (if no options are
specified). The options call_count
and meta
perform a kind of local tracing, and cannot be combined
with global
. A function can be globally or
locally traced. If global tracing is specified for a
set of functions, then local, meta, call time, and call count
tracing for the matching set of local functions is
disabled, and conversely.
When disabling trace, the option must match the type of trace
set on the function. That is, local tracing must be
disabled with option local
and global tracing with
option global
(or no option), and so on.
Part of a match specification list cannot be changed directly.
If a function has a match specification, it can be replaced
with a new one. To change an existing match specification,
use the BIF
erlang:trace_info/2
to retrieve the existing match specification.
Returns the number of functions matching
argument
. This is zero if none matched.
trunc(Number) -> integer()
Number = number()
Returns an integer by truncating
,
for example:
> trunc(5.5).
5
Allowed in guard tests.
tuple_size(Tuple) -> integer() >= 0
Tuple = tuple()
Returns an integer that is the number of elements in
, for example:
> tuple_size({morni, mulle, bwange}).
3
Allowed in guard tests.
tuple_to_list(Tuple) -> [term()]
Tuple = tuple()
Returns a list corresponding to
.
can contain any Erlang terms.
Example:
> tuple_to_list({share, {'Ericsson_B', 163}}).
[share,{'Ericsson_B',163}]
erlang:unique_integer() -> integer()
Generates and returns an
integer unique on current runtime system instance.
The same as calling
erlang:unique_integer([])
.
erlang:unique_integer(ModifierList) -> integer()
ModifierList = [Modifier]
Modifier = positive | monotonic
Generates and returns an integer unique on current runtime system instance. The integer is unique in the sense that this BIF, using the same set of modifiers, does not return the same integer more than once on the current runtime system instance. Each integer value can of course be constructed by other means.
By default, when []
is passed as
, both negative and
positive integers can be returned. This
to use the range of integers that do
not need heap memory allocation as much as possible.
By default the returned integers are also only
guaranteed to be unique, that is, any returned integer
can be smaller or larger than previously
returned integers.
s:
Returns only positive integers.
Notice that by passing the positive
modifier
you will get heap allocated integers (bignums) quicker.
Returns strictly monotonically increasing integers corresponding to creation time. That is, the integer returned is always larger than previously returned integers on the current runtime system instance.
These values can be used to determine order between events
on the runtime system instance. That is, if both
X = erlang:unique_integer([monotonic])
and
Y = erlang:unique_integer([monotonic])
are
executed by different processes (or the same
process) on the same runtime system instance and
X < Y
, we know that X
was created
before Y
.
Warning!
Strictly monotonically increasing values
are inherently quite expensive to generate and scales
poorly. This is because the values need to be synchronized
between CPU cores. That is, do not pass the monotonic
modifier unless you really need strictly monotonically
increasing values.
All valid
s
can be combined. Repeated (valid)
s in the ModifierList
are ignored.
Note!
The set of integers returned by
erlang:unique_integer/1
using different sets of
s will overlap.
For example, by calling unique_integer([monotonic])
,
and unique_integer([positive, monotonic])
repeatedly, you will eventually see some integers that are
returned by both calls.
Failures:
badarg
ModifierList
is not a
proper list.badarg
Modifier
is not a
valid modifier.erlang:universaltime() -> DateTime
DateTime = calendar:datetime()
Returns the current date and time according to Universal
Time Coordinated (UTC) in the form
{{Year, Month, Day}, {Hour, Minute, Second}}
if
supported by the underlying OS.
Otherwise erlang:universaltime()
is equivalent to
erlang:localtime()
. Example:
> erlang:universaltime().
{{1996,11,6},{14,18,43}}
erlang:universaltime_to_localtime(Universaltime) -> Localtime
Localtime = Universaltime = calendar:datetime()
Converts Universal Time Coordinated (UTC) date and time to
local date and time in the form
{{Year, Month, Day}, {Hour, Minute, Second}}
if
supported by the underlying OS.
Otherwise no conversion is done, and
is returned. Example:
> erlang:universaltime_to_localtime({{1996,11,6},{14,18,43}}).
{{1996,11,7},{15,18,43}}
Failure: badarg
if Universaltime
denotes
an invalid date and time.
unlink(Id) -> true
Id = pid() | port()
Removes the link, if there is one, between the calling
process and the process or port referred to by
.
Returns true
and does not fail, even if there is no
link to
, or if
does not exist.
Once unlink(
has returned,
it is guaranteed that
the link between the caller and the entity referred to by
has no effect on the caller
in the future (unless
the link is setup again). If the caller is trapping exits, an
{'EXIT',
message from the link
can have been placed in the caller's message queue before
the call.
Notice that the {'EXIT',
message can be the
result of the link, but can also be the result of Id
calling exit/2
. Therefore, it can be
appropriate to clean up the message queue when trapping exits
after the call to unlink(
, as follows:
unlink(Id), receive {'EXIT', Id, _} -> true after 0 -> true end
Note!
Before Erlang/OTP R11B (ERTS 5.5) unlink/1
behaved completely asynchronously, that is, the link was active
until the "unlink signal" reached the linked entity. This
had an undesirable effect, as you could never know when
you were guaranteed not to be effected by the link.
The current behavior can be viewed as two combined operations: asynchronously send an "unlink signal" to the linked entity and ignore any future results of the link.
unregister(RegName) -> true
RegName = atom()
Removes the registered name
associated with a
process identifier or a port identifier, for example:
> unregister(db).
true
Users are advised not to unregister system processes.
Failure: badarg
if RegName
is not a registered
name.
whereis(RegName) -> pid() | port() | undefined
RegName = atom()
Returns the process identifier or port identifier with
the registered name RegName
. Returns undefined
if the name is not registered. Example:
> whereis(db).
<0.43.0>
erlang:yield() -> true
Voluntarily lets other processes (if any) get a chance to
execute. Using this function is similar to
receive after 1 -> ok end
, except that yield()
is faster.
Warning!
There is seldom or never any need to use this BIF as other processes have a chance to run in another scheduler thread anyway. Using this BIF without a thorough grasp of how the scheduler works can cause performance degradation.