erlang
(erts)The Erlang BIFs.
By convention, most Built-In Functions (BIFs) are seen as being
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()
A binary data object, structured according to the Erlang external term format.
message_queue_data/0
timestamp/0
See erlang:timestamp/0.
time_unit/0
Supported time unit representations:
PartsPerSecond :: integer() >= 1
Time unit expressed in parts per second. That is,
the time unit equals 1/PartsPerSecond
second.
seconds
Symbolic representation of the time unit
represented by the integer 1
.
milli_seconds
Symbolic representation of the time unit
represented by the integer 1000
.
micro_seconds
Symbolic representation of the time unit
represented by the integer 1000000
.
nano_seconds
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,
seconds, native)
. The result equals the number
of whole native
time units per second. In case
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 at all about the
quality of time values. It sets a limit for
the
resolution
as well as for the
precision
of time values,
but it gives absolutely no information at all 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 might differ inbetween
run-time restarts. You get values of this type by calling
os:perf_counter()
The time_unit/0
type may be extended. Use
erlang:convert_time_unit/3
in order to convert time values between time units.
Functions
abs/1
Float = float()
Int = integer()
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.
adler32/1
Computes and returns the adler32 checksum for
.
adler32/2
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]).
adler32_combine/3
Combines two previously computed adler32 checksums. This computation requires the size of the data object for the second checksum to be known.
The following code:
Y = erlang:adler32(Data1),
Z = erlang:adler32(Y,Data2).
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)).
append_element/2
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/2
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 given as
{Module, Function}
, equivalent to
apply(Module, Function, Args)
. This use is
deprecated and will stop working in a future release.
apply/3
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 the reason undef
is generated.
atom_to_binary/2
Returns a binary corresponding to the text
representation of
.
If
is latin1
, there is one byte for each character
in the text representation. If
is
utf8
or
unicode
, the characters are encoded using UTF-8
(that is, characters from 128 through 255 are
encoded in two bytes).
Note!
atom_to_binary(
never
fails because the text representation of an atom can only
contain characters from 0 through 255. In a future release,
the text representation
of atoms can be allowed to contain any Unicode character and
atom_to_binary(
will then fail if the
text representation for
contains a Unicode
character greater than 255.
Example:
> atom_to_binary('Erlang', latin1).
<<"Erlang">>
atom_to_list/1
Returns a string corresponding to the text
representation of
, for example:
> atom_to_list('Erlang').
"Erlang"
binary_part/2
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 the
binary
manual page in STDLIB
.
Allowed in guard tests.
binary_part/3
The same as binary_part(
.
Allowed in guard tests.
binary_to_atom/2
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. Only Unicode characters up
to 255 are allowed.
Note!
binary_to_atom(
fails if
the binary contains Unicode characters greater than 255.
In a future release, such Unicode characters can be allowed
and binary_to_atom(
does then not fail.
For more information on Unicode support in atoms, see the
note on UTF-8
encoded atoms
in Section "External Term Format" in the User's Guide.
Examples:
>binary_to_atom(<<"Erlang">>, latin1).
'Erlang' >binary_to_atom(<<1024/utf8>>, utf8).
** exception error: bad argument in function binary_to_atom/2 called as binary_to_atom(<<208,128>>,utf8)
binary_to_existing_atom/2
As binary_to_atom/2, but the atom must exist.
Failure: badarg
if the atom does not exist.
binary_to_float/1
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/1
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/2
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/1
Returns a list of integers corresponding to the bytes of
.
binary_to_list/3
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.
bitstring_to_list/1
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.
binary_to_term/1
Returns an Erlang term that is the result of decoding
binary object
, which must be encoded
according to the Erlang external term format.
Warning!
When decoding binaries from untrusted sources,
consider using binary_to_term/2
to prevent Denial
of Service attacks.
See also term_to_binary/1 and binary_to_term/2.
binary_to_term/2
As binary_to_term/1
, but takes options that affect decoding
of the binary.
safe
Use this option when receiving binaries from an untrusted source.
When enabled, it prevents decoding data that can be used to
attack the Erlang system. In the event of receiving unsafe
data, decoding fails with a badarg
error.
This prevents creation of new atoms directly, creation of new atoms indirectly (as they are embedded in certain structures, such as process identifiers, refs, and funs), and creation of new external function references. None of those resources are garbage collected, so unchecked creation of them can exhaust available memory.
Failure: badarg
if safe
is specified and unsafe
data is decoded.
See also term_to_binary/1, binary_to_term/1, and list_to_existing_atom/1.
bit_size/1
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.
bump_reductions/1
This implementation-dependent function increments the reduction counter for the calling process. In the Beam emulator, the reduction counter is normally incremented by one for each function and BIF call. A context switch is forced when the counter reaches the maximum number of reductions for a process (2000 reductions in 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/1
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.
cancel_timer/2
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.
Available
s:
{async, Async}
Asynchronous request for cancellation. Async
defaults to false
which will cause the
cancellation to be performed synchronously. When
Async
is set to true
, the cancel
operation is performed asynchronously. That is,
erlang:cancel_timer()
will send an asynchronous
request for cancellation to the timer service that
manages the timer, and then return ok
.
{info, Info}
Request 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 the operation is performed
If Info
is true
, the Result
is
returned by erlang:cancel_timer()
; otherwise,
ok
is returned.
If Info
is true
, a message on the form
{cancel_timer,
is sent to the
caller of 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 milli-seconds 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 whether or not the timeout message has
arrived at its destination yet.
Note!
The timer service that manages the timer may be co-located
with another scheduler than the scheduler that the calling
process is executing on. If this is the case, 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
.
cancel_timer/1
Cancels a timer. The same as calling
erlang:cancel_timer(TimerRef,
[])
.
check_old_code/1
Returns true
if
has old code,
otherwise false
.
See also code(3).
check_process_code/2
The same as
erlang:check_process_code(
.
check_process_code/3
Checks if the node local process identified by
executes old code for
.
The available
s are as follows:
{allow_gc, boolean()}
Determines if garbage collection is allowed when performing
the operation. If {allow_gc, false}
is passed, and
a garbage collection is needed to determine the
result of the operation, the operation is aborted (see
information on
in the following).
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}
.
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.
convert_time_unit/3
Converts the
value of time unit
to the corresponding
value of time unit
. The result is rounded
using the floor function.
Warning!
You may lose accuracy and precision when converting
between time units. In order to minimize such loss, collect all
data at native
time unit and do the conversion on the end
result.
crc32/1
Computes and returns the crc32 (IEEE 802.3 style) checksum
for
.
crc32/2
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]).
crc32_combine/3
Combines two previously computed crc32 checksums. This computation requires the size of the data object for the second checksum to be known.
The following code:
Y = erlang:crc32(Data1),
Z = erlang:crc32(Y,Data2).
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/0
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}
decode_packet/3
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.
The following Type
s are valid:
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 latin1 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.
The following options are available:
{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. Default is 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 latin1 character $\n
.
Examples:
>erlang:decode_packet(1,<<3,"abcd">>,[]).
{ok,<<"abc">>,<<"d">>} >erlang:decode_packet(1,<<5,"abcd">>,[]).
{more,6}
delete_element/2
Returns a new tuple with element at
removed from tuple
, for example:
> erlang:delete_element(2, {one, two, three}).
{one,three}
delete_module/1
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/1
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. A {'DOWN',
message
can have been placed in the caller message queue before
the call, though. 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!
Prior to OTP release R11B (ERTS version 5.5) demonitor/1
behaved completely asynchronously, i.e., 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
due to the monitor.
Current behavior can be viewed as two combined operations: asynchronously send a "demonitor signal" to the monitored entity and ignore any future results of the monitor.
Failure: It is an error if
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/2
The returned value is true
unless info
is part
of
.
demonitor(
is equivalent to
demonitor(
.
The available
s are as follows:
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
'DOWN'
message corresponding to this
monitor has been delivered and will not be delivered.
false
'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
disconnect_node/1
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.
display/1
Prints a text representation of
on the
standard output.
Warning!
This BIF is intended for debugging only.
element/2
Returns the
th element (numbering from 1) of
, for example:
> element(2, {a, b, c}).
b
Allowed in guard tests.
erase/0
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/1
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/1
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). Since evaluating this function causes
the process to terminate, it has no return value.
Example:
> catch error(foobar).
{'EXIT',{foobar,[{erl_eval,do_apply,5},
{erl_eval,expr,5},
{shell,exprs,6},
{shell,eval_exprs,6},
{shell,eval_loop,3}]}}
error/2
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
. Since evaluating this function causes
the process to terminate, it has no return value.
exit/1
Stops the execution of the calling process with exit reason
, where
is any term. Since
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/2
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 also process_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
.
external_size/1
Calculates, without doing the encoding, the maximum byte size for a term encoded in the Erlang external term format. The following condition applies always:
>Size1 = byte_size(term_to_binary(
>Term )),Size2 = erlang:external_size(
>Term ),true = Size1 =< Size2.
true
This is equivalent to a call to:
erlang:external_size(Term , [])
external_size/2
Calculates, without doing the encoding, the maximum byte size for a term encoded in the Erlang external term format. The following condition applies always:
>Size1 = byte_size(term_to_binary(
>Term ,Options )),Size2 = erlang:external_size(
>Term ,Options ),true = Size1 =< Size2.
true
Option {minor_version,
specifies how
floats are encoded. For a detailed description, see
term_to_binary/2.
float/1
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/1
The same as
float_to_binary(
.
float_to_binary/2
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/1
The same as
float_to_list(
.
float_to_list/2
Returns a string corresponding to the text representation
of Float
using fixed decimal point formatting. The
options are as follows:
- 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 provided, the trailing zeros at the end of the list are truncated. This option is only meaningful together with optiondecimals
. - If option
scientific
is provided, the float is formatted using scientific notation withDecimals
digits of precision. - If
Options
is[]
, the function behaves as float_to_list/1.
Examples:
>float_to_list(7.12, [{decimals, 4}]).
"7.1200" >float_to_list(7.12, [{decimals, 4}, compact]).
"7.12"
fun_info/1
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.
{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 OTP R15, this integer is calculated from the
compiled code for the entire module. Before OTP R15, this
integer was based on only the body of the fun.
fun_info/2
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.
fun_to_list/1
Returns a string corresponding to the text
representation of
.
function_exported/3
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 given name, otherwise returns false
.
Note!
This function used to return false for built-in functions before the 18.0 release.
garbage_collect/0
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/1
The same as
garbage_collect(
.
garbage_collect/2
Garbage collects the node local process identified by
.
The available
s are as follows:
{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 }
.
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/0
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/1
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}
get_cookie/0
Returns the magic cookie of the local node if the node is
alive, otherwise the atom nocookie
.
get_keys/0
Returns a list of keys all keys present in the process dictionary.
>put(dog, {animal,1}),
put(cow, {animal,2}),
put(lamb, {animal,3}),
get_keys().
[dog,cow,lamb]
get_keys/1
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]
get_stacktrace/0
Gets the call stack back-trace (stacktrace) of the
last exception 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 the catch
operator
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
See also erlang:error/1 and erlang:error/2.
group_leader/0
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 start-up, init
is both
its own group leader and the group leader of all processes.
group_leader/2
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
.
See also group_leader/0.
halt/0
halt/1
halt/2
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).
Status
as slogan. Then the runtime system exits with status code 1
.
abort
Note!
On many platforms, the OS supports only status codes 0-255. A too large status code will be truncated by clearing the high bits.
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.
hash/2
Returns a hash value for
within the range
1..
. The maximum range is 1..2^27-1.
Warning!
This BIF is deprecated, as the hash value can differ on
different architectures. The hash values for integer
terms higher than 2^27 and large binaries are
poor. The BIF is retained for backward compatibility
reasons (it can have been used to hash records into a file),
but all new code is to use one of the BIFs
erlang:phash/2
or erlang:phash2/1,2
instead.
hd/1
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 []
.
hibernate/3
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 given 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, what erlang:hibernate/3
does
is the following. It 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 reinserted 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.
insert_element/3
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/1
Returns a binary corresponding to the text
representation of
, for example:
> integer_to_binary(77).
<<"77">>
integer_to_binary/2
Returns a binary corresponding to the text
representation of
in base
, for example:
> integer_to_binary(1023, 16).
<<"3FF">>
integer_to_list/1
Returns a string corresponding to the text
representation of
, for example:
> integer_to_list(77).
"77"
integer_to_list/2
Returns a string corresponding to the text
representation of
in base
, for example:
> integer_to_list(1023, 16).
"3FF"
iolist_to_binary/1
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>>
iolist_size/1
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
is_alive/0
Returns true
if the local node is alive (that is, if
the node can be part of a distributed system), otherwise
false
.
is_atom/1
Returns true
if
is an atom,
otherwise false
.
Allowed in guard tests.
is_binary/1
Returns true
if
is a binary,
otherwise false
.
A binary always contains a complete number of bytes.
Allowed in guard tests.
is_bitstring/1
Returns true
if
is a
bitstring (including a binary), otherwise false
.
Allowed in guard tests.
is_boolean/1
Returns true
if
is the
atom true
or the atom false
(that is, a boolean).
Otherwise returns false
.
Allowed in guard tests.
is_builtin/3
This BIF is useful for builders of cross-reference tools.
Returns true
if
is a BIF implemented in C, otherwise false
.
is_float/1
Returns true
if
is a floating point
number, otherwise false
.
Allowed in guard tests.
is_function/1
Returns true
if
is a fun, otherwise
false
.
Allowed in guard tests.
is_function/2
Returns true
if
is a fun that can be
applied with
number of arguments, otherwise
false
.
Allowed in guard tests.
is_integer/1
Returns true
if
is an integer,
otherwise false
.
Allowed in guard tests.
is_list/1
Returns true
if
is a list with
zero or more elements, otherwise false
.
Allowed in guard tests.
is_map/1
Returns true
if
is a map,
otherwise false
.
Allowed in guard tests.
is_number/1
Returns true
if
is an integer or a
floating point number. Otherwise returns false
.
Allowed in guard tests.
is_pid/1
Returns true
if
is a process
identifier, otherwise false
.
Allowed in guard tests.
is_port/1
Returns true
if
is a port identifier,
otherwise false
.
Allowed in guard tests.
is_process_alive/1
must refer to a process at the local node.
Returns true
if the process exists and is alive, that
is, is not exiting and has not exited. Otherwise returns
false
.
is_record/2
Returns true
if
is a tuple and its
first element is
.
Otherwise returns false
.
Note!
Normally the compiler treats calls to is_record/2
specially. 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/3
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/1
Returns true
if
is a reference,
otherwise false
.
Allowed in guard tests.
is_tuple/1
Returns true
if
is a tuple,
otherwise false
.
Allowed in guard tests.
length/1
Returns the length of
, for example:
> length([1,2,3,4,5,6,7,8,9]).
9
Allowed in guard tests.
link/1
Creates a link between the calling process and another
process (or port)
, 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/1
Returns the atom whose text representation is
.
can only contain ISO-latin-1
characters (that is,
numbers less than 256) as the implementation does not
allow unicode characters equal to or above 256 in atoms.
For more information on Unicode support in atoms, see
note on UTF-8
encoded atoms
in Section "External Term Format" in the User's Guide.
Example:
> list_to_atom("Erlang").
'Erlang'
list_to_binary/1
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/1
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/1
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
.
list_to_float/1
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/1
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/2
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/1
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_tuple/1
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/2
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 any of the following:
badfile
The object code in
has an
incorrect format or the object code contains code
for another module than
.
not_purged
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.
load_nif/2
Note!
Before OTP R14B, NIFs were an
experimental feature. Versions before OTP R14B can
have different and possibly incompatible NIF semantics and
interfaces. For example, in OTP R13B03 the return value on
failure was {error,Reason,Text}
.
Loads and links a dynamic library containing native
implemented functions (NIFs) for a module.
is a file path to the shareable object/dynamic library file minus
the OS-dependent file extension (.so
for Unix and
.dll
for Windows. For information on how to
implement a NIF library, see
erl_nif.
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 | reload | upgrade
old_code
load_nif/2
was made from the old
code of a module that has been upgraded; this is not
allowed.
loaded/0
Returns a list of all loaded Erlang modules (current and old code), including preloaded modules.
See also code(3).
localtime/0
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.
localtime_to_universaltime/1
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.
localtime_to_universaltime/2
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/0
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.
make_tuple/2
Creates a new tuple of the given
, where all
elements are
, for example:
> erlang:make_tuple(4, []).
{[],[],[],[]}
make_tuple/3
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_size/1
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.
match_spec_test/3
This function is a utility to test a match_spec used in calls to ets:select/2 and erlang:trace_pattern/3. The function both tests MatchSpec for "syntactic" correctness and runs the match_spec against the object. If the match_spec contains errors, the tuple {error, Errors} is returned where Errors is a list of natural language descriptions of what was wrong with the match_spec.
If the
is table
the object to match
against should 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_spec does
not match the object tuple.
If
is trace
the object to match
against should be a list. The function returns
{ok, Result, Flags, Warnings} where Result is true
if a trace
message should be emitted, false
if a trace message should not
be emitted or the message term to be appended to the trace message.
Flags is a list containing all the trace flags that will be enabled,
at the moment 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/2
Returns the largest of
and
.
If the terms are equal,
is returned.
md5/1
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 RFC 1321 - The MD5 Message-Digest Algorithm.
Warning!
The MD5 Message-Digest Algorithm is not considered safe for code-signing or software-integrity purposes.
md5_final/1
Finishes the update of an MD5
and returns
the computed MD5
message digest.
md5_init/0
Creates an MD5 context, to be used in subsequent calls to
md5_update/2
.
md5_update/2
Updates an MD5
with
and returns a
.
memory/0
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.
The memory types are as follows:
total
The total amount of memory currently allocated. This is
the same as the sum of the memory size for processes
and system
.
processes
The total amount of memory currently allocated for the Erlang processes.
processes_used
The total amount of memory currently used by the Erlang
processes. This is part of the memory presented as
processes
memory.
system
The total amount of memory currently allocated for
the emulator that is not directly related to any Erlang
process. Memory presented as processes
is not
included in this memory.
atom
The total amount of memory currently allocated for atoms.
This memory is part of the memory presented as
system
memory.
atom_used
The total amount of memory currently used for atoms.
This memory is part of the memory presented as
atom
memory.
binary
The total amount of memory currently allocated for
binaries. This memory is part of the memory presented
as system
memory.
code
The total amount of memory currently allocated for
Erlang code. This memory is part of the memory presented
as system
memory.
ets
The total amount of memory currently allocated for ets
tables. This memory is part of the memory presented as
system
memory.
low
Only on 64-bit halfword emulator. The total amount of memory allocated in low memory areas that are restricted to less than 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.
Furthermore, 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/1
Returns the memory size in bytes allocated for memory of
type
. The argument can also be given as a list
of memory_type()
atoms, in which case a corresponding list of
{memory_type(), Size :: integer >= 0}
tuples is returned.
Note!
As from ERTS
version 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
See also erlang:memory/0.
min/2
Returns the smallest of
and
.
If the terms are equal,
is returned.
module_loaded/1
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.
monitor/2
Send a monitor request of type
to the
entity identified by
. The caller of
monitor/2
will later be notified by a monitor message on the
following format if the monitored state is changed:
{Tag,MonitorRef ,Type , Object, Info}
Note!
The monitor request is an asynchronous signal. That is, it takes time before the signal reaches its destination.
Valid
s:
process
Monitor the existence of the process identified by
. Valid
s in combination with the
process
can be any of the following:
pid()
The process identifier of the process to monitor.
{RegisteredName, Node}
A tuple consisting of a registered name of a process and
a node name. The process residing on the node Node
with the registered name {RegisteredName, Node}
will
be monitored.
RegisteredName
The process locally registered as RegisteredName
will become monitored.
Note!
When a registered name is used, the process that has the registered name when the monitor request reach its destination will be monitored. The monitor is not effected if the registered name is unregistered, or unregistered and later registered on another process.
The monitor is triggered either when the monitored process terminates, is non existing, or if the connection to it is lost. In the case the connection to it is lost, we do not know if it still exist or not. After this type of monitor has been triggered, the monitor is automatically removed.
When the monitor is triggered a 'DOWN'
message is
sent to the monitoring process. A 'DOWN'
message has
the following pattern:
{'DOWN', MonitorRef, Type, Object, Info}
Here MonitorRef
and Type
are the same as
described earlier, and:
Object
equals:
Item
Item
is specified by a
process identifier.{RegisteredName, Node}
Item
is specified as
RegisteredName
, or {RegisteredName, Node}
where Node
corresponds to the node that the
monitored process resides on.Info
Either the exit reason of the process, noproc
(non-existing process), or noconnection
(no
connection to the node where the monitored process
resides).
The monitoring is turned off when the 'DOWN'
message is sent or when
demonitor/1
is called.
If an attempt is made to monitor a process on an older node
(where remote process monitoring is not implemented or
where remote process monitoring by registered name is not
implemented), the call fails with badarg
.
Note!
The format of the 'DOWN'
message changed in ERTS
version 5.2 (OTP R9B) for monitoring
by registered name. Element Object
of
the 'DOWN'
message could in earlier versions
sometimes be the process identifier of the monitored process and sometimes
be the registered name. Now element Object
is
always a tuple consisting of the registered name and
the node name. Processes on new nodes (ERTS version 5.2
or higher) always get 'DOWN'
messages on
the new format even if they are monitoring processes on old
nodes. Processes on old nodes always get 'DOWN'
messages on the old format.
time_offset
Monitor changes in
time offset
between
Erlang
monotonic time and
Erlang
system time. There is only one valid
in combination with the
time_offset
, namely the atom
clock_service
. Note that the atom clock_service
is
not the registered name of a process. In this specific
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 will be triggered once regardless of whether the time offset value was actually changed or not.
If the runtime system is in multi time warp mode, the time offset will be changed when the runtime system detects that the OS system time has changed. The runtime system will, however, not detect this immediately when it happens. A task checking the time offset is scheduled to execute at least once a minute, so under normal operation this should be detected within a minute, but during heavy load it might take longer time.
The monitor will not be automatically removed after it has been triggered. That is, repeated changes of the time offset will trigger the monitor repeatedly.
When the monitor is triggered a 'CHANGE'
message will
be 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()
.
Note 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/2
Monitors 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.
monitor_node/3
Behaves as
monitor_node/2
except that it allows an
extra option to be given, 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.
monotonic_time/0
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
may also place this unspecified point in time different relative
runtime system start. It may 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)
.
monotonic_time/1
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.
nif_error/1
Works exactly like
erlang:error/1, but
Dialyzer
thinks that this BIF will return an arbitrary
term. When used in a stub function for a NIF to generate an
exception when the NIF library is not loaded, Dialyzer
does not generate false warnings.
nif_error/2
Works exactly like
erlang:error/2, but
Dialyzer
thinks that this BIF will return an arbitrary
term. When used in a stub function for a NIF to generate an
exception when the NIF library is not loaded, Dialyzer
does not generate false warnings.
node/0
Returns the name of the local node. If the node is not alive,
nonode@nohost
is returned instead.
Allowed in guard tests.
node/1
Returns the node where
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/0
Returns a list of all visible nodes in the system, except
the local node. Same as nodes(visible)
.
nodes/1
Returns a list of nodes according to the argument given. The returned result when the argument is a list, is the list of nodes satisfying the disjunction(s) of the list elements.
can be any of the following:
visible
Nodes connected to this node through normal connections.
hidden
Nodes connected to this node through hidden connections.
connected
All nodes connected to this node.
this
This node.
known
Nodes 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 delayed_node_table_gc.
Some equalities: [node()] = nodes(this)
,
nodes(connected) = nodes([visible, hidden])
, and
nodes() = nodes(visible)
.
now/0
Warning!
This function is deprecated! Do not use it!
See the users guide chapter
Time and Time Correction
for more information. Specifically the
Dos and Dont's
section for information on 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),
on the assumption that the underlying OS supports this.
Otherwise some other point in time is chosen. It is also
guaranteed that subsequent calls to this BIF return
continuously increasing values. Hence, the return value from
now()
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/2
Returns a port identifier as the result of opening a new Erlang port. A port can be seen as an external Erlang process.
The name of the executable as well as the arguments
given in cd
, env
, args
, and arg0
are
subject to Unicode file name translation if the system is running
in Unicode file name 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, the function
file:native_name_encoding/0, and the
STDLIB
User's Guide.
Note!
The characters in the name (if given as a list) can only be higher than 255 if the Erlang Virtual Machine is started in Unicode file name translation mode. Otherwise the name of the executable is limited to the ISO-latin-1 character set.
can be any of the following:
{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.
When starting external programs on Solaris, the system
call vfork
is used in preference to fork
for performance reasons, although it has a history of
being less robust. If there are problems using
vfork
, setting environment variable
ERL_NO_VFORK
to any value causes fork
to be used instead.
For external programs, PATH
is searched
(or an equivalent method is used to find programs,
depending on 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 having spaces in file names or directory names.
If spaces in executable file names 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 given file is not
executable.
{fd, In , Out }
Allows an Erlang process to access any currently opened
file descriptors used by Erlang. The file descriptor
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 new line 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 new line 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 new line
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 }
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.
{args, [ string() | binary() ]}
Only valid for {spawn_executable,
and specifies arguments to the executable. Each argument
is given as a separate string and (on Unix) eventually
ends up as one element each in the argument vector. On
other platforms, a similar behavior is mimicked.
The arguments are not expanded by the shell before being supplied to the executable. Most notably this means that file wild card expansion does not happen. To expand wild cards 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, wild card expansion does not happen, and the script is provided with the untouched arguments. On Windows, wild card expansion is always up to the program itself, therefore this is not an issue issue.
The executable name (also known as argv[0]
)
is not to be given 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 also given, 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
given in {spawn_executable, Command}
does not point out an executable file.
enoent
FileName
given in
{spawn_executable, FileName }
does not point out an existing file.
During use of a port opened using {spawn, Name}
,
{spawn_driver, Name}
, or {spawn_executable, Name}
,
errors arising when sending messages to it are reported to
the owning process using signals of the form
{'EXIT', Port, PosixCode}
. For the possible values of
PosixCode
, see the
file(3)
manual page in Kernel
.
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)
.
phash/2
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.
This BIF can be used instead of the old deprecated BIF
erlang:hash/2
, as it calculates better hashes for
all data types, but consider using phash2/1,2
instead.
phash2/1
phash2/2
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/1
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.
port_close/1
Closes an open port. Roughly the same as
except for the error behavior
(see the following), 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 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. This 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/2
Sends data to a port. Same as
except
for the error
behavior and being synchronous (see the following). 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 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. This 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
Data
is an invalid I/O list.
port_command/3
Sends data to a port. port_command(Port, Data, [])
equals port_command(Port, Data)
.
If the port command is aborted, false
is returned,
otherwise true
.
If the port is busy, the calling process is suspended until the port is not busy any more.
The following
s are valid:
force
notsup
exception if the
driver of the port does not support this. For more
information, see driver flag
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.
port_connect/2
Sets the port owner (the connected port) to
.
Roughly the same as
except for the following:
-
The error behavior differs, see the following.
-
The port does not reply with
{Port,connected}
. -
port_connect/1
is synchronous, see the following. -
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 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. This 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/3
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
).
port_call/3
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
Operation
or Data
).
port_info/1
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.
port_info/2
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:
false
(emulator without SMP support)port_level
(port-specific locking)driver_level
(driver-specific locking)
Notice that these results are highly implementation-specific and can change in a future release.
If the port identified by
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 that this port
monitors.
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 being 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/1
Returns a string corresponding to the text
representation of the port identifier
.
Warning!
This BIF is intended for debugging. It is not to be used in application programs.
ports/0
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/0
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.
process_display/2
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.
process_flag/2
When trap_exit
is set to true
, exit signals
arriving to a process are converted to {'EXIT', From, Reason}
messages, which can be received as ordinary
messages. If trap_exit
is set to false
, the
process exits if it receives an exit signal other than
normal
and the exit signal is propagated to its
linked processes. Application processes are normally
not to trap exits.
Returns the old value of the flag.
See also exit/2.
Used by a process to redefine the error handler for undefined function calls and undefined registered processes. Inexperienced users are not to use this flag, as code auto-loading depends on the correct operation of the error handling module.
Returns the old value of the flag.
Changes the minimum heap size for the calling process.
Returns the old value of the flag.
Changes the minimum binary virtual heap size for the calling process.
Returns the old value of the flag.
This flag sets the maximum heap size for the calling process.
If
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 will 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 will send an
untrappable exit signal with reason kill
to the process
if the maximum heap size is reached. The garbage collection
that triggered the kill
will not be completed, instead the
process will exit as soon as is possible. When set to false
no exit signal will be sent to the process, instead it will
continue 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 the erl
+hmaxk option,
or
erlang:system_flag(max_heap_size, MaxHeapSize)
.
error_logger
When set to true
the runtime system will send a
message to the current error_logger
containing details about the process when the maximum
heap size is reached. One error_logger
report will
be sent each time the limit is reached.
If error_logger
is not defined in the map the system
default will be used. The default system default is true
.
It can be changed by either the erl +hmaxel
option, or
erlang:system_flag(max_heap_size, MaxHeapSize)
.
The heap size of a process is quite hard to predict, especially the
amount of memory that is used during the garbage collection. When
contemplating using this option, it is recommended to first run
it in production with kill
set to false
and inspect
the error_logger
reports to see what the normal peak sizes
of the processes in the system is and then tune the value
accordingly.
This flag determines how messages in the message queue are stored. When the flag is:
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 may however temporarily be stored off heap. This is how messages always have been stored up until ERTS version 8.0.
mixed
Messages may be placed either on the heap or outside of the heap.
The default message_queue_data
process flag is determined
by the +hmqd
erl
command line argument.
If the process potentially may get a hugh amount of messages,
you are recommended to set the flag to off_heap
. This
since a garbage collection with lots of messages placed on
the heap may become extremly expensive and the process may
consume large amounts of memory. Performance of the
actual message passing is however generally better when not
using the off_heap
flag.
When changing this flag messages will be moved. This work has been initiated but not completed when this function call returns.
Returns the old value of the flag.
Sets the process priority.
is an atom.
There are four priority levels: 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 there are runnable processes on priority high
,
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 there are processes
running on priority high
. On the runtime
system with SMP support, more processes can be running
in parallel than processes on priority high
, that is,
a low
and a high
priority process can
execute at the same time.
When there are runnable processes on priority max
,
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 preemptive. Regardless of priority, a process is preempted when it has consumed more than a certain number of reductions since the last time it was selected for execution.
Note!
Do not depend on the scheduling to remain exactly as it is today. Scheduling, at least on the runtime system with SMP support, is likely to be changed in a future release to use available processor cores better.
There is no automatic mechanism for avoiding priority inversion, such as priority inheritance or priority ceilings. When using priorities, take this into account and handle such scenarios by yourself.
Making calls from a high
priority process into code
that you have 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 does
most likely cause 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
is greater than 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 calls - The 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. Furthermore, send, receive,
and timeout events are still added to the list.)
Returns the old value of the flag.
process_flag/3
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/1
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
messages
links
dictionary
trap_exit
error_handler
priority
group_leader
total_heap_size
heap_size
stack_size
reductions
garbage_collection
If the process identified by
has a
registered name,
also an
with item registered_name
appears.
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/2
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 given, 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 given, the result is
.
The
s in
appear with the corresponding
s in the same order as the
s appeared
in
. Valid
s can
appear multiple times in
.
Note!
If registered_name
is part of
and the process has no name registered a
{registered_name, []}
,
will appear in the resulting
. This
behavior is different when a single
Item =:= registered_name
is given, and when
process_info/1
is used.
The following
s with corresponding
s are valid:
{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 currently being referred to by this
process. This
can be changed or
removed without prior notice.
{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}}
,
,
is
the current function call of the process.
{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.
{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.
See gc_minor_start in
erlang:trace/3 for details about
what each item means.
{group_leader, GroupLeader }
is 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 the following).
{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, Pids }
A list of process identifiers monitoring the process (with
monitor/2
).
{monitors, Monitors }
A list of monitors (started by monitor/2
)
that are active for the process. For a local process
monitor or a remote process monitor by a process
identifier, the list item is {process,
.
For a remote process
monitor by name, the list item is
{process, {
.
{message_queue_data, MQD }
Returns the current state of the message_queue_data
process flag.
is either off_heap
,
on_heap
, or mixed
. 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 name of the process. 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 one of the following BIFs:
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/0
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/1
Removes old code for
.
Before this BIF is used,
erlang: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 (OTP 19), any lingering processes
that still execute the old code will be 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/2
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.
raise/3
Stops the execution of the calling process with an exception of given class, reason, and call stack backtrace (stacktrace).
Warning!
This BIF is intended for debugging. Avoid to use it in applications, unless you really know what you are doing.
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.
Since 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.
read_timer/2
Read 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.
Available
:
{async, Async}
Asynchronous request for state information. Async
defaults to false
which will cause 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 may be added in the future.
If
is an integer, it represents the
time in milli-seconds left until the timer expires.
If
is false
, a
timer corresponding to
could not
be found. This can be because the timer had expired,
it had 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 timeout message has
arrived at its destination yet.
Note!
The timer service that manages the timer may be co-located
with another scheduler than the scheduler that the calling
process is executing on. If this is the case, 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, you want to use option {async, true}
.
If using option {async, false}
, the calling
process will be blocked until the operation has been
performed.
See also
erlang:send_after/4
,
erlang:start_timer/4
,
and
erlang:cancel_timer/2
.
read_timer/1
Read the state of a timer. The same as calling
erlang:read_timer(TimerRef,
[])
.
ref_to_list/1
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/2
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/0
Returns a list of names that have been registered using register/2, for example:
> registered().
[code_server, file_server, init, user, my_db]
resume_process/1
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/1
Returns an integer by rounding
,
for example:
round(5.5).
6
Allowed in guard tests.
self/0
Returns the process identifier of the calling process, for example:
> self().
<0.26.0>
Allowed in guard tests.
send/2
Sends a message and returns
. This
is the same as
.
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.
send/3
Either sends a message and returns ok
, or does not send
the message but returns something else (see the following).
Otherwise the same as
erlang:send/2.
For more detailed explanation and warnings, see
erlang:send_nosuspend/2,3.
The options are as follows:
nosuspend
If the sender would have to be suspended to do the send,
nosuspend
is returned instead.
noconnect
If the destination node would have to be auto-connected
to do the send, noconnect
is returned
instead.
Warning!
As with erlang:send_nosuspend/2,3
: use with extreme
care.
send_after/4
Starts a timer. When the timer expires, the message
is sent to the process
identified by
. Apart from
the format of the timeout message,
erlang:send_after/4
works exactly as
erlang:start_timer/4
.
send_after/3
Starts a timer. The same as calling
erlang:send_after(
.
send_nosuspend/2
The same as
erlang:send(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. The fact that 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.
send_nosuspend/3
The same as
erlang:send(
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.
set_cookie/2
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/3
Returns a tuple that is a copy of argument
with the element given 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/1
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/1
Returns the process identifier of a new process started by the
application of
to the empty list
[]
. Otherwise
works like spawn/3.
spawn/2
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/3
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/4
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/1
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/2
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/3
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/4
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/1
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/3
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/2
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 given, the newly created
process is monitored, and both the pid and reference for
the monitor is returned.
spawn_opt/3
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/4
Works as spawn/3, except that an extra option list is given when creating the process.
If option monitor
is given, the newly created
process is monitored, and both the pid and reference for
the monitor is returned.
The options are as follows:
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,
{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, see erlang:system_flag/2.)Number
{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 the
+hmax
erl
command line argument. 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.
should be either off_heap
,
on_heap
, or mixed
. The default
message_queue_data
process flag is determined by the
+hmqd
erl
command line argument. For more information, see the
documentation of
process_flag(message_queue_data,
.
spawn_opt/5
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/2
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
start_timer/4
Starts a timer. When the timer expires, the message
{timeout,
is sent to the process identified by
.
Available
s:
{abs, false}
This is the default. It means the
value is interpreted
as a time in milli-seconds relative current
Erlang
monotonic time.
{abs, true}
Absolute
value. The
value is interpreted as an
absolute Erlang monotonic time in milli-seconds.
More
s may be added in the future.
The absolute point in time, the timer is set to expire on,
has to be in the interval
[
erlang:system_info(start_time)
,
erlang:system_info(end_time)
]
.
Further, 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 may or may not
have terminated. 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 given 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 version 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.
start_timer/3
Starts a timer. The same as calling
erlang:start_timer(
.
statistics/1
Returns a list where each element represents the amount
of active processes and ports on each run queue and its
associated scheduler. That is, the number of processes and
ports that are ready to run, or are currently running. The
element location in the list corresponds to the scheduler
and its run queue. The first element corresponds to scheduler
number 1 and so on. The information is not gathered
atomically. That is, the result is not necessarily a
consistent snapshot of the state, but instead quite
efficiently gathered. See also,
statistics(total_active_tasks)
,
statistics(run_queue_lengths)
, and
statistics(total_run_queue_lengths)
.
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),
especially on an Erlang machine with SMP support.
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 there will be some overhead when this
is enabled. Microstate accounting is meant to be a profiling tool
to help figure out performance bottlenecks.
To start
/stop
/reset
microstate_accounting you use
the system_flag
microstate_accounting
.
erlang: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.
> 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 could 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)).
It is important to note that these values are not guaranteed to be the exact time spent in each state. This is because of various optimisation done in order to keep the overhead as small as possible.
Currently the following
are available:
scheduler
async
aux
Currently 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 will get the total run-time for that thread.
aux
check_io
emulator
gc
other
port
sleep
It is possible to add more fine grained
s
through configure.
(e.g. ./configure --with-microstate-accounting=extra
).
Enabling these states will cause a performance degradation when
microstate accounting is turned off and increase the overhead when
it is turned on.
alloc
bif
emulator
state.busy_wait
erlang: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.There is a utility module called
msacc
in
runtime_tools that can be used to more easily analyse these
statistics.
Returns undefined
if the system flag
microstate_accounting
is turned off.
The list of thread information is unsorted and may 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 (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 the run-queues. That is, the number
of processes and ports that are ready to run on all available
run-queues. The information is gathered atomically. That
is, the result is a consistent snapshot of the state, but
this operation is much more expensive compared to
statistics(total_run_queue_lengths)
.
This especially when a large amount of schedulers is used.
Returns a list where each element represents the amount
of processes and ports ready to run for each run queue. The
element location in the list corresponds to the run queue
of a scheduler. The first element corresponds to the run
queue of scheduler number 1 and so on. The information is
not gathered atomically. That is, the result is
not necessarily a consistent snapshot of the state, but
instead quite efficiently gathered. See also,
statistics(total_run_queue_lengths)
,
statistics(active_tasks)
, and
statistics(total_active_tasks)
.
Returns information about runtime, in milliseconds.
This is the sum of the runtime for all threads in the Erlang runtime system and can therefore be greater than the wall clock time.
Example:
> statistics(runtime).
{1690,1620}
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. 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 built-in-functions, 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.
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)), A/T.
0.9769136803764825
Note!
scheduler_wall_time
is by default disabled. To
enable it, use
erlang:system_flag(scheduler_wall_time, true)
.
Returns the total amount of active processes and ports in
the system. That is, the number of processes and ports that
are ready to run, or are currently running. The information
is not gathered atomically. That is, the result
is not necessarily a consistent snapshot of the state, but
instead quite efficiently gathered. See also,
statistics(active_tasks)
,
statistics(run_queue_lengths)
, and
statistics(total_run_queue_lengths)
.
Returns the total length of the run-queues. That is, the number
of processes and ports that are ready to run on all available
run-queues. The information is not gathered atomically.
That is, the result is not necessarily a consistent snapshot of
the state, but much more efficiently gathered compared to
statistics(run_queue)
.
See also,
statistics(run_queue_lengths)
,
statistics(total_active_tasks)
, and
statistics(active_tasks)
.
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.
suspend_process/2
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 will not be
scheduled for execution until the process has been resumed.
A process can be suspended by multiple processes and can
be suspended multiple times by a single process. A suspended
process does not leave the suspended state until its suspend
count reaches zero. The suspend count of
is decreased when
erlang:resume_process(erlang:suspend_process(
.
All increased suspend
counts on other processes acquired by a process are automatically
decreased when the process terminates.
The options (
s) are as follows:
asynchronous
Suspendee
. Suspendee
eventually suspends
unless it is resumed before it could suspend. The caller
of erlang:suspend_process/2
returns immediately,
regardless of whether Suspendee
has
suspended yet or not. The point in time when
Suspendee
suspends cannot be deduced
from other events in the system. It is only guaranteed that
Suspendee
eventually suspends
(unless it
is resumed). If option asynchronous
has not
been passed, the caller of erlang:suspend_process/2
is
blocked until Suspendee
has suspended.
unless_suspending
Suspendee
is
suspended unless the calling process already is suspending
Suspendee
.
If unless_suspending
is combined
with option asynchronous
, a suspend request is
sent unless the calling process already is suspending
Suspendee
or if a suspend request
already has been sent and is in transit. If the calling
process already is suspending Suspendee
,
or if combined with option asynchronous
and a send request already is in transit,
false
is returned and the suspend count on
Suspendee
remains unchanged.
If the suspend count on the process identified by
is increased, true
is returned, otherwise false
.
Warning!
This BIF is intended for debugging only.
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
higher than 2,000,000,000 suspends and will never be lower.
suspend_process/1
Suspends the process identified by
. The same as calling
erlang:suspend_process(
Warning!
This BIF is intended for debugging only.
system_flag/2
Sets the maximum depth of call stack back-traces in the
exit reason element of 'EXIT'
tuples.
Returns the old value of the flag.
Warning!
This argument is deprecated and scheduled for
removal in ERTS
5.10/OTP R16. 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 the 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.
Note!
The dirty schedulers functionality is experimental. Enable support for dirty schedulers when building OTP to try out the functionality.
For more information, see erlang:system_info(dirty_cpu_schedulers) and erlang:system_info(dirty_cpu_schedulers_online).
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. By passing reset it is possible to reset all counters to 0.
For more information see, erlang:statistics(microstate_accounting).
Sets the default minimum heap size for processes. The size
is given 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/N or
process_flag/2.
Returns the old value of the flag.
Sets the default minimum binary virtual heap size for
processes. The size is given in words.
The new min_bin_vhheap_size
effects only
processes spawned after the change of
min_bin_vhheap_size
has been made.
min_bin_vheap_size
can be set for individual
processes by using
spawn_opt/N or
process_flag/2.
Returns the old value of the flag.
Sets the default maximum heap size settings for processes.
The size is given 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/N 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 may 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 as well as 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).
Warning!
This argument is deprecated and scheduled for
removal in ERTS
5.10/OTP R16. 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,
it is reported to error_logger
. To verify that the
schedulers have bound as requested, call
erlang:system_info(scheduler_bindings).
Schedulers can be bound on newer Linux, Solaris, FreeBSD, and Windows systems, but more systems will be supported in future releases.
In order for the runtime system to be able to bind schedulers,
the CPU topology must be known. If the runtime system fails
to detect the CPU topology automatically, it can be defined.
For more information on how to define the CPU topology, see
command-line flag +sct
in erl(1)
.
The runtime system does by default not bind schedulers to logical processors.
Note!
If the Erlang runtime system is the only OS process binding threads to logical processors, this improves the performance of the runtime system. However, if other OS processes (for example, another Erlang runtime system) also bind threads to logical processors, there can be a performance penalty instead. Sometimes this performance penalty can be severe. If so, it is recommended to not bind the schedulers.
Schedulers can be bound in different ways. Argument
determines how schedulers are
bound and can be any of the following:
unbound
Same as command-line argument
+sbt u in erl(1)
.
no_spread
Same as command-line argument
+sbt ns in erl(1)
.
thread_spread
Same as command-line argument
+sbt ts in erl(1)
.
processor_spread
Same as command-line argument
+sbt ps in erl(1)
.
spread
Same as command-line argument
+sbt s in erl(1)
.
no_node_thread_spread
Same as command-line argument
+sbt nnts in erl(1)
.
no_node_processor_spread
Same as command-line argument
+sbt nnps in erl(1)
.
thread_no_node_processor_spread
Same as command-line argument
+sbt tnnps in erl(1)
.
default_bind
Same as command-line argument
+sbt db in erl(1)
.
The returned value equals
before flag
scheduler_bind_type
was changed.
Failures:
notsup
If binding of schedulers is not supported.
badarg
If
is not one of the documented
alternatives.
badarg
If CPU topology information is unavailable.
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 erlang: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 value of the node trace control word to
, which is to be an unsigned integer.
For more information, see the 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.
system_info/1
Returns various information about the 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).
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, 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.
{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,
.
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 }
LevelTag
s can be introduced in a
future release.
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 sub level to core
.
core
can be a sub level to processor
or node
. processor
can be on the
top level or a sub level to node
. node
can be on the top level or a sub level to
processor
. That is, NUMA nodes can be processor
internal or processor external. A CPU topology can
consist of a mix of processor internal and external
NUMA nodes, as long as each logical CPU belongs to
one 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. In other words, 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.
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 in the following.
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
system_flag/2.
spawn_opt/4
can spawn a process that does not use the default
settings.
max_heap_size
Returns {max_heap_size,
,
where
is the current
system-wide max heap size settings for spawned processes.
This setting can be set using the erl
command line
flags +hmax
,
+hmaxk
and
+hmaxel
. It can
also be changed at run-time using
erlang:system_flag(max_heap_size, MaxHeapSize)
.
For more details about the max_heap_size
process flag
see
process_flag(max_heap_size, MaxHeapSize)
.
min_heap_size
Returns {min_heap_size,
,
where
is the current
system-wide minimum heap size for spawned processes.
message_queue_data
Returns the default value of the message_queue_data
process flag which is either off_heap
, on_heap
, or mixed
.
This default is set by the erl
command line argument
+hmqd
. For more information on the
message_queue_data
process flag, see documentation of
process_flag(message_queue_data,
MQD)
.
min_bin_vheap_size
Returns {min_bin_vheap_size,
, where
is the current system-wide
minimum binary virtual heap size for spawned processes.
Returns various information about the current system
(emulator) as specified by
:
allocated_areas
, allocator
,
alloc_util_allocators
, allocator_sizes
See above.
build_type
Returns an atom describing the build type of the runtime
system. This is normally the atom opt
for optimized.
Other possible return values are debug
, purify
,
quantify
, purecov
, gcov
, valgrind
,
gprof
, and lcnt
. Possible return values
can be added or removed at any time without prior notice.
c_compiler_used
Returns a two-tuple describing the C compiler used when
compiling the runtime system. The first element is an
atom describing the name of the compiler, or undefined
if unknown. The second element is a term describing the
version of the compiler, or undefined
if unknown.
check_io
Returns a list containing miscellaneous information about the emulators internal I/O checking. Notice that the content of the returned list can vary between platforms and over time. It is only guaranteed that a list is returned.
compat_rel
Returns the compatibility mode of the local node as
an integer. The integer returned represents the
Erlang/OTP release that the current emulator has been
set to be backward compatible with. The compatibility
mode can be configured at startup by using command-line flag
+R in
erl(1)
.
cpu_topology
See above.
creation
Returns the creation of the local node as an integer.
The creation is changed when a node is restarted. The
creation of a node is stored in process identifiers, port
identifiers, and references. This makes it (to some
extent) possible to distinguish between identifiers from
different incarnations of a node. The valid
creations are integers in the range 1..3, but this will
probably change in a future release. If the node is not
alive, 0
is returned.
debug_compiled
Returns true
if the emulator has been debug
compiled, otherwise false
.
delayed_node_table_gc
Returns the amount of time in seconds garbage collection
of an entry in a node table is delayed. This limit can be set
on startup by passing the command line flag
+zdntgc
to erl
. For more information see the documentation of the
command line flag.
dirty_cpu_schedulers
Returns the number of dirty CPU scheduler threads used by the emulator. Dirty CPU schedulers execute CPU-bound native functions, such as NIFs, linked-in driver code, and BIFs that cannot be managed cleanly by the normal emulator schedulers.
The number of dirty CPU scheduler threads is determined
at emulator boot time and cannot be changed after that.
However, the number of dirty CPU scheduler threads online
can be changed at any time. The number of dirty CPU
schedulers can be set at startup by passing
command-line flag
+SDcpu or
+SDPcpu in
erl(1)
.
Notice that the dirty schedulers functionality is experimental. Enable support for dirty schedulers when building OTP to try out the functionality.
See also erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline), erlang:system_info(dirty_cpu_schedulers_online), erlang:system_info(dirty_io_schedulers), erlang:system_info(schedulers), erlang:system_info(schedulers_online), and erlang:system_flag(schedulers_online, SchedulersOnline).
dirty_cpu_schedulers_online
Returns the number of dirty CPU schedulers online.
The return value satisfies
1 <= DirtyCPUSchedulersOnline <= N
,
where N
is the smallest of the return values of
erlang:system_info(dirty_cpu_schedulers)
and
erlang:system_info(schedulers_online)
.
The number of dirty CPU schedulers online can be set at
startup by passing command-line flag
+SDcpu in
erl(1)
.
Notice that the dirty schedulers functionality is experimental. Enable support for dirty schedulers when building OTP to try out the functionality.
For more information, see erlang:system_info(dirty_cpu_schedulers), erlang:system_info(dirty_io_schedulers), erlang:system_info(schedulers_online), and erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline).
dirty_io_schedulers
Returns the number of dirty I/O schedulers as an integer. Dirty I/O schedulers execute I/O-bound native functions, such as NIFs and linked-in driver code, which cannot be managed cleanly by the normal emulator schedulers.
This value can be set at startup by passing command-line
argument +SDio
in erl(1)
.
Notice that the dirty schedulers functionality is experimental. Enable support for dirty schedulers when building OTP to try out the functionality.
For more information, see erlang:system_info(dirty_cpu_schedulers), erlang:system_info(dirty_cpu_schedulers_online), and erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline).
dist
Returns a binary containing a string of distribution information formatted as in Erlang crash dumps. For more information, see Section "How to interpret the Erlang crash dumps" in the User's Guide.
dist_buf_busy_limit
Returns the value of the distribution buffer busy limit
in bytes. This limit can be set at startup by passing
command-line flag
+zdbbl
to erl
.
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.
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 the
dyntrace
manual page and the
README.dtrace
/README.systemtap
files in the
Erlang source code top directory.
dynamic_trace_probes
Returns a boolean()
indicating if dynamic trace
probes (dtrace
or systemtap
) are built into
the emulator. This can only be true
if the Virtual
Machine was built for dynamic tracing (that is,
system_info(dynamic_trace)
returns
dtrace
or systemtap
).
end_time
The last Erlang monotonic
time in native
time unit that
can be represented internally in the current Erlang runtime system
instance. The time between the
start time and
the end time is at least a quarter of a millennium.
elib_malloc
This option will be removed in a future release.
The return value will always be false
, as the
elib_malloc
allocator has been removed.
eager_check_io
Returns the value of the erl
command line flag
+secio
which is either true
or false
. See the
documentation of the command line flag for information about
the different values.
ets_limit
Returns the maximum number of ETS tables allowed. This
limit can be increased at startup by passing
command-line flag
+e to
erl(1)
or by setting environment variable
ERL_MAX_ETS_TABLES
before starting the Erlang
runtime system.
heap_sizes
Returns a list of integers representing valid heap sizes in words. All Erlang heaps are sized from sizes in this list.
heap_type
Returns the heap type used by the current emulator. One heap type exists:
private
Each process has a heap reserved for its use and no references between heaps of different processes are allowed. Messages passed between processes are copied between heaps.
info
Returns a binary containing a string of miscellaneous system information formatted as in Erlang crash dumps. For more information, see Section "How to interpret the Erlang crash dumps" in the User's Guide.
kernel_poll
Returns true
if the emulator uses some kind of
kernel-poll implementation, otherwise false
.
loaded
Returns a binary containing a string of loaded module information formatted as in Erlang crash dumps. For more information, see Section "How to interpret the Erlang crash dumps" in the User's Guide.
logical_processors
Returns the detected number of logical processors configured
in the system. The return value is either an integer, or
the atom unknown
if the emulator cannot
detect the configured logical processors.
logical_processors_available
Returns the detected number of logical processors available
to the Erlang runtime system. The return value is either an
integer, or the atom unknown
if the emulator
cannot detect the available logical processors. The number
of available logical processors is less than or equal to
the number of
logical processors online.
logical_processors_online
Returns the detected number of logical processors online on
the system. The return value is either an integer,
or the atom unknown
if the emulator cannot
detect logical processors online. The number of logical
processors online is less than or equal to the number of
logical processors configured.
machine
Returns a string containing the Erlang machine name.
modified_timing_level
Returns the modified timing-level (an integer) if
modified timing is enabled, otherwise, undefined
.
For more information about modified timing, see
command-line flag
+T
in erl(1)
multi_scheduling
Returns disabled
, blocked
, blocked_normal
,
or enabled
:
disabled
The emulator has only one scheduler thread. The emulator does not have SMP support, or have been started with only one scheduler thread.
blocked
The emulator has more than one scheduler thread, but all scheduler threads except one are blocked. That is, only one scheduler thread schedules Erlang processes and executes Erlang code.
blocked_normal
The emulator has more than one scheduler thread, but all normal scheduler threads except one are blocked. Note that dirty schedulers are not blocked, and may 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).
nif_version
Returns a string containing the version of the Erlang NIF interface used by the runtime system. It is on the form "<major ver>.<minor ver>".
normal_multi_scheduling_blockers
Returns a list of
s when
normal multi-scheduling is blocked (i.e. 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).
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 OTP 17, the OTP release number corresponds to
the major OTP version number. No
erlang:system_info()
argument gives the exact OTP
version. This is because the exact OTP version in the general case
is difficult to determine. For more information, see the description
of versions in
System principles in System Documentation.
os_monotonic_time_source
Returns a list containing information about the source of OS monotonic time that is used by the runtime system.
If []
is returned, no OS monotonic time is
available. The list contains two-tuples with 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 exist if OS monotonic time is
available to the runtime system.
{clock_id, ClockId}
This tuple only exist 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
. Also note that
the resolution does not say anything about the
accuracy,
and whether the
precision
do align 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 needs to 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 needs to 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 if these tuples is undefined. The following
tuples can be part of the list, but more tuples can be
introduced in the future:
{function, Function}
Function
is the name of the funcion
used.
{clock_id, ClockId}
This tuple only exist 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 may be lower than
OsSystemTimeResolution
. Also note that
the resolution does not say anything about the
accuracy,
and whether the
precision
do align with the resolution. You do,
however, know that the precision is not better than
OsSystemTimeResolution
.
{parallel, Parallel}
Parallel
equals yes
if
Function
is called in parallel from multiple
threads. If it is not called in parallel, because
calls needs to be serialized, Parallel
equals
no
.
{time, OsSystemTime}
OsSystemTime
equals current OS
system time in native
time unit.
port_parallelism
Returns the default port parallelism scheduling hint used.
For more information, see command-line argument
+spp in erl(1)
.
port_count
Returns the number of ports currently existing at the
local node. The value is given as an integer. This is
the same value as returned by
length(erlang:ports())
, but more efficient.
port_limit
Returns the maximum number of simultaneously existing
ports at the local node as an integer. This limit can be
configured at startup by using command-line flag
+Q in erl(1)
.
process_count
Returns the number of processes currently existing at the
local node. The value is given as an integer. This is
the same value as returned by
length(processes())
, but more efficient.
process_limit
Returns the maximum number of simultaneously existing
processes at the local node. The value is given as an
integer. This limit can be configured at startup by using
command-line flag +P
in erl(1)
.
procs
Returns a binary containing a string of process and port information formatted as in Erlang crash dumps. For more information, see Section "How to interpret the Erlang crash dumps" in the User's Guide.
scheduler_bind_type
Returns information about how the user has requested schedulers to be bound or not bound.
Notice that even though 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
if the emulator has been compiled
with SMP support, otherwise false
is returned.
start_time
The Erlang monotonic
time in native
time unit at the
time when current Erlang runtime system instance started. See also
erlang:system_info(end_time)
.
system_version
Returns a string containing version number and some important properties, such as the number of schedulers.
system_architecture
Returns a string containing the processor and OS architecture the emulator is built for.
threads
Returns true
if the emulator has been compiled
with thread support, otherwise false
is returned.
thread_pool_size
Returns the number of async threads in the async thread pool used for asynchronous driver calls (driver_async()). The value is given as an integer.
time_correction
Returns a boolean value indicating whether time correction is enabled or not.
time_offset
Returns the state of the time offset:
preliminary
The time offset is preliminary, and will be changed at a later time when being finalized. 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 being used:
no_time_warp
The no time warp mode is used.
single_time_warp
The single time warp mode is used.
multi_time_warp
The multi time warp mode is used.
tolerant_timeofday
Returns whether a pre erts-7.0 backwards compatible compensation
for sudden changes of system time is enabled
or disabled
.
Such compensation is enabled
when the
time offset is
final
, and
time correction
is enabled.
trace_control_word
Returns the value of the node trace control word. For
more information, see function get_tcw
in Section
Match Specifications in Erlang in the User's Guide.
update_cpu_info
The runtime system rereads the CPU information available and updates its internally stored information about the detected CPU topology and the number of logical processors configured, online, and available.
If the CPU information has changed since the last time
it was read, the atom changed
is returned, otherwise
the atom unchanged
. If the CPU information has changed,
you probably want to
adjust the
number of schedulers online. You typically want
to have as many schedulers online as
logical
processors available.
version
Returns a string containing the version number of the emulator.
wordsize
Same as {wordsize, internal}
.
{wordsize, internal}
Returns the size of Erlang term words in bytes as an integer, that is, 4 is returned on a 32-bit architecture, and 8 is returned on a pure 64-bit architecture. On a halfword 64-bit emulator, 4 is returned, as the Erlang terms are stored using a virtual word size of half the system word size.
{wordsize, external}
Returns the true word size of the emulator, that is, the size of a pointer. The value is given in bytes as an integer. On a pure 32-bit architecture, 4 is returned. On both a half word and on a pure 64-bit architecture, 8 is returned.
Note!
Argument scheduler
has changed name to
scheduler_id
to avoid mix up with argument
schedulers
. Argument scheduler
was
introduced in ERTS
5.5 and renamed in
ERTS
5.5.1.
system_monitor/0
Returns the current system monitoring settings set by
erlang:system_monitor/2
as {
,
or undefined
if there
are no settings. The order of the options can be different
from the one that was set.
system_monitor/1
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.
system_monitor/2
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
the timeout
tuple 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 below 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
will be 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.system_profile/0
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.
system_profile/2
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
Timestamps in profile messages will use
Erlang
monotonic time. The time-stamp (Ts) has the same
format and value as produced by
erlang:monotonic_time(nano_seconds)
.
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
preempted 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
Timestamps in profile messages will consisting 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(nano_seconds),
erlang:unique_integer([monotonic])}
.
timestamp
Timestamps in profile messages will include a
time-stamp (Ts) that has the same form as returned by
erlang:now()
. This is also the default if no
timestamp flag is given. If cpu_timestamp
has
been enabled via erlang:trace/3
, this will also
effect the timestamp produced in profiling messages
when timestamp
flag is enabled.
Note!
erlang:system_profile
is considered experimental
and its behavior can change in a future release.
system_time/0
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 ERTS User's Guide.
system_time/1
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 ERTS User's Guide.
term_to_binary/1
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.
See also binary_to_term/1.
term_to_binary/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 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 OTP R11B-4.
The valid values for
are
0
and 1
.
As from OTP 17.0, {minor_version, 1}
is the default. It
forces any floats in the term to be encoded in a more
space-efficient and exact way (namely in the 64-bit IEEE format,
rather than converted to a textual representation).
As from OTP R11B-4, binary_to_term/1
can decode this
representation.
{minor_version, 0}
means that floats are encoded
using a textual representation. This option is useful to
ensure that releases before OTP R11B-4 can decode resulting
binary.
See also binary_to_term/1.
throw/1
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/0
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}
time_offset/0
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 may be observed at slightly different points in time by different processes.
If the runtime system is in multi time warp mode, the time offset will be changed when the runtime system detects that the OS system time has changed. The runtime system will, however, not detect this immediately when it happens. A task checking the time offset is scheduled to execute at least once a minute, so under normal operation this should be detected within a minute, but during heavy load it might take longer time.
time_offset/1
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.
timestamp/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
uses. The reason for the existence of erlang:timestamp()
is
purely to simplify usage for existing code that assumes this timestamp
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(micro_seconds), MegaSecs = ErlangSystemTime div 1000000000000, Secs = ErlangSystemTime div 1000000 - MegaSecs*1000000, MicroSecs = ErlangSystemTime rem 1000000, {MegaSecs, Secs, MicroSecs}.
It, however, uses a native implementation which 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 ERTS User's Guide.
tl/1
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 []
.
trace/3
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
All currently existing processes and ports and all that will be created in the future.
processes
All currently existing processes and all that will be created in the future.
ports
All currently existing ports and all that will be created in the future.
existing
All currently existing processes and ports.
existing_processes
All currently existing processes.
existing_ports
All currently existing ports.
new
All processes and ports that will be created in the future.
new_processes
All processes that will be created in the future.
new_ports
All ports that will be created in the future.
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 the timestamp
flag to be
in CPU time, not wall clock time. That is, cpu_timestamp
will 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 might 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(nano_seconds)
.
This flag overrides the cpu_timestamp
flag.
strict_monotonic_timestamp
Includes an timestamp 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(nano_seconds),
erlang:unique_integer([monotonic])}
.
This flag overrides the cpu_timestamp
flag.
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 should 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
If no tracer
is given, the calling process
will be receiving all of the trace messages
The effect of combining set_on_first_link
with
set_on_link
is the same as having
set_on_first_link
alone. Likewise for
set_on_spawn
and set_on_first_spawn
.
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 given, 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 timestamp flags are passed, timestamp
has
precedence over strict_monotonic_timestamp
which
in turn has precedence over monotonic_timestamp
. All
timestamp flags are remembered, so if two are passed
and the one with highest precedence later is disabled
the other one will become active.
{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 timeout, then a receive
statement may have timedout, 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 the Driver
.
Driver
is the name of the driver as an atom.
{trace, Port, closed, Reason}
When Port
closed 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 may 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 | 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.
trace_delivered/1
The delivery of trace messages (generated by
erlang:trace/3
,
seq_trace
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(
. A
{trace_delivered,
message is sent to
the caller of 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(
.
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 an
Tracer Module any message sent in the trace callback
is guaranteed to have reached it's 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.
trace_info/2
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
, 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.
The following Item
s are valid 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 being 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 wild cards 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.
The following Item
s are valid 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'
.
The only valid Item
for events is:
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 given, or the name of a
non-existing function, Value
is undefined
.
trace_pattern/2
The same as erlang:trace_pattern(Event, MatchSpec, []), retained for backward compatibility.
trace_pattern/3
Sets trace pattern for message sending.
Must be combined with
erlang:trace/3
to set the send
trace flag for one or more processes.
By default all messages, sent from send
traced processes,
are traced. Use erlang:trace_pattern/3
to limit
traced send events based on the message content, the sender
and/or the receiver.
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
.
See the users guide section
Match Specifications in Erlang
for more information.
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
.
Example; 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
.
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. Use erlang:trace_pattern/3
to limit
traced receive events based on the message content, the sender
and/or the receiver.
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 may
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
. See the users guide section
Match Specifications in Erlang
for more information.
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
.
Example; 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
.
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 in the following). It can be the module, function,
and arity for a function (or a BIF in any module).
The atom '_'
can be used as a wild card 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 wild cards 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 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 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 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.
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 forth.
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/1
Returns an integer by truncating
,
for example:
> trunc(5.5).
5
Allowed in guard tests.
tuple_size/1
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/1
Returns a list corresponding to
.
can contain any Erlang terms.
Example:
> tuple_to_list({share, {'Ericsson_B', 163}}).
[share,{'Ericsson_B',163}]
universaltime/0
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}}
universaltime_to_localtime/1
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.
unique_integer/0
Generates and returns an
integer
unique on current runtime system instance. The same as calling
erlang:unique_integer([])
.
unique_integer/1
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, will 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 in order
to utilize 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.
Valid
s:
Return only positive integers.
Note that by passing the positive
modifier
you will get heap allocated integers (bignums)
quicker.
Return strictly monotonically increasing integers corresponding to creation time. That is, the integer returned will always be 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!
Note that the set of integers returned by
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 being
returned by both calls.
Failures:
badarg
ModifierList
is not a
proper list.badarg
Modifier
is not a
valid modifier.unlink/1
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!
Prior to OTP release R11B (ERTS version 5.5) unlink/1
behaved completely asynchronously, i.e., 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/1
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/1
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>
yield/0
Voluntarily lets other processes (if any) get a chance to
execute. Using erlang:yield()
is similar to
receive after 1 -> ok end
, except that yield()
is faster.
Warning!
There is seldom or never any need to use this BIF, especially in the SMP emulator, as other processes 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.