![[Erlang Systems]](min_head.gif)
By convention, Built In Functions (BIFs) are seen as being in the module
erlang. Thus, both the calls atom_to_list(Erlang)
and erlang:atom_to_list(Erlang) are identical.
BIFs may fail for a variety of reasons. All BIFs fail if they
are called with arguments of an incorrect type. For example,
atom_to_list/1 will fail if it is called with an argument
which is not an atom. If this type of failure is not within the
scope of a catch (and the BIF is not called within a guard; see
below), the process making the call will exit, and an
EXIT signal with the associated reason badarg will be sent
to all linked processes. The other reasons that may make BIFs fail
are described in connection with the description of each
individual BIF.
A few BIFs may be used in guard tests, for example:
tuple_5(Something) when size(Something) == 5 ->
is_tuple_size_5;
tuple_5(_) ->
is_something_else.
Here the BIF size/1 is used in a guard. If size/1
is called with a tuple, it will return the size of the tuple
(i.e., how many elements there are in the tuple). In the above example,
size/1 is used in a guard which tests if its
argument Something is a tuple and, if it is, whether it is
of size 5. In this case, calling size with an argument other than
a tuple will cause the guard to fail and execution will continue
with the next clause. Suppose tuple_5/1 is written as
follows:
tuple_5(Something) ->
case size(Something) of
5 -> is_tuple_size_5;
_ -> is_something_else
end.
In this case, size/1 is not in a guard. If Something
is not a tuple, size/1 will fail and cause the process to
exit with the associated reason badarg (see above).
Some of the BIFs in this chapter are optional in Erlang implementations, and not all implementations will include them.
The following descriptions indicate which BIFs can be used in guards and which BIFs are optional.
Returns an integer or float which is the arithmetical
absolute value of the argument Number (integer or
float).
> abs(-3.33). 3.33000 > abs(-3). 3
This BIF is allowed in guard tests.
Failure: badarg if the argument is not an integer or
a float.
apply({Module, Function}, ArgumentList)
This is equivalent to apply(Module, Function,
ArgumentList).
apply(Module, Function, ArgumentList)
Returns the result of applying Function in
Module on ArgumentList. The applied function
must have been exported from Module. The arity of the
function is the length of ArgumentList.
> apply(lists, reverse, [[a, b, c]]). [c,b,a]
apply can be used to evaluate BIFs by using the
module name erlang.
> apply(erlang, atom_to_list, ['Erlang']). "Erlang"
Failure: error_handler:undefined_function/3 is called
if Module has not exported Function/Arity. The
error handler can be redefined (see the BIF
process_flag/2). If the error_handler is
undefined, or if the user has redefined the default
error_handler so the replacement module is undefined,
an error with the reason undef will be generated.
Returns a list of integers (Latin-1 codes), which
corresponds to the text representation of the argument
Atom.
>atom_to_list('Erlang').
"Erlang"
Failure: badarg if the argument is not an atom.
Returns a list of integers which correspond to the bytes of
Binary.
binary_to_list(Binary, Start, Stop)
As binary_to_list/1, but it only returns the list from
position Start to position Stop. Start and
Stop are integers. Positions in the binary are
numbered starting from 1.
Returns an Erlang term which is the result of decoding the
binary Binary. Binary is encoded in the Erlang
external binary representation. See term_to_binary/1.
cancel_timer(Ref) cancels a timer, where Ref was
returned by either send_after/3 or
start_timer/3. If the timer was there to be removed,
cancel_timer/1 returns the time in ms left until the
timer would have expired, otherwise false (which may
mean that Ref was never a timer, or that it had already been
cancelled, or that it had already delivered its message).
Note: usually, cancelling a timer does not guarantee that the message has not already been delivered to the message queue. However, in the special case of a process P cancelling a timer which would have sent a message to P itself, attempting to read the timeout message from the queue is guaranteed to remove the timeout in that situation:
cancel_timer(Ref),
receive
{timeout, Ref, _} ->
ok
after 0 ->
ok
end
Failure: badarg if Ref is not a reference.
erlang:check_process_code(Pid, Module)
Returns true if the process Pid is executing an
old version of Module, if the current call of the process
executes code for an old version of the module, if the
process has references to an old version of the module,
or if the process contains funs that references the old version
of the module.
Otherwise, it returns false.
> erlang:check_process_code(Pid, lists). false
This is an optional BIF.
Failure: badarg, if the process argument is not a Pid,
or the module argument is not an atom.
Concatenates a list of binaries ListOfBinaries into
one binary.
Returns the current date as {Year, Month, Day}
> date().
{1995, 2, 19}
Moves the current version of the code of Module to
the old version and deletes all export references of
Module. Returns undefined if the module does not
exist, otherwise true.
> delete_module(test). true
This is an optional BIF.
Failure: badarg if there is already an old version of
the module (see BIF purge_module/1).
 |
In normal Erlang implementations code handling - which includes loading, deleting, and replacing modules - is performed in the module |
If Ref is a reference which the current process obtained by
calling erlang:monitor/2, the monitoring is turned off.
It is an error if Ref 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 Ref is a
remote reference).
Forces the disconnection of a node. This will appear to the
node Node as if the current node has crashed. This BIF
is mainly used in the Erlang network authentication
protocols. Returns true if disconnection succeeds,
otherwise false.
Failure: badarg if Node is not an atom.
Returns the Nth element (numbering from 1) of Tuple.
> element(2, {a, b, c}).
b
Failure: badarg if N < 1, or N
> size(Tuple), or if the argument Tuple is
not a tuple. Allowed in guard tests.
Returns the process dictionary and deletes it.
> put(key1, {1, 2, 3}), put(key2, [a, b, c]), erase().
[{key1,{1, 2, 3}},{key2,[a, b, c]}]
Returns the value associated with Key and deletes it
from the process dictionary. Returns undefined if no
value is associated with Key. Key can be any
Erlang term.
> put(key1, {merry, lambs, are, playing}),
X = erase(key1), {X, erase(key1)}.
{{merry, lambs, are, playing}, undefined}
Stops the execution of the current process with the reason
Reason. Can be caught. Reason is any Erlang
term. Since evaluating this function causes the process to
terminate, it has no return value.
> exit(foobar).
** exited: foobar **
> catch exit(foobar).
{'EXIT', foobar}
Sends an EXIT message to the process Pid. Returns
true.
> exit(Pid, goodbye). true
 |
The above is not necessarily the same as: Pid ! {'EXIT', self(), goodbye}
|
The above two alternatives are the
same if the process with the process identity Pid is
trapping exits. However, if Pid is not trapping exits, the
Pid itself will exit and propagate EXIT signals in
turn to its linked processes.
If the reason is the atom kill, for example
exit(Pid, kill), an untrappable EXIT signal will be
sent to the process Pid. In other words, the process
Pid will be unconditionally killed.
Returns true.
Failure: badarg if Pid is not a Pid.
Stops the execution of the current process with the reason
Reason, where Reason is any Erlang term.
The actual EXIT term will be {Reason, Where},
where Where is a list of the functions most recently
called (the current function first).
Since evaluating this function causes the process to
terminate, it has no return value.
Stops the execution of the current process with the reason
Reason, where Reason is any Erlang term.
The actual EXIT term will be {Reason, Where},
where Where is a list of the functions most recently
called (the current function first).
The Args is expected to be the arguments for the current
function; in Beam it will be used to provide the actual arguments
for the current function in the Where term.
Since evaluating this function causes the process to
terminate, it has no return value.
Returns a float by converting Number to a float.
> float(55). 55.0000
|
-module(t). f(F) when float(F) -> float; f(F) -> not_a_float. 1> t:f(1). not_a_float 2> t:f(1.0). float 3> |
Failure: badarg if the argument is not a float or an
integer.
Returns a list containing information about the fun Fun.
In R6, the fun can be real fun type or the tuple representation;
future versions will not allow the fun representation.
This BIF is only intended for debugging.
The list returned contains the following tuples, not necessarily in
the order listed here (i.e. you should not depend on the order).
{id,Pid}Pid is the pid of the process that originally created the fun.
It will be the atom undefined if the fun is given in
the tuple representation.
{module,Module}Module (an atom) is the module in which the fun is defined.
{index,Index}Index (an integer) is an index into the module's fun table.
{index,Uniq}Uniq (an integer) is an unique value for this fun.
{env,Env}Env (a list) is the environment or free variables for the fun.
Returns information about the Fun as specified by
Item, in the form {Item, Info}.
Item can be any of the atoms id, module,
index, uniq, or env.
See the erlang:fun_info/1 BIF.
Returns a textual representation of the fun Fun.
Returns a list of integers (ASCII codes) which corresponds to
Float.
> float_to_list(7.0). "7.00000000000000000000e+00"
Failure: badarg if the argument is not a float.
Returns the process dictionary as a list of {Key, Value}
tuples.
> put(key1, merry), put(key2, lambs),
put(key3, {are, playing}), get().
[{key1, merry}, {key2, lambs}, {key3, {are, playing}}]
Returns the value associated with Key in the process
dictionary, and undefined if no value is
associated with Key. Key can be any Erlang
term.
> put(key1, merry), put(key2, lambs),
put({any, [valid, term]}, {are, playing}),
get({any, [valid, term]}).
{are, playing}
Returns the "magic cookie" of the current node, if the node is
alive; otherwise the atom nocookie.
Returns a list of keys which corresponds to Value in
the process dictionary.
> put(mary, {1, 2}), put(had, {1, 2}), put(a, {1, 2}),
put(little, {1, 2}), put(dog, {1, 3}), put(lamb, {1, 2}),
get_keys({1, 2}).
[mary, had, a, little, lamb]
Every process is a member of some process group and all groups have a leader.
This BIF returns the process identifier Pid of the group
leader for the process which evaluates the BIF. When a process
is spawned, the group leader of the spawned process is the
same as that of the process which spawned it. Initially, at
system start-up, init is both its own group leader and
the group leader of all processes.
Sets the group leader of Pid to
Leader. Typically, this is used when a processes
started from a certain shell should have another group
leader than init. The process Leader is normally
a process with an I/O protocol. All I/O from this group of
processes are thus channeled to the same place.
Halts the Erlang system and indicates normal exit to the calling environment. Has no return value.
> halt(). unix_prompt%
Status must be a non-negative integer, or a string. Halts
the Erlang system. Has no return value. If Status is an
integer, it is returned as an exit status of Erlang to the calling
environment. If Status is a string, produces an Erlang crash
dump with String as slogan, and then exits with a non-zero status
code.
Note that on many platforms, only the status codes 0-255 are supported by the operating system.
Returns a hash value for Term within the range 1..Range.
Returns the first item of List.
> hd([1,2,3,4,5]). 1
Allowed in guard tests.
Failure: badarg if List is the empty list
[], or is not a list.
This BIF is optional and may be removed or changed in
future releases of Erlang. What can be any of the
atoms info, procs, loaded, or dist.
The BIF returns information of the different `topics' as
binary data objects.
Failure: badarg if What is not one of the atoms
shown above.
Returns a list of integers (ASCII codes) which correspond
to Integer.
> integer_to_list(77). "77"
Failure: badarg if the argument is not an integer.
Returns the atom true if the current node is alive;
i.e., if the node can be part of a
distributed system. Otherwise, it returns the atom
false.
Pid must refer to a process on the current node.
Returns the atom true if the process is alive, i.e., has
not exited.
Otherwise, it returns the atom false.
This is the preferred way to check whether a process exists.
Unlike process_info/[1,2], is_process_alive/1
does not report zombie processes as alive.
Returns the length of List.
> length([1,2,3,4,5,6,7,8,9]). 9
Allowed in guard tests.
Failure: badarg if the argument is not a proper list.
Creates a link to the process (or port) Pid, if there
is not such a link already. If a process attempts to create a link
to itself, nothing is done. Returns true.
Failure: badarg if the argument is not a Pid or port.
Sends the EXIT signal noproc to the process which evaluates
link if the argument is the Pid of a process which
does not exist.
Returns an atom whose text representation is the integers
(Latin-1 codes) in CharIntegerList.
> list_to_atom([69, 114, 108, 97, 110, 103]). 'Erlang'
Failure: badarg if the argument is not a list of
integers, or if any integer in the list is not an integer
in the range [0, 255].
list_to_binary(ListOfIntegers)
Returns a binary which is made from the integer list
ListOfIntegers.
Failure: badarg if the argument is not a list of
integers, or if any integer in the list is not an integer
in the range [0, 255].
list_to_float(AsciiIntegerList)
Returns a float whose text representation is the integers
(ASCII-values) in AsciiIntegerList.
> list_to_float([50,46,50,48,49,55,55,54,52,101,43,48]). 2.20178
Failure: badarg if the argument is not a list of
integers, or if AsciiIntegerList contains a bad
representation of a float.
list_to_integer(AsciiIntegerList)
Returns an integer whose text representation is the
integers (ASCII-values) in AsciiIntegerList.
> list_to_integer([49, 50, 51]). 123
Failure: badarg if the argument is not a list of
integers, or if AsciiIntegerList contains a bad
representation of an integer.
Returns a Pid whose text representation is the integers
(ASCII-values) in AsciiIntegerList. This BIF
is intended for debugging, and in the Erlang operating
system. It should not be used in application programs.
> list_to_pid("<0.4.1>").
<0.4.1>
Failure: badarg if the argument is not a list of
integers, or AsciiIntegerList contains a bad
representation of a Pid.
Returns a tuple which corresponds to List. List
can contain any Erlang terms.
> list_to_tuple([mary, had, a, little, {dog, cat, lamb}]).
{mary, had, a, little, {dog, cat, lamb}}
Failure: badarg if List is not a proper list.
erlang:load_module(Module, Binary)
If Binary contains the object code for the module
Module, this BIF loads that object code. Also, if the
code for the module Module already exists, all export
references are replaced so they point to the newly loaded
code. The previously loaded code is kept in the system as
`old code', as there may still be processes which are
executing that code. It returns either {module,
Module}, where Module is the name of the module
which has been loaded, or {error, Reason} if
load fails. Reason is one of the following:
badfileBinary has an incorrect format.
not_purgedBinary contains a module which cannot be
loaded because old code for this module already exists (see
the BIFs purge_module and delete_module).
badfileModule
|
Code handling - which includes
loading, deleting, and replacing of modules - is done by
the module |
This is an optional BIF.
Failure: badarg if the first argument is not an atom,
or the second argument is not a binary.
Returns the current local date and time
{{Year, Month, Day}, {Hour, Minute, Second}}.
The time zone and daylight saving time correction depend on the underlying OS.
> erlang:localtime().
{{1996,11,6},{14,45,17}}
erlang:localtime_to_universaltime(DateTime)
Converts local date and time in DateTime to
Universal Time Coordinated (UTC), if this is supported by
the underlying OS. Otherwise, no conversion is done and
DateTime is returned. The return value is of the form
{{Year, Month, Day}, {Hour, Minute, Second}}.
Failure: badarg if the argument is not a valid date and
time tuple {{Year, Month, Day}, {Hour, Minute, Second}}.
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}).
{{1996,11,6},{13,45,17}}
Returns an almost unique reference.
The returned reference will reoccur after approximately 2^82 calls; therefore it is unique enough for most practical purposes.
> make_ref(). #Ref<0.0.0.135>
Returns the atom true if the module contained in atom
Module is loaded, otherwise it returns the atom
false. It does not attempt to load the module.
|
This BIF is intended for the implementation of the
module named |
> erlang:module_loaded(lists). true
This is an optional BIF.
Failure: badarg if the argument is not an atom.
The current process starts monitoring Item, and will be notified
when Item dies, with a message
{'DOWN', Ref, Type, Item, Info}, where Ref is the value
returned by the call to erlang:monitor/2, and Info gives
additional information.
The message is also sent if Item is already dead.
The value returned can be used
for disabling the monitor (see erlang:demonitor/1).
The currently allowed arguments are the atom process for Type,
and a pid for Item; Info in the message is the exit reason
of the process (or noproc or noconnection,
when the process does not exist or the remote node goes down, respectively,
in analogy with link/1). If an attempt is made to monitor a process
on an older node (where remote process monitoring is not implemented),
the call fails with badarg.
Making several calls to erlang:monitor/2 for the same item is not an
error; it results in several completely independent monitorings.
Monitors the status of the node Node. If Flag
is true, monitoring is turned on; if Flag is
false, monitoring is turned off. Calls to the BIF are
accumulated. This is shown in the following example, where a process
is already monitoring the node Node and a
library function is called:
monitor_node(Node, true),
... some operations
monitor_node(Node, false),
After the call, the process is still monitoring the node.
If Node fails or does not exist, the message
{nodedown, Node} is delivered to the process. If a
process has made two calls to monitor_node(Node, true)
and Node terminates, two nodedown messages are
delivered to the process. If there is no connection to
Node, there will be an attempt to create one. If this
fails, a nodedown message is delivered.
Returns true.
Failure: badarg if Flag is not true or
false,
and badarg if Node is not an atom indicating a
remote node, or if the local node is not alive.
Returns the name of the current node. If it is not a
networked node but a local Erlang system, the atom
nonode@nohost is returned.
Allowed in guard tests.
Returns the node where Arg is located. Arg can
be a Pid, a reference, or a port.
Allowed in guard tests.
Failure: badarg if Arg is not a Pid, reference, or port.
Returns a list of all known nodes in the system, excluding the current node.
Returns the tuple {MegaSecs, Secs, Microsecs}
which is the elapsed time since 00:00 GMT, January 1, 1970
(zero hour) on the assumption that the underlying OS supports this.
Otherwise, some other point in time is chosen. It is also
guaranteed that subsequent calls to this BIF returns
continuously increasing values. Hence, the return value from
now() can be used to generate unique time-stamps. It
can only be used to check the local time of day if the time-zone
info of the underlying operating system is properly
configured.
open_port(PortName, PortSettings)
Returns a port identifier as the result of opening a
new Erlang port. A port can be seen as an external Erlang
process. PortName is one of the following:
{spawn, Command}Command is the name
of the external program which will be run. Command
runs outside the Erlang work space unless an Erlang
driver with the name Command is found. If found,
that driver will be started. A driver runs in the Erlang
workspace, which means that it is linked with the Erlang runtime
system.
vfork is used in preference
to fork for performance reasons, although it has a
history of being less robust. If there are problems with using
vfork, setting the environment variable
ERL_NO_VFORK to any value will cause fork to be
used instead.
Atomfile
module instead.
The atom is assumed to be the name of an
external resource. A transparent connection is
established between Erlang and the resource named by the
atom Atom. The characteristics of the port depend
on the type of resource. If Atom represents a
normal file, the entire contents of the file is sent to
the Erlang process as one or more messages. When
messages are sent to the port, it causes data to be
written to the file.
{fd, In, Out}In can be used for standard input, and the file
descriptor Out for standard output. It is only
used for various servers in the Erlang operating system
(shell and user). Hence, its use is very
limited.
PortSettings is a list of settings for the
port. Valid values are:
{packet, N}N
bytes, with the most significant byte first. Valid
values for N are 1, 2, or 4.
stream{line, N}{Flag, Line}, where Flag is either
eol or noeol and Line is the actual data
delivered (without the newline sequence).N specifies the maximum line length in bytes. Lines
longer than
this will be delivered in more than one message,
with the Flag set to noeol for all but the last
message.
If end of file is encountered anywere else than immediately
following a
newline sequence, the last line will also be delivered with the
Flag set to noeol.
In all other cases, lines are delivered with
Flag set to eol.{packet, N} and {line, N} settings are mutually
exclusive.
{cd, Dir}{spawn, Command}.
The external program starts using Dir as its working directory.
Dir must be a string. Not available on VxWorks.
{env, Environment}{spawn, Command}.
The environment of the started process is extended using the
environment specifications in Environment.
Environment should be a list of tuples {Name,
Value}, where Name is the name of an
environment variable, and Value is the value it is to
have in the spawned port process. Both Name and
Value must be strings. The one exception is Value
being the atom false (in analogy with
os:getenv/1), which removes the environment variable.
Not available on VxWorks.
exit_status{spawn, Command}
where Command refers to an external program.
When the external process connected to the port exits, a
message of the form {Port, {exit_status, Status}} is
sent to the connected process, where Status is the
exit status of the external process. If the program aborts,
on Unix the same convention is used as the shells do (i.e.
128+signal).
If the eof option has been given as well, the eof
message
and the exit_status message appear in an unspecified order.
If the port program closes its stdout without exiting, the
exit_status option will not work.
use_stdio{spawn, Command}. It
allows the standard input and output (file
descriptors 0 and 1) of the spawned (UNIX) process for
communication with Erlang.
nouse_stdiostderr_to_stdoutstderr_to_stdout
and nouse_stdio are mutually exclusive.
inoutbinaryeof{Port, eof} message will be sent to the process
holding the port.
The default is stream for all types of port and
use_stdio for spawned ports.
Failure: badarg if the format of PortName or
PortSettings is incorrect. If the port cannot be
opened, the exit reason is the Posix error code which most
closely describes the error, or einval if no Posix code
is appropriate. The following Posix error codes
may appear:
enomemeagainenametoolongemfileenfile During use of a port opened using {spawn, Name}, errors arising
when sending messages to it are reported to the owning process using
exit signals of the form {'EXIT', Port, PosixCode}. Posix codes
are listed in the documentation for the file module.
Returns a list which corresponds to the process Pid.
|
This BIF is intended for debugging and for use in the Erlang operating system. It should not be used in application programs. |
> pid_to_list(whereis(init)). "<0.0.0>"
Failure: badarg if the argument is not a Pid.
Returns information about the port Port as specified by
Item, which can be any one of the atoms
id, connected,
links, name, input, or output.
{id, Index}Index is the internal index of the port. This
index may be used to separate ports.
{connected, Pid}Pid is the process connected to the port.
{links, ListOfPids}ListOfPids is a list of Pids with processes to
which the port has a link.
{name, String}String is the command name set by open_port.
{input, Bytes}Bytes is the total number of bytes read from
the port.
{output, Bytes}Bytes is the total number of bytes written to
the port.
All implementations may not support all of the above
Items. Returns undefined if the port does not
exist.
Failure: badarg if Port is not a process
identifier, or if Port is a port identifier of a
remote process.
Returns a list of all ports on the current node.
Returns a list of Erlang modules which are pre-loaded in the
system. As all loading of code is done through the file
system, the file system must have been
loaded previously. Hence, at least the module init must be pre-loaded.
erlang:process_display(Pid, Type)
Writes information about the local process Pid on standard
error. The currently allowed value for the atom Type
is backtrace, which shows the contents of the stack,
including information about the call chain, with
the most recent data printed last. The format
of the output is not further defined. Pid may be a zombie
process.
Sets certain flags for the process which calls this function. Returns the old value of the flag.
process_flag(trap_exit, Boolean)trap_exit is set to true, EXIT signals
arriving to a process are converted to {'EXIT', From,
Reason} messages, which can be received as ordinary
messages. If trap_exit is set to false, the
process exits if it receives an EXIT signal other than
normal and the EXIT signal is propagated to its
linked processes. Application processes should normally
not trap exits.
process_flag(error_handler, Module)process_flag(priority, Level)Level is an
atom. All implementations support three priority levels,
low, normal, and high. The default
is normal.
process_flag(save_calls, N)N must be an integer in the interval
[0, 10000].
If N > 0, call saving is made active for the process,
which means that information about the N most recent global
function calls, BIF calls, sends and receives made by the process
are saved in a list, which can be retrieved with
process_info(Pid, last_calls).
A global function call is one in which the module of the function
is explicitly mentioned.
Only a fixed amount of
information is saved: a tuple {Module, Function, Arity}
for function calls, and the mere atoms send,
'receive' and timeout for sends and receives
('receive' when a message is received and timeout
when a receive times out).
If N = 0, call saving is disabled for the process.
Whenever the size of the call saving list is set, its contents
are reset.
Failure: badarg if Flag is not an atom, or is
not a recognized flag value, or if Option is not a
recognized term for Flag.
process_flag(Pid, Flag, Option)
Sets certain flags for the process Pid, in the same
manner as process_flag/2.
Returns the old value of the flag. The allowed values for
Flag are only a subset of those allowed in
process_flag/2, namely: save_calls.
Failure: badarg if Pid is not a process on the
local node, or if
Flag is not an atom, or is
not a recognized flag value, or if Option is not a
recognized term for Flag.
Returns a long list which contains information about the
process Pid. This BIF is only intended for
debugging. It should not be used for any other purpose. The list returned contains the following tuples. The order in which these tuples are returned is not defined, nor are all the tuples mandatory.
{current_function, {Module, Function,
Arguments}}Module,
Function, Arguments is the current function
call of the process.
{dictionary, Dictionary}Dictionary is the dictionary of the process.
{error_handler, Module}Module is the error handler module used by the
process (for undefined function calls, for example).
{group_leader, Groupleader}Groupleader is group leader for the I/O of
the process.
{heap_size, Size}Size is the heap size of the process in heap
words.
{initial_call, {Module, Function,
Arity}}Module, Function,
Arity is the initial function call with which the
process was spawned.
{links, ListOfPids}ListOfPids is a list of Pids, with processes to
which the process has a link.
{message_queue_len,
MessageQueueLen}MessageQueueLen
is the number of messages currently in the message queue of
the process. This is the length of the list
MessageQueue returned as the info item
messages (see below).
{messages, MessageQueue}MessageQueue is a list of the messages to the
process, which have not yet been processed.
{priority, Level}Level is the current priority level for the
process. Only low and normal are always
supported.
{reductions, Number}Number is the number of reductions executed by the
process.
{registered_name, Atom}Atom is the registered name of the process. If the
process has no registered name, this tuple is not present in
the list.
{stack_size, Size}Size is the stack size of the process in stack
words.
{status, Status}Status is the status of the process.
Status is waiting (waiting for a message),
running, runnable (ready to run, but another
process is running), suspended (suspended on a "busy"
port or by the trace/3 BIF), or exiting (if
the process has exited, but remains as a zombie).
{trap_exit, Boolean}Boolean is true if the process is trapping
exits, otherwise it is false.
Failure: badarg if the argument is not a Pid, or
if Pid is a Pid of a remote process.
Returns information about the process Pid as specified by
Item, in the form
{Item, Info}. Item can be any one of the atoms
backtrace,
current_function, dictionary, error_handler,
exit,
group_leader, heap_size, initial_call,
last_calls,
links, memory, message_queue_len,
messages, priority, reductions,
registered_name, stack_size, status
or trap_exit.
Returns undefined if no information is
known about the process.
process_info can be used to
obtain information about processes which have exited but whose
data are still kept, so called zombie processes. To determine
whether to keep information about dead processes, use the BIF
erlang:system_flag/2. Since process_info does not
necessarily return undefined for a dead process, use
is_process_alive/1 to check whether a process is alive.
Item exit returns [] if the process is alive,
or {exit, Reason} if the process has exited, where Reason
is the exit reason.
Item registered_name returns [] if
the process has no registered name. If the process is a zombie,
the registered name it had when it died is returned.
Item memory returns {memory, Size}, where Size
is the size of the process in bytes. This includes stack, heap and
internal structures.
Item backtrace returns a binary, which contains the
same information as the output from
erlang:process_display(Pid, backtrace). Use
binary_to_list/1 to obtain the string of characters from the
binary.
Item last_calls returns 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.
Not all implementations support every one of the above
Items.
Failure: badarg if Pid is not a process
identifier, or if Pid is a process identifier of a
remote process.
Returns a list of all processes on the current node, including zombie processes. See system_flag/2.
> processes(). [<0.0.1>, <0.1.1>, <0.2.1>, <0.3.1>, <0.4.1>, <0.6.1>]
Removes old code for
Module. Before this BIF is used, erlang:check_process_code/2 should be
called to check that no processes
are executing old code in this module.
|
In normal Erlang implementations, code handling - which is
loading, deleting and replacing modules - is evaluated
by the module |
This is an optional BIF.
Failure: badarg if Module does not exist.
Adds a new Value to the process dictionary and
associates it with Key. If a value is already
associated with Key, that value is deleted and replaced
by the new value Value. It returns any value
previously associated with Key, or undefined if
no value was associated with Key. Key and
Value can be any valid Erlang terms.
|
The values stored when |
> X = put(name, walrus), Y = put(name, carpenter),
Z = get(name),
{X, Y, Z}.
{undefined, walrus, carpenter}
Associates the name Name with the process identity
Pid.
Name, which must be an atom, can be used instead of a pid
in the send operator (Name ! Message).
Returns true.
Failure: badarg if Pid is not an active
process, or if Pid is a process on another node,
or if the name Name is already in use,
or if the process is already registered (it already has a name),
or if the name Name is not an atom, or if Name
is the atom undefined.
Returns a list of names which have been registered using
register/2.
> registered(). [code_server, file_server, init, user, my_db]
Resume a suspended process. This should be used for debugging purposes only, not in production code.
Returns an integer by rounding the number Number.
Allowed in guard tests.
> round(5.5). 6
Failure: badarg if the argument is not a float (or an
integer).
Returns the process identity of the calling process. Allowed in guard tests.
> self(). <0.16.1>
erlang:send_after(Time, Pid, Msg)
Time is a non-negative integer, Pid is
either a pid or an atom, and Msg is any Erlang term.
The function returns a reference.
After Time ms, send_after/3 sends Msg
to Pid.
If Pid is an atom, it is supposed to be the
name of a registered process. The process referred to by the
name is looked up at the time of delivery. No error is given
if the name does not refer to a process. See also
start_timer/3 and cancel_timer/1.
Limitations: Pid must be a process on the
local node. The timeout value must fit in 32 bits.
Failure: badarg if any arguments are of the
wrong type, or do not obey the limitations noted above.
erlang:set_cookie(Node, Cookie)
Sets the "magic cookie" of Node to the atom Cookie.
If Node is the current node, the BIF also sets the
cookie of all other unknown nodes to Cookie (see
auth(3)).
setelement(Index, Tuple, Value)
Returns a tuple which is a copy of the argument Tuple
with the element given by the integer argument Index
(the first element is the element with index 1)
replaced by the argument Value.
> setelement(2, {10, green, bottles}, red).
{10, red, bottles}
Failure: badarg if Index is not an integer, or
Tuple is not a tuple, or if Index is less than 1
or greater than the size of Tuple.
Returns an integer which is the size of the argument
Item, where Item must be either a tuple or a
binary.
> size({morni, mulle, bwange}).
3
Allowed in guard tests.
Failure: badarg if Item is not a tuple or a
binary.
Returns the Pid of a new process started by the application
of Fun to the empty argument list []. Otherwise
works like spawn/3.
Returns the Pid of a new process started by the application
of Fun to the empty argument list [] on node
Node.
Otherwise works like spawn/4.
spawn(Module, Function, ArgumentList)
Returns the Pid of a new process started by the application
of Module:Function to ArgumentList. Note:
The new process created will be placed in the system
scheduler queue and will be run some time later.
error_handler:undefined_function(Module, Function,
ArgumentList) is evaluated by the new process if
Module:Function/Arity does not exist (where Arity
is the length of ArgumentList).
The error handler can be redefined (see BIF
process_flag/2)). Arity is the length of the
ArgumentList. If error_handler is undefined,
or the user has redefined the default error_handler
so its replacement is undefined, a failure with the reason
undef will occur.
> spawn(speed, regulator, [high_speed, thin_cut]). <0.13.1>
Failure: badarg if Module and/or Function
is not an atom, or if ArgumentList is not a list.
spawn(Node, Module, Function, ArgumentList)
Works like spawn/3, with the exception that
the process is spawned at Node. If Node does not
exist, a useless Pid is returned.
Failure: badarg if Node, Module, or
Function are not atoms, or ArgumentList is not a list.
Works like spawn/1 except that a link is made from the
current process to the newly created one, atomically.
Works like spawn/2 except that a link is made from the
current process to the newly created one, atomically.
spawn_link(Module, Function, ArgumentList)
This BIF is identical to the following code being evaluated in an atomic operation:
> Pid = spawn(Module, Function, ArgumentList), link(Pid), Pid.
This BIF is necessary since the process created might run
immediately and fail before link/1 is called.
Failure: See spawn/3.
spawn_link(Node, Module, Function, ArgumentList)
Works like spawn_link/3, except that the
process is spawned at Node. If an attempt is made to
spawn a process on a node which does not exist, a useless
Pid is returned, and an EXIT signal will be received.
spawn_opt(Module, Function, ArgumentList, Options)
Works exactly like spawn/3, except that the following options can be given when creating the process:
link
spawn_link/3 does).
{priority, Level}
process_flag(priority, Level) in the start function
of the new process, except that the priority will be set before the
process is scheduled in the first time.
{gc_switch, Threshold}
Threshold is 0, generational garbage collection will be
used (this is default). If Threshold is greater than zero,
the fullsweep algorithm will be until the amount of live data (counted
in words) reaches Threshold, at which point generational collection
will be used. A large Threshold or the atom infinity means
the fullsweep algorithm will be used.{min_heap_size, Size}
Size values.
Returns a tuple which contains two binaries which are the
result of splitting Binary into two parts at
position Pos. This is not a destructive
operation. After this operation, there are three
binaries altogether. Returns a tuple consisting of the two new
binaries. For example:
1> B = list_to_binary("0123456789").
#Bin
2> size(B).
10
3> {B1, B2} = split_binary(B,3).
{#Bin, #Bin}
4> size(B1).
3
5> size(B2).
7
Failure: badarg if Binary is not a binary, or
Pos is not an integer or is out of range.
erlang:start_timer(Time, Pid, Msg)
Time is a non-negative integer, Pid is
either a pid or an atom, and Msg is any Erlang term.
The function returns a reference.
After Time ms, start_timer/3 sends the
tuple {timeout, Ref, Msg} to Pid, where
Ref is the reference returned by
start_timer/3.
If Pid is an atom, it is supposed to be the
name of a registered process. The process referred to by the
name is looked up at the time of delivery. No error is given
if the name does not refer to a process. See also
send_after/3 and cancel_timer/1.
Limitations: Pid must be a process on the
local node. The timeout value must fit in 32 bits.
Failure: badarg if any arguments are of the
wrong type, or do not obey the limitations noted above.
Returns information about the system. Type is an atom
which is one of:
run_queueruntime{Total_Run_Time, Time_Since_Last_Call}.
wall_clock{Total_Wallclock_Time,
Wallclock_Time_Since_Last_Call}. wall_clock
can be used in the same manner as the atom
runtime, except that real time is measured as
opposed to runtime or CPU time.
reductions{Total_Reductions, Reductions_Since_Last_Call}.
garbage_collection{Number_of_GCs, Words_Reclaimed, 0}. This
information may not be valid for all implementations.
All times are in milliseconds.
> statistics(runtime).
{1690, 1620}
> statistics(reductions).
{2046, 11}
> statistics(garbage_collection).
{85, 23961, 0}
Failure: badarg if Type is not one of the atoms
shown above.
Suspend a process. This should be used for debugging purposes only, not in production code.
erlang:system_flag(Flag, Value)
This BIF sets various system properties of the Erlang node.
If Flag is a valid name of a system flag, its value is
set to Value, and the old value is returned.
The currently allowed value for Flag is
keep_zombies. The value of the keep_zombies flag
is an integer which indicates how many processes to keep in
memory when they exit, so that they can be inspected with
process_info. Originally, the number is 0.
Setting it to 0 disables the keeping of zombies.
A negative number -N means to keep the N
latest zombies; a positive value N means to keep the
N first zombies. Setting the flag always clears away
any already saved zombies.
The maximum number of zombies which can be saved is 100.
Resources owned by a zombie process are cleared away immediately
when the process dies, for example ets tables and ports, and
cannot be inspected.
This BIF returns the encoded value of any Erlang term and turns it into the Erlang external term format. It can be used for a variety of purposes, for example writing a term to a file in an efficient way, or sending an Erlang term to some type of communications channel not supported by distributed Erlang.
Returns a binary data object which corresponds
to an external representation of the Erlang term Term.
A non-local return from a function. If evaluated within a
catch, catch will return the value Any.
> catch throw({hello, there}).
{hello, there}
Failure: nocatch if not evaluated within a catch.
Returns the tuple {Hour, Minute, Second} of the
current system time. The time zone correction is
implementation-dependent.
> time().
{9, 42, 44}
Returns List stripped of its first element.
> tl([geesties, guilies, beasties]). [guilies, beasties]
Failure: badarg if List is the empty list
[], or is not a list. Allowed in guard tests.
erlang:trace(PidSpec, How, Flaglist)
Turns on (if How == true) or off (if How == false)
the trace flags in Flaglist for the process or processes
represented by PidSpec.
PidSpec is either a pid for a local process,
or one of the following atoms:
existingnewallFlaglist can contain any number of the following
atoms (the "message tags" refers to the list of message following
below):
sendPid sends. Message tags: send, send_to_non_existing_process.
'receive'Pid receives. Message tags: 'receive'.
procsspawn,
link, exit. Message tags: spawn, exit,
link, unlink, getting_linked.
callcall, return.
old_call_tracecall,
return.
runningin, out.
garbage_collectiongc_start, gc_end.
timestamperlang:now().
arity{Mod, Fun, Args} in call traces,
there will be {Mod, Fun, Arity}.
set_on_spawnPid
inherit the flags of Pid, including the set_on_spawn
flag.
set_on_first_spawnPid
inherit the flags of Pid That process does not
inherit the set_on_first_spawn flag.
set_on_linkPid inherit
the flags of Pid, including the set_on_link flag.
set_on_first_linkPid inherit the flags of Pid. That process does not
inherit the set_on_first_link flag.
{tracer, Tracer}Tracer should be the pid for a local process or the port identifier
for a local port.
All trace messages will be sent to the given process or port.
If this flag is not given, trace messages will be sent to the process
that called erlang:trace/3.
The effect of combining set_on_first_link with
set_on_link is the same as having set_on_first_link
alone. Likewise for set_on_spawn and set_on_first_spawn.
If the timestamp flag is not given, the tracing process
will receive the trace messages described below.
If the timestamp flag is given, the first element of the
tuple will be trace_ts and the timestamp will be in the last
element of the tuple.
{trace, Pid, 'receive', Message}Pid receives something.
{trace, Pid, send, Msg, To}Pid sends a message.
{trace, Pid, send_to_non_existing_process, Msg, To [,Ts]}Pid sends a message to a non existing process.
{trace, Pid, call, {M,F,A}}{trace, Pid, return_to, {M,F,A}}{M,F,A}. This
trace message is only sent when both the old_call_trace and
timestamp flags have been given.
{trace, Pid, return_from, {M,F,A}, ReturnValue}{M,F,A}
This trace message is sent when the call flag has been specified,
and the function has a match specification with a return_trace
action.
{trace, Pid, spawn, Pid2}Pid2.
{trace, Pid, exit, Reason}Reason.
{trace, Pid, link, Pid2}Pid2.
{trace, Pid, unlink, Pid2}Pid2.
{trace, Pid, getting_linked, Pid2}Pid2.
{trace, Pid, in, {M,F,A}}{trace, Pid, out, {M,F,A}}{trace, Pid, gc_start, Info}Info is a list of two-element tuples, where the first element
is a key, and the second is the value.
You should not depend on the tuples have any defined order
Currently, the following keys are defined.
heap_sizeold_heap_sizestack_sizerecent_sizembuf_size{trace, Pid, gc_end, Info}Info contains the same kind of list as in the gc_start
message, but the sizes reflect the new sizes after garbage collection.
If the tracing process dies, the flags will be silently removed.
Only one process can trace a particular process. For this reason, attempts to trace an already traced process will fail.
Returns: A number indicating the number of processes that matched
PidSpec. If PidSped is a pid, the return value will be
1. If PidSpec is all or existing the return
value will be the number of processes running, excluding tracer
processes. If PidSpec is new, the return value will
be 0.
Failure: badarg if bad arguments are given.
erlang:trace_info(PidOrFunc, Item)
Returns trace information about a process or exported function.
To get information about a process, PidOrFunc should be
a pid or the atom new.
The atom new means that the default trace state for
processes to be created will be returned.
Item must have one of the following values:
flagssend, 'receive', set_on_spawn,
call, old_call_trace, procs,
set_on_first_spawn, set_on_link,
running, garbage_collection,
timestamp, and arity.
The order is arbitrary.
tracer
[].
To get information about an exported function, PidOrFunc should
be three-element tuple: {Module, Function, Arity}. No wildcards
are allowed.
Item must have one of the following values:
tracedtrue if this function is traced
or false otherwise.
match_spec The return value will be {Item, Value}, where Value is
the requested information as described above.
If a pid for a dead process was given, or the name of a non-existing
function, the return value will be undefined.
erlang:trace_pattern(MFA, MatchSpec)
This BIF is used to enable or disable call tracing for exported functions.
It must be combined with erlang:trace/3
to set the call trace flag for one or more processes.
Conceptually, call tracing works like this. Inside the Erlang virtual machine there is a set of processes to be traced and a set of functions to be traced. Tracing will be enabled on the intersection of the set. That is, if a process included in the traced process set calls a function included in the traced function set, the trace action will be taken. Otherwise, nothing will happen.
Use erlang:trace/3 to add or remove
one or more processes to the set of traced processes.
Use erlang:trace_pattern/2 to add or remove exported functions
to the set of traced functions.
The erlang:trace_pattern/2 BIF can also add match specifications
to an exported function. A match spefication comprises a pattern
that the arguments to the function must match, a guard expression which
must evaluate to true and action to be performed. The default
action is to send a trace message. If the pattern doesn't match or
the guard fails, the action will not be executed.
The MFA argument should be a tuple like {Module, Function, Arity}.
It can be the module, function, and arity for an exported function
(or a BIF in any module).
The '_' atom can be used to mean any of that kind.
Wildcards can be used in any of the following ways:
{Mod,Func,'_'}Func
in module Mod.{Mod,'_','_'}Mod.{'_','_','_'} Other combinations, such as {Mod,'_',Arity}, are not allowed.
Local functions will not match any wildcard.
The MatchSpec argument can any of the following forms:
falsetrueMatchSpecListtrue. See the ERTS User's Guide for a description of
match specifications.
There is no way to directly change part of a match specification list. If a function has a match specification, you can replace it with a completely new one. If you need to change an existing match specification, use the erlang:trace_info/2 BIF to retrieve the existing match specification.
Returns the number of exported functions that matched the MFA argument.
This will be zero if none matched at all.
Failure: badarg for invalid MFA or MatchSpec.
Returns an integer by the truncation of Number.
Allowed in guard tests.
> trunc(5.5). 5
Failure: badarg if the argument is not a float, or an integer.
Returns a list which corresponds to
Tuple. Tuple may contain any valid Erlang terms.
> tuple_to_list({share, {'Ericsson_B', 163}}).
[share, {'Ericsson_B', 163}]
Failure: badarg if the argument is not a tuple.
Returns the current date and time according to Universal
Time Coordinated (UTC), also called GMT, in the form
{{Year, Month, Day}, {Hour, Minute, Second}} if supported
by the underlying operating system. If not, erlang:universaltime()
is equivalent to erlang:localtime().
> erlang:universaltime().
{{1996,11,6},{14,18,43}}
erlang:universaltime_to_localtime(DateTime)
Converts UTC date and time in DateTime to
local date and time if supported by the underlying operating system.
Otherwise, no conversion is done, and
DateTime is returned. The return value is of the form
{{Year, Month, Day}, {Hour, Minute, Second}}.
Failure: badarg if the argument is not a valid date and
time tuple {{Year, Month, Day}, {Hour, Minute, Second}}.
> erlang:universaltime_to_localtime({{1996,11,6},{14,18,43}}).
{{1996,11,7},{15,18,43}}
Removes a link, if there is one, from the calling process
to another process given by the argument Pid.
Returns true. Will not fail if not linked to
Pid, or if Pid does not exist.
Failure: badarg if the argument is not a valid Pid.
Removes the registered name for a process, given by the atom argument Name.
Returns the atom true.
> unregister(db). true
Failure: badarg if Name is not the name of a
registered process.
Users are advised not to unregister system processes.
Returns the Pid for the process registered under Name (see
register/2). Returns undefined if no such process
is registered.
> whereis(user). <0.3.1>
Failure: badarg if the argument is not an atom.