Elixir v1.2.6 Process

Conveniences for working with processes and the process dictionary.

Besides the functions available in this module, the Kernel module exposes and auto-imports some basic functionality related to processes available through the functions:

Summary

Functions

Returns true if the process exists and is alive (i.e. it is not exiting and has not exited yet). Otherwise, returns false

Cancels a timer created by send_after/3

Deletes the given key from the dictionary

If monitor_ref is a reference which the calling process obtained by calling monitor/1, this monitoring is turned off. If the monitoring is already turned off, nothing happens

Sends an exit signal with the given reason to the pid

Sets certain flags for the process which calls this function. Returns the old value of the flag

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

Returns all key-values in the dictionary

Returns the value for the given key

Returns all keys in the process dictionary

Returns all keys that have the given value

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

Sets the group leader of pid to leader. Typically, this is used when a processes started from a certain shell should have a group leader other than :init

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

Returns information about the process identified by pid or nil if the process is not alive. Use this only for debugging information

Returns information about the process identified by pid or nil if the process is not alive

Creates a link between the calling process and another process (or port) pid, if there is not such a link already

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

The calling process starts monitoring the item given. It returns the monitor reference

Stores the given key-value in the process dictionary

Reads a timer created by send_after/3

Associates the name with a pid or a port identifier. name, which must be an atom, can be used instead of the pid / port identifier with the Kernel.send/2 function

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

Sends a message to the given process

Sends msg to dest after time milliseconds

Spawns the given module and function passing the given args according to the given options

Spawns the given module and function passing the given args according to the given options

Removes the link, if there is one, between the calling process and the process or port referred to by pid. Returns true and does not fail, even if there is no link or id does not exist

Removes the registered name, associated with a pid or a port identifier

Returns the pid or port identifier with the registered name. Returns nil if the name is not registered

Types

spawn_opt()
spawn_opt ::
  :link |
  :monitor |
  {:priority, :low | :normal | :high} |
  {:fullsweep_after, non_neg_integer} |
  {:min_heap_size, non_neg_integer} |
  {:min_bin_vheap_size, non_neg_integer}
spawn_opts()

Functions

alive?(pid)
alive?(pid) :: boolean

Returns true if the process exists and is alive (i.e. it is not exiting and has not exited yet). Otherwise, returns false.

pid must refer to a process at the local node.

Inlined by the compiler.

cancel_timer(timer_ref)
cancel_timer(reference) :: non_neg_integer | false

Cancels a timer created by send_after/3.

When the result is an integer, it represents the time in milli-seconds left until the timer will expire.

When the result is false, a timer corresponding to timer_ref could not be found. This can be either because the timer expired, already has been canceled, or because timer_ref never corresponded to a timer.

If the timer has expired, the timeout message has been sent, but it does not tell you whether or not it has arrived at its destination yet.

Inlined by the compiler.

delete(key)
delete(term) :: term | nil

Deletes the given key from the dictionary.

demonitor(monitor_ref, options \\ [])
demonitor(reference, options :: [:flush | :info]) :: boolean

If monitor_ref is a reference which the calling process obtained by calling monitor/1, this monitoring is turned off. If the monitoring is already turned off, nothing happens.

See :erlang.demonitor/2 for more info.

Inlined by the compiler.

exit(pid, reason)
exit(pid, term) :: true

Sends an exit signal with the given reason to the pid.

The following behaviour applies if reason is any term except :normal or :kill:

  1. If pid is not trapping exits, pid will exit with the given reason.

  2. If pid is trapping exits, the exit signal is transformed into a message {:EXIT, from, reason} and delivered to the message queue of pid.

  3. If reason is the atom :normal, pid will not exit (unless it is the calling process’s pid, in which case it will exit with the reason :normal). If it is trapping exits, the exit signal is transformed into a message {:EXIT, from, :normal} and delivered to its message queue.

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

Inlined by the compiler.

Examples

Process.exit(pid, :kill)
flag(flag, value)
flag(process_flag, term) :: term

Sets certain flags for the process which calls this function. Returns the old value of the flag.

See :erlang.process_flag/2 for more info.

flag(pid, flag, value)
flag(pid, :save_calls, non_neg_integer) :: non_neg_integer

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

See :erlang.process_flag/3 for more info.

get()
get :: [{term, term}]

Returns all key-values in the dictionary.

Inlined by the compiler.

get(key, default \\ nil)
get(term, default :: term) :: term

Returns the value for the given key.

get_keys()
get_keys :: [term]

Returns all keys in the process dictionary.

Inlined by the compiler.

get_keys(value)
get_keys(term) :: [term]

Returns all keys that have the given value.

Inlined by the compiler.

group_leader()
group_leader :: pid

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

group_leader(pid, leader)
group_leader(pid, leader :: pid) :: true

Sets the group leader of pid to leader. Typically, this is used when a processes started from a certain shell should have a group leader other than :init.

hibernate(mod, fun, args)
hibernate(module, atom, list) :: no_return

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

See :erlang.hibernate/3 for more info.

Inlined by the compiler.

info(pid)
info(pid) :: Keyword.t

Returns information about the process identified by pid or nil if the process is not alive. Use this only for debugging information.

See :erlang.process_info/1 for more info.

info(pid, spec)
info(pid, atom | [atom]) ::
  {atom, term} |
  [{atom, term}] |
  nil

Returns information about the process identified by pid or nil if the process is not alive.

See :erlang.process_info/2 for more info.

link(pid)
link(pid | port) :: true

Creates a link between the calling process and another process (or port) pid, if there is not such a link already.

See :erlang.link/1 for more info.

Inlined by the compiler.

list()
list :: [pid]

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

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

See :erlang.processes/0 for more info.

monitor(item)
monitor(pid | {reg_name :: atom, node :: atom} | reg_name :: atom) :: reference

The calling process starts monitoring the item given. It returns the monitor reference.

See the need for monitoring for an example. See :erlang.monitor/2 for more info.

Inlined by the compiler.

put(key, value)
put(term, term) :: term | nil

Stores the given key-value in the process dictionary.

The return value is the value that was previously stored under the key key (or nil in case no value was stored under key).

read_timer(timer_ref)
read_timer(reference) :: non_neg_integer | false

Reads a timer created by send_after/3.

When the result is an integer, it represents the time in milli-seconds left until the timer will expire.

When the result is false, a timer corresponding to timer_ref could not be found. This can be either because the timer expired, already has been canceled, or because timer_ref never corresponded to a timer.

If the timer has expired, the timeout message has been sent, but it does not tell you whether or not it has arrived at its destination yet.

Inlined by the compiler.

register(pid, name)
register(pid | port, atom) :: true

Associates the name with a pid or a port identifier. name, which must be an atom, can be used instead of the pid / port identifier with the Kernel.send/2 function.

Process.register/2 will fail with ArgumentError if the pid supplied is no longer alive, (check with alive?/1 or if the name is already registered (check with whereis/1.

registered()
registered :: [atom]

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

send(dest, msg, options)
send(dest, msg, [option]) ::
  :ok |
  :noconnect |
  :nosuspend when dest: pid | port | atom | {atom, node}, msg: any, option: :noconnect | :nosuspend

Sends a message to the given process.

If the option :noconnect is used and sending the message would require an auto-connection to another node the message is not sent and :noconnect is returned.

If the option :nosuspend is used and sending the message would cause the sender to be suspended the message is not sent and :nosuspend is returned.

Otherwise the message is sent and :ok is returned.

Examples

iex> Process.send({:name, :node_does_not_exist}, :hi, [:noconnect])
:noconnect
send_after(dest, msg, time)
send_after(pid | atom, term, non_neg_integer) :: reference

Sends msg to dest after time milliseconds.

If dest is a pid, it must be the pid of a local process, dead or alive. If dest is an atom, it must be the name of a registered process which is looked up at the time of delivery. No error is given if the name does not refer to a process.

This function returns a timer reference, which can be read or canceled with read_timer/1 and cancel_timer/1.

Finally, the timer will be automatically canceled if the given dest is a pid which is not alive or when the given pid exits. Note that timers will not be automatically canceled when dest is an atom (as the atom resolution is done on delivery).

spawn(fun, opts)
spawn((() -> any), spawn_opts) :: pid | {pid, reference}

Spawns the given module and function passing the given args according to the given options.

The result depends on the given options. In particular, if :monitor is given as an option, it will return a tuple containing the pid and the monitoring reference, otherwise just the spawned process pid.

It also accepts extra options, for the list of available options check :erlang.spawn_opt/4.

Inlined by the compiler.

spawn(mod, fun, args, opts)
spawn(module, atom, list, spawn_opts) ::
  pid |
  {pid, reference}

Spawns the given module and function passing the given args according to the given options.

The result depends on the given options. In particular, if :monitor is given as an option, it will return a tuple containing the pid and the monitoring reference, otherwise just the spawned process pid.

It also accepts extra options, for the list of available options check :erlang.spawn_opt/4.

Inlined by the compiler.

unlink(pid)
unlink(pid | port) :: true

Removes the link, if there is one, between the calling process and the process or port referred to by pid. Returns true and does not fail, even if there is no link or id does not exist

See :erlang.unlink/1 for more info.

Inlined by the compiler.

unregister(name)
unregister(atom) :: true

Removes the registered name, associated with a pid or a port identifier.

See :erlang.unregister/1 for more info.

whereis(name)
whereis(atom) :: pid | port | nil

Returns the pid or port identifier with the registered name. Returns nil if the name is not registered.

See :erlang.whereis/1 for more info.