proc_lib

Module

proc_lib

Module summary

Functions for asynchronous and synchronous start of processes adhering to the OTP design principles.

Description

This module is used to start processes adhering to the OTP Design Principles. Specifically, the functions in this module are used by the OTP standard behaviors (for example, gen_server, gen_fsm, and gen_statem) when starting new processes. The functions can also be used to start special processes, user-defined processes that comply to the OTP design principles. For an example, see section sys and proc_lib in OTP Design Principles.

Some useful information is initialized when a process starts. The registered names, or the process identifiers, of the parent process, and the parent ancestors, are stored together with information about the function initially called in the process.

While in "plain Erlang", a process is said to terminate normally only for exit reason normal, a process started using proc_lib is also said to terminate normally if it exits with reason shutdown or {shutdown,Term}. shutdown is the reason used when an application (supervision tree) is stopped.

When a process that is started using proc_lib terminates abnormally (that is, with another exit reason than normal, shutdown, or {shutdown,Term}), a crash report is generated, which is written to terminal by the default SASL event handler. That is, the crash report is normally only visible if the SASL application is started; see sasl(6) and section SASL Error Logging in the SASL User's Guide.

The crash report contains the previously stored information, such as ancestors and initial function, the termination reason, and information about other processes that terminate as a result of this process terminating.

Data types

spawn_option() =
    link |     monitor |     {priority, priority_level()} |     {max_heap_size, max_heap_size()} |     {min_heap_size, integer() >= 0} |     {min_bin_vheap_size, integer() >= 0} |     {fullsweep_after, integer() >= 0} |     {message_queue_data, off_heap | on_heap | mixed}

See erlang:spawn_opt/2,3,4,5.

priority_level() = high | low | max | normal

max_heap_size() =
    integer() >= 0 |     #{size => integer() >= 0,       kill => true,       error_logger => true}

See erlang:process_flag(max_heap_size, MaxHeapSize).

dict_or_pid() =
    pid() |     (ProcInfo :: [term()]) |     {X :: integer(), Y :: integer(), Z :: integer()}

Exports

format(CrashReport) -> string()

Types:

CrashReport = [term()]

Equivalent to format(CrashReport, latin1).

format(CrashReport, Encoding) -> string()

Types:

CrashReport = [term()]
Encoding = latin1 | unicode | utf8

This function can be used by a user-defined event handler to format a crash report. The crash report is sent using error_logger:error_report(crash_report,CrashReport). That is, the event to be handled is of the format {error_report, GL, {Pid, crash_report, CrashReport}}, where GL is the group leader pid of process Pid that sent the crash report.

format(CrashReport, Encoding, Depth) -> string()

Types:

CrashReport = [term()]
Encoding = latin1 | unicode | utf8
Depth = unlimited | integer() >= 1

This function can be used by a user-defined event handler to format a crash report. When Depth is specified as a positive integer, it is used in the format string to limit the output as follows: io_lib:format("~P", [Term,Depth]).

hibernate(Module, Function, Args) -> no_return()

Types:

Module = module()
Function = atom()
Args = [term()]

This function does the same as (and does call) the hibernate/3 BIF, but ensures that exception handling and logging continues to work as expected when the process wakes up.

Always use this function instead of the BIF for processes started using proc_lib functions.

init_ack(Ret) -> okinit_ack(Parent, Ret) -> ok

Types:

Parent = pid()
Ret = term()

This function must be used by a process that has been started by a start[_link]/3,4,5 function. It tells Parent that the process has initialized itself, has started, or has failed to initialize itself.

Function init_ack/1 uses the parent value previously stored by the start function used.

If this function is not called, the start function returns an error tuple (if a link and/or a time-out is used) or hang otherwise.

The following example illustrates how this function and proc_lib:start_link/3 are used:

-module(my_proc).
-export([start_link/0]).
-export([init/1]).

start_link() ->
    proc_lib:start_link(my_proc, init, [self()]).

init(Parent) ->
    case do_initialization() of
        ok ->
            proc_lib:init_ack(Parent, {ok, self()});
        {error, Reason} ->
            exit(Reason)
    end,
    loop().

...

initial_call(Process) -> {Module, Function, Args} | false

Types:

Process = dict_or_pid()
Module = module()
Function = atom()
Args = [atom()]

Extracts the initial call of a process that was started using one of the spawn or start functions in this module. Process can either be a pid, an integer tuple (from which a pid can be created), or the process information of a process Pid fetched through an erlang:process_info(Pid) function call.

spawn(Fun) -> pid()spawn(Node, Fun) -> pid()spawn(Module, Function, Args) -> pid()spawn(Node, Module, Function, Args) -> pid()

Types:

Node = node()
Fun = function()
Module = module()
Function = atom()
Args = [term()]

Spawns a new process and initializes it as described in the beginning of this manual page. The process is spawned using the spawn BIFs.

spawn_link(Fun) -> pid()spawn_link(Node, Fun) -> pid()spawn_link(Module, Function, Args) -> pid()spawn_link(Node, Module, Function, Args) -> pid()

Types:

Node = node()
Fun = function()
Module = module()
Function = atom()
Args = [term()]

Spawns a new process and initializes it as described in the beginning of this manual page. The process is spawned using the spawn_link BIFs.

spawn_opt(Fun, SpawnOpts) -> pid()spawn_opt(Node, Function, SpawnOpts) -> pid()spawn_opt(Module, Function, Args, SpawnOpts) -> pid()spawn_opt(Node, Module, Function, Args, SpawnOpts) -> pid()

Types:

Node = node()
Fun = function()
Module = module()
Function = atom()
Args = [term()]
SpawnOpts = [spawn_option()]

Spawns a new process and initializes it as described in the beginning of this manual page. The process is spawned using the spawn_opt BIFs.

start(Module, Function, Args) -> Retstart(Module, Function, Args, Time) -> Retstart(Module, Function, Args, Time, SpawnOpts) -> Retstart_link(Module, Function, Args) -> Retstart_link(Module, Function, Args, Time) -> Retstart_link(Module, Function, Args, Time, SpawnOpts) -> Ret

Types:

Module = module()
Function = atom()
Args = [term()]
Time = timeout()
SpawnOpts = [spawn_option()]
Ret = term() | {error, Reason :: term()}

Starts a new process synchronously. Spawns the process and waits for it to start. When the process has started, it must call init_ack(Parent, Ret) or init_ack(Ret), where Parent is the process that evaluates this function. At this time, Ret is returned.

If function start_link/3,4,5 is used and the process crashes before it has called init_ack/1,2, {error, Reason} is returned if the calling process traps exits.

If Time is specified as an integer, this function waits for Time milliseconds for the new process to call init_ack, or {error, timeout} is returned, and the process is killed.

Argument SpawnOpts, if specified, is passed as the last argument to the spawn_opt/2,3,4,5 BIF.

stop(Process) -> ok

Types:

Process = pid() | RegName | {RegName, node()}

Equivalent to stop(Process, normal, infinity).

stop(Process, Reason, Timeout) -> ok

Types:

Process = pid() | RegName | {RegName, node()}
Reason = term()
Timeout = timeout()

Orders the process to exit with the specified Reason and waits for it to terminate.

Returns ok if the process exits with the specified Reason within Timeout milliseconds.

If the call times out, a timeout exception is raised.

If the process does not exist, a noproc exception is raised.

The implementation of this function is based on the terminate system message, and requires that the process handles system messages correctly. For information about system messages, see sys(3) and section sys and proc_lib in OTP Design Principles.

translate_initial_call(Process) -> {Module, Function, Arity}

Types:

Process = dict_or_pid()
Module = module()
Function = atom()
Arity = byte()

This function is used by functions c:i/0 and c:regs/0 to present process information.

This function extracts the initial call of a process that was started using one of the spawn or start functions in this module, and translates it to more useful information. Process can either be a pid, an integer tuple (from which a pid can be created), or the process information of a process Pid fetched through an erlang:process_info(Pid) function call.

If the initial call is to one of the system-defined behaviors such as gen_server or gen_event, it is translated to more useful information. If a gen_server is spawned, the returned Module is the name of the callback module and Function is init (the function that initiates the new server).

A supervisor and a supervisor_bridge are also gen_server processes. To return information that this process is a supervisor and the name of the callback module, Module is supervisor and Function is the name of the supervisor callback module. Arity is 1, as the init/1 function is called initially in the callback module.

By default, {proc_lib,init_p,5} is returned if no information about the initial call can be found. It is assumed that the caller knows that the process has been spawned with the proc_lib module.

See Also

error_logger(3)