proc_lib(3)

MODULE
proc_lib - 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 (gen_server, gen_fsm, ...) when starting new processes. The functions can also be used to start special processes, user defined processes which comply to the OTP design principles. See Sys and Proc_Lib in OTP Design Principles for an example.

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 the exit reason normal, a process started using proc_lib is also said to terminate normally if it exits with reason shutdown. This is the reason used when an application (supervision tree) is stopped.

When a process started using proc_lib terminates abnormally -- that is, with another exit reason than normal or shutdown -- 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 SASL User's Guide.

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

EXPORTS

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

    Types
        Node = node()
        Fun = fun() -> void()
        Module = Function = atom()
        Args = [term()]

    Spawns a new process and initializes it as described above. 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 = fun() -> void()
        Module = Function = atom()
        Args = [term()]

    Spawns a new process and initializes it as described above. The process is spawned using the spawn_link BIFs.

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

    Types
        Node = node()
        Fun = fun() -> void()
        Module = Function = atom()
        Args = [term()]
        SpawnOpts -- see erlang:spawn_opt/2, 3, 4, 5

    Spawns a new process and initializes it as described above. The process is spawned using the spawn_opt BIFs.

  Note:

Using the spawn option monitor is currently not allowed, but will cause the function to fail with reason badarg.

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

    Types
        Module = Function = atom()
        Args = [term()]
        Time = int() >= 0 | infinity
        SpawnOpts -- see erlang:spawn_opt/2, 3, 4, 5
        Ret = term() | {error, Reason}

    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 the start_link/3, 4, 5 function 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.

    The SpawnOpts argument, if given, will be passed as the last argument to the spawn_opt/2, 3, 4, 5 BIF.

  Note:

Using the spawn option monitor is currently not allowed, but will cause the function to fail with reason badarg.

init_ack(Parent, Ret) -> void()
init_ack(Ret) -> void()

    Types
        Parent = pid()
        Ret = term()

    This function must 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.

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

    If this function is not called, the start function will return an error tuple (if a link and/or a timeout 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().
    ...

format(CrashReport) -> string()

    Types
        CrashReport = term()

    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 the process Pid which sent the crash report.

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

    Types
        Process = pid() | {X, Y, Z} | ProcInfo
        X = Y = Z = int()
        ProcInfo = term()
        Module = Function = atom()
        Args = [term()]
        Fun = fun() -> void()

    Extracts the initial call of a process that was started using one of the spawn or start functions described above. 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.

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

    Types
        Process = pid() | {X, Y, Z} | ProcInfo
        X = Y = Z = int()
        ProcInfo = term()
        Module = Function = atom()
        Arity = int()
        Fun = fun() -> void()

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

    Extracts the initial call of a process that was started using one of the spawn or start functions described above, 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. In order to return information that this process is a supervisor and the name of the call-back module, Module is supervisor and Function is the name of the supervisor callback module. Arity is 1 since 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.

hibernate(Module, Function, Args)

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

    This function does the same as (and does call) the BIF hibernate/3, 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.

SEE ALSO

error_logger(3)

AUTHORS
Gunilla Arendt - support@erlang.ericsson.se
Magnus Froberg - support@erlang.ericsson.se