Provided by: erlang-manpages_16.b.3-dfsg-1ubuntu2.2_all 
NAME
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 or
{shutdown,Term}. shutdown 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, 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(7) 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.
DATA TYPES
spawn_option() = link
| monitor
| {priority, priority_level()}
| {min_heap_size, integer() >= 0}
| {min_bin_vheap_size, integer() >= 0}
| {fullsweep_after, integer() >= 0}
See erlang:spawn_opt/2,3,4,5.
priority_level() = high | low | max | normal
dict_or_pid() = pid()
| (ProcInfo :: [term()])
| {X :: integer(),
Y :: integer(),
Z :: integer()}
EXPORTS
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 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 = function()
Module = 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, 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 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 = 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 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(Ret) -> ok
init_ack(Parent, Ret) -> ok
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()]
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 the process Pid which sent the crash report.
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
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.
Note:
The list Args no longer contains the actual arguments, but the same number of atoms as the number
of arguments; the first atom is always 'Argument__1', the second 'Argument__2', and so on. The
reason is that the argument list could waste a significant amount of memory, and if the argument
list contained funs, it could be impossible to upgrade the code for the module.
If the process was spawned using a fun, initial_call/1 no longer returns the actual fun, but the
module, function for the local function implementing the fun, and the arity, for instance
{some_module,-work/3-fun-0-,0} (meaning that the fun was created in the function
some_module:work/3). The reason is that keeping the fun would prevent code upgrade for the module,
and that a significant amount of memory could be wasted.
translate_initial_call(Process) -> {Module, Function, Arity}
Types:
Process = dict_or_pid()
Module = module()
Function = atom()
Arity = byte()
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) -> no_return()
Types:
Module = 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(3erl)