1gen_event(3) Erlang Module Definition gen_event(3)
2
6 gen_event - Generic event handling behavior.
7
9 This behavior module provides event handling functionality. It consists
10 of a generic event manager process with any number of event handlers
11 that are added and deleted dynamically.
12 An event manager implemented using this module has a standard set of
14 interface functions and includes functionality for tracing and error
15 reporting. It also fits into an OTP supervision tree. For more informa‐
16 tion, see OTP Design Principles.
17 Each event handler is implemented as a callback module exporting a pre‐
19 defined set of functions. The relationship between the behavior func‐
20 tions and the callback functions is as follows:
21 gen_event module Callback module
23 ---------------- ---------------
24 gen_event:start
25 gen_event:start_link -----> -
26 gen_event:add_handler
28 gen_event:add_sup_handler -----> Module:init/1
29 gen_event:notify
31 gen_event:sync_notify -----> Module:handle_event/2
32 gen_event:call -----> Module:handle_call/2
34 - -----> Module:handle_info/2
36 gen_event:delete_handler -----> Module:terminate/2
38 gen_event:swap_handler
40 gen_event:swap_sup_handler -----> Module1:terminate/2
41 Module2:init/1
42 gen_event:which_handlers -----> -
44 gen_event:stop -----> Module:terminate/2
46 - -----> Module:code_change/3
48 As each event handler is one callback module, an event manager has many
50 callback modules that are added and deleted dynamically. gen_event is
51 therefore more tolerant of callback module errors than the other behav‐
52 iors. If a callback function for an installed event handler fails with
53 Reason, or returns a bad value Term, the event manager does not fail.
54 It deletes the event handler by calling callback function Module:termi‐
55 nate/2, giving as argument {error,{'EXIT',Reason}} or {error,Term},
56 respectively. No other event handler is affected.
57 A gen_event process handles system messages as described in sys(3). The
59 sys module can be used for debugging an event manager.
60 Notice that an event manager does trap exit signals automatically.
62 The gen_event process can go into hibernation (see erlang:hibernate/3)
64 if a callback function in a handler module specifies hibernate in its
65 return value. This can be useful if the server is expected to be idle
66 for a long time. However, use this feature with care, as hibernation
67 implies at least two garbage collections (when hibernating and shortly
68 after waking up) and is not something you want to do between each event
69 handled by a busy event manager.
70 Notice that when multiple event handlers are invoked, it is sufficient
72 that one single event handler returns a hibernate request for the whole
73 event manager to go into hibernation.
74 Unless otherwise stated, all functions in this module fail if the spec‐
76 ified event manager does not exist or if bad arguments are specified.
77
79 handler() = atom() | {atom(), term()}
80 handler_args() = term()
82 add_handler_ret() = ok | term() | {'EXIT', term()}
84 del_handler_ret() = ok | term() | {'EXIT', term()}
86
88 add_handler(EventMgrRef, Handler, Args) -> Result
89 Types:
91 EventMgrRef = Name | {Name,Node} | {global,GlobalName} |
93 {via,Module,ViaName} | pid()
94 Name = Node = atom()
95 GlobalName = ViaName = term()
96 Handler = Module | {Module,Id}
97 Module = atom()
98 Id = term()
99 Args = term()
100 Result = ok | {'EXIT',Reason} | term()
101 Reason = term()
102 Adds a new event handler to event manager EventMgrRef. The event
104 manager calls Module:init/1 to initiate the event handler and
105 its internal state.
106 EventMgrRef can be any of the following:
108 * The pid
110 * Name, if the event manager is locally registered
112 * {Name,Node}, if the event manager is locally registered at
114 another node
115 * {global,GlobalName}, if the event manager is globally regis‐
117 tered
118 * {via,Module,ViaName}, if the event manager is registered
120 through an alternative process registry
121 Handler is the name of the callback module Module or a tuple
123 {Module,Id}, where Id is any term. The {Module,Id} representa‐
124 tion makes it possible to identify a specific event handler when
125 many event handlers use the same callback module.
126 Args is any term that is passed as the argument to Mod‐
128 ule:init/1.
129 If Module:init/1 returns a correct value indicating successful
131 completion, the event manager adds the event handler and this
132 function returns ok. If Module:init/1 fails with Reason or
133 returns {error,Reason}, the event handler is ignored and this
134 function returns {'EXIT',Reason} or {error,Reason}, respec‐
135 tively.
136 add_sup_handler(EventMgrRef, Handler, Args) -> Result
138 Types:
140 EventMgrRef = Name | {Name,Node} | {global,GlobalName} |
142 {via,Module,ViaName} | pid()
143 Name = Node = atom()
144 GlobalName = ViaName = term()
145 Handler = Module | {Module,Id}
146 Module = atom()
147 Id = term()
148 Args = term()
149 Result = ok | {'EXIT',Reason} | term()
150 Reason = term()
151 Adds a new event handler in the same way as add_handler/3, but
153 also supervises the connection between the event handler and the
154 calling process.
155 * If the calling process later terminates with Reason, the
157 event manager deletes the event handler by calling Mod‐
158 ule:terminate/2 with {stop,Reason} as argument.
159 * If the event handler is deleted later, the event manager
161 sends a message{gen_event_EXIT,Handler,Reason} to the call‐
162 ing process. Reason is one of the following:
163 * normal, if the event handler has been removed because of a
165 call to delete_handler/3, or remove_handler has been
166 returned by a callback function (see below).
167 * shutdown, if the event handler has been removed because
169 the event manager is terminating.
170 * {swapped,NewHandler,Pid}, if the process Pid has replaced
172 the event handler with another event handler NewHandler
173 using a call to swap_handler/3 or swap_sup_handler/3.
174 * A term, if the event handler is removed because of an
176 error. Which term depends on the error.
177 For a description of the arguments and return values, see
179 add_handler/3.
180 call(EventMgrRef, Handler, Request) -> Result
182 call(EventMgrRef, Handler, Request, Timeout) -> Result
183 Types:
185 EventMgrRef = Name | {Name,Node} | {global,GlobalName} |
187 {via,Module,ViaName} | pid()
188 Name = Node = atom()
189 GlobalName = ViaName = term()
190 Handler = Module | {Module,Id}
191 Module = atom()
192 Id = term()
193 Request = term()
194 Timeout = int()>0 | infinity
195 Result = Reply | {error,Error}
196 Reply = term()
197 Error = bad_module | {'EXIT',Reason} | term()
198 Reason = term()
199 Makes a synchronous call to event handler Handler installed in
201 event manager EventMgrRef by sending a request and waiting until
202 a reply arrives or a time-out occurs. The event manager calls
203 Module:handle_call/2 to handle the request.
204 For a description of EventMgrRef and Handler, see add_handler/3.
206 Request is any term that is passed as one of the arguments to
208 Module:handle_call/2.
209 Timeout is an integer greater than zero that specifies how many
211 milliseconds to wait for a reply, or the atom infinity to wait
212 indefinitely. Defaults to 5000. If no reply is received within
213 the specified time, the function call fails.
214 The return value Reply is defined in the return value of Mod‐
216 ule:handle_call/2. If the specified event handler is not
217 installed, the function returns {error,bad_module}. If the call‐
218 back function fails with Reason or returns an unexpected value
219 Term, this function returns {error,{'EXIT',Reason}} or
220 {error,Term}, respectively.
221 delete_handler(EventMgrRef, Handler, Args) -> Result
223 Types:
225 EventMgrRef = Name | {Name,Node} | {global,GlobalName} |
227 {via,Module,ViaName} | pid()
228 Name = Node = atom()
229 GlobalName = ViaName = term()
230 Handler = Module | {Module,Id}
231 Module = atom()
232 Id = term()
233 Args = term()
234 Result = term() | {error,module_not_found} | {'EXIT',Reason}
235 Reason = term()
236 Deletes an event handler from event manager EventMgrRef. The
238 event manager calls Module:terminate/2 to terminate the event
239 handler.
240 For a description of EventMgrRef and Handler, see add_handler/3.
242 Args is any term that is passed as one of the arguments to Mod‐
244 ule:terminate/2.
245 The return value is the return value of Module:terminate/2. If
247 the specified event handler is not installed, the function
248 returns {error,module_not_found}. If the callback function fails
249 with Reason, the function returns {'EXIT',Reason}.
250 notify(EventMgrRef, Event) -> ok
252 sync_notify(EventMgrRef, Event) -> ok
253 Types:
255 EventMgrRef = Name | {Name,Node} | {global,GlobalName} |
257 {via,Module,ViaName} | pid()
258 Name = Node = atom()
259 GlobalName = ViaName = term()
260 Event = term()
261 Sends an event notification to event manager EventMgrRef. The
263 event manager calls Module:handle_event/2 for each installed
264 event handler to handle the event.
265 notify/2 is asynchronous and returns immediately after the event
267 notification has been sent. sync_notify/2 is synchronous in the
268 sense that it returns ok after the event has been handled by all
269 event handlers.
270 For a description of EventMgrRef, see add_handler/3.
272 Event is any term that is passed as one of the arguments to Mod‐
274 ule:handle_event/2.
275 notify/1 does not fail even if the specified event manager does
277 not exist, unless it is specified as Name.
278 start() -> Result
280 start(EventMgrName | Options) -> Result
281 start(EventMgrName, Options) -> Result
282 Types:
284 EventMgrName = {local,Name} | {global,GlobalName} | {via,Mod‐
286 ule,ViaName}
287 Name = atom()
288 GlobalName = ViaName = term()
289 Options = [Option]
290 Option = {debug,Dbgs} | {timeout,Time} | {hiber‐
291 nate_after,HibernateAfterTimeout} | {spawn_opt,SOpts}
292 Dbgs = [Dbg]
293 Dbg = trace | log | statistics | {log_to_file,FileName} |
294 {install,{Func,FuncState}}
295 SOpts = [term()]
296 Result = {ok,Pid} | {error,{already_started,Pid}}
297 Pid = pid()
298 Creates a stand-alone event manager process, that is, an event
300 manager that is not part of a supervision tree and thus has no
301 supervisor.
302 For a description of the arguments and return values, see
304 start_link/0,1.
305 start_link() -> Result
307 start_link(EventMgrName | Options) -> Result
308 start_link(EventMgrName, Options) -> Result
309 Types:
311 EventMgrName = {local,Name} | {global,GlobalName} | {via,Mod‐
313 ule,ViaName}
314 Name = atom()
315 GlobalName = ViaName = term()
316 Options = [Option]
317 Option = {debug,Dbgs} | {timeout,Time} | {hiber‐
318 nate_after,HibernateAfterTimeout} | {spawn_opt,SOpts}
319 Dbgs = [Dbg]
320 Dbg = trace | log | statistics | {log_to_file,FileName} |
321 {install,{Func,FuncState}}
322 SOpts = [term()]
323 Result = {ok,Pid} | {error,{already_started,Pid}}
324 Pid = pid()
325 Creates an event manager process as part of a supervision tree.
327 The function is to be called, directly or indirectly, by the
328 supervisor. For example, it ensures that the event manager is
329 linked to the supervisor.
330 * If EventMgrName={local,Name}, the event manager is regis‐
332 tered locally as Name using register/2.
333 * If EventMgrName={global,GlobalName}, the event manager is
335 registered globally as GlobalName using global:regis‐
336 ter_name/2. If no name is provided, the event manager is not
337 registered.
338 * If EventMgrName={via,Module,ViaName}, the event manager reg‐
340 isters with the registry represented by Module. The Module
341 callback is to export the functions register_name/2, unreg‐
342 ister_name/1, whereis_name/1, and send/2, which are to
343 behave as the corresponding functions in global. Thus,
344 {via,global,GlobalName} is a valid reference.
345 * If option {hibernate_after,HibernateAfterTimeout} is
347 present, the gen_event process awaits any message for Hiber‐
348 nateAfterTimeout milliseconds and if no message is received,
349 the process goes into hibernation automatically (by calling
350 proc_lib:hibernate/3).
351 If the event manager is successfully created, the function
353 returns {ok,Pid}, where Pid is the pid of the event manager. If
354 a process with the specified EventMgrName exists already, the
355 function returns {error,{already_started,Pid}}, where Pid is the
356 pid of that process.
357 stop(EventMgrRef) -> ok
359 stop(EventMgrRef, Reason, Timeout) -> ok
360 Types:
362 EventMgrRef = Name | {Name,Node} | {global,GlobalName} |
364 {via,Module,ViaName} | pid()
365 Name = Node = atom()
366 GlobalName = ViaName = term()
367 Reason = term()
368 Timeout = int()>0 | infinity
369 Orders event manager EventMgrRef to exit with the specifies Rea‐
371 son and waits for it to terminate. Before terminating, gen_event
372 calls Module:terminate(stop,...) for each installed event han‐
373 dler.
374 The function returns ok if the event manager terminates with the
376 expected reason. Any other reason than normal, shutdown, or
377 {shutdown,Term} causes an error report to be issued using
378 error_logger:format/2. The default Reason is normal.
379 Timeout is an integer greater than zero that specifies how many
381 milliseconds to wait for the event manager to terminate, or the
382 atom infinity to wait indefinitely. Defaults to infinity. If the
383 event manager has not terminated within the specified time, a
384 timeout exception is raised.
385 If the process does not exist, a noproc exception is raised.
387 For a description of EventMgrRef, see add_handler/3.
389 swap_handler(EventMgrRef, {Handler1,Args1}, {Handler2,Args2}) -> Result
391 Types:
393 EventMgrRef = Name | {Name,Node} | {global,GlobalName} |
395 {via,Module,ViaName} | pid()
396 Name = Node = atom()
397 GlobalName = ViaName = term()
398 Handler1 = Handler2 = Module | {Module,Id}
399 Module = atom()
400 Id = term()
401 Args1 = Args2 = term()
402 Result = ok | {error,Error}
403 Error = {'EXIT',Reason} | term()
404 Reason = term()
405 Replaces an old event handler with a new event handler in event
407 manager EventMgrRef.
408 For a description of the arguments, see add_handler/3.
410 First the old event handler Handler1 is deleted. The event man‐
412 ager calls Module1:terminate(Args1, ...), where Module1 is the
413 callback module of Handler1, and collects the return value.
414 Then the new event handler Handler2 is added and initiated by
416 calling Module2:init({Args2,Term}), where Module2 is the call‐
417 back module of Handler2 and Term is the return value of Mod‐
418 ule1:terminate/2. This makes it possible to transfer information
419 from Handler1 to Handler2.
420 The new handler is added even if the the specified old event
422 handler is not installed, in which case Term=error, or if Mod‐
423 ule1:terminate/2 fails with Reason, in which case
424 Term={'EXIT',Reason}. The old handler is deleted even if Mod‐
425 ule2:init/1 fails.
426 If there was a supervised connection between Handler1 and a
428 process Pid, there is a supervised connection between Handler2
429 and Pid instead.
430 If Module2:init/1 returns a correct value, this function returns
432 ok. If Module2:init/1 fails with Reason or returns an unexpected
433 value Term, this function returns {error,{'EXIT',Reason}} or
434 {error,Term}, respectively.
435 swap_sup_handler(EventMgrRef, {Handler1,Args1}, {Handler2,Args2}) ->
437 Result
438 Types:
440 EventMgrRef = Name | {Name,Node} | {global,GlobalName} |
442 {via,Module,ViaName} | pid()
443 Name = Node = atom()
444 GlobalName = ViaName = term()
445 Handler1 = Handler 2 = Module | {Module,Id}
446 Module = atom()
447 Id = term()
448 Args1 = Args2 = term()
449 Result = ok | {error,Error}
450 Error = {'EXIT',Reason} | term()
451 Reason = term()
452 Replaces an event handler in event manager EventMgrRef in the
454 same way as swap_handler/3, but also supervises the connection
455 between Handler2 and the calling process.
456 For a description of the arguments and return values, see
458 swap_handler/3.
459 which_handlers(EventMgrRef) -> [Handler]
461 Types:
463 EventMgrRef = Name | {Name,Node} | {global,GlobalName} |
465 {via,Module,ViaName} | pid()
466 Name = Node = atom()
467 GlobalName = ViaName = term()
468 Handler = Module | {Module,Id}
469 Module = atom()
470 Id = term()
471 Returns a list of all event handlers installed in event manager
473 EventMgrRef.
474 For a description of EventMgrRef and Handler, see add_handler/3.
476
478 The following functions are to be exported from a gen_event callback
479 module.
480
482 Module:code_change(OldVsn, State, Extra) -> {ok, NewState}
483 Types:
485 OldVsn = Vsn | {down, Vsn}
487 Vsn = term()
488 State = NewState = term()
489 Extra = term()
490 Note:
492 This callback is optional, so callback modules need not export
493 it. If a release upgrade/downgrade with Change={advanced,Extra}
494 specified in the .appup file is made when code_change/3 isn't
495 implemented the event handler will crash with an undef error
496 reason.
497 This function is called for an installed event handler that is
500 to update its internal state during a release upgrade/downgrade,
501 that is, when the instruction {update,Module,Change,...}, where
502 Change={advanced,Extra}, is specified in the .appup file. For
503 more information, see OTP Design Principles.
504 For an upgrade, OldVsn is Vsn, and for a downgrade, OldVsn is
506 {down,Vsn}. Vsn is defined by the vsn attribute(s) of the old
507 version of the callback module Module. If no such attribute is
508 defined, the version is the checksum of the Beam file.
509 State is the internal state of the event handler.
511 Extra is passed "as is" from the {advanced,Extra} part of the
513 update instruction.
514 The function is to return the updated internal state.
516 Module:format_status(Opt, [PDict, State]) -> Status
518 Types:
520 Opt = normal | terminate
522 PDict = [{Key, Value}]
523 State = term()
524 Status = term()
525 Note:
527 This callback is optional, so event handler modules need not
528 export it. If a handler does not export this function, the
529 gen_event module uses the handler state directly for the pur‐
530 poses described below.
531 This function is called by a gen_event process in the following
534 situations:
535 * One of sys:get_status/1,2 is invoked to get the gen_event
537 status. Opt is set to the atom normal for this case.
538 * The event handler terminates abnormally and gen_event logs
540 an error. Opt is set to the atom terminate for this case.
541 This function is useful for changing the form and appearance of
543 the event handler state for these cases. An event handler call‐
544 back module wishing to change the the sys:get_status/1,2 return
545 value as well as how its state appears in termination error
546 logs, exports an instance of format_status/2 that returns a term
547 describing the current state of the event handler.
548 PDict is the current value of the process dictionary of
550 gen_event.
551 State is the internal state of the event handler.
553 The function is to return Status, a term that change the details
555 of the current state of the event handler. Any term is allowed
556 for Status. The gen_event module uses Status as follows:
557 * When sys:get_status/1,2 is called, gen_event ensures that
559 its return value contains Status in place of the state term
560 of the event handler.
561 * When an event handler terminates abnormally, gen_event logs
563 Status in place of the state term of the event handler.
564 One use for this function is to return compact alternative state
566 representations to avoid that large state terms are printed in
567 log files.
568 Module:handle_call(Request, State) -> Result
570 Types:
572 Request = term()
574 State = term()
575 Result = {ok,Reply,NewState} | {ok,Reply,NewState,hibernate}
576 | {swap_handler,Reply,Args1,NewState,Handler2,Args2}
577 | {remove_handler, Reply}
578 Reply = term()
579 NewState = term()
580 Args1 = Args2 = term()
581 Handler2 = Module2 | {Module2,Id}
582 Module2 = atom()
583 Id = term()
584 Whenever an event manager receives a request sent using
586 call/3,4, this function is called for the specified event han‐
587 dler to handle the request.
588 Request is the Request argument of call/3,4.
590 State is the internal state of the event handler.
592 The return values are the same as for Module:handle_event/2
594 except that they also contain a term Reply, which is the reply
595 to the client as the return value of call/3,4.
596 Module:handle_event(Event, State) -> Result
598 Types:
600 Event = term()
602 State = term()
603 Result = {ok,NewState} | {ok,NewState,hibernate}
604 | {swap_handler,Args1,NewState,Handler2,Args2} | remove_han‐
605 dler
606 NewState = term()
607 Args1 = Args2 = term()
608 Handler2 = Module2 | {Module2,Id}
609 Module2 = atom()
610 Id = term()
611 Whenever an event manager receives an event sent using notify/2
613 or sync_notify/2, this function is called for each installed
614 event handler to handle the event.
615 Event is the Event argument of notify/2/sync_notify/2.
617 State is the internal state of the event handler.
619 * If {ok,NewState} or {ok,NewState,hibernate} is returned, the
621 event handler remains in the event manager with the possible
622 updated internal state NewState.
623 * If {ok,NewState,hibernate} is returned, the event manager
625 also goes into hibernation (by calling proc_lib:hiber‐
626 nate/3), waiting for the next event to occur. It is suffi‐
627 cient that one of the event handlers return {ok,New‐
628 State,hibernate} for the whole event manager process to
629 hibernate.
630 * If {swap_handler,Args1,NewState,Handler2,Args2} is returned,
632 the event handler is replaced by Handler2 by first calling
633 Module:terminate(Args1,NewState) and then Mod‐
634 ule2:init({Args2,Term}), where Term is the return value of
635 Module:terminate/2. For more information, see swap_han‐
636 dler/3.
637 * If remove_handler is returned, the event handler is deleted
639 by calling Module:terminate(remove_handler,State).
640 Module:handle_info(Info, State) -> Result
642 Types:
644 Info = term()
646 State = term()
647 Result = {ok,NewState} | {ok,NewState,hibernate}
648 | {swap_handler,Args1,NewState,Handler2,Args2} | remove_han‐
649 dler
650 NewState = term()
651 Args1 = Args2 = term()
652 Handler2 = Module2 | {Module2,Id}
653 Module2 = atom()
654 Id = term()
655 Note:
657 This callback is optional, so callback modules need not export
658 it. The gen_event module provides a default implementation of
659 this function that logs about the unexpected Info message, drops
660 it and returns {noreply, State}.
661 This function is called for each installed event handler when an
664 event manager receives any other message than an event or a syn‐
665 chronous request (or a system message).
666 Info is the received message.
668 For a description of State and possible return values, see Mod‐
670 ule:handle_event/2.
671 Module:init(InitArgs) -> {ok,State} | {ok,State,hibernate} |
673 {error,Reason}
674 Types:
676 InitArgs = Args | {Args,Term}
678 Args = Term = term()
679 State = term()
680 Reason = term()
681 Whenever a new event handler is added to an event manager, this
683 function is called to initialize the event handler.
684 If the event handler is added because of a call to add_handler/3
686 or add_sup_handler/3, InitArgs is the Args argument of these
687 functions.
688 If the event handler replaces another event handler because of a
690 call to swap_handler/3 or swap_sup_handler/3, or because of a
691 swap return tuple from one of the other callback functions, Ini‐
692 tArgs is a tuple {Args,Term}, where Args is the argument pro‐
693 vided in the function call/return tuple and Term is the result
694 of terminating the old event handler, see swap_handler/3.
695 If successful, the function returns {ok,State} or
697 {ok,State,hibernate}, where State is the initial internal state
698 of the event handler.
699 If {ok,State,hibernate} is returned, the event manager goes into
701 hibernation (by calling proc_lib:hibernate/3), waiting for the
702 next event to occur.
703 Module:terminate(Arg, State) -> term()
705 Types:
707 Arg = Args | {stop,Reason} | stop | remove_handler
709 | {error,{'EXIT',Reason}} | {error,Term}
710 Args = Reason = Term = term()
711 Note:
713 This callback is optional, so callback modules need not export
714 it. The gen_event module provides a default implementation with‐
715 out cleanup.
716 Whenever an event handler is deleted from an event manager, this
719 function is called. It is to be the opposite of Module:init/1
720 and do any necessary cleaning up.
721 If the event handler is deleted because of a call to delete_han‐
723 dler/3, swap_handler/3, or swap_sup_handler/3, Arg is the Args
724 argument of this function call.
725 Arg={stop,Reason} if the event handler has a supervised connec‐
727 tion to a process that has terminated with reason Reason.
728 Arg=stop if the event handler is deleted because the event man‐
730 ager is terminating.
731 The event manager terminates if it is part of a supervision tree
733 and it is ordered by its supervisor to terminate. Even if it is
734 not part of a supervision tree, it terminates if it receives an
735 'EXIT' message from its parent.
736 Arg=remove_handler if the event handler is deleted because
738 another callback function has returned remove_handler or
739 {remove_handler,Reply}.
740 Arg={error,Term} if the event handler is deleted because a call‐
742 back function returned an unexpected value Term, or
743 Arg={error,{'EXIT',Reason}} if a callback function failed.
744 State is the internal state of the event handler.
746 The function can return any term. If the event handler is
748 deleted because of a call to gen_event:delete_handler/3, the
749 return value of that function becomes the return value of this
750 function. If the event handler is to be replaced with another
751 event handler because of a swap, the return value is passed to
752 the init function of the new event handler. Otherwise the return
753 value is ignored.
754
756 supervisor(3), sys(3)
757Ericsson AB stdlib 3.4.5.1 gen_event(3)