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Revision 1.320 by root, Fri Oct 22 10:48:54 2010 UTC vs.
Revision 1.360 by root, Mon Jan 17 12:11:12 2011 UTC

…		…
43		43
44	int	44	int
45	main (void)	45	main (void)
46	{	46	{
47	// use the default event loop unless you have special needs	47	// use the default event loop unless you have special needs
48	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = EV_DEFAULT;
49		49
50	// initialise an io watcher, then start it	50	// initialise an io watcher, then start it
51	// this one will watch for stdin to become readable	51	// this one will watch for stdin to become readable
52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
53	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
…		…
77	on event-based programming, nor will it introduce event-based programming	77	on event-based programming, nor will it introduce event-based programming
78	with libev.	78	with libev.
79		79
80	Familiarity with event based programming techniques in general is assumed	80	Familiarity with event based programming techniques in general is assumed
81	throughout this document.	81	throughout this document.
		82
		83	=head1 WHAT TO READ WHEN IN A HURRY
		84
		85	This manual tries to be very detailed, but unfortunately, this also makes
		86	it very long. If you just want to know the basics of libev, I suggest
		87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
		88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
		89	C<ev_timer> sections in L<WATCHER TYPES>.
82		90
83	=head1 ABOUT LIBEV	91	=head1 ABOUT LIBEV
84		92
85	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
86	file descriptor being readable or a timeout occurring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
…		…
165		173
166	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
167		175
168	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
169	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
170	you actually want to know. Also interetsing is the combination of	178	you actually want to know. Also interesting is the combination of
171	C<ev_update_now> and C<ev_now>.	179	C<ev_update_now> and C<ev_now>.
172		180
173	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
174		182
175	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked until
…		…
233	the current system, you would need to look at C<ev_embeddable_backends ()	241	the current system, you would need to look at C<ev_embeddable_backends ()
234	& ev_supported_backends ()>, likewise for recommended ones.	242	& ev_supported_backends ()>, likewise for recommended ones.
235		243
236	See the description of C<ev_embed> watchers for more info.	244	See the description of C<ev_embed> watchers for more info.
237		245
238	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
239		247
240	Sets the allocation function to use (the prototype is similar - the	248	Sets the allocation function to use (the prototype is similar - the
241	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	249	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
242	used to allocate and free memory (no surprises here). If it returns zero	250	used to allocate and free memory (no surprises here). If it returns zero
243	when memory needs to be allocated (C<size != 0>), the library might abort	251	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
269	}	277	}
270		278
271	...	279	...
272	ev_set_allocator (persistent_realloc);	280	ev_set_allocator (persistent_realloc);
273		281
274	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	282	=item ev_set_syserr_cb (void (*cb)(const char *msg))
275		283
276	Set the callback function to call on a retryable system call error (such	284	Set the callback function to call on a retryable system call error (such
277	as failed select, poll, epoll_wait). The message is a printable string	285	as failed select, poll, epoll_wait). The message is a printable string
278	indicating the system call or subsystem causing the problem. If this	286	indicating the system call or subsystem causing the problem. If this
279	callback is set, then libev will expect it to remedy the situation, no	287	callback is set, then libev will expect it to remedy the situation, no
…		…
291	}	299	}
292		300
293	...	301	...
294	ev_set_syserr_cb (fatal_error);	302	ev_set_syserr_cb (fatal_error);
295		303
		304	=item ev_feed_signal (int signum)
		305
		306	This function can be used to "simulate" a signal receive. It is completely
		307	safe to call this function at any time, from any context, including signal
		308	handlers or random threads.
		309
		310	Its main use is to customise signal handling in your process, especially
		311	in the presence of threads. For example, you could block signals
		312	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		313	creating any loops), and in one thread, use C<sigwait> or any other
		314	mechanism to wait for signals, then "deliver" them to libev by calling
		315	C<ev_feed_signal>.
		316
296	=back	317	=back
297		318
298	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	319	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
299		320
300	An event loop is described by a C<struct ev_loop *> (the C<struct> is	321	An event loop is described by a C<struct ev_loop *> (the C<struct> is
301	I<not> optional in this case unless libev 3 compatibility is disabled, as	322	I<not> optional in this case unless libev 3 compatibility is disabled, as
302	libev 3 had an C<ev_loop> function colliding with the struct name).	323	libev 3 had an C<ev_loop> function colliding with the struct name).
303		324
304	The library knows two types of such loops, the I<default> loop, which	325	The library knows two types of such loops, the I<default> loop, which
305	supports signals and child events, and dynamically created event loops	326	supports child process events, and dynamically created event loops which
306	which do not.	327	do not.
307		328
308	=over 4	329	=over 4
309		330
310	=item struct ev_loop *ev_default_loop (unsigned int flags)	331	=item struct ev_loop *ev_default_loop (unsigned int flags)
311		332
312	This will initialise the default event loop if it hasn't been initialised	333	This returns the "default" event loop object, which is what you should
313	yet and return it. If the default loop could not be initialised, returns	334	normally use when you just need "the event loop". Event loop objects and
314	false. If it already was initialised it simply returns it (and ignores the	335	the C<flags> parameter are described in more detail in the entry for
315	flags. If that is troubling you, check C<ev_backend ()> afterwards).	336	C<ev_loop_new>.
		337
		338	If the default loop is already initialised then this function simply
		339	returns it (and ignores the flags. If that is troubling you, check
		340	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		341	flags, which should almost always be C<0>, unless the caller is also the
		342	one calling C<ev_run> or otherwise qualifies as "the main program".
316		343
317	If you don't know what event loop to use, use the one returned from this	344	If you don't know what event loop to use, use the one returned from this
318	function.	345	function (or via the C<EV_DEFAULT> macro).
319		346
320	Note that this function is I<not> thread-safe, so if you want to use it	347	Note that this function is I<not> thread-safe, so if you want to use it
321	from multiple threads, you have to lock (note also that this is unlikely,	348	from multiple threads, you have to employ some kind of mutex (note also
322	as loops cannot be shared easily between threads anyway).	349	that this case is unlikely, as loops cannot be shared easily between
		350	threads anyway).
323		351
324	The default loop is the only loop that can handle C<ev_signal> and	352	The default loop is the only loop that can handle C<ev_child> watchers,
325	C<ev_child> watchers, and to do this, it always registers a handler	353	and to do this, it always registers a handler for C<SIGCHLD>. If this is
326	for C<SIGCHLD>. If this is a problem for your application you can either	354	a problem for your application you can either create a dynamic loop with
327	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	355	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
328	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	356	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
329	C<ev_default_init>.	357
		358	Example: This is the most typical usage.
		359
		360	if (!ev_default_loop (0))
		361	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		362
		363	Example: Restrict libev to the select and poll backends, and do not allow
		364	environment settings to be taken into account:
		365
		366	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		367
		368	=item struct ev_loop *ev_loop_new (unsigned int flags)
		369
		370	This will create and initialise a new event loop object. If the loop
		371	could not be initialised, returns false.
		372
		373	This function is thread-safe, and one common way to use libev with
		374	threads is indeed to create one loop per thread, and using the default
		375	loop in the "main" or "initial" thread.
330		376
331	The flags argument can be used to specify special behaviour or specific	377	The flags argument can be used to specify special behaviour or specific
332	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	378	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
333		379
334	The following flags are supported:	380	The following flags are supported:
…		…
369	environment variable.	415	environment variable.
370		416
371	=item C<EVFLAG_NOINOTIFY>	417	=item C<EVFLAG_NOINOTIFY>
372		418
373	When this flag is specified, then libev will not attempt to use the	419	When this flag is specified, then libev will not attempt to use the
374	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and	420	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
375	testing, this flag can be useful to conserve inotify file descriptors, as	421	testing, this flag can be useful to conserve inotify file descriptors, as
376	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.	422	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
377		423
378	=item C<EVFLAG_SIGNALFD>	424	=item C<EVFLAG_SIGNALFD>
379		425
380	When this flag is specified, then libev will attempt to use the	426	When this flag is specified, then libev will attempt to use the
381	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API	427	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
382	delivers signals synchronously, which makes it both faster and might make	428	delivers signals synchronously, which makes it both faster and might make
383	it possible to get the queued signal data. It can also simplify signal	429	it possible to get the queued signal data. It can also simplify signal
384	handling with threads, as long as you properly block signals in your	430	handling with threads, as long as you properly block signals in your
385	threads that are not interested in handling them.	431	threads that are not interested in handling them.
386		432
387	Signalfd will not be used by default as this changes your signal mask, and	433	Signalfd will not be used by default as this changes your signal mask, and
388	there are a lot of shoddy libraries and programs (glib's threadpool for	434	there are a lot of shoddy libraries and programs (glib's threadpool for
389	example) that can't properly initialise their signal masks.	435	example) that can't properly initialise their signal masks.
		436
		437	=item C<EVFLAG_NOSIGMASK>
		438
		439	When this flag is specified, then libev will avoid to modify the signal
		440	mask. Specifically, this means you ahve to make sure signals are unblocked
		441	when you want to receive them.
		442
		443	This behaviour is useful when you want to do your own signal handling, or
		444	want to handle signals only in specific threads and want to avoid libev
		445	unblocking the signals.
		446
		447	It's also required by POSIX in a threaded program, as libev calls
		448	C<sigprocmask>, whose behaviour is officially unspecified.
		449
		450	This flag's behaviour will become the default in future versions of libev.
390		451
391	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	452	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
392		453
393	This is your standard select(2) backend. Not I<completely> standard, as	454	This is your standard select(2) backend. Not I<completely> standard, as
394	libev tries to roll its own fd_set with no limits on the number of fds,	455	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
430	epoll scales either O(1) or O(active_fds).	491	epoll scales either O(1) or O(active_fds).
431		492
432	The epoll mechanism deserves honorable mention as the most misdesigned	493	The epoll mechanism deserves honorable mention as the most misdesigned
433	of the more advanced event mechanisms: mere annoyances include silently	494	of the more advanced event mechanisms: mere annoyances include silently
434	dropping file descriptors, requiring a system call per change per file	495	dropping file descriptors, requiring a system call per change per file
435	descriptor (and unnecessary guessing of parameters), problems with dup and	496	descriptor (and unnecessary guessing of parameters), problems with dup,
		497	returning before the timeout value, resulting in additional iterations
		498	(and only giving 5ms accuracy while select on the same platform gives
436	so on. The biggest issue is fork races, however - if a program forks then	499	0.1ms) and so on. The biggest issue is fork races, however - if a program
437	I<both> parent and child process have to recreate the epoll set, which can	500	forks then I<both> parent and child process have to recreate the epoll
438	take considerable time (one syscall per file descriptor) and is of course	501	set, which can take considerable time (one syscall per file descriptor)
439	hard to detect.	502	and is of course hard to detect.
440		503
441	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	504	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
442	of course I<doesn't>, and epoll just loves to report events for totally	505	of course I<doesn't>, and epoll just loves to report events for totally
443	I<different> file descriptors (even already closed ones, so one cannot	506	I<different> file descriptors (even already closed ones, so one cannot
444	even remove them from the set) than registered in the set (especially	507	even remove them from the set) than registered in the set (especially
…		…
446	employing an additional generation counter and comparing that against the	509	employing an additional generation counter and comparing that against the
447	events to filter out spurious ones, recreating the set when required. Last	510	events to filter out spurious ones, recreating the set when required. Last
448	not least, it also refuses to work with some file descriptors which work	511	not least, it also refuses to work with some file descriptors which work
449	perfectly fine with C<select> (files, many character devices...).	512	perfectly fine with C<select> (files, many character devices...).
450		513
		514	Epoll is truly the train wreck analog among event poll mechanisms,
		515	a frankenpoll, cobbled together in a hurry, no thought to design or
		516	interaction with others.
		517
451	While stopping, setting and starting an I/O watcher in the same iteration	518	While stopping, setting and starting an I/O watcher in the same iteration
452	will result in some caching, there is still a system call per such	519	will result in some caching, there is still a system call per such
453	incident (because the same I<file descriptor> could point to a different	520	incident (because the same I<file descriptor> could point to a different
454	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	521	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
455	file descriptors might not work very well if you register events for both	522	file descriptors might not work very well if you register events for both
…		…
520	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	587	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
521		588
522	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	589	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
523	it's really slow, but it still scales very well (O(active_fds)).	590	it's really slow, but it still scales very well (O(active_fds)).
524		591
525	Please note that Solaris event ports can deliver a lot of spurious
526	notifications, so you need to use non-blocking I/O or other means to avoid
527	blocking when no data (or space) is available.
528
529	While this backend scales well, it requires one system call per active	592	While this backend scales well, it requires one system call per active
530	file descriptor per loop iteration. For small and medium numbers of file	593	file descriptor per loop iteration. For small and medium numbers of file
531	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	594	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
532	might perform better.	595	might perform better.
533		596
534	On the positive side, with the exception of the spurious readiness	597	On the positive side, this backend actually performed fully to
535	notifications, this backend actually performed fully to specification
536	in all tests and is fully embeddable, which is a rare feat among the	598	specification in all tests and is fully embeddable, which is a rare feat
537	OS-specific backends (I vastly prefer correctness over speed hacks).	599	among the OS-specific backends (I vastly prefer correctness over speed
		600	hacks).
		601
		602	On the negative side, the interface is I<bizarre> - so bizarre that
		603	even sun itself gets it wrong in their code examples: The event polling
		604	function sometimes returning events to the caller even though an error
		605	occurred, but with no indication whether it has done so or not (yes, it's
		606	even documented that way) - deadly for edge-triggered interfaces where
		607	you absolutely have to know whether an event occurred or not because you
		608	have to re-arm the watcher.
		609
		610	Fortunately libev seems to be able to work around these idiocies.
538		611
539	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	612	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
540	C<EVBACKEND_POLL>.	613	C<EVBACKEND_POLL>.
541		614
542	=item C<EVBACKEND_ALL>	615	=item C<EVBACKEND_ALL>
543		616
544	Try all backends (even potentially broken ones that wouldn't be tried	617	Try all backends (even potentially broken ones that wouldn't be tried
545	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	618	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
546	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	619	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
547		620
548	It is definitely not recommended to use this flag.	621	It is definitely not recommended to use this flag, use whatever
		622	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		623	at all.
		624
		625	=item C<EVBACKEND_MASK>
		626
		627	Not a backend at all, but a mask to select all backend bits from a
		628	C<flags> value, in case you want to mask out any backends from a flags
		629	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
549		630
550	=back	631	=back
551		632
552	If one or more of the backend flags are or'ed into the flags value,	633	If one or more of the backend flags are or'ed into the flags value,
553	then only these backends will be tried (in the reverse order as listed	634	then only these backends will be tried (in the reverse order as listed
554	here). If none are specified, all backends in C<ev_recommended_backends	635	here). If none are specified, all backends in C<ev_recommended_backends
555	()> will be tried.	636	()> will be tried.
556		637
557	Example: This is the most typical usage.
558
559	if (!ev_default_loop (0))
560	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
561
562	Example: Restrict libev to the select and poll backends, and do not allow
563	environment settings to be taken into account:
564
565	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
566
567	Example: Use whatever libev has to offer, but make sure that kqueue is
568	used if available (warning, breaks stuff, best use only with your own
569	private event loop and only if you know the OS supports your types of
570	fds):
571
572	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
573
574	=item struct ev_loop *ev_loop_new (unsigned int flags)
575
576	Similar to C<ev_default_loop>, but always creates a new event loop that is
577	always distinct from the default loop.
578
579	Note that this function I<is> thread-safe, and one common way to use
580	libev with threads is indeed to create one loop per thread, and using the
581	default loop in the "main" or "initial" thread.
582
583	Example: Try to create a event loop that uses epoll and nothing else.	638	Example: Try to create a event loop that uses epoll and nothing else.
584		639
585	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	640	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
586	if (!epoller)	641	if (!epoller)
587	fatal ("no epoll found here, maybe it hides under your chair");	642	fatal ("no epoll found here, maybe it hides under your chair");
588		643
		644	Example: Use whatever libev has to offer, but make sure that kqueue is
		645	used if available.
		646
		647	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		648
589	=item ev_default_destroy ()	649	=item ev_loop_destroy (loop)
590		650
591	Destroys the default loop (frees all memory and kernel state etc.). None	651	Destroys an event loop object (frees all memory and kernel state
592	of the active event watchers will be stopped in the normal sense, so	652	etc.). None of the active event watchers will be stopped in the normal
593	e.g. C<ev_is_active> might still return true. It is your responsibility to	653	sense, so e.g. C<ev_is_active> might still return true. It is your
594	either stop all watchers cleanly yourself I<before> calling this function,	654	responsibility to either stop all watchers cleanly yourself I<before>
595	or cope with the fact afterwards (which is usually the easiest thing, you	655	calling this function, or cope with the fact afterwards (which is usually
596	can just ignore the watchers and/or C<free ()> them for example).	656	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		657	for example).
597		658
598	Note that certain global state, such as signal state (and installed signal	659	Note that certain global state, such as signal state (and installed signal
599	handlers), will not be freed by this function, and related watchers (such	660	handlers), will not be freed by this function, and related watchers (such
600	as signal and child watchers) would need to be stopped manually.	661	as signal and child watchers) would need to be stopped manually.
601		662
602	In general it is not advisable to call this function except in the	663	This function is normally used on loop objects allocated by
603	rare occasion where you really need to free e.g. the signal handling	664	C<ev_loop_new>, but it can also be used on the default loop returned by
		665	C<ev_default_loop>, in which case it is not thread-safe.
		666
		667	Note that it is not advisable to call this function on the default loop
		668	except in the rare occasion where you really need to free its resources.
604	pipe fds. If you need dynamically allocated loops it is better to use	669	If you need dynamically allocated loops it is better to use C<ev_loop_new>
605	C<ev_loop_new> and C<ev_loop_destroy>.	670	and C<ev_loop_destroy>.
606		671
607	=item ev_loop_destroy (loop)	672	=item ev_loop_fork (loop)
608		673
609	Like C<ev_default_destroy>, but destroys an event loop created by an
610	earlier call to C<ev_loop_new>.
611
612	=item ev_default_fork ()
613
614	This function sets a flag that causes subsequent C<ev_run> iterations	674	This function sets a flag that causes subsequent C<ev_run> iterations to
615	to reinitialise the kernel state for backends that have one. Despite the	675	reinitialise the kernel state for backends that have one. Despite the
616	name, you can call it anytime, but it makes most sense after forking, in	676	name, you can call it anytime, but it makes most sense after forking, in
617	the child process (or both child and parent, but that again makes little	677	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
618	sense). You I<must> call it in the child before using any of the libev	678	child before resuming or calling C<ev_run>.
619	functions, and it will only take effect at the next C<ev_run> iteration.
620		679
621	Again, you I<have> to call it on I<any> loop that you want to re-use after	680	Again, you I<have> to call it on I<any> loop that you want to re-use after
622	a fork, I<even if you do not plan to use the loop in the parent>. This is	681	a fork, I<even if you do not plan to use the loop in the parent>. This is
623	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	682	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
624	during fork.	683	during fork.
…		…
629	call it at all (in fact, C<epoll> is so badly broken that it makes a	688	call it at all (in fact, C<epoll> is so badly broken that it makes a
630	difference, but libev will usually detect this case on its own and do a	689	difference, but libev will usually detect this case on its own and do a
631	costly reset of the backend).	690	costly reset of the backend).
632		691
633	The function itself is quite fast and it's usually not a problem to call	692	The function itself is quite fast and it's usually not a problem to call
634	it just in case after a fork. To make this easy, the function will fit in	693	it just in case after a fork.
635	quite nicely into a call to C<pthread_atfork>:
636		694
		695	Example: Automate calling C<ev_loop_fork> on the default loop when
		696	using pthreads.
		697
		698	static void
		699	post_fork_child (void)
		700	{
		701	ev_loop_fork (EV_DEFAULT);
		702	}
		703
		704	...
637	pthread_atfork (0, 0, ev_default_fork);	705	pthread_atfork (0, 0, post_fork_child);
638
639	=item ev_loop_fork (loop)
640
641	Like C<ev_default_fork>, but acts on an event loop created by
642	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
643	after fork that you want to re-use in the child, and how you keep track of
644	them is entirely your own problem.
645		706
646	=item int ev_is_default_loop (loop)	707	=item int ev_is_default_loop (loop)
647		708
648	Returns true when the given loop is, in fact, the default loop, and false	709	Returns true when the given loop is, in fact, the default loop, and false
649	otherwise.	710	otherwise.
…		…
660	prepare and check phases.	721	prepare and check phases.
661		722
662	=item unsigned int ev_depth (loop)	723	=item unsigned int ev_depth (loop)
663		724
664	Returns the number of times C<ev_run> was entered minus the number of	725	Returns the number of times C<ev_run> was entered minus the number of
665	times C<ev_run> was exited, in other words, the recursion depth.	726	times C<ev_run> was exited normally, in other words, the recursion depth.
666		727
667	Outside C<ev_run>, this number is zero. In a callback, this number is	728	Outside C<ev_run>, this number is zero. In a callback, this number is
668	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	729	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
669	in which case it is higher.	730	in which case it is higher.
670		731
671	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	732	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
672	etc.), doesn't count as "exit" - consider this as a hint to avoid such	733	throwing an exception etc.), doesn't count as "exit" - consider this
673	ungentleman-like behaviour unless it's really convenient.	734	as a hint to avoid such ungentleman-like behaviour unless it's really
		735	convenient, in which case it is fully supported.
674		736
675	=item unsigned int ev_backend (loop)	737	=item unsigned int ev_backend (loop)
676		738
677	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	739	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
678	use.	740	use.
…		…
739	relying on all watchers to be stopped when deciding when a program has	801	relying on all watchers to be stopped when deciding when a program has
740	finished (especially in interactive programs), but having a program	802	finished (especially in interactive programs), but having a program
741	that automatically loops as long as it has to and no longer by virtue	803	that automatically loops as long as it has to and no longer by virtue
742	of relying on its watchers stopping correctly, that is truly a thing of	804	of relying on its watchers stopping correctly, that is truly a thing of
743	beauty.	805	beauty.
		806
		807	This function is also I<mostly> exception-safe - you can break out of
		808	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		809	exception and so on. This does not decrement the C<ev_depth> value, nor
		810	will it clear any outstanding C<EVBREAK_ONE> breaks.
744		811
745	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	812	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
746	those events and any already outstanding ones, but will not wait and	813	those events and any already outstanding ones, but will not wait and
747	block your process in case there are no events and will return after one	814	block your process in case there are no events and will return after one
748	iteration of the loop. This is sometimes useful to poll and handle new	815	iteration of the loop. This is sometimes useful to poll and handle new
…		…
810	Can be used to make a call to C<ev_run> return early (but only after it	877	Can be used to make a call to C<ev_run> return early (but only after it
811	has processed all outstanding events). The C<how> argument must be either	878	has processed all outstanding events). The C<how> argument must be either
812	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	879	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
813	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	880	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
814		881
815	This "unloop state" will be cleared when entering C<ev_run> again.	882	This "break state" will be cleared on the next call to C<ev_run>.
816		883
817	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	884	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		885	which case it will have no effect.
818		886
819	=item ev_ref (loop)	887	=item ev_ref (loop)
820		888
821	=item ev_unref (loop)	889	=item ev_unref (loop)
822		890
…		…
843	running when nothing else is active.	911	running when nothing else is active.
844		912
845	ev_signal exitsig;	913	ev_signal exitsig;
846	ev_signal_init (&exitsig, sig_cb, SIGINT);	914	ev_signal_init (&exitsig, sig_cb, SIGINT);
847	ev_signal_start (loop, &exitsig);	915	ev_signal_start (loop, &exitsig);
848	evf_unref (loop);	916	ev_unref (loop);
849		917
850	Example: For some weird reason, unregister the above signal handler again.	918	Example: For some weird reason, unregister the above signal handler again.
851		919
852	ev_ref (loop);	920	ev_ref (loop);
853	ev_signal_stop (loop, &exitsig);	921	ev_signal_stop (loop, &exitsig);
…		…
965	See also the locking example in the C<THREADS> section later in this	1033	See also the locking example in the C<THREADS> section later in this
966	document.	1034	document.
967		1035
968	=item ev_set_userdata (loop, void *data)	1036	=item ev_set_userdata (loop, void *data)
969		1037
970	=item ev_userdata (loop)	1038	=item void *ev_userdata (loop)
971		1039
972	Set and retrieve a single C<void *> associated with a loop. When	1040	Set and retrieve a single C<void *> associated with a loop. When
973	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1041	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
974	C<0.>	1042	C<0>.
975		1043
976	These two functions can be used to associate arbitrary data with a loop,	1044	These two functions can be used to associate arbitrary data with a loop,
977	and are intended solely for the C<invoke_pending_cb>, C<release> and	1045	and are intended solely for the C<invoke_pending_cb>, C<release> and
978	C<acquire> callbacks described above, but of course can be (ab-)used for	1046	C<acquire> callbacks described above, but of course can be (ab-)used for
979	any other purpose as well.	1047	any other purpose as well.
…		…
1107	=item C<EV_FORK>	1175	=item C<EV_FORK>
1108		1176
1109	The event loop has been resumed in the child process after fork (see	1177	The event loop has been resumed in the child process after fork (see
1110	C<ev_fork>).	1178	C<ev_fork>).
1111		1179
		1180	=item C<EV_CLEANUP>
		1181
		1182	The event loop is about to be destroyed (see C<ev_cleanup>).
		1183
1112	=item C<EV_ASYNC>	1184	=item C<EV_ASYNC>
1113		1185
1114	The given async watcher has been asynchronously notified (see C<ev_async>).	1186	The given async watcher has been asynchronously notified (see C<ev_async>).
1115		1187
1116	=item C<EV_CUSTOM>	1188	=item C<EV_CUSTOM>
…		…
1137	programs, though, as the fd could already be closed and reused for another	1209	programs, though, as the fd could already be closed and reused for another
1138	thing, so beware.	1210	thing, so beware.
1139		1211
1140	=back	1212	=back
1141		1213
		1214	=head2 GENERIC WATCHER FUNCTIONS
		1215
		1216	=over 4
		1217
		1218	=item C<ev_init> (ev_TYPE *watcher, callback)
		1219
		1220	This macro initialises the generic portion of a watcher. The contents
		1221	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1222	the generic parts of the watcher are initialised, you I<need> to call
		1223	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1224	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1225	which rolls both calls into one.
		1226
		1227	You can reinitialise a watcher at any time as long as it has been stopped
		1228	(or never started) and there are no pending events outstanding.
		1229
		1230	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1231	int revents)>.
		1232
		1233	Example: Initialise an C<ev_io> watcher in two steps.
		1234
		1235	ev_io w;
		1236	ev_init (&w, my_cb);
		1237	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1238
		1239	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1240
		1241	This macro initialises the type-specific parts of a watcher. You need to
		1242	call C<ev_init> at least once before you call this macro, but you can
		1243	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1244	macro on a watcher that is active (it can be pending, however, which is a
		1245	difference to the C<ev_init> macro).
		1246
		1247	Although some watcher types do not have type-specific arguments
		1248	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1249
		1250	See C<ev_init>, above, for an example.
		1251
		1252	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1253
		1254	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1255	calls into a single call. This is the most convenient method to initialise
		1256	a watcher. The same limitations apply, of course.
		1257
		1258	Example: Initialise and set an C<ev_io> watcher in one step.
		1259
		1260	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1261
		1262	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1263
		1264	Starts (activates) the given watcher. Only active watchers will receive
		1265	events. If the watcher is already active nothing will happen.
		1266
		1267	Example: Start the C<ev_io> watcher that is being abused as example in this
		1268	whole section.
		1269
		1270	ev_io_start (EV_DEFAULT_UC, &w);
		1271
		1272	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1273
		1274	Stops the given watcher if active, and clears the pending status (whether
		1275	the watcher was active or not).
		1276
		1277	It is possible that stopped watchers are pending - for example,
		1278	non-repeating timers are being stopped when they become pending - but
		1279	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1280	pending. If you want to free or reuse the memory used by the watcher it is
		1281	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1282
		1283	=item bool ev_is_active (ev_TYPE *watcher)
		1284
		1285	Returns a true value iff the watcher is active (i.e. it has been started
		1286	and not yet been stopped). As long as a watcher is active you must not modify
		1287	it.
		1288
		1289	=item bool ev_is_pending (ev_TYPE *watcher)
		1290
		1291	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1292	events but its callback has not yet been invoked). As long as a watcher
		1293	is pending (but not active) you must not call an init function on it (but
		1294	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1295	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1296	it).
		1297
		1298	=item callback ev_cb (ev_TYPE *watcher)
		1299
		1300	Returns the callback currently set on the watcher.
		1301
		1302	=item ev_cb_set (ev_TYPE *watcher, callback)
		1303
		1304	Change the callback. You can change the callback at virtually any time
		1305	(modulo threads).
		1306
		1307	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1308
		1309	=item int ev_priority (ev_TYPE *watcher)
		1310
		1311	Set and query the priority of the watcher. The priority is a small
		1312	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1313	(default: C<-2>). Pending watchers with higher priority will be invoked
		1314	before watchers with lower priority, but priority will not keep watchers
		1315	from being executed (except for C<ev_idle> watchers).
		1316
		1317	If you need to suppress invocation when higher priority events are pending
		1318	you need to look at C<ev_idle> watchers, which provide this functionality.
		1319
		1320	You I<must not> change the priority of a watcher as long as it is active or
		1321	pending.
		1322
		1323	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1324	fine, as long as you do not mind that the priority value you query might
		1325	or might not have been clamped to the valid range.
		1326
		1327	The default priority used by watchers when no priority has been set is
		1328	always C<0>, which is supposed to not be too high and not be too low :).
		1329
		1330	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1331	priorities.
		1332
		1333	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1334
		1335	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1336	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1337	can deal with that fact, as both are simply passed through to the
		1338	callback.
		1339
		1340	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1341
		1342	If the watcher is pending, this function clears its pending status and
		1343	returns its C<revents> bitset (as if its callback was invoked). If the
		1344	watcher isn't pending it does nothing and returns C<0>.
		1345
		1346	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1347	callback to be invoked, which can be accomplished with this function.
		1348
		1349	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1350
		1351	Feeds the given event set into the event loop, as if the specified event
		1352	had happened for the specified watcher (which must be a pointer to an
		1353	initialised but not necessarily started event watcher). Obviously you must
		1354	not free the watcher as long as it has pending events.
		1355
		1356	Stopping the watcher, letting libev invoke it, or calling
		1357	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1358	not started in the first place.
		1359
		1360	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1361	functions that do not need a watcher.
		1362
		1363	=back
		1364
		1365	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1366	OWN COMPOSITE WATCHERS> idioms.
		1367
1142	=head2 WATCHER STATES	1368	=head2 WATCHER STATES
1143		1369
1144	There are various watcher states mentioned throughout this manual -	1370	There are various watcher states mentioned throughout this manual -
1145	active, pending and so on. In this section these states and the rules to	1371	active, pending and so on. In this section these states and the rules to
1146	transition between them will be described in more detail - and while these	1372	transition between them will be described in more detail - and while these
…		…
1195	While stopped (and not pending) the watcher is essentially in the	1421	While stopped (and not pending) the watcher is essentially in the
1196	initialised state, that is it can be reused, moved, modified in any way	1422	initialised state, that is it can be reused, moved, modified in any way
1197	you wish.	1423	you wish.
1198		1424
1199	=back	1425	=back
1200
1201	=head2 GENERIC WATCHER FUNCTIONS
1202
1203	=over 4
1204
1205	=item C<ev_init> (ev_TYPE *watcher, callback)
1206
1207	This macro initialises the generic portion of a watcher. The contents
1208	of the watcher object can be arbitrary (so C<malloc> will do). Only
1209	the generic parts of the watcher are initialised, you I<need> to call
1210	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1211	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1212	which rolls both calls into one.
1213
1214	You can reinitialise a watcher at any time as long as it has been stopped
1215	(or never started) and there are no pending events outstanding.
1216
1217	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1218	int revents)>.
1219
1220	Example: Initialise an C<ev_io> watcher in two steps.
1221
1222	ev_io w;
1223	ev_init (&w, my_cb);
1224	ev_io_set (&w, STDIN_FILENO, EV_READ);
1225
1226	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1227
1228	This macro initialises the type-specific parts of a watcher. You need to
1229	call C<ev_init> at least once before you call this macro, but you can
1230	call C<ev_TYPE_set> any number of times. You must not, however, call this
1231	macro on a watcher that is active (it can be pending, however, which is a
1232	difference to the C<ev_init> macro).
1233
1234	Although some watcher types do not have type-specific arguments
1235	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1236
1237	See C<ev_init>, above, for an example.
1238
1239	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1240
1241	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1242	calls into a single call. This is the most convenient method to initialise
1243	a watcher. The same limitations apply, of course.
1244
1245	Example: Initialise and set an C<ev_io> watcher in one step.
1246
1247	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1248
1249	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1250
1251	Starts (activates) the given watcher. Only active watchers will receive
1252	events. If the watcher is already active nothing will happen.
1253
1254	Example: Start the C<ev_io> watcher that is being abused as example in this
1255	whole section.
1256
1257	ev_io_start (EV_DEFAULT_UC, &w);
1258
1259	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1260
1261	Stops the given watcher if active, and clears the pending status (whether
1262	the watcher was active or not).
1263
1264	It is possible that stopped watchers are pending - for example,
1265	non-repeating timers are being stopped when they become pending - but
1266	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1267	pending. If you want to free or reuse the memory used by the watcher it is
1268	therefore a good idea to always call its C<ev_TYPE_stop> function.
1269
1270	=item bool ev_is_active (ev_TYPE *watcher)
1271
1272	Returns a true value iff the watcher is active (i.e. it has been started
1273	and not yet been stopped). As long as a watcher is active you must not modify
1274	it.
1275
1276	=item bool ev_is_pending (ev_TYPE *watcher)
1277
1278	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1279	events but its callback has not yet been invoked). As long as a watcher
1280	is pending (but not active) you must not call an init function on it (but
1281	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1282	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1283	it).
1284
1285	=item callback ev_cb (ev_TYPE *watcher)
1286
1287	Returns the callback currently set on the watcher.
1288
1289	=item ev_cb_set (ev_TYPE *watcher, callback)
1290
1291	Change the callback. You can change the callback at virtually any time
1292	(modulo threads).
1293
1294	=item ev_set_priority (ev_TYPE *watcher, int priority)
1295
1296	=item int ev_priority (ev_TYPE *watcher)
1297
1298	Set and query the priority of the watcher. The priority is a small
1299	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1300	(default: C<-2>). Pending watchers with higher priority will be invoked
1301	before watchers with lower priority, but priority will not keep watchers
1302	from being executed (except for C<ev_idle> watchers).
1303
1304	If you need to suppress invocation when higher priority events are pending
1305	you need to look at C<ev_idle> watchers, which provide this functionality.
1306
1307	You I<must not> change the priority of a watcher as long as it is active or
1308	pending.
1309
1310	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1311	fine, as long as you do not mind that the priority value you query might
1312	or might not have been clamped to the valid range.
1313
1314	The default priority used by watchers when no priority has been set is
1315	always C<0>, which is supposed to not be too high and not be too low :).
1316
1317	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1318	priorities.
1319
1320	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1321
1322	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1323	C<loop> nor C<revents> need to be valid as long as the watcher callback
1324	can deal with that fact, as both are simply passed through to the
1325	callback.
1326
1327	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1328
1329	If the watcher is pending, this function clears its pending status and
1330	returns its C<revents> bitset (as if its callback was invoked). If the
1331	watcher isn't pending it does nothing and returns C<0>.
1332
1333	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1334	callback to be invoked, which can be accomplished with this function.
1335
1336	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1337
1338	Feeds the given event set into the event loop, as if the specified event
1339	had happened for the specified watcher (which must be a pointer to an
1340	initialised but not necessarily started event watcher). Obviously you must
1341	not free the watcher as long as it has pending events.
1342
1343	Stopping the watcher, letting libev invoke it, or calling
1344	C<ev_clear_pending> will clear the pending event, even if the watcher was
1345	not started in the first place.
1346
1347	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1348	functions that do not need a watcher.
1349
1350	=back
1351
1352
1353	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1354
1355	Each watcher has, by default, a member C<void *data> that you can change
1356	and read at any time: libev will completely ignore it. This can be used
1357	to associate arbitrary data with your watcher. If you need more data and
1358	don't want to allocate memory and store a pointer to it in that data
1359	member, you can also "subclass" the watcher type and provide your own
1360	data:
1361
1362	struct my_io
1363	{
1364	ev_io io;
1365	int otherfd;
1366	void *somedata;
1367	struct whatever *mostinteresting;
1368	};
1369
1370	...
1371	struct my_io w;
1372	ev_io_init (&w.io, my_cb, fd, EV_READ);
1373
1374	And since your callback will be called with a pointer to the watcher, you
1375	can cast it back to your own type:
1376
1377	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1378	{
1379	struct my_io *w = (struct my_io *)w_;
1380	...
1381	}
1382
1383	More interesting and less C-conformant ways of casting your callback type
1384	instead have been omitted.
1385
1386	Another common scenario is to use some data structure with multiple
1387	embedded watchers:
1388
1389	struct my_biggy
1390	{
1391	int some_data;
1392	ev_timer t1;
1393	ev_timer t2;
1394	}
1395
1396	In this case getting the pointer to C<my_biggy> is a bit more
1397	complicated: Either you store the address of your C<my_biggy> struct
1398	in the C<data> member of the watcher (for woozies), or you need to use
1399	some pointer arithmetic using C<offsetof> inside your watchers (for real
1400	programmers):
1401
1402	#include <stddef.h>
1403
1404	static void
1405	t1_cb (EV_P_ ev_timer *w, int revents)
1406	{
1407	struct my_biggy big = (struct my_biggy *)
1408	(((char *)w) - offsetof (struct my_biggy, t1));
1409	}
1410
1411	static void
1412	t2_cb (EV_P_ ev_timer *w, int revents)
1413	{
1414	struct my_biggy big = (struct my_biggy *)
1415	(((char *)w) - offsetof (struct my_biggy, t2));
1416	}
1417		1426
1418	=head2 WATCHER PRIORITY MODELS	1427	=head2 WATCHER PRIORITY MODELS
1419		1428
1420	Many event loops support I<watcher priorities>, which are usually small	1429	Many event loops support I<watcher priorities>, which are usually small
1421	integers that influence the ordering of event callback invocation	1430	integers that influence the ordering of event callback invocation
…		…
1548	In general you can register as many read and/or write event watchers per	1557	In general you can register as many read and/or write event watchers per
1549	fd as you want (as long as you don't confuse yourself). Setting all file	1558	fd as you want (as long as you don't confuse yourself). Setting all file
1550	descriptors to non-blocking mode is also usually a good idea (but not	1559	descriptors to non-blocking mode is also usually a good idea (but not
1551	required if you know what you are doing).	1560	required if you know what you are doing).
1552		1561
1553	If you cannot use non-blocking mode, then force the use of a
1554	known-to-be-good backend (at the time of this writing, this includes only
1555	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1556	descriptors for which non-blocking operation makes no sense (such as
1557	files) - libev doesn't guarantee any specific behaviour in that case.
1558
1559	Another thing you have to watch out for is that it is quite easy to	1562	Another thing you have to watch out for is that it is quite easy to
1560	receive "spurious" readiness notifications, that is your callback might	1563	receive "spurious" readiness notifications, that is, your callback might
1561	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1564	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1562	because there is no data. Not only are some backends known to create a	1565	because there is no data. It is very easy to get into this situation even
1563	lot of those (for example Solaris ports), it is very easy to get into	1566	with a relatively standard program structure. Thus it is best to always
1564	this situation even with a relatively standard program structure. Thus	1567	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1565	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1566	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1568	preferable to a program hanging until some data arrives.
1567		1569
1568	If you cannot run the fd in non-blocking mode (for example you should	1570	If you cannot run the fd in non-blocking mode (for example you should
1569	not play around with an Xlib connection), then you have to separately	1571	not play around with an Xlib connection), then you have to separately
1570	re-test whether a file descriptor is really ready with a known-to-be good	1572	re-test whether a file descriptor is really ready with a known-to-be good
1571	interface such as poll (fortunately in our Xlib example, Xlib already	1573	interface such as poll (fortunately in the case of Xlib, it already does
1572	does this on its own, so its quite safe to use). Some people additionally	1574	this on its own, so its quite safe to use). Some people additionally
1573	use C<SIGALRM> and an interval timer, just to be sure you won't block	1575	use C<SIGALRM> and an interval timer, just to be sure you won't block
1574	indefinitely.	1576	indefinitely.
1575		1577
1576	But really, best use non-blocking mode.	1578	But really, best use non-blocking mode.
1577		1579
…		…
1605		1607
1606	There is no workaround possible except not registering events	1608	There is no workaround possible except not registering events
1607	for potentially C<dup ()>'ed file descriptors, or to resort to	1609	for potentially C<dup ()>'ed file descriptors, or to resort to
1608	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1610	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1609		1611
		1612	=head3 The special problem of files
		1613
		1614	Many people try to use C<select> (or libev) on file descriptors
		1615	representing files, and expect it to become ready when their program
		1616	doesn't block on disk accesses (which can take a long time on their own).
		1617
		1618	However, this cannot ever work in the "expected" way - you get a readiness
		1619	notification as soon as the kernel knows whether and how much data is
		1620	there, and in the case of open files, that's always the case, so you
		1621	always get a readiness notification instantly, and your read (or possibly
		1622	write) will still block on the disk I/O.
		1623
		1624	Another way to view it is that in the case of sockets, pipes, character
		1625	devices and so on, there is another party (the sender) that delivers data
		1626	on its own, but in the case of files, there is no such thing: the disk
		1627	will not send data on its own, simply because it doesn't know what you
		1628	wish to read - you would first have to request some data.
		1629
		1630	Since files are typically not-so-well supported by advanced notification
		1631	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1632	to files, even though you should not use it. The reason for this is
		1633	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1634	usually a tty, often a pipe, but also sometimes files or special devices
		1635	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1636	F</dev/urandom>), and even though the file might better be served with
		1637	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1638	it "just works" instead of freezing.
		1639
		1640	So avoid file descriptors pointing to files when you know it (e.g. use
		1641	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1642	when you rarely read from a file instead of from a socket, and want to
		1643	reuse the same code path.
		1644
1610	=head3 The special problem of fork	1645	=head3 The special problem of fork
1611		1646
1612	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1647	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1613	useless behaviour. Libev fully supports fork, but needs to be told about	1648	useless behaviour. Libev fully supports fork, but needs to be told about
1614	it in the child.	1649	it in the child if you want to continue to use it in the child.
1615		1650
1616	To support fork in your programs, you either have to call	1651	To support fork in your child processes, you have to call C<ev_loop_fork
1617	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1652	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1618	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1653	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1619	C<EVBACKEND_POLL>.
1620		1654
1621	=head3 The special problem of SIGPIPE	1655	=head3 The special problem of SIGPIPE
1622		1656
1623	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1657	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1624	when writing to a pipe whose other end has been closed, your program gets	1658	when writing to a pipe whose other end has been closed, your program gets
…		…
2240		2274
2241	=head2 C<ev_signal> - signal me when a signal gets signalled!	2275	=head2 C<ev_signal> - signal me when a signal gets signalled!
2242		2276
2243	Signal watchers will trigger an event when the process receives a specific	2277	Signal watchers will trigger an event when the process receives a specific
2244	signal one or more times. Even though signals are very asynchronous, libev	2278	signal one or more times. Even though signals are very asynchronous, libev
2245	will try it's best to deliver signals synchronously, i.e. as part of the	2279	will try its best to deliver signals synchronously, i.e. as part of the
2246	normal event processing, like any other event.	2280	normal event processing, like any other event.
2247		2281
2248	If you want signals to be delivered truly asynchronously, just use	2282	If you want signals to be delivered truly asynchronously, just use
2249	C<sigaction> as you would do without libev and forget about sharing	2283	C<sigaction> as you would do without libev and forget about sharing
2250	the signal. You can even use C<ev_async> from a signal handler to	2284	the signal. You can even use C<ev_async> from a signal handler to
…		…
2269	=head3 The special problem of inheritance over fork/execve/pthread_create	2303	=head3 The special problem of inheritance over fork/execve/pthread_create
2270		2304
2271	Both the signal mask (C<sigprocmask>) and the signal disposition	2305	Both the signal mask (C<sigprocmask>) and the signal disposition
2272	(C<sigaction>) are unspecified after starting a signal watcher (and after	2306	(C<sigaction>) are unspecified after starting a signal watcher (and after
2273	stopping it again), that is, libev might or might not block the signal,	2307	stopping it again), that is, libev might or might not block the signal,
2274	and might or might not set or restore the installed signal handler.	2308	and might or might not set or restore the installed signal handler (but
		2309	see C<EVFLAG_NOSIGMASK>).
2275		2310
2276	While this does not matter for the signal disposition (libev never	2311	While this does not matter for the signal disposition (libev never
2277	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2312	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2278	C<execve>), this matters for the signal mask: many programs do not expect	2313	C<execve>), this matters for the signal mask: many programs do not expect
2279	certain signals to be blocked.	2314	certain signals to be blocked.
…		…
2292	I<has> to modify the signal mask, at least temporarily.	2327	I<has> to modify the signal mask, at least temporarily.
2293		2328
2294	So I can't stress this enough: I<If you do not reset your signal mask when	2329	So I can't stress this enough: I<If you do not reset your signal mask when
2295	you expect it to be empty, you have a race condition in your code>. This	2330	you expect it to be empty, you have a race condition in your code>. This
2296	is not a libev-specific thing, this is true for most event libraries.	2331	is not a libev-specific thing, this is true for most event libraries.
		2332
		2333	=head3 The special problem of threads signal handling
		2334
		2335	POSIX threads has problematic signal handling semantics, specifically,
		2336	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2337	threads in a process block signals, which is hard to achieve.
		2338
		2339	When you want to use sigwait (or mix libev signal handling with your own
		2340	for the same signals), you can tackle this problem by globally blocking
		2341	all signals before creating any threads (or creating them with a fully set
		2342	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2343	loops. Then designate one thread as "signal receiver thread" which handles
		2344	these signals. You can pass on any signals that libev might be interested
		2345	in by calling C<ev_feed_signal>.
2297		2346
2298	=head3 Watcher-Specific Functions and Data Members	2347	=head3 Watcher-Specific Functions and Data Members
2299		2348
2300	=over 4	2349	=over 4
2301		2350
…		…
3075	disadvantage of having to use multiple event loops (which do not support	3124	disadvantage of having to use multiple event loops (which do not support
3076	signal watchers).	3125	signal watchers).
3077		3126
3078	When this is not possible, or you want to use the default loop for	3127	When this is not possible, or you want to use the default loop for
3079	other reasons, then in the process that wants to start "fresh", call	3128	other reasons, then in the process that wants to start "fresh", call
3080	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying	3129	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
3081	the default loop will "orphan" (not stop) all registered watchers, so you	3130	Destroying the default loop will "orphan" (not stop) all registered
3082	have to be careful not to execute code that modifies those watchers. Note	3131	watchers, so you have to be careful not to execute code that modifies
3083	also that in that case, you have to re-register any signal watchers.	3132	those watchers. Note also that in that case, you have to re-register any
		3133	signal watchers.
3084		3134
3085	=head3 Watcher-Specific Functions and Data Members	3135	=head3 Watcher-Specific Functions and Data Members
3086		3136
3087	=over 4	3137	=over 4
3088		3138
3089	=item ev_fork_init (ev_signal *, callback)	3139	=item ev_fork_init (ev_fork *, callback)
3090		3140
3091	Initialises and configures the fork watcher - it has no parameters of any	3141	Initialises and configures the fork watcher - it has no parameters of any
3092	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3142	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3093	believe me.	3143	really.
3094		3144
3095	=back	3145	=back
		3146
		3147
		3148	=head2 C<ev_cleanup> - even the best things end
		3149
		3150	Cleanup watchers are called just before the event loop is being destroyed
		3151	by a call to C<ev_loop_destroy>.
		3152
		3153	While there is no guarantee that the event loop gets destroyed, cleanup
		3154	watchers provide a convenient method to install cleanup hooks for your
		3155	program, worker threads and so on - you just to make sure to destroy the
		3156	loop when you want them to be invoked.
		3157
		3158	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3159	all other watchers, they do not keep a reference to the event loop (which
		3160	makes a lot of sense if you think about it). Like all other watchers, you
		3161	can call libev functions in the callback, except C<ev_cleanup_start>.
		3162
		3163	=head3 Watcher-Specific Functions and Data Members
		3164
		3165	=over 4
		3166
		3167	=item ev_cleanup_init (ev_cleanup *, callback)
		3168
		3169	Initialises and configures the cleanup watcher - it has no parameters of
		3170	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3171	pointless, I assure you.
		3172
		3173	=back
		3174
		3175	Example: Register an atexit handler to destroy the default loop, so any
		3176	cleanup functions are called.
		3177
		3178	static void
		3179	program_exits (void)
		3180	{
		3181	ev_loop_destroy (EV_DEFAULT_UC);
		3182	}
		3183
		3184	...
		3185	atexit (program_exits);
3096		3186
3097		3187
3098	=head2 C<ev_async> - how to wake up an event loop	3188	=head2 C<ev_async> - how to wake up an event loop
3099		3189
3100	In general, you cannot use an C<ev_run> from multiple threads or other	3190	In general, you cannot use an C<ev_run> from multiple threads or other
…		…
3107	it by calling C<ev_async_send>, which is thread- and signal safe.	3197	it by calling C<ev_async_send>, which is thread- and signal safe.
3108		3198
3109	This functionality is very similar to C<ev_signal> watchers, as signals,	3199	This functionality is very similar to C<ev_signal> watchers, as signals,
3110	too, are asynchronous in nature, and signals, too, will be compressed	3200	too, are asynchronous in nature, and signals, too, will be compressed
3111	(i.e. the number of callback invocations may be less than the number of	3201	(i.e. the number of callback invocations may be less than the number of
3112	C<ev_async_sent> calls).	3202	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3203	of "global async watchers" by using a watcher on an otherwise unused
		3204	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3205	even without knowing which loop owns the signal.
3113		3206
3114	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3207	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3115	just the default loop.	3208	just the default loop.
3116		3209
3117	=head3 Queueing	3210	=head3 Queueing
…		…
3293	Feed an event on the given fd, as if a file descriptor backend detected	3386	Feed an event on the given fd, as if a file descriptor backend detected
3294	the given events it.	3387	the given events it.
3295		3388
3296	=item ev_feed_signal_event (loop, int signum)	3389	=item ev_feed_signal_event (loop, int signum)
3297		3390
3298	Feed an event as if the given signal occurred (C<loop> must be the default	3391	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3299	loop!).	3392	which is async-safe.
3300		3393
3301	=back	3394	=back
		3395
		3396
		3397	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3398
		3399	This section explains some common idioms that are not immediately
		3400	obvious. Note that examples are sprinkled over the whole manual, and this
		3401	section only contains stuff that wouldn't fit anywhere else.
		3402
		3403	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3404
		3405	Each watcher has, by default, a C<void *data> member that you can read
		3406	or modify at any time: libev will completely ignore it. This can be used
		3407	to associate arbitrary data with your watcher. If you need more data and
		3408	don't want to allocate memory separately and store a pointer to it in that
		3409	data member, you can also "subclass" the watcher type and provide your own
		3410	data:
		3411
		3412	struct my_io
		3413	{
		3414	ev_io io;
		3415	int otherfd;
		3416	void *somedata;
		3417	struct whatever *mostinteresting;
		3418	};
		3419
		3420	...
		3421	struct my_io w;
		3422	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3423
		3424	And since your callback will be called with a pointer to the watcher, you
		3425	can cast it back to your own type:
		3426
		3427	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3428	{
		3429	struct my_io *w = (struct my_io *)w_;
		3430	...
		3431	}
		3432
		3433	More interesting and less C-conformant ways of casting your callback
		3434	function type instead have been omitted.
		3435
		3436	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3437
		3438	Another common scenario is to use some data structure with multiple
		3439	embedded watchers, in effect creating your own watcher that combines
		3440	multiple libev event sources into one "super-watcher":
		3441
		3442	struct my_biggy
		3443	{
		3444	int some_data;
		3445	ev_timer t1;
		3446	ev_timer t2;
		3447	}
		3448
		3449	In this case getting the pointer to C<my_biggy> is a bit more
		3450	complicated: Either you store the address of your C<my_biggy> struct in
		3451	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3452	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3453	real programmers):
		3454
		3455	#include <stddef.h>
		3456
		3457	static void
		3458	t1_cb (EV_P_ ev_timer *w, int revents)
		3459	{
		3460	struct my_biggy big = (struct my_biggy *)
		3461	(((char *)w) - offsetof (struct my_biggy, t1));
		3462	}
		3463
		3464	static void
		3465	t2_cb (EV_P_ ev_timer *w, int revents)
		3466	{
		3467	struct my_biggy big = (struct my_biggy *)
		3468	(((char *)w) - offsetof (struct my_biggy, t2));
		3469	}
		3470
		3471	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3472
		3473	Often (especially in GUI toolkits) there are places where you have
		3474	I<modal> interaction, which is most easily implemented by recursively
		3475	invoking C<ev_run>.
		3476
		3477	This brings the problem of exiting - a callback might want to finish the
		3478	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3479	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3480	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3481	other combination: In these cases, C<ev_break> will not work alone.
		3482
		3483	The solution is to maintain "break this loop" variable for each C<ev_run>
		3484	invocation, and use a loop around C<ev_run> until the condition is
		3485	triggered, using C<EVRUN_ONCE>:
		3486
		3487	// main loop
		3488	int exit_main_loop = 0;
		3489
		3490	while (!exit_main_loop)
		3491	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3492
		3493	// in a model watcher
		3494	int exit_nested_loop = 0;
		3495
		3496	while (!exit_nested_loop)
		3497	ev_run (EV_A_ EVRUN_ONCE);
		3498
		3499	To exit from any of these loops, just set the corresponding exit variable:
		3500
		3501	// exit modal loop
		3502	exit_nested_loop = 1;
		3503
		3504	// exit main program, after modal loop is finished
		3505	exit_main_loop = 1;
		3506
		3507	// exit both
		3508	exit_main_loop = exit_nested_loop = 1;
		3509
		3510	=head2 THREAD LOCKING EXAMPLE
		3511
		3512	Here is a fictitious example of how to run an event loop in a different
		3513	thread from where callbacks are being invoked and watchers are
		3514	created/added/removed.
		3515
		3516	For a real-world example, see the C<EV::Loop::Async> perl module,
		3517	which uses exactly this technique (which is suited for many high-level
		3518	languages).
		3519
		3520	The example uses a pthread mutex to protect the loop data, a condition
		3521	variable to wait for callback invocations, an async watcher to notify the
		3522	event loop thread and an unspecified mechanism to wake up the main thread.
		3523
		3524	First, you need to associate some data with the event loop:
		3525
		3526	typedef struct {
		3527	mutex_t lock; /* global loop lock */
		3528	ev_async async_w;
		3529	thread_t tid;
		3530	cond_t invoke_cv;
		3531	} userdata;
		3532
		3533	void prepare_loop (EV_P)
		3534	{
		3535	// for simplicity, we use a static userdata struct.
		3536	static userdata u;
		3537
		3538	ev_async_init (&u->async_w, async_cb);
		3539	ev_async_start (EV_A_ &u->async_w);
		3540
		3541	pthread_mutex_init (&u->lock, 0);
		3542	pthread_cond_init (&u->invoke_cv, 0);
		3543
		3544	// now associate this with the loop
		3545	ev_set_userdata (EV_A_ u);
		3546	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3547	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3548
		3549	// then create the thread running ev_loop
		3550	pthread_create (&u->tid, 0, l_run, EV_A);
		3551	}
		3552
		3553	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3554	solely to wake up the event loop so it takes notice of any new watchers
		3555	that might have been added:
		3556
		3557	static void
		3558	async_cb (EV_P_ ev_async *w, int revents)
		3559	{
		3560	// just used for the side effects
		3561	}
		3562
		3563	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3564	protecting the loop data, respectively.
		3565
		3566	static void
		3567	l_release (EV_P)
		3568	{
		3569	userdata *u = ev_userdata (EV_A);
		3570	pthread_mutex_unlock (&u->lock);
		3571	}
		3572
		3573	static void
		3574	l_acquire (EV_P)
		3575	{
		3576	userdata *u = ev_userdata (EV_A);
		3577	pthread_mutex_lock (&u->lock);
		3578	}
		3579
		3580	The event loop thread first acquires the mutex, and then jumps straight
		3581	into C<ev_run>:
		3582
		3583	void *
		3584	l_run (void *thr_arg)
		3585	{
		3586	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3587
		3588	l_acquire (EV_A);
		3589	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3590	ev_run (EV_A_ 0);
		3591	l_release (EV_A);
		3592
		3593	return 0;
		3594	}
		3595
		3596	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3597	signal the main thread via some unspecified mechanism (signals? pipe
		3598	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3599	have been called (in a while loop because a) spurious wakeups are possible
		3600	and b) skipping inter-thread-communication when there are no pending
		3601	watchers is very beneficial):
		3602
		3603	static void
		3604	l_invoke (EV_P)
		3605	{
		3606	userdata *u = ev_userdata (EV_A);
		3607
		3608	while (ev_pending_count (EV_A))
		3609	{
		3610	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3611	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3612	}
		3613	}
		3614
		3615	Now, whenever the main thread gets told to invoke pending watchers, it
		3616	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3617	thread to continue:
		3618
		3619	static void
		3620	real_invoke_pending (EV_P)
		3621	{
		3622	userdata *u = ev_userdata (EV_A);
		3623
		3624	pthread_mutex_lock (&u->lock);
		3625	ev_invoke_pending (EV_A);
		3626	pthread_cond_signal (&u->invoke_cv);
		3627	pthread_mutex_unlock (&u->lock);
		3628	}
		3629
		3630	Whenever you want to start/stop a watcher or do other modifications to an
		3631	event loop, you will now have to lock:
		3632
		3633	ev_timer timeout_watcher;
		3634	userdata *u = ev_userdata (EV_A);
		3635
		3636	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3637
		3638	pthread_mutex_lock (&u->lock);
		3639	ev_timer_start (EV_A_ &timeout_watcher);
		3640	ev_async_send (EV_A_ &u->async_w);
		3641	pthread_mutex_unlock (&u->lock);
		3642
		3643	Note that sending the C<ev_async> watcher is required because otherwise
		3644	an event loop currently blocking in the kernel will have no knowledge
		3645	about the newly added timer. By waking up the loop it will pick up any new
		3646	watchers in the next event loop iteration.
		3647
		3648	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3649
		3650	While the overhead of a callback that e.g. schedules a thread is small, it
		3651	is still an overhead. If you embed libev, and your main usage is with some
		3652	kind of threads or coroutines, you might want to customise libev so that
		3653	doesn't need callbacks anymore.
		3654
		3655	Imagine you have coroutines that you can switch to using a function
		3656	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3657	and that due to some magic, the currently active coroutine is stored in a
		3658	global called C<current_coro>. Then you can build your own "wait for libev
		3659	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3660	the differing C<;> conventions):
		3661
		3662	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3663	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3664
		3665	That means instead of having a C callback function, you store the
		3666	coroutine to switch to in each watcher, and instead of having libev call
		3667	your callback, you instead have it switch to that coroutine.
		3668
		3669	A coroutine might now wait for an event with a function called
		3670	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3671	matter when, or whether the watcher is active or not when this function is
		3672	called):
		3673
		3674	void
		3675	wait_for_event (ev_watcher *w)
		3676	{
		3677	ev_cb_set (w) = current_coro;
		3678	switch_to (libev_coro);
		3679	}
		3680
		3681	That basically suspends the coroutine inside C<wait_for_event> and
		3682	continues the libev coroutine, which, when appropriate, switches back to
		3683	this or any other coroutine. I am sure if you sue this your own :)
		3684
		3685	You can do similar tricks if you have, say, threads with an event queue -
		3686	instead of storing a coroutine, you store the queue object and instead of
		3687	switching to a coroutine, you push the watcher onto the queue and notify
		3688	any waiters.
		3689
		3690	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3691	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3692
		3693	// my_ev.h
		3694	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3695	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3696	#include "../libev/ev.h"
		3697
		3698	// my_ev.c
		3699	#define EV_H "my_ev.h"
		3700	#include "../libev/ev.c"
		3701
		3702	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3703	F<my_ev.c> into your project. When properly specifying include paths, you
		3704	can even use F<ev.h> as header file name directly.
3302		3705
3303		3706
3304	=head1 LIBEVENT EMULATION	3707	=head1 LIBEVENT EMULATION
3305		3708
3306	Libev offers a compatibility emulation layer for libevent. It cannot	3709	Libev offers a compatibility emulation layer for libevent. It cannot
3307	emulate the internals of libevent, so here are some usage hints:	3710	emulate the internals of libevent, so here are some usage hints:
3308		3711
3309	=over 4	3712	=over 4
		3713
		3714	=item * Only the libevent-1.4.1-beta API is being emulated.
		3715
		3716	This was the newest libevent version available when libev was implemented,
		3717	and is still mostly unchanged in 2010.
3310		3718
3311	=item * Use it by including <event.h>, as usual.	3719	=item * Use it by including <event.h>, as usual.
3312		3720
3313	=item * The following members are fully supported: ev_base, ev_callback,	3721	=item * The following members are fully supported: ev_base, ev_callback,
3314	ev_arg, ev_fd, ev_res, ev_events.	3722	ev_arg, ev_fd, ev_res, ev_events.
…		…
3320	=item * Priorities are not currently supported. Initialising priorities	3728	=item * Priorities are not currently supported. Initialising priorities
3321	will fail and all watchers will have the same priority, even though there	3729	will fail and all watchers will have the same priority, even though there
3322	is an ev_pri field.	3730	is an ev_pri field.
3323		3731
3324	=item * In libevent, the last base created gets the signals, in libev, the	3732	=item * In libevent, the last base created gets the signals, in libev, the
3325	first base created (== the default loop) gets the signals.	3733	base that registered the signal gets the signals.
3326		3734
3327	=item * Other members are not supported.	3735	=item * Other members are not supported.
3328		3736
3329	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3737	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3330	to use the libev header file and library.	3738	to use the libev header file and library.
…		…
3349	Care has been taken to keep the overhead low. The only data member the C++	3757	Care has been taken to keep the overhead low. The only data member the C++
3350	classes add (compared to plain C-style watchers) is the event loop pointer	3758	classes add (compared to plain C-style watchers) is the event loop pointer
3351	that the watcher is associated with (or no additional members at all if	3759	that the watcher is associated with (or no additional members at all if
3352	you disable C<EV_MULTIPLICITY> when embedding libev).	3760	you disable C<EV_MULTIPLICITY> when embedding libev).
3353		3761
3354	Currently, functions, and static and non-static member functions can be	3762	Currently, functions, static and non-static member functions and classes
3355	used as callbacks. Other types should be easy to add as long as they only	3763	with C<operator ()> can be used as callbacks. Other types should be easy
3356	need one additional pointer for context. If you need support for other	3764	to add as long as they only need one additional pointer for context. If
3357	types of functors please contact the author (preferably after implementing	3765	you need support for other types of functors please contact the author
3358	it).	3766	(preferably after implementing it).
3359		3767
3360	Here is a list of things available in the C<ev> namespace:	3768	Here is a list of things available in the C<ev> namespace:
3361		3769
3362	=over 4	3770	=over 4
3363		3771
…		…
4231	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4639	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4232		4640
4233	#include "ev_cpp.h"	4641	#include "ev_cpp.h"
4234	#include "ev.c"	4642	#include "ev.c"
4235		4643
4236	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4644	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4237		4645
4238	=head2 THREADS AND COROUTINES	4646	=head2 THREADS AND COROUTINES
4239		4647
4240	=head3 THREADS	4648	=head3 THREADS
4241		4649
…		…
4292	default loop and triggering an C<ev_async> watcher from the default loop	4700	default loop and triggering an C<ev_async> watcher from the default loop
4293	watcher callback into the event loop interested in the signal.	4701	watcher callback into the event loop interested in the signal.
4294		4702
4295	=back	4703	=back
4296		4704
4297	=head4 THREAD LOCKING EXAMPLE	4705	See also L<THREAD LOCKING EXAMPLE>.
4298
4299	Here is a fictitious example of how to run an event loop in a different
4300	thread than where callbacks are being invoked and watchers are
4301	created/added/removed.
4302
4303	For a real-world example, see the C<EV::Loop::Async> perl module,
4304	which uses exactly this technique (which is suited for many high-level
4305	languages).
4306
4307	The example uses a pthread mutex to protect the loop data, a condition
4308	variable to wait for callback invocations, an async watcher to notify the
4309	event loop thread and an unspecified mechanism to wake up the main thread.
4310
4311	First, you need to associate some data with the event loop:
4312
4313	typedef struct {
4314	mutex_t lock; /* global loop lock */
4315	ev_async async_w;
4316	thread_t tid;
4317	cond_t invoke_cv;
4318	} userdata;
4319
4320	void prepare_loop (EV_P)
4321	{
4322	// for simplicity, we use a static userdata struct.
4323	static userdata u;
4324
4325	ev_async_init (&u->async_w, async_cb);
4326	ev_async_start (EV_A_ &u->async_w);
4327
4328	pthread_mutex_init (&u->lock, 0);
4329	pthread_cond_init (&u->invoke_cv, 0);
4330
4331	// now associate this with the loop
4332	ev_set_userdata (EV_A_ u);
4333	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4334	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4335
4336	// then create the thread running ev_loop
4337	pthread_create (&u->tid, 0, l_run, EV_A);
4338	}
4339
4340	The callback for the C<ev_async> watcher does nothing: the watcher is used
4341	solely to wake up the event loop so it takes notice of any new watchers
4342	that might have been added:
4343
4344	static void
4345	async_cb (EV_P_ ev_async *w, int revents)
4346	{
4347	// just used for the side effects
4348	}
4349
4350	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4351	protecting the loop data, respectively.
4352
4353	static void
4354	l_release (EV_P)
4355	{
4356	userdata *u = ev_userdata (EV_A);
4357	pthread_mutex_unlock (&u->lock);
4358	}
4359
4360	static void
4361	l_acquire (EV_P)
4362	{
4363	userdata *u = ev_userdata (EV_A);
4364	pthread_mutex_lock (&u->lock);
4365	}
4366
4367	The event loop thread first acquires the mutex, and then jumps straight
4368	into C<ev_run>:
4369
4370	void *
4371	l_run (void *thr_arg)
4372	{
4373	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4374
4375	l_acquire (EV_A);
4376	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4377	ev_run (EV_A_ 0);
4378	l_release (EV_A);
4379
4380	return 0;
4381	}
4382
4383	Instead of invoking all pending watchers, the C<l_invoke> callback will
4384	signal the main thread via some unspecified mechanism (signals? pipe
4385	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4386	have been called (in a while loop because a) spurious wakeups are possible
4387	and b) skipping inter-thread-communication when there are no pending
4388	watchers is very beneficial):
4389
4390	static void
4391	l_invoke (EV_P)
4392	{
4393	userdata *u = ev_userdata (EV_A);
4394
4395	while (ev_pending_count (EV_A))
4396	{
4397	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4398	pthread_cond_wait (&u->invoke_cv, &u->lock);
4399	}
4400	}
4401
4402	Now, whenever the main thread gets told to invoke pending watchers, it
4403	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4404	thread to continue:
4405
4406	static void
4407	real_invoke_pending (EV_P)
4408	{
4409	userdata *u = ev_userdata (EV_A);
4410
4411	pthread_mutex_lock (&u->lock);
4412	ev_invoke_pending (EV_A);
4413	pthread_cond_signal (&u->invoke_cv);
4414	pthread_mutex_unlock (&u->lock);
4415	}
4416
4417	Whenever you want to start/stop a watcher or do other modifications to an
4418	event loop, you will now have to lock:
4419
4420	ev_timer timeout_watcher;
4421	userdata *u = ev_userdata (EV_A);
4422
4423	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4424
4425	pthread_mutex_lock (&u->lock);
4426	ev_timer_start (EV_A_ &timeout_watcher);
4427	ev_async_send (EV_A_ &u->async_w);
4428	pthread_mutex_unlock (&u->lock);
4429
4430	Note that sending the C<ev_async> watcher is required because otherwise
4431	an event loop currently blocking in the kernel will have no knowledge
4432	about the newly added timer. By waking up the loop it will pick up any new
4433	watchers in the next event loop iteration.
4434		4706
4435	=head3 COROUTINES	4707	=head3 COROUTINES
4436		4708
4437	Libev is very accommodating to coroutines ("cooperative threads"):	4709	Libev is very accommodating to coroutines ("cooperative threads"):
4438	libev fully supports nesting calls to its functions from different	4710	libev fully supports nesting calls to its functions from different
…		…
4707	structure (guaranteed by POSIX but not by ISO C for example), but it also	4979	structure (guaranteed by POSIX but not by ISO C for example), but it also
4708	assumes that the same (machine) code can be used to call any watcher	4980	assumes that the same (machine) code can be used to call any watcher
4709	callback: The watcher callbacks have different type signatures, but libev	4981	callback: The watcher callbacks have different type signatures, but libev
4710	calls them using an C<ev_watcher *> internally.	4982	calls them using an C<ev_watcher *> internally.
4711		4983
		4984	=item pointer accesses must be thread-atomic
		4985
		4986	Accessing a pointer value must be atomic, it must both be readable and
		4987	writable in one piece - this is the case on all current architectures.
		4988
4712	=item C<sig_atomic_t volatile> must be thread-atomic as well	4989	=item C<sig_atomic_t volatile> must be thread-atomic as well
4713		4990
4714	The type C<sig_atomic_t volatile> (or whatever is defined as	4991	The type C<sig_atomic_t volatile> (or whatever is defined as
4715	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	4992	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4716	threads. This is not part of the specification for C<sig_atomic_t>, but is	4993	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4822	=back	5099	=back
4823		5100
4824		5101
4825	=head1 PORTING FROM LIBEV 3.X TO 4.X	5102	=head1 PORTING FROM LIBEV 3.X TO 4.X
4826		5103
4827	The major version 4 introduced some minor incompatible changes to the API.	5104	The major version 4 introduced some incompatible changes to the API.
4828		5105
4829	At the moment, the C<ev.h> header file tries to implement superficial	5106	At the moment, the C<ev.h> header file provides compatibility definitions
4830	compatibility, so most programs should still compile. Those might be	5107	for all changes, so most programs should still compile. The compatibility
4831	removed in later versions of libev, so better update early than late.	5108	layer might be removed in later versions of libev, so better update to the
		5109	new API early than late.
4832		5110
4833	=over 4	5111	=over 4
		5112
		5113	=item C<EV_COMPAT3> backwards compatibility mechanism
		5114
		5115	The backward compatibility mechanism can be controlled by
		5116	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5117	section.
		5118
		5119	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5120
		5121	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5122
		5123	ev_loop_destroy (EV_DEFAULT_UC);
		5124	ev_loop_fork (EV_DEFAULT);
4834		5125
4835	=item function/symbol renames	5126	=item function/symbol renames
4836		5127
4837	A number of functions and symbols have been renamed:	5128	A number of functions and symbols have been renamed:
4838		5129
…		…
4857	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5148	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4858	as all other watcher types. Note that C<ev_loop_fork> is still called	5149	as all other watcher types. Note that C<ev_loop_fork> is still called
4859	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5150	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4860	typedef.	5151	typedef.
4861		5152
4862	=item C<EV_COMPAT3> backwards compatibility mechanism
4863
4864	The backward compatibility mechanism can be controlled by
4865	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4866	section.
4867
4868	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5153	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4869		5154
4870	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5155	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4871	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5156	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4872	and work, but the library code will of course be larger.	5157	and work, but the library code will of course be larger.
…		…
4946		5231
4947	=back	5232	=back
4948		5233
4949	=head1 AUTHOR	5234	=head1 AUTHOR
4950		5235
4951	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5236	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5237	Magnusson and Emanuele Giaquinta.
4952		5238

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