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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
…		…
58	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
59		61
60	// now wait for events to arrive	62	// now wait for events to arrive
61	ev_run (loop, 0);	63	ev_run (loop, 0);
62		64
63	// unloop was called, so exit	65	// break was called, so exit
64	return 0;	66	return 0;
65	}	67	}
66		68
67	=head1 ABOUT THIS DOCUMENT	69	=head1 ABOUT THIS DOCUMENT
68		70
…		…
82		84
83	=head1 WHAT TO READ WHEN IN A HURRY	85	=head1 WHAT TO READ WHEN IN A HURRY
84		86
85	This manual tries to be very detailed, but unfortunately, this also makes	87	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	88	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	89	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	90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
89	C<ev_timer> sections in L<WATCHER TYPES>.	91	C<ev_timer> sections in L</WATCHER TYPES>.
90		92
91	=head1 ABOUT LIBEV	93	=head1 ABOUT LIBEV
92		94
93	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
94	file descriptor being readable or a timeout occurring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
…		…
174	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
175		177
176	Returns the current time as libev would use it. Please note that the	178	Returns the current time as libev would use it. Please note that the
177	C<ev_now> function is usually faster and also often returns the timestamp	179	C<ev_now> function is usually faster and also often returns the timestamp
178	you actually want to know. Also interesting is the combination of	180	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	181	C<ev_now_update> and C<ev_now>.
180		182
181	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
182		184
183	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
185	this is a sub-second-resolution C<sleep ()>.	190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
186		194
187	=item int ev_version_major ()	195	=item int ev_version_major ()
188		196
189	=item int ev_version_minor ()	197	=item int ev_version_minor ()
190		198
…		…
241	the current system, you would need to look at C<ev_embeddable_backends ()	249	the current system, you would need to look at C<ev_embeddable_backends ()
242	& ev_supported_backends ()>, likewise for recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
243		251
244	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
245		253
246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
247		255
248	Sets the allocation function to use (the prototype is similar - the	256	Sets the allocation function to use (the prototype is similar - the
249	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	257	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
250	used to allocate and free memory (no surprises here). If it returns zero	258	used to allocate and free memory (no surprises here). If it returns zero
251	when memory needs to be allocated (C<size != 0>), the library might abort	259	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
257		265
258	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
259	free some memory if it cannot allocate memory, to use a special allocator,	267	free some memory if it cannot allocate memory, to use a special allocator,
260	or even to sleep a while and retry until some memory is available.	268	or even to sleep a while and retry until some memory is available.
261		269
		270	Example: The following is the C<realloc> function that libev itself uses
		271	which should work with C<realloc> and C<free> functions of all kinds and
		272	is probably a good basis for your own implementation.
		273
		274	static void *
		275	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		276	{
		277	if (size)
		278	return realloc (ptr, size);
		279
		280	free (ptr);
		281	return 0;
		282	}
		283
262	Example: Replace the libev allocator with one that waits a bit and then	284	Example: Replace the libev allocator with one that waits a bit and then
263	retries (example requires a standards-compliant C<realloc>).	285	retries.
264		286
265	static void *	287	static void *
266	persistent_realloc (void *ptr, size_t size)	288	persistent_realloc (void *ptr, size_t size)
267	{	289	{
		290	if (!size)
		291	{
		292	free (ptr);
		293	return 0;
		294	}
		295
268	for (;;)	296	for (;;)
269	{	297	{
270	void *newptr = realloc (ptr, size);	298	void *newptr = realloc (ptr, size);
271		299
272	if (newptr)	300	if (newptr)
…		…
277	}	305	}
278		306
279	...	307	...
280	ev_set_allocator (persistent_realloc);	308	ev_set_allocator (persistent_realloc);
281		309
282	=item ev_set_syserr_cb (void (*cb)(const char *msg))	310	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
283		311
284	Set the callback function to call on a retryable system call error (such	312	Set the callback function to call on a retryable system call error (such
285	as failed select, poll, epoll_wait). The message is a printable string	313	as failed select, poll, epoll_wait). The message is a printable string
286	indicating the system call or subsystem causing the problem. If this	314	indicating the system call or subsystem causing the problem. If this
287	callback is set, then libev will expect it to remedy the situation, no	315	callback is set, then libev will expect it to remedy the situation, no
…		…
390		418
391	If this flag bit is or'ed into the flag value (or the program runs setuid	419	If this flag bit is or'ed into the flag value (or the program runs setuid
392	or setgid) then libev will I<not> look at the environment variable	420	or setgid) then libev will I<not> look at the environment variable
393	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	421	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
394	override the flags completely if it is found in the environment. This is	422	override the flags completely if it is found in the environment. This is
395	useful to try out specific backends to test their performance, or to work	423	useful to try out specific backends to test their performance, to work
396	around bugs.	424	around bugs, or to make libev threadsafe (accessing environment variables
		425	cannot be done in a threadsafe way, but usually it works if no other
		426	thread modifies them).
397		427
398	=item C<EVFLAG_FORKCHECK>	428	=item C<EVFLAG_FORKCHECK>
399		429
400	Instead of calling C<ev_loop_fork> manually after a fork, you can also	430	Instead of calling C<ev_loop_fork> manually after a fork, you can also
401	make libev check for a fork in each iteration by enabling this flag.	431	make libev check for a fork in each iteration by enabling this flag.
402		432
403	This works by calling C<getpid ()> on every iteration of the loop,	433	This works by calling C<getpid ()> on every iteration of the loop,
404	and thus this might slow down your event loop if you do a lot of loop	434	and thus this might slow down your event loop if you do a lot of loop
405	iterations and little real work, but is usually not noticeable (on my	435	iterations and little real work, but is usually not noticeable (on my
406	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	436	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
407	without a system call and thus I<very> fast, but my GNU/Linux system also has	437	sequence without a system call and thus I<very> fast, but my GNU/Linux
408	C<pthread_atfork> which is even faster).	438	system also has C<pthread_atfork> which is even faster). (Update: glibc
		439	versions 2.25 apparently removed the C<getpid> optimisation again).
409		440
410	The big advantage of this flag is that you can forget about fork (and	441	The big advantage of this flag is that you can forget about fork (and
411	forget about forgetting to tell libev about forking) when you use this	442	forget about forgetting to tell libev about forking, although you still
412	flag.	443	have to ignore C<SIGPIPE>) when you use this flag.
413		444
414	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	445	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
415	environment variable.	446	environment variable.
416		447
417	=item C<EVFLAG_NOINOTIFY>	448	=item C<EVFLAG_NOINOTIFY>
…		…
435	example) that can't properly initialise their signal masks.	466	example) that can't properly initialise their signal masks.
436		467
437	=item C<EVFLAG_NOSIGMASK>	468	=item C<EVFLAG_NOSIGMASK>
438		469
439	When this flag is specified, then libev will avoid to modify the signal	470	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	471	mask. Specifically, this means you have to make sure signals are unblocked
441	when you want to receive them.	472	when you want to receive them.
442		473
443	This behaviour is useful when you want to do your own signal handling, or	474	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	475	want to handle signals only in specific threads and want to avoid libev
445	unblocking the signals.	476	unblocking the signals.
		477
		478	It's also required by POSIX in a threaded program, as libev calls
		479	C<sigprocmask>, whose behaviour is officially unspecified.
446		480
447	This flag's behaviour will become the default in future versions of libev.	481	This flag's behaviour will become the default in future versions of libev.
448		482
449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	483	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
450		484
…		…
480	=item C<EVBACKEND_EPOLL> (value 4, Linux)	514	=item C<EVBACKEND_EPOLL> (value 4, Linux)
481		515
482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	516	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
483	kernels).	517	kernels).
484		518
485	For few fds, this backend is a bit little slower than poll and select,	519	For few fds, this backend is a bit little slower than poll and select, but
486	but it scales phenomenally better. While poll and select usually scale	520	it scales phenomenally better. While poll and select usually scale like
487	like O(total_fds) where n is the total number of fds (or the highest fd),	521	O(total_fds) where total_fds is the total number of fds (or the highest
488	epoll scales either O(1) or O(active_fds).	522	fd), epoll scales either O(1) or O(active_fds).
489		523
490	The epoll mechanism deserves honorable mention as the most misdesigned	524	The epoll mechanism deserves honorable mention as the most misdesigned
491	of the more advanced event mechanisms: mere annoyances include silently	525	of the more advanced event mechanisms: mere annoyances include silently
492	dropping file descriptors, requiring a system call per change per file	526	dropping file descriptors, requiring a system call per change per file
493	descriptor (and unnecessary guessing of parameters), problems with dup,	527	descriptor (and unnecessary guessing of parameters), problems with dup,
…		…
496	0.1ms) and so on. The biggest issue is fork races, however - if a program	530	0.1ms) and so on. The biggest issue is fork races, however - if a program
497	forks then I<both> parent and child process have to recreate the epoll	531	forks then I<both> parent and child process have to recreate the epoll
498	set, which can take considerable time (one syscall per file descriptor)	532	set, which can take considerable time (one syscall per file descriptor)
499	and is of course hard to detect.	533	and is of course hard to detect.
500		534
501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	535	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
502	of course I<doesn't>, and epoll just loves to report events for totally	536	but of course I<doesn't>, and epoll just loves to report events for
503	I<different> file descriptors (even already closed ones, so one cannot	537	totally I<different> file descriptors (even already closed ones, so
504	even remove them from the set) than registered in the set (especially	538	one cannot even remove them from the set) than registered in the set
505	on SMP systems). Libev tries to counter these spurious notifications by	539	(especially on SMP systems). Libev tries to counter these spurious
506	employing an additional generation counter and comparing that against the	540	notifications by employing an additional generation counter and comparing
507	events to filter out spurious ones, recreating the set when required. Last	541	that against the events to filter out spurious ones, recreating the set
		542	when required. Epoll also erroneously rounds down timeouts, but gives you
		543	no way to know when and by how much, so sometimes you have to busy-wait
		544	because epoll returns immediately despite a nonzero timeout. And last
508	not least, it also refuses to work with some file descriptors which work	545	not least, it also refuses to work with some file descriptors which work
509	perfectly fine with C<select> (files, many character devices...).	546	perfectly fine with C<select> (files, many character devices...).
510		547
511	Epoll is truly the train wreck analog among event poll mechanisms.	548	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		549	cobbled together in a hurry, no thought to design or interaction with
		550	others. Oh, the pain, will it ever stop...
512		551
513	While stopping, setting and starting an I/O watcher in the same iteration	552	While stopping, setting and starting an I/O watcher in the same iteration
514	will result in some caching, there is still a system call per such	553	will result in some caching, there is still a system call per such
515	incident (because the same I<file descriptor> could point to a different	554	incident (because the same I<file descriptor> could point to a different
516	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	555	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
553		592
554	It scales in the same way as the epoll backend, but the interface to the	593	It scales in the same way as the epoll backend, but the interface to the
555	kernel is more efficient (which says nothing about its actual speed, of	594	kernel is more efficient (which says nothing about its actual speed, of
556	course). While stopping, setting and starting an I/O watcher does never	595	course). While stopping, setting and starting an I/O watcher does never
557	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	596	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
558	two event changes per incident. Support for C<fork ()> is very bad (but	597	two event changes per incident. Support for C<fork ()> is very bad (you
559	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	598	might have to leak fd's on fork, but it's more sane than epoll) and it
560	cases	599	drops fds silently in similarly hard-to-detect cases.
561		600
562	This backend usually performs well under most conditions.	601	This backend usually performs well under most conditions.
563		602
564	While nominally embeddable in other event loops, this doesn't work	603	While nominally embeddable in other event loops, this doesn't work
565	everywhere, so you might need to test for this. And since it is broken	604	everywhere, so you might need to test for this. And since it is broken
…		…
594	among the OS-specific backends (I vastly prefer correctness over speed	633	among the OS-specific backends (I vastly prefer correctness over speed
595	hacks).	634	hacks).
596		635
597	On the negative side, the interface is I<bizarre> - so bizarre that	636	On the negative side, the interface is I<bizarre> - so bizarre that
598	even sun itself gets it wrong in their code examples: The event polling	637	even sun itself gets it wrong in their code examples: The event polling
599	function sometimes returning events to the caller even though an error	638	function sometimes returns events to the caller even though an error
600	occurred, but with no indication whether it has done so or not (yes, it's	639	occurred, but with no indication whether it has done so or not (yes, it's
601	even documented that way) - deadly for edge-triggered interfaces where	640	even documented that way) - deadly for edge-triggered interfaces where you
602	you absolutely have to know whether an event occurred or not because you	641	absolutely have to know whether an event occurred or not because you have
603	have to re-arm the watcher.	642	to re-arm the watcher.
604		643
605	Fortunately libev seems to be able to work around these idiocies.	644	Fortunately libev seems to be able to work around these idiocies.
606		645
607	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	646	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
608	C<EVBACKEND_POLL>.	647	C<EVBACKEND_POLL>.
…		…
664	If you need dynamically allocated loops it is better to use C<ev_loop_new>	703	If you need dynamically allocated loops it is better to use C<ev_loop_new>
665	and C<ev_loop_destroy>.	704	and C<ev_loop_destroy>.
666		705
667	=item ev_loop_fork (loop)	706	=item ev_loop_fork (loop)
668		707
669	This function sets a flag that causes subsequent C<ev_run> iterations to	708	This function sets a flag that causes subsequent C<ev_run> iterations
670	reinitialise the kernel state for backends that have one. Despite the	709	to reinitialise the kernel state for backends that have one. Despite
671	name, you can call it anytime, but it makes most sense after forking, in	710	the name, you can call it anytime you are allowed to start or stop
672	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the	711	watchers (except inside an C<ev_prepare> callback), but it makes most
		712	sense after forking, in the child process. You I<must> call it (or use
673	child before resuming or calling C<ev_run>.	713	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
674		714
		715	In addition, if you want to reuse a loop (via this function or
		716	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		717
675	Again, you I<have> to call it on I<any> loop that you want to re-use after	718	Again, you I<have> to call it on I<any> loop that you want to re-use after
676	a fork, I<even if you do not plan to use the loop in the parent>. This is	719	a fork, I<even if you do not plan to use the loop in the parent>. This is
677	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	720	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
678	during fork.	721	during fork.
679		722
680	On the other hand, you only need to call this function in the child	723	On the other hand, you only need to call this function in the child
…		…
750		793
751	This function is rarely useful, but when some event callback runs for a	794	This function is rarely useful, but when some event callback runs for a
752	very long time without entering the event loop, updating libev's idea of	795	very long time without entering the event loop, updating libev's idea of
753	the current time is a good idea.	796	the current time is a good idea.
754		797
755	See also L<The special problem of time updates> in the C<ev_timer> section.	798	See also L</The special problem of time updates> in the C<ev_timer> section.
756		799
757	=item ev_suspend (loop)	800	=item ev_suspend (loop)
758		801
759	=item ev_resume (loop)	802	=item ev_resume (loop)
760		803
…		…
778	without a previous call to C<ev_suspend>.	821	without a previous call to C<ev_suspend>.
779		822
780	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	823	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
781	event loop time (see C<ev_now_update>).	824	event loop time (see C<ev_now_update>).
782		825
783	=item ev_run (loop, int flags)	826	=item bool ev_run (loop, int flags)
784		827
785	Finally, this is it, the event handler. This function usually is called	828	Finally, this is it, the event handler. This function usually is called
786	after you have initialised all your watchers and you want to start	829	after you have initialised all your watchers and you want to start
787	handling events. It will ask the operating system for any new events, call	830	handling events. It will ask the operating system for any new events, call
788	the watcher callbacks, an then repeat the whole process indefinitely: This	831	the watcher callbacks, and then repeat the whole process indefinitely: This
789	is why event loops are called I<loops>.	832	is why event loops are called I<loops>.
790		833
791	If the flags argument is specified as C<0>, it will keep handling events	834	If the flags argument is specified as C<0>, it will keep handling events
792	until either no event watchers are active anymore or C<ev_break> was	835	until either no event watchers are active anymore or C<ev_break> was
793	called.	836	called.
		837
		838	The return value is false if there are no more active watchers (which
		839	usually means "all jobs done" or "deadlock"), and true in all other cases
		840	(which usually means " you should call C<ev_run> again").
794		841
795	Please note that an explicit C<ev_break> is usually better than	842	Please note that an explicit C<ev_break> is usually better than
796	relying on all watchers to be stopped when deciding when a program has	843	relying on all watchers to be stopped when deciding when a program has
797	finished (especially in interactive programs), but having a program	844	finished (especially in interactive programs), but having a program
798	that automatically loops as long as it has to and no longer by virtue	845	that automatically loops as long as it has to and no longer by virtue
799	of relying on its watchers stopping correctly, that is truly a thing of	846	of relying on its watchers stopping correctly, that is truly a thing of
800	beauty.	847	beauty.
801		848
802	This function is also I<mostly> exception-safe - you can break out of	849	This function is I<mostly> exception-safe - you can break out of a
803	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++	850	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
804	exception and so on. This does not decrement the C<ev_depth> value, nor	851	exception and so on. This does not decrement the C<ev_depth> value, nor
805	will it clear any outstanding C<EVBREAK_ONE> breaks.	852	will it clear any outstanding C<EVBREAK_ONE> breaks.
806		853
807	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	854	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
808	those events and any already outstanding ones, but will not wait and	855	those events and any already outstanding ones, but will not wait and
…		…
820	This is useful if you are waiting for some external event in conjunction	867	This is useful if you are waiting for some external event in conjunction
821	with something not expressible using other libev watchers (i.e. "roll your	868	with something not expressible using other libev watchers (i.e. "roll your
822	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	869	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
823	usually a better approach for this kind of thing.	870	usually a better approach for this kind of thing.
824		871
825	Here are the gory details of what C<ev_run> does:	872	Here are the gory details of what C<ev_run> does (this is for your
		873	understanding, not a guarantee that things will work exactly like this in
		874	future versions):
826		875
827	- Increment loop depth.	876	- Increment loop depth.
828	- Reset the ev_break status.	877	- Reset the ev_break status.
829	- Before the first iteration, call any pending watchers.	878	- Before the first iteration, call any pending watchers.
830	LOOP:	879	LOOP:
…		…
863	anymore.	912	anymore.
864		913
865	... queue jobs here, make sure they register event watchers as long	914	... queue jobs here, make sure they register event watchers as long
866	... as they still have work to do (even an idle watcher will do..)	915	... as they still have work to do (even an idle watcher will do..)
867	ev_run (my_loop, 0);	916	ev_run (my_loop, 0);
868	... jobs done or somebody called unloop. yeah!	917	... jobs done or somebody called break. yeah!
869		918
870	=item ev_break (loop, how)	919	=item ev_break (loop, how)
871		920
872	Can be used to make a call to C<ev_run> return early (but only after it	921	Can be used to make a call to C<ev_run> return early (but only after it
873	has processed all outstanding events). The C<how> argument must be either	922	has processed all outstanding events). The C<how> argument must be either
…		…
936	overhead for the actual polling but can deliver many events at once.	985	overhead for the actual polling but can deliver many events at once.
937		986
938	By setting a higher I<io collect interval> you allow libev to spend more	987	By setting a higher I<io collect interval> you allow libev to spend more
939	time collecting I/O events, so you can handle more events per iteration,	988	time collecting I/O events, so you can handle more events per iteration,
940	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	989	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
941	C<ev_timer>) will be not affected. Setting this to a non-null value will	990	C<ev_timer>) will not be affected. Setting this to a non-null value will
942	introduce an additional C<ev_sleep ()> call into most loop iterations. The	991	introduce an additional C<ev_sleep ()> call into most loop iterations. The
943	sleep time ensures that libev will not poll for I/O events more often then	992	sleep time ensures that libev will not poll for I/O events more often then
944	once per this interval, on average.	993	once per this interval, on average (as long as the host time resolution is
		994	good enough).
945		995
946	Likewise, by setting a higher I<timeout collect interval> you allow libev	996	Likewise, by setting a higher I<timeout collect interval> you allow libev
947	to spend more time collecting timeouts, at the expense of increased	997	to spend more time collecting timeouts, at the expense of increased
948	latency/jitter/inexactness (the watcher callback will be called	998	latency/jitter/inexactness (the watcher callback will be called
949	later). C<ev_io> watchers will not be affected. Setting this to a non-null	999	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
995	invoke the actual watchers inside another context (another thread etc.).	1045	invoke the actual watchers inside another context (another thread etc.).
996		1046
997	If you want to reset the callback, use C<ev_invoke_pending> as new	1047	If you want to reset the callback, use C<ev_invoke_pending> as new
998	callback.	1048	callback.
999		1049
1000	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1050	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
1001		1051
1002	Sometimes you want to share the same loop between multiple threads. This	1052	Sometimes you want to share the same loop between multiple threads. This
1003	can be done relatively simply by putting mutex_lock/unlock calls around	1053	can be done relatively simply by putting mutex_lock/unlock calls around
1004	each call to a libev function.	1054	each call to a libev function.
1005		1055
1006	However, C<ev_run> can run an indefinite time, so it is not feasible	1056	However, C<ev_run> can run an indefinite time, so it is not feasible
1007	to wait for it to return. One way around this is to wake up the event	1057	to wait for it to return. One way around this is to wake up the event
1008	loop via C<ev_break> and C<av_async_send>, another way is to set these	1058	loop via C<ev_break> and C<ev_async_send>, another way is to set these
1009	I<release> and I<acquire> callbacks on the loop.	1059	I<release> and I<acquire> callbacks on the loop.
1010		1060
1011	When set, then C<release> will be called just before the thread is	1061	When set, then C<release> will be called just before the thread is
1012	suspended waiting for new events, and C<acquire> is called just	1062	suspended waiting for new events, and C<acquire> is called just
1013	afterwards.	1063	afterwards.
…		…
1153		1203
1154	=item C<EV_PREPARE>	1204	=item C<EV_PREPARE>
1155		1205
1156	=item C<EV_CHECK>	1206	=item C<EV_CHECK>
1157		1207
1158	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1208	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1159	to gather new events, and all C<ev_check> watchers are invoked just after	1209	gather new events, and all C<ev_check> watchers are queued (not invoked)
1160	C<ev_run> has gathered them, but before it invokes any callbacks for any	1210	just after C<ev_run> has gathered them, but before it queues any callbacks
		1211	for any received events. That means C<ev_prepare> watchers are the last
		1212	watchers invoked before the event loop sleeps or polls for new events, and
		1213	C<ev_check> watchers will be invoked before any other watchers of the same
		1214	or lower priority within an event loop iteration.
		1215
1161	received events. Callbacks of both watcher types can start and stop as	1216	Callbacks of both watcher types can start and stop as many watchers as
1162	many watchers as they want, and all of them will be taken into account	1217	they want, and all of them will be taken into account (for example, a
1163	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1218	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1164	C<ev_run> from blocking).	1219	blocking).
1165		1220
1166	=item C<EV_EMBED>	1221	=item C<EV_EMBED>
1167		1222
1168	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1223	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1169		1224
…		…
1292		1347
1293	=item callback ev_cb (ev_TYPE *watcher)	1348	=item callback ev_cb (ev_TYPE *watcher)
1294		1349
1295	Returns the callback currently set on the watcher.	1350	Returns the callback currently set on the watcher.
1296		1351
1297	=item ev_cb_set (ev_TYPE *watcher, callback)	1352	=item ev_set_cb (ev_TYPE *watcher, callback)
1298		1353
1299	Change the callback. You can change the callback at virtually any time	1354	Change the callback. You can change the callback at virtually any time
1300	(modulo threads).	1355	(modulo threads).
1301		1356
1302	=item ev_set_priority (ev_TYPE *watcher, int priority)	1357	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1320	or might not have been clamped to the valid range.	1375	or might not have been clamped to the valid range.
1321		1376
1322	The default priority used by watchers when no priority has been set is	1377	The default priority used by watchers when no priority has been set is
1323	always C<0>, which is supposed to not be too high and not be too low :).	1378	always C<0>, which is supposed to not be too high and not be too low :).
1324		1379
1325	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1380	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1326	priorities.	1381	priorities.
1327		1382
1328	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1383	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1329		1384
1330	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1385	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1355	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1410	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1356	functions that do not need a watcher.	1411	functions that do not need a watcher.
1357		1412
1358	=back	1413	=back
1359		1414
1360	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1415	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1361		1416	OWN COMPOSITE WATCHERS> idioms.
1362	Each watcher has, by default, a member C<void *data> that you can change
1363	and read at any time: libev will completely ignore it. This can be used
1364	to associate arbitrary data with your watcher. If you need more data and
1365	don't want to allocate memory and store a pointer to it in that data
1366	member, you can also "subclass" the watcher type and provide your own
1367	data:
1368
1369	struct my_io
1370	{
1371	ev_io io;
1372	int otherfd;
1373	void *somedata;
1374	struct whatever *mostinteresting;
1375	};
1376
1377	...
1378	struct my_io w;
1379	ev_io_init (&w.io, my_cb, fd, EV_READ);
1380
1381	And since your callback will be called with a pointer to the watcher, you
1382	can cast it back to your own type:
1383
1384	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1385	{
1386	struct my_io *w = (struct my_io *)w_;
1387	...
1388	}
1389
1390	More interesting and less C-conformant ways of casting your callback type
1391	instead have been omitted.
1392
1393	Another common scenario is to use some data structure with multiple
1394	embedded watchers:
1395
1396	struct my_biggy
1397	{
1398	int some_data;
1399	ev_timer t1;
1400	ev_timer t2;
1401	}
1402
1403	In this case getting the pointer to C<my_biggy> is a bit more
1404	complicated: Either you store the address of your C<my_biggy> struct
1405	in the C<data> member of the watcher (for woozies), or you need to use
1406	some pointer arithmetic using C<offsetof> inside your watchers (for real
1407	programmers):
1408
1409	#include <stddef.h>
1410
1411	static void
1412	t1_cb (EV_P_ ev_timer *w, int revents)
1413	{
1414	struct my_biggy big = (struct my_biggy *)
1415	(((char *)w) - offsetof (struct my_biggy, t1));
1416	}
1417
1418	static void
1419	t2_cb (EV_P_ ev_timer *w, int revents)
1420	{
1421	struct my_biggy big = (struct my_biggy *)
1422	(((char *)w) - offsetof (struct my_biggy, t2));
1423	}
1424		1417
1425	=head2 WATCHER STATES	1418	=head2 WATCHER STATES
1426		1419
1427	There are various watcher states mentioned throughout this manual -	1420	There are various watcher states mentioned throughout this manual -
1428	active, pending and so on. In this section these states and the rules to	1421	active, pending and so on. In this section these states and the rules to
1429	transition between them will be described in more detail - and while these	1422	transition between them will be described in more detail - and while these
1430	rules might look complicated, they usually do "the right thing".	1423	rules might look complicated, they usually do "the right thing".
1431		1424
1432	=over 4	1425	=over 4
1433		1426
1434	=item initialiased	1427	=item initialised
1435		1428
1436	Before a watcher can be registered with the event looop it has to be	1429	Before a watcher can be registered with the event loop it has to be
1437	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1430	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1438	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1431	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1439		1432
1440	In this state it is simply some block of memory that is suitable for use	1433	In this state it is simply some block of memory that is suitable for
1441	in an event loop. It can be moved around, freed, reused etc. at will.	1434	use in an event loop. It can be moved around, freed, reused etc. at
		1435	will - as long as you either keep the memory contents intact, or call
		1436	C<ev_TYPE_init> again.
1442		1437
1443	=item started/running/active	1438	=item started/running/active
1444		1439
1445	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1440	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1446	property of the event loop, and is actively waiting for events. While in	1441	property of the event loop, and is actively waiting for events. While in
…		…
1474	latter will clear any pending state the watcher might be in, regardless	1469	latter will clear any pending state the watcher might be in, regardless
1475	of whether it was active or not, so stopping a watcher explicitly before	1470	of whether it was active or not, so stopping a watcher explicitly before
1476	freeing it is often a good idea.	1471	freeing it is often a good idea.
1477		1472
1478	While stopped (and not pending) the watcher is essentially in the	1473	While stopped (and not pending) the watcher is essentially in the
1479	initialised state, that is it can be reused, moved, modified in any way	1474	initialised state, that is, it can be reused, moved, modified in any way
1480	you wish.	1475	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1476	it again).
1481		1477
1482	=back	1478	=back
1483		1479
1484	=head2 WATCHER PRIORITY MODELS	1480	=head2 WATCHER PRIORITY MODELS
1485		1481
…		…
1614	In general you can register as many read and/or write event watchers per	1610	In general you can register as many read and/or write event watchers per
1615	fd as you want (as long as you don't confuse yourself). Setting all file	1611	fd as you want (as long as you don't confuse yourself). Setting all file
1616	descriptors to non-blocking mode is also usually a good idea (but not	1612	descriptors to non-blocking mode is also usually a good idea (but not
1617	required if you know what you are doing).	1613	required if you know what you are doing).
1618		1614
1619	If you cannot use non-blocking mode, then force the use of a
1620	known-to-be-good backend (at the time of this writing, this includes only
1621	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1622	descriptors for which non-blocking operation makes no sense (such as
1623	files) - libev doesn't guarantee any specific behaviour in that case.
1624
1625	Another thing you have to watch out for is that it is quite easy to	1615	Another thing you have to watch out for is that it is quite easy to
1626	receive "spurious" readiness notifications, that is your callback might	1616	receive "spurious" readiness notifications, that is, your callback might
1627	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1617	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1628	because there is no data. Not only are some backends known to create a	1618	because there is no data. It is very easy to get into this situation even
1629	lot of those (for example Solaris ports), it is very easy to get into	1619	with a relatively standard program structure. Thus it is best to always
1630	this situation even with a relatively standard program structure. Thus	1620	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1631	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1632	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1621	preferable to a program hanging until some data arrives.
1633		1622
1634	If you cannot run the fd in non-blocking mode (for example you should	1623	If you cannot run the fd in non-blocking mode (for example you should
1635	not play around with an Xlib connection), then you have to separately	1624	not play around with an Xlib connection), then you have to separately
1636	re-test whether a file descriptor is really ready with a known-to-be good	1625	re-test whether a file descriptor is really ready with a known-to-be good
1637	interface such as poll (fortunately in our Xlib example, Xlib already	1626	interface such as poll (fortunately in the case of Xlib, it already does
1638	does this on its own, so its quite safe to use). Some people additionally	1627	this on its own, so its quite safe to use). Some people additionally
1639	use C<SIGALRM> and an interval timer, just to be sure you won't block	1628	use C<SIGALRM> and an interval timer, just to be sure you won't block
1640	indefinitely.	1629	indefinitely.
1641		1630
1642	But really, best use non-blocking mode.	1631	But really, best use non-blocking mode.
1643		1632
…		…
1671		1660
1672	There is no workaround possible except not registering events	1661	There is no workaround possible except not registering events
1673	for potentially C<dup ()>'ed file descriptors, or to resort to	1662	for potentially C<dup ()>'ed file descriptors, or to resort to
1674	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1663	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1675		1664
		1665	=head3 The special problem of files
		1666
		1667	Many people try to use C<select> (or libev) on file descriptors
		1668	representing files, and expect it to become ready when their program
		1669	doesn't block on disk accesses (which can take a long time on their own).
		1670
		1671	However, this cannot ever work in the "expected" way - you get a readiness
		1672	notification as soon as the kernel knows whether and how much data is
		1673	there, and in the case of open files, that's always the case, so you
		1674	always get a readiness notification instantly, and your read (or possibly
		1675	write) will still block on the disk I/O.
		1676
		1677	Another way to view it is that in the case of sockets, pipes, character
		1678	devices and so on, there is another party (the sender) that delivers data
		1679	on its own, but in the case of files, there is no such thing: the disk
		1680	will not send data on its own, simply because it doesn't know what you
		1681	wish to read - you would first have to request some data.
		1682
		1683	Since files are typically not-so-well supported by advanced notification
		1684	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1685	to files, even though you should not use it. The reason for this is
		1686	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1687	usually a tty, often a pipe, but also sometimes files or special devices
		1688	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1689	F</dev/urandom>), and even though the file might better be served with
		1690	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1691	it "just works" instead of freezing.
		1692
		1693	So avoid file descriptors pointing to files when you know it (e.g. use
		1694	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1695	when you rarely read from a file instead of from a socket, and want to
		1696	reuse the same code path.
		1697
1676	=head3 The special problem of fork	1698	=head3 The special problem of fork
1677		1699
1678	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1700	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1679	useless behaviour. Libev fully supports fork, but needs to be told about	1701	useless behaviour. Libev fully supports fork, but needs to be told about
1680	it in the child.	1702	it in the child if you want to continue to use it in the child.
1681		1703
1682	To support fork in your programs, you either have to call	1704	To support fork in your child processes, you have to call C<ev_loop_fork
1683	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1705	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1684	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1706	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1685	C<EVBACKEND_POLL>.
1686		1707
1687	=head3 The special problem of SIGPIPE	1708	=head3 The special problem of SIGPIPE
1688		1709
1689	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1710	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1690	when writing to a pipe whose other end has been closed, your program gets	1711	when writing to a pipe whose other end has been closed, your program gets
…		…
1788	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1809	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1789	monotonic clock option helps a lot here).	1810	monotonic clock option helps a lot here).
1790		1811
1791	The callback is guaranteed to be invoked only I<after> its timeout has	1812	The callback is guaranteed to be invoked only I<after> its timeout has
1792	passed (not I<at>, so on systems with very low-resolution clocks this	1813	passed (not I<at>, so on systems with very low-resolution clocks this
1793	might introduce a small delay). If multiple timers become ready during the	1814	might introduce a small delay, see "the special problem of being too
		1815	early", below). If multiple timers become ready during the same loop
1794	same loop iteration then the ones with earlier time-out values are invoked	1816	iteration then the ones with earlier time-out values are invoked before
1795	before ones of the same priority with later time-out values (but this is	1817	ones of the same priority with later time-out values (but this is no
1796	no longer true when a callback calls C<ev_run> recursively).	1818	longer true when a callback calls C<ev_run> recursively).
1797		1819
1798	=head3 Be smart about timeouts	1820	=head3 Be smart about timeouts
1799		1821
1800	Many real-world problems involve some kind of timeout, usually for error	1822	Many real-world problems involve some kind of timeout, usually for error
1801	recovery. A typical example is an HTTP request - if the other side hangs,	1823	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1876		1898
1877	In this case, it would be more efficient to leave the C<ev_timer> alone,	1899	In this case, it would be more efficient to leave the C<ev_timer> alone,
1878	but remember the time of last activity, and check for a real timeout only	1900	but remember the time of last activity, and check for a real timeout only
1879	within the callback:	1901	within the callback:
1880		1902
		1903	ev_tstamp timeout = 60.;
1881	ev_tstamp last_activity; // time of last activity	1904	ev_tstamp last_activity; // time of last activity
		1905	ev_timer timer;
1882		1906
1883	static void	1907	static void
1884	callback (EV_P_ ev_timer *w, int revents)	1908	callback (EV_P_ ev_timer *w, int revents)
1885	{	1909	{
1886	ev_tstamp now = ev_now (EV_A);	1910	// calculate when the timeout would happen
1887	ev_tstamp timeout = last_activity + 60.;	1911	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1888		1912
1889	// if last_activity + 60. is older than now, we did time out	1913	// if negative, it means we the timeout already occurred
1890	if (timeout < now)	1914	if (after < 0.)
1891	{	1915	{
1892	// timeout occurred, take action	1916	// timeout occurred, take action
1893	}	1917	}
1894	else	1918	else
1895	{	1919	{
1896	// callback was invoked, but there was some activity, re-arm	1920	// callback was invoked, but there was some recent
1897	// the watcher to fire in last_activity + 60, which is	1921	// activity. simply restart the timer to time out
1898	// guaranteed to be in the future, so "again" is positive:	1922	// after "after" seconds, which is the earliest time
1899	w->repeat = timeout - now;	1923	// the timeout can occur.
		1924	ev_timer_set (w, after, 0.);
1900	ev_timer_again (EV_A_ w);	1925	ev_timer_start (EV_A_ w);
1901	}	1926	}
1902	}	1927	}
1903		1928
1904	To summarise the callback: first calculate the real timeout (defined	1929	To summarise the callback: first calculate in how many seconds the
1905	as "60 seconds after the last activity"), then check if that time has	1930	timeout will occur (by calculating the absolute time when it would occur,
1906	been reached, which means something I<did>, in fact, time out. Otherwise	1931	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1907	the callback was invoked too early (C<timeout> is in the future), so	1932	(EV_A)> from that).
1908	re-schedule the timer to fire at that future time, to see if maybe we have
1909	a timeout then.
1910		1933
1911	Note how C<ev_timer_again> is used, taking advantage of the	1934	If this value is negative, then we are already past the timeout, i.e. we
1912	C<ev_timer_again> optimisation when the timer is already running.	1935	timed out, and need to do whatever is needed in this case.
		1936
		1937	Otherwise, we now the earliest time at which the timeout would trigger,
		1938	and simply start the timer with this timeout value.
		1939
		1940	In other words, each time the callback is invoked it will check whether
		1941	the timeout occurred. If not, it will simply reschedule itself to check
		1942	again at the earliest time it could time out. Rinse. Repeat.
1913		1943
1914	This scheme causes more callback invocations (about one every 60 seconds	1944	This scheme causes more callback invocations (about one every 60 seconds
1915	minus half the average time between activity), but virtually no calls to	1945	minus half the average time between activity), but virtually no calls to
1916	libev to change the timeout.	1946	libev to change the timeout.
1917		1947
1918	To start the timer, simply initialise the watcher and set C<last_activity>	1948	To start the machinery, simply initialise the watcher and set
1919	to the current time (meaning we just have some activity :), then call the	1949	C<last_activity> to the current time (meaning there was some activity just
1920	callback, which will "do the right thing" and start the timer:	1950	now), then call the callback, which will "do the right thing" and start
		1951	the timer:
1921		1952
		1953	last_activity = ev_now (EV_A);
1922	ev_init (timer, callback);	1954	ev_init (&timer, callback);
1923	last_activity = ev_now (loop);	1955	callback (EV_A_ &timer, 0);
1924	callback (loop, timer, EV_TIMER);
1925		1956
1926	And when there is some activity, simply store the current time in	1957	When there is some activity, simply store the current time in
1927	C<last_activity>, no libev calls at all:	1958	C<last_activity>, no libev calls at all:
1928		1959
		1960	if (activity detected)
1929	last_activity = ev_now (loop);	1961	last_activity = ev_now (EV_A);
		1962
		1963	When your timeout value changes, then the timeout can be changed by simply
		1964	providing a new value, stopping the timer and calling the callback, which
		1965	will again do the right thing (for example, time out immediately :).
		1966
		1967	timeout = new_value;
		1968	ev_timer_stop (EV_A_ &timer);
		1969	callback (EV_A_ &timer, 0);
1930		1970
1931	This technique is slightly more complex, but in most cases where the	1971	This technique is slightly more complex, but in most cases where the
1932	time-out is unlikely to be triggered, much more efficient.	1972	time-out is unlikely to be triggered, much more efficient.
1933
1934	Changing the timeout is trivial as well (if it isn't hard-coded in the
1935	callback :) - just change the timeout and invoke the callback, which will
1936	fix things for you.
1937		1973
1938	=item 4. Wee, just use a double-linked list for your timeouts.	1974	=item 4. Wee, just use a double-linked list for your timeouts.
1939		1975
1940	If there is not one request, but many thousands (millions...), all	1976	If there is not one request, but many thousands (millions...), all
1941	employing some kind of timeout with the same timeout value, then one can	1977	employing some kind of timeout with the same timeout value, then one can
…		…
1968	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2004	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1969	rather complicated, but extremely efficient, something that really pays	2005	rather complicated, but extremely efficient, something that really pays
1970	off after the first million or so of active timers, i.e. it's usually	2006	off after the first million or so of active timers, i.e. it's usually
1971	overkill :)	2007	overkill :)
1972		2008
		2009	=head3 The special problem of being too early
		2010
		2011	If you ask a timer to call your callback after three seconds, then
		2012	you expect it to be invoked after three seconds - but of course, this
		2013	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2014	guaranteed to any precision by libev - imagine somebody suspending the
		2015	process with a STOP signal for a few hours for example.
		2016
		2017	So, libev tries to invoke your callback as soon as possible I<after> the
		2018	delay has occurred, but cannot guarantee this.
		2019
		2020	A less obvious failure mode is calling your callback too early: many event
		2021	loops compare timestamps with a "elapsed delay >= requested delay", but
		2022	this can cause your callback to be invoked much earlier than you would
		2023	expect.
		2024
		2025	To see why, imagine a system with a clock that only offers full second
		2026	resolution (think windows if you can't come up with a broken enough OS
		2027	yourself). If you schedule a one-second timer at the time 500.9, then the
		2028	event loop will schedule your timeout to elapse at a system time of 500
		2029	(500.9 truncated to the resolution) + 1, or 501.
		2030
		2031	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2032	501" and invoke the callback 0.1s after it was started, even though a
		2033	one-second delay was requested - this is being "too early", despite best
		2034	intentions.
		2035
		2036	This is the reason why libev will never invoke the callback if the elapsed
		2037	delay equals the requested delay, but only when the elapsed delay is
		2038	larger than the requested delay. In the example above, libev would only invoke
		2039	the callback at system time 502, or 1.1s after the timer was started.
		2040
		2041	So, while libev cannot guarantee that your callback will be invoked
		2042	exactly when requested, it I<can> and I<does> guarantee that the requested
		2043	delay has actually elapsed, or in other words, it always errs on the "too
		2044	late" side of things.
		2045
1973	=head3 The special problem of time updates	2046	=head3 The special problem of time updates
1974		2047
1975	Establishing the current time is a costly operation (it usually takes at	2048	Establishing the current time is a costly operation (it usually takes
1976	least two system calls): EV therefore updates its idea of the current	2049	at least one system call): EV therefore updates its idea of the current
1977	time only before and after C<ev_run> collects new events, which causes a	2050	time only before and after C<ev_run> collects new events, which causes a
1978	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2051	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1979	lots of events in one iteration.	2052	lots of events in one iteration.
1980		2053
1981	The relative timeouts are calculated relative to the C<ev_now ()>	2054	The relative timeouts are calculated relative to the C<ev_now ()>
1982	time. This is usually the right thing as this timestamp refers to the time	2055	time. This is usually the right thing as this timestamp refers to the time
1983	of the event triggering whatever timeout you are modifying/starting. If	2056	of the event triggering whatever timeout you are modifying/starting. If
1984	you suspect event processing to be delayed and you I<need> to base the	2057	you suspect event processing to be delayed and you I<need> to base the
1985	timeout on the current time, use something like this to adjust for this:	2058	timeout on the current time, use something like the following to adjust
		2059	for it:
1986		2060
1987	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2061	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1988		2062
1989	If the event loop is suspended for a long time, you can also force an	2063	If the event loop is suspended for a long time, you can also force an
1990	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2064	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1991	()>.	2065	()>, although that will push the event time of all outstanding events
		2066	further into the future.
		2067
		2068	=head3 The special problem of unsynchronised clocks
		2069
		2070	Modern systems have a variety of clocks - libev itself uses the normal
		2071	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2072	jumps).
		2073
		2074	Neither of these clocks is synchronised with each other or any other clock
		2075	on the system, so C<ev_time ()> might return a considerably different time
		2076	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2077	a call to C<gettimeofday> might return a second count that is one higher
		2078	than a directly following call to C<time>.
		2079
		2080	The moral of this is to only compare libev-related timestamps with
		2081	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2082	a second or so.
		2083
		2084	One more problem arises due to this lack of synchronisation: if libev uses
		2085	the system monotonic clock and you compare timestamps from C<ev_time>
		2086	or C<ev_now> from when you started your timer and when your callback is
		2087	invoked, you will find that sometimes the callback is a bit "early".
		2088
		2089	This is because C<ev_timer>s work in real time, not wall clock time, so
		2090	libev makes sure your callback is not invoked before the delay happened,
		2091	I<measured according to the real time>, not the system clock.
		2092
		2093	If your timeouts are based on a physical timescale (e.g. "time out this
		2094	connection after 100 seconds") then this shouldn't bother you as it is
		2095	exactly the right behaviour.
		2096
		2097	If you want to compare wall clock/system timestamps to your timers, then
		2098	you need to use C<ev_periodic>s, as these are based on the wall clock
		2099	time, where your comparisons will always generate correct results.
1992		2100
1993	=head3 The special problems of suspended animation	2101	=head3 The special problems of suspended animation
1994		2102
1995	When you leave the server world it is quite customary to hit machines that	2103	When you leave the server world it is quite customary to hit machines that
1996	can suspend/hibernate - what happens to the clocks during such a suspend?	2104	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
2026		2134
2027	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2135	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
2028		2136
2029	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2137	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
2030		2138
2031	Configure the timer to trigger after C<after> seconds. If C<repeat>	2139	Configure the timer to trigger after C<after> seconds (fractional and
2032	is C<0.>, then it will automatically be stopped once the timeout is	2140	negative values are supported). If C<repeat> is C<0.>, then it will
2033	reached. If it is positive, then the timer will automatically be	2141	automatically be stopped once the timeout is reached. If it is positive,
2034	configured to trigger again C<repeat> seconds later, again, and again,	2142	then the timer will automatically be configured to trigger again C<repeat>
2035	until stopped manually.	2143	seconds later, again, and again, until stopped manually.
2036		2144
2037	The timer itself will do a best-effort at avoiding drift, that is, if	2145	The timer itself will do a best-effort at avoiding drift, that is, if
2038	you configure a timer to trigger every 10 seconds, then it will normally	2146	you configure a timer to trigger every 10 seconds, then it will normally
2039	trigger at exactly 10 second intervals. If, however, your program cannot	2147	trigger at exactly 10 second intervals. If, however, your program cannot
2040	keep up with the timer (because it takes longer than those 10 seconds to	2148	keep up with the timer (because it takes longer than those 10 seconds to
2041	do stuff) the timer will not fire more than once per event loop iteration.	2149	do stuff) the timer will not fire more than once per event loop iteration.
2042		2150
2043	=item ev_timer_again (loop, ev_timer *)	2151	=item ev_timer_again (loop, ev_timer *)
2044		2152
2045	This will act as if the timer timed out and restart it again if it is	2153	This will act as if the timer timed out, and restarts it again if it is
2046	repeating. The exact semantics are:	2154	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2155	timeout to the C<repeat> value and calling C<ev_timer_start>.
2047		2156
		2157	The exact semantics are as in the following rules, all of which will be
		2158	applied to the watcher:
		2159
		2160	=over 4
		2161
2048	If the timer is pending, its pending status is cleared.	2162	=item If the timer is pending, the pending status is always cleared.
2049		2163
2050	If the timer is started but non-repeating, stop it (as if it timed out).	2164	=item If the timer is started but non-repeating, stop it (as if it timed
		2165	out, without invoking it).
2051		2166
2052	If the timer is repeating, either start it if necessary (with the	2167	=item If the timer is repeating, make the C<repeat> value the new timeout
2053	C<repeat> value), or reset the running timer to the C<repeat> value.	2168	and start the timer, if necessary.
2054		2169
		2170	=back
		2171
2055	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2172	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2056	usage example.	2173	usage example.
2057		2174
2058	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2175	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2059		2176
2060	Returns the remaining time until a timer fires. If the timer is active,	2177	Returns the remaining time until a timer fires. If the timer is active,
…		…
2113	Periodic watchers are also timers of a kind, but they are very versatile	2230	Periodic watchers are also timers of a kind, but they are very versatile
2114	(and unfortunately a bit complex).	2231	(and unfortunately a bit complex).
2115		2232
2116	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2233	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2117	relative time, the physical time that passes) but on wall clock time	2234	relative time, the physical time that passes) but on wall clock time
2118	(absolute time, the thing you can read on your calender or clock). The	2235	(absolute time, the thing you can read on your calendar or clock). The
2119	difference is that wall clock time can run faster or slower than real	2236	difference is that wall clock time can run faster or slower than real
2120	time, and time jumps are not uncommon (e.g. when you adjust your	2237	time, and time jumps are not uncommon (e.g. when you adjust your
2121	wrist-watch).	2238	wrist-watch).
2122		2239
2123	You can tell a periodic watcher to trigger after some specific point	2240	You can tell a periodic watcher to trigger after some specific point
…		…
2128	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2245	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2129	it, as it uses a relative timeout).	2246	it, as it uses a relative timeout).
2130		2247
2131	C<ev_periodic> watchers can also be used to implement vastly more complex	2248	C<ev_periodic> watchers can also be used to implement vastly more complex
2132	timers, such as triggering an event on each "midnight, local time", or	2249	timers, such as triggering an event on each "midnight, local time", or
2133	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2250	other complicated rules. This cannot easily be done with C<ev_timer>
2134	those cannot react to time jumps.	2251	watchers, as those cannot react to time jumps.
2135		2252
2136	As with timers, the callback is guaranteed to be invoked only when the	2253	As with timers, the callback is guaranteed to be invoked only when the
2137	point in time where it is supposed to trigger has passed. If multiple	2254	point in time where it is supposed to trigger has passed. If multiple
2138	timers become ready during the same loop iteration then the ones with	2255	timers become ready during the same loop iteration then the ones with
2139	earlier time-out values are invoked before ones with later time-out values	2256	earlier time-out values are invoked before ones with later time-out values
…		…
2180		2297
2181	Another way to think about it (for the mathematically inclined) is that	2298	Another way to think about it (for the mathematically inclined) is that
2182	C<ev_periodic> will try to run the callback in this mode at the next possible	2299	C<ev_periodic> will try to run the callback in this mode at the next possible
2183	time where C<time = offset (mod interval)>, regardless of any time jumps.	2300	time where C<time = offset (mod interval)>, regardless of any time jumps.
2184		2301
2185	For numerical stability it is preferable that the C<offset> value is near	2302	The C<interval> I<MUST> be positive, and for numerical stability, the
2186	C<ev_now ()> (the current time), but there is no range requirement for	2303	interval value should be higher than C<1/8192> (which is around 100
2187	this value, and in fact is often specified as zero.	2304	microseconds) and C<offset> should be higher than C<0> and should have
		2305	at most a similar magnitude as the current time (say, within a factor of
		2306	ten). Typical values for offset are, in fact, C<0> or something between
		2307	C<0> and C<interval>, which is also the recommended range.
2188		2308
2189	Note also that there is an upper limit to how often a timer can fire (CPU	2309	Note also that there is an upper limit to how often a timer can fire (CPU
2190	speed for example), so if C<interval> is very small then timing stability	2310	speed for example), so if C<interval> is very small then timing stability
2191	will of course deteriorate. Libev itself tries to be exact to be about one	2311	will of course deteriorate. Libev itself tries to be exact to be about one
2192	millisecond (if the OS supports it and the machine is fast enough).	2312	millisecond (if the OS supports it and the machine is fast enough).
…		…
2222		2342
2223	NOTE: I<< This callback must always return a time that is higher than or	2343	NOTE: I<< This callback must always return a time that is higher than or
2224	equal to the passed C<now> value >>.	2344	equal to the passed C<now> value >>.
2225		2345
2226	This can be used to create very complex timers, such as a timer that	2346	This can be used to create very complex timers, such as a timer that
2227	triggers on "next midnight, local time". To do this, you would calculate the	2347	triggers on "next midnight, local time". To do this, you would calculate
2228	next midnight after C<now> and return the timestamp value for this. How	2348	the next midnight after C<now> and return the timestamp value for
2229	you do this is, again, up to you (but it is not trivial, which is the main	2349	this. Here is a (completely untested, no error checking) example on how to
2230	reason I omitted it as an example).	2350	do this:
		2351
		2352	#include <time.h>
		2353
		2354	static ev_tstamp
		2355	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2356	{
		2357	time_t tnow = (time_t)now;
		2358	struct tm tm;
		2359	localtime_r (&tnow, &tm);
		2360
		2361	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2362	++tm.tm_mday; // midnight next day
		2363
		2364	return mktime (&tm);
		2365	}
		2366
		2367	Note: this code might run into trouble on days that have more then two
		2368	midnights (beginning and end).
2231		2369
2232	=back	2370	=back
2233		2371
2234	=item ev_periodic_again (loop, ev_periodic *)	2372	=item ev_periodic_again (loop, ev_periodic *)
2235		2373
…		…
2300		2438
2301	ev_periodic hourly_tick;	2439	ev_periodic hourly_tick;
2302	ev_periodic_init (&hourly_tick, clock_cb,	2440	ev_periodic_init (&hourly_tick, clock_cb,
2303	fmod (ev_now (loop), 3600.), 3600., 0);	2441	fmod (ev_now (loop), 3600.), 3600., 0);
2304	ev_periodic_start (loop, &hourly_tick);	2442	ev_periodic_start (loop, &hourly_tick);
2305		2443
2306		2444
2307	=head2 C<ev_signal> - signal me when a signal gets signalled!	2445	=head2 C<ev_signal> - signal me when a signal gets signalled!
2308		2446
2309	Signal watchers will trigger an event when the process receives a specific	2447	Signal watchers will trigger an event when the process receives a specific
2310	signal one or more times. Even though signals are very asynchronous, libev	2448	signal one or more times. Even though signals are very asynchronous, libev
…		…
2320	only within the same loop, i.e. you can watch for C<SIGINT> in your	2458	only within the same loop, i.e. you can watch for C<SIGINT> in your
2321	default loop and for C<SIGIO> in another loop, but you cannot watch for	2459	default loop and for C<SIGIO> in another loop, but you cannot watch for
2322	C<SIGINT> in both the default loop and another loop at the same time. At	2460	C<SIGINT> in both the default loop and another loop at the same time. At
2323	the moment, C<SIGCHLD> is permanently tied to the default loop.	2461	the moment, C<SIGCHLD> is permanently tied to the default loop.
2324		2462
2325	When the first watcher gets started will libev actually register something	2463	Only after the first watcher for a signal is started will libev actually
2326	with the kernel (thus it coexists with your own signal handlers as long as	2464	register something with the kernel. It thus coexists with your own signal
2327	you don't register any with libev for the same signal).	2465	handlers as long as you don't register any with libev for the same signal.
2328		2466
2329	If possible and supported, libev will install its handlers with	2467	If possible and supported, libev will install its handlers with
2330	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2468	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2331	not be unduly interrupted. If you have a problem with system calls getting	2469	not be unduly interrupted. If you have a problem with system calls getting
2332	interrupted by signals you can block all signals in an C<ev_check> watcher	2470	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2335	=head3 The special problem of inheritance over fork/execve/pthread_create	2473	=head3 The special problem of inheritance over fork/execve/pthread_create
2336		2474
2337	Both the signal mask (C<sigprocmask>) and the signal disposition	2475	Both the signal mask (C<sigprocmask>) and the signal disposition
2338	(C<sigaction>) are unspecified after starting a signal watcher (and after	2476	(C<sigaction>) are unspecified after starting a signal watcher (and after
2339	stopping it again), that is, libev might or might not block the signal,	2477	stopping it again), that is, libev might or might not block the signal,
2340	and might or might not set or restore the installed signal handler.	2478	and might or might not set or restore the installed signal handler (but
		2479	see C<EVFLAG_NOSIGMASK>).
2341		2480
2342	While this does not matter for the signal disposition (libev never	2481	While this does not matter for the signal disposition (libev never
2343	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2482	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2344	C<execve>), this matters for the signal mask: many programs do not expect	2483	C<execve>), this matters for the signal mask: many programs do not expect
2345	certain signals to be blocked.	2484	certain signals to be blocked.
…		…
2516		2655
2517	=head2 C<ev_stat> - did the file attributes just change?	2656	=head2 C<ev_stat> - did the file attributes just change?
2518		2657
2519	This watches a file system path for attribute changes. That is, it calls	2658	This watches a file system path for attribute changes. That is, it calls
2520	C<stat> on that path in regular intervals (or when the OS says it changed)	2659	C<stat> on that path in regular intervals (or when the OS says it changed)
2521	and sees if it changed compared to the last time, invoking the callback if	2660	and sees if it changed compared to the last time, invoking the callback
2522	it did.	2661	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2662	happen after the watcher has been started will be reported.
2523		2663
2524	The path does not need to exist: changing from "path exists" to "path does	2664	The path does not need to exist: changing from "path exists" to "path does
2525	not exist" is a status change like any other. The condition "path does not	2665	not exist" is a status change like any other. The condition "path does not
2526	exist" (or more correctly "path cannot be stat'ed") is signified by the	2666	exist" (or more correctly "path cannot be stat'ed") is signified by the
2527	C<st_nlink> field being zero (which is otherwise always forced to be at	2667	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2757	Apart from keeping your process non-blocking (which is a useful	2897	Apart from keeping your process non-blocking (which is a useful
2758	effect on its own sometimes), idle watchers are a good place to do	2898	effect on its own sometimes), idle watchers are a good place to do
2759	"pseudo-background processing", or delay processing stuff to after the	2899	"pseudo-background processing", or delay processing stuff to after the
2760	event loop has handled all outstanding events.	2900	event loop has handled all outstanding events.
2761		2901
		2902	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2903
		2904	As long as there is at least one active idle watcher, libev will never
		2905	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2906	For this to work, the idle watcher doesn't need to be invoked at all - the
		2907	lowest priority will do.
		2908
		2909	This mode of operation can be useful together with an C<ev_check> watcher,
		2910	to do something on each event loop iteration - for example to balance load
		2911	between different connections.
		2912
		2913	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2914	example.
		2915
2762	=head3 Watcher-Specific Functions and Data Members	2916	=head3 Watcher-Specific Functions and Data Members
2763		2917
2764	=over 4	2918	=over 4
2765		2919
2766	=item ev_idle_init (ev_idle *, callback)	2920	=item ev_idle_init (ev_idle *, callback)
…		…
2777	callback, free it. Also, use no error checking, as usual.	2931	callback, free it. Also, use no error checking, as usual.
2778		2932
2779	static void	2933	static void
2780	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2934	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2781	{	2935	{
		2936	// stop the watcher
		2937	ev_idle_stop (loop, w);
		2938
		2939	// now we can free it
2782	free (w);	2940	free (w);
		2941
2783	// now do something you wanted to do when the program has	2942	// now do something you wanted to do when the program has
2784	// no longer anything immediate to do.	2943	// no longer anything immediate to do.
2785	}	2944	}
2786		2945
2787	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2946	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2789	ev_idle_start (loop, idle_watcher);	2948	ev_idle_start (loop, idle_watcher);
2790		2949
2791		2950
2792	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2951	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2793		2952
2794	Prepare and check watchers are usually (but not always) used in pairs:	2953	Prepare and check watchers are often (but not always) used in pairs:
2795	prepare watchers get invoked before the process blocks and check watchers	2954	prepare watchers get invoked before the process blocks and check watchers
2796	afterwards.	2955	afterwards.
2797		2956
2798	You I<must not> call C<ev_run> or similar functions that enter	2957	You I<must not> call C<ev_run> (or similar functions that enter the
2799	the current event loop from either C<ev_prepare> or C<ev_check>	2958	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2800	watchers. Other loops than the current one are fine, however. The	2959	C<ev_check> watchers. Other loops than the current one are fine,
2801	rationale behind this is that you do not need to check for recursion in	2960	however. The rationale behind this is that you do not need to check
2802	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2961	for recursion in those watchers, i.e. the sequence will always be
2803	C<ev_check> so if you have one watcher of each kind they will always be	2962	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2804	called in pairs bracketing the blocking call.	2963	kind they will always be called in pairs bracketing the blocking call.
2805		2964
2806	Their main purpose is to integrate other event mechanisms into libev and	2965	Their main purpose is to integrate other event mechanisms into libev and
2807	their use is somewhat advanced. They could be used, for example, to track	2966	their use is somewhat advanced. They could be used, for example, to track
2808	variable changes, implement your own watchers, integrate net-snmp or a	2967	variable changes, implement your own watchers, integrate net-snmp or a
2809	coroutine library and lots more. They are also occasionally useful if	2968	coroutine library and lots more. They are also occasionally useful if
…		…
2827	with priority higher than or equal to the event loop and one coroutine	2986	with priority higher than or equal to the event loop and one coroutine
2828	of lower priority, but only once, using idle watchers to keep the event	2987	of lower priority, but only once, using idle watchers to keep the event
2829	loop from blocking if lower-priority coroutines are active, thus mapping	2988	loop from blocking if lower-priority coroutines are active, thus mapping
2830	low-priority coroutines to idle/background tasks).	2989	low-priority coroutines to idle/background tasks).
2831		2990
2832	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2991	When used for this purpose, it is recommended to give C<ev_check> watchers
2833	priority, to ensure that they are being run before any other watchers	2992	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2834	after the poll (this doesn't matter for C<ev_prepare> watchers).	2993	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2994	watchers).
2835		2995
2836	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	2996	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2837	activate ("feed") events into libev. While libev fully supports this, they	2997	activate ("feed") events into libev. While libev fully supports this, they
2838	might get executed before other C<ev_check> watchers did their job. As	2998	might get executed before other C<ev_check> watchers did their job. As
2839	C<ev_check> watchers are often used to embed other (non-libev) event	2999	C<ev_check> watchers are often used to embed other (non-libev) event
2840	loops those other event loops might be in an unusable state until their	3000	loops those other event loops might be in an unusable state until their
2841	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3001	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2842	others).	3002	others).
		3003
		3004	=head3 Abusing an C<ev_check> watcher for its side-effect
		3005
		3006	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3007	useful because they are called once per event loop iteration. For
		3008	example, if you want to handle a large number of connections fairly, you
		3009	normally only do a bit of work for each active connection, and if there
		3010	is more work to do, you wait for the next event loop iteration, so other
		3011	connections have a chance of making progress.
		3012
		3013	Using an C<ev_check> watcher is almost enough: it will be called on the
		3014	next event loop iteration. However, that isn't as soon as possible -
		3015	without external events, your C<ev_check> watcher will not be invoked.
		3016
		3017	This is where C<ev_idle> watchers come in handy - all you need is a
		3018	single global idle watcher that is active as long as you have one active
		3019	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3020	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3021	invoked. Neither watcher alone can do that.
2843		3022
2844	=head3 Watcher-Specific Functions and Data Members	3023	=head3 Watcher-Specific Functions and Data Members
2845		3024
2846	=over 4	3025	=over 4
2847		3026
…		…
3048		3227
3049	=over 4	3228	=over 4
3050		3229
3051	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3230	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
3052		3231
3053	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3232	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
3054		3233
3055	Configures the watcher to embed the given loop, which must be	3234	Configures the watcher to embed the given loop, which must be
3056	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3235	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
3057	invoked automatically, otherwise it is the responsibility of the callback	3236	invoked automatically, otherwise it is the responsibility of the callback
3058	to invoke it (it will continue to be called until the sweep has been done,	3237	to invoke it (it will continue to be called until the sweep has been done,
…		…
3079	used).	3258	used).
3080		3259
3081	struct ev_loop *loop_hi = ev_default_init (0);	3260	struct ev_loop *loop_hi = ev_default_init (0);
3082	struct ev_loop *loop_lo = 0;	3261	struct ev_loop *loop_lo = 0;
3083	ev_embed embed;	3262	ev_embed embed;
3084		3263
3085	// see if there is a chance of getting one that works	3264	// see if there is a chance of getting one that works
3086	// (remember that a flags value of 0 means autodetection)	3265	// (remember that a flags value of 0 means autodetection)
3087	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3266	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3088	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3267	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3089	: 0;	3268	: 0;
…		…
3103	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3282	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3104		3283
3105	struct ev_loop *loop = ev_default_init (0);	3284	struct ev_loop *loop = ev_default_init (0);
3106	struct ev_loop *loop_socket = 0;	3285	struct ev_loop *loop_socket = 0;
3107	ev_embed embed;	3286	ev_embed embed;
3108		3287
3109	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3288	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3110	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3289	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3111	{	3290	{
3112	ev_embed_init (&embed, 0, loop_socket);	3291	ev_embed_init (&embed, 0, loop_socket);
3113	ev_embed_start (loop, &embed);	3292	ev_embed_start (loop, &embed);
…		…
3121		3300
3122	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3301	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3123		3302
3124	Fork watchers are called when a C<fork ()> was detected (usually because	3303	Fork watchers are called when a C<fork ()> was detected (usually because
3125	whoever is a good citizen cared to tell libev about it by calling	3304	whoever is a good citizen cared to tell libev about it by calling
3126	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3305	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3127	event loop blocks next and before C<ev_check> watchers are being called,	3306	and before C<ev_check> watchers are being called, and only in the child
3128	and only in the child after the fork. If whoever good citizen calling	3307	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3129	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3308	and calls it in the wrong process, the fork handlers will be invoked, too,
3130	handlers will be invoked, too, of course.	3309	of course.
3131		3310
3132	=head3 The special problem of life after fork - how is it possible?	3311	=head3 The special problem of life after fork - how is it possible?
3133		3312
3134	Most uses of C<fork()> consist of forking, then some simple calls to set	3313	Most uses of C<fork ()> consist of forking, then some simple calls to set
3135	up/change the process environment, followed by a call to C<exec()>. This	3314	up/change the process environment, followed by a call to C<exec()>. This
3136	sequence should be handled by libev without any problems.	3315	sequence should be handled by libev without any problems.
3137		3316
3138	This changes when the application actually wants to do event handling	3317	This changes when the application actually wants to do event handling
3139	in the child, or both parent in child, in effect "continuing" after the	3318	in the child, or both parent in child, in effect "continuing" after the
…		…
3216	atexit (program_exits);	3395	atexit (program_exits);
3217		3396
3218		3397
3219	=head2 C<ev_async> - how to wake up an event loop	3398	=head2 C<ev_async> - how to wake up an event loop
3220		3399
3221	In general, you cannot use an C<ev_run> from multiple threads or other	3400	In general, you cannot use an C<ev_loop> from multiple threads or other
3222	asynchronous sources such as signal handlers (as opposed to multiple event	3401	asynchronous sources such as signal handlers (as opposed to multiple event
3223	loops - those are of course safe to use in different threads).	3402	loops - those are of course safe to use in different threads).
3224		3403
3225	Sometimes, however, you need to wake up an event loop you do not control,	3404	Sometimes, however, you need to wake up an event loop you do not control,
3226	for example because it belongs to another thread. This is what C<ev_async>	3405	for example because it belongs to another thread. This is what C<ev_async>
…		…
3228	it by calling C<ev_async_send>, which is thread- and signal safe.	3407	it by calling C<ev_async_send>, which is thread- and signal safe.
3229		3408
3230	This functionality is very similar to C<ev_signal> watchers, as signals,	3409	This functionality is very similar to C<ev_signal> watchers, as signals,
3231	too, are asynchronous in nature, and signals, too, will be compressed	3410	too, are asynchronous in nature, and signals, too, will be compressed
3232	(i.e. the number of callback invocations may be less than the number of	3411	(i.e. the number of callback invocations may be less than the number of
3233	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind	3412	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3234	of "global async watchers" by using a watcher on an otherwise unused	3413	of "global async watchers" by using a watcher on an otherwise unused
3235	signal, and C<ev_feed_signal> to signal this watcher from another thread,	3414	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3236	even without knowing which loop owns the signal.	3415	even without knowing which loop owns the signal.
3237
3238	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3239	just the default loop.
3240		3416
3241	=head3 Queueing	3417	=head3 Queueing
3242		3418
3243	C<ev_async> does not support queueing of data in any way. The reason	3419	C<ev_async> does not support queueing of data in any way. The reason
3244	is that the author does not know of a simple (or any) algorithm for a	3420	is that the author does not know of a simple (or any) algorithm for a
…		…
3336	trust me.	3512	trust me.
3337		3513
3338	=item ev_async_send (loop, ev_async *)	3514	=item ev_async_send (loop, ev_async *)
3339		3515
3340	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3516	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3341	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3517	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3518	returns.
		3519
3342	C<ev_feed_event>, this call is safe to do from other threads, signal or	3520	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3343	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3521	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3344	section below on what exactly this means).	3522	embedding section below on what exactly this means).
3345		3523
3346	Note that, as with other watchers in libev, multiple events might get	3524	Note that, as with other watchers in libev, multiple events might get
3347	compressed into a single callback invocation (another way to look at this	3525	compressed into a single callback invocation (another way to look at
3348	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3526	this is that C<ev_async> watchers are level-triggered: they are set on
3349	reset when the event loop detects that).	3527	C<ev_async_send>, reset when the event loop detects that).
3350		3528
3351	This call incurs the overhead of a system call only once per event loop	3529	This call incurs the overhead of at most one extra system call per event
3352	iteration, so while the overhead might be noticeable, it doesn't apply to	3530	loop iteration, if the event loop is blocked, and no syscall at all if
3353	repeated calls to C<ev_async_send> for the same event loop.	3531	the event loop (or your program) is processing events. That means that
		3532	repeated calls are basically free (there is no need to avoid calls for
		3533	performance reasons) and that the overhead becomes smaller (typically
		3534	zero) under load.
3354		3535
3355	=item bool = ev_async_pending (ev_async *)	3536	=item bool = ev_async_pending (ev_async *)
3356		3537
3357	Returns a non-zero value when C<ev_async_send> has been called on the	3538	Returns a non-zero value when C<ev_async_send> has been called on the
3358	watcher but the event has not yet been processed (or even noted) by the	3539	watcher but the event has not yet been processed (or even noted) by the
…		…
3375		3556
3376	There are some other functions of possible interest. Described. Here. Now.	3557	There are some other functions of possible interest. Described. Here. Now.
3377		3558
3378	=over 4	3559	=over 4
3379		3560
3380	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3561	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3381		3562
3382	This function combines a simple timer and an I/O watcher, calls your	3563	This function combines a simple timer and an I/O watcher, calls your
3383	callback on whichever event happens first and automatically stops both	3564	callback on whichever event happens first and automatically stops both
3384	watchers. This is useful if you want to wait for a single event on an fd	3565	watchers. This is useful if you want to wait for a single event on an fd
3385	or timeout without having to allocate/configure/start/stop/free one or	3566	or timeout without having to allocate/configure/start/stop/free one or
…		…
3413	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3594	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3414		3595
3415	=item ev_feed_fd_event (loop, int fd, int revents)	3596	=item ev_feed_fd_event (loop, int fd, int revents)
3416		3597
3417	Feed an event on the given fd, as if a file descriptor backend detected	3598	Feed an event on the given fd, as if a file descriptor backend detected
3418	the given events it.	3599	the given events.
3419		3600
3420	=item ev_feed_signal_event (loop, int signum)	3601	=item ev_feed_signal_event (loop, int signum)
3421		3602
3422	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,	3603	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3423	which is async-safe.	3604	which is async-safe.
…		…
3429		3610
3430	This section explains some common idioms that are not immediately	3611	This section explains some common idioms that are not immediately
3431	obvious. Note that examples are sprinkled over the whole manual, and this	3612	obvious. Note that examples are sprinkled over the whole manual, and this
3432	section only contains stuff that wouldn't fit anywhere else.	3613	section only contains stuff that wouldn't fit anywhere else.
3433		3614
3434	=over 4	3615	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3435		3616
3436	=item Model/nested event loop invocations and exit conditions.	3617	Each watcher has, by default, a C<void *data> member that you can read
		3618	or modify at any time: libev will completely ignore it. This can be used
		3619	to associate arbitrary data with your watcher. If you need more data and
		3620	don't want to allocate memory separately and store a pointer to it in that
		3621	data member, you can also "subclass" the watcher type and provide your own
		3622	data:
		3623
		3624	struct my_io
		3625	{
		3626	ev_io io;
		3627	int otherfd;
		3628	void *somedata;
		3629	struct whatever *mostinteresting;
		3630	};
		3631
		3632	...
		3633	struct my_io w;
		3634	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3635
		3636	And since your callback will be called with a pointer to the watcher, you
		3637	can cast it back to your own type:
		3638
		3639	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3640	{
		3641	struct my_io *w = (struct my_io *)w_;
		3642	...
		3643	}
		3644
		3645	More interesting and less C-conformant ways of casting your callback
		3646	function type instead have been omitted.
		3647
		3648	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3649
		3650	Another common scenario is to use some data structure with multiple
		3651	embedded watchers, in effect creating your own watcher that combines
		3652	multiple libev event sources into one "super-watcher":
		3653
		3654	struct my_biggy
		3655	{
		3656	int some_data;
		3657	ev_timer t1;
		3658	ev_timer t2;
		3659	}
		3660
		3661	In this case getting the pointer to C<my_biggy> is a bit more
		3662	complicated: Either you store the address of your C<my_biggy> struct in
		3663	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3664	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3665	real programmers):
		3666
		3667	#include <stddef.h>
		3668
		3669	static void
		3670	t1_cb (EV_P_ ev_timer *w, int revents)
		3671	{
		3672	struct my_biggy big = (struct my_biggy *)
		3673	(((char *)w) - offsetof (struct my_biggy, t1));
		3674	}
		3675
		3676	static void
		3677	t2_cb (EV_P_ ev_timer *w, int revents)
		3678	{
		3679	struct my_biggy big = (struct my_biggy *)
		3680	(((char *)w) - offsetof (struct my_biggy, t2));
		3681	}
		3682
		3683	=head2 AVOIDING FINISHING BEFORE RETURNING
		3684
		3685	Often you have structures like this in event-based programs:
		3686
		3687	callback ()
		3688	{
		3689	free (request);
		3690	}
		3691
		3692	request = start_new_request (..., callback);
		3693
		3694	The intent is to start some "lengthy" operation. The C<request> could be
		3695	used to cancel the operation, or do other things with it.
		3696
		3697	It's not uncommon to have code paths in C<start_new_request> that
		3698	immediately invoke the callback, for example, to report errors. Or you add
		3699	some caching layer that finds that it can skip the lengthy aspects of the
		3700	operation and simply invoke the callback with the result.
		3701
		3702	The problem here is that this will happen I<before> C<start_new_request>
		3703	has returned, so C<request> is not set.
		3704
		3705	Even if you pass the request by some safer means to the callback, you
		3706	might want to do something to the request after starting it, such as
		3707	canceling it, which probably isn't working so well when the callback has
		3708	already been invoked.
		3709
		3710	A common way around all these issues is to make sure that
		3711	C<start_new_request> I<always> returns before the callback is invoked. If
		3712	C<start_new_request> immediately knows the result, it can artificially
		3713	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3714	example, or more sneakily, by reusing an existing (stopped) watcher and
		3715	pushing it into the pending queue:
		3716
		3717	ev_set_cb (watcher, callback);
		3718	ev_feed_event (EV_A_ watcher, 0);
		3719
		3720	This way, C<start_new_request> can safely return before the callback is
		3721	invoked, while not delaying callback invocation too much.
		3722
		3723	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3437		3724
3438	Often (especially in GUI toolkits) there are places where you have	3725	Often (especially in GUI toolkits) there are places where you have
3439	I<modal> interaction, which is most easily implemented by recursively	3726	I<modal> interaction, which is most easily implemented by recursively
3440	invoking C<ev_run>.	3727	invoking C<ev_run>.
3441		3728
3442	This brings the problem of exiting - a callback might want to finish the	3729	This brings the problem of exiting - a callback might want to finish the
3443	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but	3730	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
3444	a modal "Are you sure?" dialog is still waiting), or just the nested one	3731	a modal "Are you sure?" dialog is still waiting), or just the nested one
3445	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some	3732	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
3446	other combination: In these cases, C<ev_break> will not work alone.	3733	other combination: In these cases, a simple C<ev_break> will not work.
3447		3734
3448	The solution is to maintain "break this loop" variable for each C<ev_run>	3735	The solution is to maintain "break this loop" variable for each C<ev_run>
3449	invocation, and use a loop around C<ev_run> until the condition is	3736	invocation, and use a loop around C<ev_run> until the condition is
3450	triggered, using C<EVRUN_ONCE>:	3737	triggered, using C<EVRUN_ONCE>:
3451		3738
…		…
3453	int exit_main_loop = 0;	3740	int exit_main_loop = 0;
3454		3741
3455	while (!exit_main_loop)	3742	while (!exit_main_loop)
3456	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3743	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3457		3744
3458	// in a model watcher	3745	// in a modal watcher
3459	int exit_nested_loop = 0;	3746	int exit_nested_loop = 0;
3460		3747
3461	while (!exit_nested_loop)	3748	while (!exit_nested_loop)
3462	ev_run (EV_A_ EVRUN_ONCE);	3749	ev_run (EV_A_ EVRUN_ONCE);
3463		3750
…		…
3470	exit_main_loop = 1;	3757	exit_main_loop = 1;
3471		3758
3472	// exit both	3759	// exit both
3473	exit_main_loop = exit_nested_loop = 1;	3760	exit_main_loop = exit_nested_loop = 1;
3474		3761
3475	=back	3762	=head2 THREAD LOCKING EXAMPLE
		3763
		3764	Here is a fictitious example of how to run an event loop in a different
		3765	thread from where callbacks are being invoked and watchers are
		3766	created/added/removed.
		3767
		3768	For a real-world example, see the C<EV::Loop::Async> perl module,
		3769	which uses exactly this technique (which is suited for many high-level
		3770	languages).
		3771
		3772	The example uses a pthread mutex to protect the loop data, a condition
		3773	variable to wait for callback invocations, an async watcher to notify the
		3774	event loop thread and an unspecified mechanism to wake up the main thread.
		3775
		3776	First, you need to associate some data with the event loop:
		3777
		3778	typedef struct {
		3779	mutex_t lock; /* global loop lock */
		3780	ev_async async_w;
		3781	thread_t tid;
		3782	cond_t invoke_cv;
		3783	} userdata;
		3784
		3785	void prepare_loop (EV_P)
		3786	{
		3787	// for simplicity, we use a static userdata struct.
		3788	static userdata u;
		3789
		3790	ev_async_init (&u->async_w, async_cb);
		3791	ev_async_start (EV_A_ &u->async_w);
		3792
		3793	pthread_mutex_init (&u->lock, 0);
		3794	pthread_cond_init (&u->invoke_cv, 0);
		3795
		3796	// now associate this with the loop
		3797	ev_set_userdata (EV_A_ u);
		3798	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3799	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3800
		3801	// then create the thread running ev_run
		3802	pthread_create (&u->tid, 0, l_run, EV_A);
		3803	}
		3804
		3805	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3806	solely to wake up the event loop so it takes notice of any new watchers
		3807	that might have been added:
		3808
		3809	static void
		3810	async_cb (EV_P_ ev_async *w, int revents)
		3811	{
		3812	// just used for the side effects
		3813	}
		3814
		3815	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3816	protecting the loop data, respectively.
		3817
		3818	static void
		3819	l_release (EV_P)
		3820	{
		3821	userdata *u = ev_userdata (EV_A);
		3822	pthread_mutex_unlock (&u->lock);
		3823	}
		3824
		3825	static void
		3826	l_acquire (EV_P)
		3827	{
		3828	userdata *u = ev_userdata (EV_A);
		3829	pthread_mutex_lock (&u->lock);
		3830	}
		3831
		3832	The event loop thread first acquires the mutex, and then jumps straight
		3833	into C<ev_run>:
		3834
		3835	void *
		3836	l_run (void *thr_arg)
		3837	{
		3838	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3839
		3840	l_acquire (EV_A);
		3841	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3842	ev_run (EV_A_ 0);
		3843	l_release (EV_A);
		3844
		3845	return 0;
		3846	}
		3847
		3848	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3849	signal the main thread via some unspecified mechanism (signals? pipe
		3850	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3851	have been called (in a while loop because a) spurious wakeups are possible
		3852	and b) skipping inter-thread-communication when there are no pending
		3853	watchers is very beneficial):
		3854
		3855	static void
		3856	l_invoke (EV_P)
		3857	{
		3858	userdata *u = ev_userdata (EV_A);
		3859
		3860	while (ev_pending_count (EV_A))
		3861	{
		3862	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3863	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3864	}
		3865	}
		3866
		3867	Now, whenever the main thread gets told to invoke pending watchers, it
		3868	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3869	thread to continue:
		3870
		3871	static void
		3872	real_invoke_pending (EV_P)
		3873	{
		3874	userdata *u = ev_userdata (EV_A);
		3875
		3876	pthread_mutex_lock (&u->lock);
		3877	ev_invoke_pending (EV_A);
		3878	pthread_cond_signal (&u->invoke_cv);
		3879	pthread_mutex_unlock (&u->lock);
		3880	}
		3881
		3882	Whenever you want to start/stop a watcher or do other modifications to an
		3883	event loop, you will now have to lock:
		3884
		3885	ev_timer timeout_watcher;
		3886	userdata *u = ev_userdata (EV_A);
		3887
		3888	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3889
		3890	pthread_mutex_lock (&u->lock);
		3891	ev_timer_start (EV_A_ &timeout_watcher);
		3892	ev_async_send (EV_A_ &u->async_w);
		3893	pthread_mutex_unlock (&u->lock);
		3894
		3895	Note that sending the C<ev_async> watcher is required because otherwise
		3896	an event loop currently blocking in the kernel will have no knowledge
		3897	about the newly added timer. By waking up the loop it will pick up any new
		3898	watchers in the next event loop iteration.
		3899
		3900	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3901
		3902	While the overhead of a callback that e.g. schedules a thread is small, it
		3903	is still an overhead. If you embed libev, and your main usage is with some
		3904	kind of threads or coroutines, you might want to customise libev so that
		3905	doesn't need callbacks anymore.
		3906
		3907	Imagine you have coroutines that you can switch to using a function
		3908	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3909	and that due to some magic, the currently active coroutine is stored in a
		3910	global called C<current_coro>. Then you can build your own "wait for libev
		3911	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3912	the differing C<;> conventions):
		3913
		3914	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3915	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3916
		3917	That means instead of having a C callback function, you store the
		3918	coroutine to switch to in each watcher, and instead of having libev call
		3919	your callback, you instead have it switch to that coroutine.
		3920
		3921	A coroutine might now wait for an event with a function called
		3922	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3923	matter when, or whether the watcher is active or not when this function is
		3924	called):
		3925
		3926	void
		3927	wait_for_event (ev_watcher *w)
		3928	{
		3929	ev_set_cb (w, current_coro);
		3930	switch_to (libev_coro);
		3931	}
		3932
		3933	That basically suspends the coroutine inside C<wait_for_event> and
		3934	continues the libev coroutine, which, when appropriate, switches back to
		3935	this or any other coroutine.
		3936
		3937	You can do similar tricks if you have, say, threads with an event queue -
		3938	instead of storing a coroutine, you store the queue object and instead of
		3939	switching to a coroutine, you push the watcher onto the queue and notify
		3940	any waiters.
		3941
		3942	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3943	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3944
		3945	// my_ev.h
		3946	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3947	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3948	#include "../libev/ev.h"
		3949
		3950	// my_ev.c
		3951	#define EV_H "my_ev.h"
		3952	#include "../libev/ev.c"
		3953
		3954	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3955	F<my_ev.c> into your project. When properly specifying include paths, you
		3956	can even use F<ev.h> as header file name directly.
3476		3957
3477		3958
3478	=head1 LIBEVENT EMULATION	3959	=head1 LIBEVENT EMULATION
3479		3960
3480	Libev offers a compatibility emulation layer for libevent. It cannot	3961	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3510		3991
3511	=back	3992	=back
3512		3993
3513	=head1 C++ SUPPORT	3994	=head1 C++ SUPPORT
3514		3995
		3996	=head2 C API
		3997
		3998	The normal C API should work fine when used from C++: both ev.h and the
		3999	libev sources can be compiled as C++. Therefore, code that uses the C API
		4000	will work fine.
		4001
		4002	Proper exception specifications might have to be added to callbacks passed
		4003	to libev: exceptions may be thrown only from watcher callbacks, all other
		4004	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4005	callbacks) must not throw exceptions, and might need a C<noexcept>
		4006	specification. If you have code that needs to be compiled as both C and
		4007	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4008
		4009	static void
		4010	fatal_error (const char *msg) EV_NOEXCEPT
		4011	{
		4012	perror (msg);
		4013	abort ();
		4014	}
		4015
		4016	...
		4017	ev_set_syserr_cb (fatal_error);
		4018
		4019	The only API functions that can currently throw exceptions are C<ev_run>,
		4020	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4021	because it runs cleanup watchers).
		4022
		4023	Throwing exceptions in watcher callbacks is only supported if libev itself
		4024	is compiled with a C++ compiler or your C and C++ environments allow
		4025	throwing exceptions through C libraries (most do).
		4026
		4027	=head2 C++ API
		4028
3515	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4029	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3516	you to use some convenience methods to start/stop watchers and also change	4030	you to use some convenience methods to start/stop watchers and also change
3517	the callback model to a model using method callbacks on objects.	4031	the callback model to a model using method callbacks on objects.
3518		4032
3519	To use it,	4033	To use it,
3520		4034
3521	#include <ev++.h>	4035	#include <ev++.h>
3522		4036
3523	This automatically includes F<ev.h> and puts all of its definitions (many	4037	This automatically includes F<ev.h> and puts all of its definitions (many
3524	of them macros) into the global namespace. All C++ specific things are	4038	of them macros) into the global namespace. All C++ specific things are
3525	put into the C<ev> namespace. It should support all the same embedding	4039	put into the C<ev> namespace. It should support all the same embedding
…		…
3534	with C<operator ()> can be used as callbacks. Other types should be easy	4048	with C<operator ()> can be used as callbacks. Other types should be easy
3535	to add as long as they only need one additional pointer for context. If	4049	to add as long as they only need one additional pointer for context. If
3536	you need support for other types of functors please contact the author	4050	you need support for other types of functors please contact the author
3537	(preferably after implementing it).	4051	(preferably after implementing it).
3538		4052
		4053	For all this to work, your C++ compiler either has to use the same calling
		4054	conventions as your C compiler (for static member functions), or you have
		4055	to embed libev and compile libev itself as C++.
		4056
3539	Here is a list of things available in the C<ev> namespace:	4057	Here is a list of things available in the C<ev> namespace:
3540		4058
3541	=over 4	4059	=over 4
3542		4060
3543	=item C<ev::READ>, C<ev::WRITE> etc.	4061	=item C<ev::READ>, C<ev::WRITE> etc.
…		…
3552	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4070	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3553		4071
3554	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4072	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3555	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4073	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3556	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4074	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3557	defines by many implementations.	4075	defined by many implementations.
3558		4076
3559	All of those classes have these methods:	4077	All of those classes have these methods:
3560		4078
3561	=over 4	4079	=over 4
3562		4080
…		…
3624	void operator() (ev::io &w, int revents)	4142	void operator() (ev::io &w, int revents)
3625	{	4143	{
3626	...	4144	...
3627	}	4145	}
3628	}	4146	}
3629		4147
3630	myfunctor f;	4148	myfunctor f;
3631		4149
3632	ev::io w;	4150	ev::io w;
3633	w.set (&f);	4151	w.set (&f);
3634		4152
…		…
3652	Associates a different C<struct ev_loop> with this watcher. You can only	4170	Associates a different C<struct ev_loop> with this watcher. You can only
3653	do this when the watcher is inactive (and not pending either).	4171	do this when the watcher is inactive (and not pending either).
3654		4172
3655	=item w->set ([arguments])	4173	=item w->set ([arguments])
3656		4174
3657	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4175	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3658	method or a suitable start method must be called at least once. Unlike the	4176	with the same arguments. Either this method or a suitable start method
3659	C counterpart, an active watcher gets automatically stopped and restarted	4177	must be called at least once. Unlike the C counterpart, an active watcher
3660	when reconfiguring it with this method.	4178	gets automatically stopped and restarted when reconfiguring it with this
		4179	method.
		4180
		4181	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4182	clashing with the C<set (loop)> method.
3661		4183
3662	=item w->start ()	4184	=item w->start ()
3663		4185
3664	Starts the watcher. Note that there is no C<loop> argument, as the	4186	Starts the watcher. Note that there is no C<loop> argument, as the
3665	constructor already stores the event loop.	4187	constructor already stores the event loop.
…		…
3695	watchers in the constructor.	4217	watchers in the constructor.
3696		4218
3697	class myclass	4219	class myclass
3698	{	4220	{
3699	ev::io io ; void io_cb (ev::io &w, int revents);	4221	ev::io io ; void io_cb (ev::io &w, int revents);
3700	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4222	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3701	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4223	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3702		4224
3703	myclass (int fd)	4225	myclass (int fd)
3704	{	4226	{
3705	io .set <myclass, &myclass::io_cb > (this);	4227	io .set <myclass, &myclass::io_cb > (this);
…		…
3756	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4278	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3757		4279
3758	=item D	4280	=item D
3759		4281
3760	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4282	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3761	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4283	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3762		4284
3763	=item Ocaml	4285	=item Ocaml
3764		4286
3765	Erkki Seppala has written Ocaml bindings for libev, to be found at	4287	Erkki Seppala has written Ocaml bindings for libev, to be found at
3766	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4288	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3769		4291
3770	Brian Maher has written a partial interface to libev for lua (at the	4292	Brian Maher has written a partial interface to libev for lua (at the
3771	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4293	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3772	L<http://github.com/brimworks/lua-ev>.	4294	L<http://github.com/brimworks/lua-ev>.
3773		4295
		4296	=item Javascript
		4297
		4298	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4299
		4300	=item Others
		4301
		4302	There are others, and I stopped counting.
		4303
3774	=back	4304	=back
3775		4305
3776		4306
3777	=head1 MACRO MAGIC	4307	=head1 MACRO MAGIC
3778		4308
…		…
3814	suitable for use with C<EV_A>.	4344	suitable for use with C<EV_A>.
3815		4345
3816	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4346	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3817		4347
3818	Similar to the other two macros, this gives you the value of the default	4348	Similar to the other two macros, this gives you the value of the default
3819	loop, if multiple loops are supported ("ev loop default").	4349	loop, if multiple loops are supported ("ev loop default"). The default loop
		4350	will be initialised if it isn't already initialised.
		4351
		4352	For non-multiplicity builds, these macros do nothing, so you always have
		4353	to initialise the loop somewhere.
3820		4354
3821	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4355	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3822		4356
3823	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4357	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3824	default loop has been initialised (C<UC> == unchecked). Their behaviour	4358	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3891	ev_vars.h	4425	ev_vars.h
3892	ev_wrap.h	4426	ev_wrap.h
3893		4427
3894	ev_win32.c required on win32 platforms only	4428	ev_win32.c required on win32 platforms only
3895		4429
3896	ev_select.c only when select backend is enabled (which is enabled by default)	4430	ev_select.c only when select backend is enabled
3897	ev_poll.c only when poll backend is enabled (disabled by default)	4431	ev_poll.c only when poll backend is enabled
3898	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4432	ev_epoll.c only when the epoll backend is enabled
3899	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4433	ev_kqueue.c only when the kqueue backend is enabled
3900	ev_port.c only when the solaris port backend is enabled (disabled by default)	4434	ev_port.c only when the solaris port backend is enabled
3901		4435
3902	F<ev.c> includes the backend files directly when enabled, so you only need	4436	F<ev.c> includes the backend files directly when enabled, so you only need
3903	to compile this single file.	4437	to compile this single file.
3904		4438
3905	=head3 LIBEVENT COMPATIBILITY API	4439	=head3 LIBEVENT COMPATIBILITY API
…		…
3969	supported). It will also not define any of the structs usually found in	4503	supported). It will also not define any of the structs usually found in
3970	F<event.h> that are not directly supported by the libev core alone.	4504	F<event.h> that are not directly supported by the libev core alone.
3971		4505
3972	In standalone mode, libev will still try to automatically deduce the	4506	In standalone mode, libev will still try to automatically deduce the
3973	configuration, but has to be more conservative.	4507	configuration, but has to be more conservative.
		4508
		4509	=item EV_USE_FLOOR
		4510
		4511	If defined to be C<1>, libev will use the C<floor ()> function for its
		4512	periodic reschedule calculations, otherwise libev will fall back on a
		4513	portable (slower) implementation. If you enable this, you usually have to
		4514	link against libm or something equivalent. Enabling this when the C<floor>
		4515	function is not available will fail, so the safe default is to not enable
		4516	this.
3974		4517
3975	=item EV_USE_MONOTONIC	4518	=item EV_USE_MONOTONIC
3976		4519
3977	If defined to be C<1>, libev will try to detect the availability of the	4520	If defined to be C<1>, libev will try to detect the availability of the
3978	monotonic clock option at both compile time and runtime. Otherwise no	4521	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4063		4606
4064	If programs implement their own fd to handle mapping on win32, then this	4607	If programs implement their own fd to handle mapping on win32, then this
4065	macro can be used to override the C<close> function, useful to unregister	4608	macro can be used to override the C<close> function, useful to unregister
4066	file descriptors again. Note that the replacement function has to close	4609	file descriptors again. Note that the replacement function has to close
4067	the underlying OS handle.	4610	the underlying OS handle.
		4611
		4612	=item EV_USE_WSASOCKET
		4613
		4614	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4615	communication socket, which works better in some environments. Otherwise,
		4616	the normal C<socket> function will be used, which works better in other
		4617	environments.
4068		4618
4069	=item EV_USE_POLL	4619	=item EV_USE_POLL
4070		4620
4071	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4621	If defined to be C<1>, libev will compile in support for the C<poll>(2)
4072	backend. Otherwise it will be enabled on non-win32 platforms. It	4622	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
4108	If defined to be C<1>, libev will compile in support for the Linux inotify	4658	If defined to be C<1>, libev will compile in support for the Linux inotify
4109	interface to speed up C<ev_stat> watchers. Its actual availability will	4659	interface to speed up C<ev_stat> watchers. Its actual availability will
4110	be detected at runtime. If undefined, it will be enabled if the headers	4660	be detected at runtime. If undefined, it will be enabled if the headers
4111	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4661	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4112		4662
		4663	=item EV_NO_SMP
		4664
		4665	If defined to be C<1>, libev will assume that memory is always coherent
		4666	between threads, that is, threads can be used, but threads never run on
		4667	different cpus (or different cpu cores). This reduces dependencies
		4668	and makes libev faster.
		4669
		4670	=item EV_NO_THREADS
		4671
		4672	If defined to be C<1>, libev will assume that it will never be called from
		4673	different threads (that includes signal handlers), which is a stronger
		4674	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4675	libev faster.
		4676
4113	=item EV_ATOMIC_T	4677	=item EV_ATOMIC_T
4114		4678
4115	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4679	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4116	access is atomic with respect to other threads or signal contexts. No such	4680	access is atomic with respect to other threads or signal contexts. No
4117	type is easily found in the C language, so you can provide your own type	4681	such type is easily found in the C language, so you can provide your own
4118	that you know is safe for your purposes. It is used both for signal handler "locking"	4682	type that you know is safe for your purposes. It is used both for signal
4119	as well as for signal and thread safety in C<ev_async> watchers.	4683	handler "locking" as well as for signal and thread safety in C<ev_async>
		4684	watchers.
4120		4685
4121	In the absence of this define, libev will use C<sig_atomic_t volatile>	4686	In the absence of this define, libev will use C<sig_atomic_t volatile>
4122	(from F<signal.h>), which is usually good enough on most platforms.	4687	(from F<signal.h>), which is usually good enough on most platforms.
4123		4688
4124	=item EV_H (h)	4689	=item EV_H (h)
…		…
4151	will have the C<struct ev_loop *> as first argument, and you can create	4716	will have the C<struct ev_loop *> as first argument, and you can create
4152	additional independent event loops. Otherwise there will be no support	4717	additional independent event loops. Otherwise there will be no support
4153	for multiple event loops and there is no first event loop pointer	4718	for multiple event loops and there is no first event loop pointer
4154	argument. Instead, all functions act on the single default loop.	4719	argument. Instead, all functions act on the single default loop.
4155		4720
		4721	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4722	default loop when multiplicity is switched off - you always have to
		4723	initialise the loop manually in this case.
		4724
4156	=item EV_MINPRI	4725	=item EV_MINPRI
4157		4726
4158	=item EV_MAXPRI	4727	=item EV_MAXPRI
4159		4728
4160	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4729	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4196	#define EV_USE_POLL 1	4765	#define EV_USE_POLL 1
4197	#define EV_CHILD_ENABLE 1	4766	#define EV_CHILD_ENABLE 1
4198	#define EV_ASYNC_ENABLE 1	4767	#define EV_ASYNC_ENABLE 1
4199		4768
4200	The actual value is a bitset, it can be a combination of the following	4769	The actual value is a bitset, it can be a combination of the following
4201	values:	4770	values (by default, all of these are enabled):
4202		4771
4203	=over 4	4772	=over 4
4204		4773
4205	=item C<1> - faster/larger code	4774	=item C<1> - faster/larger code
4206		4775
…		…
4210	code size by roughly 30% on amd64).	4779	code size by roughly 30% on amd64).
4211		4780
4212	When optimising for size, use of compiler flags such as C<-Os> with	4781	When optimising for size, use of compiler flags such as C<-Os> with
4213	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4782	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4214	assertions.	4783	assertions.
		4784
		4785	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4786	(e.g. gcc with C<-Os>).
4215		4787
4216	=item C<2> - faster/larger data structures	4788	=item C<2> - faster/larger data structures
4217		4789
4218	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4790	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4219	hash table sizes and so on. This will usually further increase code size	4791	hash table sizes and so on. This will usually further increase code size
4220	and can additionally have an effect on the size of data structures at	4792	and can additionally have an effect on the size of data structures at
4221	runtime.	4793	runtime.
4222		4794
		4795	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4796	(e.g. gcc with C<-Os>).
		4797
4223	=item C<4> - full API configuration	4798	=item C<4> - full API configuration
4224		4799
4225	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4800	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4226	enables multiplicity (C<EV_MULTIPLICITY>=1).	4801	enables multiplicity (C<EV_MULTIPLICITY>=1).
4227		4802
…		…
4257		4832
4258	With an intelligent-enough linker (gcc+binutils are intelligent enough	4833	With an intelligent-enough linker (gcc+binutils are intelligent enough
4259	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4834	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4260	your program might be left out as well - a binary starting a timer and an	4835	your program might be left out as well - a binary starting a timer and an
4261	I/O watcher then might come out at only 5Kb.	4836	I/O watcher then might come out at only 5Kb.
		4837
		4838	=item EV_API_STATIC
		4839
		4840	If this symbol is defined (by default it is not), then all identifiers
		4841	will have static linkage. This means that libev will not export any
		4842	identifiers, and you cannot link against libev anymore. This can be useful
		4843	when you embed libev, only want to use libev functions in a single file,
		4844	and do not want its identifiers to be visible.
		4845
		4846	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4847	wants to use libev.
		4848
		4849	This option only works when libev is compiled with a C compiler, as C++
		4850	doesn't support the required declaration syntax.
4262		4851
4263	=item EV_AVOID_STDIO	4852	=item EV_AVOID_STDIO
4264		4853
4265	If this is set to C<1> at compiletime, then libev will avoid using stdio	4854	If this is set to C<1> at compiletime, then libev will avoid using stdio
4266	functions (printf, scanf, perror etc.). This will increase the code size	4855	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4410	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4999	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4411		5000
4412	#include "ev_cpp.h"	5001	#include "ev_cpp.h"
4413	#include "ev.c"	5002	#include "ev.c"
4414		5003
4415	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5004	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4416		5005
4417	=head2 THREADS AND COROUTINES	5006	=head2 THREADS AND COROUTINES
4418		5007
4419	=head3 THREADS	5008	=head3 THREADS
4420		5009
…		…
4471	default loop and triggering an C<ev_async> watcher from the default loop	5060	default loop and triggering an C<ev_async> watcher from the default loop
4472	watcher callback into the event loop interested in the signal.	5061	watcher callback into the event loop interested in the signal.
4473		5062
4474	=back	5063	=back
4475		5064
4476	=head4 THREAD LOCKING EXAMPLE	5065	See also L</THREAD LOCKING EXAMPLE>.
4477
4478	Here is a fictitious example of how to run an event loop in a different
4479	thread than where callbacks are being invoked and watchers are
4480	created/added/removed.
4481
4482	For a real-world example, see the C<EV::Loop::Async> perl module,
4483	which uses exactly this technique (which is suited for many high-level
4484	languages).
4485
4486	The example uses a pthread mutex to protect the loop data, a condition
4487	variable to wait for callback invocations, an async watcher to notify the
4488	event loop thread and an unspecified mechanism to wake up the main thread.
4489
4490	First, you need to associate some data with the event loop:
4491
4492	typedef struct {
4493	mutex_t lock; /* global loop lock */
4494	ev_async async_w;
4495	thread_t tid;
4496	cond_t invoke_cv;
4497	} userdata;
4498
4499	void prepare_loop (EV_P)
4500	{
4501	// for simplicity, we use a static userdata struct.
4502	static userdata u;
4503
4504	ev_async_init (&u->async_w, async_cb);
4505	ev_async_start (EV_A_ &u->async_w);
4506
4507	pthread_mutex_init (&u->lock, 0);
4508	pthread_cond_init (&u->invoke_cv, 0);
4509
4510	// now associate this with the loop
4511	ev_set_userdata (EV_A_ u);
4512	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4513	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4514
4515	// then create the thread running ev_loop
4516	pthread_create (&u->tid, 0, l_run, EV_A);
4517	}
4518
4519	The callback for the C<ev_async> watcher does nothing: the watcher is used
4520	solely to wake up the event loop so it takes notice of any new watchers
4521	that might have been added:
4522
4523	static void
4524	async_cb (EV_P_ ev_async *w, int revents)
4525	{
4526	// just used for the side effects
4527	}
4528
4529	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4530	protecting the loop data, respectively.
4531
4532	static void
4533	l_release (EV_P)
4534	{
4535	userdata *u = ev_userdata (EV_A);
4536	pthread_mutex_unlock (&u->lock);
4537	}
4538
4539	static void
4540	l_acquire (EV_P)
4541	{
4542	userdata *u = ev_userdata (EV_A);
4543	pthread_mutex_lock (&u->lock);
4544	}
4545
4546	The event loop thread first acquires the mutex, and then jumps straight
4547	into C<ev_run>:
4548
4549	void *
4550	l_run (void *thr_arg)
4551	{
4552	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4553
4554	l_acquire (EV_A);
4555	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4556	ev_run (EV_A_ 0);
4557	l_release (EV_A);
4558
4559	return 0;
4560	}
4561
4562	Instead of invoking all pending watchers, the C<l_invoke> callback will
4563	signal the main thread via some unspecified mechanism (signals? pipe
4564	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4565	have been called (in a while loop because a) spurious wakeups are possible
4566	and b) skipping inter-thread-communication when there are no pending
4567	watchers is very beneficial):
4568
4569	static void
4570	l_invoke (EV_P)
4571	{
4572	userdata *u = ev_userdata (EV_A);
4573
4574	while (ev_pending_count (EV_A))
4575	{
4576	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4577	pthread_cond_wait (&u->invoke_cv, &u->lock);
4578	}
4579	}
4580
4581	Now, whenever the main thread gets told to invoke pending watchers, it
4582	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4583	thread to continue:
4584
4585	static void
4586	real_invoke_pending (EV_P)
4587	{
4588	userdata *u = ev_userdata (EV_A);
4589
4590	pthread_mutex_lock (&u->lock);
4591	ev_invoke_pending (EV_A);
4592	pthread_cond_signal (&u->invoke_cv);
4593	pthread_mutex_unlock (&u->lock);
4594	}
4595
4596	Whenever you want to start/stop a watcher or do other modifications to an
4597	event loop, you will now have to lock:
4598
4599	ev_timer timeout_watcher;
4600	userdata *u = ev_userdata (EV_A);
4601
4602	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4603
4604	pthread_mutex_lock (&u->lock);
4605	ev_timer_start (EV_A_ &timeout_watcher);
4606	ev_async_send (EV_A_ &u->async_w);
4607	pthread_mutex_unlock (&u->lock);
4608
4609	Note that sending the C<ev_async> watcher is required because otherwise
4610	an event loop currently blocking in the kernel will have no knowledge
4611	about the newly added timer. By waking up the loop it will pick up any new
4612	watchers in the next event loop iteration.
4613		5066
4614	=head3 COROUTINES	5067	=head3 COROUTINES
4615		5068
4616	Libev is very accommodating to coroutines ("cooperative threads"):	5069	Libev is very accommodating to coroutines ("cooperative threads"):
4617	libev fully supports nesting calls to its functions from different	5070	libev fully supports nesting calls to its functions from different
…		…
4782	requires, and its I/O model is fundamentally incompatible with the POSIX	5235	requires, and its I/O model is fundamentally incompatible with the POSIX
4783	model. Libev still offers limited functionality on this platform in	5236	model. Libev still offers limited functionality on this platform in
4784	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5237	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4785	descriptors. This only applies when using Win32 natively, not when using	5238	descriptors. This only applies when using Win32 natively, not when using
4786	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5239	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4787	as every compielr comes with a slightly differently broken/incompatible	5240	as every compiler comes with a slightly differently broken/incompatible
4788	environment.	5241	environment.
4789		5242
4790	Lifting these limitations would basically require the full	5243	Lifting these limitations would basically require the full
4791	re-implementation of the I/O system. If you are into this kind of thing,	5244	re-implementation of the I/O system. If you are into this kind of thing,
4792	then note that glib does exactly that for you in a very portable way (note	5245	then note that glib does exactly that for you in a very portable way (note
…		…
4886	structure (guaranteed by POSIX but not by ISO C for example), but it also	5339	structure (guaranteed by POSIX but not by ISO C for example), but it also
4887	assumes that the same (machine) code can be used to call any watcher	5340	assumes that the same (machine) code can be used to call any watcher
4888	callback: The watcher callbacks have different type signatures, but libev	5341	callback: The watcher callbacks have different type signatures, but libev
4889	calls them using an C<ev_watcher *> internally.	5342	calls them using an C<ev_watcher *> internally.
4890		5343
		5344	=item null pointers and integer zero are represented by 0 bytes
		5345
		5346	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5347	relies on this setting pointers and integers to null.
		5348
4891	=item pointer accesses must be thread-atomic	5349	=item pointer accesses must be thread-atomic
4892		5350
4893	Accessing a pointer value must be atomic, it must both be readable and	5351	Accessing a pointer value must be atomic, it must both be readable and
4894	writable in one piece - this is the case on all current architectures.	5352	writable in one piece - this is the case on all current architectures.
4895		5353
…		…
4908	thread" or will block signals process-wide, both behaviours would	5366	thread" or will block signals process-wide, both behaviours would
4909	be compatible with libev. Interaction between C<sigprocmask> and	5367	be compatible with libev. Interaction between C<sigprocmask> and
4910	C<pthread_sigmask> could complicate things, however.	5368	C<pthread_sigmask> could complicate things, however.
4911		5369
4912	The most portable way to handle signals is to block signals in all threads	5370	The most portable way to handle signals is to block signals in all threads
4913	except the initial one, and run the default loop in the initial thread as	5371	except the initial one, and run the signal handling loop in the initial
4914	well.	5372	thread as well.
4915		5373
4916	=item C<long> must be large enough for common memory allocation sizes	5374	=item C<long> must be large enough for common memory allocation sizes
4917		5375
4918	To improve portability and simplify its API, libev uses C<long> internally	5376	To improve portability and simplify its API, libev uses C<long> internally
4919	instead of C<size_t> when allocating its data structures. On non-POSIX	5377	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4925		5383
4926	The type C<double> is used to represent timestamps. It is required to	5384	The type C<double> is used to represent timestamps. It is required to
4927	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5385	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4928	good enough for at least into the year 4000 with millisecond accuracy	5386	good enough for at least into the year 4000 with millisecond accuracy
4929	(the design goal for libev). This requirement is overfulfilled by	5387	(the design goal for libev). This requirement is overfulfilled by
4930	implementations using IEEE 754, which is basically all existing ones. With	5388	implementations using IEEE 754, which is basically all existing ones.
		5389
4931	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5390	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5391	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5392	is either obsolete or somebody patched it to use C<long double> or
		5393	something like that, just kidding).
4932		5394
4933	=back	5395	=back
4934		5396
4935	If you know of other additional requirements drop me a note.	5397	If you know of other additional requirements drop me a note.
4936		5398
…		…
4998	=item Processing ev_async_send: O(number_of_async_watchers)	5460	=item Processing ev_async_send: O(number_of_async_watchers)
4999		5461
5000	=item Processing signals: O(max_signal_number)	5462	=item Processing signals: O(max_signal_number)
5001		5463
5002	Sending involves a system call I<iff> there were no other C<ev_async_send>	5464	Sending involves a system call I<iff> there were no other C<ev_async_send>
5003	calls in the current loop iteration. Checking for async and signal events	5465	calls in the current loop iteration and the loop is currently
		5466	blocked. Checking for async and signal events involves iterating over all
5004	involves iterating over all running async watchers or all signal numbers.	5467	running async watchers or all signal numbers.
5005		5468
5006	=back	5469	=back
5007		5470
5008		5471
5009	=head1 PORTING FROM LIBEV 3.X TO 4.X	5472	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5018	=over 4	5481	=over 4
5019		5482
5020	=item C<EV_COMPAT3> backwards compatibility mechanism	5483	=item C<EV_COMPAT3> backwards compatibility mechanism
5021		5484
5022	The backward compatibility mechanism can be controlled by	5485	The backward compatibility mechanism can be controlled by
5023	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5486	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
5024	section.	5487	section.
5025		5488
5026	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5489	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
5027		5490
5028	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5491	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
5071	=over 4	5534	=over 4
5072		5535
5073	=item active	5536	=item active
5074		5537
5075	A watcher is active as long as it has been started and not yet stopped.	5538	A watcher is active as long as it has been started and not yet stopped.
5076	See L<WATCHER STATES> for details.	5539	See L</WATCHER STATES> for details.
5077		5540
5078	=item application	5541	=item application
5079		5542
5080	In this document, an application is whatever is using libev.	5543	In this document, an application is whatever is using libev.
5081		5544
…		…
5117	watchers and events.	5580	watchers and events.
5118		5581
5119	=item pending	5582	=item pending
5120		5583
5121	A watcher is pending as soon as the corresponding event has been	5584	A watcher is pending as soon as the corresponding event has been
5122	detected. See L<WATCHER STATES> for details.	5585	detected. See L</WATCHER STATES> for details.
5123		5586
5124	=item real time	5587	=item real time
5125		5588
5126	The physical time that is observed. It is apparently strictly monotonic :)	5589	The physical time that is observed. It is apparently strictly monotonic :)
5127		5590
5128	=item wall-clock time	5591	=item wall-clock time
5129		5592
5130	The time and date as shown on clocks. Unlike real time, it can actually	5593	The time and date as shown on clocks. Unlike real time, it can actually
5131	be wrong and jump forwards and backwards, e.g. when the you adjust your	5594	be wrong and jump forwards and backwards, e.g. when you adjust your
5132	clock.	5595	clock.
5133		5596
5134	=item watcher	5597	=item watcher
5135		5598
5136	A data structure that describes interest in certain events. Watchers need	5599	A data structure that describes interest in certain events. Watchers need
…		…
5139	=back	5602	=back
5140		5603
5141	=head1 AUTHOR	5604	=head1 AUTHOR
5142		5605
5143	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5606	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5144	Magnusson and Emanuele Giaquinta.	5607	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5145		5608

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