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Revision 1.442 by root, Mon Jul 30 22:23:50 2018 UTC

		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
…		…
277	}	285	}
278		286
279	...	287	...
280	ev_set_allocator (persistent_realloc);	288	ev_set_allocator (persistent_realloc);
281		289
282	=item ev_set_syserr_cb (void (*cb)(const char *msg))	290	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
283		291
284	Set the callback function to call on a retryable system call error (such	292	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	293	as failed select, poll, epoll_wait). The message is a printable string
286	indicating the system call or subsystem causing the problem. If this	294	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	295	callback is set, then libev will expect it to remedy the situation, no
…		…
299	}	307	}
300		308
301	...	309	...
302	ev_set_syserr_cb (fatal_error);	310	ev_set_syserr_cb (fatal_error);
303		311
		312	=item ev_feed_signal (int signum)
		313
		314	This function can be used to "simulate" a signal receive. It is completely
		315	safe to call this function at any time, from any context, including signal
		316	handlers or random threads.
		317
		318	Its main use is to customise signal handling in your process, especially
		319	in the presence of threads. For example, you could block signals
		320	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		321	creating any loops), and in one thread, use C<sigwait> or any other
		322	mechanism to wait for signals, then "deliver" them to libev by calling
		323	C<ev_feed_signal>.
		324
304	=back	325	=back
305		326
306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	327	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
307		328
308	An event loop is described by a C<struct ev_loop *> (the C<struct> is	329	An event loop is described by a C<struct ev_loop *> (the C<struct> is
…		…
377		398
378	If this flag bit is or'ed into the flag value (or the program runs setuid	399	If this flag bit is or'ed into the flag value (or the program runs setuid
379	or setgid) then libev will I<not> look at the environment variable	400	or setgid) then libev will I<not> look at the environment variable
380	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	401	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
381	override the flags completely if it is found in the environment. This is	402	override the flags completely if it is found in the environment. This is
382	useful to try out specific backends to test their performance, or to work	403	useful to try out specific backends to test their performance, to work
383	around bugs.	404	around bugs, or to make libev threadsafe (accessing environment variables
		405	cannot be done in a threadsafe way, but usually it works if no other
		406	thread modifies them).
384		407
385	=item C<EVFLAG_FORKCHECK>	408	=item C<EVFLAG_FORKCHECK>
386		409
387	Instead of calling C<ev_loop_fork> manually after a fork, you can also	410	Instead of calling C<ev_loop_fork> manually after a fork, you can also
388	make libev check for a fork in each iteration by enabling this flag.	411	make libev check for a fork in each iteration by enabling this flag.
389		412
390	This works by calling C<getpid ()> on every iteration of the loop,	413	This works by calling C<getpid ()> on every iteration of the loop,
391	and thus this might slow down your event loop if you do a lot of loop	414	and thus this might slow down your event loop if you do a lot of loop
392	iterations and little real work, but is usually not noticeable (on my	415	iterations and little real work, but is usually not noticeable (on my
393	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	416	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
394	without a system call and thus I<very> fast, but my GNU/Linux system also has	417	sequence without a system call and thus I<very> fast, but my GNU/Linux
395	C<pthread_atfork> which is even faster).	418	system also has C<pthread_atfork> which is even faster). (Update: glibc
		419	versions 2.25 apparently removed the C<getpid> optimisation again).
396		420
397	The big advantage of this flag is that you can forget about fork (and	421	The big advantage of this flag is that you can forget about fork (and
398	forget about forgetting to tell libev about forking) when you use this	422	forget about forgetting to tell libev about forking, although you still
399	flag.	423	have to ignore C<SIGPIPE>) when you use this flag.
400		424
401	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	425	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
402	environment variable.	426	environment variable.
403		427
404	=item C<EVFLAG_NOINOTIFY>	428	=item C<EVFLAG_NOINOTIFY>
…		…
419		443
420	Signalfd will not be used by default as this changes your signal mask, and	444	Signalfd will not be used by default as this changes your signal mask, and
421	there are a lot of shoddy libraries and programs (glib's threadpool for	445	there are a lot of shoddy libraries and programs (glib's threadpool for
422	example) that can't properly initialise their signal masks.	446	example) that can't properly initialise their signal masks.
423		447
		448	=item C<EVFLAG_NOSIGMASK>
		449
		450	When this flag is specified, then libev will avoid to modify the signal
		451	mask. Specifically, this means you have to make sure signals are unblocked
		452	when you want to receive them.
		453
		454	This behaviour is useful when you want to do your own signal handling, or
		455	want to handle signals only in specific threads and want to avoid libev
		456	unblocking the signals.
		457
		458	It's also required by POSIX in a threaded program, as libev calls
		459	C<sigprocmask>, whose behaviour is officially unspecified.
		460
		461	This flag's behaviour will become the default in future versions of libev.
		462
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	463	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		464
426	This is your standard select(2) backend. Not I<completely> standard, as	465	This is your standard select(2) backend. Not I<completely> standard, as
427	libev tries to roll its own fd_set with no limits on the number of fds,	466	libev tries to roll its own fd_set with no limits on the number of fds,
428	but if that fails, expect a fairly low limit on the number of fds when	467	but if that fails, expect a fairly low limit on the number of fds when
…		…
455	=item C<EVBACKEND_EPOLL> (value 4, Linux)	494	=item C<EVBACKEND_EPOLL> (value 4, Linux)
456		495
457	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	496	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
458	kernels).	497	kernels).
459		498
460	For few fds, this backend is a bit little slower than poll and select,	499	For few fds, this backend is a bit little slower than poll and select, but
461	but it scales phenomenally better. While poll and select usually scale	500	it scales phenomenally better. While poll and select usually scale like
462	like O(total_fds) where n is the total number of fds (or the highest fd),	501	O(total_fds) where total_fds is the total number of fds (or the highest
463	epoll scales either O(1) or O(active_fds).	502	fd), epoll scales either O(1) or O(active_fds).
464		503
465	The epoll mechanism deserves honorable mention as the most misdesigned	504	The epoll mechanism deserves honorable mention as the most misdesigned
466	of the more advanced event mechanisms: mere annoyances include silently	505	of the more advanced event mechanisms: mere annoyances include silently
467	dropping file descriptors, requiring a system call per change per file	506	dropping file descriptors, requiring a system call per change per file
468	descriptor (and unnecessary guessing of parameters), problems with dup,	507	descriptor (and unnecessary guessing of parameters), problems with dup,
…		…
471	0.1ms) and so on. The biggest issue is fork races, however - if a program	510	0.1ms) and so on. The biggest issue is fork races, however - if a program
472	forks then I<both> parent and child process have to recreate the epoll	511	forks then I<both> parent and child process have to recreate the epoll
473	set, which can take considerable time (one syscall per file descriptor)	512	set, which can take considerable time (one syscall per file descriptor)
474	and is of course hard to detect.	513	and is of course hard to detect.
475		514
476	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	515	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
477	of course I<doesn't>, and epoll just loves to report events for totally	516	but of course I<doesn't>, and epoll just loves to report events for
478	I<different> file descriptors (even already closed ones, so one cannot	517	totally I<different> file descriptors (even already closed ones, so
479	even remove them from the set) than registered in the set (especially	518	one cannot even remove them from the set) than registered in the set
480	on SMP systems). Libev tries to counter these spurious notifications by	519	(especially on SMP systems). Libev tries to counter these spurious
481	employing an additional generation counter and comparing that against the	520	notifications by employing an additional generation counter and comparing
482	events to filter out spurious ones, recreating the set when required. Last	521	that against the events to filter out spurious ones, recreating the set
		522	when required. Epoll also erroneously rounds down timeouts, but gives you
		523	no way to know when and by how much, so sometimes you have to busy-wait
		524	because epoll returns immediately despite a nonzero timeout. And last
483	not least, it also refuses to work with some file descriptors which work	525	not least, it also refuses to work with some file descriptors which work
484	perfectly fine with C<select> (files, many character devices...).	526	perfectly fine with C<select> (files, many character devices...).
485		527
486	Epoll is truly the train wreck analog among event poll mechanisms.	528	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		529	cobbled together in a hurry, no thought to design or interaction with
		530	others. Oh, the pain, will it ever stop...
487		531
488	While stopping, setting and starting an I/O watcher in the same iteration	532	While stopping, setting and starting an I/O watcher in the same iteration
489	will result in some caching, there is still a system call per such	533	will result in some caching, there is still a system call per such
490	incident (because the same I<file descriptor> could point to a different	534	incident (because the same I<file descriptor> could point to a different
491	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	535	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
528		572
529	It scales in the same way as the epoll backend, but the interface to the	573	It scales in the same way as the epoll backend, but the interface to the
530	kernel is more efficient (which says nothing about its actual speed, of	574	kernel is more efficient (which says nothing about its actual speed, of
531	course). While stopping, setting and starting an I/O watcher does never	575	course). While stopping, setting and starting an I/O watcher does never
532	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	576	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
533	two event changes per incident. Support for C<fork ()> is very bad (but	577	two event changes per incident. Support for C<fork ()> is very bad (you
534	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	578	might have to leak fd's on fork, but it's more sane than epoll) and it
535	cases	579	drops fds silently in similarly hard-to-detect cases.
536		580
537	This backend usually performs well under most conditions.	581	This backend usually performs well under most conditions.
538		582
539	While nominally embeddable in other event loops, this doesn't work	583	While nominally embeddable in other event loops, this doesn't work
540	everywhere, so you might need to test for this. And since it is broken	584	everywhere, so you might need to test for this. And since it is broken
…		…
557	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	601	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
558		602
559	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	603	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
560	it's really slow, but it still scales very well (O(active_fds)).	604	it's really slow, but it still scales very well (O(active_fds)).
561		605
562	Please note that Solaris event ports can deliver a lot of spurious
563	notifications, so you need to use non-blocking I/O or other means to avoid
564	blocking when no data (or space) is available.
565
566	While this backend scales well, it requires one system call per active	606	While this backend scales well, it requires one system call per active
567	file descriptor per loop iteration. For small and medium numbers of file	607	file descriptor per loop iteration. For small and medium numbers of file
568	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	608	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
569	might perform better.	609	might perform better.
570		610
571	On the positive side, with the exception of the spurious readiness	611	On the positive side, this backend actually performed fully to
572	notifications, this backend actually performed fully to specification
573	in all tests and is fully embeddable, which is a rare feat among the	612	specification in all tests and is fully embeddable, which is a rare feat
574	OS-specific backends (I vastly prefer correctness over speed hacks).	613	among the OS-specific backends (I vastly prefer correctness over speed
		614	hacks).
		615
		616	On the negative side, the interface is I<bizarre> - so bizarre that
		617	even sun itself gets it wrong in their code examples: The event polling
		618	function sometimes returns events to the caller even though an error
		619	occurred, but with no indication whether it has done so or not (yes, it's
		620	even documented that way) - deadly for edge-triggered interfaces where you
		621	absolutely have to know whether an event occurred or not because you have
		622	to re-arm the watcher.
		623
		624	Fortunately libev seems to be able to work around these idiocies.
575		625
576	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	626	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
577	C<EVBACKEND_POLL>.	627	C<EVBACKEND_POLL>.
578		628
579	=item C<EVBACKEND_ALL>	629	=item C<EVBACKEND_ALL>
580		630
581	Try all backends (even potentially broken ones that wouldn't be tried	631	Try all backends (even potentially broken ones that wouldn't be tried
582	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	632	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
583	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	633	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
584		634
585	It is definitely not recommended to use this flag.	635	It is definitely not recommended to use this flag, use whatever
		636	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		637	at all.
		638
		639	=item C<EVBACKEND_MASK>
		640
		641	Not a backend at all, but a mask to select all backend bits from a
		642	C<flags> value, in case you want to mask out any backends from a flags
		643	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
586		644
587	=back	645	=back
588		646
589	If one or more of the backend flags are or'ed into the flags value,	647	If one or more of the backend flags are or'ed into the flags value,
590	then only these backends will be tried (in the reverse order as listed	648	then only these backends will be tried (in the reverse order as listed
…		…
625	If you need dynamically allocated loops it is better to use C<ev_loop_new>	683	If you need dynamically allocated loops it is better to use C<ev_loop_new>
626	and C<ev_loop_destroy>.	684	and C<ev_loop_destroy>.
627		685
628	=item ev_loop_fork (loop)	686	=item ev_loop_fork (loop)
629		687
630	This function sets a flag that causes subsequent C<ev_run> iterations to	688	This function sets a flag that causes subsequent C<ev_run> iterations
631	reinitialise the kernel state for backends that have one. Despite the	689	to reinitialise the kernel state for backends that have one. Despite
632	name, you can call it anytime, but it makes most sense after forking, in	690	the name, you can call it anytime you are allowed to start or stop
633	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the	691	watchers (except inside an C<ev_prepare> callback), but it makes most
		692	sense after forking, in the child process. You I<must> call it (or use
634	child before resuming or calling C<ev_run>.	693	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
635		694
		695	In addition, if you want to reuse a loop (via this function or
		696	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		697
636	Again, you I<have> to call it on I<any> loop that you want to re-use after	698	Again, you I<have> to call it on I<any> loop that you want to re-use after
637	a fork, I<even if you do not plan to use the loop in the parent>. This is	699	a fork, I<even if you do not plan to use the loop in the parent>. This is
638	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	700	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
639	during fork.	701	during fork.
640		702
641	On the other hand, you only need to call this function in the child	703	On the other hand, you only need to call this function in the child
…		…
711		773
712	This function is rarely useful, but when some event callback runs for a	774	This function is rarely useful, but when some event callback runs for a
713	very long time without entering the event loop, updating libev's idea of	775	very long time without entering the event loop, updating libev's idea of
714	the current time is a good idea.	776	the current time is a good idea.
715		777
716	See also L<The special problem of time updates> in the C<ev_timer> section.	778	See also L</The special problem of time updates> in the C<ev_timer> section.
717		779
718	=item ev_suspend (loop)	780	=item ev_suspend (loop)
719		781
720	=item ev_resume (loop)	782	=item ev_resume (loop)
721		783
…		…
739	without a previous call to C<ev_suspend>.	801	without a previous call to C<ev_suspend>.
740		802
741	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	803	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
742	event loop time (see C<ev_now_update>).	804	event loop time (see C<ev_now_update>).
743		805
744	=item ev_run (loop, int flags)	806	=item bool ev_run (loop, int flags)
745		807
746	Finally, this is it, the event handler. This function usually is called	808	Finally, this is it, the event handler. This function usually is called
747	after you have initialised all your watchers and you want to start	809	after you have initialised all your watchers and you want to start
748	handling events. It will ask the operating system for any new events, call	810	handling events. It will ask the operating system for any new events, call
749	the watcher callbacks, an then repeat the whole process indefinitely: This	811	the watcher callbacks, and then repeat the whole process indefinitely: This
750	is why event loops are called I<loops>.	812	is why event loops are called I<loops>.
751		813
752	If the flags argument is specified as C<0>, it will keep handling events	814	If the flags argument is specified as C<0>, it will keep handling events
753	until either no event watchers are active anymore or C<ev_break> was	815	until either no event watchers are active anymore or C<ev_break> was
754	called.	816	called.
		817
		818	The return value is false if there are no more active watchers (which
		819	usually means "all jobs done" or "deadlock"), and true in all other cases
		820	(which usually means " you should call C<ev_run> again").
755		821
756	Please note that an explicit C<ev_break> is usually better than	822	Please note that an explicit C<ev_break> is usually better than
757	relying on all watchers to be stopped when deciding when a program has	823	relying on all watchers to be stopped when deciding when a program has
758	finished (especially in interactive programs), but having a program	824	finished (especially in interactive programs), but having a program
759	that automatically loops as long as it has to and no longer by virtue	825	that automatically loops as long as it has to and no longer by virtue
760	of relying on its watchers stopping correctly, that is truly a thing of	826	of relying on its watchers stopping correctly, that is truly a thing of
761	beauty.	827	beauty.
762		828
763	This function is also I<mostly> exception-safe - you can break out of	829	This function is I<mostly> exception-safe - you can break out of a
764	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++	830	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
765	exception and so on. This does not decrement the C<ev_depth> value, nor	831	exception and so on. This does not decrement the C<ev_depth> value, nor
766	will it clear any outstanding C<EVBREAK_ONE> breaks.	832	will it clear any outstanding C<EVBREAK_ONE> breaks.
767		833
768	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	834	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
769	those events and any already outstanding ones, but will not wait and	835	those events and any already outstanding ones, but will not wait and
…		…
781	This is useful if you are waiting for some external event in conjunction	847	This is useful if you are waiting for some external event in conjunction
782	with something not expressible using other libev watchers (i.e. "roll your	848	with something not expressible using other libev watchers (i.e. "roll your
783	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	849	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
784	usually a better approach for this kind of thing.	850	usually a better approach for this kind of thing.
785		851
786	Here are the gory details of what C<ev_run> does:	852	Here are the gory details of what C<ev_run> does (this is for your
		853	understanding, not a guarantee that things will work exactly like this in
		854	future versions):
787		855
788	- Increment loop depth.	856	- Increment loop depth.
789	- Reset the ev_break status.	857	- Reset the ev_break status.
790	- Before the first iteration, call any pending watchers.	858	- Before the first iteration, call any pending watchers.
791	LOOP:	859	LOOP:
…		…
824	anymore.	892	anymore.
825		893
826	... queue jobs here, make sure they register event watchers as long	894	... queue jobs here, make sure they register event watchers as long
827	... as they still have work to do (even an idle watcher will do..)	895	... as they still have work to do (even an idle watcher will do..)
828	ev_run (my_loop, 0);	896	ev_run (my_loop, 0);
829	... jobs done or somebody called unloop. yeah!	897	... jobs done or somebody called break. yeah!
830		898
831	=item ev_break (loop, how)	899	=item ev_break (loop, how)
832		900
833	Can be used to make a call to C<ev_run> return early (but only after it	901	Can be used to make a call to C<ev_run> return early (but only after it
834	has processed all outstanding events). The C<how> argument must be either	902	has processed all outstanding events). The C<how> argument must be either
…		…
897	overhead for the actual polling but can deliver many events at once.	965	overhead for the actual polling but can deliver many events at once.
898		966
899	By setting a higher I<io collect interval> you allow libev to spend more	967	By setting a higher I<io collect interval> you allow libev to spend more
900	time collecting I/O events, so you can handle more events per iteration,	968	time collecting I/O events, so you can handle more events per iteration,
901	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	969	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
902	C<ev_timer>) will be not affected. Setting this to a non-null value will	970	C<ev_timer>) will not be affected. Setting this to a non-null value will
903	introduce an additional C<ev_sleep ()> call into most loop iterations. The	971	introduce an additional C<ev_sleep ()> call into most loop iterations. The
904	sleep time ensures that libev will not poll for I/O events more often then	972	sleep time ensures that libev will not poll for I/O events more often then
905	once per this interval, on average.	973	once per this interval, on average (as long as the host time resolution is
		974	good enough).
906		975
907	Likewise, by setting a higher I<timeout collect interval> you allow libev	976	Likewise, by setting a higher I<timeout collect interval> you allow libev
908	to spend more time collecting timeouts, at the expense of increased	977	to spend more time collecting timeouts, at the expense of increased
909	latency/jitter/inexactness (the watcher callback will be called	978	latency/jitter/inexactness (the watcher callback will be called
910	later). C<ev_io> watchers will not be affected. Setting this to a non-null	979	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
956	invoke the actual watchers inside another context (another thread etc.).	1025	invoke the actual watchers inside another context (another thread etc.).
957		1026
958	If you want to reset the callback, use C<ev_invoke_pending> as new	1027	If you want to reset the callback, use C<ev_invoke_pending> as new
959	callback.	1028	callback.
960		1029
961	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1030	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
962		1031
963	Sometimes you want to share the same loop between multiple threads. This	1032	Sometimes you want to share the same loop between multiple threads. This
964	can be done relatively simply by putting mutex_lock/unlock calls around	1033	can be done relatively simply by putting mutex_lock/unlock calls around
965	each call to a libev function.	1034	each call to a libev function.
966		1035
967	However, C<ev_run> can run an indefinite time, so it is not feasible	1036	However, C<ev_run> can run an indefinite time, so it is not feasible
968	to wait for it to return. One way around this is to wake up the event	1037	to wait for it to return. One way around this is to wake up the event
969	loop via C<ev_break> and C<av_async_send>, another way is to set these	1038	loop via C<ev_break> and C<ev_async_send>, another way is to set these
970	I<release> and I<acquire> callbacks on the loop.	1039	I<release> and I<acquire> callbacks on the loop.
971		1040
972	When set, then C<release> will be called just before the thread is	1041	When set, then C<release> will be called just before the thread is
973	suspended waiting for new events, and C<acquire> is called just	1042	suspended waiting for new events, and C<acquire> is called just
974	afterwards.	1043	afterwards.
…		…
1114		1183
1115	=item C<EV_PREPARE>	1184	=item C<EV_PREPARE>
1116		1185
1117	=item C<EV_CHECK>	1186	=item C<EV_CHECK>
1118		1187
1119	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1188	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1120	to gather new events, and all C<ev_check> watchers are invoked just after	1189	gather new events, and all C<ev_check> watchers are queued (not invoked)
1121	C<ev_run> has gathered them, but before it invokes any callbacks for any	1190	just after C<ev_run> has gathered them, but before it queues any callbacks
		1191	for any received events. That means C<ev_prepare> watchers are the last
		1192	watchers invoked before the event loop sleeps or polls for new events, and
		1193	C<ev_check> watchers will be invoked before any other watchers of the same
		1194	or lower priority within an event loop iteration.
		1195
1122	received events. Callbacks of both watcher types can start and stop as	1196	Callbacks of both watcher types can start and stop as many watchers as
1123	many watchers as they want, and all of them will be taken into account	1197	they want, and all of them will be taken into account (for example, a
1124	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1198	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1125	C<ev_run> from blocking).	1199	blocking).
1126		1200
1127	=item C<EV_EMBED>	1201	=item C<EV_EMBED>
1128		1202
1129	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1203	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1130		1204
…		…
1253		1327
1254	=item callback ev_cb (ev_TYPE *watcher)	1328	=item callback ev_cb (ev_TYPE *watcher)
1255		1329
1256	Returns the callback currently set on the watcher.	1330	Returns the callback currently set on the watcher.
1257		1331
1258	=item ev_cb_set (ev_TYPE *watcher, callback)	1332	=item ev_set_cb (ev_TYPE *watcher, callback)
1259		1333
1260	Change the callback. You can change the callback at virtually any time	1334	Change the callback. You can change the callback at virtually any time
1261	(modulo threads).	1335	(modulo threads).
1262		1336
1263	=item ev_set_priority (ev_TYPE *watcher, int priority)	1337	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1281	or might not have been clamped to the valid range.	1355	or might not have been clamped to the valid range.
1282		1356
1283	The default priority used by watchers when no priority has been set is	1357	The default priority used by watchers when no priority has been set is
1284	always C<0>, which is supposed to not be too high and not be too low :).	1358	always C<0>, which is supposed to not be too high and not be too low :).
1285		1359
1286	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1360	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1287	priorities.	1361	priorities.
1288		1362
1289	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1363	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1290		1364
1291	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1365	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1316	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1390	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1317	functions that do not need a watcher.	1391	functions that do not need a watcher.
1318		1392
1319	=back	1393	=back
1320		1394
1321	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1395	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1322		1396	OWN COMPOSITE WATCHERS> idioms.
1323	Each watcher has, by default, a member C<void *data> that you can change
1324	and read at any time: libev will completely ignore it. This can be used
1325	to associate arbitrary data with your watcher. If you need more data and
1326	don't want to allocate memory and store a pointer to it in that data
1327	member, you can also "subclass" the watcher type and provide your own
1328	data:
1329
1330	struct my_io
1331	{
1332	ev_io io;
1333	int otherfd;
1334	void *somedata;
1335	struct whatever *mostinteresting;
1336	};
1337
1338	...
1339	struct my_io w;
1340	ev_io_init (&w.io, my_cb, fd, EV_READ);
1341
1342	And since your callback will be called with a pointer to the watcher, you
1343	can cast it back to your own type:
1344
1345	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1346	{
1347	struct my_io *w = (struct my_io *)w_;
1348	...
1349	}
1350
1351	More interesting and less C-conformant ways of casting your callback type
1352	instead have been omitted.
1353
1354	Another common scenario is to use some data structure with multiple
1355	embedded watchers:
1356
1357	struct my_biggy
1358	{
1359	int some_data;
1360	ev_timer t1;
1361	ev_timer t2;
1362	}
1363
1364	In this case getting the pointer to C<my_biggy> is a bit more
1365	complicated: Either you store the address of your C<my_biggy> struct
1366	in the C<data> member of the watcher (for woozies), or you need to use
1367	some pointer arithmetic using C<offsetof> inside your watchers (for real
1368	programmers):
1369
1370	#include <stddef.h>
1371
1372	static void
1373	t1_cb (EV_P_ ev_timer *w, int revents)
1374	{
1375	struct my_biggy big = (struct my_biggy *)
1376	(((char *)w) - offsetof (struct my_biggy, t1));
1377	}
1378
1379	static void
1380	t2_cb (EV_P_ ev_timer *w, int revents)
1381	{
1382	struct my_biggy big = (struct my_biggy *)
1383	(((char *)w) - offsetof (struct my_biggy, t2));
1384	}
1385		1397
1386	=head2 WATCHER STATES	1398	=head2 WATCHER STATES
1387		1399
1388	There are various watcher states mentioned throughout this manual -	1400	There are various watcher states mentioned throughout this manual -
1389	active, pending and so on. In this section these states and the rules to	1401	active, pending and so on. In this section these states and the rules to
1390	transition between them will be described in more detail - and while these	1402	transition between them will be described in more detail - and while these
1391	rules might look complicated, they usually do "the right thing".	1403	rules might look complicated, they usually do "the right thing".
1392		1404
1393	=over 4	1405	=over 4
1394		1406
1395	=item initialiased	1407	=item initialised
1396		1408
1397	Before a watcher can be registered with the event looop it has to be	1409	Before a watcher can be registered with the event loop it has to be
1398	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1410	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1399	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1411	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1400		1412
1401	In this state it is simply some block of memory that is suitable for use	1413	In this state it is simply some block of memory that is suitable for
1402	in an event loop. It can be moved around, freed, reused etc. at will.	1414	use in an event loop. It can be moved around, freed, reused etc. at
		1415	will - as long as you either keep the memory contents intact, or call
		1416	C<ev_TYPE_init> again.
1403		1417
1404	=item started/running/active	1418	=item started/running/active
1405		1419
1406	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1420	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1407	property of the event loop, and is actively waiting for events. While in	1421	property of the event loop, and is actively waiting for events. While in
…		…
1435	latter will clear any pending state the watcher might be in, regardless	1449	latter will clear any pending state the watcher might be in, regardless
1436	of whether it was active or not, so stopping a watcher explicitly before	1450	of whether it was active or not, so stopping a watcher explicitly before
1437	freeing it is often a good idea.	1451	freeing it is often a good idea.
1438		1452
1439	While stopped (and not pending) the watcher is essentially in the	1453	While stopped (and not pending) the watcher is essentially in the
1440	initialised state, that is it can be reused, moved, modified in any way	1454	initialised state, that is, it can be reused, moved, modified in any way
1441	you wish.	1455	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1456	it again).
1442		1457
1443	=back	1458	=back
1444		1459
1445	=head2 WATCHER PRIORITY MODELS	1460	=head2 WATCHER PRIORITY MODELS
1446		1461
…		…
1575	In general you can register as many read and/or write event watchers per	1590	In general you can register as many read and/or write event watchers per
1576	fd as you want (as long as you don't confuse yourself). Setting all file	1591	fd as you want (as long as you don't confuse yourself). Setting all file
1577	descriptors to non-blocking mode is also usually a good idea (but not	1592	descriptors to non-blocking mode is also usually a good idea (but not
1578	required if you know what you are doing).	1593	required if you know what you are doing).
1579		1594
1580	If you cannot use non-blocking mode, then force the use of a
1581	known-to-be-good backend (at the time of this writing, this includes only
1582	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1583	descriptors for which non-blocking operation makes no sense (such as
1584	files) - libev doesn't guarantee any specific behaviour in that case.
1585
1586	Another thing you have to watch out for is that it is quite easy to	1595	Another thing you have to watch out for is that it is quite easy to
1587	receive "spurious" readiness notifications, that is your callback might	1596	receive "spurious" readiness notifications, that is, your callback might
1588	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1597	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1589	because there is no data. Not only are some backends known to create a	1598	because there is no data. It is very easy to get into this situation even
1590	lot of those (for example Solaris ports), it is very easy to get into	1599	with a relatively standard program structure. Thus it is best to always
1591	this situation even with a relatively standard program structure. Thus	1600	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1592	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1593	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1601	preferable to a program hanging until some data arrives.
1594		1602
1595	If you cannot run the fd in non-blocking mode (for example you should	1603	If you cannot run the fd in non-blocking mode (for example you should
1596	not play around with an Xlib connection), then you have to separately	1604	not play around with an Xlib connection), then you have to separately
1597	re-test whether a file descriptor is really ready with a known-to-be good	1605	re-test whether a file descriptor is really ready with a known-to-be good
1598	interface such as poll (fortunately in our Xlib example, Xlib already	1606	interface such as poll (fortunately in the case of Xlib, it already does
1599	does this on its own, so its quite safe to use). Some people additionally	1607	this on its own, so its quite safe to use). Some people additionally
1600	use C<SIGALRM> and an interval timer, just to be sure you won't block	1608	use C<SIGALRM> and an interval timer, just to be sure you won't block
1601	indefinitely.	1609	indefinitely.
1602		1610
1603	But really, best use non-blocking mode.	1611	But really, best use non-blocking mode.
1604		1612
…		…
1632		1640
1633	There is no workaround possible except not registering events	1641	There is no workaround possible except not registering events
1634	for potentially C<dup ()>'ed file descriptors, or to resort to	1642	for potentially C<dup ()>'ed file descriptors, or to resort to
1635	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1643	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1636		1644
		1645	=head3 The special problem of files
		1646
		1647	Many people try to use C<select> (or libev) on file descriptors
		1648	representing files, and expect it to become ready when their program
		1649	doesn't block on disk accesses (which can take a long time on their own).
		1650
		1651	However, this cannot ever work in the "expected" way - you get a readiness
		1652	notification as soon as the kernel knows whether and how much data is
		1653	there, and in the case of open files, that's always the case, so you
		1654	always get a readiness notification instantly, and your read (or possibly
		1655	write) will still block on the disk I/O.
		1656
		1657	Another way to view it is that in the case of sockets, pipes, character
		1658	devices and so on, there is another party (the sender) that delivers data
		1659	on its own, but in the case of files, there is no such thing: the disk
		1660	will not send data on its own, simply because it doesn't know what you
		1661	wish to read - you would first have to request some data.
		1662
		1663	Since files are typically not-so-well supported by advanced notification
		1664	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1665	to files, even though you should not use it. The reason for this is
		1666	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1667	usually a tty, often a pipe, but also sometimes files or special devices
		1668	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1669	F</dev/urandom>), and even though the file might better be served with
		1670	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1671	it "just works" instead of freezing.
		1672
		1673	So avoid file descriptors pointing to files when you know it (e.g. use
		1674	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1675	when you rarely read from a file instead of from a socket, and want to
		1676	reuse the same code path.
		1677
1637	=head3 The special problem of fork	1678	=head3 The special problem of fork
1638		1679
1639	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1680	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1640	useless behaviour. Libev fully supports fork, but needs to be told about	1681	useless behaviour. Libev fully supports fork, but needs to be told about
1641	it in the child.	1682	it in the child if you want to continue to use it in the child.
1642		1683
1643	To support fork in your programs, you either have to call	1684	To support fork in your child processes, you have to call C<ev_loop_fork
1644	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1685	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1645	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1686	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1646	C<EVBACKEND_POLL>.
1647		1687
1648	=head3 The special problem of SIGPIPE	1688	=head3 The special problem of SIGPIPE
1649		1689
1650	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1690	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1651	when writing to a pipe whose other end has been closed, your program gets	1691	when writing to a pipe whose other end has been closed, your program gets
…		…
1749	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1789	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1750	monotonic clock option helps a lot here).	1790	monotonic clock option helps a lot here).
1751		1791
1752	The callback is guaranteed to be invoked only I<after> its timeout has	1792	The callback is guaranteed to be invoked only I<after> its timeout has
1753	passed (not I<at>, so on systems with very low-resolution clocks this	1793	passed (not I<at>, so on systems with very low-resolution clocks this
1754	might introduce a small delay). If multiple timers become ready during the	1794	might introduce a small delay, see "the special problem of being too
		1795	early", below). If multiple timers become ready during the same loop
1755	same loop iteration then the ones with earlier time-out values are invoked	1796	iteration then the ones with earlier time-out values are invoked before
1756	before ones of the same priority with later time-out values (but this is	1797	ones of the same priority with later time-out values (but this is no
1757	no longer true when a callback calls C<ev_run> recursively).	1798	longer true when a callback calls C<ev_run> recursively).
1758		1799
1759	=head3 Be smart about timeouts	1800	=head3 Be smart about timeouts
1760		1801
1761	Many real-world problems involve some kind of timeout, usually for error	1802	Many real-world problems involve some kind of timeout, usually for error
1762	recovery. A typical example is an HTTP request - if the other side hangs,	1803	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1837		1878
1838	In this case, it would be more efficient to leave the C<ev_timer> alone,	1879	In this case, it would be more efficient to leave the C<ev_timer> alone,
1839	but remember the time of last activity, and check for a real timeout only	1880	but remember the time of last activity, and check for a real timeout only
1840	within the callback:	1881	within the callback:
1841		1882
		1883	ev_tstamp timeout = 60.;
1842	ev_tstamp last_activity; // time of last activity	1884	ev_tstamp last_activity; // time of last activity
		1885	ev_timer timer;
1843		1886
1844	static void	1887	static void
1845	callback (EV_P_ ev_timer *w, int revents)	1888	callback (EV_P_ ev_timer *w, int revents)
1846	{	1889	{
1847	ev_tstamp now = ev_now (EV_A);	1890	// calculate when the timeout would happen
1848	ev_tstamp timeout = last_activity + 60.;	1891	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1849		1892
1850	// if last_activity + 60. is older than now, we did time out	1893	// if negative, it means we the timeout already occurred
1851	if (timeout < now)	1894	if (after < 0.)
1852	{	1895	{
1853	// timeout occurred, take action	1896	// timeout occurred, take action
1854	}	1897	}
1855	else	1898	else
1856	{	1899	{
1857	// callback was invoked, but there was some activity, re-arm	1900	// callback was invoked, but there was some recent
1858	// the watcher to fire in last_activity + 60, which is	1901	// activity. simply restart the timer to time out
1859	// guaranteed to be in the future, so "again" is positive:	1902	// after "after" seconds, which is the earliest time
1860	w->repeat = timeout - now;	1903	// the timeout can occur.
		1904	ev_timer_set (w, after, 0.);
1861	ev_timer_again (EV_A_ w);	1905	ev_timer_start (EV_A_ w);
1862	}	1906	}
1863	}	1907	}
1864		1908
1865	To summarise the callback: first calculate the real timeout (defined	1909	To summarise the callback: first calculate in how many seconds the
1866	as "60 seconds after the last activity"), then check if that time has	1910	timeout will occur (by calculating the absolute time when it would occur,
1867	been reached, which means something I<did>, in fact, time out. Otherwise	1911	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1868	the callback was invoked too early (C<timeout> is in the future), so	1912	(EV_A)> from that).
1869	re-schedule the timer to fire at that future time, to see if maybe we have
1870	a timeout then.
1871		1913
1872	Note how C<ev_timer_again> is used, taking advantage of the	1914	If this value is negative, then we are already past the timeout, i.e. we
1873	C<ev_timer_again> optimisation when the timer is already running.	1915	timed out, and need to do whatever is needed in this case.
		1916
		1917	Otherwise, we now the earliest time at which the timeout would trigger,
		1918	and simply start the timer with this timeout value.
		1919
		1920	In other words, each time the callback is invoked it will check whether
		1921	the timeout occurred. If not, it will simply reschedule itself to check
		1922	again at the earliest time it could time out. Rinse. Repeat.
1874		1923
1875	This scheme causes more callback invocations (about one every 60 seconds	1924	This scheme causes more callback invocations (about one every 60 seconds
1876	minus half the average time between activity), but virtually no calls to	1925	minus half the average time between activity), but virtually no calls to
1877	libev to change the timeout.	1926	libev to change the timeout.
1878		1927
1879	To start the timer, simply initialise the watcher and set C<last_activity>	1928	To start the machinery, simply initialise the watcher and set
1880	to the current time (meaning we just have some activity :), then call the	1929	C<last_activity> to the current time (meaning there was some activity just
1881	callback, which will "do the right thing" and start the timer:	1930	now), then call the callback, which will "do the right thing" and start
		1931	the timer:
1882		1932
		1933	last_activity = ev_now (EV_A);
1883	ev_init (timer, callback);	1934	ev_init (&timer, callback);
1884	last_activity = ev_now (loop);	1935	callback (EV_A_ &timer, 0);
1885	callback (loop, timer, EV_TIMER);
1886		1936
1887	And when there is some activity, simply store the current time in	1937	When there is some activity, simply store the current time in
1888	C<last_activity>, no libev calls at all:	1938	C<last_activity>, no libev calls at all:
1889		1939
		1940	if (activity detected)
1890	last_activity = ev_now (loop);	1941	last_activity = ev_now (EV_A);
		1942
		1943	When your timeout value changes, then the timeout can be changed by simply
		1944	providing a new value, stopping the timer and calling the callback, which
		1945	will again do the right thing (for example, time out immediately :).
		1946
		1947	timeout = new_value;
		1948	ev_timer_stop (EV_A_ &timer);
		1949	callback (EV_A_ &timer, 0);
1891		1950
1892	This technique is slightly more complex, but in most cases where the	1951	This technique is slightly more complex, but in most cases where the
1893	time-out is unlikely to be triggered, much more efficient.	1952	time-out is unlikely to be triggered, much more efficient.
1894
1895	Changing the timeout is trivial as well (if it isn't hard-coded in the
1896	callback :) - just change the timeout and invoke the callback, which will
1897	fix things for you.
1898		1953
1899	=item 4. Wee, just use a double-linked list for your timeouts.	1954	=item 4. Wee, just use a double-linked list for your timeouts.
1900		1955
1901	If there is not one request, but many thousands (millions...), all	1956	If there is not one request, but many thousands (millions...), all
1902	employing some kind of timeout with the same timeout value, then one can	1957	employing some kind of timeout with the same timeout value, then one can
…		…
1929	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1984	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1930	rather complicated, but extremely efficient, something that really pays	1985	rather complicated, but extremely efficient, something that really pays
1931	off after the first million or so of active timers, i.e. it's usually	1986	off after the first million or so of active timers, i.e. it's usually
1932	overkill :)	1987	overkill :)
1933		1988
		1989	=head3 The special problem of being too early
		1990
		1991	If you ask a timer to call your callback after three seconds, then
		1992	you expect it to be invoked after three seconds - but of course, this
		1993	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1994	guaranteed to any precision by libev - imagine somebody suspending the
		1995	process with a STOP signal for a few hours for example.
		1996
		1997	So, libev tries to invoke your callback as soon as possible I<after> the
		1998	delay has occurred, but cannot guarantee this.
		1999
		2000	A less obvious failure mode is calling your callback too early: many event
		2001	loops compare timestamps with a "elapsed delay >= requested delay", but
		2002	this can cause your callback to be invoked much earlier than you would
		2003	expect.
		2004
		2005	To see why, imagine a system with a clock that only offers full second
		2006	resolution (think windows if you can't come up with a broken enough OS
		2007	yourself). If you schedule a one-second timer at the time 500.9, then the
		2008	event loop will schedule your timeout to elapse at a system time of 500
		2009	(500.9 truncated to the resolution) + 1, or 501.
		2010
		2011	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2012	501" and invoke the callback 0.1s after it was started, even though a
		2013	one-second delay was requested - this is being "too early", despite best
		2014	intentions.
		2015
		2016	This is the reason why libev will never invoke the callback if the elapsed
		2017	delay equals the requested delay, but only when the elapsed delay is
		2018	larger than the requested delay. In the example above, libev would only invoke
		2019	the callback at system time 502, or 1.1s after the timer was started.
		2020
		2021	So, while libev cannot guarantee that your callback will be invoked
		2022	exactly when requested, it I<can> and I<does> guarantee that the requested
		2023	delay has actually elapsed, or in other words, it always errs on the "too
		2024	late" side of things.
		2025
1934	=head3 The special problem of time updates	2026	=head3 The special problem of time updates
1935		2027
1936	Establishing the current time is a costly operation (it usually takes at	2028	Establishing the current time is a costly operation (it usually takes
1937	least two system calls): EV therefore updates its idea of the current	2029	at least one system call): EV therefore updates its idea of the current
1938	time only before and after C<ev_run> collects new events, which causes a	2030	time only before and after C<ev_run> collects new events, which causes a
1939	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2031	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1940	lots of events in one iteration.	2032	lots of events in one iteration.
1941		2033
1942	The relative timeouts are calculated relative to the C<ev_now ()>	2034	The relative timeouts are calculated relative to the C<ev_now ()>
1943	time. This is usually the right thing as this timestamp refers to the time	2035	time. This is usually the right thing as this timestamp refers to the time
1944	of the event triggering whatever timeout you are modifying/starting. If	2036	of the event triggering whatever timeout you are modifying/starting. If
1945	you suspect event processing to be delayed and you I<need> to base the	2037	you suspect event processing to be delayed and you I<need> to base the
1946	timeout on the current time, use something like this to adjust for this:	2038	timeout on the current time, use something like the following to adjust
		2039	for it:
1947		2040
1948	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2041	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1949		2042
1950	If the event loop is suspended for a long time, you can also force an	2043	If the event loop is suspended for a long time, you can also force an
1951	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2044	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1952	()>.	2045	()>, although that will push the event time of all outstanding events
		2046	further into the future.
		2047
		2048	=head3 The special problem of unsynchronised clocks
		2049
		2050	Modern systems have a variety of clocks - libev itself uses the normal
		2051	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2052	jumps).
		2053
		2054	Neither of these clocks is synchronised with each other or any other clock
		2055	on the system, so C<ev_time ()> might return a considerably different time
		2056	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2057	a call to C<gettimeofday> might return a second count that is one higher
		2058	than a directly following call to C<time>.
		2059
		2060	The moral of this is to only compare libev-related timestamps with
		2061	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2062	a second or so.
		2063
		2064	One more problem arises due to this lack of synchronisation: if libev uses
		2065	the system monotonic clock and you compare timestamps from C<ev_time>
		2066	or C<ev_now> from when you started your timer and when your callback is
		2067	invoked, you will find that sometimes the callback is a bit "early".
		2068
		2069	This is because C<ev_timer>s work in real time, not wall clock time, so
		2070	libev makes sure your callback is not invoked before the delay happened,
		2071	I<measured according to the real time>, not the system clock.
		2072
		2073	If your timeouts are based on a physical timescale (e.g. "time out this
		2074	connection after 100 seconds") then this shouldn't bother you as it is
		2075	exactly the right behaviour.
		2076
		2077	If you want to compare wall clock/system timestamps to your timers, then
		2078	you need to use C<ev_periodic>s, as these are based on the wall clock
		2079	time, where your comparisons will always generate correct results.
1953		2080
1954	=head3 The special problems of suspended animation	2081	=head3 The special problems of suspended animation
1955		2082
1956	When you leave the server world it is quite customary to hit machines that	2083	When you leave the server world it is quite customary to hit machines that
1957	can suspend/hibernate - what happens to the clocks during such a suspend?	2084	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
2001	keep up with the timer (because it takes longer than those 10 seconds to	2128	keep up with the timer (because it takes longer than those 10 seconds to
2002	do stuff) the timer will not fire more than once per event loop iteration.	2129	do stuff) the timer will not fire more than once per event loop iteration.
2003		2130
2004	=item ev_timer_again (loop, ev_timer *)	2131	=item ev_timer_again (loop, ev_timer *)
2005		2132
2006	This will act as if the timer timed out and restart it again if it is	2133	This will act as if the timer timed out, and restarts it again if it is
2007	repeating. The exact semantics are:	2134	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2135	timeout to the C<repeat> value and calling C<ev_timer_start>.
2008		2136
		2137	The exact semantics are as in the following rules, all of which will be
		2138	applied to the watcher:
		2139
		2140	=over 4
		2141
2009	If the timer is pending, its pending status is cleared.	2142	=item If the timer is pending, the pending status is always cleared.
2010		2143
2011	If the timer is started but non-repeating, stop it (as if it timed out).	2144	=item If the timer is started but non-repeating, stop it (as if it timed
		2145	out, without invoking it).
2012		2146
2013	If the timer is repeating, either start it if necessary (with the	2147	=item If the timer is repeating, make the C<repeat> value the new timeout
2014	C<repeat> value), or reset the running timer to the C<repeat> value.	2148	and start the timer, if necessary.
2015		2149
		2150	=back
		2151
2016	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2152	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2017	usage example.	2153	usage example.
2018		2154
2019	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2155	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2020		2156
2021	Returns the remaining time until a timer fires. If the timer is active,	2157	Returns the remaining time until a timer fires. If the timer is active,
…		…
2074	Periodic watchers are also timers of a kind, but they are very versatile	2210	Periodic watchers are also timers of a kind, but they are very versatile
2075	(and unfortunately a bit complex).	2211	(and unfortunately a bit complex).
2076		2212
2077	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2213	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2078	relative time, the physical time that passes) but on wall clock time	2214	relative time, the physical time that passes) but on wall clock time
2079	(absolute time, the thing you can read on your calender or clock). The	2215	(absolute time, the thing you can read on your calendar or clock). The
2080	difference is that wall clock time can run faster or slower than real	2216	difference is that wall clock time can run faster or slower than real
2081	time, and time jumps are not uncommon (e.g. when you adjust your	2217	time, and time jumps are not uncommon (e.g. when you adjust your
2082	wrist-watch).	2218	wrist-watch).
2083		2219
2084	You can tell a periodic watcher to trigger after some specific point	2220	You can tell a periodic watcher to trigger after some specific point
…		…
2141		2277
2142	Another way to think about it (for the mathematically inclined) is that	2278	Another way to think about it (for the mathematically inclined) is that
2143	C<ev_periodic> will try to run the callback in this mode at the next possible	2279	C<ev_periodic> will try to run the callback in this mode at the next possible
2144	time where C<time = offset (mod interval)>, regardless of any time jumps.	2280	time where C<time = offset (mod interval)>, regardless of any time jumps.
2145		2281
2146	For numerical stability it is preferable that the C<offset> value is near	2282	The C<interval> I<MUST> be positive, and for numerical stability, the
2147	C<ev_now ()> (the current time), but there is no range requirement for	2283	interval value should be higher than C<1/8192> (which is around 100
2148	this value, and in fact is often specified as zero.	2284	microseconds) and C<offset> should be higher than C<0> and should have
		2285	at most a similar magnitude as the current time (say, within a factor of
		2286	ten). Typical values for offset are, in fact, C<0> or something between
		2287	C<0> and C<interval>, which is also the recommended range.
2149		2288
2150	Note also that there is an upper limit to how often a timer can fire (CPU	2289	Note also that there is an upper limit to how often a timer can fire (CPU
2151	speed for example), so if C<interval> is very small then timing stability	2290	speed for example), so if C<interval> is very small then timing stability
2152	will of course deteriorate. Libev itself tries to be exact to be about one	2291	will of course deteriorate. Libev itself tries to be exact to be about one
2153	millisecond (if the OS supports it and the machine is fast enough).	2292	millisecond (if the OS supports it and the machine is fast enough).
…		…
2261		2400
2262	ev_periodic hourly_tick;	2401	ev_periodic hourly_tick;
2263	ev_periodic_init (&hourly_tick, clock_cb,	2402	ev_periodic_init (&hourly_tick, clock_cb,
2264	fmod (ev_now (loop), 3600.), 3600., 0);	2403	fmod (ev_now (loop), 3600.), 3600., 0);
2265	ev_periodic_start (loop, &hourly_tick);	2404	ev_periodic_start (loop, &hourly_tick);
2266		2405
2267		2406
2268	=head2 C<ev_signal> - signal me when a signal gets signalled!	2407	=head2 C<ev_signal> - signal me when a signal gets signalled!
2269		2408
2270	Signal watchers will trigger an event when the process receives a specific	2409	Signal watchers will trigger an event when the process receives a specific
2271	signal one or more times. Even though signals are very asynchronous, libev	2410	signal one or more times. Even though signals are very asynchronous, libev
…		…
2281	only within the same loop, i.e. you can watch for C<SIGINT> in your	2420	only within the same loop, i.e. you can watch for C<SIGINT> in your
2282	default loop and for C<SIGIO> in another loop, but you cannot watch for	2421	default loop and for C<SIGIO> in another loop, but you cannot watch for
2283	C<SIGINT> in both the default loop and another loop at the same time. At	2422	C<SIGINT> in both the default loop and another loop at the same time. At
2284	the moment, C<SIGCHLD> is permanently tied to the default loop.	2423	the moment, C<SIGCHLD> is permanently tied to the default loop.
2285		2424
2286	When the first watcher gets started will libev actually register something	2425	Only after the first watcher for a signal is started will libev actually
2287	with the kernel (thus it coexists with your own signal handlers as long as	2426	register something with the kernel. It thus coexists with your own signal
2288	you don't register any with libev for the same signal).	2427	handlers as long as you don't register any with libev for the same signal.
2289		2428
2290	If possible and supported, libev will install its handlers with	2429	If possible and supported, libev will install its handlers with
2291	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2430	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2292	not be unduly interrupted. If you have a problem with system calls getting	2431	not be unduly interrupted. If you have a problem with system calls getting
2293	interrupted by signals you can block all signals in an C<ev_check> watcher	2432	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2296	=head3 The special problem of inheritance over fork/execve/pthread_create	2435	=head3 The special problem of inheritance over fork/execve/pthread_create
2297		2436
2298	Both the signal mask (C<sigprocmask>) and the signal disposition	2437	Both the signal mask (C<sigprocmask>) and the signal disposition
2299	(C<sigaction>) are unspecified after starting a signal watcher (and after	2438	(C<sigaction>) are unspecified after starting a signal watcher (and after
2300	stopping it again), that is, libev might or might not block the signal,	2439	stopping it again), that is, libev might or might not block the signal,
2301	and might or might not set or restore the installed signal handler.	2440	and might or might not set or restore the installed signal handler (but
		2441	see C<EVFLAG_NOSIGMASK>).
2302		2442
2303	While this does not matter for the signal disposition (libev never	2443	While this does not matter for the signal disposition (libev never
2304	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2444	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2305	C<execve>), this matters for the signal mask: many programs do not expect	2445	C<execve>), this matters for the signal mask: many programs do not expect
2306	certain signals to be blocked.	2446	certain signals to be blocked.
…		…
2319	I<has> to modify the signal mask, at least temporarily.	2459	I<has> to modify the signal mask, at least temporarily.
2320		2460
2321	So I can't stress this enough: I<If you do not reset your signal mask when	2461	So I can't stress this enough: I<If you do not reset your signal mask when
2322	you expect it to be empty, you have a race condition in your code>. This	2462	you expect it to be empty, you have a race condition in your code>. This
2323	is not a libev-specific thing, this is true for most event libraries.	2463	is not a libev-specific thing, this is true for most event libraries.
		2464
		2465	=head3 The special problem of threads signal handling
		2466
		2467	POSIX threads has problematic signal handling semantics, specifically,
		2468	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2469	threads in a process block signals, which is hard to achieve.
		2470
		2471	When you want to use sigwait (or mix libev signal handling with your own
		2472	for the same signals), you can tackle this problem by globally blocking
		2473	all signals before creating any threads (or creating them with a fully set
		2474	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2475	loops. Then designate one thread as "signal receiver thread" which handles
		2476	these signals. You can pass on any signals that libev might be interested
		2477	in by calling C<ev_feed_signal>.
2324		2478
2325	=head3 Watcher-Specific Functions and Data Members	2479	=head3 Watcher-Specific Functions and Data Members
2326		2480
2327	=over 4	2481	=over 4
2328		2482
…		…
2463		2617
2464	=head2 C<ev_stat> - did the file attributes just change?	2618	=head2 C<ev_stat> - did the file attributes just change?
2465		2619
2466	This watches a file system path for attribute changes. That is, it calls	2620	This watches a file system path for attribute changes. That is, it calls
2467	C<stat> on that path in regular intervals (or when the OS says it changed)	2621	C<stat> on that path in regular intervals (or when the OS says it changed)
2468	and sees if it changed compared to the last time, invoking the callback if	2622	and sees if it changed compared to the last time, invoking the callback
2469	it did.	2623	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2624	happen after the watcher has been started will be reported.
2470		2625
2471	The path does not need to exist: changing from "path exists" to "path does	2626	The path does not need to exist: changing from "path exists" to "path does
2472	not exist" is a status change like any other. The condition "path does not	2627	not exist" is a status change like any other. The condition "path does not
2473	exist" (or more correctly "path cannot be stat'ed") is signified by the	2628	exist" (or more correctly "path cannot be stat'ed") is signified by the
2474	C<st_nlink> field being zero (which is otherwise always forced to be at	2629	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2704	Apart from keeping your process non-blocking (which is a useful	2859	Apart from keeping your process non-blocking (which is a useful
2705	effect on its own sometimes), idle watchers are a good place to do	2860	effect on its own sometimes), idle watchers are a good place to do
2706	"pseudo-background processing", or delay processing stuff to after the	2861	"pseudo-background processing", or delay processing stuff to after the
2707	event loop has handled all outstanding events.	2862	event loop has handled all outstanding events.
2708		2863
		2864	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2865
		2866	As long as there is at least one active idle watcher, libev will never
		2867	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2868	For this to work, the idle watcher doesn't need to be invoked at all - the
		2869	lowest priority will do.
		2870
		2871	This mode of operation can be useful together with an C<ev_check> watcher,
		2872	to do something on each event loop iteration - for example to balance load
		2873	between different connections.
		2874
		2875	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2876	example.
		2877
2709	=head3 Watcher-Specific Functions and Data Members	2878	=head3 Watcher-Specific Functions and Data Members
2710		2879
2711	=over 4	2880	=over 4
2712		2881
2713	=item ev_idle_init (ev_idle *, callback)	2882	=item ev_idle_init (ev_idle *, callback)
…		…
2724	callback, free it. Also, use no error checking, as usual.	2893	callback, free it. Also, use no error checking, as usual.
2725		2894
2726	static void	2895	static void
2727	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2896	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2728	{	2897	{
		2898	// stop the watcher
		2899	ev_idle_stop (loop, w);
		2900
		2901	// now we can free it
2729	free (w);	2902	free (w);
		2903
2730	// now do something you wanted to do when the program has	2904	// now do something you wanted to do when the program has
2731	// no longer anything immediate to do.	2905	// no longer anything immediate to do.
2732	}	2906	}
2733		2907
2734	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2908	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2736	ev_idle_start (loop, idle_watcher);	2910	ev_idle_start (loop, idle_watcher);
2737		2911
2738		2912
2739	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2913	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2740		2914
2741	Prepare and check watchers are usually (but not always) used in pairs:	2915	Prepare and check watchers are often (but not always) used in pairs:
2742	prepare watchers get invoked before the process blocks and check watchers	2916	prepare watchers get invoked before the process blocks and check watchers
2743	afterwards.	2917	afterwards.
2744		2918
2745	You I<must not> call C<ev_run> or similar functions that enter	2919	You I<must not> call C<ev_run> (or similar functions that enter the
2746	the current event loop from either C<ev_prepare> or C<ev_check>	2920	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2747	watchers. Other loops than the current one are fine, however. The	2921	C<ev_check> watchers. Other loops than the current one are fine,
2748	rationale behind this is that you do not need to check for recursion in	2922	however. The rationale behind this is that you do not need to check
2749	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2923	for recursion in those watchers, i.e. the sequence will always be
2750	C<ev_check> so if you have one watcher of each kind they will always be	2924	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2751	called in pairs bracketing the blocking call.	2925	kind they will always be called in pairs bracketing the blocking call.
2752		2926
2753	Their main purpose is to integrate other event mechanisms into libev and	2927	Their main purpose is to integrate other event mechanisms into libev and
2754	their use is somewhat advanced. They could be used, for example, to track	2928	their use is somewhat advanced. They could be used, for example, to track
2755	variable changes, implement your own watchers, integrate net-snmp or a	2929	variable changes, implement your own watchers, integrate net-snmp or a
2756	coroutine library and lots more. They are also occasionally useful if	2930	coroutine library and lots more. They are also occasionally useful if
…		…
2774	with priority higher than or equal to the event loop and one coroutine	2948	with priority higher than or equal to the event loop and one coroutine
2775	of lower priority, but only once, using idle watchers to keep the event	2949	of lower priority, but only once, using idle watchers to keep the event
2776	loop from blocking if lower-priority coroutines are active, thus mapping	2950	loop from blocking if lower-priority coroutines are active, thus mapping
2777	low-priority coroutines to idle/background tasks).	2951	low-priority coroutines to idle/background tasks).
2778		2952
2779	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2953	When used for this purpose, it is recommended to give C<ev_check> watchers
2780	priority, to ensure that they are being run before any other watchers	2954	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2781	after the poll (this doesn't matter for C<ev_prepare> watchers).	2955	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2956	watchers).
2782		2957
2783	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	2958	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2784	activate ("feed") events into libev. While libev fully supports this, they	2959	activate ("feed") events into libev. While libev fully supports this, they
2785	might get executed before other C<ev_check> watchers did their job. As	2960	might get executed before other C<ev_check> watchers did their job. As
2786	C<ev_check> watchers are often used to embed other (non-libev) event	2961	C<ev_check> watchers are often used to embed other (non-libev) event
2787	loops those other event loops might be in an unusable state until their	2962	loops those other event loops might be in an unusable state until their
2788	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2963	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2789	others).	2964	others).
		2965
		2966	=head3 Abusing an C<ev_check> watcher for its side-effect
		2967
		2968	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2969	useful because they are called once per event loop iteration. For
		2970	example, if you want to handle a large number of connections fairly, you
		2971	normally only do a bit of work for each active connection, and if there
		2972	is more work to do, you wait for the next event loop iteration, so other
		2973	connections have a chance of making progress.
		2974
		2975	Using an C<ev_check> watcher is almost enough: it will be called on the
		2976	next event loop iteration. However, that isn't as soon as possible -
		2977	without external events, your C<ev_check> watcher will not be invoked.
		2978
		2979	This is where C<ev_idle> watchers come in handy - all you need is a
		2980	single global idle watcher that is active as long as you have one active
		2981	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2982	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2983	invoked. Neither watcher alone can do that.
2790		2984
2791	=head3 Watcher-Specific Functions and Data Members	2985	=head3 Watcher-Specific Functions and Data Members
2792		2986
2793	=over 4	2987	=over 4
2794		2988
…		…
2995		3189
2996	=over 4	3190	=over 4
2997		3191
2998	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3192	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2999		3193
3000	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3194	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
3001		3195
3002	Configures the watcher to embed the given loop, which must be	3196	Configures the watcher to embed the given loop, which must be
3003	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3197	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
3004	invoked automatically, otherwise it is the responsibility of the callback	3198	invoked automatically, otherwise it is the responsibility of the callback
3005	to invoke it (it will continue to be called until the sweep has been done,	3199	to invoke it (it will continue to be called until the sweep has been done,
…		…
3026	used).	3220	used).
3027		3221
3028	struct ev_loop *loop_hi = ev_default_init (0);	3222	struct ev_loop *loop_hi = ev_default_init (0);
3029	struct ev_loop *loop_lo = 0;	3223	struct ev_loop *loop_lo = 0;
3030	ev_embed embed;	3224	ev_embed embed;
3031		3225
3032	// see if there is a chance of getting one that works	3226	// see if there is a chance of getting one that works
3033	// (remember that a flags value of 0 means autodetection)	3227	// (remember that a flags value of 0 means autodetection)
3034	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3228	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3035	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3229	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3036	: 0;	3230	: 0;
…		…
3050	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3244	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3051		3245
3052	struct ev_loop *loop = ev_default_init (0);	3246	struct ev_loop *loop = ev_default_init (0);
3053	struct ev_loop *loop_socket = 0;	3247	struct ev_loop *loop_socket = 0;
3054	ev_embed embed;	3248	ev_embed embed;
3055		3249
3056	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3250	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3057	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3251	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3058	{	3252	{
3059	ev_embed_init (&embed, 0, loop_socket);	3253	ev_embed_init (&embed, 0, loop_socket);
3060	ev_embed_start (loop, &embed);	3254	ev_embed_start (loop, &embed);
…		…
3068		3262
3069	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3263	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3070		3264
3071	Fork watchers are called when a C<fork ()> was detected (usually because	3265	Fork watchers are called when a C<fork ()> was detected (usually because
3072	whoever is a good citizen cared to tell libev about it by calling	3266	whoever is a good citizen cared to tell libev about it by calling
3073	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3267	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3074	event loop blocks next and before C<ev_check> watchers are being called,	3268	and before C<ev_check> watchers are being called, and only in the child
3075	and only in the child after the fork. If whoever good citizen calling	3269	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3076	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3270	and calls it in the wrong process, the fork handlers will be invoked, too,
3077	handlers will be invoked, too, of course.	3271	of course.
3078		3272
3079	=head3 The special problem of life after fork - how is it possible?	3273	=head3 The special problem of life after fork - how is it possible?
3080		3274
3081	Most uses of C<fork()> consist of forking, then some simple calls to set	3275	Most uses of C<fork ()> consist of forking, then some simple calls to set
3082	up/change the process environment, followed by a call to C<exec()>. This	3276	up/change the process environment, followed by a call to C<exec()>. This
3083	sequence should be handled by libev without any problems.	3277	sequence should be handled by libev without any problems.
3084		3278
3085	This changes when the application actually wants to do event handling	3279	This changes when the application actually wants to do event handling
3086	in the child, or both parent in child, in effect "continuing" after the	3280	in the child, or both parent in child, in effect "continuing" after the
…		…
3163	atexit (program_exits);	3357	atexit (program_exits);
3164		3358
3165		3359
3166	=head2 C<ev_async> - how to wake up an event loop	3360	=head2 C<ev_async> - how to wake up an event loop
3167		3361
3168	In general, you cannot use an C<ev_run> from multiple threads or other	3362	In general, you cannot use an C<ev_loop> from multiple threads or other
3169	asynchronous sources such as signal handlers (as opposed to multiple event	3363	asynchronous sources such as signal handlers (as opposed to multiple event
3170	loops - those are of course safe to use in different threads).	3364	loops - those are of course safe to use in different threads).
3171		3365
3172	Sometimes, however, you need to wake up an event loop you do not control,	3366	Sometimes, however, you need to wake up an event loop you do not control,
3173	for example because it belongs to another thread. This is what C<ev_async>	3367	for example because it belongs to another thread. This is what C<ev_async>
…		…
3175	it by calling C<ev_async_send>, which is thread- and signal safe.	3369	it by calling C<ev_async_send>, which is thread- and signal safe.
3176		3370
3177	This functionality is very similar to C<ev_signal> watchers, as signals,	3371	This functionality is very similar to C<ev_signal> watchers, as signals,
3178	too, are asynchronous in nature, and signals, too, will be compressed	3372	too, are asynchronous in nature, and signals, too, will be compressed
3179	(i.e. the number of callback invocations may be less than the number of	3373	(i.e. the number of callback invocations may be less than the number of
3180	C<ev_async_sent> calls).	3374	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3181		3375	of "global async watchers" by using a watcher on an otherwise unused
3182	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3376	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3183	just the default loop.	3377	even without knowing which loop owns the signal.
3184		3378
3185	=head3 Queueing	3379	=head3 Queueing
3186		3380
3187	C<ev_async> does not support queueing of data in any way. The reason	3381	C<ev_async> does not support queueing of data in any way. The reason
3188	is that the author does not know of a simple (or any) algorithm for a	3382	is that the author does not know of a simple (or any) algorithm for a
…		…
3280	trust me.	3474	trust me.
3281		3475
3282	=item ev_async_send (loop, ev_async *)	3476	=item ev_async_send (loop, ev_async *)
3283		3477
3284	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3478	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3285	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3479	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3480	returns.
		3481
3286	C<ev_feed_event>, this call is safe to do from other threads, signal or	3482	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3287	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3483	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3288	section below on what exactly this means).	3484	embedding section below on what exactly this means).
3289		3485
3290	Note that, as with other watchers in libev, multiple events might get	3486	Note that, as with other watchers in libev, multiple events might get
3291	compressed into a single callback invocation (another way to look at this	3487	compressed into a single callback invocation (another way to look at
3292	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3488	this is that C<ev_async> watchers are level-triggered: they are set on
3293	reset when the event loop detects that).	3489	C<ev_async_send>, reset when the event loop detects that).
3294		3490
3295	This call incurs the overhead of a system call only once per event loop	3491	This call incurs the overhead of at most one extra system call per event
3296	iteration, so while the overhead might be noticeable, it doesn't apply to	3492	loop iteration, if the event loop is blocked, and no syscall at all if
3297	repeated calls to C<ev_async_send> for the same event loop.	3493	the event loop (or your program) is processing events. That means that
		3494	repeated calls are basically free (there is no need to avoid calls for
		3495	performance reasons) and that the overhead becomes smaller (typically
		3496	zero) under load.
3298		3497
3299	=item bool = ev_async_pending (ev_async *)	3498	=item bool = ev_async_pending (ev_async *)
3300		3499
3301	Returns a non-zero value when C<ev_async_send> has been called on the	3500	Returns a non-zero value when C<ev_async_send> has been called on the
3302	watcher but the event has not yet been processed (or even noted) by the	3501	watcher but the event has not yet been processed (or even noted) by the
…		…
3319		3518
3320	There are some other functions of possible interest. Described. Here. Now.	3519	There are some other functions of possible interest. Described. Here. Now.
3321		3520
3322	=over 4	3521	=over 4
3323		3522
3324	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3523	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3325		3524
3326	This function combines a simple timer and an I/O watcher, calls your	3525	This function combines a simple timer and an I/O watcher, calls your
3327	callback on whichever event happens first and automatically stops both	3526	callback on whichever event happens first and automatically stops both
3328	watchers. This is useful if you want to wait for a single event on an fd	3527	watchers. This is useful if you want to wait for a single event on an fd
3329	or timeout without having to allocate/configure/start/stop/free one or	3528	or timeout without having to allocate/configure/start/stop/free one or
…		…
3357	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3556	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3358		3557
3359	=item ev_feed_fd_event (loop, int fd, int revents)	3558	=item ev_feed_fd_event (loop, int fd, int revents)
3360		3559
3361	Feed an event on the given fd, as if a file descriptor backend detected	3560	Feed an event on the given fd, as if a file descriptor backend detected
3362	the given events it.	3561	the given events.
3363		3562
3364	=item ev_feed_signal_event (loop, int signum)	3563	=item ev_feed_signal_event (loop, int signum)
3365		3564
3366	Feed an event as if the given signal occurred (C<loop> must be the default	3565	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3367	loop!).	3566	which is async-safe.
3368		3567
3369	=back	3568	=back
3370		3569
3371		3570
3372	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)	3571	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
3373		3572
3374	This section explains some common idioms that are not immediately	3573	This section explains some common idioms that are not immediately
3375	obvious. Note that examples are sprinkled over the whole manual, and this	3574	obvious. Note that examples are sprinkled over the whole manual, and this
3376	section only contains stuff that wouldn't fit anywhere else.	3575	section only contains stuff that wouldn't fit anywhere else.
3377		3576
3378	=over 4	3577	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3379		3578
3380	=item Model/nested event loop invocations and exit conditions.	3579	Each watcher has, by default, a C<void *data> member that you can read
		3580	or modify at any time: libev will completely ignore it. This can be used
		3581	to associate arbitrary data with your watcher. If you need more data and
		3582	don't want to allocate memory separately and store a pointer to it in that
		3583	data member, you can also "subclass" the watcher type and provide your own
		3584	data:
		3585
		3586	struct my_io
		3587	{
		3588	ev_io io;
		3589	int otherfd;
		3590	void *somedata;
		3591	struct whatever *mostinteresting;
		3592	};
		3593
		3594	...
		3595	struct my_io w;
		3596	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3597
		3598	And since your callback will be called with a pointer to the watcher, you
		3599	can cast it back to your own type:
		3600
		3601	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3602	{
		3603	struct my_io *w = (struct my_io *)w_;
		3604	...
		3605	}
		3606
		3607	More interesting and less C-conformant ways of casting your callback
		3608	function type instead have been omitted.
		3609
		3610	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3611
		3612	Another common scenario is to use some data structure with multiple
		3613	embedded watchers, in effect creating your own watcher that combines
		3614	multiple libev event sources into one "super-watcher":
		3615
		3616	struct my_biggy
		3617	{
		3618	int some_data;
		3619	ev_timer t1;
		3620	ev_timer t2;
		3621	}
		3622
		3623	In this case getting the pointer to C<my_biggy> is a bit more
		3624	complicated: Either you store the address of your C<my_biggy> struct in
		3625	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3626	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3627	real programmers):
		3628
		3629	#include <stddef.h>
		3630
		3631	static void
		3632	t1_cb (EV_P_ ev_timer *w, int revents)
		3633	{
		3634	struct my_biggy big = (struct my_biggy *)
		3635	(((char *)w) - offsetof (struct my_biggy, t1));
		3636	}
		3637
		3638	static void
		3639	t2_cb (EV_P_ ev_timer *w, int revents)
		3640	{
		3641	struct my_biggy big = (struct my_biggy *)
		3642	(((char *)w) - offsetof (struct my_biggy, t2));
		3643	}
		3644
		3645	=head2 AVOIDING FINISHING BEFORE RETURNING
		3646
		3647	Often you have structures like this in event-based programs:
		3648
		3649	callback ()
		3650	{
		3651	free (request);
		3652	}
		3653
		3654	request = start_new_request (..., callback);
		3655
		3656	The intent is to start some "lengthy" operation. The C<request> could be
		3657	used to cancel the operation, or do other things with it.
		3658
		3659	It's not uncommon to have code paths in C<start_new_request> that
		3660	immediately invoke the callback, for example, to report errors. Or you add
		3661	some caching layer that finds that it can skip the lengthy aspects of the
		3662	operation and simply invoke the callback with the result.
		3663
		3664	The problem here is that this will happen I<before> C<start_new_request>
		3665	has returned, so C<request> is not set.
		3666
		3667	Even if you pass the request by some safer means to the callback, you
		3668	might want to do something to the request after starting it, such as
		3669	canceling it, which probably isn't working so well when the callback has
		3670	already been invoked.
		3671
		3672	A common way around all these issues is to make sure that
		3673	C<start_new_request> I<always> returns before the callback is invoked. If
		3674	C<start_new_request> immediately knows the result, it can artificially
		3675	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3676	example, or more sneakily, by reusing an existing (stopped) watcher and
		3677	pushing it into the pending queue:
		3678
		3679	ev_set_cb (watcher, callback);
		3680	ev_feed_event (EV_A_ watcher, 0);
		3681
		3682	This way, C<start_new_request> can safely return before the callback is
		3683	invoked, while not delaying callback invocation too much.
		3684
		3685	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3381		3686
3382	Often (especially in GUI toolkits) there are places where you have	3687	Often (especially in GUI toolkits) there are places where you have
3383	I<modal> interaction, which is most easily implemented by recursively	3688	I<modal> interaction, which is most easily implemented by recursively
3384	invoking C<ev_run>.	3689	invoking C<ev_run>.
3385		3690
3386	This brings the problem of exiting - a callback might want to finish the	3691	This brings the problem of exiting - a callback might want to finish the
3387	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but	3692	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
3388	a modal "Are you sure?" dialog is still waiting), or just the nested one	3693	a modal "Are you sure?" dialog is still waiting), or just the nested one
3389	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some	3694	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
3390	other combination: In these cases, C<ev_break> will not work alone.	3695	other combination: In these cases, a simple C<ev_break> will not work.
3391		3696
3392	The solution is to maintain "break this loop" variable for each C<ev_run>	3697	The solution is to maintain "break this loop" variable for each C<ev_run>
3393	invocation, and use a loop around C<ev_run> until the condition is	3698	invocation, and use a loop around C<ev_run> until the condition is
3394	triggered, using C<EVRUN_ONCE>:	3699	triggered, using C<EVRUN_ONCE>:
3395		3700
…		…
3397	int exit_main_loop = 0;	3702	int exit_main_loop = 0;
3398		3703
3399	while (!exit_main_loop)	3704	while (!exit_main_loop)
3400	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3705	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3401		3706
3402	// in a model watcher	3707	// in a modal watcher
3403	int exit_nested_loop = 0;	3708	int exit_nested_loop = 0;
3404		3709
3405	while (!exit_nested_loop)	3710	while (!exit_nested_loop)
3406	ev_run (EV_A_ EVRUN_ONCE);	3711	ev_run (EV_A_ EVRUN_ONCE);
3407		3712
…		…
3414	exit_main_loop = 1;	3719	exit_main_loop = 1;
3415		3720
3416	// exit both	3721	// exit both
3417	exit_main_loop = exit_nested_loop = 1;	3722	exit_main_loop = exit_nested_loop = 1;
3418		3723
3419	=back	3724	=head2 THREAD LOCKING EXAMPLE
		3725
		3726	Here is a fictitious example of how to run an event loop in a different
		3727	thread from where callbacks are being invoked and watchers are
		3728	created/added/removed.
		3729
		3730	For a real-world example, see the C<EV::Loop::Async> perl module,
		3731	which uses exactly this technique (which is suited for many high-level
		3732	languages).
		3733
		3734	The example uses a pthread mutex to protect the loop data, a condition
		3735	variable to wait for callback invocations, an async watcher to notify the
		3736	event loop thread and an unspecified mechanism to wake up the main thread.
		3737
		3738	First, you need to associate some data with the event loop:
		3739
		3740	typedef struct {
		3741	mutex_t lock; /* global loop lock */
		3742	ev_async async_w;
		3743	thread_t tid;
		3744	cond_t invoke_cv;
		3745	} userdata;
		3746
		3747	void prepare_loop (EV_P)
		3748	{
		3749	// for simplicity, we use a static userdata struct.
		3750	static userdata u;
		3751
		3752	ev_async_init (&u->async_w, async_cb);
		3753	ev_async_start (EV_A_ &u->async_w);
		3754
		3755	pthread_mutex_init (&u->lock, 0);
		3756	pthread_cond_init (&u->invoke_cv, 0);
		3757
		3758	// now associate this with the loop
		3759	ev_set_userdata (EV_A_ u);
		3760	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3761	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3762
		3763	// then create the thread running ev_run
		3764	pthread_create (&u->tid, 0, l_run, EV_A);
		3765	}
		3766
		3767	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3768	solely to wake up the event loop so it takes notice of any new watchers
		3769	that might have been added:
		3770
		3771	static void
		3772	async_cb (EV_P_ ev_async *w, int revents)
		3773	{
		3774	// just used for the side effects
		3775	}
		3776
		3777	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3778	protecting the loop data, respectively.
		3779
		3780	static void
		3781	l_release (EV_P)
		3782	{
		3783	userdata *u = ev_userdata (EV_A);
		3784	pthread_mutex_unlock (&u->lock);
		3785	}
		3786
		3787	static void
		3788	l_acquire (EV_P)
		3789	{
		3790	userdata *u = ev_userdata (EV_A);
		3791	pthread_mutex_lock (&u->lock);
		3792	}
		3793
		3794	The event loop thread first acquires the mutex, and then jumps straight
		3795	into C<ev_run>:
		3796
		3797	void *
		3798	l_run (void *thr_arg)
		3799	{
		3800	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3801
		3802	l_acquire (EV_A);
		3803	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3804	ev_run (EV_A_ 0);
		3805	l_release (EV_A);
		3806
		3807	return 0;
		3808	}
		3809
		3810	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3811	signal the main thread via some unspecified mechanism (signals? pipe
		3812	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3813	have been called (in a while loop because a) spurious wakeups are possible
		3814	and b) skipping inter-thread-communication when there are no pending
		3815	watchers is very beneficial):
		3816
		3817	static void
		3818	l_invoke (EV_P)
		3819	{
		3820	userdata *u = ev_userdata (EV_A);
		3821
		3822	while (ev_pending_count (EV_A))
		3823	{
		3824	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3825	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3826	}
		3827	}
		3828
		3829	Now, whenever the main thread gets told to invoke pending watchers, it
		3830	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3831	thread to continue:
		3832
		3833	static void
		3834	real_invoke_pending (EV_P)
		3835	{
		3836	userdata *u = ev_userdata (EV_A);
		3837
		3838	pthread_mutex_lock (&u->lock);
		3839	ev_invoke_pending (EV_A);
		3840	pthread_cond_signal (&u->invoke_cv);
		3841	pthread_mutex_unlock (&u->lock);
		3842	}
		3843
		3844	Whenever you want to start/stop a watcher or do other modifications to an
		3845	event loop, you will now have to lock:
		3846
		3847	ev_timer timeout_watcher;
		3848	userdata *u = ev_userdata (EV_A);
		3849
		3850	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3851
		3852	pthread_mutex_lock (&u->lock);
		3853	ev_timer_start (EV_A_ &timeout_watcher);
		3854	ev_async_send (EV_A_ &u->async_w);
		3855	pthread_mutex_unlock (&u->lock);
		3856
		3857	Note that sending the C<ev_async> watcher is required because otherwise
		3858	an event loop currently blocking in the kernel will have no knowledge
		3859	about the newly added timer. By waking up the loop it will pick up any new
		3860	watchers in the next event loop iteration.
		3861
		3862	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3863
		3864	While the overhead of a callback that e.g. schedules a thread is small, it
		3865	is still an overhead. If you embed libev, and your main usage is with some
		3866	kind of threads or coroutines, you might want to customise libev so that
		3867	doesn't need callbacks anymore.
		3868
		3869	Imagine you have coroutines that you can switch to using a function
		3870	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3871	and that due to some magic, the currently active coroutine is stored in a
		3872	global called C<current_coro>. Then you can build your own "wait for libev
		3873	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3874	the differing C<;> conventions):
		3875
		3876	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3877	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3878
		3879	That means instead of having a C callback function, you store the
		3880	coroutine to switch to in each watcher, and instead of having libev call
		3881	your callback, you instead have it switch to that coroutine.
		3882
		3883	A coroutine might now wait for an event with a function called
		3884	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3885	matter when, or whether the watcher is active or not when this function is
		3886	called):
		3887
		3888	void
		3889	wait_for_event (ev_watcher *w)
		3890	{
		3891	ev_set_cb (w, current_coro);
		3892	switch_to (libev_coro);
		3893	}
		3894
		3895	That basically suspends the coroutine inside C<wait_for_event> and
		3896	continues the libev coroutine, which, when appropriate, switches back to
		3897	this or any other coroutine.
		3898
		3899	You can do similar tricks if you have, say, threads with an event queue -
		3900	instead of storing a coroutine, you store the queue object and instead of
		3901	switching to a coroutine, you push the watcher onto the queue and notify
		3902	any waiters.
		3903
		3904	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3905	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3906
		3907	// my_ev.h
		3908	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3909	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3910	#include "../libev/ev.h"
		3911
		3912	// my_ev.c
		3913	#define EV_H "my_ev.h"
		3914	#include "../libev/ev.c"
		3915
		3916	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3917	F<my_ev.c> into your project. When properly specifying include paths, you
		3918	can even use F<ev.h> as header file name directly.
3420		3919
3421		3920
3422	=head1 LIBEVENT EMULATION	3921	=head1 LIBEVENT EMULATION
3423		3922
3424	Libev offers a compatibility emulation layer for libevent. It cannot	3923	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3454		3953
3455	=back	3954	=back
3456		3955
3457	=head1 C++ SUPPORT	3956	=head1 C++ SUPPORT
3458		3957
		3958	=head2 C API
		3959
		3960	The normal C API should work fine when used from C++: both ev.h and the
		3961	libev sources can be compiled as C++. Therefore, code that uses the C API
		3962	will work fine.
		3963
		3964	Proper exception specifications might have to be added to callbacks passed
		3965	to libev: exceptions may be thrown only from watcher callbacks, all
		3966	other callbacks (allocator, syserr, loop acquire/release and periodic
		3967	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3968	()> specification. If you have code that needs to be compiled as both C
		3969	and C++ you can use the C<EV_THROW> macro for this:
		3970
		3971	static void
		3972	fatal_error (const char *msg) EV_THROW
		3973	{
		3974	perror (msg);
		3975	abort ();
		3976	}
		3977
		3978	...
		3979	ev_set_syserr_cb (fatal_error);
		3980
		3981	The only API functions that can currently throw exceptions are C<ev_run>,
		3982	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3983	because it runs cleanup watchers).
		3984
		3985	Throwing exceptions in watcher callbacks is only supported if libev itself
		3986	is compiled with a C++ compiler or your C and C++ environments allow
		3987	throwing exceptions through C libraries (most do).
		3988
		3989	=head2 C++ API
		3990
3459	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3991	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3460	you to use some convenience methods to start/stop watchers and also change	3992	you to use some convenience methods to start/stop watchers and also change
3461	the callback model to a model using method callbacks on objects.	3993	the callback model to a model using method callbacks on objects.
3462		3994
3463	To use it,	3995	To use it,
3464		3996
3465	#include <ev++.h>	3997	#include <ev++.h>
3466		3998
3467	This automatically includes F<ev.h> and puts all of its definitions (many	3999	This automatically includes F<ev.h> and puts all of its definitions (many
3468	of them macros) into the global namespace. All C++ specific things are	4000	of them macros) into the global namespace. All C++ specific things are
3469	put into the C<ev> namespace. It should support all the same embedding	4001	put into the C<ev> namespace. It should support all the same embedding
…		…
3478	with C<operator ()> can be used as callbacks. Other types should be easy	4010	with C<operator ()> can be used as callbacks. Other types should be easy
3479	to add as long as they only need one additional pointer for context. If	4011	to add as long as they only need one additional pointer for context. If
3480	you need support for other types of functors please contact the author	4012	you need support for other types of functors please contact the author
3481	(preferably after implementing it).	4013	(preferably after implementing it).
3482		4014
		4015	For all this to work, your C++ compiler either has to use the same calling
		4016	conventions as your C compiler (for static member functions), or you have
		4017	to embed libev and compile libev itself as C++.
		4018
3483	Here is a list of things available in the C<ev> namespace:	4019	Here is a list of things available in the C<ev> namespace:
3484		4020
3485	=over 4	4021	=over 4
3486		4022
3487	=item C<ev::READ>, C<ev::WRITE> etc.	4023	=item C<ev::READ>, C<ev::WRITE> etc.
…		…
3496	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4032	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3497		4033
3498	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4034	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3499	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4035	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3500	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4036	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3501	defines by many implementations.	4037	defined by many implementations.
3502		4038
3503	All of those classes have these methods:	4039	All of those classes have these methods:
3504		4040
3505	=over 4	4041	=over 4
3506		4042
…		…
3568	void operator() (ev::io &w, int revents)	4104	void operator() (ev::io &w, int revents)
3569	{	4105	{
3570	...	4106	...
3571	}	4107	}
3572	}	4108	}
3573		4109
3574	myfunctor f;	4110	myfunctor f;
3575		4111
3576	ev::io w;	4112	ev::io w;
3577	w.set (&f);	4113	w.set (&f);
3578		4114
…		…
3596	Associates a different C<struct ev_loop> with this watcher. You can only	4132	Associates a different C<struct ev_loop> with this watcher. You can only
3597	do this when the watcher is inactive (and not pending either).	4133	do this when the watcher is inactive (and not pending either).
3598		4134
3599	=item w->set ([arguments])	4135	=item w->set ([arguments])
3600		4136
3601	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4137	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3602	method or a suitable start method must be called at least once. Unlike the	4138	with the same arguments. Either this method or a suitable start method
3603	C counterpart, an active watcher gets automatically stopped and restarted	4139	must be called at least once. Unlike the C counterpart, an active watcher
3604	when reconfiguring it with this method.	4140	gets automatically stopped and restarted when reconfiguring it with this
		4141	method.
		4142
		4143	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4144	clashing with the C<set (loop)> method.
3605		4145
3606	=item w->start ()	4146	=item w->start ()
3607		4147
3608	Starts the watcher. Note that there is no C<loop> argument, as the	4148	Starts the watcher. Note that there is no C<loop> argument, as the
3609	constructor already stores the event loop.	4149	constructor already stores the event loop.
…		…
3639	watchers in the constructor.	4179	watchers in the constructor.
3640		4180
3641	class myclass	4181	class myclass
3642	{	4182	{
3643	ev::io io ; void io_cb (ev::io &w, int revents);	4183	ev::io io ; void io_cb (ev::io &w, int revents);
3644	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4184	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3645	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4185	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3646		4186
3647	myclass (int fd)	4187	myclass (int fd)
3648	{	4188	{
3649	io .set <myclass, &myclass::io_cb > (this);	4189	io .set <myclass, &myclass::io_cb > (this);
…		…
3700	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4240	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3701		4241
3702	=item D	4242	=item D
3703		4243
3704	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4244	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3705	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4245	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3706		4246
3707	=item Ocaml	4247	=item Ocaml
3708		4248
3709	Erkki Seppala has written Ocaml bindings for libev, to be found at	4249	Erkki Seppala has written Ocaml bindings for libev, to be found at
3710	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4250	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3713		4253
3714	Brian Maher has written a partial interface to libev for lua (at the	4254	Brian Maher has written a partial interface to libev for lua (at the
3715	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4255	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3716	L<http://github.com/brimworks/lua-ev>.	4256	L<http://github.com/brimworks/lua-ev>.
3717		4257
		4258	=item Javascript
		4259
		4260	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4261
		4262	=item Others
		4263
		4264	There are others, and I stopped counting.
		4265
3718	=back	4266	=back
3719		4267
3720		4268
3721	=head1 MACRO MAGIC	4269	=head1 MACRO MAGIC
3722		4270
…		…
3758	suitable for use with C<EV_A>.	4306	suitable for use with C<EV_A>.
3759		4307
3760	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4308	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3761		4309
3762	Similar to the other two macros, this gives you the value of the default	4310	Similar to the other two macros, this gives you the value of the default
3763	loop, if multiple loops are supported ("ev loop default").	4311	loop, if multiple loops are supported ("ev loop default"). The default loop
		4312	will be initialised if it isn't already initialised.
		4313
		4314	For non-multiplicity builds, these macros do nothing, so you always have
		4315	to initialise the loop somewhere.
3764		4316
3765	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4317	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3766		4318
3767	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4319	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3768	default loop has been initialised (C<UC> == unchecked). Their behaviour	4320	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3835	ev_vars.h	4387	ev_vars.h
3836	ev_wrap.h	4388	ev_wrap.h
3837		4389
3838	ev_win32.c required on win32 platforms only	4390	ev_win32.c required on win32 platforms only
3839		4391
3840	ev_select.c only when select backend is enabled (which is enabled by default)	4392	ev_select.c only when select backend is enabled
3841	ev_poll.c only when poll backend is enabled (disabled by default)	4393	ev_poll.c only when poll backend is enabled
3842	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4394	ev_epoll.c only when the epoll backend is enabled
3843	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4395	ev_kqueue.c only when the kqueue backend is enabled
3844	ev_port.c only when the solaris port backend is enabled (disabled by default)	4396	ev_port.c only when the solaris port backend is enabled
3845		4397
3846	F<ev.c> includes the backend files directly when enabled, so you only need	4398	F<ev.c> includes the backend files directly when enabled, so you only need
3847	to compile this single file.	4399	to compile this single file.
3848		4400
3849	=head3 LIBEVENT COMPATIBILITY API	4401	=head3 LIBEVENT COMPATIBILITY API
…		…
3913	supported). It will also not define any of the structs usually found in	4465	supported). It will also not define any of the structs usually found in
3914	F<event.h> that are not directly supported by the libev core alone.	4466	F<event.h> that are not directly supported by the libev core alone.
3915		4467
3916	In standalone mode, libev will still try to automatically deduce the	4468	In standalone mode, libev will still try to automatically deduce the
3917	configuration, but has to be more conservative.	4469	configuration, but has to be more conservative.
		4470
		4471	=item EV_USE_FLOOR
		4472
		4473	If defined to be C<1>, libev will use the C<floor ()> function for its
		4474	periodic reschedule calculations, otherwise libev will fall back on a
		4475	portable (slower) implementation. If you enable this, you usually have to
		4476	link against libm or something equivalent. Enabling this when the C<floor>
		4477	function is not available will fail, so the safe default is to not enable
		4478	this.
3918		4479
3919	=item EV_USE_MONOTONIC	4480	=item EV_USE_MONOTONIC
3920		4481
3921	If defined to be C<1>, libev will try to detect the availability of the	4482	If defined to be C<1>, libev will try to detect the availability of the
3922	monotonic clock option at both compile time and runtime. Otherwise no	4483	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4007		4568
4008	If programs implement their own fd to handle mapping on win32, then this	4569	If programs implement their own fd to handle mapping on win32, then this
4009	macro can be used to override the C<close> function, useful to unregister	4570	macro can be used to override the C<close> function, useful to unregister
4010	file descriptors again. Note that the replacement function has to close	4571	file descriptors again. Note that the replacement function has to close
4011	the underlying OS handle.	4572	the underlying OS handle.
		4573
		4574	=item EV_USE_WSASOCKET
		4575
		4576	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4577	communication socket, which works better in some environments. Otherwise,
		4578	the normal C<socket> function will be used, which works better in other
		4579	environments.
4012		4580
4013	=item EV_USE_POLL	4581	=item EV_USE_POLL
4014		4582
4015	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4583	If defined to be C<1>, libev will compile in support for the C<poll>(2)
4016	backend. Otherwise it will be enabled on non-win32 platforms. It	4584	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
4052	If defined to be C<1>, libev will compile in support for the Linux inotify	4620	If defined to be C<1>, libev will compile in support for the Linux inotify
4053	interface to speed up C<ev_stat> watchers. Its actual availability will	4621	interface to speed up C<ev_stat> watchers. Its actual availability will
4054	be detected at runtime. If undefined, it will be enabled if the headers	4622	be detected at runtime. If undefined, it will be enabled if the headers
4055	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4623	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4056		4624
		4625	=item EV_NO_SMP
		4626
		4627	If defined to be C<1>, libev will assume that memory is always coherent
		4628	between threads, that is, threads can be used, but threads never run on
		4629	different cpus (or different cpu cores). This reduces dependencies
		4630	and makes libev faster.
		4631
		4632	=item EV_NO_THREADS
		4633
		4634	If defined to be C<1>, libev will assume that it will never be called from
		4635	different threads (that includes signal handlers), which is a stronger
		4636	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4637	libev faster.
		4638
4057	=item EV_ATOMIC_T	4639	=item EV_ATOMIC_T
4058		4640
4059	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4641	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4060	access is atomic with respect to other threads or signal contexts. No such	4642	access is atomic with respect to other threads or signal contexts. No
4061	type is easily found in the C language, so you can provide your own type	4643	such type is easily found in the C language, so you can provide your own
4062	that you know is safe for your purposes. It is used both for signal handler "locking"	4644	type that you know is safe for your purposes. It is used both for signal
4063	as well as for signal and thread safety in C<ev_async> watchers.	4645	handler "locking" as well as for signal and thread safety in C<ev_async>
		4646	watchers.
4064		4647
4065	In the absence of this define, libev will use C<sig_atomic_t volatile>	4648	In the absence of this define, libev will use C<sig_atomic_t volatile>
4066	(from F<signal.h>), which is usually good enough on most platforms.	4649	(from F<signal.h>), which is usually good enough on most platforms.
4067		4650
4068	=item EV_H (h)	4651	=item EV_H (h)
…		…
4095	will have the C<struct ev_loop *> as first argument, and you can create	4678	will have the C<struct ev_loop *> as first argument, and you can create
4096	additional independent event loops. Otherwise there will be no support	4679	additional independent event loops. Otherwise there will be no support
4097	for multiple event loops and there is no first event loop pointer	4680	for multiple event loops and there is no first event loop pointer
4098	argument. Instead, all functions act on the single default loop.	4681	argument. Instead, all functions act on the single default loop.
4099		4682
		4683	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4684	default loop when multiplicity is switched off - you always have to
		4685	initialise the loop manually in this case.
		4686
4100	=item EV_MINPRI	4687	=item EV_MINPRI
4101		4688
4102	=item EV_MAXPRI	4689	=item EV_MAXPRI
4103		4690
4104	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4691	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4140	#define EV_USE_POLL 1	4727	#define EV_USE_POLL 1
4141	#define EV_CHILD_ENABLE 1	4728	#define EV_CHILD_ENABLE 1
4142	#define EV_ASYNC_ENABLE 1	4729	#define EV_ASYNC_ENABLE 1
4143		4730
4144	The actual value is a bitset, it can be a combination of the following	4731	The actual value is a bitset, it can be a combination of the following
4145	values:	4732	values (by default, all of these are enabled):
4146		4733
4147	=over 4	4734	=over 4
4148		4735
4149	=item C<1> - faster/larger code	4736	=item C<1> - faster/larger code
4150		4737
…		…
4154	code size by roughly 30% on amd64).	4741	code size by roughly 30% on amd64).
4155		4742
4156	When optimising for size, use of compiler flags such as C<-Os> with	4743	When optimising for size, use of compiler flags such as C<-Os> with
4157	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4744	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4158	assertions.	4745	assertions.
		4746
		4747	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4748	(e.g. gcc with C<-Os>).
4159		4749
4160	=item C<2> - faster/larger data structures	4750	=item C<2> - faster/larger data structures
4161		4751
4162	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4752	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4163	hash table sizes and so on. This will usually further increase code size	4753	hash table sizes and so on. This will usually further increase code size
4164	and can additionally have an effect on the size of data structures at	4754	and can additionally have an effect on the size of data structures at
4165	runtime.	4755	runtime.
4166		4756
		4757	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4758	(e.g. gcc with C<-Os>).
		4759
4167	=item C<4> - full API configuration	4760	=item C<4> - full API configuration
4168		4761
4169	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4762	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4170	enables multiplicity (C<EV_MULTIPLICITY>=1).	4763	enables multiplicity (C<EV_MULTIPLICITY>=1).
4171		4764
…		…
4201		4794
4202	With an intelligent-enough linker (gcc+binutils are intelligent enough	4795	With an intelligent-enough linker (gcc+binutils are intelligent enough
4203	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4796	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4204	your program might be left out as well - a binary starting a timer and an	4797	your program might be left out as well - a binary starting a timer and an
4205	I/O watcher then might come out at only 5Kb.	4798	I/O watcher then might come out at only 5Kb.
		4799
		4800	=item EV_API_STATIC
		4801
		4802	If this symbol is defined (by default it is not), then all identifiers
		4803	will have static linkage. This means that libev will not export any
		4804	identifiers, and you cannot link against libev anymore. This can be useful
		4805	when you embed libev, only want to use libev functions in a single file,
		4806	and do not want its identifiers to be visible.
		4807
		4808	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4809	wants to use libev.
		4810
		4811	This option only works when libev is compiled with a C compiler, as C++
		4812	doesn't support the required declaration syntax.
4206		4813
4207	=item EV_AVOID_STDIO	4814	=item EV_AVOID_STDIO
4208		4815
4209	If this is set to C<1> at compiletime, then libev will avoid using stdio	4816	If this is set to C<1> at compiletime, then libev will avoid using stdio
4210	functions (printf, scanf, perror etc.). This will increase the code size	4817	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4354	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4961	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4355		4962
4356	#include "ev_cpp.h"	4963	#include "ev_cpp.h"
4357	#include "ev.c"	4964	#include "ev.c"
4358		4965
4359	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4966	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4360		4967
4361	=head2 THREADS AND COROUTINES	4968	=head2 THREADS AND COROUTINES
4362		4969
4363	=head3 THREADS	4970	=head3 THREADS
4364		4971
…		…
4415	default loop and triggering an C<ev_async> watcher from the default loop	5022	default loop and triggering an C<ev_async> watcher from the default loop
4416	watcher callback into the event loop interested in the signal.	5023	watcher callback into the event loop interested in the signal.
4417		5024
4418	=back	5025	=back
4419		5026
4420	=head4 THREAD LOCKING EXAMPLE	5027	See also L</THREAD LOCKING EXAMPLE>.
4421
4422	Here is a fictitious example of how to run an event loop in a different
4423	thread than where callbacks are being invoked and watchers are
4424	created/added/removed.
4425
4426	For a real-world example, see the C<EV::Loop::Async> perl module,
4427	which uses exactly this technique (which is suited for many high-level
4428	languages).
4429
4430	The example uses a pthread mutex to protect the loop data, a condition
4431	variable to wait for callback invocations, an async watcher to notify the
4432	event loop thread and an unspecified mechanism to wake up the main thread.
4433
4434	First, you need to associate some data with the event loop:
4435
4436	typedef struct {
4437	mutex_t lock; /* global loop lock */
4438	ev_async async_w;
4439	thread_t tid;
4440	cond_t invoke_cv;
4441	} userdata;
4442
4443	void prepare_loop (EV_P)
4444	{
4445	// for simplicity, we use a static userdata struct.
4446	static userdata u;
4447
4448	ev_async_init (&u->async_w, async_cb);
4449	ev_async_start (EV_A_ &u->async_w);
4450
4451	pthread_mutex_init (&u->lock, 0);
4452	pthread_cond_init (&u->invoke_cv, 0);
4453
4454	// now associate this with the loop
4455	ev_set_userdata (EV_A_ u);
4456	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4457	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4458
4459	// then create the thread running ev_loop
4460	pthread_create (&u->tid, 0, l_run, EV_A);
4461	}
4462
4463	The callback for the C<ev_async> watcher does nothing: the watcher is used
4464	solely to wake up the event loop so it takes notice of any new watchers
4465	that might have been added:
4466
4467	static void
4468	async_cb (EV_P_ ev_async *w, int revents)
4469	{
4470	// just used for the side effects
4471	}
4472
4473	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4474	protecting the loop data, respectively.
4475
4476	static void
4477	l_release (EV_P)
4478	{
4479	userdata *u = ev_userdata (EV_A);
4480	pthread_mutex_unlock (&u->lock);
4481	}
4482
4483	static void
4484	l_acquire (EV_P)
4485	{
4486	userdata *u = ev_userdata (EV_A);
4487	pthread_mutex_lock (&u->lock);
4488	}
4489
4490	The event loop thread first acquires the mutex, and then jumps straight
4491	into C<ev_run>:
4492
4493	void *
4494	l_run (void *thr_arg)
4495	{
4496	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4497
4498	l_acquire (EV_A);
4499	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4500	ev_run (EV_A_ 0);
4501	l_release (EV_A);
4502
4503	return 0;
4504	}
4505
4506	Instead of invoking all pending watchers, the C<l_invoke> callback will
4507	signal the main thread via some unspecified mechanism (signals? pipe
4508	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4509	have been called (in a while loop because a) spurious wakeups are possible
4510	and b) skipping inter-thread-communication when there are no pending
4511	watchers is very beneficial):
4512
4513	static void
4514	l_invoke (EV_P)
4515	{
4516	userdata *u = ev_userdata (EV_A);
4517
4518	while (ev_pending_count (EV_A))
4519	{
4520	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4521	pthread_cond_wait (&u->invoke_cv, &u->lock);
4522	}
4523	}
4524
4525	Now, whenever the main thread gets told to invoke pending watchers, it
4526	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4527	thread to continue:
4528
4529	static void
4530	real_invoke_pending (EV_P)
4531	{
4532	userdata *u = ev_userdata (EV_A);
4533
4534	pthread_mutex_lock (&u->lock);
4535	ev_invoke_pending (EV_A);
4536	pthread_cond_signal (&u->invoke_cv);
4537	pthread_mutex_unlock (&u->lock);
4538	}
4539
4540	Whenever you want to start/stop a watcher or do other modifications to an
4541	event loop, you will now have to lock:
4542
4543	ev_timer timeout_watcher;
4544	userdata *u = ev_userdata (EV_A);
4545
4546	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4547
4548	pthread_mutex_lock (&u->lock);
4549	ev_timer_start (EV_A_ &timeout_watcher);
4550	ev_async_send (EV_A_ &u->async_w);
4551	pthread_mutex_unlock (&u->lock);
4552
4553	Note that sending the C<ev_async> watcher is required because otherwise
4554	an event loop currently blocking in the kernel will have no knowledge
4555	about the newly added timer. By waking up the loop it will pick up any new
4556	watchers in the next event loop iteration.
4557		5028
4558	=head3 COROUTINES	5029	=head3 COROUTINES
4559		5030
4560	Libev is very accommodating to coroutines ("cooperative threads"):	5031	Libev is very accommodating to coroutines ("cooperative threads"):
4561	libev fully supports nesting calls to its functions from different	5032	libev fully supports nesting calls to its functions from different
…		…
4726	requires, and its I/O model is fundamentally incompatible with the POSIX	5197	requires, and its I/O model is fundamentally incompatible with the POSIX
4727	model. Libev still offers limited functionality on this platform in	5198	model. Libev still offers limited functionality on this platform in
4728	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5199	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4729	descriptors. This only applies when using Win32 natively, not when using	5200	descriptors. This only applies when using Win32 natively, not when using
4730	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5201	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4731	as every compielr comes with a slightly differently broken/incompatible	5202	as every compiler comes with a slightly differently broken/incompatible
4732	environment.	5203	environment.
4733		5204
4734	Lifting these limitations would basically require the full	5205	Lifting these limitations would basically require the full
4735	re-implementation of the I/O system. If you are into this kind of thing,	5206	re-implementation of the I/O system. If you are into this kind of thing,
4736	then note that glib does exactly that for you in a very portable way (note	5207	then note that glib does exactly that for you in a very portable way (note
…		…
4830	structure (guaranteed by POSIX but not by ISO C for example), but it also	5301	structure (guaranteed by POSIX but not by ISO C for example), but it also
4831	assumes that the same (machine) code can be used to call any watcher	5302	assumes that the same (machine) code can be used to call any watcher
4832	callback: The watcher callbacks have different type signatures, but libev	5303	callback: The watcher callbacks have different type signatures, but libev
4833	calls them using an C<ev_watcher *> internally.	5304	calls them using an C<ev_watcher *> internally.
4834		5305
		5306	=item null pointers and integer zero are represented by 0 bytes
		5307
		5308	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5309	relies on this setting pointers and integers to null.
		5310
4835	=item pointer accesses must be thread-atomic	5311	=item pointer accesses must be thread-atomic
4836		5312
4837	Accessing a pointer value must be atomic, it must both be readable and	5313	Accessing a pointer value must be atomic, it must both be readable and
4838	writable in one piece - this is the case on all current architectures.	5314	writable in one piece - this is the case on all current architectures.
4839		5315
…		…
4852	thread" or will block signals process-wide, both behaviours would	5328	thread" or will block signals process-wide, both behaviours would
4853	be compatible with libev. Interaction between C<sigprocmask> and	5329	be compatible with libev. Interaction between C<sigprocmask> and
4854	C<pthread_sigmask> could complicate things, however.	5330	C<pthread_sigmask> could complicate things, however.
4855		5331
4856	The most portable way to handle signals is to block signals in all threads	5332	The most portable way to handle signals is to block signals in all threads
4857	except the initial one, and run the default loop in the initial thread as	5333	except the initial one, and run the signal handling loop in the initial
4858	well.	5334	thread as well.
4859		5335
4860	=item C<long> must be large enough for common memory allocation sizes	5336	=item C<long> must be large enough for common memory allocation sizes
4861		5337
4862	To improve portability and simplify its API, libev uses C<long> internally	5338	To improve portability and simplify its API, libev uses C<long> internally
4863	instead of C<size_t> when allocating its data structures. On non-POSIX	5339	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4869		5345
4870	The type C<double> is used to represent timestamps. It is required to	5346	The type C<double> is used to represent timestamps. It is required to
4871	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5347	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4872	good enough for at least into the year 4000 with millisecond accuracy	5348	good enough for at least into the year 4000 with millisecond accuracy
4873	(the design goal for libev). This requirement is overfulfilled by	5349	(the design goal for libev). This requirement is overfulfilled by
4874	implementations using IEEE 754, which is basically all existing ones. With	5350	implementations using IEEE 754, which is basically all existing ones.
		5351
4875	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5352	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5353	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5354	is either obsolete or somebody patched it to use C<long double> or
		5355	something like that, just kidding).
4876		5356
4877	=back	5357	=back
4878		5358
4879	If you know of other additional requirements drop me a note.	5359	If you know of other additional requirements drop me a note.
4880		5360
…		…
4942	=item Processing ev_async_send: O(number_of_async_watchers)	5422	=item Processing ev_async_send: O(number_of_async_watchers)
4943		5423
4944	=item Processing signals: O(max_signal_number)	5424	=item Processing signals: O(max_signal_number)
4945		5425
4946	Sending involves a system call I<iff> there were no other C<ev_async_send>	5426	Sending involves a system call I<iff> there were no other C<ev_async_send>
4947	calls in the current loop iteration. Checking for async and signal events	5427	calls in the current loop iteration and the loop is currently
		5428	blocked. Checking for async and signal events involves iterating over all
4948	involves iterating over all running async watchers or all signal numbers.	5429	running async watchers or all signal numbers.
4949		5430
4950	=back	5431	=back
4951		5432
4952		5433
4953	=head1 PORTING FROM LIBEV 3.X TO 4.X	5434	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
4962	=over 4	5443	=over 4
4963		5444
4964	=item C<EV_COMPAT3> backwards compatibility mechanism	5445	=item C<EV_COMPAT3> backwards compatibility mechanism
4965		5446
4966	The backward compatibility mechanism can be controlled by	5447	The backward compatibility mechanism can be controlled by
4967	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5448	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
4968	section.	5449	section.
4969		5450
4970	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5451	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4971		5452
4972	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5453	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
5015	=over 4	5496	=over 4
5016		5497
5017	=item active	5498	=item active
5018		5499
5019	A watcher is active as long as it has been started and not yet stopped.	5500	A watcher is active as long as it has been started and not yet stopped.
5020	See L<WATCHER STATES> for details.	5501	See L</WATCHER STATES> for details.
5021		5502
5022	=item application	5503	=item application
5023		5504
5024	In this document, an application is whatever is using libev.	5505	In this document, an application is whatever is using libev.
5025		5506
…		…
5061	watchers and events.	5542	watchers and events.
5062		5543
5063	=item pending	5544	=item pending
5064		5545
5065	A watcher is pending as soon as the corresponding event has been	5546	A watcher is pending as soon as the corresponding event has been
5066	detected. See L<WATCHER STATES> for details.	5547	detected. See L</WATCHER STATES> for details.
5067		5548
5068	=item real time	5549	=item real time
5069		5550
5070	The physical time that is observed. It is apparently strictly monotonic :)	5551	The physical time that is observed. It is apparently strictly monotonic :)
5071		5552
5072	=item wall-clock time	5553	=item wall-clock time
5073		5554
5074	The time and date as shown on clocks. Unlike real time, it can actually	5555	The time and date as shown on clocks. Unlike real time, it can actually
5075	be wrong and jump forwards and backwards, e.g. when the you adjust your	5556	be wrong and jump forwards and backwards, e.g. when you adjust your
5076	clock.	5557	clock.
5077		5558
5078	=item watcher	5559	=item watcher
5079		5560
5080	A data structure that describes interest in certain events. Watchers need	5561	A data structure that describes interest in certain events. Watchers need
…		…
5083	=back	5564	=back
5084		5565
5085	=head1 AUTHOR	5566	=head1 AUTHOR
5086		5567
5087	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5568	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5088	Magnusson and Emanuele Giaquinta.	5569	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5089		5570

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