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Revision 1.345 by root, Wed Nov 10 14:36:42 2010 UTC vs.
Revision 1.422 by root, Thu Nov 15 01:39:45 2012 UTC

…		…
58	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
59		59
60	// now wait for events to arrive	60	// now wait for events to arrive
61	ev_run (loop, 0);	61	ev_run (loop, 0);
62		62
63	// unloop was called, so exit	63	// break was called, so exit
64	return 0;	64	return 0;
65	}	65	}
66		66
67	=head1 ABOUT THIS DOCUMENT	67	=head1 ABOUT THIS DOCUMENT
68		68
…		…
82		82
83	=head1 WHAT TO READ WHEN IN A HURRY	83	=head1 WHAT TO READ WHEN IN A HURRY
84		84
85	This manual tries to be very detailed, but unfortunately, this also makes	85	This manual tries to be very detailed, but unfortunately, this also makes
86	it very long. If you just want to know the basics of libev, I suggest	86	it very long. If you just want to know the basics of libev, I suggest
87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and	87	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and	88	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
89	C<ev_timer> sections in L<WATCHER TYPES>.	89	C<ev_timer> sections in L</WATCHER TYPES>.
90		90
91	=head1 ABOUT LIBEV	91	=head1 ABOUT LIBEV
92		92
93	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
94	file descriptor being readable or a timeout occurring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
…		…
174	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
175		175
176	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
177	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
178	you actually want to know. Also interesting is the combination of	178	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	179	C<ev_now_update> and C<ev_now>.
180		180
181	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
182		182
183	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
185	this is a sub-second-resolution C<sleep ()>.	188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
186		192
187	=item int ev_version_major ()	193	=item int ev_version_major ()
188		194
189	=item int ev_version_minor ()	195	=item int ev_version_minor ()
190		196
…		…
241	the current system, you would need to look at C<ev_embeddable_backends ()	247	the current system, you would need to look at C<ev_embeddable_backends ()
242	& ev_supported_backends ()>, likewise for recommended ones.	248	& ev_supported_backends ()>, likewise for recommended ones.
243		249
244	See the description of C<ev_embed> watchers for more info.	250	See the description of C<ev_embed> watchers for more info.
245		251
246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
247		253
248	Sets the allocation function to use (the prototype is similar - the	254	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	255	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	256	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	257	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
277	}	283	}
278		284
279	...	285	...
280	ev_set_allocator (persistent_realloc);	286	ev_set_allocator (persistent_realloc);
281		287
282	=item ev_set_syserr_cb (void (*cb)(const char *msg))	288	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
283		289
284	Set the callback function to call on a retryable system call error (such	290	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	291	as failed select, poll, epoll_wait). The message is a printable string
286	indicating the system call or subsystem causing the problem. If this	292	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	293	callback is set, then libev will expect it to remedy the situation, no
…		…
299	}	305	}
300		306
301	...	307	...
302	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
303		309
		310	=item ev_feed_signal (int signum)
		311
		312	This function can be used to "simulate" a signal receive. It is completely
		313	safe to call this function at any time, from any context, including signal
		314	handlers or random threads.
		315
		316	Its main use is to customise signal handling in your process, especially
		317	in the presence of threads. For example, you could block signals
		318	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		319	creating any loops), and in one thread, use C<sigwait> or any other
		320	mechanism to wait for signals, then "deliver" them to libev by calling
		321	C<ev_feed_signal>.
		322
304	=back	323	=back
305		324
306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
307		326
308	An event loop is described by a C<struct ev_loop *> (the C<struct> is	327	An event loop is described by a C<struct ev_loop *> (the C<struct> is
…		…
419		438
420	Signalfd will not be used by default as this changes your signal mask, and	439	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	440	there are a lot of shoddy libraries and programs (glib's threadpool for
422	example) that can't properly initialise their signal masks.	441	example) that can't properly initialise their signal masks.
423		442
		443	=item C<EVFLAG_NOSIGMASK>
		444
		445	When this flag is specified, then libev will avoid to modify the signal
		446	mask. Specifically, this means you have to make sure signals are unblocked
		447	when you want to receive them.
		448
		449	This behaviour is useful when you want to do your own signal handling, or
		450	want to handle signals only in specific threads and want to avoid libev
		451	unblocking the signals.
		452
		453	It's also required by POSIX in a threaded program, as libev calls
		454	C<sigprocmask>, whose behaviour is officially unspecified.
		455
		456	This flag's behaviour will become the default in future versions of libev.
		457
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		459
426	This is your standard select(2) backend. Not I<completely> standard, as	460	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,	461	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	462	but if that fails, expect a fairly low limit on the number of fds when
…		…
455	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
456		490
457	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
458	kernels).	492	kernels).
459		493
460	For few fds, this backend is a bit little slower than poll and select,	494	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	495	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),	496	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).	497	fd), epoll scales either O(1) or O(active_fds).
464		498
465	The epoll mechanism deserves honorable mention as the most misdesigned	499	The epoll mechanism deserves honorable mention as the most misdesigned
466	of the more advanced event mechanisms: mere annoyances include silently	500	of the more advanced event mechanisms: mere annoyances include silently
467	dropping file descriptors, requiring a system call per change per file	501	dropping file descriptors, requiring a system call per change per file
468	descriptor (and unnecessary guessing of parameters), problems with dup,	502	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	505	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	506	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)	507	set, which can take considerable time (one syscall per file descriptor)
474	and is of course hard to detect.	508	and is of course hard to detect.
475		509
476	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	510	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	511	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	512	totally I<different> file descriptors (even already closed ones, so
479	even remove them from the set) than registered in the set (especially	513	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	514	(especially on SMP systems). Libev tries to counter these spurious
481	employing an additional generation counter and comparing that against the	515	notifications by employing an additional generation counter and comparing
482	events to filter out spurious ones, recreating the set when required. Last	516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also erroneously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
483	not least, it also refuses to work with some file descriptors which work	520	not least, it also refuses to work with some file descriptors which work
484	perfectly fine with C<select> (files, many character devices...).	521	perfectly fine with C<select> (files, many character devices...).
485		522
486	Epoll is truly the train wreck analog among event poll mechanisms.	523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
487		526
488	While stopping, setting and starting an I/O watcher in the same iteration	527	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	528	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	529	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	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
528		567
529	It scales in the same way as the epoll backend, but the interface to the	568	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	569	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	570	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	571	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	572	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	573	might have to leak fd's on fork, but it's more sane than epoll) and it
535	cases	574	drops fds silently in similarly hard-to-detect cases.
536		575
537	This backend usually performs well under most conditions.	576	This backend usually performs well under most conditions.
538		577
539	While nominally embeddable in other event loops, this doesn't work	578	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	579	everywhere, so you might need to test for this. And since it is broken
…		…
557	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
558		597
559	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	598	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)).	599	it's really slow, but it still scales very well (O(active_fds)).
561		600
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	601	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	602	file descriptor per loop iteration. For small and medium numbers of file
568	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
569	might perform better.	604	might perform better.
570		605
571	On the positive side, with the exception of the spurious readiness	606	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	607	specification in all tests and is fully embeddable, which is a rare feat
574	OS-specific backends (I vastly prefer correctness over speed hacks).	608	among the OS-specific backends (I vastly prefer correctness over speed
		609	hacks).
		610
		611	On the negative side, the interface is I<bizarre> - so bizarre that
		612	even sun itself gets it wrong in their code examples: The event polling
		613	function sometimes returns events to the caller even though an error
		614	occurred, but with no indication whether it has done so or not (yes, it's
		615	even documented that way) - deadly for edge-triggered interfaces where you
		616	absolutely have to know whether an event occurred or not because you have
		617	to re-arm the watcher.
		618
		619	Fortunately libev seems to be able to work around these idiocies.
575		620
576	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	621	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
577	C<EVBACKEND_POLL>.	622	C<EVBACKEND_POLL>.
578		623
579	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
580		625
581	Try all backends (even potentially broken ones that wouldn't be tried	626	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	627	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
583	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
584		629
585	It is definitely not recommended to use this flag.	630	It is definitely not recommended to use this flag, use whatever
		631	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		632	at all.
		633
		634	=item C<EVBACKEND_MASK>
		635
		636	Not a backend at all, but a mask to select all backend bits from a
		637	C<flags> value, in case you want to mask out any backends from a flags
		638	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
586		639
587	=back	640	=back
588		641
589	If one or more of the backend flags are or'ed into the flags value,	642	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	643	then only these backends will be tried (in the reverse order as listed
…		…
711		764
712	This function is rarely useful, but when some event callback runs for a	765	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	766	very long time without entering the event loop, updating libev's idea of
714	the current time is a good idea.	767	the current time is a good idea.
715		768
716	See also L<The special problem of time updates> in the C<ev_timer> section.	769	See also L</The special problem of time updates> in the C<ev_timer> section.
717		770
718	=item ev_suspend (loop)	771	=item ev_suspend (loop)
719		772
720	=item ev_resume (loop)	773	=item ev_resume (loop)
721		774
…		…
739	without a previous call to C<ev_suspend>.	792	without a previous call to C<ev_suspend>.
740		793
741	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	794	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
742	event loop time (see C<ev_now_update>).	795	event loop time (see C<ev_now_update>).
743		796
744	=item ev_run (loop, int flags)	797	=item bool ev_run (loop, int flags)
745		798
746	Finally, this is it, the event handler. This function usually is called	799	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	800	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	801	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	802	the watcher callbacks, and then repeat the whole process indefinitely: This
750	is why event loops are called I<loops>.	803	is why event loops are called I<loops>.
751		804
752	If the flags argument is specified as C<0>, it will keep handling events	805	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	806	until either no event watchers are active anymore or C<ev_break> was
754	called.	807	called.
		808
		809	The return value is false if there are no more active watchers (which
		810	usually means "all jobs done" or "deadlock"), and true in all other cases
		811	(which usually means " you should call C<ev_run> again").
755		812
756	Please note that an explicit C<ev_break> is usually better than	813	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	814	relying on all watchers to be stopped when deciding when a program has
758	finished (especially in interactive programs), but having a program	815	finished (especially in interactive programs), but having a program
759	that automatically loops as long as it has to and no longer by virtue	816	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	817	of relying on its watchers stopping correctly, that is truly a thing of
761	beauty.	818	beauty.
762		819
763	This function is also I<mostly> exception-safe - you can break out of	820	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++	821	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	822	exception and so on. This does not decrement the C<ev_depth> value, nor
766	will it clear any outstanding C<EVBREAK_ONE> breaks.	823	will it clear any outstanding C<EVBREAK_ONE> breaks.
767		824
768	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	825	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	826	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	838	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	839	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	840	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.	841	usually a better approach for this kind of thing.
785		842
786	Here are the gory details of what C<ev_run> does:	843	Here are the gory details of what C<ev_run> does (this is for your
		844	understanding, not a guarantee that things will work exactly like this in
		845	future versions):
787		846
788	- Increment loop depth.	847	- Increment loop depth.
789	- Reset the ev_break status.	848	- Reset the ev_break status.
790	- Before the first iteration, call any pending watchers.	849	- Before the first iteration, call any pending watchers.
791	LOOP:	850	LOOP:
…		…
824	anymore.	883	anymore.
825		884
826	... queue jobs here, make sure they register event watchers as long	885	... 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..)	886	... as they still have work to do (even an idle watcher will do..)
828	ev_run (my_loop, 0);	887	ev_run (my_loop, 0);
829	... jobs done or somebody called unloop. yeah!	888	... jobs done or somebody called break. yeah!
830		889
831	=item ev_break (loop, how)	890	=item ev_break (loop, how)
832		891
833	Can be used to make a call to C<ev_run> return early (but only after it	892	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	893	has processed all outstanding events). The C<how> argument must be either
…		…
867	running when nothing else is active.	926	running when nothing else is active.
868		927
869	ev_signal exitsig;	928	ev_signal exitsig;
870	ev_signal_init (&exitsig, sig_cb, SIGINT);	929	ev_signal_init (&exitsig, sig_cb, SIGINT);
871	ev_signal_start (loop, &exitsig);	930	ev_signal_start (loop, &exitsig);
872	evf_unref (loop);	931	ev_unref (loop);
873		932
874	Example: For some weird reason, unregister the above signal handler again.	933	Example: For some weird reason, unregister the above signal handler again.
875		934
876	ev_ref (loop);	935	ev_ref (loop);
877	ev_signal_stop (loop, &exitsig);	936	ev_signal_stop (loop, &exitsig);
…		…
897	overhead for the actual polling but can deliver many events at once.	956	overhead for the actual polling but can deliver many events at once.
898		957
899	By setting a higher I<io collect interval> you allow libev to spend more	958	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,	959	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	960	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	961	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	962	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	963	sleep time ensures that libev will not poll for I/O events more often then
905	once per this interval, on average.	964	once per this interval, on average (as long as the host time resolution is
		965	good enough).
906		966
907	Likewise, by setting a higher I<timeout collect interval> you allow libev	967	Likewise, by setting a higher I<timeout collect interval> you allow libev
908	to spend more time collecting timeouts, at the expense of increased	968	to spend more time collecting timeouts, at the expense of increased
909	latency/jitter/inexactness (the watcher callback will be called	969	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	970	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.).	1016	invoke the actual watchers inside another context (another thread etc.).
957		1017
958	If you want to reset the callback, use C<ev_invoke_pending> as new	1018	If you want to reset the callback, use C<ev_invoke_pending> as new
959	callback.	1019	callback.
960		1020
961	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1021	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
962		1022
963	Sometimes you want to share the same loop between multiple threads. This	1023	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	1024	can be done relatively simply by putting mutex_lock/unlock calls around
965	each call to a libev function.	1025	each call to a libev function.
966		1026
967	However, C<ev_run> can run an indefinite time, so it is not feasible	1027	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	1028	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	1029	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.	1030	I<release> and I<acquire> callbacks on the loop.
971		1031
972	When set, then C<release> will be called just before the thread is	1032	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	1033	suspended waiting for new events, and C<acquire> is called just
974	afterwards.	1034	afterwards.
…		…
1114		1174
1115	=item C<EV_PREPARE>	1175	=item C<EV_PREPARE>
1116		1176
1117	=item C<EV_CHECK>	1177	=item C<EV_CHECK>
1118		1178
1119	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1179	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	1180	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	1181	just after C<ev_run> has gathered them, but before it queues any callbacks
		1182	for any received events. That means C<ev_prepare> watchers are the last
		1183	watchers invoked before the event loop sleeps or polls for new events, and
		1184	C<ev_check> watchers will be invoked before any other watchers of the same
		1185	or lower priority within an event loop iteration.
		1186
1122	received events. Callbacks of both watcher types can start and stop as	1187	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	1188	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	1189	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1125	C<ev_run> from blocking).	1190	blocking).
1126		1191
1127	=item C<EV_EMBED>	1192	=item C<EV_EMBED>
1128		1193
1129	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1194	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1130		1195
…		…
1253		1318
1254	=item callback ev_cb (ev_TYPE *watcher)	1319	=item callback ev_cb (ev_TYPE *watcher)
1255		1320
1256	Returns the callback currently set on the watcher.	1321	Returns the callback currently set on the watcher.
1257		1322
1258	=item ev_cb_set (ev_TYPE *watcher, callback)	1323	=item ev_set_cb (ev_TYPE *watcher, callback)
1259		1324
1260	Change the callback. You can change the callback at virtually any time	1325	Change the callback. You can change the callback at virtually any time
1261	(modulo threads).	1326	(modulo threads).
1262		1327
1263	=item ev_set_priority (ev_TYPE *watcher, int priority)	1328	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1281	or might not have been clamped to the valid range.	1346	or might not have been clamped to the valid range.
1282		1347
1283	The default priority used by watchers when no priority has been set is	1348	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 :).	1349	always C<0>, which is supposed to not be too high and not be too low :).
1285		1350
1286	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1351	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1287	priorities.	1352	priorities.
1288		1353
1289	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1354	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1290		1355
1291	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1356	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	1381	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1317	functions that do not need a watcher.	1382	functions that do not need a watcher.
1318		1383
1319	=back	1384	=back
1320		1385
1321	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1386	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1322		1387	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		1388
1386	=head2 WATCHER STATES	1389	=head2 WATCHER STATES
1387		1390
1388	There are various watcher states mentioned throughout this manual -	1391	There are various watcher states mentioned throughout this manual -
1389	active, pending and so on. In this section these states and the rules to	1392	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	1393	transition between them will be described in more detail - and while these
1391	rules might look complicated, they usually do "the right thing".	1394	rules might look complicated, they usually do "the right thing".
1392		1395
1393	=over 4	1396	=over 4
1394		1397
1395	=item initialiased	1398	=item initialised
1396		1399
1397	Before a watcher can be registered with the event looop it has to be	1400	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	1401	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.	1402	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1400		1403
1401	In this state it is simply some block of memory that is suitable for use	1404	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.	1405	use in an event loop. It can be moved around, freed, reused etc. at
		1406	will - as long as you either keep the memory contents intact, or call
		1407	C<ev_TYPE_init> again.
1403		1408
1404	=item started/running/active	1409	=item started/running/active
1405		1410
1406	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1411	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	1412	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	1440	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	1441	of whether it was active or not, so stopping a watcher explicitly before
1437	freeing it is often a good idea.	1442	freeing it is often a good idea.
1438		1443
1439	While stopped (and not pending) the watcher is essentially in the	1444	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	1445	initialised state, that is, it can be reused, moved, modified in any way
1441	you wish.	1446	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1447	it again).
1442		1448
1443	=back	1449	=back
1444		1450
1445	=head2 WATCHER PRIORITY MODELS	1451	=head2 WATCHER PRIORITY MODELS
1446		1452
…		…
1575	In general you can register as many read and/or write event watchers per	1581	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	1582	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	1583	descriptors to non-blocking mode is also usually a good idea (but not
1578	required if you know what you are doing).	1584	required if you know what you are doing).
1579		1585
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	1586	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	1587	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	1588	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	1589	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	1590	with a relatively standard program structure. Thus it is best to always
1591	this situation even with a relatively standard program structure. Thus	1591	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.	1592	preferable to a program hanging until some data arrives.
1594		1593
1595	If you cannot run the fd in non-blocking mode (for example you should	1594	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	1595	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	1596	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	1597	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	1598	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	1599	use C<SIGALRM> and an interval timer, just to be sure you won't block
1601	indefinitely.	1600	indefinitely.
1602		1601
1603	But really, best use non-blocking mode.	1602	But really, best use non-blocking mode.
1604		1603
…		…
1632		1631
1633	There is no workaround possible except not registering events	1632	There is no workaround possible except not registering events
1634	for potentially C<dup ()>'ed file descriptors, or to resort to	1633	for potentially C<dup ()>'ed file descriptors, or to resort to
1635	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1634	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1636		1635
		1636	=head3 The special problem of files
		1637
		1638	Many people try to use C<select> (or libev) on file descriptors
		1639	representing files, and expect it to become ready when their program
		1640	doesn't block on disk accesses (which can take a long time on their own).
		1641
		1642	However, this cannot ever work in the "expected" way - you get a readiness
		1643	notification as soon as the kernel knows whether and how much data is
		1644	there, and in the case of open files, that's always the case, so you
		1645	always get a readiness notification instantly, and your read (or possibly
		1646	write) will still block on the disk I/O.
		1647
		1648	Another way to view it is that in the case of sockets, pipes, character
		1649	devices and so on, there is another party (the sender) that delivers data
		1650	on its own, but in the case of files, there is no such thing: the disk
		1651	will not send data on its own, simply because it doesn't know what you
		1652	wish to read - you would first have to request some data.
		1653
		1654	Since files are typically not-so-well supported by advanced notification
		1655	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1656	to files, even though you should not use it. The reason for this is
		1657	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1658	usually a tty, often a pipe, but also sometimes files or special devices
		1659	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1660	F</dev/urandom>), and even though the file might better be served with
		1661	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1662	it "just works" instead of freezing.
		1663
		1664	So avoid file descriptors pointing to files when you know it (e.g. use
		1665	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1666	when you rarely read from a file instead of from a socket, and want to
		1667	reuse the same code path.
		1668
1637	=head3 The special problem of fork	1669	=head3 The special problem of fork
1638		1670
1639	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1671	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	1672	useless behaviour. Libev fully supports fork, but needs to be told about
1641	it in the child.	1673	it in the child if you want to continue to use it in the child.
1642		1674
1643	To support fork in your programs, you either have to call	1675	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,	1676	()> 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	1677	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1646	C<EVBACKEND_POLL>.
1647		1678
1648	=head3 The special problem of SIGPIPE	1679	=head3 The special problem of SIGPIPE
1649		1680
1650	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1681	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	1682	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	1780	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1750	monotonic clock option helps a lot here).	1781	monotonic clock option helps a lot here).
1751		1782
1752	The callback is guaranteed to be invoked only I<after> its timeout has	1783	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	1784	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	1785	might introduce a small delay, see "the special problem of being too
		1786	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	1787	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	1788	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).	1789	longer true when a callback calls C<ev_run> recursively).
1758		1790
1759	=head3 Be smart about timeouts	1791	=head3 Be smart about timeouts
1760		1792
1761	Many real-world problems involve some kind of timeout, usually for error	1793	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,	1794	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1837		1869
1838	In this case, it would be more efficient to leave the C<ev_timer> alone,	1870	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	1871	but remember the time of last activity, and check for a real timeout only
1840	within the callback:	1872	within the callback:
1841		1873
		1874	ev_tstamp timeout = 60.;
1842	ev_tstamp last_activity; // time of last activity	1875	ev_tstamp last_activity; // time of last activity
		1876	ev_timer timer;
1843		1877
1844	static void	1878	static void
1845	callback (EV_P_ ev_timer *w, int revents)	1879	callback (EV_P_ ev_timer *w, int revents)
1846	{	1880	{
1847	ev_tstamp now = ev_now (EV_A);	1881	// calculate when the timeout would happen
1848	ev_tstamp timeout = last_activity + 60.;	1882	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1849		1883
1850	// if last_activity + 60. is older than now, we did time out	1884	// if negative, it means we the timeout already occurred
1851	if (timeout < now)	1885	if (after < 0.)
1852	{	1886	{
1853	// timeout occurred, take action	1887	// timeout occurred, take action
1854	}	1888	}
1855	else	1889	else
1856	{	1890	{
1857	// callback was invoked, but there was some activity, re-arm	1891	// callback was invoked, but there was some recent
1858	// the watcher to fire in last_activity + 60, which is	1892	// activity. simply restart the timer to time out
1859	// guaranteed to be in the future, so "again" is positive:	1893	// after "after" seconds, which is the earliest time
1860	w->repeat = timeout - now;	1894	// the timeout can occur.
		1895	ev_timer_set (w, after, 0.);
1861	ev_timer_again (EV_A_ w);	1896	ev_timer_start (EV_A_ w);
1862	}	1897	}
1863	}	1898	}
1864		1899
1865	To summarise the callback: first calculate the real timeout (defined	1900	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	1901	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	1902	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	1903	(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		1904
1872	Note how C<ev_timer_again> is used, taking advantage of the	1905	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.	1906	timed out, and need to do whatever is needed in this case.
		1907
		1908	Otherwise, we now the earliest time at which the timeout would trigger,
		1909	and simply start the timer with this timeout value.
		1910
		1911	In other words, each time the callback is invoked it will check whether
		1912	the timeout occurred. If not, it will simply reschedule itself to check
		1913	again at the earliest time it could time out. Rinse. Repeat.
1874		1914
1875	This scheme causes more callback invocations (about one every 60 seconds	1915	This scheme causes more callback invocations (about one every 60 seconds
1876	minus half the average time between activity), but virtually no calls to	1916	minus half the average time between activity), but virtually no calls to
1877	libev to change the timeout.	1917	libev to change the timeout.
1878		1918
1879	To start the timer, simply initialise the watcher and set C<last_activity>	1919	To start the machinery, simply initialise the watcher and set
1880	to the current time (meaning we just have some activity :), then call the	1920	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:	1921	now), then call the callback, which will "do the right thing" and start
		1922	the timer:
1882		1923
		1924	last_activity = ev_now (EV_A);
1883	ev_init (timer, callback);	1925	ev_init (&timer, callback);
1884	last_activity = ev_now (loop);	1926	callback (EV_A_ &timer, 0);
1885	callback (loop, timer, EV_TIMER);
1886		1927
1887	And when there is some activity, simply store the current time in	1928	When there is some activity, simply store the current time in
1888	C<last_activity>, no libev calls at all:	1929	C<last_activity>, no libev calls at all:
1889		1930
		1931	if (activity detected)
1890	last_activity = ev_now (loop);	1932	last_activity = ev_now (EV_A);
		1933
		1934	When your timeout value changes, then the timeout can be changed by simply
		1935	providing a new value, stopping the timer and calling the callback, which
		1936	will again do the right thing (for example, time out immediately :).
		1937
		1938	timeout = new_value;
		1939	ev_timer_stop (EV_A_ &timer);
		1940	callback (EV_A_ &timer, 0);
1891		1941
1892	This technique is slightly more complex, but in most cases where the	1942	This technique is slightly more complex, but in most cases where the
1893	time-out is unlikely to be triggered, much more efficient.	1943	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		1944
1899	=item 4. Wee, just use a double-linked list for your timeouts.	1945	=item 4. Wee, just use a double-linked list for your timeouts.
1900		1946
1901	If there is not one request, but many thousands (millions...), all	1947	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	1948	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	1975	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	1976	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	1977	off after the first million or so of active timers, i.e. it's usually
1932	overkill :)	1978	overkill :)
1933		1979
		1980	=head3 The special problem of being too early
		1981
		1982	If you ask a timer to call your callback after three seconds, then
		1983	you expect it to be invoked after three seconds - but of course, this
		1984	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1985	guaranteed to any precision by libev - imagine somebody suspending the
		1986	process with a STOP signal for a few hours for example.
		1987
		1988	So, libev tries to invoke your callback as soon as possible I<after> the
		1989	delay has occurred, but cannot guarantee this.
		1990
		1991	A less obvious failure mode is calling your callback too early: many event
		1992	loops compare timestamps with a "elapsed delay >= requested delay", but
		1993	this can cause your callback to be invoked much earlier than you would
		1994	expect.
		1995
		1996	To see why, imagine a system with a clock that only offers full second
		1997	resolution (think windows if you can't come up with a broken enough OS
		1998	yourself). If you schedule a one-second timer at the time 500.9, then the
		1999	event loop will schedule your timeout to elapse at a system time of 500
		2000	(500.9 truncated to the resolution) + 1, or 501.
		2001
		2002	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2003	501" and invoke the callback 0.1s after it was started, even though a
		2004	one-second delay was requested - this is being "too early", despite best
		2005	intentions.
		2006
		2007	This is the reason why libev will never invoke the callback if the elapsed
		2008	delay equals the requested delay, but only when the elapsed delay is
		2009	larger than the requested delay. In the example above, libev would only invoke
		2010	the callback at system time 502, or 1.1s after the timer was started.
		2011
		2012	So, while libev cannot guarantee that your callback will be invoked
		2013	exactly when requested, it I<can> and I<does> guarantee that the requested
		2014	delay has actually elapsed, or in other words, it always errs on the "too
		2015	late" side of things.
		2016
1934	=head3 The special problem of time updates	2017	=head3 The special problem of time updates
1935		2018
1936	Establishing the current time is a costly operation (it usually takes at	2019	Establishing the current time is a costly operation (it usually takes
1937	least two system calls): EV therefore updates its idea of the current	2020	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	2021	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	2022	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1940	lots of events in one iteration.	2023	lots of events in one iteration.
1941		2024
1942	The relative timeouts are calculated relative to the C<ev_now ()>	2025	The relative timeouts are calculated relative to the C<ev_now ()>
…		…
1948	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2031	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1949		2032
1950	If the event loop is suspended for a long time, you can also force an	2033	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	2034	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1952	()>.	2035	()>.
		2036
		2037	=head3 The special problem of unsynchronised clocks
		2038
		2039	Modern systems have a variety of clocks - libev itself uses the normal
		2040	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2041	jumps).
		2042
		2043	Neither of these clocks is synchronised with each other or any other clock
		2044	on the system, so C<ev_time ()> might return a considerably different time
		2045	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2046	a call to C<gettimeofday> might return a second count that is one higher
		2047	than a directly following call to C<time>.
		2048
		2049	The moral of this is to only compare libev-related timestamps with
		2050	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2051	a second or so.
		2052
		2053	One more problem arises due to this lack of synchronisation: if libev uses
		2054	the system monotonic clock and you compare timestamps from C<ev_time>
		2055	or C<ev_now> from when you started your timer and when your callback is
		2056	invoked, you will find that sometimes the callback is a bit "early".
		2057
		2058	This is because C<ev_timer>s work in real time, not wall clock time, so
		2059	libev makes sure your callback is not invoked before the delay happened,
		2060	I<measured according to the real time>, not the system clock.
		2061
		2062	If your timeouts are based on a physical timescale (e.g. "time out this
		2063	connection after 100 seconds") then this shouldn't bother you as it is
		2064	exactly the right behaviour.
		2065
		2066	If you want to compare wall clock/system timestamps to your timers, then
		2067	you need to use C<ev_periodic>s, as these are based on the wall clock
		2068	time, where your comparisons will always generate correct results.
1953		2069
1954	=head3 The special problems of suspended animation	2070	=head3 The special problems of suspended animation
1955		2071
1956	When you leave the server world it is quite customary to hit machines that	2072	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?	2073	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	2117	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.	2118	do stuff) the timer will not fire more than once per event loop iteration.
2003		2119
2004	=item ev_timer_again (loop, ev_timer *)	2120	=item ev_timer_again (loop, ev_timer *)
2005		2121
2006	This will act as if the timer timed out and restart it again if it is	2122	This will act as if the timer timed out, and restarts it again if it is
2007	repeating. The exact semantics are:	2123	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2124	timeout to the C<repeat> value and calling C<ev_timer_start>.
2008		2125
		2126	The exact semantics are as in the following rules, all of which will be
		2127	applied to the watcher:
		2128
		2129	=over 4
		2130
2009	If the timer is pending, its pending status is cleared.	2131	=item If the timer is pending, the pending status is always cleared.
2010		2132
2011	If the timer is started but non-repeating, stop it (as if it timed out).	2133	=item If the timer is started but non-repeating, stop it (as if it timed
		2134	out, without invoking it).
2012		2135
2013	If the timer is repeating, either start it if necessary (with the	2136	=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.	2137	and start the timer, if necessary.
2015		2138
		2139	=back
		2140
2016	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2141	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2017	usage example.	2142	usage example.
2018		2143
2019	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2144	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2020		2145
2021	Returns the remaining time until a timer fires. If the timer is active,	2146	Returns the remaining time until a timer fires. If the timer is active,
…		…
2141		2266
2142	Another way to think about it (for the mathematically inclined) is that	2267	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	2268	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.	2269	time where C<time = offset (mod interval)>, regardless of any time jumps.
2145		2270
2146	For numerical stability it is preferable that the C<offset> value is near	2271	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	2272	interval value should be higher than C<1/8192> (which is around 100
2148	this value, and in fact is often specified as zero.	2273	microseconds) and C<offset> should be higher than C<0> and should have
		2274	at most a similar magnitude as the current time (say, within a factor of
		2275	ten). Typical values for offset are, in fact, C<0> or something between
		2276	C<0> and C<interval>, which is also the recommended range.
2149		2277
2150	Note also that there is an upper limit to how often a timer can fire (CPU	2278	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	2279	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	2280	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).	2281	millisecond (if the OS supports it and the machine is fast enough).
…		…
2296	=head3 The special problem of inheritance over fork/execve/pthread_create	2424	=head3 The special problem of inheritance over fork/execve/pthread_create
2297		2425
2298	Both the signal mask (C<sigprocmask>) and the signal disposition	2426	Both the signal mask (C<sigprocmask>) and the signal disposition
2299	(C<sigaction>) are unspecified after starting a signal watcher (and after	2427	(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,	2428	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.	2429	and might or might not set or restore the installed signal handler (but
		2430	see C<EVFLAG_NOSIGMASK>).
2302		2431
2303	While this does not matter for the signal disposition (libev never	2432	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	2433	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	2434	C<execve>), this matters for the signal mask: many programs do not expect
2306	certain signals to be blocked.	2435	certain signals to be blocked.
…		…
2319	I<has> to modify the signal mask, at least temporarily.	2448	I<has> to modify the signal mask, at least temporarily.
2320		2449
2321	So I can't stress this enough: I<If you do not reset your signal mask when	2450	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	2451	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.	2452	is not a libev-specific thing, this is true for most event libraries.
		2453
		2454	=head3 The special problem of threads signal handling
		2455
		2456	POSIX threads has problematic signal handling semantics, specifically,
		2457	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2458	threads in a process block signals, which is hard to achieve.
		2459
		2460	When you want to use sigwait (or mix libev signal handling with your own
		2461	for the same signals), you can tackle this problem by globally blocking
		2462	all signals before creating any threads (or creating them with a fully set
		2463	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2464	loops. Then designate one thread as "signal receiver thread" which handles
		2465	these signals. You can pass on any signals that libev might be interested
		2466	in by calling C<ev_feed_signal>.
2324		2467
2325	=head3 Watcher-Specific Functions and Data Members	2468	=head3 Watcher-Specific Functions and Data Members
2326		2469
2327	=over 4	2470	=over 4
2328		2471
…		…
2704	Apart from keeping your process non-blocking (which is a useful	2847	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	2848	effect on its own sometimes), idle watchers are a good place to do
2706	"pseudo-background processing", or delay processing stuff to after the	2849	"pseudo-background processing", or delay processing stuff to after the
2707	event loop has handled all outstanding events.	2850	event loop has handled all outstanding events.
2708		2851
		2852	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2853
		2854	As long as there is at least one active idle watcher, libev will never
		2855	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2856	For this to work, the idle watcher doesn't need to be invoked at all - the
		2857	lowest priority will do.
		2858
		2859	This mode of operation can be useful together with an C<ev_check> watcher,
		2860	to do something on each event loop iteration - for example to balance load
		2861	between different connections.
		2862
		2863	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2864	example.
		2865
2709	=head3 Watcher-Specific Functions and Data Members	2866	=head3 Watcher-Specific Functions and Data Members
2710		2867
2711	=over 4	2868	=over 4
2712		2869
2713	=item ev_idle_init (ev_idle *, callback)	2870	=item ev_idle_init (ev_idle *, callback)
…		…
2724	callback, free it. Also, use no error checking, as usual.	2881	callback, free it. Also, use no error checking, as usual.
2725		2882
2726	static void	2883	static void
2727	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2884	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2728	{	2885	{
		2886	// stop the watcher
		2887	ev_idle_stop (loop, w);
		2888
		2889	// now we can free it
2729	free (w);	2890	free (w);
		2891
2730	// now do something you wanted to do when the program has	2892	// now do something you wanted to do when the program has
2731	// no longer anything immediate to do.	2893	// no longer anything immediate to do.
2732	}	2894	}
2733		2895
2734	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2896	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2736	ev_idle_start (loop, idle_watcher);	2898	ev_idle_start (loop, idle_watcher);
2737		2899
2738		2900
2739	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2901	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2740		2902
2741	Prepare and check watchers are usually (but not always) used in pairs:	2903	Prepare and check watchers are often (but not always) used in pairs:
2742	prepare watchers get invoked before the process blocks and check watchers	2904	prepare watchers get invoked before the process blocks and check watchers
2743	afterwards.	2905	afterwards.
2744		2906
2745	You I<must not> call C<ev_run> or similar functions that enter	2907	You I<must not> call C<ev_run> or similar functions that enter
2746	the current event loop from either C<ev_prepare> or C<ev_check>	2908	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
2774	with priority higher than or equal to the event loop and one coroutine	2936	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	2937	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	2938	loop from blocking if lower-priority coroutines are active, thus mapping
2777	low-priority coroutines to idle/background tasks).	2939	low-priority coroutines to idle/background tasks).
2778		2940
2779	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2941	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	2942	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).	2943	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2944	watchers).
2782		2945
2783	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	2946	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	2947	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	2948	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	2949	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	2950	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	2951	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2789	others).	2952	others).
		2953
		2954	=head3 Abusing an C<ev_check> watcher for its side-effect
		2955
		2956	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2957	useful because they are called once per event loop iteration. For
		2958	example, if you want to handle a large number of connections fairly, you
		2959	normally only do a bit of work for each active connection, and if there
		2960	is more work to do, you wait for the next event loop iteration, so other
		2961	connections have a chance of making progress.
		2962
		2963	Using an C<ev_check> watcher is almost enough: it will be called on the
		2964	next event loop iteration. However, that isn't as soon as possible -
		2965	without external events, your C<ev_check> watcher will not be invoked.
		2966
		2967	This is where C<ev_idle> watchers come in handy - all you need is a
		2968	single global idle watcher that is active as long as you have one active
		2969	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2970	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2971	invoked. Neither watcher alone can do that.
2790		2972
2791	=head3 Watcher-Specific Functions and Data Members	2973	=head3 Watcher-Specific Functions and Data Members
2792		2974
2793	=over 4	2975	=over 4
2794		2976
…		…
3068		3250
3069	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3251	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3070		3252
3071	Fork watchers are called when a C<fork ()> was detected (usually because	3253	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	3254	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	3255	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,	3256	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	3257	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	3258	and calls it in the wrong process, the fork handlers will be invoked, too,
3077	handlers will be invoked, too, of course.	3259	of course.
3078		3260
3079	=head3 The special problem of life after fork - how is it possible?	3261	=head3 The special problem of life after fork - how is it possible?
3080		3262
3081	Most uses of C<fork()> consist of forking, then some simple calls to set	3263	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	3264	up/change the process environment, followed by a call to C<exec()>. This
…		…
3163	atexit (program_exits);	3345	atexit (program_exits);
3164		3346
3165		3347
3166	=head2 C<ev_async> - how to wake up an event loop	3348	=head2 C<ev_async> - how to wake up an event loop
3167		3349
3168	In general, you cannot use an C<ev_run> from multiple threads or other	3350	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	3351	asynchronous sources such as signal handlers (as opposed to multiple event
3170	loops - those are of course safe to use in different threads).	3352	loops - those are of course safe to use in different threads).
3171		3353
3172	Sometimes, however, you need to wake up an event loop you do not control,	3354	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>	3355	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.	3357	it by calling C<ev_async_send>, which is thread- and signal safe.
3176		3358
3177	This functionality is very similar to C<ev_signal> watchers, as signals,	3359	This functionality is very similar to C<ev_signal> watchers, as signals,
3178	too, are asynchronous in nature, and signals, too, will be compressed	3360	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	3361	(i.e. the number of callback invocations may be less than the number of
3180	C<ev_async_sent> calls).	3362	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3181		3363	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	3364	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3183	just the default loop.	3365	even without knowing which loop owns the signal.
3184		3366
3185	=head3 Queueing	3367	=head3 Queueing
3186		3368
3187	C<ev_async> does not support queueing of data in any way. The reason	3369	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	3370	is that the author does not know of a simple (or any) algorithm for a
…		…
3280	trust me.	3462	trust me.
3281		3463
3282	=item ev_async_send (loop, ev_async *)	3464	=item ev_async_send (loop, ev_async *)
3283		3465
3284	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3466	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	3467	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3468	returns.
		3469
3286	C<ev_feed_event>, this call is safe to do from other threads, signal or	3470	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	3471	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3288	section below on what exactly this means).	3472	embedding section below on what exactly this means).
3289		3473
3290	Note that, as with other watchers in libev, multiple events might get	3474	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	3475	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>,	3476	this is that C<ev_async> watchers are level-triggered: they are set on
3293	reset when the event loop detects that).	3477	C<ev_async_send>, reset when the event loop detects that).
3294		3478
3295	This call incurs the overhead of a system call only once per event loop	3479	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	3480	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.	3481	the event loop (or your program) is processing events. That means that
		3482	repeated calls are basically free (there is no need to avoid calls for
		3483	performance reasons) and that the overhead becomes smaller (typically
		3484	zero) under load.
3298		3485
3299	=item bool = ev_async_pending (ev_async *)	3486	=item bool = ev_async_pending (ev_async *)
3300		3487
3301	Returns a non-zero value when C<ev_async_send> has been called on the	3488	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	3489	watcher but the event has not yet been processed (or even noted) by the
…		…
3357	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3544	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3358		3545
3359	=item ev_feed_fd_event (loop, int fd, int revents)	3546	=item ev_feed_fd_event (loop, int fd, int revents)
3360		3547
3361	Feed an event on the given fd, as if a file descriptor backend detected	3548	Feed an event on the given fd, as if a file descriptor backend detected
3362	the given events it.	3549	the given events.
3363		3550
3364	=item ev_feed_signal_event (loop, int signum)	3551	=item ev_feed_signal_event (loop, int signum)
3365		3552
3366	Feed an event as if the given signal occurred (C<loop> must be the default	3553	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3367	loop!).	3554	which is async-safe.
3368		3555
3369	=back	3556	=back
3370		3557
3371		3558
3372	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)	3559	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
3373		3560
3374	This section explains some common idioms that are not immediately	3561	This section explains some common idioms that are not immediately
3375	obvious. Note that examples are sprinkled over the whole manual, and this	3562	obvious. Note that examples are sprinkled over the whole manual, and this
3376	section only contains stuff that wouldn't fit anywhere else.	3563	section only contains stuff that wouldn't fit anywhere else.
3377		3564
3378	=over 4	3565	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3379		3566
3380	=item Model/nested event loop invocations and exit conditions.	3567	Each watcher has, by default, a C<void *data> member that you can read
		3568	or modify at any time: libev will completely ignore it. This can be used
		3569	to associate arbitrary data with your watcher. If you need more data and
		3570	don't want to allocate memory separately and store a pointer to it in that
		3571	data member, you can also "subclass" the watcher type and provide your own
		3572	data:
		3573
		3574	struct my_io
		3575	{
		3576	ev_io io;
		3577	int otherfd;
		3578	void *somedata;
		3579	struct whatever *mostinteresting;
		3580	};
		3581
		3582	...
		3583	struct my_io w;
		3584	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3585
		3586	And since your callback will be called with a pointer to the watcher, you
		3587	can cast it back to your own type:
		3588
		3589	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3590	{
		3591	struct my_io *w = (struct my_io *)w_;
		3592	...
		3593	}
		3594
		3595	More interesting and less C-conformant ways of casting your callback
		3596	function type instead have been omitted.
		3597
		3598	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3599
		3600	Another common scenario is to use some data structure with multiple
		3601	embedded watchers, in effect creating your own watcher that combines
		3602	multiple libev event sources into one "super-watcher":
		3603
		3604	struct my_biggy
		3605	{
		3606	int some_data;
		3607	ev_timer t1;
		3608	ev_timer t2;
		3609	}
		3610
		3611	In this case getting the pointer to C<my_biggy> is a bit more
		3612	complicated: Either you store the address of your C<my_biggy> struct in
		3613	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3614	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3615	real programmers):
		3616
		3617	#include <stddef.h>
		3618
		3619	static void
		3620	t1_cb (EV_P_ ev_timer *w, int revents)
		3621	{
		3622	struct my_biggy big = (struct my_biggy *)
		3623	(((char *)w) - offsetof (struct my_biggy, t1));
		3624	}
		3625
		3626	static void
		3627	t2_cb (EV_P_ ev_timer *w, int revents)
		3628	{
		3629	struct my_biggy big = (struct my_biggy *)
		3630	(((char *)w) - offsetof (struct my_biggy, t2));
		3631	}
		3632
		3633	=head2 AVOIDING FINISHING BEFORE RETURNING
		3634
		3635	Often you have structures like this in event-based programs:
		3636
		3637	callback ()
		3638	{
		3639	free (request);
		3640	}
		3641
		3642	request = start_new_request (..., callback);
		3643
		3644	The intent is to start some "lengthy" operation. The C<request> could be
		3645	used to cancel the operation, or do other things with it.
		3646
		3647	It's not uncommon to have code paths in C<start_new_request> that
		3648	immediately invoke the callback, for example, to report errors. Or you add
		3649	some caching layer that finds that it can skip the lengthy aspects of the
		3650	operation and simply invoke the callback with the result.
		3651
		3652	The problem here is that this will happen I<before> C<start_new_request>
		3653	has returned, so C<request> is not set.
		3654
		3655	Even if you pass the request by some safer means to the callback, you
		3656	might want to do something to the request after starting it, such as
		3657	canceling it, which probably isn't working so well when the callback has
		3658	already been invoked.
		3659
		3660	A common way around all these issues is to make sure that
		3661	C<start_new_request> I<always> returns before the callback is invoked. If
		3662	C<start_new_request> immediately knows the result, it can artificially
		3663	delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher
		3664	for example, or more sneakily, by reusing an existing (stopped) watcher
		3665	and pushing it into the pending queue:
		3666
		3667	ev_set_cb (watcher, callback);
		3668	ev_feed_event (EV_A_ watcher, 0);
		3669
		3670	This way, C<start_new_request> can safely return before the callback is
		3671	invoked, while not delaying callback invocation too much.
		3672
		3673	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3381		3674
3382	Often (especially in GUI toolkits) there are places where you have	3675	Often (especially in GUI toolkits) there are places where you have
3383	I<modal> interaction, which is most easily implemented by recursively	3676	I<modal> interaction, which is most easily implemented by recursively
3384	invoking C<ev_run>.	3677	invoking C<ev_run>.
3385		3678
…		…
3397	int exit_main_loop = 0;	3690	int exit_main_loop = 0;
3398		3691
3399	while (!exit_main_loop)	3692	while (!exit_main_loop)
3400	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3693	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3401		3694
3402	// in a model watcher	3695	// in a modal watcher
3403	int exit_nested_loop = 0;	3696	int exit_nested_loop = 0;
3404		3697
3405	while (!exit_nested_loop)	3698	while (!exit_nested_loop)
3406	ev_run (EV_A_ EVRUN_ONCE);	3699	ev_run (EV_A_ EVRUN_ONCE);
3407		3700
…		…
3414	exit_main_loop = 1;	3707	exit_main_loop = 1;
3415		3708
3416	// exit both	3709	// exit both
3417	exit_main_loop = exit_nested_loop = 1;	3710	exit_main_loop = exit_nested_loop = 1;
3418		3711
3419	=back	3712	=head2 THREAD LOCKING EXAMPLE
		3713
		3714	Here is a fictitious example of how to run an event loop in a different
		3715	thread from where callbacks are being invoked and watchers are
		3716	created/added/removed.
		3717
		3718	For a real-world example, see the C<EV::Loop::Async> perl module,
		3719	which uses exactly this technique (which is suited for many high-level
		3720	languages).
		3721
		3722	The example uses a pthread mutex to protect the loop data, a condition
		3723	variable to wait for callback invocations, an async watcher to notify the
		3724	event loop thread and an unspecified mechanism to wake up the main thread.
		3725
		3726	First, you need to associate some data with the event loop:
		3727
		3728	typedef struct {
		3729	mutex_t lock; /* global loop lock */
		3730	ev_async async_w;
		3731	thread_t tid;
		3732	cond_t invoke_cv;
		3733	} userdata;
		3734
		3735	void prepare_loop (EV_P)
		3736	{
		3737	// for simplicity, we use a static userdata struct.
		3738	static userdata u;
		3739
		3740	ev_async_init (&u->async_w, async_cb);
		3741	ev_async_start (EV_A_ &u->async_w);
		3742
		3743	pthread_mutex_init (&u->lock, 0);
		3744	pthread_cond_init (&u->invoke_cv, 0);
		3745
		3746	// now associate this with the loop
		3747	ev_set_userdata (EV_A_ u);
		3748	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3749	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3750
		3751	// then create the thread running ev_run
		3752	pthread_create (&u->tid, 0, l_run, EV_A);
		3753	}
		3754
		3755	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3756	solely to wake up the event loop so it takes notice of any new watchers
		3757	that might have been added:
		3758
		3759	static void
		3760	async_cb (EV_P_ ev_async *w, int revents)
		3761	{
		3762	// just used for the side effects
		3763	}
		3764
		3765	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3766	protecting the loop data, respectively.
		3767
		3768	static void
		3769	l_release (EV_P)
		3770	{
		3771	userdata *u = ev_userdata (EV_A);
		3772	pthread_mutex_unlock (&u->lock);
		3773	}
		3774
		3775	static void
		3776	l_acquire (EV_P)
		3777	{
		3778	userdata *u = ev_userdata (EV_A);
		3779	pthread_mutex_lock (&u->lock);
		3780	}
		3781
		3782	The event loop thread first acquires the mutex, and then jumps straight
		3783	into C<ev_run>:
		3784
		3785	void *
		3786	l_run (void *thr_arg)
		3787	{
		3788	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3789
		3790	l_acquire (EV_A);
		3791	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3792	ev_run (EV_A_ 0);
		3793	l_release (EV_A);
		3794
		3795	return 0;
		3796	}
		3797
		3798	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3799	signal the main thread via some unspecified mechanism (signals? pipe
		3800	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3801	have been called (in a while loop because a) spurious wakeups are possible
		3802	and b) skipping inter-thread-communication when there are no pending
		3803	watchers is very beneficial):
		3804
		3805	static void
		3806	l_invoke (EV_P)
		3807	{
		3808	userdata *u = ev_userdata (EV_A);
		3809
		3810	while (ev_pending_count (EV_A))
		3811	{
		3812	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3813	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3814	}
		3815	}
		3816
		3817	Now, whenever the main thread gets told to invoke pending watchers, it
		3818	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3819	thread to continue:
		3820
		3821	static void
		3822	real_invoke_pending (EV_P)
		3823	{
		3824	userdata *u = ev_userdata (EV_A);
		3825
		3826	pthread_mutex_lock (&u->lock);
		3827	ev_invoke_pending (EV_A);
		3828	pthread_cond_signal (&u->invoke_cv);
		3829	pthread_mutex_unlock (&u->lock);
		3830	}
		3831
		3832	Whenever you want to start/stop a watcher or do other modifications to an
		3833	event loop, you will now have to lock:
		3834
		3835	ev_timer timeout_watcher;
		3836	userdata *u = ev_userdata (EV_A);
		3837
		3838	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3839
		3840	pthread_mutex_lock (&u->lock);
		3841	ev_timer_start (EV_A_ &timeout_watcher);
		3842	ev_async_send (EV_A_ &u->async_w);
		3843	pthread_mutex_unlock (&u->lock);
		3844
		3845	Note that sending the C<ev_async> watcher is required because otherwise
		3846	an event loop currently blocking in the kernel will have no knowledge
		3847	about the newly added timer. By waking up the loop it will pick up any new
		3848	watchers in the next event loop iteration.
		3849
		3850	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3851
		3852	While the overhead of a callback that e.g. schedules a thread is small, it
		3853	is still an overhead. If you embed libev, and your main usage is with some
		3854	kind of threads or coroutines, you might want to customise libev so that
		3855	doesn't need callbacks anymore.
		3856
		3857	Imagine you have coroutines that you can switch to using a function
		3858	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3859	and that due to some magic, the currently active coroutine is stored in a
		3860	global called C<current_coro>. Then you can build your own "wait for libev
		3861	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3862	the differing C<;> conventions):
		3863
		3864	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3865	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3866
		3867	That means instead of having a C callback function, you store the
		3868	coroutine to switch to in each watcher, and instead of having libev call
		3869	your callback, you instead have it switch to that coroutine.
		3870
		3871	A coroutine might now wait for an event with a function called
		3872	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3873	matter when, or whether the watcher is active or not when this function is
		3874	called):
		3875
		3876	void
		3877	wait_for_event (ev_watcher *w)
		3878	{
		3879	ev_set_cb (w, current_coro);
		3880	switch_to (libev_coro);
		3881	}
		3882
		3883	That basically suspends the coroutine inside C<wait_for_event> and
		3884	continues the libev coroutine, which, when appropriate, switches back to
		3885	this or any other coroutine.
		3886
		3887	You can do similar tricks if you have, say, threads with an event queue -
		3888	instead of storing a coroutine, you store the queue object and instead of
		3889	switching to a coroutine, you push the watcher onto the queue and notify
		3890	any waiters.
		3891
		3892	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3893	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3894
		3895	// my_ev.h
		3896	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3897	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3898	#include "../libev/ev.h"
		3899
		3900	// my_ev.c
		3901	#define EV_H "my_ev.h"
		3902	#include "../libev/ev.c"
		3903
		3904	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3905	F<my_ev.c> into your project. When properly specifying include paths, you
		3906	can even use F<ev.h> as header file name directly.
3420		3907
3421		3908
3422	=head1 LIBEVENT EMULATION	3909	=head1 LIBEVENT EMULATION
3423		3910
3424	Libev offers a compatibility emulation layer for libevent. It cannot	3911	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3427	=over 4	3914	=over 4
3428		3915
3429	=item * Only the libevent-1.4.1-beta API is being emulated.	3916	=item * Only the libevent-1.4.1-beta API is being emulated.
3430		3917
3431	This was the newest libevent version available when libev was implemented,	3918	This was the newest libevent version available when libev was implemented,
3432	and is still mostly uncanged in 2010.	3919	and is still mostly unchanged in 2010.
3433		3920
3434	=item * Use it by including <event.h>, as usual.	3921	=item * Use it by including <event.h>, as usual.
3435		3922
3436	=item * The following members are fully supported: ev_base, ev_callback,	3923	=item * The following members are fully supported: ev_base, ev_callback,
3437	ev_arg, ev_fd, ev_res, ev_events.	3924	ev_arg, ev_fd, ev_res, ev_events.
…		…
3453	to use the libev header file and library.	3940	to use the libev header file and library.
3454		3941
3455	=back	3942	=back
3456		3943
3457	=head1 C++ SUPPORT	3944	=head1 C++ SUPPORT
		3945
		3946	=head2 C API
		3947
		3948	The normal C API should work fine when used from C++: both ev.h and the
		3949	libev sources can be compiled as C++. Therefore, code that uses the C API
		3950	will work fine.
		3951
		3952	Proper exception specifications might have to be added to callbacks passed
		3953	to libev: exceptions may be thrown only from watcher callbacks, all
		3954	other callbacks (allocator, syserr, loop acquire/release and periodic
		3955	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3956	()> specification. If you have code that needs to be compiled as both C
		3957	and C++ you can use the C<EV_THROW> macro for this:
		3958
		3959	static void
		3960	fatal_error (const char *msg) EV_THROW
		3961	{
		3962	perror (msg);
		3963	abort ();
		3964	}
		3965
		3966	...
		3967	ev_set_syserr_cb (fatal_error);
		3968
		3969	The only API functions that can currently throw exceptions are C<ev_run>,
		3970	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3971	because it runs cleanup watchers).
		3972
		3973	Throwing exceptions in watcher callbacks is only supported if libev itself
		3974	is compiled with a C++ compiler or your C and C++ environments allow
		3975	throwing exceptions through C libraries (most do).
		3976
		3977	=head2 C++ API
3458		3978
3459	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3979	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	3980	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.	3981	the callback model to a model using method callbacks on objects.
3462		3982
…		…
3472	Care has been taken to keep the overhead low. The only data member the C++	3992	Care has been taken to keep the overhead low. The only data member the C++
3473	classes add (compared to plain C-style watchers) is the event loop pointer	3993	classes add (compared to plain C-style watchers) is the event loop pointer
3474	that the watcher is associated with (or no additional members at all if	3994	that the watcher is associated with (or no additional members at all if
3475	you disable C<EV_MULTIPLICITY> when embedding libev).	3995	you disable C<EV_MULTIPLICITY> when embedding libev).
3476		3996
3477	Currently, functions, and static and non-static member functions can be	3997	Currently, functions, static and non-static member functions and classes
3478	used as callbacks. Other types should be easy to add as long as they only	3998	with C<operator ()> can be used as callbacks. Other types should be easy
3479	need one additional pointer for context. If you need support for other	3999	to add as long as they only need one additional pointer for context. If
3480	types of functors please contact the author (preferably after implementing	4000	you need support for other types of functors please contact the author
3481	it).	4001	(preferably after implementing it).
		4002
		4003	For all this to work, your C++ compiler either has to use the same calling
		4004	conventions as your C compiler (for static member functions), or you have
		4005	to embed libev and compile libev itself as C++.
3482		4006
3483	Here is a list of things available in the C<ev> namespace:	4007	Here is a list of things available in the C<ev> namespace:
3484		4008
3485	=over 4	4009	=over 4
3486		4010
…		…
3496	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4020	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3497		4021
3498	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4022	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>	4023	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	4024	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3501	defines by many implementations.	4025	defined by many implementations.
3502		4026
3503	All of those classes have these methods:	4027	All of those classes have these methods:
3504		4028
3505	=over 4	4029	=over 4
3506		4030
…		…
3596	Associates a different C<struct ev_loop> with this watcher. You can only	4120	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).	4121	do this when the watcher is inactive (and not pending either).
3598		4122
3599	=item w->set ([arguments])	4123	=item w->set ([arguments])
3600		4124
3601	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4125	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	4126	with the same arguments. Either this method or a suitable start method
3603	C counterpart, an active watcher gets automatically stopped and restarted	4127	must be called at least once. Unlike the C counterpart, an active watcher
3604	when reconfiguring it with this method.	4128	gets automatically stopped and restarted when reconfiguring it with this
		4129	method.
		4130
		4131	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4132	clashing with the C<set (loop)> method.
3605		4133
3606	=item w->start ()	4134	=item w->start ()
3607		4135
3608	Starts the watcher. Note that there is no C<loop> argument, as the	4136	Starts the watcher. Note that there is no C<loop> argument, as the
3609	constructor already stores the event loop.	4137	constructor already stores the event loop.
…		…
3639	watchers in the constructor.	4167	watchers in the constructor.
3640		4168
3641	class myclass	4169	class myclass
3642	{	4170	{
3643	ev::io io ; void io_cb (ev::io &w, int revents);	4171	ev::io io ; void io_cb (ev::io &w, int revents);
3644	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4172	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3645	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4173	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3646		4174
3647	myclass (int fd)	4175	myclass (int fd)
3648	{	4176	{
3649	io .set <myclass, &myclass::io_cb > (this);	4177	io .set <myclass, &myclass::io_cb > (this);
…		…
3700	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4228	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3701		4229
3702	=item D	4230	=item D
3703		4231
3704	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4232	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>.	4233	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3706		4234
3707	=item Ocaml	4235	=item Ocaml
3708		4236
3709	Erkki Seppala has written Ocaml bindings for libev, to be found at	4237	Erkki Seppala has written Ocaml bindings for libev, to be found at
3710	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4238	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3713		4241
3714	Brian Maher has written a partial interface to libev for lua (at the	4242	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	4243	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3716	L<http://github.com/brimworks/lua-ev>.	4244	L<http://github.com/brimworks/lua-ev>.
3717		4245
		4246	=item Javascript
		4247
		4248	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4249
		4250	=item Others
		4251
		4252	There are others, and I stopped counting.
		4253
3718	=back	4254	=back
3719		4255
3720		4256
3721	=head1 MACRO MAGIC	4257	=head1 MACRO MAGIC
3722		4258
…		…
3758	suitable for use with C<EV_A>.	4294	suitable for use with C<EV_A>.
3759		4295
3760	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4296	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3761		4297
3762	Similar to the other two macros, this gives you the value of the default	4298	Similar to the other two macros, this gives you the value of the default
3763	loop, if multiple loops are supported ("ev loop default").	4299	loop, if multiple loops are supported ("ev loop default"). The default loop
		4300	will be initialised if it isn't already initialised.
		4301
		4302	For non-multiplicity builds, these macros do nothing, so you always have
		4303	to initialise the loop somewhere.
3764		4304
3765	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4305	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3766		4306
3767	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4307	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	4308	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3913	supported). It will also not define any of the structs usually found in	4453	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.	4454	F<event.h> that are not directly supported by the libev core alone.
3915		4455
3916	In standalone mode, libev will still try to automatically deduce the	4456	In standalone mode, libev will still try to automatically deduce the
3917	configuration, but has to be more conservative.	4457	configuration, but has to be more conservative.
		4458
		4459	=item EV_USE_FLOOR
		4460
		4461	If defined to be C<1>, libev will use the C<floor ()> function for its
		4462	periodic reschedule calculations, otherwise libev will fall back on a
		4463	portable (slower) implementation. If you enable this, you usually have to
		4464	link against libm or something equivalent. Enabling this when the C<floor>
		4465	function is not available will fail, so the safe default is to not enable
		4466	this.
3918		4467
3919	=item EV_USE_MONOTONIC	4468	=item EV_USE_MONOTONIC
3920		4469
3921	If defined to be C<1>, libev will try to detect the availability of the	4470	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	4471	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4007		4556
4008	If programs implement their own fd to handle mapping on win32, then this	4557	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	4558	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	4559	file descriptors again. Note that the replacement function has to close
4011	the underlying OS handle.	4560	the underlying OS handle.
		4561
		4562	=item EV_USE_WSASOCKET
		4563
		4564	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4565	communication socket, which works better in some environments. Otherwise,
		4566	the normal C<socket> function will be used, which works better in other
		4567	environments.
4012		4568
4013	=item EV_USE_POLL	4569	=item EV_USE_POLL
4014		4570
4015	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4571	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	4572	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	4608	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	4609	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	4610	be detected at runtime. If undefined, it will be enabled if the headers
4055	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4611	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4056		4612
		4613	=item EV_NO_SMP
		4614
		4615	If defined to be C<1>, libev will assume that memory is always coherent
		4616	between threads, that is, threads can be used, but threads never run on
		4617	different cpus (or different cpu cores). This reduces dependencies
		4618	and makes libev faster.
		4619
		4620	=item EV_NO_THREADS
		4621
		4622	If defined to be C<1>, libev will assume that it will never be called
		4623	from different threads, which is a stronger assumption than C<EV_NO_SMP>,
		4624	above. This reduces dependencies and makes libev faster.
		4625
4057	=item EV_ATOMIC_T	4626	=item EV_ATOMIC_T
4058		4627
4059	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4628	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	4629	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	4630	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"	4631	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.	4632	handler "locking" as well as for signal and thread safety in C<ev_async>
		4633	watchers.
4064		4634
4065	In the absence of this define, libev will use C<sig_atomic_t volatile>	4635	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.	4636	(from F<signal.h>), which is usually good enough on most platforms.
4067		4637
4068	=item EV_H (h)	4638	=item EV_H (h)
…		…
4095	will have the C<struct ev_loop *> as first argument, and you can create	4665	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	4666	additional independent event loops. Otherwise there will be no support
4097	for multiple event loops and there is no first event loop pointer	4667	for multiple event loops and there is no first event loop pointer
4098	argument. Instead, all functions act on the single default loop.	4668	argument. Instead, all functions act on the single default loop.
4099		4669
		4670	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4671	default loop when multiplicity is switched off - you always have to
		4672	initialise the loop manually in this case.
		4673
4100	=item EV_MINPRI	4674	=item EV_MINPRI
4101		4675
4102	=item EV_MAXPRI	4676	=item EV_MAXPRI
4103		4677
4104	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4678	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4140	#define EV_USE_POLL 1	4714	#define EV_USE_POLL 1
4141	#define EV_CHILD_ENABLE 1	4715	#define EV_CHILD_ENABLE 1
4142	#define EV_ASYNC_ENABLE 1	4716	#define EV_ASYNC_ENABLE 1
4143		4717
4144	The actual value is a bitset, it can be a combination of the following	4718	The actual value is a bitset, it can be a combination of the following
4145	values:	4719	values (by default, all of these are enabled):
4146		4720
4147	=over 4	4721	=over 4
4148		4722
4149	=item C<1> - faster/larger code	4723	=item C<1> - faster/larger code
4150		4724
…		…
4154	code size by roughly 30% on amd64).	4728	code size by roughly 30% on amd64).
4155		4729
4156	When optimising for size, use of compiler flags such as C<-Os> with	4730	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	4731	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4158	assertions.	4732	assertions.
		4733
		4734	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4735	(e.g. gcc with C<-Os>).
4159		4736
4160	=item C<2> - faster/larger data structures	4737	=item C<2> - faster/larger data structures
4161		4738
4162	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4739	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	4740	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	4741	and can additionally have an effect on the size of data structures at
4165	runtime.	4742	runtime.
4166		4743
		4744	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4745	(e.g. gcc with C<-Os>).
		4746
4167	=item C<4> - full API configuration	4747	=item C<4> - full API configuration
4168		4748
4169	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4749	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4170	enables multiplicity (C<EV_MULTIPLICITY>=1).	4750	enables multiplicity (C<EV_MULTIPLICITY>=1).
4171		4751
…		…
4201		4781
4202	With an intelligent-enough linker (gcc+binutils are intelligent enough	4782	With an intelligent-enough linker (gcc+binutils are intelligent enough
4203	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4783	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	4784	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.	4785	I/O watcher then might come out at only 5Kb.
		4786
		4787	=item EV_API_STATIC
		4788
		4789	If this symbol is defined (by default it is not), then all identifiers
		4790	will have static linkage. This means that libev will not export any
		4791	identifiers, and you cannot link against libev anymore. This can be useful
		4792	when you embed libev, only want to use libev functions in a single file,
		4793	and do not want its identifiers to be visible.
		4794
		4795	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4796	wants to use libev.
		4797
		4798	This option only works when libev is compiled with a C compiler, as C++
		4799	doesn't support the required declaration syntax.
4206		4800
4207	=item EV_AVOID_STDIO	4801	=item EV_AVOID_STDIO
4208		4802
4209	If this is set to C<1> at compiletime, then libev will avoid using stdio	4803	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	4804	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:	4948	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4355		4949
4356	#include "ev_cpp.h"	4950	#include "ev_cpp.h"
4357	#include "ev.c"	4951	#include "ev.c"
4358		4952
4359	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4953	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4360		4954
4361	=head2 THREADS AND COROUTINES	4955	=head2 THREADS AND COROUTINES
4362		4956
4363	=head3 THREADS	4957	=head3 THREADS
4364		4958
…		…
4415	default loop and triggering an C<ev_async> watcher from the default loop	5009	default loop and triggering an C<ev_async> watcher from the default loop
4416	watcher callback into the event loop interested in the signal.	5010	watcher callback into the event loop interested in the signal.
4417		5011
4418	=back	5012	=back
4419		5013
4420	=head4 THREAD LOCKING EXAMPLE	5014	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		5015
4558	=head3 COROUTINES	5016	=head3 COROUTINES
4559		5017
4560	Libev is very accommodating to coroutines ("cooperative threads"):	5018	Libev is very accommodating to coroutines ("cooperative threads"):
4561	libev fully supports nesting calls to its functions from different	5019	libev fully supports nesting calls to its functions from different
…		…
4726	requires, and its I/O model is fundamentally incompatible with the POSIX	5184	requires, and its I/O model is fundamentally incompatible with the POSIX
4727	model. Libev still offers limited functionality on this platform in	5185	model. Libev still offers limited functionality on this platform in
4728	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5186	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4729	descriptors. This only applies when using Win32 natively, not when using	5187	descriptors. This only applies when using Win32 natively, not when using
4730	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5188	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4731	as every compielr comes with a slightly differently broken/incompatible	5189	as every compiler comes with a slightly differently broken/incompatible
4732	environment.	5190	environment.
4733		5191
4734	Lifting these limitations would basically require the full	5192	Lifting these limitations would basically require the full
4735	re-implementation of the I/O system. If you are into this kind of thing,	5193	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	5194	then note that glib does exactly that for you in a very portable way (note
…		…
4852	thread" or will block signals process-wide, both behaviours would	5310	thread" or will block signals process-wide, both behaviours would
4853	be compatible with libev. Interaction between C<sigprocmask> and	5311	be compatible with libev. Interaction between C<sigprocmask> and
4854	C<pthread_sigmask> could complicate things, however.	5312	C<pthread_sigmask> could complicate things, however.
4855		5313
4856	The most portable way to handle signals is to block signals in all threads	5314	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	5315	except the initial one, and run the signal handling loop in the initial
4858	well.	5316	thread as well.
4859		5317
4860	=item C<long> must be large enough for common memory allocation sizes	5318	=item C<long> must be large enough for common memory allocation sizes
4861		5319
4862	To improve portability and simplify its API, libev uses C<long> internally	5320	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	5321	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4869		5327
4870	The type C<double> is used to represent timestamps. It is required to	5328	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	5329	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	5330	good enough for at least into the year 4000 with millisecond accuracy
4873	(the design goal for libev). This requirement is overfulfilled by	5331	(the design goal for libev). This requirement is overfulfilled by
4874	implementations using IEEE 754, which is basically all existing ones. With	5332	implementations using IEEE 754, which is basically all existing ones.
		5333
4875	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5334	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5335	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5336	is either obsolete or somebody patched it to use C<long double> or
		5337	something like that, just kidding).
4876		5338
4877	=back	5339	=back
4878		5340
4879	If you know of other additional requirements drop me a note.	5341	If you know of other additional requirements drop me a note.
4880		5342
…		…
4942	=item Processing ev_async_send: O(number_of_async_watchers)	5404	=item Processing ev_async_send: O(number_of_async_watchers)
4943		5405
4944	=item Processing signals: O(max_signal_number)	5406	=item Processing signals: O(max_signal_number)
4945		5407
4946	Sending involves a system call I<iff> there were no other C<ev_async_send>	5408	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	5409	calls in the current loop iteration and the loop is currently
		5410	blocked. Checking for async and signal events involves iterating over all
4948	involves iterating over all running async watchers or all signal numbers.	5411	running async watchers or all signal numbers.
4949		5412
4950	=back	5413	=back
4951		5414
4952		5415
4953	=head1 PORTING FROM LIBEV 3.X TO 4.X	5416	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
4962	=over 4	5425	=over 4
4963		5426
4964	=item C<EV_COMPAT3> backwards compatibility mechanism	5427	=item C<EV_COMPAT3> backwards compatibility mechanism
4965		5428
4966	The backward compatibility mechanism can be controlled by	5429	The backward compatibility mechanism can be controlled by
4967	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5430	C<EV_COMPAT3>. See L</PREPROCESSOR SYMBOLS/MACROS> in the L</EMBEDDING>
4968	section.	5431	section.
4969		5432
4970	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5433	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4971		5434
4972	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5435	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
5015	=over 4	5478	=over 4
5016		5479
5017	=item active	5480	=item active
5018		5481
5019	A watcher is active as long as it has been started and not yet stopped.	5482	A watcher is active as long as it has been started and not yet stopped.
5020	See L<WATCHER STATES> for details.	5483	See L</WATCHER STATES> for details.
5021		5484
5022	=item application	5485	=item application
5023		5486
5024	In this document, an application is whatever is using libev.	5487	In this document, an application is whatever is using libev.
5025		5488
…		…
5061	watchers and events.	5524	watchers and events.
5062		5525
5063	=item pending	5526	=item pending
5064		5527
5065	A watcher is pending as soon as the corresponding event has been	5528	A watcher is pending as soon as the corresponding event has been
5066	detected. See L<WATCHER STATES> for details.	5529	detected. See L</WATCHER STATES> for details.
5067		5530
5068	=item real time	5531	=item real time
5069		5532
5070	The physical time that is observed. It is apparently strictly monotonic :)	5533	The physical time that is observed. It is apparently strictly monotonic :)
5071		5534
5072	=item wall-clock time	5535	=item wall-clock time
5073		5536
5074	The time and date as shown on clocks. Unlike real time, it can actually	5537	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	5538	be wrong and jump forwards and backwards, e.g. when you adjust your
5076	clock.	5539	clock.
5077		5540
5078	=item watcher	5541	=item watcher
5079		5542
5080	A data structure that describes interest in certain events. Watchers need	5543	A data structure that describes interest in certain events. Watchers need
…		…
5083	=back	5546	=back
5084		5547
5085	=head1 AUTHOR	5548	=head1 AUTHOR
5086		5549
5087	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5550	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5088	Magnusson and Emanuele Giaquinta.	5551	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5089		5552

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