ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.344 by root, Wed Nov 10 13:41:48 2010 UTC vs.
Revision 1.426 by root, Sat Feb 23 23:06:40 2013 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
…		…
2463		2606
2464	=head2 C<ev_stat> - did the file attributes just change?	2607	=head2 C<ev_stat> - did the file attributes just change?
2465		2608
2466	This watches a file system path for attribute changes. That is, it calls	2609	This watches a file system path for attribute changes. That is, it calls
2467	C<stat> on that path in regular intervals (or when the OS says it changed)	2610	C<stat> on that path in regular intervals (or when the OS says it changed)
2468	and sees if it changed compared to the last time, invoking the callback if	2611	and sees if it changed compared to the last time, invoking the callback
2469	it did.	2612	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2613	happen after the watcher has been started will be reported.
2470		2614
2471	The path does not need to exist: changing from "path exists" to "path does	2615	The path does not need to exist: changing from "path exists" to "path does
2472	not exist" is a status change like any other. The condition "path does not	2616	not exist" is a status change like any other. The condition "path does not
2473	exist" (or more correctly "path cannot be stat'ed") is signified by the	2617	exist" (or more correctly "path cannot be stat'ed") is signified by the
2474	C<st_nlink> field being zero (which is otherwise always forced to be at	2618	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2704	Apart from keeping your process non-blocking (which is a useful	2848	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	2849	effect on its own sometimes), idle watchers are a good place to do
2706	"pseudo-background processing", or delay processing stuff to after the	2850	"pseudo-background processing", or delay processing stuff to after the
2707	event loop has handled all outstanding events.	2851	event loop has handled all outstanding events.
2708		2852
		2853	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2854
		2855	As long as there is at least one active idle watcher, libev will never
		2856	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2857	For this to work, the idle watcher doesn't need to be invoked at all - the
		2858	lowest priority will do.
		2859
		2860	This mode of operation can be useful together with an C<ev_check> watcher,
		2861	to do something on each event loop iteration - for example to balance load
		2862	between different connections.
		2863
		2864	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2865	example.
		2866
2709	=head3 Watcher-Specific Functions and Data Members	2867	=head3 Watcher-Specific Functions and Data Members
2710		2868
2711	=over 4	2869	=over 4
2712		2870
2713	=item ev_idle_init (ev_idle *, callback)	2871	=item ev_idle_init (ev_idle *, callback)
…		…
2724	callback, free it. Also, use no error checking, as usual.	2882	callback, free it. Also, use no error checking, as usual.
2725		2883
2726	static void	2884	static void
2727	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2885	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2728	{	2886	{
		2887	// stop the watcher
		2888	ev_idle_stop (loop, w);
		2889
		2890	// now we can free it
2729	free (w);	2891	free (w);
		2892
2730	// now do something you wanted to do when the program has	2893	// now do something you wanted to do when the program has
2731	// no longer anything immediate to do.	2894	// no longer anything immediate to do.
2732	}	2895	}
2733		2896
2734	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2897	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2736	ev_idle_start (loop, idle_watcher);	2899	ev_idle_start (loop, idle_watcher);
2737		2900
2738		2901
2739	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2902	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2740		2903
2741	Prepare and check watchers are usually (but not always) used in pairs:	2904	Prepare and check watchers are often (but not always) used in pairs:
2742	prepare watchers get invoked before the process blocks and check watchers	2905	prepare watchers get invoked before the process blocks and check watchers
2743	afterwards.	2906	afterwards.
2744		2907
2745	You I<must not> call C<ev_run> or similar functions that enter	2908	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>	2909	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	2937	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	2938	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	2939	loop from blocking if lower-priority coroutines are active, thus mapping
2777	low-priority coroutines to idle/background tasks).	2940	low-priority coroutines to idle/background tasks).
2778		2941
2779	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2942	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	2943	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).	2944	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2945	watchers).
2782		2946
2783	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	2947	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	2948	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	2949	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	2950	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	2951	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	2952	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2789	others).	2953	others).
		2954
		2955	=head3 Abusing an C<ev_check> watcher for its side-effect
		2956
		2957	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2958	useful because they are called once per event loop iteration. For
		2959	example, if you want to handle a large number of connections fairly, you
		2960	normally only do a bit of work for each active connection, and if there
		2961	is more work to do, you wait for the next event loop iteration, so other
		2962	connections have a chance of making progress.
		2963
		2964	Using an C<ev_check> watcher is almost enough: it will be called on the
		2965	next event loop iteration. However, that isn't as soon as possible -
		2966	without external events, your C<ev_check> watcher will not be invoked.
		2967
		2968	This is where C<ev_idle> watchers come in handy - all you need is a
		2969	single global idle watcher that is active as long as you have one active
		2970	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2971	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2972	invoked. Neither watcher alone can do that.
2790		2973
2791	=head3 Watcher-Specific Functions and Data Members	2974	=head3 Watcher-Specific Functions and Data Members
2792		2975
2793	=over 4	2976	=over 4
2794		2977
…		…
2995		3178
2996	=over 4	3179	=over 4
2997		3180
2998	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3181	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2999		3182
3000	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3183	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
3001		3184
3002	Configures the watcher to embed the given loop, which must be	3185	Configures the watcher to embed the given loop, which must be
3003	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3186	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
3004	invoked automatically, otherwise it is the responsibility of the callback	3187	invoked automatically, otherwise it is the responsibility of the callback
3005	to invoke it (it will continue to be called until the sweep has been done,	3188	to invoke it (it will continue to be called until the sweep has been done,
…		…
3068		3251
3069	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3252	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3070		3253
3071	Fork watchers are called when a C<fork ()> was detected (usually because	3254	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	3255	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	3256	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,	3257	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	3258	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	3259	and calls it in the wrong process, the fork handlers will be invoked, too,
3077	handlers will be invoked, too, of course.	3260	of course.
3078		3261
3079	=head3 The special problem of life after fork - how is it possible?	3262	=head3 The special problem of life after fork - how is it possible?
3080		3263
3081	Most uses of C<fork()> consist of forking, then some simple calls to set	3264	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	3265	up/change the process environment, followed by a call to C<exec()>. This
…		…
3163	atexit (program_exits);	3346	atexit (program_exits);
3164		3347
3165		3348
3166	=head2 C<ev_async> - how to wake up an event loop	3349	=head2 C<ev_async> - how to wake up an event loop
3167		3350
3168	In general, you cannot use an C<ev_run> from multiple threads or other	3351	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	3352	asynchronous sources such as signal handlers (as opposed to multiple event
3170	loops - those are of course safe to use in different threads).	3353	loops - those are of course safe to use in different threads).
3171		3354
3172	Sometimes, however, you need to wake up an event loop you do not control,	3355	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>	3356	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.	3358	it by calling C<ev_async_send>, which is thread- and signal safe.
3176		3359
3177	This functionality is very similar to C<ev_signal> watchers, as signals,	3360	This functionality is very similar to C<ev_signal> watchers, as signals,
3178	too, are asynchronous in nature, and signals, too, will be compressed	3361	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	3362	(i.e. the number of callback invocations may be less than the number of
3180	C<ev_async_sent> calls).	3363	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3181		3364	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	3365	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3183	just the default loop.	3366	even without knowing which loop owns the signal.
3184		3367
3185	=head3 Queueing	3368	=head3 Queueing
3186		3369
3187	C<ev_async> does not support queueing of data in any way. The reason	3370	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	3371	is that the author does not know of a simple (or any) algorithm for a
…		…
3280	trust me.	3463	trust me.
3281		3464
3282	=item ev_async_send (loop, ev_async *)	3465	=item ev_async_send (loop, ev_async *)
3283		3466
3284	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3467	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	3468	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3469	returns.
		3470
3286	C<ev_feed_event>, this call is safe to do from other threads, signal or	3471	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	3472	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3288	section below on what exactly this means).	3473	embedding section below on what exactly this means).
3289		3474
3290	Note that, as with other watchers in libev, multiple events might get	3475	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	3476	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>,	3477	this is that C<ev_async> watchers are level-triggered: they are set on
3293	reset when the event loop detects that).	3478	C<ev_async_send>, reset when the event loop detects that).
3294		3479
3295	This call incurs the overhead of a system call only once per event loop	3480	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	3481	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.	3482	the event loop (or your program) is processing events. That means that
		3483	repeated calls are basically free (there is no need to avoid calls for
		3484	performance reasons) and that the overhead becomes smaller (typically
		3485	zero) under load.
3298		3486
3299	=item bool = ev_async_pending (ev_async *)	3487	=item bool = ev_async_pending (ev_async *)
3300		3488
3301	Returns a non-zero value when C<ev_async_send> has been called on the	3489	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	3490	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);	3545	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3358		3546
3359	=item ev_feed_fd_event (loop, int fd, int revents)	3547	=item ev_feed_fd_event (loop, int fd, int revents)
3360		3548
3361	Feed an event on the given fd, as if a file descriptor backend detected	3549	Feed an event on the given fd, as if a file descriptor backend detected
3362	the given events it.	3550	the given events.
3363		3551
3364	=item ev_feed_signal_event (loop, int signum)	3552	=item ev_feed_signal_event (loop, int signum)
3365		3553
3366	Feed an event as if the given signal occurred (C<loop> must be the default	3554	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3367	loop!).	3555	which is async-safe.
3368		3556
3369	=back	3557	=back
		3558
		3559
		3560	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3561
		3562	This section explains some common idioms that are not immediately
		3563	obvious. Note that examples are sprinkled over the whole manual, and this
		3564	section only contains stuff that wouldn't fit anywhere else.
		3565
		3566	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3567
		3568	Each watcher has, by default, a C<void *data> member that you can read
		3569	or modify at any time: libev will completely ignore it. This can be used
		3570	to associate arbitrary data with your watcher. If you need more data and
		3571	don't want to allocate memory separately and store a pointer to it in that
		3572	data member, you can also "subclass" the watcher type and provide your own
		3573	data:
		3574
		3575	struct my_io
		3576	{
		3577	ev_io io;
		3578	int otherfd;
		3579	void *somedata;
		3580	struct whatever *mostinteresting;
		3581	};
		3582
		3583	...
		3584	struct my_io w;
		3585	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3586
		3587	And since your callback will be called with a pointer to the watcher, you
		3588	can cast it back to your own type:
		3589
		3590	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3591	{
		3592	struct my_io *w = (struct my_io *)w_;
		3593	...
		3594	}
		3595
		3596	More interesting and less C-conformant ways of casting your callback
		3597	function type instead have been omitted.
		3598
		3599	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3600
		3601	Another common scenario is to use some data structure with multiple
		3602	embedded watchers, in effect creating your own watcher that combines
		3603	multiple libev event sources into one "super-watcher":
		3604
		3605	struct my_biggy
		3606	{
		3607	int some_data;
		3608	ev_timer t1;
		3609	ev_timer t2;
		3610	}
		3611
		3612	In this case getting the pointer to C<my_biggy> is a bit more
		3613	complicated: Either you store the address of your C<my_biggy> struct in
		3614	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3615	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3616	real programmers):
		3617
		3618	#include <stddef.h>
		3619
		3620	static void
		3621	t1_cb (EV_P_ ev_timer *w, int revents)
		3622	{
		3623	struct my_biggy big = (struct my_biggy *)
		3624	(((char *)w) - offsetof (struct my_biggy, t1));
		3625	}
		3626
		3627	static void
		3628	t2_cb (EV_P_ ev_timer *w, int revents)
		3629	{
		3630	struct my_biggy big = (struct my_biggy *)
		3631	(((char *)w) - offsetof (struct my_biggy, t2));
		3632	}
		3633
		3634	=head2 AVOIDING FINISHING BEFORE RETURNING
		3635
		3636	Often you have structures like this in event-based programs:
		3637
		3638	callback ()
		3639	{
		3640	free (request);
		3641	}
		3642
		3643	request = start_new_request (..., callback);
		3644
		3645	The intent is to start some "lengthy" operation. The C<request> could be
		3646	used to cancel the operation, or do other things with it.
		3647
		3648	It's not uncommon to have code paths in C<start_new_request> that
		3649	immediately invoke the callback, for example, to report errors. Or you add
		3650	some caching layer that finds that it can skip the lengthy aspects of the
		3651	operation and simply invoke the callback with the result.
		3652
		3653	The problem here is that this will happen I<before> C<start_new_request>
		3654	has returned, so C<request> is not set.
		3655
		3656	Even if you pass the request by some safer means to the callback, you
		3657	might want to do something to the request after starting it, such as
		3658	canceling it, which probably isn't working so well when the callback has
		3659	already been invoked.
		3660
		3661	A common way around all these issues is to make sure that
		3662	C<start_new_request> I<always> returns before the callback is invoked. If
		3663	C<start_new_request> immediately knows the result, it can artificially
		3664	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3665	example, or more sneakily, by reusing an existing (stopped) watcher and
		3666	pushing it into the pending queue:
		3667
		3668	ev_set_cb (watcher, callback);
		3669	ev_feed_event (EV_A_ watcher, 0);
		3670
		3671	This way, C<start_new_request> can safely return before the callback is
		3672	invoked, while not delaying callback invocation too much.
		3673
		3674	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3675
		3676	Often (especially in GUI toolkits) there are places where you have
		3677	I<modal> interaction, which is most easily implemented by recursively
		3678	invoking C<ev_run>.
		3679
		3680	This brings the problem of exiting - a callback might want to finish the
		3681	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3682	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3683	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3684	other combination: In these cases, a simple C<ev_break> will not work.
		3685
		3686	The solution is to maintain "break this loop" variable for each C<ev_run>
		3687	invocation, and use a loop around C<ev_run> until the condition is
		3688	triggered, using C<EVRUN_ONCE>:
		3689
		3690	// main loop
		3691	int exit_main_loop = 0;
		3692
		3693	while (!exit_main_loop)
		3694	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3695
		3696	// in a modal watcher
		3697	int exit_nested_loop = 0;
		3698
		3699	while (!exit_nested_loop)
		3700	ev_run (EV_A_ EVRUN_ONCE);
		3701
		3702	To exit from any of these loops, just set the corresponding exit variable:
		3703
		3704	// exit modal loop
		3705	exit_nested_loop = 1;
		3706
		3707	// exit main program, after modal loop is finished
		3708	exit_main_loop = 1;
		3709
		3710	// exit both
		3711	exit_main_loop = exit_nested_loop = 1;
		3712
		3713	=head2 THREAD LOCKING EXAMPLE
		3714
		3715	Here is a fictitious example of how to run an event loop in a different
		3716	thread from where callbacks are being invoked and watchers are
		3717	created/added/removed.
		3718
		3719	For a real-world example, see the C<EV::Loop::Async> perl module,
		3720	which uses exactly this technique (which is suited for many high-level
		3721	languages).
		3722
		3723	The example uses a pthread mutex to protect the loop data, a condition
		3724	variable to wait for callback invocations, an async watcher to notify the
		3725	event loop thread and an unspecified mechanism to wake up the main thread.
		3726
		3727	First, you need to associate some data with the event loop:
		3728
		3729	typedef struct {
		3730	mutex_t lock; /* global loop lock */
		3731	ev_async async_w;
		3732	thread_t tid;
		3733	cond_t invoke_cv;
		3734	} userdata;
		3735
		3736	void prepare_loop (EV_P)
		3737	{
		3738	// for simplicity, we use a static userdata struct.
		3739	static userdata u;
		3740
		3741	ev_async_init (&u->async_w, async_cb);
		3742	ev_async_start (EV_A_ &u->async_w);
		3743
		3744	pthread_mutex_init (&u->lock, 0);
		3745	pthread_cond_init (&u->invoke_cv, 0);
		3746
		3747	// now associate this with the loop
		3748	ev_set_userdata (EV_A_ u);
		3749	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3750	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3751
		3752	// then create the thread running ev_run
		3753	pthread_create (&u->tid, 0, l_run, EV_A);
		3754	}
		3755
		3756	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3757	solely to wake up the event loop so it takes notice of any new watchers
		3758	that might have been added:
		3759
		3760	static void
		3761	async_cb (EV_P_ ev_async *w, int revents)
		3762	{
		3763	// just used for the side effects
		3764	}
		3765
		3766	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3767	protecting the loop data, respectively.
		3768
		3769	static void
		3770	l_release (EV_P)
		3771	{
		3772	userdata *u = ev_userdata (EV_A);
		3773	pthread_mutex_unlock (&u->lock);
		3774	}
		3775
		3776	static void
		3777	l_acquire (EV_P)
		3778	{
		3779	userdata *u = ev_userdata (EV_A);
		3780	pthread_mutex_lock (&u->lock);
		3781	}
		3782
		3783	The event loop thread first acquires the mutex, and then jumps straight
		3784	into C<ev_run>:
		3785
		3786	void *
		3787	l_run (void *thr_arg)
		3788	{
		3789	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3790
		3791	l_acquire (EV_A);
		3792	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3793	ev_run (EV_A_ 0);
		3794	l_release (EV_A);
		3795
		3796	return 0;
		3797	}
		3798
		3799	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3800	signal the main thread via some unspecified mechanism (signals? pipe
		3801	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3802	have been called (in a while loop because a) spurious wakeups are possible
		3803	and b) skipping inter-thread-communication when there are no pending
		3804	watchers is very beneficial):
		3805
		3806	static void
		3807	l_invoke (EV_P)
		3808	{
		3809	userdata *u = ev_userdata (EV_A);
		3810
		3811	while (ev_pending_count (EV_A))
		3812	{
		3813	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3814	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3815	}
		3816	}
		3817
		3818	Now, whenever the main thread gets told to invoke pending watchers, it
		3819	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3820	thread to continue:
		3821
		3822	static void
		3823	real_invoke_pending (EV_P)
		3824	{
		3825	userdata *u = ev_userdata (EV_A);
		3826
		3827	pthread_mutex_lock (&u->lock);
		3828	ev_invoke_pending (EV_A);
		3829	pthread_cond_signal (&u->invoke_cv);
		3830	pthread_mutex_unlock (&u->lock);
		3831	}
		3832
		3833	Whenever you want to start/stop a watcher or do other modifications to an
		3834	event loop, you will now have to lock:
		3835
		3836	ev_timer timeout_watcher;
		3837	userdata *u = ev_userdata (EV_A);
		3838
		3839	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3840
		3841	pthread_mutex_lock (&u->lock);
		3842	ev_timer_start (EV_A_ &timeout_watcher);
		3843	ev_async_send (EV_A_ &u->async_w);
		3844	pthread_mutex_unlock (&u->lock);
		3845
		3846	Note that sending the C<ev_async> watcher is required because otherwise
		3847	an event loop currently blocking in the kernel will have no knowledge
		3848	about the newly added timer. By waking up the loop it will pick up any new
		3849	watchers in the next event loop iteration.
		3850
		3851	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3852
		3853	While the overhead of a callback that e.g. schedules a thread is small, it
		3854	is still an overhead. If you embed libev, and your main usage is with some
		3855	kind of threads or coroutines, you might want to customise libev so that
		3856	doesn't need callbacks anymore.
		3857
		3858	Imagine you have coroutines that you can switch to using a function
		3859	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3860	and that due to some magic, the currently active coroutine is stored in a
		3861	global called C<current_coro>. Then you can build your own "wait for libev
		3862	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3863	the differing C<;> conventions):
		3864
		3865	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3866	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3867
		3868	That means instead of having a C callback function, you store the
		3869	coroutine to switch to in each watcher, and instead of having libev call
		3870	your callback, you instead have it switch to that coroutine.
		3871
		3872	A coroutine might now wait for an event with a function called
		3873	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3874	matter when, or whether the watcher is active or not when this function is
		3875	called):
		3876
		3877	void
		3878	wait_for_event (ev_watcher *w)
		3879	{
		3880	ev_set_cb (w, current_coro);
		3881	switch_to (libev_coro);
		3882	}
		3883
		3884	That basically suspends the coroutine inside C<wait_for_event> and
		3885	continues the libev coroutine, which, when appropriate, switches back to
		3886	this or any other coroutine.
		3887
		3888	You can do similar tricks if you have, say, threads with an event queue -
		3889	instead of storing a coroutine, you store the queue object and instead of
		3890	switching to a coroutine, you push the watcher onto the queue and notify
		3891	any waiters.
		3892
		3893	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3894	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3895
		3896	// my_ev.h
		3897	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3898	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3899	#include "../libev/ev.h"
		3900
		3901	// my_ev.c
		3902	#define EV_H "my_ev.h"
		3903	#include "../libev/ev.c"
		3904
		3905	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3906	F<my_ev.c> into your project. When properly specifying include paths, you
		3907	can even use F<ev.h> as header file name directly.
3370		3908
3371		3909
3372	=head1 LIBEVENT EMULATION	3910	=head1 LIBEVENT EMULATION
3373		3911
3374	Libev offers a compatibility emulation layer for libevent. It cannot	3912	Libev offers a compatibility emulation layer for libevent. It cannot
3375	emulate the internals of libevent, so here are some usage hints:	3913	emulate the internals of libevent, so here are some usage hints:
3376		3914
3377	=over 4	3915	=over 4
		3916
		3917	=item * Only the libevent-1.4.1-beta API is being emulated.
		3918
		3919	This was the newest libevent version available when libev was implemented,
		3920	and is still mostly unchanged in 2010.
3378		3921
3379	=item * Use it by including <event.h>, as usual.	3922	=item * Use it by including <event.h>, as usual.
3380		3923
3381	=item * The following members are fully supported: ev_base, ev_callback,	3924	=item * The following members are fully supported: ev_base, ev_callback,
3382	ev_arg, ev_fd, ev_res, ev_events.	3925	ev_arg, ev_fd, ev_res, ev_events.
…		…
3398	to use the libev header file and library.	3941	to use the libev header file and library.
3399		3942
3400	=back	3943	=back
3401		3944
3402	=head1 C++ SUPPORT	3945	=head1 C++ SUPPORT
		3946
		3947	=head2 C API
		3948
		3949	The normal C API should work fine when used from C++: both ev.h and the
		3950	libev sources can be compiled as C++. Therefore, code that uses the C API
		3951	will work fine.
		3952
		3953	Proper exception specifications might have to be added to callbacks passed
		3954	to libev: exceptions may be thrown only from watcher callbacks, all
		3955	other callbacks (allocator, syserr, loop acquire/release and periodic
		3956	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3957	()> specification. If you have code that needs to be compiled as both C
		3958	and C++ you can use the C<EV_THROW> macro for this:
		3959
		3960	static void
		3961	fatal_error (const char *msg) EV_THROW
		3962	{
		3963	perror (msg);
		3964	abort ();
		3965	}
		3966
		3967	...
		3968	ev_set_syserr_cb (fatal_error);
		3969
		3970	The only API functions that can currently throw exceptions are C<ev_run>,
		3971	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3972	because it runs cleanup watchers).
		3973
		3974	Throwing exceptions in watcher callbacks is only supported if libev itself
		3975	is compiled with a C++ compiler or your C and C++ environments allow
		3976	throwing exceptions through C libraries (most do).
		3977
		3978	=head2 C++ API
3403		3979
3404	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3980	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3405	you to use some convenience methods to start/stop watchers and also change	3981	you to use some convenience methods to start/stop watchers and also change
3406	the callback model to a model using method callbacks on objects.	3982	the callback model to a model using method callbacks on objects.
3407		3983
…		…
3417	Care has been taken to keep the overhead low. The only data member the C++	3993	Care has been taken to keep the overhead low. The only data member the C++
3418	classes add (compared to plain C-style watchers) is the event loop pointer	3994	classes add (compared to plain C-style watchers) is the event loop pointer
3419	that the watcher is associated with (or no additional members at all if	3995	that the watcher is associated with (or no additional members at all if
3420	you disable C<EV_MULTIPLICITY> when embedding libev).	3996	you disable C<EV_MULTIPLICITY> when embedding libev).
3421		3997
3422	Currently, functions, and static and non-static member functions can be	3998	Currently, functions, static and non-static member functions and classes
3423	used as callbacks. Other types should be easy to add as long as they only	3999	with C<operator ()> can be used as callbacks. Other types should be easy
3424	need one additional pointer for context. If you need support for other	4000	to add as long as they only need one additional pointer for context. If
3425	types of functors please contact the author (preferably after implementing	4001	you need support for other types of functors please contact the author
3426	it).	4002	(preferably after implementing it).
		4003
		4004	For all this to work, your C++ compiler either has to use the same calling
		4005	conventions as your C compiler (for static member functions), or you have
		4006	to embed libev and compile libev itself as C++.
3427		4007
3428	Here is a list of things available in the C<ev> namespace:	4008	Here is a list of things available in the C<ev> namespace:
3429		4009
3430	=over 4	4010	=over 4
3431		4011
…		…
3441	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4021	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3442		4022
3443	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4023	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3444	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4024	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3445	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4025	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3446	defines by many implementations.	4026	defined by many implementations.
3447		4027
3448	All of those classes have these methods:	4028	All of those classes have these methods:
3449		4029
3450	=over 4	4030	=over 4
3451		4031
…		…
3541	Associates a different C<struct ev_loop> with this watcher. You can only	4121	Associates a different C<struct ev_loop> with this watcher. You can only
3542	do this when the watcher is inactive (and not pending either).	4122	do this when the watcher is inactive (and not pending either).
3543		4123
3544	=item w->set ([arguments])	4124	=item w->set ([arguments])
3545		4125
3546	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4126	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3547	method or a suitable start method must be called at least once. Unlike the	4127	with the same arguments. Either this method or a suitable start method
3548	C counterpart, an active watcher gets automatically stopped and restarted	4128	must be called at least once. Unlike the C counterpart, an active watcher
3549	when reconfiguring it with this method.	4129	gets automatically stopped and restarted when reconfiguring it with this
		4130	method.
		4131
		4132	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4133	clashing with the C<set (loop)> method.
3550		4134
3551	=item w->start ()	4135	=item w->start ()
3552		4136
3553	Starts the watcher. Note that there is no C<loop> argument, as the	4137	Starts the watcher. Note that there is no C<loop> argument, as the
3554	constructor already stores the event loop.	4138	constructor already stores the event loop.
…		…
3584	watchers in the constructor.	4168	watchers in the constructor.
3585		4169
3586	class myclass	4170	class myclass
3587	{	4171	{
3588	ev::io io ; void io_cb (ev::io &w, int revents);	4172	ev::io io ; void io_cb (ev::io &w, int revents);
3589	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4173	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3590	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4174	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3591		4175
3592	myclass (int fd)	4176	myclass (int fd)
3593	{	4177	{
3594	io .set <myclass, &myclass::io_cb > (this);	4178	io .set <myclass, &myclass::io_cb > (this);
…		…
3645	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4229	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3646		4230
3647	=item D	4231	=item D
3648		4232
3649	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4233	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3650	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4234	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3651		4235
3652	=item Ocaml	4236	=item Ocaml
3653		4237
3654	Erkki Seppala has written Ocaml bindings for libev, to be found at	4238	Erkki Seppala has written Ocaml bindings for libev, to be found at
3655	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4239	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3658		4242
3659	Brian Maher has written a partial interface to libev for lua (at the	4243	Brian Maher has written a partial interface to libev for lua (at the
3660	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4244	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3661	L<http://github.com/brimworks/lua-ev>.	4245	L<http://github.com/brimworks/lua-ev>.
3662		4246
		4247	=item Javascript
		4248
		4249	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4250
		4251	=item Others
		4252
		4253	There are others, and I stopped counting.
		4254
3663	=back	4255	=back
3664		4256
3665		4257
3666	=head1 MACRO MAGIC	4258	=head1 MACRO MAGIC
3667		4259
…		…
3703	suitable for use with C<EV_A>.	4295	suitable for use with C<EV_A>.
3704		4296
3705	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4297	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3706		4298
3707	Similar to the other two macros, this gives you the value of the default	4299	Similar to the other two macros, this gives you the value of the default
3708	loop, if multiple loops are supported ("ev loop default").	4300	loop, if multiple loops are supported ("ev loop default"). The default loop
		4301	will be initialised if it isn't already initialised.
		4302
		4303	For non-multiplicity builds, these macros do nothing, so you always have
		4304	to initialise the loop somewhere.
3709		4305
3710	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4306	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3711		4307
3712	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4308	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3713	default loop has been initialised (C<UC> == unchecked). Their behaviour	4309	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3858	supported). It will also not define any of the structs usually found in	4454	supported). It will also not define any of the structs usually found in
3859	F<event.h> that are not directly supported by the libev core alone.	4455	F<event.h> that are not directly supported by the libev core alone.
3860		4456
3861	In standalone mode, libev will still try to automatically deduce the	4457	In standalone mode, libev will still try to automatically deduce the
3862	configuration, but has to be more conservative.	4458	configuration, but has to be more conservative.
		4459
		4460	=item EV_USE_FLOOR
		4461
		4462	If defined to be C<1>, libev will use the C<floor ()> function for its
		4463	periodic reschedule calculations, otherwise libev will fall back on a
		4464	portable (slower) implementation. If you enable this, you usually have to
		4465	link against libm or something equivalent. Enabling this when the C<floor>
		4466	function is not available will fail, so the safe default is to not enable
		4467	this.
3863		4468
3864	=item EV_USE_MONOTONIC	4469	=item EV_USE_MONOTONIC
3865		4470
3866	If defined to be C<1>, libev will try to detect the availability of the	4471	If defined to be C<1>, libev will try to detect the availability of the
3867	monotonic clock option at both compile time and runtime. Otherwise no	4472	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3952		4557
3953	If programs implement their own fd to handle mapping on win32, then this	4558	If programs implement their own fd to handle mapping on win32, then this
3954	macro can be used to override the C<close> function, useful to unregister	4559	macro can be used to override the C<close> function, useful to unregister
3955	file descriptors again. Note that the replacement function has to close	4560	file descriptors again. Note that the replacement function has to close
3956	the underlying OS handle.	4561	the underlying OS handle.
		4562
		4563	=item EV_USE_WSASOCKET
		4564
		4565	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4566	communication socket, which works better in some environments. Otherwise,
		4567	the normal C<socket> function will be used, which works better in other
		4568	environments.
3957		4569
3958	=item EV_USE_POLL	4570	=item EV_USE_POLL
3959		4571
3960	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4572	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3961	backend. Otherwise it will be enabled on non-win32 platforms. It	4573	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3997	If defined to be C<1>, libev will compile in support for the Linux inotify	4609	If defined to be C<1>, libev will compile in support for the Linux inotify
3998	interface to speed up C<ev_stat> watchers. Its actual availability will	4610	interface to speed up C<ev_stat> watchers. Its actual availability will
3999	be detected at runtime. If undefined, it will be enabled if the headers	4611	be detected at runtime. If undefined, it will be enabled if the headers
4000	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4612	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4001		4613
		4614	=item EV_NO_SMP
		4615
		4616	If defined to be C<1>, libev will assume that memory is always coherent
		4617	between threads, that is, threads can be used, but threads never run on
		4618	different cpus (or different cpu cores). This reduces dependencies
		4619	and makes libev faster.
		4620
		4621	=item EV_NO_THREADS
		4622
		4623	If defined to be C<1>, libev will assume that it will never be called from
		4624	different threads (that includes signal handlers), which is a stronger
		4625	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4626	libev faster.
		4627
4002	=item EV_ATOMIC_T	4628	=item EV_ATOMIC_T
4003		4629
4004	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4630	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4005	access is atomic with respect to other threads or signal contexts. No such	4631	access is atomic with respect to other threads or signal contexts. No
4006	type is easily found in the C language, so you can provide your own type	4632	such type is easily found in the C language, so you can provide your own
4007	that you know is safe for your purposes. It is used both for signal handler "locking"	4633	type that you know is safe for your purposes. It is used both for signal
4008	as well as for signal and thread safety in C<ev_async> watchers.	4634	handler "locking" as well as for signal and thread safety in C<ev_async>
		4635	watchers.
4009		4636
4010	In the absence of this define, libev will use C<sig_atomic_t volatile>	4637	In the absence of this define, libev will use C<sig_atomic_t volatile>
4011	(from F<signal.h>), which is usually good enough on most platforms.	4638	(from F<signal.h>), which is usually good enough on most platforms.
4012		4639
4013	=item EV_H (h)	4640	=item EV_H (h)
…		…
4040	will have the C<struct ev_loop *> as first argument, and you can create	4667	will have the C<struct ev_loop *> as first argument, and you can create
4041	additional independent event loops. Otherwise there will be no support	4668	additional independent event loops. Otherwise there will be no support
4042	for multiple event loops and there is no first event loop pointer	4669	for multiple event loops and there is no first event loop pointer
4043	argument. Instead, all functions act on the single default loop.	4670	argument. Instead, all functions act on the single default loop.
4044		4671
		4672	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4673	default loop when multiplicity is switched off - you always have to
		4674	initialise the loop manually in this case.
		4675
4045	=item EV_MINPRI	4676	=item EV_MINPRI
4046		4677
4047	=item EV_MAXPRI	4678	=item EV_MAXPRI
4048		4679
4049	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4680	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4085	#define EV_USE_POLL 1	4716	#define EV_USE_POLL 1
4086	#define EV_CHILD_ENABLE 1	4717	#define EV_CHILD_ENABLE 1
4087	#define EV_ASYNC_ENABLE 1	4718	#define EV_ASYNC_ENABLE 1
4088		4719
4089	The actual value is a bitset, it can be a combination of the following	4720	The actual value is a bitset, it can be a combination of the following
4090	values:	4721	values (by default, all of these are enabled):
4091		4722
4092	=over 4	4723	=over 4
4093		4724
4094	=item C<1> - faster/larger code	4725	=item C<1> - faster/larger code
4095		4726
…		…
4099	code size by roughly 30% on amd64).	4730	code size by roughly 30% on amd64).
4100		4731
4101	When optimising for size, use of compiler flags such as C<-Os> with	4732	When optimising for size, use of compiler flags such as C<-Os> with
4102	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4733	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4103	assertions.	4734	assertions.
		4735
		4736	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4737	(e.g. gcc with C<-Os>).
4104		4738
4105	=item C<2> - faster/larger data structures	4739	=item C<2> - faster/larger data structures
4106		4740
4107	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4741	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4108	hash table sizes and so on. This will usually further increase code size	4742	hash table sizes and so on. This will usually further increase code size
4109	and can additionally have an effect on the size of data structures at	4743	and can additionally have an effect on the size of data structures at
4110	runtime.	4744	runtime.
4111		4745
		4746	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4747	(e.g. gcc with C<-Os>).
		4748
4112	=item C<4> - full API configuration	4749	=item C<4> - full API configuration
4113		4750
4114	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4751	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4115	enables multiplicity (C<EV_MULTIPLICITY>=1).	4752	enables multiplicity (C<EV_MULTIPLICITY>=1).
4116		4753
…		…
4146		4783
4147	With an intelligent-enough linker (gcc+binutils are intelligent enough	4784	With an intelligent-enough linker (gcc+binutils are intelligent enough
4148	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4785	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4149	your program might be left out as well - a binary starting a timer and an	4786	your program might be left out as well - a binary starting a timer and an
4150	I/O watcher then might come out at only 5Kb.	4787	I/O watcher then might come out at only 5Kb.
		4788
		4789	=item EV_API_STATIC
		4790
		4791	If this symbol is defined (by default it is not), then all identifiers
		4792	will have static linkage. This means that libev will not export any
		4793	identifiers, and you cannot link against libev anymore. This can be useful
		4794	when you embed libev, only want to use libev functions in a single file,
		4795	and do not want its identifiers to be visible.
		4796
		4797	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4798	wants to use libev.
		4799
		4800	This option only works when libev is compiled with a C compiler, as C++
		4801	doesn't support the required declaration syntax.
4151		4802
4152	=item EV_AVOID_STDIO	4803	=item EV_AVOID_STDIO
4153		4804
4154	If this is set to C<1> at compiletime, then libev will avoid using stdio	4805	If this is set to C<1> at compiletime, then libev will avoid using stdio
4155	functions (printf, scanf, perror etc.). This will increase the code size	4806	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4299	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4950	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4300		4951
4301	#include "ev_cpp.h"	4952	#include "ev_cpp.h"
4302	#include "ev.c"	4953	#include "ev.c"
4303		4954
4304	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4955	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4305		4956
4306	=head2 THREADS AND COROUTINES	4957	=head2 THREADS AND COROUTINES
4307		4958
4308	=head3 THREADS	4959	=head3 THREADS
4309		4960
…		…
4360	default loop and triggering an C<ev_async> watcher from the default loop	5011	default loop and triggering an C<ev_async> watcher from the default loop
4361	watcher callback into the event loop interested in the signal.	5012	watcher callback into the event loop interested in the signal.
4362		5013
4363	=back	5014	=back
4364		5015
4365	=head4 THREAD LOCKING EXAMPLE	5016	See also L</THREAD LOCKING EXAMPLE>.
4366
4367	Here is a fictitious example of how to run an event loop in a different
4368	thread than where callbacks are being invoked and watchers are
4369	created/added/removed.
4370
4371	For a real-world example, see the C<EV::Loop::Async> perl module,
4372	which uses exactly this technique (which is suited for many high-level
4373	languages).
4374
4375	The example uses a pthread mutex to protect the loop data, a condition
4376	variable to wait for callback invocations, an async watcher to notify the
4377	event loop thread and an unspecified mechanism to wake up the main thread.
4378
4379	First, you need to associate some data with the event loop:
4380
4381	typedef struct {
4382	mutex_t lock; /* global loop lock */
4383	ev_async async_w;
4384	thread_t tid;
4385	cond_t invoke_cv;
4386	} userdata;
4387
4388	void prepare_loop (EV_P)
4389	{
4390	// for simplicity, we use a static userdata struct.
4391	static userdata u;
4392
4393	ev_async_init (&u->async_w, async_cb);
4394	ev_async_start (EV_A_ &u->async_w);
4395
4396	pthread_mutex_init (&u->lock, 0);
4397	pthread_cond_init (&u->invoke_cv, 0);
4398
4399	// now associate this with the loop
4400	ev_set_userdata (EV_A_ u);
4401	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4402	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4403
4404	// then create the thread running ev_loop
4405	pthread_create (&u->tid, 0, l_run, EV_A);
4406	}
4407
4408	The callback for the C<ev_async> watcher does nothing: the watcher is used
4409	solely to wake up the event loop so it takes notice of any new watchers
4410	that might have been added:
4411
4412	static void
4413	async_cb (EV_P_ ev_async *w, int revents)
4414	{
4415	// just used for the side effects
4416	}
4417
4418	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4419	protecting the loop data, respectively.
4420
4421	static void
4422	l_release (EV_P)
4423	{
4424	userdata *u = ev_userdata (EV_A);
4425	pthread_mutex_unlock (&u->lock);
4426	}
4427
4428	static void
4429	l_acquire (EV_P)
4430	{
4431	userdata *u = ev_userdata (EV_A);
4432	pthread_mutex_lock (&u->lock);
4433	}
4434
4435	The event loop thread first acquires the mutex, and then jumps straight
4436	into C<ev_run>:
4437
4438	void *
4439	l_run (void *thr_arg)
4440	{
4441	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4442
4443	l_acquire (EV_A);
4444	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4445	ev_run (EV_A_ 0);
4446	l_release (EV_A);
4447
4448	return 0;
4449	}
4450
4451	Instead of invoking all pending watchers, the C<l_invoke> callback will
4452	signal the main thread via some unspecified mechanism (signals? pipe
4453	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4454	have been called (in a while loop because a) spurious wakeups are possible
4455	and b) skipping inter-thread-communication when there are no pending
4456	watchers is very beneficial):
4457
4458	static void
4459	l_invoke (EV_P)
4460	{
4461	userdata *u = ev_userdata (EV_A);
4462
4463	while (ev_pending_count (EV_A))
4464	{
4465	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4466	pthread_cond_wait (&u->invoke_cv, &u->lock);
4467	}
4468	}
4469
4470	Now, whenever the main thread gets told to invoke pending watchers, it
4471	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4472	thread to continue:
4473
4474	static void
4475	real_invoke_pending (EV_P)
4476	{
4477	userdata *u = ev_userdata (EV_A);
4478
4479	pthread_mutex_lock (&u->lock);
4480	ev_invoke_pending (EV_A);
4481	pthread_cond_signal (&u->invoke_cv);
4482	pthread_mutex_unlock (&u->lock);
4483	}
4484
4485	Whenever you want to start/stop a watcher or do other modifications to an
4486	event loop, you will now have to lock:
4487
4488	ev_timer timeout_watcher;
4489	userdata *u = ev_userdata (EV_A);
4490
4491	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4492
4493	pthread_mutex_lock (&u->lock);
4494	ev_timer_start (EV_A_ &timeout_watcher);
4495	ev_async_send (EV_A_ &u->async_w);
4496	pthread_mutex_unlock (&u->lock);
4497
4498	Note that sending the C<ev_async> watcher is required because otherwise
4499	an event loop currently blocking in the kernel will have no knowledge
4500	about the newly added timer. By waking up the loop it will pick up any new
4501	watchers in the next event loop iteration.
4502		5017
4503	=head3 COROUTINES	5018	=head3 COROUTINES
4504		5019
4505	Libev is very accommodating to coroutines ("cooperative threads"):	5020	Libev is very accommodating to coroutines ("cooperative threads"):
4506	libev fully supports nesting calls to its functions from different	5021	libev fully supports nesting calls to its functions from different
…		…
4671	requires, and its I/O model is fundamentally incompatible with the POSIX	5186	requires, and its I/O model is fundamentally incompatible with the POSIX
4672	model. Libev still offers limited functionality on this platform in	5187	model. Libev still offers limited functionality on this platform in
4673	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5188	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4674	descriptors. This only applies when using Win32 natively, not when using	5189	descriptors. This only applies when using Win32 natively, not when using
4675	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5190	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4676	as every compielr comes with a slightly differently broken/incompatible	5191	as every compiler comes with a slightly differently broken/incompatible
4677	environment.	5192	environment.
4678		5193
4679	Lifting these limitations would basically require the full	5194	Lifting these limitations would basically require the full
4680	re-implementation of the I/O system. If you are into this kind of thing,	5195	re-implementation of the I/O system. If you are into this kind of thing,
4681	then note that glib does exactly that for you in a very portable way (note	5196	then note that glib does exactly that for you in a very portable way (note
…		…
4797	thread" or will block signals process-wide, both behaviours would	5312	thread" or will block signals process-wide, both behaviours would
4798	be compatible with libev. Interaction between C<sigprocmask> and	5313	be compatible with libev. Interaction between C<sigprocmask> and
4799	C<pthread_sigmask> could complicate things, however.	5314	C<pthread_sigmask> could complicate things, however.
4800		5315
4801	The most portable way to handle signals is to block signals in all threads	5316	The most portable way to handle signals is to block signals in all threads
4802	except the initial one, and run the default loop in the initial thread as	5317	except the initial one, and run the signal handling loop in the initial
4803	well.	5318	thread as well.
4804		5319
4805	=item C<long> must be large enough for common memory allocation sizes	5320	=item C<long> must be large enough for common memory allocation sizes
4806		5321
4807	To improve portability and simplify its API, libev uses C<long> internally	5322	To improve portability and simplify its API, libev uses C<long> internally
4808	instead of C<size_t> when allocating its data structures. On non-POSIX	5323	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4814		5329
4815	The type C<double> is used to represent timestamps. It is required to	5330	The type C<double> is used to represent timestamps. It is required to
4816	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5331	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4817	good enough for at least into the year 4000 with millisecond accuracy	5332	good enough for at least into the year 4000 with millisecond accuracy
4818	(the design goal for libev). This requirement is overfulfilled by	5333	(the design goal for libev). This requirement is overfulfilled by
4819	implementations using IEEE 754, which is basically all existing ones. With	5334	implementations using IEEE 754, which is basically all existing ones.
		5335
4820	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5336	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5337	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5338	is either obsolete or somebody patched it to use C<long double> or
		5339	something like that, just kidding).
4821		5340
4822	=back	5341	=back
4823		5342
4824	If you know of other additional requirements drop me a note.	5343	If you know of other additional requirements drop me a note.
4825		5344
…		…
4887	=item Processing ev_async_send: O(number_of_async_watchers)	5406	=item Processing ev_async_send: O(number_of_async_watchers)
4888		5407
4889	=item Processing signals: O(max_signal_number)	5408	=item Processing signals: O(max_signal_number)
4890		5409
4891	Sending involves a system call I<iff> there were no other C<ev_async_send>	5410	Sending involves a system call I<iff> there were no other C<ev_async_send>
4892	calls in the current loop iteration. Checking for async and signal events	5411	calls in the current loop iteration and the loop is currently
		5412	blocked. Checking for async and signal events involves iterating over all
4893	involves iterating over all running async watchers or all signal numbers.	5413	running async watchers or all signal numbers.
4894		5414
4895	=back	5415	=back
4896		5416
4897		5417
4898	=head1 PORTING FROM LIBEV 3.X TO 4.X	5418	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
4907	=over 4	5427	=over 4
4908		5428
4909	=item C<EV_COMPAT3> backwards compatibility mechanism	5429	=item C<EV_COMPAT3> backwards compatibility mechanism
4910		5430
4911	The backward compatibility mechanism can be controlled by	5431	The backward compatibility mechanism can be controlled by
4912	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5432	C<EV_COMPAT3>. See L</PREPROCESSOR SYMBOLS/MACROS> in the L</EMBEDDING>
4913	section.	5433	section.
4914		5434
4915	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5435	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4916		5436
4917	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5437	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
4960	=over 4	5480	=over 4
4961		5481
4962	=item active	5482	=item active
4963		5483
4964	A watcher is active as long as it has been started and not yet stopped.	5484	A watcher is active as long as it has been started and not yet stopped.
4965	See L<WATCHER STATES> for details.	5485	See L</WATCHER STATES> for details.
4966		5486
4967	=item application	5487	=item application
4968		5488
4969	In this document, an application is whatever is using libev.	5489	In this document, an application is whatever is using libev.
4970		5490
…		…
5006	watchers and events.	5526	watchers and events.
5007		5527
5008	=item pending	5528	=item pending
5009		5529
5010	A watcher is pending as soon as the corresponding event has been	5530	A watcher is pending as soon as the corresponding event has been
5011	detected. See L<WATCHER STATES> for details.	5531	detected. See L</WATCHER STATES> for details.
5012		5532
5013	=item real time	5533	=item real time
5014		5534
5015	The physical time that is observed. It is apparently strictly monotonic :)	5535	The physical time that is observed. It is apparently strictly monotonic :)
5016		5536
5017	=item wall-clock time	5537	=item wall-clock time
5018		5538
5019	The time and date as shown on clocks. Unlike real time, it can actually	5539	The time and date as shown on clocks. Unlike real time, it can actually
5020	be wrong and jump forwards and backwards, e.g. when the you adjust your	5540	be wrong and jump forwards and backwards, e.g. when you adjust your
5021	clock.	5541	clock.
5022		5542
5023	=item watcher	5543	=item watcher
5024		5544
5025	A data structure that describes interest in certain events. Watchers need	5545	A data structure that describes interest in certain events. Watchers need
…		…
5028	=back	5548	=back
5029		5549
5030	=head1 AUTHOR	5550	=head1 AUTHOR
5031		5551
5032	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5552	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5033	Magnusson and Emanuele Giaquinta.	5553	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5034		5554

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines