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Revision 1.386 by root, Mon Dec 19 20:15:28 2011 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
…		…
77	on event-based programming, nor will it introduce event-based programming	77	on event-based programming, nor will it introduce event-based programming
78	with libev.	78	with libev.
79		79
80	Familiarity with event based programming techniques in general is assumed	80	Familiarity with event based programming techniques in general is assumed
81	throughout this document.	81	throughout this document.
		82
		83	=head1 WHAT TO READ WHEN IN A HURRY
		84
		85	This manual tries to be very detailed, but unfortunately, this also makes
		86	it very long. If you just want to know the basics of libev, I suggest
		87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
		88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
		89	C<ev_timer> sections in L<WATCHER TYPES>.
82		90
83	=head1 ABOUT LIBEV	91	=head1 ABOUT LIBEV
84		92
85	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
86	file descriptor being readable or a timeout occurring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
…		…
166	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
167		175
168	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
169	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
170	you actually want to know. Also interesting is the combination of	178	you actually want to know. Also interesting is the combination of
171	C<ev_update_now> and C<ev_now>.	179	C<ev_now_update> and C<ev_now>.
172		180
173	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
174		182
175	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked
176	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
177	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 >>).
178		192
179	=item int ev_version_major ()	193	=item int ev_version_major ()
180		194
181	=item int ev_version_minor ()	195	=item int ev_version_minor ()
182		196
…		…
233	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 ()
234	& ev_supported_backends ()>, likewise for recommended ones.	248	& ev_supported_backends ()>, likewise for recommended ones.
235		249
236	See the description of C<ev_embed> watchers for more info.	250	See the description of C<ev_embed> watchers for more info.
237		251
238	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
239		253
240	Sets the allocation function to use (the prototype is similar - the	254	Sets the allocation function to use (the prototype is similar - the
241	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	255	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
242	used to allocate and free memory (no surprises here). If it returns zero	256	used to allocate and free memory (no surprises here). If it returns zero
243	when memory needs to be allocated (C<size != 0>), the library might abort	257	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
269	}	283	}
270		284
271	...	285	...
272	ev_set_allocator (persistent_realloc);	286	ev_set_allocator (persistent_realloc);
273		287
274	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	288	=item ev_set_syserr_cb (void (*cb)(const char *msg))
275		289
276	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
277	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
278	indicating the system call or subsystem causing the problem. If this	292	indicating the system call or subsystem causing the problem. If this
279	callback is set, then libev will expect it to remedy the situation, no	293	callback is set, then libev will expect it to remedy the situation, no
…		…
291	}	305	}
292		306
293	...	307	...
294	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
295		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
296	=back	323	=back
297		324
298	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
299		326
300	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
301	I<not> optional in this case unless libev 3 compatibility is disabled, as	328	I<not> optional in this case unless libev 3 compatibility is disabled, as
302	libev 3 had an C<ev_loop> function colliding with the struct name).	329	libev 3 had an C<ev_loop> function colliding with the struct name).
303		330
304	The library knows two types of such loops, the I<default> loop, which	331	The library knows two types of such loops, the I<default> loop, which
305	supports signals and child events, and dynamically created event loops	332	supports child process events, and dynamically created event loops which
306	which do not.	333	do not.
307		334
308	=over 4	335	=over 4
309		336
310	=item struct ev_loop *ev_default_loop (unsigned int flags)	337	=item struct ev_loop *ev_default_loop (unsigned int flags)
311		338
…		…
347	=item struct ev_loop *ev_loop_new (unsigned int flags)	374	=item struct ev_loop *ev_loop_new (unsigned int flags)
348		375
349	This will create and initialise a new event loop object. If the loop	376	This will create and initialise a new event loop object. If the loop
350	could not be initialised, returns false.	377	could not be initialised, returns false.
351		378
352	Note that this function I<is> thread-safe, and one common way to use	379	This function is thread-safe, and one common way to use libev with
353	libev with threads is indeed to create one loop per thread, and using the	380	threads is indeed to create one loop per thread, and using the default
354	default loop in the "main" or "initial" thread.	381	loop in the "main" or "initial" thread.
355		382
356	The flags argument can be used to specify special behaviour or specific	383	The flags argument can be used to specify special behaviour or specific
357	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	384	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
358		385
359	The following flags are supported:	386	The following flags are supported:
…		…
394	environment variable.	421	environment variable.
395		422
396	=item C<EVFLAG_NOINOTIFY>	423	=item C<EVFLAG_NOINOTIFY>
397		424
398	When this flag is specified, then libev will not attempt to use the	425	When this flag is specified, then libev will not attempt to use the
399	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and	426	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
400	testing, this flag can be useful to conserve inotify file descriptors, as	427	testing, this flag can be useful to conserve inotify file descriptors, as
401	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.	428	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
402		429
403	=item C<EVFLAG_SIGNALFD>	430	=item C<EVFLAG_SIGNALFD>
404		431
405	When this flag is specified, then libev will attempt to use the	432	When this flag is specified, then libev will attempt to use the
406	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API	433	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
407	delivers signals synchronously, which makes it both faster and might make	434	delivers signals synchronously, which makes it both faster and might make
408	it possible to get the queued signal data. It can also simplify signal	435	it possible to get the queued signal data. It can also simplify signal
409	handling with threads, as long as you properly block signals in your	436	handling with threads, as long as you properly block signals in your
410	threads that are not interested in handling them.	437	threads that are not interested in handling them.
411		438
412	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
413	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
414	example) that can't properly initialise their signal masks.	441	example) that can't properly initialise their signal masks.
		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.
415		457
416	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
417		459
418	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
419	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,
…		…
447	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
448		490
449	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
450	kernels).	492	kernels).
451		493
452	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
453	but it scales phenomenally better. While poll and select usually scale	495	it scales phenomenally better. While poll and select usually scale like
454	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
455	epoll scales either O(1) or O(active_fds).	497	fd), epoll scales either O(1) or O(active_fds).
456		498
457	The epoll mechanism deserves honorable mention as the most misdesigned	499	The epoll mechanism deserves honorable mention as the most misdesigned
458	of the more advanced event mechanisms: mere annoyances include silently	500	of the more advanced event mechanisms: mere annoyances include silently
459	dropping file descriptors, requiring a system call per change per file	501	dropping file descriptors, requiring a system call per change per file
460	descriptor (and unnecessary guessing of parameters), problems with dup and	502	descriptor (and unnecessary guessing of parameters), problems with dup,
		503	returning before the timeout value, resulting in additional iterations
		504	(and only giving 5ms accuracy while select on the same platform gives
461	so on. The biggest issue is fork races, however - if a program forks then	505	0.1ms) and so on. The biggest issue is fork races, however - if a program
462	I<both> parent and child process have to recreate the epoll set, which can	506	forks then I<both> parent and child process have to recreate the epoll
463	take considerable time (one syscall per file descriptor) and is of course	507	set, which can take considerable time (one syscall per file descriptor)
464	hard to detect.	508	and is of course hard to detect.
465		509
466	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
467	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
468	I<different> file descriptors (even already closed ones, so one cannot	512	totally I<different> file descriptors (even already closed ones, so
469	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
470	on SMP systems). Libev tries to counter these spurious notifications by	514	(especially on SMP systems). Libev tries to counter these spurious
471	employing an additional generation counter and comparing that against the	515	notifications by employing an additional generation counter and comparing
472	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
473	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
474	perfectly fine with C<select> (files, many character devices...).	521	perfectly fine with C<select> (files, many character devices...).
		522
		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...
475		526
476	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
477	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
478	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
479	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
…		…
545	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
546		597
547	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,
548	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)).
549		600
550	Please note that Solaris event ports can deliver a lot of spurious
551	notifications, so you need to use non-blocking I/O or other means to avoid
552	blocking when no data (or space) is available.
553
554	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
555	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
556	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
557	might perform better.	604	might perform better.
558		605
559	On the positive side, with the exception of the spurious readiness	606	On the positive side, this backend actually performed fully to
560	notifications, this backend actually performed fully to specification
561	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
562	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.
563		620
564	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
565	C<EVBACKEND_POLL>.	622	C<EVBACKEND_POLL>.
566		623
567	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
568		625
569	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
570	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
571	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
572		629
573	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).
574		639
575	=back	640	=back
576		641
577	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,
578	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
…		…
607	This function is normally used on loop objects allocated by	672	This function is normally used on loop objects allocated by
608	C<ev_loop_new>, but it can also be used on the default loop returned by	673	C<ev_loop_new>, but it can also be used on the default loop returned by
609	C<ev_default_loop>, in which case it is not thread-safe.	674	C<ev_default_loop>, in which case it is not thread-safe.
610		675
611	Note that it is not advisable to call this function on the default loop	676	Note that it is not advisable to call this function on the default loop
612	except in the rare occasion where you really need to free it's resources.	677	except in the rare occasion where you really need to free its resources.
613	If you need dynamically allocated loops it is better to use C<ev_loop_new>	678	If you need dynamically allocated loops it is better to use C<ev_loop_new>
614	and C<ev_loop_destroy>.	679	and C<ev_loop_destroy>.
615		680
616	=item ev_loop_fork (loop)	681	=item ev_loop_fork (loop)
617		682
…		…
665	prepare and check phases.	730	prepare and check phases.
666		731
667	=item unsigned int ev_depth (loop)	732	=item unsigned int ev_depth (loop)
668		733
669	Returns the number of times C<ev_run> was entered minus the number of	734	Returns the number of times C<ev_run> was entered minus the number of
670	times C<ev_run> was exited, in other words, the recursion depth.	735	times C<ev_run> was exited normally, in other words, the recursion depth.
671		736
672	Outside C<ev_run>, this number is zero. In a callback, this number is	737	Outside C<ev_run>, this number is zero. In a callback, this number is
673	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	738	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
674	in which case it is higher.	739	in which case it is higher.
675		740
676	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	741	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
677	etc.), doesn't count as "exit" - consider this as a hint to avoid such	742	throwing an exception etc.), doesn't count as "exit" - consider this
678	ungentleman-like behaviour unless it's really convenient.	743	as a hint to avoid such ungentleman-like behaviour unless it's really
		744	convenient, in which case it is fully supported.
679		745
680	=item unsigned int ev_backend (loop)	746	=item unsigned int ev_backend (loop)
681		747
682	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	748	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
683	use.	749	use.
…		…
745	finished (especially in interactive programs), but having a program	811	finished (especially in interactive programs), but having a program
746	that automatically loops as long as it has to and no longer by virtue	812	that automatically loops as long as it has to and no longer by virtue
747	of relying on its watchers stopping correctly, that is truly a thing of	813	of relying on its watchers stopping correctly, that is truly a thing of
748	beauty.	814	beauty.
749		815
		816	This function is also I<mostly> exception-safe - you can break out of
		817	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		818	exception and so on. This does not decrement the C<ev_depth> value, nor
		819	will it clear any outstanding C<EVBREAK_ONE> breaks.
		820
750	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	821	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
751	those events and any already outstanding ones, but will not wait and	822	those events and any already outstanding ones, but will not wait and
752	block your process in case there are no events and will return after one	823	block your process in case there are no events and will return after one
753	iteration of the loop. This is sometimes useful to poll and handle new	824	iteration of the loop. This is sometimes useful to poll and handle new
754	events while doing lengthy calculations, to keep the program responsive.	825	events while doing lengthy calculations, to keep the program responsive.
…		…
763	This is useful if you are waiting for some external event in conjunction	834	This is useful if you are waiting for some external event in conjunction
764	with something not expressible using other libev watchers (i.e. "roll your	835	with something not expressible using other libev watchers (i.e. "roll your
765	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	836	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
766	usually a better approach for this kind of thing.	837	usually a better approach for this kind of thing.
767		838
768	Here are the gory details of what C<ev_run> does:	839	Here are the gory details of what C<ev_run> does (this is for your
		840	understanding, not a guarantee that things will work exactly like this in
		841	future versions):
769		842
770	- Increment loop depth.	843	- Increment loop depth.
771	- Reset the ev_break status.	844	- Reset the ev_break status.
772	- Before the first iteration, call any pending watchers.	845	- Before the first iteration, call any pending watchers.
773	LOOP:	846	LOOP:
…		…
806	anymore.	879	anymore.
807		880
808	... queue jobs here, make sure they register event watchers as long	881	... queue jobs here, make sure they register event watchers as long
809	... as they still have work to do (even an idle watcher will do..)	882	... as they still have work to do (even an idle watcher will do..)
810	ev_run (my_loop, 0);	883	ev_run (my_loop, 0);
811	... jobs done or somebody called unloop. yeah!	884	... jobs done or somebody called break. yeah!
812		885
813	=item ev_break (loop, how)	886	=item ev_break (loop, how)
814		887
815	Can be used to make a call to C<ev_run> return early (but only after it	888	Can be used to make a call to C<ev_run> return early (but only after it
816	has processed all outstanding events). The C<how> argument must be either	889	has processed all outstanding events). The C<how> argument must be either
817	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	890	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
818	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	891	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
819		892
820	This "unloop state" will be cleared when entering C<ev_run> again.	893	This "break state" will be cleared on the next call to C<ev_run>.
821		894
822	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	895	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		896	which case it will have no effect.
823		897
824	=item ev_ref (loop)	898	=item ev_ref (loop)
825		899
826	=item ev_unref (loop)	900	=item ev_unref (loop)
827		901
…		…
848	running when nothing else is active.	922	running when nothing else is active.
849		923
850	ev_signal exitsig;	924	ev_signal exitsig;
851	ev_signal_init (&exitsig, sig_cb, SIGINT);	925	ev_signal_init (&exitsig, sig_cb, SIGINT);
852	ev_signal_start (loop, &exitsig);	926	ev_signal_start (loop, &exitsig);
853	evf_unref (loop);	927	ev_unref (loop);
854		928
855	Example: For some weird reason, unregister the above signal handler again.	929	Example: For some weird reason, unregister the above signal handler again.
856		930
857	ev_ref (loop);	931	ev_ref (loop);
858	ev_signal_stop (loop, &exitsig);	932	ev_signal_stop (loop, &exitsig);
…		…
878	overhead for the actual polling but can deliver many events at once.	952	overhead for the actual polling but can deliver many events at once.
879		953
880	By setting a higher I<io collect interval> you allow libev to spend more	954	By setting a higher I<io collect interval> you allow libev to spend more
881	time collecting I/O events, so you can handle more events per iteration,	955	time collecting I/O events, so you can handle more events per iteration,
882	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	956	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
883	C<ev_timer>) will be not affected. Setting this to a non-null value will	957	C<ev_timer>) will not be affected. Setting this to a non-null value will
884	introduce an additional C<ev_sleep ()> call into most loop iterations. The	958	introduce an additional C<ev_sleep ()> call into most loop iterations. The
885	sleep time ensures that libev will not poll for I/O events more often then	959	sleep time ensures that libev will not poll for I/O events more often then
886	once per this interval, on average.	960	once per this interval, on average (as long as the host time resolution is
		961	good enough).
887		962
888	Likewise, by setting a higher I<timeout collect interval> you allow libev	963	Likewise, by setting a higher I<timeout collect interval> you allow libev
889	to spend more time collecting timeouts, at the expense of increased	964	to spend more time collecting timeouts, at the expense of increased
890	latency/jitter/inexactness (the watcher callback will be called	965	latency/jitter/inexactness (the watcher callback will be called
891	later). C<ev_io> watchers will not be affected. Setting this to a non-null	966	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
945	can be done relatively simply by putting mutex_lock/unlock calls around	1020	can be done relatively simply by putting mutex_lock/unlock calls around
946	each call to a libev function.	1021	each call to a libev function.
947		1022
948	However, C<ev_run> can run an indefinite time, so it is not feasible	1023	However, C<ev_run> can run an indefinite time, so it is not feasible
949	to wait for it to return. One way around this is to wake up the event	1024	to wait for it to return. One way around this is to wake up the event
950	loop via C<ev_break> and C<av_async_send>, another way is to set these	1025	loop via C<ev_break> and C<ev_async_send>, another way is to set these
951	I<release> and I<acquire> callbacks on the loop.	1026	I<release> and I<acquire> callbacks on the loop.
952		1027
953	When set, then C<release> will be called just before the thread is	1028	When set, then C<release> will be called just before the thread is
954	suspended waiting for new events, and C<acquire> is called just	1029	suspended waiting for new events, and C<acquire> is called just
955	afterwards.	1030	afterwards.
…		…
970	See also the locking example in the C<THREADS> section later in this	1045	See also the locking example in the C<THREADS> section later in this
971	document.	1046	document.
972		1047
973	=item ev_set_userdata (loop, void *data)	1048	=item ev_set_userdata (loop, void *data)
974		1049
975	=item ev_userdata (loop)	1050	=item void *ev_userdata (loop)
976		1051
977	Set and retrieve a single C<void *> associated with a loop. When	1052	Set and retrieve a single C<void *> associated with a loop. When
978	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1053	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
979	C<0.>	1054	C<0>.
980		1055
981	These two functions can be used to associate arbitrary data with a loop,	1056	These two functions can be used to associate arbitrary data with a loop,
982	and are intended solely for the C<invoke_pending_cb>, C<release> and	1057	and are intended solely for the C<invoke_pending_cb>, C<release> and
983	C<acquire> callbacks described above, but of course can be (ab-)used for	1058	C<acquire> callbacks described above, but of course can be (ab-)used for
984	any other purpose as well.	1059	any other purpose as well.
…		…
1114	The event loop has been resumed in the child process after fork (see	1189	The event loop has been resumed in the child process after fork (see
1115	C<ev_fork>).	1190	C<ev_fork>).
1116		1191
1117	=item C<EV_CLEANUP>	1192	=item C<EV_CLEANUP>
1118		1193
1119	The event loop is abotu to be destroyed (see C<ev_cleanup>).	1194	The event loop is about to be destroyed (see C<ev_cleanup>).
1120		1195
1121	=item C<EV_ASYNC>	1196	=item C<EV_ASYNC>
1122		1197
1123	The given async watcher has been asynchronously notified (see C<ev_async>).	1198	The given async watcher has been asynchronously notified (see C<ev_async>).
1124		1199
…		…
1146	programs, though, as the fd could already be closed and reused for another	1221	programs, though, as the fd could already be closed and reused for another
1147	thing, so beware.	1222	thing, so beware.
1148		1223
1149	=back	1224	=back
1150		1225
		1226	=head2 GENERIC WATCHER FUNCTIONS
		1227
		1228	=over 4
		1229
		1230	=item C<ev_init> (ev_TYPE *watcher, callback)
		1231
		1232	This macro initialises the generic portion of a watcher. The contents
		1233	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1234	the generic parts of the watcher are initialised, you I<need> to call
		1235	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1236	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1237	which rolls both calls into one.
		1238
		1239	You can reinitialise a watcher at any time as long as it has been stopped
		1240	(or never started) and there are no pending events outstanding.
		1241
		1242	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1243	int revents)>.
		1244
		1245	Example: Initialise an C<ev_io> watcher in two steps.
		1246
		1247	ev_io w;
		1248	ev_init (&w, my_cb);
		1249	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1250
		1251	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1252
		1253	This macro initialises the type-specific parts of a watcher. You need to
		1254	call C<ev_init> at least once before you call this macro, but you can
		1255	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1256	macro on a watcher that is active (it can be pending, however, which is a
		1257	difference to the C<ev_init> macro).
		1258
		1259	Although some watcher types do not have type-specific arguments
		1260	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1261
		1262	See C<ev_init>, above, for an example.
		1263
		1264	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1265
		1266	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1267	calls into a single call. This is the most convenient method to initialise
		1268	a watcher. The same limitations apply, of course.
		1269
		1270	Example: Initialise and set an C<ev_io> watcher in one step.
		1271
		1272	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1273
		1274	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1275
		1276	Starts (activates) the given watcher. Only active watchers will receive
		1277	events. If the watcher is already active nothing will happen.
		1278
		1279	Example: Start the C<ev_io> watcher that is being abused as example in this
		1280	whole section.
		1281
		1282	ev_io_start (EV_DEFAULT_UC, &w);
		1283
		1284	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1285
		1286	Stops the given watcher if active, and clears the pending status (whether
		1287	the watcher was active or not).
		1288
		1289	It is possible that stopped watchers are pending - for example,
		1290	non-repeating timers are being stopped when they become pending - but
		1291	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1292	pending. If you want to free or reuse the memory used by the watcher it is
		1293	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1294
		1295	=item bool ev_is_active (ev_TYPE *watcher)
		1296
		1297	Returns a true value iff the watcher is active (i.e. it has been started
		1298	and not yet been stopped). As long as a watcher is active you must not modify
		1299	it.
		1300
		1301	=item bool ev_is_pending (ev_TYPE *watcher)
		1302
		1303	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1304	events but its callback has not yet been invoked). As long as a watcher
		1305	is pending (but not active) you must not call an init function on it (but
		1306	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1307	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1308	it).
		1309
		1310	=item callback ev_cb (ev_TYPE *watcher)
		1311
		1312	Returns the callback currently set on the watcher.
		1313
		1314	=item ev_cb_set (ev_TYPE *watcher, callback)
		1315
		1316	Change the callback. You can change the callback at virtually any time
		1317	(modulo threads).
		1318
		1319	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1320
		1321	=item int ev_priority (ev_TYPE *watcher)
		1322
		1323	Set and query the priority of the watcher. The priority is a small
		1324	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1325	(default: C<-2>). Pending watchers with higher priority will be invoked
		1326	before watchers with lower priority, but priority will not keep watchers
		1327	from being executed (except for C<ev_idle> watchers).
		1328
		1329	If you need to suppress invocation when higher priority events are pending
		1330	you need to look at C<ev_idle> watchers, which provide this functionality.
		1331
		1332	You I<must not> change the priority of a watcher as long as it is active or
		1333	pending.
		1334
		1335	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1336	fine, as long as you do not mind that the priority value you query might
		1337	or might not have been clamped to the valid range.
		1338
		1339	The default priority used by watchers when no priority has been set is
		1340	always C<0>, which is supposed to not be too high and not be too low :).
		1341
		1342	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1343	priorities.
		1344
		1345	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1346
		1347	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1348	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1349	can deal with that fact, as both are simply passed through to the
		1350	callback.
		1351
		1352	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1353
		1354	If the watcher is pending, this function clears its pending status and
		1355	returns its C<revents> bitset (as if its callback was invoked). If the
		1356	watcher isn't pending it does nothing and returns C<0>.
		1357
		1358	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1359	callback to be invoked, which can be accomplished with this function.
		1360
		1361	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1362
		1363	Feeds the given event set into the event loop, as if the specified event
		1364	had happened for the specified watcher (which must be a pointer to an
		1365	initialised but not necessarily started event watcher). Obviously you must
		1366	not free the watcher as long as it has pending events.
		1367
		1368	Stopping the watcher, letting libev invoke it, or calling
		1369	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1370	not started in the first place.
		1371
		1372	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1373	functions that do not need a watcher.
		1374
		1375	=back
		1376
		1377	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1378	OWN COMPOSITE WATCHERS> idioms.
		1379
1151	=head2 WATCHER STATES	1380	=head2 WATCHER STATES
1152		1381
1153	There are various watcher states mentioned throughout this manual -	1382	There are various watcher states mentioned throughout this manual -
1154	active, pending and so on. In this section these states and the rules to	1383	active, pending and so on. In this section these states and the rules to
1155	transition between them will be described in more detail - and while these	1384	transition between them will be described in more detail - and while these
…		…
1157		1386
1158	=over 4	1387	=over 4
1159		1388
1160	=item initialiased	1389	=item initialiased
1161		1390
1162	Before a watcher can be registered with the event looop it has to be	1391	Before a watcher can be registered with the event loop it has to be
1163	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1392	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1164	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1393	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1165		1394
1166	In this state it is simply some block of memory that is suitable for use	1395	In this state it is simply some block of memory that is suitable for
1167	in an event loop. It can be moved around, freed, reused etc. at will.	1396	use in an event loop. It can be moved around, freed, reused etc. at
		1397	will - as long as you either keep the memory contents intact, or call
		1398	C<ev_TYPE_init> again.
1168		1399
1169	=item started/running/active	1400	=item started/running/active
1170		1401
1171	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1402	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1172	property of the event loop, and is actively waiting for events. While in	1403	property of the event loop, and is actively waiting for events. While in
…		…
1200	latter will clear any pending state the watcher might be in, regardless	1431	latter will clear any pending state the watcher might be in, regardless
1201	of whether it was active or not, so stopping a watcher explicitly before	1432	of whether it was active or not, so stopping a watcher explicitly before
1202	freeing it is often a good idea.	1433	freeing it is often a good idea.
1203		1434
1204	While stopped (and not pending) the watcher is essentially in the	1435	While stopped (and not pending) the watcher is essentially in the
1205	initialised state, that is it can be reused, moved, modified in any way	1436	initialised state, that is, it can be reused, moved, modified in any way
1206	you wish.	1437	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1438	it again).
1207		1439
1208	=back	1440	=back
1209
1210	=head2 GENERIC WATCHER FUNCTIONS
1211
1212	=over 4
1213
1214	=item C<ev_init> (ev_TYPE *watcher, callback)
1215
1216	This macro initialises the generic portion of a watcher. The contents
1217	of the watcher object can be arbitrary (so C<malloc> will do). Only
1218	the generic parts of the watcher are initialised, you I<need> to call
1219	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1220	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1221	which rolls both calls into one.
1222
1223	You can reinitialise a watcher at any time as long as it has been stopped
1224	(or never started) and there are no pending events outstanding.
1225
1226	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1227	int revents)>.
1228
1229	Example: Initialise an C<ev_io> watcher in two steps.
1230
1231	ev_io w;
1232	ev_init (&w, my_cb);
1233	ev_io_set (&w, STDIN_FILENO, EV_READ);
1234
1235	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1236
1237	This macro initialises the type-specific parts of a watcher. You need to
1238	call C<ev_init> at least once before you call this macro, but you can
1239	call C<ev_TYPE_set> any number of times. You must not, however, call this
1240	macro on a watcher that is active (it can be pending, however, which is a
1241	difference to the C<ev_init> macro).
1242
1243	Although some watcher types do not have type-specific arguments
1244	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1245
1246	See C<ev_init>, above, for an example.
1247
1248	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1249
1250	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1251	calls into a single call. This is the most convenient method to initialise
1252	a watcher. The same limitations apply, of course.
1253
1254	Example: Initialise and set an C<ev_io> watcher in one step.
1255
1256	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1257
1258	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1259
1260	Starts (activates) the given watcher. Only active watchers will receive
1261	events. If the watcher is already active nothing will happen.
1262
1263	Example: Start the C<ev_io> watcher that is being abused as example in this
1264	whole section.
1265
1266	ev_io_start (EV_DEFAULT_UC, &w);
1267
1268	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1269
1270	Stops the given watcher if active, and clears the pending status (whether
1271	the watcher was active or not).
1272
1273	It is possible that stopped watchers are pending - for example,
1274	non-repeating timers are being stopped when they become pending - but
1275	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1276	pending. If you want to free or reuse the memory used by the watcher it is
1277	therefore a good idea to always call its C<ev_TYPE_stop> function.
1278
1279	=item bool ev_is_active (ev_TYPE *watcher)
1280
1281	Returns a true value iff the watcher is active (i.e. it has been started
1282	and not yet been stopped). As long as a watcher is active you must not modify
1283	it.
1284
1285	=item bool ev_is_pending (ev_TYPE *watcher)
1286
1287	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1288	events but its callback has not yet been invoked). As long as a watcher
1289	is pending (but not active) you must not call an init function on it (but
1290	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1291	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1292	it).
1293
1294	=item callback ev_cb (ev_TYPE *watcher)
1295
1296	Returns the callback currently set on the watcher.
1297
1298	=item ev_cb_set (ev_TYPE *watcher, callback)
1299
1300	Change the callback. You can change the callback at virtually any time
1301	(modulo threads).
1302
1303	=item ev_set_priority (ev_TYPE *watcher, int priority)
1304
1305	=item int ev_priority (ev_TYPE *watcher)
1306
1307	Set and query the priority of the watcher. The priority is a small
1308	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1309	(default: C<-2>). Pending watchers with higher priority will be invoked
1310	before watchers with lower priority, but priority will not keep watchers
1311	from being executed (except for C<ev_idle> watchers).
1312
1313	If you need to suppress invocation when higher priority events are pending
1314	you need to look at C<ev_idle> watchers, which provide this functionality.
1315
1316	You I<must not> change the priority of a watcher as long as it is active or
1317	pending.
1318
1319	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1320	fine, as long as you do not mind that the priority value you query might
1321	or might not have been clamped to the valid range.
1322
1323	The default priority used by watchers when no priority has been set is
1324	always C<0>, which is supposed to not be too high and not be too low :).
1325
1326	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1327	priorities.
1328
1329	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1330
1331	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1332	C<loop> nor C<revents> need to be valid as long as the watcher callback
1333	can deal with that fact, as both are simply passed through to the
1334	callback.
1335
1336	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1337
1338	If the watcher is pending, this function clears its pending status and
1339	returns its C<revents> bitset (as if its callback was invoked). If the
1340	watcher isn't pending it does nothing and returns C<0>.
1341
1342	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1343	callback to be invoked, which can be accomplished with this function.
1344
1345	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1346
1347	Feeds the given event set into the event loop, as if the specified event
1348	had happened for the specified watcher (which must be a pointer to an
1349	initialised but not necessarily started event watcher). Obviously you must
1350	not free the watcher as long as it has pending events.
1351
1352	Stopping the watcher, letting libev invoke it, or calling
1353	C<ev_clear_pending> will clear the pending event, even if the watcher was
1354	not started in the first place.
1355
1356	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1357	functions that do not need a watcher.
1358
1359	=back
1360
1361
1362	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1363
1364	Each watcher has, by default, a member C<void *data> that you can change
1365	and read at any time: libev will completely ignore it. This can be used
1366	to associate arbitrary data with your watcher. If you need more data and
1367	don't want to allocate memory and store a pointer to it in that data
1368	member, you can also "subclass" the watcher type and provide your own
1369	data:
1370
1371	struct my_io
1372	{
1373	ev_io io;
1374	int otherfd;
1375	void *somedata;
1376	struct whatever *mostinteresting;
1377	};
1378
1379	...
1380	struct my_io w;
1381	ev_io_init (&w.io, my_cb, fd, EV_READ);
1382
1383	And since your callback will be called with a pointer to the watcher, you
1384	can cast it back to your own type:
1385
1386	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1387	{
1388	struct my_io *w = (struct my_io *)w_;
1389	...
1390	}
1391
1392	More interesting and less C-conformant ways of casting your callback type
1393	instead have been omitted.
1394
1395	Another common scenario is to use some data structure with multiple
1396	embedded watchers:
1397
1398	struct my_biggy
1399	{
1400	int some_data;
1401	ev_timer t1;
1402	ev_timer t2;
1403	}
1404
1405	In this case getting the pointer to C<my_biggy> is a bit more
1406	complicated: Either you store the address of your C<my_biggy> struct
1407	in the C<data> member of the watcher (for woozies), or you need to use
1408	some pointer arithmetic using C<offsetof> inside your watchers (for real
1409	programmers):
1410
1411	#include <stddef.h>
1412
1413	static void
1414	t1_cb (EV_P_ ev_timer *w, int revents)
1415	{
1416	struct my_biggy big = (struct my_biggy *)
1417	(((char *)w) - offsetof (struct my_biggy, t1));
1418	}
1419
1420	static void
1421	t2_cb (EV_P_ ev_timer *w, int revents)
1422	{
1423	struct my_biggy big = (struct my_biggy *)
1424	(((char *)w) - offsetof (struct my_biggy, t2));
1425	}
1426		1441
1427	=head2 WATCHER PRIORITY MODELS	1442	=head2 WATCHER PRIORITY MODELS
1428		1443
1429	Many event loops support I<watcher priorities>, which are usually small	1444	Many event loops support I<watcher priorities>, which are usually small
1430	integers that influence the ordering of event callback invocation	1445	integers that influence the ordering of event callback invocation
…		…
1557	In general you can register as many read and/or write event watchers per	1572	In general you can register as many read and/or write event watchers per
1558	fd as you want (as long as you don't confuse yourself). Setting all file	1573	fd as you want (as long as you don't confuse yourself). Setting all file
1559	descriptors to non-blocking mode is also usually a good idea (but not	1574	descriptors to non-blocking mode is also usually a good idea (but not
1560	required if you know what you are doing).	1575	required if you know what you are doing).
1561		1576
1562	If you cannot use non-blocking mode, then force the use of a
1563	known-to-be-good backend (at the time of this writing, this includes only
1564	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1565	descriptors for which non-blocking operation makes no sense (such as
1566	files) - libev doesn't guarantee any specific behaviour in that case.
1567
1568	Another thing you have to watch out for is that it is quite easy to	1577	Another thing you have to watch out for is that it is quite easy to
1569	receive "spurious" readiness notifications, that is your callback might	1578	receive "spurious" readiness notifications, that is, your callback might
1570	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1579	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1571	because there is no data. Not only are some backends known to create a	1580	because there is no data. It is very easy to get into this situation even
1572	lot of those (for example Solaris ports), it is very easy to get into	1581	with a relatively standard program structure. Thus it is best to always
1573	this situation even with a relatively standard program structure. Thus	1582	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1574	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1575	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1583	preferable to a program hanging until some data arrives.
1576		1584
1577	If you cannot run the fd in non-blocking mode (for example you should	1585	If you cannot run the fd in non-blocking mode (for example you should
1578	not play around with an Xlib connection), then you have to separately	1586	not play around with an Xlib connection), then you have to separately
1579	re-test whether a file descriptor is really ready with a known-to-be good	1587	re-test whether a file descriptor is really ready with a known-to-be good
1580	interface such as poll (fortunately in our Xlib example, Xlib already	1588	interface such as poll (fortunately in the case of Xlib, it already does
1581	does this on its own, so its quite safe to use). Some people additionally	1589	this on its own, so its quite safe to use). Some people additionally
1582	use C<SIGALRM> and an interval timer, just to be sure you won't block	1590	use C<SIGALRM> and an interval timer, just to be sure you won't block
1583	indefinitely.	1591	indefinitely.
1584		1592
1585	But really, best use non-blocking mode.	1593	But really, best use non-blocking mode.
1586		1594
…		…
1614		1622
1615	There is no workaround possible except not registering events	1623	There is no workaround possible except not registering events
1616	for potentially C<dup ()>'ed file descriptors, or to resort to	1624	for potentially C<dup ()>'ed file descriptors, or to resort to
1617	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1618		1626
		1627	=head3 The special problem of files
		1628
		1629	Many people try to use C<select> (or libev) on file descriptors
		1630	representing files, and expect it to become ready when their program
		1631	doesn't block on disk accesses (which can take a long time on their own).
		1632
		1633	However, this cannot ever work in the "expected" way - you get a readiness
		1634	notification as soon as the kernel knows whether and how much data is
		1635	there, and in the case of open files, that's always the case, so you
		1636	always get a readiness notification instantly, and your read (or possibly
		1637	write) will still block on the disk I/O.
		1638
		1639	Another way to view it is that in the case of sockets, pipes, character
		1640	devices and so on, there is another party (the sender) that delivers data
		1641	on its own, but in the case of files, there is no such thing: the disk
		1642	will not send data on its own, simply because it doesn't know what you
		1643	wish to read - you would first have to request some data.
		1644
		1645	Since files are typically not-so-well supported by advanced notification
		1646	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1647	to files, even though you should not use it. The reason for this is
		1648	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1649	usually a tty, often a pipe, but also sometimes files or special devices
		1650	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1651	F</dev/urandom>), and even though the file might better be served with
		1652	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1653	it "just works" instead of freezing.
		1654
		1655	So avoid file descriptors pointing to files when you know it (e.g. use
		1656	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1657	when you rarely read from a file instead of from a socket, and want to
		1658	reuse the same code path.
		1659
1619	=head3 The special problem of fork	1660	=head3 The special problem of fork
1620		1661
1621	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1662	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1622	useless behaviour. Libev fully supports fork, but needs to be told about	1663	useless behaviour. Libev fully supports fork, but needs to be told about
1623	it in the child.	1664	it in the child if you want to continue to use it in the child.
1624		1665
1625	To support fork in your programs, you either have to call	1666	To support fork in your child processes, you have to call C<ev_loop_fork
1626	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1667	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1627	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1668	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1628	C<EVBACKEND_POLL>.
1629		1669
1630	=head3 The special problem of SIGPIPE	1670	=head3 The special problem of SIGPIPE
1631		1671
1632	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1672	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1633	when writing to a pipe whose other end has been closed, your program gets	1673	when writing to a pipe whose other end has been closed, your program gets
…		…
1731	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1771	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1732	monotonic clock option helps a lot here).	1772	monotonic clock option helps a lot here).
1733		1773
1734	The callback is guaranteed to be invoked only I<after> its timeout has	1774	The callback is guaranteed to be invoked only I<after> its timeout has
1735	passed (not I<at>, so on systems with very low-resolution clocks this	1775	passed (not I<at>, so on systems with very low-resolution clocks this
1736	might introduce a small delay). If multiple timers become ready during the	1776	might introduce a small delay, see "the special problem of being too
		1777	early", below). If multiple timers become ready during the same loop
1737	same loop iteration then the ones with earlier time-out values are invoked	1778	iteration then the ones with earlier time-out values are invoked before
1738	before ones of the same priority with later time-out values (but this is	1779	ones of the same priority with later time-out values (but this is no
1739	no longer true when a callback calls C<ev_run> recursively).	1780	longer true when a callback calls C<ev_run> recursively).
1740		1781
1741	=head3 Be smart about timeouts	1782	=head3 Be smart about timeouts
1742		1783
1743	Many real-world problems involve some kind of timeout, usually for error	1784	Many real-world problems involve some kind of timeout, usually for error
1744	recovery. A typical example is an HTTP request - if the other side hangs,	1785	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1911	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1952	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1912	rather complicated, but extremely efficient, something that really pays	1953	rather complicated, but extremely efficient, something that really pays
1913	off after the first million or so of active timers, i.e. it's usually	1954	off after the first million or so of active timers, i.e. it's usually
1914	overkill :)	1955	overkill :)
1915		1956
		1957	=head3 The special problem of being too early
		1958
		1959	If you ask a timer to call your callback after three seconds, then
		1960	you expect it to be invoked after three seconds - but of course, this
		1961	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1962	guaranteed to any precision by libev - imagine somebody suspending the
		1963	process with a STOP signal for a few hours for example.
		1964
		1965	So, libev tries to invoke your callback as soon as possible I<after> the
		1966	delay has occurred, but cannot guarantee this.
		1967
		1968	A less obvious failure mode is calling your callback too early: many event
		1969	loops compare timestamps with a "elapsed delay >= requested delay", but
		1970	this can cause your callback to be invoked much earlier than you would
		1971	expect.
		1972
		1973	To see why, imagine a system with a clock that only offers full second
		1974	resolution (think windows if you can't come up with a broken enough OS
		1975	yourself). If you schedule a one-second timer at the time 500.9, then the
		1976	event loop will schedule your timeout to elapse at a system time of 500
		1977	(500.9 truncated to the resolution) + 1, or 501.
		1978
		1979	If an event library looks at the timeout 0.1s later, it will see "501 >=
		1980	501" and invoke the callback 0.1s after it was started, even though a
		1981	one-second delay was requested - this is being "too early", despite best
		1982	intentions.
		1983
		1984	This is the reason why libev will never invoke the callback if the elapsed
		1985	delay equals the requested delay, but only when the elapsed delay is
		1986	larger than the requested delay. In the example above, libev would only invoke
		1987	the callback at system time 502, or 1.1s after the timer was started.
		1988
		1989	So, while libev cannot guarantee that your callback will be invoked
		1990	exactly when requested, it I<can> and I<does> guarantee that the requested
		1991	delay has actually elapsed, or in other words, it always errs on the "too
		1992	late" side of things.
		1993
1916	=head3 The special problem of time updates	1994	=head3 The special problem of time updates
1917		1995
1918	Establishing the current time is a costly operation (it usually takes at	1996	Establishing the current time is a costly operation (it usually takes
1919	least two system calls): EV therefore updates its idea of the current	1997	at least one system call): EV therefore updates its idea of the current
1920	time only before and after C<ev_run> collects new events, which causes a	1998	time only before and after C<ev_run> collects new events, which causes a
1921	growing difference between C<ev_now ()> and C<ev_time ()> when handling	1999	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1922	lots of events in one iteration.	2000	lots of events in one iteration.
1923		2001
1924	The relative timeouts are calculated relative to the C<ev_now ()>	2002	The relative timeouts are calculated relative to the C<ev_now ()>
…		…
1930	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2008	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1931		2009
1932	If the event loop is suspended for a long time, you can also force an	2010	If the event loop is suspended for a long time, you can also force an
1933	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2011	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1934	()>.	2012	()>.
		2013
		2014	=head3 The special problem of unsynchronised clocks
		2015
		2016	Modern systems have a variety of clocks - libev itself uses the normal
		2017	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2018	jumps).
		2019
		2020	Neither of these clocks is synchronised with each other or any other clock
		2021	on the system, so C<ev_time ()> might return a considerably different time
		2022	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2023	a call to C<gettimeofday> might return a second count that is one higher
		2024	than a directly following call to C<time>.
		2025
		2026	The moral of this is to only compare libev-related timestamps with
		2027	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2028	a second or so.
		2029
		2030	One more problem arises due to this lack of synchronisation: if libev uses
		2031	the system monotonic clock and you compare timestamps from C<ev_time>
		2032	or C<ev_now> from when you started your timer and when your callback is
		2033	invoked, you will find that sometimes the callback is a bit "early".
		2034
		2035	This is because C<ev_timer>s work in real time, not wall clock time, so
		2036	libev makes sure your callback is not invoked before the delay happened,
		2037	I<measured according to the real time>, not the system clock.
		2038
		2039	If your timeouts are based on a physical timescale (e.g. "time out this
		2040	connection after 100 seconds") then this shouldn't bother you as it is
		2041	exactly the right behaviour.
		2042
		2043	If you want to compare wall clock/system timestamps to your timers, then
		2044	you need to use C<ev_periodic>s, as these are based on the wall clock
		2045	time, where your comparisons will always generate correct results.
1935		2046
1936	=head3 The special problems of suspended animation	2047	=head3 The special problems of suspended animation
1937		2048
1938	When you leave the server world it is quite customary to hit machines that	2049	When you leave the server world it is quite customary to hit machines that
1939	can suspend/hibernate - what happens to the clocks during such a suspend?	2050	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1983	keep up with the timer (because it takes longer than those 10 seconds to	2094	keep up with the timer (because it takes longer than those 10 seconds to
1984	do stuff) the timer will not fire more than once per event loop iteration.	2095	do stuff) the timer will not fire more than once per event loop iteration.
1985		2096
1986	=item ev_timer_again (loop, ev_timer *)	2097	=item ev_timer_again (loop, ev_timer *)
1987		2098
1988	This will act as if the timer timed out and restart it again if it is	2099	This will act as if the timer timed out and restarts it again if it is
1989	repeating. The exact semantics are:	2100	repeating. The exact semantics are:
1990		2101
1991	If the timer is pending, its pending status is cleared.	2102	If the timer is pending, its pending status is cleared.
1992		2103
1993	If the timer is started but non-repeating, stop it (as if it timed out).	2104	If the timer is started but non-repeating, stop it (as if it timed out).
…		…
2123		2234
2124	Another way to think about it (for the mathematically inclined) is that	2235	Another way to think about it (for the mathematically inclined) is that
2125	C<ev_periodic> will try to run the callback in this mode at the next possible	2236	C<ev_periodic> will try to run the callback in this mode at the next possible
2126	time where C<time = offset (mod interval)>, regardless of any time jumps.	2237	time where C<time = offset (mod interval)>, regardless of any time jumps.
2127		2238
2128	For numerical stability it is preferable that the C<offset> value is near	2239	The C<interval> I<MUST> be positive, and for numerical stability, the
2129	C<ev_now ()> (the current time), but there is no range requirement for	2240	interval value should be higher than C<1/8192> (which is around 100
2130	this value, and in fact is often specified as zero.	2241	microseconds) and C<offset> should be higher than C<0> and should have
		2242	at most a similar magnitude as the current time (say, within a factor of
		2243	ten). Typical values for offset are, in fact, C<0> or something between
		2244	C<0> and C<interval>, which is also the recommended range.
2131		2245
2132	Note also that there is an upper limit to how often a timer can fire (CPU	2246	Note also that there is an upper limit to how often a timer can fire (CPU
2133	speed for example), so if C<interval> is very small then timing stability	2247	speed for example), so if C<interval> is very small then timing stability
2134	will of course deteriorate. Libev itself tries to be exact to be about one	2248	will of course deteriorate. Libev itself tries to be exact to be about one
2135	millisecond (if the OS supports it and the machine is fast enough).	2249	millisecond (if the OS supports it and the machine is fast enough).
…		…
2249		2363
2250	=head2 C<ev_signal> - signal me when a signal gets signalled!	2364	=head2 C<ev_signal> - signal me when a signal gets signalled!
2251		2365
2252	Signal watchers will trigger an event when the process receives a specific	2366	Signal watchers will trigger an event when the process receives a specific
2253	signal one or more times. Even though signals are very asynchronous, libev	2367	signal one or more times. Even though signals are very asynchronous, libev
2254	will try it's best to deliver signals synchronously, i.e. as part of the	2368	will try its best to deliver signals synchronously, i.e. as part of the
2255	normal event processing, like any other event.	2369	normal event processing, like any other event.
2256		2370
2257	If you want signals to be delivered truly asynchronously, just use	2371	If you want signals to be delivered truly asynchronously, just use
2258	C<sigaction> as you would do without libev and forget about sharing	2372	C<sigaction> as you would do without libev and forget about sharing
2259	the signal. You can even use C<ev_async> from a signal handler to	2373	the signal. You can even use C<ev_async> from a signal handler to
…		…
2278	=head3 The special problem of inheritance over fork/execve/pthread_create	2392	=head3 The special problem of inheritance over fork/execve/pthread_create
2279		2393
2280	Both the signal mask (C<sigprocmask>) and the signal disposition	2394	Both the signal mask (C<sigprocmask>) and the signal disposition
2281	(C<sigaction>) are unspecified after starting a signal watcher (and after	2395	(C<sigaction>) are unspecified after starting a signal watcher (and after
2282	stopping it again), that is, libev might or might not block the signal,	2396	stopping it again), that is, libev might or might not block the signal,
2283	and might or might not set or restore the installed signal handler.	2397	and might or might not set or restore the installed signal handler (but
		2398	see C<EVFLAG_NOSIGMASK>).
2284		2399
2285	While this does not matter for the signal disposition (libev never	2400	While this does not matter for the signal disposition (libev never
2286	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2401	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2287	C<execve>), this matters for the signal mask: many programs do not expect	2402	C<execve>), this matters for the signal mask: many programs do not expect
2288	certain signals to be blocked.	2403	certain signals to be blocked.
…		…
2301	I<has> to modify the signal mask, at least temporarily.	2416	I<has> to modify the signal mask, at least temporarily.
2302		2417
2303	So I can't stress this enough: I<If you do not reset your signal mask when	2418	So I can't stress this enough: I<If you do not reset your signal mask when
2304	you expect it to be empty, you have a race condition in your code>. This	2419	you expect it to be empty, you have a race condition in your code>. This
2305	is not a libev-specific thing, this is true for most event libraries.	2420	is not a libev-specific thing, this is true for most event libraries.
		2421
		2422	=head3 The special problem of threads signal handling
		2423
		2424	POSIX threads has problematic signal handling semantics, specifically,
		2425	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2426	threads in a process block signals, which is hard to achieve.
		2427
		2428	When you want to use sigwait (or mix libev signal handling with your own
		2429	for the same signals), you can tackle this problem by globally blocking
		2430	all signals before creating any threads (or creating them with a fully set
		2431	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2432	loops. Then designate one thread as "signal receiver thread" which handles
		2433	these signals. You can pass on any signals that libev might be interested
		2434	in by calling C<ev_feed_signal>.
2306		2435
2307	=head3 Watcher-Specific Functions and Data Members	2436	=head3 Watcher-Specific Functions and Data Members
2308		2437
2309	=over 4	2438	=over 4
2310		2439
…		…
3098		3227
3099	=item ev_fork_init (ev_fork *, callback)	3228	=item ev_fork_init (ev_fork *, callback)
3100		3229
3101	Initialises and configures the fork watcher - it has no parameters of any	3230	Initialises and configures the fork watcher - it has no parameters of any
3102	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3231	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3103	believe me.	3232	really.
3104		3233
3105	=back	3234	=back
3106		3235
3107		3236
3108	=head2 C<ev_cleanup> - even the best things end	3237	=head2 C<ev_cleanup> - even the best things end
3109		3238
3110	Cleanup watchers are called just before the event loop they are registered	3239	Cleanup watchers are called just before the event loop is being destroyed
3111	with is being destroyed.	3240	by a call to C<ev_loop_destroy>.
3112		3241
3113	While there is no guarantee that the event loop gets destroyed, cleanup	3242	While there is no guarantee that the event loop gets destroyed, cleanup
3114	watchers provide a convenient method to install cleanup hooks for your	3243	watchers provide a convenient method to install cleanup hooks for your
3115	program, worker threads and so on - you just to make sure to destroy the	3244	program, worker threads and so on - you just to make sure to destroy the
3116	loop when you want them to be invoked.	3245	loop when you want them to be invoked.
…		…
3126		3255
3127	=item ev_cleanup_init (ev_cleanup *, callback)	3256	=item ev_cleanup_init (ev_cleanup *, callback)
3128		3257
3129	Initialises and configures the cleanup watcher - it has no parameters of	3258	Initialises and configures the cleanup watcher - it has no parameters of
3130	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly	3259	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
3131	pointless, believe me.	3260	pointless, I assure you.
3132		3261
3133	=back	3262	=back
3134		3263
3135	Example: Register an atexit handler to destroy the default loop, so any	3264	Example: Register an atexit handler to destroy the default loop, so any
3136	cleanup functions are called.	3265	cleanup functions are called.
…		…
3145	atexit (program_exits);	3274	atexit (program_exits);
3146		3275
3147		3276
3148	=head2 C<ev_async> - how to wake up an event loop	3277	=head2 C<ev_async> - how to wake up an event loop
3149		3278
3150	In general, you cannot use an C<ev_run> from multiple threads or other	3279	In general, you cannot use an C<ev_loop> from multiple threads or other
3151	asynchronous sources such as signal handlers (as opposed to multiple event	3280	asynchronous sources such as signal handlers (as opposed to multiple event
3152	loops - those are of course safe to use in different threads).	3281	loops - those are of course safe to use in different threads).
3153		3282
3154	Sometimes, however, you need to wake up an event loop you do not control,	3283	Sometimes, however, you need to wake up an event loop you do not control,
3155	for example because it belongs to another thread. This is what C<ev_async>	3284	for example because it belongs to another thread. This is what C<ev_async>
…		…
3157	it by calling C<ev_async_send>, which is thread- and signal safe.	3286	it by calling C<ev_async_send>, which is thread- and signal safe.
3158		3287
3159	This functionality is very similar to C<ev_signal> watchers, as signals,	3288	This functionality is very similar to C<ev_signal> watchers, as signals,
3160	too, are asynchronous in nature, and signals, too, will be compressed	3289	too, are asynchronous in nature, and signals, too, will be compressed
3161	(i.e. the number of callback invocations may be less than the number of	3290	(i.e. the number of callback invocations may be less than the number of
3162	C<ev_async_sent> calls).	3291	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
3163		3292	of "global async watchers" by using a watcher on an otherwise unused
3164	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3293	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3165	just the default loop.	3294	even without knowing which loop owns the signal.
3166		3295
3167	=head3 Queueing	3296	=head3 Queueing
3168		3297
3169	C<ev_async> does not support queueing of data in any way. The reason	3298	C<ev_async> does not support queueing of data in any way. The reason
3170	is that the author does not know of a simple (or any) algorithm for a	3299	is that the author does not know of a simple (or any) algorithm for a
…		…
3262	trust me.	3391	trust me.
3263		3392
3264	=item ev_async_send (loop, ev_async *)	3393	=item ev_async_send (loop, ev_async *)
3265		3394
3266	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3395	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3267	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3396	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3397	returns.
		3398
3268	C<ev_feed_event>, this call is safe to do from other threads, signal or	3399	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3269	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3400	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3270	section below on what exactly this means).	3401	embedding section below on what exactly this means).
3271		3402
3272	Note that, as with other watchers in libev, multiple events might get	3403	Note that, as with other watchers in libev, multiple events might get
3273	compressed into a single callback invocation (another way to look at this	3404	compressed into a single callback invocation (another way to look at
3274	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3405	this is that C<ev_async> watchers are level-triggered: they are set on
3275	reset when the event loop detects that).	3406	C<ev_async_send>, reset when the event loop detects that).
3276		3407
3277	This call incurs the overhead of a system call only once per event loop	3408	This call incurs the overhead of at most one extra system call per event
3278	iteration, so while the overhead might be noticeable, it doesn't apply to	3409	loop iteration, if the event loop is blocked, and no syscall at all if
3279	repeated calls to C<ev_async_send> for the same event loop.	3410	the event loop (or your program) is processing events. That means that
		3411	repeated calls are basically free (there is no need to avoid calls for
		3412	performance reasons) and that the overhead becomes smaller (typically
		3413	zero) under load.
3280		3414
3281	=item bool = ev_async_pending (ev_async *)	3415	=item bool = ev_async_pending (ev_async *)
3282		3416
3283	Returns a non-zero value when C<ev_async_send> has been called on the	3417	Returns a non-zero value when C<ev_async_send> has been called on the
3284	watcher but the event has not yet been processed (or even noted) by the	3418	watcher but the event has not yet been processed (or even noted) by the
…		…
3339	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3473	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3340		3474
3341	=item ev_feed_fd_event (loop, int fd, int revents)	3475	=item ev_feed_fd_event (loop, int fd, int revents)
3342		3476
3343	Feed an event on the given fd, as if a file descriptor backend detected	3477	Feed an event on the given fd, as if a file descriptor backend detected
3344	the given events it.	3478	the given events.
3345		3479
3346	=item ev_feed_signal_event (loop, int signum)	3480	=item ev_feed_signal_event (loop, int signum)
3347		3481
3348	Feed an event as if the given signal occurred (C<loop> must be the default	3482	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3349	loop!).	3483	which is async-safe.
3350		3484
3351	=back	3485	=back
		3486
		3487
		3488	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3489
		3490	This section explains some common idioms that are not immediately
		3491	obvious. Note that examples are sprinkled over the whole manual, and this
		3492	section only contains stuff that wouldn't fit anywhere else.
		3493
		3494	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3495
		3496	Each watcher has, by default, a C<void *data> member that you can read
		3497	or modify at any time: libev will completely ignore it. This can be used
		3498	to associate arbitrary data with your watcher. If you need more data and
		3499	don't want to allocate memory separately and store a pointer to it in that
		3500	data member, you can also "subclass" the watcher type and provide your own
		3501	data:
		3502
		3503	struct my_io
		3504	{
		3505	ev_io io;
		3506	int otherfd;
		3507	void *somedata;
		3508	struct whatever *mostinteresting;
		3509	};
		3510
		3511	...
		3512	struct my_io w;
		3513	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3514
		3515	And since your callback will be called with a pointer to the watcher, you
		3516	can cast it back to your own type:
		3517
		3518	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3519	{
		3520	struct my_io *w = (struct my_io *)w_;
		3521	...
		3522	}
		3523
		3524	More interesting and less C-conformant ways of casting your callback
		3525	function type instead have been omitted.
		3526
		3527	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3528
		3529	Another common scenario is to use some data structure with multiple
		3530	embedded watchers, in effect creating your own watcher that combines
		3531	multiple libev event sources into one "super-watcher":
		3532
		3533	struct my_biggy
		3534	{
		3535	int some_data;
		3536	ev_timer t1;
		3537	ev_timer t2;
		3538	}
		3539
		3540	In this case getting the pointer to C<my_biggy> is a bit more
		3541	complicated: Either you store the address of your C<my_biggy> struct in
		3542	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3543	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3544	real programmers):
		3545
		3546	#include <stddef.h>
		3547
		3548	static void
		3549	t1_cb (EV_P_ ev_timer *w, int revents)
		3550	{
		3551	struct my_biggy big = (struct my_biggy *)
		3552	(((char *)w) - offsetof (struct my_biggy, t1));
		3553	}
		3554
		3555	static void
		3556	t2_cb (EV_P_ ev_timer *w, int revents)
		3557	{
		3558	struct my_biggy big = (struct my_biggy *)
		3559	(((char *)w) - offsetof (struct my_biggy, t2));
		3560	}
		3561
		3562	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3563
		3564	Often (especially in GUI toolkits) there are places where you have
		3565	I<modal> interaction, which is most easily implemented by recursively
		3566	invoking C<ev_run>.
		3567
		3568	This brings the problem of exiting - a callback might want to finish the
		3569	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3570	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3571	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3572	other combination: In these cases, C<ev_break> will not work alone.
		3573
		3574	The solution is to maintain "break this loop" variable for each C<ev_run>
		3575	invocation, and use a loop around C<ev_run> until the condition is
		3576	triggered, using C<EVRUN_ONCE>:
		3577
		3578	// main loop
		3579	int exit_main_loop = 0;
		3580
		3581	while (!exit_main_loop)
		3582	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3583
		3584	// in a model watcher
		3585	int exit_nested_loop = 0;
		3586
		3587	while (!exit_nested_loop)
		3588	ev_run (EV_A_ EVRUN_ONCE);
		3589
		3590	To exit from any of these loops, just set the corresponding exit variable:
		3591
		3592	// exit modal loop
		3593	exit_nested_loop = 1;
		3594
		3595	// exit main program, after modal loop is finished
		3596	exit_main_loop = 1;
		3597
		3598	// exit both
		3599	exit_main_loop = exit_nested_loop = 1;
		3600
		3601	=head2 THREAD LOCKING EXAMPLE
		3602
		3603	Here is a fictitious example of how to run an event loop in a different
		3604	thread from where callbacks are being invoked and watchers are
		3605	created/added/removed.
		3606
		3607	For a real-world example, see the C<EV::Loop::Async> perl module,
		3608	which uses exactly this technique (which is suited for many high-level
		3609	languages).
		3610
		3611	The example uses a pthread mutex to protect the loop data, a condition
		3612	variable to wait for callback invocations, an async watcher to notify the
		3613	event loop thread and an unspecified mechanism to wake up the main thread.
		3614
		3615	First, you need to associate some data with the event loop:
		3616
		3617	typedef struct {
		3618	mutex_t lock; /* global loop lock */
		3619	ev_async async_w;
		3620	thread_t tid;
		3621	cond_t invoke_cv;
		3622	} userdata;
		3623
		3624	void prepare_loop (EV_P)
		3625	{
		3626	// for simplicity, we use a static userdata struct.
		3627	static userdata u;
		3628
		3629	ev_async_init (&u->async_w, async_cb);
		3630	ev_async_start (EV_A_ &u->async_w);
		3631
		3632	pthread_mutex_init (&u->lock, 0);
		3633	pthread_cond_init (&u->invoke_cv, 0);
		3634
		3635	// now associate this with the loop
		3636	ev_set_userdata (EV_A_ u);
		3637	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3638	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3639
		3640	// then create the thread running ev_run
		3641	pthread_create (&u->tid, 0, l_run, EV_A);
		3642	}
		3643
		3644	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3645	solely to wake up the event loop so it takes notice of any new watchers
		3646	that might have been added:
		3647
		3648	static void
		3649	async_cb (EV_P_ ev_async *w, int revents)
		3650	{
		3651	// just used for the side effects
		3652	}
		3653
		3654	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3655	protecting the loop data, respectively.
		3656
		3657	static void
		3658	l_release (EV_P)
		3659	{
		3660	userdata *u = ev_userdata (EV_A);
		3661	pthread_mutex_unlock (&u->lock);
		3662	}
		3663
		3664	static void
		3665	l_acquire (EV_P)
		3666	{
		3667	userdata *u = ev_userdata (EV_A);
		3668	pthread_mutex_lock (&u->lock);
		3669	}
		3670
		3671	The event loop thread first acquires the mutex, and then jumps straight
		3672	into C<ev_run>:
		3673
		3674	void *
		3675	l_run (void *thr_arg)
		3676	{
		3677	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3678
		3679	l_acquire (EV_A);
		3680	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3681	ev_run (EV_A_ 0);
		3682	l_release (EV_A);
		3683
		3684	return 0;
		3685	}
		3686
		3687	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3688	signal the main thread via some unspecified mechanism (signals? pipe
		3689	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3690	have been called (in a while loop because a) spurious wakeups are possible
		3691	and b) skipping inter-thread-communication when there are no pending
		3692	watchers is very beneficial):
		3693
		3694	static void
		3695	l_invoke (EV_P)
		3696	{
		3697	userdata *u = ev_userdata (EV_A);
		3698
		3699	while (ev_pending_count (EV_A))
		3700	{
		3701	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3702	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3703	}
		3704	}
		3705
		3706	Now, whenever the main thread gets told to invoke pending watchers, it
		3707	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3708	thread to continue:
		3709
		3710	static void
		3711	real_invoke_pending (EV_P)
		3712	{
		3713	userdata *u = ev_userdata (EV_A);
		3714
		3715	pthread_mutex_lock (&u->lock);
		3716	ev_invoke_pending (EV_A);
		3717	pthread_cond_signal (&u->invoke_cv);
		3718	pthread_mutex_unlock (&u->lock);
		3719	}
		3720
		3721	Whenever you want to start/stop a watcher or do other modifications to an
		3722	event loop, you will now have to lock:
		3723
		3724	ev_timer timeout_watcher;
		3725	userdata *u = ev_userdata (EV_A);
		3726
		3727	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3728
		3729	pthread_mutex_lock (&u->lock);
		3730	ev_timer_start (EV_A_ &timeout_watcher);
		3731	ev_async_send (EV_A_ &u->async_w);
		3732	pthread_mutex_unlock (&u->lock);
		3733
		3734	Note that sending the C<ev_async> watcher is required because otherwise
		3735	an event loop currently blocking in the kernel will have no knowledge
		3736	about the newly added timer. By waking up the loop it will pick up any new
		3737	watchers in the next event loop iteration.
		3738
		3739	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3740
		3741	While the overhead of a callback that e.g. schedules a thread is small, it
		3742	is still an overhead. If you embed libev, and your main usage is with some
		3743	kind of threads or coroutines, you might want to customise libev so that
		3744	doesn't need callbacks anymore.
		3745
		3746	Imagine you have coroutines that you can switch to using a function
		3747	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3748	and that due to some magic, the currently active coroutine is stored in a
		3749	global called C<current_coro>. Then you can build your own "wait for libev
		3750	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3751	the differing C<;> conventions):
		3752
		3753	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3754	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3755
		3756	That means instead of having a C callback function, you store the
		3757	coroutine to switch to in each watcher, and instead of having libev call
		3758	your callback, you instead have it switch to that coroutine.
		3759
		3760	A coroutine might now wait for an event with a function called
		3761	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3762	matter when, or whether the watcher is active or not when this function is
		3763	called):
		3764
		3765	void
		3766	wait_for_event (ev_watcher *w)
		3767	{
		3768	ev_cb_set (w) = current_coro;
		3769	switch_to (libev_coro);
		3770	}
		3771
		3772	That basically suspends the coroutine inside C<wait_for_event> and
		3773	continues the libev coroutine, which, when appropriate, switches back to
		3774	this or any other coroutine. I am sure if you sue this your own :)
		3775
		3776	You can do similar tricks if you have, say, threads with an event queue -
		3777	instead of storing a coroutine, you store the queue object and instead of
		3778	switching to a coroutine, you push the watcher onto the queue and notify
		3779	any waiters.
		3780
		3781	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3782	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3783
		3784	// my_ev.h
		3785	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3786	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3787	#include "../libev/ev.h"
		3788
		3789	// my_ev.c
		3790	#define EV_H "my_ev.h"
		3791	#include "../libev/ev.c"
		3792
		3793	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3794	F<my_ev.c> into your project. When properly specifying include paths, you
		3795	can even use F<ev.h> as header file name directly.
3352		3796
3353		3797
3354	=head1 LIBEVENT EMULATION	3798	=head1 LIBEVENT EMULATION
3355		3799
3356	Libev offers a compatibility emulation layer for libevent. It cannot	3800	Libev offers a compatibility emulation layer for libevent. It cannot
3357	emulate the internals of libevent, so here are some usage hints:	3801	emulate the internals of libevent, so here are some usage hints:
3358		3802
3359	=over 4	3803	=over 4
		3804
		3805	=item * Only the libevent-1.4.1-beta API is being emulated.
		3806
		3807	This was the newest libevent version available when libev was implemented,
		3808	and is still mostly unchanged in 2010.
3360		3809
3361	=item * Use it by including <event.h>, as usual.	3810	=item * Use it by including <event.h>, as usual.
3362		3811
3363	=item * The following members are fully supported: ev_base, ev_callback,	3812	=item * The following members are fully supported: ev_base, ev_callback,
3364	ev_arg, ev_fd, ev_res, ev_events.	3813	ev_arg, ev_fd, ev_res, ev_events.
…		…
3370	=item * Priorities are not currently supported. Initialising priorities	3819	=item * Priorities are not currently supported. Initialising priorities
3371	will fail and all watchers will have the same priority, even though there	3820	will fail and all watchers will have the same priority, even though there
3372	is an ev_pri field.	3821	is an ev_pri field.
3373		3822
3374	=item * In libevent, the last base created gets the signals, in libev, the	3823	=item * In libevent, the last base created gets the signals, in libev, the
3375	first base created (== the default loop) gets the signals.	3824	base that registered the signal gets the signals.
3376		3825
3377	=item * Other members are not supported.	3826	=item * Other members are not supported.
3378		3827
3379	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3828	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3380	to use the libev header file and library.	3829	to use the libev header file and library.
…		…
3399	Care has been taken to keep the overhead low. The only data member the C++	3848	Care has been taken to keep the overhead low. The only data member the C++
3400	classes add (compared to plain C-style watchers) is the event loop pointer	3849	classes add (compared to plain C-style watchers) is the event loop pointer
3401	that the watcher is associated with (or no additional members at all if	3850	that the watcher is associated with (or no additional members at all if
3402	you disable C<EV_MULTIPLICITY> when embedding libev).	3851	you disable C<EV_MULTIPLICITY> when embedding libev).
3403		3852
3404	Currently, functions, and static and non-static member functions can be	3853	Currently, functions, static and non-static member functions and classes
3405	used as callbacks. Other types should be easy to add as long as they only	3854	with C<operator ()> can be used as callbacks. Other types should be easy
3406	need one additional pointer for context. If you need support for other	3855	to add as long as they only need one additional pointer for context. If
3407	types of functors please contact the author (preferably after implementing	3856	you need support for other types of functors please contact the author
3408	it).	3857	(preferably after implementing it).
3409		3858
3410	Here is a list of things available in the C<ev> namespace:	3859	Here is a list of things available in the C<ev> namespace:
3411		3860
3412	=over 4	3861	=over 4
3413		3862
…		…
3566	watchers in the constructor.	4015	watchers in the constructor.
3567		4016
3568	class myclass	4017	class myclass
3569	{	4018	{
3570	ev::io io ; void io_cb (ev::io &w, int revents);	4019	ev::io io ; void io_cb (ev::io &w, int revents);
3571	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4020	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3572	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4021	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3573		4022
3574	myclass (int fd)	4023	myclass (int fd)
3575	{	4024	{
3576	io .set <myclass, &myclass::io_cb > (this);	4025	io .set <myclass, &myclass::io_cb > (this);
…		…
3627	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4076	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3628		4077
3629	=item D	4078	=item D
3630		4079
3631	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4080	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3632	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4081	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3633		4082
3634	=item Ocaml	4083	=item Ocaml
3635		4084
3636	Erkki Seppala has written Ocaml bindings for libev, to be found at	4085	Erkki Seppala has written Ocaml bindings for libev, to be found at
3637	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4086	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3685	suitable for use with C<EV_A>.	4134	suitable for use with C<EV_A>.
3686		4135
3687	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4136	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3688		4137
3689	Similar to the other two macros, this gives you the value of the default	4138	Similar to the other two macros, this gives you the value of the default
3690	loop, if multiple loops are supported ("ev loop default").	4139	loop, if multiple loops are supported ("ev loop default"). The default loop
		4140	will be initialised if it isn't already initialised.
		4141
		4142	For non-multiplicity builds, these macros do nothing, so you always have
		4143	to initialise the loop somewhere.
3691		4144
3692	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4145	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3693		4146
3694	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4147	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3695	default loop has been initialised (C<UC> == unchecked). Their behaviour	4148	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3840	supported). It will also not define any of the structs usually found in	4293	supported). It will also not define any of the structs usually found in
3841	F<event.h> that are not directly supported by the libev core alone.	4294	F<event.h> that are not directly supported by the libev core alone.
3842		4295
3843	In standalone mode, libev will still try to automatically deduce the	4296	In standalone mode, libev will still try to automatically deduce the
3844	configuration, but has to be more conservative.	4297	configuration, but has to be more conservative.
		4298
		4299	=item EV_USE_FLOOR
		4300
		4301	If defined to be C<1>, libev will use the C<floor ()> function for its
		4302	periodic reschedule calculations, otherwise libev will fall back on a
		4303	portable (slower) implementation. If you enable this, you usually have to
		4304	link against libm or something equivalent. Enabling this when the C<floor>
		4305	function is not available will fail, so the safe default is to not enable
		4306	this.
3845		4307
3846	=item EV_USE_MONOTONIC	4308	=item EV_USE_MONOTONIC
3847		4309
3848	If defined to be C<1>, libev will try to detect the availability of the	4310	If defined to be C<1>, libev will try to detect the availability of the
3849	monotonic clock option at both compile time and runtime. Otherwise no	4311	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3982	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4444	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3983		4445
3984	=item EV_ATOMIC_T	4446	=item EV_ATOMIC_T
3985		4447
3986	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4448	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3987	access is atomic with respect to other threads or signal contexts. No such	4449	access is atomic and serialised with respect to other threads or signal
3988	type is easily found in the C language, so you can provide your own type	4450	contexts. No such type is easily found in the C language, so you can
3989	that you know is safe for your purposes. It is used both for signal handler "locking"	4451	provide your own type that you know is safe for your purposes. It is used
3990	as well as for signal and thread safety in C<ev_async> watchers.	4452	both for signal handler "locking" as well as for signal and thread safety
		4453	in C<ev_async> watchers.
3991		4454
3992	In the absence of this define, libev will use C<sig_atomic_t volatile>	4455	In the absence of this define, libev will use C<sig_atomic_t volatile>
3993	(from F<signal.h>), which is usually good enough on most platforms.	4456	(from F<signal.h>), which is usually good enough on most platforms,
		4457	although strictly speaking using a type that also implies a memory fence
		4458	is required.
3994		4459
3995	=item EV_H (h)	4460	=item EV_H (h)
3996		4461
3997	The name of the F<ev.h> header file used to include it. The default if	4462	The name of the F<ev.h> header file used to include it. The default if
3998	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4463	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
…		…
4021	If undefined or defined to C<1>, then all event-loop-specific functions	4486	If undefined or defined to C<1>, then all event-loop-specific functions
4022	will have the C<struct ev_loop *> as first argument, and you can create	4487	will have the C<struct ev_loop *> as first argument, and you can create
4023	additional independent event loops. Otherwise there will be no support	4488	additional independent event loops. Otherwise there will be no support
4024	for multiple event loops and there is no first event loop pointer	4489	for multiple event loops and there is no first event loop pointer
4025	argument. Instead, all functions act on the single default loop.	4490	argument. Instead, all functions act on the single default loop.
		4491
		4492	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4493	default loop when multiplicity is switched off - you always have to
		4494	initialise the loop manually in this case.
4026		4495
4027	=item EV_MINPRI	4496	=item EV_MINPRI
4028		4497
4029	=item EV_MAXPRI	4498	=item EV_MAXPRI
4030		4499
…		…
4281	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4750	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4282		4751
4283	#include "ev_cpp.h"	4752	#include "ev_cpp.h"
4284	#include "ev.c"	4753	#include "ev.c"
4285		4754
4286	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4755	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4287		4756
4288	=head2 THREADS AND COROUTINES	4757	=head2 THREADS AND COROUTINES
4289		4758
4290	=head3 THREADS	4759	=head3 THREADS
4291		4760
…		…
4342	default loop and triggering an C<ev_async> watcher from the default loop	4811	default loop and triggering an C<ev_async> watcher from the default loop
4343	watcher callback into the event loop interested in the signal.	4812	watcher callback into the event loop interested in the signal.
4344		4813
4345	=back	4814	=back
4346		4815
4347	=head4 THREAD LOCKING EXAMPLE	4816	See also L<THREAD LOCKING EXAMPLE>.
4348
4349	Here is a fictitious example of how to run an event loop in a different
4350	thread than where callbacks are being invoked and watchers are
4351	created/added/removed.
4352
4353	For a real-world example, see the C<EV::Loop::Async> perl module,
4354	which uses exactly this technique (which is suited for many high-level
4355	languages).
4356
4357	The example uses a pthread mutex to protect the loop data, a condition
4358	variable to wait for callback invocations, an async watcher to notify the
4359	event loop thread and an unspecified mechanism to wake up the main thread.
4360
4361	First, you need to associate some data with the event loop:
4362
4363	typedef struct {
4364	mutex_t lock; /* global loop lock */
4365	ev_async async_w;
4366	thread_t tid;
4367	cond_t invoke_cv;
4368	} userdata;
4369
4370	void prepare_loop (EV_P)
4371	{
4372	// for simplicity, we use a static userdata struct.
4373	static userdata u;
4374
4375	ev_async_init (&u->async_w, async_cb);
4376	ev_async_start (EV_A_ &u->async_w);
4377
4378	pthread_mutex_init (&u->lock, 0);
4379	pthread_cond_init (&u->invoke_cv, 0);
4380
4381	// now associate this with the loop
4382	ev_set_userdata (EV_A_ u);
4383	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4384	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4385
4386	// then create the thread running ev_loop
4387	pthread_create (&u->tid, 0, l_run, EV_A);
4388	}
4389
4390	The callback for the C<ev_async> watcher does nothing: the watcher is used
4391	solely to wake up the event loop so it takes notice of any new watchers
4392	that might have been added:
4393
4394	static void
4395	async_cb (EV_P_ ev_async *w, int revents)
4396	{
4397	// just used for the side effects
4398	}
4399
4400	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4401	protecting the loop data, respectively.
4402
4403	static void
4404	l_release (EV_P)
4405	{
4406	userdata *u = ev_userdata (EV_A);
4407	pthread_mutex_unlock (&u->lock);
4408	}
4409
4410	static void
4411	l_acquire (EV_P)
4412	{
4413	userdata *u = ev_userdata (EV_A);
4414	pthread_mutex_lock (&u->lock);
4415	}
4416
4417	The event loop thread first acquires the mutex, and then jumps straight
4418	into C<ev_run>:
4419
4420	void *
4421	l_run (void *thr_arg)
4422	{
4423	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4424
4425	l_acquire (EV_A);
4426	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4427	ev_run (EV_A_ 0);
4428	l_release (EV_A);
4429
4430	return 0;
4431	}
4432
4433	Instead of invoking all pending watchers, the C<l_invoke> callback will
4434	signal the main thread via some unspecified mechanism (signals? pipe
4435	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4436	have been called (in a while loop because a) spurious wakeups are possible
4437	and b) skipping inter-thread-communication when there are no pending
4438	watchers is very beneficial):
4439
4440	static void
4441	l_invoke (EV_P)
4442	{
4443	userdata *u = ev_userdata (EV_A);
4444
4445	while (ev_pending_count (EV_A))
4446	{
4447	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4448	pthread_cond_wait (&u->invoke_cv, &u->lock);
4449	}
4450	}
4451
4452	Now, whenever the main thread gets told to invoke pending watchers, it
4453	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4454	thread to continue:
4455
4456	static void
4457	real_invoke_pending (EV_P)
4458	{
4459	userdata *u = ev_userdata (EV_A);
4460
4461	pthread_mutex_lock (&u->lock);
4462	ev_invoke_pending (EV_A);
4463	pthread_cond_signal (&u->invoke_cv);
4464	pthread_mutex_unlock (&u->lock);
4465	}
4466
4467	Whenever you want to start/stop a watcher or do other modifications to an
4468	event loop, you will now have to lock:
4469
4470	ev_timer timeout_watcher;
4471	userdata *u = ev_userdata (EV_A);
4472
4473	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4474
4475	pthread_mutex_lock (&u->lock);
4476	ev_timer_start (EV_A_ &timeout_watcher);
4477	ev_async_send (EV_A_ &u->async_w);
4478	pthread_mutex_unlock (&u->lock);
4479
4480	Note that sending the C<ev_async> watcher is required because otherwise
4481	an event loop currently blocking in the kernel will have no knowledge
4482	about the newly added timer. By waking up the loop it will pick up any new
4483	watchers in the next event loop iteration.
4484		4817
4485	=head3 COROUTINES	4818	=head3 COROUTINES
4486		4819
4487	Libev is very accommodating to coroutines ("cooperative threads"):	4820	Libev is very accommodating to coroutines ("cooperative threads"):
4488	libev fully supports nesting calls to its functions from different	4821	libev fully supports nesting calls to its functions from different
…		…
4653	requires, and its I/O model is fundamentally incompatible with the POSIX	4986	requires, and its I/O model is fundamentally incompatible with the POSIX
4654	model. Libev still offers limited functionality on this platform in	4987	model. Libev still offers limited functionality on this platform in
4655	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4988	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4656	descriptors. This only applies when using Win32 natively, not when using	4989	descriptors. This only applies when using Win32 natively, not when using
4657	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	4990	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4658	as every compielr comes with a slightly differently broken/incompatible	4991	as every compiler comes with a slightly differently broken/incompatible
4659	environment.	4992	environment.
4660		4993
4661	Lifting these limitations would basically require the full	4994	Lifting these limitations would basically require the full
4662	re-implementation of the I/O system. If you are into this kind of thing,	4995	re-implementation of the I/O system. If you are into this kind of thing,
4663	then note that glib does exactly that for you in a very portable way (note	4996	then note that glib does exactly that for you in a very portable way (note
…		…
4757	structure (guaranteed by POSIX but not by ISO C for example), but it also	5090	structure (guaranteed by POSIX but not by ISO C for example), but it also
4758	assumes that the same (machine) code can be used to call any watcher	5091	assumes that the same (machine) code can be used to call any watcher
4759	callback: The watcher callbacks have different type signatures, but libev	5092	callback: The watcher callbacks have different type signatures, but libev
4760	calls them using an C<ev_watcher *> internally.	5093	calls them using an C<ev_watcher *> internally.
4761		5094
		5095	=item pointer accesses must be thread-atomic
		5096
		5097	Accessing a pointer value must be atomic, it must both be readable and
		5098	writable in one piece - this is the case on all current architectures.
		5099
4762	=item C<sig_atomic_t volatile> must be thread-atomic as well	5100	=item C<sig_atomic_t volatile> must be thread-atomic as well
4763		5101
4764	The type C<sig_atomic_t volatile> (or whatever is defined as	5102	The type C<sig_atomic_t volatile> (or whatever is defined as
4765	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5103	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4766	threads. This is not part of the specification for C<sig_atomic_t>, but is	5104	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4791		5129
4792	The type C<double> is used to represent timestamps. It is required to	5130	The type C<double> is used to represent timestamps. It is required to
4793	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5131	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4794	good enough for at least into the year 4000 with millisecond accuracy	5132	good enough for at least into the year 4000 with millisecond accuracy
4795	(the design goal for libev). This requirement is overfulfilled by	5133	(the design goal for libev). This requirement is overfulfilled by
4796	implementations using IEEE 754, which is basically all existing ones. With	5134	implementations using IEEE 754, which is basically all existing ones.
		5135
4797	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5136	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5137	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5138	is either obsolete or somebody patched it to use C<long double> or
		5139	something like that, just kidding).
4798		5140
4799	=back	5141	=back
4800		5142
4801	If you know of other additional requirements drop me a note.	5143	If you know of other additional requirements drop me a note.
4802		5144
…		…
4864	=item Processing ev_async_send: O(number_of_async_watchers)	5206	=item Processing ev_async_send: O(number_of_async_watchers)
4865		5207
4866	=item Processing signals: O(max_signal_number)	5208	=item Processing signals: O(max_signal_number)
4867		5209
4868	Sending involves a system call I<iff> there were no other C<ev_async_send>	5210	Sending involves a system call I<iff> there were no other C<ev_async_send>
4869	calls in the current loop iteration. Checking for async and signal events	5211	calls in the current loop iteration and the loop is currently
		5212	blocked. Checking for async and signal events involves iterating over all
4870	involves iterating over all running async watchers or all signal numbers.	5213	running async watchers or all signal numbers.
4871		5214
4872	=back	5215	=back
4873		5216
4874		5217
4875	=head1 PORTING FROM LIBEV 3.X TO 4.X	5218	=head1 PORTING FROM LIBEV 3.X TO 4.X
4876		5219
4877	The major version 4 introduced some minor incompatible changes to the API.	5220	The major version 4 introduced some incompatible changes to the API.
4878		5221
4879	At the moment, the C<ev.h> header file tries to implement superficial	5222	At the moment, the C<ev.h> header file provides compatibility definitions
4880	compatibility, so most programs should still compile. Those might be	5223	for all changes, so most programs should still compile. The compatibility
4881	removed in later versions of libev, so better update early than late.	5224	layer might be removed in later versions of libev, so better update to the
		5225	new API early than late.
4882		5226
4883	=over 4	5227	=over 4
		5228
		5229	=item C<EV_COMPAT3> backwards compatibility mechanism
		5230
		5231	The backward compatibility mechanism can be controlled by
		5232	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5233	section.
4884		5234
4885	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5235	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4886		5236
4887	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5237	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
4888		5238
…		…
4914	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5264	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4915	as all other watcher types. Note that C<ev_loop_fork> is still called	5265	as all other watcher types. Note that C<ev_loop_fork> is still called
4916	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5266	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4917	typedef.	5267	typedef.
4918		5268
4919	=item C<EV_COMPAT3> backwards compatibility mechanism
4920
4921	The backward compatibility mechanism can be controlled by
4922	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4923	section.
4924
4925	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5269	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4926		5270
4927	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5271	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4928	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5272	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4929	and work, but the library code will of course be larger.	5273	and work, but the library code will of course be larger.
…		…
4991	The physical time that is observed. It is apparently strictly monotonic :)	5335	The physical time that is observed. It is apparently strictly monotonic :)
4992		5336
4993	=item wall-clock time	5337	=item wall-clock time
4994		5338
4995	The time and date as shown on clocks. Unlike real time, it can actually	5339	The time and date as shown on clocks. Unlike real time, it can actually
4996	be wrong and jump forwards and backwards, e.g. when the you adjust your	5340	be wrong and jump forwards and backwards, e.g. when you adjust your
4997	clock.	5341	clock.
4998		5342
4999	=item watcher	5343	=item watcher
5000		5344
5001	A data structure that describes interest in certain events. Watchers need	5345	A data structure that describes interest in certain events. Watchers need
…		…
5003		5347
5004	=back	5348	=back
5005		5349
5006	=head1 AUTHOR	5350	=head1 AUTHOR
5007		5351
5008	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5352	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5353	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5009		5354

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