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Revision 1.352 by root, Mon Jan 10 14:30:15 2011 UTC vs.
Revision 1.415 by root, Fri May 4 20:51:08 2012 UTC

…		…
58	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
59		59
60	// now wait for events to arrive	60	// now wait for events to arrive
61	ev_run (loop, 0);	61	ev_run (loop, 0);
62		62
63	// unloop was called, so exit	63	// break was called, so exit
64	return 0;	64	return 0;
65	}	65	}
66		66
67	=head1 ABOUT THIS DOCUMENT	67	=head1 ABOUT THIS DOCUMENT
68		68
…		…
82		82
83	=head1 WHAT TO READ WHEN IN A HURRY	83	=head1 WHAT TO READ WHEN IN A HURRY
84		84
85	This manual tries to be very detailed, but unfortunately, this also makes	85	This manual tries to be very detailed, but unfortunately, this also makes
86	it very long. If you just want to know the basics of libev, I suggest	86	it very long. If you just want to know the basics of libev, I suggest
87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and	87	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and	88	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
89	C<ev_timer> sections in L<WATCHER TYPES>.	89	C<ev_timer> sections in L</WATCHER TYPES>.
90		90
91	=head1 ABOUT LIBEV	91	=head1 ABOUT LIBEV
92		92
93	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
94	file descriptor being readable or a timeout occurring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
…		…
174	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
175		175
176	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
177	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
178	you actually want to know. Also interesting is the combination of	178	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	179	C<ev_now_update> and C<ev_now>.
180		180
181	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
182		182
183	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
185	this is a sub-second-resolution C<sleep ()>.	188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
186		192
187	=item int ev_version_major ()	193	=item int ev_version_major ()
188		194
189	=item int ev_version_minor ()	195	=item int ev_version_minor ()
190		196
…		…
241	the current system, you would need to look at C<ev_embeddable_backends ()	247	the current system, you would need to look at C<ev_embeddable_backends ()
242	& ev_supported_backends ()>, likewise for recommended ones.	248	& ev_supported_backends ()>, likewise for recommended ones.
243		249
244	See the description of C<ev_embed> watchers for more info.	250	See the description of C<ev_embed> watchers for more info.
245		251
246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
247		253
248	Sets the allocation function to use (the prototype is similar - the	254	Sets the allocation function to use (the prototype is similar - the
249	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	255	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
250	used to allocate and free memory (no surprises here). If it returns zero	256	used to allocate and free memory (no surprises here). If it returns zero
251	when memory needs to be allocated (C<size != 0>), the library might abort	257	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
277	}	283	}
278		284
279	...	285	...
280	ev_set_allocator (persistent_realloc);	286	ev_set_allocator (persistent_realloc);
281		287
282	=item ev_set_syserr_cb (void (*cb)(const char *msg))	288	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
283		289
284	Set the callback function to call on a retryable system call error (such	290	Set the callback function to call on a retryable system call error (such
285	as failed select, poll, epoll_wait). The message is a printable string	291	as failed select, poll, epoll_wait). The message is a printable string
286	indicating the system call or subsystem causing the problem. If this	292	indicating the system call or subsystem causing the problem. If this
287	callback is set, then libev will expect it to remedy the situation, no	293	callback is set, then libev will expect it to remedy the situation, no
…		…
435	example) that can't properly initialise their signal masks.	441	example) that can't properly initialise their signal masks.
436		442
437	=item C<EVFLAG_NOSIGMASK>	443	=item C<EVFLAG_NOSIGMASK>
438		444
439	When this flag is specified, then libev will avoid to modify the signal	445	When this flag is specified, then libev will avoid to modify the signal
440	mask. Specifically, this means you ahve to make sure signals are unblocked	446	mask. Specifically, this means you have to make sure signals are unblocked
441	when you want to receive them.	447	when you want to receive them.
442		448
443	This behaviour is useful when you want to do your own signal handling, or	449	This behaviour is useful when you want to do your own signal handling, or
444	want to handle signals only in specific threads and want to avoid libev	450	want to handle signals only in specific threads and want to avoid libev
445	unblocking the signals.	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.
446		455
447	This flag's behaviour will become the default in future versions of libev.	456	This flag's behaviour will become the default in future versions of libev.
448		457
449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
450		459
…		…
480	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
481		490
482	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
483	kernels).	492	kernels).
484		493
485	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
486	but it scales phenomenally better. While poll and select usually scale	495	it scales phenomenally better. While poll and select usually scale like
487	like O(total_fds) where n is the total number of fds (or the highest fd),	496	O(total_fds) where total_fds is the total number of fds (or the highest
488	epoll scales either O(1) or O(active_fds).	497	fd), epoll scales either O(1) or O(active_fds).
489		498
490	The epoll mechanism deserves honorable mention as the most misdesigned	499	The epoll mechanism deserves honorable mention as the most misdesigned
491	of the more advanced event mechanisms: mere annoyances include silently	500	of the more advanced event mechanisms: mere annoyances include silently
492	dropping file descriptors, requiring a system call per change per file	501	dropping file descriptors, requiring a system call per change per file
493	descriptor (and unnecessary guessing of parameters), problems with dup,	502	descriptor (and unnecessary guessing of parameters), problems with dup,
…		…
496	0.1ms) and so on. The biggest issue is fork races, however - if a program	505	0.1ms) and so on. The biggest issue is fork races, however - if a program
497	forks then I<both> parent and child process have to recreate the epoll	506	forks then I<both> parent and child process have to recreate the epoll
498	set, which can take considerable time (one syscall per file descriptor)	507	set, which can take considerable time (one syscall per file descriptor)
499	and is of course hard to detect.	508	and is of course hard to detect.
500		509
501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
502	of course I<doesn't>, and epoll just loves to report events for totally	511	but of course I<doesn't>, and epoll just loves to report events for
503	I<different> file descriptors (even already closed ones, so one cannot	512	totally I<different> file descriptors (even already closed ones, so
504	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
505	on SMP systems). Libev tries to counter these spurious notifications by	514	(especially on SMP systems). Libev tries to counter these spurious
506	employing an additional generation counter and comparing that against the	515	notifications by employing an additional generation counter and comparing
507	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
508	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
509	perfectly fine with C<select> (files, many character devices...).	521	perfectly fine with C<select> (files, many character devices...).
510		522
511	Epoll is truly the train wreck analog among event poll mechanisms.	523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
512		526
513	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
514	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
515	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
516	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
…		…
553		567
554	It scales in the same way as the epoll backend, but the interface to the	568	It scales in the same way as the epoll backend, but the interface to the
555	kernel is more efficient (which says nothing about its actual speed, of	569	kernel is more efficient (which says nothing about its actual speed, of
556	course). While stopping, setting and starting an I/O watcher does never	570	course). While stopping, setting and starting an I/O watcher does never
557	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	571	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
558	two event changes per incident. Support for C<fork ()> is very bad (but	572	two event changes per incident. Support for C<fork ()> is very bad (you
559	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	573	might have to leak fd's on fork, but it's more sane than epoll) and it
560	cases	574	drops fds silently in similarly hard-to-detect cases
561		575
562	This backend usually performs well under most conditions.	576	This backend usually performs well under most conditions.
563		577
564	While nominally embeddable in other event loops, this doesn't work	578	While nominally embeddable in other event loops, this doesn't work
565	everywhere, so you might need to test for this. And since it is broken	579	everywhere, so you might need to test for this. And since it is broken
…		…
594	among the OS-specific backends (I vastly prefer correctness over speed	608	among the OS-specific backends (I vastly prefer correctness over speed
595	hacks).	609	hacks).
596		610
597	On the negative side, the interface is I<bizarre> - so bizarre that	611	On the negative side, the interface is I<bizarre> - so bizarre that
598	even sun itself gets it wrong in their code examples: The event polling	612	even sun itself gets it wrong in their code examples: The event polling
599	function sometimes returning events to the caller even though an error	613	function sometimes returns events to the caller even though an error
600	occured, but with no indication whether it has done so or not (yes, it's	614	occurred, but with no indication whether it has done so or not (yes, it's
601	even documented that way) - deadly for edge-triggered interfaces where	615	even documented that way) - deadly for edge-triggered interfaces where you
602	you absolutely have to know whether an event occured or not because you	616	absolutely have to know whether an event occurred or not because you have
603	have to re-arm the watcher.	617	to re-arm the watcher.
604		618
605	Fortunately libev seems to be able to work around these idiocies.	619	Fortunately libev seems to be able to work around these idiocies.
606		620
607	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
608	C<EVBACKEND_POLL>.	622	C<EVBACKEND_POLL>.
…		…
750		764
751	This function is rarely useful, but when some event callback runs for a	765	This function is rarely useful, but when some event callback runs for a
752	very long time without entering the event loop, updating libev's idea of	766	very long time without entering the event loop, updating libev's idea of
753	the current time is a good idea.	767	the current time is a good idea.
754		768
755	See also L<The special problem of time updates> in the C<ev_timer> section.	769	See also L</The special problem of time updates> in the C<ev_timer> section.
756		770
757	=item ev_suspend (loop)	771	=item ev_suspend (loop)
758		772
759	=item ev_resume (loop)	773	=item ev_resume (loop)
760		774
…		…
778	without a previous call to C<ev_suspend>.	792	without a previous call to C<ev_suspend>.
779		793
780	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	794	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
781	event loop time (see C<ev_now_update>).	795	event loop time (see C<ev_now_update>).
782		796
783	=item ev_run (loop, int flags)	797	=item bool ev_run (loop, int flags)
784		798
785	Finally, this is it, the event handler. This function usually is called	799	Finally, this is it, the event handler. This function usually is called
786	after you have initialised all your watchers and you want to start	800	after you have initialised all your watchers and you want to start
787	handling events. It will ask the operating system for any new events, call	801	handling events. It will ask the operating system for any new events, call
788	the watcher callbacks, an then repeat the whole process indefinitely: This	802	the watcher callbacks, and then repeat the whole process indefinitely: This
789	is why event loops are called I<loops>.	803	is why event loops are called I<loops>.
790		804
791	If the flags argument is specified as C<0>, it will keep handling events	805	If the flags argument is specified as C<0>, it will keep handling events
792	until either no event watchers are active anymore or C<ev_break> was	806	until either no event watchers are active anymore or C<ev_break> was
793	called.	807	called.
		808
		809	The return value is false if there are no more active watchers (which
		810	usually means "all jobs done" or "deadlock"), and true in all other cases
		811	(which usually means " you should call C<ev_run> again").
794		812
795	Please note that an explicit C<ev_break> is usually better than	813	Please note that an explicit C<ev_break> is usually better than
796	relying on all watchers to be stopped when deciding when a program has	814	relying on all watchers to be stopped when deciding when a program has
797	finished (especially in interactive programs), but having a program	815	finished (especially in interactive programs), but having a program
798	that automatically loops as long as it has to and no longer by virtue	816	that automatically loops as long as it has to and no longer by virtue
799	of relying on its watchers stopping correctly, that is truly a thing of	817	of relying on its watchers stopping correctly, that is truly a thing of
800	beauty.	818	beauty.
801		819
802	This function is also I<mostly> exception-safe - you can break out of	820	This function is I<mostly> exception-safe - you can break out of a
803	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++	821	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
804	exception and so on. This does not decrement the C<ev_depth> value, nor	822	exception and so on. This does not decrement the C<ev_depth> value, nor
805	will it clear any outstanding C<EVBREAK_ONE> breaks.	823	will it clear any outstanding C<EVBREAK_ONE> breaks.
806		824
807	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	825	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
808	those events and any already outstanding ones, but will not wait and	826	those events and any already outstanding ones, but will not wait and
…		…
820	This is useful if you are waiting for some external event in conjunction	838	This is useful if you are waiting for some external event in conjunction
821	with something not expressible using other libev watchers (i.e. "roll your	839	with something not expressible using other libev watchers (i.e. "roll your
822	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	840	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
823	usually a better approach for this kind of thing.	841	usually a better approach for this kind of thing.
824		842
825	Here are the gory details of what C<ev_run> does:	843	Here are the gory details of what C<ev_run> does (this is for your
		844	understanding, not a guarantee that things will work exactly like this in
		845	future versions):
826		846
827	- Increment loop depth.	847	- Increment loop depth.
828	- Reset the ev_break status.	848	- Reset the ev_break status.
829	- Before the first iteration, call any pending watchers.	849	- Before the first iteration, call any pending watchers.
830	LOOP:	850	LOOP:
…		…
863	anymore.	883	anymore.
864		884
865	... queue jobs here, make sure they register event watchers as long	885	... queue jobs here, make sure they register event watchers as long
866	... as they still have work to do (even an idle watcher will do..)	886	... as they still have work to do (even an idle watcher will do..)
867	ev_run (my_loop, 0);	887	ev_run (my_loop, 0);
868	... jobs done or somebody called unloop. yeah!	888	... jobs done or somebody called break. yeah!
869		889
870	=item ev_break (loop, how)	890	=item ev_break (loop, how)
871		891
872	Can be used to make a call to C<ev_run> return early (but only after it	892	Can be used to make a call to C<ev_run> return early (but only after it
873	has processed all outstanding events). The C<how> argument must be either	893	has processed all outstanding events). The C<how> argument must be either
…		…
936	overhead for the actual polling but can deliver many events at once.	956	overhead for the actual polling but can deliver many events at once.
937		957
938	By setting a higher I<io collect interval> you allow libev to spend more	958	By setting a higher I<io collect interval> you allow libev to spend more
939	time collecting I/O events, so you can handle more events per iteration,	959	time collecting I/O events, so you can handle more events per iteration,
940	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	960	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
941	C<ev_timer>) will be not affected. Setting this to a non-null value will	961	C<ev_timer>) will not be affected. Setting this to a non-null value will
942	introduce an additional C<ev_sleep ()> call into most loop iterations. The	962	introduce an additional C<ev_sleep ()> call into most loop iterations. The
943	sleep time ensures that libev will not poll for I/O events more often then	963	sleep time ensures that libev will not poll for I/O events more often then
944	once per this interval, on average.	964	once per this interval, on average (as long as the host time resolution is
		965	good enough).
945		966
946	Likewise, by setting a higher I<timeout collect interval> you allow libev	967	Likewise, by setting a higher I<timeout collect interval> you allow libev
947	to spend more time collecting timeouts, at the expense of increased	968	to spend more time collecting timeouts, at the expense of increased
948	latency/jitter/inexactness (the watcher callback will be called	969	latency/jitter/inexactness (the watcher callback will be called
949	later). C<ev_io> watchers will not be affected. Setting this to a non-null	970	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
995	invoke the actual watchers inside another context (another thread etc.).	1016	invoke the actual watchers inside another context (another thread etc.).
996		1017
997	If you want to reset the callback, use C<ev_invoke_pending> as new	1018	If you want to reset the callback, use C<ev_invoke_pending> as new
998	callback.	1019	callback.
999		1020
1000	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1021	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
1001		1022
1002	Sometimes you want to share the same loop between multiple threads. This	1023	Sometimes you want to share the same loop between multiple threads. This
1003	can be done relatively simply by putting mutex_lock/unlock calls around	1024	can be done relatively simply by putting mutex_lock/unlock calls around
1004	each call to a libev function.	1025	each call to a libev function.
1005		1026
1006	However, C<ev_run> can run an indefinite time, so it is not feasible	1027	However, C<ev_run> can run an indefinite time, so it is not feasible
1007	to wait for it to return. One way around this is to wake up the event	1028	to wait for it to return. One way around this is to wake up the event
1008	loop via C<ev_break> and C<av_async_send>, another way is to set these	1029	loop via C<ev_break> and C<ev_async_send>, another way is to set these
1009	I<release> and I<acquire> callbacks on the loop.	1030	I<release> and I<acquire> callbacks on the loop.
1010		1031
1011	When set, then C<release> will be called just before the thread is	1032	When set, then C<release> will be called just before the thread is
1012	suspended waiting for new events, and C<acquire> is called just	1033	suspended waiting for new events, and C<acquire> is called just
1013	afterwards.	1034	afterwards.
…		…
1153		1174
1154	=item C<EV_PREPARE>	1175	=item C<EV_PREPARE>
1155		1176
1156	=item C<EV_CHECK>	1177	=item C<EV_CHECK>
1157		1178
1158	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1179	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1159	to gather new events, and all C<ev_check> watchers are invoked just after	1180	gather new events, and all C<ev_check> watchers are queued (not invoked)
1160	C<ev_run> has gathered them, but before it invokes any callbacks for any	1181	just after C<ev_run> has gathered them, but before it queues any callbacks
		1182	for any received events. That means C<ev_prepare> watchers are the last
		1183	watchers invoked before the event loop sleeps or polls for new events, and
		1184	C<ev_check> watchers will be invoked before any other watchers of the same
		1185	or lower priority within an event loop iteration.
		1186
1161	received events. Callbacks of both watcher types can start and stop as	1187	Callbacks of both watcher types can start and stop as many watchers as
1162	many watchers as they want, and all of them will be taken into account	1188	they want, and all of them will be taken into account (for example, a
1163	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1189	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1164	C<ev_run> from blocking).	1190	blocking).
1165		1191
1166	=item C<EV_EMBED>	1192	=item C<EV_EMBED>
1167		1193
1168	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1194	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1169		1195
…		…
1292		1318
1293	=item callback ev_cb (ev_TYPE *watcher)	1319	=item callback ev_cb (ev_TYPE *watcher)
1294		1320
1295	Returns the callback currently set on the watcher.	1321	Returns the callback currently set on the watcher.
1296		1322
1297	=item ev_cb_set (ev_TYPE *watcher, callback)	1323	=item ev_set_cb (ev_TYPE *watcher, callback)
1298		1324
1299	Change the callback. You can change the callback at virtually any time	1325	Change the callback. You can change the callback at virtually any time
1300	(modulo threads).	1326	(modulo threads).
1301		1327
1302	=item ev_set_priority (ev_TYPE *watcher, int priority)	1328	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1320	or might not have been clamped to the valid range.	1346	or might not have been clamped to the valid range.
1321		1347
1322	The default priority used by watchers when no priority has been set is	1348	The default priority used by watchers when no priority has been set is
1323	always C<0>, which is supposed to not be too high and not be too low :).	1349	always C<0>, which is supposed to not be too high and not be too low :).
1324		1350
1325	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1351	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1326	priorities.	1352	priorities.
1327		1353
1328	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1354	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1329		1355
1330	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1356	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1355	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1381	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1356	functions that do not need a watcher.	1382	functions that do not need a watcher.
1357		1383
1358	=back	1384	=back
1359		1385
1360	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1386	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1361		1387	OWN COMPOSITE WATCHERS> idioms.
1362	Each watcher has, by default, a member C<void *data> that you can change
1363	and read at any time: libev will completely ignore it. This can be used
1364	to associate arbitrary data with your watcher. If you need more data and
1365	don't want to allocate memory and store a pointer to it in that data
1366	member, you can also "subclass" the watcher type and provide your own
1367	data:
1368
1369	struct my_io
1370	{
1371	ev_io io;
1372	int otherfd;
1373	void *somedata;
1374	struct whatever *mostinteresting;
1375	};
1376
1377	...
1378	struct my_io w;
1379	ev_io_init (&w.io, my_cb, fd, EV_READ);
1380
1381	And since your callback will be called with a pointer to the watcher, you
1382	can cast it back to your own type:
1383
1384	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1385	{
1386	struct my_io *w = (struct my_io *)w_;
1387	...
1388	}
1389
1390	More interesting and less C-conformant ways of casting your callback type
1391	instead have been omitted.
1392
1393	Another common scenario is to use some data structure with multiple
1394	embedded watchers:
1395
1396	struct my_biggy
1397	{
1398	int some_data;
1399	ev_timer t1;
1400	ev_timer t2;
1401	}
1402
1403	In this case getting the pointer to C<my_biggy> is a bit more
1404	complicated: Either you store the address of your C<my_biggy> struct
1405	in the C<data> member of the watcher (for woozies), or you need to use
1406	some pointer arithmetic using C<offsetof> inside your watchers (for real
1407	programmers):
1408
1409	#include <stddef.h>
1410
1411	static void
1412	t1_cb (EV_P_ ev_timer *w, int revents)
1413	{
1414	struct my_biggy big = (struct my_biggy *)
1415	(((char *)w) - offsetof (struct my_biggy, t1));
1416	}
1417
1418	static void
1419	t2_cb (EV_P_ ev_timer *w, int revents)
1420	{
1421	struct my_biggy big = (struct my_biggy *)
1422	(((char *)w) - offsetof (struct my_biggy, t2));
1423	}
1424		1388
1425	=head2 WATCHER STATES	1389	=head2 WATCHER STATES
1426		1390
1427	There are various watcher states mentioned throughout this manual -	1391	There are various watcher states mentioned throughout this manual -
1428	active, pending and so on. In this section these states and the rules to	1392	active, pending and so on. In this section these states and the rules to
…		…
1431		1395
1432	=over 4	1396	=over 4
1433		1397
1434	=item initialiased	1398	=item initialiased
1435		1399
1436	Before a watcher can be registered with the event looop it has to be	1400	Before a watcher can be registered with the event loop it has to be
1437	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1401	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1438	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1402	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1439		1403
1440	In this state it is simply some block of memory that is suitable for use	1404	In this state it is simply some block of memory that is suitable for
1441	in an event loop. It can be moved around, freed, reused etc. at will.	1405	use in an event loop. It can be moved around, freed, reused etc. at
		1406	will - as long as you either keep the memory contents intact, or call
		1407	C<ev_TYPE_init> again.
1442		1408
1443	=item started/running/active	1409	=item started/running/active
1444		1410
1445	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1411	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1446	property of the event loop, and is actively waiting for events. While in	1412	property of the event loop, and is actively waiting for events. While in
…		…
1474	latter will clear any pending state the watcher might be in, regardless	1440	latter will clear any pending state the watcher might be in, regardless
1475	of whether it was active or not, so stopping a watcher explicitly before	1441	of whether it was active or not, so stopping a watcher explicitly before
1476	freeing it is often a good idea.	1442	freeing it is often a good idea.
1477		1443
1478	While stopped (and not pending) the watcher is essentially in the	1444	While stopped (and not pending) the watcher is essentially in the
1479	initialised state, that is it can be reused, moved, modified in any way	1445	initialised state, that is, it can be reused, moved, modified in any way
1480	you wish.	1446	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1447	it again).
1481		1448
1482	=back	1449	=back
1483		1450
1484	=head2 WATCHER PRIORITY MODELS	1451	=head2 WATCHER PRIORITY MODELS
1485		1452
…		…
1614	In general you can register as many read and/or write event watchers per	1581	In general you can register as many read and/or write event watchers per
1615	fd as you want (as long as you don't confuse yourself). Setting all file	1582	fd as you want (as long as you don't confuse yourself). Setting all file
1616	descriptors to non-blocking mode is also usually a good idea (but not	1583	descriptors to non-blocking mode is also usually a good idea (but not
1617	required if you know what you are doing).	1584	required if you know what you are doing).
1618		1585
1619	If you cannot use non-blocking mode, then force the use of a
1620	known-to-be-good backend (at the time of this writing, this includes only
1621	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1622	descriptors for which non-blocking operation makes no sense (such as
1623	files) - libev doesn't guarantee any specific behaviour in that case.
1624
1625	Another thing you have to watch out for is that it is quite easy to	1586	Another thing you have to watch out for is that it is quite easy to
1626	receive "spurious" readiness notifications, that is your callback might	1587	receive "spurious" readiness notifications, that is, your callback might
1627	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1588	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1628	because there is no data. Not only are some backends known to create a	1589	because there is no data. It is very easy to get into this situation even
1629	lot of those (for example Solaris ports), it is very easy to get into	1590	with a relatively standard program structure. Thus it is best to always
1630	this situation even with a relatively standard program structure. Thus	1591	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1631	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1632	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1592	preferable to a program hanging until some data arrives.
1633		1593
1634	If you cannot run the fd in non-blocking mode (for example you should	1594	If you cannot run the fd in non-blocking mode (for example you should
1635	not play around with an Xlib connection), then you have to separately	1595	not play around with an Xlib connection), then you have to separately
1636	re-test whether a file descriptor is really ready with a known-to-be good	1596	re-test whether a file descriptor is really ready with a known-to-be good
1637	interface such as poll (fortunately in our Xlib example, Xlib already	1597	interface such as poll (fortunately in the case of Xlib, it already does
1638	does this on its own, so its quite safe to use). Some people additionally	1598	this on its own, so its quite safe to use). Some people additionally
1639	use C<SIGALRM> and an interval timer, just to be sure you won't block	1599	use C<SIGALRM> and an interval timer, just to be sure you won't block
1640	indefinitely.	1600	indefinitely.
1641		1601
1642	But really, best use non-blocking mode.	1602	But really, best use non-blocking mode.
1643		1603
…		…
1671		1631
1672	There is no workaround possible except not registering events	1632	There is no workaround possible except not registering events
1673	for potentially C<dup ()>'ed file descriptors, or to resort to	1633	for potentially C<dup ()>'ed file descriptors, or to resort to
1674	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1634	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1675		1635
		1636	=head3 The special problem of files
		1637
		1638	Many people try to use C<select> (or libev) on file descriptors
		1639	representing files, and expect it to become ready when their program
		1640	doesn't block on disk accesses (which can take a long time on their own).
		1641
		1642	However, this cannot ever work in the "expected" way - you get a readiness
		1643	notification as soon as the kernel knows whether and how much data is
		1644	there, and in the case of open files, that's always the case, so you
		1645	always get a readiness notification instantly, and your read (or possibly
		1646	write) will still block on the disk I/O.
		1647
		1648	Another way to view it is that in the case of sockets, pipes, character
		1649	devices and so on, there is another party (the sender) that delivers data
		1650	on its own, but in the case of files, there is no such thing: the disk
		1651	will not send data on its own, simply because it doesn't know what you
		1652	wish to read - you would first have to request some data.
		1653
		1654	Since files are typically not-so-well supported by advanced notification
		1655	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1656	to files, even though you should not use it. The reason for this is
		1657	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1658	usually a tty, often a pipe, but also sometimes files or special devices
		1659	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1660	F</dev/urandom>), and even though the file might better be served with
		1661	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1662	it "just works" instead of freezing.
		1663
		1664	So avoid file descriptors pointing to files when you know it (e.g. use
		1665	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1666	when you rarely read from a file instead of from a socket, and want to
		1667	reuse the same code path.
		1668
1676	=head3 The special problem of fork	1669	=head3 The special problem of fork
1677		1670
1678	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1671	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1679	useless behaviour. Libev fully supports fork, but needs to be told about	1672	useless behaviour. Libev fully supports fork, but needs to be told about
1680	it in the child.	1673	it in the child if you want to continue to use it in the child.
1681		1674
1682	To support fork in your programs, you either have to call	1675	To support fork in your child processes, you have to call C<ev_loop_fork
1683	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1676	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1684	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1677	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1685	C<EVBACKEND_POLL>.
1686		1678
1687	=head3 The special problem of SIGPIPE	1679	=head3 The special problem of SIGPIPE
1688		1680
1689	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1681	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1690	when writing to a pipe whose other end has been closed, your program gets	1682	when writing to a pipe whose other end has been closed, your program gets
…		…
1788	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1780	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1789	monotonic clock option helps a lot here).	1781	monotonic clock option helps a lot here).
1790		1782
1791	The callback is guaranteed to be invoked only I<after> its timeout has	1783	The callback is guaranteed to be invoked only I<after> its timeout has
1792	passed (not I<at>, so on systems with very low-resolution clocks this	1784	passed (not I<at>, so on systems with very low-resolution clocks this
1793	might introduce a small delay). If multiple timers become ready during the	1785	might introduce a small delay, see "the special problem of being too
		1786	early", below). If multiple timers become ready during the same loop
1794	same loop iteration then the ones with earlier time-out values are invoked	1787	iteration then the ones with earlier time-out values are invoked before
1795	before ones of the same priority with later time-out values (but this is	1788	ones of the same priority with later time-out values (but this is no
1796	no longer true when a callback calls C<ev_run> recursively).	1789	longer true when a callback calls C<ev_run> recursively).
1797		1790
1798	=head3 Be smart about timeouts	1791	=head3 Be smart about timeouts
1799		1792
1800	Many real-world problems involve some kind of timeout, usually for error	1793	Many real-world problems involve some kind of timeout, usually for error
1801	recovery. A typical example is an HTTP request - if the other side hangs,	1794	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1876		1869
1877	In this case, it would be more efficient to leave the C<ev_timer> alone,	1870	In this case, it would be more efficient to leave the C<ev_timer> alone,
1878	but remember the time of last activity, and check for a real timeout only	1871	but remember the time of last activity, and check for a real timeout only
1879	within the callback:	1872	within the callback:
1880		1873
		1874	ev_tstamp timeout = 60.;
1881	ev_tstamp last_activity; // time of last activity	1875	ev_tstamp last_activity; // time of last activity
		1876	ev_timer timer;
1882		1877
1883	static void	1878	static void
1884	callback (EV_P_ ev_timer *w, int revents)	1879	callback (EV_P_ ev_timer *w, int revents)
1885	{	1880	{
1886	ev_tstamp now = ev_now (EV_A);	1881	// calculate when the timeout would happen
1887	ev_tstamp timeout = last_activity + 60.;	1882	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1888		1883
1889	// if last_activity + 60. is older than now, we did time out	1884	// if negative, it means we the timeout already occurred
1890	if (timeout < now)	1885	if (after < 0.)
1891	{	1886	{
1892	// timeout occurred, take action	1887	// timeout occurred, take action
1893	}	1888	}
1894	else	1889	else
1895	{	1890	{
1896	// callback was invoked, but there was some activity, re-arm	1891	// callback was invoked, but there was some recent
1897	// the watcher to fire in last_activity + 60, which is	1892	// activity. simply restart the timer to time out
1898	// guaranteed to be in the future, so "again" is positive:	1893	// after "after" seconds, which is the earliest time
1899	w->repeat = timeout - now;	1894	// the timeout can occur.
		1895	ev_timer_set (w, after, 0.);
1900	ev_timer_again (EV_A_ w);	1896	ev_timer_start (EV_A_ w);
1901	}	1897	}
1902	}	1898	}
1903		1899
1904	To summarise the callback: first calculate the real timeout (defined	1900	To summarise the callback: first calculate in how many seconds the
1905	as "60 seconds after the last activity"), then check if that time has	1901	timeout will occur (by calculating the absolute time when it would occur,
1906	been reached, which means something I<did>, in fact, time out. Otherwise	1902	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1907	the callback was invoked too early (C<timeout> is in the future), so	1903	(EV_A)> from that).
1908	re-schedule the timer to fire at that future time, to see if maybe we have
1909	a timeout then.
1910		1904
1911	Note how C<ev_timer_again> is used, taking advantage of the	1905	If this value is negative, then we are already past the timeout, i.e. we
1912	C<ev_timer_again> optimisation when the timer is already running.	1906	timed out, and need to do whatever is needed in this case.
		1907
		1908	Otherwise, we now the earliest time at which the timeout would trigger,
		1909	and simply start the timer with this timeout value.
		1910
		1911	In other words, each time the callback is invoked it will check whether
		1912	the timeout occurred. If not, it will simply reschedule itself to check
		1913	again at the earliest time it could time out. Rinse. Repeat.
1913		1914
1914	This scheme causes more callback invocations (about one every 60 seconds	1915	This scheme causes more callback invocations (about one every 60 seconds
1915	minus half the average time between activity), but virtually no calls to	1916	minus half the average time between activity), but virtually no calls to
1916	libev to change the timeout.	1917	libev to change the timeout.
1917		1918
1918	To start the timer, simply initialise the watcher and set C<last_activity>	1919	To start the machinery, simply initialise the watcher and set
1919	to the current time (meaning we just have some activity :), then call the	1920	C<last_activity> to the current time (meaning there was some activity just
1920	callback, which will "do the right thing" and start the timer:	1921	now), then call the callback, which will "do the right thing" and start
		1922	the timer:
1921		1923
		1924	last_activity = ev_now (EV_A);
1922	ev_init (timer, callback);	1925	ev_init (&timer, callback);
1923	last_activity = ev_now (loop);	1926	callback (EV_A_ &timer, 0);
1924	callback (loop, timer, EV_TIMER);
1925		1927
1926	And when there is some activity, simply store the current time in	1928	When there is some activity, simply store the current time in
1927	C<last_activity>, no libev calls at all:	1929	C<last_activity>, no libev calls at all:
1928		1930
		1931	if (activity detected)
1929	last_activity = ev_now (loop);	1932	last_activity = ev_now (EV_A);
		1933
		1934	When your timeout value changes, then the timeout can be changed by simply
		1935	providing a new value, stopping the timer and calling the callback, which
		1936	will again do the right thing (for example, time out immediately :).
		1937
		1938	timeout = new_value;
		1939	ev_timer_stop (EV_A_ &timer);
		1940	callback (EV_A_ &timer, 0);
1930		1941
1931	This technique is slightly more complex, but in most cases where the	1942	This technique is slightly more complex, but in most cases where the
1932	time-out is unlikely to be triggered, much more efficient.	1943	time-out is unlikely to be triggered, much more efficient.
1933
1934	Changing the timeout is trivial as well (if it isn't hard-coded in the
1935	callback :) - just change the timeout and invoke the callback, which will
1936	fix things for you.
1937		1944
1938	=item 4. Wee, just use a double-linked list for your timeouts.	1945	=item 4. Wee, just use a double-linked list for your timeouts.
1939		1946
1940	If there is not one request, but many thousands (millions...), all	1947	If there is not one request, but many thousands (millions...), all
1941	employing some kind of timeout with the same timeout value, then one can	1948	employing some kind of timeout with the same timeout value, then one can
…		…
1968	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1975	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1969	rather complicated, but extremely efficient, something that really pays	1976	rather complicated, but extremely efficient, something that really pays
1970	off after the first million or so of active timers, i.e. it's usually	1977	off after the first million or so of active timers, i.e. it's usually
1971	overkill :)	1978	overkill :)
1972		1979
		1980	=head3 The special problem of being too early
		1981
		1982	If you ask a timer to call your callback after three seconds, then
		1983	you expect it to be invoked after three seconds - but of course, this
		1984	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1985	guaranteed to any precision by libev - imagine somebody suspending the
		1986	process with a STOP signal for a few hours for example.
		1987
		1988	So, libev tries to invoke your callback as soon as possible I<after> the
		1989	delay has occurred, but cannot guarantee this.
		1990
		1991	A less obvious failure mode is calling your callback too early: many event
		1992	loops compare timestamps with a "elapsed delay >= requested delay", but
		1993	this can cause your callback to be invoked much earlier than you would
		1994	expect.
		1995
		1996	To see why, imagine a system with a clock that only offers full second
		1997	resolution (think windows if you can't come up with a broken enough OS
		1998	yourself). If you schedule a one-second timer at the time 500.9, then the
		1999	event loop will schedule your timeout to elapse at a system time of 500
		2000	(500.9 truncated to the resolution) + 1, or 501.
		2001
		2002	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2003	501" and invoke the callback 0.1s after it was started, even though a
		2004	one-second delay was requested - this is being "too early", despite best
		2005	intentions.
		2006
		2007	This is the reason why libev will never invoke the callback if the elapsed
		2008	delay equals the requested delay, but only when the elapsed delay is
		2009	larger than the requested delay. In the example above, libev would only invoke
		2010	the callback at system time 502, or 1.1s after the timer was started.
		2011
		2012	So, while libev cannot guarantee that your callback will be invoked
		2013	exactly when requested, it I<can> and I<does> guarantee that the requested
		2014	delay has actually elapsed, or in other words, it always errs on the "too
		2015	late" side of things.
		2016
1973	=head3 The special problem of time updates	2017	=head3 The special problem of time updates
1974		2018
1975	Establishing the current time is a costly operation (it usually takes at	2019	Establishing the current time is a costly operation (it usually takes
1976	least two system calls): EV therefore updates its idea of the current	2020	at least one system call): EV therefore updates its idea of the current
1977	time only before and after C<ev_run> collects new events, which causes a	2021	time only before and after C<ev_run> collects new events, which causes a
1978	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2022	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1979	lots of events in one iteration.	2023	lots of events in one iteration.
1980		2024
1981	The relative timeouts are calculated relative to the C<ev_now ()>	2025	The relative timeouts are calculated relative to the C<ev_now ()>
…		…
1987	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2031	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1988		2032
1989	If the event loop is suspended for a long time, you can also force an	2033	If the event loop is suspended for a long time, you can also force an
1990	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2034	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1991	()>.	2035	()>.
		2036
		2037	=head3 The special problem of unsynchronised clocks
		2038
		2039	Modern systems have a variety of clocks - libev itself uses the normal
		2040	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2041	jumps).
		2042
		2043	Neither of these clocks is synchronised with each other or any other clock
		2044	on the system, so C<ev_time ()> might return a considerably different time
		2045	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2046	a call to C<gettimeofday> might return a second count that is one higher
		2047	than a directly following call to C<time>.
		2048
		2049	The moral of this is to only compare libev-related timestamps with
		2050	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2051	a second or so.
		2052
		2053	One more problem arises due to this lack of synchronisation: if libev uses
		2054	the system monotonic clock and you compare timestamps from C<ev_time>
		2055	or C<ev_now> from when you started your timer and when your callback is
		2056	invoked, you will find that sometimes the callback is a bit "early".
		2057
		2058	This is because C<ev_timer>s work in real time, not wall clock time, so
		2059	libev makes sure your callback is not invoked before the delay happened,
		2060	I<measured according to the real time>, not the system clock.
		2061
		2062	If your timeouts are based on a physical timescale (e.g. "time out this
		2063	connection after 100 seconds") then this shouldn't bother you as it is
		2064	exactly the right behaviour.
		2065
		2066	If you want to compare wall clock/system timestamps to your timers, then
		2067	you need to use C<ev_periodic>s, as these are based on the wall clock
		2068	time, where your comparisons will always generate correct results.
1992		2069
1993	=head3 The special problems of suspended animation	2070	=head3 The special problems of suspended animation
1994		2071
1995	When you leave the server world it is quite customary to hit machines that	2072	When you leave the server world it is quite customary to hit machines that
1996	can suspend/hibernate - what happens to the clocks during such a suspend?	2073	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
2040	keep up with the timer (because it takes longer than those 10 seconds to	2117	keep up with the timer (because it takes longer than those 10 seconds to
2041	do stuff) the timer will not fire more than once per event loop iteration.	2118	do stuff) the timer will not fire more than once per event loop iteration.
2042		2119
2043	=item ev_timer_again (loop, ev_timer *)	2120	=item ev_timer_again (loop, ev_timer *)
2044		2121
2045	This will act as if the timer timed out and restart it again if it is	2122	This will act as if the timer timed out, and restarts it again if it is
2046	repeating. The exact semantics are:	2123	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2124	timeout to the C<repeat> value and calling C<ev_timer_start>.
2047		2125
		2126	The exact semantics are as in the following rules, all of which will be
		2127	applied to the watcher:
		2128
		2129	=over 4
		2130
2048	If the timer is pending, its pending status is cleared.	2131	=item If the timer is pending, the pending status is always cleared.
2049		2132
2050	If the timer is started but non-repeating, stop it (as if it timed out).	2133	=item If the timer is started but non-repeating, stop it (as if it timed
		2134	out, without invoking it).
2051		2135
2052	If the timer is repeating, either start it if necessary (with the	2136	=item If the timer is repeating, make the C<repeat> value the new timeout
2053	C<repeat> value), or reset the running timer to the C<repeat> value.	2137	and start the timer, if necessary.
2054		2138
		2139	=back
		2140
2055	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2141	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2056	usage example.	2142	usage example.
2057		2143
2058	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2144	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2059		2145
2060	Returns the remaining time until a timer fires. If the timer is active,	2146	Returns the remaining time until a timer fires. If the timer is active,
…		…
2180		2266
2181	Another way to think about it (for the mathematically inclined) is that	2267	Another way to think about it (for the mathematically inclined) is that
2182	C<ev_periodic> will try to run the callback in this mode at the next possible	2268	C<ev_periodic> will try to run the callback in this mode at the next possible
2183	time where C<time = offset (mod interval)>, regardless of any time jumps.	2269	time where C<time = offset (mod interval)>, regardless of any time jumps.
2184		2270
2185	For numerical stability it is preferable that the C<offset> value is near	2271	The C<interval> I<MUST> be positive, and for numerical stability, the
2186	C<ev_now ()> (the current time), but there is no range requirement for	2272	interval value should be higher than C<1/8192> (which is around 100
2187	this value, and in fact is often specified as zero.	2273	microseconds) and C<offset> should be higher than C<0> and should have
		2274	at most a similar magnitude as the current time (say, within a factor of
		2275	ten). Typical values for offset are, in fact, C<0> or something between
		2276	C<0> and C<interval>, which is also the recommended range.
2188		2277
2189	Note also that there is an upper limit to how often a timer can fire (CPU	2278	Note also that there is an upper limit to how often a timer can fire (CPU
2190	speed for example), so if C<interval> is very small then timing stability	2279	speed for example), so if C<interval> is very small then timing stability
2191	will of course deteriorate. Libev itself tries to be exact to be about one	2280	will of course deteriorate. Libev itself tries to be exact to be about one
2192	millisecond (if the OS supports it and the machine is fast enough).	2281	millisecond (if the OS supports it and the machine is fast enough).
…		…
2335	=head3 The special problem of inheritance over fork/execve/pthread_create	2424	=head3 The special problem of inheritance over fork/execve/pthread_create
2336		2425
2337	Both the signal mask (C<sigprocmask>) and the signal disposition	2426	Both the signal mask (C<sigprocmask>) and the signal disposition
2338	(C<sigaction>) are unspecified after starting a signal watcher (and after	2427	(C<sigaction>) are unspecified after starting a signal watcher (and after
2339	stopping it again), that is, libev might or might not block the signal,	2428	stopping it again), that is, libev might or might not block the signal,
2340	and might or might not set or restore the installed signal handler.	2429	and might or might not set or restore the installed signal handler (but
		2430	see C<EVFLAG_NOSIGMASK>).
2341		2431
2342	While this does not matter for the signal disposition (libev never	2432	While this does not matter for the signal disposition (libev never
2343	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2433	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2344	C<execve>), this matters for the signal mask: many programs do not expect	2434	C<execve>), this matters for the signal mask: many programs do not expect
2345	certain signals to be blocked.	2435	certain signals to be blocked.
…		…
2757	Apart from keeping your process non-blocking (which is a useful	2847	Apart from keeping your process non-blocking (which is a useful
2758	effect on its own sometimes), idle watchers are a good place to do	2848	effect on its own sometimes), idle watchers are a good place to do
2759	"pseudo-background processing", or delay processing stuff to after the	2849	"pseudo-background processing", or delay processing stuff to after the
2760	event loop has handled all outstanding events.	2850	event loop has handled all outstanding events.
2761		2851
		2852	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2853
		2854	As long as there is at least one active idle watcher, libev will never
		2855	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2856	For this to work, the idle watcher doesn't need to be invoked at all - the
		2857	lowest priority will do.
		2858
		2859	This mode of operation can be useful together with an C<ev_check> watcher,
		2860	to do something on each event loop iteration - for example to balance load
		2861	between different connections.
		2862
		2863	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2864	example.
		2865
2762	=head3 Watcher-Specific Functions and Data Members	2866	=head3 Watcher-Specific Functions and Data Members
2763		2867
2764	=over 4	2868	=over 4
2765		2869
2766	=item ev_idle_init (ev_idle *, callback)	2870	=item ev_idle_init (ev_idle *, callback)
…		…
2777	callback, free it. Also, use no error checking, as usual.	2881	callback, free it. Also, use no error checking, as usual.
2778		2882
2779	static void	2883	static void
2780	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2884	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2781	{	2885	{
		2886	// stop the watcher
		2887	ev_idle_stop (loop, w);
		2888
		2889	// now we can free it
2782	free (w);	2890	free (w);
		2891
2783	// now do something you wanted to do when the program has	2892	// now do something you wanted to do when the program has
2784	// no longer anything immediate to do.	2893	// no longer anything immediate to do.
2785	}	2894	}
2786		2895
2787	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2896	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2789	ev_idle_start (loop, idle_watcher);	2898	ev_idle_start (loop, idle_watcher);
2790		2899
2791		2900
2792	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2901	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2793		2902
2794	Prepare and check watchers are usually (but not always) used in pairs:	2903	Prepare and check watchers are often (but not always) used in pairs:
2795	prepare watchers get invoked before the process blocks and check watchers	2904	prepare watchers get invoked before the process blocks and check watchers
2796	afterwards.	2905	afterwards.
2797		2906
2798	You I<must not> call C<ev_run> or similar functions that enter	2907	You I<must not> call C<ev_run> or similar functions that enter
2799	the current event loop from either C<ev_prepare> or C<ev_check>	2908	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
2827	with priority higher than or equal to the event loop and one coroutine	2936	with priority higher than or equal to the event loop and one coroutine
2828	of lower priority, but only once, using idle watchers to keep the event	2937	of lower priority, but only once, using idle watchers to keep the event
2829	loop from blocking if lower-priority coroutines are active, thus mapping	2938	loop from blocking if lower-priority coroutines are active, thus mapping
2830	low-priority coroutines to idle/background tasks).	2939	low-priority coroutines to idle/background tasks).
2831		2940
2832	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2941	When used for this purpose, it is recommended to give C<ev_check> watchers
2833	priority, to ensure that they are being run before any other watchers	2942	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2834	after the poll (this doesn't matter for C<ev_prepare> watchers).	2943	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2944	watchers).
2835		2945
2836	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	2946	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2837	activate ("feed") events into libev. While libev fully supports this, they	2947	activate ("feed") events into libev. While libev fully supports this, they
2838	might get executed before other C<ev_check> watchers did their job. As	2948	might get executed before other C<ev_check> watchers did their job. As
2839	C<ev_check> watchers are often used to embed other (non-libev) event	2949	C<ev_check> watchers are often used to embed other (non-libev) event
2840	loops those other event loops might be in an unusable state until their	2950	loops those other event loops might be in an unusable state until their
2841	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2951	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2842	others).	2952	others).
		2953
		2954	=head3 Abusing an C<ev_check> watcher for its side-effect
		2955
		2956	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2957	useful because they are called once per event loop iteration. For
		2958	example, if you want to handle a large number of connections fairly, you
		2959	normally only do a bit of work for each active connection, and if there
		2960	is more work to do, you wait for the next event loop iteration, so other
		2961	connections have a chance of making progress.
		2962
		2963	Using an C<ev_check> watcher is almost enough: it will be called on the
		2964	next event loop iteration. However, that isn't as soon as possible -
		2965	without external events, your C<ev_check> watcher will not be invoked.
		2966
		2967
		2968	This is where C<ev_idle> watchers come in handy - all you need is a
		2969	single global idle watcher that is active as long as you have one active
		2970	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2971	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2972	invoked. Neither watcher alone can do that.
2843		2973
2844	=head3 Watcher-Specific Functions and Data Members	2974	=head3 Watcher-Specific Functions and Data Members
2845		2975
2846	=over 4	2976	=over 4
2847		2977
…		…
3216	atexit (program_exits);	3346	atexit (program_exits);
3217		3347
3218		3348
3219	=head2 C<ev_async> - how to wake up an event loop	3349	=head2 C<ev_async> - how to wake up an event loop
3220		3350
3221	In general, you cannot use an C<ev_run> from multiple threads or other	3351	In general, you cannot use an C<ev_loop> from multiple threads or other
3222	asynchronous sources such as signal handlers (as opposed to multiple event	3352	asynchronous sources such as signal handlers (as opposed to multiple event
3223	loops - those are of course safe to use in different threads).	3353	loops - those are of course safe to use in different threads).
3224		3354
3225	Sometimes, however, you need to wake up an event loop you do not control,	3355	Sometimes, however, you need to wake up an event loop you do not control,
3226	for example because it belongs to another thread. This is what C<ev_async>	3356	for example because it belongs to another thread. This is what C<ev_async>
…		…
3228	it by calling C<ev_async_send>, which is thread- and signal safe.	3358	it by calling C<ev_async_send>, which is thread- and signal safe.
3229		3359
3230	This functionality is very similar to C<ev_signal> watchers, as signals,	3360	This functionality is very similar to C<ev_signal> watchers, as signals,
3231	too, are asynchronous in nature, and signals, too, will be compressed	3361	too, are asynchronous in nature, and signals, too, will be compressed
3232	(i.e. the number of callback invocations may be less than the number of	3362	(i.e. the number of callback invocations may be less than the number of
3233	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind	3363	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3234	of "global async watchers" by using a watcher on an otherwise unused	3364	of "global async watchers" by using a watcher on an otherwise unused
3235	signal, and C<ev_feed_signal> to signal this watcher from another thread,	3365	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3236	even without knowing which loop owns the signal.	3366	even without knowing which loop owns the signal.
3237
3238	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3239	just the default loop.
3240		3367
3241	=head3 Queueing	3368	=head3 Queueing
3242		3369
3243	C<ev_async> does not support queueing of data in any way. The reason	3370	C<ev_async> does not support queueing of data in any way. The reason
3244	is that the author does not know of a simple (or any) algorithm for a	3371	is that the author does not know of a simple (or any) algorithm for a
…		…
3336	trust me.	3463	trust me.
3337		3464
3338	=item ev_async_send (loop, ev_async *)	3465	=item ev_async_send (loop, ev_async *)
3339		3466
3340	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3467	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3341	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3468	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3469	returns.
		3470
3342	C<ev_feed_event>, this call is safe to do from other threads, signal or	3471	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3343	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3472	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3344	section below on what exactly this means).	3473	embedding section below on what exactly this means).
3345		3474
3346	Note that, as with other watchers in libev, multiple events might get	3475	Note that, as with other watchers in libev, multiple events might get
3347	compressed into a single callback invocation (another way to look at this	3476	compressed into a single callback invocation (another way to look at
3348	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3477	this is that C<ev_async> watchers are level-triggered: they are set on
3349	reset when the event loop detects that).	3478	C<ev_async_send>, reset when the event loop detects that).
3350		3479
3351	This call incurs the overhead of a system call only once per event loop	3480	This call incurs the overhead of at most one extra system call per event
3352	iteration, so while the overhead might be noticeable, it doesn't apply to	3481	loop iteration, if the event loop is blocked, and no syscall at all if
3353	repeated calls to C<ev_async_send> for the same event loop.	3482	the event loop (or your program) is processing events. That means that
		3483	repeated calls are basically free (there is no need to avoid calls for
		3484	performance reasons) and that the overhead becomes smaller (typically
		3485	zero) under load.
3354		3486
3355	=item bool = ev_async_pending (ev_async *)	3487	=item bool = ev_async_pending (ev_async *)
3356		3488
3357	Returns a non-zero value when C<ev_async_send> has been called on the	3489	Returns a non-zero value when C<ev_async_send> has been called on the
3358	watcher but the event has not yet been processed (or even noted) by the	3490	watcher but the event has not yet been processed (or even noted) by the
…		…
3413	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3545	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3414		3546
3415	=item ev_feed_fd_event (loop, int fd, int revents)	3547	=item ev_feed_fd_event (loop, int fd, int revents)
3416		3548
3417	Feed an event on the given fd, as if a file descriptor backend detected	3549	Feed an event on the given fd, as if a file descriptor backend detected
3418	the given events it.	3550	the given events.
3419		3551
3420	=item ev_feed_signal_event (loop, int signum)	3552	=item ev_feed_signal_event (loop, int signum)
3421		3553
3422	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,	3554	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3423	which is async-safe.	3555	which is async-safe.
…		…
3429		3561
3430	This section explains some common idioms that are not immediately	3562	This section explains some common idioms that are not immediately
3431	obvious. Note that examples are sprinkled over the whole manual, and this	3563	obvious. Note that examples are sprinkled over the whole manual, and this
3432	section only contains stuff that wouldn't fit anywhere else.	3564	section only contains stuff that wouldn't fit anywhere else.
3433		3565
3434	=over 4	3566	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3435		3567
3436	=item Model/nested event loop invocations and exit conditions.	3568	Each watcher has, by default, a C<void *data> member that you can read
		3569	or modify at any time: libev will completely ignore it. This can be used
		3570	to associate arbitrary data with your watcher. If you need more data and
		3571	don't want to allocate memory separately and store a pointer to it in that
		3572	data member, you can also "subclass" the watcher type and provide your own
		3573	data:
		3574
		3575	struct my_io
		3576	{
		3577	ev_io io;
		3578	int otherfd;
		3579	void *somedata;
		3580	struct whatever *mostinteresting;
		3581	};
		3582
		3583	...
		3584	struct my_io w;
		3585	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3586
		3587	And since your callback will be called with a pointer to the watcher, you
		3588	can cast it back to your own type:
		3589
		3590	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3591	{
		3592	struct my_io *w = (struct my_io *)w_;
		3593	...
		3594	}
		3595
		3596	More interesting and less C-conformant ways of casting your callback
		3597	function type instead have been omitted.
		3598
		3599	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3600
		3601	Another common scenario is to use some data structure with multiple
		3602	embedded watchers, in effect creating your own watcher that combines
		3603	multiple libev event sources into one "super-watcher":
		3604
		3605	struct my_biggy
		3606	{
		3607	int some_data;
		3608	ev_timer t1;
		3609	ev_timer t2;
		3610	}
		3611
		3612	In this case getting the pointer to C<my_biggy> is a bit more
		3613	complicated: Either you store the address of your C<my_biggy> struct in
		3614	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3615	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3616	real programmers):
		3617
		3618	#include <stddef.h>
		3619
		3620	static void
		3621	t1_cb (EV_P_ ev_timer *w, int revents)
		3622	{
		3623	struct my_biggy big = (struct my_biggy *)
		3624	(((char *)w) - offsetof (struct my_biggy, t1));
		3625	}
		3626
		3627	static void
		3628	t2_cb (EV_P_ ev_timer *w, int revents)
		3629	{
		3630	struct my_biggy big = (struct my_biggy *)
		3631	(((char *)w) - offsetof (struct my_biggy, t2));
		3632	}
		3633
		3634	=head2 AVOIDING FINISHING BEFORE RETURNING
		3635
		3636	Often you have structures like this in event-based programs:
		3637
		3638	callback ()
		3639	{
		3640	free (request);
		3641	}
		3642
		3643	request = start_new_request (..., callback);
		3644
		3645	The intent is to start some "lengthy" operation. The C<request> could be
		3646	used to cancel the operation, or do other things with it.
		3647
		3648	It's not uncommon to have code paths in C<start_new_request> that
		3649	immediately invoke the callback, for example, to report errors. Or you add
		3650	some caching layer that finds that it can skip the lengthy aspects of the
		3651	operation and simply invoke the callback with the result.
		3652
		3653	The problem here is that this will happen I<before> C<start_new_request>
		3654	has returned, so C<request> is not set.
		3655
		3656	Even if you pass the request by some safer means to the callback, you
		3657	might want to do something to the request after starting it, such as
		3658	canceling it, which probably isn't working so well when the callback has
		3659	already been invoked.
		3660
		3661	A common way around all these issues is to make sure that
		3662	C<start_new_request> I<always> returns before the callback is invoked. If
		3663	C<start_new_request> immediately knows the result, it can artificially
		3664	delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher
		3665	for example, or more sneakily, by reusing an existing (stopped) watcher
		3666	and pushing it into the pending queue:
		3667
		3668	ev_set_cb (watcher, callback);
		3669	ev_feed_event (EV_A_ watcher, 0);
		3670
		3671	This way, C<start_new_request> can safely return before the callback is
		3672	invoked, while not delaying callback invocation too much.
		3673
		3674	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3437		3675
3438	Often (especially in GUI toolkits) there are places where you have	3676	Often (especially in GUI toolkits) there are places where you have
3439	I<modal> interaction, which is most easily implemented by recursively	3677	I<modal> interaction, which is most easily implemented by recursively
3440	invoking C<ev_run>.	3678	invoking C<ev_run>.
3441		3679
…		…
3453	int exit_main_loop = 0;	3691	int exit_main_loop = 0;
3454		3692
3455	while (!exit_main_loop)	3693	while (!exit_main_loop)
3456	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3694	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3457		3695
3458	// in a model watcher	3696	// in a modal watcher
3459	int exit_nested_loop = 0;	3697	int exit_nested_loop = 0;
3460		3698
3461	while (!exit_nested_loop)	3699	while (!exit_nested_loop)
3462	ev_run (EV_A_ EVRUN_ONCE);	3700	ev_run (EV_A_ EVRUN_ONCE);
3463		3701
…		…
3470	exit_main_loop = 1;	3708	exit_main_loop = 1;
3471		3709
3472	// exit both	3710	// exit both
3473	exit_main_loop = exit_nested_loop = 1;	3711	exit_main_loop = exit_nested_loop = 1;
3474		3712
3475	=back	3713	=head2 THREAD LOCKING EXAMPLE
		3714
		3715	Here is a fictitious example of how to run an event loop in a different
		3716	thread from where callbacks are being invoked and watchers are
		3717	created/added/removed.
		3718
		3719	For a real-world example, see the C<EV::Loop::Async> perl module,
		3720	which uses exactly this technique (which is suited for many high-level
		3721	languages).
		3722
		3723	The example uses a pthread mutex to protect the loop data, a condition
		3724	variable to wait for callback invocations, an async watcher to notify the
		3725	event loop thread and an unspecified mechanism to wake up the main thread.
		3726
		3727	First, you need to associate some data with the event loop:
		3728
		3729	typedef struct {
		3730	mutex_t lock; /* global loop lock */
		3731	ev_async async_w;
		3732	thread_t tid;
		3733	cond_t invoke_cv;
		3734	} userdata;
		3735
		3736	void prepare_loop (EV_P)
		3737	{
		3738	// for simplicity, we use a static userdata struct.
		3739	static userdata u;
		3740
		3741	ev_async_init (&u->async_w, async_cb);
		3742	ev_async_start (EV_A_ &u->async_w);
		3743
		3744	pthread_mutex_init (&u->lock, 0);
		3745	pthread_cond_init (&u->invoke_cv, 0);
		3746
		3747	// now associate this with the loop
		3748	ev_set_userdata (EV_A_ u);
		3749	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3750	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3751
		3752	// then create the thread running ev_run
		3753	pthread_create (&u->tid, 0, l_run, EV_A);
		3754	}
		3755
		3756	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3757	solely to wake up the event loop so it takes notice of any new watchers
		3758	that might have been added:
		3759
		3760	static void
		3761	async_cb (EV_P_ ev_async *w, int revents)
		3762	{
		3763	// just used for the side effects
		3764	}
		3765
		3766	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3767	protecting the loop data, respectively.
		3768
		3769	static void
		3770	l_release (EV_P)
		3771	{
		3772	userdata *u = ev_userdata (EV_A);
		3773	pthread_mutex_unlock (&u->lock);
		3774	}
		3775
		3776	static void
		3777	l_acquire (EV_P)
		3778	{
		3779	userdata *u = ev_userdata (EV_A);
		3780	pthread_mutex_lock (&u->lock);
		3781	}
		3782
		3783	The event loop thread first acquires the mutex, and then jumps straight
		3784	into C<ev_run>:
		3785
		3786	void *
		3787	l_run (void *thr_arg)
		3788	{
		3789	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3790
		3791	l_acquire (EV_A);
		3792	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3793	ev_run (EV_A_ 0);
		3794	l_release (EV_A);
		3795
		3796	return 0;
		3797	}
		3798
		3799	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3800	signal the main thread via some unspecified mechanism (signals? pipe
		3801	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3802	have been called (in a while loop because a) spurious wakeups are possible
		3803	and b) skipping inter-thread-communication when there are no pending
		3804	watchers is very beneficial):
		3805
		3806	static void
		3807	l_invoke (EV_P)
		3808	{
		3809	userdata *u = ev_userdata (EV_A);
		3810
		3811	while (ev_pending_count (EV_A))
		3812	{
		3813	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3814	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3815	}
		3816	}
		3817
		3818	Now, whenever the main thread gets told to invoke pending watchers, it
		3819	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3820	thread to continue:
		3821
		3822	static void
		3823	real_invoke_pending (EV_P)
		3824	{
		3825	userdata *u = ev_userdata (EV_A);
		3826
		3827	pthread_mutex_lock (&u->lock);
		3828	ev_invoke_pending (EV_A);
		3829	pthread_cond_signal (&u->invoke_cv);
		3830	pthread_mutex_unlock (&u->lock);
		3831	}
		3832
		3833	Whenever you want to start/stop a watcher or do other modifications to an
		3834	event loop, you will now have to lock:
		3835
		3836	ev_timer timeout_watcher;
		3837	userdata *u = ev_userdata (EV_A);
		3838
		3839	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3840
		3841	pthread_mutex_lock (&u->lock);
		3842	ev_timer_start (EV_A_ &timeout_watcher);
		3843	ev_async_send (EV_A_ &u->async_w);
		3844	pthread_mutex_unlock (&u->lock);
		3845
		3846	Note that sending the C<ev_async> watcher is required because otherwise
		3847	an event loop currently blocking in the kernel will have no knowledge
		3848	about the newly added timer. By waking up the loop it will pick up any new
		3849	watchers in the next event loop iteration.
		3850
		3851	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3852
		3853	While the overhead of a callback that e.g. schedules a thread is small, it
		3854	is still an overhead. If you embed libev, and your main usage is with some
		3855	kind of threads or coroutines, you might want to customise libev so that
		3856	doesn't need callbacks anymore.
		3857
		3858	Imagine you have coroutines that you can switch to using a function
		3859	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3860	and that due to some magic, the currently active coroutine is stored in a
		3861	global called C<current_coro>. Then you can build your own "wait for libev
		3862	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3863	the differing C<;> conventions):
		3864
		3865	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3866	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3867
		3868	That means instead of having a C callback function, you store the
		3869	coroutine to switch to in each watcher, and instead of having libev call
		3870	your callback, you instead have it switch to that coroutine.
		3871
		3872	A coroutine might now wait for an event with a function called
		3873	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3874	matter when, or whether the watcher is active or not when this function is
		3875	called):
		3876
		3877	void
		3878	wait_for_event (ev_watcher *w)
		3879	{
		3880	ev_set_cb (w, current_coro);
		3881	switch_to (libev_coro);
		3882	}
		3883
		3884	That basically suspends the coroutine inside C<wait_for_event> and
		3885	continues the libev coroutine, which, when appropriate, switches back to
		3886	this or any other coroutine.
		3887
		3888	You can do similar tricks if you have, say, threads with an event queue -
		3889	instead of storing a coroutine, you store the queue object and instead of
		3890	switching to a coroutine, you push the watcher onto the queue and notify
		3891	any waiters.
		3892
		3893	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3894	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3895
		3896	// my_ev.h
		3897	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3898	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3899	#include "../libev/ev.h"
		3900
		3901	// my_ev.c
		3902	#define EV_H "my_ev.h"
		3903	#include "../libev/ev.c"
		3904
		3905	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3906	F<my_ev.c> into your project. When properly specifying include paths, you
		3907	can even use F<ev.h> as header file name directly.
3476		3908
3477		3909
3478	=head1 LIBEVENT EMULATION	3910	=head1 LIBEVENT EMULATION
3479		3911
3480	Libev offers a compatibility emulation layer for libevent. It cannot	3912	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3509	to use the libev header file and library.	3941	to use the libev header file and library.
3510		3942
3511	=back	3943	=back
3512		3944
3513	=head1 C++ SUPPORT	3945	=head1 C++ SUPPORT
		3946
		3947	=head2 C API
		3948
		3949	The normal C API should work fine when used from C++: both ev.h and the
		3950	libev sources can be compiled as C++. Therefore, code that uses the C API
		3951	will work fine.
		3952
		3953	Proper exception specifications might have to be added to callbacks passed
		3954	to libev: exceptions may be thrown only from watcher callbacks, all
		3955	other callbacks (allocator, syserr, loop acquire/release and periodioc
		3956	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3957	()> specification. If you have code that needs to be compiled as both C
		3958	and C++ you can use the C<EV_THROW> macro for this:
		3959
		3960	static void
		3961	fatal_error (const char *msg) EV_THROW
		3962	{
		3963	perror (msg);
		3964	abort ();
		3965	}
		3966
		3967	...
		3968	ev_set_syserr_cb (fatal_error);
		3969
		3970	The only API functions that can currently throw exceptions are C<ev_run>,
		3971	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3972	because it runs cleanup watchers).
		3973
		3974	Throwing exceptions in watcher callbacks is only supported if libev itself
		3975	is compiled with a C++ compiler or your C and C++ environments allow
		3976	throwing exceptions through C libraries (most do).
		3977
		3978	=head2 C++ API
3514		3979
3515	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3980	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3516	you to use some convenience methods to start/stop watchers and also change	3981	you to use some convenience methods to start/stop watchers and also change
3517	the callback model to a model using method callbacks on objects.	3982	the callback model to a model using method callbacks on objects.
3518		3983
…		…
3534	with C<operator ()> can be used as callbacks. Other types should be easy	3999	with C<operator ()> can be used as callbacks. Other types should be easy
3535	to add as long as they only need one additional pointer for context. If	4000	to add as long as they only need one additional pointer for context. If
3536	you need support for other types of functors please contact the author	4001	you need support for other types of functors please contact the author
3537	(preferably after implementing it).	4002	(preferably after implementing it).
3538		4003
		4004	For all this to work, your C++ compiler either has to use the same calling
		4005	conventions as your C compiler (for static member functions), or you have
		4006	to embed libev and compile libev itself as C++.
		4007
3539	Here is a list of things available in the C<ev> namespace:	4008	Here is a list of things available in the C<ev> namespace:
3540		4009
3541	=over 4	4010	=over 4
3542		4011
3543	=item C<ev::READ>, C<ev::WRITE> etc.	4012	=item C<ev::READ>, C<ev::WRITE> etc.
…		…
3552	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4021	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3553		4022
3554	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4023	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3555	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4024	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3556	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4025	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3557	defines by many implementations.	4026	defined by many implementations.
3558		4027
3559	All of those classes have these methods:	4028	All of those classes have these methods:
3560		4029
3561	=over 4	4030	=over 4
3562		4031
…		…
3695	watchers in the constructor.	4164	watchers in the constructor.
3696		4165
3697	class myclass	4166	class myclass
3698	{	4167	{
3699	ev::io io ; void io_cb (ev::io &w, int revents);	4168	ev::io io ; void io_cb (ev::io &w, int revents);
3700	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4169	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3701	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4170	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3702		4171
3703	myclass (int fd)	4172	myclass (int fd)
3704	{	4173	{
3705	io .set <myclass, &myclass::io_cb > (this);	4174	io .set <myclass, &myclass::io_cb > (this);
…		…
3756	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4225	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3757		4226
3758	=item D	4227	=item D
3759		4228
3760	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4229	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3761	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4230	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3762		4231
3763	=item Ocaml	4232	=item Ocaml
3764		4233
3765	Erkki Seppala has written Ocaml bindings for libev, to be found at	4234	Erkki Seppala has written Ocaml bindings for libev, to be found at
3766	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4235	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3814	suitable for use with C<EV_A>.	4283	suitable for use with C<EV_A>.
3815		4284
3816	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4285	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3817		4286
3818	Similar to the other two macros, this gives you the value of the default	4287	Similar to the other two macros, this gives you the value of the default
3819	loop, if multiple loops are supported ("ev loop default").	4288	loop, if multiple loops are supported ("ev loop default"). The default loop
		4289	will be initialised if it isn't already initialised.
		4290
		4291	For non-multiplicity builds, these macros do nothing, so you always have
		4292	to initialise the loop somewhere.
3820		4293
3821	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4294	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3822		4295
3823	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4296	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3824	default loop has been initialised (C<UC> == unchecked). Their behaviour	4297	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3969	supported). It will also not define any of the structs usually found in	4442	supported). It will also not define any of the structs usually found in
3970	F<event.h> that are not directly supported by the libev core alone.	4443	F<event.h> that are not directly supported by the libev core alone.
3971		4444
3972	In standalone mode, libev will still try to automatically deduce the	4445	In standalone mode, libev will still try to automatically deduce the
3973	configuration, but has to be more conservative.	4446	configuration, but has to be more conservative.
		4447
		4448	=item EV_USE_FLOOR
		4449
		4450	If defined to be C<1>, libev will use the C<floor ()> function for its
		4451	periodic reschedule calculations, otherwise libev will fall back on a
		4452	portable (slower) implementation. If you enable this, you usually have to
		4453	link against libm or something equivalent. Enabling this when the C<floor>
		4454	function is not available will fail, so the safe default is to not enable
		4455	this.
3974		4456
3975	=item EV_USE_MONOTONIC	4457	=item EV_USE_MONOTONIC
3976		4458
3977	If defined to be C<1>, libev will try to detect the availability of the	4459	If defined to be C<1>, libev will try to detect the availability of the
3978	monotonic clock option at both compile time and runtime. Otherwise no	4460	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4108	If defined to be C<1>, libev will compile in support for the Linux inotify	4590	If defined to be C<1>, libev will compile in support for the Linux inotify
4109	interface to speed up C<ev_stat> watchers. Its actual availability will	4591	interface to speed up C<ev_stat> watchers. Its actual availability will
4110	be detected at runtime. If undefined, it will be enabled if the headers	4592	be detected at runtime. If undefined, it will be enabled if the headers
4111	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4593	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4112		4594
		4595	=item EV_NO_SMP
		4596
		4597	If defined to be C<1>, libev will assume that memory is always coherent
		4598	between threads, that is, threads can be used, but threads never run on
		4599	different cpus (or different cpu cores). This reduces dependencies
		4600	and makes libev faster.
		4601
		4602	=item EV_NO_THREADS
		4603
		4604	If defined to be C<1>, libev will assume that it will never be called
		4605	from different threads, which is a stronger assumption than C<EV_NO_SMP>,
		4606	above. This reduces dependencies and makes libev faster.
		4607
4113	=item EV_ATOMIC_T	4608	=item EV_ATOMIC_T
4114		4609
4115	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4610	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4116	access is atomic with respect to other threads or signal contexts. No such	4611	access is atomic and serialised with respect to other threads or signal
4117	type is easily found in the C language, so you can provide your own type	4612	contexts. No such type is easily found in the C language, so you can
4118	that you know is safe for your purposes. It is used both for signal handler "locking"	4613	provide your own type that you know is safe for your purposes. It is used
4119	as well as for signal and thread safety in C<ev_async> watchers.	4614	both for signal handler "locking" as well as for signal and thread safety
		4615	in C<ev_async> watchers.
4120		4616
4121	In the absence of this define, libev will use C<sig_atomic_t volatile>	4617	In the absence of this define, libev will use C<sig_atomic_t volatile>
4122	(from F<signal.h>), which is usually good enough on most platforms.	4618	(from F<signal.h>), which is usually good enough on most platforms,
		4619	although strictly speaking using a type that also implies a memory fence
		4620	is required.
4123		4621
4124	=item EV_H (h)	4622	=item EV_H (h)
4125		4623
4126	The name of the F<ev.h> header file used to include it. The default if	4624	The name of the F<ev.h> header file used to include it. The default if
4127	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4625	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
…		…
4151	will have the C<struct ev_loop *> as first argument, and you can create	4649	will have the C<struct ev_loop *> as first argument, and you can create
4152	additional independent event loops. Otherwise there will be no support	4650	additional independent event loops. Otherwise there will be no support
4153	for multiple event loops and there is no first event loop pointer	4651	for multiple event loops and there is no first event loop pointer
4154	argument. Instead, all functions act on the single default loop.	4652	argument. Instead, all functions act on the single default loop.
4155		4653
		4654	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4655	default loop when multiplicity is switched off - you always have to
		4656	initialise the loop manually in this case.
		4657
4156	=item EV_MINPRI	4658	=item EV_MINPRI
4157		4659
4158	=item EV_MAXPRI	4660	=item EV_MAXPRI
4159		4661
4160	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4662	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4196	#define EV_USE_POLL 1	4698	#define EV_USE_POLL 1
4197	#define EV_CHILD_ENABLE 1	4699	#define EV_CHILD_ENABLE 1
4198	#define EV_ASYNC_ENABLE 1	4700	#define EV_ASYNC_ENABLE 1
4199		4701
4200	The actual value is a bitset, it can be a combination of the following	4702	The actual value is a bitset, it can be a combination of the following
4201	values:	4703	values (by default, all of these are enabled):
4202		4704
4203	=over 4	4705	=over 4
4204		4706
4205	=item C<1> - faster/larger code	4707	=item C<1> - faster/larger code
4206		4708
…		…
4210	code size by roughly 30% on amd64).	4712	code size by roughly 30% on amd64).
4211		4713
4212	When optimising for size, use of compiler flags such as C<-Os> with	4714	When optimising for size, use of compiler flags such as C<-Os> with
4213	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4715	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4214	assertions.	4716	assertions.
		4717
		4718	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4719	(e.g. gcc with C<-Os>).
4215		4720
4216	=item C<2> - faster/larger data structures	4721	=item C<2> - faster/larger data structures
4217		4722
4218	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4723	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4219	hash table sizes and so on. This will usually further increase code size	4724	hash table sizes and so on. This will usually further increase code size
4220	and can additionally have an effect on the size of data structures at	4725	and can additionally have an effect on the size of data structures at
4221	runtime.	4726	runtime.
4222		4727
		4728	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4729	(e.g. gcc with C<-Os>).
		4730
4223	=item C<4> - full API configuration	4731	=item C<4> - full API configuration
4224		4732
4225	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4733	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4226	enables multiplicity (C<EV_MULTIPLICITY>=1).	4734	enables multiplicity (C<EV_MULTIPLICITY>=1).
4227		4735
…		…
4257		4765
4258	With an intelligent-enough linker (gcc+binutils are intelligent enough	4766	With an intelligent-enough linker (gcc+binutils are intelligent enough
4259	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4767	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4260	your program might be left out as well - a binary starting a timer and an	4768	your program might be left out as well - a binary starting a timer and an
4261	I/O watcher then might come out at only 5Kb.	4769	I/O watcher then might come out at only 5Kb.
		4770
		4771	=item EV_API_STATIC
		4772
		4773	If this symbol is defined (by default it is not), then all identifiers
		4774	will have static linkage. This means that libev will not export any
		4775	identifiers, and you cannot link against libev anymore. This can be useful
		4776	when you embed libev, only want to use libev functions in a single file,
		4777	and do not want its identifiers to be visible.
		4778
		4779	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4780	wants to use libev.
		4781
		4782	This option only works when libev is compiled with a C compiler, as C++
		4783	doesn't support the required declaration syntax.
4262		4784
4263	=item EV_AVOID_STDIO	4785	=item EV_AVOID_STDIO
4264		4786
4265	If this is set to C<1> at compiletime, then libev will avoid using stdio	4787	If this is set to C<1> at compiletime, then libev will avoid using stdio
4266	functions (printf, scanf, perror etc.). This will increase the code size	4788	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4410	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4932	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4411		4933
4412	#include "ev_cpp.h"	4934	#include "ev_cpp.h"
4413	#include "ev.c"	4935	#include "ev.c"
4414		4936
4415	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4937	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4416		4938
4417	=head2 THREADS AND COROUTINES	4939	=head2 THREADS AND COROUTINES
4418		4940
4419	=head3 THREADS	4941	=head3 THREADS
4420		4942
…		…
4471	default loop and triggering an C<ev_async> watcher from the default loop	4993	default loop and triggering an C<ev_async> watcher from the default loop
4472	watcher callback into the event loop interested in the signal.	4994	watcher callback into the event loop interested in the signal.
4473		4995
4474	=back	4996	=back
4475		4997
4476	=head4 THREAD LOCKING EXAMPLE	4998	See also L</THREAD LOCKING EXAMPLE>.
4477
4478	Here is a fictitious example of how to run an event loop in a different
4479	thread than where callbacks are being invoked and watchers are
4480	created/added/removed.
4481
4482	For a real-world example, see the C<EV::Loop::Async> perl module,
4483	which uses exactly this technique (which is suited for many high-level
4484	languages).
4485
4486	The example uses a pthread mutex to protect the loop data, a condition
4487	variable to wait for callback invocations, an async watcher to notify the
4488	event loop thread and an unspecified mechanism to wake up the main thread.
4489
4490	First, you need to associate some data with the event loop:
4491
4492	typedef struct {
4493	mutex_t lock; /* global loop lock */
4494	ev_async async_w;
4495	thread_t tid;
4496	cond_t invoke_cv;
4497	} userdata;
4498
4499	void prepare_loop (EV_P)
4500	{
4501	// for simplicity, we use a static userdata struct.
4502	static userdata u;
4503
4504	ev_async_init (&u->async_w, async_cb);
4505	ev_async_start (EV_A_ &u->async_w);
4506
4507	pthread_mutex_init (&u->lock, 0);
4508	pthread_cond_init (&u->invoke_cv, 0);
4509
4510	// now associate this with the loop
4511	ev_set_userdata (EV_A_ u);
4512	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4513	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4514
4515	// then create the thread running ev_loop
4516	pthread_create (&u->tid, 0, l_run, EV_A);
4517	}
4518
4519	The callback for the C<ev_async> watcher does nothing: the watcher is used
4520	solely to wake up the event loop so it takes notice of any new watchers
4521	that might have been added:
4522
4523	static void
4524	async_cb (EV_P_ ev_async *w, int revents)
4525	{
4526	// just used for the side effects
4527	}
4528
4529	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4530	protecting the loop data, respectively.
4531
4532	static void
4533	l_release (EV_P)
4534	{
4535	userdata *u = ev_userdata (EV_A);
4536	pthread_mutex_unlock (&u->lock);
4537	}
4538
4539	static void
4540	l_acquire (EV_P)
4541	{
4542	userdata *u = ev_userdata (EV_A);
4543	pthread_mutex_lock (&u->lock);
4544	}
4545
4546	The event loop thread first acquires the mutex, and then jumps straight
4547	into C<ev_run>:
4548
4549	void *
4550	l_run (void *thr_arg)
4551	{
4552	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4553
4554	l_acquire (EV_A);
4555	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4556	ev_run (EV_A_ 0);
4557	l_release (EV_A);
4558
4559	return 0;
4560	}
4561
4562	Instead of invoking all pending watchers, the C<l_invoke> callback will
4563	signal the main thread via some unspecified mechanism (signals? pipe
4564	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4565	have been called (in a while loop because a) spurious wakeups are possible
4566	and b) skipping inter-thread-communication when there are no pending
4567	watchers is very beneficial):
4568
4569	static void
4570	l_invoke (EV_P)
4571	{
4572	userdata *u = ev_userdata (EV_A);
4573
4574	while (ev_pending_count (EV_A))
4575	{
4576	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4577	pthread_cond_wait (&u->invoke_cv, &u->lock);
4578	}
4579	}
4580
4581	Now, whenever the main thread gets told to invoke pending watchers, it
4582	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4583	thread to continue:
4584
4585	static void
4586	real_invoke_pending (EV_P)
4587	{
4588	userdata *u = ev_userdata (EV_A);
4589
4590	pthread_mutex_lock (&u->lock);
4591	ev_invoke_pending (EV_A);
4592	pthread_cond_signal (&u->invoke_cv);
4593	pthread_mutex_unlock (&u->lock);
4594	}
4595
4596	Whenever you want to start/stop a watcher or do other modifications to an
4597	event loop, you will now have to lock:
4598
4599	ev_timer timeout_watcher;
4600	userdata *u = ev_userdata (EV_A);
4601
4602	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4603
4604	pthread_mutex_lock (&u->lock);
4605	ev_timer_start (EV_A_ &timeout_watcher);
4606	ev_async_send (EV_A_ &u->async_w);
4607	pthread_mutex_unlock (&u->lock);
4608
4609	Note that sending the C<ev_async> watcher is required because otherwise
4610	an event loop currently blocking in the kernel will have no knowledge
4611	about the newly added timer. By waking up the loop it will pick up any new
4612	watchers in the next event loop iteration.
4613		4999
4614	=head3 COROUTINES	5000	=head3 COROUTINES
4615		5001
4616	Libev is very accommodating to coroutines ("cooperative threads"):	5002	Libev is very accommodating to coroutines ("cooperative threads"):
4617	libev fully supports nesting calls to its functions from different	5003	libev fully supports nesting calls to its functions from different
…		…
4782	requires, and its I/O model is fundamentally incompatible with the POSIX	5168	requires, and its I/O model is fundamentally incompatible with the POSIX
4783	model. Libev still offers limited functionality on this platform in	5169	model. Libev still offers limited functionality on this platform in
4784	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5170	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4785	descriptors. This only applies when using Win32 natively, not when using	5171	descriptors. This only applies when using Win32 natively, not when using
4786	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5172	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4787	as every compielr comes with a slightly differently broken/incompatible	5173	as every compiler comes with a slightly differently broken/incompatible
4788	environment.	5174	environment.
4789		5175
4790	Lifting these limitations would basically require the full	5176	Lifting these limitations would basically require the full
4791	re-implementation of the I/O system. If you are into this kind of thing,	5177	re-implementation of the I/O system. If you are into this kind of thing,
4792	then note that glib does exactly that for you in a very portable way (note	5178	then note that glib does exactly that for you in a very portable way (note
…		…
4925		5311
4926	The type C<double> is used to represent timestamps. It is required to	5312	The type C<double> is used to represent timestamps. It is required to
4927	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5313	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4928	good enough for at least into the year 4000 with millisecond accuracy	5314	good enough for at least into the year 4000 with millisecond accuracy
4929	(the design goal for libev). This requirement is overfulfilled by	5315	(the design goal for libev). This requirement is overfulfilled by
4930	implementations using IEEE 754, which is basically all existing ones. With	5316	implementations using IEEE 754, which is basically all existing ones.
		5317
4931	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5318	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5319	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5320	is either obsolete or somebody patched it to use C<long double> or
		5321	something like that, just kidding).
4932		5322
4933	=back	5323	=back
4934		5324
4935	If you know of other additional requirements drop me a note.	5325	If you know of other additional requirements drop me a note.
4936		5326
…		…
4998	=item Processing ev_async_send: O(number_of_async_watchers)	5388	=item Processing ev_async_send: O(number_of_async_watchers)
4999		5389
5000	=item Processing signals: O(max_signal_number)	5390	=item Processing signals: O(max_signal_number)
5001		5391
5002	Sending involves a system call I<iff> there were no other C<ev_async_send>	5392	Sending involves a system call I<iff> there were no other C<ev_async_send>
5003	calls in the current loop iteration. Checking for async and signal events	5393	calls in the current loop iteration and the loop is currently
		5394	blocked. Checking for async and signal events involves iterating over all
5004	involves iterating over all running async watchers or all signal numbers.	5395	running async watchers or all signal numbers.
5005		5396
5006	=back	5397	=back
5007		5398
5008		5399
5009	=head1 PORTING FROM LIBEV 3.X TO 4.X	5400	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5018	=over 4	5409	=over 4
5019		5410
5020	=item C<EV_COMPAT3> backwards compatibility mechanism	5411	=item C<EV_COMPAT3> backwards compatibility mechanism
5021		5412
5022	The backward compatibility mechanism can be controlled by	5413	The backward compatibility mechanism can be controlled by
5023	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5414	C<EV_COMPAT3>. See L</PREPROCESSOR SYMBOLS/MACROS> in the L</EMBEDDING>
5024	section.	5415	section.
5025		5416
5026	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5417	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
5027		5418
5028	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5419	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
5071	=over 4	5462	=over 4
5072		5463
5073	=item active	5464	=item active
5074		5465
5075	A watcher is active as long as it has been started and not yet stopped.	5466	A watcher is active as long as it has been started and not yet stopped.
5076	See L<WATCHER STATES> for details.	5467	See L</WATCHER STATES> for details.
5077		5468
5078	=item application	5469	=item application
5079		5470
5080	In this document, an application is whatever is using libev.	5471	In this document, an application is whatever is using libev.
5081		5472
…		…
5117	watchers and events.	5508	watchers and events.
5118		5509
5119	=item pending	5510	=item pending
5120		5511
5121	A watcher is pending as soon as the corresponding event has been	5512	A watcher is pending as soon as the corresponding event has been
5122	detected. See L<WATCHER STATES> for details.	5513	detected. See L</WATCHER STATES> for details.
5123		5514
5124	=item real time	5515	=item real time
5125		5516
5126	The physical time that is observed. It is apparently strictly monotonic :)	5517	The physical time that is observed. It is apparently strictly monotonic :)
5127		5518
5128	=item wall-clock time	5519	=item wall-clock time
5129		5520
5130	The time and date as shown on clocks. Unlike real time, it can actually	5521	The time and date as shown on clocks. Unlike real time, it can actually
5131	be wrong and jump forwards and backwards, e.g. when the you adjust your	5522	be wrong and jump forwards and backwards, e.g. when you adjust your
5132	clock.	5523	clock.
5133		5524
5134	=item watcher	5525	=item watcher
5135		5526
5136	A data structure that describes interest in certain events. Watchers need	5527	A data structure that describes interest in certain events. Watchers need
…		…
5139	=back	5530	=back
5140		5531
5141	=head1 AUTHOR	5532	=head1 AUTHOR
5142		5533
5143	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5534	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5144	Magnusson and Emanuele Giaquinta.	5535	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5145		5536

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