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…		…
8		8
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
		13
		14	#include <stdio.h> // for puts
13		15
14	// every watcher type has its own typedef'd struct	16	// every watcher type has its own typedef'd struct
15	// with the name ev_TYPE	17	// with the name ev_TYPE
16	ev_io stdin_watcher;	18	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
…		…
41		43
42	int	44	int
43	main (void)	45	main (void)
44	{	46	{
45	// use the default event loop unless you have special needs	47	// use the default event loop unless you have special needs
46	ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
47		49
48	// initialise an io watcher, then start it	50	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	51	// this one will watch for stdin to become readable
50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
51	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
…		…
60		62
61	// unloop was called, so exit	63	// unloop was called, so exit
62	return 0;	64	return 0;
63	}	65	}
64		66
65	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
66		70
67	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
70		84
71	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	87	these event sources and provide your program with events.
74		88
…		…
108	name C<loop> (which is always of type C<ev_loop *>) will not have	122	name C<loop> (which is always of type C<ev_loop *>) will not have
109	this argument.	123	this argument.
110		124
111	=head2 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
112		126
113	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
115	the beginning of 1970, details are complicated, don't ask). This type is	129	near the beginning of 1970, details are complicated, don't ask). This
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	type is called C<ev_tstamp>, which is what you should use too. It usually
117	to the C<double> type in C, and when you need to do any calculations on	131	aliases to the C<double> type in C. When you need to do any calculations
118	it, you should treat it as some floating point value. Unlike the name	132	on it, you should treat it as some floating point value. Unlike the name
119	component C<stamp> might indicate, it is also used for time differences	133	component C<stamp> might indicate, it is also used for time differences
120	throughout libev.	134	throughout libev.
121		135
122	=head1 ERROR HANDLING	136	=head1 ERROR HANDLING
123		137
…		…
347	forget about forgetting to tell libev about forking) when you use this	361	forget about forgetting to tell libev about forking) when you use this
348	flag.	362	flag.
349		363
350	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
351	environment variable.	365	environment variable.
		366
		367	=item C<EVFLAG_NOINOTIFY>
		368
		369	When this flag is specified, then libev will not attempt to use the
		370	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		371	testing, this flag can be useful to conserve inotify file descriptors, as
		372	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		373
		374	=item C<EVFLAG_NOSIGNALFD>
		375
		376	When this flag is specified, then libev will not attempt to use the
		377	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		378	probably only useful to work around any bugs in libev. Consequently, this
		379	flag might go away once the signalfd functionality is considered stable,
		380	so it's useful mostly in environment variables and not in program code.
352		381
353	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	382	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
354		383
355	This is your standard select(2) backend. Not I<completely> standard, as	384	This is your standard select(2) backend. Not I<completely> standard, as
356	libev tries to roll its own fd_set with no limits on the number of fds,	385	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
417	i.e. keep at least one watcher active per fd at all times. Stopping and	446	i.e. keep at least one watcher active per fd at all times. Stopping and
418	starting a watcher (without re-setting it) also usually doesn't cause	447	starting a watcher (without re-setting it) also usually doesn't cause
419	extra overhead. A fork can both result in spurious notifications as well	448	extra overhead. A fork can both result in spurious notifications as well
420	as in libev having to destroy and recreate the epoll object, which can	449	as in libev having to destroy and recreate the epoll object, which can
421	take considerable time and thus should be avoided.	450	take considerable time and thus should be avoided.
		451
		452	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		453	faster than epoll for maybe up to a hundred file descriptors, depending on
		454	the usage. So sad.
422		455
423	While nominally embeddable in other event loops, this feature is broken in	456	While nominally embeddable in other event loops, this feature is broken in
424	all kernel versions tested so far.	457	all kernel versions tested so far.
425		458
426	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	459	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
…		…
454		487
455	While nominally embeddable in other event loops, this doesn't work	488	While nominally embeddable in other event loops, this doesn't work
456	everywhere, so you might need to test for this. And since it is broken	489	everywhere, so you might need to test for this. And since it is broken
457	almost everywhere, you should only use it when you have a lot of sockets	490	almost everywhere, you should only use it when you have a lot of sockets
458	(for which it usually works), by embedding it into another event loop	491	(for which it usually works), by embedding it into another event loop
459	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,	492	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
460	using it only for sockets.	493	also broken on OS X)) and, did I mention it, using it only for sockets.
461		494
462	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with	495	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
463	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with	496	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
464	C<NOTE_EOF>.	497	C<NOTE_EOF>.
465		498
…		…
500		533
501	It is definitely not recommended to use this flag.	534	It is definitely not recommended to use this flag.
502		535
503	=back	536	=back
504		537
505	If one or more of these are or'ed into the flags value, then only these	538	If one or more of the backend flags are or'ed into the flags value,
506	backends will be tried (in the reverse order as listed here). If none are	539	then only these backends will be tried (in the reverse order as listed
507	specified, all backends in C<ev_recommended_backends ()> will be tried.	540	here). If none are specified, all backends in C<ev_recommended_backends
		541	()> will be tried.
508		542
509	Example: This is the most typical usage.	543	Example: This is the most typical usage.
510		544
511	if (!ev_default_loop (0))	545	if (!ev_default_loop (0))
512	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	546	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
…		…
603		637
604	This value can sometimes be useful as a generation counter of sorts (it	638	This value can sometimes be useful as a generation counter of sorts (it
605	"ticks" the number of loop iterations), as it roughly corresponds with	639	"ticks" the number of loop iterations), as it roughly corresponds with
606	C<ev_prepare> and C<ev_check> calls.	640	C<ev_prepare> and C<ev_check> calls.
607		641
		642	=item unsigned int ev_loop_depth (loop)
		643
		644	Returns the number of times C<ev_loop> was entered minus the number of
		645	times C<ev_loop> was exited, in other words, the recursion depth.
		646
		647	Outside C<ev_loop>, this number is zero. In a callback, this number is
		648	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		649	in which case it is higher.
		650
		651	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		652	etc.), doesn't count as exit.
		653
608	=item unsigned int ev_backend (loop)	654	=item unsigned int ev_backend (loop)
609		655
610	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	656	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
611	use.	657	use.
612		658
…		…
626		672
627	This function is rarely useful, but when some event callback runs for a	673	This function is rarely useful, but when some event callback runs for a
628	very long time without entering the event loop, updating libev's idea of	674	very long time without entering the event loop, updating libev's idea of
629	the current time is a good idea.	675	the current time is a good idea.
630		676
631	See also "The special problem of time updates" in the C<ev_timer> section.	677	See also L<The special problem of time updates> in the C<ev_timer> section.
		678
		679	=item ev_suspend (loop)
		680
		681	=item ev_resume (loop)
		682
		683	These two functions suspend and resume a loop, for use when the loop is
		684	not used for a while and timeouts should not be processed.
		685
		686	A typical use case would be an interactive program such as a game: When
		687	the user presses C<^Z> to suspend the game and resumes it an hour later it
		688	would be best to handle timeouts as if no time had actually passed while
		689	the program was suspended. This can be achieved by calling C<ev_suspend>
		690	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		691	C<ev_resume> directly afterwards to resume timer processing.
		692
		693	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		694	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		695	will be rescheduled (that is, they will lose any events that would have
		696	occured while suspended).
		697
		698	After calling C<ev_suspend> you B<must not> call I<any> function on the
		699	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		700	without a previous call to C<ev_suspend>.
		701
		702	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		703	event loop time (see C<ev_now_update>).
632		704
633	=item ev_loop (loop, int flags)	705	=item ev_loop (loop, int flags)
634		706
635	Finally, this is it, the event handler. This function usually is called	707	Finally, this is it, the event handler. This function usually is called
636	after you initialised all your watchers and you want to start handling	708	after you initialised all your watchers and you want to start handling
…		…
720		792
721	If you have a watcher you never unregister that should not keep C<ev_loop>	793	If you have a watcher you never unregister that should not keep C<ev_loop>
722	from returning, call ev_unref() after starting, and ev_ref() before	794	from returning, call ev_unref() after starting, and ev_ref() before
723	stopping it.	795	stopping it.
724		796
725	As an example, libev itself uses this for its internal signal pipe: It is	797	As an example, libev itself uses this for its internal signal pipe: It
726	not visible to the libev user and should not keep C<ev_loop> from exiting	798	is not visible to the libev user and should not keep C<ev_loop> from
727	if no event watchers registered by it are active. It is also an excellent	799	exiting if no event watchers registered by it are active. It is also an
728	way to do this for generic recurring timers or from within third-party	800	excellent way to do this for generic recurring timers or from within
729	libraries. Just remember to I<unref after start> and I<ref before stop>	801	third-party libraries. Just remember to I<unref after start> and I<ref
730	(but only if the watcher wasn't active before, or was active before,	802	before stop> (but only if the watcher wasn't active before, or was active
731	respectively).	803	before, respectively. Note also that libev might stop watchers itself
		804	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		805	in the callback).
732		806
733	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	807	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
734	running when nothing else is active.	808	running when nothing else is active.
735		809
736	ev_signal exitsig;	810	ev_signal exitsig;
…		…
765		839
766	By setting a higher I<io collect interval> you allow libev to spend more	840	By setting a higher I<io collect interval> you allow libev to spend more
767	time collecting I/O events, so you can handle more events per iteration,	841	time collecting I/O events, so you can handle more events per iteration,
768	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	842	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
769	C<ev_timer>) will be not affected. Setting this to a non-null value will	843	C<ev_timer>) will be not affected. Setting this to a non-null value will
770	introduce an additional C<ev_sleep ()> call into most loop iterations.	844	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		845	sleep time ensures that libev will not poll for I/O events more often then
		846	once per this interval, on average.
771		847
772	Likewise, by setting a higher I<timeout collect interval> you allow libev	848	Likewise, by setting a higher I<timeout collect interval> you allow libev
773	to spend more time collecting timeouts, at the expense of increased	849	to spend more time collecting timeouts, at the expense of increased
774	latency/jitter/inexactness (the watcher callback will be called	850	latency/jitter/inexactness (the watcher callback will be called
775	later). C<ev_io> watchers will not be affected. Setting this to a non-null	851	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
777		853
778	Many (busy) programs can usually benefit by setting the I/O collect	854	Many (busy) programs can usually benefit by setting the I/O collect
779	interval to a value near C<0.1> or so, which is often enough for	855	interval to a value near C<0.1> or so, which is often enough for
780	interactive servers (of course not for games), likewise for timeouts. It	856	interactive servers (of course not for games), likewise for timeouts. It
781	usually doesn't make much sense to set it to a lower value than C<0.01>,	857	usually doesn't make much sense to set it to a lower value than C<0.01>,
782	as this approaches the timing granularity of most systems.	858	as this approaches the timing granularity of most systems. Note that if
		859	you do transactions with the outside world and you can't increase the
		860	parallelity, then this setting will limit your transaction rate (if you
		861	need to poll once per transaction and the I/O collect interval is 0.01,
		862	then you can't do more than 100 transations per second).
783		863
784	Setting the I<timeout collect interval> can improve the opportunity for	864	Setting the I<timeout collect interval> can improve the opportunity for
785	saving power, as the program will "bundle" timer callback invocations that	865	saving power, as the program will "bundle" timer callback invocations that
786	are "near" in time together, by delaying some, thus reducing the number of	866	are "near" in time together, by delaying some, thus reducing the number of
787	times the process sleeps and wakes up again. Another useful technique to	867	times the process sleeps and wakes up again. Another useful technique to
788	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	868	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
789	they fire on, say, one-second boundaries only.	869	they fire on, say, one-second boundaries only.
		870
		871	Example: we only need 0.1s timeout granularity, and we wish not to poll
		872	more often than 100 times per second:
		873
		874	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		875	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		876
		877	=item ev_invoke_pending (loop)
		878
		879	This call will simply invoke all pending watchers while resetting their
		880	pending state. Normally, C<ev_loop> does this automatically when required,
		881	but when overriding the invoke callback this call comes handy.
		882
		883	=item int ev_pending_count (loop)
		884
		885	Returns the number of pending watchers - zero indicates that no watchers
		886	are pending.
		887
		888	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		889
		890	This overrides the invoke pending functionality of the loop: Instead of
		891	invoking all pending watchers when there are any, C<ev_loop> will call
		892	this callback instead. This is useful, for example, when you want to
		893	invoke the actual watchers inside another context (another thread etc.).
		894
		895	If you want to reset the callback, use C<ev_invoke_pending> as new
		896	callback.
		897
		898	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		899
		900	Sometimes you want to share the same loop between multiple threads. This
		901	can be done relatively simply by putting mutex_lock/unlock calls around
		902	each call to a libev function.
		903
		904	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		905	wait for it to return. One way around this is to wake up the loop via
		906	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		907	and I<acquire> callbacks on the loop.
		908
		909	When set, then C<release> will be called just before the thread is
		910	suspended waiting for new events, and C<acquire> is called just
		911	afterwards.
		912
		913	Ideally, C<release> will just call your mutex_unlock function, and
		914	C<acquire> will just call the mutex_lock function again.
		915
		916	While event loop modifications are allowed between invocations of
		917	C<release> and C<acquire> (that's their only purpose after all), no
		918	modifications done will affect the event loop, i.e. adding watchers will
		919	have no effect on the set of file descriptors being watched, or the time
		920	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		921	to take note of any changes you made.
		922
		923	In theory, threads executing C<ev_loop> will be async-cancel safe between
		924	invocations of C<release> and C<acquire>.
		925
		926	See also the locking example in the C<THREADS> section later in this
		927	document.
		928
		929	=item ev_set_userdata (loop, void *data)
		930
		931	=item ev_userdata (loop)
		932
		933	Set and retrieve a single C<void *> associated with a loop. When
		934	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		935	C<0.>
		936
		937	These two functions can be used to associate arbitrary data with a loop,
		938	and are intended solely for the C<invoke_pending_cb>, C<release> and
		939	C<acquire> callbacks described above, but of course can be (ab-)used for
		940	any other purpose as well.
790		941
791	=item ev_loop_verify (loop)	942	=item ev_loop_verify (loop)
792		943
793	This function only does something when C<EV_VERIFY> support has been	944	This function only does something when C<EV_VERIFY> support has been
794	compiled in, which is the default for non-minimal builds. It tries to go	945	compiled in, which is the default for non-minimal builds. It tries to go
…		…
920		1071
921	=item C<EV_ASYNC>	1072	=item C<EV_ASYNC>
922		1073
923	The given async watcher has been asynchronously notified (see C<ev_async>).	1074	The given async watcher has been asynchronously notified (see C<ev_async>).
924		1075
		1076	=item C<EV_CUSTOM>
		1077
		1078	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1079	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1080
925	=item C<EV_ERROR>	1081	=item C<EV_ERROR>
926		1082
927	An unspecified error has occurred, the watcher has been stopped. This might	1083	An unspecified error has occurred, the watcher has been stopped. This might
928	happen because the watcher could not be properly started because libev	1084	happen because the watcher could not be properly started because libev
929	ran out of memory, a file descriptor was found to be closed or any other	1085	ran out of memory, a file descriptor was found to be closed or any other
…		…
1044	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1200	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1045	(default: C<-2>). Pending watchers with higher priority will be invoked	1201	(default: C<-2>). Pending watchers with higher priority will be invoked
1046	before watchers with lower priority, but priority will not keep watchers	1202	before watchers with lower priority, but priority will not keep watchers
1047	from being executed (except for C<ev_idle> watchers).	1203	from being executed (except for C<ev_idle> watchers).
1048		1204
1049	This means that priorities are I<only> used for ordering callback
1050	invocation after new events have been received. This is useful, for
1051	example, to reduce latency after idling, or more often, to bind two
1052	watchers on the same event and make sure one is called first.
1053
1054	If you need to suppress invocation when higher priority events are pending	1205	If you need to suppress invocation when higher priority events are pending
1055	you need to look at C<ev_idle> watchers, which provide this functionality.	1206	you need to look at C<ev_idle> watchers, which provide this functionality.
1056		1207
1057	You I<must not> change the priority of a watcher as long as it is active or	1208	You I<must not> change the priority of a watcher as long as it is active or
1058	pending.	1209	pending.
1059
1060	The default priority used by watchers when no priority has been set is
1061	always C<0>, which is supposed to not be too high and not be too low :).
1062		1210
1063	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1211	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1064	fine, as long as you do not mind that the priority value you query might	1212	fine, as long as you do not mind that the priority value you query might
1065	or might not have been clamped to the valid range.	1213	or might not have been clamped to the valid range.
		1214
		1215	The default priority used by watchers when no priority has been set is
		1216	always C<0>, which is supposed to not be too high and not be too low :).
		1217
		1218	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1219	priorities.
1066		1220
1067	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1221	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1068		1222
1069	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1223	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1070	C<loop> nor C<revents> need to be valid as long as the watcher callback	1224	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1135	#include <stddef.h>	1289	#include <stddef.h>
1136		1290
1137	static void	1291	static void
1138	t1_cb (EV_P_ ev_timer *w, int revents)	1292	t1_cb (EV_P_ ev_timer *w, int revents)
1139	{	1293	{
1140	struct my_biggy big = (struct my_biggy *	1294	struct my_biggy big = (struct my_biggy *)
1141	(((char *)w) - offsetof (struct my_biggy, t1));	1295	(((char *)w) - offsetof (struct my_biggy, t1));
1142	}	1296	}
1143		1297
1144	static void	1298	static void
1145	t2_cb (EV_P_ ev_timer *w, int revents)	1299	t2_cb (EV_P_ ev_timer *w, int revents)
1146	{	1300	{
1147	struct my_biggy big = (struct my_biggy *	1301	struct my_biggy big = (struct my_biggy *)
1148	(((char *)w) - offsetof (struct my_biggy, t2));	1302	(((char *)w) - offsetof (struct my_biggy, t2));
1149	}	1303	}
		1304
		1305	=head2 WATCHER PRIORITY MODELS
		1306
		1307	Many event loops support I<watcher priorities>, which are usually small
		1308	integers that influence the ordering of event callback invocation
		1309	between watchers in some way, all else being equal.
		1310
		1311	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1312	description for the more technical details such as the actual priority
		1313	range.
		1314
		1315	There are two common ways how these these priorities are being interpreted
		1316	by event loops:
		1317
		1318	In the more common lock-out model, higher priorities "lock out" invocation
		1319	of lower priority watchers, which means as long as higher priority
		1320	watchers receive events, lower priority watchers are not being invoked.
		1321
		1322	The less common only-for-ordering model uses priorities solely to order
		1323	callback invocation within a single event loop iteration: Higher priority
		1324	watchers are invoked before lower priority ones, but they all get invoked
		1325	before polling for new events.
		1326
		1327	Libev uses the second (only-for-ordering) model for all its watchers
		1328	except for idle watchers (which use the lock-out model).
		1329
		1330	The rationale behind this is that implementing the lock-out model for
		1331	watchers is not well supported by most kernel interfaces, and most event
		1332	libraries will just poll for the same events again and again as long as
		1333	their callbacks have not been executed, which is very inefficient in the
		1334	common case of one high-priority watcher locking out a mass of lower
		1335	priority ones.
		1336
		1337	Static (ordering) priorities are most useful when you have two or more
		1338	watchers handling the same resource: a typical usage example is having an
		1339	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1340	timeouts. Under load, data might be received while the program handles
		1341	other jobs, but since timers normally get invoked first, the timeout
		1342	handler will be executed before checking for data. In that case, giving
		1343	the timer a lower priority than the I/O watcher ensures that I/O will be
		1344	handled first even under adverse conditions (which is usually, but not
		1345	always, what you want).
		1346
		1347	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1348	will only be executed when no same or higher priority watchers have
		1349	received events, they can be used to implement the "lock-out" model when
		1350	required.
		1351
		1352	For example, to emulate how many other event libraries handle priorities,
		1353	you can associate an C<ev_idle> watcher to each such watcher, and in
		1354	the normal watcher callback, you just start the idle watcher. The real
		1355	processing is done in the idle watcher callback. This causes libev to
		1356	continously poll and process kernel event data for the watcher, but when
		1357	the lock-out case is known to be rare (which in turn is rare :), this is
		1358	workable.
		1359
		1360	Usually, however, the lock-out model implemented that way will perform
		1361	miserably under the type of load it was designed to handle. In that case,
		1362	it might be preferable to stop the real watcher before starting the
		1363	idle watcher, so the kernel will not have to process the event in case
		1364	the actual processing will be delayed for considerable time.
		1365
		1366	Here is an example of an I/O watcher that should run at a strictly lower
		1367	priority than the default, and which should only process data when no
		1368	other events are pending:
		1369
		1370	ev_idle idle; // actual processing watcher
		1371	ev_io io; // actual event watcher
		1372
		1373	static void
		1374	io_cb (EV_P_ ev_io *w, int revents)
		1375	{
		1376	// stop the I/O watcher, we received the event, but
		1377	// are not yet ready to handle it.
		1378	ev_io_stop (EV_A_ w);
		1379
		1380	// start the idle watcher to ahndle the actual event.
		1381	// it will not be executed as long as other watchers
		1382	// with the default priority are receiving events.
		1383	ev_idle_start (EV_A_ &idle);
		1384	}
		1385
		1386	static void
		1387	idle_cb (EV_P_ ev_idle *w, int revents)
		1388	{
		1389	// actual processing
		1390	read (STDIN_FILENO, ...);
		1391
		1392	// have to start the I/O watcher again, as
		1393	// we have handled the event
		1394	ev_io_start (EV_P_ &io);
		1395	}
		1396
		1397	// initialisation
		1398	ev_idle_init (&idle, idle_cb);
		1399	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1400	ev_io_start (EV_DEFAULT_ &io);
		1401
		1402	In the "real" world, it might also be beneficial to start a timer, so that
		1403	low-priority connections can not be locked out forever under load. This
		1404	enables your program to keep a lower latency for important connections
		1405	during short periods of high load, while not completely locking out less
		1406	important ones.
1150		1407
1151		1408
1152	=head1 WATCHER TYPES	1409	=head1 WATCHER TYPES
1153		1410
1154	This section describes each watcher in detail, but will not repeat	1411	This section describes each watcher in detail, but will not repeat
…		…
1180	descriptors to non-blocking mode is also usually a good idea (but not	1437	descriptors to non-blocking mode is also usually a good idea (but not
1181	required if you know what you are doing).	1438	required if you know what you are doing).
1182		1439
1183	If you cannot use non-blocking mode, then force the use of a	1440	If you cannot use non-blocking mode, then force the use of a
1184	known-to-be-good backend (at the time of this writing, this includes only	1441	known-to-be-good backend (at the time of this writing, this includes only
1185	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1442	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1443	descriptors for which non-blocking operation makes no sense (such as
		1444	files) - libev doesn't guarentee any specific behaviour in that case.
1186		1445
1187	Another thing you have to watch out for is that it is quite easy to	1446	Another thing you have to watch out for is that it is quite easy to
1188	receive "spurious" readiness notifications, that is your callback might	1447	receive "spurious" readiness notifications, that is your callback might
1189	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1448	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1190	because there is no data. Not only are some backends known to create a	1449	because there is no data. Not only are some backends known to create a
…		…
1311	year, it will still time out after (roughly) one hour. "Roughly" because	1570	year, it will still time out after (roughly) one hour. "Roughly" because
1312	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1571	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1313	monotonic clock option helps a lot here).	1572	monotonic clock option helps a lot here).
1314		1573
1315	The callback is guaranteed to be invoked only I<after> its timeout has	1574	The callback is guaranteed to be invoked only I<after> its timeout has
1316	passed, but if multiple timers become ready during the same loop iteration	1575	passed (not I<at>, so on systems with very low-resolution clocks this
1317	then order of execution is undefined.	1576	might introduce a small delay). If multiple timers become ready during the
		1577	same loop iteration then the ones with earlier time-out values are invoked
		1578	before ones of the same priority with later time-out values (but this is
		1579	no longer true when a callback calls C<ev_loop> recursively).
1318		1580
1319	=head3 Be smart about timeouts	1581	=head3 Be smart about timeouts
1320		1582
1321	Many real-world problems involve some kind of timeout, usually for error	1583	Many real-world problems involve some kind of timeout, usually for error
1322	recovery. A typical example is an HTTP request - if the other side hangs,	1584	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1366	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>	1628	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
1367	member and C<ev_timer_again>.	1629	member and C<ev_timer_again>.
1368		1630
1369	At start:	1631	At start:
1370		1632
1371	ev_timer_init (timer, callback);	1633	ev_init (timer, callback);
1372	timer->repeat = 60.;	1634	timer->repeat = 60.;
1373	ev_timer_again (loop, timer);	1635	ev_timer_again (loop, timer);
1374		1636
1375	Each time there is some activity:	1637	Each time there is some activity:
1376		1638
…		…
1415	else	1677	else
1416	{	1678	{
1417	// callback was invoked, but there was some activity, re-arm	1679	// callback was invoked, but there was some activity, re-arm
1418	// the watcher to fire in last_activity + 60, which is	1680	// the watcher to fire in last_activity + 60, which is
1419	// guaranteed to be in the future, so "again" is positive:	1681	// guaranteed to be in the future, so "again" is positive:
1420	w->again = timeout - now;	1682	w->repeat = timeout - now;
1421	ev_timer_again (EV_A_ w);	1683	ev_timer_again (EV_A_ w);
1422	}	1684	}
1423	}	1685	}
1424		1686
1425	To summarise the callback: first calculate the real timeout (defined	1687	To summarise the callback: first calculate the real timeout (defined
…		…
1438		1700
1439	To start the timer, simply initialise the watcher and set C<last_activity>	1701	To start the timer, simply initialise the watcher and set C<last_activity>
1440	to the current time (meaning we just have some activity :), then call the	1702	to the current time (meaning we just have some activity :), then call the
1441	callback, which will "do the right thing" and start the timer:	1703	callback, which will "do the right thing" and start the timer:
1442		1704
1443	ev_timer_init (timer, callback);	1705	ev_init (timer, callback);
1444	last_activity = ev_now (loop);	1706	last_activity = ev_now (loop);
1445	callback (loop, timer, EV_TIMEOUT);	1707	callback (loop, timer, EV_TIMEOUT);
1446		1708
1447	And when there is some activity, simply store the current time in	1709	And when there is some activity, simply store the current time in
1448	C<last_activity>, no libev calls at all:	1710	C<last_activity>, no libev calls at all:
…		…
1509		1771
1510	If the event loop is suspended for a long time, you can also force an	1772	If the event loop is suspended for a long time, you can also force an
1511	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1773	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1512	()>.	1774	()>.
1513		1775
		1776	=head3 The special problems of suspended animation
		1777
		1778	When you leave the server world it is quite customary to hit machines that
		1779	can suspend/hibernate - what happens to the clocks during such a suspend?
		1780
		1781	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1782	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1783	to run until the system is suspended, but they will not advance while the
		1784	system is suspended. That means, on resume, it will be as if the program
		1785	was frozen for a few seconds, but the suspend time will not be counted
		1786	towards C<ev_timer> when a monotonic clock source is used. The real time
		1787	clock advanced as expected, but if it is used as sole clocksource, then a
		1788	long suspend would be detected as a time jump by libev, and timers would
		1789	be adjusted accordingly.
		1790
		1791	I would not be surprised to see different behaviour in different between
		1792	operating systems, OS versions or even different hardware.
		1793
		1794	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1795	time jump in the monotonic clocks and the realtime clock. If the program
		1796	is suspended for a very long time, and monotonic clock sources are in use,
		1797	then you can expect C<ev_timer>s to expire as the full suspension time
		1798	will be counted towards the timers. When no monotonic clock source is in
		1799	use, then libev will again assume a timejump and adjust accordingly.
		1800
		1801	It might be beneficial for this latter case to call C<ev_suspend>
		1802	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1803	deterministic behaviour in this case (you can do nothing against
		1804	C<SIGSTOP>).
		1805
1514	=head3 Watcher-Specific Functions and Data Members	1806	=head3 Watcher-Specific Functions and Data Members
1515		1807
1516	=over 4	1808	=over 4
1517		1809
1518	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1810	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1541	If the timer is started but non-repeating, stop it (as if it timed out).	1833	If the timer is started but non-repeating, stop it (as if it timed out).
1542		1834
1543	If the timer is repeating, either start it if necessary (with the	1835	If the timer is repeating, either start it if necessary (with the
1544	C<repeat> value), or reset the running timer to the C<repeat> value.	1836	C<repeat> value), or reset the running timer to the C<repeat> value.
1545		1837
1546	This sounds a bit complicated, see "Be smart about timeouts", above, for a	1838	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1547	usage example.	1839	usage example.
		1840
		1841	=item ev_timer_remaining (loop, ev_timer *)
		1842
		1843	Returns the remaining time until a timer fires. If the timer is active,
		1844	then this time is relative to the current event loop time, otherwise it's
		1845	the timeout value currently configured.
		1846
		1847	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1848	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1849	will return C<4>. When the timer expires and is restarted, it will return
		1850	roughly C<7> (likely slightly less as callback invocation takes some time,
		1851	too), and so on.
1548		1852
1549	=item ev_tstamp repeat [read-write]	1853	=item ev_tstamp repeat [read-write]
1550		1854
1551	The current C<repeat> value. Will be used each time the watcher times out	1855	The current C<repeat> value. Will be used each time the watcher times out
1552	or C<ev_timer_again> is called, and determines the next timeout (if any),	1856	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1590	=head2 C<ev_periodic> - to cron or not to cron?	1894	=head2 C<ev_periodic> - to cron or not to cron?
1591		1895
1592	Periodic watchers are also timers of a kind, but they are very versatile	1896	Periodic watchers are also timers of a kind, but they are very versatile
1593	(and unfortunately a bit complex).	1897	(and unfortunately a bit complex).
1594		1898
1595	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1899	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1596	but on wall clock time (absolute time). You can tell a periodic watcher	1900	relative time, the physical time that passes) but on wall clock time
1597	to trigger after some specific point in time. For example, if you tell a	1901	(absolute time, the thing you can read on your calender or clock). The
1598	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1902	difference is that wall clock time can run faster or slower than real
1599	+ 10.>, that is, an absolute time not a delay) and then reset your system	1903	time, and time jumps are not uncommon (e.g. when you adjust your
1600	clock to January of the previous year, then it will take more than year	1904	wrist-watch).
1601	to trigger the event (unlike an C<ev_timer>, which would still trigger
1602	roughly 10 seconds later as it uses a relative timeout).
1603		1905
		1906	You can tell a periodic watcher to trigger after some specific point
		1907	in time: for example, if you tell a periodic watcher to trigger "in 10
		1908	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1909	not a delay) and then reset your system clock to January of the previous
		1910	year, then it will take a year or more to trigger the event (unlike an
		1911	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1912	it, as it uses a relative timeout).
		1913
1604	C<ev_periodic>s can also be used to implement vastly more complex timers,	1914	C<ev_periodic> watchers can also be used to implement vastly more complex
1605	such as triggering an event on each "midnight, local time", or other	1915	timers, such as triggering an event on each "midnight, local time", or
1606	complicated rules.	1916	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1917	those cannot react to time jumps.
1607		1918
1608	As with timers, the callback is guaranteed to be invoked only when the	1919	As with timers, the callback is guaranteed to be invoked only when the
1609	time (C<at>) has passed, but if multiple periodic timers become ready	1920	point in time where it is supposed to trigger has passed. If multiple
1610	during the same loop iteration, then order of execution is undefined.	1921	timers become ready during the same loop iteration then the ones with
		1922	earlier time-out values are invoked before ones with later time-out values
		1923	(but this is no longer true when a callback calls C<ev_loop> recursively).
1611		1924
1612	=head3 Watcher-Specific Functions and Data Members	1925	=head3 Watcher-Specific Functions and Data Members
1613		1926
1614	=over 4	1927	=over 4
1615		1928
1616	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1929	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1617		1930
1618	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1931	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1619		1932
1620	Lots of arguments, lets sort it out... There are basically three modes of	1933	Lots of arguments, let's sort it out... There are basically three modes of
1621	operation, and we will explain them from simplest to most complex:	1934	operation, and we will explain them from simplest to most complex:
1622		1935
1623	=over 4	1936	=over 4
1624		1937
1625	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1938	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1626		1939
1627	In this configuration the watcher triggers an event after the wall clock	1940	In this configuration the watcher triggers an event after the wall clock
1628	time C<at> has passed. It will not repeat and will not adjust when a time	1941	time C<offset> has passed. It will not repeat and will not adjust when a
1629	jump occurs, that is, if it is to be run at January 1st 2011 then it will	1942	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1630	only run when the system clock reaches or surpasses this time.	1943	will be stopped and invoked when the system clock reaches or surpasses
		1944	this point in time.
1631		1945
1632	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1946	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1633		1947
1634	In this mode the watcher will always be scheduled to time out at the next	1948	In this mode the watcher will always be scheduled to time out at the next
1635	C<at + N * interval> time (for some integer N, which can also be negative)	1949	C<offset + N * interval> time (for some integer N, which can also be
1636	and then repeat, regardless of any time jumps.	1950	negative) and then repeat, regardless of any time jumps. The C<offset>
		1951	argument is merely an offset into the C<interval> periods.
1637		1952
1638	This can be used to create timers that do not drift with respect to the	1953	This can be used to create timers that do not drift with respect to the
1639	system clock, for example, here is a C<ev_periodic> that triggers each	1954	system clock, for example, here is an C<ev_periodic> that triggers each
1640	hour, on the hour:	1955	hour, on the hour (with respect to UTC):
1641		1956
1642	ev_periodic_set (&periodic, 0., 3600., 0);	1957	ev_periodic_set (&periodic, 0., 3600., 0);
1643		1958
1644	This doesn't mean there will always be 3600 seconds in between triggers,	1959	This doesn't mean there will always be 3600 seconds in between triggers,
1645	but only that the callback will be called when the system time shows a	1960	but only that the callback will be called when the system time shows a
1646	full hour (UTC), or more correctly, when the system time is evenly divisible	1961	full hour (UTC), or more correctly, when the system time is evenly divisible
1647	by 3600.	1962	by 3600.
1648		1963
1649	Another way to think about it (for the mathematically inclined) is that	1964	Another way to think about it (for the mathematically inclined) is that
1650	C<ev_periodic> will try to run the callback in this mode at the next possible	1965	C<ev_periodic> will try to run the callback in this mode at the next possible
1651	time where C<time = at (mod interval)>, regardless of any time jumps.	1966	time where C<time = offset (mod interval)>, regardless of any time jumps.
1652		1967
1653	For numerical stability it is preferable that the C<at> value is near	1968	For numerical stability it is preferable that the C<offset> value is near
1654	C<ev_now ()> (the current time), but there is no range requirement for	1969	C<ev_now ()> (the current time), but there is no range requirement for
1655	this value, and in fact is often specified as zero.	1970	this value, and in fact is often specified as zero.
1656		1971
1657	Note also that there is an upper limit to how often a timer can fire (CPU	1972	Note also that there is an upper limit to how often a timer can fire (CPU
1658	speed for example), so if C<interval> is very small then timing stability	1973	speed for example), so if C<interval> is very small then timing stability
1659	will of course deteriorate. Libev itself tries to be exact to be about one	1974	will of course deteriorate. Libev itself tries to be exact to be about one
1660	millisecond (if the OS supports it and the machine is fast enough).	1975	millisecond (if the OS supports it and the machine is fast enough).
1661		1976
1662	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1977	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1663		1978
1664	In this mode the values for C<interval> and C<at> are both being	1979	In this mode the values for C<interval> and C<offset> are both being
1665	ignored. Instead, each time the periodic watcher gets scheduled, the	1980	ignored. Instead, each time the periodic watcher gets scheduled, the
1666	reschedule callback will be called with the watcher as first, and the	1981	reschedule callback will be called with the watcher as first, and the
1667	current time as second argument.	1982	current time as second argument.
1668		1983
1669	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1984	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1670	ever, or make ANY event loop modifications whatsoever>.	1985	or make ANY other event loop modifications whatsoever, unless explicitly
		1986	allowed by documentation here>.
1671		1987
1672	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1988	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1673	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1989	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1674	only event loop modification you are allowed to do).	1990	only event loop modification you are allowed to do).
1675		1991
…		…
1705	a different time than the last time it was called (e.g. in a crond like	2021	a different time than the last time it was called (e.g. in a crond like
1706	program when the crontabs have changed).	2022	program when the crontabs have changed).
1707		2023
1708	=item ev_tstamp ev_periodic_at (ev_periodic *)	2024	=item ev_tstamp ev_periodic_at (ev_periodic *)
1709		2025
1710	When active, returns the absolute time that the watcher is supposed to	2026	When active, returns the absolute time that the watcher is supposed
1711	trigger next.	2027	to trigger next. This is not the same as the C<offset> argument to
		2028	C<ev_periodic_set>, but indeed works even in interval and manual
		2029	rescheduling modes.
1712		2030
1713	=item ev_tstamp offset [read-write]	2031	=item ev_tstamp offset [read-write]
1714		2032
1715	When repeating, this contains the offset value, otherwise this is the	2033	When repeating, this contains the offset value, otherwise this is the
1716	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2034	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2035	although libev might modify this value for better numerical stability).
1717		2036
1718	Can be modified any time, but changes only take effect when the periodic	2037	Can be modified any time, but changes only take effect when the periodic
1719	timer fires or C<ev_periodic_again> is being called.	2038	timer fires or C<ev_periodic_again> is being called.
1720		2039
1721	=item ev_tstamp interval [read-write]	2040	=item ev_tstamp interval [read-write]
…		…
1773	Signal watchers will trigger an event when the process receives a specific	2092	Signal watchers will trigger an event when the process receives a specific
1774	signal one or more times. Even though signals are very asynchronous, libev	2093	signal one or more times. Even though signals are very asynchronous, libev
1775	will try it's best to deliver signals synchronously, i.e. as part of the	2094	will try it's best to deliver signals synchronously, i.e. as part of the
1776	normal event processing, like any other event.	2095	normal event processing, like any other event.
1777		2096
1778	If you want signals asynchronously, just use C<sigaction> as you would	2097	If you want signals to be delivered truly asynchronously, just use
1779	do without libev and forget about sharing the signal. You can even use	2098	C<sigaction> as you would do without libev and forget about sharing
1780	C<ev_async> from a signal handler to synchronously wake up an event loop.	2099	the signal. You can even use C<ev_async> from a signal handler to
		2100	synchronously wake up an event loop.
1781		2101
1782	You can configure as many watchers as you like per signal. Only when the	2102	You can configure as many watchers as you like for the same signal, but
		2103	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2104	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2105	C<SIGINT> in both the default loop and another loop at the same time. At
		2106	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2107
1783	first watcher gets started will libev actually register a signal handler	2108	When the first watcher gets started will libev actually register something
1784	with the kernel (thus it coexists with your own signal handlers as long as	2109	with the kernel (thus it coexists with your own signal handlers as long as
1785	you don't register any with libev for the same signal). Similarly, when	2110	you don't register any with libev for the same signal).
1786	the last signal watcher for a signal is stopped, libev will reset the	2111
1787	signal handler to SIG_DFL (regardless of what it was set to before).	2112	Both the signal mask state (C<sigprocmask>) and the signal handler state
		2113	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2114	sotpping it again), that is, libev might or might not block the signal,
		2115	and might or might not set or restore the installed signal handler.
1788		2116
1789	If possible and supported, libev will install its handlers with	2117	If possible and supported, libev will install its handlers with
1790	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2118	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1791	interrupted. If you have a problem with system calls getting interrupted by	2119	not be unduly interrupted. If you have a problem with system calls getting
1792	signals you can block all signals in an C<ev_check> watcher and unblock	2120	interrupted by signals you can block all signals in an C<ev_check> watcher
1793	them in an C<ev_prepare> watcher.	2121	and unblock them in an C<ev_prepare> watcher.
1794		2122
1795	=head3 Watcher-Specific Functions and Data Members	2123	=head3 Watcher-Specific Functions and Data Members
1796		2124
1797	=over 4	2125	=over 4
1798		2126
…		…
1830	some child status changes (most typically when a child of yours dies or	2158	some child status changes (most typically when a child of yours dies or
1831	exits). It is permissible to install a child watcher I<after> the child	2159	exits). It is permissible to install a child watcher I<after> the child
1832	has been forked (which implies it might have already exited), as long	2160	has been forked (which implies it might have already exited), as long
1833	as the event loop isn't entered (or is continued from a watcher), i.e.,	2161	as the event loop isn't entered (or is continued from a watcher), i.e.,
1834	forking and then immediately registering a watcher for the child is fine,	2162	forking and then immediately registering a watcher for the child is fine,
1835	but forking and registering a watcher a few event loop iterations later is	2163	but forking and registering a watcher a few event loop iterations later or
1836	not.	2164	in the next callback invocation is not.
1837		2165
1838	Only the default event loop is capable of handling signals, and therefore	2166	Only the default event loop is capable of handling signals, and therefore
1839	you can only register child watchers in the default event loop.	2167	you can only register child watchers in the default event loop.
1840		2168
		2169	Due to some design glitches inside libev, child watchers will always be
		2170	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2171	libev)
		2172
1841	=head3 Process Interaction	2173	=head3 Process Interaction
1842		2174
1843	Libev grabs C<SIGCHLD> as soon as the default event loop is	2175	Libev grabs C<SIGCHLD> as soon as the default event loop is
1844	initialised. This is necessary to guarantee proper behaviour even if	2176	initialised. This is necessary to guarantee proper behaviour even if the
1845	the first child watcher is started after the child exits. The occurrence	2177	first child watcher is started after the child exits. The occurrence
1846	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2178	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1847	synchronously as part of the event loop processing. Libev always reaps all	2179	synchronously as part of the event loop processing. Libev always reaps all
1848	children, even ones not watched.	2180	children, even ones not watched.
1849		2181
1850	=head3 Overriding the Built-In Processing	2182	=head3 Overriding the Built-In Processing
…		…
1860	=head3 Stopping the Child Watcher	2192	=head3 Stopping the Child Watcher
1861		2193
1862	Currently, the child watcher never gets stopped, even when the	2194	Currently, the child watcher never gets stopped, even when the
1863	child terminates, so normally one needs to stop the watcher in the	2195	child terminates, so normally one needs to stop the watcher in the
1864	callback. Future versions of libev might stop the watcher automatically	2196	callback. Future versions of libev might stop the watcher automatically
1865	when a child exit is detected.	2197	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2198	problem).
1866		2199
1867	=head3 Watcher-Specific Functions and Data Members	2200	=head3 Watcher-Specific Functions and Data Members
1868		2201
1869	=over 4	2202	=over 4
1870		2203
…		…
1998	There is no support for kqueue, as apparently it cannot be used to	2331	There is no support for kqueue, as apparently it cannot be used to
1999	implement this functionality, due to the requirement of having a file	2332	implement this functionality, due to the requirement of having a file
2000	descriptor open on the object at all times, and detecting renames, unlinks	2333	descriptor open on the object at all times, and detecting renames, unlinks
2001	etc. is difficult.	2334	etc. is difficult.
2002		2335
		2336	=head3 C<stat ()> is a synchronous operation
		2337
		2338	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2339	the process. The exception are C<ev_stat> watchers - those call C<stat
		2340	()>, which is a synchronous operation.
		2341
		2342	For local paths, this usually doesn't matter: unless the system is very
		2343	busy or the intervals between stat's are large, a stat call will be fast,
		2344	as the path data is usually in memory already (except when starting the
		2345	watcher).
		2346
		2347	For networked file systems, calling C<stat ()> can block an indefinite
		2348	time due to network issues, and even under good conditions, a stat call
		2349	often takes multiple milliseconds.
		2350
		2351	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2352	paths, although this is fully supported by libev.
		2353
2003	=head3 The special problem of stat time resolution	2354	=head3 The special problem of stat time resolution
2004		2355
2005	The C<stat ()> system call only supports full-second resolution portably,	2356	The C<stat ()> system call only supports full-second resolution portably,
2006	and even on systems where the resolution is higher, most file systems	2357	and even on systems where the resolution is higher, most file systems
2007	still only support whole seconds.	2358	still only support whole seconds.
…		…
2155		2506
2156	=head3 Watcher-Specific Functions and Data Members	2507	=head3 Watcher-Specific Functions and Data Members
2157		2508
2158	=over 4	2509	=over 4
2159		2510
2160	=item ev_idle_init (ev_signal *, callback)	2511	=item ev_idle_init (ev_idle *, callback)
2161		2512
2162	Initialises and configures the idle watcher - it has no parameters of any	2513	Initialises and configures the idle watcher - it has no parameters of any
2163	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2514	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
2164	believe me.	2515	believe me.
2165		2516
…		…
2178	// no longer anything immediate to do.	2529	// no longer anything immediate to do.
2179	}	2530	}
2180		2531
2181	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2532	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2182	ev_idle_init (idle_watcher, idle_cb);	2533	ev_idle_init (idle_watcher, idle_cb);
2183	ev_idle_start (loop, idle_cb);	2534	ev_idle_start (loop, idle_watcher);
2184		2535
2185		2536
2186	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2537	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2187		2538
2188	Prepare and check watchers are usually (but not always) used in pairs:	2539	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2281	struct pollfd fds [nfd];	2632	struct pollfd fds [nfd];
2282	// actual code will need to loop here and realloc etc.	2633	// actual code will need to loop here and realloc etc.
2283	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2634	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2284		2635
2285	/* the callback is illegal, but won't be called as we stop during check */	2636	/* the callback is illegal, but won't be called as we stop during check */
2286	ev_timer_init (&tw, 0, timeout * 1e-3);	2637	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2287	ev_timer_start (loop, &tw);	2638	ev_timer_start (loop, &tw);
2288		2639
2289	// create one ev_io per pollfd	2640	// create one ev_io per pollfd
2290	for (int i = 0; i < nfd; ++i)	2641	for (int i = 0; i < nfd; ++i)
2291	{	2642	{
…		…
2404	some fds have to be watched and handled very quickly (with low latency),	2755	some fds have to be watched and handled very quickly (with low latency),
2405	and even priorities and idle watchers might have too much overhead. In	2756	and even priorities and idle watchers might have too much overhead. In
2406	this case you would put all the high priority stuff in one loop and all	2757	this case you would put all the high priority stuff in one loop and all
2407	the rest in a second one, and embed the second one in the first.	2758	the rest in a second one, and embed the second one in the first.
2408		2759
2409	As long as the watcher is active, the callback will be invoked every time	2760	As long as the watcher is active, the callback will be invoked every
2410	there might be events pending in the embedded loop. The callback must then	2761	time there might be events pending in the embedded loop. The callback
2411	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2762	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2412	their callbacks (you could also start an idle watcher to give the embedded	2763	sweep and invoke their callbacks (the callback doesn't need to invoke the
2413	loop strictly lower priority for example). You can also set the callback	2764	C<ev_embed_sweep> function directly, it could also start an idle watcher
2414	to C<0>, in which case the embed watcher will automatically execute the	2765	to give the embedded loop strictly lower priority for example).
2415	embedded loop sweep.
2416		2766
2417	As long as the watcher is started it will automatically handle events. The	2767	You can also set the callback to C<0>, in which case the embed watcher
2418	callback will be invoked whenever some events have been handled. You can	2768	will automatically execute the embedded loop sweep whenever necessary.
2419	set the callback to C<0> to avoid having to specify one if you are not
2420	interested in that.
2421		2769
2422	Also, there have not currently been made special provisions for forking:	2770	Fork detection will be handled transparently while the C<ev_embed> watcher
2423	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2771	is active, i.e., the embedded loop will automatically be forked when the
2424	but you will also have to stop and restart any C<ev_embed> watchers	2772	embedding loop forks. In other cases, the user is responsible for calling
2425	yourself - but you can use a fork watcher to handle this automatically,	2773	C<ev_loop_fork> on the embedded loop.
2426	and future versions of libev might do just that.
2427		2774
2428	Unfortunately, not all backends are embeddable: only the ones returned by	2775	Unfortunately, not all backends are embeddable: only the ones returned by
2429	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2776	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2430	portable one.	2777	portable one.
2431		2778
…		…
2525	event loop blocks next and before C<ev_check> watchers are being called,	2872	event loop blocks next and before C<ev_check> watchers are being called,
2526	and only in the child after the fork. If whoever good citizen calling	2873	and only in the child after the fork. If whoever good citizen calling
2527	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2874	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2528	handlers will be invoked, too, of course.	2875	handlers will be invoked, too, of course.
2529		2876
		2877	=head3 The special problem of life after fork - how is it possible?
		2878
		2879	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2880	up/change the process environment, followed by a call to C<exec()>. This
		2881	sequence should be handled by libev without any problems.
		2882
		2883	This changes when the application actually wants to do event handling
		2884	in the child, or both parent in child, in effect "continuing" after the
		2885	fork.
		2886
		2887	The default mode of operation (for libev, with application help to detect
		2888	forks) is to duplicate all the state in the child, as would be expected
		2889	when I<either> the parent I<or> the child process continues.
		2890
		2891	When both processes want to continue using libev, then this is usually the
		2892	wrong result. In that case, usually one process (typically the parent) is
		2893	supposed to continue with all watchers in place as before, while the other
		2894	process typically wants to start fresh, i.e. without any active watchers.
		2895
		2896	The cleanest and most efficient way to achieve that with libev is to
		2897	simply create a new event loop, which of course will be "empty", and
		2898	use that for new watchers. This has the advantage of not touching more
		2899	memory than necessary, and thus avoiding the copy-on-write, and the
		2900	disadvantage of having to use multiple event loops (which do not support
		2901	signal watchers).
		2902
		2903	When this is not possible, or you want to use the default loop for
		2904	other reasons, then in the process that wants to start "fresh", call
		2905	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2906	the default loop will "orphan" (not stop) all registered watchers, so you
		2907	have to be careful not to execute code that modifies those watchers. Note
		2908	also that in that case, you have to re-register any signal watchers.
		2909
2530	=head3 Watcher-Specific Functions and Data Members	2910	=head3 Watcher-Specific Functions and Data Members
2531		2911
2532	=over 4	2912	=over 4
2533		2913
2534	=item ev_fork_init (ev_signal *, callback)	2914	=item ev_fork_init (ev_signal *, callback)
…		…
2662	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3042	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2663	C<ev_feed_event>, this call is safe to do from other threads, signal or	3043	C<ev_feed_event>, this call is safe to do from other threads, signal or
2664	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3044	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2665	section below on what exactly this means).	3045	section below on what exactly this means).
2666		3046
		3047	Note that, as with other watchers in libev, multiple events might get
		3048	compressed into a single callback invocation (another way to look at this
		3049	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3050	reset when the event loop detects that).
		3051
2667	This call incurs the overhead of a system call only once per loop iteration,	3052	This call incurs the overhead of a system call only once per event loop
2668	so while the overhead might be noticeable, it doesn't apply to repeated	3053	iteration, so while the overhead might be noticeable, it doesn't apply to
2669	calls to C<ev_async_send>.	3054	repeated calls to C<ev_async_send> for the same event loop.
2670		3055
2671	=item bool = ev_async_pending (ev_async *)	3056	=item bool = ev_async_pending (ev_async *)
2672		3057
2673	Returns a non-zero value when C<ev_async_send> has been called on the	3058	Returns a non-zero value when C<ev_async_send> has been called on the
2674	watcher but the event has not yet been processed (or even noted) by the	3059	watcher but the event has not yet been processed (or even noted) by the
…		…
2677	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3062	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2678	the loop iterates next and checks for the watcher to have become active,	3063	the loop iterates next and checks for the watcher to have become active,
2679	it will reset the flag again. C<ev_async_pending> can be used to very	3064	it will reset the flag again. C<ev_async_pending> can be used to very
2680	quickly check whether invoking the loop might be a good idea.	3065	quickly check whether invoking the loop might be a good idea.
2681		3066
2682	Not that this does I<not> check whether the watcher itself is pending, only	3067	Not that this does I<not> check whether the watcher itself is pending,
2683	whether it has been requested to make this watcher pending.	3068	only whether it has been requested to make this watcher pending: there
		3069	is a time window between the event loop checking and resetting the async
		3070	notification, and the callback being invoked.
2684		3071
2685	=back	3072	=back
2686		3073
2687		3074
2688	=head1 OTHER FUNCTIONS	3075	=head1 OTHER FUNCTIONS
…		…
2867		3254
2868	myclass obj;	3255	myclass obj;
2869	ev::io iow;	3256	ev::io iow;
2870	iow.set <myclass, &myclass::io_cb> (&obj);	3257	iow.set <myclass, &myclass::io_cb> (&obj);
2871		3258
		3259	=item w->set (object *)
		3260
		3261	This is an B<experimental> feature that might go away in a future version.
		3262
		3263	This is a variation of a method callback - leaving out the method to call
		3264	will default the method to C<operator ()>, which makes it possible to use
		3265	functor objects without having to manually specify the C<operator ()> all
		3266	the time. Incidentally, you can then also leave out the template argument
		3267	list.
		3268
		3269	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3270	int revents)>.
		3271
		3272	See the method-C<set> above for more details.
		3273
		3274	Example: use a functor object as callback.
		3275
		3276	struct myfunctor
		3277	{
		3278	void operator() (ev::io &w, int revents)
		3279	{
		3280	...
		3281	}
		3282	}
		3283
		3284	myfunctor f;
		3285
		3286	ev::io w;
		3287	w.set (&f);
		3288
2872	=item w->set<function> (void *data = 0)	3289	=item w->set<function> (void *data = 0)
2873		3290
2874	Also sets a callback, but uses a static method or plain function as	3291	Also sets a callback, but uses a static method or plain function as
2875	callback. The optional C<data> argument will be stored in the watcher's	3292	callback. The optional C<data> argument will be stored in the watcher's
2876	C<data> member and is free for you to use.	3293	C<data> member and is free for you to use.
…		…
2962	L<http://software.schmorp.de/pkg/EV>.	3379	L<http://software.schmorp.de/pkg/EV>.
2963		3380
2964	=item Python	3381	=item Python
2965		3382
2966	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3383	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2967	seems to be quite complete and well-documented. Note, however, that the	3384	seems to be quite complete and well-documented.
2968	patch they require for libev is outright dangerous as it breaks the ABI
2969	for everybody else, and therefore, should never be applied in an installed
2970	libev (if python requires an incompatible ABI then it needs to embed
2971	libev).
2972		3385
2973	=item Ruby	3386	=item Ruby
2974		3387
2975	Tony Arcieri has written a ruby extension that offers access to a subset	3388	Tony Arcieri has written a ruby extension that offers access to a subset
2976	of the libev API and adds file handle abstractions, asynchronous DNS and	3389	of the libev API and adds file handle abstractions, asynchronous DNS and
2977	more on top of it. It can be found via gem servers. Its homepage is at	3390	more on top of it. It can be found via gem servers. Its homepage is at
2978	L<http://rev.rubyforge.org/>.	3391	L<http://rev.rubyforge.org/>.
		3392
		3393	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3394	makes rev work even on mingw.
		3395
		3396	=item Haskell
		3397
		3398	A haskell binding to libev is available at
		3399	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
2979		3400
2980	=item D	3401	=item D
2981		3402
2982	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3403	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2983	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3404	be found at L<http://proj.llucax.com.ar/wiki/evd>.
…		…
3160	keeps libev from including F<config.h>, and it also defines dummy	3581	keeps libev from including F<config.h>, and it also defines dummy
3161	implementations for some libevent functions (such as logging, which is not	3582	implementations for some libevent functions (such as logging, which is not
3162	supported). It will also not define any of the structs usually found in	3583	supported). It will also not define any of the structs usually found in
3163	F<event.h> that are not directly supported by the libev core alone.	3584	F<event.h> that are not directly supported by the libev core alone.
3164		3585
		3586	In stanbdalone mode, libev will still try to automatically deduce the
		3587	configuration, but has to be more conservative.
		3588
3165	=item EV_USE_MONOTONIC	3589	=item EV_USE_MONOTONIC
3166		3590
3167	If defined to be C<1>, libev will try to detect the availability of the	3591	If defined to be C<1>, libev will try to detect the availability of the
3168	monotonic clock option at both compile time and runtime. Otherwise no use	3592	monotonic clock option at both compile time and runtime. Otherwise no
3169	of the monotonic clock option will be attempted. If you enable this, you	3593	use of the monotonic clock option will be attempted. If you enable this,
3170	usually have to link against librt or something similar. Enabling it when	3594	you usually have to link against librt or something similar. Enabling it
3171	the functionality isn't available is safe, though, although you have	3595	when the functionality isn't available is safe, though, although you have
3172	to make sure you link against any libraries where the C<clock_gettime>	3596	to make sure you link against any libraries where the C<clock_gettime>
3173	function is hiding in (often F<-lrt>).	3597	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
3174		3598
3175	=item EV_USE_REALTIME	3599	=item EV_USE_REALTIME
3176		3600
3177	If defined to be C<1>, libev will try to detect the availability of the	3601	If defined to be C<1>, libev will try to detect the availability of the
3178	real-time clock option at compile time (and assume its availability at	3602	real-time clock option at compile time (and assume its availability
3179	runtime if successful). Otherwise no use of the real-time clock option will	3603	at runtime if successful). Otherwise no use of the real-time clock
3180	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3604	option will be attempted. This effectively replaces C<gettimeofday>
3181	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3605	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
3182	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3606	correctness. See the note about libraries in the description of
		3607	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3608	C<EV_USE_CLOCK_SYSCALL>.
		3609
		3610	=item EV_USE_CLOCK_SYSCALL
		3611
		3612	If defined to be C<1>, libev will try to use a direct syscall instead
		3613	of calling the system-provided C<clock_gettime> function. This option
		3614	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3615	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3616	programs needlessly. Using a direct syscall is slightly slower (in
		3617	theory), because no optimised vdso implementation can be used, but avoids
		3618	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3619	higher, as it simplifies linking (no need for C<-lrt>).
3183		3620
3184	=item EV_USE_NANOSLEEP	3621	=item EV_USE_NANOSLEEP
3185		3622
3186	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3623	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
3187	and will use it for delays. Otherwise it will use C<select ()>.	3624	and will use it for delays. Otherwise it will use C<select ()>.
…		…
3203		3640
3204	=item EV_SELECT_USE_FD_SET	3641	=item EV_SELECT_USE_FD_SET
3205		3642
3206	If defined to C<1>, then the select backend will use the system C<fd_set>	3643	If defined to C<1>, then the select backend will use the system C<fd_set>
3207	structure. This is useful if libev doesn't compile due to a missing	3644	structure. This is useful if libev doesn't compile due to a missing
3208	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3645	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
3209	exotic systems. This usually limits the range of file descriptors to some	3646	on exotic systems. This usually limits the range of file descriptors to
3210	low limit such as 1024 or might have other limitations (winsocket only	3647	some low limit such as 1024 or might have other limitations (winsocket
3211	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3648	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
3212	influence the size of the C<fd_set> used.	3649	configures the maximum size of the C<fd_set>.
3213		3650
3214	=item EV_SELECT_IS_WINSOCKET	3651	=item EV_SELECT_IS_WINSOCKET
3215		3652
3216	When defined to C<1>, the select backend will assume that	3653	When defined to C<1>, the select backend will assume that
3217	select/socket/connect etc. don't understand file descriptors but	3654	select/socket/connect etc. don't understand file descriptors but
…		…
3367	defined to be C<0>, then they are not.	3804	defined to be C<0>, then they are not.
3368		3805
3369	=item EV_MINIMAL	3806	=item EV_MINIMAL
3370		3807
3371	If you need to shave off some kilobytes of code at the expense of some	3808	If you need to shave off some kilobytes of code at the expense of some
3372	speed, define this symbol to C<1>. Currently this is used to override some	3809	speed (but with the full API), define this symbol to C<1>. Currently this
3373	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3810	is used to override some inlining decisions, saves roughly 30% code size
3374	much smaller 2-heap for timer management over the default 4-heap.	3811	on amd64. It also selects a much smaller 2-heap for timer management over
		3812	the default 4-heap.
		3813
		3814	You can save even more by disabling watcher types you do not need
		3815	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3816	(C<-DNDEBUG>) will usually reduce code size a lot.
		3817
		3818	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3819	provide a bare-bones event library. See C<ev.h> for details on what parts
		3820	of the API are still available, and do not complain if this subset changes
		3821	over time.
		3822
		3823	=item EV_NSIG
		3824
		3825	The highest supported signal number, +1 (or, the number of
		3826	signals): Normally, libev tries to deduce the maximum number of signals
		3827	automatically, but sometimes this fails, in which case it can be
		3828	specified. Also, using a lower number than detected (C<32> should be
		3829	good for about any system in existance) can save some memory, as libev
		3830	statically allocates some 12-24 bytes per signal number.
3375		3831
3376	=item EV_PID_HASHSIZE	3832	=item EV_PID_HASHSIZE
3377		3833
3378	C<ev_child> watchers use a small hash table to distribute workload by	3834	C<ev_child> watchers use a small hash table to distribute workload by
3379	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3835	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3565	default loop and triggering an C<ev_async> watcher from the default loop	4021	default loop and triggering an C<ev_async> watcher from the default loop
3566	watcher callback into the event loop interested in the signal.	4022	watcher callback into the event loop interested in the signal.
3567		4023
3568	=back	4024	=back
3569		4025
		4026	=head4 THREAD LOCKING EXAMPLE
		4027
		4028	Here is a fictitious example of how to run an event loop in a different
		4029	thread than where callbacks are being invoked and watchers are
		4030	created/added/removed.
		4031
		4032	For a real-world example, see the C<EV::Loop::Async> perl module,
		4033	which uses exactly this technique (which is suited for many high-level
		4034	languages).
		4035
		4036	The example uses a pthread mutex to protect the loop data, a condition
		4037	variable to wait for callback invocations, an async watcher to notify the
		4038	event loop thread and an unspecified mechanism to wake up the main thread.
		4039
		4040	First, you need to associate some data with the event loop:
		4041
		4042	typedef struct {
		4043	mutex_t lock; /* global loop lock */
		4044	ev_async async_w;
		4045	thread_t tid;
		4046	cond_t invoke_cv;
		4047	} userdata;
		4048
		4049	void prepare_loop (EV_P)
		4050	{
		4051	// for simplicity, we use a static userdata struct.
		4052	static userdata u;
		4053
		4054	ev_async_init (&u->async_w, async_cb);
		4055	ev_async_start (EV_A_ &u->async_w);
		4056
		4057	pthread_mutex_init (&u->lock, 0);
		4058	pthread_cond_init (&u->invoke_cv, 0);
		4059
		4060	// now associate this with the loop
		4061	ev_set_userdata (EV_A_ u);
		4062	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4063	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4064
		4065	// then create the thread running ev_loop
		4066	pthread_create (&u->tid, 0, l_run, EV_A);
		4067	}
		4068
		4069	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4070	solely to wake up the event loop so it takes notice of any new watchers
		4071	that might have been added:
		4072
		4073	static void
		4074	async_cb (EV_P_ ev_async *w, int revents)
		4075	{
		4076	// just used for the side effects
		4077	}
		4078
		4079	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4080	protecting the loop data, respectively.
		4081
		4082	static void
		4083	l_release (EV_P)
		4084	{
		4085	userdata *u = ev_userdata (EV_A);
		4086	pthread_mutex_unlock (&u->lock);
		4087	}
		4088
		4089	static void
		4090	l_acquire (EV_P)
		4091	{
		4092	userdata *u = ev_userdata (EV_A);
		4093	pthread_mutex_lock (&u->lock);
		4094	}
		4095
		4096	The event loop thread first acquires the mutex, and then jumps straight
		4097	into C<ev_loop>:
		4098
		4099	void *
		4100	l_run (void *thr_arg)
		4101	{
		4102	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4103
		4104	l_acquire (EV_A);
		4105	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4106	ev_loop (EV_A_ 0);
		4107	l_release (EV_A);
		4108
		4109	return 0;
		4110	}
		4111
		4112	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4113	signal the main thread via some unspecified mechanism (signals? pipe
		4114	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4115	have been called (in a while loop because a) spurious wakeups are possible
		4116	and b) skipping inter-thread-communication when there are no pending
		4117	watchers is very beneficial):
		4118
		4119	static void
		4120	l_invoke (EV_P)
		4121	{
		4122	userdata *u = ev_userdata (EV_A);
		4123
		4124	while (ev_pending_count (EV_A))
		4125	{
		4126	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4127	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4128	}
		4129	}
		4130
		4131	Now, whenever the main thread gets told to invoke pending watchers, it
		4132	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4133	thread to continue:
		4134
		4135	static void
		4136	real_invoke_pending (EV_P)
		4137	{
		4138	userdata *u = ev_userdata (EV_A);
		4139
		4140	pthread_mutex_lock (&u->lock);
		4141	ev_invoke_pending (EV_A);
		4142	pthread_cond_signal (&u->invoke_cv);
		4143	pthread_mutex_unlock (&u->lock);
		4144	}
		4145
		4146	Whenever you want to start/stop a watcher or do other modifications to an
		4147	event loop, you will now have to lock:
		4148
		4149	ev_timer timeout_watcher;
		4150	userdata *u = ev_userdata (EV_A);
		4151
		4152	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4153
		4154	pthread_mutex_lock (&u->lock);
		4155	ev_timer_start (EV_A_ &timeout_watcher);
		4156	ev_async_send (EV_A_ &u->async_w);
		4157	pthread_mutex_unlock (&u->lock);
		4158
		4159	Note that sending the C<ev_async> watcher is required because otherwise
		4160	an event loop currently blocking in the kernel will have no knowledge
		4161	about the newly added timer. By waking up the loop it will pick up any new
		4162	watchers in the next event loop iteration.
		4163
3570	=head3 COROUTINES	4164	=head3 COROUTINES
3571		4165
3572	Libev is very accommodating to coroutines ("cooperative threads"):	4166	Libev is very accommodating to coroutines ("cooperative threads"):
3573	libev fully supports nesting calls to its functions from different	4167	libev fully supports nesting calls to its functions from different
3574	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4168	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3575	different coroutines, and switch freely between both coroutines running the	4169	different coroutines, and switch freely between both coroutines running
3576	loop, as long as you don't confuse yourself). The only exception is that	4170	the loop, as long as you don't confuse yourself). The only exception is
3577	you must not do this from C<ev_periodic> reschedule callbacks.	4171	that you must not do this from C<ev_periodic> reschedule callbacks.
3578		4172
3579	Care has been taken to ensure that libev does not keep local state inside	4173	Care has been taken to ensure that libev does not keep local state inside
3580	C<ev_loop>, and other calls do not usually allow for coroutine switches as	4174	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3581	they do not call any callbacks.	4175	they do not call any callbacks.
3582		4176
…		…
3659	way (note also that glib is the slowest event library known to man).	4253	way (note also that glib is the slowest event library known to man).
3660		4254
3661	There is no supported compilation method available on windows except	4255	There is no supported compilation method available on windows except
3662	embedding it into other applications.	4256	embedding it into other applications.
3663		4257
		4258	Sensible signal handling is officially unsupported by Microsoft - libev
		4259	tries its best, but under most conditions, signals will simply not work.
		4260
3664	Not a libev limitation but worth mentioning: windows apparently doesn't	4261	Not a libev limitation but worth mentioning: windows apparently doesn't
3665	accept large writes: instead of resulting in a partial write, windows will	4262	accept large writes: instead of resulting in a partial write, windows will
3666	either accept everything or return C<ENOBUFS> if the buffer is too large,	4263	either accept everything or return C<ENOBUFS> if the buffer is too large,
3667	so make sure you only write small amounts into your sockets (less than a	4264	so make sure you only write small amounts into your sockets (less than a
3668	megabyte seems safe, but this apparently depends on the amount of memory	4265	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3672	the abysmal performance of winsockets, using a large number of sockets	4269	the abysmal performance of winsockets, using a large number of sockets
3673	is not recommended (and not reasonable). If your program needs to use	4270	is not recommended (and not reasonable). If your program needs to use
3674	more than a hundred or so sockets, then likely it needs to use a totally	4271	more than a hundred or so sockets, then likely it needs to use a totally
3675	different implementation for windows, as libev offers the POSIX readiness	4272	different implementation for windows, as libev offers the POSIX readiness
3676	notification model, which cannot be implemented efficiently on windows	4273	notification model, which cannot be implemented efficiently on windows
3677	(Microsoft monopoly games).	4274	(due to Microsoft monopoly games).
3678		4275
3679	A typical way to use libev under windows is to embed it (see the embedding	4276	A typical way to use libev under windows is to embed it (see the embedding
3680	section for details) and use the following F<evwrap.h> header file instead	4277	section for details) and use the following F<evwrap.h> header file instead
3681	of F<ev.h>:	4278	of F<ev.h>:
3682		4279
…		…
3718		4315
3719	Early versions of winsocket's select only supported waiting for a maximum	4316	Early versions of winsocket's select only supported waiting for a maximum
3720	of C<64> handles (probably owning to the fact that all windows kernels	4317	of C<64> handles (probably owning to the fact that all windows kernels
3721	can only wait for C<64> things at the same time internally; Microsoft	4318	can only wait for C<64> things at the same time internally; Microsoft
3722	recommends spawning a chain of threads and wait for 63 handles and the	4319	recommends spawning a chain of threads and wait for 63 handles and the
3723	previous thread in each. Great).	4320	previous thread in each. Sounds great!).
3724		4321
3725	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4322	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3726	to some high number (e.g. C<2048>) before compiling the winsocket select	4323	to some high number (e.g. C<2048>) before compiling the winsocket select
3727	call (which might be in libev or elsewhere, for example, perl does its own	4324	call (which might be in libev or elsewhere, for example, perl and many
3728	select emulation on windows).	4325	other interpreters do their own select emulation on windows).
3729		4326
3730	Another limit is the number of file descriptors in the Microsoft runtime	4327	Another limit is the number of file descriptors in the Microsoft runtime
3731	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4328	libraries, which by default is C<64> (there must be a hidden I<64>
3732	or something like this inside Microsoft). You can increase this by calling	4329	fetish or something like this inside Microsoft). You can increase this
3733	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4330	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3734	arbitrary limit), but is broken in many versions of the Microsoft runtime	4331	(another arbitrary limit), but is broken in many versions of the Microsoft
3735	libraries.
3736
3737	This might get you to about C<512> or C<2048> sockets (depending on	4332	runtime libraries. This might get you to about C<512> or C<2048> sockets
3738	windows version and/or the phase of the moon). To get more, you need to	4333	(depending on windows version and/or the phase of the moon). To get more,
3739	wrap all I/O functions and provide your own fd management, but the cost of	4334	you need to wrap all I/O functions and provide your own fd management, but
3740	calling select (O(n²)) will likely make this unworkable.	4335	the cost of calling select (O(n²)) will likely make this unworkable.
3741		4336
3742	=back	4337	=back
3743		4338
3744	=head2 PORTABILITY REQUIREMENTS	4339	=head2 PORTABILITY REQUIREMENTS
3745		4340
…		…
3788	=item C<double> must hold a time value in seconds with enough accuracy	4383	=item C<double> must hold a time value in seconds with enough accuracy
3789		4384
3790	The type C<double> is used to represent timestamps. It is required to	4385	The type C<double> is used to represent timestamps. It is required to
3791	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4386	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3792	enough for at least into the year 4000. This requirement is fulfilled by	4387	enough for at least into the year 4000. This requirement is fulfilled by
3793	implementations implementing IEEE 754 (basically all existing ones).	4388	implementations implementing IEEE 754, which is basically all existing
		4389	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4390	2200.
3794		4391
3795	=back	4392	=back
3796		4393
3797	If you know of other additional requirements drop me a note.	4394	If you know of other additional requirements drop me a note.
3798		4395
…		…
3866	involves iterating over all running async watchers or all signal numbers.	4463	involves iterating over all running async watchers or all signal numbers.
3867		4464
3868	=back	4465	=back
3869		4466
3870		4467
		4468	=head1 GLOSSARY
		4469
		4470	=over 4
		4471
		4472	=item active
		4473
		4474	A watcher is active as long as it has been started (has been attached to
		4475	an event loop) but not yet stopped (disassociated from the event loop).
		4476
		4477	=item application
		4478
		4479	In this document, an application is whatever is using libev.
		4480
		4481	=item callback
		4482
		4483	The address of a function that is called when some event has been
		4484	detected. Callbacks are being passed the event loop, the watcher that
		4485	received the event, and the actual event bitset.
		4486
		4487	=item callback invocation
		4488
		4489	The act of calling the callback associated with a watcher.
		4490
		4491	=item event
		4492
		4493	A change of state of some external event, such as data now being available
		4494	for reading on a file descriptor, time having passed or simply not having
		4495	any other events happening anymore.
		4496
		4497	In libev, events are represented as single bits (such as C<EV_READ> or
		4498	C<EV_TIMEOUT>).
		4499
		4500	=item event library
		4501
		4502	A software package implementing an event model and loop.
		4503
		4504	=item event loop
		4505
		4506	An entity that handles and processes external events and converts them
		4507	into callback invocations.
		4508
		4509	=item event model
		4510
		4511	The model used to describe how an event loop handles and processes
		4512	watchers and events.
		4513
		4514	=item pending
		4515
		4516	A watcher is pending as soon as the corresponding event has been detected,
		4517	and stops being pending as soon as the watcher will be invoked or its
		4518	pending status is explicitly cleared by the application.
		4519
		4520	A watcher can be pending, but not active. Stopping a watcher also clears
		4521	its pending status.
		4522
		4523	=item real time
		4524
		4525	The physical time that is observed. It is apparently strictly monotonic :)
		4526
		4527	=item wall-clock time
		4528
		4529	The time and date as shown on clocks. Unlike real time, it can actually
		4530	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4531	clock.
		4532
		4533	=item watcher
		4534
		4535	A data structure that describes interest in certain events. Watchers need
		4536	to be started (attached to an event loop) before they can receive events.
		4537
		4538	=item watcher invocation
		4539
		4540	The act of calling the callback associated with a watcher.
		4541
		4542	=back
		4543
3871	=head1 AUTHOR	4544	=head1 AUTHOR
3872		4545
3873	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	4546	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3874		4547

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