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Revision 1.226 by root, Wed Mar 4 12:51:37 2009 UTC vs.
Revision 1.254 by root, Tue Jul 14 19:02:43 2009 UTC

…		…
62		62
63	// unloop was called, so exit	63	// unloop was called, so exit
64	return 0;	64	return 0;
65	}	65	}
66		66
67	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
68		70
69	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
70	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
71	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
72		84
73	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
74	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
75	these event sources and provide your program with events.	87	these event sources and provide your program with events.
76		88
…		…
110	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
111	this argument.	123	this argument.
112		124
113	=head2 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
114		126
115	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
116	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
117	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
118	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
119	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
120	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
121	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
122	throughout libev.	134	throughout libev.
123		135
124	=head1 ERROR HANDLING	136	=head1 ERROR HANDLING
125		137
…		…
609		621
610	This value can sometimes be useful as a generation counter of sorts (it	622	This value can sometimes be useful as a generation counter of sorts (it
611	"ticks" the number of loop iterations), as it roughly corresponds with	623	"ticks" the number of loop iterations), as it roughly corresponds with
612	C<ev_prepare> and C<ev_check> calls.	624	C<ev_prepare> and C<ev_check> calls.
613		625
		626	=item unsigned int ev_loop_depth (loop)
		627
		628	Returns the number of times C<ev_loop> was entered minus the number of
		629	times C<ev_loop> was exited, in other words, the recursion depth.
		630
		631	Outside C<ev_loop>, this number is zero. In a callback, this number is
		632	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		633	in which case it is higher.
		634
		635	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		636	etc.), doesn't count as exit.
		637
614	=item unsigned int ev_backend (loop)	638	=item unsigned int ev_backend (loop)
615		639
616	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	640	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
617	use.	641	use.
618		642
…		…
632		656
633	This function is rarely useful, but when some event callback runs for a	657	This function is rarely useful, but when some event callback runs for a
634	very long time without entering the event loop, updating libev's idea of	658	very long time without entering the event loop, updating libev's idea of
635	the current time is a good idea.	659	the current time is a good idea.
636		660
637	See also "The special problem of time updates" in the C<ev_timer> section.	661	See also L<The special problem of time updates> in the C<ev_timer> section.
		662
		663	=item ev_suspend (loop)
		664
		665	=item ev_resume (loop)
		666
		667	These two functions suspend and resume a loop, for use when the loop is
		668	not used for a while and timeouts should not be processed.
		669
		670	A typical use case would be an interactive program such as a game: When
		671	the user presses C<^Z> to suspend the game and resumes it an hour later it
		672	would be best to handle timeouts as if no time had actually passed while
		673	the program was suspended. This can be achieved by calling C<ev_suspend>
		674	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		675	C<ev_resume> directly afterwards to resume timer processing.
		676
		677	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		678	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		679	will be rescheduled (that is, they will lose any events that would have
		680	occured while suspended).
		681
		682	After calling C<ev_suspend> you B<must not> call I<any> function on the
		683	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		684	without a previous call to C<ev_suspend>.
		685
		686	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		687	event loop time (see C<ev_now_update>).
638		688
639	=item ev_loop (loop, int flags)	689	=item ev_loop (loop, int flags)
640		690
641	Finally, this is it, the event handler. This function usually is called	691	Finally, this is it, the event handler. This function usually is called
642	after you initialised all your watchers and you want to start handling	692	after you initialised all your watchers and you want to start handling
…		…
726		776
727	If you have a watcher you never unregister that should not keep C<ev_loop>	777	If you have a watcher you never unregister that should not keep C<ev_loop>
728	from returning, call ev_unref() after starting, and ev_ref() before	778	from returning, call ev_unref() after starting, and ev_ref() before
729	stopping it.	779	stopping it.
730		780
731	As an example, libev itself uses this for its internal signal pipe: It is	781	As an example, libev itself uses this for its internal signal pipe: It
732	not visible to the libev user and should not keep C<ev_loop> from exiting	782	is not visible to the libev user and should not keep C<ev_loop> from
733	if no event watchers registered by it are active. It is also an excellent	783	exiting if no event watchers registered by it are active. It is also an
734	way to do this for generic recurring timers or from within third-party	784	excellent way to do this for generic recurring timers or from within
735	libraries. Just remember to I<unref after start> and I<ref before stop>	785	third-party libraries. Just remember to I<unref after start> and I<ref
736	(but only if the watcher wasn't active before, or was active before,	786	before stop> (but only if the watcher wasn't active before, or was active
737	respectively).	787	before, respectively. Note also that libev might stop watchers itself
		788	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		789	in the callback).
738		790
739	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	791	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
740	running when nothing else is active.	792	running when nothing else is active.
741		793
742	ev_signal exitsig;	794	ev_signal exitsig;
…		…
771		823
772	By setting a higher I<io collect interval> you allow libev to spend more	824	By setting a higher I<io collect interval> you allow libev to spend more
773	time collecting I/O events, so you can handle more events per iteration,	825	time collecting I/O events, so you can handle more events per iteration,
774	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	826	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
775	C<ev_timer>) will be not affected. Setting this to a non-null value will	827	C<ev_timer>) will be not affected. Setting this to a non-null value will
776	introduce an additional C<ev_sleep ()> call into most loop iterations.	828	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		829	sleep time ensures that libev will not poll for I/O events more often then
		830	once per this interval, on average.
777		831
778	Likewise, by setting a higher I<timeout collect interval> you allow libev	832	Likewise, by setting a higher I<timeout collect interval> you allow libev
779	to spend more time collecting timeouts, at the expense of increased	833	to spend more time collecting timeouts, at the expense of increased
780	latency/jitter/inexactness (the watcher callback will be called	834	latency/jitter/inexactness (the watcher callback will be called
781	later). C<ev_io> watchers will not be affected. Setting this to a non-null	835	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
783		837
784	Many (busy) programs can usually benefit by setting the I/O collect	838	Many (busy) programs can usually benefit by setting the I/O collect
785	interval to a value near C<0.1> or so, which is often enough for	839	interval to a value near C<0.1> or so, which is often enough for
786	interactive servers (of course not for games), likewise for timeouts. It	840	interactive servers (of course not for games), likewise for timeouts. It
787	usually doesn't make much sense to set it to a lower value than C<0.01>,	841	usually doesn't make much sense to set it to a lower value than C<0.01>,
788	as this approaches the timing granularity of most systems.	842	as this approaches the timing granularity of most systems. Note that if
		843	you do transactions with the outside world and you can't increase the
		844	parallelity, then this setting will limit your transaction rate (if you
		845	need to poll once per transaction and the I/O collect interval is 0.01,
		846	then you can't do more than 100 transations per second).
789		847
790	Setting the I<timeout collect interval> can improve the opportunity for	848	Setting the I<timeout collect interval> can improve the opportunity for
791	saving power, as the program will "bundle" timer callback invocations that	849	saving power, as the program will "bundle" timer callback invocations that
792	are "near" in time together, by delaying some, thus reducing the number of	850	are "near" in time together, by delaying some, thus reducing the number of
793	times the process sleeps and wakes up again. Another useful technique to	851	times the process sleeps and wakes up again. Another useful technique to
794	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	852	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
795	they fire on, say, one-second boundaries only.	853	they fire on, say, one-second boundaries only.
		854
		855	Example: we only need 0.1s timeout granularity, and we wish not to poll
		856	more often than 100 times per second:
		857
		858	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		859	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		860
		861	=item ev_invoke_pending (loop)
		862
		863	This call will simply invoke all pending watchers while resetting their
		864	pending state. Normally, C<ev_loop> does this automatically when required,
		865	but when overriding the invoke callback this call comes handy.
		866
		867	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		868
		869	This overrides the invoke pending functionality of the loop: Instead of
		870	invoking all pending watchers when there are any, C<ev_loop> will call
		871	this callback instead. This is useful, for example, when you want to
		872	invoke the actual watchers inside another context (another thread etc.).
		873
		874	If you want to reset the callback, use C<ev_invoke_pending> as new
		875	callback.
		876
		877	=item ev_set_loop_release_cb (loop, void (release)(EV_P), void (acquire)(EV_P))
		878
		879	Sometimes you want to share the same loop between multiple threads. This
		880	can be done relatively simply by putting mutex_lock/unlock calls around
		881	each call to a libev function.
		882
		883	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		884	wait for it to return. One way around this is to wake up the loop via
		885	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		886	and I<acquire> callbacks on the loop.
		887
		888	When set, then C<release> will be called just before the thread is
		889	suspended waiting for new events, and C<acquire> is called just
		890	afterwards.
		891
		892	Ideally, C<release> will just call your mutex_unlock function, and
		893	C<acquire> will just call the mutex_lock function again.
		894
		895	While event loop modifications are allowed between invocations of
		896	C<release> and C<acquire> (that's their only purpose after all), no
		897	modifications done will affect the event loop, i.e. adding watchers will
		898	have no effect on the set of file descriptors being watched, or the time
		899	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		900	to take note of any changes you made.
		901
		902	In theory, threads executing C<ev_loop> will be async-cancel safe between
		903	invocations of C<release> and C<acquire>.
		904
		905	See also the locking example in the C<THREADS> section later in this
		906	document.
		907
		908	=item ev_set_userdata (loop, void *data)
		909
		910	=item ev_userdata (loop)
		911
		912	Set and retrieve a single C<void *> associated with a loop. When
		913	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		914	C<0.>
		915
		916	These two functions can be used to associate arbitrary data with a loop,
		917	and are intended solely for the C<invoke_pending_cb>, C<release> and
		918	C<acquire> callbacks described above, but of course can be (ab-)used for
		919	any other purpose as well.
796		920
797	=item ev_loop_verify (loop)	921	=item ev_loop_verify (loop)
798		922
799	This function only does something when C<EV_VERIFY> support has been	923	This function only does something when C<EV_VERIFY> support has been
800	compiled in, which is the default for non-minimal builds. It tries to go	924	compiled in, which is the default for non-minimal builds. It tries to go
…		…
926		1050
927	=item C<EV_ASYNC>	1051	=item C<EV_ASYNC>
928		1052
929	The given async watcher has been asynchronously notified (see C<ev_async>).	1053	The given async watcher has been asynchronously notified (see C<ev_async>).
930		1054
		1055	=item C<EV_CUSTOM>
		1056
		1057	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1058	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1059
931	=item C<EV_ERROR>	1060	=item C<EV_ERROR>
932		1061
933	An unspecified error has occurred, the watcher has been stopped. This might	1062	An unspecified error has occurred, the watcher has been stopped. This might
934	happen because the watcher could not be properly started because libev	1063	happen because the watcher could not be properly started because libev
935	ran out of memory, a file descriptor was found to be closed or any other	1064	ran out of memory, a file descriptor was found to be closed or any other
…		…
1050	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1179	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1051	(default: C<-2>). Pending watchers with higher priority will be invoked	1180	(default: C<-2>). Pending watchers with higher priority will be invoked
1052	before watchers with lower priority, but priority will not keep watchers	1181	before watchers with lower priority, but priority will not keep watchers
1053	from being executed (except for C<ev_idle> watchers).	1182	from being executed (except for C<ev_idle> watchers).
1054		1183
1055	This means that priorities are I<only> used for ordering callback
1056	invocation after new events have been received. This is useful, for
1057	example, to reduce latency after idling, or more often, to bind two
1058	watchers on the same event and make sure one is called first.
1059
1060	If you need to suppress invocation when higher priority events are pending	1184	If you need to suppress invocation when higher priority events are pending
1061	you need to look at C<ev_idle> watchers, which provide this functionality.	1185	you need to look at C<ev_idle> watchers, which provide this functionality.
1062		1186
1063	You I<must not> change the priority of a watcher as long as it is active or	1187	You I<must not> change the priority of a watcher as long as it is active or
1064	pending.	1188	pending.
1065
1066	The default priority used by watchers when no priority has been set is
1067	always C<0>, which is supposed to not be too high and not be too low :).
1068		1189
1069	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1190	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1070	fine, as long as you do not mind that the priority value you query might	1191	fine, as long as you do not mind that the priority value you query might
1071	or might not have been clamped to the valid range.	1192	or might not have been clamped to the valid range.
		1193
		1194	The default priority used by watchers when no priority has been set is
		1195	always C<0>, which is supposed to not be too high and not be too low :).
		1196
		1197	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1198	priorities.
1072		1199
1073	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1200	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1074		1201
1075	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1202	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1076	C<loop> nor C<revents> need to be valid as long as the watcher callback	1203	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1141	#include <stddef.h>	1268	#include <stddef.h>
1142		1269
1143	static void	1270	static void
1144	t1_cb (EV_P_ ev_timer *w, int revents)	1271	t1_cb (EV_P_ ev_timer *w, int revents)
1145	{	1272	{
1146	struct my_biggy big = (struct my_biggy *	1273	struct my_biggy big = (struct my_biggy *)
1147	(((char *)w) - offsetof (struct my_biggy, t1));	1274	(((char *)w) - offsetof (struct my_biggy, t1));
1148	}	1275	}
1149		1276
1150	static void	1277	static void
1151	t2_cb (EV_P_ ev_timer *w, int revents)	1278	t2_cb (EV_P_ ev_timer *w, int revents)
1152	{	1279	{
1153	struct my_biggy big = (struct my_biggy *	1280	struct my_biggy big = (struct my_biggy *)
1154	(((char *)w) - offsetof (struct my_biggy, t2));	1281	(((char *)w) - offsetof (struct my_biggy, t2));
1155	}	1282	}
		1283
		1284	=head2 WATCHER PRIORITY MODELS
		1285
		1286	Many event loops support I<watcher priorities>, which are usually small
		1287	integers that influence the ordering of event callback invocation
		1288	between watchers in some way, all else being equal.
		1289
		1290	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1291	description for the more technical details such as the actual priority
		1292	range.
		1293
		1294	There are two common ways how these these priorities are being interpreted
		1295	by event loops:
		1296
		1297	In the more common lock-out model, higher priorities "lock out" invocation
		1298	of lower priority watchers, which means as long as higher priority
		1299	watchers receive events, lower priority watchers are not being invoked.
		1300
		1301	The less common only-for-ordering model uses priorities solely to order
		1302	callback invocation within a single event loop iteration: Higher priority
		1303	watchers are invoked before lower priority ones, but they all get invoked
		1304	before polling for new events.
		1305
		1306	Libev uses the second (only-for-ordering) model for all its watchers
		1307	except for idle watchers (which use the lock-out model).
		1308
		1309	The rationale behind this is that implementing the lock-out model for
		1310	watchers is not well supported by most kernel interfaces, and most event
		1311	libraries will just poll for the same events again and again as long as
		1312	their callbacks have not been executed, which is very inefficient in the
		1313	common case of one high-priority watcher locking out a mass of lower
		1314	priority ones.
		1315
		1316	Static (ordering) priorities are most useful when you have two or more
		1317	watchers handling the same resource: a typical usage example is having an
		1318	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1319	timeouts. Under load, data might be received while the program handles
		1320	other jobs, but since timers normally get invoked first, the timeout
		1321	handler will be executed before checking for data. In that case, giving
		1322	the timer a lower priority than the I/O watcher ensures that I/O will be
		1323	handled first even under adverse conditions (which is usually, but not
		1324	always, what you want).
		1325
		1326	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1327	will only be executed when no same or higher priority watchers have
		1328	received events, they can be used to implement the "lock-out" model when
		1329	required.
		1330
		1331	For example, to emulate how many other event libraries handle priorities,
		1332	you can associate an C<ev_idle> watcher to each such watcher, and in
		1333	the normal watcher callback, you just start the idle watcher. The real
		1334	processing is done in the idle watcher callback. This causes libev to
		1335	continously poll and process kernel event data for the watcher, but when
		1336	the lock-out case is known to be rare (which in turn is rare :), this is
		1337	workable.
		1338
		1339	Usually, however, the lock-out model implemented that way will perform
		1340	miserably under the type of load it was designed to handle. In that case,
		1341	it might be preferable to stop the real watcher before starting the
		1342	idle watcher, so the kernel will not have to process the event in case
		1343	the actual processing will be delayed for considerable time.
		1344
		1345	Here is an example of an I/O watcher that should run at a strictly lower
		1346	priority than the default, and which should only process data when no
		1347	other events are pending:
		1348
		1349	ev_idle idle; // actual processing watcher
		1350	ev_io io; // actual event watcher
		1351
		1352	static void
		1353	io_cb (EV_P_ ev_io *w, int revents)
		1354	{
		1355	// stop the I/O watcher, we received the event, but
		1356	// are not yet ready to handle it.
		1357	ev_io_stop (EV_A_ w);
		1358
		1359	// start the idle watcher to ahndle the actual event.
		1360	// it will not be executed as long as other watchers
		1361	// with the default priority are receiving events.
		1362	ev_idle_start (EV_A_ &idle);
		1363	}
		1364
		1365	static void
		1366	idle_cb (EV_P_ ev_idle *w, int revents)
		1367	{
		1368	// actual processing
		1369	read (STDIN_FILENO, ...);
		1370
		1371	// have to start the I/O watcher again, as
		1372	// we have handled the event
		1373	ev_io_start (EV_P_ &io);
		1374	}
		1375
		1376	// initialisation
		1377	ev_idle_init (&idle, idle_cb);
		1378	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1379	ev_io_start (EV_DEFAULT_ &io);
		1380
		1381	In the "real" world, it might also be beneficial to start a timer, so that
		1382	low-priority connections can not be locked out forever under load. This
		1383	enables your program to keep a lower latency for important connections
		1384	during short periods of high load, while not completely locking out less
		1385	important ones.
1156		1386
1157		1387
1158	=head1 WATCHER TYPES	1388	=head1 WATCHER TYPES
1159		1389
1160	This section describes each watcher in detail, but will not repeat	1390	This section describes each watcher in detail, but will not repeat
…		…
1186	descriptors to non-blocking mode is also usually a good idea (but not	1416	descriptors to non-blocking mode is also usually a good idea (but not
1187	required if you know what you are doing).	1417	required if you know what you are doing).
1188		1418
1189	If you cannot use non-blocking mode, then force the use of a	1419	If you cannot use non-blocking mode, then force the use of a
1190	known-to-be-good backend (at the time of this writing, this includes only	1420	known-to-be-good backend (at the time of this writing, this includes only
1191	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1421	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1422	descriptors for which non-blocking operation makes no sense (such as
		1423	files) - libev doesn't guarentee any specific behaviour in that case.
1192		1424
1193	Another thing you have to watch out for is that it is quite easy to	1425	Another thing you have to watch out for is that it is quite easy to
1194	receive "spurious" readiness notifications, that is your callback might	1426	receive "spurious" readiness notifications, that is your callback might
1195	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1427	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1196	because there is no data. Not only are some backends known to create a	1428	because there is no data. Not only are some backends known to create a
…		…
1317	year, it will still time out after (roughly) one hour. "Roughly" because	1549	year, it will still time out after (roughly) one hour. "Roughly" because
1318	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1550	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1319	monotonic clock option helps a lot here).	1551	monotonic clock option helps a lot here).
1320		1552
1321	The callback is guaranteed to be invoked only I<after> its timeout has	1553	The callback is guaranteed to be invoked only I<after> its timeout has
1322	passed, but if multiple timers become ready during the same loop iteration	1554	passed (not I<at>, so on systems with very low-resolution clocks this
1323	then order of execution is undefined.	1555	might introduce a small delay). If multiple timers become ready during the
		1556	same loop iteration then the ones with earlier time-out values are invoked
		1557	before ones of the same priority with later time-out values (but this is
		1558	no longer true when a callback calls C<ev_loop> recursively).
1324		1559
1325	=head3 Be smart about timeouts	1560	=head3 Be smart about timeouts
1326		1561
1327	Many real-world problems involve some kind of timeout, usually for error	1562	Many real-world problems involve some kind of timeout, usually for error
1328	recovery. A typical example is an HTTP request - if the other side hangs,	1563	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1372	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>	1607	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
1373	member and C<ev_timer_again>.	1608	member and C<ev_timer_again>.
1374		1609
1375	At start:	1610	At start:
1376		1611
1377	ev_timer_init (timer, callback);	1612	ev_init (timer, callback);
1378	timer->repeat = 60.;	1613	timer->repeat = 60.;
1379	ev_timer_again (loop, timer);	1614	ev_timer_again (loop, timer);
1380		1615
1381	Each time there is some activity:	1616	Each time there is some activity:
1382		1617
…		…
1444		1679
1445	To start the timer, simply initialise the watcher and set C<last_activity>	1680	To start the timer, simply initialise the watcher and set C<last_activity>
1446	to the current time (meaning we just have some activity :), then call the	1681	to the current time (meaning we just have some activity :), then call the
1447	callback, which will "do the right thing" and start the timer:	1682	callback, which will "do the right thing" and start the timer:
1448		1683
1449	ev_timer_init (timer, callback);	1684	ev_init (timer, callback);
1450	last_activity = ev_now (loop);	1685	last_activity = ev_now (loop);
1451	callback (loop, timer, EV_TIMEOUT);	1686	callback (loop, timer, EV_TIMEOUT);
1452		1687
1453	And when there is some activity, simply store the current time in	1688	And when there is some activity, simply store the current time in
1454	C<last_activity>, no libev calls at all:	1689	C<last_activity>, no libev calls at all:
…		…
1547	If the timer is started but non-repeating, stop it (as if it timed out).	1782	If the timer is started but non-repeating, stop it (as if it timed out).
1548		1783
1549	If the timer is repeating, either start it if necessary (with the	1784	If the timer is repeating, either start it if necessary (with the
1550	C<repeat> value), or reset the running timer to the C<repeat> value.	1785	C<repeat> value), or reset the running timer to the C<repeat> value.
1551		1786
1552	This sounds a bit complicated, see "Be smart about timeouts", above, for a	1787	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1553	usage example.	1788	usage example.
1554		1789
1555	=item ev_tstamp repeat [read-write]	1790	=item ev_tstamp repeat [read-write]
1556		1791
1557	The current C<repeat> value. Will be used each time the watcher times out	1792	The current C<repeat> value. Will be used each time the watcher times out
…		…
1596	=head2 C<ev_periodic> - to cron or not to cron?	1831	=head2 C<ev_periodic> - to cron or not to cron?
1597		1832
1598	Periodic watchers are also timers of a kind, but they are very versatile	1833	Periodic watchers are also timers of a kind, but they are very versatile
1599	(and unfortunately a bit complex).	1834	(and unfortunately a bit complex).
1600		1835
1601	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1836	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1602	but on wall clock time (absolute time). You can tell a periodic watcher	1837	relative time, the physical time that passes) but on wall clock time
1603	to trigger after some specific point in time. For example, if you tell a	1838	(absolute time, the thing you can read on your calender or clock). The
1604	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1839	difference is that wall clock time can run faster or slower than real
1605	+ 10.>, that is, an absolute time not a delay) and then reset your system	1840	time, and time jumps are not uncommon (e.g. when you adjust your
1606	clock to January of the previous year, then it will take more than year	1841	wrist-watch).
1607	to trigger the event (unlike an C<ev_timer>, which would still trigger
1608	roughly 10 seconds later as it uses a relative timeout).
1609		1842
		1843	You can tell a periodic watcher to trigger after some specific point
		1844	in time: for example, if you tell a periodic watcher to trigger "in 10
		1845	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1846	not a delay) and then reset your system clock to January of the previous
		1847	year, then it will take a year or more to trigger the event (unlike an
		1848	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1849	it, as it uses a relative timeout).
		1850
1610	C<ev_periodic>s can also be used to implement vastly more complex timers,	1851	C<ev_periodic> watchers can also be used to implement vastly more complex
1611	such as triggering an event on each "midnight, local time", or other	1852	timers, such as triggering an event on each "midnight, local time", or
1612	complicated rules.	1853	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1854	those cannot react to time jumps.
1613		1855
1614	As with timers, the callback is guaranteed to be invoked only when the	1856	As with timers, the callback is guaranteed to be invoked only when the
1615	time (C<at>) has passed, but if multiple periodic timers become ready	1857	point in time where it is supposed to trigger has passed. If multiple
1616	during the same loop iteration, then order of execution is undefined.	1858	timers become ready during the same loop iteration then the ones with
		1859	earlier time-out values are invoked before ones with later time-out values
		1860	(but this is no longer true when a callback calls C<ev_loop> recursively).
1617		1861
1618	=head3 Watcher-Specific Functions and Data Members	1862	=head3 Watcher-Specific Functions and Data Members
1619		1863
1620	=over 4	1864	=over 4
1621		1865
1622	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1866	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1623		1867
1624	=item ev_periodic_set (ev_periodic *, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1868	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1625		1869
1626	Lots of arguments, lets sort it out... There are basically three modes of	1870	Lots of arguments, let's sort it out... There are basically three modes of
1627	operation, and we will explain them from simplest to most complex:	1871	operation, and we will explain them from simplest to most complex:
1628		1872
1629	=over 4	1873	=over 4
1630		1874
1631	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1875	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1632		1876
1633	In this configuration the watcher triggers an event after the wall clock	1877	In this configuration the watcher triggers an event after the wall clock
1634	time C<at> has passed. It will not repeat and will not adjust when a time	1878	time C<offset> has passed. It will not repeat and will not adjust when a
1635	jump occurs, that is, if it is to be run at January 1st 2011 then it will	1879	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1636	only run when the system clock reaches or surpasses this time.	1880	will be stopped and invoked when the system clock reaches or surpasses
		1881	this point in time.
1637		1882
1638	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1883	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1639		1884
1640	In this mode the watcher will always be scheduled to time out at the next	1885	In this mode the watcher will always be scheduled to time out at the next
1641	C<at + N * interval> time (for some integer N, which can also be negative)	1886	C<offset + N * interval> time (for some integer N, which can also be
1642	and then repeat, regardless of any time jumps.	1887	negative) and then repeat, regardless of any time jumps. The C<offset>
		1888	argument is merely an offset into the C<interval> periods.
1643		1889
1644	This can be used to create timers that do not drift with respect to the	1890	This can be used to create timers that do not drift with respect to the
1645	system clock, for example, here is a C<ev_periodic> that triggers each	1891	system clock, for example, here is an C<ev_periodic> that triggers each
1646	hour, on the hour:	1892	hour, on the hour (with respect to UTC):
1647		1893
1648	ev_periodic_set (&periodic, 0., 3600., 0);	1894	ev_periodic_set (&periodic, 0., 3600., 0);
1649		1895
1650	This doesn't mean there will always be 3600 seconds in between triggers,	1896	This doesn't mean there will always be 3600 seconds in between triggers,
1651	but only that the callback will be called when the system time shows a	1897	but only that the callback will be called when the system time shows a
1652	full hour (UTC), or more correctly, when the system time is evenly divisible	1898	full hour (UTC), or more correctly, when the system time is evenly divisible
1653	by 3600.	1899	by 3600.
1654		1900
1655	Another way to think about it (for the mathematically inclined) is that	1901	Another way to think about it (for the mathematically inclined) is that
1656	C<ev_periodic> will try to run the callback in this mode at the next possible	1902	C<ev_periodic> will try to run the callback in this mode at the next possible
1657	time where C<time = at (mod interval)>, regardless of any time jumps.	1903	time where C<time = offset (mod interval)>, regardless of any time jumps.
1658		1904
1659	For numerical stability it is preferable that the C<at> value is near	1905	For numerical stability it is preferable that the C<offset> value is near
1660	C<ev_now ()> (the current time), but there is no range requirement for	1906	C<ev_now ()> (the current time), but there is no range requirement for
1661	this value, and in fact is often specified as zero.	1907	this value, and in fact is often specified as zero.
1662		1908
1663	Note also that there is an upper limit to how often a timer can fire (CPU	1909	Note also that there is an upper limit to how often a timer can fire (CPU
1664	speed for example), so if C<interval> is very small then timing stability	1910	speed for example), so if C<interval> is very small then timing stability
1665	will of course deteriorate. Libev itself tries to be exact to be about one	1911	will of course deteriorate. Libev itself tries to be exact to be about one
1666	millisecond (if the OS supports it and the machine is fast enough).	1912	millisecond (if the OS supports it and the machine is fast enough).
1667		1913
1668	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1914	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1669		1915
1670	In this mode the values for C<interval> and C<at> are both being	1916	In this mode the values for C<interval> and C<offset> are both being
1671	ignored. Instead, each time the periodic watcher gets scheduled, the	1917	ignored. Instead, each time the periodic watcher gets scheduled, the
1672	reschedule callback will be called with the watcher as first, and the	1918	reschedule callback will be called with the watcher as first, and the
1673	current time as second argument.	1919	current time as second argument.
1674		1920
1675	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1921	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1676	ever, or make ANY other event loop modifications whatsoever>.	1922	or make ANY other event loop modifications whatsoever, unless explicitly
		1923	allowed by documentation here>.
1677		1924
1678	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1925	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1679	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1926	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1680	only event loop modification you are allowed to do).	1927	only event loop modification you are allowed to do).
1681		1928
…		…
1711	a different time than the last time it was called (e.g. in a crond like	1958	a different time than the last time it was called (e.g. in a crond like
1712	program when the crontabs have changed).	1959	program when the crontabs have changed).
1713		1960
1714	=item ev_tstamp ev_periodic_at (ev_periodic *)	1961	=item ev_tstamp ev_periodic_at (ev_periodic *)
1715		1962
1716	When active, returns the absolute time that the watcher is supposed to	1963	When active, returns the absolute time that the watcher is supposed
1717	trigger next.	1964	to trigger next. This is not the same as the C<offset> argument to
		1965	C<ev_periodic_set>, but indeed works even in interval and manual
		1966	rescheduling modes.
1718		1967
1719	=item ev_tstamp offset [read-write]	1968	=item ev_tstamp offset [read-write]
1720		1969
1721	When repeating, this contains the offset value, otherwise this is the	1970	When repeating, this contains the offset value, otherwise this is the
1722	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1971	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1972	although libev might modify this value for better numerical stability).
1723		1973
1724	Can be modified any time, but changes only take effect when the periodic	1974	Can be modified any time, but changes only take effect when the periodic
1725	timer fires or C<ev_periodic_again> is being called.	1975	timer fires or C<ev_periodic_again> is being called.
1726		1976
1727	=item ev_tstamp interval [read-write]	1977	=item ev_tstamp interval [read-write]
…		…
1836	some child status changes (most typically when a child of yours dies or	2086	some child status changes (most typically when a child of yours dies or
1837	exits). It is permissible to install a child watcher I<after> the child	2087	exits). It is permissible to install a child watcher I<after> the child
1838	has been forked (which implies it might have already exited), as long	2088	has been forked (which implies it might have already exited), as long
1839	as the event loop isn't entered (or is continued from a watcher), i.e.,	2089	as the event loop isn't entered (or is continued from a watcher), i.e.,
1840	forking and then immediately registering a watcher for the child is fine,	2090	forking and then immediately registering a watcher for the child is fine,
1841	but forking and registering a watcher a few event loop iterations later is	2091	but forking and registering a watcher a few event loop iterations later or
1842	not.	2092	in the next callback invocation is not.
1843		2093
1844	Only the default event loop is capable of handling signals, and therefore	2094	Only the default event loop is capable of handling signals, and therefore
1845	you can only register child watchers in the default event loop.	2095	you can only register child watchers in the default event loop.
		2096
		2097	Due to some design glitches inside libev, child watchers will always be
		2098	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2099	libev)
1846		2100
1847	=head3 Process Interaction	2101	=head3 Process Interaction
1848		2102
1849	Libev grabs C<SIGCHLD> as soon as the default event loop is	2103	Libev grabs C<SIGCHLD> as soon as the default event loop is
1850	initialised. This is necessary to guarantee proper behaviour even if	2104	initialised. This is necessary to guarantee proper behaviour even if
…		…
2202	// no longer anything immediate to do.	2456	// no longer anything immediate to do.
2203	}	2457	}
2204		2458
2205	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2459	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2206	ev_idle_init (idle_watcher, idle_cb);	2460	ev_idle_init (idle_watcher, idle_cb);
2207	ev_idle_start (loop, idle_cb);	2461	ev_idle_start (loop, idle_watcher);
2208		2462
2209		2463
2210	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2464	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2211		2465
2212	Prepare and check watchers are usually (but not always) used in pairs:	2466	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2305	struct pollfd fds [nfd];	2559	struct pollfd fds [nfd];
2306	// actual code will need to loop here and realloc etc.	2560	// actual code will need to loop here and realloc etc.
2307	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2561	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2308		2562
2309	/* the callback is illegal, but won't be called as we stop during check */	2563	/* the callback is illegal, but won't be called as we stop during check */
2310	ev_timer_init (&tw, 0, timeout * 1e-3);	2564	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2311	ev_timer_start (loop, &tw);	2565	ev_timer_start (loop, &tw);
2312		2566
2313	// create one ev_io per pollfd	2567	// create one ev_io per pollfd
2314	for (int i = 0; i < nfd; ++i)	2568	for (int i = 0; i < nfd; ++i)
2315	{	2569	{
…		…
2545	event loop blocks next and before C<ev_check> watchers are being called,	2799	event loop blocks next and before C<ev_check> watchers are being called,
2546	and only in the child after the fork. If whoever good citizen calling	2800	and only in the child after the fork. If whoever good citizen calling
2547	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2801	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2548	handlers will be invoked, too, of course.	2802	handlers will be invoked, too, of course.
2549		2803
		2804	=head3 The special problem of life after fork - how is it possible?
		2805
		2806	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2807	up/change the process environment, followed by a call to C<exec()>. This
		2808	sequence should be handled by libev without any problems.
		2809
		2810	This changes when the application actually wants to do event handling
		2811	in the child, or both parent in child, in effect "continuing" after the
		2812	fork.
		2813
		2814	The default mode of operation (for libev, with application help to detect
		2815	forks) is to duplicate all the state in the child, as would be expected
		2816	when I<either> the parent I<or> the child process continues.
		2817
		2818	When both processes want to continue using libev, then this is usually the
		2819	wrong result. In that case, usually one process (typically the parent) is
		2820	supposed to continue with all watchers in place as before, while the other
		2821	process typically wants to start fresh, i.e. without any active watchers.
		2822
		2823	The cleanest and most efficient way to achieve that with libev is to
		2824	simply create a new event loop, which of course will be "empty", and
		2825	use that for new watchers. This has the advantage of not touching more
		2826	memory than necessary, and thus avoiding the copy-on-write, and the
		2827	disadvantage of having to use multiple event loops (which do not support
		2828	signal watchers).
		2829
		2830	When this is not possible, or you want to use the default loop for
		2831	other reasons, then in the process that wants to start "fresh", call
		2832	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2833	the default loop will "orphan" (not stop) all registered watchers, so you
		2834	have to be careful not to execute code that modifies those watchers. Note
		2835	also that in that case, you have to re-register any signal watchers.
		2836
2550	=head3 Watcher-Specific Functions and Data Members	2837	=head3 Watcher-Specific Functions and Data Members
2551		2838
2552	=over 4	2839	=over 4
2553		2840
2554	=item ev_fork_init (ev_signal *, callback)	2841	=item ev_fork_init (ev_signal *, callback)
…		…
2682	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	2969	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2683	C<ev_feed_event>, this call is safe to do from other threads, signal or	2970	C<ev_feed_event>, this call is safe to do from other threads, signal or
2684	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	2971	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2685	section below on what exactly this means).	2972	section below on what exactly this means).
2686		2973
		2974	Note that, as with other watchers in libev, multiple events might get
		2975	compressed into a single callback invocation (another way to look at this
		2976	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2977	reset when the event loop detects that).
		2978
2687	This call incurs the overhead of a system call only once per loop iteration,	2979	This call incurs the overhead of a system call only once per event loop
2688	so while the overhead might be noticeable, it doesn't apply to repeated	2980	iteration, so while the overhead might be noticeable, it doesn't apply to
2689	calls to C<ev_async_send>.	2981	repeated calls to C<ev_async_send> for the same event loop.
2690		2982
2691	=item bool = ev_async_pending (ev_async *)	2983	=item bool = ev_async_pending (ev_async *)
2692		2984
2693	Returns a non-zero value when C<ev_async_send> has been called on the	2985	Returns a non-zero value when C<ev_async_send> has been called on the
2694	watcher but the event has not yet been processed (or even noted) by the	2986	watcher but the event has not yet been processed (or even noted) by the
…		…
2697	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	2989	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2698	the loop iterates next and checks for the watcher to have become active,	2990	the loop iterates next and checks for the watcher to have become active,
2699	it will reset the flag again. C<ev_async_pending> can be used to very	2991	it will reset the flag again. C<ev_async_pending> can be used to very
2700	quickly check whether invoking the loop might be a good idea.	2992	quickly check whether invoking the loop might be a good idea.
2701		2993
2702	Not that this does I<not> check whether the watcher itself is pending, only	2994	Not that this does I<not> check whether the watcher itself is pending,
2703	whether it has been requested to make this watcher pending.	2995	only whether it has been requested to make this watcher pending: there
		2996	is a time window between the event loop checking and resetting the async
		2997	notification, and the callback being invoked.
2704		2998
2705	=back	2999	=back
2706		3000
2707		3001
2708	=head1 OTHER FUNCTIONS	3002	=head1 OTHER FUNCTIONS
…		…
3012	L<http://software.schmorp.de/pkg/EV>.	3306	L<http://software.schmorp.de/pkg/EV>.
3013		3307
3014	=item Python	3308	=item Python
3015		3309
3016	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3310	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
3017	seems to be quite complete and well-documented. Note, however, that the	3311	seems to be quite complete and well-documented.
3018	patch they require for libev is outright dangerous as it breaks the ABI
3019	for everybody else, and therefore, should never be applied in an installed
3020	libev (if python requires an incompatible ABI then it needs to embed
3021	libev).
3022		3312
3023	=item Ruby	3313	=item Ruby
3024		3314
3025	Tony Arcieri has written a ruby extension that offers access to a subset	3315	Tony Arcieri has written a ruby extension that offers access to a subset
3026	of the libev API and adds file handle abstractions, asynchronous DNS and	3316	of the libev API and adds file handle abstractions, asynchronous DNS and
3027	more on top of it. It can be found via gem servers. Its homepage is at	3317	more on top of it. It can be found via gem servers. Its homepage is at
3028	L<http://rev.rubyforge.org/>.	3318	L<http://rev.rubyforge.org/>.
3029		3319
3030	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>	3320	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
3031	makes rev work even on mingw.	3321	makes rev work even on mingw.
		3322
		3323	=item Haskell
		3324
		3325	A haskell binding to libev is available at
		3326	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3032		3327
3033	=item D	3328	=item D
3034		3329
3035	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3330	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3036	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3331	be found at L<http://proj.llucax.com.ar/wiki/evd>.
…		…
3436	defined to be C<0>, then they are not.	3731	defined to be C<0>, then they are not.
3437		3732
3438	=item EV_MINIMAL	3733	=item EV_MINIMAL
3439		3734
3440	If you need to shave off some kilobytes of code at the expense of some	3735	If you need to shave off some kilobytes of code at the expense of some
3441	speed, define this symbol to C<1>. Currently this is used to override some	3736	speed (but with the full API), define this symbol to C<1>. Currently this
3442	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3737	is used to override some inlining decisions, saves roughly 30% code size
3443	much smaller 2-heap for timer management over the default 4-heap.	3738	on amd64. It also selects a much smaller 2-heap for timer management over
		3739	the default 4-heap.
		3740
		3741	You can save even more by disabling watcher types you do not need
		3742	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3743	(C<-DNDEBUG>) will usually reduce code size a lot.
		3744
		3745	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3746	provide a bare-bones event library. See C<ev.h> for details on what parts
		3747	of the API are still available, and do not complain if this subset changes
		3748	over time.
3444		3749
3445	=item EV_PID_HASHSIZE	3750	=item EV_PID_HASHSIZE
3446		3751
3447	C<ev_child> watchers use a small hash table to distribute workload by	3752	C<ev_child> watchers use a small hash table to distribute workload by
3448	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3753	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3634	default loop and triggering an C<ev_async> watcher from the default loop	3939	default loop and triggering an C<ev_async> watcher from the default loop
3635	watcher callback into the event loop interested in the signal.	3940	watcher callback into the event loop interested in the signal.
3636		3941
3637	=back	3942	=back
3638		3943
		3944	=head4 THREAD LOCKING EXAMPLE
		3945
		3946	Here is a fictitious example of how to run an event loop in a different
		3947	thread than where callbacks are being invoked and watchers are
		3948	created/added/removed.
		3949
		3950	For a real-world example, see the C<EV::Loop::Async> perl module,
		3951	which uses exactly this technique (which is suited for many high-level
		3952	languages).
		3953
		3954	The example uses a pthread mutex to protect the loop data, a condition
		3955	variable to wait for callback invocations, an async watcher to notify the
		3956	event loop thread and an unspecified mechanism to wake up the main thread.
		3957
		3958	First, you need to associate some data with the event loop:
		3959
		3960	typedef struct {
		3961	mutex_t lock; /* global loop lock */
		3962	ev_async async_w;
		3963	thread_t tid;
		3964	cond_t invoke_cv;
		3965	} userdata;
		3966
		3967	void prepare_loop (EV_P)
		3968	{
		3969	// for simplicity, we use a static userdata struct.
		3970	static userdata u;
		3971
		3972	ev_async_init (&u->async_w, async_cb);
		3973	ev_async_start (EV_A_ &u->async_w);
		3974
		3975	pthread_mutex_init (&u->lock, 0);
		3976	pthread_cond_init (&u->invoke_cv, 0);
		3977
		3978	// now associate this with the loop
		3979	ev_set_userdata (EV_A_ u);
		3980	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3981	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3982
		3983	// then create the thread running ev_loop
		3984	pthread_create (&u->tid, 0, l_run, EV_A);
		3985	}
		3986
		3987	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3988	solely to wake up the event loop so it takes notice of any new watchers
		3989	that might have been added:
		3990
		3991	static void
		3992	async_cb (EV_P_ ev_async *w, int revents)
		3993	{
		3994	// just used for the side effects
		3995	}
		3996
		3997	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3998	protecting the loop data, respectively.
		3999
		4000	static void
		4001	l_release (EV_P)
		4002	{
		4003	udat *u = ev_userdata (EV_A);
		4004	pthread_mutex_unlock (&u->lock);
		4005	}
		4006
		4007	static void
		4008	l_acquire (EV_P)
		4009	{
		4010	udat *u = ev_userdata (EV_A);
		4011	pthread_mutex_lock (&u->lock);
		4012	}
		4013
		4014	The event loop thread first acquires the mutex, and then jumps straight
		4015	into C<ev_loop>:
		4016
		4017	void *
		4018	l_run (void *thr_arg)
		4019	{
		4020	struct ev_loop loop = (struct ev_loop )thr_arg;
		4021
		4022	l_acquire (EV_A);
		4023	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4024	ev_loop (EV_A_ 0);
		4025	l_release (EV_A);
		4026
		4027	return 0;
		4028	}
		4029
		4030	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4031	signal the main thread via some unspecified mechanism (signals? pipe
		4032	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4033	have been called:
		4034
		4035	static void
		4036	l_invoke (EV_P)
		4037	{
		4038	udat *u = ev_userdata (EV_A);
		4039
		4040	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4041
		4042	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4043	}
		4044
		4045	Now, whenever the main thread gets told to invoke pending watchers, it
		4046	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4047	thread to continue:
		4048
		4049	static void
		4050	real_invoke_pending (EV_P)
		4051	{
		4052	udat *u = ev_userdata (EV_A);
		4053
		4054	pthread_mutex_lock (&u->lock);
		4055	ev_invoke_pending (EV_A);
		4056	pthread_cond_signal (&u->invoke_cv);
		4057	pthread_mutex_unlock (&u->lock);
		4058	}
		4059
		4060	Whenever you want to start/stop a watcher or do other modifications to an
		4061	event loop, you will now have to lock:
		4062
		4063	ev_timer timeout_watcher;
		4064	udat *u = ev_userdata (EV_A);
		4065
		4066	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4067
		4068	pthread_mutex_lock (&u->lock);
		4069	ev_timer_start (EV_A_ &timeout_watcher);
		4070	ev_async_send (EV_A_ &u->async_w);
		4071	pthread_mutex_unlock (&u->lock);
		4072
		4073	Note that sending the C<ev_async> watcher is required because otherwise
		4074	an event loop currently blocking in the kernel will have no knowledge
		4075	about the newly added timer. By waking up the loop it will pick up any new
		4076	watchers in the next event loop iteration.
		4077
3639	=head3 COROUTINES	4078	=head3 COROUTINES
3640		4079
3641	Libev is very accommodating to coroutines ("cooperative threads"):	4080	Libev is very accommodating to coroutines ("cooperative threads"):
3642	libev fully supports nesting calls to its functions from different	4081	libev fully supports nesting calls to its functions from different
3643	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4082	coroutines (e.g. you can call C<ev_loop> on the same loop from two
…		…
3728	way (note also that glib is the slowest event library known to man).	4167	way (note also that glib is the slowest event library known to man).
3729		4168
3730	There is no supported compilation method available on windows except	4169	There is no supported compilation method available on windows except
3731	embedding it into other applications.	4170	embedding it into other applications.
3732		4171
		4172	Sensible signal handling is officially unsupported by Microsoft - libev
		4173	tries its best, but under most conditions, signals will simply not work.
		4174
3733	Not a libev limitation but worth mentioning: windows apparently doesn't	4175	Not a libev limitation but worth mentioning: windows apparently doesn't
3734	accept large writes: instead of resulting in a partial write, windows will	4176	accept large writes: instead of resulting in a partial write, windows will
3735	either accept everything or return C<ENOBUFS> if the buffer is too large,	4177	either accept everything or return C<ENOBUFS> if the buffer is too large,
3736	so make sure you only write small amounts into your sockets (less than a	4178	so make sure you only write small amounts into your sockets (less than a
3737	megabyte seems safe, but this apparently depends on the amount of memory	4179	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3741	the abysmal performance of winsockets, using a large number of sockets	4183	the abysmal performance of winsockets, using a large number of sockets
3742	is not recommended (and not reasonable). If your program needs to use	4184	is not recommended (and not reasonable). If your program needs to use
3743	more than a hundred or so sockets, then likely it needs to use a totally	4185	more than a hundred or so sockets, then likely it needs to use a totally
3744	different implementation for windows, as libev offers the POSIX readiness	4186	different implementation for windows, as libev offers the POSIX readiness
3745	notification model, which cannot be implemented efficiently on windows	4187	notification model, which cannot be implemented efficiently on windows
3746	(Microsoft monopoly games).	4188	(due to Microsoft monopoly games).
3747		4189
3748	A typical way to use libev under windows is to embed it (see the embedding	4190	A typical way to use libev under windows is to embed it (see the embedding
3749	section for details) and use the following F<evwrap.h> header file instead	4191	section for details) and use the following F<evwrap.h> header file instead
3750	of F<ev.h>:	4192	of F<ev.h>:
3751		4193
…		…
3787		4229
3788	Early versions of winsocket's select only supported waiting for a maximum	4230	Early versions of winsocket's select only supported waiting for a maximum
3789	of C<64> handles (probably owning to the fact that all windows kernels	4231	of C<64> handles (probably owning to the fact that all windows kernels
3790	can only wait for C<64> things at the same time internally; Microsoft	4232	can only wait for C<64> things at the same time internally; Microsoft
3791	recommends spawning a chain of threads and wait for 63 handles and the	4233	recommends spawning a chain of threads and wait for 63 handles and the
3792	previous thread in each. Great).	4234	previous thread in each. Sounds great!).
3793		4235
3794	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4236	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3795	to some high number (e.g. C<2048>) before compiling the winsocket select	4237	to some high number (e.g. C<2048>) before compiling the winsocket select
3796	call (which might be in libev or elsewhere, for example, perl does its own	4238	call (which might be in libev or elsewhere, for example, perl and many
3797	select emulation on windows).	4239	other interpreters do their own select emulation on windows).
3798		4240
3799	Another limit is the number of file descriptors in the Microsoft runtime	4241	Another limit is the number of file descriptors in the Microsoft runtime
3800	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4242	libraries, which by default is C<64> (there must be a hidden I<64>
3801	or something like this inside Microsoft). You can increase this by calling	4243	fetish or something like this inside Microsoft). You can increase this
3802	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4244	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3803	arbitrary limit), but is broken in many versions of the Microsoft runtime	4245	(another arbitrary limit), but is broken in many versions of the Microsoft
3804	libraries.
3805
3806	This might get you to about C<512> or C<2048> sockets (depending on	4246	runtime libraries. This might get you to about C<512> or C<2048> sockets
3807	windows version and/or the phase of the moon). To get more, you need to	4247	(depending on windows version and/or the phase of the moon). To get more,
3808	wrap all I/O functions and provide your own fd management, but the cost of	4248	you need to wrap all I/O functions and provide your own fd management, but
3809	calling select (O(n²)) will likely make this unworkable.	4249	the cost of calling select (O(n²)) will likely make this unworkable.
3810		4250
3811	=back	4251	=back
3812		4252
3813	=head2 PORTABILITY REQUIREMENTS	4253	=head2 PORTABILITY REQUIREMENTS
3814		4254
…		…
3857	=item C<double> must hold a time value in seconds with enough accuracy	4297	=item C<double> must hold a time value in seconds with enough accuracy
3858		4298
3859	The type C<double> is used to represent timestamps. It is required to	4299	The type C<double> is used to represent timestamps. It is required to
3860	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4300	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3861	enough for at least into the year 4000. This requirement is fulfilled by	4301	enough for at least into the year 4000. This requirement is fulfilled by
3862	implementations implementing IEEE 754 (basically all existing ones).	4302	implementations implementing IEEE 754, which is basically all existing
		4303	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4304	2200.
3863		4305
3864	=back	4306	=back
3865		4307
3866	If you know of other additional requirements drop me a note.	4308	If you know of other additional requirements drop me a note.
3867		4309
…		…
3935	involves iterating over all running async watchers or all signal numbers.	4377	involves iterating over all running async watchers or all signal numbers.
3936		4378
3937	=back	4379	=back
3938		4380
3939		4381
		4382	=head1 GLOSSARY
		4383
		4384	=over 4
		4385
		4386	=item active
		4387
		4388	A watcher is active as long as it has been started (has been attached to
		4389	an event loop) but not yet stopped (disassociated from the event loop).
		4390
		4391	=item application
		4392
		4393	In this document, an application is whatever is using libev.
		4394
		4395	=item callback
		4396
		4397	The address of a function that is called when some event has been
		4398	detected. Callbacks are being passed the event loop, the watcher that
		4399	received the event, and the actual event bitset.
		4400
		4401	=item callback invocation
		4402
		4403	The act of calling the callback associated with a watcher.
		4404
		4405	=item event
		4406
		4407	A change of state of some external event, such as data now being available
		4408	for reading on a file descriptor, time having passed or simply not having
		4409	any other events happening anymore.
		4410
		4411	In libev, events are represented as single bits (such as C<EV_READ> or
		4412	C<EV_TIMEOUT>).
		4413
		4414	=item event library
		4415
		4416	A software package implementing an event model and loop.
		4417
		4418	=item event loop
		4419
		4420	An entity that handles and processes external events and converts them
		4421	into callback invocations.
		4422
		4423	=item event model
		4424
		4425	The model used to describe how an event loop handles and processes
		4426	watchers and events.
		4427
		4428	=item pending
		4429
		4430	A watcher is pending as soon as the corresponding event has been detected,
		4431	and stops being pending as soon as the watcher will be invoked or its
		4432	pending status is explicitly cleared by the application.
		4433
		4434	A watcher can be pending, but not active. Stopping a watcher also clears
		4435	its pending status.
		4436
		4437	=item real time
		4438
		4439	The physical time that is observed. It is apparently strictly monotonic :)
		4440
		4441	=item wall-clock time
		4442
		4443	The time and date as shown on clocks. Unlike real time, it can actually
		4444	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4445	clock.
		4446
		4447	=item watcher
		4448
		4449	A data structure that describes interest in certain events. Watchers need
		4450	to be started (attached to an event loop) before they can receive events.
		4451
		4452	=item watcher invocation
		4453
		4454	The act of calling the callback associated with a watcher.
		4455
		4456	=back
		4457
3940	=head1 AUTHOR	4458	=head1 AUTHOR
3941		4459
3942	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	4460	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3943		4461

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Comparing libev/ev.pod (file contents):
Revision 1.226 by root, Wed Mar 4 12:51:37 2009 UTC vs.
Revision 1.254 by root, Tue Jul 14 19:02:43 2009 UTC