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Revision 1.224 by root, Fri Feb 6 20:17:43 2009 UTC vs.
Revision 1.258 by root, Wed Jul 15 16:58:53 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 int ev_pending_count (loop)
		868
		869	Returns the number of pending watchers - zero indicates that no watchers
		870	are pending.
		871
		872	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		873
		874	This overrides the invoke pending functionality of the loop: Instead of
		875	invoking all pending watchers when there are any, C<ev_loop> will call
		876	this callback instead. This is useful, for example, when you want to
		877	invoke the actual watchers inside another context (another thread etc.).
		878
		879	If you want to reset the callback, use C<ev_invoke_pending> as new
		880	callback.
		881
		882	=item ev_set_loop_release_cb (loop, void (release)(EV_P), void (acquire)(EV_P))
		883
		884	Sometimes you want to share the same loop between multiple threads. This
		885	can be done relatively simply by putting mutex_lock/unlock calls around
		886	each call to a libev function.
		887
		888	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		889	wait for it to return. One way around this is to wake up the loop via
		890	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		891	and I<acquire> callbacks on the loop.
		892
		893	When set, then C<release> will be called just before the thread is
		894	suspended waiting for new events, and C<acquire> is called just
		895	afterwards.
		896
		897	Ideally, C<release> will just call your mutex_unlock function, and
		898	C<acquire> will just call the mutex_lock function again.
		899
		900	While event loop modifications are allowed between invocations of
		901	C<release> and C<acquire> (that's their only purpose after all), no
		902	modifications done will affect the event loop, i.e. adding watchers will
		903	have no effect on the set of file descriptors being watched, or the time
		904	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		905	to take note of any changes you made.
		906
		907	In theory, threads executing C<ev_loop> will be async-cancel safe between
		908	invocations of C<release> and C<acquire>.
		909
		910	See also the locking example in the C<THREADS> section later in this
		911	document.
		912
		913	=item ev_set_userdata (loop, void *data)
		914
		915	=item ev_userdata (loop)
		916
		917	Set and retrieve a single C<void *> associated with a loop. When
		918	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		919	C<0.>
		920
		921	These two functions can be used to associate arbitrary data with a loop,
		922	and are intended solely for the C<invoke_pending_cb>, C<release> and
		923	C<acquire> callbacks described above, but of course can be (ab-)used for
		924	any other purpose as well.
796		925
797	=item ev_loop_verify (loop)	926	=item ev_loop_verify (loop)
798		927
799	This function only does something when C<EV_VERIFY> support has been	928	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	929	compiled in, which is the default for non-minimal builds. It tries to go
…		…
926		1055
927	=item C<EV_ASYNC>	1056	=item C<EV_ASYNC>
928		1057
929	The given async watcher has been asynchronously notified (see C<ev_async>).	1058	The given async watcher has been asynchronously notified (see C<ev_async>).
930		1059
		1060	=item C<EV_CUSTOM>
		1061
		1062	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1063	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1064
931	=item C<EV_ERROR>	1065	=item C<EV_ERROR>
932		1066
933	An unspecified error has occurred, the watcher has been stopped. This might	1067	An unspecified error has occurred, the watcher has been stopped. This might
934	happen because the watcher could not be properly started because libev	1068	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	1069	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>	1184	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1051	(default: C<-2>). Pending watchers with higher priority will be invoked	1185	(default: C<-2>). Pending watchers with higher priority will be invoked
1052	before watchers with lower priority, but priority will not keep watchers	1186	before watchers with lower priority, but priority will not keep watchers
1053	from being executed (except for C<ev_idle> watchers).	1187	from being executed (except for C<ev_idle> watchers).
1054		1188
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	1189	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.	1190	you need to look at C<ev_idle> watchers, which provide this functionality.
1062		1191
1063	You I<must not> change the priority of a watcher as long as it is active or	1192	You I<must not> change the priority of a watcher as long as it is active or
1064	pending.	1193	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		1194
1069	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1195	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	1196	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.	1197	or might not have been clamped to the valid range.
		1198
		1199	The default priority used by watchers when no priority has been set is
		1200	always C<0>, which is supposed to not be too high and not be too low :).
		1201
		1202	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1203	priorities.
1072		1204
1073	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1205	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1074		1206
1075	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1207	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	1208	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1141	#include <stddef.h>	1273	#include <stddef.h>
1142		1274
1143	static void	1275	static void
1144	t1_cb (EV_P_ ev_timer *w, int revents)	1276	t1_cb (EV_P_ ev_timer *w, int revents)
1145	{	1277	{
1146	struct my_biggy big = (struct my_biggy *	1278	struct my_biggy big = (struct my_biggy *)
1147	(((char *)w) - offsetof (struct my_biggy, t1));	1279	(((char *)w) - offsetof (struct my_biggy, t1));
1148	}	1280	}
1149		1281
1150	static void	1282	static void
1151	t2_cb (EV_P_ ev_timer *w, int revents)	1283	t2_cb (EV_P_ ev_timer *w, int revents)
1152	{	1284	{
1153	struct my_biggy big = (struct my_biggy *	1285	struct my_biggy big = (struct my_biggy *)
1154	(((char *)w) - offsetof (struct my_biggy, t2));	1286	(((char *)w) - offsetof (struct my_biggy, t2));
1155	}	1287	}
		1288
		1289	=head2 WATCHER PRIORITY MODELS
		1290
		1291	Many event loops support I<watcher priorities>, which are usually small
		1292	integers that influence the ordering of event callback invocation
		1293	between watchers in some way, all else being equal.
		1294
		1295	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1296	description for the more technical details such as the actual priority
		1297	range.
		1298
		1299	There are two common ways how these these priorities are being interpreted
		1300	by event loops:
		1301
		1302	In the more common lock-out model, higher priorities "lock out" invocation
		1303	of lower priority watchers, which means as long as higher priority
		1304	watchers receive events, lower priority watchers are not being invoked.
		1305
		1306	The less common only-for-ordering model uses priorities solely to order
		1307	callback invocation within a single event loop iteration: Higher priority
		1308	watchers are invoked before lower priority ones, but they all get invoked
		1309	before polling for new events.
		1310
		1311	Libev uses the second (only-for-ordering) model for all its watchers
		1312	except for idle watchers (which use the lock-out model).
		1313
		1314	The rationale behind this is that implementing the lock-out model for
		1315	watchers is not well supported by most kernel interfaces, and most event
		1316	libraries will just poll for the same events again and again as long as
		1317	their callbacks have not been executed, which is very inefficient in the
		1318	common case of one high-priority watcher locking out a mass of lower
		1319	priority ones.
		1320
		1321	Static (ordering) priorities are most useful when you have two or more
		1322	watchers handling the same resource: a typical usage example is having an
		1323	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1324	timeouts. Under load, data might be received while the program handles
		1325	other jobs, but since timers normally get invoked first, the timeout
		1326	handler will be executed before checking for data. In that case, giving
		1327	the timer a lower priority than the I/O watcher ensures that I/O will be
		1328	handled first even under adverse conditions (which is usually, but not
		1329	always, what you want).
		1330
		1331	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1332	will only be executed when no same or higher priority watchers have
		1333	received events, they can be used to implement the "lock-out" model when
		1334	required.
		1335
		1336	For example, to emulate how many other event libraries handle priorities,
		1337	you can associate an C<ev_idle> watcher to each such watcher, and in
		1338	the normal watcher callback, you just start the idle watcher. The real
		1339	processing is done in the idle watcher callback. This causes libev to
		1340	continously poll and process kernel event data for the watcher, but when
		1341	the lock-out case is known to be rare (which in turn is rare :), this is
		1342	workable.
		1343
		1344	Usually, however, the lock-out model implemented that way will perform
		1345	miserably under the type of load it was designed to handle. In that case,
		1346	it might be preferable to stop the real watcher before starting the
		1347	idle watcher, so the kernel will not have to process the event in case
		1348	the actual processing will be delayed for considerable time.
		1349
		1350	Here is an example of an I/O watcher that should run at a strictly lower
		1351	priority than the default, and which should only process data when no
		1352	other events are pending:
		1353
		1354	ev_idle idle; // actual processing watcher
		1355	ev_io io; // actual event watcher
		1356
		1357	static void
		1358	io_cb (EV_P_ ev_io *w, int revents)
		1359	{
		1360	// stop the I/O watcher, we received the event, but
		1361	// are not yet ready to handle it.
		1362	ev_io_stop (EV_A_ w);
		1363
		1364	// start the idle watcher to ahndle the actual event.
		1365	// it will not be executed as long as other watchers
		1366	// with the default priority are receiving events.
		1367	ev_idle_start (EV_A_ &idle);
		1368	}
		1369
		1370	static void
		1371	idle_cb (EV_P_ ev_idle *w, int revents)
		1372	{
		1373	// actual processing
		1374	read (STDIN_FILENO, ...);
		1375
		1376	// have to start the I/O watcher again, as
		1377	// we have handled the event
		1378	ev_io_start (EV_P_ &io);
		1379	}
		1380
		1381	// initialisation
		1382	ev_idle_init (&idle, idle_cb);
		1383	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1384	ev_io_start (EV_DEFAULT_ &io);
		1385
		1386	In the "real" world, it might also be beneficial to start a timer, so that
		1387	low-priority connections can not be locked out forever under load. This
		1388	enables your program to keep a lower latency for important connections
		1389	during short periods of high load, while not completely locking out less
		1390	important ones.
1156		1391
1157		1392
1158	=head1 WATCHER TYPES	1393	=head1 WATCHER TYPES
1159		1394
1160	This section describes each watcher in detail, but will not repeat	1395	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	1421	descriptors to non-blocking mode is also usually a good idea (but not
1187	required if you know what you are doing).	1422	required if you know what you are doing).
1188		1423
1189	If you cannot use non-blocking mode, then force the use of a	1424	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	1425	known-to-be-good backend (at the time of this writing, this includes only
1191	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1426	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1427	descriptors for which non-blocking operation makes no sense (such as
		1428	files) - libev doesn't guarentee any specific behaviour in that case.
1192		1429
1193	Another thing you have to watch out for is that it is quite easy to	1430	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	1431	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	1432	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	1433	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	1554	year, it will still time out after (roughly) one hour. "Roughly" because
1318	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1555	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1319	monotonic clock option helps a lot here).	1556	monotonic clock option helps a lot here).
1320		1557
1321	The callback is guaranteed to be invoked only I<after> its timeout has	1558	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	1559	passed (not I<at>, so on systems with very low-resolution clocks this
1323	then order of execution is undefined.	1560	might introduce a small delay). If multiple timers become ready during the
		1561	same loop iteration then the ones with earlier time-out values are invoked
		1562	before ones of the same priority with later time-out values (but this is
		1563	no longer true when a callback calls C<ev_loop> recursively).
1324		1564
1325	=head3 Be smart about timeouts	1565	=head3 Be smart about timeouts
1326		1566
1327	Many real-world problems involve some kind of timeout, usually for error	1567	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,	1568	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>	1612	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
1373	member and C<ev_timer_again>.	1613	member and C<ev_timer_again>.
1374		1614
1375	At start:	1615	At start:
1376		1616
1377	ev_timer_init (timer, callback);	1617	ev_init (timer, callback);
1378	timer->repeat = 60.;	1618	timer->repeat = 60.;
1379	ev_timer_again (loop, timer);	1619	ev_timer_again (loop, timer);
1380		1620
1381	Each time there is some activity:	1621	Each time there is some activity:
1382		1622
…		…
1444		1684
1445	To start the timer, simply initialise the watcher and set C<last_activity>	1685	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	1686	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:	1687	callback, which will "do the right thing" and start the timer:
1448		1688
1449	ev_timer_init (timer, callback);	1689	ev_init (timer, callback);
1450	last_activity = ev_now (loop);	1690	last_activity = ev_now (loop);
1451	callback (loop, timer, EV_TIMEOUT);	1691	callback (loop, timer, EV_TIMEOUT);
1452		1692
1453	And when there is some activity, simply store the current time in	1693	And when there is some activity, simply store the current time in
1454	C<last_activity>, no libev calls at all:	1694	C<last_activity>, no libev calls at all:
…		…
1515		1755
1516	If the event loop is suspended for a long time, you can also force an	1756	If the event loop is suspended for a long time, you can also force an
1517	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1757	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1518	()>.	1758	()>.
1519		1759
		1760	=head3 The special problems of suspended animation
		1761
		1762	When you leave the server world it is quite customary to hit machines that
		1763	can suspend/hibernate - what happens to the clocks during such a suspend?
		1764
		1765	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1766	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1767	to run until the system is suspended, but they will not advance while the
		1768	system is suspended. That means, on resume, it will be as if the program
		1769	was frozen for a few seconds, but the suspend time will not be counted
		1770	towards C<ev_timer> when a monotonic clock source is used. The real time
		1771	clock advanced as expected, but if it is used as sole clocksource, then a
		1772	long suspend would be detected as a time jump by libev, and timers would
		1773	be adjusted accordingly.
		1774
		1775	I would not be surprised to see different behaviour in different between
		1776	operating systems, OS versions or even different hardware.
		1777
		1778	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1779	time jump in the monotonic clocks and the realtime clock. If the program
		1780	is suspended for a very long time, and monotonic clock sources are in use,
		1781	then you can expect C<ev_timer>s to expire as the full suspension time
		1782	will be counted towards the timers. When no monotonic clock source is in
		1783	use, then libev will again assume a timejump and adjust accordingly.
		1784
		1785	It might be beneficial for this latter case to call C<ev_suspend>
		1786	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1787	deterministic behaviour in this case (you can do nothing against
		1788	C<SIGSTOP>).
		1789
1520	=head3 Watcher-Specific Functions and Data Members	1790	=head3 Watcher-Specific Functions and Data Members
1521		1791
1522	=over 4	1792	=over 4
1523		1793
1524	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1794	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1547	If the timer is started but non-repeating, stop it (as if it timed out).	1817	If the timer is started but non-repeating, stop it (as if it timed out).
1548		1818
1549	If the timer is repeating, either start it if necessary (with the	1819	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.	1820	C<repeat> value), or reset the running timer to the C<repeat> value.
1551		1821
1552	This sounds a bit complicated, see "Be smart about timeouts", above, for a	1822	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1553	usage example.	1823	usage example.
		1824
		1825	=item ev_timer_remaining (loop, ev_timer *)
		1826
		1827	Returns the remaining time until a timer fires. If the timer is active,
		1828	then this time is relative to the current event loop time, otherwise it's
		1829	the timeout value currently configured.
		1830
		1831	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1832	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1833	will return C<4>. When the timer expires and is restarted, it will return
		1834	roughly C<7> (likely slightly less as callback invocation takes some time,
		1835	too), and so on.
1554		1836
1555	=item ev_tstamp repeat [read-write]	1837	=item ev_tstamp repeat [read-write]
1556		1838
1557	The current C<repeat> value. Will be used each time the watcher times out	1839	The current C<repeat> value. Will be used each time the watcher times out
1558	or C<ev_timer_again> is called, and determines the next timeout (if any),	1840	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1596	=head2 C<ev_periodic> - to cron or not to cron?	1878	=head2 C<ev_periodic> - to cron or not to cron?
1597		1879
1598	Periodic watchers are also timers of a kind, but they are very versatile	1880	Periodic watchers are also timers of a kind, but they are very versatile
1599	(and unfortunately a bit complex).	1881	(and unfortunately a bit complex).
1600		1882
1601	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1883	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	1884	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	1885	(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 ()	1886	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	1887	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	1888	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		1889
		1890	You can tell a periodic watcher to trigger after some specific point
		1891	in time: for example, if you tell a periodic watcher to trigger "in 10
		1892	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1893	not a delay) and then reset your system clock to January of the previous
		1894	year, then it will take a year or more to trigger the event (unlike an
		1895	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1896	it, as it uses a relative timeout).
		1897
1610	C<ev_periodic>s can also be used to implement vastly more complex timers,	1898	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	1899	timers, such as triggering an event on each "midnight, local time", or
1612	complicated rules.	1900	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1901	those cannot react to time jumps.
1613		1902
1614	As with timers, the callback is guaranteed to be invoked only when the	1903	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	1904	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.	1905	timers become ready during the same loop iteration then the ones with
		1906	earlier time-out values are invoked before ones with later time-out values
		1907	(but this is no longer true when a callback calls C<ev_loop> recursively).
1617		1908
1618	=head3 Watcher-Specific Functions and Data Members	1909	=head3 Watcher-Specific Functions and Data Members
1619		1910
1620	=over 4	1911	=over 4
1621		1912
1622	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1913	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1623		1914
1624	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1915	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1625		1916
1626	Lots of arguments, lets sort it out... There are basically three modes of	1917	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:	1918	operation, and we will explain them from simplest to most complex:
1628		1919
1629	=over 4	1920	=over 4
1630		1921
1631	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1922	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1632		1923
1633	In this configuration the watcher triggers an event after the wall clock	1924	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	1925	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	1926	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.	1927	will be stopped and invoked when the system clock reaches or surpasses
		1928	this point in time.
1637		1929
1638	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1930	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1639		1931
1640	In this mode the watcher will always be scheduled to time out at the next	1932	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)	1933	C<offset + N * interval> time (for some integer N, which can also be
1642	and then repeat, regardless of any time jumps.	1934	negative) and then repeat, regardless of any time jumps. The C<offset>
		1935	argument is merely an offset into the C<interval> periods.
1643		1936
1644	This can be used to create timers that do not drift with respect to the	1937	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	1938	system clock, for example, here is an C<ev_periodic> that triggers each
1646	hour, on the hour:	1939	hour, on the hour (with respect to UTC):
1647		1940
1648	ev_periodic_set (&periodic, 0., 3600., 0);	1941	ev_periodic_set (&periodic, 0., 3600., 0);
1649		1942
1650	This doesn't mean there will always be 3600 seconds in between triggers,	1943	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	1944	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	1945	full hour (UTC), or more correctly, when the system time is evenly divisible
1653	by 3600.	1946	by 3600.
1654		1947
1655	Another way to think about it (for the mathematically inclined) is that	1948	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	1949	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.	1950	time where C<time = offset (mod interval)>, regardless of any time jumps.
1658		1951
1659	For numerical stability it is preferable that the C<at> value is near	1952	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	1953	C<ev_now ()> (the current time), but there is no range requirement for
1661	this value, and in fact is often specified as zero.	1954	this value, and in fact is often specified as zero.
1662		1955
1663	Note also that there is an upper limit to how often a timer can fire (CPU	1956	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	1957	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	1958	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).	1959	millisecond (if the OS supports it and the machine is fast enough).
1667		1960
1668	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1961	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1669		1962
1670	In this mode the values for C<interval> and C<at> are both being	1963	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	1964	ignored. Instead, each time the periodic watcher gets scheduled, the
1672	reschedule callback will be called with the watcher as first, and the	1965	reschedule callback will be called with the watcher as first, and the
1673	current time as second argument.	1966	current time as second argument.
1674		1967
1675	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1968	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1676	ever, or make ANY event loop modifications whatsoever>.	1969	or make ANY other event loop modifications whatsoever, unless explicitly
		1970	allowed by documentation here>.
1677		1971
1678	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1972	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	1973	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1680	only event loop modification you are allowed to do).	1974	only event loop modification you are allowed to do).
1681		1975
…		…
1711	a different time than the last time it was called (e.g. in a crond like	2005	a different time than the last time it was called (e.g. in a crond like
1712	program when the crontabs have changed).	2006	program when the crontabs have changed).
1713		2007
1714	=item ev_tstamp ev_periodic_at (ev_periodic *)	2008	=item ev_tstamp ev_periodic_at (ev_periodic *)
1715		2009
1716	When active, returns the absolute time that the watcher is supposed to	2010	When active, returns the absolute time that the watcher is supposed
1717	trigger next.	2011	to trigger next. This is not the same as the C<offset> argument to
		2012	C<ev_periodic_set>, but indeed works even in interval and manual
		2013	rescheduling modes.
1718		2014
1719	=item ev_tstamp offset [read-write]	2015	=item ev_tstamp offset [read-write]
1720		2016
1721	When repeating, this contains the offset value, otherwise this is the	2017	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>).	2018	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2019	although libev might modify this value for better numerical stability).
1723		2020
1724	Can be modified any time, but changes only take effect when the periodic	2021	Can be modified any time, but changes only take effect when the periodic
1725	timer fires or C<ev_periodic_again> is being called.	2022	timer fires or C<ev_periodic_again> is being called.
1726		2023
1727	=item ev_tstamp interval [read-write]	2024	=item ev_tstamp interval [read-write]
…		…
1836	some child status changes (most typically when a child of yours dies or	2133	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	2134	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	2135	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.,	2136	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,	2137	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	2138	but forking and registering a watcher a few event loop iterations later or
1842	not.	2139	in the next callback invocation is not.
1843		2140
1844	Only the default event loop is capable of handling signals, and therefore	2141	Only the default event loop is capable of handling signals, and therefore
1845	you can only register child watchers in the default event loop.	2142	you can only register child watchers in the default event loop.
		2143
		2144	Due to some design glitches inside libev, child watchers will always be
		2145	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2146	libev)
1846		2147
1847	=head3 Process Interaction	2148	=head3 Process Interaction
1848		2149
1849	Libev grabs C<SIGCHLD> as soon as the default event loop is	2150	Libev grabs C<SIGCHLD> as soon as the default event loop is
1850	initialised. This is necessary to guarantee proper behaviour even if	2151	initialised. This is necessary to guarantee proper behaviour even if
…		…
2179		2480
2180	=head3 Watcher-Specific Functions and Data Members	2481	=head3 Watcher-Specific Functions and Data Members
2181		2482
2182	=over 4	2483	=over 4
2183		2484
2184	=item ev_idle_init (ev_signal *, callback)	2485	=item ev_idle_init (ev_idle *, callback)
2185		2486
2186	Initialises and configures the idle watcher - it has no parameters of any	2487	Initialises and configures the idle watcher - it has no parameters of any
2187	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2488	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
2188	believe me.	2489	believe me.
2189		2490
…		…
2202	// no longer anything immediate to do.	2503	// no longer anything immediate to do.
2203	}	2504	}
2204		2505
2205	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2506	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2206	ev_idle_init (idle_watcher, idle_cb);	2507	ev_idle_init (idle_watcher, idle_cb);
2207	ev_idle_start (loop, idle_cb);	2508	ev_idle_start (loop, idle_watcher);
2208		2509
2209		2510
2210	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2511	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2211		2512
2212	Prepare and check watchers are usually (but not always) used in pairs:	2513	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2305	struct pollfd fds [nfd];	2606	struct pollfd fds [nfd];
2306	// actual code will need to loop here and realloc etc.	2607	// actual code will need to loop here and realloc etc.
2307	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2608	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2308		2609
2309	/* the callback is illegal, but won't be called as we stop during check */	2610	/* the callback is illegal, but won't be called as we stop during check */
2310	ev_timer_init (&tw, 0, timeout * 1e-3);	2611	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2311	ev_timer_start (loop, &tw);	2612	ev_timer_start (loop, &tw);
2312		2613
2313	// create one ev_io per pollfd	2614	// create one ev_io per pollfd
2314	for (int i = 0; i < nfd; ++i)	2615	for (int i = 0; i < nfd; ++i)
2315	{	2616	{
…		…
2545	event loop blocks next and before C<ev_check> watchers are being called,	2846	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	2847	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	2848	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2548	handlers will be invoked, too, of course.	2849	handlers will be invoked, too, of course.
2549		2850
		2851	=head3 The special problem of life after fork - how is it possible?
		2852
		2853	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2854	up/change the process environment, followed by a call to C<exec()>. This
		2855	sequence should be handled by libev without any problems.
		2856
		2857	This changes when the application actually wants to do event handling
		2858	in the child, or both parent in child, in effect "continuing" after the
		2859	fork.
		2860
		2861	The default mode of operation (for libev, with application help to detect
		2862	forks) is to duplicate all the state in the child, as would be expected
		2863	when I<either> the parent I<or> the child process continues.
		2864
		2865	When both processes want to continue using libev, then this is usually the
		2866	wrong result. In that case, usually one process (typically the parent) is
		2867	supposed to continue with all watchers in place as before, while the other
		2868	process typically wants to start fresh, i.e. without any active watchers.
		2869
		2870	The cleanest and most efficient way to achieve that with libev is to
		2871	simply create a new event loop, which of course will be "empty", and
		2872	use that for new watchers. This has the advantage of not touching more
		2873	memory than necessary, and thus avoiding the copy-on-write, and the
		2874	disadvantage of having to use multiple event loops (which do not support
		2875	signal watchers).
		2876
		2877	When this is not possible, or you want to use the default loop for
		2878	other reasons, then in the process that wants to start "fresh", call
		2879	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2880	the default loop will "orphan" (not stop) all registered watchers, so you
		2881	have to be careful not to execute code that modifies those watchers. Note
		2882	also that in that case, you have to re-register any signal watchers.
		2883
2550	=head3 Watcher-Specific Functions and Data Members	2884	=head3 Watcher-Specific Functions and Data Members
2551		2885
2552	=over 4	2886	=over 4
2553		2887
2554	=item ev_fork_init (ev_signal *, callback)	2888	=item ev_fork_init (ev_signal *, callback)
…		…
2682	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3016	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	3017	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	3018	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2685	section below on what exactly this means).	3019	section below on what exactly this means).
2686		3020
		3021	Note that, as with other watchers in libev, multiple events might get
		3022	compressed into a single callback invocation (another way to look at this
		3023	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3024	reset when the event loop detects that).
		3025
2687	This call incurs the overhead of a system call only once per loop iteration,	3026	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	3027	iteration, so while the overhead might be noticeable, it doesn't apply to
2689	calls to C<ev_async_send>.	3028	repeated calls to C<ev_async_send> for the same event loop.
2690		3029
2691	=item bool = ev_async_pending (ev_async *)	3030	=item bool = ev_async_pending (ev_async *)
2692		3031
2693	Returns a non-zero value when C<ev_async_send> has been called on the	3032	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	3033	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	3036	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,	3037	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	3038	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.	3039	quickly check whether invoking the loop might be a good idea.
2701		3040
2702	Not that this does I<not> check whether the watcher itself is pending, only	3041	Not that this does I<not> check whether the watcher itself is pending,
2703	whether it has been requested to make this watcher pending.	3042	only whether it has been requested to make this watcher pending: there
		3043	is a time window between the event loop checking and resetting the async
		3044	notification, and the callback being invoked.
2704		3045
2705	=back	3046	=back
2706		3047
2707		3048
2708	=head1 OTHER FUNCTIONS	3049	=head1 OTHER FUNCTIONS
…		…
3012	L<http://software.schmorp.de/pkg/EV>.	3353	L<http://software.schmorp.de/pkg/EV>.
3013		3354
3014	=item Python	3355	=item Python
3015		3356
3016	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3357	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	3358	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		3359
3023	=item Ruby	3360	=item Ruby
3024		3361
3025	Tony Arcieri has written a ruby extension that offers access to a subset	3362	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	3363	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	3364	more on top of it. It can be found via gem servers. Its homepage is at
3028	L<http://rev.rubyforge.org/>.	3365	L<http://rev.rubyforge.org/>.
3029		3366
3030	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>	3367	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
3031	makes rev work even on mingw.	3368	makes rev work even on mingw.
		3369
		3370	=item Haskell
		3371
		3372	A haskell binding to libev is available at
		3373	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3032		3374
3033	=item D	3375	=item D
3034		3376
3035	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3377	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>.	3378	be found at L<http://proj.llucax.com.ar/wiki/evd>.
…		…
3436	defined to be C<0>, then they are not.	3778	defined to be C<0>, then they are not.
3437		3779
3438	=item EV_MINIMAL	3780	=item EV_MINIMAL
3439		3781
3440	If you need to shave off some kilobytes of code at the expense of some	3782	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	3783	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	3784	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.	3785	on amd64. It also selects a much smaller 2-heap for timer management over
		3786	the default 4-heap.
		3787
		3788	You can save even more by disabling watcher types you do not need
		3789	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3790	(C<-DNDEBUG>) will usually reduce code size a lot.
		3791
		3792	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3793	provide a bare-bones event library. See C<ev.h> for details on what parts
		3794	of the API are still available, and do not complain if this subset changes
		3795	over time.
3444		3796
3445	=item EV_PID_HASHSIZE	3797	=item EV_PID_HASHSIZE
3446		3798
3447	C<ev_child> watchers use a small hash table to distribute workload by	3799	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	3800	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	3986	default loop and triggering an C<ev_async> watcher from the default loop
3635	watcher callback into the event loop interested in the signal.	3987	watcher callback into the event loop interested in the signal.
3636		3988
3637	=back	3989	=back
3638		3990
		3991	=head4 THREAD LOCKING EXAMPLE
		3992
		3993	Here is a fictitious example of how to run an event loop in a different
		3994	thread than where callbacks are being invoked and watchers are
		3995	created/added/removed.
		3996
		3997	For a real-world example, see the C<EV::Loop::Async> perl module,
		3998	which uses exactly this technique (which is suited for many high-level
		3999	languages).
		4000
		4001	The example uses a pthread mutex to protect the loop data, a condition
		4002	variable to wait for callback invocations, an async watcher to notify the
		4003	event loop thread and an unspecified mechanism to wake up the main thread.
		4004
		4005	First, you need to associate some data with the event loop:
		4006
		4007	typedef struct {
		4008	mutex_t lock; /* global loop lock */
		4009	ev_async async_w;
		4010	thread_t tid;
		4011	cond_t invoke_cv;
		4012	} userdata;
		4013
		4014	void prepare_loop (EV_P)
		4015	{
		4016	// for simplicity, we use a static userdata struct.
		4017	static userdata u;
		4018
		4019	ev_async_init (&u->async_w, async_cb);
		4020	ev_async_start (EV_A_ &u->async_w);
		4021
		4022	pthread_mutex_init (&u->lock, 0);
		4023	pthread_cond_init (&u->invoke_cv, 0);
		4024
		4025	// now associate this with the loop
		4026	ev_set_userdata (EV_A_ u);
		4027	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4028	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4029
		4030	// then create the thread running ev_loop
		4031	pthread_create (&u->tid, 0, l_run, EV_A);
		4032	}
		4033
		4034	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4035	solely to wake up the event loop so it takes notice of any new watchers
		4036	that might have been added:
		4037
		4038	static void
		4039	async_cb (EV_P_ ev_async *w, int revents)
		4040	{
		4041	// just used for the side effects
		4042	}
		4043
		4044	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4045	protecting the loop data, respectively.
		4046
		4047	static void
		4048	l_release (EV_P)
		4049	{
		4050	userdata *u = ev_userdata (EV_A);
		4051	pthread_mutex_unlock (&u->lock);
		4052	}
		4053
		4054	static void
		4055	l_acquire (EV_P)
		4056	{
		4057	userdata *u = ev_userdata (EV_A);
		4058	pthread_mutex_lock (&u->lock);
		4059	}
		4060
		4061	The event loop thread first acquires the mutex, and then jumps straight
		4062	into C<ev_loop>:
		4063
		4064	void *
		4065	l_run (void *thr_arg)
		4066	{
		4067	struct ev_loop loop = (struct ev_loop )thr_arg;
		4068
		4069	l_acquire (EV_A);
		4070	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4071	ev_loop (EV_A_ 0);
		4072	l_release (EV_A);
		4073
		4074	return 0;
		4075	}
		4076
		4077	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4078	signal the main thread via some unspecified mechanism (signals? pipe
		4079	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4080	have been called (in a while loop because a) spurious wakeups are possible
		4081	and b) skipping inter-thread-communication when there are no pending
		4082	watchers is very beneficial):
		4083
		4084	static void
		4085	l_invoke (EV_P)
		4086	{
		4087	userdata *u = ev_userdata (EV_A);
		4088
		4089	while (ev_pending_count (EV_A))
		4090	{
		4091	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4092	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4093	}
		4094	}
		4095
		4096	Now, whenever the main thread gets told to invoke pending watchers, it
		4097	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4098	thread to continue:
		4099
		4100	static void
		4101	real_invoke_pending (EV_P)
		4102	{
		4103	userdata *u = ev_userdata (EV_A);
		4104
		4105	pthread_mutex_lock (&u->lock);
		4106	ev_invoke_pending (EV_A);
		4107	pthread_cond_signal (&u->invoke_cv);
		4108	pthread_mutex_unlock (&u->lock);
		4109	}
		4110
		4111	Whenever you want to start/stop a watcher or do other modifications to an
		4112	event loop, you will now have to lock:
		4113
		4114	ev_timer timeout_watcher;
		4115	userdata *u = ev_userdata (EV_A);
		4116
		4117	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4118
		4119	pthread_mutex_lock (&u->lock);
		4120	ev_timer_start (EV_A_ &timeout_watcher);
		4121	ev_async_send (EV_A_ &u->async_w);
		4122	pthread_mutex_unlock (&u->lock);
		4123
		4124	Note that sending the C<ev_async> watcher is required because otherwise
		4125	an event loop currently blocking in the kernel will have no knowledge
		4126	about the newly added timer. By waking up the loop it will pick up any new
		4127	watchers in the next event loop iteration.
		4128
3639	=head3 COROUTINES	4129	=head3 COROUTINES
3640		4130
3641	Libev is very accommodating to coroutines ("cooperative threads"):	4131	Libev is very accommodating to coroutines ("cooperative threads"):
3642	libev fully supports nesting calls to its functions from different	4132	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	4133	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3644	different coroutines, and switch freely between both coroutines running the	4134	different coroutines, and switch freely between both coroutines running
3645	loop, as long as you don't confuse yourself). The only exception is that	4135	the loop, as long as you don't confuse yourself). The only exception is
3646	you must not do this from C<ev_periodic> reschedule callbacks.	4136	that you must not do this from C<ev_periodic> reschedule callbacks.
3647		4137
3648	Care has been taken to ensure that libev does not keep local state inside	4138	Care has been taken to ensure that libev does not keep local state inside
3649	C<ev_loop>, and other calls do not usually allow for coroutine switches as	4139	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3650	they do not call any callbacks.	4140	they do not call any callbacks.
3651		4141
…		…
3728	way (note also that glib is the slowest event library known to man).	4218	way (note also that glib is the slowest event library known to man).
3729		4219
3730	There is no supported compilation method available on windows except	4220	There is no supported compilation method available on windows except
3731	embedding it into other applications.	4221	embedding it into other applications.
3732		4222
		4223	Sensible signal handling is officially unsupported by Microsoft - libev
		4224	tries its best, but under most conditions, signals will simply not work.
		4225
3733	Not a libev limitation but worth mentioning: windows apparently doesn't	4226	Not a libev limitation but worth mentioning: windows apparently doesn't
3734	accept large writes: instead of resulting in a partial write, windows will	4227	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,	4228	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	4229	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	4230	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3741	the abysmal performance of winsockets, using a large number of sockets	4234	the abysmal performance of winsockets, using a large number of sockets
3742	is not recommended (and not reasonable). If your program needs to use	4235	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	4236	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	4237	different implementation for windows, as libev offers the POSIX readiness
3745	notification model, which cannot be implemented efficiently on windows	4238	notification model, which cannot be implemented efficiently on windows
3746	(Microsoft monopoly games).	4239	(due to Microsoft monopoly games).
3747		4240
3748	A typical way to use libev under windows is to embed it (see the embedding	4241	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	4242	section for details) and use the following F<evwrap.h> header file instead
3750	of F<ev.h>:	4243	of F<ev.h>:
3751		4244
…		…
3787		4280
3788	Early versions of winsocket's select only supported waiting for a maximum	4281	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	4282	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	4283	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	4284	recommends spawning a chain of threads and wait for 63 handles and the
3792	previous thread in each. Great).	4285	previous thread in each. Sounds great!).
3793		4286
3794	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4287	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	4288	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	4289	call (which might be in libev or elsewhere, for example, perl and many
3797	select emulation on windows).	4290	other interpreters do their own select emulation on windows).
3798		4291
3799	Another limit is the number of file descriptors in the Microsoft runtime	4292	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	4293	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	4294	fetish or something like this inside Microsoft). You can increase this
3802	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4295	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	4296	(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	4297	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	4298	(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	4299	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.	4300	the cost of calling select (O(n²)) will likely make this unworkable.
3810		4301
3811	=back	4302	=back
3812		4303
3813	=head2 PORTABILITY REQUIREMENTS	4304	=head2 PORTABILITY REQUIREMENTS
3814		4305
…		…
3857	=item C<double> must hold a time value in seconds with enough accuracy	4348	=item C<double> must hold a time value in seconds with enough accuracy
3858		4349
3859	The type C<double> is used to represent timestamps. It is required to	4350	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	4351	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	4352	enough for at least into the year 4000. This requirement is fulfilled by
3862	implementations implementing IEEE 754 (basically all existing ones).	4353	implementations implementing IEEE 754, which is basically all existing
		4354	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4355	2200.
3863		4356
3864	=back	4357	=back
3865		4358
3866	If you know of other additional requirements drop me a note.	4359	If you know of other additional requirements drop me a note.
3867		4360
…		…
3935	involves iterating over all running async watchers or all signal numbers.	4428	involves iterating over all running async watchers or all signal numbers.
3936		4429
3937	=back	4430	=back
3938		4431
3939		4432
		4433	=head1 GLOSSARY
		4434
		4435	=over 4
		4436
		4437	=item active
		4438
		4439	A watcher is active as long as it has been started (has been attached to
		4440	an event loop) but not yet stopped (disassociated from the event loop).
		4441
		4442	=item application
		4443
		4444	In this document, an application is whatever is using libev.
		4445
		4446	=item callback
		4447
		4448	The address of a function that is called when some event has been
		4449	detected. Callbacks are being passed the event loop, the watcher that
		4450	received the event, and the actual event bitset.
		4451
		4452	=item callback invocation
		4453
		4454	The act of calling the callback associated with a watcher.
		4455
		4456	=item event
		4457
		4458	A change of state of some external event, such as data now being available
		4459	for reading on a file descriptor, time having passed or simply not having
		4460	any other events happening anymore.
		4461
		4462	In libev, events are represented as single bits (such as C<EV_READ> or
		4463	C<EV_TIMEOUT>).
		4464
		4465	=item event library
		4466
		4467	A software package implementing an event model and loop.
		4468
		4469	=item event loop
		4470
		4471	An entity that handles and processes external events and converts them
		4472	into callback invocations.
		4473
		4474	=item event model
		4475
		4476	The model used to describe how an event loop handles and processes
		4477	watchers and events.
		4478
		4479	=item pending
		4480
		4481	A watcher is pending as soon as the corresponding event has been detected,
		4482	and stops being pending as soon as the watcher will be invoked or its
		4483	pending status is explicitly cleared by the application.
		4484
		4485	A watcher can be pending, but not active. Stopping a watcher also clears
		4486	its pending status.
		4487
		4488	=item real time
		4489
		4490	The physical time that is observed. It is apparently strictly monotonic :)
		4491
		4492	=item wall-clock time
		4493
		4494	The time and date as shown on clocks. Unlike real time, it can actually
		4495	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4496	clock.
		4497
		4498	=item watcher
		4499
		4500	A data structure that describes interest in certain events. Watchers need
		4501	to be started (attached to an event loop) before they can receive events.
		4502
		4503	=item watcher invocation
		4504
		4505	The act of calling the callback associated with a watcher.
		4506
		4507	=back
		4508
3940	=head1 AUTHOR	4509	=head1 AUTHOR
3941		4510
3942	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	4511	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3943		4512

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Comparing libev/ev.pod (file contents): Revision 1.224 by root, Fri Feb 6 20:17:43 2009 UTC vs. Revision 1.258 by root, Wed Jul 15 16:58:53 2009 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.224 by root, Fri Feb 6 20:17:43 2009 UTC vs.
Revision 1.258 by root, Wed Jul 15 16:58:53 2009 UTC