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Revision 1.230 by root, Wed Apr 15 18:47:07 2009 UTC vs.
Revision 1.265 by root, Wed Aug 26 17:11:42 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
…		…
86	=head2 FEATURES	98	=head2 FEATURES
87		99
88	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
89	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
90	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
91	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
92	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
93	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
94	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
95	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
96	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
97	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
98		111
99	It also is quite fast (see this	112	It also is quite fast (see this
100	L<benchmark\|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark\|http://libev.schmorp.de/bench.html> comparing it to libevent
101	for example).	114	for example).
102		115
…		…
110	name C<loop> (which is always of type C<ev_loop *>) will not have	123	name C<loop> (which is always of type C<ev_loop *>) will not have
111	this argument.	124	this argument.
112		125
113	=head2 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
114		127
115	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
116	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
117	the beginning of 1970, details are complicated, don't ask). This type is	130	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	131	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	132	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	133	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	134	component C<stamp> might indicate, it is also used for time differences
122	throughout libev.	135	throughout libev.
123		136
124	=head1 ERROR HANDLING	137	=head1 ERROR HANDLING
125		138
…		…
349	forget about forgetting to tell libev about forking) when you use this	362	forget about forgetting to tell libev about forking) when you use this
350	flag.	363	flag.
351		364
352	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
353	environment variable.	366	environment variable.
		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_NOSIGNALFD>
		376
		377	When this flag is specified, then libev will not attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		379	probably only useful to work around any bugs in libev. Consequently, this
		380	flag might go away once the signalfd functionality is considered stable,
		381	so it's useful mostly in environment variables and not in program code.
354		382
355	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	383	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
356		384
357	This is your standard select(2) backend. Not I<completely> standard, as	385	This is your standard select(2) backend. Not I<completely> standard, as
358	libev tries to roll its own fd_set with no limits on the number of fds,	386	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
506		534
507	It is definitely not recommended to use this flag.	535	It is definitely not recommended to use this flag.
508		536
509	=back	537	=back
510		538
511	If one or more of these are or'ed into the flags value, then only these	539	If one or more of the backend flags are or'ed into the flags value,
512	backends will be tried (in the reverse order as listed here). If none are	540	then only these backends will be tried (in the reverse order as listed
513	specified, all backends in C<ev_recommended_backends ()> will be tried.	541	here). If none are specified, all backends in C<ev_recommended_backends
		542	()> will be tried.
514		543
515	Example: This is the most typical usage.	544	Example: This is the most typical usage.
516		545
517	if (!ev_default_loop (0))	546	if (!ev_default_loop (0))
518	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	547	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
…		…
609		638
610	This value can sometimes be useful as a generation counter of sorts (it	639	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	640	"ticks" the number of loop iterations), as it roughly corresponds with
612	C<ev_prepare> and C<ev_check> calls.	641	C<ev_prepare> and C<ev_check> calls.
613		642
		643	=item unsigned int ev_loop_depth (loop)
		644
		645	Returns the number of times C<ev_loop> was entered minus the number of
		646	times C<ev_loop> was exited, in other words, the recursion depth.
		647
		648	Outside C<ev_loop>, this number is zero. In a callback, this number is
		649	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		650	in which case it is higher.
		651
		652	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		653	etc.), doesn't count as exit.
		654
614	=item unsigned int ev_backend (loop)	655	=item unsigned int ev_backend (loop)
615		656
616	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	657	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
617	use.	658	use.
618		659
…		…
632		673
633	This function is rarely useful, but when some event callback runs for a	674	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	675	very long time without entering the event loop, updating libev's idea of
635	the current time is a good idea.	676	the current time is a good idea.
636		677
637	See also "The special problem of time updates" in the C<ev_timer> section.	678	See also L<The special problem of time updates> in the C<ev_timer> section.
		679
		680	=item ev_suspend (loop)
		681
		682	=item ev_resume (loop)
		683
		684	These two functions suspend and resume a loop, for use when the loop is
		685	not used for a while and timeouts should not be processed.
		686
		687	A typical use case would be an interactive program such as a game: When
		688	the user presses C<^Z> to suspend the game and resumes it an hour later it
		689	would be best to handle timeouts as if no time had actually passed while
		690	the program was suspended. This can be achieved by calling C<ev_suspend>
		691	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		692	C<ev_resume> directly afterwards to resume timer processing.
		693
		694	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		695	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		696	will be rescheduled (that is, they will lose any events that would have
		697	occured while suspended).
		698
		699	After calling C<ev_suspend> you B<must not> call I<any> function on the
		700	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		701	without a previous call to C<ev_suspend>.
		702
		703	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		704	event loop time (see C<ev_now_update>).
638		705
639	=item ev_loop (loop, int flags)	706	=item ev_loop (loop, int flags)
640		707
641	Finally, this is it, the event handler. This function usually is called	708	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	709	after you initialised all your watchers and you want to start handling
…		…
773		840
774	By setting a higher I<io collect interval> you allow libev to spend more	841	By setting a higher I<io collect interval> you allow libev to spend more
775	time collecting I/O events, so you can handle more events per iteration,	842	time collecting I/O events, so you can handle more events per iteration,
776	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	843	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
777	C<ev_timer>) will be not affected. Setting this to a non-null value will	844	C<ev_timer>) will be not affected. Setting this to a non-null value will
778	introduce an additional C<ev_sleep ()> call into most loop iterations.	845	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		846	sleep time ensures that libev will not poll for I/O events more often then
		847	once per this interval, on average.
779		848
780	Likewise, by setting a higher I<timeout collect interval> you allow libev	849	Likewise, by setting a higher I<timeout collect interval> you allow libev
781	to spend more time collecting timeouts, at the expense of increased	850	to spend more time collecting timeouts, at the expense of increased
782	latency/jitter/inexactness (the watcher callback will be called	851	latency/jitter/inexactness (the watcher callback will be called
783	later). C<ev_io> watchers will not be affected. Setting this to a non-null	852	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
785		854
786	Many (busy) programs can usually benefit by setting the I/O collect	855	Many (busy) programs can usually benefit by setting the I/O collect
787	interval to a value near C<0.1> or so, which is often enough for	856	interval to a value near C<0.1> or so, which is often enough for
788	interactive servers (of course not for games), likewise for timeouts. It	857	interactive servers (of course not for games), likewise for timeouts. It
789	usually doesn't make much sense to set it to a lower value than C<0.01>,	858	usually doesn't make much sense to set it to a lower value than C<0.01>,
790	as this approaches the timing granularity of most systems.	859	as this approaches the timing granularity of most systems. Note that if
		860	you do transactions with the outside world and you can't increase the
		861	parallelity, then this setting will limit your transaction rate (if you
		862	need to poll once per transaction and the I/O collect interval is 0.01,
		863	then you can't do more than 100 transations per second).
791		864
792	Setting the I<timeout collect interval> can improve the opportunity for	865	Setting the I<timeout collect interval> can improve the opportunity for
793	saving power, as the program will "bundle" timer callback invocations that	866	saving power, as the program will "bundle" timer callback invocations that
794	are "near" in time together, by delaying some, thus reducing the number of	867	are "near" in time together, by delaying some, thus reducing the number of
795	times the process sleeps and wakes up again. Another useful technique to	868	times the process sleeps and wakes up again. Another useful technique to
796	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	869	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
797	they fire on, say, one-second boundaries only.	870	they fire on, say, one-second boundaries only.
		871
		872	Example: we only need 0.1s timeout granularity, and we wish not to poll
		873	more often than 100 times per second:
		874
		875	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		876	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		877
		878	=item ev_invoke_pending (loop)
		879
		880	This call will simply invoke all pending watchers while resetting their
		881	pending state. Normally, C<ev_loop> does this automatically when required,
		882	but when overriding the invoke callback this call comes handy.
		883
		884	=item int ev_pending_count (loop)
		885
		886	Returns the number of pending watchers - zero indicates that no watchers
		887	are pending.
		888
		889	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		890
		891	This overrides the invoke pending functionality of the loop: Instead of
		892	invoking all pending watchers when there are any, C<ev_loop> will call
		893	this callback instead. This is useful, for example, when you want to
		894	invoke the actual watchers inside another context (another thread etc.).
		895
		896	If you want to reset the callback, use C<ev_invoke_pending> as new
		897	callback.
		898
		899	=item ev_set_loop_release_cb (loop, void (release)(EV_P), void (acquire)(EV_P))
		900
		901	Sometimes you want to share the same loop between multiple threads. This
		902	can be done relatively simply by putting mutex_lock/unlock calls around
		903	each call to a libev function.
		904
		905	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		906	wait for it to return. One way around this is to wake up the loop via
		907	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		908	and I<acquire> callbacks on the loop.
		909
		910	When set, then C<release> will be called just before the thread is
		911	suspended waiting for new events, and C<acquire> is called just
		912	afterwards.
		913
		914	Ideally, C<release> will just call your mutex_unlock function, and
		915	C<acquire> will just call the mutex_lock function again.
		916
		917	While event loop modifications are allowed between invocations of
		918	C<release> and C<acquire> (that's their only purpose after all), no
		919	modifications done will affect the event loop, i.e. adding watchers will
		920	have no effect on the set of file descriptors being watched, or the time
		921	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		922	to take note of any changes you made.
		923
		924	In theory, threads executing C<ev_loop> will be async-cancel safe between
		925	invocations of C<release> and C<acquire>.
		926
		927	See also the locking example in the C<THREADS> section later in this
		928	document.
		929
		930	=item ev_set_userdata (loop, void *data)
		931
		932	=item ev_userdata (loop)
		933
		934	Set and retrieve a single C<void *> associated with a loop. When
		935	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		936	C<0.>
		937
		938	These two functions can be used to associate arbitrary data with a loop,
		939	and are intended solely for the C<invoke_pending_cb>, C<release> and
		940	C<acquire> callbacks described above, but of course can be (ab-)used for
		941	any other purpose as well.
798		942
799	=item ev_loop_verify (loop)	943	=item ev_loop_verify (loop)
800		944
801	This function only does something when C<EV_VERIFY> support has been	945	This function only does something when C<EV_VERIFY> support has been
802	compiled in, which is the default for non-minimal builds. It tries to go	946	compiled in, which is the default for non-minimal builds. It tries to go
…		…
1057	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1201	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1058	(default: C<-2>). Pending watchers with higher priority will be invoked	1202	(default: C<-2>). Pending watchers with higher priority will be invoked
1059	before watchers with lower priority, but priority will not keep watchers	1203	before watchers with lower priority, but priority will not keep watchers
1060	from being executed (except for C<ev_idle> watchers).	1204	from being executed (except for C<ev_idle> watchers).
1061		1205
1062	This means that priorities are I<only> used for ordering callback
1063	invocation after new events have been received. This is useful, for
1064	example, to reduce latency after idling, or more often, to bind two
1065	watchers on the same event and make sure one is called first.
1066
1067	If you need to suppress invocation when higher priority events are pending	1206	If you need to suppress invocation when higher priority events are pending
1068	you need to look at C<ev_idle> watchers, which provide this functionality.	1207	you need to look at C<ev_idle> watchers, which provide this functionality.
1069		1208
1070	You I<must not> change the priority of a watcher as long as it is active or	1209	You I<must not> change the priority of a watcher as long as it is active or
1071	pending.	1210	pending.
1072
1073	The default priority used by watchers when no priority has been set is
1074	always C<0>, which is supposed to not be too high and not be too low :).
1075		1211
1076	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1212	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1077	fine, as long as you do not mind that the priority value you query might	1213	fine, as long as you do not mind that the priority value you query might
1078	or might not have been clamped to the valid range.	1214	or might not have been clamped to the valid range.
		1215
		1216	The default priority used by watchers when no priority has been set is
		1217	always C<0>, which is supposed to not be too high and not be too low :).
		1218
		1219	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1220	priorities.
1079		1221
1080	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1222	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1081		1223
1082	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1224	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1083	C<loop> nor C<revents> need to be valid as long as the watcher callback	1225	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1148	#include <stddef.h>	1290	#include <stddef.h>
1149		1291
1150	static void	1292	static void
1151	t1_cb (EV_P_ ev_timer *w, int revents)	1293	t1_cb (EV_P_ ev_timer *w, int revents)
1152	{	1294	{
1153	struct my_biggy big = (struct my_biggy *	1295	struct my_biggy big = (struct my_biggy *)
1154	(((char *)w) - offsetof (struct my_biggy, t1));	1296	(((char *)w) - offsetof (struct my_biggy, t1));
1155	}	1297	}
1156		1298
1157	static void	1299	static void
1158	t2_cb (EV_P_ ev_timer *w, int revents)	1300	t2_cb (EV_P_ ev_timer *w, int revents)
1159	{	1301	{
1160	struct my_biggy big = (struct my_biggy *	1302	struct my_biggy big = (struct my_biggy *)
1161	(((char *)w) - offsetof (struct my_biggy, t2));	1303	(((char *)w) - offsetof (struct my_biggy, t2));
1162	}	1304	}
		1305
		1306	=head2 WATCHER PRIORITY MODELS
		1307
		1308	Many event loops support I<watcher priorities>, which are usually small
		1309	integers that influence the ordering of event callback invocation
		1310	between watchers in some way, all else being equal.
		1311
		1312	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1313	description for the more technical details such as the actual priority
		1314	range.
		1315
		1316	There are two common ways how these these priorities are being interpreted
		1317	by event loops:
		1318
		1319	In the more common lock-out model, higher priorities "lock out" invocation
		1320	of lower priority watchers, which means as long as higher priority
		1321	watchers receive events, lower priority watchers are not being invoked.
		1322
		1323	The less common only-for-ordering model uses priorities solely to order
		1324	callback invocation within a single event loop iteration: Higher priority
		1325	watchers are invoked before lower priority ones, but they all get invoked
		1326	before polling for new events.
		1327
		1328	Libev uses the second (only-for-ordering) model for all its watchers
		1329	except for idle watchers (which use the lock-out model).
		1330
		1331	The rationale behind this is that implementing the lock-out model for
		1332	watchers is not well supported by most kernel interfaces, and most event
		1333	libraries will just poll for the same events again and again as long as
		1334	their callbacks have not been executed, which is very inefficient in the
		1335	common case of one high-priority watcher locking out a mass of lower
		1336	priority ones.
		1337
		1338	Static (ordering) priorities are most useful when you have two or more
		1339	watchers handling the same resource: a typical usage example is having an
		1340	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1341	timeouts. Under load, data might be received while the program handles
		1342	other jobs, but since timers normally get invoked first, the timeout
		1343	handler will be executed before checking for data. In that case, giving
		1344	the timer a lower priority than the I/O watcher ensures that I/O will be
		1345	handled first even under adverse conditions (which is usually, but not
		1346	always, what you want).
		1347
		1348	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1349	will only be executed when no same or higher priority watchers have
		1350	received events, they can be used to implement the "lock-out" model when
		1351	required.
		1352
		1353	For example, to emulate how many other event libraries handle priorities,
		1354	you can associate an C<ev_idle> watcher to each such watcher, and in
		1355	the normal watcher callback, you just start the idle watcher. The real
		1356	processing is done in the idle watcher callback. This causes libev to
		1357	continously poll and process kernel event data for the watcher, but when
		1358	the lock-out case is known to be rare (which in turn is rare :), this is
		1359	workable.
		1360
		1361	Usually, however, the lock-out model implemented that way will perform
		1362	miserably under the type of load it was designed to handle. In that case,
		1363	it might be preferable to stop the real watcher before starting the
		1364	idle watcher, so the kernel will not have to process the event in case
		1365	the actual processing will be delayed for considerable time.
		1366
		1367	Here is an example of an I/O watcher that should run at a strictly lower
		1368	priority than the default, and which should only process data when no
		1369	other events are pending:
		1370
		1371	ev_idle idle; // actual processing watcher
		1372	ev_io io; // actual event watcher
		1373
		1374	static void
		1375	io_cb (EV_P_ ev_io *w, int revents)
		1376	{
		1377	// stop the I/O watcher, we received the event, but
		1378	// are not yet ready to handle it.
		1379	ev_io_stop (EV_A_ w);
		1380
		1381	// start the idle watcher to ahndle the actual event.
		1382	// it will not be executed as long as other watchers
		1383	// with the default priority are receiving events.
		1384	ev_idle_start (EV_A_ &idle);
		1385	}
		1386
		1387	static void
		1388	idle_cb (EV_P_ ev_idle *w, int revents)
		1389	{
		1390	// actual processing
		1391	read (STDIN_FILENO, ...);
		1392
		1393	// have to start the I/O watcher again, as
		1394	// we have handled the event
		1395	ev_io_start (EV_P_ &io);
		1396	}
		1397
		1398	// initialisation
		1399	ev_idle_init (&idle, idle_cb);
		1400	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1401	ev_io_start (EV_DEFAULT_ &io);
		1402
		1403	In the "real" world, it might also be beneficial to start a timer, so that
		1404	low-priority connections can not be locked out forever under load. This
		1405	enables your program to keep a lower latency for important connections
		1406	during short periods of high load, while not completely locking out less
		1407	important ones.
1163		1408
1164		1409
1165	=head1 WATCHER TYPES	1410	=head1 WATCHER TYPES
1166		1411
1167	This section describes each watcher in detail, but will not repeat	1412	This section describes each watcher in detail, but will not repeat
…		…
1193	descriptors to non-blocking mode is also usually a good idea (but not	1438	descriptors to non-blocking mode is also usually a good idea (but not
1194	required if you know what you are doing).	1439	required if you know what you are doing).
1195		1440
1196	If you cannot use non-blocking mode, then force the use of a	1441	If you cannot use non-blocking mode, then force the use of a
1197	known-to-be-good backend (at the time of this writing, this includes only	1442	known-to-be-good backend (at the time of this writing, this includes only
1198	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1443	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1444	descriptors for which non-blocking operation makes no sense (such as
		1445	files) - libev doesn't guarentee any specific behaviour in that case.
1199		1446
1200	Another thing you have to watch out for is that it is quite easy to	1447	Another thing you have to watch out for is that it is quite easy to
1201	receive "spurious" readiness notifications, that is your callback might	1448	receive "spurious" readiness notifications, that is your callback might
1202	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1449	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1203	because there is no data. Not only are some backends known to create a	1450	because there is no data. Not only are some backends known to create a
…		…
1324	year, it will still time out after (roughly) one hour. "Roughly" because	1571	year, it will still time out after (roughly) one hour. "Roughly" because
1325	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1572	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1326	monotonic clock option helps a lot here).	1573	monotonic clock option helps a lot here).
1327		1574
1328	The callback is guaranteed to be invoked only I<after> its timeout has	1575	The callback is guaranteed to be invoked only I<after> its timeout has
1329	passed. If multiple timers become ready during the same loop iteration	1576	passed (not I<at>, so on systems with very low-resolution clocks this
1330	then the ones with earlier time-out values are invoked before ones with	1577	might introduce a small delay). If multiple timers become ready during the
1331	later time-out values (but this is no longer true when a callback calls	1578	same loop iteration then the ones with earlier time-out values are invoked
1332	C<ev_loop> recursively).	1579	before ones of the same priority with later time-out values (but this is
		1580	no longer true when a callback calls C<ev_loop> recursively).
1333		1581
1334	=head3 Be smart about timeouts	1582	=head3 Be smart about timeouts
1335		1583
1336	Many real-world problems involve some kind of timeout, usually for error	1584	Many real-world problems involve some kind of timeout, usually for error
1337	recovery. A typical example is an HTTP request - if the other side hangs,	1585	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1381	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>	1629	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
1382	member and C<ev_timer_again>.	1630	member and C<ev_timer_again>.
1383		1631
1384	At start:	1632	At start:
1385		1633
1386	ev_timer_init (timer, callback);	1634	ev_init (timer, callback);
1387	timer->repeat = 60.;	1635	timer->repeat = 60.;
1388	ev_timer_again (loop, timer);	1636	ev_timer_again (loop, timer);
1389		1637
1390	Each time there is some activity:	1638	Each time there is some activity:
1391		1639
…		…
1453		1701
1454	To start the timer, simply initialise the watcher and set C<last_activity>	1702	To start the timer, simply initialise the watcher and set C<last_activity>
1455	to the current time (meaning we just have some activity :), then call the	1703	to the current time (meaning we just have some activity :), then call the
1456	callback, which will "do the right thing" and start the timer:	1704	callback, which will "do the right thing" and start the timer:
1457		1705
1458	ev_timer_init (timer, callback);	1706	ev_init (timer, callback);
1459	last_activity = ev_now (loop);	1707	last_activity = ev_now (loop);
1460	callback (loop, timer, EV_TIMEOUT);	1708	callback (loop, timer, EV_TIMEOUT);
1461		1709
1462	And when there is some activity, simply store the current time in	1710	And when there is some activity, simply store the current time in
1463	C<last_activity>, no libev calls at all:	1711	C<last_activity>, no libev calls at all:
…		…
1524		1772
1525	If the event loop is suspended for a long time, you can also force an	1773	If the event loop is suspended for a long time, you can also force an
1526	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1774	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1527	()>.	1775	()>.
1528		1776
		1777	=head3 The special problems of suspended animation
		1778
		1779	When you leave the server world it is quite customary to hit machines that
		1780	can suspend/hibernate - what happens to the clocks during such a suspend?
		1781
		1782	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1783	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1784	to run until the system is suspended, but they will not advance while the
		1785	system is suspended. That means, on resume, it will be as if the program
		1786	was frozen for a few seconds, but the suspend time will not be counted
		1787	towards C<ev_timer> when a monotonic clock source is used. The real time
		1788	clock advanced as expected, but if it is used as sole clocksource, then a
		1789	long suspend would be detected as a time jump by libev, and timers would
		1790	be adjusted accordingly.
		1791
		1792	I would not be surprised to see different behaviour in different between
		1793	operating systems, OS versions or even different hardware.
		1794
		1795	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1796	time jump in the monotonic clocks and the realtime clock. If the program
		1797	is suspended for a very long time, and monotonic clock sources are in use,
		1798	then you can expect C<ev_timer>s to expire as the full suspension time
		1799	will be counted towards the timers. When no monotonic clock source is in
		1800	use, then libev will again assume a timejump and adjust accordingly.
		1801
		1802	It might be beneficial for this latter case to call C<ev_suspend>
		1803	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1804	deterministic behaviour in this case (you can do nothing against
		1805	C<SIGSTOP>).
		1806
1529	=head3 Watcher-Specific Functions and Data Members	1807	=head3 Watcher-Specific Functions and Data Members
1530		1808
1531	=over 4	1809	=over 4
1532		1810
1533	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1811	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1556	If the timer is started but non-repeating, stop it (as if it timed out).	1834	If the timer is started but non-repeating, stop it (as if it timed out).
1557		1835
1558	If the timer is repeating, either start it if necessary (with the	1836	If the timer is repeating, either start it if necessary (with the
1559	C<repeat> value), or reset the running timer to the C<repeat> value.	1837	C<repeat> value), or reset the running timer to the C<repeat> value.
1560		1838
1561	This sounds a bit complicated, see "Be smart about timeouts", above, for a	1839	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1562	usage example.	1840	usage example.
		1841
		1842	=item ev_timer_remaining (loop, ev_timer *)
		1843
		1844	Returns the remaining time until a timer fires. If the timer is active,
		1845	then this time is relative to the current event loop time, otherwise it's
		1846	the timeout value currently configured.
		1847
		1848	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1849	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1850	will return C<4>. When the timer expires and is restarted, it will return
		1851	roughly C<7> (likely slightly less as callback invocation takes some time,
		1852	too), and so on.
1563		1853
1564	=item ev_tstamp repeat [read-write]	1854	=item ev_tstamp repeat [read-write]
1565		1855
1566	The current C<repeat> value. Will be used each time the watcher times out	1856	The current C<repeat> value. Will be used each time the watcher times out
1567	or C<ev_timer_again> is called, and determines the next timeout (if any),	1857	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1803	Signal watchers will trigger an event when the process receives a specific	2093	Signal watchers will trigger an event when the process receives a specific
1804	signal one or more times. Even though signals are very asynchronous, libev	2094	signal one or more times. Even though signals are very asynchronous, libev
1805	will try it's best to deliver signals synchronously, i.e. as part of the	2095	will try it's best to deliver signals synchronously, i.e. as part of the
1806	normal event processing, like any other event.	2096	normal event processing, like any other event.
1807		2097
1808	If you want signals asynchronously, just use C<sigaction> as you would	2098	If you want signals to be delivered truly asynchronously, just use
1809	do without libev and forget about sharing the signal. You can even use	2099	C<sigaction> as you would do without libev and forget about sharing
1810	C<ev_async> from a signal handler to synchronously wake up an event loop.	2100	the signal. You can even use C<ev_async> from a signal handler to
		2101	synchronously wake up an event loop.
1811		2102
1812	You can configure as many watchers as you like per signal. Only when the	2103	You can configure as many watchers as you like for the same signal, but
		2104	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2105	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2106	C<SIGINT> in both the default loop and another loop at the same time. At
		2107	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2108
1813	first watcher gets started will libev actually register a signal handler	2109	When the first watcher gets started will libev actually register something
1814	with the kernel (thus it coexists with your own signal handlers as long as	2110	with the kernel (thus it coexists with your own signal handlers as long as
1815	you don't register any with libev for the same signal). Similarly, when	2111	you don't register any with libev for the same signal).
1816	the last signal watcher for a signal is stopped, libev will reset the
1817	signal handler to SIG_DFL (regardless of what it was set to before).
1818		2112
1819	If possible and supported, libev will install its handlers with	2113	If possible and supported, libev will install its handlers with
1820	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2114	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1821	interrupted. If you have a problem with system calls getting interrupted by	2115	not be unduly interrupted. If you have a problem with system calls getting
1822	signals you can block all signals in an C<ev_check> watcher and unblock	2116	interrupted by signals you can block all signals in an C<ev_check> watcher
1823	them in an C<ev_prepare> watcher.	2117	and unblock them in an C<ev_prepare> watcher.
		2118
		2119	=head3 The special problem of inheritance over execve
		2120
		2121	Both the signal mask (C<sigprocmask>) and the signal disposition
		2122	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2123	stopping it again), that is, libev might or might not block the signal,
		2124	and might or might not set or restore the installed signal handler.
		2125
		2126	While this does not matter for the signal disposition (libev never
		2127	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2128	C<execve>), this matters for the signal mask: many programs do not expect
		2129	many signals to be blocked.
		2130
		2131	This means that before calling C<exec> (from the child) you should reset
		2132	the signal mask to whatever "default" you expect (all clear is a good
		2133	choice usually).
1824		2134
1825	=head3 Watcher-Specific Functions and Data Members	2135	=head3 Watcher-Specific Functions and Data Members
1826		2136
1827	=over 4	2137	=over 4
1828		2138
…		…
1860	some child status changes (most typically when a child of yours dies or	2170	some child status changes (most typically when a child of yours dies or
1861	exits). It is permissible to install a child watcher I<after> the child	2171	exits). It is permissible to install a child watcher I<after> the child
1862	has been forked (which implies it might have already exited), as long	2172	has been forked (which implies it might have already exited), as long
1863	as the event loop isn't entered (or is continued from a watcher), i.e.,	2173	as the event loop isn't entered (or is continued from a watcher), i.e.,
1864	forking and then immediately registering a watcher for the child is fine,	2174	forking and then immediately registering a watcher for the child is fine,
1865	but forking and registering a watcher a few event loop iterations later is	2175	but forking and registering a watcher a few event loop iterations later or
1866	not.	2176	in the next callback invocation is not.
1867		2177
1868	Only the default event loop is capable of handling signals, and therefore	2178	Only the default event loop is capable of handling signals, and therefore
1869	you can only register child watchers in the default event loop.	2179	you can only register child watchers in the default event loop.
1870		2180
		2181	Due to some design glitches inside libev, child watchers will always be
		2182	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2183	libev)
		2184
1871	=head3 Process Interaction	2185	=head3 Process Interaction
1872		2186
1873	Libev grabs C<SIGCHLD> as soon as the default event loop is	2187	Libev grabs C<SIGCHLD> as soon as the default event loop is
1874	initialised. This is necessary to guarantee proper behaviour even if	2188	initialised. This is necessary to guarantee proper behaviour even if the
1875	the first child watcher is started after the child exits. The occurrence	2189	first child watcher is started after the child exits. The occurrence
1876	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2190	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1877	synchronously as part of the event loop processing. Libev always reaps all	2191	synchronously as part of the event loop processing. Libev always reaps all
1878	children, even ones not watched.	2192	children, even ones not watched.
1879		2193
1880	=head3 Overriding the Built-In Processing	2194	=head3 Overriding the Built-In Processing
…		…
1890	=head3 Stopping the Child Watcher	2204	=head3 Stopping the Child Watcher
1891		2205
1892	Currently, the child watcher never gets stopped, even when the	2206	Currently, the child watcher never gets stopped, even when the
1893	child terminates, so normally one needs to stop the watcher in the	2207	child terminates, so normally one needs to stop the watcher in the
1894	callback. Future versions of libev might stop the watcher automatically	2208	callback. Future versions of libev might stop the watcher automatically
1895	when a child exit is detected.	2209	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2210	problem).
1896		2211
1897	=head3 Watcher-Specific Functions and Data Members	2212	=head3 Watcher-Specific Functions and Data Members
1898		2213
1899	=over 4	2214	=over 4
1900		2215
…		…
2226	// no longer anything immediate to do.	2541	// no longer anything immediate to do.
2227	}	2542	}
2228		2543
2229	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2544	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2230	ev_idle_init (idle_watcher, idle_cb);	2545	ev_idle_init (idle_watcher, idle_cb);
2231	ev_idle_start (loop, idle_cb);	2546	ev_idle_start (loop, idle_watcher);
2232		2547
2233		2548
2234	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2549	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2235		2550
2236	Prepare and check watchers are usually (but not always) used in pairs:	2551	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2329	struct pollfd fds [nfd];	2644	struct pollfd fds [nfd];
2330	// actual code will need to loop here and realloc etc.	2645	// actual code will need to loop here and realloc etc.
2331	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2646	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2332		2647
2333	/* the callback is illegal, but won't be called as we stop during check */	2648	/* the callback is illegal, but won't be called as we stop during check */
2334	ev_timer_init (&tw, 0, timeout * 1e-3);	2649	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2335	ev_timer_start (loop, &tw);	2650	ev_timer_start (loop, &tw);
2336		2651
2337	// create one ev_io per pollfd	2652	// create one ev_io per pollfd
2338	for (int i = 0; i < nfd; ++i)	2653	for (int i = 0; i < nfd; ++i)
2339	{	2654	{
…		…
2569	event loop blocks next and before C<ev_check> watchers are being called,	2884	event loop blocks next and before C<ev_check> watchers are being called,
2570	and only in the child after the fork. If whoever good citizen calling	2885	and only in the child after the fork. If whoever good citizen calling
2571	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2886	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2572	handlers will be invoked, too, of course.	2887	handlers will be invoked, too, of course.
2573		2888
		2889	=head3 The special problem of life after fork - how is it possible?
		2890
		2891	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2892	up/change the process environment, followed by a call to C<exec()>. This
		2893	sequence should be handled by libev without any problems.
		2894
		2895	This changes when the application actually wants to do event handling
		2896	in the child, or both parent in child, in effect "continuing" after the
		2897	fork.
		2898
		2899	The default mode of operation (for libev, with application help to detect
		2900	forks) is to duplicate all the state in the child, as would be expected
		2901	when I<either> the parent I<or> the child process continues.
		2902
		2903	When both processes want to continue using libev, then this is usually the
		2904	wrong result. In that case, usually one process (typically the parent) is
		2905	supposed to continue with all watchers in place as before, while the other
		2906	process typically wants to start fresh, i.e. without any active watchers.
		2907
		2908	The cleanest and most efficient way to achieve that with libev is to
		2909	simply create a new event loop, which of course will be "empty", and
		2910	use that for new watchers. This has the advantage of not touching more
		2911	memory than necessary, and thus avoiding the copy-on-write, and the
		2912	disadvantage of having to use multiple event loops (which do not support
		2913	signal watchers).
		2914
		2915	When this is not possible, or you want to use the default loop for
		2916	other reasons, then in the process that wants to start "fresh", call
		2917	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2918	the default loop will "orphan" (not stop) all registered watchers, so you
		2919	have to be careful not to execute code that modifies those watchers. Note
		2920	also that in that case, you have to re-register any signal watchers.
		2921
2574	=head3 Watcher-Specific Functions and Data Members	2922	=head3 Watcher-Specific Functions and Data Members
2575		2923
2576	=over 4	2924	=over 4
2577		2925
2578	=item ev_fork_init (ev_signal *, callback)	2926	=item ev_fork_init (ev_signal *, callback)
…		…
3070	=item Ocaml	3418	=item Ocaml
3071		3419
3072	Erkki Seppala has written Ocaml bindings for libev, to be found at	3420	Erkki Seppala has written Ocaml bindings for libev, to be found at
3073	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	3421	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
3074		3422
		3423	=item Lua
		3424
		3425	Brian Maher has written a partial interface to libev
		3426	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3427	L<http://github.com/brimworks/lua-ev>.
		3428
3075	=back	3429	=back
3076		3430
3077		3431
3078	=head1 MACRO MAGIC	3432	=head1 MACRO MAGIC
3079		3433
…		…
3245	keeps libev from including F<config.h>, and it also defines dummy	3599	keeps libev from including F<config.h>, and it also defines dummy
3246	implementations for some libevent functions (such as logging, which is not	3600	implementations for some libevent functions (such as logging, which is not
3247	supported). It will also not define any of the structs usually found in	3601	supported). It will also not define any of the structs usually found in
3248	F<event.h> that are not directly supported by the libev core alone.	3602	F<event.h> that are not directly supported by the libev core alone.
3249		3603
3250	In stanbdalone mode, libev will still try to automatically deduce the	3604	In standalone mode, libev will still try to automatically deduce the
3251	configuration, but has to be more conservative.	3605	configuration, but has to be more conservative.
3252		3606
3253	=item EV_USE_MONOTONIC	3607	=item EV_USE_MONOTONIC
3254		3608
3255	If defined to be C<1>, libev will try to detect the availability of the	3609	If defined to be C<1>, libev will try to detect the availability of the
…		…
3320	be used is the winsock select). This means that it will call	3674	be used is the winsock select). This means that it will call
3321	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3675	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
3322	it is assumed that all these functions actually work on fds, even	3676	it is assumed that all these functions actually work on fds, even
3323	on win32. Should not be defined on non-win32 platforms.	3677	on win32. Should not be defined on non-win32 platforms.
3324		3678
3325	=item EV_FD_TO_WIN32_HANDLE	3679	=item EV_FD_TO_WIN32_HANDLE(fd)
3326		3680
3327	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3681	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
3328	file descriptors to socket handles. When not defining this symbol (the	3682	file descriptors to socket handles. When not defining this symbol (the
3329	default), then libev will call C<_get_osfhandle>, which is usually	3683	default), then libev will call C<_get_osfhandle>, which is usually
3330	correct. In some cases, programs use their own file descriptor management,	3684	correct. In some cases, programs use their own file descriptor management,
3331	in which case they can provide this function to map fds to socket handles.	3685	in which case they can provide this function to map fds to socket handles.
		3686
		3687	=item EV_WIN32_HANDLE_TO_FD(handle)
		3688
		3689	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3690	using the standard C<_open_osfhandle> function. For programs implementing
		3691	their own fd to handle mapping, overwriting this function makes it easier
		3692	to do so. This can be done by defining this macro to an appropriate value.
		3693
		3694	=item EV_WIN32_CLOSE_FD(fd)
		3695
		3696	If programs implement their own fd to handle mapping on win32, then this
		3697	macro can be used to override the C<close> function, useful to unregister
		3698	file descriptors again. Note that the replacement function has to close
		3699	the underlying OS handle.
3332		3700
3333	=item EV_USE_POLL	3701	=item EV_USE_POLL
3334		3702
3335	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3703	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3336	backend. Otherwise it will be enabled on non-win32 platforms. It	3704	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3468	defined to be C<0>, then they are not.	3836	defined to be C<0>, then they are not.
3469		3837
3470	=item EV_MINIMAL	3838	=item EV_MINIMAL
3471		3839
3472	If you need to shave off some kilobytes of code at the expense of some	3840	If you need to shave off some kilobytes of code at the expense of some
3473	speed, define this symbol to C<1>. Currently this is used to override some	3841	speed (but with the full API), define this symbol to C<1>. Currently this
3474	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3842	is used to override some inlining decisions, saves roughly 30% code size
3475	much smaller 2-heap for timer management over the default 4-heap.	3843	on amd64. It also selects a much smaller 2-heap for timer management over
		3844	the default 4-heap.
		3845
		3846	You can save even more by disabling watcher types you do not need
		3847	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3848	(C<-DNDEBUG>) will usually reduce code size a lot.
		3849
		3850	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3851	provide a bare-bones event library. See C<ev.h> for details on what parts
		3852	of the API are still available, and do not complain if this subset changes
		3853	over time.
		3854
		3855	=item EV_NSIG
		3856
		3857	The highest supported signal number, +1 (or, the number of
		3858	signals): Normally, libev tries to deduce the maximum number of signals
		3859	automatically, but sometimes this fails, in which case it can be
		3860	specified. Also, using a lower number than detected (C<32> should be
		3861	good for about any system in existance) can save some memory, as libev
		3862	statically allocates some 12-24 bytes per signal number.
3476		3863
3477	=item EV_PID_HASHSIZE	3864	=item EV_PID_HASHSIZE
3478		3865
3479	C<ev_child> watchers use a small hash table to distribute workload by	3866	C<ev_child> watchers use a small hash table to distribute workload by
3480	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3867	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3666	default loop and triggering an C<ev_async> watcher from the default loop	4053	default loop and triggering an C<ev_async> watcher from the default loop
3667	watcher callback into the event loop interested in the signal.	4054	watcher callback into the event loop interested in the signal.
3668		4055
3669	=back	4056	=back
3670		4057
		4058	=head4 THREAD LOCKING EXAMPLE
		4059
		4060	Here is a fictitious example of how to run an event loop in a different
		4061	thread than where callbacks are being invoked and watchers are
		4062	created/added/removed.
		4063
		4064	For a real-world example, see the C<EV::Loop::Async> perl module,
		4065	which uses exactly this technique (which is suited for many high-level
		4066	languages).
		4067
		4068	The example uses a pthread mutex to protect the loop data, a condition
		4069	variable to wait for callback invocations, an async watcher to notify the
		4070	event loop thread and an unspecified mechanism to wake up the main thread.
		4071
		4072	First, you need to associate some data with the event loop:
		4073
		4074	typedef struct {
		4075	mutex_t lock; /* global loop lock */
		4076	ev_async async_w;
		4077	thread_t tid;
		4078	cond_t invoke_cv;
		4079	} userdata;
		4080
		4081	void prepare_loop (EV_P)
		4082	{
		4083	// for simplicity, we use a static userdata struct.
		4084	static userdata u;
		4085
		4086	ev_async_init (&u->async_w, async_cb);
		4087	ev_async_start (EV_A_ &u->async_w);
		4088
		4089	pthread_mutex_init (&u->lock, 0);
		4090	pthread_cond_init (&u->invoke_cv, 0);
		4091
		4092	// now associate this with the loop
		4093	ev_set_userdata (EV_A_ u);
		4094	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4095	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4096
		4097	// then create the thread running ev_loop
		4098	pthread_create (&u->tid, 0, l_run, EV_A);
		4099	}
		4100
		4101	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4102	solely to wake up the event loop so it takes notice of any new watchers
		4103	that might have been added:
		4104
		4105	static void
		4106	async_cb (EV_P_ ev_async *w, int revents)
		4107	{
		4108	// just used for the side effects
		4109	}
		4110
		4111	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4112	protecting the loop data, respectively.
		4113
		4114	static void
		4115	l_release (EV_P)
		4116	{
		4117	userdata *u = ev_userdata (EV_A);
		4118	pthread_mutex_unlock (&u->lock);
		4119	}
		4120
		4121	static void
		4122	l_acquire (EV_P)
		4123	{
		4124	userdata *u = ev_userdata (EV_A);
		4125	pthread_mutex_lock (&u->lock);
		4126	}
		4127
		4128	The event loop thread first acquires the mutex, and then jumps straight
		4129	into C<ev_loop>:
		4130
		4131	void *
		4132	l_run (void *thr_arg)
		4133	{
		4134	struct ev_loop loop = (struct ev_loop )thr_arg;
		4135
		4136	l_acquire (EV_A);
		4137	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4138	ev_loop (EV_A_ 0);
		4139	l_release (EV_A);
		4140
		4141	return 0;
		4142	}
		4143
		4144	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4145	signal the main thread via some unspecified mechanism (signals? pipe
		4146	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4147	have been called (in a while loop because a) spurious wakeups are possible
		4148	and b) skipping inter-thread-communication when there are no pending
		4149	watchers is very beneficial):
		4150
		4151	static void
		4152	l_invoke (EV_P)
		4153	{
		4154	userdata *u = ev_userdata (EV_A);
		4155
		4156	while (ev_pending_count (EV_A))
		4157	{
		4158	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4159	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4160	}
		4161	}
		4162
		4163	Now, whenever the main thread gets told to invoke pending watchers, it
		4164	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4165	thread to continue:
		4166
		4167	static void
		4168	real_invoke_pending (EV_P)
		4169	{
		4170	userdata *u = ev_userdata (EV_A);
		4171
		4172	pthread_mutex_lock (&u->lock);
		4173	ev_invoke_pending (EV_A);
		4174	pthread_cond_signal (&u->invoke_cv);
		4175	pthread_mutex_unlock (&u->lock);
		4176	}
		4177
		4178	Whenever you want to start/stop a watcher or do other modifications to an
		4179	event loop, you will now have to lock:
		4180
		4181	ev_timer timeout_watcher;
		4182	userdata *u = ev_userdata (EV_A);
		4183
		4184	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4185
		4186	pthread_mutex_lock (&u->lock);
		4187	ev_timer_start (EV_A_ &timeout_watcher);
		4188	ev_async_send (EV_A_ &u->async_w);
		4189	pthread_mutex_unlock (&u->lock);
		4190
		4191	Note that sending the C<ev_async> watcher is required because otherwise
		4192	an event loop currently blocking in the kernel will have no knowledge
		4193	about the newly added timer. By waking up the loop it will pick up any new
		4194	watchers in the next event loop iteration.
		4195
3671	=head3 COROUTINES	4196	=head3 COROUTINES
3672		4197
3673	Libev is very accommodating to coroutines ("cooperative threads"):	4198	Libev is very accommodating to coroutines ("cooperative threads"):
3674	libev fully supports nesting calls to its functions from different	4199	libev fully supports nesting calls to its functions from different
3675	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4200	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3676	different coroutines, and switch freely between both coroutines running the	4201	different coroutines, and switch freely between both coroutines running
3677	loop, as long as you don't confuse yourself). The only exception is that	4202	the loop, as long as you don't confuse yourself). The only exception is
3678	you must not do this from C<ev_periodic> reschedule callbacks.	4203	that you must not do this from C<ev_periodic> reschedule callbacks.
3679		4204
3680	Care has been taken to ensure that libev does not keep local state inside	4205	Care has been taken to ensure that libev does not keep local state inside
3681	C<ev_loop>, and other calls do not usually allow for coroutine switches as	4206	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3682	they do not call any callbacks.	4207	they do not call any callbacks.
3683		4208
…		…
3760	way (note also that glib is the slowest event library known to man).	4285	way (note also that glib is the slowest event library known to man).
3761		4286
3762	There is no supported compilation method available on windows except	4287	There is no supported compilation method available on windows except
3763	embedding it into other applications.	4288	embedding it into other applications.
3764		4289
		4290	Sensible signal handling is officially unsupported by Microsoft - libev
		4291	tries its best, but under most conditions, signals will simply not work.
		4292
3765	Not a libev limitation but worth mentioning: windows apparently doesn't	4293	Not a libev limitation but worth mentioning: windows apparently doesn't
3766	accept large writes: instead of resulting in a partial write, windows will	4294	accept large writes: instead of resulting in a partial write, windows will
3767	either accept everything or return C<ENOBUFS> if the buffer is too large,	4295	either accept everything or return C<ENOBUFS> if the buffer is too large,
3768	so make sure you only write small amounts into your sockets (less than a	4296	so make sure you only write small amounts into your sockets (less than a
3769	megabyte seems safe, but this apparently depends on the amount of memory	4297	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3773	the abysmal performance of winsockets, using a large number of sockets	4301	the abysmal performance of winsockets, using a large number of sockets
3774	is not recommended (and not reasonable). If your program needs to use	4302	is not recommended (and not reasonable). If your program needs to use
3775	more than a hundred or so sockets, then likely it needs to use a totally	4303	more than a hundred or so sockets, then likely it needs to use a totally
3776	different implementation for windows, as libev offers the POSIX readiness	4304	different implementation for windows, as libev offers the POSIX readiness
3777	notification model, which cannot be implemented efficiently on windows	4305	notification model, which cannot be implemented efficiently on windows
3778	(Microsoft monopoly games).	4306	(due to Microsoft monopoly games).
3779		4307
3780	A typical way to use libev under windows is to embed it (see the embedding	4308	A typical way to use libev under windows is to embed it (see the embedding
3781	section for details) and use the following F<evwrap.h> header file instead	4309	section for details) and use the following F<evwrap.h> header file instead
3782	of F<ev.h>:	4310	of F<ev.h>:
3783		4311
…		…
3819		4347
3820	Early versions of winsocket's select only supported waiting for a maximum	4348	Early versions of winsocket's select only supported waiting for a maximum
3821	of C<64> handles (probably owning to the fact that all windows kernels	4349	of C<64> handles (probably owning to the fact that all windows kernels
3822	can only wait for C<64> things at the same time internally; Microsoft	4350	can only wait for C<64> things at the same time internally; Microsoft
3823	recommends spawning a chain of threads and wait for 63 handles and the	4351	recommends spawning a chain of threads and wait for 63 handles and the
3824	previous thread in each. Great).	4352	previous thread in each. Sounds great!).
3825		4353
3826	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4354	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3827	to some high number (e.g. C<2048>) before compiling the winsocket select	4355	to some high number (e.g. C<2048>) before compiling the winsocket select
3828	call (which might be in libev or elsewhere, for example, perl does its own	4356	call (which might be in libev or elsewhere, for example, perl and many
3829	select emulation on windows).	4357	other interpreters do their own select emulation on windows).
3830		4358
3831	Another limit is the number of file descriptors in the Microsoft runtime	4359	Another limit is the number of file descriptors in the Microsoft runtime
3832	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4360	libraries, which by default is C<64> (there must be a hidden I<64>
3833	or something like this inside Microsoft). You can increase this by calling	4361	fetish or something like this inside Microsoft). You can increase this
3834	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4362	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3835	arbitrary limit), but is broken in many versions of the Microsoft runtime	4363	(another arbitrary limit), but is broken in many versions of the Microsoft
3836	libraries.
3837
3838	This might get you to about C<512> or C<2048> sockets (depending on	4364	runtime libraries. This might get you to about C<512> or C<2048> sockets
3839	windows version and/or the phase of the moon). To get more, you need to	4365	(depending on windows version and/or the phase of the moon). To get more,
3840	wrap all I/O functions and provide your own fd management, but the cost of	4366	you need to wrap all I/O functions and provide your own fd management, but
3841	calling select (O(n²)) will likely make this unworkable.	4367	the cost of calling select (O(n²)) will likely make this unworkable.
3842		4368
3843	=back	4369	=back
3844		4370
3845	=head2 PORTABILITY REQUIREMENTS	4371	=head2 PORTABILITY REQUIREMENTS
3846		4372
…		…
3889	=item C<double> must hold a time value in seconds with enough accuracy	4415	=item C<double> must hold a time value in seconds with enough accuracy
3890		4416
3891	The type C<double> is used to represent timestamps. It is required to	4417	The type C<double> is used to represent timestamps. It is required to
3892	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4418	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3893	enough for at least into the year 4000. This requirement is fulfilled by	4419	enough for at least into the year 4000. This requirement is fulfilled by
3894	implementations implementing IEEE 754 (basically all existing ones).	4420	implementations implementing IEEE 754, which is basically all existing
		4421	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4422	2200.
3895		4423
3896	=back	4424	=back
3897		4425
3898	If you know of other additional requirements drop me a note.	4426	If you know of other additional requirements drop me a note.
3899		4427
…		…
3967	involves iterating over all running async watchers or all signal numbers.	4495	involves iterating over all running async watchers or all signal numbers.
3968		4496
3969	=back	4497	=back
3970		4498
3971		4499
		4500	=head1 GLOSSARY
		4501
		4502	=over 4
		4503
		4504	=item active
		4505
		4506	A watcher is active as long as it has been started (has been attached to
		4507	an event loop) but not yet stopped (disassociated from the event loop).
		4508
		4509	=item application
		4510
		4511	In this document, an application is whatever is using libev.
		4512
		4513	=item callback
		4514
		4515	The address of a function that is called when some event has been
		4516	detected. Callbacks are being passed the event loop, the watcher that
		4517	received the event, and the actual event bitset.
		4518
		4519	=item callback invocation
		4520
		4521	The act of calling the callback associated with a watcher.
		4522
		4523	=item event
		4524
		4525	A change of state of some external event, such as data now being available
		4526	for reading on a file descriptor, time having passed or simply not having
		4527	any other events happening anymore.
		4528
		4529	In libev, events are represented as single bits (such as C<EV_READ> or
		4530	C<EV_TIMEOUT>).
		4531
		4532	=item event library
		4533
		4534	A software package implementing an event model and loop.
		4535
		4536	=item event loop
		4537
		4538	An entity that handles and processes external events and converts them
		4539	into callback invocations.
		4540
		4541	=item event model
		4542
		4543	The model used to describe how an event loop handles and processes
		4544	watchers and events.
		4545
		4546	=item pending
		4547
		4548	A watcher is pending as soon as the corresponding event has been detected,
		4549	and stops being pending as soon as the watcher will be invoked or its
		4550	pending status is explicitly cleared by the application.
		4551
		4552	A watcher can be pending, but not active. Stopping a watcher also clears
		4553	its pending status.
		4554
		4555	=item real time
		4556
		4557	The physical time that is observed. It is apparently strictly monotonic :)
		4558
		4559	=item wall-clock time
		4560
		4561	The time and date as shown on clocks. Unlike real time, it can actually
		4562	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4563	clock.
		4564
		4565	=item watcher
		4566
		4567	A data structure that describes interest in certain events. Watchers need
		4568	to be started (attached to an event loop) before they can receive events.
		4569
		4570	=item watcher invocation
		4571
		4572	The act of calling the callback associated with a watcher.
		4573
		4574	=back
		4575
3972	=head1 AUTHOR	4576	=head1 AUTHOR
3973		4577
3974	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	4578	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3975		4579

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Comparing libev/ev.pod (file contents): Revision 1.230 by root, Wed Apr 15 18:47:07 2009 UTC vs. Revision 1.265 by root, Wed Aug 26 17:11:42 2009 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.230 by root, Wed Apr 15 18:47:07 2009 UTC vs.
Revision 1.265 by root, Wed Aug 26 17:11:42 2009 UTC