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Comparing libev/ev.pod (file contents):
Revision 1.232 by root, Thu Apr 16 06:17:26 2009 UTC vs.
Revision 1.257 by root, Wed Jul 15 16:08:24 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.
638		662
639	=item ev_suspend (loop)	663	=item ev_suspend (loop)
640		664
641	=item ev_resume (loop)	665	=item ev_resume (loop)
642		666
…		…
799		823
800	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
801	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,
802	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
803	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
804	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.
805		831
806	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
807	to spend more time collecting timeouts, at the expense of increased	833	to spend more time collecting timeouts, at the expense of increased
808	latency/jitter/inexactness (the watcher callback will be called	834	latency/jitter/inexactness (the watcher callback will be called
809	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
…		…
811		837
812	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
813	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
814	interactive servers (of course not for games), likewise for timeouts. It	840	interactive servers (of course not for games), likewise for timeouts. It
815	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>,
816	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).
817		847
818	Setting the I<timeout collect interval> can improve the opportunity for	848	Setting the I<timeout collect interval> can improve the opportunity for
819	saving power, as the program will "bundle" timer callback invocations that	849	saving power, as the program will "bundle" timer callback invocations that
820	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
821	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
822	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
823	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.
824		925
825	=item ev_loop_verify (loop)	926	=item ev_loop_verify (loop)
826		927
827	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
828	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
…		…
1083	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>
1084	(default: C<-2>). Pending watchers with higher priority will be invoked	1185	(default: C<-2>). Pending watchers with higher priority will be invoked
1085	before watchers with lower priority, but priority will not keep watchers	1186	before watchers with lower priority, but priority will not keep watchers
1086	from being executed (except for C<ev_idle> watchers).	1187	from being executed (except for C<ev_idle> watchers).
1087		1188
1088	See L<
1089
1090	This means that priorities are I<only> used for ordering callback
1091	invocation after new events have been received. This is useful, for
1092	example, to reduce latency after idling, or more often, to bind two
1093	watchers on the same event and make sure one is called first.
1094
1095	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
1096	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.
1097		1191
1098	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
1099	pending.	1193	pending.
1100
1101	The default priority used by watchers when no priority has been set is
1102	always C<0>, which is supposed to not be too high and not be too low :).
1103		1194
1104	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
1105	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
1106	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.
1107		1204
1108	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1205	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1109		1206
1110	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
1111	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
…		…
1176	#include <stddef.h>	1273	#include <stddef.h>
1177		1274
1178	static void	1275	static void
1179	t1_cb (EV_P_ ev_timer *w, int revents)	1276	t1_cb (EV_P_ ev_timer *w, int revents)
1180	{	1277	{
1181	struct my_biggy big = (struct my_biggy *	1278	struct my_biggy big = (struct my_biggy *)
1182	(((char *)w) - offsetof (struct my_biggy, t1));	1279	(((char *)w) - offsetof (struct my_biggy, t1));
1183	}	1280	}
1184		1281
1185	static void	1282	static void
1186	t2_cb (EV_P_ ev_timer *w, int revents)	1283	t2_cb (EV_P_ ev_timer *w, int revents)
1187	{	1284	{
1188	struct my_biggy big = (struct my_biggy *	1285	struct my_biggy big = (struct my_biggy *)
1189	(((char *)w) - offsetof (struct my_biggy, t2));	1286	(((char *)w) - offsetof (struct my_biggy, t2));
1190	}	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.
1191		1391
1192		1392
1193	=head1 WATCHER TYPES	1393	=head1 WATCHER TYPES
1194		1394
1195	This section describes each watcher in detail, but will not repeat	1395	This section describes each watcher in detail, but will not repeat
…		…
1221	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
1222	required if you know what you are doing).	1422	required if you know what you are doing).
1223		1423
1224	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
1225	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
1226	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.
1227		1429
1228	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
1229	receive "spurious" readiness notifications, that is your callback might	1431	receive "spurious" readiness notifications, that is your callback might
1230	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
1231	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
…		…
1352	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
1353	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1555	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1354	monotonic clock option helps a lot here).	1556	monotonic clock option helps a lot here).
1355		1557
1356	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
1357	passed. If multiple timers become ready during the same loop iteration	1559	passed (not I<at>, so on systems with very low-resolution clocks this
1358	then the ones with earlier time-out values are invoked before ones with	1560	might introduce a small delay). If multiple timers become ready during the
1359	later time-out values (but this is no longer true when a callback calls	1561	same loop iteration then the ones with earlier time-out values are invoked
1360	C<ev_loop> recursively).	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).
1361		1564
1362	=head3 Be smart about timeouts	1565	=head3 Be smart about timeouts
1363		1566
1364	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
1365	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,
…		…
1409	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>
1410	member and C<ev_timer_again>.	1613	member and C<ev_timer_again>.
1411		1614
1412	At start:	1615	At start:
1413		1616
1414	ev_timer_init (timer, callback);	1617	ev_init (timer, callback);
1415	timer->repeat = 60.;	1618	timer->repeat = 60.;
1416	ev_timer_again (loop, timer);	1619	ev_timer_again (loop, timer);
1417		1620
1418	Each time there is some activity:	1621	Each time there is some activity:
1419		1622
…		…
1481		1684
1482	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>
1483	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
1484	callback, which will "do the right thing" and start the timer:	1687	callback, which will "do the right thing" and start the timer:
1485		1688
1486	ev_timer_init (timer, callback);	1689	ev_init (timer, callback);
1487	last_activity = ev_now (loop);	1690	last_activity = ev_now (loop);
1488	callback (loop, timer, EV_TIMEOUT);	1691	callback (loop, timer, EV_TIMEOUT);
1489		1692
1490	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
1491	C<last_activity>, no libev calls at all:	1694	C<last_activity>, no libev calls at all:
…		…
1551	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1754	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1552		1755
1553	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
1554	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
1555	()>.	1758	()>.
		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>).
1556		1789
1557	=head3 Watcher-Specific Functions and Data Members	1790	=head3 Watcher-Specific Functions and Data Members
1558		1791
1559	=over 4	1792	=over 4
1560		1793
…		…
1888	some child status changes (most typically when a child of yours dies or	2121	some child status changes (most typically when a child of yours dies or
1889	exits). It is permissible to install a child watcher I<after> the child	2122	exits). It is permissible to install a child watcher I<after> the child
1890	has been forked (which implies it might have already exited), as long	2123	has been forked (which implies it might have already exited), as long
1891	as the event loop isn't entered (or is continued from a watcher), i.e.,	2124	as the event loop isn't entered (or is continued from a watcher), i.e.,
1892	forking and then immediately registering a watcher for the child is fine,	2125	forking and then immediately registering a watcher for the child is fine,
1893	but forking and registering a watcher a few event loop iterations later is	2126	but forking and registering a watcher a few event loop iterations later or
1894	not.	2127	in the next callback invocation is not.
1895		2128
1896	Only the default event loop is capable of handling signals, and therefore	2129	Only the default event loop is capable of handling signals, and therefore
1897	you can only register child watchers in the default event loop.	2130	you can only register child watchers in the default event loop.
		2131
		2132	Due to some design glitches inside libev, child watchers will always be
		2133	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2134	libev)
1898		2135
1899	=head3 Process Interaction	2136	=head3 Process Interaction
1900		2137
1901	Libev grabs C<SIGCHLD> as soon as the default event loop is	2138	Libev grabs C<SIGCHLD> as soon as the default event loop is
1902	initialised. This is necessary to guarantee proper behaviour even if	2139	initialised. This is necessary to guarantee proper behaviour even if
…		…
2254	// no longer anything immediate to do.	2491	// no longer anything immediate to do.
2255	}	2492	}
2256		2493
2257	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2494	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2258	ev_idle_init (idle_watcher, idle_cb);	2495	ev_idle_init (idle_watcher, idle_cb);
2259	ev_idle_start (loop, idle_cb);	2496	ev_idle_start (loop, idle_watcher);
2260		2497
2261		2498
2262	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2499	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2263		2500
2264	Prepare and check watchers are usually (but not always) used in pairs:	2501	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2357	struct pollfd fds [nfd];	2594	struct pollfd fds [nfd];
2358	// actual code will need to loop here and realloc etc.	2595	// actual code will need to loop here and realloc etc.
2359	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2596	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2360		2597
2361	/* the callback is illegal, but won't be called as we stop during check */	2598	/* the callback is illegal, but won't be called as we stop during check */
2362	ev_timer_init (&tw, 0, timeout * 1e-3);	2599	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2363	ev_timer_start (loop, &tw);	2600	ev_timer_start (loop, &tw);
2364		2601
2365	// create one ev_io per pollfd	2602	// create one ev_io per pollfd
2366	for (int i = 0; i < nfd; ++i)	2603	for (int i = 0; i < nfd; ++i)
2367	{	2604	{
…		…
2597	event loop blocks next and before C<ev_check> watchers are being called,	2834	event loop blocks next and before C<ev_check> watchers are being called,
2598	and only in the child after the fork. If whoever good citizen calling	2835	and only in the child after the fork. If whoever good citizen calling
2599	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2836	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2600	handlers will be invoked, too, of course.	2837	handlers will be invoked, too, of course.
2601		2838
		2839	=head3 The special problem of life after fork - how is it possible?
		2840
		2841	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2842	up/change the process environment, followed by a call to C<exec()>. This
		2843	sequence should be handled by libev without any problems.
		2844
		2845	This changes when the application actually wants to do event handling
		2846	in the child, or both parent in child, in effect "continuing" after the
		2847	fork.
		2848
		2849	The default mode of operation (for libev, with application help to detect
		2850	forks) is to duplicate all the state in the child, as would be expected
		2851	when I<either> the parent I<or> the child process continues.
		2852
		2853	When both processes want to continue using libev, then this is usually the
		2854	wrong result. In that case, usually one process (typically the parent) is
		2855	supposed to continue with all watchers in place as before, while the other
		2856	process typically wants to start fresh, i.e. without any active watchers.
		2857
		2858	The cleanest and most efficient way to achieve that with libev is to
		2859	simply create a new event loop, which of course will be "empty", and
		2860	use that for new watchers. This has the advantage of not touching more
		2861	memory than necessary, and thus avoiding the copy-on-write, and the
		2862	disadvantage of having to use multiple event loops (which do not support
		2863	signal watchers).
		2864
		2865	When this is not possible, or you want to use the default loop for
		2866	other reasons, then in the process that wants to start "fresh", call
		2867	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2868	the default loop will "orphan" (not stop) all registered watchers, so you
		2869	have to be careful not to execute code that modifies those watchers. Note
		2870	also that in that case, you have to re-register any signal watchers.
		2871
2602	=head3 Watcher-Specific Functions and Data Members	2872	=head3 Watcher-Specific Functions and Data Members
2603		2873
2604	=over 4	2874	=over 4
2605		2875
2606	=item ev_fork_init (ev_signal *, callback)	2876	=item ev_fork_init (ev_signal *, callback)
…		…
3496	defined to be C<0>, then they are not.	3766	defined to be C<0>, then they are not.
3497		3767
3498	=item EV_MINIMAL	3768	=item EV_MINIMAL
3499		3769
3500	If you need to shave off some kilobytes of code at the expense of some	3770	If you need to shave off some kilobytes of code at the expense of some
3501	speed, define this symbol to C<1>. Currently this is used to override some	3771	speed (but with the full API), define this symbol to C<1>. Currently this
3502	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3772	is used to override some inlining decisions, saves roughly 30% code size
3503	much smaller 2-heap for timer management over the default 4-heap.	3773	on amd64. It also selects a much smaller 2-heap for timer management over
		3774	the default 4-heap.
		3775
		3776	You can save even more by disabling watcher types you do not need
		3777	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3778	(C<-DNDEBUG>) will usually reduce code size a lot.
		3779
		3780	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3781	provide a bare-bones event library. See C<ev.h> for details on what parts
		3782	of the API are still available, and do not complain if this subset changes
		3783	over time.
3504		3784
3505	=item EV_PID_HASHSIZE	3785	=item EV_PID_HASHSIZE
3506		3786
3507	C<ev_child> watchers use a small hash table to distribute workload by	3787	C<ev_child> watchers use a small hash table to distribute workload by
3508	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3788	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3694	default loop and triggering an C<ev_async> watcher from the default loop	3974	default loop and triggering an C<ev_async> watcher from the default loop
3695	watcher callback into the event loop interested in the signal.	3975	watcher callback into the event loop interested in the signal.
3696		3976
3697	=back	3977	=back
3698		3978
		3979	=head4 THREAD LOCKING EXAMPLE
		3980
		3981	Here is a fictitious example of how to run an event loop in a different
		3982	thread than where callbacks are being invoked and watchers are
		3983	created/added/removed.
		3984
		3985	For a real-world example, see the C<EV::Loop::Async> perl module,
		3986	which uses exactly this technique (which is suited for many high-level
		3987	languages).
		3988
		3989	The example uses a pthread mutex to protect the loop data, a condition
		3990	variable to wait for callback invocations, an async watcher to notify the
		3991	event loop thread and an unspecified mechanism to wake up the main thread.
		3992
		3993	First, you need to associate some data with the event loop:
		3994
		3995	typedef struct {
		3996	mutex_t lock; /* global loop lock */
		3997	ev_async async_w;
		3998	thread_t tid;
		3999	cond_t invoke_cv;
		4000	} userdata;
		4001
		4002	void prepare_loop (EV_P)
		4003	{
		4004	// for simplicity, we use a static userdata struct.
		4005	static userdata u;
		4006
		4007	ev_async_init (&u->async_w, async_cb);
		4008	ev_async_start (EV_A_ &u->async_w);
		4009
		4010	pthread_mutex_init (&u->lock, 0);
		4011	pthread_cond_init (&u->invoke_cv, 0);
		4012
		4013	// now associate this with the loop
		4014	ev_set_userdata (EV_A_ u);
		4015	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4016	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4017
		4018	// then create the thread running ev_loop
		4019	pthread_create (&u->tid, 0, l_run, EV_A);
		4020	}
		4021
		4022	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4023	solely to wake up the event loop so it takes notice of any new watchers
		4024	that might have been added:
		4025
		4026	static void
		4027	async_cb (EV_P_ ev_async *w, int revents)
		4028	{
		4029	// just used for the side effects
		4030	}
		4031
		4032	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4033	protecting the loop data, respectively.
		4034
		4035	static void
		4036	l_release (EV_P)
		4037	{
		4038	userdata *u = ev_userdata (EV_A);
		4039	pthread_mutex_unlock (&u->lock);
		4040	}
		4041
		4042	static void
		4043	l_acquire (EV_P)
		4044	{
		4045	userdata *u = ev_userdata (EV_A);
		4046	pthread_mutex_lock (&u->lock);
		4047	}
		4048
		4049	The event loop thread first acquires the mutex, and then jumps straight
		4050	into C<ev_loop>:
		4051
		4052	void *
		4053	l_run (void *thr_arg)
		4054	{
		4055	struct ev_loop loop = (struct ev_loop )thr_arg;
		4056
		4057	l_acquire (EV_A);
		4058	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4059	ev_loop (EV_A_ 0);
		4060	l_release (EV_A);
		4061
		4062	return 0;
		4063	}
		4064
		4065	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4066	signal the main thread via some unspecified mechanism (signals? pipe
		4067	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4068	have been called (in a while loop because a) spurious wakeups are possible
		4069	and b) skipping inter-thread-communication when there are no pending
		4070	watchers is very beneficial):
		4071
		4072	static void
		4073	l_invoke (EV_P)
		4074	{
		4075	userdata *u = ev_userdata (EV_A);
		4076
		4077	while (ev_pending_count (EV_A))
		4078	{
		4079	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4080	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4081	}
		4082	}
		4083
		4084	Now, whenever the main thread gets told to invoke pending watchers, it
		4085	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4086	thread to continue:
		4087
		4088	static void
		4089	real_invoke_pending (EV_P)
		4090	{
		4091	userdata *u = ev_userdata (EV_A);
		4092
		4093	pthread_mutex_lock (&u->lock);
		4094	ev_invoke_pending (EV_A);
		4095	pthread_cond_signal (&u->invoke_cv);
		4096	pthread_mutex_unlock (&u->lock);
		4097	}
		4098
		4099	Whenever you want to start/stop a watcher or do other modifications to an
		4100	event loop, you will now have to lock:
		4101
		4102	ev_timer timeout_watcher;
		4103	userdata *u = ev_userdata (EV_A);
		4104
		4105	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4106
		4107	pthread_mutex_lock (&u->lock);
		4108	ev_timer_start (EV_A_ &timeout_watcher);
		4109	ev_async_send (EV_A_ &u->async_w);
		4110	pthread_mutex_unlock (&u->lock);
		4111
		4112	Note that sending the C<ev_async> watcher is required because otherwise
		4113	an event loop currently blocking in the kernel will have no knowledge
		4114	about the newly added timer. By waking up the loop it will pick up any new
		4115	watchers in the next event loop iteration.
		4116
3699	=head3 COROUTINES	4117	=head3 COROUTINES
3700		4118
3701	Libev is very accommodating to coroutines ("cooperative threads"):	4119	Libev is very accommodating to coroutines ("cooperative threads"):
3702	libev fully supports nesting calls to its functions from different	4120	libev fully supports nesting calls to its functions from different
3703	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4121	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3704	different coroutines, and switch freely between both coroutines running the	4122	different coroutines, and switch freely between both coroutines running
3705	loop, as long as you don't confuse yourself). The only exception is that	4123	the loop, as long as you don't confuse yourself). The only exception is
3706	you must not do this from C<ev_periodic> reschedule callbacks.	4124	that you must not do this from C<ev_periodic> reschedule callbacks.
3707		4125
3708	Care has been taken to ensure that libev does not keep local state inside	4126	Care has been taken to ensure that libev does not keep local state inside
3709	C<ev_loop>, and other calls do not usually allow for coroutine switches as	4127	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3710	they do not call any callbacks.	4128	they do not call any callbacks.
3711		4129
…		…
3788	way (note also that glib is the slowest event library known to man).	4206	way (note also that glib is the slowest event library known to man).
3789		4207
3790	There is no supported compilation method available on windows except	4208	There is no supported compilation method available on windows except
3791	embedding it into other applications.	4209	embedding it into other applications.
3792		4210
		4211	Sensible signal handling is officially unsupported by Microsoft - libev
		4212	tries its best, but under most conditions, signals will simply not work.
		4213
3793	Not a libev limitation but worth mentioning: windows apparently doesn't	4214	Not a libev limitation but worth mentioning: windows apparently doesn't
3794	accept large writes: instead of resulting in a partial write, windows will	4215	accept large writes: instead of resulting in a partial write, windows will
3795	either accept everything or return C<ENOBUFS> if the buffer is too large,	4216	either accept everything or return C<ENOBUFS> if the buffer is too large,
3796	so make sure you only write small amounts into your sockets (less than a	4217	so make sure you only write small amounts into your sockets (less than a
3797	megabyte seems safe, but this apparently depends on the amount of memory	4218	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3801	the abysmal performance of winsockets, using a large number of sockets	4222	the abysmal performance of winsockets, using a large number of sockets
3802	is not recommended (and not reasonable). If your program needs to use	4223	is not recommended (and not reasonable). If your program needs to use
3803	more than a hundred or so sockets, then likely it needs to use a totally	4224	more than a hundred or so sockets, then likely it needs to use a totally
3804	different implementation for windows, as libev offers the POSIX readiness	4225	different implementation for windows, as libev offers the POSIX readiness
3805	notification model, which cannot be implemented efficiently on windows	4226	notification model, which cannot be implemented efficiently on windows
3806	(Microsoft monopoly games).	4227	(due to Microsoft monopoly games).
3807		4228
3808	A typical way to use libev under windows is to embed it (see the embedding	4229	A typical way to use libev under windows is to embed it (see the embedding
3809	section for details) and use the following F<evwrap.h> header file instead	4230	section for details) and use the following F<evwrap.h> header file instead
3810	of F<ev.h>:	4231	of F<ev.h>:
3811		4232
…		…
3847		4268
3848	Early versions of winsocket's select only supported waiting for a maximum	4269	Early versions of winsocket's select only supported waiting for a maximum
3849	of C<64> handles (probably owning to the fact that all windows kernels	4270	of C<64> handles (probably owning to the fact that all windows kernels
3850	can only wait for C<64> things at the same time internally; Microsoft	4271	can only wait for C<64> things at the same time internally; Microsoft
3851	recommends spawning a chain of threads and wait for 63 handles and the	4272	recommends spawning a chain of threads and wait for 63 handles and the
3852	previous thread in each. Great).	4273	previous thread in each. Sounds great!).
3853		4274
3854	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4275	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3855	to some high number (e.g. C<2048>) before compiling the winsocket select	4276	to some high number (e.g. C<2048>) before compiling the winsocket select
3856	call (which might be in libev or elsewhere, for example, perl does its own	4277	call (which might be in libev or elsewhere, for example, perl and many
3857	select emulation on windows).	4278	other interpreters do their own select emulation on windows).
3858		4279
3859	Another limit is the number of file descriptors in the Microsoft runtime	4280	Another limit is the number of file descriptors in the Microsoft runtime
3860	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4281	libraries, which by default is C<64> (there must be a hidden I<64>
3861	or something like this inside Microsoft). You can increase this by calling	4282	fetish or something like this inside Microsoft). You can increase this
3862	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4283	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3863	arbitrary limit), but is broken in many versions of the Microsoft runtime	4284	(another arbitrary limit), but is broken in many versions of the Microsoft
3864	libraries.
3865
3866	This might get you to about C<512> or C<2048> sockets (depending on	4285	runtime libraries. This might get you to about C<512> or C<2048> sockets
3867	windows version and/or the phase of the moon). To get more, you need to	4286	(depending on windows version and/or the phase of the moon). To get more,
3868	wrap all I/O functions and provide your own fd management, but the cost of	4287	you need to wrap all I/O functions and provide your own fd management, but
3869	calling select (O(n²)) will likely make this unworkable.	4288	the cost of calling select (O(n²)) will likely make this unworkable.
3870		4289
3871	=back	4290	=back
3872		4291
3873	=head2 PORTABILITY REQUIREMENTS	4292	=head2 PORTABILITY REQUIREMENTS
3874		4293
…		…
3917	=item C<double> must hold a time value in seconds with enough accuracy	4336	=item C<double> must hold a time value in seconds with enough accuracy
3918		4337
3919	The type C<double> is used to represent timestamps. It is required to	4338	The type C<double> is used to represent timestamps. It is required to
3920	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4339	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3921	enough for at least into the year 4000. This requirement is fulfilled by	4340	enough for at least into the year 4000. This requirement is fulfilled by
3922	implementations implementing IEEE 754 (basically all existing ones).	4341	implementations implementing IEEE 754, which is basically all existing
		4342	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4343	2200.
3923		4344
3924	=back	4345	=back
3925		4346
3926	If you know of other additional requirements drop me a note.	4347	If you know of other additional requirements drop me a note.
3927		4348
…		…
3995	involves iterating over all running async watchers or all signal numbers.	4416	involves iterating over all running async watchers or all signal numbers.
3996		4417
3997	=back	4418	=back
3998		4419
3999		4420
		4421	=head1 GLOSSARY
		4422
		4423	=over 4
		4424
		4425	=item active
		4426
		4427	A watcher is active as long as it has been started (has been attached to
		4428	an event loop) but not yet stopped (disassociated from the event loop).
		4429
		4430	=item application
		4431
		4432	In this document, an application is whatever is using libev.
		4433
		4434	=item callback
		4435
		4436	The address of a function that is called when some event has been
		4437	detected. Callbacks are being passed the event loop, the watcher that
		4438	received the event, and the actual event bitset.
		4439
		4440	=item callback invocation
		4441
		4442	The act of calling the callback associated with a watcher.
		4443
		4444	=item event
		4445
		4446	A change of state of some external event, such as data now being available
		4447	for reading on a file descriptor, time having passed or simply not having
		4448	any other events happening anymore.
		4449
		4450	In libev, events are represented as single bits (such as C<EV_READ> or
		4451	C<EV_TIMEOUT>).
		4452
		4453	=item event library
		4454
		4455	A software package implementing an event model and loop.
		4456
		4457	=item event loop
		4458
		4459	An entity that handles and processes external events and converts them
		4460	into callback invocations.
		4461
		4462	=item event model
		4463
		4464	The model used to describe how an event loop handles and processes
		4465	watchers and events.
		4466
		4467	=item pending
		4468
		4469	A watcher is pending as soon as the corresponding event has been detected,
		4470	and stops being pending as soon as the watcher will be invoked or its
		4471	pending status is explicitly cleared by the application.
		4472
		4473	A watcher can be pending, but not active. Stopping a watcher also clears
		4474	its pending status.
		4475
		4476	=item real time
		4477
		4478	The physical time that is observed. It is apparently strictly monotonic :)
		4479
		4480	=item wall-clock time
		4481
		4482	The time and date as shown on clocks. Unlike real time, it can actually
		4483	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4484	clock.
		4485
		4486	=item watcher
		4487
		4488	A data structure that describes interest in certain events. Watchers need
		4489	to be started (attached to an event loop) before they can receive events.
		4490
		4491	=item watcher invocation
		4492
		4493	The act of calling the callback associated with a watcher.
		4494
		4495	=back
		4496
4000	=head1 AUTHOR	4497	=head1 AUTHOR
4001		4498
4002	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	4499	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
4003		4500

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Comparing libev/ev.pod (file contents): Revision 1.232 by root, Thu Apr 16 06:17:26 2009 UTC vs. Revision 1.257 by root, Wed Jul 15 16:08:24 2009 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.232 by root, Thu Apr 16 06:17:26 2009 UTC vs.
Revision 1.257 by root, Wed Jul 15 16:08:24 2009 UTC