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Comparing libev/ev.pod (file contents):
Revision 1.231 by root, Wed Apr 15 19:35:53 2009 UTC vs.
Revision 1.254 by root, Tue Jul 14 19:02:43 2009 UTC

…		…
62		62
63	// unloop was called, so exit	63	// unloop was called, so exit
64	return 0;	64	return 0;
65	}	65	}
66		66
67	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
68		70
69	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
70	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
71	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
72		84
73	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
74	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
75	these event sources and provide your program with events.	87	these event sources and provide your program with events.
76		88
…		…
110	name C<loop> (which is always of type C<ev_loop *>) will not have	122	name C<loop> (which is always of type C<ev_loop *>) will not have
111	this argument.	123	this argument.
112		124
113	=head2 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
114		126
115	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
116	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
117	the beginning of 1970, details are complicated, don't ask). This type is	129	near the beginning of 1970, details are complicated, don't ask). This
118	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	type is called C<ev_tstamp>, which is what you should use too. It usually
119	to the C<double> type in C, and when you need to do any calculations on	131	aliases to the C<double> type in C. When you need to do any calculations
120	it, you should treat it as some floating point value. Unlike the name	132	on it, you should treat it as some floating point value. Unlike the name
121	component C<stamp> might indicate, it is also used for time differences	133	component C<stamp> might indicate, it is also used for time differences
122	throughout libev.	134	throughout libev.
123		135
124	=head1 ERROR HANDLING	136	=head1 ERROR HANDLING
125		137
…		…
609		621
610	This value can sometimes be useful as a generation counter of sorts (it	622	This value can sometimes be useful as a generation counter of sorts (it
611	"ticks" the number of loop iterations), as it roughly corresponds with	623	"ticks" the number of loop iterations), as it roughly corresponds with
612	C<ev_prepare> and C<ev_check> calls.	624	C<ev_prepare> and C<ev_check> calls.
613		625
		626	=item unsigned int ev_loop_depth (loop)
		627
		628	Returns the number of times C<ev_loop> was entered minus the number of
		629	times C<ev_loop> was exited, in other words, the recursion depth.
		630
		631	Outside C<ev_loop>, this number is zero. In a callback, this number is
		632	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		633	in which case it is higher.
		634
		635	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		636	etc.), doesn't count as exit.
		637
614	=item unsigned int ev_backend (loop)	638	=item unsigned int ev_backend (loop)
615		639
616	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	640	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
617	use.	641	use.
618		642
…		…
632		656
633	This function is rarely useful, but when some event callback runs for a	657	This function is rarely useful, but when some event callback runs for a
634	very long time without entering the event loop, updating libev's idea of	658	very long time without entering the event loop, updating libev's idea of
635	the current time is a good idea.	659	the current time is a good idea.
636		660
637	See also "The special problem of time updates" in the C<ev_timer> section.	661	See also L<The special problem of time updates> in the C<ev_timer> section.
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 ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		868
		869	This overrides the invoke pending functionality of the loop: Instead of
		870	invoking all pending watchers when there are any, C<ev_loop> will call
		871	this callback instead. This is useful, for example, when you want to
		872	invoke the actual watchers inside another context (another thread etc.).
		873
		874	If you want to reset the callback, use C<ev_invoke_pending> as new
		875	callback.
		876
		877	=item ev_set_loop_release_cb (loop, void (release)(EV_P), void (acquire)(EV_P))
		878
		879	Sometimes you want to share the same loop between multiple threads. This
		880	can be done relatively simply by putting mutex_lock/unlock calls around
		881	each call to a libev function.
		882
		883	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		884	wait for it to return. One way around this is to wake up the loop via
		885	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		886	and I<acquire> callbacks on the loop.
		887
		888	When set, then C<release> will be called just before the thread is
		889	suspended waiting for new events, and C<acquire> is called just
		890	afterwards.
		891
		892	Ideally, C<release> will just call your mutex_unlock function, and
		893	C<acquire> will just call the mutex_lock function again.
		894
		895	While event loop modifications are allowed between invocations of
		896	C<release> and C<acquire> (that's their only purpose after all), no
		897	modifications done will affect the event loop, i.e. adding watchers will
		898	have no effect on the set of file descriptors being watched, or the time
		899	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		900	to take note of any changes you made.
		901
		902	In theory, threads executing C<ev_loop> will be async-cancel safe between
		903	invocations of C<release> and C<acquire>.
		904
		905	See also the locking example in the C<THREADS> section later in this
		906	document.
		907
		908	=item ev_set_userdata (loop, void *data)
		909
		910	=item ev_userdata (loop)
		911
		912	Set and retrieve a single C<void *> associated with a loop. When
		913	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		914	C<0.>
		915
		916	These two functions can be used to associate arbitrary data with a loop,
		917	and are intended solely for the C<invoke_pending_cb>, C<release> and
		918	C<acquire> callbacks described above, but of course can be (ab-)used for
		919	any other purpose as well.
824		920
825	=item ev_loop_verify (loop)	921	=item ev_loop_verify (loop)
826		922
827	This function only does something when C<EV_VERIFY> support has been	923	This function only does something when C<EV_VERIFY> support has been
828	compiled in, which is the default for non-minimal builds. It tries to go	924	compiled in, which is the default for non-minimal builds. It tries to go
…		…
1083	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1179	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1084	(default: C<-2>). Pending watchers with higher priority will be invoked	1180	(default: C<-2>). Pending watchers with higher priority will be invoked
1085	before watchers with lower priority, but priority will not keep watchers	1181	before watchers with lower priority, but priority will not keep watchers
1086	from being executed (except for C<ev_idle> watchers).	1182	from being executed (except for C<ev_idle> watchers).
1087		1183
1088	This means that priorities are I<only> used for ordering callback
1089	invocation after new events have been received. This is useful, for
1090	example, to reduce latency after idling, or more often, to bind two
1091	watchers on the same event and make sure one is called first.
1092
1093	If you need to suppress invocation when higher priority events are pending	1184	If you need to suppress invocation when higher priority events are pending
1094	you need to look at C<ev_idle> watchers, which provide this functionality.	1185	you need to look at C<ev_idle> watchers, which provide this functionality.
1095		1186
1096	You I<must not> change the priority of a watcher as long as it is active or	1187	You I<must not> change the priority of a watcher as long as it is active or
1097	pending.	1188	pending.
1098
1099	The default priority used by watchers when no priority has been set is
1100	always C<0>, which is supposed to not be too high and not be too low :).
1101		1189
1102	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1190	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1103	fine, as long as you do not mind that the priority value you query might	1191	fine, as long as you do not mind that the priority value you query might
1104	or might not have been clamped to the valid range.	1192	or might not have been clamped to the valid range.
		1193
		1194	The default priority used by watchers when no priority has been set is
		1195	always C<0>, which is supposed to not be too high and not be too low :).
		1196
		1197	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1198	priorities.
1105		1199
1106	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1200	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1107		1201
1108	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1202	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1109	C<loop> nor C<revents> need to be valid as long as the watcher callback	1203	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1174	#include <stddef.h>	1268	#include <stddef.h>
1175		1269
1176	static void	1270	static void
1177	t1_cb (EV_P_ ev_timer *w, int revents)	1271	t1_cb (EV_P_ ev_timer *w, int revents)
1178	{	1272	{
1179	struct my_biggy big = (struct my_biggy *	1273	struct my_biggy big = (struct my_biggy *)
1180	(((char *)w) - offsetof (struct my_biggy, t1));	1274	(((char *)w) - offsetof (struct my_biggy, t1));
1181	}	1275	}
1182		1276
1183	static void	1277	static void
1184	t2_cb (EV_P_ ev_timer *w, int revents)	1278	t2_cb (EV_P_ ev_timer *w, int revents)
1185	{	1279	{
1186	struct my_biggy big = (struct my_biggy *	1280	struct my_biggy big = (struct my_biggy *)
1187	(((char *)w) - offsetof (struct my_biggy, t2));	1281	(((char *)w) - offsetof (struct my_biggy, t2));
1188	}	1282	}
		1283
		1284	=head2 WATCHER PRIORITY MODELS
		1285
		1286	Many event loops support I<watcher priorities>, which are usually small
		1287	integers that influence the ordering of event callback invocation
		1288	between watchers in some way, all else being equal.
		1289
		1290	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1291	description for the more technical details such as the actual priority
		1292	range.
		1293
		1294	There are two common ways how these these priorities are being interpreted
		1295	by event loops:
		1296
		1297	In the more common lock-out model, higher priorities "lock out" invocation
		1298	of lower priority watchers, which means as long as higher priority
		1299	watchers receive events, lower priority watchers are not being invoked.
		1300
		1301	The less common only-for-ordering model uses priorities solely to order
		1302	callback invocation within a single event loop iteration: Higher priority
		1303	watchers are invoked before lower priority ones, but they all get invoked
		1304	before polling for new events.
		1305
		1306	Libev uses the second (only-for-ordering) model for all its watchers
		1307	except for idle watchers (which use the lock-out model).
		1308
		1309	The rationale behind this is that implementing the lock-out model for
		1310	watchers is not well supported by most kernel interfaces, and most event
		1311	libraries will just poll for the same events again and again as long as
		1312	their callbacks have not been executed, which is very inefficient in the
		1313	common case of one high-priority watcher locking out a mass of lower
		1314	priority ones.
		1315
		1316	Static (ordering) priorities are most useful when you have two or more
		1317	watchers handling the same resource: a typical usage example is having an
		1318	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1319	timeouts. Under load, data might be received while the program handles
		1320	other jobs, but since timers normally get invoked first, the timeout
		1321	handler will be executed before checking for data. In that case, giving
		1322	the timer a lower priority than the I/O watcher ensures that I/O will be
		1323	handled first even under adverse conditions (which is usually, but not
		1324	always, what you want).
		1325
		1326	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1327	will only be executed when no same or higher priority watchers have
		1328	received events, they can be used to implement the "lock-out" model when
		1329	required.
		1330
		1331	For example, to emulate how many other event libraries handle priorities,
		1332	you can associate an C<ev_idle> watcher to each such watcher, and in
		1333	the normal watcher callback, you just start the idle watcher. The real
		1334	processing is done in the idle watcher callback. This causes libev to
		1335	continously poll and process kernel event data for the watcher, but when
		1336	the lock-out case is known to be rare (which in turn is rare :), this is
		1337	workable.
		1338
		1339	Usually, however, the lock-out model implemented that way will perform
		1340	miserably under the type of load it was designed to handle. In that case,
		1341	it might be preferable to stop the real watcher before starting the
		1342	idle watcher, so the kernel will not have to process the event in case
		1343	the actual processing will be delayed for considerable time.
		1344
		1345	Here is an example of an I/O watcher that should run at a strictly lower
		1346	priority than the default, and which should only process data when no
		1347	other events are pending:
		1348
		1349	ev_idle idle; // actual processing watcher
		1350	ev_io io; // actual event watcher
		1351
		1352	static void
		1353	io_cb (EV_P_ ev_io *w, int revents)
		1354	{
		1355	// stop the I/O watcher, we received the event, but
		1356	// are not yet ready to handle it.
		1357	ev_io_stop (EV_A_ w);
		1358
		1359	// start the idle watcher to ahndle the actual event.
		1360	// it will not be executed as long as other watchers
		1361	// with the default priority are receiving events.
		1362	ev_idle_start (EV_A_ &idle);
		1363	}
		1364
		1365	static void
		1366	idle_cb (EV_P_ ev_idle *w, int revents)
		1367	{
		1368	// actual processing
		1369	read (STDIN_FILENO, ...);
		1370
		1371	// have to start the I/O watcher again, as
		1372	// we have handled the event
		1373	ev_io_start (EV_P_ &io);
		1374	}
		1375
		1376	// initialisation
		1377	ev_idle_init (&idle, idle_cb);
		1378	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1379	ev_io_start (EV_DEFAULT_ &io);
		1380
		1381	In the "real" world, it might also be beneficial to start a timer, so that
		1382	low-priority connections can not be locked out forever under load. This
		1383	enables your program to keep a lower latency for important connections
		1384	during short periods of high load, while not completely locking out less
		1385	important ones.
1189		1386
1190		1387
1191	=head1 WATCHER TYPES	1388	=head1 WATCHER TYPES
1192		1389
1193	This section describes each watcher in detail, but will not repeat	1390	This section describes each watcher in detail, but will not repeat
…		…
1219	descriptors to non-blocking mode is also usually a good idea (but not	1416	descriptors to non-blocking mode is also usually a good idea (but not
1220	required if you know what you are doing).	1417	required if you know what you are doing).
1221		1418
1222	If you cannot use non-blocking mode, then force the use of a	1419	If you cannot use non-blocking mode, then force the use of a
1223	known-to-be-good backend (at the time of this writing, this includes only	1420	known-to-be-good backend (at the time of this writing, this includes only
1224	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1421	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1422	descriptors for which non-blocking operation makes no sense (such as
		1423	files) - libev doesn't guarentee any specific behaviour in that case.
1225		1424
1226	Another thing you have to watch out for is that it is quite easy to	1425	Another thing you have to watch out for is that it is quite easy to
1227	receive "spurious" readiness notifications, that is your callback might	1426	receive "spurious" readiness notifications, that is your callback might
1228	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1427	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1229	because there is no data. Not only are some backends known to create a	1428	because there is no data. Not only are some backends known to create a
…		…
1350	year, it will still time out after (roughly) one hour. "Roughly" because	1549	year, it will still time out after (roughly) one hour. "Roughly" because
1351	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1550	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1352	monotonic clock option helps a lot here).	1551	monotonic clock option helps a lot here).
1353		1552
1354	The callback is guaranteed to be invoked only I<after> its timeout has	1553	The callback is guaranteed to be invoked only I<after> its timeout has
1355	passed. If multiple timers become ready during the same loop iteration	1554	passed (not I<at>, so on systems with very low-resolution clocks this
1356	then the ones with earlier time-out values are invoked before ones with	1555	might introduce a small delay). If multiple timers become ready during the
1357	later time-out values (but this is no longer true when a callback calls	1556	same loop iteration then the ones with earlier time-out values are invoked
1358	C<ev_loop> recursively).	1557	before ones of the same priority with later time-out values (but this is
		1558	no longer true when a callback calls C<ev_loop> recursively).
1359		1559
1360	=head3 Be smart about timeouts	1560	=head3 Be smart about timeouts
1361		1561
1362	Many real-world problems involve some kind of timeout, usually for error	1562	Many real-world problems involve some kind of timeout, usually for error
1363	recovery. A typical example is an HTTP request - if the other side hangs,	1563	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1407	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>	1607	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
1408	member and C<ev_timer_again>.	1608	member and C<ev_timer_again>.
1409		1609
1410	At start:	1610	At start:
1411		1611
1412	ev_timer_init (timer, callback);	1612	ev_init (timer, callback);
1413	timer->repeat = 60.;	1613	timer->repeat = 60.;
1414	ev_timer_again (loop, timer);	1614	ev_timer_again (loop, timer);
1415		1615
1416	Each time there is some activity:	1616	Each time there is some activity:
1417		1617
…		…
1479		1679
1480	To start the timer, simply initialise the watcher and set C<last_activity>	1680	To start the timer, simply initialise the watcher and set C<last_activity>
1481	to the current time (meaning we just have some activity :), then call the	1681	to the current time (meaning we just have some activity :), then call the
1482	callback, which will "do the right thing" and start the timer:	1682	callback, which will "do the right thing" and start the timer:
1483		1683
1484	ev_timer_init (timer, callback);	1684	ev_init (timer, callback);
1485	last_activity = ev_now (loop);	1685	last_activity = ev_now (loop);
1486	callback (loop, timer, EV_TIMEOUT);	1686	callback (loop, timer, EV_TIMEOUT);
1487		1687
1488	And when there is some activity, simply store the current time in	1688	And when there is some activity, simply store the current time in
1489	C<last_activity>, no libev calls at all:	1689	C<last_activity>, no libev calls at all:
…		…
1582	If the timer is started but non-repeating, stop it (as if it timed out).	1782	If the timer is started but non-repeating, stop it (as if it timed out).
1583		1783
1584	If the timer is repeating, either start it if necessary (with the	1784	If the timer is repeating, either start it if necessary (with the
1585	C<repeat> value), or reset the running timer to the C<repeat> value.	1785	C<repeat> value), or reset the running timer to the C<repeat> value.
1586		1786
1587	This sounds a bit complicated, see "Be smart about timeouts", above, for a	1787	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1588	usage example.	1788	usage example.
1589		1789
1590	=item ev_tstamp repeat [read-write]	1790	=item ev_tstamp repeat [read-write]
1591		1791
1592	The current C<repeat> value. Will be used each time the watcher times out	1792	The current C<repeat> value. Will be used each time the watcher times out
…		…
1886	some child status changes (most typically when a child of yours dies or	2086	some child status changes (most typically when a child of yours dies or
1887	exits). It is permissible to install a child watcher I<after> the child	2087	exits). It is permissible to install a child watcher I<after> the child
1888	has been forked (which implies it might have already exited), as long	2088	has been forked (which implies it might have already exited), as long
1889	as the event loop isn't entered (or is continued from a watcher), i.e.,	2089	as the event loop isn't entered (or is continued from a watcher), i.e.,
1890	forking and then immediately registering a watcher for the child is fine,	2090	forking and then immediately registering a watcher for the child is fine,
1891	but forking and registering a watcher a few event loop iterations later is	2091	but forking and registering a watcher a few event loop iterations later or
1892	not.	2092	in the next callback invocation is not.
1893		2093
1894	Only the default event loop is capable of handling signals, and therefore	2094	Only the default event loop is capable of handling signals, and therefore
1895	you can only register child watchers in the default event loop.	2095	you can only register child watchers in the default event loop.
		2096
		2097	Due to some design glitches inside libev, child watchers will always be
		2098	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2099	libev)
1896		2100
1897	=head3 Process Interaction	2101	=head3 Process Interaction
1898		2102
1899	Libev grabs C<SIGCHLD> as soon as the default event loop is	2103	Libev grabs C<SIGCHLD> as soon as the default event loop is
1900	initialised. This is necessary to guarantee proper behaviour even if	2104	initialised. This is necessary to guarantee proper behaviour even if
…		…
2252	// no longer anything immediate to do.	2456	// no longer anything immediate to do.
2253	}	2457	}
2254		2458
2255	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2459	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2256	ev_idle_init (idle_watcher, idle_cb);	2460	ev_idle_init (idle_watcher, idle_cb);
2257	ev_idle_start (loop, idle_cb);	2461	ev_idle_start (loop, idle_watcher);
2258		2462
2259		2463
2260	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2464	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2261		2465
2262	Prepare and check watchers are usually (but not always) used in pairs:	2466	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2355	struct pollfd fds [nfd];	2559	struct pollfd fds [nfd];
2356	// actual code will need to loop here and realloc etc.	2560	// actual code will need to loop here and realloc etc.
2357	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2561	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2358		2562
2359	/* the callback is illegal, but won't be called as we stop during check */	2563	/* the callback is illegal, but won't be called as we stop during check */
2360	ev_timer_init (&tw, 0, timeout * 1e-3);	2564	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2361	ev_timer_start (loop, &tw);	2565	ev_timer_start (loop, &tw);
2362		2566
2363	// create one ev_io per pollfd	2567	// create one ev_io per pollfd
2364	for (int i = 0; i < nfd; ++i)	2568	for (int i = 0; i < nfd; ++i)
2365	{	2569	{
…		…
2595	event loop blocks next and before C<ev_check> watchers are being called,	2799	event loop blocks next and before C<ev_check> watchers are being called,
2596	and only in the child after the fork. If whoever good citizen calling	2800	and only in the child after the fork. If whoever good citizen calling
2597	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2801	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2598	handlers will be invoked, too, of course.	2802	handlers will be invoked, too, of course.
2599		2803
		2804	=head3 The special problem of life after fork - how is it possible?
		2805
		2806	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2807	up/change the process environment, followed by a call to C<exec()>. This
		2808	sequence should be handled by libev without any problems.
		2809
		2810	This changes when the application actually wants to do event handling
		2811	in the child, or both parent in child, in effect "continuing" after the
		2812	fork.
		2813
		2814	The default mode of operation (for libev, with application help to detect
		2815	forks) is to duplicate all the state in the child, as would be expected
		2816	when I<either> the parent I<or> the child process continues.
		2817
		2818	When both processes want to continue using libev, then this is usually the
		2819	wrong result. In that case, usually one process (typically the parent) is
		2820	supposed to continue with all watchers in place as before, while the other
		2821	process typically wants to start fresh, i.e. without any active watchers.
		2822
		2823	The cleanest and most efficient way to achieve that with libev is to
		2824	simply create a new event loop, which of course will be "empty", and
		2825	use that for new watchers. This has the advantage of not touching more
		2826	memory than necessary, and thus avoiding the copy-on-write, and the
		2827	disadvantage of having to use multiple event loops (which do not support
		2828	signal watchers).
		2829
		2830	When this is not possible, or you want to use the default loop for
		2831	other reasons, then in the process that wants to start "fresh", call
		2832	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2833	the default loop will "orphan" (not stop) all registered watchers, so you
		2834	have to be careful not to execute code that modifies those watchers. Note
		2835	also that in that case, you have to re-register any signal watchers.
		2836
2600	=head3 Watcher-Specific Functions and Data Members	2837	=head3 Watcher-Specific Functions and Data Members
2601		2838
2602	=over 4	2839	=over 4
2603		2840
2604	=item ev_fork_init (ev_signal *, callback)	2841	=item ev_fork_init (ev_signal *, callback)
…		…
3494	defined to be C<0>, then they are not.	3731	defined to be C<0>, then they are not.
3495		3732
3496	=item EV_MINIMAL	3733	=item EV_MINIMAL
3497		3734
3498	If you need to shave off some kilobytes of code at the expense of some	3735	If you need to shave off some kilobytes of code at the expense of some
3499	speed, define this symbol to C<1>. Currently this is used to override some	3736	speed (but with the full API), define this symbol to C<1>. Currently this
3500	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3737	is used to override some inlining decisions, saves roughly 30% code size
3501	much smaller 2-heap for timer management over the default 4-heap.	3738	on amd64. It also selects a much smaller 2-heap for timer management over
		3739	the default 4-heap.
		3740
		3741	You can save even more by disabling watcher types you do not need
		3742	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3743	(C<-DNDEBUG>) will usually reduce code size a lot.
		3744
		3745	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3746	provide a bare-bones event library. See C<ev.h> for details on what parts
		3747	of the API are still available, and do not complain if this subset changes
		3748	over time.
3502		3749
3503	=item EV_PID_HASHSIZE	3750	=item EV_PID_HASHSIZE
3504		3751
3505	C<ev_child> watchers use a small hash table to distribute workload by	3752	C<ev_child> watchers use a small hash table to distribute workload by
3506	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3753	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3692	default loop and triggering an C<ev_async> watcher from the default loop	3939	default loop and triggering an C<ev_async> watcher from the default loop
3693	watcher callback into the event loop interested in the signal.	3940	watcher callback into the event loop interested in the signal.
3694		3941
3695	=back	3942	=back
3696		3943
		3944	=head4 THREAD LOCKING EXAMPLE
		3945
		3946	Here is a fictitious example of how to run an event loop in a different
		3947	thread than where callbacks are being invoked and watchers are
		3948	created/added/removed.
		3949
		3950	For a real-world example, see the C<EV::Loop::Async> perl module,
		3951	which uses exactly this technique (which is suited for many high-level
		3952	languages).
		3953
		3954	The example uses a pthread mutex to protect the loop data, a condition
		3955	variable to wait for callback invocations, an async watcher to notify the
		3956	event loop thread and an unspecified mechanism to wake up the main thread.
		3957
		3958	First, you need to associate some data with the event loop:
		3959
		3960	typedef struct {
		3961	mutex_t lock; /* global loop lock */
		3962	ev_async async_w;
		3963	thread_t tid;
		3964	cond_t invoke_cv;
		3965	} userdata;
		3966
		3967	void prepare_loop (EV_P)
		3968	{
		3969	// for simplicity, we use a static userdata struct.
		3970	static userdata u;
		3971
		3972	ev_async_init (&u->async_w, async_cb);
		3973	ev_async_start (EV_A_ &u->async_w);
		3974
		3975	pthread_mutex_init (&u->lock, 0);
		3976	pthread_cond_init (&u->invoke_cv, 0);
		3977
		3978	// now associate this with the loop
		3979	ev_set_userdata (EV_A_ u);
		3980	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3981	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3982
		3983	// then create the thread running ev_loop
		3984	pthread_create (&u->tid, 0, l_run, EV_A);
		3985	}
		3986
		3987	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3988	solely to wake up the event loop so it takes notice of any new watchers
		3989	that might have been added:
		3990
		3991	static void
		3992	async_cb (EV_P_ ev_async *w, int revents)
		3993	{
		3994	// just used for the side effects
		3995	}
		3996
		3997	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3998	protecting the loop data, respectively.
		3999
		4000	static void
		4001	l_release (EV_P)
		4002	{
		4003	udat *u = ev_userdata (EV_A);
		4004	pthread_mutex_unlock (&u->lock);
		4005	}
		4006
		4007	static void
		4008	l_acquire (EV_P)
		4009	{
		4010	udat *u = ev_userdata (EV_A);
		4011	pthread_mutex_lock (&u->lock);
		4012	}
		4013
		4014	The event loop thread first acquires the mutex, and then jumps straight
		4015	into C<ev_loop>:
		4016
		4017	void *
		4018	l_run (void *thr_arg)
		4019	{
		4020	struct ev_loop loop = (struct ev_loop )thr_arg;
		4021
		4022	l_acquire (EV_A);
		4023	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4024	ev_loop (EV_A_ 0);
		4025	l_release (EV_A);
		4026
		4027	return 0;
		4028	}
		4029
		4030	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4031	signal the main thread via some unspecified mechanism (signals? pipe
		4032	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4033	have been called:
		4034
		4035	static void
		4036	l_invoke (EV_P)
		4037	{
		4038	udat *u = ev_userdata (EV_A);
		4039
		4040	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4041
		4042	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4043	}
		4044
		4045	Now, whenever the main thread gets told to invoke pending watchers, it
		4046	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4047	thread to continue:
		4048
		4049	static void
		4050	real_invoke_pending (EV_P)
		4051	{
		4052	udat *u = ev_userdata (EV_A);
		4053
		4054	pthread_mutex_lock (&u->lock);
		4055	ev_invoke_pending (EV_A);
		4056	pthread_cond_signal (&u->invoke_cv);
		4057	pthread_mutex_unlock (&u->lock);
		4058	}
		4059
		4060	Whenever you want to start/stop a watcher or do other modifications to an
		4061	event loop, you will now have to lock:
		4062
		4063	ev_timer timeout_watcher;
		4064	udat *u = ev_userdata (EV_A);
		4065
		4066	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4067
		4068	pthread_mutex_lock (&u->lock);
		4069	ev_timer_start (EV_A_ &timeout_watcher);
		4070	ev_async_send (EV_A_ &u->async_w);
		4071	pthread_mutex_unlock (&u->lock);
		4072
		4073	Note that sending the C<ev_async> watcher is required because otherwise
		4074	an event loop currently blocking in the kernel will have no knowledge
		4075	about the newly added timer. By waking up the loop it will pick up any new
		4076	watchers in the next event loop iteration.
		4077
3697	=head3 COROUTINES	4078	=head3 COROUTINES
3698		4079
3699	Libev is very accommodating to coroutines ("cooperative threads"):	4080	Libev is very accommodating to coroutines ("cooperative threads"):
3700	libev fully supports nesting calls to its functions from different	4081	libev fully supports nesting calls to its functions from different
3701	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4082	coroutines (e.g. you can call C<ev_loop> on the same loop from two
…		…
3786	way (note also that glib is the slowest event library known to man).	4167	way (note also that glib is the slowest event library known to man).
3787		4168
3788	There is no supported compilation method available on windows except	4169	There is no supported compilation method available on windows except
3789	embedding it into other applications.	4170	embedding it into other applications.
3790		4171
		4172	Sensible signal handling is officially unsupported by Microsoft - libev
		4173	tries its best, but under most conditions, signals will simply not work.
		4174
3791	Not a libev limitation but worth mentioning: windows apparently doesn't	4175	Not a libev limitation but worth mentioning: windows apparently doesn't
3792	accept large writes: instead of resulting in a partial write, windows will	4176	accept large writes: instead of resulting in a partial write, windows will
3793	either accept everything or return C<ENOBUFS> if the buffer is too large,	4177	either accept everything or return C<ENOBUFS> if the buffer is too large,
3794	so make sure you only write small amounts into your sockets (less than a	4178	so make sure you only write small amounts into your sockets (less than a
3795	megabyte seems safe, but this apparently depends on the amount of memory	4179	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3799	the abysmal performance of winsockets, using a large number of sockets	4183	the abysmal performance of winsockets, using a large number of sockets
3800	is not recommended (and not reasonable). If your program needs to use	4184	is not recommended (and not reasonable). If your program needs to use
3801	more than a hundred or so sockets, then likely it needs to use a totally	4185	more than a hundred or so sockets, then likely it needs to use a totally
3802	different implementation for windows, as libev offers the POSIX readiness	4186	different implementation for windows, as libev offers the POSIX readiness
3803	notification model, which cannot be implemented efficiently on windows	4187	notification model, which cannot be implemented efficiently on windows
3804	(Microsoft monopoly games).	4188	(due to Microsoft monopoly games).
3805		4189
3806	A typical way to use libev under windows is to embed it (see the embedding	4190	A typical way to use libev under windows is to embed it (see the embedding
3807	section for details) and use the following F<evwrap.h> header file instead	4191	section for details) and use the following F<evwrap.h> header file instead
3808	of F<ev.h>:	4192	of F<ev.h>:
3809		4193
…		…
3845		4229
3846	Early versions of winsocket's select only supported waiting for a maximum	4230	Early versions of winsocket's select only supported waiting for a maximum
3847	of C<64> handles (probably owning to the fact that all windows kernels	4231	of C<64> handles (probably owning to the fact that all windows kernels
3848	can only wait for C<64> things at the same time internally; Microsoft	4232	can only wait for C<64> things at the same time internally; Microsoft
3849	recommends spawning a chain of threads and wait for 63 handles and the	4233	recommends spawning a chain of threads and wait for 63 handles and the
3850	previous thread in each. Great).	4234	previous thread in each. Sounds great!).
3851		4235
3852	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4236	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3853	to some high number (e.g. C<2048>) before compiling the winsocket select	4237	to some high number (e.g. C<2048>) before compiling the winsocket select
3854	call (which might be in libev or elsewhere, for example, perl does its own	4238	call (which might be in libev or elsewhere, for example, perl and many
3855	select emulation on windows).	4239	other interpreters do their own select emulation on windows).
3856		4240
3857	Another limit is the number of file descriptors in the Microsoft runtime	4241	Another limit is the number of file descriptors in the Microsoft runtime
3858	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4242	libraries, which by default is C<64> (there must be a hidden I<64>
3859	or something like this inside Microsoft). You can increase this by calling	4243	fetish or something like this inside Microsoft). You can increase this
3860	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4244	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3861	arbitrary limit), but is broken in many versions of the Microsoft runtime	4245	(another arbitrary limit), but is broken in many versions of the Microsoft
3862	libraries.
3863
3864	This might get you to about C<512> or C<2048> sockets (depending on	4246	runtime libraries. This might get you to about C<512> or C<2048> sockets
3865	windows version and/or the phase of the moon). To get more, you need to	4247	(depending on windows version and/or the phase of the moon). To get more,
3866	wrap all I/O functions and provide your own fd management, but the cost of	4248	you need to wrap all I/O functions and provide your own fd management, but
3867	calling select (O(n²)) will likely make this unworkable.	4249	the cost of calling select (O(n²)) will likely make this unworkable.
3868		4250
3869	=back	4251	=back
3870		4252
3871	=head2 PORTABILITY REQUIREMENTS	4253	=head2 PORTABILITY REQUIREMENTS
3872		4254
…		…
3915	=item C<double> must hold a time value in seconds with enough accuracy	4297	=item C<double> must hold a time value in seconds with enough accuracy
3916		4298
3917	The type C<double> is used to represent timestamps. It is required to	4299	The type C<double> is used to represent timestamps. It is required to
3918	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4300	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3919	enough for at least into the year 4000. This requirement is fulfilled by	4301	enough for at least into the year 4000. This requirement is fulfilled by
3920	implementations implementing IEEE 754 (basically all existing ones).	4302	implementations implementing IEEE 754, which is basically all existing
		4303	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4304	2200.
3921		4305
3922	=back	4306	=back
3923		4307
3924	If you know of other additional requirements drop me a note.	4308	If you know of other additional requirements drop me a note.
3925		4309
…		…
3993	involves iterating over all running async watchers or all signal numbers.	4377	involves iterating over all running async watchers or all signal numbers.
3994		4378
3995	=back	4379	=back
3996		4380
3997		4381
		4382	=head1 GLOSSARY
		4383
		4384	=over 4
		4385
		4386	=item active
		4387
		4388	A watcher is active as long as it has been started (has been attached to
		4389	an event loop) but not yet stopped (disassociated from the event loop).
		4390
		4391	=item application
		4392
		4393	In this document, an application is whatever is using libev.
		4394
		4395	=item callback
		4396
		4397	The address of a function that is called when some event has been
		4398	detected. Callbacks are being passed the event loop, the watcher that
		4399	received the event, and the actual event bitset.
		4400
		4401	=item callback invocation
		4402
		4403	The act of calling the callback associated with a watcher.
		4404
		4405	=item event
		4406
		4407	A change of state of some external event, such as data now being available
		4408	for reading on a file descriptor, time having passed or simply not having
		4409	any other events happening anymore.
		4410
		4411	In libev, events are represented as single bits (such as C<EV_READ> or
		4412	C<EV_TIMEOUT>).
		4413
		4414	=item event library
		4415
		4416	A software package implementing an event model and loop.
		4417
		4418	=item event loop
		4419
		4420	An entity that handles and processes external events and converts them
		4421	into callback invocations.
		4422
		4423	=item event model
		4424
		4425	The model used to describe how an event loop handles and processes
		4426	watchers and events.
		4427
		4428	=item pending
		4429
		4430	A watcher is pending as soon as the corresponding event has been detected,
		4431	and stops being pending as soon as the watcher will be invoked or its
		4432	pending status is explicitly cleared by the application.
		4433
		4434	A watcher can be pending, but not active. Stopping a watcher also clears
		4435	its pending status.
		4436
		4437	=item real time
		4438
		4439	The physical time that is observed. It is apparently strictly monotonic :)
		4440
		4441	=item wall-clock time
		4442
		4443	The time and date as shown on clocks. Unlike real time, it can actually
		4444	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4445	clock.
		4446
		4447	=item watcher
		4448
		4449	A data structure that describes interest in certain events. Watchers need
		4450	to be started (attached to an event loop) before they can receive events.
		4451
		4452	=item watcher invocation
		4453
		4454	The act of calling the callback associated with a watcher.
		4455
		4456	=back
		4457
3998	=head1 AUTHOR	4458	=head1 AUTHOR
3999		4459
4000	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	4460	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
4001		4461

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Comparing libev/ev.pod (file contents): Revision 1.231 by root, Wed Apr 15 19:35:53 2009 UTC vs. Revision 1.254 by root, Tue Jul 14 19:02:43 2009 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.231 by root, Wed Apr 15 19:35:53 2009 UTC vs.
Revision 1.254 by root, Tue Jul 14 19:02:43 2009 UTC