[ViewVC] Diff of: cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.230 by root, Wed Apr 15 18:47:07 2009 UTC vs.
Revision 1.256 by root, Tue Jul 14 20:31:21 2009 UTC

…		…
62		62
63	// unloop was called, so exit	63	// unloop was called, so exit
64	return 0;	64	return 0;
65	}	65	}
66		66
67	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
68		70
69	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
70	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
71	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
72		84
73	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
74	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
75	these event sources and provide your program with events.	87	these event sources and provide your program with events.
76		88
…		…
110	name C<loop> (which is always of type C<ev_loop *>) will not have	122	name C<loop> (which is always of type C<ev_loop *>) will not have
111	this argument.	123	this argument.
112		124
113	=head2 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
114		126
115	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
116	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
117	the beginning of 1970, details are complicated, don't ask). This type is	129	near the beginning of 1970, details are complicated, don't ask). This
118	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	type is called C<ev_tstamp>, which is what you should use too. It usually
119	to the C<double> type in C, and when you need to do any calculations on	131	aliases to the C<double> type in C. When you need to do any calculations
120	it, you should treat it as some floating point value. Unlike the name	132	on it, you should treat it as some floating point value. Unlike the name
121	component C<stamp> might indicate, it is also used for time differences	133	component C<stamp> might indicate, it is also used for time differences
122	throughout libev.	134	throughout libev.
123		135
124	=head1 ERROR HANDLING	136	=head1 ERROR HANDLING
125		137
…		…
609		621
610	This value can sometimes be useful as a generation counter of sorts (it	622	This value can sometimes be useful as a generation counter of sorts (it
611	"ticks" the number of loop iterations), as it roughly corresponds with	623	"ticks" the number of loop iterations), as it roughly corresponds with
612	C<ev_prepare> and C<ev_check> calls.	624	C<ev_prepare> and C<ev_check> calls.
613		625
		626	=item unsigned int ev_loop_depth (loop)
		627
		628	Returns the number of times C<ev_loop> was entered minus the number of
		629	times C<ev_loop> was exited, in other words, the recursion depth.
		630
		631	Outside C<ev_loop>, this number is zero. In a callback, this number is
		632	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		633	in which case it is higher.
		634
		635	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		636	etc.), doesn't count as exit.
		637
614	=item unsigned int ev_backend (loop)	638	=item unsigned int ev_backend (loop)
615		639
616	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	640	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
617	use.	641	use.
618		642
…		…
632		656
633	This function is rarely useful, but when some event callback runs for a	657	This function is rarely useful, but when some event callback runs for a
634	very long time without entering the event loop, updating libev's idea of	658	very long time without entering the event loop, updating libev's idea of
635	the current time is a good idea.	659	the current time is a good idea.
636		660
637	See also "The special problem of time updates" in the C<ev_timer> section.	661	See also L<The special problem of time updates> in the C<ev_timer> section.
		662
		663	=item ev_suspend (loop)
		664
		665	=item ev_resume (loop)
		666
		667	These two functions suspend and resume a loop, for use when the loop is
		668	not used for a while and timeouts should not be processed.
		669
		670	A typical use case would be an interactive program such as a game: When
		671	the user presses C<^Z> to suspend the game and resumes it an hour later it
		672	would be best to handle timeouts as if no time had actually passed while
		673	the program was suspended. This can be achieved by calling C<ev_suspend>
		674	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		675	C<ev_resume> directly afterwards to resume timer processing.
		676
		677	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		678	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		679	will be rescheduled (that is, they will lose any events that would have
		680	occured while suspended).
		681
		682	After calling C<ev_suspend> you B<must not> call I<any> function on the
		683	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		684	without a previous call to C<ev_suspend>.
		685
		686	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		687	event loop time (see C<ev_now_update>).
638		688
639	=item ev_loop (loop, int flags)	689	=item ev_loop (loop, int flags)
640		690
641	Finally, this is it, the event handler. This function usually is called	691	Finally, this is it, the event handler. This function usually is called
642	after you initialised all your watchers and you want to start handling	692	after you initialised all your watchers and you want to start handling
…		…
773		823
774	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
775	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,
776	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
777	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
778	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.
779		831
780	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
781	to spend more time collecting timeouts, at the expense of increased	833	to spend more time collecting timeouts, at the expense of increased
782	latency/jitter/inexactness (the watcher callback will be called	834	latency/jitter/inexactness (the watcher callback will be called
783	later). C<ev_io> watchers will not be affected. Setting this to a non-null	835	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
785		837
786	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
787	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
788	interactive servers (of course not for games), likewise for timeouts. It	840	interactive servers (of course not for games), likewise for timeouts. It
789	usually doesn't make much sense to set it to a lower value than C<0.01>,	841	usually doesn't make much sense to set it to a lower value than C<0.01>,
790	as this approaches the timing granularity of most systems.	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).
791		847
792	Setting the I<timeout collect interval> can improve the opportunity for	848	Setting the I<timeout collect interval> can improve the opportunity for
793	saving power, as the program will "bundle" timer callback invocations that	849	saving power, as the program will "bundle" timer callback invocations that
794	are "near" in time together, by delaying some, thus reducing the number of	850	are "near" in time together, by delaying some, thus reducing the number of
795	times the process sleeps and wakes up again. Another useful technique to	851	times the process sleeps and wakes up again. Another useful technique to
796	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	852	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
797	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.
798		925
799	=item ev_loop_verify (loop)	926	=item ev_loop_verify (loop)
800		927
801	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
802	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
…		…
1057	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>
1058	(default: C<-2>). Pending watchers with higher priority will be invoked	1185	(default: C<-2>). Pending watchers with higher priority will be invoked
1059	before watchers with lower priority, but priority will not keep watchers	1186	before watchers with lower priority, but priority will not keep watchers
1060	from being executed (except for C<ev_idle> watchers).	1187	from being executed (except for C<ev_idle> watchers).
1061		1188
1062	This means that priorities are I<only> used for ordering callback
1063	invocation after new events have been received. This is useful, for
1064	example, to reduce latency after idling, or more often, to bind two
1065	watchers on the same event and make sure one is called first.
1066
1067	If you need to suppress invocation when higher priority events are pending	1189	If you need to suppress invocation when higher priority events are pending
1068	you need to look at C<ev_idle> watchers, which provide this functionality.	1190	you need to look at C<ev_idle> watchers, which provide this functionality.
1069		1191
1070	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
1071	pending.	1193	pending.
1072
1073	The default priority used by watchers when no priority has been set is
1074	always C<0>, which is supposed to not be too high and not be too low :).
1075		1194
1076	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
1077	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
1078	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.
1079		1204
1080	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1205	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1081		1206
1082	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
1083	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
…		…
1148	#include <stddef.h>	1273	#include <stddef.h>
1149		1274
1150	static void	1275	static void
1151	t1_cb (EV_P_ ev_timer *w, int revents)	1276	t1_cb (EV_P_ ev_timer *w, int revents)
1152	{	1277	{
1153	struct my_biggy big = (struct my_biggy *	1278	struct my_biggy big = (struct my_biggy *)
1154	(((char *)w) - offsetof (struct my_biggy, t1));	1279	(((char *)w) - offsetof (struct my_biggy, t1));
1155	}	1280	}
1156		1281
1157	static void	1282	static void
1158	t2_cb (EV_P_ ev_timer *w, int revents)	1283	t2_cb (EV_P_ ev_timer *w, int revents)
1159	{	1284	{
1160	struct my_biggy big = (struct my_biggy *	1285	struct my_biggy big = (struct my_biggy *)
1161	(((char *)w) - offsetof (struct my_biggy, t2));	1286	(((char *)w) - offsetof (struct my_biggy, t2));
1162	}	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.
1163		1391
1164		1392
1165	=head1 WATCHER TYPES	1393	=head1 WATCHER TYPES
1166		1394
1167	This section describes each watcher in detail, but will not repeat	1395	This section describes each watcher in detail, but will not repeat
…		…
1193	descriptors to non-blocking mode is also usually a good idea (but not	1421	descriptors to non-blocking mode is also usually a good idea (but not
1194	required if you know what you are doing).	1422	required if you know what you are doing).
1195		1423
1196	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
1197	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
1198	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.
1199		1429
1200	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
1201	receive "spurious" readiness notifications, that is your callback might	1431	receive "spurious" readiness notifications, that is your callback might
1202	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1432	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1203	because there is no data. Not only are some backends known to create a	1433	because there is no data. Not only are some backends known to create a
…		…
1324	year, it will still time out after (roughly) one hour. "Roughly" because	1554	year, it will still time out after (roughly) one hour. "Roughly" because
1325	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1555	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1326	monotonic clock option helps a lot here).	1556	monotonic clock option helps a lot here).
1327		1557
1328	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
1329	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
1330	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
1331	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
1332	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).
1333		1564
1334	=head3 Be smart about timeouts	1565	=head3 Be smart about timeouts
1335		1566
1336	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
1337	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,
…		…
1381	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>
1382	member and C<ev_timer_again>.	1613	member and C<ev_timer_again>.
1383		1614
1384	At start:	1615	At start:
1385		1616
1386	ev_timer_init (timer, callback);	1617	ev_init (timer, callback);
1387	timer->repeat = 60.;	1618	timer->repeat = 60.;
1388	ev_timer_again (loop, timer);	1619	ev_timer_again (loop, timer);
1389		1620
1390	Each time there is some activity:	1621	Each time there is some activity:
1391		1622
…		…
1453		1684
1454	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>
1455	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
1456	callback, which will "do the right thing" and start the timer:	1687	callback, which will "do the right thing" and start the timer:
1457		1688
1458	ev_timer_init (timer, callback);	1689	ev_init (timer, callback);
1459	last_activity = ev_now (loop);	1690	last_activity = ev_now (loop);
1460	callback (loop, timer, EV_TIMEOUT);	1691	callback (loop, timer, EV_TIMEOUT);
1461		1692
1462	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
1463	C<last_activity>, no libev calls at all:	1694	C<last_activity>, no libev calls at all:
…		…
1556	If the timer is started but non-repeating, stop it (as if it timed out).	1787	If the timer is started but non-repeating, stop it (as if it timed out).
1557		1788
1558	If the timer is repeating, either start it if necessary (with the	1789	If the timer is repeating, either start it if necessary (with the
1559	C<repeat> value), or reset the running timer to the C<repeat> value.	1790	C<repeat> value), or reset the running timer to the C<repeat> value.
1560		1791
1561	This sounds a bit complicated, see "Be smart about timeouts", above, for a	1792	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1562	usage example.	1793	usage example.
1563		1794
1564	=item ev_tstamp repeat [read-write]	1795	=item ev_tstamp repeat [read-write]
1565		1796
1566	The current C<repeat> value. Will be used each time the watcher times out	1797	The current C<repeat> value. Will be used each time the watcher times out
…		…
1860	some child status changes (most typically when a child of yours dies or	2091	some child status changes (most typically when a child of yours dies or
1861	exits). It is permissible to install a child watcher I<after> the child	2092	exits). It is permissible to install a child watcher I<after> the child
1862	has been forked (which implies it might have already exited), as long	2093	has been forked (which implies it might have already exited), as long
1863	as the event loop isn't entered (or is continued from a watcher), i.e.,	2094	as the event loop isn't entered (or is continued from a watcher), i.e.,
1864	forking and then immediately registering a watcher for the child is fine,	2095	forking and then immediately registering a watcher for the child is fine,
1865	but forking and registering a watcher a few event loop iterations later is	2096	but forking and registering a watcher a few event loop iterations later or
1866	not.	2097	in the next callback invocation is not.
1867		2098
1868	Only the default event loop is capable of handling signals, and therefore	2099	Only the default event loop is capable of handling signals, and therefore
1869	you can only register child watchers in the default event loop.	2100	you can only register child watchers in the default event loop.
		2101
		2102	Due to some design glitches inside libev, child watchers will always be
		2103	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2104	libev)
1870		2105
1871	=head3 Process Interaction	2106	=head3 Process Interaction
1872		2107
1873	Libev grabs C<SIGCHLD> as soon as the default event loop is	2108	Libev grabs C<SIGCHLD> as soon as the default event loop is
1874	initialised. This is necessary to guarantee proper behaviour even if	2109	initialised. This is necessary to guarantee proper behaviour even if
…		…
2226	// no longer anything immediate to do.	2461	// no longer anything immediate to do.
2227	}	2462	}
2228		2463
2229	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2464	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2230	ev_idle_init (idle_watcher, idle_cb);	2465	ev_idle_init (idle_watcher, idle_cb);
2231	ev_idle_start (loop, idle_cb);	2466	ev_idle_start (loop, idle_watcher);
2232		2467
2233		2468
2234	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2469	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2235		2470
2236	Prepare and check watchers are usually (but not always) used in pairs:	2471	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2329	struct pollfd fds [nfd];	2564	struct pollfd fds [nfd];
2330	// actual code will need to loop here and realloc etc.	2565	// actual code will need to loop here and realloc etc.
2331	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2566	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2332		2567
2333	/* the callback is illegal, but won't be called as we stop during check */	2568	/* the callback is illegal, but won't be called as we stop during check */
2334	ev_timer_init (&tw, 0, timeout * 1e-3);	2569	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2335	ev_timer_start (loop, &tw);	2570	ev_timer_start (loop, &tw);
2336		2571
2337	// create one ev_io per pollfd	2572	// create one ev_io per pollfd
2338	for (int i = 0; i < nfd; ++i)	2573	for (int i = 0; i < nfd; ++i)
2339	{	2574	{
…		…
2569	event loop blocks next and before C<ev_check> watchers are being called,	2804	event loop blocks next and before C<ev_check> watchers are being called,
2570	and only in the child after the fork. If whoever good citizen calling	2805	and only in the child after the fork. If whoever good citizen calling
2571	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2806	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2572	handlers will be invoked, too, of course.	2807	handlers will be invoked, too, of course.
2573		2808
		2809	=head3 The special problem of life after fork - how is it possible?
		2810
		2811	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2812	up/change the process environment, followed by a call to C<exec()>. This
		2813	sequence should be handled by libev without any problems.
		2814
		2815	This changes when the application actually wants to do event handling
		2816	in the child, or both parent in child, in effect "continuing" after the
		2817	fork.
		2818
		2819	The default mode of operation (for libev, with application help to detect
		2820	forks) is to duplicate all the state in the child, as would be expected
		2821	when I<either> the parent I<or> the child process continues.
		2822
		2823	When both processes want to continue using libev, then this is usually the
		2824	wrong result. In that case, usually one process (typically the parent) is
		2825	supposed to continue with all watchers in place as before, while the other
		2826	process typically wants to start fresh, i.e. without any active watchers.
		2827
		2828	The cleanest and most efficient way to achieve that with libev is to
		2829	simply create a new event loop, which of course will be "empty", and
		2830	use that for new watchers. This has the advantage of not touching more
		2831	memory than necessary, and thus avoiding the copy-on-write, and the
		2832	disadvantage of having to use multiple event loops (which do not support
		2833	signal watchers).
		2834
		2835	When this is not possible, or you want to use the default loop for
		2836	other reasons, then in the process that wants to start "fresh", call
		2837	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2838	the default loop will "orphan" (not stop) all registered watchers, so you
		2839	have to be careful not to execute code that modifies those watchers. Note
		2840	also that in that case, you have to re-register any signal watchers.
		2841
2574	=head3 Watcher-Specific Functions and Data Members	2842	=head3 Watcher-Specific Functions and Data Members
2575		2843
2576	=over 4	2844	=over 4
2577		2845
2578	=item ev_fork_init (ev_signal *, callback)	2846	=item ev_fork_init (ev_signal *, callback)
…		…
3468	defined to be C<0>, then they are not.	3736	defined to be C<0>, then they are not.
3469		3737
3470	=item EV_MINIMAL	3738	=item EV_MINIMAL
3471		3739
3472	If you need to shave off some kilobytes of code at the expense of some	3740	If you need to shave off some kilobytes of code at the expense of some
3473	speed, define this symbol to C<1>. Currently this is used to override some	3741	speed (but with the full API), define this symbol to C<1>. Currently this
3474	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3742	is used to override some inlining decisions, saves roughly 30% code size
3475	much smaller 2-heap for timer management over the default 4-heap.	3743	on amd64. It also selects a much smaller 2-heap for timer management over
		3744	the default 4-heap.
		3745
		3746	You can save even more by disabling watcher types you do not need
		3747	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3748	(C<-DNDEBUG>) will usually reduce code size a lot.
		3749
		3750	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3751	provide a bare-bones event library. See C<ev.h> for details on what parts
		3752	of the API are still available, and do not complain if this subset changes
		3753	over time.
3476		3754
3477	=item EV_PID_HASHSIZE	3755	=item EV_PID_HASHSIZE
3478		3756
3479	C<ev_child> watchers use a small hash table to distribute workload by	3757	C<ev_child> watchers use a small hash table to distribute workload by
3480	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3758	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3666	default loop and triggering an C<ev_async> watcher from the default loop	3944	default loop and triggering an C<ev_async> watcher from the default loop
3667	watcher callback into the event loop interested in the signal.	3945	watcher callback into the event loop interested in the signal.
3668		3946
3669	=back	3947	=back
3670		3948
		3949	=head4 THREAD LOCKING EXAMPLE
		3950
		3951	Here is a fictitious example of how to run an event loop in a different
		3952	thread than where callbacks are being invoked and watchers are
		3953	created/added/removed.
		3954
		3955	For a real-world example, see the C<EV::Loop::Async> perl module,
		3956	which uses exactly this technique (which is suited for many high-level
		3957	languages).
		3958
		3959	The example uses a pthread mutex to protect the loop data, a condition
		3960	variable to wait for callback invocations, an async watcher to notify the
		3961	event loop thread and an unspecified mechanism to wake up the main thread.
		3962
		3963	First, you need to associate some data with the event loop:
		3964
		3965	typedef struct {
		3966	mutex_t lock; /* global loop lock */
		3967	ev_async async_w;
		3968	thread_t tid;
		3969	cond_t invoke_cv;
		3970	} userdata;
		3971
		3972	void prepare_loop (EV_P)
		3973	{
		3974	// for simplicity, we use a static userdata struct.
		3975	static userdata u;
		3976
		3977	ev_async_init (&u->async_w, async_cb);
		3978	ev_async_start (EV_A_ &u->async_w);
		3979
		3980	pthread_mutex_init (&u->lock, 0);
		3981	pthread_cond_init (&u->invoke_cv, 0);
		3982
		3983	// now associate this with the loop
		3984	ev_set_userdata (EV_A_ u);
		3985	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3986	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3987
		3988	// then create the thread running ev_loop
		3989	pthread_create (&u->tid, 0, l_run, EV_A);
		3990	}
		3991
		3992	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3993	solely to wake up the event loop so it takes notice of any new watchers
		3994	that might have been added:
		3995
		3996	static void
		3997	async_cb (EV_P_ ev_async *w, int revents)
		3998	{
		3999	// just used for the side effects
		4000	}
		4001
		4002	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4003	protecting the loop data, respectively.
		4004
		4005	static void
		4006	l_release (EV_P)
		4007	{
		4008	userdata *u = ev_userdata (EV_A);
		4009	pthread_mutex_unlock (&u->lock);
		4010	}
		4011
		4012	static void
		4013	l_acquire (EV_P)
		4014	{
		4015	userdata *u = ev_userdata (EV_A);
		4016	pthread_mutex_lock (&u->lock);
		4017	}
		4018
		4019	The event loop thread first acquires the mutex, and then jumps straight
		4020	into C<ev_loop>:
		4021
		4022	void *
		4023	l_run (void *thr_arg)
		4024	{
		4025	struct ev_loop loop = (struct ev_loop )thr_arg;
		4026
		4027	l_acquire (EV_A);
		4028	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4029	ev_loop (EV_A_ 0);
		4030	l_release (EV_A);
		4031
		4032	return 0;
		4033	}
		4034
		4035	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4036	signal the main thread via some unspecified mechanism (signals? pipe
		4037	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4038	have been called (in a while loop because a) spurious wakeups are possible
		4039	and b) skipping inter-thread-communication when there are no pending
		4040	watchers is very beneficial):
		4041
		4042	static void
		4043	l_invoke (EV_P)
		4044	{
		4045	userdata *u = ev_userdata (EV_A);
		4046
		4047	while (ev_pending_count (EV_A))
		4048	{
		4049	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4050	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4051	}
		4052	}
		4053
		4054	Now, whenever the main thread gets told to invoke pending watchers, it
		4055	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4056	thread to continue:
		4057
		4058	static void
		4059	real_invoke_pending (EV_P)
		4060	{
		4061	userdata *u = ev_userdata (EV_A);
		4062
		4063	pthread_mutex_lock (&u->lock);
		4064	ev_invoke_pending (EV_A);
		4065	pthread_cond_signal (&u->invoke_cv);
		4066	pthread_mutex_unlock (&u->lock);
		4067	}
		4068
		4069	Whenever you want to start/stop a watcher or do other modifications to an
		4070	event loop, you will now have to lock:
		4071
		4072	ev_timer timeout_watcher;
		4073	userdata *u = ev_userdata (EV_A);
		4074
		4075	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4076
		4077	pthread_mutex_lock (&u->lock);
		4078	ev_timer_start (EV_A_ &timeout_watcher);
		4079	ev_async_send (EV_A_ &u->async_w);
		4080	pthread_mutex_unlock (&u->lock);
		4081
		4082	Note that sending the C<ev_async> watcher is required because otherwise
		4083	an event loop currently blocking in the kernel will have no knowledge
		4084	about the newly added timer. By waking up the loop it will pick up any new
		4085	watchers in the next event loop iteration.
		4086
3671	=head3 COROUTINES	4087	=head3 COROUTINES
3672		4088
3673	Libev is very accommodating to coroutines ("cooperative threads"):	4089	Libev is very accommodating to coroutines ("cooperative threads"):
3674	libev fully supports nesting calls to its functions from different	4090	libev fully supports nesting calls to its functions from different
3675	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4091	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3676	different coroutines, and switch freely between both coroutines running the	4092	different coroutines, and switch freely between both coroutines running
3677	loop, as long as you don't confuse yourself). The only exception is that	4093	the loop, as long as you don't confuse yourself). The only exception is
3678	you must not do this from C<ev_periodic> reschedule callbacks.	4094	that you must not do this from C<ev_periodic> reschedule callbacks.
3679		4095
3680	Care has been taken to ensure that libev does not keep local state inside	4096	Care has been taken to ensure that libev does not keep local state inside
3681	C<ev_loop>, and other calls do not usually allow for coroutine switches as	4097	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3682	they do not call any callbacks.	4098	they do not call any callbacks.
3683		4099
…		…
3760	way (note also that glib is the slowest event library known to man).	4176	way (note also that glib is the slowest event library known to man).
3761		4177
3762	There is no supported compilation method available on windows except	4178	There is no supported compilation method available on windows except
3763	embedding it into other applications.	4179	embedding it into other applications.
3764		4180
		4181	Sensible signal handling is officially unsupported by Microsoft - libev
		4182	tries its best, but under most conditions, signals will simply not work.
		4183
3765	Not a libev limitation but worth mentioning: windows apparently doesn't	4184	Not a libev limitation but worth mentioning: windows apparently doesn't
3766	accept large writes: instead of resulting in a partial write, windows will	4185	accept large writes: instead of resulting in a partial write, windows will
3767	either accept everything or return C<ENOBUFS> if the buffer is too large,	4186	either accept everything or return C<ENOBUFS> if the buffer is too large,
3768	so make sure you only write small amounts into your sockets (less than a	4187	so make sure you only write small amounts into your sockets (less than a
3769	megabyte seems safe, but this apparently depends on the amount of memory	4188	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3773	the abysmal performance of winsockets, using a large number of sockets	4192	the abysmal performance of winsockets, using a large number of sockets
3774	is not recommended (and not reasonable). If your program needs to use	4193	is not recommended (and not reasonable). If your program needs to use
3775	more than a hundred or so sockets, then likely it needs to use a totally	4194	more than a hundred or so sockets, then likely it needs to use a totally
3776	different implementation for windows, as libev offers the POSIX readiness	4195	different implementation for windows, as libev offers the POSIX readiness
3777	notification model, which cannot be implemented efficiently on windows	4196	notification model, which cannot be implemented efficiently on windows
3778	(Microsoft monopoly games).	4197	(due to Microsoft monopoly games).
3779		4198
3780	A typical way to use libev under windows is to embed it (see the embedding	4199	A typical way to use libev under windows is to embed it (see the embedding
3781	section for details) and use the following F<evwrap.h> header file instead	4200	section for details) and use the following F<evwrap.h> header file instead
3782	of F<ev.h>:	4201	of F<ev.h>:
3783		4202
…		…
3819		4238
3820	Early versions of winsocket's select only supported waiting for a maximum	4239	Early versions of winsocket's select only supported waiting for a maximum
3821	of C<64> handles (probably owning to the fact that all windows kernels	4240	of C<64> handles (probably owning to the fact that all windows kernels
3822	can only wait for C<64> things at the same time internally; Microsoft	4241	can only wait for C<64> things at the same time internally; Microsoft
3823	recommends spawning a chain of threads and wait for 63 handles and the	4242	recommends spawning a chain of threads and wait for 63 handles and the
3824	previous thread in each. Great).	4243	previous thread in each. Sounds great!).
3825		4244
3826	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4245	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3827	to some high number (e.g. C<2048>) before compiling the winsocket select	4246	to some high number (e.g. C<2048>) before compiling the winsocket select
3828	call (which might be in libev or elsewhere, for example, perl does its own	4247	call (which might be in libev or elsewhere, for example, perl and many
3829	select emulation on windows).	4248	other interpreters do their own select emulation on windows).
3830		4249
3831	Another limit is the number of file descriptors in the Microsoft runtime	4250	Another limit is the number of file descriptors in the Microsoft runtime
3832	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4251	libraries, which by default is C<64> (there must be a hidden I<64>
3833	or something like this inside Microsoft). You can increase this by calling	4252	fetish or something like this inside Microsoft). You can increase this
3834	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4253	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3835	arbitrary limit), but is broken in many versions of the Microsoft runtime	4254	(another arbitrary limit), but is broken in many versions of the Microsoft
3836	libraries.
3837
3838	This might get you to about C<512> or C<2048> sockets (depending on	4255	runtime libraries. This might get you to about C<512> or C<2048> sockets
3839	windows version and/or the phase of the moon). To get more, you need to	4256	(depending on windows version and/or the phase of the moon). To get more,
3840	wrap all I/O functions and provide your own fd management, but the cost of	4257	you need to wrap all I/O functions and provide your own fd management, but
3841	calling select (O(n²)) will likely make this unworkable.	4258	the cost of calling select (O(n²)) will likely make this unworkable.
3842		4259
3843	=back	4260	=back
3844		4261
3845	=head2 PORTABILITY REQUIREMENTS	4262	=head2 PORTABILITY REQUIREMENTS
3846		4263
…		…
3889	=item C<double> must hold a time value in seconds with enough accuracy	4306	=item C<double> must hold a time value in seconds with enough accuracy
3890		4307
3891	The type C<double> is used to represent timestamps. It is required to	4308	The type C<double> is used to represent timestamps. It is required to
3892	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4309	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3893	enough for at least into the year 4000. This requirement is fulfilled by	4310	enough for at least into the year 4000. This requirement is fulfilled by
3894	implementations implementing IEEE 754 (basically all existing ones).	4311	implementations implementing IEEE 754, which is basically all existing
		4312	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4313	2200.
3895		4314
3896	=back	4315	=back
3897		4316
3898	If you know of other additional requirements drop me a note.	4317	If you know of other additional requirements drop me a note.
3899		4318
…		…
3967	involves iterating over all running async watchers or all signal numbers.	4386	involves iterating over all running async watchers or all signal numbers.
3968		4387
3969	=back	4388	=back
3970		4389
3971		4390
		4391	=head1 GLOSSARY
		4392
		4393	=over 4
		4394
		4395	=item active
		4396
		4397	A watcher is active as long as it has been started (has been attached to
		4398	an event loop) but not yet stopped (disassociated from the event loop).
		4399
		4400	=item application
		4401
		4402	In this document, an application is whatever is using libev.
		4403
		4404	=item callback
		4405
		4406	The address of a function that is called when some event has been
		4407	detected. Callbacks are being passed the event loop, the watcher that
		4408	received the event, and the actual event bitset.
		4409
		4410	=item callback invocation
		4411
		4412	The act of calling the callback associated with a watcher.
		4413
		4414	=item event
		4415
		4416	A change of state of some external event, such as data now being available
		4417	for reading on a file descriptor, time having passed or simply not having
		4418	any other events happening anymore.
		4419
		4420	In libev, events are represented as single bits (such as C<EV_READ> or
		4421	C<EV_TIMEOUT>).
		4422
		4423	=item event library
		4424
		4425	A software package implementing an event model and loop.
		4426
		4427	=item event loop
		4428
		4429	An entity that handles and processes external events and converts them
		4430	into callback invocations.
		4431
		4432	=item event model
		4433
		4434	The model used to describe how an event loop handles and processes
		4435	watchers and events.
		4436
		4437	=item pending
		4438
		4439	A watcher is pending as soon as the corresponding event has been detected,
		4440	and stops being pending as soon as the watcher will be invoked or its
		4441	pending status is explicitly cleared by the application.
		4442
		4443	A watcher can be pending, but not active. Stopping a watcher also clears
		4444	its pending status.
		4445
		4446	=item real time
		4447
		4448	The physical time that is observed. It is apparently strictly monotonic :)
		4449
		4450	=item wall-clock time
		4451
		4452	The time and date as shown on clocks. Unlike real time, it can actually
		4453	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4454	clock.
		4455
		4456	=item watcher
		4457
		4458	A data structure that describes interest in certain events. Watchers need
		4459	to be started (attached to an event loop) before they can receive events.
		4460
		4461	=item watcher invocation
		4462
		4463	The act of calling the callback associated with a watcher.
		4464
		4465	=back
		4466
3972	=head1 AUTHOR	4467	=head1 AUTHOR
3973		4468
3974	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	4469	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3975		4470

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Comparing libev/ev.pod (file contents): Revision 1.230 by root, Wed Apr 15 18:47:07 2009 UTC vs. Revision 1.256 by root, Tue Jul 14 20:31:21 2009 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.230 by root, Wed Apr 15 18:47:07 2009 UTC vs.
Revision 1.256 by root, Tue Jul 14 20:31:21 2009 UTC