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

Comparing libev/ev.pod (file contents):
Revision 1.232 by root, Thu Apr 16 06:17:26 2009 UTC vs.
Revision 1.253 by root, Tue Jul 14 18:33:48 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	=item ev_set_userdata (loop, void *data)
		896
		897	=item ev_userdata (loop)
		898
		899	Set and retrieve a single C<void *> associated with a loop. When
		900	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		901	C<0.>
		902
		903	These two functions can be used to associate arbitrary data with a loop,
		904	and are intended solely for the C<invoke_pending_cb>, C<release> and
		905	C<acquire> callbacks described above, but of course can be (ab-)used for
		906	any other purpose as well.
824		907
825	=item ev_loop_verify (loop)	908	=item ev_loop_verify (loop)
826		909
827	This function only does something when C<EV_VERIFY> support has been	910	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	911	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>	1166	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1084	(default: C<-2>). Pending watchers with higher priority will be invoked	1167	(default: C<-2>). Pending watchers with higher priority will be invoked
1085	before watchers with lower priority, but priority will not keep watchers	1168	before watchers with lower priority, but priority will not keep watchers
1086	from being executed (except for C<ev_idle> watchers).	1169	from being executed (except for C<ev_idle> watchers).
1087		1170
1088	See L<
1089
1090	This means that priorities are I<only> used for ordering callback
1091	invocation after new events have been received. This is useful, for
1092	example, to reduce latency after idling, or more often, to bind two
1093	watchers on the same event and make sure one is called first.
1094
1095	If you need to suppress invocation when higher priority events are pending	1171	If you need to suppress invocation when higher priority events are pending
1096	you need to look at C<ev_idle> watchers, which provide this functionality.	1172	you need to look at C<ev_idle> watchers, which provide this functionality.
1097		1173
1098	You I<must not> change the priority of a watcher as long as it is active or	1174	You I<must not> change the priority of a watcher as long as it is active or
1099	pending.	1175	pending.
1100
1101	The default priority used by watchers when no priority has been set is
1102	always C<0>, which is supposed to not be too high and not be too low :).
1103		1176
1104	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1177	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1105	fine, as long as you do not mind that the priority value you query might	1178	fine, as long as you do not mind that the priority value you query might
1106	or might not have been clamped to the valid range.	1179	or might not have been clamped to the valid range.
		1180
		1181	The default priority used by watchers when no priority has been set is
		1182	always C<0>, which is supposed to not be too high and not be too low :).
		1183
		1184	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1185	priorities.
1107		1186
1108	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1187	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1109		1188
1110	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1189	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1111	C<loop> nor C<revents> need to be valid as long as the watcher callback	1190	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1176	#include <stddef.h>	1255	#include <stddef.h>
1177		1256
1178	static void	1257	static void
1179	t1_cb (EV_P_ ev_timer *w, int revents)	1258	t1_cb (EV_P_ ev_timer *w, int revents)
1180	{	1259	{
1181	struct my_biggy big = (struct my_biggy *	1260	struct my_biggy big = (struct my_biggy *)
1182	(((char *)w) - offsetof (struct my_biggy, t1));	1261	(((char *)w) - offsetof (struct my_biggy, t1));
1183	}	1262	}
1184		1263
1185	static void	1264	static void
1186	t2_cb (EV_P_ ev_timer *w, int revents)	1265	t2_cb (EV_P_ ev_timer *w, int revents)
1187	{	1266	{
1188	struct my_biggy big = (struct my_biggy *	1267	struct my_biggy big = (struct my_biggy *)
1189	(((char *)w) - offsetof (struct my_biggy, t2));	1268	(((char *)w) - offsetof (struct my_biggy, t2));
1190	}	1269	}
		1270
		1271	=head2 WATCHER PRIORITY MODELS
		1272
		1273	Many event loops support I<watcher priorities>, which are usually small
		1274	integers that influence the ordering of event callback invocation
		1275	between watchers in some way, all else being equal.
		1276
		1277	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1278	description for the more technical details such as the actual priority
		1279	range.
		1280
		1281	There are two common ways how these these priorities are being interpreted
		1282	by event loops:
		1283
		1284	In the more common lock-out model, higher priorities "lock out" invocation
		1285	of lower priority watchers, which means as long as higher priority
		1286	watchers receive events, lower priority watchers are not being invoked.
		1287
		1288	The less common only-for-ordering model uses priorities solely to order
		1289	callback invocation within a single event loop iteration: Higher priority
		1290	watchers are invoked before lower priority ones, but they all get invoked
		1291	before polling for new events.
		1292
		1293	Libev uses the second (only-for-ordering) model for all its watchers
		1294	except for idle watchers (which use the lock-out model).
		1295
		1296	The rationale behind this is that implementing the lock-out model for
		1297	watchers is not well supported by most kernel interfaces, and most event
		1298	libraries will just poll for the same events again and again as long as
		1299	their callbacks have not been executed, which is very inefficient in the
		1300	common case of one high-priority watcher locking out a mass of lower
		1301	priority ones.
		1302
		1303	Static (ordering) priorities are most useful when you have two or more
		1304	watchers handling the same resource: a typical usage example is having an
		1305	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1306	timeouts. Under load, data might be received while the program handles
		1307	other jobs, but since timers normally get invoked first, the timeout
		1308	handler will be executed before checking for data. In that case, giving
		1309	the timer a lower priority than the I/O watcher ensures that I/O will be
		1310	handled first even under adverse conditions (which is usually, but not
		1311	always, what you want).
		1312
		1313	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1314	will only be executed when no same or higher priority watchers have
		1315	received events, they can be used to implement the "lock-out" model when
		1316	required.
		1317
		1318	For example, to emulate how many other event libraries handle priorities,
		1319	you can associate an C<ev_idle> watcher to each such watcher, and in
		1320	the normal watcher callback, you just start the idle watcher. The real
		1321	processing is done in the idle watcher callback. This causes libev to
		1322	continously poll and process kernel event data for the watcher, but when
		1323	the lock-out case is known to be rare (which in turn is rare :), this is
		1324	workable.
		1325
		1326	Usually, however, the lock-out model implemented that way will perform
		1327	miserably under the type of load it was designed to handle. In that case,
		1328	it might be preferable to stop the real watcher before starting the
		1329	idle watcher, so the kernel will not have to process the event in case
		1330	the actual processing will be delayed for considerable time.
		1331
		1332	Here is an example of an I/O watcher that should run at a strictly lower
		1333	priority than the default, and which should only process data when no
		1334	other events are pending:
		1335
		1336	ev_idle idle; // actual processing watcher
		1337	ev_io io; // actual event watcher
		1338
		1339	static void
		1340	io_cb (EV_P_ ev_io *w, int revents)
		1341	{
		1342	// stop the I/O watcher, we received the event, but
		1343	// are not yet ready to handle it.
		1344	ev_io_stop (EV_A_ w);
		1345
		1346	// start the idle watcher to ahndle the actual event.
		1347	// it will not be executed as long as other watchers
		1348	// with the default priority are receiving events.
		1349	ev_idle_start (EV_A_ &idle);
		1350	}
		1351
		1352	static void
		1353	idle_cb (EV_P_ ev_idle *w, int revents)
		1354	{
		1355	// actual processing
		1356	read (STDIN_FILENO, ...);
		1357
		1358	// have to start the I/O watcher again, as
		1359	// we have handled the event
		1360	ev_io_start (EV_P_ &io);
		1361	}
		1362
		1363	// initialisation
		1364	ev_idle_init (&idle, idle_cb);
		1365	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1366	ev_io_start (EV_DEFAULT_ &io);
		1367
		1368	In the "real" world, it might also be beneficial to start a timer, so that
		1369	low-priority connections can not be locked out forever under load. This
		1370	enables your program to keep a lower latency for important connections
		1371	during short periods of high load, while not completely locking out less
		1372	important ones.
1191		1373
1192		1374
1193	=head1 WATCHER TYPES	1375	=head1 WATCHER TYPES
1194		1376
1195	This section describes each watcher in detail, but will not repeat	1377	This section describes each watcher in detail, but will not repeat
…		…
1221	descriptors to non-blocking mode is also usually a good idea (but not	1403	descriptors to non-blocking mode is also usually a good idea (but not
1222	required if you know what you are doing).	1404	required if you know what you are doing).
1223		1405
1224	If you cannot use non-blocking mode, then force the use of a	1406	If you cannot use non-blocking mode, then force the use of a
1225	known-to-be-good backend (at the time of this writing, this includes only	1407	known-to-be-good backend (at the time of this writing, this includes only
1226	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1408	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1409	descriptors for which non-blocking operation makes no sense (such as
		1410	files) - libev doesn't guarentee any specific behaviour in that case.
1227		1411
1228	Another thing you have to watch out for is that it is quite easy to	1412	Another thing you have to watch out for is that it is quite easy to
1229	receive "spurious" readiness notifications, that is your callback might	1413	receive "spurious" readiness notifications, that is your callback might
1230	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1414	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1231	because there is no data. Not only are some backends known to create a	1415	because there is no data. Not only are some backends known to create a
…		…
1352	year, it will still time out after (roughly) one hour. "Roughly" because	1536	year, it will still time out after (roughly) one hour. "Roughly" because
1353	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1537	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1354	monotonic clock option helps a lot here).	1538	monotonic clock option helps a lot here).
1355		1539
1356	The callback is guaranteed to be invoked only I<after> its timeout has	1540	The callback is guaranteed to be invoked only I<after> its timeout has
1357	passed. If multiple timers become ready during the same loop iteration	1541	passed (not I<at>, so on systems with very low-resolution clocks this
1358	then the ones with earlier time-out values are invoked before ones with	1542	might introduce a small delay). If multiple timers become ready during the
1359	later time-out values (but this is no longer true when a callback calls	1543	same loop iteration then the ones with earlier time-out values are invoked
1360	C<ev_loop> recursively).	1544	before ones of the same priority with later time-out values (but this is
		1545	no longer true when a callback calls C<ev_loop> recursively).
1361		1546
1362	=head3 Be smart about timeouts	1547	=head3 Be smart about timeouts
1363		1548
1364	Many real-world problems involve some kind of timeout, usually for error	1549	Many real-world problems involve some kind of timeout, usually for error
1365	recovery. A typical example is an HTTP request - if the other side hangs,	1550	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1409	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>	1594	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
1410	member and C<ev_timer_again>.	1595	member and C<ev_timer_again>.
1411		1596
1412	At start:	1597	At start:
1413		1598
1414	ev_timer_init (timer, callback);	1599	ev_init (timer, callback);
1415	timer->repeat = 60.;	1600	timer->repeat = 60.;
1416	ev_timer_again (loop, timer);	1601	ev_timer_again (loop, timer);
1417		1602
1418	Each time there is some activity:	1603	Each time there is some activity:
1419		1604
…		…
1481		1666
1482	To start the timer, simply initialise the watcher and set C<last_activity>	1667	To start the timer, simply initialise the watcher and set C<last_activity>
1483	to the current time (meaning we just have some activity :), then call the	1668	to the current time (meaning we just have some activity :), then call the
1484	callback, which will "do the right thing" and start the timer:	1669	callback, which will "do the right thing" and start the timer:
1485		1670
1486	ev_timer_init (timer, callback);	1671	ev_init (timer, callback);
1487	last_activity = ev_now (loop);	1672	last_activity = ev_now (loop);
1488	callback (loop, timer, EV_TIMEOUT);	1673	callback (loop, timer, EV_TIMEOUT);
1489		1674
1490	And when there is some activity, simply store the current time in	1675	And when there is some activity, simply store the current time in
1491	C<last_activity>, no libev calls at all:	1676	C<last_activity>, no libev calls at all:
…		…
1888	some child status changes (most typically when a child of yours dies or	2073	some child status changes (most typically when a child of yours dies or
1889	exits). It is permissible to install a child watcher I<after> the child	2074	exits). It is permissible to install a child watcher I<after> the child
1890	has been forked (which implies it might have already exited), as long	2075	has been forked (which implies it might have already exited), as long
1891	as the event loop isn't entered (or is continued from a watcher), i.e.,	2076	as the event loop isn't entered (or is continued from a watcher), i.e.,
1892	forking and then immediately registering a watcher for the child is fine,	2077	forking and then immediately registering a watcher for the child is fine,
1893	but forking and registering a watcher a few event loop iterations later is	2078	but forking and registering a watcher a few event loop iterations later or
1894	not.	2079	in the next callback invocation is not.
1895		2080
1896	Only the default event loop is capable of handling signals, and therefore	2081	Only the default event loop is capable of handling signals, and therefore
1897	you can only register child watchers in the default event loop.	2082	you can only register child watchers in the default event loop.
		2083
		2084	Due to some design glitches inside libev, child watchers will always be
		2085	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2086	libev)
1898		2087
1899	=head3 Process Interaction	2088	=head3 Process Interaction
1900		2089
1901	Libev grabs C<SIGCHLD> as soon as the default event loop is	2090	Libev grabs C<SIGCHLD> as soon as the default event loop is
1902	initialised. This is necessary to guarantee proper behaviour even if	2091	initialised. This is necessary to guarantee proper behaviour even if
…		…
2254	// no longer anything immediate to do.	2443	// no longer anything immediate to do.
2255	}	2444	}
2256		2445
2257	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2446	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2258	ev_idle_init (idle_watcher, idle_cb);	2447	ev_idle_init (idle_watcher, idle_cb);
2259	ev_idle_start (loop, idle_cb);	2448	ev_idle_start (loop, idle_watcher);
2260		2449
2261		2450
2262	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2451	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2263		2452
2264	Prepare and check watchers are usually (but not always) used in pairs:	2453	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2357	struct pollfd fds [nfd];	2546	struct pollfd fds [nfd];
2358	// actual code will need to loop here and realloc etc.	2547	// actual code will need to loop here and realloc etc.
2359	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2548	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2360		2549
2361	/* the callback is illegal, but won't be called as we stop during check */	2550	/* the callback is illegal, but won't be called as we stop during check */
2362	ev_timer_init (&tw, 0, timeout * 1e-3);	2551	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2363	ev_timer_start (loop, &tw);	2552	ev_timer_start (loop, &tw);
2364		2553
2365	// create one ev_io per pollfd	2554	// create one ev_io per pollfd
2366	for (int i = 0; i < nfd; ++i)	2555	for (int i = 0; i < nfd; ++i)
2367	{	2556	{
…		…
2597	event loop blocks next and before C<ev_check> watchers are being called,	2786	event loop blocks next and before C<ev_check> watchers are being called,
2598	and only in the child after the fork. If whoever good citizen calling	2787	and only in the child after the fork. If whoever good citizen calling
2599	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2788	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2600	handlers will be invoked, too, of course.	2789	handlers will be invoked, too, of course.
2601		2790
		2791	=head3 The special problem of life after fork - how is it possible?
		2792
		2793	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2794	up/change the process environment, followed by a call to C<exec()>. This
		2795	sequence should be handled by libev without any problems.
		2796
		2797	This changes when the application actually wants to do event handling
		2798	in the child, or both parent in child, in effect "continuing" after the
		2799	fork.
		2800
		2801	The default mode of operation (for libev, with application help to detect
		2802	forks) is to duplicate all the state in the child, as would be expected
		2803	when I<either> the parent I<or> the child process continues.
		2804
		2805	When both processes want to continue using libev, then this is usually the
		2806	wrong result. In that case, usually one process (typically the parent) is
		2807	supposed to continue with all watchers in place as before, while the other
		2808	process typically wants to start fresh, i.e. without any active watchers.
		2809
		2810	The cleanest and most efficient way to achieve that with libev is to
		2811	simply create a new event loop, which of course will be "empty", and
		2812	use that for new watchers. This has the advantage of not touching more
		2813	memory than necessary, and thus avoiding the copy-on-write, and the
		2814	disadvantage of having to use multiple event loops (which do not support
		2815	signal watchers).
		2816
		2817	When this is not possible, or you want to use the default loop for
		2818	other reasons, then in the process that wants to start "fresh", call
		2819	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2820	the default loop will "orphan" (not stop) all registered watchers, so you
		2821	have to be careful not to execute code that modifies those watchers. Note
		2822	also that in that case, you have to re-register any signal watchers.
		2823
2602	=head3 Watcher-Specific Functions and Data Members	2824	=head3 Watcher-Specific Functions and Data Members
2603		2825
2604	=over 4	2826	=over 4
2605		2827
2606	=item ev_fork_init (ev_signal *, callback)	2828	=item ev_fork_init (ev_signal *, callback)
…		…
3496	defined to be C<0>, then they are not.	3718	defined to be C<0>, then they are not.
3497		3719
3498	=item EV_MINIMAL	3720	=item EV_MINIMAL
3499		3721
3500	If you need to shave off some kilobytes of code at the expense of some	3722	If you need to shave off some kilobytes of code at the expense of some
3501	speed, define this symbol to C<1>. Currently this is used to override some	3723	speed (but with the full API), define this symbol to C<1>. Currently this
3502	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3724	is used to override some inlining decisions, saves roughly 30% code size
3503	much smaller 2-heap for timer management over the default 4-heap.	3725	on amd64. It also selects a much smaller 2-heap for timer management over
		3726	the default 4-heap.
		3727
		3728	You can save even more by disabling watcher types you do not need
		3729	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3730	(C<-DNDEBUG>) will usually reduce code size a lot.
		3731
		3732	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3733	provide a bare-bones event library. See C<ev.h> for details on what parts
		3734	of the API are still available, and do not complain if this subset changes
		3735	over time.
3504		3736
3505	=item EV_PID_HASHSIZE	3737	=item EV_PID_HASHSIZE
3506		3738
3507	C<ev_child> watchers use a small hash table to distribute workload by	3739	C<ev_child> watchers use a small hash table to distribute workload by
3508	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3740	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3694	default loop and triggering an C<ev_async> watcher from the default loop	3926	default loop and triggering an C<ev_async> watcher from the default loop
3695	watcher callback into the event loop interested in the signal.	3927	watcher callback into the event loop interested in the signal.
3696		3928
3697	=back	3929	=back
3698		3930
		3931	=head4 THREAD LOCKING EXAMPLE
		3932
3699	=head3 COROUTINES	3933	=head3 COROUTINES
3700		3934
3701	Libev is very accommodating to coroutines ("cooperative threads"):	3935	Libev is very accommodating to coroutines ("cooperative threads"):
3702	libev fully supports nesting calls to its functions from different	3936	libev fully supports nesting calls to its functions from different
3703	coroutines (e.g. you can call C<ev_loop> on the same loop from two	3937	coroutines (e.g. you can call C<ev_loop> on the same loop from two
…		…
3788	way (note also that glib is the slowest event library known to man).	4022	way (note also that glib is the slowest event library known to man).
3789		4023
3790	There is no supported compilation method available on windows except	4024	There is no supported compilation method available on windows except
3791	embedding it into other applications.	4025	embedding it into other applications.
3792		4026
		4027	Sensible signal handling is officially unsupported by Microsoft - libev
		4028	tries its best, but under most conditions, signals will simply not work.
		4029
3793	Not a libev limitation but worth mentioning: windows apparently doesn't	4030	Not a libev limitation but worth mentioning: windows apparently doesn't
3794	accept large writes: instead of resulting in a partial write, windows will	4031	accept large writes: instead of resulting in a partial write, windows will
3795	either accept everything or return C<ENOBUFS> if the buffer is too large,	4032	either accept everything or return C<ENOBUFS> if the buffer is too large,
3796	so make sure you only write small amounts into your sockets (less than a	4033	so make sure you only write small amounts into your sockets (less than a
3797	megabyte seems safe, but this apparently depends on the amount of memory	4034	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3801	the abysmal performance of winsockets, using a large number of sockets	4038	the abysmal performance of winsockets, using a large number of sockets
3802	is not recommended (and not reasonable). If your program needs to use	4039	is not recommended (and not reasonable). If your program needs to use
3803	more than a hundred or so sockets, then likely it needs to use a totally	4040	more than a hundred or so sockets, then likely it needs to use a totally
3804	different implementation for windows, as libev offers the POSIX readiness	4041	different implementation for windows, as libev offers the POSIX readiness
3805	notification model, which cannot be implemented efficiently on windows	4042	notification model, which cannot be implemented efficiently on windows
3806	(Microsoft monopoly games).	4043	(due to Microsoft monopoly games).
3807		4044
3808	A typical way to use libev under windows is to embed it (see the embedding	4045	A typical way to use libev under windows is to embed it (see the embedding
3809	section for details) and use the following F<evwrap.h> header file instead	4046	section for details) and use the following F<evwrap.h> header file instead
3810	of F<ev.h>:	4047	of F<ev.h>:
3811		4048
…		…
3847		4084
3848	Early versions of winsocket's select only supported waiting for a maximum	4085	Early versions of winsocket's select only supported waiting for a maximum
3849	of C<64> handles (probably owning to the fact that all windows kernels	4086	of C<64> handles (probably owning to the fact that all windows kernels
3850	can only wait for C<64> things at the same time internally; Microsoft	4087	can only wait for C<64> things at the same time internally; Microsoft
3851	recommends spawning a chain of threads and wait for 63 handles and the	4088	recommends spawning a chain of threads and wait for 63 handles and the
3852	previous thread in each. Great).	4089	previous thread in each. Sounds great!).
3853		4090
3854	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4091	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3855	to some high number (e.g. C<2048>) before compiling the winsocket select	4092	to some high number (e.g. C<2048>) before compiling the winsocket select
3856	call (which might be in libev or elsewhere, for example, perl does its own	4093	call (which might be in libev or elsewhere, for example, perl and many
3857	select emulation on windows).	4094	other interpreters do their own select emulation on windows).
3858		4095
3859	Another limit is the number of file descriptors in the Microsoft runtime	4096	Another limit is the number of file descriptors in the Microsoft runtime
3860	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4097	libraries, which by default is C<64> (there must be a hidden I<64>
3861	or something like this inside Microsoft). You can increase this by calling	4098	fetish or something like this inside Microsoft). You can increase this
3862	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4099	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3863	arbitrary limit), but is broken in many versions of the Microsoft runtime	4100	(another arbitrary limit), but is broken in many versions of the Microsoft
3864	libraries.
3865
3866	This might get you to about C<512> or C<2048> sockets (depending on	4101	runtime libraries. This might get you to about C<512> or C<2048> sockets
3867	windows version and/or the phase of the moon). To get more, you need to	4102	(depending on windows version and/or the phase of the moon). To get more,
3868	wrap all I/O functions and provide your own fd management, but the cost of	4103	you need to wrap all I/O functions and provide your own fd management, but
3869	calling select (O(n²)) will likely make this unworkable.	4104	the cost of calling select (O(n²)) will likely make this unworkable.
3870		4105
3871	=back	4106	=back
3872		4107
3873	=head2 PORTABILITY REQUIREMENTS	4108	=head2 PORTABILITY REQUIREMENTS
3874		4109
…		…
3917	=item C<double> must hold a time value in seconds with enough accuracy	4152	=item C<double> must hold a time value in seconds with enough accuracy
3918		4153
3919	The type C<double> is used to represent timestamps. It is required to	4154	The type C<double> is used to represent timestamps. It is required to
3920	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4155	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3921	enough for at least into the year 4000. This requirement is fulfilled by	4156	enough for at least into the year 4000. This requirement is fulfilled by
3922	implementations implementing IEEE 754 (basically all existing ones).	4157	implementations implementing IEEE 754, which is basically all existing
		4158	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4159	2200.
3923		4160
3924	=back	4161	=back
3925		4162
3926	If you know of other additional requirements drop me a note.	4163	If you know of other additional requirements drop me a note.
3927		4164
…		…
3995	involves iterating over all running async watchers or all signal numbers.	4232	involves iterating over all running async watchers or all signal numbers.
3996		4233
3997	=back	4234	=back
3998		4235
3999		4236
		4237	=head1 GLOSSARY
		4238
		4239	=over 4
		4240
		4241	=item active
		4242
		4243	A watcher is active as long as it has been started (has been attached to
		4244	an event loop) but not yet stopped (disassociated from the event loop).
		4245
		4246	=item application
		4247
		4248	In this document, an application is whatever is using libev.
		4249
		4250	=item callback
		4251
		4252	The address of a function that is called when some event has been
		4253	detected. Callbacks are being passed the event loop, the watcher that
		4254	received the event, and the actual event bitset.
		4255
		4256	=item callback invocation
		4257
		4258	The act of calling the callback associated with a watcher.
		4259
		4260	=item event
		4261
		4262	A change of state of some external event, such as data now being available
		4263	for reading on a file descriptor, time having passed or simply not having
		4264	any other events happening anymore.
		4265
		4266	In libev, events are represented as single bits (such as C<EV_READ> or
		4267	C<EV_TIMEOUT>).
		4268
		4269	=item event library
		4270
		4271	A software package implementing an event model and loop.
		4272
		4273	=item event loop
		4274
		4275	An entity that handles and processes external events and converts them
		4276	into callback invocations.
		4277
		4278	=item event model
		4279
		4280	The model used to describe how an event loop handles and processes
		4281	watchers and events.
		4282
		4283	=item pending
		4284
		4285	A watcher is pending as soon as the corresponding event has been detected,
		4286	and stops being pending as soon as the watcher will be invoked or its
		4287	pending status is explicitly cleared by the application.
		4288
		4289	A watcher can be pending, but not active. Stopping a watcher also clears
		4290	its pending status.
		4291
		4292	=item real time
		4293
		4294	The physical time that is observed. It is apparently strictly monotonic :)
		4295
		4296	=item wall-clock time
		4297
		4298	The time and date as shown on clocks. Unlike real time, it can actually
		4299	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4300	clock.
		4301
		4302	=item watcher
		4303
		4304	A data structure that describes interest in certain events. Watchers need
		4305	to be started (attached to an event loop) before they can receive events.
		4306
		4307	=item watcher invocation
		4308
		4309	The act of calling the callback associated with a watcher.
		4310
		4311	=back
		4312
4000	=head1 AUTHOR	4313	=head1 AUTHOR
4001		4314
4002	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	4315	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
4003		4316

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing libev/ev.pod (file contents): Revision 1.232 by root, Thu Apr 16 06:17:26 2009 UTC vs. Revision 1.253 by root, Tue Jul 14 18:33:48 2009 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.232 by root, Thu Apr 16 06:17:26 2009 UTC vs.
Revision 1.253 by root, Tue Jul 14 18:33:48 2009 UTC