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

Comparing libev/ev.pod (file contents):
Revision 1.234 by root, Thu Apr 16 07:49:23 2009 UTC vs.
Revision 1.260 by root, Sun Jul 19 21:18:03 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
…		…
349	forget about forgetting to tell libev about forking) when you use this	361	forget about forgetting to tell libev about forking) when you use this
350	flag.	362	flag.
351		363
352	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
353	environment variable.	365	environment variable.
		366
		367	=item C<EVFLAG_NOINOTIFY>
		368
		369	When this flag is specified, then libev will not attempt to use the
		370	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		371	testing, this flag can be useful to conserve inotify file descriptors, as
		372	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		373
		374	=item C<EVFLAG_NOSIGNALFD>
		375
		376	When this flag is specified, then libev will not attempt to use the
		377	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		378	probably only useful to work around any bugs in libev. Consequently, this
		379	flag might go away once the signalfd functionality is considered stable,
		380	so it's useful mostly in environment variables and not in program code.
354		381
355	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	382	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
356		383
357	This is your standard select(2) backend. Not I<completely> standard, as	384	This is your standard select(2) backend. Not I<completely> standard, as
358	libev tries to roll its own fd_set with no limits on the number of fds,	385	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
506		533
507	It is definitely not recommended to use this flag.	534	It is definitely not recommended to use this flag.
508		535
509	=back	536	=back
510		537
511	If one or more of these are or'ed into the flags value, then only these	538	If one or more of the backend flags are or'ed into the flags value,
512	backends will be tried (in the reverse order as listed here). If none are	539	then only these backends will be tried (in the reverse order as listed
513	specified, all backends in C<ev_recommended_backends ()> will be tried.	540	here). If none are specified, all backends in C<ev_recommended_backends
		541	()> will be tried.
514		542
515	Example: This is the most typical usage.	543	Example: This is the most typical usage.
516		544
517	if (!ev_default_loop (0))	545	if (!ev_default_loop (0))
518	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	546	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
…		…
609		637
610	This value can sometimes be useful as a generation counter of sorts (it	638	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	639	"ticks" the number of loop iterations), as it roughly corresponds with
612	C<ev_prepare> and C<ev_check> calls.	640	C<ev_prepare> and C<ev_check> calls.
613		641
		642	=item unsigned int ev_loop_depth (loop)
		643
		644	Returns the number of times C<ev_loop> was entered minus the number of
		645	times C<ev_loop> was exited, in other words, the recursion depth.
		646
		647	Outside C<ev_loop>, this number is zero. In a callback, this number is
		648	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		649	in which case it is higher.
		650
		651	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		652	etc.), doesn't count as exit.
		653
614	=item unsigned int ev_backend (loop)	654	=item unsigned int ev_backend (loop)
615		655
616	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	656	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
617	use.	657	use.
618		658
…		…
632		672
633	This function is rarely useful, but when some event callback runs for a	673	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	674	very long time without entering the event loop, updating libev's idea of
635	the current time is a good idea.	675	the current time is a good idea.
636		676
637	See also "The special problem of time updates" in the C<ev_timer> section.	677	See also L<The special problem of time updates> in the C<ev_timer> section.
638		678
639	=item ev_suspend (loop)	679	=item ev_suspend (loop)
640		680
641	=item ev_resume (loop)	681	=item ev_resume (loop)
642		682
…		…
799		839
800	By setting a higher I<io collect interval> you allow libev to spend more	840	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,	841	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	842	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	843	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.	844	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		845	sleep time ensures that libev will not poll for I/O events more often then
		846	once per this interval, on average.
805		847
806	Likewise, by setting a higher I<timeout collect interval> you allow libev	848	Likewise, by setting a higher I<timeout collect interval> you allow libev
807	to spend more time collecting timeouts, at the expense of increased	849	to spend more time collecting timeouts, at the expense of increased
808	latency/jitter/inexactness (the watcher callback will be called	850	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	851	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
811		853
812	Many (busy) programs can usually benefit by setting the I/O collect	854	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	855	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	856	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>,	857	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.	858	as this approaches the timing granularity of most systems. Note that if
		859	you do transactions with the outside world and you can't increase the
		860	parallelity, then this setting will limit your transaction rate (if you
		861	need to poll once per transaction and the I/O collect interval is 0.01,
		862	then you can't do more than 100 transations per second).
817		863
818	Setting the I<timeout collect interval> can improve the opportunity for	864	Setting the I<timeout collect interval> can improve the opportunity for
819	saving power, as the program will "bundle" timer callback invocations that	865	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	866	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	867	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	868	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
823	they fire on, say, one-second boundaries only.	869	they fire on, say, one-second boundaries only.
		870
		871	Example: we only need 0.1s timeout granularity, and we wish not to poll
		872	more often than 100 times per second:
		873
		874	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		875	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		876
		877	=item ev_invoke_pending (loop)
		878
		879	This call will simply invoke all pending watchers while resetting their
		880	pending state. Normally, C<ev_loop> does this automatically when required,
		881	but when overriding the invoke callback this call comes handy.
		882
		883	=item int ev_pending_count (loop)
		884
		885	Returns the number of pending watchers - zero indicates that no watchers
		886	are pending.
		887
		888	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		889
		890	This overrides the invoke pending functionality of the loop: Instead of
		891	invoking all pending watchers when there are any, C<ev_loop> will call
		892	this callback instead. This is useful, for example, when you want to
		893	invoke the actual watchers inside another context (another thread etc.).
		894
		895	If you want to reset the callback, use C<ev_invoke_pending> as new
		896	callback.
		897
		898	=item ev_set_loop_release_cb (loop, void (release)(EV_P), void (acquire)(EV_P))
		899
		900	Sometimes you want to share the same loop between multiple threads. This
		901	can be done relatively simply by putting mutex_lock/unlock calls around
		902	each call to a libev function.
		903
		904	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		905	wait for it to return. One way around this is to wake up the loop via
		906	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		907	and I<acquire> callbacks on the loop.
		908
		909	When set, then C<release> will be called just before the thread is
		910	suspended waiting for new events, and C<acquire> is called just
		911	afterwards.
		912
		913	Ideally, C<release> will just call your mutex_unlock function, and
		914	C<acquire> will just call the mutex_lock function again.
		915
		916	While event loop modifications are allowed between invocations of
		917	C<release> and C<acquire> (that's their only purpose after all), no
		918	modifications done will affect the event loop, i.e. adding watchers will
		919	have no effect on the set of file descriptors being watched, or the time
		920	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		921	to take note of any changes you made.
		922
		923	In theory, threads executing C<ev_loop> will be async-cancel safe between
		924	invocations of C<release> and C<acquire>.
		925
		926	See also the locking example in the C<THREADS> section later in this
		927	document.
		928
		929	=item ev_set_userdata (loop, void *data)
		930
		931	=item ev_userdata (loop)
		932
		933	Set and retrieve a single C<void *> associated with a loop. When
		934	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		935	C<0.>
		936
		937	These two functions can be used to associate arbitrary data with a loop,
		938	and are intended solely for the C<invoke_pending_cb>, C<release> and
		939	C<acquire> callbacks described above, but of course can be (ab-)used for
		940	any other purpose as well.
824		941
825	=item ev_loop_verify (loop)	942	=item ev_loop_verify (loop)
826		943
827	This function only does something when C<EV_VERIFY> support has been	944	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	945	compiled in, which is the default for non-minimal builds. It tries to go
…		…
1096	or might not have been clamped to the valid range.	1213	or might not have been clamped to the valid range.
1097		1214
1098	The default priority used by watchers when no priority has been set is	1215	The default priority used by watchers when no priority has been set is
1099	always C<0>, which is supposed to not be too high and not be too low :).	1216	always C<0>, which is supposed to not be too high and not be too low :).
1100		1217
1101	See L<WATCHER PRIORITIES>, below, for a more thorough treatment of	1218	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1102	priorities.	1219	priorities.
1103		1220
1104	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1221	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1105		1222
1106	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1223	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1172	#include <stddef.h>	1289	#include <stddef.h>
1173		1290
1174	static void	1291	static void
1175	t1_cb (EV_P_ ev_timer *w, int revents)	1292	t1_cb (EV_P_ ev_timer *w, int revents)
1176	{	1293	{
1177	struct my_biggy big = (struct my_biggy *	1294	struct my_biggy big = (struct my_biggy *)
1178	(((char *)w) - offsetof (struct my_biggy, t1));	1295	(((char *)w) - offsetof (struct my_biggy, t1));
1179	}	1296	}
1180		1297
1181	static void	1298	static void
1182	t2_cb (EV_P_ ev_timer *w, int revents)	1299	t2_cb (EV_P_ ev_timer *w, int revents)
1183	{	1300	{
1184	struct my_biggy big = (struct my_biggy *	1301	struct my_biggy big = (struct my_biggy *)
1185	(((char *)w) - offsetof (struct my_biggy, t2));	1302	(((char *)w) - offsetof (struct my_biggy, t2));
1186	}	1303	}
1187		1304
1188	=head2 WATCHER PRIORITY MODELS	1305	=head2 WATCHER PRIORITY MODELS
1189		1306
…		…
1265	// with the default priority are receiving events.	1382	// with the default priority are receiving events.
1266	ev_idle_start (EV_A_ &idle);	1383	ev_idle_start (EV_A_ &idle);
1267	}	1384	}
1268		1385
1269	static void	1386	static void
1270	idle-cb (EV_P_ ev_idle *w, int revents)	1387	idle_cb (EV_P_ ev_idle *w, int revents)
1271	{	1388	{
1272	// actual processing	1389	// actual processing
1273	read (STDIN_FILENO, ...);	1390	read (STDIN_FILENO, ...);
1274		1391
1275	// have to start the I/O watcher again, as	1392	// have to start the I/O watcher again, as
…		…
1320	descriptors to non-blocking mode is also usually a good idea (but not	1437	descriptors to non-blocking mode is also usually a good idea (but not
1321	required if you know what you are doing).	1438	required if you know what you are doing).
1322		1439
1323	If you cannot use non-blocking mode, then force the use of a	1440	If you cannot use non-blocking mode, then force the use of a
1324	known-to-be-good backend (at the time of this writing, this includes only	1441	known-to-be-good backend (at the time of this writing, this includes only
1325	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1442	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1443	descriptors for which non-blocking operation makes no sense (such as
		1444	files) - libev doesn't guarentee any specific behaviour in that case.
1326		1445
1327	Another thing you have to watch out for is that it is quite easy to	1446	Another thing you have to watch out for is that it is quite easy to
1328	receive "spurious" readiness notifications, that is your callback might	1447	receive "spurious" readiness notifications, that is your callback might
1329	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1448	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1330	because there is no data. Not only are some backends known to create a	1449	because there is no data. Not only are some backends known to create a
…		…
1451	year, it will still time out after (roughly) one hour. "Roughly" because	1570	year, it will still time out after (roughly) one hour. "Roughly" because
1452	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1571	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1453	monotonic clock option helps a lot here).	1572	monotonic clock option helps a lot here).
1454		1573
1455	The callback is guaranteed to be invoked only I<after> its timeout has	1574	The callback is guaranteed to be invoked only I<after> its timeout has
1456	passed. If multiple timers become ready during the same loop iteration	1575	passed (not I<at>, so on systems with very low-resolution clocks this
1457	then the ones with earlier time-out values are invoked before ones with	1576	might introduce a small delay). If multiple timers become ready during the
1458	later time-out values (but this is no longer true when a callback calls	1577	same loop iteration then the ones with earlier time-out values are invoked
1459	C<ev_loop> recursively).	1578	before ones of the same priority with later time-out values (but this is
		1579	no longer true when a callback calls C<ev_loop> recursively).
1460		1580
1461	=head3 Be smart about timeouts	1581	=head3 Be smart about timeouts
1462		1582
1463	Many real-world problems involve some kind of timeout, usually for error	1583	Many real-world problems involve some kind of timeout, usually for error
1464	recovery. A typical example is an HTTP request - if the other side hangs,	1584	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1508	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>	1628	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
1509	member and C<ev_timer_again>.	1629	member and C<ev_timer_again>.
1510		1630
1511	At start:	1631	At start:
1512		1632
1513	ev_timer_init (timer, callback);	1633	ev_init (timer, callback);
1514	timer->repeat = 60.;	1634	timer->repeat = 60.;
1515	ev_timer_again (loop, timer);	1635	ev_timer_again (loop, timer);
1516		1636
1517	Each time there is some activity:	1637	Each time there is some activity:
1518		1638
…		…
1580		1700
1581	To start the timer, simply initialise the watcher and set C<last_activity>	1701	To start the timer, simply initialise the watcher and set C<last_activity>
1582	to the current time (meaning we just have some activity :), then call the	1702	to the current time (meaning we just have some activity :), then call the
1583	callback, which will "do the right thing" and start the timer:	1703	callback, which will "do the right thing" and start the timer:
1584		1704
1585	ev_timer_init (timer, callback);	1705	ev_init (timer, callback);
1586	last_activity = ev_now (loop);	1706	last_activity = ev_now (loop);
1587	callback (loop, timer, EV_TIMEOUT);	1707	callback (loop, timer, EV_TIMEOUT);
1588		1708
1589	And when there is some activity, simply store the current time in	1709	And when there is some activity, simply store the current time in
1590	C<last_activity>, no libev calls at all:	1710	C<last_activity>, no libev calls at all:
…		…
1651		1771
1652	If the event loop is suspended for a long time, you can also force an	1772	If the event loop is suspended for a long time, you can also force an
1653	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1773	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1654	()>.	1774	()>.
1655		1775
		1776	=head3 The special problems of suspended animation
		1777
		1778	When you leave the server world it is quite customary to hit machines that
		1779	can suspend/hibernate - what happens to the clocks during such a suspend?
		1780
		1781	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1782	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1783	to run until the system is suspended, but they will not advance while the
		1784	system is suspended. That means, on resume, it will be as if the program
		1785	was frozen for a few seconds, but the suspend time will not be counted
		1786	towards C<ev_timer> when a monotonic clock source is used. The real time
		1787	clock advanced as expected, but if it is used as sole clocksource, then a
		1788	long suspend would be detected as a time jump by libev, and timers would
		1789	be adjusted accordingly.
		1790
		1791	I would not be surprised to see different behaviour in different between
		1792	operating systems, OS versions or even different hardware.
		1793
		1794	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1795	time jump in the monotonic clocks and the realtime clock. If the program
		1796	is suspended for a very long time, and monotonic clock sources are in use,
		1797	then you can expect C<ev_timer>s to expire as the full suspension time
		1798	will be counted towards the timers. When no monotonic clock source is in
		1799	use, then libev will again assume a timejump and adjust accordingly.
		1800
		1801	It might be beneficial for this latter case to call C<ev_suspend>
		1802	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1803	deterministic behaviour in this case (you can do nothing against
		1804	C<SIGSTOP>).
		1805
1656	=head3 Watcher-Specific Functions and Data Members	1806	=head3 Watcher-Specific Functions and Data Members
1657		1807
1658	=over 4	1808	=over 4
1659		1809
1660	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1810	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1685	If the timer is repeating, either start it if necessary (with the	1835	If the timer is repeating, either start it if necessary (with the
1686	C<repeat> value), or reset the running timer to the C<repeat> value.	1836	C<repeat> value), or reset the running timer to the C<repeat> value.
1687		1837
1688	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	1838	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1689	usage example.	1839	usage example.
		1840
		1841	=item ev_timer_remaining (loop, ev_timer *)
		1842
		1843	Returns the remaining time until a timer fires. If the timer is active,
		1844	then this time is relative to the current event loop time, otherwise it's
		1845	the timeout value currently configured.
		1846
		1847	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1848	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1849	will return C<4>. When the timer expires and is restarted, it will return
		1850	roughly C<7> (likely slightly less as callback invocation takes some time,
		1851	too), and so on.
1690		1852
1691	=item ev_tstamp repeat [read-write]	1853	=item ev_tstamp repeat [read-write]
1692		1854
1693	The current C<repeat> value. Will be used each time the watcher times out	1855	The current C<repeat> value. Will be used each time the watcher times out
1694	or C<ev_timer_again> is called, and determines the next timeout (if any),	1856	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1930	Signal watchers will trigger an event when the process receives a specific	2092	Signal watchers will trigger an event when the process receives a specific
1931	signal one or more times. Even though signals are very asynchronous, libev	2093	signal one or more times. Even though signals are very asynchronous, libev
1932	will try it's best to deliver signals synchronously, i.e. as part of the	2094	will try it's best to deliver signals synchronously, i.e. as part of the
1933	normal event processing, like any other event.	2095	normal event processing, like any other event.
1934		2096
1935	If you want signals asynchronously, just use C<sigaction> as you would	2097	If you want signals to be delivered truly asynchronously, just use
1936	do without libev and forget about sharing the signal. You can even use	2098	C<sigaction> as you would do without libev and forget about sharing
1937	C<ev_async> from a signal handler to synchronously wake up an event loop.	2099	the signal. You can even use C<ev_async> from a signal handler to
		2100	synchronously wake up an event loop.
1938		2101
1939	You can configure as many watchers as you like per signal. Only when the	2102	You can configure as many watchers as you like for the same signal, but
		2103	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2104	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2105	C<SIGINT> in both the default loop and another loop at the same time. At
		2106	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2107
1940	first watcher gets started will libev actually register a signal handler	2108	When the first watcher gets started will libev actually register something
1941	with the kernel (thus it coexists with your own signal handlers as long as	2109	with the kernel (thus it coexists with your own signal handlers as long as
1942	you don't register any with libev for the same signal). Similarly, when	2110	you don't register any with libev for the same signal).
1943	the last signal watcher for a signal is stopped, libev will reset the	2111
1944	signal handler to SIG_DFL (regardless of what it was set to before).	2112	Both the signal mask state (C<sigprocmask>) and the signal handler state
		2113	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2114	sotpping it again), that is, libev might or might not block the signal,
		2115	and might or might not set or restore the installed signal handler.
1945		2116
1946	If possible and supported, libev will install its handlers with	2117	If possible and supported, libev will install its handlers with
1947	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2118	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1948	interrupted. If you have a problem with system calls getting interrupted by	2119	not be unduly interrupted. If you have a problem with system calls getting
1949	signals you can block all signals in an C<ev_check> watcher and unblock	2120	interrupted by signals you can block all signals in an C<ev_check> watcher
1950	them in an C<ev_prepare> watcher.	2121	and unblock them in an C<ev_prepare> watcher.
1951		2122
1952	=head3 Watcher-Specific Functions and Data Members	2123	=head3 Watcher-Specific Functions and Data Members
1953		2124
1954	=over 4	2125	=over 4
1955		2126
…		…
1987	some child status changes (most typically when a child of yours dies or	2158	some child status changes (most typically when a child of yours dies or
1988	exits). It is permissible to install a child watcher I<after> the child	2159	exits). It is permissible to install a child watcher I<after> the child
1989	has been forked (which implies it might have already exited), as long	2160	has been forked (which implies it might have already exited), as long
1990	as the event loop isn't entered (or is continued from a watcher), i.e.,	2161	as the event loop isn't entered (or is continued from a watcher), i.e.,
1991	forking and then immediately registering a watcher for the child is fine,	2162	forking and then immediately registering a watcher for the child is fine,
1992	but forking and registering a watcher a few event loop iterations later is	2163	but forking and registering a watcher a few event loop iterations later or
1993	not.	2164	in the next callback invocation is not.
1994		2165
1995	Only the default event loop is capable of handling signals, and therefore	2166	Only the default event loop is capable of handling signals, and therefore
1996	you can only register child watchers in the default event loop.	2167	you can only register child watchers in the default event loop.
1997		2168
		2169	Due to some design glitches inside libev, child watchers will always be
		2170	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2171	libev)
		2172
1998	=head3 Process Interaction	2173	=head3 Process Interaction
1999		2174
2000	Libev grabs C<SIGCHLD> as soon as the default event loop is	2175	Libev grabs C<SIGCHLD> as soon as the default event loop is
2001	initialised. This is necessary to guarantee proper behaviour even if	2176	initialised. This is necessary to guarantee proper behaviour even if the
2002	the first child watcher is started after the child exits. The occurrence	2177	first child watcher is started after the child exits. The occurrence
2003	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2178	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
2004	synchronously as part of the event loop processing. Libev always reaps all	2179	synchronously as part of the event loop processing. Libev always reaps all
2005	children, even ones not watched.	2180	children, even ones not watched.
2006		2181
2007	=head3 Overriding the Built-In Processing	2182	=head3 Overriding the Built-In Processing
…		…
2017	=head3 Stopping the Child Watcher	2192	=head3 Stopping the Child Watcher
2018		2193
2019	Currently, the child watcher never gets stopped, even when the	2194	Currently, the child watcher never gets stopped, even when the
2020	child terminates, so normally one needs to stop the watcher in the	2195	child terminates, so normally one needs to stop the watcher in the
2021	callback. Future versions of libev might stop the watcher automatically	2196	callback. Future versions of libev might stop the watcher automatically
2022	when a child exit is detected.	2197	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2198	problem).
2023		2199
2024	=head3 Watcher-Specific Functions and Data Members	2200	=head3 Watcher-Specific Functions and Data Members
2025		2201
2026	=over 4	2202	=over 4
2027		2203
…		…
2353	// no longer anything immediate to do.	2529	// no longer anything immediate to do.
2354	}	2530	}
2355		2531
2356	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2532	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2357	ev_idle_init (idle_watcher, idle_cb);	2533	ev_idle_init (idle_watcher, idle_cb);
2358	ev_idle_start (loop, idle_cb);	2534	ev_idle_start (loop, idle_watcher);
2359		2535
2360		2536
2361	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2537	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2362		2538
2363	Prepare and check watchers are usually (but not always) used in pairs:	2539	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2456	struct pollfd fds [nfd];	2632	struct pollfd fds [nfd];
2457	// actual code will need to loop here and realloc etc.	2633	// actual code will need to loop here and realloc etc.
2458	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2634	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2459		2635
2460	/* the callback is illegal, but won't be called as we stop during check */	2636	/* the callback is illegal, but won't be called as we stop during check */
2461	ev_timer_init (&tw, 0, timeout * 1e-3);	2637	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2462	ev_timer_start (loop, &tw);	2638	ev_timer_start (loop, &tw);
2463		2639
2464	// create one ev_io per pollfd	2640	// create one ev_io per pollfd
2465	for (int i = 0; i < nfd; ++i)	2641	for (int i = 0; i < nfd; ++i)
2466	{	2642	{
…		…
2696	event loop blocks next and before C<ev_check> watchers are being called,	2872	event loop blocks next and before C<ev_check> watchers are being called,
2697	and only in the child after the fork. If whoever good citizen calling	2873	and only in the child after the fork. If whoever good citizen calling
2698	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2874	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2699	handlers will be invoked, too, of course.	2875	handlers will be invoked, too, of course.
2700		2876
		2877	=head3 The special problem of life after fork - how is it possible?
		2878
		2879	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2880	up/change the process environment, followed by a call to C<exec()>. This
		2881	sequence should be handled by libev without any problems.
		2882
		2883	This changes when the application actually wants to do event handling
		2884	in the child, or both parent in child, in effect "continuing" after the
		2885	fork.
		2886
		2887	The default mode of operation (for libev, with application help to detect
		2888	forks) is to duplicate all the state in the child, as would be expected
		2889	when I<either> the parent I<or> the child process continues.
		2890
		2891	When both processes want to continue using libev, then this is usually the
		2892	wrong result. In that case, usually one process (typically the parent) is
		2893	supposed to continue with all watchers in place as before, while the other
		2894	process typically wants to start fresh, i.e. without any active watchers.
		2895
		2896	The cleanest and most efficient way to achieve that with libev is to
		2897	simply create a new event loop, which of course will be "empty", and
		2898	use that for new watchers. This has the advantage of not touching more
		2899	memory than necessary, and thus avoiding the copy-on-write, and the
		2900	disadvantage of having to use multiple event loops (which do not support
		2901	signal watchers).
		2902
		2903	When this is not possible, or you want to use the default loop for
		2904	other reasons, then in the process that wants to start "fresh", call
		2905	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2906	the default loop will "orphan" (not stop) all registered watchers, so you
		2907	have to be careful not to execute code that modifies those watchers. Note
		2908	also that in that case, you have to re-register any signal watchers.
		2909
2701	=head3 Watcher-Specific Functions and Data Members	2910	=head3 Watcher-Specific Functions and Data Members
2702		2911
2703	=over 4	2912	=over 4
2704		2913
2705	=item ev_fork_init (ev_signal *, callback)	2914	=item ev_fork_init (ev_signal *, callback)
…		…
3595	defined to be C<0>, then they are not.	3804	defined to be C<0>, then they are not.
3596		3805
3597	=item EV_MINIMAL	3806	=item EV_MINIMAL
3598		3807
3599	If you need to shave off some kilobytes of code at the expense of some	3808	If you need to shave off some kilobytes of code at the expense of some
3600	speed, define this symbol to C<1>. Currently this is used to override some	3809	speed (but with the full API), define this symbol to C<1>. Currently this
3601	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3810	is used to override some inlining decisions, saves roughly 30% code size
3602	much smaller 2-heap for timer management over the default 4-heap.	3811	on amd64. It also selects a much smaller 2-heap for timer management over
		3812	the default 4-heap.
		3813
		3814	You can save even more by disabling watcher types you do not need
		3815	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3816	(C<-DNDEBUG>) will usually reduce code size a lot.
		3817
		3818	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3819	provide a bare-bones event library. See C<ev.h> for details on what parts
		3820	of the API are still available, and do not complain if this subset changes
		3821	over time.
		3822
		3823	=item EV_NSIG
		3824
		3825	The highest supported signal number, +1 (or, the number of
		3826	signals): Normally, libev tries to deduce the maximum number of signals
		3827	automatically, but sometimes this fails, in which case it can be
		3828	specified. Also, using a lower number than detected (C<32> should be
		3829	good for about any system in existance) can save some memory, as libev
		3830	statically allocates some 12-24 bytes per signal number.
3603		3831
3604	=item EV_PID_HASHSIZE	3832	=item EV_PID_HASHSIZE
3605		3833
3606	C<ev_child> watchers use a small hash table to distribute workload by	3834	C<ev_child> watchers use a small hash table to distribute workload by
3607	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3835	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3793	default loop and triggering an C<ev_async> watcher from the default loop	4021	default loop and triggering an C<ev_async> watcher from the default loop
3794	watcher callback into the event loop interested in the signal.	4022	watcher callback into the event loop interested in the signal.
3795		4023
3796	=back	4024	=back
3797		4025
		4026	=head4 THREAD LOCKING EXAMPLE
		4027
		4028	Here is a fictitious example of how to run an event loop in a different
		4029	thread than where callbacks are being invoked and watchers are
		4030	created/added/removed.
		4031
		4032	For a real-world example, see the C<EV::Loop::Async> perl module,
		4033	which uses exactly this technique (which is suited for many high-level
		4034	languages).
		4035
		4036	The example uses a pthread mutex to protect the loop data, a condition
		4037	variable to wait for callback invocations, an async watcher to notify the
		4038	event loop thread and an unspecified mechanism to wake up the main thread.
		4039
		4040	First, you need to associate some data with the event loop:
		4041
		4042	typedef struct {
		4043	mutex_t lock; /* global loop lock */
		4044	ev_async async_w;
		4045	thread_t tid;
		4046	cond_t invoke_cv;
		4047	} userdata;
		4048
		4049	void prepare_loop (EV_P)
		4050	{
		4051	// for simplicity, we use a static userdata struct.
		4052	static userdata u;
		4053
		4054	ev_async_init (&u->async_w, async_cb);
		4055	ev_async_start (EV_A_ &u->async_w);
		4056
		4057	pthread_mutex_init (&u->lock, 0);
		4058	pthread_cond_init (&u->invoke_cv, 0);
		4059
		4060	// now associate this with the loop
		4061	ev_set_userdata (EV_A_ u);
		4062	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4063	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4064
		4065	// then create the thread running ev_loop
		4066	pthread_create (&u->tid, 0, l_run, EV_A);
		4067	}
		4068
		4069	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4070	solely to wake up the event loop so it takes notice of any new watchers
		4071	that might have been added:
		4072
		4073	static void
		4074	async_cb (EV_P_ ev_async *w, int revents)
		4075	{
		4076	// just used for the side effects
		4077	}
		4078
		4079	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4080	protecting the loop data, respectively.
		4081
		4082	static void
		4083	l_release (EV_P)
		4084	{
		4085	userdata *u = ev_userdata (EV_A);
		4086	pthread_mutex_unlock (&u->lock);
		4087	}
		4088
		4089	static void
		4090	l_acquire (EV_P)
		4091	{
		4092	userdata *u = ev_userdata (EV_A);
		4093	pthread_mutex_lock (&u->lock);
		4094	}
		4095
		4096	The event loop thread first acquires the mutex, and then jumps straight
		4097	into C<ev_loop>:
		4098
		4099	void *
		4100	l_run (void *thr_arg)
		4101	{
		4102	struct ev_loop loop = (struct ev_loop )thr_arg;
		4103
		4104	l_acquire (EV_A);
		4105	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4106	ev_loop (EV_A_ 0);
		4107	l_release (EV_A);
		4108
		4109	return 0;
		4110	}
		4111
		4112	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4113	signal the main thread via some unspecified mechanism (signals? pipe
		4114	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4115	have been called (in a while loop because a) spurious wakeups are possible
		4116	and b) skipping inter-thread-communication when there are no pending
		4117	watchers is very beneficial):
		4118
		4119	static void
		4120	l_invoke (EV_P)
		4121	{
		4122	userdata *u = ev_userdata (EV_A);
		4123
		4124	while (ev_pending_count (EV_A))
		4125	{
		4126	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4127	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4128	}
		4129	}
		4130
		4131	Now, whenever the main thread gets told to invoke pending watchers, it
		4132	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4133	thread to continue:
		4134
		4135	static void
		4136	real_invoke_pending (EV_P)
		4137	{
		4138	userdata *u = ev_userdata (EV_A);
		4139
		4140	pthread_mutex_lock (&u->lock);
		4141	ev_invoke_pending (EV_A);
		4142	pthread_cond_signal (&u->invoke_cv);
		4143	pthread_mutex_unlock (&u->lock);
		4144	}
		4145
		4146	Whenever you want to start/stop a watcher or do other modifications to an
		4147	event loop, you will now have to lock:
		4148
		4149	ev_timer timeout_watcher;
		4150	userdata *u = ev_userdata (EV_A);
		4151
		4152	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4153
		4154	pthread_mutex_lock (&u->lock);
		4155	ev_timer_start (EV_A_ &timeout_watcher);
		4156	ev_async_send (EV_A_ &u->async_w);
		4157	pthread_mutex_unlock (&u->lock);
		4158
		4159	Note that sending the C<ev_async> watcher is required because otherwise
		4160	an event loop currently blocking in the kernel will have no knowledge
		4161	about the newly added timer. By waking up the loop it will pick up any new
		4162	watchers in the next event loop iteration.
		4163
3798	=head3 COROUTINES	4164	=head3 COROUTINES
3799		4165
3800	Libev is very accommodating to coroutines ("cooperative threads"):	4166	Libev is very accommodating to coroutines ("cooperative threads"):
3801	libev fully supports nesting calls to its functions from different	4167	libev fully supports nesting calls to its functions from different
3802	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4168	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3803	different coroutines, and switch freely between both coroutines running the	4169	different coroutines, and switch freely between both coroutines running
3804	loop, as long as you don't confuse yourself). The only exception is that	4170	the loop, as long as you don't confuse yourself). The only exception is
3805	you must not do this from C<ev_periodic> reschedule callbacks.	4171	that you must not do this from C<ev_periodic> reschedule callbacks.
3806		4172
3807	Care has been taken to ensure that libev does not keep local state inside	4173	Care has been taken to ensure that libev does not keep local state inside
3808	C<ev_loop>, and other calls do not usually allow for coroutine switches as	4174	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3809	they do not call any callbacks.	4175	they do not call any callbacks.
3810		4176
…		…
3887	way (note also that glib is the slowest event library known to man).	4253	way (note also that glib is the slowest event library known to man).
3888		4254
3889	There is no supported compilation method available on windows except	4255	There is no supported compilation method available on windows except
3890	embedding it into other applications.	4256	embedding it into other applications.
3891		4257
		4258	Sensible signal handling is officially unsupported by Microsoft - libev
		4259	tries its best, but under most conditions, signals will simply not work.
		4260
3892	Not a libev limitation but worth mentioning: windows apparently doesn't	4261	Not a libev limitation but worth mentioning: windows apparently doesn't
3893	accept large writes: instead of resulting in a partial write, windows will	4262	accept large writes: instead of resulting in a partial write, windows will
3894	either accept everything or return C<ENOBUFS> if the buffer is too large,	4263	either accept everything or return C<ENOBUFS> if the buffer is too large,
3895	so make sure you only write small amounts into your sockets (less than a	4264	so make sure you only write small amounts into your sockets (less than a
3896	megabyte seems safe, but this apparently depends on the amount of memory	4265	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3900	the abysmal performance of winsockets, using a large number of sockets	4269	the abysmal performance of winsockets, using a large number of sockets
3901	is not recommended (and not reasonable). If your program needs to use	4270	is not recommended (and not reasonable). If your program needs to use
3902	more than a hundred or so sockets, then likely it needs to use a totally	4271	more than a hundred or so sockets, then likely it needs to use a totally
3903	different implementation for windows, as libev offers the POSIX readiness	4272	different implementation for windows, as libev offers the POSIX readiness
3904	notification model, which cannot be implemented efficiently on windows	4273	notification model, which cannot be implemented efficiently on windows
3905	(Microsoft monopoly games).	4274	(due to Microsoft monopoly games).
3906		4275
3907	A typical way to use libev under windows is to embed it (see the embedding	4276	A typical way to use libev under windows is to embed it (see the embedding
3908	section for details) and use the following F<evwrap.h> header file instead	4277	section for details) and use the following F<evwrap.h> header file instead
3909	of F<ev.h>:	4278	of F<ev.h>:
3910		4279
…		…
3946		4315
3947	Early versions of winsocket's select only supported waiting for a maximum	4316	Early versions of winsocket's select only supported waiting for a maximum
3948	of C<64> handles (probably owning to the fact that all windows kernels	4317	of C<64> handles (probably owning to the fact that all windows kernels
3949	can only wait for C<64> things at the same time internally; Microsoft	4318	can only wait for C<64> things at the same time internally; Microsoft
3950	recommends spawning a chain of threads and wait for 63 handles and the	4319	recommends spawning a chain of threads and wait for 63 handles and the
3951	previous thread in each. Great).	4320	previous thread in each. Sounds great!).
3952		4321
3953	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4322	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3954	to some high number (e.g. C<2048>) before compiling the winsocket select	4323	to some high number (e.g. C<2048>) before compiling the winsocket select
3955	call (which might be in libev or elsewhere, for example, perl does its own	4324	call (which might be in libev or elsewhere, for example, perl and many
3956	select emulation on windows).	4325	other interpreters do their own select emulation on windows).
3957		4326
3958	Another limit is the number of file descriptors in the Microsoft runtime	4327	Another limit is the number of file descriptors in the Microsoft runtime
3959	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4328	libraries, which by default is C<64> (there must be a hidden I<64>
3960	or something like this inside Microsoft). You can increase this by calling	4329	fetish or something like this inside Microsoft). You can increase this
3961	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4330	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3962	arbitrary limit), but is broken in many versions of the Microsoft runtime	4331	(another arbitrary limit), but is broken in many versions of the Microsoft
3963	libraries.
3964
3965	This might get you to about C<512> or C<2048> sockets (depending on	4332	runtime libraries. This might get you to about C<512> or C<2048> sockets
3966	windows version and/or the phase of the moon). To get more, you need to	4333	(depending on windows version and/or the phase of the moon). To get more,
3967	wrap all I/O functions and provide your own fd management, but the cost of	4334	you need to wrap all I/O functions and provide your own fd management, but
3968	calling select (O(n²)) will likely make this unworkable.	4335	the cost of calling select (O(n²)) will likely make this unworkable.
3969		4336
3970	=back	4337	=back
3971		4338
3972	=head2 PORTABILITY REQUIREMENTS	4339	=head2 PORTABILITY REQUIREMENTS
3973		4340
…		…
4016	=item C<double> must hold a time value in seconds with enough accuracy	4383	=item C<double> must hold a time value in seconds with enough accuracy
4017		4384
4018	The type C<double> is used to represent timestamps. It is required to	4385	The type C<double> is used to represent timestamps. It is required to
4019	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4386	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
4020	enough for at least into the year 4000. This requirement is fulfilled by	4387	enough for at least into the year 4000. This requirement is fulfilled by
4021	implementations implementing IEEE 754 (basically all existing ones).	4388	implementations implementing IEEE 754, which is basically all existing
		4389	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4390	2200.
4022		4391
4023	=back	4392	=back
4024		4393
4025	If you know of other additional requirements drop me a note.	4394	If you know of other additional requirements drop me a note.
4026		4395

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Comparing libev/ev.pod (file contents): Revision 1.234 by root, Thu Apr 16 07:49:23 2009 UTC vs. Revision 1.260 by root, Sun Jul 19 21:18:03 2009 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.234 by root, Thu Apr 16 07:49:23 2009 UTC vs.
Revision 1.260 by root, Sun Jul 19 21:18:03 2009 UTC