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

Comparing libev/ev.pod (file contents):
Revision 1.235 by root, Thu Apr 16 07:50:39 2009 UTC vs.
Revision 1.258 by root, Wed Jul 15 16:58:53 2009 UTC

…		…
62		62
63	// unloop was called, so exit	63	// unloop was called, so exit
64	return 0;	64	return 0;
65	}	65	}
66		66
67	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
68		70
69	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
70	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
71	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
72		84
73	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
74	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
75	these event sources and provide your program with events.	87	these event sources and provide your program with events.
76		88
…		…
110	name C<loop> (which is always of type C<ev_loop *>) will not have	122	name C<loop> (which is always of type C<ev_loop *>) will not have
111	this argument.	123	this argument.
112		124
113	=head2 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
114		126
115	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
116	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
117	the beginning of 1970, details are complicated, don't ask). This type is	129	near the beginning of 1970, details are complicated, don't ask). This
118	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	type is called C<ev_tstamp>, which is what you should use too. It usually
119	to the C<double> type in C, and when you need to do any calculations on	131	aliases to the C<double> type in C. When you need to do any calculations
120	it, you should treat it as some floating point value. Unlike the name	132	on it, you should treat it as some floating point value. Unlike the name
121	component C<stamp> might indicate, it is also used for time differences	133	component C<stamp> might indicate, it is also used for time differences
122	throughout libev.	134	throughout libev.
123		135
124	=head1 ERROR HANDLING	136	=head1 ERROR HANDLING
125		137
…		…
609		621
610	This value can sometimes be useful as a generation counter of sorts (it	622	This value can sometimes be useful as a generation counter of sorts (it
611	"ticks" the number of loop iterations), as it roughly corresponds with	623	"ticks" the number of loop iterations), as it roughly corresponds with
612	C<ev_prepare> and C<ev_check> calls.	624	C<ev_prepare> and C<ev_check> calls.
613		625
		626	=item unsigned int ev_loop_depth (loop)
		627
		628	Returns the number of times C<ev_loop> was entered minus the number of
		629	times C<ev_loop> was exited, in other words, the recursion depth.
		630
		631	Outside C<ev_loop>, this number is zero. In a callback, this number is
		632	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		633	in which case it is higher.
		634
		635	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		636	etc.), doesn't count as exit.
		637
614	=item unsigned int ev_backend (loop)	638	=item unsigned int ev_backend (loop)
615		639
616	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	640	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
617	use.	641	use.
618		642
…		…
632		656
633	This function is rarely useful, but when some event callback runs for a	657	This function is rarely useful, but when some event callback runs for a
634	very long time without entering the event loop, updating libev's idea of	658	very long time without entering the event loop, updating libev's idea of
635	the current time is a good idea.	659	the current time is a good idea.
636		660
637	See also "The special problem of time updates" in the C<ev_timer> section.	661	See also L<The special problem of time updates> in the C<ev_timer> section.
638		662
639	=item ev_suspend (loop)	663	=item ev_suspend (loop)
640		664
641	=item ev_resume (loop)	665	=item ev_resume (loop)
642		666
…		…
799		823
800	By setting a higher I<io collect interval> you allow libev to spend more	824	By setting a higher I<io collect interval> you allow libev to spend more
801	time collecting I/O events, so you can handle more events per iteration,	825	time collecting I/O events, so you can handle more events per iteration,
802	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	826	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
803	C<ev_timer>) will be not affected. Setting this to a non-null value will	827	C<ev_timer>) will be not affected. Setting this to a non-null value will
804	introduce an additional C<ev_sleep ()> call into most loop iterations.	828	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		829	sleep time ensures that libev will not poll for I/O events more often then
		830	once per this interval, on average.
805		831
806	Likewise, by setting a higher I<timeout collect interval> you allow libev	832	Likewise, by setting a higher I<timeout collect interval> you allow libev
807	to spend more time collecting timeouts, at the expense of increased	833	to spend more time collecting timeouts, at the expense of increased
808	latency/jitter/inexactness (the watcher callback will be called	834	latency/jitter/inexactness (the watcher callback will be called
809	later). C<ev_io> watchers will not be affected. Setting this to a non-null	835	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
811		837
812	Many (busy) programs can usually benefit by setting the I/O collect	838	Many (busy) programs can usually benefit by setting the I/O collect
813	interval to a value near C<0.1> or so, which is often enough for	839	interval to a value near C<0.1> or so, which is often enough for
814	interactive servers (of course not for games), likewise for timeouts. It	840	interactive servers (of course not for games), likewise for timeouts. It
815	usually doesn't make much sense to set it to a lower value than C<0.01>,	841	usually doesn't make much sense to set it to a lower value than C<0.01>,
816	as this approaches the timing granularity of most systems.	842	as this approaches the timing granularity of most systems. Note that if
		843	you do transactions with the outside world and you can't increase the
		844	parallelity, then this setting will limit your transaction rate (if you
		845	need to poll once per transaction and the I/O collect interval is 0.01,
		846	then you can't do more than 100 transations per second).
817		847
818	Setting the I<timeout collect interval> can improve the opportunity for	848	Setting the I<timeout collect interval> can improve the opportunity for
819	saving power, as the program will "bundle" timer callback invocations that	849	saving power, as the program will "bundle" timer callback invocations that
820	are "near" in time together, by delaying some, thus reducing the number of	850	are "near" in time together, by delaying some, thus reducing the number of
821	times the process sleeps and wakes up again. Another useful technique to	851	times the process sleeps and wakes up again. Another useful technique to
822	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	852	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
823	they fire on, say, one-second boundaries only.	853	they fire on, say, one-second boundaries only.
		854
		855	Example: we only need 0.1s timeout granularity, and we wish not to poll
		856	more often than 100 times per second:
		857
		858	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		859	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		860
		861	=item ev_invoke_pending (loop)
		862
		863	This call will simply invoke all pending watchers while resetting their
		864	pending state. Normally, C<ev_loop> does this automatically when required,
		865	but when overriding the invoke callback this call comes handy.
		866
		867	=item int ev_pending_count (loop)
		868
		869	Returns the number of pending watchers - zero indicates that no watchers
		870	are pending.
		871
		872	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		873
		874	This overrides the invoke pending functionality of the loop: Instead of
		875	invoking all pending watchers when there are any, C<ev_loop> will call
		876	this callback instead. This is useful, for example, when you want to
		877	invoke the actual watchers inside another context (another thread etc.).
		878
		879	If you want to reset the callback, use C<ev_invoke_pending> as new
		880	callback.
		881
		882	=item ev_set_loop_release_cb (loop, void (release)(EV_P), void (acquire)(EV_P))
		883
		884	Sometimes you want to share the same loop between multiple threads. This
		885	can be done relatively simply by putting mutex_lock/unlock calls around
		886	each call to a libev function.
		887
		888	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		889	wait for it to return. One way around this is to wake up the loop via
		890	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		891	and I<acquire> callbacks on the loop.
		892
		893	When set, then C<release> will be called just before the thread is
		894	suspended waiting for new events, and C<acquire> is called just
		895	afterwards.
		896
		897	Ideally, C<release> will just call your mutex_unlock function, and
		898	C<acquire> will just call the mutex_lock function again.
		899
		900	While event loop modifications are allowed between invocations of
		901	C<release> and C<acquire> (that's their only purpose after all), no
		902	modifications done will affect the event loop, i.e. adding watchers will
		903	have no effect on the set of file descriptors being watched, or the time
		904	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		905	to take note of any changes you made.
		906
		907	In theory, threads executing C<ev_loop> will be async-cancel safe between
		908	invocations of C<release> and C<acquire>.
		909
		910	See also the locking example in the C<THREADS> section later in this
		911	document.
		912
		913	=item ev_set_userdata (loop, void *data)
		914
		915	=item ev_userdata (loop)
		916
		917	Set and retrieve a single C<void *> associated with a loop. When
		918	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		919	C<0.>
		920
		921	These two functions can be used to associate arbitrary data with a loop,
		922	and are intended solely for the C<invoke_pending_cb>, C<release> and
		923	C<acquire> callbacks described above, but of course can be (ab-)used for
		924	any other purpose as well.
824		925
825	=item ev_loop_verify (loop)	926	=item ev_loop_verify (loop)
826		927
827	This function only does something when C<EV_VERIFY> support has been	928	This function only does something when C<EV_VERIFY> support has been
828	compiled in, which is the default for non-minimal builds. It tries to go	929	compiled in, which is the default for non-minimal builds. It tries to go
…		…
1172	#include <stddef.h>	1273	#include <stddef.h>
1173		1274
1174	static void	1275	static void
1175	t1_cb (EV_P_ ev_timer *w, int revents)	1276	t1_cb (EV_P_ ev_timer *w, int revents)
1176	{	1277	{
1177	struct my_biggy big = (struct my_biggy *	1278	struct my_biggy big = (struct my_biggy *)
1178	(((char *)w) - offsetof (struct my_biggy, t1));	1279	(((char *)w) - offsetof (struct my_biggy, t1));
1179	}	1280	}
1180		1281
1181	static void	1282	static void
1182	t2_cb (EV_P_ ev_timer *w, int revents)	1283	t2_cb (EV_P_ ev_timer *w, int revents)
1183	{	1284	{
1184	struct my_biggy big = (struct my_biggy *	1285	struct my_biggy big = (struct my_biggy *)
1185	(((char *)w) - offsetof (struct my_biggy, t2));	1286	(((char *)w) - offsetof (struct my_biggy, t2));
1186	}	1287	}
1187		1288
1188	=head2 WATCHER PRIORITY MODELS	1289	=head2 WATCHER PRIORITY MODELS
1189		1290
…		…
1265	// with the default priority are receiving events.	1366	// with the default priority are receiving events.
1266	ev_idle_start (EV_A_ &idle);	1367	ev_idle_start (EV_A_ &idle);
1267	}	1368	}
1268		1369
1269	static void	1370	static void
1270	idle-cb (EV_P_ ev_idle *w, int revents)	1371	idle_cb (EV_P_ ev_idle *w, int revents)
1271	{	1372	{
1272	// actual processing	1373	// actual processing
1273	read (STDIN_FILENO, ...);	1374	read (STDIN_FILENO, ...);
1274		1375
1275	// have to start the I/O watcher again, as	1376	// have to start the I/O watcher again, as
…		…
1320	descriptors to non-blocking mode is also usually a good idea (but not	1421	descriptors to non-blocking mode is also usually a good idea (but not
1321	required if you know what you are doing).	1422	required if you know what you are doing).
1322		1423
1323	If you cannot use non-blocking mode, then force the use of a	1424	If you cannot use non-blocking mode, then force the use of a
1324	known-to-be-good backend (at the time of this writing, this includes only	1425	known-to-be-good backend (at the time of this writing, this includes only
1325	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1426	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1427	descriptors for which non-blocking operation makes no sense (such as
		1428	files) - libev doesn't guarentee any specific behaviour in that case.
1326		1429
1327	Another thing you have to watch out for is that it is quite easy to	1430	Another thing you have to watch out for is that it is quite easy to
1328	receive "spurious" readiness notifications, that is your callback might	1431	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	1432	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	1433	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	1554	year, it will still time out after (roughly) one hour. "Roughly" because
1452	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1555	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1453	monotonic clock option helps a lot here).	1556	monotonic clock option helps a lot here).
1454		1557
1455	The callback is guaranteed to be invoked only I<after> its timeout has	1558	The callback is guaranteed to be invoked only I<after> its timeout has
1456	passed. If multiple timers become ready during the same loop iteration	1559	passed (not I<at>, so on systems with very low-resolution clocks this
1457	then the ones with earlier time-out values are invoked before ones with	1560	might introduce a small delay). If multiple timers become ready during the
1458	later time-out values (but this is no longer true when a callback calls	1561	same loop iteration then the ones with earlier time-out values are invoked
1459	C<ev_loop> recursively).	1562	before ones of the same priority with later time-out values (but this is
		1563	no longer true when a callback calls C<ev_loop> recursively).
1460		1564
1461	=head3 Be smart about timeouts	1565	=head3 Be smart about timeouts
1462		1566
1463	Many real-world problems involve some kind of timeout, usually for error	1567	Many real-world problems involve some kind of timeout, usually for error
1464	recovery. A typical example is an HTTP request - if the other side hangs,	1568	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1508	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>	1612	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
1509	member and C<ev_timer_again>.	1613	member and C<ev_timer_again>.
1510		1614
1511	At start:	1615	At start:
1512		1616
1513	ev_timer_init (timer, callback);	1617	ev_init (timer, callback);
1514	timer->repeat = 60.;	1618	timer->repeat = 60.;
1515	ev_timer_again (loop, timer);	1619	ev_timer_again (loop, timer);
1516		1620
1517	Each time there is some activity:	1621	Each time there is some activity:
1518		1622
…		…
1580		1684
1581	To start the timer, simply initialise the watcher and set C<last_activity>	1685	To start the timer, simply initialise the watcher and set C<last_activity>
1582	to the current time (meaning we just have some activity :), then call the	1686	to the current time (meaning we just have some activity :), then call the
1583	callback, which will "do the right thing" and start the timer:	1687	callback, which will "do the right thing" and start the timer:
1584		1688
1585	ev_timer_init (timer, callback);	1689	ev_init (timer, callback);
1586	last_activity = ev_now (loop);	1690	last_activity = ev_now (loop);
1587	callback (loop, timer, EV_TIMEOUT);	1691	callback (loop, timer, EV_TIMEOUT);
1588		1692
1589	And when there is some activity, simply store the current time in	1693	And when there is some activity, simply store the current time in
1590	C<last_activity>, no libev calls at all:	1694	C<last_activity>, no libev calls at all:
…		…
1651		1755
1652	If the event loop is suspended for a long time, you can also force an	1756	If the event loop is suspended for a long time, you can also force an
1653	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1757	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1654	()>.	1758	()>.
1655		1759
		1760	=head3 The special problems of suspended animation
		1761
		1762	When you leave the server world it is quite customary to hit machines that
		1763	can suspend/hibernate - what happens to the clocks during such a suspend?
		1764
		1765	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1766	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1767	to run until the system is suspended, but they will not advance while the
		1768	system is suspended. That means, on resume, it will be as if the program
		1769	was frozen for a few seconds, but the suspend time will not be counted
		1770	towards C<ev_timer> when a monotonic clock source is used. The real time
		1771	clock advanced as expected, but if it is used as sole clocksource, then a
		1772	long suspend would be detected as a time jump by libev, and timers would
		1773	be adjusted accordingly.
		1774
		1775	I would not be surprised to see different behaviour in different between
		1776	operating systems, OS versions or even different hardware.
		1777
		1778	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1779	time jump in the monotonic clocks and the realtime clock. If the program
		1780	is suspended for a very long time, and monotonic clock sources are in use,
		1781	then you can expect C<ev_timer>s to expire as the full suspension time
		1782	will be counted towards the timers. When no monotonic clock source is in
		1783	use, then libev will again assume a timejump and adjust accordingly.
		1784
		1785	It might be beneficial for this latter case to call C<ev_suspend>
		1786	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1787	deterministic behaviour in this case (you can do nothing against
		1788	C<SIGSTOP>).
		1789
1656	=head3 Watcher-Specific Functions and Data Members	1790	=head3 Watcher-Specific Functions and Data Members
1657		1791
1658	=over 4	1792	=over 4
1659		1793
1660	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1794	=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	1819	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.	1820	C<repeat> value), or reset the running timer to the C<repeat> value.
1687		1821
1688	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	1822	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1689	usage example.	1823	usage example.
		1824
		1825	=item ev_timer_remaining (loop, ev_timer *)
		1826
		1827	Returns the remaining time until a timer fires. If the timer is active,
		1828	then this time is relative to the current event loop time, otherwise it's
		1829	the timeout value currently configured.
		1830
		1831	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1832	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1833	will return C<4>. When the timer expires and is restarted, it will return
		1834	roughly C<7> (likely slightly less as callback invocation takes some time,
		1835	too), and so on.
1690		1836
1691	=item ev_tstamp repeat [read-write]	1837	=item ev_tstamp repeat [read-write]
1692		1838
1693	The current C<repeat> value. Will be used each time the watcher times out	1839	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),	1840	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1987	some child status changes (most typically when a child of yours dies or	2133	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	2134	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	2135	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.,	2136	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,	2137	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	2138	but forking and registering a watcher a few event loop iterations later or
1993	not.	2139	in the next callback invocation is not.
1994		2140
1995	Only the default event loop is capable of handling signals, and therefore	2141	Only the default event loop is capable of handling signals, and therefore
1996	you can only register child watchers in the default event loop.	2142	you can only register child watchers in the default event loop.
		2143
		2144	Due to some design glitches inside libev, child watchers will always be
		2145	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2146	libev)
1997		2147
1998	=head3 Process Interaction	2148	=head3 Process Interaction
1999		2149
2000	Libev grabs C<SIGCHLD> as soon as the default event loop is	2150	Libev grabs C<SIGCHLD> as soon as the default event loop is
2001	initialised. This is necessary to guarantee proper behaviour even if	2151	initialised. This is necessary to guarantee proper behaviour even if
…		…
2353	// no longer anything immediate to do.	2503	// no longer anything immediate to do.
2354	}	2504	}
2355		2505
2356	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2506	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2357	ev_idle_init (idle_watcher, idle_cb);	2507	ev_idle_init (idle_watcher, idle_cb);
2358	ev_idle_start (loop, idle_cb);	2508	ev_idle_start (loop, idle_watcher);
2359		2509
2360		2510
2361	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2511	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2362		2512
2363	Prepare and check watchers are usually (but not always) used in pairs:	2513	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2456	struct pollfd fds [nfd];	2606	struct pollfd fds [nfd];
2457	// actual code will need to loop here and realloc etc.	2607	// actual code will need to loop here and realloc etc.
2458	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2608	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2459		2609
2460	/* the callback is illegal, but won't be called as we stop during check */	2610	/* the callback is illegal, but won't be called as we stop during check */
2461	ev_timer_init (&tw, 0, timeout * 1e-3);	2611	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2462	ev_timer_start (loop, &tw);	2612	ev_timer_start (loop, &tw);
2463		2613
2464	// create one ev_io per pollfd	2614	// create one ev_io per pollfd
2465	for (int i = 0; i < nfd; ++i)	2615	for (int i = 0; i < nfd; ++i)
2466	{	2616	{
…		…
2696	event loop blocks next and before C<ev_check> watchers are being called,	2846	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	2847	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	2848	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2699	handlers will be invoked, too, of course.	2849	handlers will be invoked, too, of course.
2700		2850
		2851	=head3 The special problem of life after fork - how is it possible?
		2852
		2853	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2854	up/change the process environment, followed by a call to C<exec()>. This
		2855	sequence should be handled by libev without any problems.
		2856
		2857	This changes when the application actually wants to do event handling
		2858	in the child, or both parent in child, in effect "continuing" after the
		2859	fork.
		2860
		2861	The default mode of operation (for libev, with application help to detect
		2862	forks) is to duplicate all the state in the child, as would be expected
		2863	when I<either> the parent I<or> the child process continues.
		2864
		2865	When both processes want to continue using libev, then this is usually the
		2866	wrong result. In that case, usually one process (typically the parent) is
		2867	supposed to continue with all watchers in place as before, while the other
		2868	process typically wants to start fresh, i.e. without any active watchers.
		2869
		2870	The cleanest and most efficient way to achieve that with libev is to
		2871	simply create a new event loop, which of course will be "empty", and
		2872	use that for new watchers. This has the advantage of not touching more
		2873	memory than necessary, and thus avoiding the copy-on-write, and the
		2874	disadvantage of having to use multiple event loops (which do not support
		2875	signal watchers).
		2876
		2877	When this is not possible, or you want to use the default loop for
		2878	other reasons, then in the process that wants to start "fresh", call
		2879	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2880	the default loop will "orphan" (not stop) all registered watchers, so you
		2881	have to be careful not to execute code that modifies those watchers. Note
		2882	also that in that case, you have to re-register any signal watchers.
		2883
2701	=head3 Watcher-Specific Functions and Data Members	2884	=head3 Watcher-Specific Functions and Data Members
2702		2885
2703	=over 4	2886	=over 4
2704		2887
2705	=item ev_fork_init (ev_signal *, callback)	2888	=item ev_fork_init (ev_signal *, callback)
…		…
3595	defined to be C<0>, then they are not.	3778	defined to be C<0>, then they are not.
3596		3779
3597	=item EV_MINIMAL	3780	=item EV_MINIMAL
3598		3781
3599	If you need to shave off some kilobytes of code at the expense of some	3782	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	3783	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	3784	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.	3785	on amd64. It also selects a much smaller 2-heap for timer management over
		3786	the default 4-heap.
		3787
		3788	You can save even more by disabling watcher types you do not need
		3789	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3790	(C<-DNDEBUG>) will usually reduce code size a lot.
		3791
		3792	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3793	provide a bare-bones event library. See C<ev.h> for details on what parts
		3794	of the API are still available, and do not complain if this subset changes
		3795	over time.
3603		3796
3604	=item EV_PID_HASHSIZE	3797	=item EV_PID_HASHSIZE
3605		3798
3606	C<ev_child> watchers use a small hash table to distribute workload by	3799	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	3800	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	3986	default loop and triggering an C<ev_async> watcher from the default loop
3794	watcher callback into the event loop interested in the signal.	3987	watcher callback into the event loop interested in the signal.
3795		3988
3796	=back	3989	=back
3797		3990
		3991	=head4 THREAD LOCKING EXAMPLE
		3992
		3993	Here is a fictitious example of how to run an event loop in a different
		3994	thread than where callbacks are being invoked and watchers are
		3995	created/added/removed.
		3996
		3997	For a real-world example, see the C<EV::Loop::Async> perl module,
		3998	which uses exactly this technique (which is suited for many high-level
		3999	languages).
		4000
		4001	The example uses a pthread mutex to protect the loop data, a condition
		4002	variable to wait for callback invocations, an async watcher to notify the
		4003	event loop thread and an unspecified mechanism to wake up the main thread.
		4004
		4005	First, you need to associate some data with the event loop:
		4006
		4007	typedef struct {
		4008	mutex_t lock; /* global loop lock */
		4009	ev_async async_w;
		4010	thread_t tid;
		4011	cond_t invoke_cv;
		4012	} userdata;
		4013
		4014	void prepare_loop (EV_P)
		4015	{
		4016	// for simplicity, we use a static userdata struct.
		4017	static userdata u;
		4018
		4019	ev_async_init (&u->async_w, async_cb);
		4020	ev_async_start (EV_A_ &u->async_w);
		4021
		4022	pthread_mutex_init (&u->lock, 0);
		4023	pthread_cond_init (&u->invoke_cv, 0);
		4024
		4025	// now associate this with the loop
		4026	ev_set_userdata (EV_A_ u);
		4027	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4028	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4029
		4030	// then create the thread running ev_loop
		4031	pthread_create (&u->tid, 0, l_run, EV_A);
		4032	}
		4033
		4034	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4035	solely to wake up the event loop so it takes notice of any new watchers
		4036	that might have been added:
		4037
		4038	static void
		4039	async_cb (EV_P_ ev_async *w, int revents)
		4040	{
		4041	// just used for the side effects
		4042	}
		4043
		4044	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4045	protecting the loop data, respectively.
		4046
		4047	static void
		4048	l_release (EV_P)
		4049	{
		4050	userdata *u = ev_userdata (EV_A);
		4051	pthread_mutex_unlock (&u->lock);
		4052	}
		4053
		4054	static void
		4055	l_acquire (EV_P)
		4056	{
		4057	userdata *u = ev_userdata (EV_A);
		4058	pthread_mutex_lock (&u->lock);
		4059	}
		4060
		4061	The event loop thread first acquires the mutex, and then jumps straight
		4062	into C<ev_loop>:
		4063
		4064	void *
		4065	l_run (void *thr_arg)
		4066	{
		4067	struct ev_loop loop = (struct ev_loop )thr_arg;
		4068
		4069	l_acquire (EV_A);
		4070	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4071	ev_loop (EV_A_ 0);
		4072	l_release (EV_A);
		4073
		4074	return 0;
		4075	}
		4076
		4077	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4078	signal the main thread via some unspecified mechanism (signals? pipe
		4079	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4080	have been called (in a while loop because a) spurious wakeups are possible
		4081	and b) skipping inter-thread-communication when there are no pending
		4082	watchers is very beneficial):
		4083
		4084	static void
		4085	l_invoke (EV_P)
		4086	{
		4087	userdata *u = ev_userdata (EV_A);
		4088
		4089	while (ev_pending_count (EV_A))
		4090	{
		4091	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4092	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4093	}
		4094	}
		4095
		4096	Now, whenever the main thread gets told to invoke pending watchers, it
		4097	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4098	thread to continue:
		4099
		4100	static void
		4101	real_invoke_pending (EV_P)
		4102	{
		4103	userdata *u = ev_userdata (EV_A);
		4104
		4105	pthread_mutex_lock (&u->lock);
		4106	ev_invoke_pending (EV_A);
		4107	pthread_cond_signal (&u->invoke_cv);
		4108	pthread_mutex_unlock (&u->lock);
		4109	}
		4110
		4111	Whenever you want to start/stop a watcher or do other modifications to an
		4112	event loop, you will now have to lock:
		4113
		4114	ev_timer timeout_watcher;
		4115	userdata *u = ev_userdata (EV_A);
		4116
		4117	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4118
		4119	pthread_mutex_lock (&u->lock);
		4120	ev_timer_start (EV_A_ &timeout_watcher);
		4121	ev_async_send (EV_A_ &u->async_w);
		4122	pthread_mutex_unlock (&u->lock);
		4123
		4124	Note that sending the C<ev_async> watcher is required because otherwise
		4125	an event loop currently blocking in the kernel will have no knowledge
		4126	about the newly added timer. By waking up the loop it will pick up any new
		4127	watchers in the next event loop iteration.
		4128
3798	=head3 COROUTINES	4129	=head3 COROUTINES
3799		4130
3800	Libev is very accommodating to coroutines ("cooperative threads"):	4131	Libev is very accommodating to coroutines ("cooperative threads"):
3801	libev fully supports nesting calls to its functions from different	4132	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	4133	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	4134	different coroutines, and switch freely between both coroutines running
3804	loop, as long as you don't confuse yourself). The only exception is that	4135	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.	4136	that you must not do this from C<ev_periodic> reschedule callbacks.
3806		4137
3807	Care has been taken to ensure that libev does not keep local state inside	4138	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	4139	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3809	they do not call any callbacks.	4140	they do not call any callbacks.
3810		4141
…		…
3887	way (note also that glib is the slowest event library known to man).	4218	way (note also that glib is the slowest event library known to man).
3888		4219
3889	There is no supported compilation method available on windows except	4220	There is no supported compilation method available on windows except
3890	embedding it into other applications.	4221	embedding it into other applications.
3891		4222
		4223	Sensible signal handling is officially unsupported by Microsoft - libev
		4224	tries its best, but under most conditions, signals will simply not work.
		4225
3892	Not a libev limitation but worth mentioning: windows apparently doesn't	4226	Not a libev limitation but worth mentioning: windows apparently doesn't
3893	accept large writes: instead of resulting in a partial write, windows will	4227	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,	4228	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	4229	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	4230	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3900	the abysmal performance of winsockets, using a large number of sockets	4234	the abysmal performance of winsockets, using a large number of sockets
3901	is not recommended (and not reasonable). If your program needs to use	4235	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	4236	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	4237	different implementation for windows, as libev offers the POSIX readiness
3904	notification model, which cannot be implemented efficiently on windows	4238	notification model, which cannot be implemented efficiently on windows
3905	(Microsoft monopoly games).	4239	(due to Microsoft monopoly games).
3906		4240
3907	A typical way to use libev under windows is to embed it (see the embedding	4241	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	4242	section for details) and use the following F<evwrap.h> header file instead
3909	of F<ev.h>:	4243	of F<ev.h>:
3910		4244
…		…
3946		4280
3947	Early versions of winsocket's select only supported waiting for a maximum	4281	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	4282	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	4283	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	4284	recommends spawning a chain of threads and wait for 63 handles and the
3951	previous thread in each. Great).	4285	previous thread in each. Sounds great!).
3952		4286
3953	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4287	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	4288	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	4289	call (which might be in libev or elsewhere, for example, perl and many
3956	select emulation on windows).	4290	other interpreters do their own select emulation on windows).
3957		4291
3958	Another limit is the number of file descriptors in the Microsoft runtime	4292	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	4293	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	4294	fetish or something like this inside Microsoft). You can increase this
3961	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4295	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	4296	(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	4297	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	4298	(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	4299	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.	4300	the cost of calling select (O(n²)) will likely make this unworkable.
3969		4301
3970	=back	4302	=back
3971		4303
3972	=head2 PORTABILITY REQUIREMENTS	4304	=head2 PORTABILITY REQUIREMENTS
3973		4305
…		…
4016	=item C<double> must hold a time value in seconds with enough accuracy	4348	=item C<double> must hold a time value in seconds with enough accuracy
4017		4349
4018	The type C<double> is used to represent timestamps. It is required to	4350	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	4351	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	4352	enough for at least into the year 4000. This requirement is fulfilled by
4021	implementations implementing IEEE 754 (basically all existing ones).	4353	implementations implementing IEEE 754, which is basically all existing
		4354	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4355	2200.
4022		4356
4023	=back	4357	=back
4024		4358
4025	If you know of other additional requirements drop me a note.	4359	If you know of other additional requirements drop me a note.
4026		4360

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Comparing libev/ev.pod (file contents): Revision 1.235 by root, Thu Apr 16 07:50:39 2009 UTC vs. Revision 1.258 by root, Wed Jul 15 16:58:53 2009 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.235 by root, Thu Apr 16 07:50:39 2009 UTC vs.
Revision 1.258 by root, Wed Jul 15 16:58:53 2009 UTC