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

Comparing libev/ev.pod (file contents):
Revision 1.97 by root, Sat Dec 22 05:48:02 2007 UTC vs.
Revision 1.112 by root, Wed Dec 26 08:06:09 2007 UTC

…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	#include <ev.h>	11	#include <ev.h>
12		12
13	ev_io stdin_watcher;	13	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	14	ev_timer timeout_watcher;
…		…
65	You register interest in certain events by registering so-called I<event	65	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	66	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	67	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	68	watcher.
69		69
70	=head1 FEATURES	70	=head2 FEATURES
71		71
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
…		…
82		82
83	It also is quite fast (see this	83	It also is quite fast (see this
84	L<benchmark\|http://libev.schmorp.de/bench.html> comparing it to libevent	84	L<benchmark\|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	85	for example).
86		86
87	=head1 CONVENTIONS	87	=head2 CONVENTIONS
88		88
89	Libev is very configurable. In this manual the default configuration will	89	Libev is very configurable. In this manual the default configuration will
90	be described, which supports multiple event loops. For more info about	90	be described, which supports multiple event loops. For more info about
91	various configuration options please have a look at B<EMBED> section in	91	various configuration options please have a look at B<EMBED> section in
92	this manual. If libev was configured without support for multiple event	92	this manual. If libev was configured without support for multiple event
93	loops, then all functions taking an initial argument of name C<loop>	93	loops, then all functions taking an initial argument of name C<loop>
94	(which is always of type C<struct ev_loop *>) will not have this argument.	94	(which is always of type C<struct ev_loop *>) will not have this argument.
95		95
96	=head1 TIME REPRESENTATION	96	=head2 TIME REPRESENTATION
97		97
98	Libev represents time as a single floating point number, representing the	98	Libev represents time as a single floating point number, representing the
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	99	(fractional) number of seconds since the (POSIX) epoch (somewhere near
100	the beginning of 1970, details are complicated, don't ask). This type is	100	the beginning of 1970, details are complicated, don't ask). This type is
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	101	called C<ev_tstamp>, which is what you should use too. It usually aliases
…		…
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		307
308	This is your standard select(2) backend. Not I<completely> standard, as	308	This is your standard select(2) backend. Not I<completely> standard, as
309	libev tries to roll its own fd_set with no limits on the number of fds,	309	libev tries to roll its own fd_set with no limits on the number of fds,
310	but if that fails, expect a fairly low limit on the number of fds when	310	but if that fails, expect a fairly low limit on the number of fds when
311	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	311	using this backend. It doesn't scale too well (O(highest_fd)), but its
312	the fastest backend for a low number of fds.	312	usually the fastest backend for a low number of (low-numbered :) fds.
		313
		314	To get good performance out of this backend you need a high amount of
		315	parallelity (most of the file descriptors should be busy). If you are
		316	writing a server, you should C<accept ()> in a loop to accept as many
		317	connections as possible during one iteration. You might also want to have
		318	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		319	readyness notifications you get per iteration.
313		320
314	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	321	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
315		322
316	And this is your standard poll(2) backend. It's more complicated than	323	And this is your standard poll(2) backend. It's more complicated
317	select, but handles sparse fds better and has no artificial limit on the	324	than select, but handles sparse fds better and has no artificial
318	number of fds you can use (except it will slow down considerably with a	325	limit on the number of fds you can use (except it will slow down
319	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	326	considerably with a lot of inactive fds). It scales similarly to select,
		327	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		328	performance tips.
320		329
321	=item C<EVBACKEND_EPOLL> (value 4, Linux)	330	=item C<EVBACKEND_EPOLL> (value 4, Linux)
322		331
323	For few fds, this backend is a bit little slower than poll and select,	332	For few fds, this backend is a bit little slower than poll and select,
324	but it scales phenomenally better. While poll and select usually scale	333	but it scales phenomenally better. While poll and select usually scale
325	like O(total_fds) where n is the total number of fds (or the highest fd),	334	like O(total_fds) where n is the total number of fds (or the highest fd),
326	epoll scales either O(1) or O(active_fds). The epoll design has a number	335	epoll scales either O(1) or O(active_fds). The epoll design has a number
327	of shortcomings, such as silently dropping events in some hard-to-detect	336	of shortcomings, such as silently dropping events in some hard-to-detect
328	cases and rewiring a syscall per fd change, no fork support and bad	337	cases and rewiring a syscall per fd change, no fork support and bad
329	support for dup:	338	support for dup.
330		339
331	While stopping, setting and starting an I/O watcher in the same iteration	340	While stopping, setting and starting an I/O watcher in the same iteration
332	will result in some caching, there is still a syscall per such incident	341	will result in some caching, there is still a syscall per such incident
333	(because the fd could point to a different file description now), so its	342	(because the fd could point to a different file description now), so its
334	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	343	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
…		…
336		345
337	Please note that epoll sometimes generates spurious notifications, so you	346	Please note that epoll sometimes generates spurious notifications, so you
338	need to use non-blocking I/O or other means to avoid blocking when no data	347	need to use non-blocking I/O or other means to avoid blocking when no data
339	(or space) is available.	348	(or space) is available.
340		349
		350	Best performance from this backend is achieved by not unregistering all
		351	watchers for a file descriptor until it has been closed, if possible, i.e.
		352	keep at least one watcher active per fd at all times.
		353
		354	While nominally embeddeble in other event loops, this feature is broken in
		355	all kernel versions tested so far.
		356
341	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	357	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
342		358
343	Kqueue deserves special mention, as at the time of this writing, it	359	Kqueue deserves special mention, as at the time of this writing, it
344	was broken on I<all> BSDs (usually it doesn't work with anything but	360	was broken on all BSDs except NetBSD (usually it doesn't work reliably
345	sockets and pipes, except on Darwin, where of course it's completely	361	with anything but sockets and pipes, except on Darwin, where of course
346	useless. On NetBSD, it seems to work for all the FD types I tested, so it
347	is used by default there). For this reason it's not being "autodetected"	362	it's completely useless). For this reason it's not being "autodetected"
348	unless you explicitly specify it explicitly in the flags (i.e. using	363	unless you explicitly specify it explicitly in the flags (i.e. using
349	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	364	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
350	system like NetBSD.	365	system like NetBSD.
351		366
		367	You still can embed kqueue into a normal poll or select backend and use it
		368	only for sockets (after having made sure that sockets work with kqueue on
		369	the target platform). See C<ev_embed> watchers for more info.
		370
352	It scales in the same way as the epoll backend, but the interface to the	371	It scales in the same way as the epoll backend, but the interface to the
353	kernel is more efficient (which says nothing about its actual speed,	372	kernel is more efficient (which says nothing about its actual speed, of
354	of course). While stopping, setting and starting an I/O watcher does	373	course). While stopping, setting and starting an I/O watcher does never
355	never cause an extra syscall as with epoll, it still adds up to two event	374	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
356	changes per incident, support for C<fork ()> is very bad and it drops fds	375	two event changes per incident, support for C<fork ()> is very bad and it
357	silently in similarly hard-to-detetc cases.	376	drops fds silently in similarly hard-to-detect cases.
		377
		378	This backend usually performs well under most conditions.
		379
		380	While nominally embeddable in other event loops, this doesn't work
		381	everywhere, so you might need to test for this. And since it is broken
		382	almost everywhere, you should only use it when you have a lot of sockets
		383	(for which it usually works), by embedding it into another event loop
		384	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		385	sockets.
358		386
359	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	387	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
360		388
361	This is not implemented yet (and might never be).	389	This is not implemented yet (and might never be, unless you send me an
		390	implementation). According to reports, C</dev/poll> only supports sockets
		391	and is not embeddable, which would limit the usefulness of this backend
		392	immensely.
362		393
363	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	394	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
364		395
365	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	396	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
366	it's really slow, but it still scales very well (O(active_fds)).	397	it's really slow, but it still scales very well (O(active_fds)).
367		398
368	Please note that solaris event ports can deliver a lot of spurious	399	Please note that solaris event ports can deliver a lot of spurious
369	notifications, so you need to use non-blocking I/O or other means to avoid	400	notifications, so you need to use non-blocking I/O or other means to avoid
370	blocking when no data (or space) is available.	401	blocking when no data (or space) is available.
371		402
		403	While this backend scales well, it requires one system call per active
		404	file descriptor per loop iteration. For small and medium numbers of file
		405	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		406	might perform better.
		407
372	=item C<EVBACKEND_ALL>	408	=item C<EVBACKEND_ALL>
373		409
374	Try all backends (even potentially broken ones that wouldn't be tried	410	Try all backends (even potentially broken ones that wouldn't be tried
375	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	411	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
376	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	412	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		413
		414	It is definitely not recommended to use this flag.
377		415
378	=back	416	=back
379		417
380	If one or more of these are ored into the flags value, then only these	418	If one or more of these are ored into the flags value, then only these
381	backends will be tried (in the reverse order as given here). If none are	419	backends will be tried (in the reverse order as given here). If none are
…		…
596	overhead for the actual polling but can deliver many events at once.	634	overhead for the actual polling but can deliver many events at once.
597		635
598	By setting a higher I<io collect interval> you allow libev to spend more	636	By setting a higher I<io collect interval> you allow libev to spend more
599	time collecting I/O events, so you can handle more events per iteration,	637	time collecting I/O events, so you can handle more events per iteration,
600	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	638	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
601	C<ev_timer>) will be not affected.	639	C<ev_timer>) will be not affected. Setting this to a non-null value will
		640	introduce an additional C<ev_sleep ()> call into most loop iterations.
602		641
603	Likewise, by setting a higher I<timeout collect interval> you allow libev	642	Likewise, by setting a higher I<timeout collect interval> you allow libev
604	to spend more time collecting timeouts, at the expense of increased	643	to spend more time collecting timeouts, at the expense of increased
605	latency (the watcher callback will be called later). C<ev_io> watchers	644	latency (the watcher callback will be called later). C<ev_io> watchers
606	will not be affected.	645	will not be affected. Setting this to a non-null value will not introduce
		646	any overhead in libev.
607		647
608	Many programs can usually benefit by setting the io collect interval to	648	Many (busy) programs can usually benefit by setting the io collect
609	a value near C<0.1> or so, which is often enough for interactive servers	649	interval to a value near C<0.1> or so, which is often enough for
610	(of course not for games), likewise for timeouts. It usually doesn't make	650	interactive servers (of course not for games), likewise for timeouts. It
611	much sense to set it to a lower value than C<0.01>, as this approsaches	651	usually doesn't make much sense to set it to a lower value than C<0.01>,
612	the timing granularity of most systems.	652	as this approsaches the timing granularity of most systems.
613		653
614	=back	654	=back
615		655
616		656
617	=head1 ANATOMY OF A WATCHER	657	=head1 ANATOMY OF A WATCHER
…		…
943	In general you can register as many read and/or write event watchers per	983	In general you can register as many read and/or write event watchers per
944	fd as you want (as long as you don't confuse yourself). Setting all file	984	fd as you want (as long as you don't confuse yourself). Setting all file
945	descriptors to non-blocking mode is also usually a good idea (but not	985	descriptors to non-blocking mode is also usually a good idea (but not
946	required if you know what you are doing).	986	required if you know what you are doing).
947		987
948	You have to be careful with dup'ed file descriptors, though. Some backends
949	(the linux epoll backend is a notable example) cannot handle dup'ed file
950	descriptors correctly if you register interest in two or more fds pointing
951	to the same underlying file/socket/etc. description (that is, they share
952	the same underlying "file open").
953
954	If you must do this, then force the use of a known-to-be-good backend	988	If you must do this, then force the use of a known-to-be-good backend
955	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	989	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
956	C<EVBACKEND_POLL>).	990	C<EVBACKEND_POLL>).
957		991
958	Another thing you have to watch out for is that it is quite easy to	992	Another thing you have to watch out for is that it is quite easy to
…		…
992	optimisations to libev.	1026	optimisations to libev.
993		1027
994	=head3 The special problem of dup'ed file descriptors	1028	=head3 The special problem of dup'ed file descriptors
995		1029
996	Some backends (e.g. epoll), cannot register events for file descriptors,	1030	Some backends (e.g. epoll), cannot register events for file descriptors,
997	but only events for the underlying file descriptions. That menas when you	1031	but only events for the underlying file descriptions. That means when you
998	have C<dup ()>'ed file descriptors and register events for them, only one	1032	have C<dup ()>'ed file descriptors or weirder constellations, and register
999	file descriptor might actually receive events.	1033	events for them, only one file descriptor might actually receive events.
1000		1034
1001	There is no workaorund possible except not registering events	1035	There is no workaround possible except not registering events
1002	for potentially C<dup ()>'ed file descriptors or to resort to	1036	for potentially C<dup ()>'ed file descriptors, or to resort to
1003	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1037	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1004		1038
1005	=head3 The special problem of fork	1039	=head3 The special problem of fork
1006		1040
1007	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1041	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
…		…
1033	=item int events [read-only]	1067	=item int events [read-only]
1034		1068
1035	The events being watched.	1069	The events being watched.
1036		1070
1037	=back	1071	=back
		1072
		1073	=head3 Examples
1038		1074
1039	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1075	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1040	readable, but only once. Since it is likely line-buffered, you could	1076	readable, but only once. Since it is likely line-buffered, you could
1041	attempt to read a whole line in the callback.	1077	attempt to read a whole line in the callback.
1042		1078
…		…
1140	or C<ev_timer_again> is called and determines the next timeout (if any),	1176	or C<ev_timer_again> is called and determines the next timeout (if any),
1141	which is also when any modifications are taken into account.	1177	which is also when any modifications are taken into account.
1142		1178
1143	=back	1179	=back
1144		1180
		1181	=head3 Examples
		1182
1145	Example: Create a timer that fires after 60 seconds.	1183	Example: Create a timer that fires after 60 seconds.
1146		1184
1147	static void	1185	static void
1148	one_minute_cb (struct ev_loop loop, struct ev_timer w, int revents)	1186	one_minute_cb (struct ev_loop loop, struct ev_timer w, int revents)
1149	{	1187	{
…		…
1306	When active, contains the absolute time that the watcher is supposed to	1344	When active, contains the absolute time that the watcher is supposed to
1307	trigger next.	1345	trigger next.
1308		1346
1309	=back	1347	=back
1310		1348
		1349	=head3 Examples
		1350
1311	Example: Call a callback every hour, or, more precisely, whenever the	1351	Example: Call a callback every hour, or, more precisely, whenever the
1312	system clock is divisible by 3600. The callback invocation times have	1352	system clock is divisible by 3600. The callback invocation times have
1313	potentially a lot of jittering, but good long-term stability.	1353	potentially a lot of jittering, but good long-term stability.
1314		1354
1315	static void	1355	static void
…		…
1406		1446
1407	The process exit/trace status caused by C<rpid> (see your systems	1447	The process exit/trace status caused by C<rpid> (see your systems
1408	C<waitpid> and C<sys/wait.h> documentation for details).	1448	C<waitpid> and C<sys/wait.h> documentation for details).
1409		1449
1410	=back	1450	=back
		1451
		1452	=head3 Examples
1411		1453
1412	Example: Try to exit cleanly on SIGINT and SIGTERM.	1454	Example: Try to exit cleanly on SIGINT and SIGTERM.
1413		1455
1414	static void	1456	static void
1415	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)	1457	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)
…		…
1456	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1498	semantics of C<ev_stat> watchers, which means that libev sometimes needs
1457	to fall back to regular polling again even with inotify, but changes are	1499	to fall back to regular polling again even with inotify, but changes are
1458	usually detected immediately, and if the file exists there will be no	1500	usually detected immediately, and if the file exists there will be no
1459	polling.	1501	polling.
1460		1502
		1503	=head3 Inotify
		1504
		1505	When C<inotify (7)> support has been compiled into libev (generally only
		1506	available on Linux) and present at runtime, it will be used to speed up
		1507	change detection where possible. The inotify descriptor will be created lazily
		1508	when the first C<ev_stat> watcher is being started.
		1509
		1510	Inotify presense does not change the semantics of C<ev_stat> watchers
		1511	except that changes might be detected earlier, and in some cases, to avoid
		1512	making regular C<stat> calls. Even in the presense of inotify support
		1513	there are many cases where libev has to resort to regular C<stat> polling.
		1514
		1515	(There is no support for kqueue, as apparently it cannot be used to
		1516	implement this functionality, due to the requirement of having a file
		1517	descriptor open on the object at all times).
		1518
		1519	=head3 The special problem of stat time resolution
		1520
		1521	The C<stat ()> syscall only supports full-second resolution portably, and
		1522	even on systems where the resolution is higher, many filesystems still
		1523	only support whole seconds.
		1524
		1525	That means that, if the time is the only thing that changes, you might
		1526	miss updates: on the first update, C<ev_stat> detects a change and calls
		1527	your callback, which does something. When there is another update within
		1528	the same second, C<ev_stat> will be unable to detect it.
		1529
		1530	The solution to this is to delay acting on a change for a second (or till
		1531	the next second boundary), using a roughly one-second delay C<ev_timer>
		1532	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
		1533	is added to work around small timing inconsistencies of some operating
		1534	systems.
		1535
1461	=head3 Watcher-Specific Functions and Data Members	1536	=head3 Watcher-Specific Functions and Data Members
1462		1537
1463	=over 4	1538	=over 4
1464		1539
1465	=item ev_stat_init (ev_stat , callback, const char path, ev_tstamp interval)	1540	=item ev_stat_init (ev_stat , callback, const char path, ev_tstamp interval)
…		…
1502	=item const char *path [read-only]	1577	=item const char *path [read-only]
1503		1578
1504	The filesystem path that is being watched.	1579	The filesystem path that is being watched.
1505		1580
1506	=back	1581	=back
		1582
		1583	=head3 Examples
1507		1584
1508	Example: Watch C</etc/passwd> for attribute changes.	1585	Example: Watch C</etc/passwd> for attribute changes.
1509		1586
1510	static void	1587	static void
1511	passwd_cb (struct ev_loop loop, ev_stat w, int revents)	1588	passwd_cb (struct ev_loop loop, ev_stat w, int revents)
…		…
1524	}	1601	}
1525		1602
1526	...	1603	...
1527	ev_stat passwd;	1604	ev_stat passwd;
1528		1605
1529	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	1606	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1530	ev_stat_start (loop, &passwd);	1607	ev_stat_start (loop, &passwd);
		1608
		1609	Example: Like above, but additionally use a one-second delay so we do not
		1610	miss updates (however, frequent updates will delay processing, too, so
		1611	one might do the work both on C<ev_stat> callback invocation I<and> on
		1612	C<ev_timer> callback invocation).
		1613
		1614	static ev_stat passwd;
		1615	static ev_timer timer;
		1616
		1617	static void
		1618	timer_cb (EV_P_ ev_timer *w, int revents)
		1619	{
		1620	ev_timer_stop (EV_A_ w);
		1621
		1622	/* now it's one second after the most recent passwd change */
		1623	}
		1624
		1625	static void
		1626	stat_cb (EV_P_ ev_stat *w, int revents)
		1627	{
		1628	/* reset the one-second timer */
		1629	ev_timer_again (EV_A_ &timer);
		1630	}
		1631
		1632	...
		1633	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1634	ev_stat_start (loop, &passwd);
		1635	ev_timer_init (&timer, timer_cb, 0., 1.01);
1531		1636
1532		1637
1533	=head2 C<ev_idle> - when you've got nothing better to do...	1638	=head2 C<ev_idle> - when you've got nothing better to do...
1534		1639
1535	Idle watchers trigger events when no other events of the same or higher	1640	Idle watchers trigger events when no other events of the same or higher
…		…
1560	Initialises and configures the idle watcher - it has no parameters of any	1665	Initialises and configures the idle watcher - it has no parameters of any
1561	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1666	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1562	believe me.	1667	believe me.
1563		1668
1564	=back	1669	=back
		1670
		1671	=head3 Examples
1565		1672
1566	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	1673	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1567	callback, free it. Also, use no error checking, as usual.	1674	callback, free it. Also, use no error checking, as usual.
1568		1675
1569	static void	1676	static void
…		…
1621		1728
1622	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	1729	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1623	priority, to ensure that they are being run before any other watchers	1730	priority, to ensure that they are being run before any other watchers
1624	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	1731	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
1625	too) should not activate ("feed") events into libev. While libev fully	1732	too) should not activate ("feed") events into libev. While libev fully
1626	supports this, they will be called before other C<ev_check> watchers did	1733	supports this, they will be called before other C<ev_check> watchers
1627	their job. As C<ev_check> watchers are often used to embed other event	1734	did their job. As C<ev_check> watchers are often used to embed other
1628	loops those other event loops might be in an unusable state until their	1735	(non-libev) event loops those other event loops might be in an unusable
1629	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	1736	state until their C<ev_check> watcher ran (always remind yourself to
1630	others).	1737	coexist peacefully with others).
1631		1738
1632	=head3 Watcher-Specific Functions and Data Members	1739	=head3 Watcher-Specific Functions and Data Members
1633		1740
1634	=over 4	1741	=over 4
1635		1742
…		…
1640	Initialises and configures the prepare or check watcher - they have no	1747	Initialises and configures the prepare or check watcher - they have no
1641	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1748	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1642	macros, but using them is utterly, utterly and completely pointless.	1749	macros, but using them is utterly, utterly and completely pointless.
1643		1750
1644	=back	1751	=back
		1752
		1753	=head3 Examples
1645		1754
1646	There are a number of principal ways to embed other event loops or modules	1755	There are a number of principal ways to embed other event loops or modules
1647	into libev. Here are some ideas on how to include libadns into libev	1756	into libev. Here are some ideas on how to include libadns into libev
1648	(there is a Perl module named C<EV::ADNS> that does this, which you could	1757	(there is a Perl module named C<EV::ADNS> that does this, which you could
1649	use for an actually working example. Another Perl module named C<EV::Glib>	1758	use for an actually working example. Another Perl module named C<EV::Glib>
…		…
1774	=head2 C<ev_embed> - when one backend isn't enough...	1883	=head2 C<ev_embed> - when one backend isn't enough...
1775		1884
1776	This is a rather advanced watcher type that lets you embed one event loop	1885	This is a rather advanced watcher type that lets you embed one event loop
1777	into another (currently only C<ev_io> events are supported in the embedded	1886	into another (currently only C<ev_io> events are supported in the embedded
1778	loop, other types of watchers might be handled in a delayed or incorrect	1887	loop, other types of watchers might be handled in a delayed or incorrect
1779	fashion and must not be used). (See portability notes, below).	1888	fashion and must not be used).
1780		1889
1781	There are primarily two reasons you would want that: work around bugs and	1890	There are primarily two reasons you would want that: work around bugs and
1782	prioritise I/O.	1891	prioritise I/O.
1783		1892
1784	As an example for a bug workaround, the kqueue backend might only support	1893	As an example for a bug workaround, the kqueue backend might only support
…		…
1818	portable one.	1927	portable one.
1819		1928
1820	So when you want to use this feature you will always have to be prepared	1929	So when you want to use this feature you will always have to be prepared
1821	that you cannot get an embeddable loop. The recommended way to get around	1930	that you cannot get an embeddable loop. The recommended way to get around
1822	this is to have a separate variables for your embeddable loop, try to	1931	this is to have a separate variables for your embeddable loop, try to
1823	create it, and if that fails, use the normal loop for everything:	1932	create it, and if that fails, use the normal loop for everything.
		1933
		1934	=head3 Watcher-Specific Functions and Data Members
		1935
		1936	=over 4
		1937
		1938	=item ev_embed_init (ev_embed , callback, struct ev_loop embedded_loop)
		1939
		1940	=item ev_embed_set (ev_embed , callback, struct ev_loop embedded_loop)
		1941
		1942	Configures the watcher to embed the given loop, which must be
		1943	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		1944	invoked automatically, otherwise it is the responsibility of the callback
		1945	to invoke it (it will continue to be called until the sweep has been done,
		1946	if you do not want thta, you need to temporarily stop the embed watcher).
		1947
		1948	=item ev_embed_sweep (loop, ev_embed *)
		1949
		1950	Make a single, non-blocking sweep over the embedded loop. This works
		1951	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		1952	apropriate way for embedded loops.
		1953
		1954	=item struct ev_loop *other [read-only]
		1955
		1956	The embedded event loop.
		1957
		1958	=back
		1959
		1960	=head3 Examples
		1961
		1962	Example: Try to get an embeddable event loop and embed it into the default
		1963	event loop. If that is not possible, use the default loop. The default
		1964	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		1965	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		1966	used).
1824		1967
1825	struct ev_loop *loop_hi = ev_default_init (0);	1968	struct ev_loop *loop_hi = ev_default_init (0);
1826	struct ev_loop *loop_lo = 0;	1969	struct ev_loop *loop_lo = 0;
1827	struct ev_embed embed;	1970	struct ev_embed embed;
1828		1971
…		…
1839	ev_embed_start (loop_hi, &embed);	1982	ev_embed_start (loop_hi, &embed);
1840	}	1983	}
1841	else	1984	else
1842	loop_lo = loop_hi;	1985	loop_lo = loop_hi;
1843		1986
1844	=head2 Portability notes	1987	Example: Check if kqueue is available but not recommended and create
		1988	a kqueue backend for use with sockets (which usually work with any
		1989	kqueue implementation). Store the kqueue/socket-only event loop in
		1990	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
1845		1991
1846	Kqueue is nominally embeddable, but this is broken on all BSDs that I	1992	struct ev_loop *loop = ev_default_init (0);
1847	tried, in various ways. Usually the embedded event loop will simply never	1993	struct ev_loop *loop_socket = 0;
1848	receive events, sometimes it will only trigger a few times, sometimes in a	1994	struct ev_embed embed;
1849	loop. Epoll is also nominally embeddable, but many Linux kernel versions	1995
1850	will always eport the epoll fd as ready, even when no events are pending.	1996	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		1997	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		1998	{
		1999	ev_embed_init (&embed, 0, loop_socket);
		2000	ev_embed_start (loop, &embed);
		2001	}
1851		2002
1852	While libev allows embedding these backends (they are contained in	2003	if (!loop_socket)
1853	C<ev_embeddable_backends ()>), take extreme care that it will actually	2004	loop_socket = loop;
1854	work.
1855		2005
1856	When in doubt, create a dynamic event loop forced to use sockets (this	2006	// now use loop_socket for all sockets, and loop for everything else
1857	usually works) and possibly another thread and a pipe or so to report to
1858	your main event loop.
1859
1860	=head3 Watcher-Specific Functions and Data Members
1861
1862	=over 4
1863
1864	=item ev_embed_init (ev_embed , callback, struct ev_loop embedded_loop)
1865
1866	=item ev_embed_set (ev_embed , callback, struct ev_loop embedded_loop)
1867
1868	Configures the watcher to embed the given loop, which must be
1869	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1870	invoked automatically, otherwise it is the responsibility of the callback
1871	to invoke it (it will continue to be called until the sweep has been done,
1872	if you do not want thta, you need to temporarily stop the embed watcher).
1873
1874	=item ev_embed_sweep (loop, ev_embed *)
1875
1876	Make a single, non-blocking sweep over the embedded loop. This works
1877	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1878	apropriate way for embedded loops.
1879
1880	=item struct ev_loop *other [read-only]
1881
1882	The embedded event loop.
1883
1884	=back
1885		2007
1886		2008
1887	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2009	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1888		2010
1889	Fork watchers are called when a C<fork ()> was detected (usually because	2011	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2368	wants osf handles on win32 (this is the case when the select to	2490	wants osf handles on win32 (this is the case when the select to
2369	be used is the winsock select). This means that it will call	2491	be used is the winsock select). This means that it will call
2370	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	2492	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2371	it is assumed that all these functions actually work on fds, even	2493	it is assumed that all these functions actually work on fds, even
2372	on win32. Should not be defined on non-win32 platforms.	2494	on win32. Should not be defined on non-win32 platforms.
		2495
		2496	=item EV_FD_TO_WIN32_HANDLE
		2497
		2498	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2499	file descriptors to socket handles. When not defining this symbol (the
		2500	default), then libev will call C<_get_osfhandle>, which is usually
		2501	correct. In some cases, programs use their own file descriptor management,
		2502	in which case they can provide this function to map fds to socket handles.
2373		2503
2374	=item EV_USE_POLL	2504	=item EV_USE_POLL
2375		2505
2376	If defined to be C<1>, libev will compile in support for the C<poll>(2)	2506	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2377	backend. Otherwise it will be enabled on non-win32 platforms. It	2507	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
2414	be detected at runtime.	2544	be detected at runtime.
2415		2545
2416	=item EV_H	2546	=item EV_H
2417		2547
2418	The name of the F<ev.h> header file used to include it. The default if	2548	The name of the F<ev.h> header file used to include it. The default if
2419	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	2549	undefined is C<"ev.h"> in F<event.h> and F<ev.c>. This can be used to
2420	can be used to virtually rename the F<ev.h> header file in case of conflicts.	2550	virtually rename the F<ev.h> header file in case of conflicts.
2421		2551
2422	=item EV_CONFIG_H	2552	=item EV_CONFIG_H
2423		2553
2424	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	2554	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2425	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	2555	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2426	C<EV_H>, above.	2556	C<EV_H>, above.
2427		2557
2428	=item EV_EVENT_H	2558	=item EV_EVENT_H
2429		2559
2430	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	2560	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2431	of how the F<event.h> header can be found.	2561	of how the F<event.h> header can be found, the dfeault is C<"event.h">.
2432		2562
2433	=item EV_PROTOTYPES	2563	=item EV_PROTOTYPES
2434		2564
2435	If defined to be C<0>, then F<ev.h> will not define any function	2565	If defined to be C<0>, then F<ev.h> will not define any function
2436	prototypes, but still define all the structs and other symbols. This is	2566	prototypes, but still define all the structs and other symbols. This is
…		…
2502	than enough. If you need to manage thousands of children you might want to	2632	than enough. If you need to manage thousands of children you might want to
2503	increase this value (I<must> be a power of two).	2633	increase this value (I<must> be a power of two).
2504		2634
2505	=item EV_INOTIFY_HASHSIZE	2635	=item EV_INOTIFY_HASHSIZE
2506		2636
2507	C<ev_staz> watchers use a small hash table to distribute workload by	2637	C<ev_stat> watchers use a small hash table to distribute workload by
2508	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	2638	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2509	usually more than enough. If you need to manage thousands of C<ev_stat>	2639	usually more than enough. If you need to manage thousands of C<ev_stat>
2510	watchers you might want to increase this value (I<must> be a power of	2640	watchers you might want to increase this value (I<must> be a power of
2511	two).	2641	two).
2512		2642
…		…
2608		2738
2609	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	2739	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2610		2740
2611	This means that, when you have a watcher that triggers in one hour and	2741	This means that, when you have a watcher that triggers in one hour and
2612	there are 100 watchers that would trigger before that then inserting will	2742	there are 100 watchers that would trigger before that then inserting will
2613	have to skip those 100 watchers.	2743	have to skip roughly seven (C<ld 100>) of these watchers.
2614		2744
2615	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	2745	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2616		2746
2617	That means that for changing a timer costs less than removing/adding them	2747	That means that changing a timer costs less than removing/adding them
2618	as only the relative motion in the event queue has to be paid for.	2748	as only the relative motion in the event queue has to be paid for.
2619		2749
2620	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	2750	=item Starting io/check/prepare/idle/signal/child watchers: O(1)
2621		2751
2622	These just add the watcher into an array or at the head of a list.	2752	These just add the watcher into an array or at the head of a list.
		2753
2623	=item Stopping check/prepare/idle watchers: O(1)	2754	=item Stopping check/prepare/idle watchers: O(1)
2624		2755
2625	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	2756	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2626		2757
2627	These watchers are stored in lists then need to be walked to find the	2758	These watchers are stored in lists then need to be walked to find the
2628	correct watcher to remove. The lists are usually short (you don't usually	2759	correct watcher to remove. The lists are usually short (you don't usually
2629	have many watchers waiting for the same fd or signal).	2760	have many watchers waiting for the same fd or signal).
2630		2761
2631	=item Finding the next timer per loop iteration: O(1)	2762	=item Finding the next timer in each loop iteration: O(1)
		2763
		2764	By virtue of using a binary heap, the next timer is always found at the
		2765	beginning of the storage array.
2632		2766
2633	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	2767	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2634		2768
2635	A change means an I/O watcher gets started or stopped, which requires	2769	A change means an I/O watcher gets started or stopped, which requires
2636	libev to recalculate its status (and possibly tell the kernel).	2770	libev to recalculate its status (and possibly tell the kernel, depending
		2771	on backend and wether C<ev_io_set> was used).
2637		2772
2638	=item Activating one watcher: O(1)	2773	=item Activating one watcher (putting it into the pending state): O(1)
2639		2774
2640	=item Priority handling: O(number_of_priorities)	2775	=item Priority handling: O(number_of_priorities)
2641		2776
2642	Priorities are implemented by allocating some space for each	2777	Priorities are implemented by allocating some space for each
2643	priority. When doing priority-based operations, libev usually has to	2778	priority. When doing priority-based operations, libev usually has to
2644	linearly search all the priorities.	2779	linearly search all the priorities, but starting/stopping and activating
		2780	watchers becomes O(1) w.r.t. prioritiy handling.
2645		2781
2646	=back	2782	=back
2647		2783
2648		2784
		2785	=head1 Win32 platform limitations and workarounds
		2786
		2787	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		2788	requires, and its I/O model is fundamentally incompatible with the POSIX
		2789	model. Libev still offers limited functionality on this platform in
		2790	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		2791	descriptors. This only applies when using Win32 natively, not when using
		2792	e.g. cygwin.
		2793
		2794	There is no supported compilation method available on windows except
		2795	embedding it into other applications.
		2796
		2797	Due to the many, low, and arbitrary limits on the win32 platform and the
		2798	abysmal performance of winsockets, using a large number of sockets is not
		2799	recommended (and not reasonable). If your program needs to use more than
		2800	a hundred or so sockets, then likely it needs to use a totally different
		2801	implementation for windows, as libev offers the POSIX model, which cannot
		2802	be implemented efficiently on windows (microsoft monopoly games).
		2803
		2804	=over 4
		2805
		2806	=item The winsocket select function
		2807
		2808	The winsocket C<select> function doesn't follow POSIX in that it requires
		2809	socket I<handles> and not socket I<file descriptors>. This makes select
		2810	very inefficient, and also requires a mapping from file descriptors
		2811	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
		2812	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
		2813	symbols for more info.
		2814
		2815	The configuration for a "naked" win32 using the microsoft runtime
		2816	libraries and raw winsocket select is:
		2817
		2818	#define EV_USE_SELECT 1
		2819	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		2820
		2821	Note that winsockets handling of fd sets is O(n), so you can easily get a
		2822	complexity in the O(n²) range when using win32.
		2823
		2824	=item Limited number of file descriptors
		2825
		2826	Windows has numerous arbitrary (and low) limits on things. Early versions
		2827	of winsocket's select only supported waiting for a max. of C<64> handles
		2828	(probably owning to the fact that all windows kernels can only wait for
		2829	C<64> things at the same time internally; microsoft recommends spawning a
		2830	chain of threads and wait for 63 handles and the previous thread in each).
		2831
		2832	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		2833	to some high number (e.g. C<2048>) before compiling the winsocket select
		2834	call (which might be in libev or elsewhere, for example, perl does its own
		2835	select emulation on windows).
		2836
		2837	Another limit is the number of file descriptors in the microsoft runtime
		2838	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		2839	or something like this inside microsoft). You can increase this by calling
		2840	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		2841	arbitrary limit), but is broken in many versions of the microsoft runtime
		2842	libraries.
		2843
		2844	This might get you to about C<512> or C<2048> sockets (depending on
		2845	windows version and/or the phase of the moon). To get more, you need to
		2846	wrap all I/O functions and provide your own fd management, but the cost of
		2847	calling select (O(n²)) will likely make this unworkable.
		2848
		2849	=back
		2850
		2851
2649	=head1 AUTHOR	2852	=head1 AUTHOR
2650		2853
2651	Marc Lehmann <libev@schmorp.de>.	2854	Marc Lehmann <libev@schmorp.de>.
2652		2855

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Comparing libev/ev.pod (file contents): Revision 1.97 by root, Sat Dec 22 05:48:02 2007 UTC vs. Revision 1.112 by root, Wed Dec 26 08:06:09 2007 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.97 by root, Sat Dec 22 05:48:02 2007 UTC vs.
Revision 1.112 by root, Wed Dec 26 08:06:09 2007 UTC