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

Comparing libev/ev.pod (file contents):
Revision 1.98 by root, Sat Dec 22 06:10:25 2007 UTC vs.
Revision 1.115 by root, Mon Dec 31 01:32:59 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
…		…
513	usually a better approach for this kind of thing.	551	usually a better approach for this kind of thing.
514		552
515	Here are the gory details of what C<ev_loop> does:	553	Here are the gory details of what C<ev_loop> does:
516		554
517	- Before the first iteration, call any pending watchers.	555	- Before the first iteration, call any pending watchers.
518	* If there are no active watchers (reference count is zero), return.	556	* If EVFLAG_FORKCHECK was used, check for a fork.
519	- Queue all prepare watchers and then call all outstanding watchers.	557	- If a fork was detected, queue and call all fork watchers.
		558	- Queue and call all prepare watchers.
520	- If we have been forked, recreate the kernel state.	559	- If we have been forked, recreate the kernel state.
521	- Update the kernel state with all outstanding changes.	560	- Update the kernel state with all outstanding changes.
522	- Update the "event loop time".	561	- Update the "event loop time".
523	- Calculate for how long to block.	562	- Calculate for how long to sleep or block, if at all
		563	(active idle watchers, EVLOOP_NONBLOCK or not having
		564	any active watchers at all will result in not sleeping).
		565	- Sleep if the I/O and timer collect interval say so.
524	- Block the process, waiting for any events.	566	- Block the process, waiting for any events.
525	- Queue all outstanding I/O (fd) events.	567	- Queue all outstanding I/O (fd) events.
526	- Update the "event loop time" and do time jump handling.	568	- Update the "event loop time" and do time jump handling.
527	- Queue all outstanding timers.	569	- Queue all outstanding timers.
528	- Queue all outstanding periodics.	570	- Queue all outstanding periodics.
529	- If no events are pending now, queue all idle watchers.	571	- If no events are pending now, queue all idle watchers.
530	- Queue all check watchers.	572	- Queue all check watchers.
531	- Call all queued watchers in reverse order (i.e. check watchers first).	573	- Call all queued watchers in reverse order (i.e. check watchers first).
532	Signals and child watchers are implemented as I/O watchers, and will	574	Signals and child watchers are implemented as I/O watchers, and will
533	be handled here by queueing them when their watcher gets executed.	575	be handled here by queueing them when their watcher gets executed.
534	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	576	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
535	were used, return, otherwise continue with step *.	577	were used, or there are no active watchers, return, otherwise
		578	continue with step *.
536		579
537	Example: Queue some jobs and then loop until no events are outsanding	580	Example: Queue some jobs and then loop until no events are outstanding
538	anymore.	581	anymore.
539		582
540	... queue jobs here, make sure they register event watchers as long	583	... queue jobs here, make sure they register event watchers as long
541	... as they still have work to do (even an idle watcher will do..)	584	... as they still have work to do (even an idle watcher will do..)
542	ev_loop (my_loop, 0);	585	ev_loop (my_loop, 0);
…		…
546		589
547	Can be used to make a call to C<ev_loop> return early (but only after it	590	Can be used to make a call to C<ev_loop> return early (but only after it
548	has processed all outstanding events). The C<how> argument must be either	591	has processed all outstanding events). The C<how> argument must be either
549	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	592	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
550	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	593	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		594
		595	This "unloop state" will be cleared when entering C<ev_loop> again.
551		596
552	=item ev_ref (loop)	597	=item ev_ref (loop)
553		598
554	=item ev_unref (loop)	599	=item ev_unref (loop)
555		600
…		…
596	overhead for the actual polling but can deliver many events at once.	641	overhead for the actual polling but can deliver many events at once.
597		642
598	By setting a higher I<io collect interval> you allow libev to spend more	643	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,	644	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	645	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
601	C<ev_timer>) will be not affected.	646	C<ev_timer>) will be not affected. Setting this to a non-null value will
		647	introduce an additional C<ev_sleep ()> call into most loop iterations.
602		648
603	Likewise, by setting a higher I<timeout collect interval> you allow libev	649	Likewise, by setting a higher I<timeout collect interval> you allow libev
604	to spend more time collecting timeouts, at the expense of increased	650	to spend more time collecting timeouts, at the expense of increased
605	latency (the watcher callback will be called later). C<ev_io> watchers	651	latency (the watcher callback will be called later). C<ev_io> watchers
606	will not be affected.	652	will not be affected. Setting this to a non-null value will not introduce
		653	any overhead in libev.
607		654
608	Many (busy) programs can usually benefit by setting the io collect	655	Many (busy) programs can usually benefit by setting the io collect
609	interval to a value near C<0.1> or so, which is often enough for	656	interval to a value near C<0.1> or so, which is often enough for
610	interactive servers (of course not for games), likewise for timeouts. It	657	interactive servers (of course not for games), likewise for timeouts. It
611	usually doesn't make much sense to set it to a lower value than C<0.01>,	658	usually doesn't make much sense to set it to a lower value than C<0.01>,
…		…
943	In general you can register as many read and/or write event watchers per	990	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	991	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	992	descriptors to non-blocking mode is also usually a good idea (but not
946	required if you know what you are doing).	993	required if you know what you are doing).
947		994
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	995	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	996	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
956	C<EVBACKEND_POLL>).	997	C<EVBACKEND_POLL>).
957		998
958	Another thing you have to watch out for is that it is quite easy to	999	Another thing you have to watch out for is that it is quite easy to
…		…
992	optimisations to libev.	1033	optimisations to libev.
993		1034
994	=head3 The special problem of dup'ed file descriptors	1035	=head3 The special problem of dup'ed file descriptors
995		1036
996	Some backends (e.g. epoll), cannot register events for file descriptors,	1037	Some backends (e.g. epoll), cannot register events for file descriptors,
997	but only events for the underlying file descriptions. That menas when you	1038	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	1039	have C<dup ()>'ed file descriptors or weirder constellations, and register
999	file descriptor might actually receive events.	1040	events for them, only one file descriptor might actually receive events.
1000		1041
1001	There is no workaorund possible except not registering events	1042	There is no workaround possible except not registering events
1002	for potentially C<dup ()>'ed file descriptors or to resort to	1043	for potentially C<dup ()>'ed file descriptors, or to resort to
1003	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1044	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1004		1045
1005	=head3 The special problem of fork	1046	=head3 The special problem of fork
1006		1047
1007	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1048	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
…		…
1033	=item int events [read-only]	1074	=item int events [read-only]
1034		1075
1035	The events being watched.	1076	The events being watched.
1036		1077
1037	=back	1078	=back
		1079
		1080	=head3 Examples
1038		1081
1039	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1082	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	1083	readable, but only once. Since it is likely line-buffered, you could
1041	attempt to read a whole line in the callback.	1084	attempt to read a whole line in the callback.
1042		1085
…		…
1140	or C<ev_timer_again> is called and determines the next timeout (if any),	1183	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.	1184	which is also when any modifications are taken into account.
1142		1185
1143	=back	1186	=back
1144		1187
		1188	=head3 Examples
		1189
1145	Example: Create a timer that fires after 60 seconds.	1190	Example: Create a timer that fires after 60 seconds.
1146		1191
1147	static void	1192	static void
1148	one_minute_cb (struct ev_loop loop, struct ev_timer w, int revents)	1193	one_minute_cb (struct ev_loop loop, struct ev_timer w, int revents)
1149	{	1194	{
…		…
1306	When active, contains the absolute time that the watcher is supposed to	1351	When active, contains the absolute time that the watcher is supposed to
1307	trigger next.	1352	trigger next.
1308		1353
1309	=back	1354	=back
1310		1355
		1356	=head3 Examples
		1357
1311	Example: Call a callback every hour, or, more precisely, whenever the	1358	Example: Call a callback every hour, or, more precisely, whenever the
1312	system clock is divisible by 3600. The callback invocation times have	1359	system clock is divisible by 3600. The callback invocation times have
1313	potentially a lot of jittering, but good long-term stability.	1360	potentially a lot of jittering, but good long-term stability.
1314		1361
1315	static void	1362	static void
…		…
1406		1453
1407	The process exit/trace status caused by C<rpid> (see your systems	1454	The process exit/trace status caused by C<rpid> (see your systems
1408	C<waitpid> and C<sys/wait.h> documentation for details).	1455	C<waitpid> and C<sys/wait.h> documentation for details).
1409		1456
1410	=back	1457	=back
		1458
		1459	=head3 Examples
1411		1460
1412	Example: Try to exit cleanly on SIGINT and SIGTERM.	1461	Example: Try to exit cleanly on SIGINT and SIGTERM.
1413		1462
1414	static void	1463	static void
1415	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)	1464	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	1505	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	1506	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	1507	usually detected immediately, and if the file exists there will be no
1459	polling.	1508	polling.
1460		1509
		1510	=head3 Inotify
		1511
		1512	When C<inotify (7)> support has been compiled into libev (generally only
		1513	available on Linux) and present at runtime, it will be used to speed up
		1514	change detection where possible. The inotify descriptor will be created lazily
		1515	when the first C<ev_stat> watcher is being started.
		1516
		1517	Inotify presense does not change the semantics of C<ev_stat> watchers
		1518	except that changes might be detected earlier, and in some cases, to avoid
		1519	making regular C<stat> calls. Even in the presense of inotify support
		1520	there are many cases where libev has to resort to regular C<stat> polling.
		1521
		1522	(There is no support for kqueue, as apparently it cannot be used to
		1523	implement this functionality, due to the requirement of having a file
		1524	descriptor open on the object at all times).
		1525
		1526	=head3 The special problem of stat time resolution
		1527
		1528	The C<stat ()> syscall only supports full-second resolution portably, and
		1529	even on systems where the resolution is higher, many filesystems still
		1530	only support whole seconds.
		1531
		1532	That means that, if the time is the only thing that changes, you might
		1533	miss updates: on the first update, C<ev_stat> detects a change and calls
		1534	your callback, which does something. When there is another update within
		1535	the same second, C<ev_stat> will be unable to detect it.
		1536
		1537	The solution to this is to delay acting on a change for a second (or till
		1538	the next second boundary), using a roughly one-second delay C<ev_timer>
		1539	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
		1540	is added to work around small timing inconsistencies of some operating
		1541	systems.
		1542
1461	=head3 Watcher-Specific Functions and Data Members	1543	=head3 Watcher-Specific Functions and Data Members
1462		1544
1463	=over 4	1545	=over 4
1464		1546
1465	=item ev_stat_init (ev_stat , callback, const char path, ev_tstamp interval)	1547	=item ev_stat_init (ev_stat , callback, const char path, ev_tstamp interval)
…		…
1502	=item const char *path [read-only]	1584	=item const char *path [read-only]
1503		1585
1504	The filesystem path that is being watched.	1586	The filesystem path that is being watched.
1505		1587
1506	=back	1588	=back
		1589
		1590	=head3 Examples
1507		1591
1508	Example: Watch C</etc/passwd> for attribute changes.	1592	Example: Watch C</etc/passwd> for attribute changes.
1509		1593
1510	static void	1594	static void
1511	passwd_cb (struct ev_loop loop, ev_stat w, int revents)	1595	passwd_cb (struct ev_loop loop, ev_stat w, int revents)
…		…
1524	}	1608	}
1525		1609
1526	...	1610	...
1527	ev_stat passwd;	1611	ev_stat passwd;
1528		1612
1529	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	1613	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1530	ev_stat_start (loop, &passwd);	1614	ev_stat_start (loop, &passwd);
		1615
		1616	Example: Like above, but additionally use a one-second delay so we do not
		1617	miss updates (however, frequent updates will delay processing, too, so
		1618	one might do the work both on C<ev_stat> callback invocation I<and> on
		1619	C<ev_timer> callback invocation).
		1620
		1621	static ev_stat passwd;
		1622	static ev_timer timer;
		1623
		1624	static void
		1625	timer_cb (EV_P_ ev_timer *w, int revents)
		1626	{
		1627	ev_timer_stop (EV_A_ w);
		1628
		1629	/* now it's one second after the most recent passwd change */
		1630	}
		1631
		1632	static void
		1633	stat_cb (EV_P_ ev_stat *w, int revents)
		1634	{
		1635	/* reset the one-second timer */
		1636	ev_timer_again (EV_A_ &timer);
		1637	}
		1638
		1639	...
		1640	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1641	ev_stat_start (loop, &passwd);
		1642	ev_timer_init (&timer, timer_cb, 0., 1.01);
1531		1643
1532		1644
1533	=head2 C<ev_idle> - when you've got nothing better to do...	1645	=head2 C<ev_idle> - when you've got nothing better to do...
1534		1646
1535	Idle watchers trigger events when no other events of the same or higher	1647	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	1672	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,	1673	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1562	believe me.	1674	believe me.
1563		1675
1564	=back	1676	=back
		1677
		1678	=head3 Examples
1565		1679
1566	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	1680	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1567	callback, free it. Also, use no error checking, as usual.	1681	callback, free it. Also, use no error checking, as usual.
1568		1682
1569	static void	1683	static void
…		…
1621		1735
1622	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	1736	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	1737	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,	1738	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	1739	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	1740	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	1741	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	1742	(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	1743	state until their C<ev_check> watcher ran (always remind yourself to
1630	others).	1744	coexist peacefully with others).
1631		1745
1632	=head3 Watcher-Specific Functions and Data Members	1746	=head3 Watcher-Specific Functions and Data Members
1633		1747
1634	=over 4	1748	=over 4
1635		1749
…		…
1640	Initialises and configures the prepare or check watcher - they have no	1754	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>	1755	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.	1756	macros, but using them is utterly, utterly and completely pointless.
1643		1757
1644	=back	1758	=back
		1759
		1760	=head3 Examples
1645		1761
1646	There are a number of principal ways to embed other event loops or modules	1762	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	1763	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	1764	(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>	1765	use for an actually working example. Another Perl module named C<EV::Glib>
…		…
1774	=head2 C<ev_embed> - when one backend isn't enough...	1890	=head2 C<ev_embed> - when one backend isn't enough...
1775		1891
1776	This is a rather advanced watcher type that lets you embed one event loop	1892	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	1893	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	1894	loop, other types of watchers might be handled in a delayed or incorrect
1779	fashion and must not be used). (See portability notes, below).	1895	fashion and must not be used).
1780		1896
1781	There are primarily two reasons you would want that: work around bugs and	1897	There are primarily two reasons you would want that: work around bugs and
1782	prioritise I/O.	1898	prioritise I/O.
1783		1899
1784	As an example for a bug workaround, the kqueue backend might only support	1900	As an example for a bug workaround, the kqueue backend might only support
…		…
1818	portable one.	1934	portable one.
1819		1935
1820	So when you want to use this feature you will always have to be prepared	1936	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	1937	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	1938	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:	1939	create it, and if that fails, use the normal loop for everything.
		1940
		1941	=head3 Watcher-Specific Functions and Data Members
		1942
		1943	=over 4
		1944
		1945	=item ev_embed_init (ev_embed , callback, struct ev_loop embedded_loop)
		1946
		1947	=item ev_embed_set (ev_embed , callback, struct ev_loop embedded_loop)
		1948
		1949	Configures the watcher to embed the given loop, which must be
		1950	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		1951	invoked automatically, otherwise it is the responsibility of the callback
		1952	to invoke it (it will continue to be called until the sweep has been done,
		1953	if you do not want thta, you need to temporarily stop the embed watcher).
		1954
		1955	=item ev_embed_sweep (loop, ev_embed *)
		1956
		1957	Make a single, non-blocking sweep over the embedded loop. This works
		1958	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		1959	apropriate way for embedded loops.
		1960
		1961	=item struct ev_loop *other [read-only]
		1962
		1963	The embedded event loop.
		1964
		1965	=back
		1966
		1967	=head3 Examples
		1968
		1969	Example: Try to get an embeddable event loop and embed it into the default
		1970	event loop. If that is not possible, use the default loop. The default
		1971	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		1972	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		1973	used).
1824		1974
1825	struct ev_loop *loop_hi = ev_default_init (0);	1975	struct ev_loop *loop_hi = ev_default_init (0);
1826	struct ev_loop *loop_lo = 0;	1976	struct ev_loop *loop_lo = 0;
1827	struct ev_embed embed;	1977	struct ev_embed embed;
1828		1978
…		…
1839	ev_embed_start (loop_hi, &embed);	1989	ev_embed_start (loop_hi, &embed);
1840	}	1990	}
1841	else	1991	else
1842	loop_lo = loop_hi;	1992	loop_lo = loop_hi;
1843		1993
1844	=head2 Portability notes	1994	Example: Check if kqueue is available but not recommended and create
		1995	a kqueue backend for use with sockets (which usually work with any
		1996	kqueue implementation). Store the kqueue/socket-only event loop in
		1997	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
1845		1998
1846	Kqueue is nominally embeddable, but this is broken on all BSDs that I	1999	struct ev_loop *loop = ev_default_init (0);
1847	tried, in various ways. Usually the embedded event loop will simply never	2000	struct ev_loop *loop_socket = 0;
1848	receive events, sometimes it will only trigger a few times, sometimes in a	2001	struct ev_embed embed;
1849	loop. Epoll is also nominally embeddable, but many Linux kernel versions	2002
1850	will always eport the epoll fd as ready, even when no events are pending.	2003	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2004	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2005	{
		2006	ev_embed_init (&embed, 0, loop_socket);
		2007	ev_embed_start (loop, &embed);
		2008	}
1851		2009
1852	While libev allows embedding these backends (they are contained in	2010	if (!loop_socket)
1853	C<ev_embeddable_backends ()>), take extreme care that it will actually	2011	loop_socket = loop;
1854	work.
1855		2012
1856	When in doubt, create a dynamic event loop forced to use sockets (this	2013	// 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		2014
1886		2015
1887	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2016	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1888		2017
1889	Fork watchers are called when a C<fork ()> was detected (usually because	2018	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	2497	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	2498	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,	2499	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	2500	it is assumed that all these functions actually work on fds, even
2372	on win32. Should not be defined on non-win32 platforms.	2501	on win32. Should not be defined on non-win32 platforms.
		2502
		2503	=item EV_FD_TO_WIN32_HANDLE
		2504
		2505	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2506	file descriptors to socket handles. When not defining this symbol (the
		2507	default), then libev will call C<_get_osfhandle>, which is usually
		2508	correct. In some cases, programs use their own file descriptor management,
		2509	in which case they can provide this function to map fds to socket handles.
2373		2510
2374	=item EV_USE_POLL	2511	=item EV_USE_POLL
2375		2512
2376	If defined to be C<1>, libev will compile in support for the C<poll>(2)	2513	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	2514	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
2414	be detected at runtime.	2551	be detected at runtime.
2415		2552
2416	=item EV_H	2553	=item EV_H
2417		2554
2418	The name of the F<ev.h> header file used to include it. The default if	2555	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	2556	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.	2557	virtually rename the F<ev.h> header file in case of conflicts.
2421		2558
2422	=item EV_CONFIG_H	2559	=item EV_CONFIG_H
2423		2560
2424	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	2561	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	2562	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2426	C<EV_H>, above.	2563	C<EV_H>, above.
2427		2564
2428	=item EV_EVENT_H	2565	=item EV_EVENT_H
2429		2566
2430	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	2567	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.	2568	of how the F<event.h> header can be found, the dfeault is C<"event.h">.
2432		2569
2433	=item EV_PROTOTYPES	2570	=item EV_PROTOTYPES
2434		2571
2435	If defined to be C<0>, then F<ev.h> will not define any function	2572	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	2573	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	2639	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).	2640	increase this value (I<must> be a power of two).
2504		2641
2505	=item EV_INOTIFY_HASHSIZE	2642	=item EV_INOTIFY_HASHSIZE
2506		2643
2507	C<ev_staz> watchers use a small hash table to distribute workload by	2644	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>),	2645	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>	2646	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	2647	watchers you might want to increase this value (I<must> be a power of
2511	two).	2648	two).
2512		2649
…		…
2608		2745
2609	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	2746	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2610		2747
2611	This means that, when you have a watcher that triggers in one hour and	2748	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	2749	there are 100 watchers that would trigger before that then inserting will
2613	have to skip those 100 watchers.	2750	have to skip roughly seven (C<ld 100>) of these watchers.
2614		2751
2615	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	2752	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2616		2753
2617	That means that for changing a timer costs less than removing/adding them	2754	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.	2755	as only the relative motion in the event queue has to be paid for.
2619		2756
2620	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	2757	=item Starting io/check/prepare/idle/signal/child watchers: O(1)
2621		2758
2622	These just add the watcher into an array or at the head of a list.	2759	These just add the watcher into an array or at the head of a list.
		2760
2623	=item Stopping check/prepare/idle watchers: O(1)	2761	=item Stopping check/prepare/idle watchers: O(1)
2624		2762
2625	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	2763	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2626		2764
2627	These watchers are stored in lists then need to be walked to find the	2765	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	2766	correct watcher to remove. The lists are usually short (you don't usually
2629	have many watchers waiting for the same fd or signal).	2767	have many watchers waiting for the same fd or signal).
2630		2768
2631	=item Finding the next timer per loop iteration: O(1)	2769	=item Finding the next timer in each loop iteration: O(1)
		2770
		2771	By virtue of using a binary heap, the next timer is always found at the
		2772	beginning of the storage array.
2632		2773
2633	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	2774	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2634		2775
2635	A change means an I/O watcher gets started or stopped, which requires	2776	A change means an I/O watcher gets started or stopped, which requires
2636	libev to recalculate its status (and possibly tell the kernel).	2777	libev to recalculate its status (and possibly tell the kernel, depending
		2778	on backend and wether C<ev_io_set> was used).
2637		2779
2638	=item Activating one watcher: O(1)	2780	=item Activating one watcher (putting it into the pending state): O(1)
2639		2781
2640	=item Priority handling: O(number_of_priorities)	2782	=item Priority handling: O(number_of_priorities)
2641		2783
2642	Priorities are implemented by allocating some space for each	2784	Priorities are implemented by allocating some space for each
2643	priority. When doing priority-based operations, libev usually has to	2785	priority. When doing priority-based operations, libev usually has to
2644	linearly search all the priorities.	2786	linearly search all the priorities, but starting/stopping and activating
		2787	watchers becomes O(1) w.r.t. prioritiy handling.
2645		2788
2646	=back	2789	=back
2647		2790
2648		2791
		2792	=head1 Win32 platform limitations and workarounds
		2793
		2794	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		2795	requires, and its I/O model is fundamentally incompatible with the POSIX
		2796	model. Libev still offers limited functionality on this platform in
		2797	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		2798	descriptors. This only applies when using Win32 natively, not when using
		2799	e.g. cygwin.
		2800
		2801	There is no supported compilation method available on windows except
		2802	embedding it into other applications.
		2803
		2804	Due to the many, low, and arbitrary limits on the win32 platform and the
		2805	abysmal performance of winsockets, using a large number of sockets is not
		2806	recommended (and not reasonable). If your program needs to use more than
		2807	a hundred or so sockets, then likely it needs to use a totally different
		2808	implementation for windows, as libev offers the POSIX model, which cannot
		2809	be implemented efficiently on windows (microsoft monopoly games).
		2810
		2811	=over 4
		2812
		2813	=item The winsocket select function
		2814
		2815	The winsocket C<select> function doesn't follow POSIX in that it requires
		2816	socket I<handles> and not socket I<file descriptors>. This makes select
		2817	very inefficient, and also requires a mapping from file descriptors
		2818	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
		2819	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
		2820	symbols for more info.
		2821
		2822	The configuration for a "naked" win32 using the microsoft runtime
		2823	libraries and raw winsocket select is:
		2824
		2825	#define EV_USE_SELECT 1
		2826	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		2827
		2828	Note that winsockets handling of fd sets is O(n), so you can easily get a
		2829	complexity in the O(n²) range when using win32.
		2830
		2831	=item Limited number of file descriptors
		2832
		2833	Windows has numerous arbitrary (and low) limits on things. Early versions
		2834	of winsocket's select only supported waiting for a max. of C<64> handles
		2835	(probably owning to the fact that all windows kernels can only wait for
		2836	C<64> things at the same time internally; microsoft recommends spawning a
		2837	chain of threads and wait for 63 handles and the previous thread in each).
		2838
		2839	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		2840	to some high number (e.g. C<2048>) before compiling the winsocket select
		2841	call (which might be in libev or elsewhere, for example, perl does its own
		2842	select emulation on windows).
		2843
		2844	Another limit is the number of file descriptors in the microsoft runtime
		2845	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		2846	or something like this inside microsoft). You can increase this by calling
		2847	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		2848	arbitrary limit), but is broken in many versions of the microsoft runtime
		2849	libraries.
		2850
		2851	This might get you to about C<512> or C<2048> sockets (depending on
		2852	windows version and/or the phase of the moon). To get more, you need to
		2853	wrap all I/O functions and provide your own fd management, but the cost of
		2854	calling select (O(n²)) will likely make this unworkable.
		2855
		2856	=back
		2857
		2858
2649	=head1 AUTHOR	2859	=head1 AUTHOR
2650		2860
2651	Marc Lehmann <libev@schmorp.de>.	2861	Marc Lehmann <libev@schmorp.de>.
2652		2862

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Comparing libev/ev.pod (file contents): Revision 1.98 by root, Sat Dec 22 06:10:25 2007 UTC vs. Revision 1.115 by root, Mon Dec 31 01:32:59 2007 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.98 by root, Sat Dec 22 06:10:25 2007 UTC vs.
Revision 1.115 by root, Mon Dec 31 01:32:59 2007 UTC