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

Comparing libev/ev.pod (file contents):
Revision 1.99 by root, Sat Dec 22 06:16:36 2007 UTC vs.
Revision 1.132 by root, Wed Feb 20 17:45:29 2008 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
…		…
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	260	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		261
262	If you don't know what event loop to use, use the one returned from this	262	If you don't know what event loop to use, use the one returned from this
263	function.	263	function.
264		264
		265	The default loop is the only loop that can handle C<ev_signal> and
		266	C<ev_child> watchers, and to do this, it always registers a handler
		267	for C<SIGCHLD>. If this is a problem for your app you can either
		268	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		269	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		270	C<ev_default_init>.
		271
265	The flags argument can be used to specify special behaviour or specific	272	The flags argument can be used to specify special behaviour or specific
266	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	273	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
267		274
268	The following flags are supported:	275	The following flags are supported:
269		276
…		…
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	313	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		314
308	This is your standard select(2) backend. Not I<completely> standard, as	315	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,	316	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	317	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	318	using this backend. It doesn't scale too well (O(highest_fd)), but its
312	the fastest backend for a low number of fds.	319	usually the fastest backend for a low number of (low-numbered :) fds.
		320
		321	To get good performance out of this backend you need a high amount of
		322	parallelity (most of the file descriptors should be busy). If you are
		323	writing a server, you should C<accept ()> in a loop to accept as many
		324	connections as possible during one iteration. You might also want to have
		325	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		326	readyness notifications you get per iteration.
313		327
314	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	328	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
315		329
316	And this is your standard poll(2) backend. It's more complicated than	330	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	331	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	332	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).	333	considerably with a lot of inactive fds). It scales similarly to select,
		334	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		335	performance tips.
320		336
321	=item C<EVBACKEND_EPOLL> (value 4, Linux)	337	=item C<EVBACKEND_EPOLL> (value 4, Linux)
322		338
323	For few fds, this backend is a bit little slower than poll and select,	339	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	340	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),	341	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	342	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	343	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	344	cases and rewiring a syscall per fd change, no fork support and bad
329	support for dup:	345	support for dup.
330		346
331	While stopping, setting and starting an I/O watcher in the same iteration	347	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	348	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	349	(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	350	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
…		…
336		352
337	Please note that epoll sometimes generates spurious notifications, so you	353	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	354	need to use non-blocking I/O or other means to avoid blocking when no data
339	(or space) is available.	355	(or space) is available.
340		356
		357	Best performance from this backend is achieved by not unregistering all
		358	watchers for a file descriptor until it has been closed, if possible, i.e.
		359	keep at least one watcher active per fd at all times.
		360
		361	While nominally embeddeble in other event loops, this feature is broken in
		362	all kernel versions tested so far.
		363
341	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	364	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
342		365
343	Kqueue deserves special mention, as at the time of this writing, it	366	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	367	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	368	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"	369	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	370	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)	371	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
350	system like NetBSD.	372	system like NetBSD.
351		373
		374	You still can embed kqueue into a normal poll or select backend and use it
		375	only for sockets (after having made sure that sockets work with kqueue on
		376	the target platform). See C<ev_embed> watchers for more info.
		377
352	It scales in the same way as the epoll backend, but the interface to the	378	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,	379	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	380	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	381	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	382	two event changes per incident, support for C<fork ()> is very bad and it
357	silently in similarly hard-to-detetc cases.	383	drops fds silently in similarly hard-to-detect cases.
		384
		385	This backend usually performs well under most conditions.
		386
		387	While nominally embeddable in other event loops, this doesn't work
		388	everywhere, so you might need to test for this. And since it is broken
		389	almost everywhere, you should only use it when you have a lot of sockets
		390	(for which it usually works), by embedding it into another event loop
		391	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		392	sockets.
358		393
359	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	394	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
360		395
361	This is not implemented yet (and might never be).	396	This is not implemented yet (and might never be, unless you send me an
		397	implementation). According to reports, C</dev/poll> only supports sockets
		398	and is not embeddable, which would limit the usefulness of this backend
		399	immensely.
362		400
363	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	401	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
364		402
365	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	403	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)).	404	it's really slow, but it still scales very well (O(active_fds)).
367		405
368	Please note that solaris event ports can deliver a lot of spurious	406	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	407	notifications, so you need to use non-blocking I/O or other means to avoid
370	blocking when no data (or space) is available.	408	blocking when no data (or space) is available.
371		409
		410	While this backend scales well, it requires one system call per active
		411	file descriptor per loop iteration. For small and medium numbers of file
		412	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		413	might perform better.
		414
		415	On the positive side, ignoring the spurious readyness notifications, this
		416	backend actually performed to specification in all tests and is fully
		417	embeddable, which is a rare feat among the OS-specific backends.
		418
372	=item C<EVBACKEND_ALL>	419	=item C<EVBACKEND_ALL>
373		420
374	Try all backends (even potentially broken ones that wouldn't be tried	421	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	422	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
376	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	423	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
377		424
		425	It is definitely not recommended to use this flag.
		426
378	=back	427	=back
379		428
380	If one or more of these are ored into the flags value, then only these	429	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	430	backends will be tried (in the reverse order as listed here). If none are
382	specified, most compiled-in backend will be tried, usually in reverse	431	specified, all backends in C<ev_recommended_backends ()> will be tried.
383	order of their flag values :)
384		432
385	The most typical usage is like this:	433	The most typical usage is like this:
386		434
387	if (!ev_default_loop (0))	435	if (!ev_default_loop (0))
388	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	436	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
…		…
435	Like C<ev_default_destroy>, but destroys an event loop created by an	483	Like C<ev_default_destroy>, but destroys an event loop created by an
436	earlier call to C<ev_loop_new>.	484	earlier call to C<ev_loop_new>.
437		485
438	=item ev_default_fork ()	486	=item ev_default_fork ()
439		487
		488	This function sets a flag that causes subsequent C<ev_loop> iterations
440	This function reinitialises the kernel state for backends that have	489	to reinitialise the kernel state for backends that have one. Despite the
441	one. Despite the name, you can call it anytime, but it makes most sense	490	name, you can call it anytime, but it makes most sense after forking, in
442	after forking, in either the parent or child process (or both, but that	491	the child process (or both child and parent, but that again makes little
443	again makes little sense).	492	sense). You I<must> call it in the child before using any of the libev
		493	functions, and it will only take effect at the next C<ev_loop> iteration.
444		494
445	You I<must> call this function in the child process after forking if and	495	On the other hand, you only need to call this function in the child
446	only if you want to use the event library in both processes. If you just	496	process if and only if you want to use the event library in the child. If
447	fork+exec, you don't have to call it.	497	you just fork+exec, you don't have to call it at all.
448		498
449	The function itself is quite fast and it's usually not a problem to call	499	The function itself is quite fast and it's usually not a problem to call
450	it just in case after a fork. To make this easy, the function will fit in	500	it just in case after a fork. To make this easy, the function will fit in
451	quite nicely into a call to C<pthread_atfork>:	501	quite nicely into a call to C<pthread_atfork>:
452		502
453	pthread_atfork (0, 0, ev_default_fork);	503	pthread_atfork (0, 0, ev_default_fork);
454		504
455	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
456	without calling this function, so if you force one of those backends you
457	do not need to care.
458
459	=item ev_loop_fork (loop)	505	=item ev_loop_fork (loop)
460		506
461	Like C<ev_default_fork>, but acts on an event loop created by	507	Like C<ev_default_fork>, but acts on an event loop created by
462	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	508	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
463	after fork, and how you do this is entirely your own problem.	509	after fork, and how you do this is entirely your own problem.
		510
		511	=item int ev_is_default_loop (loop)
		512
		513	Returns true when the given loop actually is the default loop, false otherwise.
464		514
465	=item unsigned int ev_loop_count (loop)	515	=item unsigned int ev_loop_count (loop)
466		516
467	Returns the count of loop iterations for the loop, which is identical to	517	Returns the count of loop iterations for the loop, which is identical to
468	the number of times libev did poll for new events. It starts at C<0> and	518	the number of times libev did poll for new events. It starts at C<0> and
…		…
513	usually a better approach for this kind of thing.	563	usually a better approach for this kind of thing.
514		564
515	Here are the gory details of what C<ev_loop> does:	565	Here are the gory details of what C<ev_loop> does:
516		566
517	- Before the first iteration, call any pending watchers.	567	- Before the first iteration, call any pending watchers.
518	* If there are no active watchers (reference count is zero), return.	568	* If EVFLAG_FORKCHECK was used, check for a fork.
519	- Queue all prepare watchers and then call all outstanding watchers.	569	- If a fork was detected, queue and call all fork watchers.
		570	- Queue and call all prepare watchers.
520	- If we have been forked, recreate the kernel state.	571	- If we have been forked, recreate the kernel state.
521	- Update the kernel state with all outstanding changes.	572	- Update the kernel state with all outstanding changes.
522	- Update the "event loop time".	573	- Update the "event loop time".
523	- Calculate for how long to block.	574	- Calculate for how long to sleep or block, if at all
		575	(active idle watchers, EVLOOP_NONBLOCK or not having
		576	any active watchers at all will result in not sleeping).
		577	- Sleep if the I/O and timer collect interval say so.
524	- Block the process, waiting for any events.	578	- Block the process, waiting for any events.
525	- Queue all outstanding I/O (fd) events.	579	- Queue all outstanding I/O (fd) events.
526	- Update the "event loop time" and do time jump handling.	580	- Update the "event loop time" and do time jump handling.
527	- Queue all outstanding timers.	581	- Queue all outstanding timers.
528	- Queue all outstanding periodics.	582	- Queue all outstanding periodics.
529	- If no events are pending now, queue all idle watchers.	583	- If no events are pending now, queue all idle watchers.
530	- Queue all check watchers.	584	- Queue all check watchers.
531	- Call all queued watchers in reverse order (i.e. check watchers first).	585	- 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	586	Signals and child watchers are implemented as I/O watchers, and will
533	be handled here by queueing them when their watcher gets executed.	587	be handled here by queueing them when their watcher gets executed.
534	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	588	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
535	were used, return, otherwise continue with step *.	589	were used, or there are no active watchers, return, otherwise
		590	continue with step *.
536		591
537	Example: Queue some jobs and then loop until no events are outsanding	592	Example: Queue some jobs and then loop until no events are outstanding
538	anymore.	593	anymore.
539		594
540	... queue jobs here, make sure they register event watchers as long	595	... 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..)	596	... as they still have work to do (even an idle watcher will do..)
542	ev_loop (my_loop, 0);	597	ev_loop (my_loop, 0);
…		…
546		601
547	Can be used to make a call to C<ev_loop> return early (but only after it	602	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	603	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	604	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.	605	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		606
		607	This "unloop state" will be cleared when entering C<ev_loop> again.
551		608
552	=item ev_ref (loop)	609	=item ev_ref (loop)
553		610
554	=item ev_unref (loop)	611	=item ev_unref (loop)
555		612
…		…
560	returning, ev_unref() after starting, and ev_ref() before stopping it. For	617	returning, ev_unref() after starting, and ev_ref() before stopping it. For
561	example, libev itself uses this for its internal signal pipe: It is not	618	example, libev itself uses this for its internal signal pipe: It is not
562	visible to the libev user and should not keep C<ev_loop> from exiting if	619	visible to the libev user and should not keep C<ev_loop> from exiting if
563	no event watchers registered by it are active. It is also an excellent	620	no event watchers registered by it are active. It is also an excellent
564	way to do this for generic recurring timers or from within third-party	621	way to do this for generic recurring timers or from within third-party
565	libraries. Just remember to I<unref after start> and I<ref before stop>.	622	libraries. Just remember to I<unref after start> and I<ref before stop>
		623	(but only if the watcher wasn't active before, or was active before,
		624	respectively).
566		625
567	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	626	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
568	running when nothing else is active.	627	running when nothing else is active.
569		628
570	struct ev_signal exitsig;	629	struct ev_signal exitsig;
…		…
596	overhead for the actual polling but can deliver many events at once.	655	overhead for the actual polling but can deliver many events at once.
597		656
598	By setting a higher I<io collect interval> you allow libev to spend more	657	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,	658	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	659	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
601	C<ev_timer>) will be not affected. Setting this to a non-null bvalue will	660	C<ev_timer>) will be not affected. Setting this to a non-null value will
602	introduce an additional C<ev_sleep ()> call into most loop iterations.	661	introduce an additional C<ev_sleep ()> call into most loop iterations.
603		662
604	Likewise, by setting a higher I<timeout collect interval> you allow libev	663	Likewise, by setting a higher I<timeout collect interval> you allow libev
605	to spend more time collecting timeouts, at the expense of increased	664	to spend more time collecting timeouts, at the expense of increased
606	latency (the watcher callback will be called later). C<ev_io> watchers	665	latency (the watcher callback will be called later). C<ev_io> watchers
…		…
718		777
719	=item C<EV_FORK>	778	=item C<EV_FORK>
720		779
721	The event loop has been resumed in the child process after fork (see	780	The event loop has been resumed in the child process after fork (see
722	C<ev_fork>).	781	C<ev_fork>).
		782
		783	=item C<EV_ASYNC>
		784
		785	The given async watcher has been asynchronously notified (see C<ev_async>).
723		786
724	=item C<EV_ERROR>	787	=item C<EV_ERROR>
725		788
726	An unspecified error has occured, the watcher has been stopped. This might	789	An unspecified error has occured, the watcher has been stopped. This might
727	happen because the watcher could not be properly started because libev	790	happen because the watcher could not be properly started because libev
…		…
945	In general you can register as many read and/or write event watchers per	1008	In general you can register as many read and/or write event watchers per
946	fd as you want (as long as you don't confuse yourself). Setting all file	1009	fd as you want (as long as you don't confuse yourself). Setting all file
947	descriptors to non-blocking mode is also usually a good idea (but not	1010	descriptors to non-blocking mode is also usually a good idea (but not
948	required if you know what you are doing).	1011	required if you know what you are doing).
949		1012
950	You have to be careful with dup'ed file descriptors, though. Some backends
951	(the linux epoll backend is a notable example) cannot handle dup'ed file
952	descriptors correctly if you register interest in two or more fds pointing
953	to the same underlying file/socket/etc. description (that is, they share
954	the same underlying "file open").
955
956	If you must do this, then force the use of a known-to-be-good backend	1013	If you must do this, then force the use of a known-to-be-good backend
957	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1014	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
958	C<EVBACKEND_POLL>).	1015	C<EVBACKEND_POLL>).
959		1016
960	Another thing you have to watch out for is that it is quite easy to	1017	Another thing you have to watch out for is that it is quite easy to
…		…
994	optimisations to libev.	1051	optimisations to libev.
995		1052
996	=head3 The special problem of dup'ed file descriptors	1053	=head3 The special problem of dup'ed file descriptors
997		1054
998	Some backends (e.g. epoll), cannot register events for file descriptors,	1055	Some backends (e.g. epoll), cannot register events for file descriptors,
999	but only events for the underlying file descriptions. That menas when you	1056	but only events for the underlying file descriptions. That means when you
1000	have C<dup ()>'ed file descriptors and register events for them, only one	1057	have C<dup ()>'ed file descriptors or weirder constellations, and register
1001	file descriptor might actually receive events.	1058	events for them, only one file descriptor might actually receive events.
1002		1059
1003	There is no workaorund possible except not registering events	1060	There is no workaround possible except not registering events
1004	for potentially C<dup ()>'ed file descriptors or to resort to	1061	for potentially C<dup ()>'ed file descriptors, or to resort to
1005	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1062	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1006		1063
1007	=head3 The special problem of fork	1064	=head3 The special problem of fork
1008		1065
1009	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1066	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
…		…
1035	=item int events [read-only]	1092	=item int events [read-only]
1036		1093
1037	The events being watched.	1094	The events being watched.
1038		1095
1039	=back	1096	=back
		1097
		1098	=head3 Examples
1040		1099
1041	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1100	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1042	readable, but only once. Since it is likely line-buffered, you could	1101	readable, but only once. Since it is likely line-buffered, you could
1043	attempt to read a whole line in the callback.	1102	attempt to read a whole line in the callback.
1044		1103
…		…
1097	configure a timer to trigger every 10 seconds, then it will trigger at	1156	configure a timer to trigger every 10 seconds, then it will trigger at
1098	exactly 10 second intervals. If, however, your program cannot keep up with	1157	exactly 10 second intervals. If, however, your program cannot keep up with
1099	the timer (because it takes longer than those 10 seconds to do stuff) the	1158	the timer (because it takes longer than those 10 seconds to do stuff) the
1100	timer will not fire more than once per event loop iteration.	1159	timer will not fire more than once per event loop iteration.
1101		1160
1102	=item ev_timer_again (loop)	1161	=item ev_timer_again (loop, ev_timer *)
1103		1162
1104	This will act as if the timer timed out and restart it again if it is	1163	This will act as if the timer timed out and restart it again if it is
1105	repeating. The exact semantics are:	1164	repeating. The exact semantics are:
1106		1165
1107	If the timer is pending, its pending status is cleared.	1166	If the timer is pending, its pending status is cleared.
…		…
1142	or C<ev_timer_again> is called and determines the next timeout (if any),	1201	or C<ev_timer_again> is called and determines the next timeout (if any),
1143	which is also when any modifications are taken into account.	1202	which is also when any modifications are taken into account.
1144		1203
1145	=back	1204	=back
1146		1205
		1206	=head3 Examples
		1207
1147	Example: Create a timer that fires after 60 seconds.	1208	Example: Create a timer that fires after 60 seconds.
1148		1209
1149	static void	1210	static void
1150	one_minute_cb (struct ev_loop loop, struct ev_timer w, int revents)	1211	one_minute_cb (struct ev_loop loop, struct ev_timer w, int revents)
1151	{	1212	{
…		…
1214	In this configuration the watcher triggers an event at the wallclock time	1275	In this configuration the watcher triggers an event at the wallclock time
1215	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1276	C<at> and doesn't repeat. It will not adjust when a time jump occurs,
1216	that is, if it is to be run at January 1st 2011 then it will run when the	1277	that is, if it is to be run at January 1st 2011 then it will run when the
1217	system time reaches or surpasses this time.	1278	system time reaches or surpasses this time.
1218		1279
1219	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1280	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1220		1281
1221	In this mode the watcher will always be scheduled to time out at the next	1282	In this mode the watcher will always be scheduled to time out at the next
1222	C<at + N * interval> time (for some integer N, which can also be negative)	1283	C<at + N * interval> time (for some integer N, which can also be negative)
1223	and then repeat, regardless of any time jumps.	1284	and then repeat, regardless of any time jumps.
1224		1285
…		…
1307		1368
1308	When active, contains the absolute time that the watcher is supposed to	1369	When active, contains the absolute time that the watcher is supposed to
1309	trigger next.	1370	trigger next.
1310		1371
1311	=back	1372	=back
		1373
		1374	=head3 Examples
1312		1375
1313	Example: Call a callback every hour, or, more precisely, whenever the	1376	Example: Call a callback every hour, or, more precisely, whenever the
1314	system clock is divisible by 3600. The callback invocation times have	1377	system clock is divisible by 3600. The callback invocation times have
1315	potentially a lot of jittering, but good long-term stability.	1378	potentially a lot of jittering, but good long-term stability.
1316		1379
…		…
1373		1436
1374	The signal the watcher watches out for.	1437	The signal the watcher watches out for.
1375		1438
1376	=back	1439	=back
1377		1440
		1441	=head3 Examples
		1442
		1443	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1444
		1445	static void
		1446	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)
		1447	{
		1448	ev_unloop (loop, EVUNLOOP_ALL);
		1449	}
		1450
		1451	struct ev_signal signal_watcher;
		1452	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1453	ev_signal_start (loop, &sigint_cb);
		1454
1378		1455
1379	=head2 C<ev_child> - watch out for process status changes	1456	=head2 C<ev_child> - watch out for process status changes
1380		1457
1381	Child watchers trigger when your process receives a SIGCHLD in response to	1458	Child watchers trigger when your process receives a SIGCHLD in response to
1382	some child status changes (most typically when a child of yours dies).	1459	some child status changes (most typically when a child of yours dies).
1383		1460
1384	=head3 Watcher-Specific Functions and Data Members	1461	=head3 Watcher-Specific Functions and Data Members
1385		1462
1386	=over 4	1463	=over 4
1387		1464
1388	=item ev_child_init (ev_child *, callback, int pid)	1465	=item ev_child_init (ev_child *, callback, int pid, int trace)
1389		1466
1390	=item ev_child_set (ev_child *, int pid)	1467	=item ev_child_set (ev_child *, int pid, int trace)
1391		1468
1392	Configures the watcher to wait for status changes of process C<pid> (or	1469	Configures the watcher to wait for status changes of process C<pid> (or
1393	I<any> process if C<pid> is specified as C<0>). The callback can look	1470	I<any> process if C<pid> is specified as C<0>). The callback can look
1394	at the C<rstatus> member of the C<ev_child> watcher structure to see	1471	at the C<rstatus> member of the C<ev_child> watcher structure to see
1395	the status word (use the macros from C<sys/wait.h> and see your systems	1472	the status word (use the macros from C<sys/wait.h> and see your systems
1396	C<waitpid> documentation). The C<rpid> member contains the pid of the	1473	C<waitpid> documentation). The C<rpid> member contains the pid of the
1397	process causing the status change.	1474	process causing the status change. C<trace> must be either C<0> (only
		1475	activate the watcher when the process terminates) or C<1> (additionally
		1476	activate the watcher when the process is stopped or continued).
1398		1477
1399	=item int pid [read-only]	1478	=item int pid [read-only]
1400		1479
1401	The process id this watcher watches out for, or C<0>, meaning any process id.	1480	The process id this watcher watches out for, or C<0>, meaning any process id.
1402		1481
…		…
1408		1487
1409	The process exit/trace status caused by C<rpid> (see your systems	1488	The process exit/trace status caused by C<rpid> (see your systems
1410	C<waitpid> and C<sys/wait.h> documentation for details).	1489	C<waitpid> and C<sys/wait.h> documentation for details).
1411		1490
1412	=back	1491	=back
1413
1414	Example: Try to exit cleanly on SIGINT and SIGTERM.
1415
1416	static void
1417	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)
1418	{
1419	ev_unloop (loop, EVUNLOOP_ALL);
1420	}
1421
1422	struct ev_signal signal_watcher;
1423	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1424	ev_signal_start (loop, &sigint_cb);
1425		1492
1426		1493
1427	=head2 C<ev_stat> - did the file attributes just change?	1494	=head2 C<ev_stat> - did the file attributes just change?
1428		1495
1429	This watches a filesystem path for attribute changes. That is, it calls	1496	This watches a filesystem path for attribute changes. That is, it calls
…		…
1458	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1525	semantics of C<ev_stat> watchers, which means that libev sometimes needs
1459	to fall back to regular polling again even with inotify, but changes are	1526	to fall back to regular polling again even with inotify, but changes are
1460	usually detected immediately, and if the file exists there will be no	1527	usually detected immediately, and if the file exists there will be no
1461	polling.	1528	polling.
1462		1529
		1530	=head3 Inotify
		1531
		1532	When C<inotify (7)> support has been compiled into libev (generally only
		1533	available on Linux) and present at runtime, it will be used to speed up
		1534	change detection where possible. The inotify descriptor will be created lazily
		1535	when the first C<ev_stat> watcher is being started.
		1536
		1537	Inotify presense does not change the semantics of C<ev_stat> watchers
		1538	except that changes might be detected earlier, and in some cases, to avoid
		1539	making regular C<stat> calls. Even in the presense of inotify support
		1540	there are many cases where libev has to resort to regular C<stat> polling.
		1541
		1542	(There is no support for kqueue, as apparently it cannot be used to
		1543	implement this functionality, due to the requirement of having a file
		1544	descriptor open on the object at all times).
		1545
		1546	=head3 The special problem of stat time resolution
		1547
		1548	The C<stat ()> syscall only supports full-second resolution portably, and
		1549	even on systems where the resolution is higher, many filesystems still
		1550	only support whole seconds.
		1551
		1552	That means that, if the time is the only thing that changes, you might
		1553	miss updates: on the first update, C<ev_stat> detects a change and calls
		1554	your callback, which does something. When there is another update within
		1555	the same second, C<ev_stat> will be unable to detect it.
		1556
		1557	The solution to this is to delay acting on a change for a second (or till
		1558	the next second boundary), using a roughly one-second delay C<ev_timer>
		1559	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
		1560	is added to work around small timing inconsistencies of some operating
		1561	systems.
		1562
1463	=head3 Watcher-Specific Functions and Data Members	1563	=head3 Watcher-Specific Functions and Data Members
1464		1564
1465	=over 4	1565	=over 4
1466		1566
1467	=item ev_stat_init (ev_stat , callback, const char path, ev_tstamp interval)	1567	=item ev_stat_init (ev_stat , callback, const char path, ev_tstamp interval)
…		…
1476		1576
1477	The callback will be receive C<EV_STAT> when a change was detected,	1577	The callback will be receive C<EV_STAT> when a change was detected,
1478	relative to the attributes at the time the watcher was started (or the	1578	relative to the attributes at the time the watcher was started (or the
1479	last change was detected).	1579	last change was detected).
1480		1580
1481	=item ev_stat_stat (ev_stat *)	1581	=item ev_stat_stat (loop, ev_stat *)
1482		1582
1483	Updates the stat buffer immediately with new values. If you change the	1583	Updates the stat buffer immediately with new values. If you change the
1484	watched path in your callback, you could call this fucntion to avoid	1584	watched path in your callback, you could call this fucntion to avoid
1485	detecting this change (while introducing a race condition). Can also be	1585	detecting this change (while introducing a race condition). Can also be
1486	useful simply to find out the new values.	1586	useful simply to find out the new values.
…		…
1504	=item const char *path [read-only]	1604	=item const char *path [read-only]
1505		1605
1506	The filesystem path that is being watched.	1606	The filesystem path that is being watched.
1507		1607
1508	=back	1608	=back
		1609
		1610	=head3 Examples
1509		1611
1510	Example: Watch C</etc/passwd> for attribute changes.	1612	Example: Watch C</etc/passwd> for attribute changes.
1511		1613
1512	static void	1614	static void
1513	passwd_cb (struct ev_loop loop, ev_stat w, int revents)	1615	passwd_cb (struct ev_loop loop, ev_stat w, int revents)
…		…
1526	}	1628	}
1527		1629
1528	...	1630	...
1529	ev_stat passwd;	1631	ev_stat passwd;
1530		1632
1531	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	1633	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1532	ev_stat_start (loop, &passwd);	1634	ev_stat_start (loop, &passwd);
		1635
		1636	Example: Like above, but additionally use a one-second delay so we do not
		1637	miss updates (however, frequent updates will delay processing, too, so
		1638	one might do the work both on C<ev_stat> callback invocation I<and> on
		1639	C<ev_timer> callback invocation).
		1640
		1641	static ev_stat passwd;
		1642	static ev_timer timer;
		1643
		1644	static void
		1645	timer_cb (EV_P_ ev_timer *w, int revents)
		1646	{
		1647	ev_timer_stop (EV_A_ w);
		1648
		1649	/* now it's one second after the most recent passwd change */
		1650	}
		1651
		1652	static void
		1653	stat_cb (EV_P_ ev_stat *w, int revents)
		1654	{
		1655	/* reset the one-second timer */
		1656	ev_timer_again (EV_A_ &timer);
		1657	}
		1658
		1659	...
		1660	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1661	ev_stat_start (loop, &passwd);
		1662	ev_timer_init (&timer, timer_cb, 0., 1.01);
1533		1663
1534		1664
1535	=head2 C<ev_idle> - when you've got nothing better to do...	1665	=head2 C<ev_idle> - when you've got nothing better to do...
1536		1666
1537	Idle watchers trigger events when no other events of the same or higher	1667	Idle watchers trigger events when no other events of the same or higher
…		…
1563	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1693	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1564	believe me.	1694	believe me.
1565		1695
1566	=back	1696	=back
1567		1697
		1698	=head3 Examples
		1699
1568	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	1700	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1569	callback, free it. Also, use no error checking, as usual.	1701	callback, free it. Also, use no error checking, as usual.
1570		1702
1571	static void	1703	static void
1572	idle_cb (struct ev_loop loop, struct ev_idle w, int revents)	1704	idle_cb (struct ev_loop loop, struct ev_idle w, int revents)
1573	{	1705	{
1574	free (w);	1706	free (w);
1575	// now do something you wanted to do when the program has	1707	// now do something you wanted to do when the program has
1576	// no longer asnything immediate to do.	1708	// no longer anything immediate to do.
1577	}	1709	}
1578		1710
1579	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	1711	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1580	ev_idle_init (idle_watcher, idle_cb);	1712	ev_idle_init (idle_watcher, idle_cb);
1581	ev_idle_start (loop, idle_cb);	1713	ev_idle_start (loop, idle_cb);
…		…
1623		1755
1624	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	1756	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1625	priority, to ensure that they are being run before any other watchers	1757	priority, to ensure that they are being run before any other watchers
1626	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	1758	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
1627	too) should not activate ("feed") events into libev. While libev fully	1759	too) should not activate ("feed") events into libev. While libev fully
1628	supports this, they will be called before other C<ev_check> watchers did	1760	supports this, they will be called before other C<ev_check> watchers
1629	their job. As C<ev_check> watchers are often used to embed other event	1761	did their job. As C<ev_check> watchers are often used to embed other
1630	loops those other event loops might be in an unusable state until their	1762	(non-libev) event loops those other event loops might be in an unusable
1631	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	1763	state until their C<ev_check> watcher ran (always remind yourself to
1632	others).	1764	coexist peacefully with others).
1633		1765
1634	=head3 Watcher-Specific Functions and Data Members	1766	=head3 Watcher-Specific Functions and Data Members
1635		1767
1636	=over 4	1768	=over 4
1637		1769
…		…
1642	Initialises and configures the prepare or check watcher - they have no	1774	Initialises and configures the prepare or check watcher - they have no
1643	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1775	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1644	macros, but using them is utterly, utterly and completely pointless.	1776	macros, but using them is utterly, utterly and completely pointless.
1645		1777
1646	=back	1778	=back
		1779
		1780	=head3 Examples
1647		1781
1648	There are a number of principal ways to embed other event loops or modules	1782	There are a number of principal ways to embed other event loops or modules
1649	into libev. Here are some ideas on how to include libadns into libev	1783	into libev. Here are some ideas on how to include libadns into libev
1650	(there is a Perl module named C<EV::ADNS> that does this, which you could	1784	(there is a Perl module named C<EV::ADNS> that does this, which you could
1651	use for an actually working example. Another Perl module named C<EV::Glib>	1785	use for an actually working example. Another Perl module named C<EV::Glib>
…		…
1776	=head2 C<ev_embed> - when one backend isn't enough...	1910	=head2 C<ev_embed> - when one backend isn't enough...
1777		1911
1778	This is a rather advanced watcher type that lets you embed one event loop	1912	This is a rather advanced watcher type that lets you embed one event loop
1779	into another (currently only C<ev_io> events are supported in the embedded	1913	into another (currently only C<ev_io> events are supported in the embedded
1780	loop, other types of watchers might be handled in a delayed or incorrect	1914	loop, other types of watchers might be handled in a delayed or incorrect
1781	fashion and must not be used). (See portability notes, below).	1915	fashion and must not be used).
1782		1916
1783	There are primarily two reasons you would want that: work around bugs and	1917	There are primarily two reasons you would want that: work around bugs and
1784	prioritise I/O.	1918	prioritise I/O.
1785		1919
1786	As an example for a bug workaround, the kqueue backend might only support	1920	As an example for a bug workaround, the kqueue backend might only support
…		…
1820	portable one.	1954	portable one.
1821		1955
1822	So when you want to use this feature you will always have to be prepared	1956	So when you want to use this feature you will always have to be prepared
1823	that you cannot get an embeddable loop. The recommended way to get around	1957	that you cannot get an embeddable loop. The recommended way to get around
1824	this is to have a separate variables for your embeddable loop, try to	1958	this is to have a separate variables for your embeddable loop, try to
1825	create it, and if that fails, use the normal loop for everything:	1959	create it, and if that fails, use the normal loop for everything.
		1960
		1961	=head3 Watcher-Specific Functions and Data Members
		1962
		1963	=over 4
		1964
		1965	=item ev_embed_init (ev_embed , callback, struct ev_loop embedded_loop)
		1966
		1967	=item ev_embed_set (ev_embed , callback, struct ev_loop embedded_loop)
		1968
		1969	Configures the watcher to embed the given loop, which must be
		1970	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		1971	invoked automatically, otherwise it is the responsibility of the callback
		1972	to invoke it (it will continue to be called until the sweep has been done,
		1973	if you do not want thta, you need to temporarily stop the embed watcher).
		1974
		1975	=item ev_embed_sweep (loop, ev_embed *)
		1976
		1977	Make a single, non-blocking sweep over the embedded loop. This works
		1978	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		1979	apropriate way for embedded loops.
		1980
		1981	=item struct ev_loop *other [read-only]
		1982
		1983	The embedded event loop.
		1984
		1985	=back
		1986
		1987	=head3 Examples
		1988
		1989	Example: Try to get an embeddable event loop and embed it into the default
		1990	event loop. If that is not possible, use the default loop. The default
		1991	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		1992	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		1993	used).
1826		1994
1827	struct ev_loop *loop_hi = ev_default_init (0);	1995	struct ev_loop *loop_hi = ev_default_init (0);
1828	struct ev_loop *loop_lo = 0;	1996	struct ev_loop *loop_lo = 0;
1829	struct ev_embed embed;	1997	struct ev_embed embed;
1830		1998
…		…
1841	ev_embed_start (loop_hi, &embed);	2009	ev_embed_start (loop_hi, &embed);
1842	}	2010	}
1843	else	2011	else
1844	loop_lo = loop_hi;	2012	loop_lo = loop_hi;
1845		2013
1846	=head2 Portability notes	2014	Example: Check if kqueue is available but not recommended and create
		2015	a kqueue backend for use with sockets (which usually work with any
		2016	kqueue implementation). Store the kqueue/socket-only event loop in
		2017	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
1847		2018
1848	Kqueue is nominally embeddable, but this is broken on all BSDs that I	2019	struct ev_loop *loop = ev_default_init (0);
1849	tried, in various ways. Usually the embedded event loop will simply never	2020	struct ev_loop *loop_socket = 0;
1850	receive events, sometimes it will only trigger a few times, sometimes in a	2021	struct ev_embed embed;
1851	loop. Epoll is also nominally embeddable, but many Linux kernel versions	2022
1852	will always eport the epoll fd as ready, even when no events are pending.	2023	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2024	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2025	{
		2026	ev_embed_init (&embed, 0, loop_socket);
		2027	ev_embed_start (loop, &embed);
		2028	}
1853		2029
1854	While libev allows embedding these backends (they are contained in	2030	if (!loop_socket)
1855	C<ev_embeddable_backends ()>), take extreme care that it will actually	2031	loop_socket = loop;
1856	work.
1857		2032
1858	When in doubt, create a dynamic event loop forced to use sockets (this	2033	// now use loop_socket for all sockets, and loop for everything else
1859	usually works) and possibly another thread and a pipe or so to report to
1860	your main event loop.
1861
1862	=head3 Watcher-Specific Functions and Data Members
1863
1864	=over 4
1865
1866	=item ev_embed_init (ev_embed , callback, struct ev_loop embedded_loop)
1867
1868	=item ev_embed_set (ev_embed , callback, struct ev_loop embedded_loop)
1869
1870	Configures the watcher to embed the given loop, which must be
1871	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1872	invoked automatically, otherwise it is the responsibility of the callback
1873	to invoke it (it will continue to be called until the sweep has been done,
1874	if you do not want thta, you need to temporarily stop the embed watcher).
1875
1876	=item ev_embed_sweep (loop, ev_embed *)
1877
1878	Make a single, non-blocking sweep over the embedded loop. This works
1879	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1880	apropriate way for embedded loops.
1881
1882	=item struct ev_loop *other [read-only]
1883
1884	The embedded event loop.
1885
1886	=back
1887		2034
1888		2035
1889	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2036	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1890		2037
1891	Fork watchers are called when a C<fork ()> was detected (usually because	2038	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1907	believe me.	2054	believe me.
1908		2055
1909	=back	2056	=back
1910		2057
1911		2058
		2059	=head2 C<ev_async> - how to wake up another event loop
		2060
		2061	In general, you cannot use an C<ev_loop> from multiple threads or other
		2062	asynchronous sources such as signal handlers (as opposed to multiple event
		2063	loops - those are of course safe to use in different threads).
		2064
		2065	Sometimes, however, you need to wake up another event loop you do not
		2066	control, for example because it belongs to another thread. This is what
		2067	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2068	can signal it by calling C<ev_async_send>, which is thread- and signal
		2069	safe.
		2070
		2071	This functionality is very similar to C<ev_signal> watchers, as signals,
		2072	too, are asynchronous in nature, and signals, too, will be compressed
		2073	(i.e. the number of callback invocations may be less than the number of
		2074	C<ev_async_sent> calls).
		2075
		2076	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2077	just the default loop.
		2078
		2079	=head3 Queueing
		2080
		2081	C<ev_async> does not support queueing of data in any way. The reason
		2082	is that the author does not know of a simple (or any) algorithm for a
		2083	multiple-writer-single-reader queue that works in all cases and doesn't
		2084	need elaborate support such as pthreads.
		2085
		2086	That means that if you want to queue data, you have to provide your own
		2087	queue. But at least I can tell you would implement locking around your
		2088	queue:
		2089
		2090	=over 4
		2091
		2092	=item queueing from a signal handler context
		2093
		2094	To implement race-free queueing, you simply add to the queue in the signal
		2095	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2096	some fictitiuous SIGUSR1 handler:
		2097
		2098	static ev_async mysig;
		2099
		2100	static void
		2101	sigusr1_handler (void)
		2102	{
		2103	sometype data;
		2104
		2105	// no locking etc.
		2106	queue_put (data);
		2107	ev_async_send (DEFAULT_ &mysig);
		2108	}
		2109
		2110	static void
		2111	mysig_cb (EV_P_ ev_async *w, int revents)
		2112	{
		2113	sometype data;
		2114	sigset_t block, prev;
		2115
		2116	sigemptyset (&block);
		2117	sigaddset (&block, SIGUSR1);
		2118	sigprocmask (SIG_BLOCK, &block, &prev);
		2119
		2120	while (queue_get (&data))
		2121	process (data);
		2122
		2123	if (sigismember (&prev, SIGUSR1)
		2124	sigprocmask (SIG_UNBLOCK, &block, 0);
		2125	}
		2126
		2127	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2128	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2129	either...).
		2130
		2131	=item queueing from a thread context
		2132
		2133	The strategy for threads is different, as you cannot (easily) block
		2134	threads but you can easily preempt them, so to queue safely you need to
		2135	employ a traditional mutex lock, such as in this pthread example:
		2136
		2137	static ev_async mysig;
		2138	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2139
		2140	static void
		2141	otherthread (void)
		2142	{
		2143	// only need to lock the actual queueing operation
		2144	pthread_mutex_lock (&mymutex);
		2145	queue_put (data);
		2146	pthread_mutex_unlock (&mymutex);
		2147
		2148	ev_async_send (DEFAULT_ &mysig);
		2149	}
		2150
		2151	static void
		2152	mysig_cb (EV_P_ ev_async *w, int revents)
		2153	{
		2154	pthread_mutex_lock (&mymutex);
		2155
		2156	while (queue_get (&data))
		2157	process (data);
		2158
		2159	pthread_mutex_unlock (&mymutex);
		2160	}
		2161
		2162	=back
		2163
		2164
		2165	=head3 Watcher-Specific Functions and Data Members
		2166
		2167	=over 4
		2168
		2169	=item ev_async_init (ev_async *, callback)
		2170
		2171	Initialises and configures the async watcher - it has no parameters of any
		2172	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2173	believe me.
		2174
		2175	=item ev_async_send (loop, ev_async *)
		2176
		2177	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2178	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2179	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2180	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
		2181	section below on what exactly this means).
		2182
		2183	This call incurs the overhead of a syscall only once per loop iteration,
		2184	so while the overhead might be noticable, it doesn't apply to repeated
		2185	calls to C<ev_async_send>.
		2186
		2187	=back
		2188
		2189
1912	=head1 OTHER FUNCTIONS	2190	=head1 OTHER FUNCTIONS
1913		2191
1914	There are some other functions of possible interest. Described. Here. Now.	2192	There are some other functions of possible interest. Described. Here. Now.
1915		2193
1916	=over 4	2194	=over 4
…		…
2143	Example: Define a class with an IO and idle watcher, start one of them in	2421	Example: Define a class with an IO and idle watcher, start one of them in
2144	the constructor.	2422	the constructor.
2145		2423
2146	class myclass	2424	class myclass
2147	{	2425	{
2148	ev_io io; void io_cb (ev::io &w, int revents);	2426	ev::io io; void io_cb (ev::io &w, int revents);
2149	ev_idle idle void idle_cb (ev::idle &w, int revents);	2427	ev:idle idle void idle_cb (ev::idle &w, int revents);
2150		2428
2151	myclass ();	2429	myclass (int fd)
2152	}
2153
2154	myclass::myclass (int fd)
2155	{	2430	{
2156	io .set <myclass, &myclass::io_cb > (this);	2431	io .set <myclass, &myclass::io_cb > (this);
2157	idle.set <myclass, &myclass::idle_cb> (this);	2432	idle.set <myclass, &myclass::idle_cb> (this);
2158		2433
2159	io.start (fd, ev::READ);	2434	io.start (fd, ev::READ);
		2435	}
2160	}	2436	};
2161		2437
2162		2438
2163	=head1 MACRO MAGIC	2439	=head1 MACRO MAGIC
2164		2440
2165	Libev can be compiled with a variety of options, the most fundamantal	2441	Libev can be compiled with a variety of options, the most fundamantal
…		…
2370	wants osf handles on win32 (this is the case when the select to	2646	wants osf handles on win32 (this is the case when the select to
2371	be used is the winsock select). This means that it will call	2647	be used is the winsock select). This means that it will call
2372	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	2648	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2373	it is assumed that all these functions actually work on fds, even	2649	it is assumed that all these functions actually work on fds, even
2374	on win32. Should not be defined on non-win32 platforms.	2650	on win32. Should not be defined on non-win32 platforms.
		2651
		2652	=item EV_FD_TO_WIN32_HANDLE
		2653
		2654	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2655	file descriptors to socket handles. When not defining this symbol (the
		2656	default), then libev will call C<_get_osfhandle>, which is usually
		2657	correct. In some cases, programs use their own file descriptor management,
		2658	in which case they can provide this function to map fds to socket handles.
2375		2659
2376	=item EV_USE_POLL	2660	=item EV_USE_POLL
2377		2661
2378	If defined to be C<1>, libev will compile in support for the C<poll>(2)	2662	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2379	backend. Otherwise it will be enabled on non-win32 platforms. It	2663	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
2413		2697
2414	If defined to be C<1>, libev will compile in support for the Linux inotify	2698	If defined to be C<1>, libev will compile in support for the Linux inotify
2415	interface to speed up C<ev_stat> watchers. Its actual availability will	2699	interface to speed up C<ev_stat> watchers. Its actual availability will
2416	be detected at runtime.	2700	be detected at runtime.
2417		2701
		2702	=item EV_ATOMIC_T
		2703
		2704	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2705	access is atomic with respect to other threads or signal contexts. No such
		2706	type is easily found in the C language, so you can provide your own type
		2707	that you know is safe for your purposes. It is used both for signal handler "locking"
		2708	as well as for signal and thread safety in C<ev_async> watchers.
		2709
		2710	In the absense of this define, libev will use C<sig_atomic_t volatile>
		2711	(from F<signal.h>), which is usually good enough on most platforms.
		2712
2418	=item EV_H	2713	=item EV_H
2419		2714
2420	The name of the F<ev.h> header file used to include it. The default if	2715	The name of the F<ev.h> header file used to include it. The default if
2421	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	2716	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2422	can be used to virtually rename the F<ev.h> header file in case of conflicts.	2717	used to virtually rename the F<ev.h> header file in case of conflicts.
2423		2718
2424	=item EV_CONFIG_H	2719	=item EV_CONFIG_H
2425		2720
2426	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	2721	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2427	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	2722	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2428	C<EV_H>, above.	2723	C<EV_H>, above.
2429		2724
2430	=item EV_EVENT_H	2725	=item EV_EVENT_H
2431		2726
2432	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	2727	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2433	of how the F<event.h> header can be found.	2728	of how the F<event.h> header can be found, the default is C<"event.h">.
2434		2729
2435	=item EV_PROTOTYPES	2730	=item EV_PROTOTYPES
2436		2731
2437	If defined to be C<0>, then F<ev.h> will not define any function	2732	If defined to be C<0>, then F<ev.h> will not define any function
2438	prototypes, but still define all the structs and other symbols. This is	2733	prototypes, but still define all the structs and other symbols. This is
…		…
2489	=item EV_FORK_ENABLE	2784	=item EV_FORK_ENABLE
2490		2785
2491	If undefined or defined to be C<1>, then fork watchers are supported. If	2786	If undefined or defined to be C<1>, then fork watchers are supported. If
2492	defined to be C<0>, then they are not.	2787	defined to be C<0>, then they are not.
2493		2788
		2789	=item EV_ASYNC_ENABLE
		2790
		2791	If undefined or defined to be C<1>, then async watchers are supported. If
		2792	defined to be C<0>, then they are not.
		2793
2494	=item EV_MINIMAL	2794	=item EV_MINIMAL
2495		2795
2496	If you need to shave off some kilobytes of code at the expense of some	2796	If you need to shave off some kilobytes of code at the expense of some
2497	speed, define this symbol to C<1>. Currently only used for gcc to override	2797	speed, define this symbol to C<1>. Currently only used for gcc to override
2498	some inlining decisions, saves roughly 30% codesize of amd64.	2798	some inlining decisions, saves roughly 30% codesize of amd64.
…		…
2504	than enough. If you need to manage thousands of children you might want to	2804	than enough. If you need to manage thousands of children you might want to
2505	increase this value (I<must> be a power of two).	2805	increase this value (I<must> be a power of two).
2506		2806
2507	=item EV_INOTIFY_HASHSIZE	2807	=item EV_INOTIFY_HASHSIZE
2508		2808
2509	C<ev_staz> watchers use a small hash table to distribute workload by	2809	C<ev_stat> watchers use a small hash table to distribute workload by
2510	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	2810	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2511	usually more than enough. If you need to manage thousands of C<ev_stat>	2811	usually more than enough. If you need to manage thousands of C<ev_stat>
2512	watchers you might want to increase this value (I<must> be a power of	2812	watchers you might want to increase this value (I<must> be a power of
2513	two).	2813	two).
2514		2814
…		…
2610		2910
2611	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	2911	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2612		2912
2613	This means that, when you have a watcher that triggers in one hour and	2913	This means that, when you have a watcher that triggers in one hour and
2614	there are 100 watchers that would trigger before that then inserting will	2914	there are 100 watchers that would trigger before that then inserting will
2615	have to skip those 100 watchers.	2915	have to skip roughly seven (C<ld 100>) of these watchers.
2616		2916
2617	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	2917	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2618		2918
2619	That means that for changing a timer costs less than removing/adding them	2919	That means that changing a timer costs less than removing/adding them
2620	as only the relative motion in the event queue has to be paid for.	2920	as only the relative motion in the event queue has to be paid for.
2621		2921
2622	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	2922	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2623		2923
2624	These just add the watcher into an array or at the head of a list.	2924	These just add the watcher into an array or at the head of a list.
		2925
2625	=item Stopping check/prepare/idle watchers: O(1)	2926	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2626		2927
2627	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	2928	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2628		2929
2629	These watchers are stored in lists then need to be walked to find the	2930	These watchers are stored in lists then need to be walked to find the
2630	correct watcher to remove. The lists are usually short (you don't usually	2931	correct watcher to remove. The lists are usually short (you don't usually
2631	have many watchers waiting for the same fd or signal).	2932	have many watchers waiting for the same fd or signal).
2632		2933
2633	=item Finding the next timer per loop iteration: O(1)	2934	=item Finding the next timer in each loop iteration: O(1)
		2935
		2936	By virtue of using a binary heap, the next timer is always found at the
		2937	beginning of the storage array.
2634		2938
2635	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	2939	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2636		2940
2637	A change means an I/O watcher gets started or stopped, which requires	2941	A change means an I/O watcher gets started or stopped, which requires
2638	libev to recalculate its status (and possibly tell the kernel).	2942	libev to recalculate its status (and possibly tell the kernel, depending
		2943	on backend and wether C<ev_io_set> was used).
2639		2944
2640	=item Activating one watcher: O(1)	2945	=item Activating one watcher (putting it into the pending state): O(1)
2641		2946
2642	=item Priority handling: O(number_of_priorities)	2947	=item Priority handling: O(number_of_priorities)
2643		2948
2644	Priorities are implemented by allocating some space for each	2949	Priorities are implemented by allocating some space for each
2645	priority. When doing priority-based operations, libev usually has to	2950	priority. When doing priority-based operations, libev usually has to
2646	linearly search all the priorities.	2951	linearly search all the priorities, but starting/stopping and activating
		2952	watchers becomes O(1) w.r.t. priority handling.
		2953
		2954	=item Sending an ev_async: O(1)
		2955
		2956	=item Processing ev_async_send: O(number_of_async_watchers)
		2957
		2958	=item Processing signals: O(max_signal_number)
		2959
		2960	Sending involves a syscall I<iff> there were no other C<ev_async_send>
		2961	calls in the current loop iteration. Checking for async and signal events
		2962	involves iterating over all running async watchers or all signal numbers.
2647		2963
2648	=back	2964	=back
2649		2965
2650		2966
		2967	=head1 Win32 platform limitations and workarounds
		2968
		2969	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		2970	requires, and its I/O model is fundamentally incompatible with the POSIX
		2971	model. Libev still offers limited functionality on this platform in
		2972	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		2973	descriptors. This only applies when using Win32 natively, not when using
		2974	e.g. cygwin.
		2975
		2976	There is no supported compilation method available on windows except
		2977	embedding it into other applications.
		2978
		2979	Due to the many, low, and arbitrary limits on the win32 platform and the
		2980	abysmal performance of winsockets, using a large number of sockets is not
		2981	recommended (and not reasonable). If your program needs to use more than
		2982	a hundred or so sockets, then likely it needs to use a totally different
		2983	implementation for windows, as libev offers the POSIX model, which cannot
		2984	be implemented efficiently on windows (microsoft monopoly games).
		2985
		2986	=over 4
		2987
		2988	=item The winsocket select function
		2989
		2990	The winsocket C<select> function doesn't follow POSIX in that it requires
		2991	socket I<handles> and not socket I<file descriptors>. This makes select
		2992	very inefficient, and also requires a mapping from file descriptors
		2993	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
		2994	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
		2995	symbols for more info.
		2996
		2997	The configuration for a "naked" win32 using the microsoft runtime
		2998	libraries and raw winsocket select is:
		2999
		3000	#define EV_USE_SELECT 1
		3001	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3002
		3003	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3004	complexity in the O(n²) range when using win32.
		3005
		3006	=item Limited number of file descriptors
		3007
		3008	Windows has numerous arbitrary (and low) limits on things. Early versions
		3009	of winsocket's select only supported waiting for a max. of C<64> handles
		3010	(probably owning to the fact that all windows kernels can only wait for
		3011	C<64> things at the same time internally; microsoft recommends spawning a
		3012	chain of threads and wait for 63 handles and the previous thread in each).
		3013
		3014	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3015	to some high number (e.g. C<2048>) before compiling the winsocket select
		3016	call (which might be in libev or elsewhere, for example, perl does its own
		3017	select emulation on windows).
		3018
		3019	Another limit is the number of file descriptors in the microsoft runtime
		3020	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3021	or something like this inside microsoft). You can increase this by calling
		3022	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3023	arbitrary limit), but is broken in many versions of the microsoft runtime
		3024	libraries.
		3025
		3026	This might get you to about C<512> or C<2048> sockets (depending on
		3027	windows version and/or the phase of the moon). To get more, you need to
		3028	wrap all I/O functions and provide your own fd management, but the cost of
		3029	calling select (O(n²)) will likely make this unworkable.
		3030
		3031	=back
		3032
		3033
2651	=head1 AUTHOR	3034	=head1 AUTHOR
2652		3035
2653	Marc Lehmann <libev@schmorp.de>.	3036	Marc Lehmann <libev@schmorp.de>.
2654		3037

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Comparing libev/ev.pod (file contents): Revision 1.99 by root, Sat Dec 22 06:16:36 2007 UTC vs. Revision 1.132 by root, Wed Feb 20 17:45:29 2008 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.99 by root, Sat Dec 22 06:16:36 2007 UTC vs.
Revision 1.132 by root, Wed Feb 20 17:45:29 2008 UTC