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

Comparing libev/ev.pod (file contents):
Revision 1.95 by root, Fri Dec 21 05:10:01 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
…		…
115		115
116	Returns the current time as libev would use it. Please note that the	116	Returns the current time as libev would use it. Please note that the
117	C<ev_now> function is usually faster and also often returns the timestamp	117	C<ev_now> function is usually faster and also often returns the timestamp
118	you actually want to know.	118	you actually want to know.
119		119
		120	=item ev_sleep (ev_tstamp interval)
		121
		122	Sleep for the given interval: The current thread will be blocked until
		123	either it is interrupted or the given time interval has passed. Basically
		124	this is a subsecond-resolution C<sleep ()>.
		125
120	=item int ev_version_major ()	126	=item int ev_version_major ()
121		127
122	=item int ev_version_minor ()	128	=item int ev_version_minor ()
123		129
124	You can find out the major and minor ABI version numbers of the library	130	You can find out the major and minor ABI version numbers of the library
…		…
254	flags. If that is troubling you, check C<ev_backend ()> afterwards).	260	flags. If that is troubling you, check C<ev_backend ()> afterwards).
255		261
256	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
257	function.	263	function.
258		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
259	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
260	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>).
261		274
262	The following flags are supported:	275	The following flags are supported:
263		276
…		…
300	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	313	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
301		314
302	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
303	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,
304	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
305	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
306	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.
307		327
308	=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)
309		329
310	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
311	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
312	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
313	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.
314		336
315	=item C<EVBACKEND_EPOLL> (value 4, Linux)	337	=item C<EVBACKEND_EPOLL> (value 4, Linux)
316		338
317	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,
318	but it scales phenomenally better. While poll and select usually scale	340	but it scales phenomenally better. While poll and select usually scale
319	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),
320	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
321	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
322	cases and rewuiring a syscall per fd change, no fork support and bad	344	cases and rewiring a syscall per fd change, no fork support and bad
323	support for dup:	345	support for dup.
324		346
325	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
326	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
327	(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
328	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
…		…
330		352
331	Please note that epoll sometimes generates spurious notifications, so you	353	Please note that epoll sometimes generates spurious notifications, so you
332	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
333	(or space) is available.	355	(or space) is available.
334		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
335	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	364	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
336		365
337	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
338	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
339	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
340	useless. On NetBSD, it seems to work for all the FD types I tested, so it
341	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"
342	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
343	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)
344	system like NetBSD.	372	system like NetBSD.
345		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
346	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
347	kernel is more efficient (which says nothing about its actual speed,	379	kernel is more efficient (which says nothing about its actual speed, of
348	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
349	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
350	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
351	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.
352		393
353	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	394	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
354		395
355	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.
356		400
357	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	401	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
358		402
359	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,
360	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)).
361		405
362	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
363	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
364	blocking when no data (or space) is available.	408	blocking when no data (or space) is available.
365		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
366	=item C<EVBACKEND_ALL>	419	=item C<EVBACKEND_ALL>
367		420
368	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
369	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
370	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	423	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
371		424
		425	It is definitely not recommended to use this flag.
		426
372	=back	427	=back
373		428
374	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
375	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
376	specified, most compiled-in backend will be tried, usually in reverse	431	specified, all backends in C<ev_recommended_backends ()> will be tried.
377	order of their flag values :)
378		432
379	The most typical usage is like this:	433	The most typical usage is like this:
380		434
381	if (!ev_default_loop (0))	435	if (!ev_default_loop (0))
382	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	436	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
…		…
429	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
430	earlier call to C<ev_loop_new>.	484	earlier call to C<ev_loop_new>.
431		485
432	=item ev_default_fork ()	486	=item ev_default_fork ()
433		487
		488	This function sets a flag that causes subsequent C<ev_loop> iterations
434	This function reinitialises the kernel state for backends that have	489	to reinitialise the kernel state for backends that have one. Despite the
435	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
436	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
437	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.
438		494
439	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
440	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
441	fork+exec, you don't have to call it.	497	you just fork+exec, you don't have to call it at all.
442		498
443	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
444	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
445	quite nicely into a call to C<pthread_atfork>:	501	quite nicely into a call to C<pthread_atfork>:
446		502
447	pthread_atfork (0, 0, ev_default_fork);	503	pthread_atfork (0, 0, ev_default_fork);
448		504
449	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
450	without calling this function, so if you force one of those backends you
451	do not need to care.
452
453	=item ev_loop_fork (loop)	505	=item ev_loop_fork (loop)
454		506
455	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
456	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
457	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.
458		514
459	=item unsigned int ev_loop_count (loop)	515	=item unsigned int ev_loop_count (loop)
460		516
461	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
462	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
…		…
507	usually a better approach for this kind of thing.	563	usually a better approach for this kind of thing.
508		564
509	Here are the gory details of what C<ev_loop> does:	565	Here are the gory details of what C<ev_loop> does:
510		566
511	- Before the first iteration, call any pending watchers.	567	- Before the first iteration, call any pending watchers.
512	* If there are no active watchers (reference count is zero), return.	568	* If EVFLAG_FORKCHECK was used, check for a fork.
513	- 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.
514	- If we have been forked, recreate the kernel state.	571	- If we have been forked, recreate the kernel state.
515	- Update the kernel state with all outstanding changes.	572	- Update the kernel state with all outstanding changes.
516	- Update the "event loop time".	573	- Update the "event loop time".
517	- 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.
518	- Block the process, waiting for any events.	578	- Block the process, waiting for any events.
519	- Queue all outstanding I/O (fd) events.	579	- Queue all outstanding I/O (fd) events.
520	- Update the "event loop time" and do time jump handling.	580	- Update the "event loop time" and do time jump handling.
521	- Queue all outstanding timers.	581	- Queue all outstanding timers.
522	- Queue all outstanding periodics.	582	- Queue all outstanding periodics.
523	- If no events are pending now, queue all idle watchers.	583	- If no events are pending now, queue all idle watchers.
524	- Queue all check watchers.	584	- Queue all check watchers.
525	- 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).
526	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
527	be handled here by queueing them when their watcher gets executed.	587	be handled here by queueing them when their watcher gets executed.
528	- 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
529	were used, return, otherwise continue with step *.	589	were used, or there are no active watchers, return, otherwise
		590	continue with step *.
530		591
531	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
532	anymore.	593	anymore.
533		594
534	... queue jobs here, make sure they register event watchers as long	595	... queue jobs here, make sure they register event watchers as long
535	... 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..)
536	ev_loop (my_loop, 0);	597	ev_loop (my_loop, 0);
…		…
540		601
541	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
542	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
543	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
544	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.
545		608
546	=item ev_ref (loop)	609	=item ev_ref (loop)
547		610
548	=item ev_unref (loop)	611	=item ev_unref (loop)
549		612
…		…
554	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
555	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
556	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
557	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
558	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
559	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).
560		625
561	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>
562	running when nothing else is active.	627	running when nothing else is active.
563		628
564	struct ev_signal exitsig;	629	struct ev_signal exitsig;
…		…
568		633
569	Example: For some weird reason, unregister the above signal handler again.	634	Example: For some weird reason, unregister the above signal handler again.
570		635
571	ev_ref (loop);	636	ev_ref (loop);
572	ev_signal_stop (loop, &exitsig);	637	ev_signal_stop (loop, &exitsig);
		638
		639	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		640
		641	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		642
		643	These advanced functions influence the time that libev will spend waiting
		644	for events. Both are by default C<0>, meaning that libev will try to
		645	invoke timer/periodic callbacks and I/O callbacks with minimum latency.
		646
		647	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		648	allows libev to delay invocation of I/O and timer/periodic callbacks to
		649	increase efficiency of loop iterations.
		650
		651	The background is that sometimes your program runs just fast enough to
		652	handle one (or very few) event(s) per loop iteration. While this makes
		653	the program responsive, it also wastes a lot of CPU time to poll for new
		654	events, especially with backends like C<select ()> which have a high
		655	overhead for the actual polling but can deliver many events at once.
		656
		657	By setting a higher I<io collect interval> you allow libev to spend more
		658	time collecting I/O events, so you can handle more events per iteration,
		659	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		660	C<ev_timer>) will be not affected. Setting this to a non-null value will
		661	introduce an additional C<ev_sleep ()> call into most loop iterations.
		662
		663	Likewise, by setting a higher I<timeout collect interval> you allow libev
		664	to spend more time collecting timeouts, at the expense of increased
		665	latency (the watcher callback will be called later). C<ev_io> watchers
		666	will not be affected. Setting this to a non-null value will not introduce
		667	any overhead in libev.
		668
		669	Many (busy) programs can usually benefit by setting the io collect
		670	interval to a value near C<0.1> or so, which is often enough for
		671	interactive servers (of course not for games), likewise for timeouts. It
		672	usually doesn't make much sense to set it to a lower value than C<0.01>,
		673	as this approsaches the timing granularity of most systems.
573		674
574	=back	675	=back
575		676
576		677
577	=head1 ANATOMY OF A WATCHER	678	=head1 ANATOMY OF A WATCHER
…		…
676		777
677	=item C<EV_FORK>	778	=item C<EV_FORK>
678		779
679	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
680	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>).
681		786
682	=item C<EV_ERROR>	787	=item C<EV_ERROR>
683		788
684	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
685	happen because the watcher could not be properly started because libev	790	happen because the watcher could not be properly started because libev
…		…
903	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
904	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
905	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
906	required if you know what you are doing).	1011	required if you know what you are doing).
907		1012
908	You have to be careful with dup'ed file descriptors, though. Some backends
909	(the linux epoll backend is a notable example) cannot handle dup'ed file
910	descriptors correctly if you register interest in two or more fds pointing
911	to the same underlying file/socket/etc. description (that is, they share
912	the same underlying "file open").
913
914	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
915	(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
916	C<EVBACKEND_POLL>).	1015	C<EVBACKEND_POLL>).
917		1016
918	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
…		…
952	optimisations to libev.	1051	optimisations to libev.
953		1052
954	=head3 The special problem of dup'ed file descriptors	1053	=head3 The special problem of dup'ed file descriptors
955		1054
956	Some backends (e.g. epoll), cannot register events for file descriptors,	1055	Some backends (e.g. epoll), cannot register events for file descriptors,
957	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
958	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
959	file descriptor might actually receive events.	1058	events for them, only one file descriptor might actually receive events.
960		1059
961	There is no workaorund possible except not registering events	1060	There is no workaround possible except not registering events
962	for potentially C<dup ()>'ed file descriptors or to resort to	1061	for potentially C<dup ()>'ed file descriptors, or to resort to
963	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1062	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
964		1063
965	=head3 The special problem of fork	1064	=head3 The special problem of fork
966		1065
967	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
…		…
993	=item int events [read-only]	1092	=item int events [read-only]
994		1093
995	The events being watched.	1094	The events being watched.
996		1095
997	=back	1096	=back
		1097
		1098	=head3 Examples
998		1099
999	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
1000	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
1001	attempt to read a whole line in the callback.	1102	attempt to read a whole line in the callback.
1002		1103
…		…
1055	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
1056	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
1057	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
1058	timer will not fire more than once per event loop iteration.	1159	timer will not fire more than once per event loop iteration.
1059		1160
1060	=item ev_timer_again (loop)	1161	=item ev_timer_again (loop, ev_timer *)
1061		1162
1062	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
1063	repeating. The exact semantics are:	1164	repeating. The exact semantics are:
1064		1165
1065	If the timer is pending, its pending status is cleared.	1166	If the timer is pending, its pending status is cleared.
…		…
1100	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),
1101	which is also when any modifications are taken into account.	1202	which is also when any modifications are taken into account.
1102		1203
1103	=back	1204	=back
1104		1205
		1206	=head3 Examples
		1207
1105	Example: Create a timer that fires after 60 seconds.	1208	Example: Create a timer that fires after 60 seconds.
1106		1209
1107	static void	1210	static void
1108	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)
1109	{	1212	{
…		…
1172	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
1173	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,
1174	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
1175	system time reaches or surpasses this time.	1278	system time reaches or surpasses this time.
1176		1279
1177	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1280	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1178		1281
1179	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
1180	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)
1181	and then repeat, regardless of any time jumps.	1284	and then repeat, regardless of any time jumps.
1182		1285
…		…
1265		1368
1266	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
1267	trigger next.	1370	trigger next.
1268		1371
1269	=back	1372	=back
		1373
		1374	=head3 Examples
1270		1375
1271	Example: Call a callback every hour, or, more precisely, whenever the	1376	Example: Call a callback every hour, or, more precisely, whenever the
1272	system clock is divisible by 3600. The callback invocation times have	1377	system clock is divisible by 3600. The callback invocation times have
1273	potentially a lot of jittering, but good long-term stability.	1378	potentially a lot of jittering, but good long-term stability.
1274		1379
…		…
1331		1436
1332	The signal the watcher watches out for.	1437	The signal the watcher watches out for.
1333		1438
1334	=back	1439	=back
1335		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
1336		1455
1337	=head2 C<ev_child> - watch out for process status changes	1456	=head2 C<ev_child> - watch out for process status changes
1338		1457
1339	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
1340	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).
1341		1460
1342	=head3 Watcher-Specific Functions and Data Members	1461	=head3 Watcher-Specific Functions and Data Members
1343		1462
1344	=over 4	1463	=over 4
1345		1464
1346	=item ev_child_init (ev_child *, callback, int pid)	1465	=item ev_child_init (ev_child *, callback, int pid, int trace)
1347		1466
1348	=item ev_child_set (ev_child *, int pid)	1467	=item ev_child_set (ev_child *, int pid, int trace)
1349		1468
1350	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
1351	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
1352	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
1353	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
1354	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
1355	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).
1356		1477
1357	=item int pid [read-only]	1478	=item int pid [read-only]
1358		1479
1359	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.
1360		1481
…		…
1366		1487
1367	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
1368	C<waitpid> and C<sys/wait.h> documentation for details).	1489	C<waitpid> and C<sys/wait.h> documentation for details).
1369		1490
1370	=back	1491	=back
1371
1372	Example: Try to exit cleanly on SIGINT and SIGTERM.
1373
1374	static void
1375	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)
1376	{
1377	ev_unloop (loop, EVUNLOOP_ALL);
1378	}
1379
1380	struct ev_signal signal_watcher;
1381	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1382	ev_signal_start (loop, &sigint_cb);
1383		1492
1384		1493
1385	=head2 C<ev_stat> - did the file attributes just change?	1494	=head2 C<ev_stat> - did the file attributes just change?
1386		1495
1387	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
…		…
1416	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
1417	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
1418	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
1419	polling.	1528	polling.
1420		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
1421	=head3 Watcher-Specific Functions and Data Members	1563	=head3 Watcher-Specific Functions and Data Members
1422		1564
1423	=over 4	1565	=over 4
1424		1566
1425	=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)
…		…
1434		1576
1435	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,
1436	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
1437	last change was detected).	1579	last change was detected).
1438		1580
1439	=item ev_stat_stat (ev_stat *)	1581	=item ev_stat_stat (loop, ev_stat *)
1440		1582
1441	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
1442	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
1443	detecting this change (while introducing a race condition). Can also be	1585	detecting this change (while introducing a race condition). Can also be
1444	useful simply to find out the new values.	1586	useful simply to find out the new values.
…		…
1462	=item const char *path [read-only]	1604	=item const char *path [read-only]
1463		1605
1464	The filesystem path that is being watched.	1606	The filesystem path that is being watched.
1465		1607
1466	=back	1608	=back
		1609
		1610	=head3 Examples
1467		1611
1468	Example: Watch C</etc/passwd> for attribute changes.	1612	Example: Watch C</etc/passwd> for attribute changes.
1469		1613
1470	static void	1614	static void
1471	passwd_cb (struct ev_loop loop, ev_stat w, int revents)	1615	passwd_cb (struct ev_loop loop, ev_stat w, int revents)
…		…
1484	}	1628	}
1485		1629
1486	...	1630	...
1487	ev_stat passwd;	1631	ev_stat passwd;
1488		1632
1489	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	1633	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1490	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);
1491		1663
1492		1664
1493	=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...
1494		1666
1495	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
…		…
1521	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,
1522	believe me.	1694	believe me.
1523		1695
1524	=back	1696	=back
1525		1697
		1698	=head3 Examples
		1699
1526	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
1527	callback, free it. Also, use no error checking, as usual.	1701	callback, free it. Also, use no error checking, as usual.
1528		1702
1529	static void	1703	static void
1530	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)
1531	{	1705	{
1532	free (w);	1706	free (w);
1533	// now do something you wanted to do when the program has	1707	// now do something you wanted to do when the program has
1534	// no longer asnything immediate to do.	1708	// no longer anything immediate to do.
1535	}	1709	}
1536		1710
1537	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	1711	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1538	ev_idle_init (idle_watcher, idle_cb);	1712	ev_idle_init (idle_watcher, idle_cb);
1539	ev_idle_start (loop, idle_cb);	1713	ev_idle_start (loop, idle_cb);
…		…
1581		1755
1582	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>)
1583	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
1584	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,
1585	too) should not activate ("feed") events into libev. While libev fully	1759	too) should not activate ("feed") events into libev. While libev fully
1586	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
1587	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
1588	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
1589	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
1590	others).	1764	coexist peacefully with others).
1591		1765
1592	=head3 Watcher-Specific Functions and Data Members	1766	=head3 Watcher-Specific Functions and Data Members
1593		1767
1594	=over 4	1768	=over 4
1595		1769
…		…
1600	Initialises and configures the prepare or check watcher - they have no	1774	Initialises and configures the prepare or check watcher - they have no
1601	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>
1602	macros, but using them is utterly, utterly and completely pointless.	1776	macros, but using them is utterly, utterly and completely pointless.
1603		1777
1604	=back	1778	=back
		1779
		1780	=head3 Examples
1605		1781
1606	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
1607	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
1608	(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
1609	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>
…		…
1734	=head2 C<ev_embed> - when one backend isn't enough...	1910	=head2 C<ev_embed> - when one backend isn't enough...
1735		1911
1736	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
1737	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
1738	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
1739	fashion and must not be used). (See portability notes, below).	1915	fashion and must not be used).
1740		1916
1741	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
1742	prioritise I/O.	1918	prioritise I/O.
1743		1919
1744	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
…		…
1778	portable one.	1954	portable one.
1779		1955
1780	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
1781	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
1782	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
1783	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).
1784		1994
1785	struct ev_loop *loop_hi = ev_default_init (0);	1995	struct ev_loop *loop_hi = ev_default_init (0);
1786	struct ev_loop *loop_lo = 0;	1996	struct ev_loop *loop_lo = 0;
1787	struct ev_embed embed;	1997	struct ev_embed embed;
1788		1998
…		…
1799	ev_embed_start (loop_hi, &embed);	2009	ev_embed_start (loop_hi, &embed);
1800	}	2010	}
1801	else	2011	else
1802	loop_lo = loop_hi;	2012	loop_lo = loop_hi;
1803		2013
1804	=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).
1805		2018
1806	Kqueue is nominally embeddable, but this is broken on all BSDs that I	2019	struct ev_loop *loop = ev_default_init (0);
1807	tried, in various ways. Usually the embedded event loop will simply never	2020	struct ev_loop *loop_socket = 0;
1808	receive events, sometimes it will only trigger a few times, sometimes in a	2021	struct ev_embed embed;
1809	loop. Epoll is also nominally embeddable, but many Linux kernel versions	2022
1810	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	}
1811		2029
1812	While libev allows embedding these backends (they are contained in	2030	if (!loop_socket)
1813	C<ev_embeddable_backends ()>), take extreme care that it will actually	2031	loop_socket = loop;
1814	work.
1815		2032
1816	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
1817	usually works) and possibly another thread and a pipe or so to report to
1818	your main event loop.
1819
1820	=head3 Watcher-Specific Functions and Data Members
1821
1822	=over 4
1823
1824	=item ev_embed_init (ev_embed , callback, struct ev_loop embedded_loop)
1825
1826	=item ev_embed_set (ev_embed , callback, struct ev_loop embedded_loop)
1827
1828	Configures the watcher to embed the given loop, which must be
1829	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1830	invoked automatically, otherwise it is the responsibility of the callback
1831	to invoke it (it will continue to be called until the sweep has been done,
1832	if you do not want thta, you need to temporarily stop the embed watcher).
1833
1834	=item ev_embed_sweep (loop, ev_embed *)
1835
1836	Make a single, non-blocking sweep over the embedded loop. This works
1837	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1838	apropriate way for embedded loops.
1839
1840	=item struct ev_loop *other [read-only]
1841
1842	The embedded event loop.
1843
1844	=back
1845		2034
1846		2035
1847	=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
1848		2037
1849	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
…		…
1865	believe me.	2054	believe me.
1866		2055
1867	=back	2056	=back
1868		2057
1869		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
1870	=head1 OTHER FUNCTIONS	2190	=head1 OTHER FUNCTIONS
1871		2191
1872	There are some other functions of possible interest. Described. Here. Now.	2192	There are some other functions of possible interest. Described. Here. Now.
1873		2193
1874	=over 4	2194	=over 4
…		…
2101	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
2102	the constructor.	2422	the constructor.
2103		2423
2104	class myclass	2424	class myclass
2105	{	2425	{
2106	ev_io io; void io_cb (ev::io &w, int revents);	2426	ev::io io; void io_cb (ev::io &w, int revents);
2107	ev_idle idle void idle_cb (ev::idle &w, int revents);	2427	ev:idle idle void idle_cb (ev::idle &w, int revents);
2108		2428
2109	myclass ();	2429	myclass (int fd)
2110	}
2111
2112	myclass::myclass (int fd)
2113	{	2430	{
2114	io .set <myclass, &myclass::io_cb > (this);	2431	io .set <myclass, &myclass::io_cb > (this);
2115	idle.set <myclass, &myclass::idle_cb> (this);	2432	idle.set <myclass, &myclass::idle_cb> (this);
2116		2433
2117	io.start (fd, ev::READ);	2434	io.start (fd, ev::READ);
		2435	}
2118	}	2436	};
2119		2437
2120		2438
2121	=head1 MACRO MAGIC	2439	=head1 MACRO MAGIC
2122		2440
2123	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
…		…
2297	runtime if successful). Otherwise no use of the realtime clock option will	2615	runtime if successful). Otherwise no use of the realtime clock option will
2298	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	2616	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
2299	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	2617	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
2300	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	2618	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
2301		2619
		2620	=item EV_USE_NANOSLEEP
		2621
		2622	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2623	and will use it for delays. Otherwise it will use C<select ()>.
		2624
2302	=item EV_USE_SELECT	2625	=item EV_USE_SELECT
2303		2626
2304	If undefined or defined to be C<1>, libev will compile in support for the	2627	If undefined or defined to be C<1>, libev will compile in support for the
2305	C<select>(2) backend. No attempt at autodetection will be done: if no	2628	C<select>(2) backend. No attempt at autodetection will be done: if no
2306	other method takes over, select will be it. Otherwise the select backend	2629	other method takes over, select will be it. Otherwise the select backend
…		…
2323	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
2324	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
2325	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,
2326	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
2327	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.
2328		2659
2329	=item EV_USE_POLL	2660	=item EV_USE_POLL
2330		2661
2331	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)
2332	backend. Otherwise it will be enabled on non-win32 platforms. It	2663	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
2366		2697
2367	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
2368	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
2369	be detected at runtime.	2700	be detected at runtime.
2370		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
2371	=item EV_H	2713	=item EV_H
2372		2714
2373	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
2374	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
2375	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.
2376		2718
2377	=item EV_CONFIG_H	2719	=item EV_CONFIG_H
2378		2720
2379	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
2380	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
2381	C<EV_H>, above.	2723	C<EV_H>, above.
2382		2724
2383	=item EV_EVENT_H	2725	=item EV_EVENT_H
2384		2726
2385	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
2386	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">.
2387		2729
2388	=item EV_PROTOTYPES	2730	=item EV_PROTOTYPES
2389		2731
2390	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
2391	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
…		…
2442	=item EV_FORK_ENABLE	2784	=item EV_FORK_ENABLE
2443		2785
2444	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
2445	defined to be C<0>, then they are not.	2787	defined to be C<0>, then they are not.
2446		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
2447	=item EV_MINIMAL	2794	=item EV_MINIMAL
2448		2795
2449	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
2450	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
2451	some inlining decisions, saves roughly 30% codesize of amd64.	2798	some inlining decisions, saves roughly 30% codesize of amd64.
…		…
2457	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
2458	increase this value (I<must> be a power of two).	2805	increase this value (I<must> be a power of two).
2459		2806
2460	=item EV_INOTIFY_HASHSIZE	2807	=item EV_INOTIFY_HASHSIZE
2461		2808
2462	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
2463	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>),
2464	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>
2465	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
2466	two).	2813	two).
2467		2814
…		…
2563		2910
2564	=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)
2565		2912
2566	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
2567	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
2568	have to skip those 100 watchers.	2915	have to skip roughly seven (C<ld 100>) of these watchers.
2569		2916
2570	=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)
2571		2918
2572	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
2573	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.
2574		2921
2575	=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)
2576		2923
2577	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
2578	=item Stopping check/prepare/idle watchers: O(1)	2926	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2579		2927
2580	=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))
2581		2929
2582	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
2583	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
2584	have many watchers waiting for the same fd or signal).	2932	have many watchers waiting for the same fd or signal).
2585		2933
2586	=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.
2587		2938
2588	=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)
2589		2940
2590	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
2591	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).
2592		2944
2593	=item Activating one watcher: O(1)	2945	=item Activating one watcher (putting it into the pending state): O(1)
2594		2946
2595	=item Priority handling: O(number_of_priorities)	2947	=item Priority handling: O(number_of_priorities)
2596		2948
2597	Priorities are implemented by allocating some space for each	2949	Priorities are implemented by allocating some space for each
2598	priority. When doing priority-based operations, libev usually has to	2950	priority. When doing priority-based operations, libev usually has to
2599	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.
2600		2963
2601	=back	2964	=back
2602		2965
2603		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
2604	=head1 AUTHOR	3034	=head1 AUTHOR
2605		3035
2606	Marc Lehmann <libev@schmorp.de>.	3036	Marc Lehmann <libev@schmorp.de>.
2607		3037

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Comparing libev/ev.pod (file contents): Revision 1.95 by root, Fri Dec 21 05:10:01 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 1.95 by root, Fri Dec 21 05:10:01 2007 UTC vs.
Revision 1.132 by root, Wed Feb 20 17:45:29 2008 UTC