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…		…
8		8
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
		13
		14	#include <stdio.h> // for puts
13		15
14	// every watcher type has its own typedef'd struct	16	// every watcher type has its own typedef'd struct
15	// with the name ev_TYPE	17	// with the name ev_TYPE
16	ev_io stdin_watcher;	18	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
…		…
41		43
42	int	44	int
43	main (void)	45	main (void)
44	{	46	{
45	// use the default event loop unless you have special needs	47	// use the default event loop unless you have special needs
46	ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
47		49
48	// initialise an io watcher, then start it	50	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	51	// this one will watch for stdin to become readable
50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
51	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
…		…
60		62
61	// unloop was called, so exit	63	// unloop was called, so exit
62	return 0;	64	return 0;
63	}	65	}
64		66
65	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
66		70
67	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
70		84
71	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	87	these event sources and provide your program with events.
74		88
…		…
84	=head2 FEATURES	98	=head2 FEATURES
85		99
86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
91	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
94	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
96		111
97	It also is quite fast (see this	112	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	114	for example).
100		115
…		…
108	name C<loop> (which is always of type C<ev_loop *>) will not have	123	name C<loop> (which is always of type C<ev_loop *>) will not have
109	this argument.	124	this argument.
110		125
111	=head2 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
112		127
113	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
115	the beginning of 1970, details are complicated, don't ask). This type is	130	near the beginning of 1970, details are complicated, don't ask). This
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	type is called C<ev_tstamp>, which is what you should use too. It usually
117	to the C<double> type in C, and when you need to do any calculations on	132	aliases to the C<double> type in C. When you need to do any calculations
118	it, you should treat it as some floating point value. Unlike the name	133	on it, you should treat it as some floating point value. Unlike the name
119	component C<stamp> might indicate, it is also used for time differences	134	component C<stamp> might indicate, it is also used for time differences
120	throughout libev.	135	throughout libev.
121		136
122	=head1 ERROR HANDLING	137	=head1 ERROR HANDLING
123		138
…		…
298	If you don't know what event loop to use, use the one returned from this	313	If you don't know what event loop to use, use the one returned from this
299	function.	314	function.
300		315
301	Note that this function is I<not> thread-safe, so if you want to use it	316	Note that this function is I<not> thread-safe, so if you want to use it
302	from multiple threads, you have to lock (note also that this is unlikely,	317	from multiple threads, you have to lock (note also that this is unlikely,
303	as loops cannot bes hared easily between threads anyway).	318	as loops cannot be shared easily between threads anyway).
304		319
305	The default loop is the only loop that can handle C<ev_signal> and	320	The default loop is the only loop that can handle C<ev_signal> and
306	C<ev_child> watchers, and to do this, it always registers a handler	321	C<ev_child> watchers, and to do this, it always registers a handler
307	for C<SIGCHLD>. If this is a problem for your application you can either	322	for C<SIGCHLD>. If this is a problem for your application you can either
308	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	323	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
348	flag.	363	flag.
349		364
350	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
351	environment variable.	366	environment variable.
352		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_NOSIGNALFD>
		376
		377	When this flag is specified, then libev will not attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		379	probably only useful to work around any bugs in libev. Consequently, this
		380	flag might go away once the signalfd functionality is considered stable,
		381	so it's useful mostly in environment variables and not in program code.
		382
353	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	383	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
354		384
355	This is your standard select(2) backend. Not I<completely> standard, as	385	This is your standard select(2) backend. Not I<completely> standard, as
356	libev tries to roll its own fd_set with no limits on the number of fds,	386	libev tries to roll its own fd_set with no limits on the number of fds,
357	but if that fails, expect a fairly low limit on the number of fds when	387	but if that fails, expect a fairly low limit on the number of fds when
…		…
384	=item C<EVBACKEND_EPOLL> (value 4, Linux)	414	=item C<EVBACKEND_EPOLL> (value 4, Linux)
385		415
386	For few fds, this backend is a bit little slower than poll and select,	416	For few fds, this backend is a bit little slower than poll and select,
387	but it scales phenomenally better. While poll and select usually scale	417	but it scales phenomenally better. While poll and select usually scale
388	like O(total_fds) where n is the total number of fds (or the highest fd),	418	like O(total_fds) where n is the total number of fds (or the highest fd),
389	epoll scales either O(1) or O(active_fds). The epoll design has a number	419	epoll scales either O(1) or O(active_fds).
390	of shortcomings, such as silently dropping events in some hard-to-detect	420
391	cases and requiring a system call per fd change, no fork support and bad	421	The epoll mechanism deserves honorable mention as the most misdesigned
392	support for dup.	422	of the more advanced event mechanisms: mere annoyances include silently
		423	dropping file descriptors, requiring a system call per change per file
		424	descriptor (and unnecessary guessing of parameters), problems with dup and
		425	so on. The biggest issue is fork races, however - if a program forks then
		426	I<both> parent and child process have to recreate the epoll set, which can
		427	take considerable time (one syscall per file descriptor) and is of course
		428	hard to detect.
		429
		430	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		431	of course I<doesn't>, and epoll just loves to report events for totally
		432	I<different> file descriptors (even already closed ones, so one cannot
		433	even remove them from the set) than registered in the set (especially
		434	on SMP systems). Libev tries to counter these spurious notifications by
		435	employing an additional generation counter and comparing that against the
		436	events to filter out spurious ones, recreating the set when required.
393		437
394	While stopping, setting and starting an I/O watcher in the same iteration	438	While stopping, setting and starting an I/O watcher in the same iteration
395	will result in some caching, there is still a system call per such incident	439	will result in some caching, there is still a system call per such
396	(because the fd could point to a different file description now), so its	440	incident (because the same I<file descriptor> could point to a different
397	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	441	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
398	very well if you register events for both fds.	442	file descriptors might not work very well if you register events for both
399		443	file descriptors.
400	Please note that epoll sometimes generates spurious notifications, so you
401	need to use non-blocking I/O or other means to avoid blocking when no data
402	(or space) is available.
403		444
404	Best performance from this backend is achieved by not unregistering all	445	Best performance from this backend is achieved by not unregistering all
405	watchers for a file descriptor until it has been closed, if possible,	446	watchers for a file descriptor until it has been closed, if possible,
406	i.e. keep at least one watcher active per fd at all times. Stopping and	447	i.e. keep at least one watcher active per fd at all times. Stopping and
407	starting a watcher (without re-setting it) also usually doesn't cause	448	starting a watcher (without re-setting it) also usually doesn't cause
408	extra overhead.	449	extra overhead. A fork can both result in spurious notifications as well
		450	as in libev having to destroy and recreate the epoll object, which can
		451	take considerable time and thus should be avoided.
		452
		453	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		454	faster than epoll for maybe up to a hundred file descriptors, depending on
		455	the usage. So sad.
409		456
410	While nominally embeddable in other event loops, this feature is broken in	457	While nominally embeddable in other event loops, this feature is broken in
411	all kernel versions tested so far.	458	all kernel versions tested so far.
412		459
413	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	460	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
414	C<EVBACKEND_POLL>.	461	C<EVBACKEND_POLL>.
415		462
416	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	463	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
417		464
418	Kqueue deserves special mention, as at the time of this writing, it was	465	Kqueue deserves special mention, as at the time of this writing, it
419	broken on all BSDs except NetBSD (usually it doesn't work reliably with	466	was broken on all BSDs except NetBSD (usually it doesn't work reliably
420	anything but sockets and pipes, except on Darwin, where of course it's	467	with anything but sockets and pipes, except on Darwin, where of course
421	completely useless). For this reason it's not being "auto-detected" unless	468	it's completely useless). Unlike epoll, however, whose brokenness
422	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or	469	is by design, these kqueue bugs can (and eventually will) be fixed
423	libev was compiled on a known-to-be-good (-enough) system like NetBSD.	470	without API changes to existing programs. For this reason it's not being
		471	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		472	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		473	system like NetBSD.
424		474
425	You still can embed kqueue into a normal poll or select backend and use it	475	You still can embed kqueue into a normal poll or select backend and use it
426	only for sockets (after having made sure that sockets work with kqueue on	476	only for sockets (after having made sure that sockets work with kqueue on
427	the target platform). See C<ev_embed> watchers for more info.	477	the target platform). See C<ev_embed> watchers for more info.
428		478
429	It scales in the same way as the epoll backend, but the interface to the	479	It scales in the same way as the epoll backend, but the interface to the
430	kernel is more efficient (which says nothing about its actual speed, of	480	kernel is more efficient (which says nothing about its actual speed, of
431	course). While stopping, setting and starting an I/O watcher does never	481	course). While stopping, setting and starting an I/O watcher does never
432	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	482	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
433	two event changes per incident. Support for C<fork ()> is very bad and it	483	two event changes per incident. Support for C<fork ()> is very bad (but
434	drops fds silently in similarly hard-to-detect cases.	484	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		485	cases
435		486
436	This backend usually performs well under most conditions.	487	This backend usually performs well under most conditions.
437		488
438	While nominally embeddable in other event loops, this doesn't work	489	While nominally embeddable in other event loops, this doesn't work
439	everywhere, so you might need to test for this. And since it is broken	490	everywhere, so you might need to test for this. And since it is broken
440	almost everywhere, you should only use it when you have a lot of sockets	491	almost everywhere, you should only use it when you have a lot of sockets
441	(for which it usually works), by embedding it into another event loop	492	(for which it usually works), by embedding it into another event loop
442	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,	493	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
443	using it only for sockets.	494	also broken on OS X)) and, did I mention it, using it only for sockets.
444		495
445	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with	496	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
446	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with	497	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
447	C<NOTE_EOF>.	498	C<NOTE_EOF>.
448		499
…		…
468	might perform better.	519	might perform better.
469		520
470	On the positive side, with the exception of the spurious readiness	521	On the positive side, with the exception of the spurious readiness
471	notifications, this backend actually performed fully to specification	522	notifications, this backend actually performed fully to specification
472	in all tests and is fully embeddable, which is a rare feat among the	523	in all tests and is fully embeddable, which is a rare feat among the
473	OS-specific backends.	524	OS-specific backends (I vastly prefer correctness over speed hacks).
474		525
475	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	526	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
476	C<EVBACKEND_POLL>.	527	C<EVBACKEND_POLL>.
477		528
478	=item C<EVBACKEND_ALL>	529	=item C<EVBACKEND_ALL>
…		…
483		534
484	It is definitely not recommended to use this flag.	535	It is definitely not recommended to use this flag.
485		536
486	=back	537	=back
487		538
488	If one or more of these are or'ed into the flags value, then only these	539	If one or more of the backend flags are or'ed into the flags value,
489	backends will be tried (in the reverse order as listed here). If none are	540	then only these backends will be tried (in the reverse order as listed
490	specified, all backends in C<ev_recommended_backends ()> will be tried.	541	here). If none are specified, all backends in C<ev_recommended_backends
		542	()> will be tried.
491		543
492	Example: This is the most typical usage.	544	Example: This is the most typical usage.
493		545
494	if (!ev_default_loop (0))	546	if (!ev_default_loop (0))
495	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	547	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
…		…
531	responsibility to either stop all watchers cleanly yourself I<before>	583	responsibility to either stop all watchers cleanly yourself I<before>
532	calling this function, or cope with the fact afterwards (which is usually	584	calling this function, or cope with the fact afterwards (which is usually
533	the easiest thing, you can just ignore the watchers and/or C<free ()> them	585	the easiest thing, you can just ignore the watchers and/or C<free ()> them
534	for example).	586	for example).
535		587
536	Note that certain global state, such as signal state, will not be freed by	588	Note that certain global state, such as signal state (and installed signal
537	this function, and related watchers (such as signal and child watchers)	589	handlers), will not be freed by this function, and related watchers (such
538	would need to be stopped manually.	590	as signal and child watchers) would need to be stopped manually.
539		591
540	In general it is not advisable to call this function except in the	592	In general it is not advisable to call this function except in the
541	rare occasion where you really need to free e.g. the signal handling	593	rare occasion where you really need to free e.g. the signal handling
542	pipe fds. If you need dynamically allocated loops it is better to use	594	pipe fds. If you need dynamically allocated loops it is better to use
543	C<ev_loop_new> and C<ev_loop_destroy>).	595	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
586		638
587	This value can sometimes be useful as a generation counter of sorts (it	639	This value can sometimes be useful as a generation counter of sorts (it
588	"ticks" the number of loop iterations), as it roughly corresponds with	640	"ticks" the number of loop iterations), as it roughly corresponds with
589	C<ev_prepare> and C<ev_check> calls.	641	C<ev_prepare> and C<ev_check> calls.
590		642
		643	=item unsigned int ev_loop_depth (loop)
		644
		645	Returns the number of times C<ev_loop> was entered minus the number of
		646	times C<ev_loop> was exited, in other words, the recursion depth.
		647
		648	Outside C<ev_loop>, this number is zero. In a callback, this number is
		649	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		650	in which case it is higher.
		651
		652	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		653	etc.), doesn't count as exit.
		654
591	=item unsigned int ev_backend (loop)	655	=item unsigned int ev_backend (loop)
592		656
593	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	657	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
594	use.	658	use.
595		659
…		…
609		673
610	This function is rarely useful, but when some event callback runs for a	674	This function is rarely useful, but when some event callback runs for a
611	very long time without entering the event loop, updating libev's idea of	675	very long time without entering the event loop, updating libev's idea of
612	the current time is a good idea.	676	the current time is a good idea.
613		677
614	See also "The special problem of time updates" in the C<ev_timer> section.	678	See also L<The special problem of time updates> in the C<ev_timer> section.
		679
		680	=item ev_suspend (loop)
		681
		682	=item ev_resume (loop)
		683
		684	These two functions suspend and resume a loop, for use when the loop is
		685	not used for a while and timeouts should not be processed.
		686
		687	A typical use case would be an interactive program such as a game: When
		688	the user presses C<^Z> to suspend the game and resumes it an hour later it
		689	would be best to handle timeouts as if no time had actually passed while
		690	the program was suspended. This can be achieved by calling C<ev_suspend>
		691	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		692	C<ev_resume> directly afterwards to resume timer processing.
		693
		694	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		695	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		696	will be rescheduled (that is, they will lose any events that would have
		697	occured while suspended).
		698
		699	After calling C<ev_suspend> you B<must not> call I<any> function on the
		700	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		701	without a previous call to C<ev_suspend>.
		702
		703	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		704	event loop time (see C<ev_now_update>).
615		705
616	=item ev_loop (loop, int flags)	706	=item ev_loop (loop, int flags)
617		707
618	Finally, this is it, the event handler. This function usually is called	708	Finally, this is it, the event handler. This function usually is called
619	after you initialised all your watchers and you want to start handling	709	after you initialised all your watchers and you want to start handling
…		…
635	the loop.	725	the loop.
636		726
637	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	727	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
638	necessary) and will handle those and any already outstanding ones. It	728	necessary) and will handle those and any already outstanding ones. It
639	will block your process until at least one new event arrives (which could	729	will block your process until at least one new event arrives (which could
640	be an event internal to libev itself, so there is no guarentee that a	730	be an event internal to libev itself, so there is no guarantee that a
641	user-registered callback will be called), and will return after one	731	user-registered callback will be called), and will return after one
642	iteration of the loop.	732	iteration of the loop.
643		733
644	This is useful if you are waiting for some external event in conjunction	734	This is useful if you are waiting for some external event in conjunction
645	with something not expressible using other libev watchers (i.e. "roll your	735	with something not expressible using other libev watchers (i.e. "roll your
…		…
703		793
704	If you have a watcher you never unregister that should not keep C<ev_loop>	794	If you have a watcher you never unregister that should not keep C<ev_loop>
705	from returning, call ev_unref() after starting, and ev_ref() before	795	from returning, call ev_unref() after starting, and ev_ref() before
706	stopping it.	796	stopping it.
707		797
708	As an example, libev itself uses this for its internal signal pipe: It is	798	As an example, libev itself uses this for its internal signal pipe: It
709	not visible to the libev user and should not keep C<ev_loop> from exiting	799	is not visible to the libev user and should not keep C<ev_loop> from
710	if no event watchers registered by it are active. It is also an excellent	800	exiting if no event watchers registered by it are active. It is also an
711	way to do this for generic recurring timers or from within third-party	801	excellent way to do this for generic recurring timers or from within
712	libraries. Just remember to I<unref after start> and I<ref before stop>	802	third-party libraries. Just remember to I<unref after start> and I<ref
713	(but only if the watcher wasn't active before, or was active before,	803	before stop> (but only if the watcher wasn't active before, or was active
714	respectively).	804	before, respectively. Note also that libev might stop watchers itself
		805	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		806	in the callback).
715		807
716	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	808	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
717	running when nothing else is active.	809	running when nothing else is active.
718		810
719	ev_signal exitsig;	811	ev_signal exitsig;
…		…
748		840
749	By setting a higher I<io collect interval> you allow libev to spend more	841	By setting a higher I<io collect interval> you allow libev to spend more
750	time collecting I/O events, so you can handle more events per iteration,	842	time collecting I/O events, so you can handle more events per iteration,
751	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	843	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
752	C<ev_timer>) will be not affected. Setting this to a non-null value will	844	C<ev_timer>) will be not affected. Setting this to a non-null value will
753	introduce an additional C<ev_sleep ()> call into most loop iterations.	845	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		846	sleep time ensures that libev will not poll for I/O events more often then
		847	once per this interval, on average.
754		848
755	Likewise, by setting a higher I<timeout collect interval> you allow libev	849	Likewise, by setting a higher I<timeout collect interval> you allow libev
756	to spend more time collecting timeouts, at the expense of increased	850	to spend more time collecting timeouts, at the expense of increased
757	latency/jitter/inexactness (the watcher callback will be called	851	latency/jitter/inexactness (the watcher callback will be called
758	later). C<ev_io> watchers will not be affected. Setting this to a non-null	852	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
760		854
761	Many (busy) programs can usually benefit by setting the I/O collect	855	Many (busy) programs can usually benefit by setting the I/O collect
762	interval to a value near C<0.1> or so, which is often enough for	856	interval to a value near C<0.1> or so, which is often enough for
763	interactive servers (of course not for games), likewise for timeouts. It	857	interactive servers (of course not for games), likewise for timeouts. It
764	usually doesn't make much sense to set it to a lower value than C<0.01>,	858	usually doesn't make much sense to set it to a lower value than C<0.01>,
765	as this approaches the timing granularity of most systems.	859	as this approaches the timing granularity of most systems. Note that if
		860	you do transactions with the outside world and you can't increase the
		861	parallelity, then this setting will limit your transaction rate (if you
		862	need to poll once per transaction and the I/O collect interval is 0.01,
		863	then you can't do more than 100 transations per second).
766		864
767	Setting the I<timeout collect interval> can improve the opportunity for	865	Setting the I<timeout collect interval> can improve the opportunity for
768	saving power, as the program will "bundle" timer callback invocations that	866	saving power, as the program will "bundle" timer callback invocations that
769	are "near" in time together, by delaying some, thus reducing the number of	867	are "near" in time together, by delaying some, thus reducing the number of
770	times the process sleeps and wakes up again. Another useful technique to	868	times the process sleeps and wakes up again. Another useful technique to
771	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	869	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
772	they fire on, say, one-second boundaries only.	870	they fire on, say, one-second boundaries only.
		871
		872	Example: we only need 0.1s timeout granularity, and we wish not to poll
		873	more often than 100 times per second:
		874
		875	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		876	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		877
		878	=item ev_invoke_pending (loop)
		879
		880	This call will simply invoke all pending watchers while resetting their
		881	pending state. Normally, C<ev_loop> does this automatically when required,
		882	but when overriding the invoke callback this call comes handy.
		883
		884	=item int ev_pending_count (loop)
		885
		886	Returns the number of pending watchers - zero indicates that no watchers
		887	are pending.
		888
		889	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		890
		891	This overrides the invoke pending functionality of the loop: Instead of
		892	invoking all pending watchers when there are any, C<ev_loop> will call
		893	this callback instead. This is useful, for example, when you want to
		894	invoke the actual watchers inside another context (another thread etc.).
		895
		896	If you want to reset the callback, use C<ev_invoke_pending> as new
		897	callback.
		898
		899	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		900
		901	Sometimes you want to share the same loop between multiple threads. This
		902	can be done relatively simply by putting mutex_lock/unlock calls around
		903	each call to a libev function.
		904
		905	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		906	wait for it to return. One way around this is to wake up the loop via
		907	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		908	and I<acquire> callbacks on the loop.
		909
		910	When set, then C<release> will be called just before the thread is
		911	suspended waiting for new events, and C<acquire> is called just
		912	afterwards.
		913
		914	Ideally, C<release> will just call your mutex_unlock function, and
		915	C<acquire> will just call the mutex_lock function again.
		916
		917	While event loop modifications are allowed between invocations of
		918	C<release> and C<acquire> (that's their only purpose after all), no
		919	modifications done will affect the event loop, i.e. adding watchers will
		920	have no effect on the set of file descriptors being watched, or the time
		921	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		922	to take note of any changes you made.
		923
		924	In theory, threads executing C<ev_loop> will be async-cancel safe between
		925	invocations of C<release> and C<acquire>.
		926
		927	See also the locking example in the C<THREADS> section later in this
		928	document.
		929
		930	=item ev_set_userdata (loop, void *data)
		931
		932	=item ev_userdata (loop)
		933
		934	Set and retrieve a single C<void *> associated with a loop. When
		935	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		936	C<0.>
		937
		938	These two functions can be used to associate arbitrary data with a loop,
		939	and are intended solely for the C<invoke_pending_cb>, C<release> and
		940	C<acquire> callbacks described above, but of course can be (ab-)used for
		941	any other purpose as well.
773		942
774	=item ev_loop_verify (loop)	943	=item ev_loop_verify (loop)
775		944
776	This function only does something when C<EV_VERIFY> support has been	945	This function only does something when C<EV_VERIFY> support has been
777	compiled in, which is the default for non-minimal builds. It tries to go	946	compiled in, which is the default for non-minimal builds. It tries to go
…		…
903		1072
904	=item C<EV_ASYNC>	1073	=item C<EV_ASYNC>
905		1074
906	The given async watcher has been asynchronously notified (see C<ev_async>).	1075	The given async watcher has been asynchronously notified (see C<ev_async>).
907		1076
		1077	=item C<EV_CUSTOM>
		1078
		1079	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1080	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1081
908	=item C<EV_ERROR>	1082	=item C<EV_ERROR>
909		1083
910	An unspecified error has occurred, the watcher has been stopped. This might	1084	An unspecified error has occurred, the watcher has been stopped. This might
911	happen because the watcher could not be properly started because libev	1085	happen because the watcher could not be properly started because libev
912	ran out of memory, a file descriptor was found to be closed or any other	1086	ran out of memory, a file descriptor was found to be closed or any other
…		…
1027	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1201	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1028	(default: C<-2>). Pending watchers with higher priority will be invoked	1202	(default: C<-2>). Pending watchers with higher priority will be invoked
1029	before watchers with lower priority, but priority will not keep watchers	1203	before watchers with lower priority, but priority will not keep watchers
1030	from being executed (except for C<ev_idle> watchers).	1204	from being executed (except for C<ev_idle> watchers).
1031		1205
1032	This means that priorities are I<only> used for ordering callback
1033	invocation after new events have been received. This is useful, for
1034	example, to reduce latency after idling, or more often, to bind two
1035	watchers on the same event and make sure one is called first.
1036
1037	If you need to suppress invocation when higher priority events are pending	1206	If you need to suppress invocation when higher priority events are pending
1038	you need to look at C<ev_idle> watchers, which provide this functionality.	1207	you need to look at C<ev_idle> watchers, which provide this functionality.
1039		1208
1040	You I<must not> change the priority of a watcher as long as it is active or	1209	You I<must not> change the priority of a watcher as long as it is active or
1041	pending.	1210	pending.
1042
1043	The default priority used by watchers when no priority has been set is
1044	always C<0>, which is supposed to not be too high and not be too low :).
1045		1211
1046	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1212	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1047	fine, as long as you do not mind that the priority value you query might	1213	fine, as long as you do not mind that the priority value you query might
1048	or might not have been clamped to the valid range.	1214	or might not have been clamped to the valid range.
		1215
		1216	The default priority used by watchers when no priority has been set is
		1217	always C<0>, which is supposed to not be too high and not be too low :).
		1218
		1219	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1220	priorities.
1049		1221
1050	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1222	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1051		1223
1052	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1224	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1053	C<loop> nor C<revents> need to be valid as long as the watcher callback	1225	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1118	#include <stddef.h>	1290	#include <stddef.h>
1119		1291
1120	static void	1292	static void
1121	t1_cb (EV_P_ ev_timer *w, int revents)	1293	t1_cb (EV_P_ ev_timer *w, int revents)
1122	{	1294	{
1123	struct my_biggy big = (struct my_biggy *	1295	struct my_biggy big = (struct my_biggy *)
1124	(((char *)w) - offsetof (struct my_biggy, t1));	1296	(((char *)w) - offsetof (struct my_biggy, t1));
1125	}	1297	}
1126		1298
1127	static void	1299	static void
1128	t2_cb (EV_P_ ev_timer *w, int revents)	1300	t2_cb (EV_P_ ev_timer *w, int revents)
1129	{	1301	{
1130	struct my_biggy big = (struct my_biggy *	1302	struct my_biggy big = (struct my_biggy *)
1131	(((char *)w) - offsetof (struct my_biggy, t2));	1303	(((char *)w) - offsetof (struct my_biggy, t2));
1132	}	1304	}
		1305
		1306	=head2 WATCHER PRIORITY MODELS
		1307
		1308	Many event loops support I<watcher priorities>, which are usually small
		1309	integers that influence the ordering of event callback invocation
		1310	between watchers in some way, all else being equal.
		1311
		1312	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1313	description for the more technical details such as the actual priority
		1314	range.
		1315
		1316	There are two common ways how these these priorities are being interpreted
		1317	by event loops:
		1318
		1319	In the more common lock-out model, higher priorities "lock out" invocation
		1320	of lower priority watchers, which means as long as higher priority
		1321	watchers receive events, lower priority watchers are not being invoked.
		1322
		1323	The less common only-for-ordering model uses priorities solely to order
		1324	callback invocation within a single event loop iteration: Higher priority
		1325	watchers are invoked before lower priority ones, but they all get invoked
		1326	before polling for new events.
		1327
		1328	Libev uses the second (only-for-ordering) model for all its watchers
		1329	except for idle watchers (which use the lock-out model).
		1330
		1331	The rationale behind this is that implementing the lock-out model for
		1332	watchers is not well supported by most kernel interfaces, and most event
		1333	libraries will just poll for the same events again and again as long as
		1334	their callbacks have not been executed, which is very inefficient in the
		1335	common case of one high-priority watcher locking out a mass of lower
		1336	priority ones.
		1337
		1338	Static (ordering) priorities are most useful when you have two or more
		1339	watchers handling the same resource: a typical usage example is having an
		1340	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1341	timeouts. Under load, data might be received while the program handles
		1342	other jobs, but since timers normally get invoked first, the timeout
		1343	handler will be executed before checking for data. In that case, giving
		1344	the timer a lower priority than the I/O watcher ensures that I/O will be
		1345	handled first even under adverse conditions (which is usually, but not
		1346	always, what you want).
		1347
		1348	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1349	will only be executed when no same or higher priority watchers have
		1350	received events, they can be used to implement the "lock-out" model when
		1351	required.
		1352
		1353	For example, to emulate how many other event libraries handle priorities,
		1354	you can associate an C<ev_idle> watcher to each such watcher, and in
		1355	the normal watcher callback, you just start the idle watcher. The real
		1356	processing is done in the idle watcher callback. This causes libev to
		1357	continously poll and process kernel event data for the watcher, but when
		1358	the lock-out case is known to be rare (which in turn is rare :), this is
		1359	workable.
		1360
		1361	Usually, however, the lock-out model implemented that way will perform
		1362	miserably under the type of load it was designed to handle. In that case,
		1363	it might be preferable to stop the real watcher before starting the
		1364	idle watcher, so the kernel will not have to process the event in case
		1365	the actual processing will be delayed for considerable time.
		1366
		1367	Here is an example of an I/O watcher that should run at a strictly lower
		1368	priority than the default, and which should only process data when no
		1369	other events are pending:
		1370
		1371	ev_idle idle; // actual processing watcher
		1372	ev_io io; // actual event watcher
		1373
		1374	static void
		1375	io_cb (EV_P_ ev_io *w, int revents)
		1376	{
		1377	// stop the I/O watcher, we received the event, but
		1378	// are not yet ready to handle it.
		1379	ev_io_stop (EV_A_ w);
		1380
		1381	// start the idle watcher to ahndle the actual event.
		1382	// it will not be executed as long as other watchers
		1383	// with the default priority are receiving events.
		1384	ev_idle_start (EV_A_ &idle);
		1385	}
		1386
		1387	static void
		1388	idle_cb (EV_P_ ev_idle *w, int revents)
		1389	{
		1390	// actual processing
		1391	read (STDIN_FILENO, ...);
		1392
		1393	// have to start the I/O watcher again, as
		1394	// we have handled the event
		1395	ev_io_start (EV_P_ &io);
		1396	}
		1397
		1398	// initialisation
		1399	ev_idle_init (&idle, idle_cb);
		1400	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1401	ev_io_start (EV_DEFAULT_ &io);
		1402
		1403	In the "real" world, it might also be beneficial to start a timer, so that
		1404	low-priority connections can not be locked out forever under load. This
		1405	enables your program to keep a lower latency for important connections
		1406	during short periods of high load, while not completely locking out less
		1407	important ones.
1133		1408
1134		1409
1135	=head1 WATCHER TYPES	1410	=head1 WATCHER TYPES
1136		1411
1137	This section describes each watcher in detail, but will not repeat	1412	This section describes each watcher in detail, but will not repeat
…		…
1163	descriptors to non-blocking mode is also usually a good idea (but not	1438	descriptors to non-blocking mode is also usually a good idea (but not
1164	required if you know what you are doing).	1439	required if you know what you are doing).
1165		1440
1166	If you cannot use non-blocking mode, then force the use of a	1441	If you cannot use non-blocking mode, then force the use of a
1167	known-to-be-good backend (at the time of this writing, this includes only	1442	known-to-be-good backend (at the time of this writing, this includes only
1168	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1443	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1444	descriptors for which non-blocking operation makes no sense (such as
		1445	files) - libev doesn't guarentee any specific behaviour in that case.
1169		1446
1170	Another thing you have to watch out for is that it is quite easy to	1447	Another thing you have to watch out for is that it is quite easy to
1171	receive "spurious" readiness notifications, that is your callback might	1448	receive "spurious" readiness notifications, that is your callback might
1172	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1449	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1173	because there is no data. Not only are some backends known to create a	1450	because there is no data. Not only are some backends known to create a
…		…
1294	year, it will still time out after (roughly) one hour. "Roughly" because	1571	year, it will still time out after (roughly) one hour. "Roughly" because
1295	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1572	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1296	monotonic clock option helps a lot here).	1573	monotonic clock option helps a lot here).
1297		1574
1298	The callback is guaranteed to be invoked only I<after> its timeout has	1575	The callback is guaranteed to be invoked only I<after> its timeout has
1299	passed, but if multiple timers become ready during the same loop iteration	1576	passed (not I<at>, so on systems with very low-resolution clocks this
1300	then order of execution is undefined.	1577	might introduce a small delay). If multiple timers become ready during the
		1578	same loop iteration then the ones with earlier time-out values are invoked
		1579	before ones of the same priority with later time-out values (but this is
		1580	no longer true when a callback calls C<ev_loop> recursively).
1301		1581
1302	=head3 Be smart about timeouts	1582	=head3 Be smart about timeouts
1303		1583
1304	Many real-world problems involve some kind of timeout, usually for error	1584	Many real-world problems involve some kind of timeout, usually for error
1305	recovery. A typical example is an HTTP request - if the other side hangs,	1585	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1349	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>	1629	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
1350	member and C<ev_timer_again>.	1630	member and C<ev_timer_again>.
1351		1631
1352	At start:	1632	At start:
1353		1633
1354	ev_timer_init (timer, callback);	1634	ev_init (timer, callback);
1355	timer->repeat = 60.;	1635	timer->repeat = 60.;
1356	ev_timer_again (loop, timer);	1636	ev_timer_again (loop, timer);
1357		1637
1358	Each time there is some activity:	1638	Each time there is some activity:
1359		1639
…		…
1398	else	1678	else
1399	{	1679	{
1400	// callback was invoked, but there was some activity, re-arm	1680	// callback was invoked, but there was some activity, re-arm
1401	// the watcher to fire in last_activity + 60, which is	1681	// the watcher to fire in last_activity + 60, which is
1402	// guaranteed to be in the future, so "again" is positive:	1682	// guaranteed to be in the future, so "again" is positive:
1403	w->again = timeout - now;	1683	w->repeat = timeout - now;
1404	ev_timer_again (EV_A_ w);	1684	ev_timer_again (EV_A_ w);
1405	}	1685	}
1406	}	1686	}
1407		1687
1408	To summarise the callback: first calculate the real timeout (defined	1688	To summarise the callback: first calculate the real timeout (defined
…		…
1421		1701
1422	To start the timer, simply initialise the watcher and set C<last_activity>	1702	To start the timer, simply initialise the watcher and set C<last_activity>
1423	to the current time (meaning we just have some activity :), then call the	1703	to the current time (meaning we just have some activity :), then call the
1424	callback, which will "do the right thing" and start the timer:	1704	callback, which will "do the right thing" and start the timer:
1425		1705
1426	ev_timer_init (timer, callback);	1706	ev_init (timer, callback);
1427	last_activity = ev_now (loop);	1707	last_activity = ev_now (loop);
1428	callback (loop, timer, EV_TIMEOUT);	1708	callback (loop, timer, EV_TIMEOUT);
1429		1709
1430	And when there is some activity, simply store the current time in	1710	And when there is some activity, simply store the current time in
1431	C<last_activity>, no libev calls at all:	1711	C<last_activity>, no libev calls at all:
…		…
1492		1772
1493	If the event loop is suspended for a long time, you can also force an	1773	If the event loop is suspended for a long time, you can also force an
1494	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1774	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1495	()>.	1775	()>.
1496		1776
		1777	=head3 The special problems of suspended animation
		1778
		1779	When you leave the server world it is quite customary to hit machines that
		1780	can suspend/hibernate - what happens to the clocks during such a suspend?
		1781
		1782	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1783	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1784	to run until the system is suspended, but they will not advance while the
		1785	system is suspended. That means, on resume, it will be as if the program
		1786	was frozen for a few seconds, but the suspend time will not be counted
		1787	towards C<ev_timer> when a monotonic clock source is used. The real time
		1788	clock advanced as expected, but if it is used as sole clocksource, then a
		1789	long suspend would be detected as a time jump by libev, and timers would
		1790	be adjusted accordingly.
		1791
		1792	I would not be surprised to see different behaviour in different between
		1793	operating systems, OS versions or even different hardware.
		1794
		1795	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1796	time jump in the monotonic clocks and the realtime clock. If the program
		1797	is suspended for a very long time, and monotonic clock sources are in use,
		1798	then you can expect C<ev_timer>s to expire as the full suspension time
		1799	will be counted towards the timers. When no monotonic clock source is in
		1800	use, then libev will again assume a timejump and adjust accordingly.
		1801
		1802	It might be beneficial for this latter case to call C<ev_suspend>
		1803	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1804	deterministic behaviour in this case (you can do nothing against
		1805	C<SIGSTOP>).
		1806
1497	=head3 Watcher-Specific Functions and Data Members	1807	=head3 Watcher-Specific Functions and Data Members
1498		1808
1499	=over 4	1809	=over 4
1500		1810
1501	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1811	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1524	If the timer is started but non-repeating, stop it (as if it timed out).	1834	If the timer is started but non-repeating, stop it (as if it timed out).
1525		1835
1526	If the timer is repeating, either start it if necessary (with the	1836	If the timer is repeating, either start it if necessary (with the
1527	C<repeat> value), or reset the running timer to the C<repeat> value.	1837	C<repeat> value), or reset the running timer to the C<repeat> value.
1528		1838
1529	This sounds a bit complicated, see "Be smart about timeouts", above, for a	1839	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1530	usage example.	1840	usage example.
		1841
		1842	=item ev_timer_remaining (loop, ev_timer *)
		1843
		1844	Returns the remaining time until a timer fires. If the timer is active,
		1845	then this time is relative to the current event loop time, otherwise it's
		1846	the timeout value currently configured.
		1847
		1848	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1849	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1850	will return C<4>. When the timer expires and is restarted, it will return
		1851	roughly C<7> (likely slightly less as callback invocation takes some time,
		1852	too), and so on.
1531		1853
1532	=item ev_tstamp repeat [read-write]	1854	=item ev_tstamp repeat [read-write]
1533		1855
1534	The current C<repeat> value. Will be used each time the watcher times out	1856	The current C<repeat> value. Will be used each time the watcher times out
1535	or C<ev_timer_again> is called, and determines the next timeout (if any),	1857	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1573	=head2 C<ev_periodic> - to cron or not to cron?	1895	=head2 C<ev_periodic> - to cron or not to cron?
1574		1896
1575	Periodic watchers are also timers of a kind, but they are very versatile	1897	Periodic watchers are also timers of a kind, but they are very versatile
1576	(and unfortunately a bit complex).	1898	(and unfortunately a bit complex).
1577		1899
1578	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1900	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1579	but on wall clock time (absolute time). You can tell a periodic watcher	1901	relative time, the physical time that passes) but on wall clock time
1580	to trigger after some specific point in time. For example, if you tell a	1902	(absolute time, the thing you can read on your calender or clock). The
1581	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1903	difference is that wall clock time can run faster or slower than real
1582	+ 10.>, that is, an absolute time not a delay) and then reset your system	1904	time, and time jumps are not uncommon (e.g. when you adjust your
1583	clock to January of the previous year, then it will take more than year	1905	wrist-watch).
1584	to trigger the event (unlike an C<ev_timer>, which would still trigger
1585	roughly 10 seconds later as it uses a relative timeout).
1586		1906
		1907	You can tell a periodic watcher to trigger after some specific point
		1908	in time: for example, if you tell a periodic watcher to trigger "in 10
		1909	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1910	not a delay) and then reset your system clock to January of the previous
		1911	year, then it will take a year or more to trigger the event (unlike an
		1912	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1913	it, as it uses a relative timeout).
		1914
1587	C<ev_periodic>s can also be used to implement vastly more complex timers,	1915	C<ev_periodic> watchers can also be used to implement vastly more complex
1588	such as triggering an event on each "midnight, local time", or other	1916	timers, such as triggering an event on each "midnight, local time", or
1589	complicated rules.	1917	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1918	those cannot react to time jumps.
1590		1919
1591	As with timers, the callback is guaranteed to be invoked only when the	1920	As with timers, the callback is guaranteed to be invoked only when the
1592	time (C<at>) has passed, but if multiple periodic timers become ready	1921	point in time where it is supposed to trigger has passed. If multiple
1593	during the same loop iteration, then order of execution is undefined.	1922	timers become ready during the same loop iteration then the ones with
		1923	earlier time-out values are invoked before ones with later time-out values
		1924	(but this is no longer true when a callback calls C<ev_loop> recursively).
1594		1925
1595	=head3 Watcher-Specific Functions and Data Members	1926	=head3 Watcher-Specific Functions and Data Members
1596		1927
1597	=over 4	1928	=over 4
1598		1929
1599	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1930	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1600		1931
1601	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1932	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1602		1933
1603	Lots of arguments, lets sort it out... There are basically three modes of	1934	Lots of arguments, let's sort it out... There are basically three modes of
1604	operation, and we will explain them from simplest to most complex:	1935	operation, and we will explain them from simplest to most complex:
1605		1936
1606	=over 4	1937	=over 4
1607		1938
1608	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1939	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1609		1940
1610	In this configuration the watcher triggers an event after the wall clock	1941	In this configuration the watcher triggers an event after the wall clock
1611	time C<at> has passed. It will not repeat and will not adjust when a time	1942	time C<offset> has passed. It will not repeat and will not adjust when a
1612	jump occurs, that is, if it is to be run at January 1st 2011 then it will	1943	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1613	only run when the system clock reaches or surpasses this time.	1944	will be stopped and invoked when the system clock reaches or surpasses
		1945	this point in time.
1614		1946
1615	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1947	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1616		1948
1617	In this mode the watcher will always be scheduled to time out at the next	1949	In this mode the watcher will always be scheduled to time out at the next
1618	C<at + N * interval> time (for some integer N, which can also be negative)	1950	C<offset + N * interval> time (for some integer N, which can also be
1619	and then repeat, regardless of any time jumps.	1951	negative) and then repeat, regardless of any time jumps. The C<offset>
		1952	argument is merely an offset into the C<interval> periods.
1620		1953
1621	This can be used to create timers that do not drift with respect to the	1954	This can be used to create timers that do not drift with respect to the
1622	system clock, for example, here is a C<ev_periodic> that triggers each	1955	system clock, for example, here is an C<ev_periodic> that triggers each
1623	hour, on the hour:	1956	hour, on the hour (with respect to UTC):
1624		1957
1625	ev_periodic_set (&periodic, 0., 3600., 0);	1958	ev_periodic_set (&periodic, 0., 3600., 0);
1626		1959
1627	This doesn't mean there will always be 3600 seconds in between triggers,	1960	This doesn't mean there will always be 3600 seconds in between triggers,
1628	but only that the callback will be called when the system time shows a	1961	but only that the callback will be called when the system time shows a
1629	full hour (UTC), or more correctly, when the system time is evenly divisible	1962	full hour (UTC), or more correctly, when the system time is evenly divisible
1630	by 3600.	1963	by 3600.
1631		1964
1632	Another way to think about it (for the mathematically inclined) is that	1965	Another way to think about it (for the mathematically inclined) is that
1633	C<ev_periodic> will try to run the callback in this mode at the next possible	1966	C<ev_periodic> will try to run the callback in this mode at the next possible
1634	time where C<time = at (mod interval)>, regardless of any time jumps.	1967	time where C<time = offset (mod interval)>, regardless of any time jumps.
1635		1968
1636	For numerical stability it is preferable that the C<at> value is near	1969	For numerical stability it is preferable that the C<offset> value is near
1637	C<ev_now ()> (the current time), but there is no range requirement for	1970	C<ev_now ()> (the current time), but there is no range requirement for
1638	this value, and in fact is often specified as zero.	1971	this value, and in fact is often specified as zero.
1639		1972
1640	Note also that there is an upper limit to how often a timer can fire (CPU	1973	Note also that there is an upper limit to how often a timer can fire (CPU
1641	speed for example), so if C<interval> is very small then timing stability	1974	speed for example), so if C<interval> is very small then timing stability
1642	will of course deteriorate. Libev itself tries to be exact to be about one	1975	will of course deteriorate. Libev itself tries to be exact to be about one
1643	millisecond (if the OS supports it and the machine is fast enough).	1976	millisecond (if the OS supports it and the machine is fast enough).
1644		1977
1645	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1978	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1646		1979
1647	In this mode the values for C<interval> and C<at> are both being	1980	In this mode the values for C<interval> and C<offset> are both being
1648	ignored. Instead, each time the periodic watcher gets scheduled, the	1981	ignored. Instead, each time the periodic watcher gets scheduled, the
1649	reschedule callback will be called with the watcher as first, and the	1982	reschedule callback will be called with the watcher as first, and the
1650	current time as second argument.	1983	current time as second argument.
1651		1984
1652	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1985	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1653	ever, or make ANY event loop modifications whatsoever>.	1986	or make ANY other event loop modifications whatsoever, unless explicitly
		1987	allowed by documentation here>.
1654		1988
1655	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1989	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1656	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1990	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1657	only event loop modification you are allowed to do).	1991	only event loop modification you are allowed to do).
1658		1992
…		…
1688	a different time than the last time it was called (e.g. in a crond like	2022	a different time than the last time it was called (e.g. in a crond like
1689	program when the crontabs have changed).	2023	program when the crontabs have changed).
1690		2024
1691	=item ev_tstamp ev_periodic_at (ev_periodic *)	2025	=item ev_tstamp ev_periodic_at (ev_periodic *)
1692		2026
1693	When active, returns the absolute time that the watcher is supposed to	2027	When active, returns the absolute time that the watcher is supposed
1694	trigger next.	2028	to trigger next. This is not the same as the C<offset> argument to
		2029	C<ev_periodic_set>, but indeed works even in interval and manual
		2030	rescheduling modes.
1695		2031
1696	=item ev_tstamp offset [read-write]	2032	=item ev_tstamp offset [read-write]
1697		2033
1698	When repeating, this contains the offset value, otherwise this is the	2034	When repeating, this contains the offset value, otherwise this is the
1699	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2035	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2036	although libev might modify this value for better numerical stability).
1700		2037
1701	Can be modified any time, but changes only take effect when the periodic	2038	Can be modified any time, but changes only take effect when the periodic
1702	timer fires or C<ev_periodic_again> is being called.	2039	timer fires or C<ev_periodic_again> is being called.
1703		2040
1704	=item ev_tstamp interval [read-write]	2041	=item ev_tstamp interval [read-write]
…		…
1756	Signal watchers will trigger an event when the process receives a specific	2093	Signal watchers will trigger an event when the process receives a specific
1757	signal one or more times. Even though signals are very asynchronous, libev	2094	signal one or more times. Even though signals are very asynchronous, libev
1758	will try it's best to deliver signals synchronously, i.e. as part of the	2095	will try it's best to deliver signals synchronously, i.e. as part of the
1759	normal event processing, like any other event.	2096	normal event processing, like any other event.
1760		2097
1761	If you want signals asynchronously, just use C<sigaction> as you would	2098	If you want signals to be delivered truly asynchronously, just use
1762	do without libev and forget about sharing the signal. You can even use	2099	C<sigaction> as you would do without libev and forget about sharing
1763	C<ev_async> from a signal handler to synchronously wake up an event loop.	2100	the signal. You can even use C<ev_async> from a signal handler to
		2101	synchronously wake up an event loop.
1764		2102
1765	You can configure as many watchers as you like per signal. Only when the	2103	You can configure as many watchers as you like for the same signal, but
		2104	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2105	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2106	C<SIGINT> in both the default loop and another loop at the same time. At
		2107	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2108
1766	first watcher gets started will libev actually register a signal handler	2109	When the first watcher gets started will libev actually register something
1767	with the kernel (thus it coexists with your own signal handlers as long as	2110	with the kernel (thus it coexists with your own signal handlers as long as
1768	you don't register any with libev for the same signal). Similarly, when	2111	you don't register any with libev for the same signal).
1769	the last signal watcher for a signal is stopped, libev will reset the	2112
1770	signal handler to SIG_DFL (regardless of what it was set to before).	2113	Both the signal mask state (C<sigprocmask>) and the signal handler state
		2114	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2115	sotpping it again), that is, libev might or might not block the signal,
		2116	and might or might not set or restore the installed signal handler.
1771		2117
1772	If possible and supported, libev will install its handlers with	2118	If possible and supported, libev will install its handlers with
1773	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2119	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1774	interrupted. If you have a problem with system calls getting interrupted by	2120	not be unduly interrupted. If you have a problem with system calls getting
1775	signals you can block all signals in an C<ev_check> watcher and unblock	2121	interrupted by signals you can block all signals in an C<ev_check> watcher
1776	them in an C<ev_prepare> watcher.	2122	and unblock them in an C<ev_prepare> watcher.
1777		2123
1778	=head3 Watcher-Specific Functions and Data Members	2124	=head3 Watcher-Specific Functions and Data Members
1779		2125
1780	=over 4	2126	=over 4
1781		2127
…		…
1813	some child status changes (most typically when a child of yours dies or	2159	some child status changes (most typically when a child of yours dies or
1814	exits). It is permissible to install a child watcher I<after> the child	2160	exits). It is permissible to install a child watcher I<after> the child
1815	has been forked (which implies it might have already exited), as long	2161	has been forked (which implies it might have already exited), as long
1816	as the event loop isn't entered (or is continued from a watcher), i.e.,	2162	as the event loop isn't entered (or is continued from a watcher), i.e.,
1817	forking and then immediately registering a watcher for the child is fine,	2163	forking and then immediately registering a watcher for the child is fine,
1818	but forking and registering a watcher a few event loop iterations later is	2164	but forking and registering a watcher a few event loop iterations later or
1819	not.	2165	in the next callback invocation is not.
1820		2166
1821	Only the default event loop is capable of handling signals, and therefore	2167	Only the default event loop is capable of handling signals, and therefore
1822	you can only register child watchers in the default event loop.	2168	you can only register child watchers in the default event loop.
1823		2169
		2170	Due to some design glitches inside libev, child watchers will always be
		2171	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2172	libev)
		2173
1824	=head3 Process Interaction	2174	=head3 Process Interaction
1825		2175
1826	Libev grabs C<SIGCHLD> as soon as the default event loop is	2176	Libev grabs C<SIGCHLD> as soon as the default event loop is
1827	initialised. This is necessary to guarantee proper behaviour even if	2177	initialised. This is necessary to guarantee proper behaviour even if the
1828	the first child watcher is started after the child exits. The occurrence	2178	first child watcher is started after the child exits. The occurrence
1829	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2179	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1830	synchronously as part of the event loop processing. Libev always reaps all	2180	synchronously as part of the event loop processing. Libev always reaps all
1831	children, even ones not watched.	2181	children, even ones not watched.
1832		2182
1833	=head3 Overriding the Built-In Processing	2183	=head3 Overriding the Built-In Processing
…		…
1843	=head3 Stopping the Child Watcher	2193	=head3 Stopping the Child Watcher
1844		2194
1845	Currently, the child watcher never gets stopped, even when the	2195	Currently, the child watcher never gets stopped, even when the
1846	child terminates, so normally one needs to stop the watcher in the	2196	child terminates, so normally one needs to stop the watcher in the
1847	callback. Future versions of libev might stop the watcher automatically	2197	callback. Future versions of libev might stop the watcher automatically
1848	when a child exit is detected.	2198	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2199	problem).
1849		2200
1850	=head3 Watcher-Specific Functions and Data Members	2201	=head3 Watcher-Specific Functions and Data Members
1851		2202
1852	=over 4	2203	=over 4
1853		2204
…		…
1910		2261
1911		2262
1912	=head2 C<ev_stat> - did the file attributes just change?	2263	=head2 C<ev_stat> - did the file attributes just change?
1913		2264
1914	This watches a file system path for attribute changes. That is, it calls	2265	This watches a file system path for attribute changes. That is, it calls
1915	C<stat> regularly (or when the OS says it changed) and sees if it changed	2266	C<stat> on that path in regular intervals (or when the OS says it changed)
1916	compared to the last time, invoking the callback if it did.	2267	and sees if it changed compared to the last time, invoking the callback if
		2268	it did.
1917		2269
1918	The path does not need to exist: changing from "path exists" to "path does	2270	The path does not need to exist: changing from "path exists" to "path does
1919	not exist" is a status change like any other. The condition "path does	2271	not exist" is a status change like any other. The condition "path does not
1920	not exist" is signified by the C<st_nlink> field being zero (which is	2272	exist" (or more correctly "path cannot be stat'ed") is signified by the
1921	otherwise always forced to be at least one) and all the other fields of	2273	C<st_nlink> field being zero (which is otherwise always forced to be at
1922	the stat buffer having unspecified contents.	2274	least one) and all the other fields of the stat buffer having unspecified
		2275	contents.
1923		2276
1924	The path I<should> be absolute and I<must not> end in a slash. If it is	2277	The path I<must not> end in a slash or contain special components such as
		2278	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1925	relative and your working directory changes, the behaviour is undefined.	2279	your working directory changes, then the behaviour is undefined.
1926		2280
1927	Since there is no standard kernel interface to do this, the portable	2281	Since there is no portable change notification interface available, the
1928	implementation simply calls C<stat (2)> regularly on the path to see if	2282	portable implementation simply calls C<stat(2)> regularly on the path
1929	it changed somehow. You can specify a recommended polling interval for	2283	to see if it changed somehow. You can specify a recommended polling
1930	this case. If you specify a polling interval of C<0> (highly recommended!)	2284	interval for this case. If you specify a polling interval of C<0> (highly
1931	then a I<suitable, unspecified default> value will be used (which	2285	recommended!) then a I<suitable, unspecified default> value will be used
1932	you can expect to be around five seconds, although this might change	2286	(which you can expect to be around five seconds, although this might
1933	dynamically). Libev will also impose a minimum interval which is currently	2287	change dynamically). Libev will also impose a minimum interval which is
1934	around C<0.1>, but thats usually overkill.	2288	currently around C<0.1>, but that's usually overkill.
1935		2289
1936	This watcher type is not meant for massive numbers of stat watchers,	2290	This watcher type is not meant for massive numbers of stat watchers,
1937	as even with OS-supported change notifications, this can be	2291	as even with OS-supported change notifications, this can be
1938	resource-intensive.	2292	resource-intensive.
1939		2293
1940	At the time of this writing, the only OS-specific interface implemented	2294	At the time of this writing, the only OS-specific interface implemented
1941	is the Linux inotify interface (implementing kqueue support is left as	2295	is the Linux inotify interface (implementing kqueue support is left as an
1942	an exercise for the reader. Note, however, that the author sees no way	2296	exercise for the reader. Note, however, that the author sees no way of
1943	of implementing C<ev_stat> semantics with kqueue).	2297	implementing C<ev_stat> semantics with kqueue, except as a hint).
1944		2298
1945	=head3 ABI Issues (Largefile Support)	2299	=head3 ABI Issues (Largefile Support)
1946		2300
1947	Libev by default (unless the user overrides this) uses the default	2301	Libev by default (unless the user overrides this) uses the default
1948	compilation environment, which means that on systems with large file	2302	compilation environment, which means that on systems with large file
1949	support disabled by default, you get the 32 bit version of the stat	2303	support disabled by default, you get the 32 bit version of the stat
1950	structure. When using the library from programs that change the ABI to	2304	structure. When using the library from programs that change the ABI to
1951	use 64 bit file offsets the programs will fail. In that case you have to	2305	use 64 bit file offsets the programs will fail. In that case you have to
1952	compile libev with the same flags to get binary compatibility. This is	2306	compile libev with the same flags to get binary compatibility. This is
1953	obviously the case with any flags that change the ABI, but the problem is	2307	obviously the case with any flags that change the ABI, but the problem is
1954	most noticeably disabled with ev_stat and large file support.	2308	most noticeably displayed with ev_stat and large file support.
1955		2309
1956	The solution for this is to lobby your distribution maker to make large	2310	The solution for this is to lobby your distribution maker to make large
1957	file interfaces available by default (as e.g. FreeBSD does) and not	2311	file interfaces available by default (as e.g. FreeBSD does) and not
1958	optional. Libev cannot simply switch on large file support because it has	2312	optional. Libev cannot simply switch on large file support because it has
1959	to exchange stat structures with application programs compiled using the	2313	to exchange stat structures with application programs compiled using the
1960	default compilation environment.	2314	default compilation environment.
1961		2315
1962	=head3 Inotify and Kqueue	2316	=head3 Inotify and Kqueue
1963		2317
1964	When C<inotify (7)> support has been compiled into libev (generally	2318	When C<inotify (7)> support has been compiled into libev and present at
1965	only available with Linux 2.6.25 or above due to bugs in earlier	2319	runtime, it will be used to speed up change detection where possible. The
1966	implementations) and present at runtime, it will be used to speed up	2320	inotify descriptor will be created lazily when the first C<ev_stat>
1967	change detection where possible. The inotify descriptor will be created	2321	watcher is being started.
1968	lazily when the first C<ev_stat> watcher is being started.
1969		2322
1970	Inotify presence does not change the semantics of C<ev_stat> watchers	2323	Inotify presence does not change the semantics of C<ev_stat> watchers
1971	except that changes might be detected earlier, and in some cases, to avoid	2324	except that changes might be detected earlier, and in some cases, to avoid
1972	making regular C<stat> calls. Even in the presence of inotify support	2325	making regular C<stat> calls. Even in the presence of inotify support
1973	there are many cases where libev has to resort to regular C<stat> polling,	2326	there are many cases where libev has to resort to regular C<stat> polling,
1974	but as long as the path exists, libev usually gets away without polling.	2327	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2328	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2329	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2330	xfs are fully working) libev usually gets away without polling.
1975		2331
1976	There is no support for kqueue, as apparently it cannot be used to	2332	There is no support for kqueue, as apparently it cannot be used to
1977	implement this functionality, due to the requirement of having a file	2333	implement this functionality, due to the requirement of having a file
1978	descriptor open on the object at all times, and detecting renames, unlinks	2334	descriptor open on the object at all times, and detecting renames, unlinks
1979	etc. is difficult.	2335	etc. is difficult.
1980		2336
		2337	=head3 C<stat ()> is a synchronous operation
		2338
		2339	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2340	the process. The exception are C<ev_stat> watchers - those call C<stat
		2341	()>, which is a synchronous operation.
		2342
		2343	For local paths, this usually doesn't matter: unless the system is very
		2344	busy or the intervals between stat's are large, a stat call will be fast,
		2345	as the path data is usually in memory already (except when starting the
		2346	watcher).
		2347
		2348	For networked file systems, calling C<stat ()> can block an indefinite
		2349	time due to network issues, and even under good conditions, a stat call
		2350	often takes multiple milliseconds.
		2351
		2352	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2353	paths, although this is fully supported by libev.
		2354
1981	=head3 The special problem of stat time resolution	2355	=head3 The special problem of stat time resolution
1982		2356
1983	The C<stat ()> system call only supports full-second resolution portably, and	2357	The C<stat ()> system call only supports full-second resolution portably,
1984	even on systems where the resolution is higher, most file systems still	2358	and even on systems where the resolution is higher, most file systems
1985	only support whole seconds.	2359	still only support whole seconds.
1986		2360
1987	That means that, if the time is the only thing that changes, you can	2361	That means that, if the time is the only thing that changes, you can
1988	easily miss updates: on the first update, C<ev_stat> detects a change and	2362	easily miss updates: on the first update, C<ev_stat> detects a change and
1989	calls your callback, which does something. When there is another update	2363	calls your callback, which does something. When there is another update
1990	within the same second, C<ev_stat> will be unable to detect unless the	2364	within the same second, C<ev_stat> will be unable to detect unless the
…		…
2133		2507
2134	=head3 Watcher-Specific Functions and Data Members	2508	=head3 Watcher-Specific Functions and Data Members
2135		2509
2136	=over 4	2510	=over 4
2137		2511
2138	=item ev_idle_init (ev_signal *, callback)	2512	=item ev_idle_init (ev_idle *, callback)
2139		2513
2140	Initialises and configures the idle watcher - it has no parameters of any	2514	Initialises and configures the idle watcher - it has no parameters of any
2141	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2515	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
2142	believe me.	2516	believe me.
2143		2517
…		…
2156	// no longer anything immediate to do.	2530	// no longer anything immediate to do.
2157	}	2531	}
2158		2532
2159	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2533	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2160	ev_idle_init (idle_watcher, idle_cb);	2534	ev_idle_init (idle_watcher, idle_cb);
2161	ev_idle_start (loop, idle_cb);	2535	ev_idle_start (loop, idle_watcher);
2162		2536
2163		2537
2164	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2538	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2165		2539
2166	Prepare and check watchers are usually (but not always) used in pairs:	2540	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2259	struct pollfd fds [nfd];	2633	struct pollfd fds [nfd];
2260	// actual code will need to loop here and realloc etc.	2634	// actual code will need to loop here and realloc etc.
2261	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2635	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2262		2636
2263	/* the callback is illegal, but won't be called as we stop during check */	2637	/* the callback is illegal, but won't be called as we stop during check */
2264	ev_timer_init (&tw, 0, timeout * 1e-3);	2638	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2265	ev_timer_start (loop, &tw);	2639	ev_timer_start (loop, &tw);
2266		2640
2267	// create one ev_io per pollfd	2641	// create one ev_io per pollfd
2268	for (int i = 0; i < nfd; ++i)	2642	for (int i = 0; i < nfd; ++i)
2269	{	2643	{
…		…
2382	some fds have to be watched and handled very quickly (with low latency),	2756	some fds have to be watched and handled very quickly (with low latency),
2383	and even priorities and idle watchers might have too much overhead. In	2757	and even priorities and idle watchers might have too much overhead. In
2384	this case you would put all the high priority stuff in one loop and all	2758	this case you would put all the high priority stuff in one loop and all
2385	the rest in a second one, and embed the second one in the first.	2759	the rest in a second one, and embed the second one in the first.
2386		2760
2387	As long as the watcher is active, the callback will be invoked every time	2761	As long as the watcher is active, the callback will be invoked every
2388	there might be events pending in the embedded loop. The callback must then	2762	time there might be events pending in the embedded loop. The callback
2389	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2763	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2390	their callbacks (you could also start an idle watcher to give the embedded	2764	sweep and invoke their callbacks (the callback doesn't need to invoke the
2391	loop strictly lower priority for example). You can also set the callback	2765	C<ev_embed_sweep> function directly, it could also start an idle watcher
2392	to C<0>, in which case the embed watcher will automatically execute the	2766	to give the embedded loop strictly lower priority for example).
2393	embedded loop sweep.
2394		2767
2395	As long as the watcher is started it will automatically handle events. The	2768	You can also set the callback to C<0>, in which case the embed watcher
2396	callback will be invoked whenever some events have been handled. You can	2769	will automatically execute the embedded loop sweep whenever necessary.
2397	set the callback to C<0> to avoid having to specify one if you are not
2398	interested in that.
2399		2770
2400	Also, there have not currently been made special provisions for forking:	2771	Fork detection will be handled transparently while the C<ev_embed> watcher
2401	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2772	is active, i.e., the embedded loop will automatically be forked when the
2402	but you will also have to stop and restart any C<ev_embed> watchers	2773	embedding loop forks. In other cases, the user is responsible for calling
2403	yourself - but you can use a fork watcher to handle this automatically,	2774	C<ev_loop_fork> on the embedded loop.
2404	and future versions of libev might do just that.
2405		2775
2406	Unfortunately, not all backends are embeddable: only the ones returned by	2776	Unfortunately, not all backends are embeddable: only the ones returned by
2407	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2777	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2408	portable one.	2778	portable one.
2409		2779
…		…
2503	event loop blocks next and before C<ev_check> watchers are being called,	2873	event loop blocks next and before C<ev_check> watchers are being called,
2504	and only in the child after the fork. If whoever good citizen calling	2874	and only in the child after the fork. If whoever good citizen calling
2505	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2875	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2506	handlers will be invoked, too, of course.	2876	handlers will be invoked, too, of course.
2507		2877
		2878	=head3 The special problem of life after fork - how is it possible?
		2879
		2880	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2881	up/change the process environment, followed by a call to C<exec()>. This
		2882	sequence should be handled by libev without any problems.
		2883
		2884	This changes when the application actually wants to do event handling
		2885	in the child, or both parent in child, in effect "continuing" after the
		2886	fork.
		2887
		2888	The default mode of operation (for libev, with application help to detect
		2889	forks) is to duplicate all the state in the child, as would be expected
		2890	when I<either> the parent I<or> the child process continues.
		2891
		2892	When both processes want to continue using libev, then this is usually the
		2893	wrong result. In that case, usually one process (typically the parent) is
		2894	supposed to continue with all watchers in place as before, while the other
		2895	process typically wants to start fresh, i.e. without any active watchers.
		2896
		2897	The cleanest and most efficient way to achieve that with libev is to
		2898	simply create a new event loop, which of course will be "empty", and
		2899	use that for new watchers. This has the advantage of not touching more
		2900	memory than necessary, and thus avoiding the copy-on-write, and the
		2901	disadvantage of having to use multiple event loops (which do not support
		2902	signal watchers).
		2903
		2904	When this is not possible, or you want to use the default loop for
		2905	other reasons, then in the process that wants to start "fresh", call
		2906	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2907	the default loop will "orphan" (not stop) all registered watchers, so you
		2908	have to be careful not to execute code that modifies those watchers. Note
		2909	also that in that case, you have to re-register any signal watchers.
		2910
2508	=head3 Watcher-Specific Functions and Data Members	2911	=head3 Watcher-Specific Functions and Data Members
2509		2912
2510	=over 4	2913	=over 4
2511		2914
2512	=item ev_fork_init (ev_signal *, callback)	2915	=item ev_fork_init (ev_signal *, callback)
…		…
2629	=over 4	3032	=over 4
2630		3033
2631	=item ev_async_init (ev_async *, callback)	3034	=item ev_async_init (ev_async *, callback)
2632		3035
2633	Initialises and configures the async watcher - it has no parameters of any	3036	Initialises and configures the async watcher - it has no parameters of any
2634	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3037	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2635	trust me.	3038	trust me.
2636		3039
2637	=item ev_async_send (loop, ev_async *)	3040	=item ev_async_send (loop, ev_async *)
2638		3041
2639	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3042	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2640	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3043	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2641	C<ev_feed_event>, this call is safe to do from other threads, signal or	3044	C<ev_feed_event>, this call is safe to do from other threads, signal or
2642	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3045	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2643	section below on what exactly this means).	3046	section below on what exactly this means).
2644		3047
		3048	Note that, as with other watchers in libev, multiple events might get
		3049	compressed into a single callback invocation (another way to look at this
		3050	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3051	reset when the event loop detects that).
		3052
2645	This call incurs the overhead of a system call only once per loop iteration,	3053	This call incurs the overhead of a system call only once per event loop
2646	so while the overhead might be noticeable, it doesn't apply to repeated	3054	iteration, so while the overhead might be noticeable, it doesn't apply to
2647	calls to C<ev_async_send>.	3055	repeated calls to C<ev_async_send> for the same event loop.
2648		3056
2649	=item bool = ev_async_pending (ev_async *)	3057	=item bool = ev_async_pending (ev_async *)
2650		3058
2651	Returns a non-zero value when C<ev_async_send> has been called on the	3059	Returns a non-zero value when C<ev_async_send> has been called on the
2652	watcher but the event has not yet been processed (or even noted) by the	3060	watcher but the event has not yet been processed (or even noted) by the
…		…
2655	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3063	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2656	the loop iterates next and checks for the watcher to have become active,	3064	the loop iterates next and checks for the watcher to have become active,
2657	it will reset the flag again. C<ev_async_pending> can be used to very	3065	it will reset the flag again. C<ev_async_pending> can be used to very
2658	quickly check whether invoking the loop might be a good idea.	3066	quickly check whether invoking the loop might be a good idea.
2659		3067
2660	Not that this does I<not> check whether the watcher itself is pending, only	3068	Not that this does I<not> check whether the watcher itself is pending,
2661	whether it has been requested to make this watcher pending.	3069	only whether it has been requested to make this watcher pending: there
		3070	is a time window between the event loop checking and resetting the async
		3071	notification, and the callback being invoked.
2662		3072
2663	=back	3073	=back
2664		3074
2665		3075
2666	=head1 OTHER FUNCTIONS	3076	=head1 OTHER FUNCTIONS
…		…
2845		3255
2846	myclass obj;	3256	myclass obj;
2847	ev::io iow;	3257	ev::io iow;
2848	iow.set <myclass, &myclass::io_cb> (&obj);	3258	iow.set <myclass, &myclass::io_cb> (&obj);
2849		3259
		3260	=item w->set (object *)
		3261
		3262	This is an B<experimental> feature that might go away in a future version.
		3263
		3264	This is a variation of a method callback - leaving out the method to call
		3265	will default the method to C<operator ()>, which makes it possible to use
		3266	functor objects without having to manually specify the C<operator ()> all
		3267	the time. Incidentally, you can then also leave out the template argument
		3268	list.
		3269
		3270	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3271	int revents)>.
		3272
		3273	See the method-C<set> above for more details.
		3274
		3275	Example: use a functor object as callback.
		3276
		3277	struct myfunctor
		3278	{
		3279	void operator() (ev::io &w, int revents)
		3280	{
		3281	...
		3282	}
		3283	}
		3284
		3285	myfunctor f;
		3286
		3287	ev::io w;
		3288	w.set (&f);
		3289
2850	=item w->set<function> (void *data = 0)	3290	=item w->set<function> (void *data = 0)
2851		3291
2852	Also sets a callback, but uses a static method or plain function as	3292	Also sets a callback, but uses a static method or plain function as
2853	callback. The optional C<data> argument will be stored in the watcher's	3293	callback. The optional C<data> argument will be stored in the watcher's
2854	C<data> member and is free for you to use.	3294	C<data> member and is free for you to use.
…		…
2940	L<http://software.schmorp.de/pkg/EV>.	3380	L<http://software.schmorp.de/pkg/EV>.
2941		3381
2942	=item Python	3382	=item Python
2943		3383
2944	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3384	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2945	seems to be quite complete and well-documented. Note, however, that the	3385	seems to be quite complete and well-documented.
2946	patch they require for libev is outright dangerous as it breaks the ABI
2947	for everybody else, and therefore, should never be applied in an installed
2948	libev (if python requires an incompatible ABI then it needs to embed
2949	libev).
2950		3386
2951	=item Ruby	3387	=item Ruby
2952		3388
2953	Tony Arcieri has written a ruby extension that offers access to a subset	3389	Tony Arcieri has written a ruby extension that offers access to a subset
2954	of the libev API and adds file handle abstractions, asynchronous DNS and	3390	of the libev API and adds file handle abstractions, asynchronous DNS and
2955	more on top of it. It can be found via gem servers. Its homepage is at	3391	more on top of it. It can be found via gem servers. Its homepage is at
2956	L<http://rev.rubyforge.org/>.	3392	L<http://rev.rubyforge.org/>.
		3393
		3394	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3395	makes rev work even on mingw.
		3396
		3397	=item Haskell
		3398
		3399	A haskell binding to libev is available at
		3400	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
2957		3401
2958	=item D	3402	=item D
2959		3403
2960	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3404	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2961	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3405	be found at L<http://proj.llucax.com.ar/wiki/evd>.
…		…
3072		3516
3073	#define EV_STANDALONE 1	3517	#define EV_STANDALONE 1
3074	#include "ev.h"	3518	#include "ev.h"
3075		3519
3076	Both header files and implementation files can be compiled with a C++	3520	Both header files and implementation files can be compiled with a C++
3077	compiler (at least, thats a stated goal, and breakage will be treated	3521	compiler (at least, that's a stated goal, and breakage will be treated
3078	as a bug).	3522	as a bug).
3079		3523
3080	You need the following files in your source tree, or in a directory	3524	You need the following files in your source tree, or in a directory
3081	in your include path (e.g. in libev/ when using -Ilibev):	3525	in your include path (e.g. in libev/ when using -Ilibev):
3082		3526
…		…
3138	keeps libev from including F<config.h>, and it also defines dummy	3582	keeps libev from including F<config.h>, and it also defines dummy
3139	implementations for some libevent functions (such as logging, which is not	3583	implementations for some libevent functions (such as logging, which is not
3140	supported). It will also not define any of the structs usually found in	3584	supported). It will also not define any of the structs usually found in
3141	F<event.h> that are not directly supported by the libev core alone.	3585	F<event.h> that are not directly supported by the libev core alone.
3142		3586
		3587	In stanbdalone mode, libev will still try to automatically deduce the
		3588	configuration, but has to be more conservative.
		3589
3143	=item EV_USE_MONOTONIC	3590	=item EV_USE_MONOTONIC
3144		3591
3145	If defined to be C<1>, libev will try to detect the availability of the	3592	If defined to be C<1>, libev will try to detect the availability of the
3146	monotonic clock option at both compile time and runtime. Otherwise no use	3593	monotonic clock option at both compile time and runtime. Otherwise no
3147	of the monotonic clock option will be attempted. If you enable this, you	3594	use of the monotonic clock option will be attempted. If you enable this,
3148	usually have to link against librt or something similar. Enabling it when	3595	you usually have to link against librt or something similar. Enabling it
3149	the functionality isn't available is safe, though, although you have	3596	when the functionality isn't available is safe, though, although you have
3150	to make sure you link against any libraries where the C<clock_gettime>	3597	to make sure you link against any libraries where the C<clock_gettime>
3151	function is hiding in (often F<-lrt>).	3598	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
3152		3599
3153	=item EV_USE_REALTIME	3600	=item EV_USE_REALTIME
3154		3601
3155	If defined to be C<1>, libev will try to detect the availability of the	3602	If defined to be C<1>, libev will try to detect the availability of the
3156	real-time clock option at compile time (and assume its availability at	3603	real-time clock option at compile time (and assume its availability
3157	runtime if successful). Otherwise no use of the real-time clock option will	3604	at runtime if successful). Otherwise no use of the real-time clock
3158	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3605	option will be attempted. This effectively replaces C<gettimeofday>
3159	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3606	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
3160	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3607	correctness. See the note about libraries in the description of
		3608	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3609	C<EV_USE_CLOCK_SYSCALL>.
		3610
		3611	=item EV_USE_CLOCK_SYSCALL
		3612
		3613	If defined to be C<1>, libev will try to use a direct syscall instead
		3614	of calling the system-provided C<clock_gettime> function. This option
		3615	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3616	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3617	programs needlessly. Using a direct syscall is slightly slower (in
		3618	theory), because no optimised vdso implementation can be used, but avoids
		3619	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3620	higher, as it simplifies linking (no need for C<-lrt>).
3161		3621
3162	=item EV_USE_NANOSLEEP	3622	=item EV_USE_NANOSLEEP
3163		3623
3164	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3624	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
3165	and will use it for delays. Otherwise it will use C<select ()>.	3625	and will use it for delays. Otherwise it will use C<select ()>.
…		…
3181		3641
3182	=item EV_SELECT_USE_FD_SET	3642	=item EV_SELECT_USE_FD_SET
3183		3643
3184	If defined to C<1>, then the select backend will use the system C<fd_set>	3644	If defined to C<1>, then the select backend will use the system C<fd_set>
3185	structure. This is useful if libev doesn't compile due to a missing	3645	structure. This is useful if libev doesn't compile due to a missing
3186	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3646	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
3187	exotic systems. This usually limits the range of file descriptors to some	3647	on exotic systems. This usually limits the range of file descriptors to
3188	low limit such as 1024 or might have other limitations (winsocket only	3648	some low limit such as 1024 or might have other limitations (winsocket
3189	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3649	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
3190	influence the size of the C<fd_set> used.	3650	configures the maximum size of the C<fd_set>.
3191		3651
3192	=item EV_SELECT_IS_WINSOCKET	3652	=item EV_SELECT_IS_WINSOCKET
3193		3653
3194	When defined to C<1>, the select backend will assume that	3654	When defined to C<1>, the select backend will assume that
3195	select/socket/connect etc. don't understand file descriptors but	3655	select/socket/connect etc. don't understand file descriptors but
…		…
3345	defined to be C<0>, then they are not.	3805	defined to be C<0>, then they are not.
3346		3806
3347	=item EV_MINIMAL	3807	=item EV_MINIMAL
3348		3808
3349	If you need to shave off some kilobytes of code at the expense of some	3809	If you need to shave off some kilobytes of code at the expense of some
3350	speed, define this symbol to C<1>. Currently this is used to override some	3810	speed (but with the full API), define this symbol to C<1>. Currently this
3351	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3811	is used to override some inlining decisions, saves roughly 30% code size
3352	much smaller 2-heap for timer management over the default 4-heap.	3812	on amd64. It also selects a much smaller 2-heap for timer management over
		3813	the default 4-heap.
		3814
		3815	You can save even more by disabling watcher types you do not need
		3816	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3817	(C<-DNDEBUG>) will usually reduce code size a lot.
		3818
		3819	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3820	provide a bare-bones event library. See C<ev.h> for details on what parts
		3821	of the API are still available, and do not complain if this subset changes
		3822	over time.
		3823
		3824	=item EV_NSIG
		3825
		3826	The highest supported signal number, +1 (or, the number of
		3827	signals): Normally, libev tries to deduce the maximum number of signals
		3828	automatically, but sometimes this fails, in which case it can be
		3829	specified. Also, using a lower number than detected (C<32> should be
		3830	good for about any system in existance) can save some memory, as libev
		3831	statically allocates some 12-24 bytes per signal number.
3353		3832
3354	=item EV_PID_HASHSIZE	3833	=item EV_PID_HASHSIZE
3355		3834
3356	C<ev_child> watchers use a small hash table to distribute workload by	3835	C<ev_child> watchers use a small hash table to distribute workload by
3357	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3836	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3543	default loop and triggering an C<ev_async> watcher from the default loop	4022	default loop and triggering an C<ev_async> watcher from the default loop
3544	watcher callback into the event loop interested in the signal.	4023	watcher callback into the event loop interested in the signal.
3545		4024
3546	=back	4025	=back
3547		4026
		4027	=head4 THREAD LOCKING EXAMPLE
		4028
		4029	Here is a fictitious example of how to run an event loop in a different
		4030	thread than where callbacks are being invoked and watchers are
		4031	created/added/removed.
		4032
		4033	For a real-world example, see the C<EV::Loop::Async> perl module,
		4034	which uses exactly this technique (which is suited for many high-level
		4035	languages).
		4036
		4037	The example uses a pthread mutex to protect the loop data, a condition
		4038	variable to wait for callback invocations, an async watcher to notify the
		4039	event loop thread and an unspecified mechanism to wake up the main thread.
		4040
		4041	First, you need to associate some data with the event loop:
		4042
		4043	typedef struct {
		4044	mutex_t lock; /* global loop lock */
		4045	ev_async async_w;
		4046	thread_t tid;
		4047	cond_t invoke_cv;
		4048	} userdata;
		4049
		4050	void prepare_loop (EV_P)
		4051	{
		4052	// for simplicity, we use a static userdata struct.
		4053	static userdata u;
		4054
		4055	ev_async_init (&u->async_w, async_cb);
		4056	ev_async_start (EV_A_ &u->async_w);
		4057
		4058	pthread_mutex_init (&u->lock, 0);
		4059	pthread_cond_init (&u->invoke_cv, 0);
		4060
		4061	// now associate this with the loop
		4062	ev_set_userdata (EV_A_ u);
		4063	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4064	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4065
		4066	// then create the thread running ev_loop
		4067	pthread_create (&u->tid, 0, l_run, EV_A);
		4068	}
		4069
		4070	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4071	solely to wake up the event loop so it takes notice of any new watchers
		4072	that might have been added:
		4073
		4074	static void
		4075	async_cb (EV_P_ ev_async *w, int revents)
		4076	{
		4077	// just used for the side effects
		4078	}
		4079
		4080	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4081	protecting the loop data, respectively.
		4082
		4083	static void
		4084	l_release (EV_P)
		4085	{
		4086	userdata *u = ev_userdata (EV_A);
		4087	pthread_mutex_unlock (&u->lock);
		4088	}
		4089
		4090	static void
		4091	l_acquire (EV_P)
		4092	{
		4093	userdata *u = ev_userdata (EV_A);
		4094	pthread_mutex_lock (&u->lock);
		4095	}
		4096
		4097	The event loop thread first acquires the mutex, and then jumps straight
		4098	into C<ev_loop>:
		4099
		4100	void *
		4101	l_run (void *thr_arg)
		4102	{
		4103	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4104
		4105	l_acquire (EV_A);
		4106	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4107	ev_loop (EV_A_ 0);
		4108	l_release (EV_A);
		4109
		4110	return 0;
		4111	}
		4112
		4113	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4114	signal the main thread via some unspecified mechanism (signals? pipe
		4115	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4116	have been called (in a while loop because a) spurious wakeups are possible
		4117	and b) skipping inter-thread-communication when there are no pending
		4118	watchers is very beneficial):
		4119
		4120	static void
		4121	l_invoke (EV_P)
		4122	{
		4123	userdata *u = ev_userdata (EV_A);
		4124
		4125	while (ev_pending_count (EV_A))
		4126	{
		4127	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4128	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4129	}
		4130	}
		4131
		4132	Now, whenever the main thread gets told to invoke pending watchers, it
		4133	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4134	thread to continue:
		4135
		4136	static void
		4137	real_invoke_pending (EV_P)
		4138	{
		4139	userdata *u = ev_userdata (EV_A);
		4140
		4141	pthread_mutex_lock (&u->lock);
		4142	ev_invoke_pending (EV_A);
		4143	pthread_cond_signal (&u->invoke_cv);
		4144	pthread_mutex_unlock (&u->lock);
		4145	}
		4146
		4147	Whenever you want to start/stop a watcher or do other modifications to an
		4148	event loop, you will now have to lock:
		4149
		4150	ev_timer timeout_watcher;
		4151	userdata *u = ev_userdata (EV_A);
		4152
		4153	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4154
		4155	pthread_mutex_lock (&u->lock);
		4156	ev_timer_start (EV_A_ &timeout_watcher);
		4157	ev_async_send (EV_A_ &u->async_w);
		4158	pthread_mutex_unlock (&u->lock);
		4159
		4160	Note that sending the C<ev_async> watcher is required because otherwise
		4161	an event loop currently blocking in the kernel will have no knowledge
		4162	about the newly added timer. By waking up the loop it will pick up any new
		4163	watchers in the next event loop iteration.
		4164
3548	=head3 COROUTINES	4165	=head3 COROUTINES
3549		4166
3550	Libev is very accommodating to coroutines ("cooperative threads"):	4167	Libev is very accommodating to coroutines ("cooperative threads"):
3551	libev fully supports nesting calls to its functions from different	4168	libev fully supports nesting calls to its functions from different
3552	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4169	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3553	different coroutines, and switch freely between both coroutines running the	4170	different coroutines, and switch freely between both coroutines running
3554	loop, as long as you don't confuse yourself). The only exception is that	4171	the loop, as long as you don't confuse yourself). The only exception is
3555	you must not do this from C<ev_periodic> reschedule callbacks.	4172	that you must not do this from C<ev_periodic> reschedule callbacks.
3556		4173
3557	Care has been taken to ensure that libev does not keep local state inside	4174	Care has been taken to ensure that libev does not keep local state inside
3558	C<ev_loop>, and other calls do not usually allow for coroutine switches as	4175	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3559	they do not clal any callbacks.	4176	they do not call any callbacks.
3560		4177
3561	=head2 COMPILER WARNINGS	4178	=head2 COMPILER WARNINGS
3562		4179
3563	Depending on your compiler and compiler settings, you might get no or a	4180	Depending on your compiler and compiler settings, you might get no or a
3564	lot of warnings when compiling libev code. Some people are apparently	4181	lot of warnings when compiling libev code. Some people are apparently
…		…
3598	==2274== definitely lost: 0 bytes in 0 blocks.	4215	==2274== definitely lost: 0 bytes in 0 blocks.
3599	==2274== possibly lost: 0 bytes in 0 blocks.	4216	==2274== possibly lost: 0 bytes in 0 blocks.
3600	==2274== still reachable: 256 bytes in 1 blocks.	4217	==2274== still reachable: 256 bytes in 1 blocks.
3601		4218
3602	Then there is no memory leak, just as memory accounted to global variables	4219	Then there is no memory leak, just as memory accounted to global variables
3603	is not a memleak - the memory is still being refernced, and didn't leak.	4220	is not a memleak - the memory is still being referenced, and didn't leak.
3604		4221
3605	Similarly, under some circumstances, valgrind might report kernel bugs	4222	Similarly, under some circumstances, valgrind might report kernel bugs
3606	as if it were a bug in libev (e.g. in realloc or in the poll backend,	4223	as if it were a bug in libev (e.g. in realloc or in the poll backend,
3607	although an acceptable workaround has been found here), or it might be	4224	although an acceptable workaround has been found here), or it might be
3608	confused.	4225	confused.
…		…
3637	way (note also that glib is the slowest event library known to man).	4254	way (note also that glib is the slowest event library known to man).
3638		4255
3639	There is no supported compilation method available on windows except	4256	There is no supported compilation method available on windows except
3640	embedding it into other applications.	4257	embedding it into other applications.
3641		4258
		4259	Sensible signal handling is officially unsupported by Microsoft - libev
		4260	tries its best, but under most conditions, signals will simply not work.
		4261
3642	Not a libev limitation but worth mentioning: windows apparently doesn't	4262	Not a libev limitation but worth mentioning: windows apparently doesn't
3643	accept large writes: instead of resulting in a partial write, windows will	4263	accept large writes: instead of resulting in a partial write, windows will
3644	either accept everything or return C<ENOBUFS> if the buffer is too large,	4264	either accept everything or return C<ENOBUFS> if the buffer is too large,
3645	so make sure you only write small amounts into your sockets (less than a	4265	so make sure you only write small amounts into your sockets (less than a
3646	megabyte seems safe, but this apparently depends on the amount of memory	4266	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3650	the abysmal performance of winsockets, using a large number of sockets	4270	the abysmal performance of winsockets, using a large number of sockets
3651	is not recommended (and not reasonable). If your program needs to use	4271	is not recommended (and not reasonable). If your program needs to use
3652	more than a hundred or so sockets, then likely it needs to use a totally	4272	more than a hundred or so sockets, then likely it needs to use a totally
3653	different implementation for windows, as libev offers the POSIX readiness	4273	different implementation for windows, as libev offers the POSIX readiness
3654	notification model, which cannot be implemented efficiently on windows	4274	notification model, which cannot be implemented efficiently on windows
3655	(Microsoft monopoly games).	4275	(due to Microsoft monopoly games).
3656		4276
3657	A typical way to use libev under windows is to embed it (see the embedding	4277	A typical way to use libev under windows is to embed it (see the embedding
3658	section for details) and use the following F<evwrap.h> header file instead	4278	section for details) and use the following F<evwrap.h> header file instead
3659	of F<ev.h>:	4279	of F<ev.h>:
3660		4280
…		…
3696		4316
3697	Early versions of winsocket's select only supported waiting for a maximum	4317	Early versions of winsocket's select only supported waiting for a maximum
3698	of C<64> handles (probably owning to the fact that all windows kernels	4318	of C<64> handles (probably owning to the fact that all windows kernels
3699	can only wait for C<64> things at the same time internally; Microsoft	4319	can only wait for C<64> things at the same time internally; Microsoft
3700	recommends spawning a chain of threads and wait for 63 handles and the	4320	recommends spawning a chain of threads and wait for 63 handles and the
3701	previous thread in each. Great).	4321	previous thread in each. Sounds great!).
3702		4322
3703	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4323	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3704	to some high number (e.g. C<2048>) before compiling the winsocket select	4324	to some high number (e.g. C<2048>) before compiling the winsocket select
3705	call (which might be in libev or elsewhere, for example, perl does its own	4325	call (which might be in libev or elsewhere, for example, perl and many
3706	select emulation on windows).	4326	other interpreters do their own select emulation on windows).
3707		4327
3708	Another limit is the number of file descriptors in the Microsoft runtime	4328	Another limit is the number of file descriptors in the Microsoft runtime
3709	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4329	libraries, which by default is C<64> (there must be a hidden I<64>
3710	or something like this inside Microsoft). You can increase this by calling	4330	fetish or something like this inside Microsoft). You can increase this
3711	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4331	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3712	arbitrary limit), but is broken in many versions of the Microsoft runtime	4332	(another arbitrary limit), but is broken in many versions of the Microsoft
3713	libraries.
3714
3715	This might get you to about C<512> or C<2048> sockets (depending on	4333	runtime libraries. This might get you to about C<512> or C<2048> sockets
3716	windows version and/or the phase of the moon). To get more, you need to	4334	(depending on windows version and/or the phase of the moon). To get more,
3717	wrap all I/O functions and provide your own fd management, but the cost of	4335	you need to wrap all I/O functions and provide your own fd management, but
3718	calling select (O(n²)) will likely make this unworkable.	4336	the cost of calling select (O(n²)) will likely make this unworkable.
3719		4337
3720	=back	4338	=back
3721		4339
3722	=head2 PORTABILITY REQUIREMENTS	4340	=head2 PORTABILITY REQUIREMENTS
3723		4341
…		…
3766	=item C<double> must hold a time value in seconds with enough accuracy	4384	=item C<double> must hold a time value in seconds with enough accuracy
3767		4385
3768	The type C<double> is used to represent timestamps. It is required to	4386	The type C<double> is used to represent timestamps. It is required to
3769	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4387	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3770	enough for at least into the year 4000. This requirement is fulfilled by	4388	enough for at least into the year 4000. This requirement is fulfilled by
3771	implementations implementing IEEE 754 (basically all existing ones).	4389	implementations implementing IEEE 754, which is basically all existing
		4390	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4391	2200.
3772		4392
3773	=back	4393	=back
3774		4394
3775	If you know of other additional requirements drop me a note.	4395	If you know of other additional requirements drop me a note.
3776		4396
…		…
3844	involves iterating over all running async watchers or all signal numbers.	4464	involves iterating over all running async watchers or all signal numbers.
3845		4465
3846	=back	4466	=back
3847		4467
3848		4468
		4469	=head1 GLOSSARY
		4470
		4471	=over 4
		4472
		4473	=item active
		4474
		4475	A watcher is active as long as it has been started (has been attached to
		4476	an event loop) but not yet stopped (disassociated from the event loop).
		4477
		4478	=item application
		4479
		4480	In this document, an application is whatever is using libev.
		4481
		4482	=item callback
		4483
		4484	The address of a function that is called when some event has been
		4485	detected. Callbacks are being passed the event loop, the watcher that
		4486	received the event, and the actual event bitset.
		4487
		4488	=item callback invocation
		4489
		4490	The act of calling the callback associated with a watcher.
		4491
		4492	=item event
		4493
		4494	A change of state of some external event, such as data now being available
		4495	for reading on a file descriptor, time having passed or simply not having
		4496	any other events happening anymore.
		4497
		4498	In libev, events are represented as single bits (such as C<EV_READ> or
		4499	C<EV_TIMEOUT>).
		4500
		4501	=item event library
		4502
		4503	A software package implementing an event model and loop.
		4504
		4505	=item event loop
		4506
		4507	An entity that handles and processes external events and converts them
		4508	into callback invocations.
		4509
		4510	=item event model
		4511
		4512	The model used to describe how an event loop handles and processes
		4513	watchers and events.
		4514
		4515	=item pending
		4516
		4517	A watcher is pending as soon as the corresponding event has been detected,
		4518	and stops being pending as soon as the watcher will be invoked or its
		4519	pending status is explicitly cleared by the application.
		4520
		4521	A watcher can be pending, but not active. Stopping a watcher also clears
		4522	its pending status.
		4523
		4524	=item real time
		4525
		4526	The physical time that is observed. It is apparently strictly monotonic :)
		4527
		4528	=item wall-clock time
		4529
		4530	The time and date as shown on clocks. Unlike real time, it can actually
		4531	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4532	clock.
		4533
		4534	=item watcher
		4535
		4536	A data structure that describes interest in certain events. Watchers need
		4537	to be started (attached to an event loop) before they can receive events.
		4538
		4539	=item watcher invocation
		4540
		4541	The act of calling the callback associated with a watcher.
		4542
		4543	=back
		4544
3849	=head1 AUTHOR	4545	=head1 AUTHOR
3850		4546
3851	Marc Lehmann <libev@schmorp.de>.	4547	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3852		4548

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