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…		…
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		13
		14	#include <stdio.h> // for puts
		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;
18		20
19	// all watcher callbacks have a similar signature	21	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	22	// this callback is called when data is readable on stdin
21	static void	23	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	25	{
24	puts ("stdin ready");	26	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	27	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	28	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	29	ev_io_stop (EV_A_ w);
…		…
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	32	ev_unloop (EV_A_ EVUNLOOP_ALL);
31	}	33	}
32		34
33	// another callback, this time for a time-out	35	// another callback, this time for a time-out
34	static void	36	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	38	{
37	puts ("timeout");	39	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	40	// this causes the innermost ev_loop to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	41	ev_unloop (EV_A_ EVUNLOOP_ONE);
40	}	42	}
…		…
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
…		…
103	Libev is very configurable. In this manual the default (and most common)	118	Libev is very configurable. In this manual the default (and most common)
104	configuration will be described, which supports multiple event loops. For	119	configuration will be described, which supports multiple event loops. For
105	more info about various configuration options please have a look at	120	more info about various configuration options please have a look at
106	B<EMBED> section in this manual. If libev was configured without support	121	B<EMBED> section in this manual. If libev was configured without support
107	for multiple event loops, then all functions taking an initial argument of	122	for multiple event loops, then all functions taking an initial argument of
108	name C<loop> (which is always of type C<struct 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
…		…
276		291
277	=back	292	=back
278		293
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	294	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280		295
281	An event loop is described by a C<struct ev_loop *>. The library knows two	296	An event loop is described by a C<struct ev_loop *> (the C<struct>
282	types of such loops, the I<default> loop, which supports signals and child	297	is I<not> optional in this case, as there is also an C<ev_loop>
283	events, and dynamically created loops which do not.	298	I<function>).
		299
		300	The library knows two types of such loops, the I<default> loop, which
		301	supports signals and child events, and dynamically created loops which do
		302	not.
284		303
285	=over 4	304	=over 4
286		305
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	306	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		307
…		…
294	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
295	function.	314	function.
296		315
297	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
298	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,
299	as loops cannot bes hared easily between threads anyway).	318	as loops cannot be shared easily between threads anyway).
300		319
301	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
302	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
303	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
304	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
…		…
344	flag.	363	flag.
345		364
346	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>
347	environment variable.	366	environment variable.
348		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_NOSIGFD>
		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
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	383	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		384
351	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
352	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,
353	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
…		…
377	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and	411	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
378	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	412	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
379		413
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	414	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		415
		416	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		417	kernels).
		418
382	For few fds, this backend is a bit little slower than poll and select,	419	For few fds, this backend is a bit little slower than poll and select,
383	but it scales phenomenally better. While poll and select usually scale	420	but it scales phenomenally better. While poll and select usually scale
384	like O(total_fds) where n is the total number of fds (or the highest fd),	421	like O(total_fds) where n is the total number of fds (or the highest fd),
385	epoll scales either O(1) or O(active_fds). The epoll design has a number	422	epoll scales either O(1) or O(active_fds).
386	of shortcomings, such as silently dropping events in some hard-to-detect	423
387	cases and requiring a system call per fd change, no fork support and bad	424	The epoll mechanism deserves honorable mention as the most misdesigned
388	support for dup.	425	of the more advanced event mechanisms: mere annoyances include silently
		426	dropping file descriptors, requiring a system call per change per file
		427	descriptor (and unnecessary guessing of parameters), problems with dup and
		428	so on. The biggest issue is fork races, however - if a program forks then
		429	I<both> parent and child process have to recreate the epoll set, which can
		430	take considerable time (one syscall per file descriptor) and is of course
		431	hard to detect.
		432
		433	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		434	of course I<doesn't>, and epoll just loves to report events for totally
		435	I<different> file descriptors (even already closed ones, so one cannot
		436	even remove them from the set) than registered in the set (especially
		437	on SMP systems). Libev tries to counter these spurious notifications by
		438	employing an additional generation counter and comparing that against the
		439	events to filter out spurious ones, recreating the set when required.
389		440
390	While stopping, setting and starting an I/O watcher in the same iteration	441	While stopping, setting and starting an I/O watcher in the same iteration
391	will result in some caching, there is still a system call per such incident	442	will result in some caching, there is still a system call per such
392	(because the fd could point to a different file description now), so its	443	incident (because the same I<file descriptor> could point to a different
393	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	444	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
394	very well if you register events for both fds.	445	file descriptors might not work very well if you register events for both
395		446	file descriptors.
396	Please note that epoll sometimes generates spurious notifications, so you
397	need to use non-blocking I/O or other means to avoid blocking when no data
398	(or space) is available.
399		447
400	Best performance from this backend is achieved by not unregistering all	448	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible,	449	watchers for a file descriptor until it has been closed, if possible,
402	i.e. keep at least one watcher active per fd at all times. Stopping and	450	i.e. keep at least one watcher active per fd at all times. Stopping and
403	starting a watcher (without re-setting it) also usually doesn't cause	451	starting a watcher (without re-setting it) also usually doesn't cause
404	extra overhead.	452	extra overhead. A fork can both result in spurious notifications as well
		453	as in libev having to destroy and recreate the epoll object, which can
		454	take considerable time and thus should be avoided.
		455
		456	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		457	faster than epoll for maybe up to a hundred file descriptors, depending on
		458	the usage. So sad.
405		459
406	While nominally embeddable in other event loops, this feature is broken in	460	While nominally embeddable in other event loops, this feature is broken in
407	all kernel versions tested so far.	461	all kernel versions tested so far.
408		462
409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	463	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
410	C<EVBACKEND_POLL>.	464	C<EVBACKEND_POLL>.
411		465
412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	466	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
413		467
414	Kqueue deserves special mention, as at the time of this writing, it was	468	Kqueue deserves special mention, as at the time of this writing, it
415	broken on all BSDs except NetBSD (usually it doesn't work reliably with	469	was broken on all BSDs except NetBSD (usually it doesn't work reliably
416	anything but sockets and pipes, except on Darwin, where of course it's	470	with anything but sockets and pipes, except on Darwin, where of course
417	completely useless). For this reason it's not being "auto-detected" unless	471	it's completely useless). Unlike epoll, however, whose brokenness
418	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or	472	is by design, these kqueue bugs can (and eventually will) be fixed
419	libev was compiled on a known-to-be-good (-enough) system like NetBSD.	473	without API changes to existing programs. For this reason it's not being
		474	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		475	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		476	system like NetBSD.
420		477
421	You still can embed kqueue into a normal poll or select backend and use it	478	You still can embed kqueue into a normal poll or select backend and use it
422	only for sockets (after having made sure that sockets work with kqueue on	479	only for sockets (after having made sure that sockets work with kqueue on
423	the target platform). See C<ev_embed> watchers for more info.	480	the target platform). See C<ev_embed> watchers for more info.
424		481
425	It scales in the same way as the epoll backend, but the interface to the	482	It scales in the same way as the epoll backend, but the interface to the
426	kernel is more efficient (which says nothing about its actual speed, of	483	kernel is more efficient (which says nothing about its actual speed, of
427	course). While stopping, setting and starting an I/O watcher does never	484	course). While stopping, setting and starting an I/O watcher does never
428	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	485	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
429	two event changes per incident. Support for C<fork ()> is very bad and it	486	two event changes per incident. Support for C<fork ()> is very bad (but
430	drops fds silently in similarly hard-to-detect cases.	487	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		488	cases
431		489
432	This backend usually performs well under most conditions.	490	This backend usually performs well under most conditions.
433		491
434	While nominally embeddable in other event loops, this doesn't work	492	While nominally embeddable in other event loops, this doesn't work
435	everywhere, so you might need to test for this. And since it is broken	493	everywhere, so you might need to test for this. And since it is broken
436	almost everywhere, you should only use it when you have a lot of sockets	494	almost everywhere, you should only use it when you have a lot of sockets
437	(for which it usually works), by embedding it into another event loop	495	(for which it usually works), by embedding it into another event loop
438	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,	496	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
439	using it only for sockets.	497	also broken on OS X)) and, did I mention it, using it only for sockets.
440		498
441	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with	499	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
442	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with	500	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
443	C<NOTE_EOF>.	501	C<NOTE_EOF>.
444		502
…		…
464	might perform better.	522	might perform better.
465		523
466	On the positive side, with the exception of the spurious readiness	524	On the positive side, with the exception of the spurious readiness
467	notifications, this backend actually performed fully to specification	525	notifications, this backend actually performed fully to specification
468	in all tests and is fully embeddable, which is a rare feat among the	526	in all tests and is fully embeddable, which is a rare feat among the
469	OS-specific backends.	527	OS-specific backends (I vastly prefer correctness over speed hacks).
470		528
471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	529	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
472	C<EVBACKEND_POLL>.	530	C<EVBACKEND_POLL>.
473		531
474	=item C<EVBACKEND_ALL>	532	=item C<EVBACKEND_ALL>
…		…
479		537
480	It is definitely not recommended to use this flag.	538	It is definitely not recommended to use this flag.
481		539
482	=back	540	=back
483		541
484	If one or more of these are or'ed into the flags value, then only these	542	If one or more of the backend flags are or'ed into the flags value,
485	backends will be tried (in the reverse order as listed here). If none are	543	then only these backends will be tried (in the reverse order as listed
486	specified, all backends in C<ev_recommended_backends ()> will be tried.	544	here). If none are specified, all backends in C<ev_recommended_backends
		545	()> will be tried.
487		546
488	Example: This is the most typical usage.	547	Example: This is the most typical usage.
489		548
490	if (!ev_default_loop (0))	549	if (!ev_default_loop (0))
491	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	550	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
…		…
527	responsibility to either stop all watchers cleanly yourself I<before>	586	responsibility to either stop all watchers cleanly yourself I<before>
528	calling this function, or cope with the fact afterwards (which is usually	587	calling this function, or cope with the fact afterwards (which is usually
529	the easiest thing, you can just ignore the watchers and/or C<free ()> them	588	the easiest thing, you can just ignore the watchers and/or C<free ()> them
530	for example).	589	for example).
531		590
532	Note that certain global state, such as signal state, will not be freed by	591	Note that certain global state, such as signal state (and installed signal
533	this function, and related watchers (such as signal and child watchers)	592	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	593	as signal and child watchers) would need to be stopped manually.
535		594
536	In general it is not advisable to call this function except in the	595	In general it is not advisable to call this function except in the
537	rare occasion where you really need to free e.g. the signal handling	596	rare occasion where you really need to free e.g. the signal handling
538	pipe fds. If you need dynamically allocated loops it is better to use	597	pipe fds. If you need dynamically allocated loops it is better to use
539	C<ev_loop_new> and C<ev_loop_destroy>).	598	C<ev_loop_new> and C<ev_loop_destroy>.
540		599
541	=item ev_loop_destroy (loop)	600	=item ev_loop_destroy (loop)
542		601
543	Like C<ev_default_destroy>, but destroys an event loop created by an	602	Like C<ev_default_destroy>, but destroys an event loop created by an
544	earlier call to C<ev_loop_new>.	603	earlier call to C<ev_loop_new>.
…		…
582		641
583	This value can sometimes be useful as a generation counter of sorts (it	642	This value can sometimes be useful as a generation counter of sorts (it
584	"ticks" the number of loop iterations), as it roughly corresponds with	643	"ticks" the number of loop iterations), as it roughly corresponds with
585	C<ev_prepare> and C<ev_check> calls.	644	C<ev_prepare> and C<ev_check> calls.
586		645
		646	=item unsigned int ev_loop_depth (loop)
		647
		648	Returns the number of times C<ev_loop> was entered minus the number of
		649	times C<ev_loop> was exited, in other words, the recursion depth.
		650
		651	Outside C<ev_loop>, this number is zero. In a callback, this number is
		652	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		653	in which case it is higher.
		654
		655	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		656	etc.), doesn't count as exit.
		657
587	=item unsigned int ev_backend (loop)	658	=item unsigned int ev_backend (loop)
588		659
589	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	660	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
590	use.	661	use.
591		662
…		…
605		676
606	This function is rarely useful, but when some event callback runs for a	677	This function is rarely useful, but when some event callback runs for a
607	very long time without entering the event loop, updating libev's idea of	678	very long time without entering the event loop, updating libev's idea of
608	the current time is a good idea.	679	the current time is a good idea.
609		680
610	See also "The special problem of time updates" in the C<ev_timer> section.	681	See also L<The special problem of time updates> in the C<ev_timer> section.
		682
		683	=item ev_suspend (loop)
		684
		685	=item ev_resume (loop)
		686
		687	These two functions suspend and resume a loop, for use when the loop is
		688	not used for a while and timeouts should not be processed.
		689
		690	A typical use case would be an interactive program such as a game: When
		691	the user presses C<^Z> to suspend the game and resumes it an hour later it
		692	would be best to handle timeouts as if no time had actually passed while
		693	the program was suspended. This can be achieved by calling C<ev_suspend>
		694	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		695	C<ev_resume> directly afterwards to resume timer processing.
		696
		697	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		698	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		699	will be rescheduled (that is, they will lose any events that would have
		700	occured while suspended).
		701
		702	After calling C<ev_suspend> you B<must not> call I<any> function on the
		703	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		704	without a previous call to C<ev_suspend>.
		705
		706	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		707	event loop time (see C<ev_now_update>).
611		708
612	=item ev_loop (loop, int flags)	709	=item ev_loop (loop, int flags)
613		710
614	Finally, this is it, the event handler. This function usually is called	711	Finally, this is it, the event handler. This function usually is called
615	after you initialised all your watchers and you want to start handling	712	after you have initialised all your watchers and you want to start
616	events.	713	handling events.
617		714
618	If the flags argument is specified as C<0>, it will not return until	715	If the flags argument is specified as C<0>, it will not return until
619	either no event watchers are active anymore or C<ev_unloop> was called.	716	either no event watchers are active anymore or C<ev_unloop> was called.
620		717
621	Please note that an explicit C<ev_unloop> is usually better than	718	Please note that an explicit C<ev_unloop> is usually better than
…		…
631	the loop.	728	the loop.
632		729
633	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	730	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
634	necessary) and will handle those and any already outstanding ones. It	731	necessary) and will handle those and any already outstanding ones. It
635	will block your process until at least one new event arrives (which could	732	will block your process until at least one new event arrives (which could
636	be an event internal to libev itself, so there is no guarentee that a	733	be an event internal to libev itself, so there is no guarantee that a
637	user-registered callback will be called), and will return after one	734	user-registered callback will be called), and will return after one
638	iteration of the loop.	735	iteration of the loop.
639		736
640	This is useful if you are waiting for some external event in conjunction	737	This is useful if you are waiting for some external event in conjunction
641	with something not expressible using other libev watchers (i.e. "roll your	738	with something not expressible using other libev watchers (i.e. "roll your
…		…
699		796
700	If you have a watcher you never unregister that should not keep C<ev_loop>	797	If you have a watcher you never unregister that should not keep C<ev_loop>
701	from returning, call ev_unref() after starting, and ev_ref() before	798	from returning, call ev_unref() after starting, and ev_ref() before
702	stopping it.	799	stopping it.
703		800
704	As an example, libev itself uses this for its internal signal pipe: It is	801	As an example, libev itself uses this for its internal signal pipe: It
705	not visible to the libev user and should not keep C<ev_loop> from exiting	802	is not visible to the libev user and should not keep C<ev_loop> from
706	if no event watchers registered by it are active. It is also an excellent	803	exiting if no event watchers registered by it are active. It is also an
707	way to do this for generic recurring timers or from within third-party	804	excellent way to do this for generic recurring timers or from within
708	libraries. Just remember to I<unref after start> and I<ref before stop>	805	third-party libraries. Just remember to I<unref after start> and I<ref
709	(but only if the watcher wasn't active before, or was active before,	806	before stop> (but only if the watcher wasn't active before, or was active
710	respectively).	807	before, respectively. Note also that libev might stop watchers itself
		808	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		809	in the callback).
711		810
712	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	811	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
713	running when nothing else is active.	812	running when nothing else is active.
714		813
715	struct ev_signal exitsig;	814	ev_signal exitsig;
716	ev_signal_init (&exitsig, sig_cb, SIGINT);	815	ev_signal_init (&exitsig, sig_cb, SIGINT);
717	ev_signal_start (loop, &exitsig);	816	ev_signal_start (loop, &exitsig);
718	evf_unref (loop);	817	evf_unref (loop);
719		818
720	Example: For some weird reason, unregister the above signal handler again.	819	Example: For some weird reason, unregister the above signal handler again.
…		…
744		843
745	By setting a higher I<io collect interval> you allow libev to spend more	844	By setting a higher I<io collect interval> you allow libev to spend more
746	time collecting I/O events, so you can handle more events per iteration,	845	time collecting I/O events, so you can handle more events per iteration,
747	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	846	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
748	C<ev_timer>) will be not affected. Setting this to a non-null value will	847	C<ev_timer>) will be not affected. Setting this to a non-null value will
749	introduce an additional C<ev_sleep ()> call into most loop iterations.	848	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		849	sleep time ensures that libev will not poll for I/O events more often then
		850	once per this interval, on average.
750		851
751	Likewise, by setting a higher I<timeout collect interval> you allow libev	852	Likewise, by setting a higher I<timeout collect interval> you allow libev
752	to spend more time collecting timeouts, at the expense of increased	853	to spend more time collecting timeouts, at the expense of increased
753	latency/jitter/inexactness (the watcher callback will be called	854	latency/jitter/inexactness (the watcher callback will be called
754	later). C<ev_io> watchers will not be affected. Setting this to a non-null	855	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
756		857
757	Many (busy) programs can usually benefit by setting the I/O collect	858	Many (busy) programs can usually benefit by setting the I/O collect
758	interval to a value near C<0.1> or so, which is often enough for	859	interval to a value near C<0.1> or so, which is often enough for
759	interactive servers (of course not for games), likewise for timeouts. It	860	interactive servers (of course not for games), likewise for timeouts. It
760	usually doesn't make much sense to set it to a lower value than C<0.01>,	861	usually doesn't make much sense to set it to a lower value than C<0.01>,
761	as this approaches the timing granularity of most systems.	862	as this approaches the timing granularity of most systems. Note that if
		863	you do transactions with the outside world and you can't increase the
		864	parallelity, then this setting will limit your transaction rate (if you
		865	need to poll once per transaction and the I/O collect interval is 0.01,
		866	then you can't do more than 100 transations per second).
762		867
763	Setting the I<timeout collect interval> can improve the opportunity for	868	Setting the I<timeout collect interval> can improve the opportunity for
764	saving power, as the program will "bundle" timer callback invocations that	869	saving power, as the program will "bundle" timer callback invocations that
765	are "near" in time together, by delaying some, thus reducing the number of	870	are "near" in time together, by delaying some, thus reducing the number of
766	times the process sleeps and wakes up again. Another useful technique to	871	times the process sleeps and wakes up again. Another useful technique to
767	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	872	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
768	they fire on, say, one-second boundaries only.	873	they fire on, say, one-second boundaries only.
769		874
		875	Example: we only need 0.1s timeout granularity, and we wish not to poll
		876	more often than 100 times per second:
		877
		878	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		879	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		880
		881	=item ev_invoke_pending (loop)
		882
		883	This call will simply invoke all pending watchers while resetting their
		884	pending state. Normally, C<ev_loop> does this automatically when required,
		885	but when overriding the invoke callback this call comes handy.
		886
		887	=item int ev_pending_count (loop)
		888
		889	Returns the number of pending watchers - zero indicates that no watchers
		890	are pending.
		891
		892	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		893
		894	This overrides the invoke pending functionality of the loop: Instead of
		895	invoking all pending watchers when there are any, C<ev_loop> will call
		896	this callback instead. This is useful, for example, when you want to
		897	invoke the actual watchers inside another context (another thread etc.).
		898
		899	If you want to reset the callback, use C<ev_invoke_pending> as new
		900	callback.
		901
		902	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		903
		904	Sometimes you want to share the same loop between multiple threads. This
		905	can be done relatively simply by putting mutex_lock/unlock calls around
		906	each call to a libev function.
		907
		908	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		909	wait for it to return. One way around this is to wake up the loop via
		910	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		911	and I<acquire> callbacks on the loop.
		912
		913	When set, then C<release> will be called just before the thread is
		914	suspended waiting for new events, and C<acquire> is called just
		915	afterwards.
		916
		917	Ideally, C<release> will just call your mutex_unlock function, and
		918	C<acquire> will just call the mutex_lock function again.
		919
		920	While event loop modifications are allowed between invocations of
		921	C<release> and C<acquire> (that's their only purpose after all), no
		922	modifications done will affect the event loop, i.e. adding watchers will
		923	have no effect on the set of file descriptors being watched, or the time
		924	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		925	to take note of any changes you made.
		926
		927	In theory, threads executing C<ev_loop> will be async-cancel safe between
		928	invocations of C<release> and C<acquire>.
		929
		930	See also the locking example in the C<THREADS> section later in this
		931	document.
		932
		933	=item ev_set_userdata (loop, void *data)
		934
		935	=item ev_userdata (loop)
		936
		937	Set and retrieve a single C<void *> associated with a loop. When
		938	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		939	C<0.>
		940
		941	These two functions can be used to associate arbitrary data with a loop,
		942	and are intended solely for the C<invoke_pending_cb>, C<release> and
		943	C<acquire> callbacks described above, but of course can be (ab-)used for
		944	any other purpose as well.
		945
770	=item ev_loop_verify (loop)	946	=item ev_loop_verify (loop)
771		947
772	This function only does something when C<EV_VERIFY> support has been	948	This function only does something when C<EV_VERIFY> support has been
773	compiled in. which is the default for non-minimal builds. It tries to go	949	compiled in, which is the default for non-minimal builds. It tries to go
774	through all internal structures and checks them for validity. If anything	950	through all internal structures and checks them for validity. If anything
775	is found to be inconsistent, it will print an error message to standard	951	is found to be inconsistent, it will print an error message to standard
776	error and call C<abort ()>.	952	error and call C<abort ()>.
777		953
778	This can be used to catch bugs inside libev itself: under normal	954	This can be used to catch bugs inside libev itself: under normal
…		…
782	=back	958	=back
783		959
784		960
785	=head1 ANATOMY OF A WATCHER	961	=head1 ANATOMY OF A WATCHER
786		962
		963	In the following description, uppercase C<TYPE> in names stands for the
		964	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		965	watchers and C<ev_io_start> for I/O watchers.
		966
787	A watcher is a structure that you create and register to record your	967	A watcher is a structure that you create and register to record your
788	interest in some event. For instance, if you want to wait for STDIN to	968	interest in some event. For instance, if you want to wait for STDIN to
789	become readable, you would create an C<ev_io> watcher for that:	969	become readable, you would create an C<ev_io> watcher for that:
790		970
791	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	971	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
792	{	972	{
793	ev_io_stop (w);	973	ev_io_stop (w);
794	ev_unloop (loop, EVUNLOOP_ALL);	974	ev_unloop (loop, EVUNLOOP_ALL);
795	}	975	}
796		976
797	struct ev_loop *loop = ev_default_loop (0);	977	struct ev_loop *loop = ev_default_loop (0);
		978
798	struct ev_io stdin_watcher;	979	ev_io stdin_watcher;
		980
799	ev_init (&stdin_watcher, my_cb);	981	ev_init (&stdin_watcher, my_cb);
800	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	982	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
801	ev_io_start (loop, &stdin_watcher);	983	ev_io_start (loop, &stdin_watcher);
		984
802	ev_loop (loop, 0);	985	ev_loop (loop, 0);
803		986
804	As you can see, you are responsible for allocating the memory for your	987	As you can see, you are responsible for allocating the memory for your
805	watcher structures (and it is usually a bad idea to do this on the stack,	988	watcher structures (and it is I<usually> a bad idea to do this on the
806	although this can sometimes be quite valid).	989	stack).
		990
		991	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		992	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
807		993
808	Each watcher structure must be initialised by a call to C<ev_init	994	Each watcher structure must be initialised by a call to C<ev_init
809	(watcher *, callback)>, which expects a callback to be provided. This	995	(watcher *, callback)>, which expects a callback to be provided. This
810	callback gets invoked each time the event occurs (or, in the case of I/O	996	callback gets invoked each time the event occurs (or, in the case of I/O
811	watchers, each time the event loop detects that the file descriptor given	997	watchers, each time the event loop detects that the file descriptor given
812	is readable and/or writable).	998	is readable and/or writable).
813		999
814	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1000	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
815	with arguments specific to this watcher type. There is also a macro	1001	macro to configure it, with arguments specific to the watcher type. There
816	to combine initialisation and setting in one call: C<< ev_<type>_init	1002	is also a macro to combine initialisation and setting in one call: C<<
817	(watcher *, callback, ...) >>.	1003	ev_TYPE_init (watcher *, callback, ...) >>.
818		1004
819	To make the watcher actually watch out for events, you have to start it	1005	To make the watcher actually watch out for events, you have to start it
820	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1006	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
821	*) >>), and you can stop watching for events at any time by calling the	1007	*) >>), and you can stop watching for events at any time by calling the
822	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1008	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
823		1009
824	As long as your watcher is active (has been started but not stopped) you	1010	As long as your watcher is active (has been started but not stopped) you
825	must not touch the values stored in it. Most specifically you must never	1011	must not touch the values stored in it. Most specifically you must never
826	reinitialise it or call its C<set> macro.	1012	reinitialise it or call its C<ev_TYPE_set> macro.
827		1013
828	Each and every callback receives the event loop pointer as first, the	1014	Each and every callback receives the event loop pointer as first, the
829	registered watcher structure as second, and a bitset of received events as	1015	registered watcher structure as second, and a bitset of received events as
830	third argument.	1016	third argument.
831		1017
…		…
889		1075
890	=item C<EV_ASYNC>	1076	=item C<EV_ASYNC>
891		1077
892	The given async watcher has been asynchronously notified (see C<ev_async>).	1078	The given async watcher has been asynchronously notified (see C<ev_async>).
893		1079
		1080	=item C<EV_CUSTOM>
		1081
		1082	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1083	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1084
894	=item C<EV_ERROR>	1085	=item C<EV_ERROR>
895		1086
896	An unspecified error has occurred, the watcher has been stopped. This might	1087	An unspecified error has occurred, the watcher has been stopped. This might
897	happen because the watcher could not be properly started because libev	1088	happen because the watcher could not be properly started because libev
898	ran out of memory, a file descriptor was found to be closed or any other	1089	ran out of memory, a file descriptor was found to be closed or any other
		1090	problem. Libev considers these application bugs.
		1091
899	problem. You best act on it by reporting the problem and somehow coping	1092	You best act on it by reporting the problem and somehow coping with the
900	with the watcher being stopped.	1093	watcher being stopped. Note that well-written programs should not receive
		1094	an error ever, so when your watcher receives it, this usually indicates a
		1095	bug in your program.
901		1096
902	Libev will usually signal a few "dummy" events together with an error, for	1097	Libev will usually signal a few "dummy" events together with an error, for
903	example it might indicate that a fd is readable or writable, and if your	1098	example it might indicate that a fd is readable or writable, and if your
904	callbacks is well-written it can just attempt the operation and cope with	1099	callbacks is well-written it can just attempt the operation and cope with
905	the error from read() or write(). This will not work in multi-threaded	1100	the error from read() or write(). This will not work in multi-threaded
…		…
908		1103
909	=back	1104	=back
910		1105
911	=head2 GENERIC WATCHER FUNCTIONS	1106	=head2 GENERIC WATCHER FUNCTIONS
912		1107
913	In the following description, C<TYPE> stands for the watcher type,
914	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
915
916	=over 4	1108	=over 4
917		1109
918	=item C<ev_init> (ev_TYPE *watcher, callback)	1110	=item C<ev_init> (ev_TYPE *watcher, callback)
919		1111
920	This macro initialises the generic portion of a watcher. The contents	1112	This macro initialises the generic portion of a watcher. The contents
…		…
925	which rolls both calls into one.	1117	which rolls both calls into one.
926		1118
927	You can reinitialise a watcher at any time as long as it has been stopped	1119	You can reinitialise a watcher at any time as long as it has been stopped
928	(or never started) and there are no pending events outstanding.	1120	(or never started) and there are no pending events outstanding.
929		1121
930	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1122	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
931	int revents)>.	1123	int revents)>.
932		1124
933	Example: Initialise an C<ev_io> watcher in two steps.	1125	Example: Initialise an C<ev_io> watcher in two steps.
934		1126
935	ev_io w;	1127	ev_io w;
…		…
1012	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1204	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1013	(default: C<-2>). Pending watchers with higher priority will be invoked	1205	(default: C<-2>). Pending watchers with higher priority will be invoked
1014	before watchers with lower priority, but priority will not keep watchers	1206	before watchers with lower priority, but priority will not keep watchers
1015	from being executed (except for C<ev_idle> watchers).	1207	from being executed (except for C<ev_idle> watchers).
1016		1208
1017	This means that priorities are I<only> used for ordering callback
1018	invocation after new events have been received. This is useful, for
1019	example, to reduce latency after idling, or more often, to bind two
1020	watchers on the same event and make sure one is called first.
1021
1022	If you need to suppress invocation when higher priority events are pending	1209	If you need to suppress invocation when higher priority events are pending
1023	you need to look at C<ev_idle> watchers, which provide this functionality.	1210	you need to look at C<ev_idle> watchers, which provide this functionality.
1024		1211
1025	You I<must not> change the priority of a watcher as long as it is active or	1212	You I<must not> change the priority of a watcher as long as it is active or
1026	pending.	1213	pending.
1027		1214
		1215	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1216	fine, as long as you do not mind that the priority value you query might
		1217	or might not have been clamped to the valid range.
		1218
1028	The default priority used by watchers when no priority has been set is	1219	The default priority used by watchers when no priority has been set is
1029	always C<0>, which is supposed to not be too high and not be too low :).	1220	always C<0>, which is supposed to not be too high and not be too low :).
1030		1221
1031	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1222	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1032	fine, as long as you do not mind that the priority value you query might	1223	priorities.
1033	or might not have been adjusted to be within valid range.
1034		1224
1035	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1225	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1036		1226
1037	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1227	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1038	C<loop> nor C<revents> need to be valid as long as the watcher callback	1228	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1060	member, you can also "subclass" the watcher type and provide your own	1250	member, you can also "subclass" the watcher type and provide your own
1061	data:	1251	data:
1062		1252
1063	struct my_io	1253	struct my_io
1064	{	1254	{
1065	struct ev_io io;	1255	ev_io io;
1066	int otherfd;	1256	int otherfd;
1067	void *somedata;	1257	void *somedata;
1068	struct whatever *mostinteresting;	1258	struct whatever *mostinteresting;
1069	};	1259	};
1070		1260
…		…
1073	ev_io_init (&w.io, my_cb, fd, EV_READ);	1263	ev_io_init (&w.io, my_cb, fd, EV_READ);
1074		1264
1075	And since your callback will be called with a pointer to the watcher, you	1265	And since your callback will be called with a pointer to the watcher, you
1076	can cast it back to your own type:	1266	can cast it back to your own type:
1077		1267
1078	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1268	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1079	{	1269	{
1080	struct my_io *w = (struct my_io *)w_;	1270	struct my_io *w = (struct my_io *)w_;
1081	...	1271	...
1082	}	1272	}
1083		1273
…		…
1101	programmers):	1291	programmers):
1102		1292
1103	#include <stddef.h>	1293	#include <stddef.h>
1104		1294
1105	static void	1295	static void
1106	t1_cb (EV_P_ struct ev_timer *w, int revents)	1296	t1_cb (EV_P_ ev_timer *w, int revents)
1107	{	1297	{
1108	struct my_biggy big = (struct my_biggy *	1298	struct my_biggy big = (struct my_biggy *)
1109	(((char *)w) - offsetof (struct my_biggy, t1));	1299	(((char *)w) - offsetof (struct my_biggy, t1));
1110	}	1300	}
1111		1301
1112	static void	1302	static void
1113	t2_cb (EV_P_ struct ev_timer *w, int revents)	1303	t2_cb (EV_P_ ev_timer *w, int revents)
1114	{	1304	{
1115	struct my_biggy big = (struct my_biggy *	1305	struct my_biggy big = (struct my_biggy *)
1116	(((char *)w) - offsetof (struct my_biggy, t2));	1306	(((char *)w) - offsetof (struct my_biggy, t2));
1117	}	1307	}
		1308
		1309	=head2 WATCHER PRIORITY MODELS
		1310
		1311	Many event loops support I<watcher priorities>, which are usually small
		1312	integers that influence the ordering of event callback invocation
		1313	between watchers in some way, all else being equal.
		1314
		1315	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1316	description for the more technical details such as the actual priority
		1317	range.
		1318
		1319	There are two common ways how these these priorities are being interpreted
		1320	by event loops:
		1321
		1322	In the more common lock-out model, higher priorities "lock out" invocation
		1323	of lower priority watchers, which means as long as higher priority
		1324	watchers receive events, lower priority watchers are not being invoked.
		1325
		1326	The less common only-for-ordering model uses priorities solely to order
		1327	callback invocation within a single event loop iteration: Higher priority
		1328	watchers are invoked before lower priority ones, but they all get invoked
		1329	before polling for new events.
		1330
		1331	Libev uses the second (only-for-ordering) model for all its watchers
		1332	except for idle watchers (which use the lock-out model).
		1333
		1334	The rationale behind this is that implementing the lock-out model for
		1335	watchers is not well supported by most kernel interfaces, and most event
		1336	libraries will just poll for the same events again and again as long as
		1337	their callbacks have not been executed, which is very inefficient in the
		1338	common case of one high-priority watcher locking out a mass of lower
		1339	priority ones.
		1340
		1341	Static (ordering) priorities are most useful when you have two or more
		1342	watchers handling the same resource: a typical usage example is having an
		1343	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1344	timeouts. Under load, data might be received while the program handles
		1345	other jobs, but since timers normally get invoked first, the timeout
		1346	handler will be executed before checking for data. In that case, giving
		1347	the timer a lower priority than the I/O watcher ensures that I/O will be
		1348	handled first even under adverse conditions (which is usually, but not
		1349	always, what you want).
		1350
		1351	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1352	will only be executed when no same or higher priority watchers have
		1353	received events, they can be used to implement the "lock-out" model when
		1354	required.
		1355
		1356	For example, to emulate how many other event libraries handle priorities,
		1357	you can associate an C<ev_idle> watcher to each such watcher, and in
		1358	the normal watcher callback, you just start the idle watcher. The real
		1359	processing is done in the idle watcher callback. This causes libev to
		1360	continously poll and process kernel event data for the watcher, but when
		1361	the lock-out case is known to be rare (which in turn is rare :), this is
		1362	workable.
		1363
		1364	Usually, however, the lock-out model implemented that way will perform
		1365	miserably under the type of load it was designed to handle. In that case,
		1366	it might be preferable to stop the real watcher before starting the
		1367	idle watcher, so the kernel will not have to process the event in case
		1368	the actual processing will be delayed for considerable time.
		1369
		1370	Here is an example of an I/O watcher that should run at a strictly lower
		1371	priority than the default, and which should only process data when no
		1372	other events are pending:
		1373
		1374	ev_idle idle; // actual processing watcher
		1375	ev_io io; // actual event watcher
		1376
		1377	static void
		1378	io_cb (EV_P_ ev_io *w, int revents)
		1379	{
		1380	// stop the I/O watcher, we received the event, but
		1381	// are not yet ready to handle it.
		1382	ev_io_stop (EV_A_ w);
		1383
		1384	// start the idle watcher to ahndle the actual event.
		1385	// it will not be executed as long as other watchers
		1386	// with the default priority are receiving events.
		1387	ev_idle_start (EV_A_ &idle);
		1388	}
		1389
		1390	static void
		1391	idle_cb (EV_P_ ev_idle *w, int revents)
		1392	{
		1393	// actual processing
		1394	read (STDIN_FILENO, ...);
		1395
		1396	// have to start the I/O watcher again, as
		1397	// we have handled the event
		1398	ev_io_start (EV_P_ &io);
		1399	}
		1400
		1401	// initialisation
		1402	ev_idle_init (&idle, idle_cb);
		1403	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1404	ev_io_start (EV_DEFAULT_ &io);
		1405
		1406	In the "real" world, it might also be beneficial to start a timer, so that
		1407	low-priority connections can not be locked out forever under load. This
		1408	enables your program to keep a lower latency for important connections
		1409	during short periods of high load, while not completely locking out less
		1410	important ones.
1118		1411
1119		1412
1120	=head1 WATCHER TYPES	1413	=head1 WATCHER TYPES
1121		1414
1122	This section describes each watcher in detail, but will not repeat	1415	This section describes each watcher in detail, but will not repeat
…		…
1148	descriptors to non-blocking mode is also usually a good idea (but not	1441	descriptors to non-blocking mode is also usually a good idea (but not
1149	required if you know what you are doing).	1442	required if you know what you are doing).
1150		1443
1151	If you cannot use non-blocking mode, then force the use of a	1444	If you cannot use non-blocking mode, then force the use of a
1152	known-to-be-good backend (at the time of this writing, this includes only	1445	known-to-be-good backend (at the time of this writing, this includes only
1153	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1446	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1447	descriptors for which non-blocking operation makes no sense (such as
		1448	files) - libev doesn't guarentee any specific behaviour in that case.
1154		1449
1155	Another thing you have to watch out for is that it is quite easy to	1450	Another thing you have to watch out for is that it is quite easy to
1156	receive "spurious" readiness notifications, that is your callback might	1451	receive "spurious" readiness notifications, that is your callback might
1157	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1452	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1158	because there is no data. Not only are some backends known to create a	1453	because there is no data. Not only are some backends known to create a
…		…
1253	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1548	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1254	readable, but only once. Since it is likely line-buffered, you could	1549	readable, but only once. Since it is likely line-buffered, you could
1255	attempt to read a whole line in the callback.	1550	attempt to read a whole line in the callback.
1256		1551
1257	static void	1552	static void
1258	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1553	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1259	{	1554	{
1260	ev_io_stop (loop, w);	1555	ev_io_stop (loop, w);
1261	.. read from stdin here (or from w->fd) and handle any I/O errors	1556	.. read from stdin here (or from w->fd) and handle any I/O errors
1262	}	1557	}
1263		1558
1264	...	1559	...
1265	struct ev_loop *loop = ev_default_init (0);	1560	struct ev_loop *loop = ev_default_init (0);
1266	struct ev_io stdin_readable;	1561	ev_io stdin_readable;
1267	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1562	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1268	ev_io_start (loop, &stdin_readable);	1563	ev_io_start (loop, &stdin_readable);
1269	ev_loop (loop, 0);	1564	ev_loop (loop, 0);
1270		1565
1271		1566
…		…
1279	year, it will still time out after (roughly) one hour. "Roughly" because	1574	year, it will still time out after (roughly) one hour. "Roughly" because
1280	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1575	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1281	monotonic clock option helps a lot here).	1576	monotonic clock option helps a lot here).
1282		1577
1283	The callback is guaranteed to be invoked only I<after> its timeout has	1578	The callback is guaranteed to be invoked only I<after> its timeout has
1284	passed, but if multiple timers become ready during the same loop iteration	1579	passed (not I<at>, so on systems with very low-resolution clocks this
1285	then order of execution is undefined.	1580	might introduce a small delay). If multiple timers become ready during the
		1581	same loop iteration then the ones with earlier time-out values are invoked
		1582	before ones of the same priority with later time-out values (but this is
		1583	no longer true when a callback calls C<ev_loop> recursively).
		1584
		1585	=head3 Be smart about timeouts
		1586
		1587	Many real-world problems involve some kind of timeout, usually for error
		1588	recovery. A typical example is an HTTP request - if the other side hangs,
		1589	you want to raise some error after a while.
		1590
		1591	What follows are some ways to handle this problem, from obvious and
		1592	inefficient to smart and efficient.
		1593
		1594	In the following, a 60 second activity timeout is assumed - a timeout that
		1595	gets reset to 60 seconds each time there is activity (e.g. each time some
		1596	data or other life sign was received).
		1597
		1598	=over 4
		1599
		1600	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1601
		1602	This is the most obvious, but not the most simple way: In the beginning,
		1603	start the watcher:
		1604
		1605	ev_timer_init (timer, callback, 60., 0.);
		1606	ev_timer_start (loop, timer);
		1607
		1608	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1609	and start it again:
		1610
		1611	ev_timer_stop (loop, timer);
		1612	ev_timer_set (timer, 60., 0.);
		1613	ev_timer_start (loop, timer);
		1614
		1615	This is relatively simple to implement, but means that each time there is
		1616	some activity, libev will first have to remove the timer from its internal
		1617	data structure and then add it again. Libev tries to be fast, but it's
		1618	still not a constant-time operation.
		1619
		1620	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1621
		1622	This is the easiest way, and involves using C<ev_timer_again> instead of
		1623	C<ev_timer_start>.
		1624
		1625	To implement this, configure an C<ev_timer> with a C<repeat> value
		1626	of C<60> and then call C<ev_timer_again> at start and each time you
		1627	successfully read or write some data. If you go into an idle state where
		1628	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1629	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1630
		1631	That means you can ignore both the C<ev_timer_start> function and the
		1632	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1633	member and C<ev_timer_again>.
		1634
		1635	At start:
		1636
		1637	ev_init (timer, callback);
		1638	timer->repeat = 60.;
		1639	ev_timer_again (loop, timer);
		1640
		1641	Each time there is some activity:
		1642
		1643	ev_timer_again (loop, timer);
		1644
		1645	It is even possible to change the time-out on the fly, regardless of
		1646	whether the watcher is active or not:
		1647
		1648	timer->repeat = 30.;
		1649	ev_timer_again (loop, timer);
		1650
		1651	This is slightly more efficient then stopping/starting the timer each time
		1652	you want to modify its timeout value, as libev does not have to completely
		1653	remove and re-insert the timer from/into its internal data structure.
		1654
		1655	It is, however, even simpler than the "obvious" way to do it.
		1656
		1657	=item 3. Let the timer time out, but then re-arm it as required.
		1658
		1659	This method is more tricky, but usually most efficient: Most timeouts are
		1660	relatively long compared to the intervals between other activity - in
		1661	our example, within 60 seconds, there are usually many I/O events with
		1662	associated activity resets.
		1663
		1664	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1665	but remember the time of last activity, and check for a real timeout only
		1666	within the callback:
		1667
		1668	ev_tstamp last_activity; // time of last activity
		1669
		1670	static void
		1671	callback (EV_P_ ev_timer *w, int revents)
		1672	{
		1673	ev_tstamp now = ev_now (EV_A);
		1674	ev_tstamp timeout = last_activity + 60.;
		1675
		1676	// if last_activity + 60. is older than now, we did time out
		1677	if (timeout < now)
		1678	{
		1679	// timeout occured, take action
		1680	}
		1681	else
		1682	{
		1683	// callback was invoked, but there was some activity, re-arm
		1684	// the watcher to fire in last_activity + 60, which is
		1685	// guaranteed to be in the future, so "again" is positive:
		1686	w->repeat = timeout - now;
		1687	ev_timer_again (EV_A_ w);
		1688	}
		1689	}
		1690
		1691	To summarise the callback: first calculate the real timeout (defined
		1692	as "60 seconds after the last activity"), then check if that time has
		1693	been reached, which means something I<did>, in fact, time out. Otherwise
		1694	the callback was invoked too early (C<timeout> is in the future), so
		1695	re-schedule the timer to fire at that future time, to see if maybe we have
		1696	a timeout then.
		1697
		1698	Note how C<ev_timer_again> is used, taking advantage of the
		1699	C<ev_timer_again> optimisation when the timer is already running.
		1700
		1701	This scheme causes more callback invocations (about one every 60 seconds
		1702	minus half the average time between activity), but virtually no calls to
		1703	libev to change the timeout.
		1704
		1705	To start the timer, simply initialise the watcher and set C<last_activity>
		1706	to the current time (meaning we just have some activity :), then call the
		1707	callback, which will "do the right thing" and start the timer:
		1708
		1709	ev_init (timer, callback);
		1710	last_activity = ev_now (loop);
		1711	callback (loop, timer, EV_TIMEOUT);
		1712
		1713	And when there is some activity, simply store the current time in
		1714	C<last_activity>, no libev calls at all:
		1715
		1716	last_actiivty = ev_now (loop);
		1717
		1718	This technique is slightly more complex, but in most cases where the
		1719	time-out is unlikely to be triggered, much more efficient.
		1720
		1721	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1722	callback :) - just change the timeout and invoke the callback, which will
		1723	fix things for you.
		1724
		1725	=item 4. Wee, just use a double-linked list for your timeouts.
		1726
		1727	If there is not one request, but many thousands (millions...), all
		1728	employing some kind of timeout with the same timeout value, then one can
		1729	do even better:
		1730
		1731	When starting the timeout, calculate the timeout value and put the timeout
		1732	at the I<end> of the list.
		1733
		1734	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1735	the list is expected to fire (for example, using the technique #3).
		1736
		1737	When there is some activity, remove the timer from the list, recalculate
		1738	the timeout, append it to the end of the list again, and make sure to
		1739	update the C<ev_timer> if it was taken from the beginning of the list.
		1740
		1741	This way, one can manage an unlimited number of timeouts in O(1) time for
		1742	starting, stopping and updating the timers, at the expense of a major
		1743	complication, and having to use a constant timeout. The constant timeout
		1744	ensures that the list stays sorted.
		1745
		1746	=back
		1747
		1748	So which method the best?
		1749
		1750	Method #2 is a simple no-brain-required solution that is adequate in most
		1751	situations. Method #3 requires a bit more thinking, but handles many cases
		1752	better, and isn't very complicated either. In most case, choosing either
		1753	one is fine, with #3 being better in typical situations.
		1754
		1755	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1756	rather complicated, but extremely efficient, something that really pays
		1757	off after the first million or so of active timers, i.e. it's usually
		1758	overkill :)
1286		1759
1287	=head3 The special problem of time updates	1760	=head3 The special problem of time updates
1288		1761
1289	Establishing the current time is a costly operation (it usually takes at	1762	Establishing the current time is a costly operation (it usually takes at
1290	least two system calls): EV therefore updates its idea of the current	1763	least two system calls): EV therefore updates its idea of the current
…		…
1302		1775
1303	If the event loop is suspended for a long time, you can also force an	1776	If the event loop is suspended for a long time, you can also force an
1304	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1777	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1305	()>.	1778	()>.
1306		1779
		1780	=head3 The special problems of suspended animation
		1781
		1782	When you leave the server world it is quite customary to hit machines that
		1783	can suspend/hibernate - what happens to the clocks during such a suspend?
		1784
		1785	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1786	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1787	to run until the system is suspended, but they will not advance while the
		1788	system is suspended. That means, on resume, it will be as if the program
		1789	was frozen for a few seconds, but the suspend time will not be counted
		1790	towards C<ev_timer> when a monotonic clock source is used. The real time
		1791	clock advanced as expected, but if it is used as sole clocksource, then a
		1792	long suspend would be detected as a time jump by libev, and timers would
		1793	be adjusted accordingly.
		1794
		1795	I would not be surprised to see different behaviour in different between
		1796	operating systems, OS versions or even different hardware.
		1797
		1798	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1799	time jump in the monotonic clocks and the realtime clock. If the program
		1800	is suspended for a very long time, and monotonic clock sources are in use,
		1801	then you can expect C<ev_timer>s to expire as the full suspension time
		1802	will be counted towards the timers. When no monotonic clock source is in
		1803	use, then libev will again assume a timejump and adjust accordingly.
		1804
		1805	It might be beneficial for this latter case to call C<ev_suspend>
		1806	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1807	deterministic behaviour in this case (you can do nothing against
		1808	C<SIGSTOP>).
		1809
1307	=head3 Watcher-Specific Functions and Data Members	1810	=head3 Watcher-Specific Functions and Data Members
1308		1811
1309	=over 4	1812	=over 4
1310		1813
1311	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1814	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1334	If the timer is started but non-repeating, stop it (as if it timed out).	1837	If the timer is started but non-repeating, stop it (as if it timed out).
1335		1838
1336	If the timer is repeating, either start it if necessary (with the	1839	If the timer is repeating, either start it if necessary (with the
1337	C<repeat> value), or reset the running timer to the C<repeat> value.	1840	C<repeat> value), or reset the running timer to the C<repeat> value.
1338		1841
1339	This sounds a bit complicated, but here is a useful and typical	1842	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1340	example: Imagine you have a TCP connection and you want a so-called idle	1843	usage example.
1341	timeout, that is, you want to be called when there have been, say, 60
1342	seconds of inactivity on the socket. The easiest way to do this is to
1343	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1344	C<ev_timer_again> each time you successfully read or write some data. If
1345	you go into an idle state where you do not expect data to travel on the
1346	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1347	automatically restart it if need be.
1348		1844
1349	That means you can ignore the C<after> value and C<ev_timer_start>	1845	=item ev_timer_remaining (loop, ev_timer *)
1350	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1351		1846
1352	ev_timer_init (timer, callback, 0., 5.);	1847	Returns the remaining time until a timer fires. If the timer is active,
1353	ev_timer_again (loop, timer);	1848	then this time is relative to the current event loop time, otherwise it's
1354	...	1849	the timeout value currently configured.
1355	timer->again = 17.;
1356	ev_timer_again (loop, timer);
1357	...
1358	timer->again = 10.;
1359	ev_timer_again (loop, timer);
1360		1850
1361	This is more slightly efficient then stopping/starting the timer each time	1851	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1362	you want to modify its timeout value.	1852	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
1363		1853	will return C<4>. When the timer expires and is restarted, it will return
1364	Note, however, that it is often even more efficient to remember the	1854	roughly C<7> (likely slightly less as callback invocation takes some time,
1365	time of the last activity and let the timer time-out naturally. In the	1855	too), and so on.
1366	callback, you then check whether the time-out is real, or, if there was
1367	some activity, you reschedule the watcher to time-out in "last_activity +
1368	timeout - ev_now ()" seconds.
1369		1856
1370	=item ev_tstamp repeat [read-write]	1857	=item ev_tstamp repeat [read-write]
1371		1858
1372	The current C<repeat> value. Will be used each time the watcher times out	1859	The current C<repeat> value. Will be used each time the watcher times out
1373	or C<ev_timer_again> is called, and determines the next timeout (if any),	1860	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1378	=head3 Examples	1865	=head3 Examples
1379		1866
1380	Example: Create a timer that fires after 60 seconds.	1867	Example: Create a timer that fires after 60 seconds.
1381		1868
1382	static void	1869	static void
1383	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1870	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1384	{	1871	{
1385	.. one minute over, w is actually stopped right here	1872	.. one minute over, w is actually stopped right here
1386	}	1873	}
1387		1874
1388	struct ev_timer mytimer;	1875	ev_timer mytimer;
1389	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1876	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1390	ev_timer_start (loop, &mytimer);	1877	ev_timer_start (loop, &mytimer);
1391		1878
1392	Example: Create a timeout timer that times out after 10 seconds of	1879	Example: Create a timeout timer that times out after 10 seconds of
1393	inactivity.	1880	inactivity.
1394		1881
1395	static void	1882	static void
1396	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1883	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1397	{	1884	{
1398	.. ten seconds without any activity	1885	.. ten seconds without any activity
1399	}	1886	}
1400		1887
1401	struct ev_timer mytimer;	1888	ev_timer mytimer;
1402	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1889	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1403	ev_timer_again (&mytimer); /* start timer */	1890	ev_timer_again (&mytimer); /* start timer */
1404	ev_loop (loop, 0);	1891	ev_loop (loop, 0);
1405		1892
1406	// and in some piece of code that gets executed on any "activity":	1893	// and in some piece of code that gets executed on any "activity":
…		…
1411	=head2 C<ev_periodic> - to cron or not to cron?	1898	=head2 C<ev_periodic> - to cron or not to cron?
1412		1899
1413	Periodic watchers are also timers of a kind, but they are very versatile	1900	Periodic watchers are also timers of a kind, but they are very versatile
1414	(and unfortunately a bit complex).	1901	(and unfortunately a bit complex).
1415		1902
1416	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1903	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1417	but on wall clock time (absolute time). You can tell a periodic watcher	1904	relative time, the physical time that passes) but on wall clock time
1418	to trigger after some specific point in time. For example, if you tell a	1905	(absolute time, the thing you can read on your calender or clock). The
1419	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1906	difference is that wall clock time can run faster or slower than real
1420	+ 10.>, that is, an absolute time not a delay) and then reset your system	1907	time, and time jumps are not uncommon (e.g. when you adjust your
1421	clock to January of the previous year, then it will take more than year	1908	wrist-watch).
1422	to trigger the event (unlike an C<ev_timer>, which would still trigger
1423	roughly 10 seconds later as it uses a relative timeout).
1424		1909
		1910	You can tell a periodic watcher to trigger after some specific point
		1911	in time: for example, if you tell a periodic watcher to trigger "in 10
		1912	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1913	not a delay) and then reset your system clock to January of the previous
		1914	year, then it will take a year or more to trigger the event (unlike an
		1915	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1916	it, as it uses a relative timeout).
		1917
1425	C<ev_periodic>s can also be used to implement vastly more complex timers,	1918	C<ev_periodic> watchers can also be used to implement vastly more complex
1426	such as triggering an event on each "midnight, local time", or other	1919	timers, such as triggering an event on each "midnight, local time", or
1427	complicated rules.	1920	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1921	those cannot react to time jumps.
1428		1922
1429	As with timers, the callback is guaranteed to be invoked only when the	1923	As with timers, the callback is guaranteed to be invoked only when the
1430	time (C<at>) has passed, but if multiple periodic timers become ready	1924	point in time where it is supposed to trigger has passed. If multiple
1431	during the same loop iteration, then order of execution is undefined.	1925	timers become ready during the same loop iteration then the ones with
		1926	earlier time-out values are invoked before ones with later time-out values
		1927	(but this is no longer true when a callback calls C<ev_loop> recursively).
1432		1928
1433	=head3 Watcher-Specific Functions and Data Members	1929	=head3 Watcher-Specific Functions and Data Members
1434		1930
1435	=over 4	1931	=over 4
1436		1932
1437	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1933	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1438		1934
1439	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1935	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1440		1936
1441	Lots of arguments, lets sort it out... There are basically three modes of	1937	Lots of arguments, let's sort it out... There are basically three modes of
1442	operation, and we will explain them from simplest to most complex:	1938	operation, and we will explain them from simplest to most complex:
1443		1939
1444	=over 4	1940	=over 4
1445		1941
1446	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1942	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1447		1943
1448	In this configuration the watcher triggers an event after the wall clock	1944	In this configuration the watcher triggers an event after the wall clock
1449	time C<at> has passed. It will not repeat and will not adjust when a time	1945	time C<offset> has passed. It will not repeat and will not adjust when a
1450	jump occurs, that is, if it is to be run at January 1st 2011 then it will	1946	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1451	only run when the system clock reaches or surpasses this time.	1947	will be stopped and invoked when the system clock reaches or surpasses
		1948	this point in time.
1452		1949
1453	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1950	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1454		1951
1455	In this mode the watcher will always be scheduled to time out at the next	1952	In this mode the watcher will always be scheduled to time out at the next
1456	C<at + N * interval> time (for some integer N, which can also be negative)	1953	C<offset + N * interval> time (for some integer N, which can also be
1457	and then repeat, regardless of any time jumps.	1954	negative) and then repeat, regardless of any time jumps. The C<offset>
		1955	argument is merely an offset into the C<interval> periods.
1458		1956
1459	This can be used to create timers that do not drift with respect to the	1957	This can be used to create timers that do not drift with respect to the
1460	system clock, for example, here is a C<ev_periodic> that triggers each	1958	system clock, for example, here is an C<ev_periodic> that triggers each
1461	hour, on the hour:	1959	hour, on the hour (with respect to UTC):
1462		1960
1463	ev_periodic_set (&periodic, 0., 3600., 0);	1961	ev_periodic_set (&periodic, 0., 3600., 0);
1464		1962
1465	This doesn't mean there will always be 3600 seconds in between triggers,	1963	This doesn't mean there will always be 3600 seconds in between triggers,
1466	but only that the callback will be called when the system time shows a	1964	but only that the callback will be called when the system time shows a
1467	full hour (UTC), or more correctly, when the system time is evenly divisible	1965	full hour (UTC), or more correctly, when the system time is evenly divisible
1468	by 3600.	1966	by 3600.
1469		1967
1470	Another way to think about it (for the mathematically inclined) is that	1968	Another way to think about it (for the mathematically inclined) is that
1471	C<ev_periodic> will try to run the callback in this mode at the next possible	1969	C<ev_periodic> will try to run the callback in this mode at the next possible
1472	time where C<time = at (mod interval)>, regardless of any time jumps.	1970	time where C<time = offset (mod interval)>, regardless of any time jumps.
1473		1971
1474	For numerical stability it is preferable that the C<at> value is near	1972	For numerical stability it is preferable that the C<offset> value is near
1475	C<ev_now ()> (the current time), but there is no range requirement for	1973	C<ev_now ()> (the current time), but there is no range requirement for
1476	this value, and in fact is often specified as zero.	1974	this value, and in fact is often specified as zero.
1477		1975
1478	Note also that there is an upper limit to how often a timer can fire (CPU	1976	Note also that there is an upper limit to how often a timer can fire (CPU
1479	speed for example), so if C<interval> is very small then timing stability	1977	speed for example), so if C<interval> is very small then timing stability
1480	will of course deteriorate. Libev itself tries to be exact to be about one	1978	will of course deteriorate. Libev itself tries to be exact to be about one
1481	millisecond (if the OS supports it and the machine is fast enough).	1979	millisecond (if the OS supports it and the machine is fast enough).
1482		1980
1483	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1981	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1484		1982
1485	In this mode the values for C<interval> and C<at> are both being	1983	In this mode the values for C<interval> and C<offset> are both being
1486	ignored. Instead, each time the periodic watcher gets scheduled, the	1984	ignored. Instead, each time the periodic watcher gets scheduled, the
1487	reschedule callback will be called with the watcher as first, and the	1985	reschedule callback will be called with the watcher as first, and the
1488	current time as second argument.	1986	current time as second argument.
1489		1987
1490	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1988	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1491	ever, or make ANY event loop modifications whatsoever>.	1989	or make ANY other event loop modifications whatsoever, unless explicitly
		1990	allowed by documentation here>.
1492		1991
1493	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1992	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1494	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1993	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1495	only event loop modification you are allowed to do).	1994	only event loop modification you are allowed to do).
1496		1995
1497	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	1996	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1498	*w, ev_tstamp now)>, e.g.:	1997	*w, ev_tstamp now)>, e.g.:
1499		1998
		1999	static ev_tstamp
1500	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2000	my_rescheduler (ev_periodic *w, ev_tstamp now)
1501	{	2001	{
1502	return now + 60.;	2002	return now + 60.;
1503	}	2003	}
1504		2004
1505	It must return the next time to trigger, based on the passed time value	2005	It must return the next time to trigger, based on the passed time value
…		…
1525	a different time than the last time it was called (e.g. in a crond like	2025	a different time than the last time it was called (e.g. in a crond like
1526	program when the crontabs have changed).	2026	program when the crontabs have changed).
1527		2027
1528	=item ev_tstamp ev_periodic_at (ev_periodic *)	2028	=item ev_tstamp ev_periodic_at (ev_periodic *)
1529		2029
1530	When active, returns the absolute time that the watcher is supposed to	2030	When active, returns the absolute time that the watcher is supposed
1531	trigger next.	2031	to trigger next. This is not the same as the C<offset> argument to
		2032	C<ev_periodic_set>, but indeed works even in interval and manual
		2033	rescheduling modes.
1532		2034
1533	=item ev_tstamp offset [read-write]	2035	=item ev_tstamp offset [read-write]
1534		2036
1535	When repeating, this contains the offset value, otherwise this is the	2037	When repeating, this contains the offset value, otherwise this is the
1536	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2038	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2039	although libev might modify this value for better numerical stability).
1537		2040
1538	Can be modified any time, but changes only take effect when the periodic	2041	Can be modified any time, but changes only take effect when the periodic
1539	timer fires or C<ev_periodic_again> is being called.	2042	timer fires or C<ev_periodic_again> is being called.
1540		2043
1541	=item ev_tstamp interval [read-write]	2044	=item ev_tstamp interval [read-write]
1542		2045
1543	The current interval value. Can be modified any time, but changes only	2046	The current interval value. Can be modified any time, but changes only
1544	take effect when the periodic timer fires or C<ev_periodic_again> is being	2047	take effect when the periodic timer fires or C<ev_periodic_again> is being
1545	called.	2048	called.
1546		2049
1547	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2050	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1548		2051
1549	The current reschedule callback, or C<0>, if this functionality is	2052	The current reschedule callback, or C<0>, if this functionality is
1550	switched off. Can be changed any time, but changes only take effect when	2053	switched off. Can be changed any time, but changes only take effect when
1551	the periodic timer fires or C<ev_periodic_again> is being called.	2054	the periodic timer fires or C<ev_periodic_again> is being called.
1552		2055
…		…
1557	Example: Call a callback every hour, or, more precisely, whenever the	2060	Example: Call a callback every hour, or, more precisely, whenever the
1558	system time is divisible by 3600. The callback invocation times have	2061	system time is divisible by 3600. The callback invocation times have
1559	potentially a lot of jitter, but good long-term stability.	2062	potentially a lot of jitter, but good long-term stability.
1560		2063
1561	static void	2064	static void
1562	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2065	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1563	{	2066	{
1564	... its now a full hour (UTC, or TAI or whatever your clock follows)	2067	... its now a full hour (UTC, or TAI or whatever your clock follows)
1565	}	2068	}
1566		2069
1567	struct ev_periodic hourly_tick;	2070	ev_periodic hourly_tick;
1568	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2071	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1569	ev_periodic_start (loop, &hourly_tick);	2072	ev_periodic_start (loop, &hourly_tick);
1570		2073
1571	Example: The same as above, but use a reschedule callback to do it:	2074	Example: The same as above, but use a reschedule callback to do it:
1572		2075
1573	#include <math.h>	2076	#include <math.h>
1574		2077
1575	static ev_tstamp	2078	static ev_tstamp
1576	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2079	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1577	{	2080	{
1578	return now + (3600. - fmod (now, 3600.));	2081	return now + (3600. - fmod (now, 3600.));
1579	}	2082	}
1580		2083
1581	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2084	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1582		2085
1583	Example: Call a callback every hour, starting now:	2086	Example: Call a callback every hour, starting now:
1584		2087
1585	struct ev_periodic hourly_tick;	2088	ev_periodic hourly_tick;
1586	ev_periodic_init (&hourly_tick, clock_cb,	2089	ev_periodic_init (&hourly_tick, clock_cb,
1587	fmod (ev_now (loop), 3600.), 3600., 0);	2090	fmod (ev_now (loop), 3600.), 3600., 0);
1588	ev_periodic_start (loop, &hourly_tick);	2091	ev_periodic_start (loop, &hourly_tick);
1589		2092
1590		2093
…		…
1593	Signal watchers will trigger an event when the process receives a specific	2096	Signal watchers will trigger an event when the process receives a specific
1594	signal one or more times. Even though signals are very asynchronous, libev	2097	signal one or more times. Even though signals are very asynchronous, libev
1595	will try it's best to deliver signals synchronously, i.e. as part of the	2098	will try it's best to deliver signals synchronously, i.e. as part of the
1596	normal event processing, like any other event.	2099	normal event processing, like any other event.
1597		2100
1598	If you want signals asynchronously, just use C<sigaction> as you would	2101	If you want signals to be delivered truly asynchronously, just use
1599	do without libev and forget about sharing the signal. You can even use	2102	C<sigaction> as you would do without libev and forget about sharing
1600	C<ev_async> from a signal handler to synchronously wake up an event loop.	2103	the signal. You can even use C<ev_async> from a signal handler to
		2104	synchronously wake up an event loop.
1601		2105
1602	You can configure as many watchers as you like per signal. Only when the	2106	You can configure as many watchers as you like for the same signal, but
		2107	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2108	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2109	C<SIGINT> in both the default loop and another loop at the same time. At
		2110	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2111
1603	first watcher gets started will libev actually register a signal handler	2112	When the first watcher gets started will libev actually register something
1604	with the kernel (thus it coexists with your own signal handlers as long as	2113	with the kernel (thus it coexists with your own signal handlers as long as
1605	you don't register any with libev for the same signal). Similarly, when	2114	you don't register any with libev for the same signal).
1606	the last signal watcher for a signal is stopped, libev will reset the
1607	signal handler to SIG_DFL (regardless of what it was set to before).
1608		2115
1609	If possible and supported, libev will install its handlers with	2116	If possible and supported, libev will install its handlers with
1610	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2117	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1611	interrupted. If you have a problem with system calls getting interrupted by	2118	not be unduly interrupted. If you have a problem with system calls getting
1612	signals you can block all signals in an C<ev_check> watcher and unblock	2119	interrupted by signals you can block all signals in an C<ev_check> watcher
1613	them in an C<ev_prepare> watcher.	2120	and unblock them in an C<ev_prepare> watcher.
		2121
		2122	=head3 The special problem of inheritance over execve
		2123
		2124	Both the signal mask (C<sigprocmask>) and the signal disposition
		2125	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2126	stopping it again), that is, libev might or might not block the signal,
		2127	and might or might not set or restore the installed signal handler.
		2128
		2129	While this does not matter for the signal disposition (libev never
		2130	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2131	C<execve>), this matters for the signal mask: many programs do not expect
		2132	certain signals to be blocked.
		2133
		2134	This means that before calling C<exec> (from the child) you should reset
		2135	the signal mask to whatever "default" you expect (all clear is a good
		2136	choice usually).
		2137
		2138	The simplest way to ensure that the signal mask is reset in the child is
		2139	to install a fork handler with C<pthread_atfork> that resets it. That will
		2140	catch fork calls done by libraries (such as the libc) as well.
		2141
		2142	In current versions of libev, you can also ensure that the signal mask is
		2143	not blocking any signals (except temporarily, so thread users watch out)
		2144	by specifying the C<EVFLAG_NOSIGFD> when creating the event loop. This
		2145	is not guaranteed for future versions, however.
1614		2146
1615	=head3 Watcher-Specific Functions and Data Members	2147	=head3 Watcher-Specific Functions and Data Members
1616		2148
1617	=over 4	2149	=over 4
1618		2150
…		…
1632	=head3 Examples	2164	=head3 Examples
1633		2165
1634	Example: Try to exit cleanly on SIGINT.	2166	Example: Try to exit cleanly on SIGINT.
1635		2167
1636	static void	2168	static void
1637	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2169	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1638	{	2170	{
1639	ev_unloop (loop, EVUNLOOP_ALL);	2171	ev_unloop (loop, EVUNLOOP_ALL);
1640	}	2172	}
1641		2173
1642	struct ev_signal signal_watcher;	2174	ev_signal signal_watcher;
1643	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2175	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1644	ev_signal_start (loop, &signal_watcher);	2176	ev_signal_start (loop, &signal_watcher);
1645		2177
1646		2178
1647	=head2 C<ev_child> - watch out for process status changes	2179	=head2 C<ev_child> - watch out for process status changes
…		…
1650	some child status changes (most typically when a child of yours dies or	2182	some child status changes (most typically when a child of yours dies or
1651	exits). It is permissible to install a child watcher I<after> the child	2183	exits). It is permissible to install a child watcher I<after> the child
1652	has been forked (which implies it might have already exited), as long	2184	has been forked (which implies it might have already exited), as long
1653	as the event loop isn't entered (or is continued from a watcher), i.e.,	2185	as the event loop isn't entered (or is continued from a watcher), i.e.,
1654	forking and then immediately registering a watcher for the child is fine,	2186	forking and then immediately registering a watcher for the child is fine,
1655	but forking and registering a watcher a few event loop iterations later is	2187	but forking and registering a watcher a few event loop iterations later or
1656	not.	2188	in the next callback invocation is not.
1657		2189
1658	Only the default event loop is capable of handling signals, and therefore	2190	Only the default event loop is capable of handling signals, and therefore
1659	you can only register child watchers in the default event loop.	2191	you can only register child watchers in the default event loop.
1660		2192
		2193	Due to some design glitches inside libev, child watchers will always be
		2194	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2195	libev)
		2196
1661	=head3 Process Interaction	2197	=head3 Process Interaction
1662		2198
1663	Libev grabs C<SIGCHLD> as soon as the default event loop is	2199	Libev grabs C<SIGCHLD> as soon as the default event loop is
1664	initialised. This is necessary to guarantee proper behaviour even if	2200	initialised. This is necessary to guarantee proper behaviour even if the
1665	the first child watcher is started after the child exits. The occurrence	2201	first child watcher is started after the child exits. The occurrence
1666	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2202	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1667	synchronously as part of the event loop processing. Libev always reaps all	2203	synchronously as part of the event loop processing. Libev always reaps all
1668	children, even ones not watched.	2204	children, even ones not watched.
1669		2205
1670	=head3 Overriding the Built-In Processing	2206	=head3 Overriding the Built-In Processing
…		…
1680	=head3 Stopping the Child Watcher	2216	=head3 Stopping the Child Watcher
1681		2217
1682	Currently, the child watcher never gets stopped, even when the	2218	Currently, the child watcher never gets stopped, even when the
1683	child terminates, so normally one needs to stop the watcher in the	2219	child terminates, so normally one needs to stop the watcher in the
1684	callback. Future versions of libev might stop the watcher automatically	2220	callback. Future versions of libev might stop the watcher automatically
1685	when a child exit is detected.	2221	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2222	problem).
1686		2223
1687	=head3 Watcher-Specific Functions and Data Members	2224	=head3 Watcher-Specific Functions and Data Members
1688		2225
1689	=over 4	2226	=over 4
1690		2227
…		…
1722	its completion.	2259	its completion.
1723		2260
1724	ev_child cw;	2261	ev_child cw;
1725		2262
1726	static void	2263	static void
1727	child_cb (EV_P_ struct ev_child *w, int revents)	2264	child_cb (EV_P_ ev_child *w, int revents)
1728	{	2265	{
1729	ev_child_stop (EV_A_ w);	2266	ev_child_stop (EV_A_ w);
1730	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2267	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1731	}	2268	}
1732		2269
…		…
1747		2284
1748		2285
1749	=head2 C<ev_stat> - did the file attributes just change?	2286	=head2 C<ev_stat> - did the file attributes just change?
1750		2287
1751	This watches a file system path for attribute changes. That is, it calls	2288	This watches a file system path for attribute changes. That is, it calls
1752	C<stat> regularly (or when the OS says it changed) and sees if it changed	2289	C<stat> on that path in regular intervals (or when the OS says it changed)
1753	compared to the last time, invoking the callback if it did.	2290	and sees if it changed compared to the last time, invoking the callback if
		2291	it did.
1754		2292
1755	The path does not need to exist: changing from "path exists" to "path does	2293	The path does not need to exist: changing from "path exists" to "path does
1756	not exist" is a status change like any other. The condition "path does	2294	not exist" is a status change like any other. The condition "path does not
1757	not exist" is signified by the C<st_nlink> field being zero (which is	2295	exist" (or more correctly "path cannot be stat'ed") is signified by the
1758	otherwise always forced to be at least one) and all the other fields of	2296	C<st_nlink> field being zero (which is otherwise always forced to be at
1759	the stat buffer having unspecified contents.	2297	least one) and all the other fields of the stat buffer having unspecified
		2298	contents.
1760		2299
1761	The path I<should> be absolute and I<must not> end in a slash. If it is	2300	The path I<must not> end in a slash or contain special components such as
		2301	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1762	relative and your working directory changes, the behaviour is undefined.	2302	your working directory changes, then the behaviour is undefined.
1763		2303
1764	Since there is no standard kernel interface to do this, the portable	2304	Since there is no portable change notification interface available, the
1765	implementation simply calls C<stat (2)> regularly on the path to see if	2305	portable implementation simply calls C<stat(2)> regularly on the path
1766	it changed somehow. You can specify a recommended polling interval for	2306	to see if it changed somehow. You can specify a recommended polling
1767	this case. If you specify a polling interval of C<0> (highly recommended!)	2307	interval for this case. If you specify a polling interval of C<0> (highly
1768	then a I<suitable, unspecified default> value will be used (which	2308	recommended!) then a I<suitable, unspecified default> value will be used
1769	you can expect to be around five seconds, although this might change	2309	(which you can expect to be around five seconds, although this might
1770	dynamically). Libev will also impose a minimum interval which is currently	2310	change dynamically). Libev will also impose a minimum interval which is
1771	around C<0.1>, but thats usually overkill.	2311	currently around C<0.1>, but that's usually overkill.
1772		2312
1773	This watcher type is not meant for massive numbers of stat watchers,	2313	This watcher type is not meant for massive numbers of stat watchers,
1774	as even with OS-supported change notifications, this can be	2314	as even with OS-supported change notifications, this can be
1775	resource-intensive.	2315	resource-intensive.
1776		2316
1777	At the time of this writing, the only OS-specific interface implemented	2317	At the time of this writing, the only OS-specific interface implemented
1778	is the Linux inotify interface (implementing kqueue support is left as	2318	is the Linux inotify interface (implementing kqueue support is left as an
1779	an exercise for the reader. Note, however, that the author sees no way	2319	exercise for the reader. Note, however, that the author sees no way of
1780	of implementing C<ev_stat> semantics with kqueue).	2320	implementing C<ev_stat> semantics with kqueue, except as a hint).
1781		2321
1782	=head3 ABI Issues (Largefile Support)	2322	=head3 ABI Issues (Largefile Support)
1783		2323
1784	Libev by default (unless the user overrides this) uses the default	2324	Libev by default (unless the user overrides this) uses the default
1785	compilation environment, which means that on systems with large file	2325	compilation environment, which means that on systems with large file
1786	support disabled by default, you get the 32 bit version of the stat	2326	support disabled by default, you get the 32 bit version of the stat
1787	structure. When using the library from programs that change the ABI to	2327	structure. When using the library from programs that change the ABI to
1788	use 64 bit file offsets the programs will fail. In that case you have to	2328	use 64 bit file offsets the programs will fail. In that case you have to
1789	compile libev with the same flags to get binary compatibility. This is	2329	compile libev with the same flags to get binary compatibility. This is
1790	obviously the case with any flags that change the ABI, but the problem is	2330	obviously the case with any flags that change the ABI, but the problem is
1791	most noticeably disabled with ev_stat and large file support.	2331	most noticeably displayed with ev_stat and large file support.
1792		2332
1793	The solution for this is to lobby your distribution maker to make large	2333	The solution for this is to lobby your distribution maker to make large
1794	file interfaces available by default (as e.g. FreeBSD does) and not	2334	file interfaces available by default (as e.g. FreeBSD does) and not
1795	optional. Libev cannot simply switch on large file support because it has	2335	optional. Libev cannot simply switch on large file support because it has
1796	to exchange stat structures with application programs compiled using the	2336	to exchange stat structures with application programs compiled using the
1797	default compilation environment.	2337	default compilation environment.
1798		2338
1799	=head3 Inotify and Kqueue	2339	=head3 Inotify and Kqueue
1800		2340
1801	When C<inotify (7)> support has been compiled into libev (generally only	2341	When C<inotify (7)> support has been compiled into libev and present at
1802	available with Linux) and present at runtime, it will be used to speed up	2342	runtime, it will be used to speed up change detection where possible. The
1803	change detection where possible. The inotify descriptor will be created lazily	2343	inotify descriptor will be created lazily when the first C<ev_stat>
1804	when the first C<ev_stat> watcher is being started.	2344	watcher is being started.
1805		2345
1806	Inotify presence does not change the semantics of C<ev_stat> watchers	2346	Inotify presence does not change the semantics of C<ev_stat> watchers
1807	except that changes might be detected earlier, and in some cases, to avoid	2347	except that changes might be detected earlier, and in some cases, to avoid
1808	making regular C<stat> calls. Even in the presence of inotify support	2348	making regular C<stat> calls. Even in the presence of inotify support
1809	there are many cases where libev has to resort to regular C<stat> polling,	2349	there are many cases where libev has to resort to regular C<stat> polling,
1810	but as long as the path exists, libev usually gets away without polling.	2350	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2351	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2352	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2353	xfs are fully working) libev usually gets away without polling.
1811		2354
1812	There is no support for kqueue, as apparently it cannot be used to	2355	There is no support for kqueue, as apparently it cannot be used to
1813	implement this functionality, due to the requirement of having a file	2356	implement this functionality, due to the requirement of having a file
1814	descriptor open on the object at all times, and detecting renames, unlinks	2357	descriptor open on the object at all times, and detecting renames, unlinks
1815	etc. is difficult.	2358	etc. is difficult.
1816		2359
		2360	=head3 C<stat ()> is a synchronous operation
		2361
		2362	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2363	the process. The exception are C<ev_stat> watchers - those call C<stat
		2364	()>, which is a synchronous operation.
		2365
		2366	For local paths, this usually doesn't matter: unless the system is very
		2367	busy or the intervals between stat's are large, a stat call will be fast,
		2368	as the path data is usually in memory already (except when starting the
		2369	watcher).
		2370
		2371	For networked file systems, calling C<stat ()> can block an indefinite
		2372	time due to network issues, and even under good conditions, a stat call
		2373	often takes multiple milliseconds.
		2374
		2375	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2376	paths, although this is fully supported by libev.
		2377
1817	=head3 The special problem of stat time resolution	2378	=head3 The special problem of stat time resolution
1818		2379
1819	The C<stat ()> system call only supports full-second resolution portably, and	2380	The C<stat ()> system call only supports full-second resolution portably,
1820	even on systems where the resolution is higher, most file systems still	2381	and even on systems where the resolution is higher, most file systems
1821	only support whole seconds.	2382	still only support whole seconds.
1822		2383
1823	That means that, if the time is the only thing that changes, you can	2384	That means that, if the time is the only thing that changes, you can
1824	easily miss updates: on the first update, C<ev_stat> detects a change and	2385	easily miss updates: on the first update, C<ev_stat> detects a change and
1825	calls your callback, which does something. When there is another update	2386	calls your callback, which does something. When there is another update
1826	within the same second, C<ev_stat> will be unable to detect unless the	2387	within the same second, C<ev_stat> will be unable to detect unless the
…		…
1969		2530
1970	=head3 Watcher-Specific Functions and Data Members	2531	=head3 Watcher-Specific Functions and Data Members
1971		2532
1972	=over 4	2533	=over 4
1973		2534
1974	=item ev_idle_init (ev_signal *, callback)	2535	=item ev_idle_init (ev_idle *, callback)
1975		2536
1976	Initialises and configures the idle watcher - it has no parameters of any	2537	Initialises and configures the idle watcher - it has no parameters of any
1977	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2538	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1978	believe me.	2539	believe me.
1979		2540
…		…
1983		2544
1984	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2545	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1985	callback, free it. Also, use no error checking, as usual.	2546	callback, free it. Also, use no error checking, as usual.
1986		2547
1987	static void	2548	static void
1988	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2549	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1989	{	2550	{
1990	free (w);	2551	free (w);
1991	// now do something you wanted to do when the program has	2552	// now do something you wanted to do when the program has
1992	// no longer anything immediate to do.	2553	// no longer anything immediate to do.
1993	}	2554	}
1994		2555
1995	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2556	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1996	ev_idle_init (idle_watcher, idle_cb);	2557	ev_idle_init (idle_watcher, idle_cb);
1997	ev_idle_start (loop, idle_cb);	2558	ev_idle_start (loop, idle_watcher);
1998		2559
1999		2560
2000	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2561	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2001		2562
2002	Prepare and check watchers are usually (but not always) used in pairs:	2563	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2081		2642
2082	static ev_io iow [nfd];	2643	static ev_io iow [nfd];
2083	static ev_timer tw;	2644	static ev_timer tw;
2084		2645
2085	static void	2646	static void
2086	io_cb (ev_loop *loop, ev_io *w, int revents)	2647	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2087	{	2648	{
2088	}	2649	}
2089		2650
2090	// create io watchers for each fd and a timer before blocking	2651	// create io watchers for each fd and a timer before blocking
2091	static void	2652	static void
2092	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2653	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2093	{	2654	{
2094	int timeout = 3600000;	2655	int timeout = 3600000;
2095	struct pollfd fds [nfd];	2656	struct pollfd fds [nfd];
2096	// actual code will need to loop here and realloc etc.	2657	// actual code will need to loop here and realloc etc.
2097	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2658	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2098		2659
2099	/* the callback is illegal, but won't be called as we stop during check */	2660	/* the callback is illegal, but won't be called as we stop during check */
2100	ev_timer_init (&tw, 0, timeout * 1e-3);	2661	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2101	ev_timer_start (loop, &tw);	2662	ev_timer_start (loop, &tw);
2102		2663
2103	// create one ev_io per pollfd	2664	// create one ev_io per pollfd
2104	for (int i = 0; i < nfd; ++i)	2665	for (int i = 0; i < nfd; ++i)
2105	{	2666	{
…		…
2112	}	2673	}
2113	}	2674	}
2114		2675
2115	// stop all watchers after blocking	2676	// stop all watchers after blocking
2116	static void	2677	static void
2117	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2678	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2118	{	2679	{
2119	ev_timer_stop (loop, &tw);	2680	ev_timer_stop (loop, &tw);
2120		2681
2121	for (int i = 0; i < nfd; ++i)	2682	for (int i = 0; i < nfd; ++i)
2122	{	2683	{
…		…
2218	some fds have to be watched and handled very quickly (with low latency),	2779	some fds have to be watched and handled very quickly (with low latency),
2219	and even priorities and idle watchers might have too much overhead. In	2780	and even priorities and idle watchers might have too much overhead. In
2220	this case you would put all the high priority stuff in one loop and all	2781	this case you would put all the high priority stuff in one loop and all
2221	the rest in a second one, and embed the second one in the first.	2782	the rest in a second one, and embed the second one in the first.
2222		2783
2223	As long as the watcher is active, the callback will be invoked every time	2784	As long as the watcher is active, the callback will be invoked every
2224	there might be events pending in the embedded loop. The callback must then	2785	time there might be events pending in the embedded loop. The callback
2225	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2786	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2226	their callbacks (you could also start an idle watcher to give the embedded	2787	sweep and invoke their callbacks (the callback doesn't need to invoke the
2227	loop strictly lower priority for example). You can also set the callback	2788	C<ev_embed_sweep> function directly, it could also start an idle watcher
2228	to C<0>, in which case the embed watcher will automatically execute the	2789	to give the embedded loop strictly lower priority for example).
2229	embedded loop sweep.
2230		2790
2231	As long as the watcher is started it will automatically handle events. The	2791	You can also set the callback to C<0>, in which case the embed watcher
2232	callback will be invoked whenever some events have been handled. You can	2792	will automatically execute the embedded loop sweep whenever necessary.
2233	set the callback to C<0> to avoid having to specify one if you are not
2234	interested in that.
2235		2793
2236	Also, there have not currently been made special provisions for forking:	2794	Fork detection will be handled transparently while the C<ev_embed> watcher
2237	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2795	is active, i.e., the embedded loop will automatically be forked when the
2238	but you will also have to stop and restart any C<ev_embed> watchers	2796	embedding loop forks. In other cases, the user is responsible for calling
2239	yourself - but you can use a fork watcher to handle this automatically,	2797	C<ev_loop_fork> on the embedded loop.
2240	and future versions of libev might do just that.
2241		2798
2242	Unfortunately, not all backends are embeddable: only the ones returned by	2799	Unfortunately, not all backends are embeddable: only the ones returned by
2243	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2800	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2244	portable one.	2801	portable one.
2245		2802
…		…
2290	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2847	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2291	used).	2848	used).
2292		2849
2293	struct ev_loop *loop_hi = ev_default_init (0);	2850	struct ev_loop *loop_hi = ev_default_init (0);
2294	struct ev_loop *loop_lo = 0;	2851	struct ev_loop *loop_lo = 0;
2295	struct ev_embed embed;	2852	ev_embed embed;
2296		2853
2297	// see if there is a chance of getting one that works	2854	// see if there is a chance of getting one that works
2298	// (remember that a flags value of 0 means autodetection)	2855	// (remember that a flags value of 0 means autodetection)
2299	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2856	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2300	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2857	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2314	kqueue implementation). Store the kqueue/socket-only event loop in	2871	kqueue implementation). Store the kqueue/socket-only event loop in
2315	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2872	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2316		2873
2317	struct ev_loop *loop = ev_default_init (0);	2874	struct ev_loop *loop = ev_default_init (0);
2318	struct ev_loop *loop_socket = 0;	2875	struct ev_loop *loop_socket = 0;
2319	struct ev_embed embed;	2876	ev_embed embed;
2320		2877
2321	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2878	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2322	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2879	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2323	{	2880	{
2324	ev_embed_init (&embed, 0, loop_socket);	2881	ev_embed_init (&embed, 0, loop_socket);
…		…
2339	event loop blocks next and before C<ev_check> watchers are being called,	2896	event loop blocks next and before C<ev_check> watchers are being called,
2340	and only in the child after the fork. If whoever good citizen calling	2897	and only in the child after the fork. If whoever good citizen calling
2341	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2898	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2342	handlers will be invoked, too, of course.	2899	handlers will be invoked, too, of course.
2343		2900
		2901	=head3 The special problem of life after fork - how is it possible?
		2902
		2903	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2904	up/change the process environment, followed by a call to C<exec()>. This
		2905	sequence should be handled by libev without any problems.
		2906
		2907	This changes when the application actually wants to do event handling
		2908	in the child, or both parent in child, in effect "continuing" after the
		2909	fork.
		2910
		2911	The default mode of operation (for libev, with application help to detect
		2912	forks) is to duplicate all the state in the child, as would be expected
		2913	when I<either> the parent I<or> the child process continues.
		2914
		2915	When both processes want to continue using libev, then this is usually the
		2916	wrong result. In that case, usually one process (typically the parent) is
		2917	supposed to continue with all watchers in place as before, while the other
		2918	process typically wants to start fresh, i.e. without any active watchers.
		2919
		2920	The cleanest and most efficient way to achieve that with libev is to
		2921	simply create a new event loop, which of course will be "empty", and
		2922	use that for new watchers. This has the advantage of not touching more
		2923	memory than necessary, and thus avoiding the copy-on-write, and the
		2924	disadvantage of having to use multiple event loops (which do not support
		2925	signal watchers).
		2926
		2927	When this is not possible, or you want to use the default loop for
		2928	other reasons, then in the process that wants to start "fresh", call
		2929	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2930	the default loop will "orphan" (not stop) all registered watchers, so you
		2931	have to be careful not to execute code that modifies those watchers. Note
		2932	also that in that case, you have to re-register any signal watchers.
		2933
2344	=head3 Watcher-Specific Functions and Data Members	2934	=head3 Watcher-Specific Functions and Data Members
2345		2935
2346	=over 4	2936	=over 4
2347		2937
2348	=item ev_fork_init (ev_signal *, callback)	2938	=item ev_fork_init (ev_signal *, callback)
…		…
2465	=over 4	3055	=over 4
2466		3056
2467	=item ev_async_init (ev_async *, callback)	3057	=item ev_async_init (ev_async *, callback)
2468		3058
2469	Initialises and configures the async watcher - it has no parameters of any	3059	Initialises and configures the async watcher - it has no parameters of any
2470	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3060	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2471	trust me.	3061	trust me.
2472		3062
2473	=item ev_async_send (loop, ev_async *)	3063	=item ev_async_send (loop, ev_async *)
2474		3064
2475	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3065	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2476	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3066	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2477	C<ev_feed_event>, this call is safe to do from other threads, signal or	3067	C<ev_feed_event>, this call is safe to do from other threads, signal or
2478	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3068	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2479	section below on what exactly this means).	3069	section below on what exactly this means).
2480		3070
		3071	Note that, as with other watchers in libev, multiple events might get
		3072	compressed into a single callback invocation (another way to look at this
		3073	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3074	reset when the event loop detects that).
		3075
2481	This call incurs the overhead of a system call only once per loop iteration,	3076	This call incurs the overhead of a system call only once per event loop
2482	so while the overhead might be noticeable, it doesn't apply to repeated	3077	iteration, so while the overhead might be noticeable, it doesn't apply to
2483	calls to C<ev_async_send>.	3078	repeated calls to C<ev_async_send> for the same event loop.
2484		3079
2485	=item bool = ev_async_pending (ev_async *)	3080	=item bool = ev_async_pending (ev_async *)
2486		3081
2487	Returns a non-zero value when C<ev_async_send> has been called on the	3082	Returns a non-zero value when C<ev_async_send> has been called on the
2488	watcher but the event has not yet been processed (or even noted) by the	3083	watcher but the event has not yet been processed (or even noted) by the
…		…
2491	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3086	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2492	the loop iterates next and checks for the watcher to have become active,	3087	the loop iterates next and checks for the watcher to have become active,
2493	it will reset the flag again. C<ev_async_pending> can be used to very	3088	it will reset the flag again. C<ev_async_pending> can be used to very
2494	quickly check whether invoking the loop might be a good idea.	3089	quickly check whether invoking the loop might be a good idea.
2495		3090
2496	Not that this does I<not> check whether the watcher itself is pending, only	3091	Not that this does I<not> check whether the watcher itself is pending,
2497	whether it has been requested to make this watcher pending.	3092	only whether it has been requested to make this watcher pending: there
		3093	is a time window between the event loop checking and resetting the async
		3094	notification, and the callback being invoked.
2498		3095
2499	=back	3096	=back
2500		3097
2501		3098
2502	=head1 OTHER FUNCTIONS	3099	=head1 OTHER FUNCTIONS
…		…
2538	/* doh, nothing entered */;	3135	/* doh, nothing entered */;
2539	}	3136	}
2540		3137
2541	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3138	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2542		3139
2543	=item ev_feed_event (ev_loop *, watcher *, int revents)	3140	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2544		3141
2545	Feeds the given event set into the event loop, as if the specified event	3142	Feeds the given event set into the event loop, as if the specified event
2546	had happened for the specified watcher (which must be a pointer to an	3143	had happened for the specified watcher (which must be a pointer to an
2547	initialised but not necessarily started event watcher).	3144	initialised but not necessarily started event watcher).
2548		3145
2549	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3146	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2550		3147
2551	Feed an event on the given fd, as if a file descriptor backend detected	3148	Feed an event on the given fd, as if a file descriptor backend detected
2552	the given events it.	3149	the given events it.
2553		3150
2554	=item ev_feed_signal_event (ev_loop *loop, int signum)	3151	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2555		3152
2556	Feed an event as if the given signal occurred (C<loop> must be the default	3153	Feed an event as if the given signal occurred (C<loop> must be the default
2557	loop!).	3154	loop!).
2558		3155
2559	=back	3156	=back
…		…
2680	}	3277	}
2681		3278
2682	myclass obj;	3279	myclass obj;
2683	ev::io iow;	3280	ev::io iow;
2684	iow.set <myclass, &myclass::io_cb> (&obj);	3281	iow.set <myclass, &myclass::io_cb> (&obj);
		3282
		3283	=item w->set (object *)
		3284
		3285	This is an B<experimental> feature that might go away in a future version.
		3286
		3287	This is a variation of a method callback - leaving out the method to call
		3288	will default the method to C<operator ()>, which makes it possible to use
		3289	functor objects without having to manually specify the C<operator ()> all
		3290	the time. Incidentally, you can then also leave out the template argument
		3291	list.
		3292
		3293	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3294	int revents)>.
		3295
		3296	See the method-C<set> above for more details.
		3297
		3298	Example: use a functor object as callback.
		3299
		3300	struct myfunctor
		3301	{
		3302	void operator() (ev::io &w, int revents)
		3303	{
		3304	...
		3305	}
		3306	}
		3307
		3308	myfunctor f;
		3309
		3310	ev::io w;
		3311	w.set (&f);
2685		3312
2686	=item w->set<function> (void *data = 0)	3313	=item w->set<function> (void *data = 0)
2687		3314
2688	Also sets a callback, but uses a static method or plain function as	3315	Also sets a callback, but uses a static method or plain function as
2689	callback. The optional C<data> argument will be stored in the watcher's	3316	callback. The optional C<data> argument will be stored in the watcher's
…		…
2776	L<http://software.schmorp.de/pkg/EV>.	3403	L<http://software.schmorp.de/pkg/EV>.
2777		3404
2778	=item Python	3405	=item Python
2779		3406
2780	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3407	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2781	seems to be quite complete and well-documented. Note, however, that the	3408	seems to be quite complete and well-documented.
2782	patch they require for libev is outright dangerous as it breaks the ABI
2783	for everybody else, and therefore, should never be applied in an installed
2784	libev (if python requires an incompatible ABI then it needs to embed
2785	libev).
2786		3409
2787	=item Ruby	3410	=item Ruby
2788		3411
2789	Tony Arcieri has written a ruby extension that offers access to a subset	3412	Tony Arcieri has written a ruby extension that offers access to a subset
2790	of the libev API and adds file handle abstractions, asynchronous DNS and	3413	of the libev API and adds file handle abstractions, asynchronous DNS and
2791	more on top of it. It can be found via gem servers. Its homepage is at	3414	more on top of it. It can be found via gem servers. Its homepage is at
2792	L<http://rev.rubyforge.org/>.	3415	L<http://rev.rubyforge.org/>.
2793		3416
		3417	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3418	makes rev work even on mingw.
		3419
		3420	=item Haskell
		3421
		3422	A haskell binding to libev is available at
		3423	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3424
2794	=item D	3425	=item D
2795		3426
2796	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3427	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2797	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3428	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3429
		3430	=item Ocaml
		3431
		3432	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3433	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3434
		3435	=item Lua
		3436
		3437	Brian Maher has written a partial interface to libev
		3438	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3439	L<http://github.com/brimworks/lua-ev>.
2798		3440
2799	=back	3441	=back
2800		3442
2801		3443
2802	=head1 MACRO MAGIC	3444	=head1 MACRO MAGIC
…		…
2903		3545
2904	#define EV_STANDALONE 1	3546	#define EV_STANDALONE 1
2905	#include "ev.h"	3547	#include "ev.h"
2906		3548
2907	Both header files and implementation files can be compiled with a C++	3549	Both header files and implementation files can be compiled with a C++
2908	compiler (at least, thats a stated goal, and breakage will be treated	3550	compiler (at least, that's a stated goal, and breakage will be treated
2909	as a bug).	3551	as a bug).
2910		3552
2911	You need the following files in your source tree, or in a directory	3553	You need the following files in your source tree, or in a directory
2912	in your include path (e.g. in libev/ when using -Ilibev):	3554	in your include path (e.g. in libev/ when using -Ilibev):
2913		3555
…		…
2969	keeps libev from including F<config.h>, and it also defines dummy	3611	keeps libev from including F<config.h>, and it also defines dummy
2970	implementations for some libevent functions (such as logging, which is not	3612	implementations for some libevent functions (such as logging, which is not
2971	supported). It will also not define any of the structs usually found in	3613	supported). It will also not define any of the structs usually found in
2972	F<event.h> that are not directly supported by the libev core alone.	3614	F<event.h> that are not directly supported by the libev core alone.
2973		3615
		3616	In standalone mode, libev will still try to automatically deduce the
		3617	configuration, but has to be more conservative.
		3618
2974	=item EV_USE_MONOTONIC	3619	=item EV_USE_MONOTONIC
2975		3620
2976	If defined to be C<1>, libev will try to detect the availability of the	3621	If defined to be C<1>, libev will try to detect the availability of the
2977	monotonic clock option at both compile time and runtime. Otherwise no use	3622	monotonic clock option at both compile time and runtime. Otherwise no
2978	of the monotonic clock option will be attempted. If you enable this, you	3623	use of the monotonic clock option will be attempted. If you enable this,
2979	usually have to link against librt or something similar. Enabling it when	3624	you usually have to link against librt or something similar. Enabling it
2980	the functionality isn't available is safe, though, although you have	3625	when the functionality isn't available is safe, though, although you have
2981	to make sure you link against any libraries where the C<clock_gettime>	3626	to make sure you link against any libraries where the C<clock_gettime>
2982	function is hiding in (often F<-lrt>).	3627	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2983		3628
2984	=item EV_USE_REALTIME	3629	=item EV_USE_REALTIME
2985		3630
2986	If defined to be C<1>, libev will try to detect the availability of the	3631	If defined to be C<1>, libev will try to detect the availability of the
2987	real-time clock option at compile time (and assume its availability at	3632	real-time clock option at compile time (and assume its availability
2988	runtime if successful). Otherwise no use of the real-time clock option will	3633	at runtime if successful). Otherwise no use of the real-time clock
2989	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3634	option will be attempted. This effectively replaces C<gettimeofday>
2990	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3635	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2991	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3636	correctness. See the note about libraries in the description of
		3637	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3638	C<EV_USE_CLOCK_SYSCALL>.
		3639
		3640	=item EV_USE_CLOCK_SYSCALL
		3641
		3642	If defined to be C<1>, libev will try to use a direct syscall instead
		3643	of calling the system-provided C<clock_gettime> function. This option
		3644	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3645	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3646	programs needlessly. Using a direct syscall is slightly slower (in
		3647	theory), because no optimised vdso implementation can be used, but avoids
		3648	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3649	higher, as it simplifies linking (no need for C<-lrt>).
2992		3650
2993	=item EV_USE_NANOSLEEP	3651	=item EV_USE_NANOSLEEP
2994		3652
2995	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3653	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2996	and will use it for delays. Otherwise it will use C<select ()>.	3654	and will use it for delays. Otherwise it will use C<select ()>.
…		…
3012		3670
3013	=item EV_SELECT_USE_FD_SET	3671	=item EV_SELECT_USE_FD_SET
3014		3672
3015	If defined to C<1>, then the select backend will use the system C<fd_set>	3673	If defined to C<1>, then the select backend will use the system C<fd_set>
3016	structure. This is useful if libev doesn't compile due to a missing	3674	structure. This is useful if libev doesn't compile due to a missing
3017	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3675	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
3018	exotic systems. This usually limits the range of file descriptors to some	3676	on exotic systems. This usually limits the range of file descriptors to
3019	low limit such as 1024 or might have other limitations (winsocket only	3677	some low limit such as 1024 or might have other limitations (winsocket
3020	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3678	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
3021	influence the size of the C<fd_set> used.	3679	configures the maximum size of the C<fd_set>.
3022		3680
3023	=item EV_SELECT_IS_WINSOCKET	3681	=item EV_SELECT_IS_WINSOCKET
3024		3682
3025	When defined to C<1>, the select backend will assume that	3683	When defined to C<1>, the select backend will assume that
3026	select/socket/connect etc. don't understand file descriptors but	3684	select/socket/connect etc. don't understand file descriptors but
…		…
3028	be used is the winsock select). This means that it will call	3686	be used is the winsock select). This means that it will call
3029	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3687	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
3030	it is assumed that all these functions actually work on fds, even	3688	it is assumed that all these functions actually work on fds, even
3031	on win32. Should not be defined on non-win32 platforms.	3689	on win32. Should not be defined on non-win32 platforms.
3032		3690
3033	=item EV_FD_TO_WIN32_HANDLE	3691	=item EV_FD_TO_WIN32_HANDLE(fd)
3034		3692
3035	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3693	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
3036	file descriptors to socket handles. When not defining this symbol (the	3694	file descriptors to socket handles. When not defining this symbol (the
3037	default), then libev will call C<_get_osfhandle>, which is usually	3695	default), then libev will call C<_get_osfhandle>, which is usually
3038	correct. In some cases, programs use their own file descriptor management,	3696	correct. In some cases, programs use their own file descriptor management,
3039	in which case they can provide this function to map fds to socket handles.	3697	in which case they can provide this function to map fds to socket handles.
		3698
		3699	=item EV_WIN32_HANDLE_TO_FD(handle)
		3700
		3701	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3702	using the standard C<_open_osfhandle> function. For programs implementing
		3703	their own fd to handle mapping, overwriting this function makes it easier
		3704	to do so. This can be done by defining this macro to an appropriate value.
		3705
		3706	=item EV_WIN32_CLOSE_FD(fd)
		3707
		3708	If programs implement their own fd to handle mapping on win32, then this
		3709	macro can be used to override the C<close> function, useful to unregister
		3710	file descriptors again. Note that the replacement function has to close
		3711	the underlying OS handle.
3040		3712
3041	=item EV_USE_POLL	3713	=item EV_USE_POLL
3042		3714
3043	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3715	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3044	backend. Otherwise it will be enabled on non-win32 platforms. It	3716	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3176	defined to be C<0>, then they are not.	3848	defined to be C<0>, then they are not.
3177		3849
3178	=item EV_MINIMAL	3850	=item EV_MINIMAL
3179		3851
3180	If you need to shave off some kilobytes of code at the expense of some	3852	If you need to shave off some kilobytes of code at the expense of some
3181	speed, define this symbol to C<1>. Currently this is used to override some	3853	speed (but with the full API), define this symbol to C<1>. Currently this
3182	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3854	is used to override some inlining decisions, saves roughly 30% code size
3183	much smaller 2-heap for timer management over the default 4-heap.	3855	on amd64. It also selects a much smaller 2-heap for timer management over
		3856	the default 4-heap.
		3857
		3858	You can save even more by disabling watcher types you do not need
		3859	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3860	(C<-DNDEBUG>) will usually reduce code size a lot.
		3861
		3862	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3863	provide a bare-bones event library. See C<ev.h> for details on what parts
		3864	of the API are still available, and do not complain if this subset changes
		3865	over time.
		3866
		3867	=item EV_NSIG
		3868
		3869	The highest supported signal number, +1 (or, the number of
		3870	signals): Normally, libev tries to deduce the maximum number of signals
		3871	automatically, but sometimes this fails, in which case it can be
		3872	specified. Also, using a lower number than detected (C<32> should be
		3873	good for about any system in existance) can save some memory, as libev
		3874	statically allocates some 12-24 bytes per signal number.
3184		3875
3185	=item EV_PID_HASHSIZE	3876	=item EV_PID_HASHSIZE
3186		3877
3187	C<ev_child> watchers use a small hash table to distribute workload by	3878	C<ev_child> watchers use a small hash table to distribute workload by
3188	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3879	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3374	default loop and triggering an C<ev_async> watcher from the default loop	4065	default loop and triggering an C<ev_async> watcher from the default loop
3375	watcher callback into the event loop interested in the signal.	4066	watcher callback into the event loop interested in the signal.
3376		4067
3377	=back	4068	=back
3378		4069
		4070	=head4 THREAD LOCKING EXAMPLE
		4071
		4072	Here is a fictitious example of how to run an event loop in a different
		4073	thread than where callbacks are being invoked and watchers are
		4074	created/added/removed.
		4075
		4076	For a real-world example, see the C<EV::Loop::Async> perl module,
		4077	which uses exactly this technique (which is suited for many high-level
		4078	languages).
		4079
		4080	The example uses a pthread mutex to protect the loop data, a condition
		4081	variable to wait for callback invocations, an async watcher to notify the
		4082	event loop thread and an unspecified mechanism to wake up the main thread.
		4083
		4084	First, you need to associate some data with the event loop:
		4085
		4086	typedef struct {
		4087	mutex_t lock; /* global loop lock */
		4088	ev_async async_w;
		4089	thread_t tid;
		4090	cond_t invoke_cv;
		4091	} userdata;
		4092
		4093	void prepare_loop (EV_P)
		4094	{
		4095	// for simplicity, we use a static userdata struct.
		4096	static userdata u;
		4097
		4098	ev_async_init (&u->async_w, async_cb);
		4099	ev_async_start (EV_A_ &u->async_w);
		4100
		4101	pthread_mutex_init (&u->lock, 0);
		4102	pthread_cond_init (&u->invoke_cv, 0);
		4103
		4104	// now associate this with the loop
		4105	ev_set_userdata (EV_A_ u);
		4106	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4107	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4108
		4109	// then create the thread running ev_loop
		4110	pthread_create (&u->tid, 0, l_run, EV_A);
		4111	}
		4112
		4113	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4114	solely to wake up the event loop so it takes notice of any new watchers
		4115	that might have been added:
		4116
		4117	static void
		4118	async_cb (EV_P_ ev_async *w, int revents)
		4119	{
		4120	// just used for the side effects
		4121	}
		4122
		4123	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4124	protecting the loop data, respectively.
		4125
		4126	static void
		4127	l_release (EV_P)
		4128	{
		4129	userdata *u = ev_userdata (EV_A);
		4130	pthread_mutex_unlock (&u->lock);
		4131	}
		4132
		4133	static void
		4134	l_acquire (EV_P)
		4135	{
		4136	userdata *u = ev_userdata (EV_A);
		4137	pthread_mutex_lock (&u->lock);
		4138	}
		4139
		4140	The event loop thread first acquires the mutex, and then jumps straight
		4141	into C<ev_loop>:
		4142
		4143	void *
		4144	l_run (void *thr_arg)
		4145	{
		4146	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4147
		4148	l_acquire (EV_A);
		4149	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4150	ev_loop (EV_A_ 0);
		4151	l_release (EV_A);
		4152
		4153	return 0;
		4154	}
		4155
		4156	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4157	signal the main thread via some unspecified mechanism (signals? pipe
		4158	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4159	have been called (in a while loop because a) spurious wakeups are possible
		4160	and b) skipping inter-thread-communication when there are no pending
		4161	watchers is very beneficial):
		4162
		4163	static void
		4164	l_invoke (EV_P)
		4165	{
		4166	userdata *u = ev_userdata (EV_A);
		4167
		4168	while (ev_pending_count (EV_A))
		4169	{
		4170	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4171	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4172	}
		4173	}
		4174
		4175	Now, whenever the main thread gets told to invoke pending watchers, it
		4176	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4177	thread to continue:
		4178
		4179	static void
		4180	real_invoke_pending (EV_P)
		4181	{
		4182	userdata *u = ev_userdata (EV_A);
		4183
		4184	pthread_mutex_lock (&u->lock);
		4185	ev_invoke_pending (EV_A);
		4186	pthread_cond_signal (&u->invoke_cv);
		4187	pthread_mutex_unlock (&u->lock);
		4188	}
		4189
		4190	Whenever you want to start/stop a watcher or do other modifications to an
		4191	event loop, you will now have to lock:
		4192
		4193	ev_timer timeout_watcher;
		4194	userdata *u = ev_userdata (EV_A);
		4195
		4196	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4197
		4198	pthread_mutex_lock (&u->lock);
		4199	ev_timer_start (EV_A_ &timeout_watcher);
		4200	ev_async_send (EV_A_ &u->async_w);
		4201	pthread_mutex_unlock (&u->lock);
		4202
		4203	Note that sending the C<ev_async> watcher is required because otherwise
		4204	an event loop currently blocking in the kernel will have no knowledge
		4205	about the newly added timer. By waking up the loop it will pick up any new
		4206	watchers in the next event loop iteration.
		4207
3379	=head3 COROUTINES	4208	=head3 COROUTINES
3380		4209
3381	Libev is very accommodating to coroutines ("cooperative threads"):	4210	Libev is very accommodating to coroutines ("cooperative threads"):
3382	libev fully supports nesting calls to its functions from different	4211	libev fully supports nesting calls to its functions from different
3383	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4212	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3384	different coroutines, and switch freely between both coroutines running the	4213	different coroutines, and switch freely between both coroutines running
3385	loop, as long as you don't confuse yourself). The only exception is that	4214	the loop, as long as you don't confuse yourself). The only exception is
3386	you must not do this from C<ev_periodic> reschedule callbacks.	4215	that you must not do this from C<ev_periodic> reschedule callbacks.
3387		4216
3388	Care has been taken to ensure that libev does not keep local state inside	4217	Care has been taken to ensure that libev does not keep local state inside
3389	C<ev_loop>, and other calls do not usually allow for coroutine switches as	4218	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3390	they do not clal any callbacks.	4219	they do not call any callbacks.
3391		4220
3392	=head2 COMPILER WARNINGS	4221	=head2 COMPILER WARNINGS
3393		4222
3394	Depending on your compiler and compiler settings, you might get no or a	4223	Depending on your compiler and compiler settings, you might get no or a
3395	lot of warnings when compiling libev code. Some people are apparently	4224	lot of warnings when compiling libev code. Some people are apparently
…		…
3429	==2274== definitely lost: 0 bytes in 0 blocks.	4258	==2274== definitely lost: 0 bytes in 0 blocks.
3430	==2274== possibly lost: 0 bytes in 0 blocks.	4259	==2274== possibly lost: 0 bytes in 0 blocks.
3431	==2274== still reachable: 256 bytes in 1 blocks.	4260	==2274== still reachable: 256 bytes in 1 blocks.
3432		4261
3433	Then there is no memory leak, just as memory accounted to global variables	4262	Then there is no memory leak, just as memory accounted to global variables
3434	is not a memleak - the memory is still being refernced, and didn't leak.	4263	is not a memleak - the memory is still being referenced, and didn't leak.
3435		4264
3436	Similarly, under some circumstances, valgrind might report kernel bugs	4265	Similarly, under some circumstances, valgrind might report kernel bugs
3437	as if it were a bug in libev (e.g. in realloc or in the poll backend,	4266	as if it were a bug in libev (e.g. in realloc or in the poll backend,
3438	although an acceptable workaround has been found here), or it might be	4267	although an acceptable workaround has been found here), or it might be
3439	confused.	4268	confused.
…		…
3468	way (note also that glib is the slowest event library known to man).	4297	way (note also that glib is the slowest event library known to man).
3469		4298
3470	There is no supported compilation method available on windows except	4299	There is no supported compilation method available on windows except
3471	embedding it into other applications.	4300	embedding it into other applications.
3472		4301
		4302	Sensible signal handling is officially unsupported by Microsoft - libev
		4303	tries its best, but under most conditions, signals will simply not work.
		4304
3473	Not a libev limitation but worth mentioning: windows apparently doesn't	4305	Not a libev limitation but worth mentioning: windows apparently doesn't
3474	accept large writes: instead of resulting in a partial write, windows will	4306	accept large writes: instead of resulting in a partial write, windows will
3475	either accept everything or return C<ENOBUFS> if the buffer is too large,	4307	either accept everything or return C<ENOBUFS> if the buffer is too large,
3476	so make sure you only write small amounts into your sockets (less than a	4308	so make sure you only write small amounts into your sockets (less than a
3477	megabyte seems safe, but this apparently depends on the amount of memory	4309	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3481	the abysmal performance of winsockets, using a large number of sockets	4313	the abysmal performance of winsockets, using a large number of sockets
3482	is not recommended (and not reasonable). If your program needs to use	4314	is not recommended (and not reasonable). If your program needs to use
3483	more than a hundred or so sockets, then likely it needs to use a totally	4315	more than a hundred or so sockets, then likely it needs to use a totally
3484	different implementation for windows, as libev offers the POSIX readiness	4316	different implementation for windows, as libev offers the POSIX readiness
3485	notification model, which cannot be implemented efficiently on windows	4317	notification model, which cannot be implemented efficiently on windows
3486	(Microsoft monopoly games).	4318	(due to Microsoft monopoly games).
3487		4319
3488	A typical way to use libev under windows is to embed it (see the embedding	4320	A typical way to use libev under windows is to embed it (see the embedding
3489	section for details) and use the following F<evwrap.h> header file instead	4321	section for details) and use the following F<evwrap.h> header file instead
3490	of F<ev.h>:	4322	of F<ev.h>:
3491		4323
…		…
3527		4359
3528	Early versions of winsocket's select only supported waiting for a maximum	4360	Early versions of winsocket's select only supported waiting for a maximum
3529	of C<64> handles (probably owning to the fact that all windows kernels	4361	of C<64> handles (probably owning to the fact that all windows kernels
3530	can only wait for C<64> things at the same time internally; Microsoft	4362	can only wait for C<64> things at the same time internally; Microsoft
3531	recommends spawning a chain of threads and wait for 63 handles and the	4363	recommends spawning a chain of threads and wait for 63 handles and the
3532	previous thread in each. Great).	4364	previous thread in each. Sounds great!).
3533		4365
3534	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4366	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3535	to some high number (e.g. C<2048>) before compiling the winsocket select	4367	to some high number (e.g. C<2048>) before compiling the winsocket select
3536	call (which might be in libev or elsewhere, for example, perl does its own	4368	call (which might be in libev or elsewhere, for example, perl and many
3537	select emulation on windows).	4369	other interpreters do their own select emulation on windows).
3538		4370
3539	Another limit is the number of file descriptors in the Microsoft runtime	4371	Another limit is the number of file descriptors in the Microsoft runtime
3540	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4372	libraries, which by default is C<64> (there must be a hidden I<64>
3541	or something like this inside Microsoft). You can increase this by calling	4373	fetish or something like this inside Microsoft). You can increase this
3542	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4374	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3543	arbitrary limit), but is broken in many versions of the Microsoft runtime	4375	(another arbitrary limit), but is broken in many versions of the Microsoft
3544	libraries.
3545
3546	This might get you to about C<512> or C<2048> sockets (depending on	4376	runtime libraries. This might get you to about C<512> or C<2048> sockets
3547	windows version and/or the phase of the moon). To get more, you need to	4377	(depending on windows version and/or the phase of the moon). To get more,
3548	wrap all I/O functions and provide your own fd management, but the cost of	4378	you need to wrap all I/O functions and provide your own fd management, but
3549	calling select (O(n²)) will likely make this unworkable.	4379	the cost of calling select (O(n²)) will likely make this unworkable.
3550		4380
3551	=back	4381	=back
3552		4382
3553	=head2 PORTABILITY REQUIREMENTS	4383	=head2 PORTABILITY REQUIREMENTS
3554		4384
…		…
3597	=item C<double> must hold a time value in seconds with enough accuracy	4427	=item C<double> must hold a time value in seconds with enough accuracy
3598		4428
3599	The type C<double> is used to represent timestamps. It is required to	4429	The type C<double> is used to represent timestamps. It is required to
3600	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4430	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3601	enough for at least into the year 4000. This requirement is fulfilled by	4431	enough for at least into the year 4000. This requirement is fulfilled by
3602	implementations implementing IEEE 754 (basically all existing ones).	4432	implementations implementing IEEE 754, which is basically all existing
		4433	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4434	2200.
3603		4435
3604	=back	4436	=back
3605		4437
3606	If you know of other additional requirements drop me a note.	4438	If you know of other additional requirements drop me a note.
3607		4439
…		…
3675	involves iterating over all running async watchers or all signal numbers.	4507	involves iterating over all running async watchers or all signal numbers.
3676		4508
3677	=back	4509	=back
3678		4510
3679		4511
		4512	=head1 GLOSSARY
		4513
		4514	=over 4
		4515
		4516	=item active
		4517
		4518	A watcher is active as long as it has been started (has been attached to
		4519	an event loop) but not yet stopped (disassociated from the event loop).
		4520
		4521	=item application
		4522
		4523	In this document, an application is whatever is using libev.
		4524
		4525	=item callback
		4526
		4527	The address of a function that is called when some event has been
		4528	detected. Callbacks are being passed the event loop, the watcher that
		4529	received the event, and the actual event bitset.
		4530
		4531	=item callback invocation
		4532
		4533	The act of calling the callback associated with a watcher.
		4534
		4535	=item event
		4536
		4537	A change of state of some external event, such as data now being available
		4538	for reading on a file descriptor, time having passed or simply not having
		4539	any other events happening anymore.
		4540
		4541	In libev, events are represented as single bits (such as C<EV_READ> or
		4542	C<EV_TIMEOUT>).
		4543
		4544	=item event library
		4545
		4546	A software package implementing an event model and loop.
		4547
		4548	=item event loop
		4549
		4550	An entity that handles and processes external events and converts them
		4551	into callback invocations.
		4552
		4553	=item event model
		4554
		4555	The model used to describe how an event loop handles and processes
		4556	watchers and events.
		4557
		4558	=item pending
		4559
		4560	A watcher is pending as soon as the corresponding event has been detected,
		4561	and stops being pending as soon as the watcher will be invoked or its
		4562	pending status is explicitly cleared by the application.
		4563
		4564	A watcher can be pending, but not active. Stopping a watcher also clears
		4565	its pending status.
		4566
		4567	=item real time
		4568
		4569	The physical time that is observed. It is apparently strictly monotonic :)
		4570
		4571	=item wall-clock time
		4572
		4573	The time and date as shown on clocks. Unlike real time, it can actually
		4574	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4575	clock.
		4576
		4577	=item watcher
		4578
		4579	A data structure that describes interest in certain events. Watchers need
		4580	to be started (attached to an event loop) before they can receive events.
		4581
		4582	=item watcher invocation
		4583
		4584	The act of calling the callback associated with a watcher.
		4585
		4586	=back
		4587
3680	=head1 AUTHOR	4588	=head1 AUTHOR
3681		4589
3682	Marc Lehmann <libev@schmorp.de>.	4590	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3683		4591

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