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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
…		…
41		43
42	int	44	int
43	main (void)	45	main (void)
44	{	46	{
45	// use the default event loop unless you have special needs	47	// use the default event loop unless you have special needs
46	ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
47		49
48	// initialise an io watcher, then start it	50	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	51	// this one will watch for stdin to become readable
50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
51	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
…		…
60		62
61	// unloop was called, so exit	63	// unloop was called, so exit
62	return 0;	64	return 0;
63	}	65	}
64		66
65	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
66		70
67	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
70		84
71	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	87	these event sources and provide your program with events.
74		88
…		…
84	=head2 FEATURES	98	=head2 FEATURES
85		99
86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
91	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
94	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
96		111
97	It also is quite fast (see this	112	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	114	for example).
100		115
…		…
108	name C<loop> (which is always of type C<ev_loop *>) will not have	123	name C<loop> (which is always of type C<ev_loop *>) will not have
109	this argument.	124	this argument.
110		125
111	=head2 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
112		127
113	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
115	the beginning of 1970, details are complicated, don't ask). This type is	130	near the beginning of 1970, details are complicated, don't ask). This
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	type is called C<ev_tstamp>, which is what you should use too. It usually
117	to the C<double> type in C, and when you need to do any calculations on	132	aliases to the C<double> type in C. When you need to do any calculations
118	it, you should treat it as some floating point value. Unlike the name	133	on it, you should treat it as some floating point value. Unlike the name
119	component C<stamp> might indicate, it is also used for time differences	134	component C<stamp> might indicate, it is also used for time differences
120	throughout libev.	135	throughout libev.
121		136
122	=head1 ERROR HANDLING	137	=head1 ERROR HANDLING
123		138
…		…
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<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_NOSIGNALFD>
		376
		377	When this flag is specified, then libev will not attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		379	probably only useful to work around any bugs in libev. Consequently, this
		380	flag might go away once the signalfd functionality is considered stable,
		381	so it's useful mostly in environment variables and not in program code.
		382
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
…		…
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	414	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		415
382	For few fds, this backend is a bit little slower than poll and select,	416	For few fds, this backend is a bit little slower than poll and select,
383	but it scales phenomenally better. While poll and select usually scale	417	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),	418	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	419	epoll scales either O(1) or O(active_fds).
386	of shortcomings, such as silently dropping events in some hard-to-detect	420
387	cases and requiring a system call per fd change, no fork support and bad	421	The epoll mechanism deserves honorable mention as the most misdesigned
388	support for dup.	422	of the more advanced event mechanisms: mere annoyances include silently
		423	dropping file descriptors, requiring a system call per change per file
		424	descriptor (and unnecessary guessing of parameters), problems with dup and
		425	so on. The biggest issue is fork races, however - if a program forks then
		426	I<both> parent and child process have to recreate the epoll set, which can
		427	take considerable time (one syscall per file descriptor) and is of course
		428	hard to detect.
		429
		430	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		431	of course I<doesn't>, and epoll just loves to report events for totally
		432	I<different> file descriptors (even already closed ones, so one cannot
		433	even remove them from the set) than registered in the set (especially
		434	on SMP systems). Libev tries to counter these spurious notifications by
		435	employing an additional generation counter and comparing that against the
		436	events to filter out spurious ones, recreating the set when required.
389		437
390	While stopping, setting and starting an I/O watcher in the same iteration	438	While stopping, setting and starting an I/O watcher in the same iteration
391	will result in some caching, there is still a system call per such incident	439	will result in some caching, there is still a system call per such
392	(because the fd could point to a different file description now), so its	440	incident (because the same I<file descriptor> could point to a different
393	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	441	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
394	very well if you register events for both fds.	442	file descriptors might not work very well if you register events for both
395		443	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		444
400	Best performance from this backend is achieved by not unregistering all	445	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible,	446	watchers for a file descriptor until it has been closed, if possible,
402	i.e. keep at least one watcher active per fd at all times. Stopping and	447	i.e. keep at least one watcher active per fd at all times. Stopping and
403	starting a watcher (without re-setting it) also usually doesn't cause	448	starting a watcher (without re-setting it) also usually doesn't cause
404	extra overhead.	449	extra overhead. A fork can both result in spurious notifications as well
		450	as in libev having to destroy and recreate the epoll object, which can
		451	take considerable time and thus should be avoided.
		452
		453	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		454	faster than epoll for maybe up to a hundred file descriptors, depending on
		455	the usage. So sad.
405		456
406	While nominally embeddable in other event loops, this feature is broken in	457	While nominally embeddable in other event loops, this feature is broken in
407	all kernel versions tested so far.	458	all kernel versions tested so far.
408		459
409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	460	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
410	C<EVBACKEND_POLL>.	461	C<EVBACKEND_POLL>.
411		462
412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	463	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
413		464
414	Kqueue deserves special mention, as at the time of this writing, it was	465	Kqueue deserves special mention, as at the time of this writing, it
415	broken on all BSDs except NetBSD (usually it doesn't work reliably with	466	was broken on all BSDs except NetBSD (usually it doesn't work reliably
416	anything but sockets and pipes, except on Darwin, where of course it's	467	with anything but sockets and pipes, except on Darwin, where of course
417	completely useless). For this reason it's not being "auto-detected" unless	468	it's completely useless). Unlike epoll, however, whose brokenness
418	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or	469	is by design, these kqueue bugs can (and eventually will) be fixed
419	libev was compiled on a known-to-be-good (-enough) system like NetBSD.	470	without API changes to existing programs. For this reason it's not being
		471	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		472	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		473	system like NetBSD.
420		474
421	You still can embed kqueue into a normal poll or select backend and use it	475	You still can embed kqueue into a normal poll or select backend and use it
422	only for sockets (after having made sure that sockets work with kqueue on	476	only for sockets (after having made sure that sockets work with kqueue on
423	the target platform). See C<ev_embed> watchers for more info.	477	the target platform). See C<ev_embed> watchers for more info.
424		478
425	It scales in the same way as the epoll backend, but the interface to the	479	It scales in the same way as the epoll backend, but the interface to the
426	kernel is more efficient (which says nothing about its actual speed, of	480	kernel is more efficient (which says nothing about its actual speed, of
427	course). While stopping, setting and starting an I/O watcher does never	481	course). While stopping, setting and starting an I/O watcher does never
428	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	482	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
429	two event changes per incident. Support for C<fork ()> is very bad and it	483	two event changes per incident. Support for C<fork ()> is very bad (but
430	drops fds silently in similarly hard-to-detect cases.	484	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		485	cases
431		486
432	This backend usually performs well under most conditions.	487	This backend usually performs well under most conditions.
433		488
434	While nominally embeddable in other event loops, this doesn't work	489	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	490	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	491	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	492	(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,	493	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
439	using it only for sockets.	494	also broken on OS X)) and, did I mention it, using it only for sockets.
440		495
441	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with	496	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
442	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with	497	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
443	C<NOTE_EOF>.	498	C<NOTE_EOF>.
444		499
…		…
464	might perform better.	519	might perform better.
465		520
466	On the positive side, with the exception of the spurious readiness	521	On the positive side, with the exception of the spurious readiness
467	notifications, this backend actually performed fully to specification	522	notifications, this backend actually performed fully to specification
468	in all tests and is fully embeddable, which is a rare feat among the	523	in all tests and is fully embeddable, which is a rare feat among the
469	OS-specific backends.	524	OS-specific backends (I vastly prefer correctness over speed hacks).
470		525
471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	526	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
472	C<EVBACKEND_POLL>.	527	C<EVBACKEND_POLL>.
473		528
474	=item C<EVBACKEND_ALL>	529	=item C<EVBACKEND_ALL>
…		…
479		534
480	It is definitely not recommended to use this flag.	535	It is definitely not recommended to use this flag.
481		536
482	=back	537	=back
483		538
484	If one or more of these are or'ed into the flags value, then only these	539	If one or more of the backend flags are or'ed into the flags value,
485	backends will be tried (in the reverse order as listed here). If none are	540	then only these backends will be tried (in the reverse order as listed
486	specified, all backends in C<ev_recommended_backends ()> will be tried.	541	here). If none are specified, all backends in C<ev_recommended_backends
		542	()> will be tried.
487		543
488	Example: This is the most typical usage.	544	Example: This is the most typical usage.
489		545
490	if (!ev_default_loop (0))	546	if (!ev_default_loop (0))
491	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	547	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
…		…
527	responsibility to either stop all watchers cleanly yourself I<before>	583	responsibility to either stop all watchers cleanly yourself I<before>
528	calling this function, or cope with the fact afterwards (which is usually	584	calling this function, or cope with the fact afterwards (which is usually
529	the easiest thing, you can just ignore the watchers and/or C<free ()> them	585	the easiest thing, you can just ignore the watchers and/or C<free ()> them
530	for example).	586	for example).
531		587
532	Note that certain global state, such as signal state, will not be freed by	588	Note that certain global state, such as signal state (and installed signal
533	this function, and related watchers (such as signal and child watchers)	589	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	590	as signal and child watchers) would need to be stopped manually.
535		591
536	In general it is not advisable to call this function except in the	592	In general it is not advisable to call this function except in the
537	rare occasion where you really need to free e.g. the signal handling	593	rare occasion where you really need to free e.g. the signal handling
538	pipe fds. If you need dynamically allocated loops it is better to use	594	pipe fds. If you need dynamically allocated loops it is better to use
539	C<ev_loop_new> and C<ev_loop_destroy>).	595	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
582		638
583	This value can sometimes be useful as a generation counter of sorts (it	639	This value can sometimes be useful as a generation counter of sorts (it
584	"ticks" the number of loop iterations), as it roughly corresponds with	640	"ticks" the number of loop iterations), as it roughly corresponds with
585	C<ev_prepare> and C<ev_check> calls.	641	C<ev_prepare> and C<ev_check> calls.
586		642
		643	=item unsigned int ev_loop_depth (loop)
		644
		645	Returns the number of times C<ev_loop> was entered minus the number of
		646	times C<ev_loop> was exited, in other words, the recursion depth.
		647
		648	Outside C<ev_loop>, this number is zero. In a callback, this number is
		649	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		650	in which case it is higher.
		651
		652	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		653	etc.), doesn't count as exit.
		654
587	=item unsigned int ev_backend (loop)	655	=item unsigned int ev_backend (loop)
588		656
589	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	657	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
590	use.	658	use.
591		659
…		…
605		673
606	This function is rarely useful, but when some event callback runs for a	674	This function is rarely useful, but when some event callback runs for a
607	very long time without entering the event loop, updating libev's idea of	675	very long time without entering the event loop, updating libev's idea of
608	the current time is a good idea.	676	the current time is a good idea.
609		677
610	See also "The special problem of time updates" in the C<ev_timer> section.	678	See also L<The special problem of time updates> in the C<ev_timer> section.
		679
		680	=item ev_suspend (loop)
		681
		682	=item ev_resume (loop)
		683
		684	These two functions suspend and resume a loop, for use when the loop is
		685	not used for a while and timeouts should not be processed.
		686
		687	A typical use case would be an interactive program such as a game: When
		688	the user presses C<^Z> to suspend the game and resumes it an hour later it
		689	would be best to handle timeouts as if no time had actually passed while
		690	the program was suspended. This can be achieved by calling C<ev_suspend>
		691	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		692	C<ev_resume> directly afterwards to resume timer processing.
		693
		694	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		695	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		696	will be rescheduled (that is, they will lose any events that would have
		697	occured while suspended).
		698
		699	After calling C<ev_suspend> you B<must not> call I<any> function on the
		700	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		701	without a previous call to C<ev_suspend>.
		702
		703	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		704	event loop time (see C<ev_now_update>).
611		705
612	=item ev_loop (loop, int flags)	706	=item ev_loop (loop, int flags)
613		707
614	Finally, this is it, the event handler. This function usually is called	708	Finally, this is it, the event handler. This function usually is called
615	after you initialised all your watchers and you want to start handling	709	after you initialised all your watchers and you want to start handling
…		…
631	the loop.	725	the loop.
632		726
633	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	727	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
634	necessary) and will handle those and any already outstanding ones. It	728	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	729	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	730	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	731	user-registered callback will be called), and will return after one
638	iteration of the loop.	732	iteration of the loop.
639		733
640	This is useful if you are waiting for some external event in conjunction	734	This is useful if you are waiting for some external event in conjunction
641	with something not expressible using other libev watchers (i.e. "roll your	735	with something not expressible using other libev watchers (i.e. "roll your
…		…
699		793
700	If you have a watcher you never unregister that should not keep C<ev_loop>	794	If you have a watcher you never unregister that should not keep C<ev_loop>
701	from returning, call ev_unref() after starting, and ev_ref() before	795	from returning, call ev_unref() after starting, and ev_ref() before
702	stopping it.	796	stopping it.
703		797
704	As an example, libev itself uses this for its internal signal pipe: It is	798	As an example, libev itself uses this for its internal signal pipe: It
705	not visible to the libev user and should not keep C<ev_loop> from exiting	799	is not visible to the libev user and should not keep C<ev_loop> from
706	if no event watchers registered by it are active. It is also an excellent	800	exiting if no event watchers registered by it are active. It is also an
707	way to do this for generic recurring timers or from within third-party	801	excellent way to do this for generic recurring timers or from within
708	libraries. Just remember to I<unref after start> and I<ref before stop>	802	third-party libraries. Just remember to I<unref after start> and I<ref
709	(but only if the watcher wasn't active before, or was active before,	803	before stop> (but only if the watcher wasn't active before, or was active
710	respectively).	804	before, respectively. Note also that libev might stop watchers itself
		805	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		806	in the callback).
711		807
712	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	808	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
713	running when nothing else is active.	809	running when nothing else is active.
714		810
715	ev_signal exitsig;	811	ev_signal exitsig;
…		…
744		840
745	By setting a higher I<io collect interval> you allow libev to spend more	841	By setting a higher I<io collect interval> you allow libev to spend more
746	time collecting I/O events, so you can handle more events per iteration,	842	time collecting I/O events, so you can handle more events per iteration,
747	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	843	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
748	C<ev_timer>) will be not affected. Setting this to a non-null value will	844	C<ev_timer>) will be not affected. Setting this to a non-null value will
749	introduce an additional C<ev_sleep ()> call into most loop iterations.	845	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		846	sleep time ensures that libev will not poll for I/O events more often then
		847	once per this interval, on average.
750		848
751	Likewise, by setting a higher I<timeout collect interval> you allow libev	849	Likewise, by setting a higher I<timeout collect interval> you allow libev
752	to spend more time collecting timeouts, at the expense of increased	850	to spend more time collecting timeouts, at the expense of increased
753	latency/jitter/inexactness (the watcher callback will be called	851	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	852	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
756		854
757	Many (busy) programs can usually benefit by setting the I/O collect	855	Many (busy) programs can usually benefit by setting the I/O collect
758	interval to a value near C<0.1> or so, which is often enough for	856	interval to a value near C<0.1> or so, which is often enough for
759	interactive servers (of course not for games), likewise for timeouts. It	857	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>,	858	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.	859	as this approaches the timing granularity of most systems. Note that if
		860	you do transactions with the outside world and you can't increase the
		861	parallelity, then this setting will limit your transaction rate (if you
		862	need to poll once per transaction and the I/O collect interval is 0.01,
		863	then you can't do more than 100 transations per second).
762		864
763	Setting the I<timeout collect interval> can improve the opportunity for	865	Setting the I<timeout collect interval> can improve the opportunity for
764	saving power, as the program will "bundle" timer callback invocations that	866	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	867	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	868	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	869	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
768	they fire on, say, one-second boundaries only.	870	they fire on, say, one-second boundaries only.
769		871
		872	Example: we only need 0.1s timeout granularity, and we wish not to poll
		873	more often than 100 times per second:
		874
		875	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		876	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		877
		878	=item ev_invoke_pending (loop)
		879
		880	This call will simply invoke all pending watchers while resetting their
		881	pending state. Normally, C<ev_loop> does this automatically when required,
		882	but when overriding the invoke callback this call comes handy.
		883
		884	=item int ev_pending_count (loop)
		885
		886	Returns the number of pending watchers - zero indicates that no watchers
		887	are pending.
		888
		889	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		890
		891	This overrides the invoke pending functionality of the loop: Instead of
		892	invoking all pending watchers when there are any, C<ev_loop> will call
		893	this callback instead. This is useful, for example, when you want to
		894	invoke the actual watchers inside another context (another thread etc.).
		895
		896	If you want to reset the callback, use C<ev_invoke_pending> as new
		897	callback.
		898
		899	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		900
		901	Sometimes you want to share the same loop between multiple threads. This
		902	can be done relatively simply by putting mutex_lock/unlock calls around
		903	each call to a libev function.
		904
		905	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		906	wait for it to return. One way around this is to wake up the loop via
		907	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		908	and I<acquire> callbacks on the loop.
		909
		910	When set, then C<release> will be called just before the thread is
		911	suspended waiting for new events, and C<acquire> is called just
		912	afterwards.
		913
		914	Ideally, C<release> will just call your mutex_unlock function, and
		915	C<acquire> will just call the mutex_lock function again.
		916
		917	While event loop modifications are allowed between invocations of
		918	C<release> and C<acquire> (that's their only purpose after all), no
		919	modifications done will affect the event loop, i.e. adding watchers will
		920	have no effect on the set of file descriptors being watched, or the time
		921	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		922	to take note of any changes you made.
		923
		924	In theory, threads executing C<ev_loop> will be async-cancel safe between
		925	invocations of C<release> and C<acquire>.
		926
		927	See also the locking example in the C<THREADS> section later in this
		928	document.
		929
		930	=item ev_set_userdata (loop, void *data)
		931
		932	=item ev_userdata (loop)
		933
		934	Set and retrieve a single C<void *> associated with a loop. When
		935	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		936	C<0.>
		937
		938	These two functions can be used to associate arbitrary data with a loop,
		939	and are intended solely for the C<invoke_pending_cb>, C<release> and
		940	C<acquire> callbacks described above, but of course can be (ab-)used for
		941	any other purpose as well.
		942
770	=item ev_loop_verify (loop)	943	=item ev_loop_verify (loop)
771		944
772	This function only does something when C<EV_VERIFY> support has been	945	This function only does something when C<EV_VERIFY> support has been
773	compiled in. which is the default for non-minimal builds. It tries to go	946	compiled in, which is the default for non-minimal builds. It tries to go
774	through all internal structures and checks them for validity. If anything	947	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	948	is found to be inconsistent, it will print an error message to standard
776	error and call C<abort ()>.	949	error and call C<abort ()>.
777		950
778	This can be used to catch bugs inside libev itself: under normal	951	This can be used to catch bugs inside libev itself: under normal
…		…
782	=back	955	=back
783		956
784		957
785	=head1 ANATOMY OF A WATCHER	958	=head1 ANATOMY OF A WATCHER
786		959
		960	In the following description, uppercase C<TYPE> in names stands for the
		961	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		962	watchers and C<ev_io_start> for I/O watchers.
		963
787	A watcher is a structure that you create and register to record your	964	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	965	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:	966	become readable, you would create an C<ev_io> watcher for that:
790		967
791	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)	968	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
…		…
793	ev_io_stop (w);	970	ev_io_stop (w);
794	ev_unloop (loop, EVUNLOOP_ALL);	971	ev_unloop (loop, EVUNLOOP_ALL);
795	}	972	}
796		973
797	struct ev_loop *loop = ev_default_loop (0);	974	struct ev_loop *loop = ev_default_loop (0);
		975
798	ev_io stdin_watcher;	976	ev_io stdin_watcher;
		977
799	ev_init (&stdin_watcher, my_cb);	978	ev_init (&stdin_watcher, my_cb);
800	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	979	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
801	ev_io_start (loop, &stdin_watcher);	980	ev_io_start (loop, &stdin_watcher);
		981
802	ev_loop (loop, 0);	982	ev_loop (loop, 0);
803		983
804	As you can see, you are responsible for allocating the memory for your	984	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,	985	watcher structures (and it is I<usually> a bad idea to do this on the
806	although this can sometimes be quite valid).	986	stack).
		987
		988	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		989	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
807		990
808	Each watcher structure must be initialised by a call to C<ev_init	991	Each watcher structure must be initialised by a call to C<ev_init
809	(watcher *, callback)>, which expects a callback to be provided. This	992	(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	993	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	994	watchers, each time the event loop detects that the file descriptor given
812	is readable and/or writable).	995	is readable and/or writable).
813		996
814	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	997	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	998	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	999	is also a macro to combine initialisation and setting in one call: C<<
817	(watcher *, callback, ...) >>.	1000	ev_TYPE_init (watcher *, callback, ...) >>.
818		1001
819	To make the watcher actually watch out for events, you have to start it	1002	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	1003	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	1004	*) >>), and you can stop watching for events at any time by calling the
822	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1005	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
823		1006
824	As long as your watcher is active (has been started but not stopped) you	1007	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	1008	must not touch the values stored in it. Most specifically you must never
826	reinitialise it or call its C<set> macro.	1009	reinitialise it or call its C<ev_TYPE_set> macro.
827		1010
828	Each and every callback receives the event loop pointer as first, the	1011	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	1012	registered watcher structure as second, and a bitset of received events as
830	third argument.	1013	third argument.
831		1014
…		…
889		1072
890	=item C<EV_ASYNC>	1073	=item C<EV_ASYNC>
891		1074
892	The given async watcher has been asynchronously notified (see C<ev_async>).	1075	The given async watcher has been asynchronously notified (see C<ev_async>).
893		1076
		1077	=item C<EV_CUSTOM>
		1078
		1079	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1080	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1081
894	=item C<EV_ERROR>	1082	=item C<EV_ERROR>
895		1083
896	An unspecified error has occurred, the watcher has been stopped. This might	1084	An unspecified error has occurred, the watcher has been stopped. This might
897	happen because the watcher could not be properly started because libev	1085	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	1086	ran out of memory, a file descriptor was found to be closed or any other
…		…
912		1100
913	=back	1101	=back
914		1102
915	=head2 GENERIC WATCHER FUNCTIONS	1103	=head2 GENERIC WATCHER FUNCTIONS
916		1104
917	In the following description, C<TYPE> stands for the watcher type,
918	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
919
920	=over 4	1105	=over 4
921		1106
922	=item C<ev_init> (ev_TYPE *watcher, callback)	1107	=item C<ev_init> (ev_TYPE *watcher, callback)
923		1108
924	This macro initialises the generic portion of a watcher. The contents	1109	This macro initialises the generic portion of a watcher. The contents
…		…
1016	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1201	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1017	(default: C<-2>). Pending watchers with higher priority will be invoked	1202	(default: C<-2>). Pending watchers with higher priority will be invoked
1018	before watchers with lower priority, but priority will not keep watchers	1203	before watchers with lower priority, but priority will not keep watchers
1019	from being executed (except for C<ev_idle> watchers).	1204	from being executed (except for C<ev_idle> watchers).
1020		1205
1021	This means that priorities are I<only> used for ordering callback
1022	invocation after new events have been received. This is useful, for
1023	example, to reduce latency after idling, or more often, to bind two
1024	watchers on the same event and make sure one is called first.
1025
1026	If you need to suppress invocation when higher priority events are pending	1206	If you need to suppress invocation when higher priority events are pending
1027	you need to look at C<ev_idle> watchers, which provide this functionality.	1207	you need to look at C<ev_idle> watchers, which provide this functionality.
1028		1208
1029	You I<must not> change the priority of a watcher as long as it is active or	1209	You I<must not> change the priority of a watcher as long as it is active or
1030	pending.	1210	pending.
1031		1211
		1212	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1213	fine, as long as you do not mind that the priority value you query might
		1214	or might not have been clamped to the valid range.
		1215
1032	The default priority used by watchers when no priority has been set is	1216	The default priority used by watchers when no priority has been set is
1033	always C<0>, which is supposed to not be too high and not be too low :).	1217	always C<0>, which is supposed to not be too high and not be too low :).
1034		1218
1035	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1219	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1036	fine, as long as you do not mind that the priority value you query might	1220	priorities.
1037	or might not have been adjusted to be within valid range.
1038		1221
1039	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1222	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1040		1223
1041	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1224	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1042	C<loop> nor C<revents> need to be valid as long as the watcher callback	1225	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1107	#include <stddef.h>	1290	#include <stddef.h>
1108		1291
1109	static void	1292	static void
1110	t1_cb (EV_P_ ev_timer *w, int revents)	1293	t1_cb (EV_P_ ev_timer *w, int revents)
1111	{	1294	{
1112	struct my_biggy big = (struct my_biggy *	1295	struct my_biggy big = (struct my_biggy *)
1113	(((char *)w) - offsetof (struct my_biggy, t1));	1296	(((char *)w) - offsetof (struct my_biggy, t1));
1114	}	1297	}
1115		1298
1116	static void	1299	static void
1117	t2_cb (EV_P_ ev_timer *w, int revents)	1300	t2_cb (EV_P_ ev_timer *w, int revents)
1118	{	1301	{
1119	struct my_biggy big = (struct my_biggy *	1302	struct my_biggy big = (struct my_biggy *)
1120	(((char *)w) - offsetof (struct my_biggy, t2));	1303	(((char *)w) - offsetof (struct my_biggy, t2));
1121	}	1304	}
		1305
		1306	=head2 WATCHER PRIORITY MODELS
		1307
		1308	Many event loops support I<watcher priorities>, which are usually small
		1309	integers that influence the ordering of event callback invocation
		1310	between watchers in some way, all else being equal.
		1311
		1312	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1313	description for the more technical details such as the actual priority
		1314	range.
		1315
		1316	There are two common ways how these these priorities are being interpreted
		1317	by event loops:
		1318
		1319	In the more common lock-out model, higher priorities "lock out" invocation
		1320	of lower priority watchers, which means as long as higher priority
		1321	watchers receive events, lower priority watchers are not being invoked.
		1322
		1323	The less common only-for-ordering model uses priorities solely to order
		1324	callback invocation within a single event loop iteration: Higher priority
		1325	watchers are invoked before lower priority ones, but they all get invoked
		1326	before polling for new events.
		1327
		1328	Libev uses the second (only-for-ordering) model for all its watchers
		1329	except for idle watchers (which use the lock-out model).
		1330
		1331	The rationale behind this is that implementing the lock-out model for
		1332	watchers is not well supported by most kernel interfaces, and most event
		1333	libraries will just poll for the same events again and again as long as
		1334	their callbacks have not been executed, which is very inefficient in the
		1335	common case of one high-priority watcher locking out a mass of lower
		1336	priority ones.
		1337
		1338	Static (ordering) priorities are most useful when you have two or more
		1339	watchers handling the same resource: a typical usage example is having an
		1340	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1341	timeouts. Under load, data might be received while the program handles
		1342	other jobs, but since timers normally get invoked first, the timeout
		1343	handler will be executed before checking for data. In that case, giving
		1344	the timer a lower priority than the I/O watcher ensures that I/O will be
		1345	handled first even under adverse conditions (which is usually, but not
		1346	always, what you want).
		1347
		1348	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1349	will only be executed when no same or higher priority watchers have
		1350	received events, they can be used to implement the "lock-out" model when
		1351	required.
		1352
		1353	For example, to emulate how many other event libraries handle priorities,
		1354	you can associate an C<ev_idle> watcher to each such watcher, and in
		1355	the normal watcher callback, you just start the idle watcher. The real
		1356	processing is done in the idle watcher callback. This causes libev to
		1357	continously poll and process kernel event data for the watcher, but when
		1358	the lock-out case is known to be rare (which in turn is rare :), this is
		1359	workable.
		1360
		1361	Usually, however, the lock-out model implemented that way will perform
		1362	miserably under the type of load it was designed to handle. In that case,
		1363	it might be preferable to stop the real watcher before starting the
		1364	idle watcher, so the kernel will not have to process the event in case
		1365	the actual processing will be delayed for considerable time.
		1366
		1367	Here is an example of an I/O watcher that should run at a strictly lower
		1368	priority than the default, and which should only process data when no
		1369	other events are pending:
		1370
		1371	ev_idle idle; // actual processing watcher
		1372	ev_io io; // actual event watcher
		1373
		1374	static void
		1375	io_cb (EV_P_ ev_io *w, int revents)
		1376	{
		1377	// stop the I/O watcher, we received the event, but
		1378	// are not yet ready to handle it.
		1379	ev_io_stop (EV_A_ w);
		1380
		1381	// start the idle watcher to ahndle the actual event.
		1382	// it will not be executed as long as other watchers
		1383	// with the default priority are receiving events.
		1384	ev_idle_start (EV_A_ &idle);
		1385	}
		1386
		1387	static void
		1388	idle_cb (EV_P_ ev_idle *w, int revents)
		1389	{
		1390	// actual processing
		1391	read (STDIN_FILENO, ...);
		1392
		1393	// have to start the I/O watcher again, as
		1394	// we have handled the event
		1395	ev_io_start (EV_P_ &io);
		1396	}
		1397
		1398	// initialisation
		1399	ev_idle_init (&idle, idle_cb);
		1400	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1401	ev_io_start (EV_DEFAULT_ &io);
		1402
		1403	In the "real" world, it might also be beneficial to start a timer, so that
		1404	low-priority connections can not be locked out forever under load. This
		1405	enables your program to keep a lower latency for important connections
		1406	during short periods of high load, while not completely locking out less
		1407	important ones.
1122		1408
1123		1409
1124	=head1 WATCHER TYPES	1410	=head1 WATCHER TYPES
1125		1411
1126	This section describes each watcher in detail, but will not repeat	1412	This section describes each watcher in detail, but will not repeat
…		…
1152	descriptors to non-blocking mode is also usually a good idea (but not	1438	descriptors to non-blocking mode is also usually a good idea (but not
1153	required if you know what you are doing).	1439	required if you know what you are doing).
1154		1440
1155	If you cannot use non-blocking mode, then force the use of a	1441	If you cannot use non-blocking mode, then force the use of a
1156	known-to-be-good backend (at the time of this writing, this includes only	1442	known-to-be-good backend (at the time of this writing, this includes only
1157	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1443	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1444	descriptors for which non-blocking operation makes no sense (such as
		1445	files) - libev doesn't guarentee any specific behaviour in that case.
1158		1446
1159	Another thing you have to watch out for is that it is quite easy to	1447	Another thing you have to watch out for is that it is quite easy to
1160	receive "spurious" readiness notifications, that is your callback might	1448	receive "spurious" readiness notifications, that is your callback might
1161	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1449	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1162	because there is no data. Not only are some backends known to create a	1450	because there is no data. Not only are some backends known to create a
…		…
1283	year, it will still time out after (roughly) one hour. "Roughly" because	1571	year, it will still time out after (roughly) one hour. "Roughly" because
1284	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1572	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1285	monotonic clock option helps a lot here).	1573	monotonic clock option helps a lot here).
1286		1574
1287	The callback is guaranteed to be invoked only I<after> its timeout has	1575	The callback is guaranteed to be invoked only I<after> its timeout has
1288	passed, but if multiple timers become ready during the same loop iteration	1576	passed (not I<at>, so on systems with very low-resolution clocks this
1289	then order of execution is undefined.	1577	might introduce a small delay). If multiple timers become ready during the
		1578	same loop iteration then the ones with earlier time-out values are invoked
		1579	before ones of the same priority with later time-out values (but this is
		1580	no longer true when a callback calls C<ev_loop> recursively).
1290		1581
1291	=head3 Be smart about timeouts	1582	=head3 Be smart about timeouts
1292		1583
1293	Many real-world problems invole some kind of time-out, usually for error	1584	Many real-world problems involve some kind of timeout, usually for error
1294	recovery. A typical example is an HTTP request - if the other side hangs,	1585	recovery. A typical example is an HTTP request - if the other side hangs,
1295	you want to raise some error after a while.	1586	you want to raise some error after a while.
1296		1587
1297	Here are some ways on how to handle this problem, from simple and	1588	What follows are some ways to handle this problem, from obvious and
1298	inefficient to very efficient.	1589	inefficient to smart and efficient.
1299		1590
1300	In the following examples a 60 second activity timeout is assumed - a	1591	In the following, a 60 second activity timeout is assumed - a timeout that
1301	timeout that gets reset to 60 seconds each time some data ("a lifesign")	1592	gets reset to 60 seconds each time there is activity (e.g. each time some
1302	was received.	1593	data or other life sign was received).
1303		1594
1304	=over 4	1595	=over 4
1305		1596
1306	=item 1. Use a timer and stop, reinitialise, start it on activity.	1597	=item 1. Use a timer and stop, reinitialise and start it on activity.
1307		1598
1308	This is the most obvious, but not the most simple way: In the beginning,	1599	This is the most obvious, but not the most simple way: In the beginning,
1309	start the watcher:	1600	start the watcher:
1310		1601
1311	ev_timer_init (timer, callback, 60., 0.);	1602	ev_timer_init (timer, callback, 60., 0.);
1312	ev_timer_start (loop, timer);	1603	ev_timer_start (loop, timer);
1313		1604
1314	Then, each time there is some activity, C<ev_timer_stop> the timer,	1605	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
1315	initialise it again, and start it:	1606	and start it again:
1316		1607
1317	ev_timer_stop (loop, timer);	1608	ev_timer_stop (loop, timer);
1318	ev_timer_set (timer, 60., 0.);	1609	ev_timer_set (timer, 60., 0.);
1319	ev_timer_start (loop, timer);	1610	ev_timer_start (loop, timer);
1320		1611
1321	This is relatively simple to implement, but means that each time there	1612	This is relatively simple to implement, but means that each time there is
1322	is some activity, libev will first have to remove the timer from it's	1613	some activity, libev will first have to remove the timer from its internal
1323	internal data strcuture and then add it again.	1614	data structure and then add it again. Libev tries to be fast, but it's
		1615	still not a constant-time operation.
1324		1616
1325	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.	1617	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
1326		1618
1327	This is the easiest way, and involves using C<ev_timer_again> instead of	1619	This is the easiest way, and involves using C<ev_timer_again> instead of
1328	C<ev_timer_start>.	1620	C<ev_timer_start>.
1329		1621
1330	For this, configure an C<ev_timer> with a C<repeat> value of C<60> and	1622	To implement this, configure an C<ev_timer> with a C<repeat> value
1331	then call C<ev_timer_again> at start and each time you successfully read	1623	of C<60> and then call C<ev_timer_again> at start and each time you
1332	or write some data. If you go into an idle state where you do not expect	1624	successfully read or write some data. If you go into an idle state where
1333	data to travel on the socket, you can C<ev_timer_stop> the timer, and	1625	you do not expect data to travel on the socket, you can C<ev_timer_stop>
1334	C<ev_timer_again> will automatically restart it if need be.	1626	the timer, and C<ev_timer_again> will automatically restart it if need be.
1335		1627
1336	That means you can ignore the C<after> value and C<ev_timer_start>	1628	That means you can ignore both the C<ev_timer_start> function and the
1337	altogether and only ever use the C<repeat> value and C<ev_timer_again>.	1629	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1630	member and C<ev_timer_again>.
1338		1631
1339	At start:	1632	At start:
1340		1633
1341	ev_timer_init (timer, callback, 0., 60.);	1634	ev_init (timer, callback);
		1635	timer->repeat = 60.;
1342	ev_timer_again (loop, timer);	1636	ev_timer_again (loop, timer);
1343		1637
1344	Each time you receive some data:	1638	Each time there is some activity:
1345		1639
1346	ev_timer_again (loop, timer);	1640	ev_timer_again (loop, timer);
1347		1641
1348	It is even possible to change the time-out on the fly:	1642	It is even possible to change the time-out on the fly, regardless of
		1643	whether the watcher is active or not:
1349		1644
1350	timer->repeat = 30.;	1645	timer->repeat = 30.;
1351	ev_timer_again (loop, timer);	1646	ev_timer_again (loop, timer);
1352		1647
1353	This is slightly more efficient then stopping/starting the timer each time	1648	This is slightly more efficient then stopping/starting the timer each time
1354	you want to modify its timeout value, as libev does not have to completely	1649	you want to modify its timeout value, as libev does not have to completely
1355	remove and re-insert the timer from/into it's internal data structure.	1650	remove and re-insert the timer from/into its internal data structure.
		1651
		1652	It is, however, even simpler than the "obvious" way to do it.
1356		1653
1357	=item 3. Let the timer time out, but then re-arm it as required.	1654	=item 3. Let the timer time out, but then re-arm it as required.
1358		1655
1359	This method is more tricky, but usually most efficient: Most timeouts are	1656	This method is more tricky, but usually most efficient: Most timeouts are
1360	relatively long compared to the loop iteration time - in our example,	1657	relatively long compared to the intervals between other activity - in
1361	within 60 seconds, there are usually many I/O events with associated	1658	our example, within 60 seconds, there are usually many I/O events with
1362	activity resets.	1659	associated activity resets.
1363		1660
1364	In this case, it would be more efficient to leave the C<ev_timer> alone,	1661	In this case, it would be more efficient to leave the C<ev_timer> alone,
1365	but remember the time of last activity, and check for a real timeout only	1662	but remember the time of last activity, and check for a real timeout only
1366	within the callback:	1663	within the callback:
1367		1664
1368	ev_tstamp last_activity; // time of last activity	1665	ev_tstamp last_activity; // time of last activity
1369		1666
1370	static void	1667	static void
1371	callback (EV_P_ ev_timer *w, int revents)	1668	callback (EV_P_ ev_timer *w, int revents)
1372	{	1669	{
1373	ev_tstamp now = ev_now (EV_A);	1670	ev_tstamp now = ev_now (EV_A);
1374	ev_tstamp timeout = last_activity + 60.;	1671	ev_tstamp timeout = last_activity + 60.;
1375		1672
1376	// if last_activity is older than now - timeout, we did time out	1673	// if last_activity + 60. is older than now, we did time out
1377	if (timeout < now)	1674	if (timeout < now)
1378	{	1675	{
1379	// timeout occured, take action	1676	// timeout occured, take action
1380	}	1677	}
1381	else	1678	else
1382	{	1679	{
1383	// callback was invoked, but there was some activity, re-arm	1680	// callback was invoked, but there was some activity, re-arm
1384	// to fire in last_activity + 60.	1681	// the watcher to fire in last_activity + 60, which is
		1682	// guaranteed to be in the future, so "again" is positive:
1385	w->again = timeout - now;	1683	w->repeat = timeout - now;
1386	ev_timer_again (EV_A_ w);	1684	ev_timer_again (EV_A_ w);
1387	}	1685	}
1388	}	1686	}
1389		1687
1390	To summarise the callback: first calculate the real time-out (defined as	1688	To summarise the callback: first calculate the real timeout (defined
1391	"60 seconds after the last activity"), then check if that time has been	1689	as "60 seconds after the last activity"), then check if that time has
1392	reached, which means there was a real timeout. Otherwise the callback was	1690	been reached, which means something I<did>, in fact, time out. Otherwise
1393	invoked too early (timeout is in the future), so re-schedule the timer to	1691	the callback was invoked too early (C<timeout> is in the future), so
1394	fire at that future time.	1692	re-schedule the timer to fire at that future time, to see if maybe we have
		1693	a timeout then.
1395		1694
1396	Note how C<ev_timer_again> is used, taking advantage of the	1695	Note how C<ev_timer_again> is used, taking advantage of the
1397	C<ev_timer_again> optimisation when the timer is already running.	1696	C<ev_timer_again> optimisation when the timer is already running.
1398		1697
1399	This scheme causes more callback invocations (about one every 60 seconds),	1698	This scheme causes more callback invocations (about one every 60 seconds
1400	but virtually no calls to libev to change the timeout.	1699	minus half the average time between activity), but virtually no calls to
		1700	libev to change the timeout.
1401		1701
1402	To start the timer, simply intiialise the watcher and C<last_activity>,	1702	To start the timer, simply initialise the watcher and set C<last_activity>
1403	then call the callback:	1703	to the current time (meaning we just have some activity :), then call the
		1704	callback, which will "do the right thing" and start the timer:
1404		1705
1405	ev_timer_init (timer, callback);	1706	ev_init (timer, callback);
1406	last_activity = ev_now (loop);	1707	last_activity = ev_now (loop);
1407	callback (loop, timer, EV_TIMEOUT);	1708	callback (loop, timer, EV_TIMEOUT);
1408		1709
1409	And when there is some activity, simply remember the time in	1710	And when there is some activity, simply store the current time in
1410	C<last_activity>:	1711	C<last_activity>, no libev calls at all:
1411		1712
1412	last_actiivty = ev_now (loop);	1713	last_actiivty = ev_now (loop);
1413		1714
1414	This technique is slightly more complex, but in most cases where the	1715	This technique is slightly more complex, but in most cases where the
1415	time-out is unlikely to be triggered, much more efficient.	1716	time-out is unlikely to be triggered, much more efficient.
1416		1717
		1718	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1719	callback :) - just change the timeout and invoke the callback, which will
		1720	fix things for you.
		1721
		1722	=item 4. Wee, just use a double-linked list for your timeouts.
		1723
		1724	If there is not one request, but many thousands (millions...), all
		1725	employing some kind of timeout with the same timeout value, then one can
		1726	do even better:
		1727
		1728	When starting the timeout, calculate the timeout value and put the timeout
		1729	at the I<end> of the list.
		1730
		1731	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1732	the list is expected to fire (for example, using the technique #3).
		1733
		1734	When there is some activity, remove the timer from the list, recalculate
		1735	the timeout, append it to the end of the list again, and make sure to
		1736	update the C<ev_timer> if it was taken from the beginning of the list.
		1737
		1738	This way, one can manage an unlimited number of timeouts in O(1) time for
		1739	starting, stopping and updating the timers, at the expense of a major
		1740	complication, and having to use a constant timeout. The constant timeout
		1741	ensures that the list stays sorted.
		1742
1417	=back	1743	=back
		1744
		1745	So which method the best?
		1746
		1747	Method #2 is a simple no-brain-required solution that is adequate in most
		1748	situations. Method #3 requires a bit more thinking, but handles many cases
		1749	better, and isn't very complicated either. In most case, choosing either
		1750	one is fine, with #3 being better in typical situations.
		1751
		1752	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1753	rather complicated, but extremely efficient, something that really pays
		1754	off after the first million or so of active timers, i.e. it's usually
		1755	overkill :)
1418		1756
1419	=head3 The special problem of time updates	1757	=head3 The special problem of time updates
1420		1758
1421	Establishing the current time is a costly operation (it usually takes at	1759	Establishing the current time is a costly operation (it usually takes at
1422	least two system calls): EV therefore updates its idea of the current	1760	least two system calls): EV therefore updates its idea of the current
…		…
1434		1772
1435	If the event loop is suspended for a long time, you can also force an	1773	If the event loop is suspended for a long time, you can also force an
1436	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1774	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1437	()>.	1775	()>.
1438		1776
		1777	=head3 The special problems of suspended animation
		1778
		1779	When you leave the server world it is quite customary to hit machines that
		1780	can suspend/hibernate - what happens to the clocks during such a suspend?
		1781
		1782	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1783	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1784	to run until the system is suspended, but they will not advance while the
		1785	system is suspended. That means, on resume, it will be as if the program
		1786	was frozen for a few seconds, but the suspend time will not be counted
		1787	towards C<ev_timer> when a monotonic clock source is used. The real time
		1788	clock advanced as expected, but if it is used as sole clocksource, then a
		1789	long suspend would be detected as a time jump by libev, and timers would
		1790	be adjusted accordingly.
		1791
		1792	I would not be surprised to see different behaviour in different between
		1793	operating systems, OS versions or even different hardware.
		1794
		1795	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1796	time jump in the monotonic clocks and the realtime clock. If the program
		1797	is suspended for a very long time, and monotonic clock sources are in use,
		1798	then you can expect C<ev_timer>s to expire as the full suspension time
		1799	will be counted towards the timers. When no monotonic clock source is in
		1800	use, then libev will again assume a timejump and adjust accordingly.
		1801
		1802	It might be beneficial for this latter case to call C<ev_suspend>
		1803	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1804	deterministic behaviour in this case (you can do nothing against
		1805	C<SIGSTOP>).
		1806
1439	=head3 Watcher-Specific Functions and Data Members	1807	=head3 Watcher-Specific Functions and Data Members
1440		1808
1441	=over 4	1809	=over 4
1442		1810
1443	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1811	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1466	If the timer is started but non-repeating, stop it (as if it timed out).	1834	If the timer is started but non-repeating, stop it (as if it timed out).
1467		1835
1468	If the timer is repeating, either start it if necessary (with the	1836	If the timer is repeating, either start it if necessary (with the
1469	C<repeat> value), or reset the running timer to the C<repeat> value.	1837	C<repeat> value), or reset the running timer to the C<repeat> value.
1470		1838
1471	This sounds a bit complicated, see "Be smart about timeouts", above, for a	1839	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1472	usage example.	1840	usage example.
		1841
		1842	=item ev_timer_remaining (loop, ev_timer *)
		1843
		1844	Returns the remaining time until a timer fires. If the timer is active,
		1845	then this time is relative to the current event loop time, otherwise it's
		1846	the timeout value currently configured.
		1847
		1848	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1849	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1850	will return C<4>. When the timer expires and is restarted, it will return
		1851	roughly C<7> (likely slightly less as callback invocation takes some time,
		1852	too), and so on.
1473		1853
1474	=item ev_tstamp repeat [read-write]	1854	=item ev_tstamp repeat [read-write]
1475		1855
1476	The current C<repeat> value. Will be used each time the watcher times out	1856	The current C<repeat> value. Will be used each time the watcher times out
1477	or C<ev_timer_again> is called, and determines the next timeout (if any),	1857	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1515	=head2 C<ev_periodic> - to cron or not to cron?	1895	=head2 C<ev_periodic> - to cron or not to cron?
1516		1896
1517	Periodic watchers are also timers of a kind, but they are very versatile	1897	Periodic watchers are also timers of a kind, but they are very versatile
1518	(and unfortunately a bit complex).	1898	(and unfortunately a bit complex).
1519		1899
1520	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1900	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1521	but on wall clock time (absolute time). You can tell a periodic watcher	1901	relative time, the physical time that passes) but on wall clock time
1522	to trigger after some specific point in time. For example, if you tell a	1902	(absolute time, the thing you can read on your calender or clock). The
1523	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1903	difference is that wall clock time can run faster or slower than real
1524	+ 10.>, that is, an absolute time not a delay) and then reset your system	1904	time, and time jumps are not uncommon (e.g. when you adjust your
1525	clock to January of the previous year, then it will take more than year	1905	wrist-watch).
1526	to trigger the event (unlike an C<ev_timer>, which would still trigger
1527	roughly 10 seconds later as it uses a relative timeout).
1528		1906
		1907	You can tell a periodic watcher to trigger after some specific point
		1908	in time: for example, if you tell a periodic watcher to trigger "in 10
		1909	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1910	not a delay) and then reset your system clock to January of the previous
		1911	year, then it will take a year or more to trigger the event (unlike an
		1912	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1913	it, as it uses a relative timeout).
		1914
1529	C<ev_periodic>s can also be used to implement vastly more complex timers,	1915	C<ev_periodic> watchers can also be used to implement vastly more complex
1530	such as triggering an event on each "midnight, local time", or other	1916	timers, such as triggering an event on each "midnight, local time", or
1531	complicated rules.	1917	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1918	those cannot react to time jumps.
1532		1919
1533	As with timers, the callback is guaranteed to be invoked only when the	1920	As with timers, the callback is guaranteed to be invoked only when the
1534	time (C<at>) has passed, but if multiple periodic timers become ready	1921	point in time where it is supposed to trigger has passed. If multiple
1535	during the same loop iteration, then order of execution is undefined.	1922	timers become ready during the same loop iteration then the ones with
		1923	earlier time-out values are invoked before ones with later time-out values
		1924	(but this is no longer true when a callback calls C<ev_loop> recursively).
1536		1925
1537	=head3 Watcher-Specific Functions and Data Members	1926	=head3 Watcher-Specific Functions and Data Members
1538		1927
1539	=over 4	1928	=over 4
1540		1929
1541	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1930	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1542		1931
1543	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1932	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1544		1933
1545	Lots of arguments, lets sort it out... There are basically three modes of	1934	Lots of arguments, let's sort it out... There are basically three modes of
1546	operation, and we will explain them from simplest to most complex:	1935	operation, and we will explain them from simplest to most complex:
1547		1936
1548	=over 4	1937	=over 4
1549		1938
1550	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1939	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1551		1940
1552	In this configuration the watcher triggers an event after the wall clock	1941	In this configuration the watcher triggers an event after the wall clock
1553	time C<at> has passed. It will not repeat and will not adjust when a time	1942	time C<offset> has passed. It will not repeat and will not adjust when a
1554	jump occurs, that is, if it is to be run at January 1st 2011 then it will	1943	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1555	only run when the system clock reaches or surpasses this time.	1944	will be stopped and invoked when the system clock reaches or surpasses
		1945	this point in time.
1556		1946
1557	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1947	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1558		1948
1559	In this mode the watcher will always be scheduled to time out at the next	1949	In this mode the watcher will always be scheduled to time out at the next
1560	C<at + N * interval> time (for some integer N, which can also be negative)	1950	C<offset + N * interval> time (for some integer N, which can also be
1561	and then repeat, regardless of any time jumps.	1951	negative) and then repeat, regardless of any time jumps. The C<offset>
		1952	argument is merely an offset into the C<interval> periods.
1562		1953
1563	This can be used to create timers that do not drift with respect to the	1954	This can be used to create timers that do not drift with respect to the
1564	system clock, for example, here is a C<ev_periodic> that triggers each	1955	system clock, for example, here is an C<ev_periodic> that triggers each
1565	hour, on the hour:	1956	hour, on the hour (with respect to UTC):
1566		1957
1567	ev_periodic_set (&periodic, 0., 3600., 0);	1958	ev_periodic_set (&periodic, 0., 3600., 0);
1568		1959
1569	This doesn't mean there will always be 3600 seconds in between triggers,	1960	This doesn't mean there will always be 3600 seconds in between triggers,
1570	but only that the callback will be called when the system time shows a	1961	but only that the callback will be called when the system time shows a
1571	full hour (UTC), or more correctly, when the system time is evenly divisible	1962	full hour (UTC), or more correctly, when the system time is evenly divisible
1572	by 3600.	1963	by 3600.
1573		1964
1574	Another way to think about it (for the mathematically inclined) is that	1965	Another way to think about it (for the mathematically inclined) is that
1575	C<ev_periodic> will try to run the callback in this mode at the next possible	1966	C<ev_periodic> will try to run the callback in this mode at the next possible
1576	time where C<time = at (mod interval)>, regardless of any time jumps.	1967	time where C<time = offset (mod interval)>, regardless of any time jumps.
1577		1968
1578	For numerical stability it is preferable that the C<at> value is near	1969	For numerical stability it is preferable that the C<offset> value is near
1579	C<ev_now ()> (the current time), but there is no range requirement for	1970	C<ev_now ()> (the current time), but there is no range requirement for
1580	this value, and in fact is often specified as zero.	1971	this value, and in fact is often specified as zero.
1581		1972
1582	Note also that there is an upper limit to how often a timer can fire (CPU	1973	Note also that there is an upper limit to how often a timer can fire (CPU
1583	speed for example), so if C<interval> is very small then timing stability	1974	speed for example), so if C<interval> is very small then timing stability
1584	will of course deteriorate. Libev itself tries to be exact to be about one	1975	will of course deteriorate. Libev itself tries to be exact to be about one
1585	millisecond (if the OS supports it and the machine is fast enough).	1976	millisecond (if the OS supports it and the machine is fast enough).
1586		1977
1587	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1978	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1588		1979
1589	In this mode the values for C<interval> and C<at> are both being	1980	In this mode the values for C<interval> and C<offset> are both being
1590	ignored. Instead, each time the periodic watcher gets scheduled, the	1981	ignored. Instead, each time the periodic watcher gets scheduled, the
1591	reschedule callback will be called with the watcher as first, and the	1982	reschedule callback will be called with the watcher as first, and the
1592	current time as second argument.	1983	current time as second argument.
1593		1984
1594	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1985	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1595	ever, or make ANY event loop modifications whatsoever>.	1986	or make ANY other event loop modifications whatsoever, unless explicitly
		1987	allowed by documentation here>.
1596		1988
1597	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1989	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1598	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1990	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1599	only event loop modification you are allowed to do).	1991	only event loop modification you are allowed to do).
1600		1992
…		…
1630	a different time than the last time it was called (e.g. in a crond like	2022	a different time than the last time it was called (e.g. in a crond like
1631	program when the crontabs have changed).	2023	program when the crontabs have changed).
1632		2024
1633	=item ev_tstamp ev_periodic_at (ev_periodic *)	2025	=item ev_tstamp ev_periodic_at (ev_periodic *)
1634		2026
1635	When active, returns the absolute time that the watcher is supposed to	2027	When active, returns the absolute time that the watcher is supposed
1636	trigger next.	2028	to trigger next. This is not the same as the C<offset> argument to
		2029	C<ev_periodic_set>, but indeed works even in interval and manual
		2030	rescheduling modes.
1637		2031
1638	=item ev_tstamp offset [read-write]	2032	=item ev_tstamp offset [read-write]
1639		2033
1640	When repeating, this contains the offset value, otherwise this is the	2034	When repeating, this contains the offset value, otherwise this is the
1641	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2035	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2036	although libev might modify this value for better numerical stability).
1642		2037
1643	Can be modified any time, but changes only take effect when the periodic	2038	Can be modified any time, but changes only take effect when the periodic
1644	timer fires or C<ev_periodic_again> is being called.	2039	timer fires or C<ev_periodic_again> is being called.
1645		2040
1646	=item ev_tstamp interval [read-write]	2041	=item ev_tstamp interval [read-write]
…		…
1698	Signal watchers will trigger an event when the process receives a specific	2093	Signal watchers will trigger an event when the process receives a specific
1699	signal one or more times. Even though signals are very asynchronous, libev	2094	signal one or more times. Even though signals are very asynchronous, libev
1700	will try it's best to deliver signals synchronously, i.e. as part of the	2095	will try it's best to deliver signals synchronously, i.e. as part of the
1701	normal event processing, like any other event.	2096	normal event processing, like any other event.
1702		2097
1703	If you want signals asynchronously, just use C<sigaction> as you would	2098	If you want signals to be delivered truly asynchronously, just use
1704	do without libev and forget about sharing the signal. You can even use	2099	C<sigaction> as you would do without libev and forget about sharing
1705	C<ev_async> from a signal handler to synchronously wake up an event loop.	2100	the signal. You can even use C<ev_async> from a signal handler to
		2101	synchronously wake up an event loop.
1706		2102
1707	You can configure as many watchers as you like per signal. Only when the	2103	You can configure as many watchers as you like for the same signal, but
		2104	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2105	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2106	C<SIGINT> in both the default loop and another loop at the same time. At
		2107	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2108
1708	first watcher gets started will libev actually register a signal handler	2109	When the first watcher gets started will libev actually register something
1709	with the kernel (thus it coexists with your own signal handlers as long as	2110	with the kernel (thus it coexists with your own signal handlers as long as
1710	you don't register any with libev for the same signal). Similarly, when	2111	you don't register any with libev for the same signal).
1711	the last signal watcher for a signal is stopped, libev will reset the	2112
1712	signal handler to SIG_DFL (regardless of what it was set to before).	2113	Both the signal mask state (C<sigprocmask>) and the signal handler state
		2114	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2115	sotpping it again), that is, libev might or might not block the signal,
		2116	and might or might not set or restore the installed signal handler.
1713		2117
1714	If possible and supported, libev will install its handlers with	2118	If possible and supported, libev will install its handlers with
1715	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2119	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1716	interrupted. If you have a problem with system calls getting interrupted by	2120	not be unduly interrupted. If you have a problem with system calls getting
1717	signals you can block all signals in an C<ev_check> watcher and unblock	2121	interrupted by signals you can block all signals in an C<ev_check> watcher
1718	them in an C<ev_prepare> watcher.	2122	and unblock them in an C<ev_prepare> watcher.
1719		2123
1720	=head3 Watcher-Specific Functions and Data Members	2124	=head3 Watcher-Specific Functions and Data Members
1721		2125
1722	=over 4	2126	=over 4
1723		2127
…		…
1755	some child status changes (most typically when a child of yours dies or	2159	some child status changes (most typically when a child of yours dies or
1756	exits). It is permissible to install a child watcher I<after> the child	2160	exits). It is permissible to install a child watcher I<after> the child
1757	has been forked (which implies it might have already exited), as long	2161	has been forked (which implies it might have already exited), as long
1758	as the event loop isn't entered (or is continued from a watcher), i.e.,	2162	as the event loop isn't entered (or is continued from a watcher), i.e.,
1759	forking and then immediately registering a watcher for the child is fine,	2163	forking and then immediately registering a watcher for the child is fine,
1760	but forking and registering a watcher a few event loop iterations later is	2164	but forking and registering a watcher a few event loop iterations later or
1761	not.	2165	in the next callback invocation is not.
1762		2166
1763	Only the default event loop is capable of handling signals, and therefore	2167	Only the default event loop is capable of handling signals, and therefore
1764	you can only register child watchers in the default event loop.	2168	you can only register child watchers in the default event loop.
1765		2169
		2170	Due to some design glitches inside libev, child watchers will always be
		2171	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2172	libev)
		2173
1766	=head3 Process Interaction	2174	=head3 Process Interaction
1767		2175
1768	Libev grabs C<SIGCHLD> as soon as the default event loop is	2176	Libev grabs C<SIGCHLD> as soon as the default event loop is
1769	initialised. This is necessary to guarantee proper behaviour even if	2177	initialised. This is necessary to guarantee proper behaviour even if the
1770	the first child watcher is started after the child exits. The occurrence	2178	first child watcher is started after the child exits. The occurrence
1771	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2179	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1772	synchronously as part of the event loop processing. Libev always reaps all	2180	synchronously as part of the event loop processing. Libev always reaps all
1773	children, even ones not watched.	2181	children, even ones not watched.
1774		2182
1775	=head3 Overriding the Built-In Processing	2183	=head3 Overriding the Built-In Processing
…		…
1785	=head3 Stopping the Child Watcher	2193	=head3 Stopping the Child Watcher
1786		2194
1787	Currently, the child watcher never gets stopped, even when the	2195	Currently, the child watcher never gets stopped, even when the
1788	child terminates, so normally one needs to stop the watcher in the	2196	child terminates, so normally one needs to stop the watcher in the
1789	callback. Future versions of libev might stop the watcher automatically	2197	callback. Future versions of libev might stop the watcher automatically
1790	when a child exit is detected.	2198	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2199	problem).
1791		2200
1792	=head3 Watcher-Specific Functions and Data Members	2201	=head3 Watcher-Specific Functions and Data Members
1793		2202
1794	=over 4	2203	=over 4
1795		2204
…		…
1852		2261
1853		2262
1854	=head2 C<ev_stat> - did the file attributes just change?	2263	=head2 C<ev_stat> - did the file attributes just change?
1855		2264
1856	This watches a file system path for attribute changes. That is, it calls	2265	This watches a file system path for attribute changes. That is, it calls
1857	C<stat> regularly (or when the OS says it changed) and sees if it changed	2266	C<stat> on that path in regular intervals (or when the OS says it changed)
1858	compared to the last time, invoking the callback if it did.	2267	and sees if it changed compared to the last time, invoking the callback if
		2268	it did.
1859		2269
1860	The path does not need to exist: changing from "path exists" to "path does	2270	The path does not need to exist: changing from "path exists" to "path does
1861	not exist" is a status change like any other. The condition "path does	2271	not exist" is a status change like any other. The condition "path does not
1862	not exist" is signified by the C<st_nlink> field being zero (which is	2272	exist" (or more correctly "path cannot be stat'ed") is signified by the
1863	otherwise always forced to be at least one) and all the other fields of	2273	C<st_nlink> field being zero (which is otherwise always forced to be at
1864	the stat buffer having unspecified contents.	2274	least one) and all the other fields of the stat buffer having unspecified
		2275	contents.
1865		2276
1866	The path I<should> be absolute and I<must not> end in a slash. If it is	2277	The path I<must not> end in a slash or contain special components such as
		2278	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1867	relative and your working directory changes, the behaviour is undefined.	2279	your working directory changes, then the behaviour is undefined.
1868		2280
1869	Since there is no standard kernel interface to do this, the portable	2281	Since there is no portable change notification interface available, the
1870	implementation simply calls C<stat (2)> regularly on the path to see if	2282	portable implementation simply calls C<stat(2)> regularly on the path
1871	it changed somehow. You can specify a recommended polling interval for	2283	to see if it changed somehow. You can specify a recommended polling
1872	this case. If you specify a polling interval of C<0> (highly recommended!)	2284	interval for this case. If you specify a polling interval of C<0> (highly
1873	then a I<suitable, unspecified default> value will be used (which	2285	recommended!) then a I<suitable, unspecified default> value will be used
1874	you can expect to be around five seconds, although this might change	2286	(which you can expect to be around five seconds, although this might
1875	dynamically). Libev will also impose a minimum interval which is currently	2287	change dynamically). Libev will also impose a minimum interval which is
1876	around C<0.1>, but thats usually overkill.	2288	currently around C<0.1>, but that's usually overkill.
1877		2289
1878	This watcher type is not meant for massive numbers of stat watchers,	2290	This watcher type is not meant for massive numbers of stat watchers,
1879	as even with OS-supported change notifications, this can be	2291	as even with OS-supported change notifications, this can be
1880	resource-intensive.	2292	resource-intensive.
1881		2293
1882	At the time of this writing, the only OS-specific interface implemented	2294	At the time of this writing, the only OS-specific interface implemented
1883	is the Linux inotify interface (implementing kqueue support is left as	2295	is the Linux inotify interface (implementing kqueue support is left as an
1884	an exercise for the reader. Note, however, that the author sees no way	2296	exercise for the reader. Note, however, that the author sees no way of
1885	of implementing C<ev_stat> semantics with kqueue).	2297	implementing C<ev_stat> semantics with kqueue, except as a hint).
1886		2298
1887	=head3 ABI Issues (Largefile Support)	2299	=head3 ABI Issues (Largefile Support)
1888		2300
1889	Libev by default (unless the user overrides this) uses the default	2301	Libev by default (unless the user overrides this) uses the default
1890	compilation environment, which means that on systems with large file	2302	compilation environment, which means that on systems with large file
1891	support disabled by default, you get the 32 bit version of the stat	2303	support disabled by default, you get the 32 bit version of the stat
1892	structure. When using the library from programs that change the ABI to	2304	structure. When using the library from programs that change the ABI to
1893	use 64 bit file offsets the programs will fail. In that case you have to	2305	use 64 bit file offsets the programs will fail. In that case you have to
1894	compile libev with the same flags to get binary compatibility. This is	2306	compile libev with the same flags to get binary compatibility. This is
1895	obviously the case with any flags that change the ABI, but the problem is	2307	obviously the case with any flags that change the ABI, but the problem is
1896	most noticeably disabled with ev_stat and large file support.	2308	most noticeably displayed with ev_stat and large file support.
1897		2309
1898	The solution for this is to lobby your distribution maker to make large	2310	The solution for this is to lobby your distribution maker to make large
1899	file interfaces available by default (as e.g. FreeBSD does) and not	2311	file interfaces available by default (as e.g. FreeBSD does) and not
1900	optional. Libev cannot simply switch on large file support because it has	2312	optional. Libev cannot simply switch on large file support because it has
1901	to exchange stat structures with application programs compiled using the	2313	to exchange stat structures with application programs compiled using the
1902	default compilation environment.	2314	default compilation environment.
1903		2315
1904	=head3 Inotify and Kqueue	2316	=head3 Inotify and Kqueue
1905		2317
1906	When C<inotify (7)> support has been compiled into libev (generally	2318	When C<inotify (7)> support has been compiled into libev and present at
1907	only available with Linux 2.6.25 or above due to bugs in earlier	2319	runtime, it will be used to speed up change detection where possible. The
1908	implementations) and present at runtime, it will be used to speed up	2320	inotify descriptor will be created lazily when the first C<ev_stat>
1909	change detection where possible. The inotify descriptor will be created	2321	watcher is being started.
1910	lazily when the first C<ev_stat> watcher is being started.
1911		2322
1912	Inotify presence does not change the semantics of C<ev_stat> watchers	2323	Inotify presence does not change the semantics of C<ev_stat> watchers
1913	except that changes might be detected earlier, and in some cases, to avoid	2324	except that changes might be detected earlier, and in some cases, to avoid
1914	making regular C<stat> calls. Even in the presence of inotify support	2325	making regular C<stat> calls. Even in the presence of inotify support
1915	there are many cases where libev has to resort to regular C<stat> polling,	2326	there are many cases where libev has to resort to regular C<stat> polling,
1916	but as long as the path exists, libev usually gets away without polling.	2327	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2328	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2329	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2330	xfs are fully working) libev usually gets away without polling.
1917		2331
1918	There is no support for kqueue, as apparently it cannot be used to	2332	There is no support for kqueue, as apparently it cannot be used to
1919	implement this functionality, due to the requirement of having a file	2333	implement this functionality, due to the requirement of having a file
1920	descriptor open on the object at all times, and detecting renames, unlinks	2334	descriptor open on the object at all times, and detecting renames, unlinks
1921	etc. is difficult.	2335	etc. is difficult.
1922		2336
		2337	=head3 C<stat ()> is a synchronous operation
		2338
		2339	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2340	the process. The exception are C<ev_stat> watchers - those call C<stat
		2341	()>, which is a synchronous operation.
		2342
		2343	For local paths, this usually doesn't matter: unless the system is very
		2344	busy or the intervals between stat's are large, a stat call will be fast,
		2345	as the path data is usually in memory already (except when starting the
		2346	watcher).
		2347
		2348	For networked file systems, calling C<stat ()> can block an indefinite
		2349	time due to network issues, and even under good conditions, a stat call
		2350	often takes multiple milliseconds.
		2351
		2352	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2353	paths, although this is fully supported by libev.
		2354
1923	=head3 The special problem of stat time resolution	2355	=head3 The special problem of stat time resolution
1924		2356
1925	The C<stat ()> system call only supports full-second resolution portably, and	2357	The C<stat ()> system call only supports full-second resolution portably,
1926	even on systems where the resolution is higher, most file systems still	2358	and even on systems where the resolution is higher, most file systems
1927	only support whole seconds.	2359	still only support whole seconds.
1928		2360
1929	That means that, if the time is the only thing that changes, you can	2361	That means that, if the time is the only thing that changes, you can
1930	easily miss updates: on the first update, C<ev_stat> detects a change and	2362	easily miss updates: on the first update, C<ev_stat> detects a change and
1931	calls your callback, which does something. When there is another update	2363	calls your callback, which does something. When there is another update
1932	within the same second, C<ev_stat> will be unable to detect unless the	2364	within the same second, C<ev_stat> will be unable to detect unless the
…		…
2075		2507
2076	=head3 Watcher-Specific Functions and Data Members	2508	=head3 Watcher-Specific Functions and Data Members
2077		2509
2078	=over 4	2510	=over 4
2079		2511
2080	=item ev_idle_init (ev_signal *, callback)	2512	=item ev_idle_init (ev_idle *, callback)
2081		2513
2082	Initialises and configures the idle watcher - it has no parameters of any	2514	Initialises and configures the idle watcher - it has no parameters of any
2083	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2515	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
2084	believe me.	2516	believe me.
2085		2517
…		…
2098	// no longer anything immediate to do.	2530	// no longer anything immediate to do.
2099	}	2531	}
2100		2532
2101	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2533	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2102	ev_idle_init (idle_watcher, idle_cb);	2534	ev_idle_init (idle_watcher, idle_cb);
2103	ev_idle_start (loop, idle_cb);	2535	ev_idle_start (loop, idle_watcher);
2104		2536
2105		2537
2106	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2538	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2107		2539
2108	Prepare and check watchers are usually (but not always) used in pairs:	2540	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2201	struct pollfd fds [nfd];	2633	struct pollfd fds [nfd];
2202	// actual code will need to loop here and realloc etc.	2634	// actual code will need to loop here and realloc etc.
2203	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2635	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2204		2636
2205	/* the callback is illegal, but won't be called as we stop during check */	2637	/* the callback is illegal, but won't be called as we stop during check */
2206	ev_timer_init (&tw, 0, timeout * 1e-3);	2638	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2207	ev_timer_start (loop, &tw);	2639	ev_timer_start (loop, &tw);
2208		2640
2209	// create one ev_io per pollfd	2641	// create one ev_io per pollfd
2210	for (int i = 0; i < nfd; ++i)	2642	for (int i = 0; i < nfd; ++i)
2211	{	2643	{
…		…
2324	some fds have to be watched and handled very quickly (with low latency),	2756	some fds have to be watched and handled very quickly (with low latency),
2325	and even priorities and idle watchers might have too much overhead. In	2757	and even priorities and idle watchers might have too much overhead. In
2326	this case you would put all the high priority stuff in one loop and all	2758	this case you would put all the high priority stuff in one loop and all
2327	the rest in a second one, and embed the second one in the first.	2759	the rest in a second one, and embed the second one in the first.
2328		2760
2329	As long as the watcher is active, the callback will be invoked every time	2761	As long as the watcher is active, the callback will be invoked every
2330	there might be events pending in the embedded loop. The callback must then	2762	time there might be events pending in the embedded loop. The callback
2331	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2763	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2332	their callbacks (you could also start an idle watcher to give the embedded	2764	sweep and invoke their callbacks (the callback doesn't need to invoke the
2333	loop strictly lower priority for example). You can also set the callback	2765	C<ev_embed_sweep> function directly, it could also start an idle watcher
2334	to C<0>, in which case the embed watcher will automatically execute the	2766	to give the embedded loop strictly lower priority for example).
2335	embedded loop sweep.
2336		2767
2337	As long as the watcher is started it will automatically handle events. The	2768	You can also set the callback to C<0>, in which case the embed watcher
2338	callback will be invoked whenever some events have been handled. You can	2769	will automatically execute the embedded loop sweep whenever necessary.
2339	set the callback to C<0> to avoid having to specify one if you are not
2340	interested in that.
2341		2770
2342	Also, there have not currently been made special provisions for forking:	2771	Fork detection will be handled transparently while the C<ev_embed> watcher
2343	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2772	is active, i.e., the embedded loop will automatically be forked when the
2344	but you will also have to stop and restart any C<ev_embed> watchers	2773	embedding loop forks. In other cases, the user is responsible for calling
2345	yourself - but you can use a fork watcher to handle this automatically,	2774	C<ev_loop_fork> on the embedded loop.
2346	and future versions of libev might do just that.
2347		2775
2348	Unfortunately, not all backends are embeddable: only the ones returned by	2776	Unfortunately, not all backends are embeddable: only the ones returned by
2349	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2777	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2350	portable one.	2778	portable one.
2351		2779
…		…
2445	event loop blocks next and before C<ev_check> watchers are being called,	2873	event loop blocks next and before C<ev_check> watchers are being called,
2446	and only in the child after the fork. If whoever good citizen calling	2874	and only in the child after the fork. If whoever good citizen calling
2447	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2875	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2448	handlers will be invoked, too, of course.	2876	handlers will be invoked, too, of course.
2449		2877
		2878	=head3 The special problem of life after fork - how is it possible?
		2879
		2880	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2881	up/change the process environment, followed by a call to C<exec()>. This
		2882	sequence should be handled by libev without any problems.
		2883
		2884	This changes when the application actually wants to do event handling
		2885	in the child, or both parent in child, in effect "continuing" after the
		2886	fork.
		2887
		2888	The default mode of operation (for libev, with application help to detect
		2889	forks) is to duplicate all the state in the child, as would be expected
		2890	when I<either> the parent I<or> the child process continues.
		2891
		2892	When both processes want to continue using libev, then this is usually the
		2893	wrong result. In that case, usually one process (typically the parent) is
		2894	supposed to continue with all watchers in place as before, while the other
		2895	process typically wants to start fresh, i.e. without any active watchers.
		2896
		2897	The cleanest and most efficient way to achieve that with libev is to
		2898	simply create a new event loop, which of course will be "empty", and
		2899	use that for new watchers. This has the advantage of not touching more
		2900	memory than necessary, and thus avoiding the copy-on-write, and the
		2901	disadvantage of having to use multiple event loops (which do not support
		2902	signal watchers).
		2903
		2904	When this is not possible, or you want to use the default loop for
		2905	other reasons, then in the process that wants to start "fresh", call
		2906	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2907	the default loop will "orphan" (not stop) all registered watchers, so you
		2908	have to be careful not to execute code that modifies those watchers. Note
		2909	also that in that case, you have to re-register any signal watchers.
		2910
2450	=head3 Watcher-Specific Functions and Data Members	2911	=head3 Watcher-Specific Functions and Data Members
2451		2912
2452	=over 4	2913	=over 4
2453		2914
2454	=item ev_fork_init (ev_signal *, callback)	2915	=item ev_fork_init (ev_signal *, callback)
…		…
2571	=over 4	3032	=over 4
2572		3033
2573	=item ev_async_init (ev_async *, callback)	3034	=item ev_async_init (ev_async *, callback)
2574		3035
2575	Initialises and configures the async watcher - it has no parameters of any	3036	Initialises and configures the async watcher - it has no parameters of any
2576	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3037	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2577	trust me.	3038	trust me.
2578		3039
2579	=item ev_async_send (loop, ev_async *)	3040	=item ev_async_send (loop, ev_async *)
2580		3041
2581	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3042	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2582	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3043	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2583	C<ev_feed_event>, this call is safe to do from other threads, signal or	3044	C<ev_feed_event>, this call is safe to do from other threads, signal or
2584	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3045	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2585	section below on what exactly this means).	3046	section below on what exactly this means).
2586		3047
		3048	Note that, as with other watchers in libev, multiple events might get
		3049	compressed into a single callback invocation (another way to look at this
		3050	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3051	reset when the event loop detects that).
		3052
2587	This call incurs the overhead of a system call only once per loop iteration,	3053	This call incurs the overhead of a system call only once per event loop
2588	so while the overhead might be noticeable, it doesn't apply to repeated	3054	iteration, so while the overhead might be noticeable, it doesn't apply to
2589	calls to C<ev_async_send>.	3055	repeated calls to C<ev_async_send> for the same event loop.
2590		3056
2591	=item bool = ev_async_pending (ev_async *)	3057	=item bool = ev_async_pending (ev_async *)
2592		3058
2593	Returns a non-zero value when C<ev_async_send> has been called on the	3059	Returns a non-zero value when C<ev_async_send> has been called on the
2594	watcher but the event has not yet been processed (or even noted) by the	3060	watcher but the event has not yet been processed (or even noted) by the
…		…
2597	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3063	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2598	the loop iterates next and checks for the watcher to have become active,	3064	the loop iterates next and checks for the watcher to have become active,
2599	it will reset the flag again. C<ev_async_pending> can be used to very	3065	it will reset the flag again. C<ev_async_pending> can be used to very
2600	quickly check whether invoking the loop might be a good idea.	3066	quickly check whether invoking the loop might be a good idea.
2601		3067
2602	Not that this does I<not> check whether the watcher itself is pending, only	3068	Not that this does I<not> check whether the watcher itself is pending,
2603	whether it has been requested to make this watcher pending.	3069	only whether it has been requested to make this watcher pending: there
		3070	is a time window between the event loop checking and resetting the async
		3071	notification, and the callback being invoked.
2604		3072
2605	=back	3073	=back
2606		3074
2607		3075
2608	=head1 OTHER FUNCTIONS	3076	=head1 OTHER FUNCTIONS
…		…
2787		3255
2788	myclass obj;	3256	myclass obj;
2789	ev::io iow;	3257	ev::io iow;
2790	iow.set <myclass, &myclass::io_cb> (&obj);	3258	iow.set <myclass, &myclass::io_cb> (&obj);
2791		3259
		3260	=item w->set (object *)
		3261
		3262	This is an B<experimental> feature that might go away in a future version.
		3263
		3264	This is a variation of a method callback - leaving out the method to call
		3265	will default the method to C<operator ()>, which makes it possible to use
		3266	functor objects without having to manually specify the C<operator ()> all
		3267	the time. Incidentally, you can then also leave out the template argument
		3268	list.
		3269
		3270	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3271	int revents)>.
		3272
		3273	See the method-C<set> above for more details.
		3274
		3275	Example: use a functor object as callback.
		3276
		3277	struct myfunctor
		3278	{
		3279	void operator() (ev::io &w, int revents)
		3280	{
		3281	...
		3282	}
		3283	}
		3284
		3285	myfunctor f;
		3286
		3287	ev::io w;
		3288	w.set (&f);
		3289
2792	=item w->set<function> (void *data = 0)	3290	=item w->set<function> (void *data = 0)
2793		3291
2794	Also sets a callback, but uses a static method or plain function as	3292	Also sets a callback, but uses a static method or plain function as
2795	callback. The optional C<data> argument will be stored in the watcher's	3293	callback. The optional C<data> argument will be stored in the watcher's
2796	C<data> member and is free for you to use.	3294	C<data> member and is free for you to use.
…		…
2882	L<http://software.schmorp.de/pkg/EV>.	3380	L<http://software.schmorp.de/pkg/EV>.
2883		3381
2884	=item Python	3382	=item Python
2885		3383
2886	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3384	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2887	seems to be quite complete and well-documented. Note, however, that the	3385	seems to be quite complete and well-documented.
2888	patch they require for libev is outright dangerous as it breaks the ABI
2889	for everybody else, and therefore, should never be applied in an installed
2890	libev (if python requires an incompatible ABI then it needs to embed
2891	libev).
2892		3386
2893	=item Ruby	3387	=item Ruby
2894		3388
2895	Tony Arcieri has written a ruby extension that offers access to a subset	3389	Tony Arcieri has written a ruby extension that offers access to a subset
2896	of the libev API and adds file handle abstractions, asynchronous DNS and	3390	of the libev API and adds file handle abstractions, asynchronous DNS and
2897	more on top of it. It can be found via gem servers. Its homepage is at	3391	more on top of it. It can be found via gem servers. Its homepage is at
2898	L<http://rev.rubyforge.org/>.	3392	L<http://rev.rubyforge.org/>.
2899		3393
		3394	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3395	makes rev work even on mingw.
		3396
		3397	=item Haskell
		3398
		3399	A haskell binding to libev is available at
		3400	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3401
2900	=item D	3402	=item D
2901		3403
2902	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3404	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2903	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3405	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3406
		3407	=item Ocaml
		3408
		3409	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3410	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3411
		3412	=item Lua
		3413
		3414	Brian Maher has written a partial interface to libev
		3415	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3416	L<http://github.com/brimworks/lua-ev>.
2904		3417
2905	=back	3418	=back
2906		3419
2907		3420
2908	=head1 MACRO MAGIC	3421	=head1 MACRO MAGIC
…		…
3009		3522
3010	#define EV_STANDALONE 1	3523	#define EV_STANDALONE 1
3011	#include "ev.h"	3524	#include "ev.h"
3012		3525
3013	Both header files and implementation files can be compiled with a C++	3526	Both header files and implementation files can be compiled with a C++
3014	compiler (at least, thats a stated goal, and breakage will be treated	3527	compiler (at least, that's a stated goal, and breakage will be treated
3015	as a bug).	3528	as a bug).
3016		3529
3017	You need the following files in your source tree, or in a directory	3530	You need the following files in your source tree, or in a directory
3018	in your include path (e.g. in libev/ when using -Ilibev):	3531	in your include path (e.g. in libev/ when using -Ilibev):
3019		3532
…		…
3075	keeps libev from including F<config.h>, and it also defines dummy	3588	keeps libev from including F<config.h>, and it also defines dummy
3076	implementations for some libevent functions (such as logging, which is not	3589	implementations for some libevent functions (such as logging, which is not
3077	supported). It will also not define any of the structs usually found in	3590	supported). It will also not define any of the structs usually found in
3078	F<event.h> that are not directly supported by the libev core alone.	3591	F<event.h> that are not directly supported by the libev core alone.
3079		3592
		3593	In standalone mode, libev will still try to automatically deduce the
		3594	configuration, but has to be more conservative.
		3595
3080	=item EV_USE_MONOTONIC	3596	=item EV_USE_MONOTONIC
3081		3597
3082	If defined to be C<1>, libev will try to detect the availability of the	3598	If defined to be C<1>, libev will try to detect the availability of the
3083	monotonic clock option at both compile time and runtime. Otherwise no use	3599	monotonic clock option at both compile time and runtime. Otherwise no
3084	of the monotonic clock option will be attempted. If you enable this, you	3600	use of the monotonic clock option will be attempted. If you enable this,
3085	usually have to link against librt or something similar. Enabling it when	3601	you usually have to link against librt or something similar. Enabling it
3086	the functionality isn't available is safe, though, although you have	3602	when the functionality isn't available is safe, though, although you have
3087	to make sure you link against any libraries where the C<clock_gettime>	3603	to make sure you link against any libraries where the C<clock_gettime>
3088	function is hiding in (often F<-lrt>).	3604	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
3089		3605
3090	=item EV_USE_REALTIME	3606	=item EV_USE_REALTIME
3091		3607
3092	If defined to be C<1>, libev will try to detect the availability of the	3608	If defined to be C<1>, libev will try to detect the availability of the
3093	real-time clock option at compile time (and assume its availability at	3609	real-time clock option at compile time (and assume its availability
3094	runtime if successful). Otherwise no use of the real-time clock option will	3610	at runtime if successful). Otherwise no use of the real-time clock
3095	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3611	option will be attempted. This effectively replaces C<gettimeofday>
3096	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3612	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
3097	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3613	correctness. See the note about libraries in the description of
		3614	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3615	C<EV_USE_CLOCK_SYSCALL>.
		3616
		3617	=item EV_USE_CLOCK_SYSCALL
		3618
		3619	If defined to be C<1>, libev will try to use a direct syscall instead
		3620	of calling the system-provided C<clock_gettime> function. This option
		3621	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3622	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3623	programs needlessly. Using a direct syscall is slightly slower (in
		3624	theory), because no optimised vdso implementation can be used, but avoids
		3625	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3626	higher, as it simplifies linking (no need for C<-lrt>).
3098		3627
3099	=item EV_USE_NANOSLEEP	3628	=item EV_USE_NANOSLEEP
3100		3629
3101	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3630	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
3102	and will use it for delays. Otherwise it will use C<select ()>.	3631	and will use it for delays. Otherwise it will use C<select ()>.
…		…
3118		3647
3119	=item EV_SELECT_USE_FD_SET	3648	=item EV_SELECT_USE_FD_SET
3120		3649
3121	If defined to C<1>, then the select backend will use the system C<fd_set>	3650	If defined to C<1>, then the select backend will use the system C<fd_set>
3122	structure. This is useful if libev doesn't compile due to a missing	3651	structure. This is useful if libev doesn't compile due to a missing
3123	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3652	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
3124	exotic systems. This usually limits the range of file descriptors to some	3653	on exotic systems. This usually limits the range of file descriptors to
3125	low limit such as 1024 or might have other limitations (winsocket only	3654	some low limit such as 1024 or might have other limitations (winsocket
3126	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3655	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
3127	influence the size of the C<fd_set> used.	3656	configures the maximum size of the C<fd_set>.
3128		3657
3129	=item EV_SELECT_IS_WINSOCKET	3658	=item EV_SELECT_IS_WINSOCKET
3130		3659
3131	When defined to C<1>, the select backend will assume that	3660	When defined to C<1>, the select backend will assume that
3132	select/socket/connect etc. don't understand file descriptors but	3661	select/socket/connect etc. don't understand file descriptors but
…		…
3282	defined to be C<0>, then they are not.	3811	defined to be C<0>, then they are not.
3283		3812
3284	=item EV_MINIMAL	3813	=item EV_MINIMAL
3285		3814
3286	If you need to shave off some kilobytes of code at the expense of some	3815	If you need to shave off some kilobytes of code at the expense of some
3287	speed, define this symbol to C<1>. Currently this is used to override some	3816	speed (but with the full API), define this symbol to C<1>. Currently this
3288	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3817	is used to override some inlining decisions, saves roughly 30% code size
3289	much smaller 2-heap for timer management over the default 4-heap.	3818	on amd64. It also selects a much smaller 2-heap for timer management over
		3819	the default 4-heap.
		3820
		3821	You can save even more by disabling watcher types you do not need
		3822	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3823	(C<-DNDEBUG>) will usually reduce code size a lot.
		3824
		3825	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3826	provide a bare-bones event library. See C<ev.h> for details on what parts
		3827	of the API are still available, and do not complain if this subset changes
		3828	over time.
		3829
		3830	=item EV_NSIG
		3831
		3832	The highest supported signal number, +1 (or, the number of
		3833	signals): Normally, libev tries to deduce the maximum number of signals
		3834	automatically, but sometimes this fails, in which case it can be
		3835	specified. Also, using a lower number than detected (C<32> should be
		3836	good for about any system in existance) can save some memory, as libev
		3837	statically allocates some 12-24 bytes per signal number.
3290		3838
3291	=item EV_PID_HASHSIZE	3839	=item EV_PID_HASHSIZE
3292		3840
3293	C<ev_child> watchers use a small hash table to distribute workload by	3841	C<ev_child> watchers use a small hash table to distribute workload by
3294	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3842	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3480	default loop and triggering an C<ev_async> watcher from the default loop	4028	default loop and triggering an C<ev_async> watcher from the default loop
3481	watcher callback into the event loop interested in the signal.	4029	watcher callback into the event loop interested in the signal.
3482		4030
3483	=back	4031	=back
3484		4032
		4033	=head4 THREAD LOCKING EXAMPLE
		4034
		4035	Here is a fictitious example of how to run an event loop in a different
		4036	thread than where callbacks are being invoked and watchers are
		4037	created/added/removed.
		4038
		4039	For a real-world example, see the C<EV::Loop::Async> perl module,
		4040	which uses exactly this technique (which is suited for many high-level
		4041	languages).
		4042
		4043	The example uses a pthread mutex to protect the loop data, a condition
		4044	variable to wait for callback invocations, an async watcher to notify the
		4045	event loop thread and an unspecified mechanism to wake up the main thread.
		4046
		4047	First, you need to associate some data with the event loop:
		4048
		4049	typedef struct {
		4050	mutex_t lock; /* global loop lock */
		4051	ev_async async_w;
		4052	thread_t tid;
		4053	cond_t invoke_cv;
		4054	} userdata;
		4055
		4056	void prepare_loop (EV_P)
		4057	{
		4058	// for simplicity, we use a static userdata struct.
		4059	static userdata u;
		4060
		4061	ev_async_init (&u->async_w, async_cb);
		4062	ev_async_start (EV_A_ &u->async_w);
		4063
		4064	pthread_mutex_init (&u->lock, 0);
		4065	pthread_cond_init (&u->invoke_cv, 0);
		4066
		4067	// now associate this with the loop
		4068	ev_set_userdata (EV_A_ u);
		4069	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4070	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4071
		4072	// then create the thread running ev_loop
		4073	pthread_create (&u->tid, 0, l_run, EV_A);
		4074	}
		4075
		4076	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4077	solely to wake up the event loop so it takes notice of any new watchers
		4078	that might have been added:
		4079
		4080	static void
		4081	async_cb (EV_P_ ev_async *w, int revents)
		4082	{
		4083	// just used for the side effects
		4084	}
		4085
		4086	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4087	protecting the loop data, respectively.
		4088
		4089	static void
		4090	l_release (EV_P)
		4091	{
		4092	userdata *u = ev_userdata (EV_A);
		4093	pthread_mutex_unlock (&u->lock);
		4094	}
		4095
		4096	static void
		4097	l_acquire (EV_P)
		4098	{
		4099	userdata *u = ev_userdata (EV_A);
		4100	pthread_mutex_lock (&u->lock);
		4101	}
		4102
		4103	The event loop thread first acquires the mutex, and then jumps straight
		4104	into C<ev_loop>:
		4105
		4106	void *
		4107	l_run (void *thr_arg)
		4108	{
		4109	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4110
		4111	l_acquire (EV_A);
		4112	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4113	ev_loop (EV_A_ 0);
		4114	l_release (EV_A);
		4115
		4116	return 0;
		4117	}
		4118
		4119	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4120	signal the main thread via some unspecified mechanism (signals? pipe
		4121	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4122	have been called (in a while loop because a) spurious wakeups are possible
		4123	and b) skipping inter-thread-communication when there are no pending
		4124	watchers is very beneficial):
		4125
		4126	static void
		4127	l_invoke (EV_P)
		4128	{
		4129	userdata *u = ev_userdata (EV_A);
		4130
		4131	while (ev_pending_count (EV_A))
		4132	{
		4133	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4134	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4135	}
		4136	}
		4137
		4138	Now, whenever the main thread gets told to invoke pending watchers, it
		4139	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4140	thread to continue:
		4141
		4142	static void
		4143	real_invoke_pending (EV_P)
		4144	{
		4145	userdata *u = ev_userdata (EV_A);
		4146
		4147	pthread_mutex_lock (&u->lock);
		4148	ev_invoke_pending (EV_A);
		4149	pthread_cond_signal (&u->invoke_cv);
		4150	pthread_mutex_unlock (&u->lock);
		4151	}
		4152
		4153	Whenever you want to start/stop a watcher or do other modifications to an
		4154	event loop, you will now have to lock:
		4155
		4156	ev_timer timeout_watcher;
		4157	userdata *u = ev_userdata (EV_A);
		4158
		4159	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4160
		4161	pthread_mutex_lock (&u->lock);
		4162	ev_timer_start (EV_A_ &timeout_watcher);
		4163	ev_async_send (EV_A_ &u->async_w);
		4164	pthread_mutex_unlock (&u->lock);
		4165
		4166	Note that sending the C<ev_async> watcher is required because otherwise
		4167	an event loop currently blocking in the kernel will have no knowledge
		4168	about the newly added timer. By waking up the loop it will pick up any new
		4169	watchers in the next event loop iteration.
		4170
3485	=head3 COROUTINES	4171	=head3 COROUTINES
3486		4172
3487	Libev is very accommodating to coroutines ("cooperative threads"):	4173	Libev is very accommodating to coroutines ("cooperative threads"):
3488	libev fully supports nesting calls to its functions from different	4174	libev fully supports nesting calls to its functions from different
3489	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4175	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3490	different coroutines, and switch freely between both coroutines running the	4176	different coroutines, and switch freely between both coroutines running
3491	loop, as long as you don't confuse yourself). The only exception is that	4177	the loop, as long as you don't confuse yourself). The only exception is
3492	you must not do this from C<ev_periodic> reschedule callbacks.	4178	that you must not do this from C<ev_periodic> reschedule callbacks.
3493		4179
3494	Care has been taken to ensure that libev does not keep local state inside	4180	Care has been taken to ensure that libev does not keep local state inside
3495	C<ev_loop>, and other calls do not usually allow for coroutine switches as	4181	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3496	they do not clal any callbacks.	4182	they do not call any callbacks.
3497		4183
3498	=head2 COMPILER WARNINGS	4184	=head2 COMPILER WARNINGS
3499		4185
3500	Depending on your compiler and compiler settings, you might get no or a	4186	Depending on your compiler and compiler settings, you might get no or a
3501	lot of warnings when compiling libev code. Some people are apparently	4187	lot of warnings when compiling libev code. Some people are apparently
…		…
3535	==2274== definitely lost: 0 bytes in 0 blocks.	4221	==2274== definitely lost: 0 bytes in 0 blocks.
3536	==2274== possibly lost: 0 bytes in 0 blocks.	4222	==2274== possibly lost: 0 bytes in 0 blocks.
3537	==2274== still reachable: 256 bytes in 1 blocks.	4223	==2274== still reachable: 256 bytes in 1 blocks.
3538		4224
3539	Then there is no memory leak, just as memory accounted to global variables	4225	Then there is no memory leak, just as memory accounted to global variables
3540	is not a memleak - the memory is still being refernced, and didn't leak.	4226	is not a memleak - the memory is still being referenced, and didn't leak.
3541		4227
3542	Similarly, under some circumstances, valgrind might report kernel bugs	4228	Similarly, under some circumstances, valgrind might report kernel bugs
3543	as if it were a bug in libev (e.g. in realloc or in the poll backend,	4229	as if it were a bug in libev (e.g. in realloc or in the poll backend,
3544	although an acceptable workaround has been found here), or it might be	4230	although an acceptable workaround has been found here), or it might be
3545	confused.	4231	confused.
…		…
3574	way (note also that glib is the slowest event library known to man).	4260	way (note also that glib is the slowest event library known to man).
3575		4261
3576	There is no supported compilation method available on windows except	4262	There is no supported compilation method available on windows except
3577	embedding it into other applications.	4263	embedding it into other applications.
3578		4264
		4265	Sensible signal handling is officially unsupported by Microsoft - libev
		4266	tries its best, but under most conditions, signals will simply not work.
		4267
3579	Not a libev limitation but worth mentioning: windows apparently doesn't	4268	Not a libev limitation but worth mentioning: windows apparently doesn't
3580	accept large writes: instead of resulting in a partial write, windows will	4269	accept large writes: instead of resulting in a partial write, windows will
3581	either accept everything or return C<ENOBUFS> if the buffer is too large,	4270	either accept everything or return C<ENOBUFS> if the buffer is too large,
3582	so make sure you only write small amounts into your sockets (less than a	4271	so make sure you only write small amounts into your sockets (less than a
3583	megabyte seems safe, but this apparently depends on the amount of memory	4272	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3587	the abysmal performance of winsockets, using a large number of sockets	4276	the abysmal performance of winsockets, using a large number of sockets
3588	is not recommended (and not reasonable). If your program needs to use	4277	is not recommended (and not reasonable). If your program needs to use
3589	more than a hundred or so sockets, then likely it needs to use a totally	4278	more than a hundred or so sockets, then likely it needs to use a totally
3590	different implementation for windows, as libev offers the POSIX readiness	4279	different implementation for windows, as libev offers the POSIX readiness
3591	notification model, which cannot be implemented efficiently on windows	4280	notification model, which cannot be implemented efficiently on windows
3592	(Microsoft monopoly games).	4281	(due to Microsoft monopoly games).
3593		4282
3594	A typical way to use libev under windows is to embed it (see the embedding	4283	A typical way to use libev under windows is to embed it (see the embedding
3595	section for details) and use the following F<evwrap.h> header file instead	4284	section for details) and use the following F<evwrap.h> header file instead
3596	of F<ev.h>:	4285	of F<ev.h>:
3597		4286
…		…
3633		4322
3634	Early versions of winsocket's select only supported waiting for a maximum	4323	Early versions of winsocket's select only supported waiting for a maximum
3635	of C<64> handles (probably owning to the fact that all windows kernels	4324	of C<64> handles (probably owning to the fact that all windows kernels
3636	can only wait for C<64> things at the same time internally; Microsoft	4325	can only wait for C<64> things at the same time internally; Microsoft
3637	recommends spawning a chain of threads and wait for 63 handles and the	4326	recommends spawning a chain of threads and wait for 63 handles and the
3638	previous thread in each. Great).	4327	previous thread in each. Sounds great!).
3639		4328
3640	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4329	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3641	to some high number (e.g. C<2048>) before compiling the winsocket select	4330	to some high number (e.g. C<2048>) before compiling the winsocket select
3642	call (which might be in libev or elsewhere, for example, perl does its own	4331	call (which might be in libev or elsewhere, for example, perl and many
3643	select emulation on windows).	4332	other interpreters do their own select emulation on windows).
3644		4333
3645	Another limit is the number of file descriptors in the Microsoft runtime	4334	Another limit is the number of file descriptors in the Microsoft runtime
3646	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4335	libraries, which by default is C<64> (there must be a hidden I<64>
3647	or something like this inside Microsoft). You can increase this by calling	4336	fetish or something like this inside Microsoft). You can increase this
3648	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4337	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3649	arbitrary limit), but is broken in many versions of the Microsoft runtime	4338	(another arbitrary limit), but is broken in many versions of the Microsoft
3650	libraries.
3651
3652	This might get you to about C<512> or C<2048> sockets (depending on	4339	runtime libraries. This might get you to about C<512> or C<2048> sockets
3653	windows version and/or the phase of the moon). To get more, you need to	4340	(depending on windows version and/or the phase of the moon). To get more,
3654	wrap all I/O functions and provide your own fd management, but the cost of	4341	you need to wrap all I/O functions and provide your own fd management, but
3655	calling select (O(n²)) will likely make this unworkable.	4342	the cost of calling select (O(n²)) will likely make this unworkable.
3656		4343
3657	=back	4344	=back
3658		4345
3659	=head2 PORTABILITY REQUIREMENTS	4346	=head2 PORTABILITY REQUIREMENTS
3660		4347
…		…
3703	=item C<double> must hold a time value in seconds with enough accuracy	4390	=item C<double> must hold a time value in seconds with enough accuracy
3704		4391
3705	The type C<double> is used to represent timestamps. It is required to	4392	The type C<double> is used to represent timestamps. It is required to
3706	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4393	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3707	enough for at least into the year 4000. This requirement is fulfilled by	4394	enough for at least into the year 4000. This requirement is fulfilled by
3708	implementations implementing IEEE 754 (basically all existing ones).	4395	implementations implementing IEEE 754, which is basically all existing
		4396	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4397	2200.
3709		4398
3710	=back	4399	=back
3711		4400
3712	If you know of other additional requirements drop me a note.	4401	If you know of other additional requirements drop me a note.
3713		4402
…		…
3781	involves iterating over all running async watchers or all signal numbers.	4470	involves iterating over all running async watchers or all signal numbers.
3782		4471
3783	=back	4472	=back
3784		4473
3785		4474
		4475	=head1 GLOSSARY
		4476
		4477	=over 4
		4478
		4479	=item active
		4480
		4481	A watcher is active as long as it has been started (has been attached to
		4482	an event loop) but not yet stopped (disassociated from the event loop).
		4483
		4484	=item application
		4485
		4486	In this document, an application is whatever is using libev.
		4487
		4488	=item callback
		4489
		4490	The address of a function that is called when some event has been
		4491	detected. Callbacks are being passed the event loop, the watcher that
		4492	received the event, and the actual event bitset.
		4493
		4494	=item callback invocation
		4495
		4496	The act of calling the callback associated with a watcher.
		4497
		4498	=item event
		4499
		4500	A change of state of some external event, such as data now being available
		4501	for reading on a file descriptor, time having passed or simply not having
		4502	any other events happening anymore.
		4503
		4504	In libev, events are represented as single bits (such as C<EV_READ> or
		4505	C<EV_TIMEOUT>).
		4506
		4507	=item event library
		4508
		4509	A software package implementing an event model and loop.
		4510
		4511	=item event loop
		4512
		4513	An entity that handles and processes external events and converts them
		4514	into callback invocations.
		4515
		4516	=item event model
		4517
		4518	The model used to describe how an event loop handles and processes
		4519	watchers and events.
		4520
		4521	=item pending
		4522
		4523	A watcher is pending as soon as the corresponding event has been detected,
		4524	and stops being pending as soon as the watcher will be invoked or its
		4525	pending status is explicitly cleared by the application.
		4526
		4527	A watcher can be pending, but not active. Stopping a watcher also clears
		4528	its pending status.
		4529
		4530	=item real time
		4531
		4532	The physical time that is observed. It is apparently strictly monotonic :)
		4533
		4534	=item wall-clock time
		4535
		4536	The time and date as shown on clocks. Unlike real time, it can actually
		4537	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4538	clock.
		4539
		4540	=item watcher
		4541
		4542	A data structure that describes interest in certain events. Watchers need
		4543	to be started (attached to an event loop) before they can receive events.
		4544
		4545	=item watcher invocation
		4546
		4547	The act of calling the callback associated with a watcher.
		4548
		4549	=back
		4550
3786	=head1 AUTHOR	4551	=head1 AUTHOR
3787		4552
3788	Marc Lehmann <libev@schmorp.de>.	4553	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3789		4554

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