ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.188 by root, Tue Sep 30 18:35:47 2008 UTC vs.
Revision 1.282 by root, Wed Mar 10 08:19:39 2010 UTC

…		…
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
		14	#include <stdio.h> // for puts
		15
14	// every watcher type has its own typedef'd struct	16	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	17	// with the name ev_TYPE
16	ev_io stdin_watcher;	18	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
18		20
19	// all watcher callbacks have a similar signature	21	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	22	// this callback is called when data is readable on stdin
21	static void	23	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	25	{
24	puts ("stdin ready");	26	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	27	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	28	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	29	ev_io_stop (EV_A_ w);
…		…
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	32	ev_unloop (EV_A_ EVUNLOOP_ALL);
31	}	33	}
32		34
33	// another callback, this time for a time-out	35	// another callback, this time for a time-out
34	static void	36	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	38	{
37	puts ("timeout");	39	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	40	// this causes the innermost ev_loop to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	41	ev_unloop (EV_A_ EVUNLOOP_ONE);
40	}	42	}
…		…
60		62
61	// unloop was called, so exit	63	// unloop was called, so exit
62	return 0;	64	return 0;
63	}	65	}
64		66
65	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
66		70
67	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
70		84
71	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	87	these event sources and provide your program with events.
74		88
…		…
84	=head2 FEATURES	98	=head2 FEATURES
85		99
86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
91	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
94	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
96		111
97	It also is quite fast (see this	112	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	114	for example).
100		115
…		…
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
109	this argument.	124	this argument.
110		125
111	=head2 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
112		127
113	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
115	the beginning of 1970, details are complicated, don't ask). This type is	130	near the beginning of 1970, details are complicated, don't ask). This
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	type is called C<ev_tstamp>, which is what you should use too. It usually
117	to the C<double> type in C, and when you need to do any calculations on	132	aliases to the C<double> type in C. When you need to do any calculations
118	it, you should treat it as some floating point value. Unlike the name	133	on it, you should treat it as some floating point value. Unlike the name
119	component C<stamp> might indicate, it is also used for time differences	134	component C<stamp> might indicate, it is also used for time differences
120	throughout libev.	135	throughout libev.
121		136
122	=head1 ERROR HANDLING	137	=head1 ERROR HANDLING
123		138
…		…
276		291
277	=back	292	=back
278		293
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	294	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280		295
281	An event loop is described by a C<struct ev_loop *>. The library knows two	296	An event loop is described by a C<struct ev_loop *> (the C<struct>
282	types of such loops, the I<default> loop, which supports signals and child	297	is I<not> optional in this case, as there is also an C<ev_loop>
283	events, and dynamically created loops which do not.	298	I<function>).
		299
		300	The library knows two types of such loops, the I<default> loop, which
		301	supports signals and child events, and dynamically created loops which do
		302	not.
284		303
285	=over 4	304	=over 4
286		305
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	306	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		307
…		…
294	If you don't know what event loop to use, use the one returned from this	313	If you don't know what event loop to use, use the one returned from this
295	function.	314	function.
296		315
297	Note that this function is I<not> thread-safe, so if you want to use it	316	Note that this function is I<not> thread-safe, so if you want to use it
298	from multiple threads, you have to lock (note also that this is unlikely,	317	from multiple threads, you have to lock (note also that this is unlikely,
299	as loops cannot bes hared easily between threads anyway).	318	as loops cannot be shared easily between threads anyway).
300		319
301	The default loop is the only loop that can handle C<ev_signal> and	320	The default loop is the only loop that can handle C<ev_signal> and
302	C<ev_child> watchers, and to do this, it always registers a handler	321	C<ev_child> watchers, and to do this, it always registers a handler
303	for C<SIGCHLD>. If this is a problem for your application you can either	322	for C<SIGCHLD>. If this is a problem for your application you can either
304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	323	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
344	flag.	363	flag.
345		364
346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
347	environment variable.	366	environment variable.
348		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_SIGNALFD>
		376
		377	When this flag is specified, then libev will attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		379	delivers signals synchronously, which makes it both faster and might make
		380	it possible to get the queued signal data. It can also simplify signal
		381	handling with threads, as long as you properly block signals in your
		382	threads that are not interested in handling them.
		383
		384	Signalfd will not be used by default as this changes your signal mask, and
		385	there are a lot of shoddy libraries and programs (glib's threadpool for
		386	example) that can't properly initialise their signal masks.
		387
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		389
351	This is your standard select(2) backend. Not I<completely> standard, as	390	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,	391	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	392	but if that fails, expect a fairly low limit on the number of fds when
…		…
377	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and	416	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
378	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	417	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
379		418
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	419	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		420
		421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		422	kernels).
		423
382	For few fds, this backend is a bit little slower than poll and select,	424	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	425	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),	426	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	427	epoll scales either O(1) or O(active_fds).
386	of shortcomings, such as silently dropping events in some hard-to-detect	428
387	cases and requiring a system call per fd change, no fork support and bad	429	The epoll mechanism deserves honorable mention as the most misdesigned
388	support for dup.	430	of the more advanced event mechanisms: mere annoyances include silently
		431	dropping file descriptors, requiring a system call per change per file
		432	descriptor (and unnecessary guessing of parameters), problems with dup and
		433	so on. The biggest issue is fork races, however - if a program forks then
		434	I<both> parent and child process have to recreate the epoll set, which can
		435	take considerable time (one syscall per file descriptor) and is of course
		436	hard to detect.
		437
		438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		439	of course I<doesn't>, and epoll just loves to report events for totally
		440	I<different> file descriptors (even already closed ones, so one cannot
		441	even remove them from the set) than registered in the set (especially
		442	on SMP systems). Libev tries to counter these spurious notifications by
		443	employing an additional generation counter and comparing that against the
		444	events to filter out spurious ones, recreating the set when required.
389		445
390	While stopping, setting and starting an I/O watcher in the same iteration	446	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	447	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	448	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	449	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
394	very well if you register events for both fds.	450	file descriptors might not work very well if you register events for both
395		451	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		452
400	Best performance from this backend is achieved by not unregistering all	453	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible,	454	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	455	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	456	starting a watcher (without re-setting it) also usually doesn't cause
404	extra overhead.	457	extra overhead. A fork can both result in spurious notifications as well
		458	as in libev having to destroy and recreate the epoll object, which can
		459	take considerable time and thus should be avoided.
		460
		461	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		462	faster than epoll for maybe up to a hundred file descriptors, depending on
		463	the usage. So sad.
405		464
406	While nominally embeddable in other event loops, this feature is broken in	465	While nominally embeddable in other event loops, this feature is broken in
407	all kernel versions tested so far.	466	all kernel versions tested so far.
408		467
409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	468	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
410	C<EVBACKEND_POLL>.	469	C<EVBACKEND_POLL>.
411		470
412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	471	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
413		472
414	Kqueue deserves special mention, as at the time of this writing, it was	473	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	474	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	475	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	476	it's completely useless). Unlike epoll, however, whose brokenness
418	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or	477	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.	478	without API changes to existing programs. For this reason it's not being
		479	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		480	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		481	system like NetBSD.
420		482
421	You still can embed kqueue into a normal poll or select backend and use it	483	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	484	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.	485	the target platform). See C<ev_embed> watchers for more info.
424		486
425	It scales in the same way as the epoll backend, but the interface to the	487	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	488	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	489	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	490	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	491	two event changes per incident. Support for C<fork ()> is very bad (but
430	drops fds silently in similarly hard-to-detect cases.	492	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		493	cases
431		494
432	This backend usually performs well under most conditions.	495	This backend usually performs well under most conditions.
433		496
434	While nominally embeddable in other event loops, this doesn't work	497	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	498	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	499	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	500	(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,	501	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
439	using it only for sockets.	502	also broken on OS X)) and, did I mention it, using it only for sockets.
440		503
441	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with	504	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	505	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
443	C<NOTE_EOF>.	506	C<NOTE_EOF>.
444		507
…		…
464	might perform better.	527	might perform better.
465		528
466	On the positive side, with the exception of the spurious readiness	529	On the positive side, with the exception of the spurious readiness
467	notifications, this backend actually performed fully to specification	530	notifications, this backend actually performed fully to specification
468	in all tests and is fully embeddable, which is a rare feat among the	531	in all tests and is fully embeddable, which is a rare feat among the
469	OS-specific backends.	532	OS-specific backends (I vastly prefer correctness over speed hacks).
470		533
471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	534	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
472	C<EVBACKEND_POLL>.	535	C<EVBACKEND_POLL>.
473		536
474	=item C<EVBACKEND_ALL>	537	=item C<EVBACKEND_ALL>
…		…
479		542
480	It is definitely not recommended to use this flag.	543	It is definitely not recommended to use this flag.
481		544
482	=back	545	=back
483		546
484	If one or more of these are or'ed into the flags value, then only these	547	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	548	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.	549	here). If none are specified, all backends in C<ev_recommended_backends
		550	()> will be tried.
487		551
488	Example: This is the most typical usage.	552	Example: This is the most typical usage.
489		553
490	if (!ev_default_loop (0))	554	if (!ev_default_loop (0))
491	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	555	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
…		…
527	responsibility to either stop all watchers cleanly yourself I<before>	591	responsibility to either stop all watchers cleanly yourself I<before>
528	calling this function, or cope with the fact afterwards (which is usually	592	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	593	the easiest thing, you can just ignore the watchers and/or C<free ()> them
530	for example).	594	for example).
531		595
532	Note that certain global state, such as signal state, will not be freed by	596	Note that certain global state, such as signal state (and installed signal
533	this function, and related watchers (such as signal and child watchers)	597	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	598	as signal and child watchers) would need to be stopped manually.
535		599
536	In general it is not advisable to call this function except in the	600	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	601	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	602	pipe fds. If you need dynamically allocated loops it is better to use
539	C<ev_loop_new> and C<ev_loop_destroy>).	603	C<ev_loop_new> and C<ev_loop_destroy>.
540		604
541	=item ev_loop_destroy (loop)	605	=item ev_loop_destroy (loop)
542		606
543	Like C<ev_default_destroy>, but destroys an event loop created by an	607	Like C<ev_default_destroy>, but destroys an event loop created by an
544	earlier call to C<ev_loop_new>.	608	earlier call to C<ev_loop_new>.
…		…
582		646
583	This value can sometimes be useful as a generation counter of sorts (it	647	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	648	"ticks" the number of loop iterations), as it roughly corresponds with
585	C<ev_prepare> and C<ev_check> calls.	649	C<ev_prepare> and C<ev_check> calls.
586		650
		651	=item unsigned int ev_loop_depth (loop)
		652
		653	Returns the number of times C<ev_loop> was entered minus the number of
		654	times C<ev_loop> was exited, in other words, the recursion depth.
		655
		656	Outside C<ev_loop>, this number is zero. In a callback, this number is
		657	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		658	in which case it is higher.
		659
		660	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		661	etc.), doesn't count as exit.
		662
587	=item unsigned int ev_backend (loop)	663	=item unsigned int ev_backend (loop)
588		664
589	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	665	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
590	use.	666	use.
591		667
…		…
605		681
606	This function is rarely useful, but when some event callback runs for a	682	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	683	very long time without entering the event loop, updating libev's idea of
608	the current time is a good idea.	684	the current time is a good idea.
609		685
610	See also "The special problem of time updates" in the C<ev_timer> section.	686	See also L<The special problem of time updates> in the C<ev_timer> section.
		687
		688	=item ev_suspend (loop)
		689
		690	=item ev_resume (loop)
		691
		692	These two functions suspend and resume a loop, for use when the loop is
		693	not used for a while and timeouts should not be processed.
		694
		695	A typical use case would be an interactive program such as a game: When
		696	the user presses C<^Z> to suspend the game and resumes it an hour later it
		697	would be best to handle timeouts as if no time had actually passed while
		698	the program was suspended. This can be achieved by calling C<ev_suspend>
		699	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		700	C<ev_resume> directly afterwards to resume timer processing.
		701
		702	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		703	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		704	will be rescheduled (that is, they will lose any events that would have
		705	occured while suspended).
		706
		707	After calling C<ev_suspend> you B<must not> call I<any> function on the
		708	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		709	without a previous call to C<ev_suspend>.
		710
		711	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		712	event loop time (see C<ev_now_update>).
611		713
612	=item ev_loop (loop, int flags)	714	=item ev_loop (loop, int flags)
613		715
614	Finally, this is it, the event handler. This function usually is called	716	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	717	after you have initialised all your watchers and you want to start
616	events.	718	handling events.
617		719
618	If the flags argument is specified as C<0>, it will not return until	720	If the flags argument is specified as C<0>, it will not return until
619	either no event watchers are active anymore or C<ev_unloop> was called.	721	either no event watchers are active anymore or C<ev_unloop> was called.
620		722
621	Please note that an explicit C<ev_unloop> is usually better than	723	Please note that an explicit C<ev_unloop> is usually better than
…		…
631	the loop.	733	the loop.
632		734
633	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	735	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	736	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	737	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	738	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	739	user-registered callback will be called), and will return after one
638	iteration of the loop.	740	iteration of the loop.
639		741
640	This is useful if you are waiting for some external event in conjunction	742	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	743	with something not expressible using other libev watchers (i.e. "roll your
…		…
685	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	787	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
686	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	788	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
687		789
688	This "unloop state" will be cleared when entering C<ev_loop> again.	790	This "unloop state" will be cleared when entering C<ev_loop> again.
689		791
		792	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		793
690	=item ev_ref (loop)	794	=item ev_ref (loop)
691		795
692	=item ev_unref (loop)	796	=item ev_unref (loop)
693		797
694	Ref/unref can be used to add or remove a reference count on the event	798	Ref/unref can be used to add or remove a reference count on the event
695	loop: Every watcher keeps one reference, and as long as the reference	799	loop: Every watcher keeps one reference, and as long as the reference
696	count is nonzero, C<ev_loop> will not return on its own.	800	count is nonzero, C<ev_loop> will not return on its own.
697		801
698	If you have a watcher you never unregister that should not keep C<ev_loop>	802	This is useful when you have a watcher that you never intend to
699	from returning, call ev_unref() after starting, and ev_ref() before	803	unregister, but that nevertheless should not keep C<ev_loop> from
		804	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
700	stopping it.	805	before stopping it.
701		806
702	As an example, libev itself uses this for its internal signal pipe: It is	807	As an example, libev itself uses this for its internal signal pipe: It
703	not visible to the libev user and should not keep C<ev_loop> from exiting	808	is not visible to the libev user and should not keep C<ev_loop> from
704	if no event watchers registered by it are active. It is also an excellent	809	exiting if no event watchers registered by it are active. It is also an
705	way to do this for generic recurring timers or from within third-party	810	excellent way to do this for generic recurring timers or from within
706	libraries. Just remember to I<unref after start> and I<ref before stop>	811	third-party libraries. Just remember to I<unref after start> and I<ref
707	(but only if the watcher wasn't active before, or was active before,	812	before stop> (but only if the watcher wasn't active before, or was active
708	respectively).	813	before, respectively. Note also that libev might stop watchers itself
		814	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		815	in the callback).
709		816
710	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	817	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
711	running when nothing else is active.	818	running when nothing else is active.
712		819
713	struct ev_signal exitsig;	820	ev_signal exitsig;
714	ev_signal_init (&exitsig, sig_cb, SIGINT);	821	ev_signal_init (&exitsig, sig_cb, SIGINT);
715	ev_signal_start (loop, &exitsig);	822	ev_signal_start (loop, &exitsig);
716	evf_unref (loop);	823	evf_unref (loop);
717		824
718	Example: For some weird reason, unregister the above signal handler again.	825	Example: For some weird reason, unregister the above signal handler again.
…		…
742		849
743	By setting a higher I<io collect interval> you allow libev to spend more	850	By setting a higher I<io collect interval> you allow libev to spend more
744	time collecting I/O events, so you can handle more events per iteration,	851	time collecting I/O events, so you can handle more events per iteration,
745	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	852	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
746	C<ev_timer>) will be not affected. Setting this to a non-null value will	853	C<ev_timer>) will be not affected. Setting this to a non-null value will
747	introduce an additional C<ev_sleep ()> call into most loop iterations.	854	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		855	sleep time ensures that libev will not poll for I/O events more often then
		856	once per this interval, on average.
748		857
749	Likewise, by setting a higher I<timeout collect interval> you allow libev	858	Likewise, by setting a higher I<timeout collect interval> you allow libev
750	to spend more time collecting timeouts, at the expense of increased	859	to spend more time collecting timeouts, at the expense of increased
751	latency/jitter/inexactness (the watcher callback will be called	860	latency/jitter/inexactness (the watcher callback will be called
752	later). C<ev_io> watchers will not be affected. Setting this to a non-null	861	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
754		863
755	Many (busy) programs can usually benefit by setting the I/O collect	864	Many (busy) programs can usually benefit by setting the I/O collect
756	interval to a value near C<0.1> or so, which is often enough for	865	interval to a value near C<0.1> or so, which is often enough for
757	interactive servers (of course not for games), likewise for timeouts. It	866	interactive servers (of course not for games), likewise for timeouts. It
758	usually doesn't make much sense to set it to a lower value than C<0.01>,	867	usually doesn't make much sense to set it to a lower value than C<0.01>,
759	as this approaches the timing granularity of most systems.	868	as this approaches the timing granularity of most systems. Note that if
		869	you do transactions with the outside world and you can't increase the
		870	parallelity, then this setting will limit your transaction rate (if you
		871	need to poll once per transaction and the I/O collect interval is 0.01,
		872	then you can't do more than 100 transations per second).
760		873
761	Setting the I<timeout collect interval> can improve the opportunity for	874	Setting the I<timeout collect interval> can improve the opportunity for
762	saving power, as the program will "bundle" timer callback invocations that	875	saving power, as the program will "bundle" timer callback invocations that
763	are "near" in time together, by delaying some, thus reducing the number of	876	are "near" in time together, by delaying some, thus reducing the number of
764	times the process sleeps and wakes up again. Another useful technique to	877	times the process sleeps and wakes up again. Another useful technique to
765	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	878	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
766	they fire on, say, one-second boundaries only.	879	they fire on, say, one-second boundaries only.
767		880
		881	Example: we only need 0.1s timeout granularity, and we wish not to poll
		882	more often than 100 times per second:
		883
		884	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		885	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		886
		887	=item ev_invoke_pending (loop)
		888
		889	This call will simply invoke all pending watchers while resetting their
		890	pending state. Normally, C<ev_loop> does this automatically when required,
		891	but when overriding the invoke callback this call comes handy.
		892
		893	=item int ev_pending_count (loop)
		894
		895	Returns the number of pending watchers - zero indicates that no watchers
		896	are pending.
		897
		898	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		899
		900	This overrides the invoke pending functionality of the loop: Instead of
		901	invoking all pending watchers when there are any, C<ev_loop> will call
		902	this callback instead. This is useful, for example, when you want to
		903	invoke the actual watchers inside another context (another thread etc.).
		904
		905	If you want to reset the callback, use C<ev_invoke_pending> as new
		906	callback.
		907
		908	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		909
		910	Sometimes you want to share the same loop between multiple threads. This
		911	can be done relatively simply by putting mutex_lock/unlock calls around
		912	each call to a libev function.
		913
		914	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		915	wait for it to return. One way around this is to wake up the loop via
		916	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		917	and I<acquire> callbacks on the loop.
		918
		919	When set, then C<release> will be called just before the thread is
		920	suspended waiting for new events, and C<acquire> is called just
		921	afterwards.
		922
		923	Ideally, C<release> will just call your mutex_unlock function, and
		924	C<acquire> will just call the mutex_lock function again.
		925
		926	While event loop modifications are allowed between invocations of
		927	C<release> and C<acquire> (that's their only purpose after all), no
		928	modifications done will affect the event loop, i.e. adding watchers will
		929	have no effect on the set of file descriptors being watched, or the time
		930	waited. Use an C<ev_async> watcher to wake up C<ev_loop> when you want it
		931	to take note of any changes you made.
		932
		933	In theory, threads executing C<ev_loop> will be async-cancel safe between
		934	invocations of C<release> and C<acquire>.
		935
		936	See also the locking example in the C<THREADS> section later in this
		937	document.
		938
		939	=item ev_set_userdata (loop, void *data)
		940
		941	=item ev_userdata (loop)
		942
		943	Set and retrieve a single C<void *> associated with a loop. When
		944	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		945	C<0.>
		946
		947	These two functions can be used to associate arbitrary data with a loop,
		948	and are intended solely for the C<invoke_pending_cb>, C<release> and
		949	C<acquire> callbacks described above, but of course can be (ab-)used for
		950	any other purpose as well.
		951
768	=item ev_loop_verify (loop)	952	=item ev_loop_verify (loop)
769		953
770	This function only does something when C<EV_VERIFY> support has been	954	This function only does something when C<EV_VERIFY> support has been
771	compiled in. which is the default for non-minimal builds. It tries to go	955	compiled in, which is the default for non-minimal builds. It tries to go
772	through all internal structures and checks them for validity. If anything	956	through all internal structures and checks them for validity. If anything
773	is found to be inconsistent, it will print an error message to standard	957	is found to be inconsistent, it will print an error message to standard
774	error and call C<abort ()>.	958	error and call C<abort ()>.
775		959
776	This can be used to catch bugs inside libev itself: under normal	960	This can be used to catch bugs inside libev itself: under normal
…		…
780	=back	964	=back
781		965
782		966
783	=head1 ANATOMY OF A WATCHER	967	=head1 ANATOMY OF A WATCHER
784		968
		969	In the following description, uppercase C<TYPE> in names stands for the
		970	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		971	watchers and C<ev_io_start> for I/O watchers.
		972
785	A watcher is a structure that you create and register to record your	973	A watcher is a structure that you create and register to record your
786	interest in some event. For instance, if you want to wait for STDIN to	974	interest in some event. For instance, if you want to wait for STDIN to
787	become readable, you would create an C<ev_io> watcher for that:	975	become readable, you would create an C<ev_io> watcher for that:
788		976
789	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	977	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
790	{	978	{
791	ev_io_stop (w);	979	ev_io_stop (w);
792	ev_unloop (loop, EVUNLOOP_ALL);	980	ev_unloop (loop, EVUNLOOP_ALL);
793	}	981	}
794		982
795	struct ev_loop *loop = ev_default_loop (0);	983	struct ev_loop *loop = ev_default_loop (0);
		984
796	struct ev_io stdin_watcher;	985	ev_io stdin_watcher;
		986
797	ev_init (&stdin_watcher, my_cb);	987	ev_init (&stdin_watcher, my_cb);
798	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	988	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
799	ev_io_start (loop, &stdin_watcher);	989	ev_io_start (loop, &stdin_watcher);
		990
800	ev_loop (loop, 0);	991	ev_loop (loop, 0);
801		992
802	As you can see, you are responsible for allocating the memory for your	993	As you can see, you are responsible for allocating the memory for your
803	watcher structures (and it is usually a bad idea to do this on the stack,	994	watcher structures (and it is I<usually> a bad idea to do this on the
804	although this can sometimes be quite valid).	995	stack).
		996
		997	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		998	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
805		999
806	Each watcher structure must be initialised by a call to C<ev_init	1000	Each watcher structure must be initialised by a call to C<ev_init
807	(watcher *, callback)>, which expects a callback to be provided. This	1001	(watcher *, callback)>, which expects a callback to be provided. This
808	callback gets invoked each time the event occurs (or, in the case of I/O	1002	callback gets invoked each time the event occurs (or, in the case of I/O
809	watchers, each time the event loop detects that the file descriptor given	1003	watchers, each time the event loop detects that the file descriptor given
810	is readable and/or writable).	1004	is readable and/or writable).
811		1005
812	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1006	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
813	with arguments specific to this watcher type. There is also a macro	1007	macro to configure it, with arguments specific to the watcher type. There
814	to combine initialisation and setting in one call: C<< ev_<type>_init	1008	is also a macro to combine initialisation and setting in one call: C<<
815	(watcher *, callback, ...) >>.	1009	ev_TYPE_init (watcher *, callback, ...) >>.
816		1010
817	To make the watcher actually watch out for events, you have to start it	1011	To make the watcher actually watch out for events, you have to start it
818	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1012	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
819	*) >>), and you can stop watching for events at any time by calling the	1013	*) >>), and you can stop watching for events at any time by calling the
820	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1014	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
821		1015
822	As long as your watcher is active (has been started but not stopped) you	1016	As long as your watcher is active (has been started but not stopped) you
823	must not touch the values stored in it. Most specifically you must never	1017	must not touch the values stored in it. Most specifically you must never
824	reinitialise it or call its C<set> macro.	1018	reinitialise it or call its C<ev_TYPE_set> macro.
825		1019
826	Each and every callback receives the event loop pointer as first, the	1020	Each and every callback receives the event loop pointer as first, the
827	registered watcher structure as second, and a bitset of received events as	1021	registered watcher structure as second, and a bitset of received events as
828	third argument.	1022	third argument.
829		1023
…		…
887		1081
888	=item C<EV_ASYNC>	1082	=item C<EV_ASYNC>
889		1083
890	The given async watcher has been asynchronously notified (see C<ev_async>).	1084	The given async watcher has been asynchronously notified (see C<ev_async>).
891		1085
		1086	=item C<EV_CUSTOM>
		1087
		1088	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1089	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1090
892	=item C<EV_ERROR>	1091	=item C<EV_ERROR>
893		1092
894	An unspecified error has occurred, the watcher has been stopped. This might	1093	An unspecified error has occurred, the watcher has been stopped. This might
895	happen because the watcher could not be properly started because libev	1094	happen because the watcher could not be properly started because libev
896	ran out of memory, a file descriptor was found to be closed or any other	1095	ran out of memory, a file descriptor was found to be closed or any other
		1096	problem. Libev considers these application bugs.
		1097
897	problem. You best act on it by reporting the problem and somehow coping	1098	You best act on it by reporting the problem and somehow coping with the
898	with the watcher being stopped.	1099	watcher being stopped. Note that well-written programs should not receive
		1100	an error ever, so when your watcher receives it, this usually indicates a
		1101	bug in your program.
899		1102
900	Libev will usually signal a few "dummy" events together with an error, for	1103	Libev will usually signal a few "dummy" events together with an error, for
901	example it might indicate that a fd is readable or writable, and if your	1104	example it might indicate that a fd is readable or writable, and if your
902	callbacks is well-written it can just attempt the operation and cope with	1105	callbacks is well-written it can just attempt the operation and cope with
903	the error from read() or write(). This will not work in multi-threaded	1106	the error from read() or write(). This will not work in multi-threaded
…		…
906		1109
907	=back	1110	=back
908		1111
909	=head2 GENERIC WATCHER FUNCTIONS	1112	=head2 GENERIC WATCHER FUNCTIONS
910		1113
911	In the following description, C<TYPE> stands for the watcher type,
912	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
913
914	=over 4	1114	=over 4
915		1115
916	=item C<ev_init> (ev_TYPE *watcher, callback)	1116	=item C<ev_init> (ev_TYPE *watcher, callback)
917		1117
918	This macro initialises the generic portion of a watcher. The contents	1118	This macro initialises the generic portion of a watcher. The contents
…		…
923	which rolls both calls into one.	1123	which rolls both calls into one.
924		1124
925	You can reinitialise a watcher at any time as long as it has been stopped	1125	You can reinitialise a watcher at any time as long as it has been stopped
926	(or never started) and there are no pending events outstanding.	1126	(or never started) and there are no pending events outstanding.
927		1127
928	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1128	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
929	int revents)>.	1129	int revents)>.
930		1130
931	Example: Initialise an C<ev_io> watcher in two steps.	1131	Example: Initialise an C<ev_io> watcher in two steps.
932		1132
933	ev_io w;	1133	ev_io w;
934	ev_init (&w, my_cb);	1134	ev_init (&w, my_cb);
935	ev_io_set (&w, STDIN_FILENO, EV_READ);	1135	ev_io_set (&w, STDIN_FILENO, EV_READ);
936		1136
937	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1137	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
938		1138
939	This macro initialises the type-specific parts of a watcher. You need to	1139	This macro initialises the type-specific parts of a watcher. You need to
940	call C<ev_init> at least once before you call this macro, but you can	1140	call C<ev_init> at least once before you call this macro, but you can
941	call C<ev_TYPE_set> any number of times. You must not, however, call this	1141	call C<ev_TYPE_set> any number of times. You must not, however, call this
942	macro on a watcher that is active (it can be pending, however, which is a	1142	macro on a watcher that is active (it can be pending, however, which is a
…		…
955		1155
956	Example: Initialise and set an C<ev_io> watcher in one step.	1156	Example: Initialise and set an C<ev_io> watcher in one step.
957		1157
958	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);	1158	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
959		1159
960	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1160	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
961		1161
962	Starts (activates) the given watcher. Only active watchers will receive	1162	Starts (activates) the given watcher. Only active watchers will receive
963	events. If the watcher is already active nothing will happen.	1163	events. If the watcher is already active nothing will happen.
964		1164
965	Example: Start the C<ev_io> watcher that is being abused as example in this	1165	Example: Start the C<ev_io> watcher that is being abused as example in this
966	whole section.	1166	whole section.
967		1167
968	ev_io_start (EV_DEFAULT_UC, &w);	1168	ev_io_start (EV_DEFAULT_UC, &w);
969		1169
970	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1170	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
971		1171
972	Stops the given watcher again (if active) and clears the pending	1172	Stops the given watcher if active, and clears the pending status (whether
		1173	the watcher was active or not).
		1174
973	status. It is possible that stopped watchers are pending (for example,	1175	It is possible that stopped watchers are pending - for example,
974	non-repeating timers are being stopped when they become pending), but	1176	non-repeating timers are being stopped when they become pending - but
975	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1177	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
976	you want to free or reuse the memory used by the watcher it is therefore a	1178	pending. If you want to free or reuse the memory used by the watcher it is
977	good idea to always call its C<ev_TYPE_stop> function.	1179	therefore a good idea to always call its C<ev_TYPE_stop> function.
978		1180
979	=item bool ev_is_active (ev_TYPE *watcher)	1181	=item bool ev_is_active (ev_TYPE *watcher)
980		1182
981	Returns a true value iff the watcher is active (i.e. it has been started	1183	Returns a true value iff the watcher is active (i.e. it has been started
982	and not yet been stopped). As long as a watcher is active you must not modify	1184	and not yet been stopped). As long as a watcher is active you must not modify
…		…
998	=item ev_cb_set (ev_TYPE *watcher, callback)	1200	=item ev_cb_set (ev_TYPE *watcher, callback)
999		1201
1000	Change the callback. You can change the callback at virtually any time	1202	Change the callback. You can change the callback at virtually any time
1001	(modulo threads).	1203	(modulo threads).
1002		1204
1003	=item ev_set_priority (ev_TYPE *watcher, priority)	1205	=item ev_set_priority (ev_TYPE *watcher, int priority)
1004		1206
1005	=item int ev_priority (ev_TYPE *watcher)	1207	=item int ev_priority (ev_TYPE *watcher)
1006		1208
1007	Set and query the priority of the watcher. The priority is a small	1209	Set and query the priority of the watcher. The priority is a small
1008	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1210	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1009	(default: C<-2>). Pending watchers with higher priority will be invoked	1211	(default: C<-2>). Pending watchers with higher priority will be invoked
1010	before watchers with lower priority, but priority will not keep watchers	1212	before watchers with lower priority, but priority will not keep watchers
1011	from being executed (except for C<ev_idle> watchers).	1213	from being executed (except for C<ev_idle> watchers).
1012		1214
1013	This means that priorities are I<only> used for ordering callback
1014	invocation after new events have been received. This is useful, for
1015	example, to reduce latency after idling, or more often, to bind two
1016	watchers on the same event and make sure one is called first.
1017
1018	If you need to suppress invocation when higher priority events are pending	1215	If you need to suppress invocation when higher priority events are pending
1019	you need to look at C<ev_idle> watchers, which provide this functionality.	1216	you need to look at C<ev_idle> watchers, which provide this functionality.
1020		1217
1021	You I<must not> change the priority of a watcher as long as it is active or	1218	You I<must not> change the priority of a watcher as long as it is active or
1022	pending.	1219	pending.
1023		1220
		1221	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1222	fine, as long as you do not mind that the priority value you query might
		1223	or might not have been clamped to the valid range.
		1224
1024	The default priority used by watchers when no priority has been set is	1225	The default priority used by watchers when no priority has been set is
1025	always C<0>, which is supposed to not be too high and not be too low :).	1226	always C<0>, which is supposed to not be too high and not be too low :).
1026		1227
1027	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1228	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1028	fine, as long as you do not mind that the priority value you query might	1229	priorities.
1029	or might not have been adjusted to be within valid range.
1030		1230
1031	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1231	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1032		1232
1033	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1233	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1034	C<loop> nor C<revents> need to be valid as long as the watcher callback	1234	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1041	returns its C<revents> bitset (as if its callback was invoked). If the	1241	returns its C<revents> bitset (as if its callback was invoked). If the
1042	watcher isn't pending it does nothing and returns C<0>.	1242	watcher isn't pending it does nothing and returns C<0>.
1043		1243
1044	Sometimes it can be useful to "poll" a watcher instead of waiting for its	1244	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1045	callback to be invoked, which can be accomplished with this function.	1245	callback to be invoked, which can be accomplished with this function.
		1246
		1247	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1248
		1249	Feeds the given event set into the event loop, as if the specified event
		1250	had happened for the specified watcher (which must be a pointer to an
		1251	initialised but not necessarily started event watcher). Obviously you must
		1252	not free the watcher as long as it has pending events.
		1253
		1254	Stopping the watcher, letting libev invoke it, or calling
		1255	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1256	not started in the first place.
		1257
		1258	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1259	functions that do not need a watcher.
1046		1260
1047	=back	1261	=back
1048		1262
1049		1263
1050	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1264	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
…		…
1056	member, you can also "subclass" the watcher type and provide your own	1270	member, you can also "subclass" the watcher type and provide your own
1057	data:	1271	data:
1058		1272
1059	struct my_io	1273	struct my_io
1060	{	1274	{
1061	struct ev_io io;	1275	ev_io io;
1062	int otherfd;	1276	int otherfd;
1063	void *somedata;	1277	void *somedata;
1064	struct whatever *mostinteresting;	1278	struct whatever *mostinteresting;
1065	};	1279	};
1066		1280
…		…
1069	ev_io_init (&w.io, my_cb, fd, EV_READ);	1283	ev_io_init (&w.io, my_cb, fd, EV_READ);
1070		1284
1071	And since your callback will be called with a pointer to the watcher, you	1285	And since your callback will be called with a pointer to the watcher, you
1072	can cast it back to your own type:	1286	can cast it back to your own type:
1073		1287
1074	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1288	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1075	{	1289	{
1076	struct my_io *w = (struct my_io *)w_;	1290	struct my_io *w = (struct my_io *)w_;
1077	...	1291	...
1078	}	1292	}
1079		1293
…		…
1097	programmers):	1311	programmers):
1098		1312
1099	#include <stddef.h>	1313	#include <stddef.h>
1100		1314
1101	static void	1315	static void
1102	t1_cb (EV_P_ struct ev_timer *w, int revents)	1316	t1_cb (EV_P_ ev_timer *w, int revents)
1103	{	1317	{
1104	struct my_biggy big = (struct my_biggy *	1318	struct my_biggy big = (struct my_biggy *)
1105	(((char *)w) - offsetof (struct my_biggy, t1));	1319	(((char *)w) - offsetof (struct my_biggy, t1));
1106	}	1320	}
1107		1321
1108	static void	1322	static void
1109	t2_cb (EV_P_ struct ev_timer *w, int revents)	1323	t2_cb (EV_P_ ev_timer *w, int revents)
1110	{	1324	{
1111	struct my_biggy big = (struct my_biggy *	1325	struct my_biggy big = (struct my_biggy *)
1112	(((char *)w) - offsetof (struct my_biggy, t2));	1326	(((char *)w) - offsetof (struct my_biggy, t2));
1113	}	1327	}
		1328
		1329	=head2 WATCHER PRIORITY MODELS
		1330
		1331	Many event loops support I<watcher priorities>, which are usually small
		1332	integers that influence the ordering of event callback invocation
		1333	between watchers in some way, all else being equal.
		1334
		1335	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1336	description for the more technical details such as the actual priority
		1337	range.
		1338
		1339	There are two common ways how these these priorities are being interpreted
		1340	by event loops:
		1341
		1342	In the more common lock-out model, higher priorities "lock out" invocation
		1343	of lower priority watchers, which means as long as higher priority
		1344	watchers receive events, lower priority watchers are not being invoked.
		1345
		1346	The less common only-for-ordering model uses priorities solely to order
		1347	callback invocation within a single event loop iteration: Higher priority
		1348	watchers are invoked before lower priority ones, but they all get invoked
		1349	before polling for new events.
		1350
		1351	Libev uses the second (only-for-ordering) model for all its watchers
		1352	except for idle watchers (which use the lock-out model).
		1353
		1354	The rationale behind this is that implementing the lock-out model for
		1355	watchers is not well supported by most kernel interfaces, and most event
		1356	libraries will just poll for the same events again and again as long as
		1357	their callbacks have not been executed, which is very inefficient in the
		1358	common case of one high-priority watcher locking out a mass of lower
		1359	priority ones.
		1360
		1361	Static (ordering) priorities are most useful when you have two or more
		1362	watchers handling the same resource: a typical usage example is having an
		1363	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1364	timeouts. Under load, data might be received while the program handles
		1365	other jobs, but since timers normally get invoked first, the timeout
		1366	handler will be executed before checking for data. In that case, giving
		1367	the timer a lower priority than the I/O watcher ensures that I/O will be
		1368	handled first even under adverse conditions (which is usually, but not
		1369	always, what you want).
		1370
		1371	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1372	will only be executed when no same or higher priority watchers have
		1373	received events, they can be used to implement the "lock-out" model when
		1374	required.
		1375
		1376	For example, to emulate how many other event libraries handle priorities,
		1377	you can associate an C<ev_idle> watcher to each such watcher, and in
		1378	the normal watcher callback, you just start the idle watcher. The real
		1379	processing is done in the idle watcher callback. This causes libev to
		1380	continously poll and process kernel event data for the watcher, but when
		1381	the lock-out case is known to be rare (which in turn is rare :), this is
		1382	workable.
		1383
		1384	Usually, however, the lock-out model implemented that way will perform
		1385	miserably under the type of load it was designed to handle. In that case,
		1386	it might be preferable to stop the real watcher before starting the
		1387	idle watcher, so the kernel will not have to process the event in case
		1388	the actual processing will be delayed for considerable time.
		1389
		1390	Here is an example of an I/O watcher that should run at a strictly lower
		1391	priority than the default, and which should only process data when no
		1392	other events are pending:
		1393
		1394	ev_idle idle; // actual processing watcher
		1395	ev_io io; // actual event watcher
		1396
		1397	static void
		1398	io_cb (EV_P_ ev_io *w, int revents)
		1399	{
		1400	// stop the I/O watcher, we received the event, but
		1401	// are not yet ready to handle it.
		1402	ev_io_stop (EV_A_ w);
		1403
		1404	// start the idle watcher to ahndle the actual event.
		1405	// it will not be executed as long as other watchers
		1406	// with the default priority are receiving events.
		1407	ev_idle_start (EV_A_ &idle);
		1408	}
		1409
		1410	static void
		1411	idle_cb (EV_P_ ev_idle *w, int revents)
		1412	{
		1413	// actual processing
		1414	read (STDIN_FILENO, ...);
		1415
		1416	// have to start the I/O watcher again, as
		1417	// we have handled the event
		1418	ev_io_start (EV_P_ &io);
		1419	}
		1420
		1421	// initialisation
		1422	ev_idle_init (&idle, idle_cb);
		1423	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1424	ev_io_start (EV_DEFAULT_ &io);
		1425
		1426	In the "real" world, it might also be beneficial to start a timer, so that
		1427	low-priority connections can not be locked out forever under load. This
		1428	enables your program to keep a lower latency for important connections
		1429	during short periods of high load, while not completely locking out less
		1430	important ones.
1114		1431
1115		1432
1116	=head1 WATCHER TYPES	1433	=head1 WATCHER TYPES
1117		1434
1118	This section describes each watcher in detail, but will not repeat	1435	This section describes each watcher in detail, but will not repeat
…		…
1144	descriptors to non-blocking mode is also usually a good idea (but not	1461	descriptors to non-blocking mode is also usually a good idea (but not
1145	required if you know what you are doing).	1462	required if you know what you are doing).
1146		1463
1147	If you cannot use non-blocking mode, then force the use of a	1464	If you cannot use non-blocking mode, then force the use of a
1148	known-to-be-good backend (at the time of this writing, this includes only	1465	known-to-be-good backend (at the time of this writing, this includes only
1149	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1466	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1467	descriptors for which non-blocking operation makes no sense (such as
		1468	files) - libev doesn't guarentee any specific behaviour in that case.
1150		1469
1151	Another thing you have to watch out for is that it is quite easy to	1470	Another thing you have to watch out for is that it is quite easy to
1152	receive "spurious" readiness notifications, that is your callback might	1471	receive "spurious" readiness notifications, that is your callback might
1153	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1472	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1154	because there is no data. Not only are some backends known to create a	1473	because there is no data. Not only are some backends known to create a
…		…
1249	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1568	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1250	readable, but only once. Since it is likely line-buffered, you could	1569	readable, but only once. Since it is likely line-buffered, you could
1251	attempt to read a whole line in the callback.	1570	attempt to read a whole line in the callback.
1252		1571
1253	static void	1572	static void
1254	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1573	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1255	{	1574	{
1256	ev_io_stop (loop, w);	1575	ev_io_stop (loop, w);
1257	.. read from stdin here (or from w->fd) and handle any I/O errors	1576	.. read from stdin here (or from w->fd) and handle any I/O errors
1258	}	1577	}
1259		1578
1260	...	1579	...
1261	struct ev_loop *loop = ev_default_init (0);	1580	struct ev_loop *loop = ev_default_init (0);
1262	struct ev_io stdin_readable;	1581	ev_io stdin_readable;
1263	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1582	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1264	ev_io_start (loop, &stdin_readable);	1583	ev_io_start (loop, &stdin_readable);
1265	ev_loop (loop, 0);	1584	ev_loop (loop, 0);
1266		1585
1267		1586
…		…
1275	year, it will still time out after (roughly) one hour. "Roughly" because	1594	year, it will still time out after (roughly) one hour. "Roughly" because
1276	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1595	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1277	monotonic clock option helps a lot here).	1596	monotonic clock option helps a lot here).
1278		1597
1279	The callback is guaranteed to be invoked only I<after> its timeout has	1598	The callback is guaranteed to be invoked only I<after> its timeout has
1280	passed, but if multiple timers become ready during the same loop iteration	1599	passed (not I<at>, so on systems with very low-resolution clocks this
1281	then order of execution is undefined.	1600	might introduce a small delay). If multiple timers become ready during the
		1601	same loop iteration then the ones with earlier time-out values are invoked
		1602	before ones of the same priority with later time-out values (but this is
		1603	no longer true when a callback calls C<ev_loop> recursively).
		1604
		1605	=head3 Be smart about timeouts
		1606
		1607	Many real-world problems involve some kind of timeout, usually for error
		1608	recovery. A typical example is an HTTP request - if the other side hangs,
		1609	you want to raise some error after a while.
		1610
		1611	What follows are some ways to handle this problem, from obvious and
		1612	inefficient to smart and efficient.
		1613
		1614	In the following, a 60 second activity timeout is assumed - a timeout that
		1615	gets reset to 60 seconds each time there is activity (e.g. each time some
		1616	data or other life sign was received).
		1617
		1618	=over 4
		1619
		1620	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1621
		1622	This is the most obvious, but not the most simple way: In the beginning,
		1623	start the watcher:
		1624
		1625	ev_timer_init (timer, callback, 60., 0.);
		1626	ev_timer_start (loop, timer);
		1627
		1628	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1629	and start it again:
		1630
		1631	ev_timer_stop (loop, timer);
		1632	ev_timer_set (timer, 60., 0.);
		1633	ev_timer_start (loop, timer);
		1634
		1635	This is relatively simple to implement, but means that each time there is
		1636	some activity, libev will first have to remove the timer from its internal
		1637	data structure and then add it again. Libev tries to be fast, but it's
		1638	still not a constant-time operation.
		1639
		1640	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1641
		1642	This is the easiest way, and involves using C<ev_timer_again> instead of
		1643	C<ev_timer_start>.
		1644
		1645	To implement this, configure an C<ev_timer> with a C<repeat> value
		1646	of C<60> and then call C<ev_timer_again> at start and each time you
		1647	successfully read or write some data. If you go into an idle state where
		1648	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1649	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1650
		1651	That means you can ignore both the C<ev_timer_start> function and the
		1652	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1653	member and C<ev_timer_again>.
		1654
		1655	At start:
		1656
		1657	ev_init (timer, callback);
		1658	timer->repeat = 60.;
		1659	ev_timer_again (loop, timer);
		1660
		1661	Each time there is some activity:
		1662
		1663	ev_timer_again (loop, timer);
		1664
		1665	It is even possible to change the time-out on the fly, regardless of
		1666	whether the watcher is active or not:
		1667
		1668	timer->repeat = 30.;
		1669	ev_timer_again (loop, timer);
		1670
		1671	This is slightly more efficient then stopping/starting the timer each time
		1672	you want to modify its timeout value, as libev does not have to completely
		1673	remove and re-insert the timer from/into its internal data structure.
		1674
		1675	It is, however, even simpler than the "obvious" way to do it.
		1676
		1677	=item 3. Let the timer time out, but then re-arm it as required.
		1678
		1679	This method is more tricky, but usually most efficient: Most timeouts are
		1680	relatively long compared to the intervals between other activity - in
		1681	our example, within 60 seconds, there are usually many I/O events with
		1682	associated activity resets.
		1683
		1684	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1685	but remember the time of last activity, and check for a real timeout only
		1686	within the callback:
		1687
		1688	ev_tstamp last_activity; // time of last activity
		1689
		1690	static void
		1691	callback (EV_P_ ev_timer *w, int revents)
		1692	{
		1693	ev_tstamp now = ev_now (EV_A);
		1694	ev_tstamp timeout = last_activity + 60.;
		1695
		1696	// if last_activity + 60. is older than now, we did time out
		1697	if (timeout < now)
		1698	{
		1699	// timeout occured, take action
		1700	}
		1701	else
		1702	{
		1703	// callback was invoked, but there was some activity, re-arm
		1704	// the watcher to fire in last_activity + 60, which is
		1705	// guaranteed to be in the future, so "again" is positive:
		1706	w->repeat = timeout - now;
		1707	ev_timer_again (EV_A_ w);
		1708	}
		1709	}
		1710
		1711	To summarise the callback: first calculate the real timeout (defined
		1712	as "60 seconds after the last activity"), then check if that time has
		1713	been reached, which means something I<did>, in fact, time out. Otherwise
		1714	the callback was invoked too early (C<timeout> is in the future), so
		1715	re-schedule the timer to fire at that future time, to see if maybe we have
		1716	a timeout then.
		1717
		1718	Note how C<ev_timer_again> is used, taking advantage of the
		1719	C<ev_timer_again> optimisation when the timer is already running.
		1720
		1721	This scheme causes more callback invocations (about one every 60 seconds
		1722	minus half the average time between activity), but virtually no calls to
		1723	libev to change the timeout.
		1724
		1725	To start the timer, simply initialise the watcher and set C<last_activity>
		1726	to the current time (meaning we just have some activity :), then call the
		1727	callback, which will "do the right thing" and start the timer:
		1728
		1729	ev_init (timer, callback);
		1730	last_activity = ev_now (loop);
		1731	callback (loop, timer, EV_TIMEOUT);
		1732
		1733	And when there is some activity, simply store the current time in
		1734	C<last_activity>, no libev calls at all:
		1735
		1736	last_actiivty = ev_now (loop);
		1737
		1738	This technique is slightly more complex, but in most cases where the
		1739	time-out is unlikely to be triggered, much more efficient.
		1740
		1741	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1742	callback :) - just change the timeout and invoke the callback, which will
		1743	fix things for you.
		1744
		1745	=item 4. Wee, just use a double-linked list for your timeouts.
		1746
		1747	If there is not one request, but many thousands (millions...), all
		1748	employing some kind of timeout with the same timeout value, then one can
		1749	do even better:
		1750
		1751	When starting the timeout, calculate the timeout value and put the timeout
		1752	at the I<end> of the list.
		1753
		1754	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1755	the list is expected to fire (for example, using the technique #3).
		1756
		1757	When there is some activity, remove the timer from the list, recalculate
		1758	the timeout, append it to the end of the list again, and make sure to
		1759	update the C<ev_timer> if it was taken from the beginning of the list.
		1760
		1761	This way, one can manage an unlimited number of timeouts in O(1) time for
		1762	starting, stopping and updating the timers, at the expense of a major
		1763	complication, and having to use a constant timeout. The constant timeout
		1764	ensures that the list stays sorted.
		1765
		1766	=back
		1767
		1768	So which method the best?
		1769
		1770	Method #2 is a simple no-brain-required solution that is adequate in most
		1771	situations. Method #3 requires a bit more thinking, but handles many cases
		1772	better, and isn't very complicated either. In most case, choosing either
		1773	one is fine, with #3 being better in typical situations.
		1774
		1775	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1776	rather complicated, but extremely efficient, something that really pays
		1777	off after the first million or so of active timers, i.e. it's usually
		1778	overkill :)
1282		1779
1283	=head3 The special problem of time updates	1780	=head3 The special problem of time updates
1284		1781
1285	Establishing the current time is a costly operation (it usually takes at	1782	Establishing the current time is a costly operation (it usually takes at
1286	least two system calls): EV therefore updates its idea of the current	1783	least two system calls): EV therefore updates its idea of the current
…		…
1298		1795
1299	If the event loop is suspended for a long time, you can also force an	1796	If the event loop is suspended for a long time, you can also force an
1300	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1797	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1301	()>.	1798	()>.
1302		1799
		1800	=head3 The special problems of suspended animation
		1801
		1802	When you leave the server world it is quite customary to hit machines that
		1803	can suspend/hibernate - what happens to the clocks during such a suspend?
		1804
		1805	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1806	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1807	to run until the system is suspended, but they will not advance while the
		1808	system is suspended. That means, on resume, it will be as if the program
		1809	was frozen for a few seconds, but the suspend time will not be counted
		1810	towards C<ev_timer> when a monotonic clock source is used. The real time
		1811	clock advanced as expected, but if it is used as sole clocksource, then a
		1812	long suspend would be detected as a time jump by libev, and timers would
		1813	be adjusted accordingly.
		1814
		1815	I would not be surprised to see different behaviour in different between
		1816	operating systems, OS versions or even different hardware.
		1817
		1818	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1819	time jump in the monotonic clocks and the realtime clock. If the program
		1820	is suspended for a very long time, and monotonic clock sources are in use,
		1821	then you can expect C<ev_timer>s to expire as the full suspension time
		1822	will be counted towards the timers. When no monotonic clock source is in
		1823	use, then libev will again assume a timejump and adjust accordingly.
		1824
		1825	It might be beneficial for this latter case to call C<ev_suspend>
		1826	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1827	deterministic behaviour in this case (you can do nothing against
		1828	C<SIGSTOP>).
		1829
1303	=head3 Watcher-Specific Functions and Data Members	1830	=head3 Watcher-Specific Functions and Data Members
1304		1831
1305	=over 4	1832	=over 4
1306		1833
1307	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1834	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1330	If the timer is started but non-repeating, stop it (as if it timed out).	1857	If the timer is started but non-repeating, stop it (as if it timed out).
1331		1858
1332	If the timer is repeating, either start it if necessary (with the	1859	If the timer is repeating, either start it if necessary (with the
1333	C<repeat> value), or reset the running timer to the C<repeat> value.	1860	C<repeat> value), or reset the running timer to the C<repeat> value.
1334		1861
1335	This sounds a bit complicated, but here is a useful and typical	1862	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1336	example: Imagine you have a TCP connection and you want a so-called idle	1863	usage example.
1337	timeout, that is, you want to be called when there have been, say, 60
1338	seconds of inactivity on the socket. The easiest way to do this is to
1339	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1340	C<ev_timer_again> each time you successfully read or write some data. If
1341	you go into an idle state where you do not expect data to travel on the
1342	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1343	automatically restart it if need be.
1344		1864
1345	That means you can ignore the C<after> value and C<ev_timer_start>	1865	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1346	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1347		1866
1348	ev_timer_init (timer, callback, 0., 5.);	1867	Returns the remaining time until a timer fires. If the timer is active,
1349	ev_timer_again (loop, timer);	1868	then this time is relative to the current event loop time, otherwise it's
1350	...	1869	the timeout value currently configured.
1351	timer->again = 17.;
1352	ev_timer_again (loop, timer);
1353	...
1354	timer->again = 10.;
1355	ev_timer_again (loop, timer);
1356		1870
1357	This is more slightly efficient then stopping/starting the timer each time	1871	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1358	you want to modify its timeout value.	1872	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
1359		1873	will return C<4>. When the timer expires and is restarted, it will return
1360	Note, however, that it is often even more efficient to remember the	1874	roughly C<7> (likely slightly less as callback invocation takes some time,
1361	time of the last activity and let the timer time-out naturally. In the	1875	too), and so on.
1362	callback, you then check whether the time-out is real, or, if there was
1363	some activity, you reschedule the watcher to time-out in "last_activity +
1364	timeout - ev_now ()" seconds.
1365		1876
1366	=item ev_tstamp repeat [read-write]	1877	=item ev_tstamp repeat [read-write]
1367		1878
1368	The current C<repeat> value. Will be used each time the watcher times out	1879	The current C<repeat> value. Will be used each time the watcher times out
1369	or C<ev_timer_again> is called, and determines the next timeout (if any),	1880	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1374	=head3 Examples	1885	=head3 Examples
1375		1886
1376	Example: Create a timer that fires after 60 seconds.	1887	Example: Create a timer that fires after 60 seconds.
1377		1888
1378	static void	1889	static void
1379	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1890	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1380	{	1891	{
1381	.. one minute over, w is actually stopped right here	1892	.. one minute over, w is actually stopped right here
1382	}	1893	}
1383		1894
1384	struct ev_timer mytimer;	1895	ev_timer mytimer;
1385	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1896	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1386	ev_timer_start (loop, &mytimer);	1897	ev_timer_start (loop, &mytimer);
1387		1898
1388	Example: Create a timeout timer that times out after 10 seconds of	1899	Example: Create a timeout timer that times out after 10 seconds of
1389	inactivity.	1900	inactivity.
1390		1901
1391	static void	1902	static void
1392	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1903	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1393	{	1904	{
1394	.. ten seconds without any activity	1905	.. ten seconds without any activity
1395	}	1906	}
1396		1907
1397	struct ev_timer mytimer;	1908	ev_timer mytimer;
1398	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1909	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1399	ev_timer_again (&mytimer); /* start timer */	1910	ev_timer_again (&mytimer); /* start timer */
1400	ev_loop (loop, 0);	1911	ev_loop (loop, 0);
1401		1912
1402	// and in some piece of code that gets executed on any "activity":	1913	// and in some piece of code that gets executed on any "activity":
…		…
1407	=head2 C<ev_periodic> - to cron or not to cron?	1918	=head2 C<ev_periodic> - to cron or not to cron?
1408		1919
1409	Periodic watchers are also timers of a kind, but they are very versatile	1920	Periodic watchers are also timers of a kind, but they are very versatile
1410	(and unfortunately a bit complex).	1921	(and unfortunately a bit complex).
1411		1922
1412	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1923	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1413	but on wall clock time (absolute time). You can tell a periodic watcher	1924	relative time, the physical time that passes) but on wall clock time
1414	to trigger after some specific point in time. For example, if you tell a	1925	(absolute time, the thing you can read on your calender or clock). The
1415	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1926	difference is that wall clock time can run faster or slower than real
1416	+ 10.>, that is, an absolute time not a delay) and then reset your system	1927	time, and time jumps are not uncommon (e.g. when you adjust your
1417	clock to January of the previous year, then it will take more than year	1928	wrist-watch).
1418	to trigger the event (unlike an C<ev_timer>, which would still trigger
1419	roughly 10 seconds later as it uses a relative timeout).
1420		1929
		1930	You can tell a periodic watcher to trigger after some specific point
		1931	in time: for example, if you tell a periodic watcher to trigger "in 10
		1932	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1933	not a delay) and then reset your system clock to January of the previous
		1934	year, then it will take a year or more to trigger the event (unlike an
		1935	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1936	it, as it uses a relative timeout).
		1937
1421	C<ev_periodic>s can also be used to implement vastly more complex timers,	1938	C<ev_periodic> watchers can also be used to implement vastly more complex
1422	such as triggering an event on each "midnight, local time", or other	1939	timers, such as triggering an event on each "midnight, local time", or
1423	complicated rules.	1940	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1941	those cannot react to time jumps.
1424		1942
1425	As with timers, the callback is guaranteed to be invoked only when the	1943	As with timers, the callback is guaranteed to be invoked only when the
1426	time (C<at>) has passed, but if multiple periodic timers become ready	1944	point in time where it is supposed to trigger has passed. If multiple
1427	during the same loop iteration, then order of execution is undefined.	1945	timers become ready during the same loop iteration then the ones with
		1946	earlier time-out values are invoked before ones with later time-out values
		1947	(but this is no longer true when a callback calls C<ev_loop> recursively).
1428		1948
1429	=head3 Watcher-Specific Functions and Data Members	1949	=head3 Watcher-Specific Functions and Data Members
1430		1950
1431	=over 4	1951	=over 4
1432		1952
1433	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1953	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1434		1954
1435	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1955	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1436		1956
1437	Lots of arguments, lets sort it out... There are basically three modes of	1957	Lots of arguments, let's sort it out... There are basically three modes of
1438	operation, and we will explain them from simplest to most complex:	1958	operation, and we will explain them from simplest to most complex:
1439		1959
1440	=over 4	1960	=over 4
1441		1961
1442	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1962	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1443		1963
1444	In this configuration the watcher triggers an event after the wall clock	1964	In this configuration the watcher triggers an event after the wall clock
1445	time C<at> has passed. It will not repeat and will not adjust when a time	1965	time C<offset> has passed. It will not repeat and will not adjust when a
1446	jump occurs, that is, if it is to be run at January 1st 2011 then it will	1966	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1447	only run when the system clock reaches or surpasses this time.	1967	will be stopped and invoked when the system clock reaches or surpasses
		1968	this point in time.
1448		1969
1449	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1970	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1450		1971
1451	In this mode the watcher will always be scheduled to time out at the next	1972	In this mode the watcher will always be scheduled to time out at the next
1452	C<at + N * interval> time (for some integer N, which can also be negative)	1973	C<offset + N * interval> time (for some integer N, which can also be
1453	and then repeat, regardless of any time jumps.	1974	negative) and then repeat, regardless of any time jumps. The C<offset>
		1975	argument is merely an offset into the C<interval> periods.
1454		1976
1455	This can be used to create timers that do not drift with respect to the	1977	This can be used to create timers that do not drift with respect to the
1456	system clock, for example, here is a C<ev_periodic> that triggers each	1978	system clock, for example, here is an C<ev_periodic> that triggers each
1457	hour, on the hour:	1979	hour, on the hour (with respect to UTC):
1458		1980
1459	ev_periodic_set (&periodic, 0., 3600., 0);	1981	ev_periodic_set (&periodic, 0., 3600., 0);
1460		1982
1461	This doesn't mean there will always be 3600 seconds in between triggers,	1983	This doesn't mean there will always be 3600 seconds in between triggers,
1462	but only that the callback will be called when the system time shows a	1984	but only that the callback will be called when the system time shows a
1463	full hour (UTC), or more correctly, when the system time is evenly divisible	1985	full hour (UTC), or more correctly, when the system time is evenly divisible
1464	by 3600.	1986	by 3600.
1465		1987
1466	Another way to think about it (for the mathematically inclined) is that	1988	Another way to think about it (for the mathematically inclined) is that
1467	C<ev_periodic> will try to run the callback in this mode at the next possible	1989	C<ev_periodic> will try to run the callback in this mode at the next possible
1468	time where C<time = at (mod interval)>, regardless of any time jumps.	1990	time where C<time = offset (mod interval)>, regardless of any time jumps.
1469		1991
1470	For numerical stability it is preferable that the C<at> value is near	1992	For numerical stability it is preferable that the C<offset> value is near
1471	C<ev_now ()> (the current time), but there is no range requirement for	1993	C<ev_now ()> (the current time), but there is no range requirement for
1472	this value, and in fact is often specified as zero.	1994	this value, and in fact is often specified as zero.
1473		1995
1474	Note also that there is an upper limit to how often a timer can fire (CPU	1996	Note also that there is an upper limit to how often a timer can fire (CPU
1475	speed for example), so if C<interval> is very small then timing stability	1997	speed for example), so if C<interval> is very small then timing stability
1476	will of course deteriorate. Libev itself tries to be exact to be about one	1998	will of course deteriorate. Libev itself tries to be exact to be about one
1477	millisecond (if the OS supports it and the machine is fast enough).	1999	millisecond (if the OS supports it and the machine is fast enough).
1478		2000
1479	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2001	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1480		2002
1481	In this mode the values for C<interval> and C<at> are both being	2003	In this mode the values for C<interval> and C<offset> are both being
1482	ignored. Instead, each time the periodic watcher gets scheduled, the	2004	ignored. Instead, each time the periodic watcher gets scheduled, the
1483	reschedule callback will be called with the watcher as first, and the	2005	reschedule callback will be called with the watcher as first, and the
1484	current time as second argument.	2006	current time as second argument.
1485		2007
1486	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2008	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1487	ever, or make ANY event loop modifications whatsoever>.	2009	or make ANY other event loop modifications whatsoever, unless explicitly
		2010	allowed by documentation here>.
1488		2011
1489	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2012	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1490	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2013	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1491	only event loop modification you are allowed to do).	2014	only event loop modification you are allowed to do).
1492		2015
1493	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2016	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1494	*w, ev_tstamp now)>, e.g.:	2017	*w, ev_tstamp now)>, e.g.:
1495		2018
		2019	static ev_tstamp
1496	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2020	my_rescheduler (ev_periodic *w, ev_tstamp now)
1497	{	2021	{
1498	return now + 60.;	2022	return now + 60.;
1499	}	2023	}
1500		2024
1501	It must return the next time to trigger, based on the passed time value	2025	It must return the next time to trigger, based on the passed time value
…		…
1521	a different time than the last time it was called (e.g. in a crond like	2045	a different time than the last time it was called (e.g. in a crond like
1522	program when the crontabs have changed).	2046	program when the crontabs have changed).
1523		2047
1524	=item ev_tstamp ev_periodic_at (ev_periodic *)	2048	=item ev_tstamp ev_periodic_at (ev_periodic *)
1525		2049
1526	When active, returns the absolute time that the watcher is supposed to	2050	When active, returns the absolute time that the watcher is supposed
1527	trigger next.	2051	to trigger next. This is not the same as the C<offset> argument to
		2052	C<ev_periodic_set>, but indeed works even in interval and manual
		2053	rescheduling modes.
1528		2054
1529	=item ev_tstamp offset [read-write]	2055	=item ev_tstamp offset [read-write]
1530		2056
1531	When repeating, this contains the offset value, otherwise this is the	2057	When repeating, this contains the offset value, otherwise this is the
1532	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2058	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2059	although libev might modify this value for better numerical stability).
1533		2060
1534	Can be modified any time, but changes only take effect when the periodic	2061	Can be modified any time, but changes only take effect when the periodic
1535	timer fires or C<ev_periodic_again> is being called.	2062	timer fires or C<ev_periodic_again> is being called.
1536		2063
1537	=item ev_tstamp interval [read-write]	2064	=item ev_tstamp interval [read-write]
1538		2065
1539	The current interval value. Can be modified any time, but changes only	2066	The current interval value. Can be modified any time, but changes only
1540	take effect when the periodic timer fires or C<ev_periodic_again> is being	2067	take effect when the periodic timer fires or C<ev_periodic_again> is being
1541	called.	2068	called.
1542		2069
1543	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2070	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1544		2071
1545	The current reschedule callback, or C<0>, if this functionality is	2072	The current reschedule callback, or C<0>, if this functionality is
1546	switched off. Can be changed any time, but changes only take effect when	2073	switched off. Can be changed any time, but changes only take effect when
1547	the periodic timer fires or C<ev_periodic_again> is being called.	2074	the periodic timer fires or C<ev_periodic_again> is being called.
1548		2075
…		…
1553	Example: Call a callback every hour, or, more precisely, whenever the	2080	Example: Call a callback every hour, or, more precisely, whenever the
1554	system time is divisible by 3600. The callback invocation times have	2081	system time is divisible by 3600. The callback invocation times have
1555	potentially a lot of jitter, but good long-term stability.	2082	potentially a lot of jitter, but good long-term stability.
1556		2083
1557	static void	2084	static void
1558	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2085	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1559	{	2086	{
1560	... its now a full hour (UTC, or TAI or whatever your clock follows)	2087	... its now a full hour (UTC, or TAI or whatever your clock follows)
1561	}	2088	}
1562		2089
1563	struct ev_periodic hourly_tick;	2090	ev_periodic hourly_tick;
1564	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2091	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1565	ev_periodic_start (loop, &hourly_tick);	2092	ev_periodic_start (loop, &hourly_tick);
1566		2093
1567	Example: The same as above, but use a reschedule callback to do it:	2094	Example: The same as above, but use a reschedule callback to do it:
1568		2095
1569	#include <math.h>	2096	#include <math.h>
1570		2097
1571	static ev_tstamp	2098	static ev_tstamp
1572	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2099	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1573	{	2100	{
1574	return now + (3600. - fmod (now, 3600.));	2101	return now + (3600. - fmod (now, 3600.));
1575	}	2102	}
1576		2103
1577	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2104	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1578		2105
1579	Example: Call a callback every hour, starting now:	2106	Example: Call a callback every hour, starting now:
1580		2107
1581	struct ev_periodic hourly_tick;	2108	ev_periodic hourly_tick;
1582	ev_periodic_init (&hourly_tick, clock_cb,	2109	ev_periodic_init (&hourly_tick, clock_cb,
1583	fmod (ev_now (loop), 3600.), 3600., 0);	2110	fmod (ev_now (loop), 3600.), 3600., 0);
1584	ev_periodic_start (loop, &hourly_tick);	2111	ev_periodic_start (loop, &hourly_tick);
1585		2112
1586		2113
…		…
1589	Signal watchers will trigger an event when the process receives a specific	2116	Signal watchers will trigger an event when the process receives a specific
1590	signal one or more times. Even though signals are very asynchronous, libev	2117	signal one or more times. Even though signals are very asynchronous, libev
1591	will try it's best to deliver signals synchronously, i.e. as part of the	2118	will try it's best to deliver signals synchronously, i.e. as part of the
1592	normal event processing, like any other event.	2119	normal event processing, like any other event.
1593		2120
1594	If you want signals asynchronously, just use C<sigaction> as you would	2121	If you want signals to be delivered truly asynchronously, just use
1595	do without libev and forget about sharing the signal. You can even use	2122	C<sigaction> as you would do without libev and forget about sharing
1596	C<ev_async> from a signal handler to synchronously wake up an event loop.	2123	the signal. You can even use C<ev_async> from a signal handler to
		2124	synchronously wake up an event loop.
1597		2125
1598	You can configure as many watchers as you like per signal. Only when the	2126	You can configure as many watchers as you like for the same signal, but
		2127	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2128	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2129	C<SIGINT> in both the default loop and another loop at the same time. At
		2130	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2131
1599	first watcher gets started will libev actually register a signal handler	2132	When the first watcher gets started will libev actually register something
1600	with the kernel (thus it coexists with your own signal handlers as long as	2133	with the kernel (thus it coexists with your own signal handlers as long as
1601	you don't register any with libev for the same signal). Similarly, when	2134	you don't register any with libev for the same signal).
1602	the last signal watcher for a signal is stopped, libev will reset the
1603	signal handler to SIG_DFL (regardless of what it was set to before).
1604		2135
1605	If possible and supported, libev will install its handlers with	2136	If possible and supported, libev will install its handlers with
1606	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2137	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1607	interrupted. If you have a problem with system calls getting interrupted by	2138	not be unduly interrupted. If you have a problem with system calls getting
1608	signals you can block all signals in an C<ev_check> watcher and unblock	2139	interrupted by signals you can block all signals in an C<ev_check> watcher
1609	them in an C<ev_prepare> watcher.	2140	and unblock them in an C<ev_prepare> watcher.
		2141
		2142	=head3 The special problem of inheritance over fork/execve/pthread_create
		2143
		2144	Both the signal mask (C<sigprocmask>) and the signal disposition
		2145	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2146	stopping it again), that is, libev might or might not block the signal,
		2147	and might or might not set or restore the installed signal handler.
		2148
		2149	While this does not matter for the signal disposition (libev never
		2150	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2151	C<execve>), this matters for the signal mask: many programs do not expect
		2152	certain signals to be blocked.
		2153
		2154	This means that before calling C<exec> (from the child) you should reset
		2155	the signal mask to whatever "default" you expect (all clear is a good
		2156	choice usually).
		2157
		2158	The simplest way to ensure that the signal mask is reset in the child is
		2159	to install a fork handler with C<pthread_atfork> that resets it. That will
		2160	catch fork calls done by libraries (such as the libc) as well.
		2161
		2162	In current versions of libev, the signal will not be blocked indefinitely
		2163	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2164	the window of opportunity for problems, it will not go away, as libev
		2165	I<has> to modify the signal mask, at least temporarily.
		2166
		2167	So I can't stress this enough: I<If you do not reset your signal mask when
		2168	you expect it to be empty, you have a race condition in your code>. This
		2169	is not a libev-specific thing, this is true for most event libraries.
1610		2170
1611	=head3 Watcher-Specific Functions and Data Members	2171	=head3 Watcher-Specific Functions and Data Members
1612		2172
1613	=over 4	2173	=over 4
1614		2174
…		…
1628	=head3 Examples	2188	=head3 Examples
1629		2189
1630	Example: Try to exit cleanly on SIGINT.	2190	Example: Try to exit cleanly on SIGINT.
1631		2191
1632	static void	2192	static void
1633	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2193	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1634	{	2194	{
1635	ev_unloop (loop, EVUNLOOP_ALL);	2195	ev_unloop (loop, EVUNLOOP_ALL);
1636	}	2196	}
1637		2197
1638	struct ev_signal signal_watcher;	2198	ev_signal signal_watcher;
1639	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2199	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1640	ev_signal_start (loop, &signal_watcher);	2200	ev_signal_start (loop, &signal_watcher);
1641		2201
1642		2202
1643	=head2 C<ev_child> - watch out for process status changes	2203	=head2 C<ev_child> - watch out for process status changes
…		…
1646	some child status changes (most typically when a child of yours dies or	2206	some child status changes (most typically when a child of yours dies or
1647	exits). It is permissible to install a child watcher I<after> the child	2207	exits). It is permissible to install a child watcher I<after> the child
1648	has been forked (which implies it might have already exited), as long	2208	has been forked (which implies it might have already exited), as long
1649	as the event loop isn't entered (or is continued from a watcher), i.e.,	2209	as the event loop isn't entered (or is continued from a watcher), i.e.,
1650	forking and then immediately registering a watcher for the child is fine,	2210	forking and then immediately registering a watcher for the child is fine,
1651	but forking and registering a watcher a few event loop iterations later is	2211	but forking and registering a watcher a few event loop iterations later or
1652	not.	2212	in the next callback invocation is not.
1653		2213
1654	Only the default event loop is capable of handling signals, and therefore	2214	Only the default event loop is capable of handling signals, and therefore
1655	you can only register child watchers in the default event loop.	2215	you can only register child watchers in the default event loop.
1656		2216
		2217	Due to some design glitches inside libev, child watchers will always be
		2218	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2219	libev)
		2220
1657	=head3 Process Interaction	2221	=head3 Process Interaction
1658		2222
1659	Libev grabs C<SIGCHLD> as soon as the default event loop is	2223	Libev grabs C<SIGCHLD> as soon as the default event loop is
1660	initialised. This is necessary to guarantee proper behaviour even if	2224	initialised. This is necessary to guarantee proper behaviour even if the
1661	the first child watcher is started after the child exits. The occurrence	2225	first child watcher is started after the child exits. The occurrence
1662	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2226	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1663	synchronously as part of the event loop processing. Libev always reaps all	2227	synchronously as part of the event loop processing. Libev always reaps all
1664	children, even ones not watched.	2228	children, even ones not watched.
1665		2229
1666	=head3 Overriding the Built-In Processing	2230	=head3 Overriding the Built-In Processing
…		…
1676	=head3 Stopping the Child Watcher	2240	=head3 Stopping the Child Watcher
1677		2241
1678	Currently, the child watcher never gets stopped, even when the	2242	Currently, the child watcher never gets stopped, even when the
1679	child terminates, so normally one needs to stop the watcher in the	2243	child terminates, so normally one needs to stop the watcher in the
1680	callback. Future versions of libev might stop the watcher automatically	2244	callback. Future versions of libev might stop the watcher automatically
1681	when a child exit is detected.	2245	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2246	problem).
1682		2247
1683	=head3 Watcher-Specific Functions and Data Members	2248	=head3 Watcher-Specific Functions and Data Members
1684		2249
1685	=over 4	2250	=over 4
1686		2251
…		…
1718	its completion.	2283	its completion.
1719		2284
1720	ev_child cw;	2285	ev_child cw;
1721		2286
1722	static void	2287	static void
1723	child_cb (EV_P_ struct ev_child *w, int revents)	2288	child_cb (EV_P_ ev_child *w, int revents)
1724	{	2289	{
1725	ev_child_stop (EV_A_ w);	2290	ev_child_stop (EV_A_ w);
1726	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2291	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1727	}	2292	}
1728		2293
…		…
1743		2308
1744		2309
1745	=head2 C<ev_stat> - did the file attributes just change?	2310	=head2 C<ev_stat> - did the file attributes just change?
1746		2311
1747	This watches a file system path for attribute changes. That is, it calls	2312	This watches a file system path for attribute changes. That is, it calls
1748	C<stat> regularly (or when the OS says it changed) and sees if it changed	2313	C<stat> on that path in regular intervals (or when the OS says it changed)
1749	compared to the last time, invoking the callback if it did.	2314	and sees if it changed compared to the last time, invoking the callback if
		2315	it did.
1750		2316
1751	The path does not need to exist: changing from "path exists" to "path does	2317	The path does not need to exist: changing from "path exists" to "path does
1752	not exist" is a status change like any other. The condition "path does	2318	not exist" is a status change like any other. The condition "path does not
1753	not exist" is signified by the C<st_nlink> field being zero (which is	2319	exist" (or more correctly "path cannot be stat'ed") is signified by the
1754	otherwise always forced to be at least one) and all the other fields of	2320	C<st_nlink> field being zero (which is otherwise always forced to be at
1755	the stat buffer having unspecified contents.	2321	least one) and all the other fields of the stat buffer having unspecified
		2322	contents.
1756		2323
1757	The path I<should> be absolute and I<must not> end in a slash. If it is	2324	The path I<must not> end in a slash or contain special components such as
		2325	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1758	relative and your working directory changes, the behaviour is undefined.	2326	your working directory changes, then the behaviour is undefined.
1759		2327
1760	Since there is no standard kernel interface to do this, the portable	2328	Since there is no portable change notification interface available, the
1761	implementation simply calls C<stat (2)> regularly on the path to see if	2329	portable implementation simply calls C<stat(2)> regularly on the path
1762	it changed somehow. You can specify a recommended polling interval for	2330	to see if it changed somehow. You can specify a recommended polling
1763	this case. If you specify a polling interval of C<0> (highly recommended!)	2331	interval for this case. If you specify a polling interval of C<0> (highly
1764	then a I<suitable, unspecified default> value will be used (which	2332	recommended!) then a I<suitable, unspecified default> value will be used
1765	you can expect to be around five seconds, although this might change	2333	(which you can expect to be around five seconds, although this might
1766	dynamically). Libev will also impose a minimum interval which is currently	2334	change dynamically). Libev will also impose a minimum interval which is
1767	around C<0.1>, but thats usually overkill.	2335	currently around C<0.1>, but that's usually overkill.
1768		2336
1769	This watcher type is not meant for massive numbers of stat watchers,	2337	This watcher type is not meant for massive numbers of stat watchers,
1770	as even with OS-supported change notifications, this can be	2338	as even with OS-supported change notifications, this can be
1771	resource-intensive.	2339	resource-intensive.
1772		2340
1773	At the time of this writing, the only OS-specific interface implemented	2341	At the time of this writing, the only OS-specific interface implemented
1774	is the Linux inotify interface (implementing kqueue support is left as	2342	is the Linux inotify interface (implementing kqueue support is left as an
1775	an exercise for the reader. Note, however, that the author sees no way	2343	exercise for the reader. Note, however, that the author sees no way of
1776	of implementing C<ev_stat> semantics with kqueue).	2344	implementing C<ev_stat> semantics with kqueue, except as a hint).
1777		2345
1778	=head3 ABI Issues (Largefile Support)	2346	=head3 ABI Issues (Largefile Support)
1779		2347
1780	Libev by default (unless the user overrides this) uses the default	2348	Libev by default (unless the user overrides this) uses the default
1781	compilation environment, which means that on systems with large file	2349	compilation environment, which means that on systems with large file
1782	support disabled by default, you get the 32 bit version of the stat	2350	support disabled by default, you get the 32 bit version of the stat
1783	structure. When using the library from programs that change the ABI to	2351	structure. When using the library from programs that change the ABI to
1784	use 64 bit file offsets the programs will fail. In that case you have to	2352	use 64 bit file offsets the programs will fail. In that case you have to
1785	compile libev with the same flags to get binary compatibility. This is	2353	compile libev with the same flags to get binary compatibility. This is
1786	obviously the case with any flags that change the ABI, but the problem is	2354	obviously the case with any flags that change the ABI, but the problem is
1787	most noticeably disabled with ev_stat and large file support.	2355	most noticeably displayed with ev_stat and large file support.
1788		2356
1789	The solution for this is to lobby your distribution maker to make large	2357	The solution for this is to lobby your distribution maker to make large
1790	file interfaces available by default (as e.g. FreeBSD does) and not	2358	file interfaces available by default (as e.g. FreeBSD does) and not
1791	optional. Libev cannot simply switch on large file support because it has	2359	optional. Libev cannot simply switch on large file support because it has
1792	to exchange stat structures with application programs compiled using the	2360	to exchange stat structures with application programs compiled using the
1793	default compilation environment.	2361	default compilation environment.
1794		2362
1795	=head3 Inotify and Kqueue	2363	=head3 Inotify and Kqueue
1796		2364
1797	When C<inotify (7)> support has been compiled into libev (generally only	2365	When C<inotify (7)> support has been compiled into libev and present at
1798	available with Linux) and present at runtime, it will be used to speed up	2366	runtime, it will be used to speed up change detection where possible. The
1799	change detection where possible. The inotify descriptor will be created lazily	2367	inotify descriptor will be created lazily when the first C<ev_stat>
1800	when the first C<ev_stat> watcher is being started.	2368	watcher is being started.
1801		2369
1802	Inotify presence does not change the semantics of C<ev_stat> watchers	2370	Inotify presence does not change the semantics of C<ev_stat> watchers
1803	except that changes might be detected earlier, and in some cases, to avoid	2371	except that changes might be detected earlier, and in some cases, to avoid
1804	making regular C<stat> calls. Even in the presence of inotify support	2372	making regular C<stat> calls. Even in the presence of inotify support
1805	there are many cases where libev has to resort to regular C<stat> polling,	2373	there are many cases where libev has to resort to regular C<stat> polling,
1806	but as long as the path exists, libev usually gets away without polling.	2374	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2375	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2376	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2377	xfs are fully working) libev usually gets away without polling.
1807		2378
1808	There is no support for kqueue, as apparently it cannot be used to	2379	There is no support for kqueue, as apparently it cannot be used to
1809	implement this functionality, due to the requirement of having a file	2380	implement this functionality, due to the requirement of having a file
1810	descriptor open on the object at all times, and detecting renames, unlinks	2381	descriptor open on the object at all times, and detecting renames, unlinks
1811	etc. is difficult.	2382	etc. is difficult.
1812		2383
		2384	=head3 C<stat ()> is a synchronous operation
		2385
		2386	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2387	the process. The exception are C<ev_stat> watchers - those call C<stat
		2388	()>, which is a synchronous operation.
		2389
		2390	For local paths, this usually doesn't matter: unless the system is very
		2391	busy or the intervals between stat's are large, a stat call will be fast,
		2392	as the path data is usually in memory already (except when starting the
		2393	watcher).
		2394
		2395	For networked file systems, calling C<stat ()> can block an indefinite
		2396	time due to network issues, and even under good conditions, a stat call
		2397	often takes multiple milliseconds.
		2398
		2399	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2400	paths, although this is fully supported by libev.
		2401
1813	=head3 The special problem of stat time resolution	2402	=head3 The special problem of stat time resolution
1814		2403
1815	The C<stat ()> system call only supports full-second resolution portably, and	2404	The C<stat ()> system call only supports full-second resolution portably,
1816	even on systems where the resolution is higher, most file systems still	2405	and even on systems where the resolution is higher, most file systems
1817	only support whole seconds.	2406	still only support whole seconds.
1818		2407
1819	That means that, if the time is the only thing that changes, you can	2408	That means that, if the time is the only thing that changes, you can
1820	easily miss updates: on the first update, C<ev_stat> detects a change and	2409	easily miss updates: on the first update, C<ev_stat> detects a change and
1821	calls your callback, which does something. When there is another update	2410	calls your callback, which does something. When there is another update
1822	within the same second, C<ev_stat> will be unable to detect unless the	2411	within the same second, C<ev_stat> will be unable to detect unless the
…		…
1965		2554
1966	=head3 Watcher-Specific Functions and Data Members	2555	=head3 Watcher-Specific Functions and Data Members
1967		2556
1968	=over 4	2557	=over 4
1969		2558
1970	=item ev_idle_init (ev_signal *, callback)	2559	=item ev_idle_init (ev_idle *, callback)
1971		2560
1972	Initialises and configures the idle watcher - it has no parameters of any	2561	Initialises and configures the idle watcher - it has no parameters of any
1973	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2562	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1974	believe me.	2563	believe me.
1975		2564
…		…
1979		2568
1980	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2569	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1981	callback, free it. Also, use no error checking, as usual.	2570	callback, free it. Also, use no error checking, as usual.
1982		2571
1983	static void	2572	static void
1984	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2573	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1985	{	2574	{
1986	free (w);	2575	free (w);
1987	// now do something you wanted to do when the program has	2576	// now do something you wanted to do when the program has
1988	// no longer anything immediate to do.	2577	// no longer anything immediate to do.
1989	}	2578	}
1990		2579
1991	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2580	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1992	ev_idle_init (idle_watcher, idle_cb);	2581	ev_idle_init (idle_watcher, idle_cb);
1993	ev_idle_start (loop, idle_cb);	2582	ev_idle_start (loop, idle_watcher);
1994		2583
1995		2584
1996	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2585	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1997		2586
1998	Prepare and check watchers are usually (but not always) used in pairs:	2587	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2077		2666
2078	static ev_io iow [nfd];	2667	static ev_io iow [nfd];
2079	static ev_timer tw;	2668	static ev_timer tw;
2080		2669
2081	static void	2670	static void
2082	io_cb (ev_loop *loop, ev_io *w, int revents)	2671	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2083	{	2672	{
2084	}	2673	}
2085		2674
2086	// create io watchers for each fd and a timer before blocking	2675	// create io watchers for each fd and a timer before blocking
2087	static void	2676	static void
2088	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2677	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2089	{	2678	{
2090	int timeout = 3600000;	2679	int timeout = 3600000;
2091	struct pollfd fds [nfd];	2680	struct pollfd fds [nfd];
2092	// actual code will need to loop here and realloc etc.	2681	// actual code will need to loop here and realloc etc.
2093	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2682	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2094		2683
2095	/* the callback is illegal, but won't be called as we stop during check */	2684	/* the callback is illegal, but won't be called as we stop during check */
2096	ev_timer_init (&tw, 0, timeout * 1e-3);	2685	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2097	ev_timer_start (loop, &tw);	2686	ev_timer_start (loop, &tw);
2098		2687
2099	// create one ev_io per pollfd	2688	// create one ev_io per pollfd
2100	for (int i = 0; i < nfd; ++i)	2689	for (int i = 0; i < nfd; ++i)
2101	{	2690	{
…		…
2108	}	2697	}
2109	}	2698	}
2110		2699
2111	// stop all watchers after blocking	2700	// stop all watchers after blocking
2112	static void	2701	static void
2113	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2702	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2114	{	2703	{
2115	ev_timer_stop (loop, &tw);	2704	ev_timer_stop (loop, &tw);
2116		2705
2117	for (int i = 0; i < nfd; ++i)	2706	for (int i = 0; i < nfd; ++i)
2118	{	2707	{
…		…
2214	some fds have to be watched and handled very quickly (with low latency),	2803	some fds have to be watched and handled very quickly (with low latency),
2215	and even priorities and idle watchers might have too much overhead. In	2804	and even priorities and idle watchers might have too much overhead. In
2216	this case you would put all the high priority stuff in one loop and all	2805	this case you would put all the high priority stuff in one loop and all
2217	the rest in a second one, and embed the second one in the first.	2806	the rest in a second one, and embed the second one in the first.
2218		2807
2219	As long as the watcher is active, the callback will be invoked every time	2808	As long as the watcher is active, the callback will be invoked every
2220	there might be events pending in the embedded loop. The callback must then	2809	time there might be events pending in the embedded loop. The callback
2221	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2810	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2222	their callbacks (you could also start an idle watcher to give the embedded	2811	sweep and invoke their callbacks (the callback doesn't need to invoke the
2223	loop strictly lower priority for example). You can also set the callback	2812	C<ev_embed_sweep> function directly, it could also start an idle watcher
2224	to C<0>, in which case the embed watcher will automatically execute the	2813	to give the embedded loop strictly lower priority for example).
2225	embedded loop sweep.
2226		2814
2227	As long as the watcher is started it will automatically handle events. The	2815	You can also set the callback to C<0>, in which case the embed watcher
2228	callback will be invoked whenever some events have been handled. You can	2816	will automatically execute the embedded loop sweep whenever necessary.
2229	set the callback to C<0> to avoid having to specify one if you are not
2230	interested in that.
2231		2817
2232	Also, there have not currently been made special provisions for forking:	2818	Fork detection will be handled transparently while the C<ev_embed> watcher
2233	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2819	is active, i.e., the embedded loop will automatically be forked when the
2234	but you will also have to stop and restart any C<ev_embed> watchers	2820	embedding loop forks. In other cases, the user is responsible for calling
2235	yourself - but you can use a fork watcher to handle this automatically,	2821	C<ev_loop_fork> on the embedded loop.
2236	and future versions of libev might do just that.
2237		2822
2238	Unfortunately, not all backends are embeddable: only the ones returned by	2823	Unfortunately, not all backends are embeddable: only the ones returned by
2239	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2824	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2240	portable one.	2825	portable one.
2241		2826
…		…
2286	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2871	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2287	used).	2872	used).
2288		2873
2289	struct ev_loop *loop_hi = ev_default_init (0);	2874	struct ev_loop *loop_hi = ev_default_init (0);
2290	struct ev_loop *loop_lo = 0;	2875	struct ev_loop *loop_lo = 0;
2291	struct ev_embed embed;	2876	ev_embed embed;
2292		2877
2293	// see if there is a chance of getting one that works	2878	// see if there is a chance of getting one that works
2294	// (remember that a flags value of 0 means autodetection)	2879	// (remember that a flags value of 0 means autodetection)
2295	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2880	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2296	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2881	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2310	kqueue implementation). Store the kqueue/socket-only event loop in	2895	kqueue implementation). Store the kqueue/socket-only event loop in
2311	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2896	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2312		2897
2313	struct ev_loop *loop = ev_default_init (0);	2898	struct ev_loop *loop = ev_default_init (0);
2314	struct ev_loop *loop_socket = 0;	2899	struct ev_loop *loop_socket = 0;
2315	struct ev_embed embed;	2900	ev_embed embed;
2316		2901
2317	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2902	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2318	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2903	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2319	{	2904	{
2320	ev_embed_init (&embed, 0, loop_socket);	2905	ev_embed_init (&embed, 0, loop_socket);
…		…
2335	event loop blocks next and before C<ev_check> watchers are being called,	2920	event loop blocks next and before C<ev_check> watchers are being called,
2336	and only in the child after the fork. If whoever good citizen calling	2921	and only in the child after the fork. If whoever good citizen calling
2337	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2922	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2338	handlers will be invoked, too, of course.	2923	handlers will be invoked, too, of course.
2339		2924
		2925	=head3 The special problem of life after fork - how is it possible?
		2926
		2927	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2928	up/change the process environment, followed by a call to C<exec()>. This
		2929	sequence should be handled by libev without any problems.
		2930
		2931	This changes when the application actually wants to do event handling
		2932	in the child, or both parent in child, in effect "continuing" after the
		2933	fork.
		2934
		2935	The default mode of operation (for libev, with application help to detect
		2936	forks) is to duplicate all the state in the child, as would be expected
		2937	when I<either> the parent I<or> the child process continues.
		2938
		2939	When both processes want to continue using libev, then this is usually the
		2940	wrong result. In that case, usually one process (typically the parent) is
		2941	supposed to continue with all watchers in place as before, while the other
		2942	process typically wants to start fresh, i.e. without any active watchers.
		2943
		2944	The cleanest and most efficient way to achieve that with libev is to
		2945	simply create a new event loop, which of course will be "empty", and
		2946	use that for new watchers. This has the advantage of not touching more
		2947	memory than necessary, and thus avoiding the copy-on-write, and the
		2948	disadvantage of having to use multiple event loops (which do not support
		2949	signal watchers).
		2950
		2951	When this is not possible, or you want to use the default loop for
		2952	other reasons, then in the process that wants to start "fresh", call
		2953	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2954	the default loop will "orphan" (not stop) all registered watchers, so you
		2955	have to be careful not to execute code that modifies those watchers. Note
		2956	also that in that case, you have to re-register any signal watchers.
		2957
2340	=head3 Watcher-Specific Functions and Data Members	2958	=head3 Watcher-Specific Functions and Data Members
2341		2959
2342	=over 4	2960	=over 4
2343		2961
2344	=item ev_fork_init (ev_signal *, callback)	2962	=item ev_fork_init (ev_signal *, callback)
…		…
2373	=head3 Queueing	2991	=head3 Queueing
2374		2992
2375	C<ev_async> does not support queueing of data in any way. The reason	2993	C<ev_async> does not support queueing of data in any way. The reason
2376	is that the author does not know of a simple (or any) algorithm for a	2994	is that the author does not know of a simple (or any) algorithm for a
2377	multiple-writer-single-reader queue that works in all cases and doesn't	2995	multiple-writer-single-reader queue that works in all cases and doesn't
2378	need elaborate support such as pthreads.	2996	need elaborate support such as pthreads or unportable memory access
		2997	semantics.
2379		2998
2380	That means that if you want to queue data, you have to provide your own	2999	That means that if you want to queue data, you have to provide your own
2381	queue. But at least I can tell you how to implement locking around your	3000	queue. But at least I can tell you how to implement locking around your
2382	queue:	3001	queue:
2383		3002
2384	=over 4	3003	=over 4
2385		3004
2386	=item queueing from a signal handler context	3005	=item queueing from a signal handler context
2387		3006
2388	To implement race-free queueing, you simply add to the queue in the signal	3007	To implement race-free queueing, you simply add to the queue in the signal
2389	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3008	handler but you block the signal handler in the watcher callback. Here is
2390	some fictitious SIGUSR1 handler:	3009	an example that does that for some fictitious SIGUSR1 handler:
2391		3010
2392	static ev_async mysig;	3011	static ev_async mysig;
2393		3012
2394	static void	3013	static void
2395	sigusr1_handler (void)	3014	sigusr1_handler (void)
…		…
2461	=over 4	3080	=over 4
2462		3081
2463	=item ev_async_init (ev_async *, callback)	3082	=item ev_async_init (ev_async *, callback)
2464		3083
2465	Initialises and configures the async watcher - it has no parameters of any	3084	Initialises and configures the async watcher - it has no parameters of any
2466	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3085	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2467	trust me.	3086	trust me.
2468		3087
2469	=item ev_async_send (loop, ev_async *)	3088	=item ev_async_send (loop, ev_async *)
2470		3089
2471	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3090	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2472	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3091	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2473	C<ev_feed_event>, this call is safe to do from other threads, signal or	3092	C<ev_feed_event>, this call is safe to do from other threads, signal or
2474	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3093	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2475	section below on what exactly this means).	3094	section below on what exactly this means).
2476		3095
		3096	Note that, as with other watchers in libev, multiple events might get
		3097	compressed into a single callback invocation (another way to look at this
		3098	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3099	reset when the event loop detects that).
		3100
2477	This call incurs the overhead of a system call only once per loop iteration,	3101	This call incurs the overhead of a system call only once per event loop
2478	so while the overhead might be noticeable, it doesn't apply to repeated	3102	iteration, so while the overhead might be noticeable, it doesn't apply to
2479	calls to C<ev_async_send>.	3103	repeated calls to C<ev_async_send> for the same event loop.
2480		3104
2481	=item bool = ev_async_pending (ev_async *)	3105	=item bool = ev_async_pending (ev_async *)
2482		3106
2483	Returns a non-zero value when C<ev_async_send> has been called on the	3107	Returns a non-zero value when C<ev_async_send> has been called on the
2484	watcher but the event has not yet been processed (or even noted) by the	3108	watcher but the event has not yet been processed (or even noted) by the
…		…
2487	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3111	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2488	the loop iterates next and checks for the watcher to have become active,	3112	the loop iterates next and checks for the watcher to have become active,
2489	it will reset the flag again. C<ev_async_pending> can be used to very	3113	it will reset the flag again. C<ev_async_pending> can be used to very
2490	quickly check whether invoking the loop might be a good idea.	3114	quickly check whether invoking the loop might be a good idea.
2491		3115
2492	Not that this does I<not> check whether the watcher itself is pending, only	3116	Not that this does I<not> check whether the watcher itself is pending,
2493	whether it has been requested to make this watcher pending.	3117	only whether it has been requested to make this watcher pending: there
		3118	is a time window between the event loop checking and resetting the async
		3119	notification, and the callback being invoked.
2494		3120
2495	=back	3121	=back
2496		3122
2497		3123
2498	=head1 OTHER FUNCTIONS	3124	=head1 OTHER FUNCTIONS
…		…
2502	=over 4	3128	=over 4
2503		3129
2504	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3130	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2505		3131
2506	This function combines a simple timer and an I/O watcher, calls your	3132	This function combines a simple timer and an I/O watcher, calls your
2507	callback on whichever event happens first and automatically stop both	3133	callback on whichever event happens first and automatically stops both
2508	watchers. This is useful if you want to wait for a single event on an fd	3134	watchers. This is useful if you want to wait for a single event on an fd
2509	or timeout without having to allocate/configure/start/stop/free one or	3135	or timeout without having to allocate/configure/start/stop/free one or
2510	more watchers yourself.	3136	more watchers yourself.
2511		3137
2512	If C<fd> is less than 0, then no I/O watcher will be started and events	3138	If C<fd> is less than 0, then no I/O watcher will be started and the
2513	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3139	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2514	C<events> set will be created and started.	3140	the given C<fd> and C<events> set will be created and started.
2515		3141
2516	If C<timeout> is less than 0, then no timeout watcher will be	3142	If C<timeout> is less than 0, then no timeout watcher will be
2517	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3143	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2518	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3144	repeat = 0) will be started. C<0> is a valid timeout.
2519	dubious value.
2520		3145
2521	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3146	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
2522	passed an C<revents> set like normal event callbacks (a combination of	3147	passed an C<revents> set like normal event callbacks (a combination of
2523	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3148	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2524	value passed to C<ev_once>:	3149	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3150	a timeout and an io event at the same time - you probably should give io
		3151	events precedence.
		3152
		3153	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2525		3154
2526	static void stdin_ready (int revents, void *arg)	3155	static void stdin_ready (int revents, void *arg)
2527	{	3156	{
		3157	if (revents & EV_READ)
		3158	/* stdin might have data for us, joy! */;
2528	if (revents & EV_TIMEOUT)	3159	else if (revents & EV_TIMEOUT)
2529	/* doh, nothing entered */;	3160	/* doh, nothing entered */;
2530	else if (revents & EV_READ)
2531	/* stdin might have data for us, joy! */;
2532	}	3161	}
2533		3162
2534	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3163	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2535		3164
2536	=item ev_feed_event (ev_loop *, watcher *, int revents)
2537
2538	Feeds the given event set into the event loop, as if the specified event
2539	had happened for the specified watcher (which must be a pointer to an
2540	initialised but not necessarily started event watcher).
2541
2542	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3165	=item ev_feed_fd_event (loop, int fd, int revents)
2543		3166
2544	Feed an event on the given fd, as if a file descriptor backend detected	3167	Feed an event on the given fd, as if a file descriptor backend detected
2545	the given events it.	3168	the given events it.
2546		3169
2547	=item ev_feed_signal_event (ev_loop *loop, int signum)	3170	=item ev_feed_signal_event (loop, int signum)
2548		3171
2549	Feed an event as if the given signal occurred (C<loop> must be the default	3172	Feed an event as if the given signal occurred (C<loop> must be the default
2550	loop!).	3173	loop!).
2551		3174
2552	=back	3175	=back
…		…
2632		3255
2633	=over 4	3256	=over 4
2634		3257
2635	=item ev::TYPE::TYPE ()	3258	=item ev::TYPE::TYPE ()
2636		3259
2637	=item ev::TYPE::TYPE (struct ev_loop *)	3260	=item ev::TYPE::TYPE (loop)
2638		3261
2639	=item ev::TYPE::~TYPE	3262	=item ev::TYPE::~TYPE
2640		3263
2641	The constructor (optionally) takes an event loop to associate the watcher	3264	The constructor (optionally) takes an event loop to associate the watcher
2642	with. If it is omitted, it will use C<EV_DEFAULT>.	3265	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2674		3297
2675	myclass obj;	3298	myclass obj;
2676	ev::io iow;	3299	ev::io iow;
2677	iow.set <myclass, &myclass::io_cb> (&obj);	3300	iow.set <myclass, &myclass::io_cb> (&obj);
2678		3301
		3302	=item w->set (object *)
		3303
		3304	This is an B<experimental> feature that might go away in a future version.
		3305
		3306	This is a variation of a method callback - leaving out the method to call
		3307	will default the method to C<operator ()>, which makes it possible to use
		3308	functor objects without having to manually specify the C<operator ()> all
		3309	the time. Incidentally, you can then also leave out the template argument
		3310	list.
		3311
		3312	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3313	int revents)>.
		3314
		3315	See the method-C<set> above for more details.
		3316
		3317	Example: use a functor object as callback.
		3318
		3319	struct myfunctor
		3320	{
		3321	void operator() (ev::io &w, int revents)
		3322	{
		3323	...
		3324	}
		3325	}
		3326
		3327	myfunctor f;
		3328
		3329	ev::io w;
		3330	w.set (&f);
		3331
2679	=item w->set<function> (void *data = 0)	3332	=item w->set<function> (void *data = 0)
2680		3333
2681	Also sets a callback, but uses a static method or plain function as	3334	Also sets a callback, but uses a static method or plain function as
2682	callback. The optional C<data> argument will be stored in the watcher's	3335	callback. The optional C<data> argument will be stored in the watcher's
2683	C<data> member and is free for you to use.	3336	C<data> member and is free for you to use.
…		…
2689	Example: Use a plain function as callback.	3342	Example: Use a plain function as callback.
2690		3343
2691	static void io_cb (ev::io &w, int revents) { }	3344	static void io_cb (ev::io &w, int revents) { }
2692	iow.set <io_cb> ();	3345	iow.set <io_cb> ();
2693		3346
2694	=item w->set (struct ev_loop *)	3347	=item w->set (loop)
2695		3348
2696	Associates a different C<struct ev_loop> with this watcher. You can only	3349	Associates a different C<struct ev_loop> with this watcher. You can only
2697	do this when the watcher is inactive (and not pending either).	3350	do this when the watcher is inactive (and not pending either).
2698		3351
2699	=item w->set ([arguments])	3352	=item w->set ([arguments])
…		…
2769	L<http://software.schmorp.de/pkg/EV>.	3422	L<http://software.schmorp.de/pkg/EV>.
2770		3423
2771	=item Python	3424	=item Python
2772		3425
2773	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3426	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2774	seems to be quite complete and well-documented. Note, however, that the	3427	seems to be quite complete and well-documented.
2775	patch they require for libev is outright dangerous as it breaks the ABI
2776	for everybody else, and therefore, should never be applied in an installed
2777	libev (if python requires an incompatible ABI then it needs to embed
2778	libev).
2779		3428
2780	=item Ruby	3429	=item Ruby
2781		3430
2782	Tony Arcieri has written a ruby extension that offers access to a subset	3431	Tony Arcieri has written a ruby extension that offers access to a subset
2783	of the libev API and adds file handle abstractions, asynchronous DNS and	3432	of the libev API and adds file handle abstractions, asynchronous DNS and
2784	more on top of it. It can be found via gem servers. Its homepage is at	3433	more on top of it. It can be found via gem servers. Its homepage is at
2785	L<http://rev.rubyforge.org/>.	3434	L<http://rev.rubyforge.org/>.
2786		3435
		3436	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3437	makes rev work even on mingw.
		3438
		3439	=item Haskell
		3440
		3441	A haskell binding to libev is available at
		3442	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3443
2787	=item D	3444	=item D
2788		3445
2789	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3446	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2790	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3447	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3448
		3449	=item Ocaml
		3450
		3451	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3452	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3453
		3454	=item Lua
		3455
		3456	Brian Maher has written a partial interface to libev for lua (at the
		3457	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3458	L<http://github.com/brimworks/lua-ev>.
2791		3459
2792	=back	3460	=back
2793		3461
2794		3462
2795	=head1 MACRO MAGIC	3463	=head1 MACRO MAGIC
…		…
2896		3564
2897	#define EV_STANDALONE 1	3565	#define EV_STANDALONE 1
2898	#include "ev.h"	3566	#include "ev.h"
2899		3567
2900	Both header files and implementation files can be compiled with a C++	3568	Both header files and implementation files can be compiled with a C++
2901	compiler (at least, thats a stated goal, and breakage will be treated	3569	compiler (at least, that's a stated goal, and breakage will be treated
2902	as a bug).	3570	as a bug).
2903		3571
2904	You need the following files in your source tree, or in a directory	3572	You need the following files in your source tree, or in a directory
2905	in your include path (e.g. in libev/ when using -Ilibev):	3573	in your include path (e.g. in libev/ when using -Ilibev):
2906		3574
…		…
2949	libev.m4	3617	libev.m4
2950		3618
2951	=head2 PREPROCESSOR SYMBOLS/MACROS	3619	=head2 PREPROCESSOR SYMBOLS/MACROS
2952		3620
2953	Libev can be configured via a variety of preprocessor symbols you have to	3621	Libev can be configured via a variety of preprocessor symbols you have to
2954	define before including any of its files. The default in the absence of	3622	define before including (or compiling) any of its files. The default in
2955	autoconf is documented for every option.	3623	the absence of autoconf is documented for every option.
		3624
		3625	Symbols marked with "(h)" do not change the ABI, and can have different
		3626	values when compiling libev vs. including F<ev.h>, so it is permissible
		3627	to redefine them before including F<ev.h> without breakign compatibility
		3628	to a compiled library. All other symbols change the ABI, which means all
		3629	users of libev and the libev code itself must be compiled with compatible
		3630	settings.
2956		3631
2957	=over 4	3632	=over 4
2958		3633
2959	=item EV_STANDALONE	3634	=item EV_STANDALONE (h)
2960		3635
2961	Must always be C<1> if you do not use autoconf configuration, which	3636	Must always be C<1> if you do not use autoconf configuration, which
2962	keeps libev from including F<config.h>, and it also defines dummy	3637	keeps libev from including F<config.h>, and it also defines dummy
2963	implementations for some libevent functions (such as logging, which is not	3638	implementations for some libevent functions (such as logging, which is not
2964	supported). It will also not define any of the structs usually found in	3639	supported). It will also not define any of the structs usually found in
2965	F<event.h> that are not directly supported by the libev core alone.	3640	F<event.h> that are not directly supported by the libev core alone.
2966		3641
		3642	In standalone mode, libev will still try to automatically deduce the
		3643	configuration, but has to be more conservative.
		3644
2967	=item EV_USE_MONOTONIC	3645	=item EV_USE_MONOTONIC
2968		3646
2969	If defined to be C<1>, libev will try to detect the availability of the	3647	If defined to be C<1>, libev will try to detect the availability of the
2970	monotonic clock option at both compile time and runtime. Otherwise no use	3648	monotonic clock option at both compile time and runtime. Otherwise no
2971	of the monotonic clock option will be attempted. If you enable this, you	3649	use of the monotonic clock option will be attempted. If you enable this,
2972	usually have to link against librt or something similar. Enabling it when	3650	you usually have to link against librt or something similar. Enabling it
2973	the functionality isn't available is safe, though, although you have	3651	when the functionality isn't available is safe, though, although you have
2974	to make sure you link against any libraries where the C<clock_gettime>	3652	to make sure you link against any libraries where the C<clock_gettime>
2975	function is hiding in (often F<-lrt>).	3653	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2976		3654
2977	=item EV_USE_REALTIME	3655	=item EV_USE_REALTIME
2978		3656
2979	If defined to be C<1>, libev will try to detect the availability of the	3657	If defined to be C<1>, libev will try to detect the availability of the
2980	real-time clock option at compile time (and assume its availability at	3658	real-time clock option at compile time (and assume its availability
2981	runtime if successful). Otherwise no use of the real-time clock option will	3659	at runtime if successful). Otherwise no use of the real-time clock
2982	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3660	option will be attempted. This effectively replaces C<gettimeofday>
2983	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3661	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2984	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3662	correctness. See the note about libraries in the description of
		3663	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3664	C<EV_USE_CLOCK_SYSCALL>.
		3665
		3666	=item EV_USE_CLOCK_SYSCALL
		3667
		3668	If defined to be C<1>, libev will try to use a direct syscall instead
		3669	of calling the system-provided C<clock_gettime> function. This option
		3670	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3671	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3672	programs needlessly. Using a direct syscall is slightly slower (in
		3673	theory), because no optimised vdso implementation can be used, but avoids
		3674	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3675	higher, as it simplifies linking (no need for C<-lrt>).
2985		3676
2986	=item EV_USE_NANOSLEEP	3677	=item EV_USE_NANOSLEEP
2987		3678
2988	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3679	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2989	and will use it for delays. Otherwise it will use C<select ()>.	3680	and will use it for delays. Otherwise it will use C<select ()>.
…		…
3005		3696
3006	=item EV_SELECT_USE_FD_SET	3697	=item EV_SELECT_USE_FD_SET
3007		3698
3008	If defined to C<1>, then the select backend will use the system C<fd_set>	3699	If defined to C<1>, then the select backend will use the system C<fd_set>
3009	structure. This is useful if libev doesn't compile due to a missing	3700	structure. This is useful if libev doesn't compile due to a missing
3010	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3701	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
3011	exotic systems. This usually limits the range of file descriptors to some	3702	on exotic systems. This usually limits the range of file descriptors to
3012	low limit such as 1024 or might have other limitations (winsocket only	3703	some low limit such as 1024 or might have other limitations (winsocket
3013	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3704	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
3014	influence the size of the C<fd_set> used.	3705	configures the maximum size of the C<fd_set>.
3015		3706
3016	=item EV_SELECT_IS_WINSOCKET	3707	=item EV_SELECT_IS_WINSOCKET
3017		3708
3018	When defined to C<1>, the select backend will assume that	3709	When defined to C<1>, the select backend will assume that
3019	select/socket/connect etc. don't understand file descriptors but	3710	select/socket/connect etc. don't understand file descriptors but
…		…
3021	be used is the winsock select). This means that it will call	3712	be used is the winsock select). This means that it will call
3022	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3713	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
3023	it is assumed that all these functions actually work on fds, even	3714	it is assumed that all these functions actually work on fds, even
3024	on win32. Should not be defined on non-win32 platforms.	3715	on win32. Should not be defined on non-win32 platforms.
3025		3716
3026	=item EV_FD_TO_WIN32_HANDLE	3717	=item EV_FD_TO_WIN32_HANDLE(fd)
3027		3718
3028	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3719	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
3029	file descriptors to socket handles. When not defining this symbol (the	3720	file descriptors to socket handles. When not defining this symbol (the
3030	default), then libev will call C<_get_osfhandle>, which is usually	3721	default), then libev will call C<_get_osfhandle>, which is usually
3031	correct. In some cases, programs use their own file descriptor management,	3722	correct. In some cases, programs use their own file descriptor management,
3032	in which case they can provide this function to map fds to socket handles.	3723	in which case they can provide this function to map fds to socket handles.
		3724
		3725	=item EV_WIN32_HANDLE_TO_FD(handle)
		3726
		3727	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3728	using the standard C<_open_osfhandle> function. For programs implementing
		3729	their own fd to handle mapping, overwriting this function makes it easier
		3730	to do so. This can be done by defining this macro to an appropriate value.
		3731
		3732	=item EV_WIN32_CLOSE_FD(fd)
		3733
		3734	If programs implement their own fd to handle mapping on win32, then this
		3735	macro can be used to override the C<close> function, useful to unregister
		3736	file descriptors again. Note that the replacement function has to close
		3737	the underlying OS handle.
3033		3738
3034	=item EV_USE_POLL	3739	=item EV_USE_POLL
3035		3740
3036	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3741	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3037	backend. Otherwise it will be enabled on non-win32 platforms. It	3742	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3084	as well as for signal and thread safety in C<ev_async> watchers.	3789	as well as for signal and thread safety in C<ev_async> watchers.
3085		3790
3086	In the absence of this define, libev will use C<sig_atomic_t volatile>	3791	In the absence of this define, libev will use C<sig_atomic_t volatile>
3087	(from F<signal.h>), which is usually good enough on most platforms.	3792	(from F<signal.h>), which is usually good enough on most platforms.
3088		3793
3089	=item EV_H	3794	=item EV_H (h)
3090		3795
3091	The name of the F<ev.h> header file used to include it. The default if	3796	The name of the F<ev.h> header file used to include it. The default if
3092	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	3797	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
3093	used to virtually rename the F<ev.h> header file in case of conflicts.	3798	used to virtually rename the F<ev.h> header file in case of conflicts.
3094		3799
3095	=item EV_CONFIG_H	3800	=item EV_CONFIG_H (h)
3096		3801
3097	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3802	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
3098	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3803	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
3099	C<EV_H>, above.	3804	C<EV_H>, above.
3100		3805
3101	=item EV_EVENT_H	3806	=item EV_EVENT_H (h)
3102		3807
3103	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3808	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
3104	of how the F<event.h> header can be found, the default is C<"event.h">.	3809	of how the F<event.h> header can be found, the default is C<"event.h">.
3105		3810
3106	=item EV_PROTOTYPES	3811	=item EV_PROTOTYPES (h)
3107		3812
3108	If defined to be C<0>, then F<ev.h> will not define any function	3813	If defined to be C<0>, then F<ev.h> will not define any function
3109	prototypes, but still define all the structs and other symbols. This is	3814	prototypes, but still define all the structs and other symbols. This is
3110	occasionally useful if you want to provide your own wrapper functions	3815	occasionally useful if you want to provide your own wrapper functions
3111	around libev functions.	3816	around libev functions.
…		…
3161	=item EV_FORK_ENABLE	3866	=item EV_FORK_ENABLE
3162		3867
3163	If undefined or defined to be C<1>, then fork watchers are supported. If	3868	If undefined or defined to be C<1>, then fork watchers are supported. If
3164	defined to be C<0>, then they are not.	3869	defined to be C<0>, then they are not.
3165		3870
		3871	=item EV_SIGNAL_ENABLE
		3872
		3873	If undefined or defined to be C<1>, then signal watchers are supported. If
		3874	defined to be C<0>, then they are not.
		3875
3166	=item EV_ASYNC_ENABLE	3876	=item EV_ASYNC_ENABLE
3167		3877
3168	If undefined or defined to be C<1>, then async watchers are supported. If	3878	If undefined or defined to be C<1>, then async watchers are supported. If
3169	defined to be C<0>, then they are not.	3879	defined to be C<0>, then they are not.
3170		3880
		3881	=item EV_CHILD_ENABLE
		3882
		3883	If undefined or defined to be C<1> (and C<_WIN32> is not defined), then
		3884	child watchers are supported. If defined to be C<0>, then they are not.
		3885
3171	=item EV_MINIMAL	3886	=item EV_MINIMAL
3172		3887
3173	If you need to shave off some kilobytes of code at the expense of some	3888	If you need to shave off some kilobytes of code at the expense of some
3174	speed, define this symbol to C<1>. Currently this is used to override some	3889	speed (but with the full API), define this symbol to C<1>. Currently this
3175	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3890	is used to override some inlining decisions, saves roughly 30% code size
3176	much smaller 2-heap for timer management over the default 4-heap.	3891	on amd64. It also selects a much smaller 2-heap for timer management over
		3892	the default 4-heap.
		3893
		3894	You can save even more by disabling watcher types you do not need
		3895	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3896	(C<-DNDEBUG>) will usually reduce code size a lot. Disabling inotify,
		3897	eventfd and signalfd will further help, and disabling backends one doesn't
		3898	need (e.g. poll, epoll, kqueue, ports) will help further.
		3899
		3900	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3901	provide a bare-bones event library. See C<ev.h> for details on what parts
		3902	of the API are still available, and do not complain if this subset changes
		3903	over time.
		3904
		3905	This example set of settings reduces the compiled size of libev from 24Kb
		3906	to 8Kb on my GNU/Linux amd64 system (and leaves little in - there is also
		3907	an effect on the amount of memory used). With an intelligent-enough linker
		3908	further unused functions might be left out as well automatically.
		3909
		3910	// tuning and API changes
		3911	#define EV_MINIMAL 2
		3912	#define EV_MULTIPLICITY 0
		3913	#define EV_MINPRI 0
		3914	#define EV_MAXPRI 0
		3915
		3916	// OS-specific backends
		3917	#define EV_USE_INOTIFY 0
		3918	#define EV_USE_EVENTFD 0
		3919	#define EV_USE_SIGNALFD 0
		3920	#define EV_USE_REALTIME 0
		3921	#define EV_USE_MONOTONIC 0
		3922	#define EV_USE_CLOCK_SYSCALL 0
		3923
		3924	// disable all backends except select
		3925	#define EV_USE_POLL 0
		3926	#define EV_USE_PORT 0
		3927	#define EV_USE_KQUEUE 0
		3928	#define EV_USE_EPOLL 0
		3929
		3930	// disable all watcher types that cna be disabled
		3931	#define EV_STAT_ENABLE 0
		3932	#define EV_PERIODIC_ENABLE 0
		3933	#define EV_IDLE_ENABLE 0
		3934	#define EV_FORK_ENABLE 0
		3935	#define EV_SIGNAL_ENABLE 0
		3936	#define EV_CHILD_ENABLE 0
		3937	#define EV_ASYNC_ENABLE 0
		3938	#define EV_EMBED_ENABLE 0
		3939
		3940	=item EV_AVOID_STDIO
		3941
		3942	If this is set to C<1> at compiletime, then libev will avoid using stdio
		3943	functions (printf, scanf, perror etc.). This will increase the codesize
		3944	somewhat, but if your program doesn't otherwise depend on stdio and your
		3945	libc allows it, this avoids linking in the stdio library which is quite
		3946	big.
		3947
		3948	Note that error messages might become less precise when this option is
		3949	enabled.
		3950
		3951	=item EV_NSIG
		3952
		3953	The highest supported signal number, +1 (or, the number of
		3954	signals): Normally, libev tries to deduce the maximum number of signals
		3955	automatically, but sometimes this fails, in which case it can be
		3956	specified. Also, using a lower number than detected (C<32> should be
		3957	good for about any system in existance) can save some memory, as libev
		3958	statically allocates some 12-24 bytes per signal number.
3177		3959
3178	=item EV_PID_HASHSIZE	3960	=item EV_PID_HASHSIZE
3179		3961
3180	C<ev_child> watchers use a small hash table to distribute workload by	3962	C<ev_child> watchers use a small hash table to distribute workload by
3181	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3963	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3306	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4088	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3307		4089
3308	#include "ev_cpp.h"	4090	#include "ev_cpp.h"
3309	#include "ev.c"	4091	#include "ev.c"
3310		4092
		4093	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3311		4094
3312	=head1 THREADS AND COROUTINES	4095	=head2 THREADS AND COROUTINES
3313		4096
3314	=head2 THREADS	4097	=head3 THREADS
3315		4098
3316	All libev functions are reentrant and thread-safe unless explicitly	4099	All libev functions are reentrant and thread-safe unless explicitly
3317	documented otherwise, but it uses no locking itself. This means that you	4100	documented otherwise, but libev implements no locking itself. This means
3318	can use as many loops as you want in parallel, as long as there are no	4101	that you can use as many loops as you want in parallel, as long as there
3319	concurrent calls into any libev function with the same loop parameter	4102	are no concurrent calls into any libev function with the same loop
3320	(C<ev_default_*> calls have an implicit default loop parameter, of	4103	parameter (C<ev_default_*> calls have an implicit default loop parameter,
3321	course): libev guarantees that different event loops share no data	4104	of course): libev guarantees that different event loops share no data
3322	structures that need any locking.	4105	structures that need any locking.
3323		4106
3324	Or to put it differently: calls with different loop parameters can be done	4107	Or to put it differently: calls with different loop parameters can be done
3325	concurrently from multiple threads, calls with the same loop parameter	4108	concurrently from multiple threads, calls with the same loop parameter
3326	must be done serially (but can be done from different threads, as long as	4109	must be done serially (but can be done from different threads, as long as
…		…
3366	default loop and triggering an C<ev_async> watcher from the default loop	4149	default loop and triggering an C<ev_async> watcher from the default loop
3367	watcher callback into the event loop interested in the signal.	4150	watcher callback into the event loop interested in the signal.
3368		4151
3369	=back	4152	=back
3370		4153
		4154	=head4 THREAD LOCKING EXAMPLE
		4155
		4156	Here is a fictitious example of how to run an event loop in a different
		4157	thread than where callbacks are being invoked and watchers are
		4158	created/added/removed.
		4159
		4160	For a real-world example, see the C<EV::Loop::Async> perl module,
		4161	which uses exactly this technique (which is suited for many high-level
		4162	languages).
		4163
		4164	The example uses a pthread mutex to protect the loop data, a condition
		4165	variable to wait for callback invocations, an async watcher to notify the
		4166	event loop thread and an unspecified mechanism to wake up the main thread.
		4167
		4168	First, you need to associate some data with the event loop:
		4169
		4170	typedef struct {
		4171	mutex_t lock; /* global loop lock */
		4172	ev_async async_w;
		4173	thread_t tid;
		4174	cond_t invoke_cv;
		4175	} userdata;
		4176
		4177	void prepare_loop (EV_P)
		4178	{
		4179	// for simplicity, we use a static userdata struct.
		4180	static userdata u;
		4181
		4182	ev_async_init (&u->async_w, async_cb);
		4183	ev_async_start (EV_A_ &u->async_w);
		4184
		4185	pthread_mutex_init (&u->lock, 0);
		4186	pthread_cond_init (&u->invoke_cv, 0);
		4187
		4188	// now associate this with the loop
		4189	ev_set_userdata (EV_A_ u);
		4190	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4191	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4192
		4193	// then create the thread running ev_loop
		4194	pthread_create (&u->tid, 0, l_run, EV_A);
		4195	}
		4196
		4197	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4198	solely to wake up the event loop so it takes notice of any new watchers
		4199	that might have been added:
		4200
		4201	static void
		4202	async_cb (EV_P_ ev_async *w, int revents)
		4203	{
		4204	// just used for the side effects
		4205	}
		4206
		4207	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4208	protecting the loop data, respectively.
		4209
		4210	static void
		4211	l_release (EV_P)
		4212	{
		4213	userdata *u = ev_userdata (EV_A);
		4214	pthread_mutex_unlock (&u->lock);
		4215	}
		4216
		4217	static void
		4218	l_acquire (EV_P)
		4219	{
		4220	userdata *u = ev_userdata (EV_A);
		4221	pthread_mutex_lock (&u->lock);
		4222	}
		4223
		4224	The event loop thread first acquires the mutex, and then jumps straight
		4225	into C<ev_loop>:
		4226
		4227	void *
		4228	l_run (void *thr_arg)
		4229	{
		4230	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4231
		4232	l_acquire (EV_A);
		4233	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4234	ev_loop (EV_A_ 0);
		4235	l_release (EV_A);
		4236
		4237	return 0;
		4238	}
		4239
		4240	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4241	signal the main thread via some unspecified mechanism (signals? pipe
		4242	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4243	have been called (in a while loop because a) spurious wakeups are possible
		4244	and b) skipping inter-thread-communication when there are no pending
		4245	watchers is very beneficial):
		4246
		4247	static void
		4248	l_invoke (EV_P)
		4249	{
		4250	userdata *u = ev_userdata (EV_A);
		4251
		4252	while (ev_pending_count (EV_A))
		4253	{
		4254	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4255	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4256	}
		4257	}
		4258
		4259	Now, whenever the main thread gets told to invoke pending watchers, it
		4260	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4261	thread to continue:
		4262
		4263	static void
		4264	real_invoke_pending (EV_P)
		4265	{
		4266	userdata *u = ev_userdata (EV_A);
		4267
		4268	pthread_mutex_lock (&u->lock);
		4269	ev_invoke_pending (EV_A);
		4270	pthread_cond_signal (&u->invoke_cv);
		4271	pthread_mutex_unlock (&u->lock);
		4272	}
		4273
		4274	Whenever you want to start/stop a watcher or do other modifications to an
		4275	event loop, you will now have to lock:
		4276
		4277	ev_timer timeout_watcher;
		4278	userdata *u = ev_userdata (EV_A);
		4279
		4280	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4281
		4282	pthread_mutex_lock (&u->lock);
		4283	ev_timer_start (EV_A_ &timeout_watcher);
		4284	ev_async_send (EV_A_ &u->async_w);
		4285	pthread_mutex_unlock (&u->lock);
		4286
		4287	Note that sending the C<ev_async> watcher is required because otherwise
		4288	an event loop currently blocking in the kernel will have no knowledge
		4289	about the newly added timer. By waking up the loop it will pick up any new
		4290	watchers in the next event loop iteration.
		4291
3371	=head2 COROUTINES	4292	=head3 COROUTINES
3372		4293
3373	Libev is much more accommodating to coroutines ("cooperative threads"):	4294	Libev is very accommodating to coroutines ("cooperative threads"):
3374	libev fully supports nesting calls to it's functions from different	4295	libev fully supports nesting calls to its functions from different
3375	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4296	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3376	different coroutines and switch freely between both coroutines running the	4297	different coroutines, and switch freely between both coroutines running
3377	loop, as long as you don't confuse yourself). The only exception is that	4298	the loop, as long as you don't confuse yourself). The only exception is
3378	you must not do this from C<ev_periodic> reschedule callbacks.	4299	that you must not do this from C<ev_periodic> reschedule callbacks.
3379		4300
3380	Care has been taken to ensure that libev does not keep local state inside	4301	Care has been taken to ensure that libev does not keep local state inside
3381	C<ev_loop>, and other calls do not usually allow coroutine switches.	4302	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4303	they do not call any callbacks.
3382		4304
		4305	=head2 COMPILER WARNINGS
3383		4306
3384	=head1 COMPLEXITIES	4307	Depending on your compiler and compiler settings, you might get no or a
		4308	lot of warnings when compiling libev code. Some people are apparently
		4309	scared by this.
3385		4310
3386	In this section the complexities of (many of) the algorithms used inside	4311	However, these are unavoidable for many reasons. For one, each compiler
3387	libev will be explained. For complexity discussions about backends see the	4312	has different warnings, and each user has different tastes regarding
3388	documentation for C<ev_default_init>.	4313	warning options. "Warn-free" code therefore cannot be a goal except when
		4314	targeting a specific compiler and compiler-version.
3389		4315
3390	All of the following are about amortised time: If an array needs to be	4316	Another reason is that some compiler warnings require elaborate
3391	extended, libev needs to realloc and move the whole array, but this	4317	workarounds, or other changes to the code that make it less clear and less
3392	happens asymptotically never with higher number of elements, so O(1) might	4318	maintainable.
3393	mean it might do a lengthy realloc operation in rare cases, but on average
3394	it is much faster and asymptotically approaches constant time.
3395		4319
3396	=over 4	4320	And of course, some compiler warnings are just plain stupid, or simply
		4321	wrong (because they don't actually warn about the condition their message
		4322	seems to warn about). For example, certain older gcc versions had some
		4323	warnings that resulted an extreme number of false positives. These have
		4324	been fixed, but some people still insist on making code warn-free with
		4325	such buggy versions.
3397		4326
3398	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4327	While libev is written to generate as few warnings as possible,
		4328	"warn-free" code is not a goal, and it is recommended not to build libev
		4329	with any compiler warnings enabled unless you are prepared to cope with
		4330	them (e.g. by ignoring them). Remember that warnings are just that:
		4331	warnings, not errors, or proof of bugs.
3399		4332
3400	This means that, when you have a watcher that triggers in one hour and
3401	there are 100 watchers that would trigger before that then inserting will
3402	have to skip roughly seven (C<ld 100>) of these watchers.
3403		4333
3404	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4334	=head2 VALGRIND
3405		4335
3406	That means that changing a timer costs less than removing/adding them	4336	Valgrind has a special section here because it is a popular tool that is
3407	as only the relative motion in the event queue has to be paid for.	4337	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3408		4338
3409	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4339	If you think you found a bug (memory leak, uninitialised data access etc.)
		4340	in libev, then check twice: If valgrind reports something like:
3410		4341
3411	These just add the watcher into an array or at the head of a list.	4342	==2274== definitely lost: 0 bytes in 0 blocks.
		4343	==2274== possibly lost: 0 bytes in 0 blocks.
		4344	==2274== still reachable: 256 bytes in 1 blocks.
3412		4345
3413	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4346	Then there is no memory leak, just as memory accounted to global variables
		4347	is not a memleak - the memory is still being referenced, and didn't leak.
3414		4348
3415	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4349	Similarly, under some circumstances, valgrind might report kernel bugs
		4350	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4351	although an acceptable workaround has been found here), or it might be
		4352	confused.
3416		4353
3417	These watchers are stored in lists then need to be walked to find the	4354	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3418	correct watcher to remove. The lists are usually short (you don't usually	4355	make it into some kind of religion.
3419	have many watchers waiting for the same fd or signal).
3420		4356
3421	=item Finding the next timer in each loop iteration: O(1)	4357	If you are unsure about something, feel free to contact the mailing list
		4358	with the full valgrind report and an explanation on why you think this
		4359	is a bug in libev (best check the archives, too :). However, don't be
		4360	annoyed when you get a brisk "this is no bug" answer and take the chance
		4361	of learning how to interpret valgrind properly.
3422		4362
3423	By virtue of using a binary or 4-heap, the next timer is always found at a	4363	If you need, for some reason, empty reports from valgrind for your project
3424	fixed position in the storage array.	4364	I suggest using suppression lists.
3425		4365
3426	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3427		4366
3428	A change means an I/O watcher gets started or stopped, which requires	4367	=head1 PORTABILITY NOTES
3429	libev to recalculate its status (and possibly tell the kernel, depending
3430	on backend and whether C<ev_io_set> was used).
3431		4368
3432	=item Activating one watcher (putting it into the pending state): O(1)
3433
3434	=item Priority handling: O(number_of_priorities)
3435
3436	Priorities are implemented by allocating some space for each
3437	priority. When doing priority-based operations, libev usually has to
3438	linearly search all the priorities, but starting/stopping and activating
3439	watchers becomes O(1) with respect to priority handling.
3440
3441	=item Sending an ev_async: O(1)
3442
3443	=item Processing ev_async_send: O(number_of_async_watchers)
3444
3445	=item Processing signals: O(max_signal_number)
3446
3447	Sending involves a system call I<iff> there were no other C<ev_async_send>
3448	calls in the current loop iteration. Checking for async and signal events
3449	involves iterating over all running async watchers or all signal numbers.
3450
3451	=back
3452
3453
3454	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	4369	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3455		4370
3456	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4371	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3457	requires, and its I/O model is fundamentally incompatible with the POSIX	4372	requires, and its I/O model is fundamentally incompatible with the POSIX
3458	model. Libev still offers limited functionality on this platform in	4373	model. Libev still offers limited functionality on this platform in
3459	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4374	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
…		…
3466	way (note also that glib is the slowest event library known to man).	4381	way (note also that glib is the slowest event library known to man).
3467		4382
3468	There is no supported compilation method available on windows except	4383	There is no supported compilation method available on windows except
3469	embedding it into other applications.	4384	embedding it into other applications.
3470		4385
		4386	Sensible signal handling is officially unsupported by Microsoft - libev
		4387	tries its best, but under most conditions, signals will simply not work.
		4388
3471	Not a libev limitation but worth mentioning: windows apparently doesn't	4389	Not a libev limitation but worth mentioning: windows apparently doesn't
3472	accept large writes: instead of resulting in a partial write, windows will	4390	accept large writes: instead of resulting in a partial write, windows will
3473	either accept everything or return C<ENOBUFS> if the buffer is too large,	4391	either accept everything or return C<ENOBUFS> if the buffer is too large,
3474	so make sure you only write small amounts into your sockets (less than a	4392	so make sure you only write small amounts into your sockets (less than a
3475	megabyte seems safe, but this apparently depends on the amount of memory	4393	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3479	the abysmal performance of winsockets, using a large number of sockets	4397	the abysmal performance of winsockets, using a large number of sockets
3480	is not recommended (and not reasonable). If your program needs to use	4398	is not recommended (and not reasonable). If your program needs to use
3481	more than a hundred or so sockets, then likely it needs to use a totally	4399	more than a hundred or so sockets, then likely it needs to use a totally
3482	different implementation for windows, as libev offers the POSIX readiness	4400	different implementation for windows, as libev offers the POSIX readiness
3483	notification model, which cannot be implemented efficiently on windows	4401	notification model, which cannot be implemented efficiently on windows
3484	(Microsoft monopoly games).	4402	(due to Microsoft monopoly games).
3485		4403
3486	A typical way to use libev under windows is to embed it (see the embedding	4404	A typical way to use libev under windows is to embed it (see the embedding
3487	section for details) and use the following F<evwrap.h> header file instead	4405	section for details) and use the following F<evwrap.h> header file instead
3488	of F<ev.h>:	4406	of F<ev.h>:
3489		4407
…		…
3525		4443
3526	Early versions of winsocket's select only supported waiting for a maximum	4444	Early versions of winsocket's select only supported waiting for a maximum
3527	of C<64> handles (probably owning to the fact that all windows kernels	4445	of C<64> handles (probably owning to the fact that all windows kernels
3528	can only wait for C<64> things at the same time internally; Microsoft	4446	can only wait for C<64> things at the same time internally; Microsoft
3529	recommends spawning a chain of threads and wait for 63 handles and the	4447	recommends spawning a chain of threads and wait for 63 handles and the
3530	previous thread in each. Great).	4448	previous thread in each. Sounds great!).
3531		4449
3532	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4450	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3533	to some high number (e.g. C<2048>) before compiling the winsocket select	4451	to some high number (e.g. C<2048>) before compiling the winsocket select
3534	call (which might be in libev or elsewhere, for example, perl does its own	4452	call (which might be in libev or elsewhere, for example, perl and many
3535	select emulation on windows).	4453	other interpreters do their own select emulation on windows).
3536		4454
3537	Another limit is the number of file descriptors in the Microsoft runtime	4455	Another limit is the number of file descriptors in the Microsoft runtime
3538	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4456	libraries, which by default is C<64> (there must be a hidden I<64>
3539	or something like this inside Microsoft). You can increase this by calling	4457	fetish or something like this inside Microsoft). You can increase this
3540	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4458	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3541	arbitrary limit), but is broken in many versions of the Microsoft runtime	4459	(another arbitrary limit), but is broken in many versions of the Microsoft
3542	libraries.
3543
3544	This might get you to about C<512> or C<2048> sockets (depending on	4460	runtime libraries. This might get you to about C<512> or C<2048> sockets
3545	windows version and/or the phase of the moon). To get more, you need to	4461	(depending on windows version and/or the phase of the moon). To get more,
3546	wrap all I/O functions and provide your own fd management, but the cost of	4462	you need to wrap all I/O functions and provide your own fd management, but
3547	calling select (O(n²)) will likely make this unworkable.	4463	the cost of calling select (O(n²)) will likely make this unworkable.
3548		4464
3549	=back	4465	=back
3550		4466
3551
3552	=head1 PORTABILITY REQUIREMENTS	4467	=head2 PORTABILITY REQUIREMENTS
3553		4468
3554	In addition to a working ISO-C implementation, libev relies on a few	4469	In addition to a working ISO-C implementation and of course the
3555	additional extensions:	4470	backend-specific APIs, libev relies on a few additional extensions:
3556		4471
3557	=over 4	4472	=over 4
3558		4473
3559	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	4474	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3560	calling conventions regardless of C<ev_watcher_type *>.	4475	calling conventions regardless of C<ev_watcher_type *>.
…		…
3585	except the initial one, and run the default loop in the initial thread as	4500	except the initial one, and run the default loop in the initial thread as
3586	well.	4501	well.
3587		4502
3588	=item C<long> must be large enough for common memory allocation sizes	4503	=item C<long> must be large enough for common memory allocation sizes
3589		4504
3590	To improve portability and simplify using libev, libev uses C<long>	4505	To improve portability and simplify its API, libev uses C<long> internally
3591	internally instead of C<size_t> when allocating its data structures. On	4506	instead of C<size_t> when allocating its data structures. On non-POSIX
3592	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	4507	systems (Microsoft...) this might be unexpectedly low, but is still at
3593	is still at least 31 bits everywhere, which is enough for hundreds of	4508	least 31 bits everywhere, which is enough for hundreds of millions of
3594	millions of watchers.	4509	watchers.
3595		4510
3596	=item C<double> must hold a time value in seconds with enough accuracy	4511	=item C<double> must hold a time value in seconds with enough accuracy
3597		4512
3598	The type C<double> is used to represent timestamps. It is required to	4513	The type C<double> is used to represent timestamps. It is required to
3599	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4514	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3600	enough for at least into the year 4000. This requirement is fulfilled by	4515	enough for at least into the year 4000. This requirement is fulfilled by
3601	implementations implementing IEEE 754 (basically all existing ones).	4516	implementations implementing IEEE 754, which is basically all existing
		4517	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4518	2200.
3602		4519
3603	=back	4520	=back
3604		4521
3605	If you know of other additional requirements drop me a note.	4522	If you know of other additional requirements drop me a note.
3606		4523
3607		4524
3608	=head1 COMPILER WARNINGS	4525	=head1 ALGORITHMIC COMPLEXITIES
3609		4526
3610	Depending on your compiler and compiler settings, you might get no or a	4527	In this section the complexities of (many of) the algorithms used inside
3611	lot of warnings when compiling libev code. Some people are apparently	4528	libev will be documented. For complexity discussions about backends see
3612	scared by this.	4529	the documentation for C<ev_default_init>.
3613		4530
3614	However, these are unavoidable for many reasons. For one, each compiler	4531	All of the following are about amortised time: If an array needs to be
3615	has different warnings, and each user has different tastes regarding	4532	extended, libev needs to realloc and move the whole array, but this
3616	warning options. "Warn-free" code therefore cannot be a goal except when	4533	happens asymptotically rarer with higher number of elements, so O(1) might
3617	targeting a specific compiler and compiler-version.	4534	mean that libev does a lengthy realloc operation in rare cases, but on
		4535	average it is much faster and asymptotically approaches constant time.
3618		4536
3619	Another reason is that some compiler warnings require elaborate	4537	=over 4
3620	workarounds, or other changes to the code that make it less clear and less
3621	maintainable.
3622		4538
3623	And of course, some compiler warnings are just plain stupid, or simply	4539	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3624	wrong (because they don't actually warn about the condition their message
3625	seems to warn about).
3626		4540
3627	While libev is written to generate as few warnings as possible,	4541	This means that, when you have a watcher that triggers in one hour and
3628	"warn-free" code is not a goal, and it is recommended not to build libev	4542	there are 100 watchers that would trigger before that, then inserting will
3629	with any compiler warnings enabled unless you are prepared to cope with	4543	have to skip roughly seven (C<ld 100>) of these watchers.
3630	them (e.g. by ignoring them). Remember that warnings are just that:
3631	warnings, not errors, or proof of bugs.
3632		4544
		4545	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3633		4546
3634	=head1 VALGRIND	4547	That means that changing a timer costs less than removing/adding them,
		4548	as only the relative motion in the event queue has to be paid for.
3635		4549
3636	Valgrind has a special section here because it is a popular tool that is	4550	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3637	highly useful, but valgrind reports are very hard to interpret.
3638		4551
3639	If you think you found a bug (memory leak, uninitialised data access etc.)	4552	These just add the watcher into an array or at the head of a list.
3640	in libev, then check twice: If valgrind reports something like:
3641		4553
3642	==2274== definitely lost: 0 bytes in 0 blocks.	4554	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3643	==2274== possibly lost: 0 bytes in 0 blocks.
3644	==2274== still reachable: 256 bytes in 1 blocks.
3645		4555
3646	Then there is no memory leak. Similarly, under some circumstances,	4556	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3647	valgrind might report kernel bugs as if it were a bug in libev, or it
3648	might be confused (it is a very good tool, but only a tool).
3649		4557
3650	If you are unsure about something, feel free to contact the mailing list	4558	These watchers are stored in lists, so they need to be walked to find the
3651	with the full valgrind report and an explanation on why you think this is	4559	correct watcher to remove. The lists are usually short (you don't usually
3652	a bug in libev. However, don't be annoyed when you get a brisk "this is	4560	have many watchers waiting for the same fd or signal: one is typical, two
3653	no bug" answer and take the chance of learning how to interpret valgrind	4561	is rare).
3654	properly.
3655		4562
3656	If you need, for some reason, empty reports from valgrind for your project	4563	=item Finding the next timer in each loop iteration: O(1)
3657	I suggest using suppression lists.
3658		4564
		4565	By virtue of using a binary or 4-heap, the next timer is always found at a
		4566	fixed position in the storage array.
		4567
		4568	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4569
		4570	A change means an I/O watcher gets started or stopped, which requires
		4571	libev to recalculate its status (and possibly tell the kernel, depending
		4572	on backend and whether C<ev_io_set> was used).
		4573
		4574	=item Activating one watcher (putting it into the pending state): O(1)
		4575
		4576	=item Priority handling: O(number_of_priorities)
		4577
		4578	Priorities are implemented by allocating some space for each
		4579	priority. When doing priority-based operations, libev usually has to
		4580	linearly search all the priorities, but starting/stopping and activating
		4581	watchers becomes O(1) with respect to priority handling.
		4582
		4583	=item Sending an ev_async: O(1)
		4584
		4585	=item Processing ev_async_send: O(number_of_async_watchers)
		4586
		4587	=item Processing signals: O(max_signal_number)
		4588
		4589	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4590	calls in the current loop iteration. Checking for async and signal events
		4591	involves iterating over all running async watchers or all signal numbers.
		4592
		4593	=back
		4594
		4595
		4596	=head1 GLOSSARY
		4597
		4598	=over 4
		4599
		4600	=item active
		4601
		4602	A watcher is active as long as it has been started (has been attached to
		4603	an event loop) but not yet stopped (disassociated from the event loop).
		4604
		4605	=item application
		4606
		4607	In this document, an application is whatever is using libev.
		4608
		4609	=item callback
		4610
		4611	The address of a function that is called when some event has been
		4612	detected. Callbacks are being passed the event loop, the watcher that
		4613	received the event, and the actual event bitset.
		4614
		4615	=item callback invocation
		4616
		4617	The act of calling the callback associated with a watcher.
		4618
		4619	=item event
		4620
		4621	A change of state of some external event, such as data now being available
		4622	for reading on a file descriptor, time having passed or simply not having
		4623	any other events happening anymore.
		4624
		4625	In libev, events are represented as single bits (such as C<EV_READ> or
		4626	C<EV_TIMEOUT>).
		4627
		4628	=item event library
		4629
		4630	A software package implementing an event model and loop.
		4631
		4632	=item event loop
		4633
		4634	An entity that handles and processes external events and converts them
		4635	into callback invocations.
		4636
		4637	=item event model
		4638
		4639	The model used to describe how an event loop handles and processes
		4640	watchers and events.
		4641
		4642	=item pending
		4643
		4644	A watcher is pending as soon as the corresponding event has been detected,
		4645	and stops being pending as soon as the watcher will be invoked or its
		4646	pending status is explicitly cleared by the application.
		4647
		4648	A watcher can be pending, but not active. Stopping a watcher also clears
		4649	its pending status.
		4650
		4651	=item real time
		4652
		4653	The physical time that is observed. It is apparently strictly monotonic :)
		4654
		4655	=item wall-clock time
		4656
		4657	The time and date as shown on clocks. Unlike real time, it can actually
		4658	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4659	clock.
		4660
		4661	=item watcher
		4662
		4663	A data structure that describes interest in certain events. Watchers need
		4664	to be started (attached to an event loop) before they can receive events.
		4665
		4666	=item watcher invocation
		4667
		4668	The act of calling the callback associated with a watcher.
		4669
		4670	=back
3659		4671
3660	=head1 AUTHOR	4672	=head1 AUTHOR
3661		4673
3662	Marc Lehmann <libev@schmorp.de>.	4674	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3663		4675

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines