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…		…
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
		14	#include <stdio.h> // for puts
		15
14	// every watcher type has its own typedef'd struct	16	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	17	// with the name ev_TYPE
16	ev_io stdin_watcher;	18	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
18		20
19	// all watcher callbacks have a similar signature	21	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	22	// this callback is called when data is readable on stdin
…		…
41		43
42	int	44	int
43	main (void)	45	main (void)
44	{	46	{
45	// use the default event loop unless you have special needs	47	// use the default event loop unless you have special needs
46	ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
47		49
48	// initialise an io watcher, then start it	50	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	51	// this one will watch for stdin to become readable
50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
51	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
…		…
60		62
61	// unloop was called, so exit	63	// unloop was called, so exit
62	return 0;	64	return 0;
63	}	65	}
64		66
65	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
66		70
67	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
70		84
71	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	87	these event sources and provide your program with events.
74		88
…		…
108	name C<loop> (which is always of type C<ev_loop *>) will not have	122	name C<loop> (which is always of type C<ev_loop *>) will not have
109	this argument.	123	this argument.
110		124
111	=head2 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
112		126
113	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
115	the beginning of 1970, details are complicated, don't ask). This type is	129	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	130	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	131	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	132	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	133	component C<stamp> might indicate, it is also used for time differences
120	throughout libev.	134	throughout libev.
121		135
122	=head1 ERROR HANDLING	136	=head1 ERROR HANDLING
123		137
…		…
276		290
277	=back	291	=back
278		292
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280		294
281	An event loop is described by a C<ev_loop *>. The library knows two	295	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	296	is I<not> optional in this case, as there is also an C<ev_loop>
283	events, and dynamically created loops which do not.	297	I<function>).
		298
		299	The library knows two types of such loops, the I<default> loop, which
		300	supports signals and child events, and dynamically created loops which do
		301	not.
284		302
285	=over 4	303	=over 4
286		304
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		306
…		…
294	If you don't know what event loop to use, use the one returned from this	312	If you don't know what event loop to use, use the one returned from this
295	function.	313	function.
296		314
297	Note that this function is I<not> thread-safe, so if you want to use it	315	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,	316	from multiple threads, you have to lock (note also that this is unlikely,
299	as loops cannot bes hared easily between threads anyway).	317	as loops cannot be shared easily between threads anyway).
300		318
301	The default loop is the only loop that can handle C<ev_signal> and	319	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	320	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	321	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	322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		399
382	For few fds, this backend is a bit little slower than poll and select,	400	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	401	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),	402	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	403	epoll scales either O(1) or O(active_fds).
386	of shortcomings, such as silently dropping events in some hard-to-detect	404
387	cases and requiring a system call per fd change, no fork support and bad	405	The epoll mechanism deserves honorable mention as the most misdesigned
388	support for dup.	406	of the more advanced event mechanisms: mere annoyances include silently
		407	dropping file descriptors, requiring a system call per change per file
		408	descriptor (and unnecessary guessing of parameters), problems with dup and
		409	so on. The biggest issue is fork races, however - if a program forks then
		410	I<both> parent and child process have to recreate the epoll set, which can
		411	take considerable time (one syscall per file descriptor) and is of course
		412	hard to detect.
		413
		414	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		415	of course I<doesn't>, and epoll just loves to report events for totally
		416	I<different> file descriptors (even already closed ones, so one cannot
		417	even remove them from the set) than registered in the set (especially
		418	on SMP systems). Libev tries to counter these spurious notifications by
		419	employing an additional generation counter and comparing that against the
		420	events to filter out spurious ones, recreating the set when required.
389		421
390	While stopping, setting and starting an I/O watcher in the same iteration	422	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	423	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	424	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	425	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
394	very well if you register events for both fds.	426	file descriptors might not work very well if you register events for both
395		427	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		428
400	Best performance from this backend is achieved by not unregistering all	429	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible,	430	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	431	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	432	starting a watcher (without re-setting it) also usually doesn't cause
404	extra overhead.	433	extra overhead. A fork can both result in spurious notifications as well
		434	as in libev having to destroy and recreate the epoll object, which can
		435	take considerable time and thus should be avoided.
		436
		437	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		438	faster than epoll for maybe up to a hundred file descriptors, depending on
		439	the usage. So sad.
405		440
406	While nominally embeddable in other event loops, this feature is broken in	441	While nominally embeddable in other event loops, this feature is broken in
407	all kernel versions tested so far.	442	all kernel versions tested so far.
408		443
409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	444	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
410	C<EVBACKEND_POLL>.	445	C<EVBACKEND_POLL>.
411		446
412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
413		448
414	Kqueue deserves special mention, as at the time of this writing, it was	449	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	450	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	451	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	452	it's completely useless). Unlike epoll, however, whose brokenness
418	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or	453	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.	454	without API changes to existing programs. For this reason it's not being
		455	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		457	system like NetBSD.
420		458
421	You still can embed kqueue into a normal poll or select backend and use it	459	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	460	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.	461	the target platform). See C<ev_embed> watchers for more info.
424		462
425	It scales in the same way as the epoll backend, but the interface to the	463	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	464	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	465	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	466	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	467	two event changes per incident. Support for C<fork ()> is very bad (but
430	drops fds silently in similarly hard-to-detect cases.	468	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		469	cases
431		470
432	This backend usually performs well under most conditions.	471	This backend usually performs well under most conditions.
433		472
434	While nominally embeddable in other event loops, this doesn't work	473	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	474	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	475	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	476	(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,	477	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
439	using it only for sockets.	478	also broken on OS X)) and, did I mention it, using it only for sockets.
440		479
441	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with	480	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	481	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
443	C<NOTE_EOF>.	482	C<NOTE_EOF>.
444		483
…		…
464	might perform better.	503	might perform better.
465		504
466	On the positive side, with the exception of the spurious readiness	505	On the positive side, with the exception of the spurious readiness
467	notifications, this backend actually performed fully to specification	506	notifications, this backend actually performed fully to specification
468	in all tests and is fully embeddable, which is a rare feat among the	507	in all tests and is fully embeddable, which is a rare feat among the
469	OS-specific backends.	508	OS-specific backends (I vastly prefer correctness over speed hacks).
470		509
471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	510	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
472	C<EVBACKEND_POLL>.	511	C<EVBACKEND_POLL>.
473		512
474	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
…		…
527	responsibility to either stop all watchers cleanly yourself I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
528	calling this function, or cope with the fact afterwards (which is usually	567	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	568	the easiest thing, you can just ignore the watchers and/or C<free ()> them
530	for example).	569	for example).
531		570
532	Note that certain global state, such as signal state, will not be freed by	571	Note that certain global state, such as signal state (and installed signal
533	this function, and related watchers (such as signal and child watchers)	572	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	573	as signal and child watchers) would need to be stopped manually.
535		574
536	In general it is not advisable to call this function except in the	575	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	576	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	577	pipe fds. If you need dynamically allocated loops it is better to use
539	C<ev_loop_new> and C<ev_loop_destroy>).	578	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
582		621
583	This value can sometimes be useful as a generation counter of sorts (it	622	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	623	"ticks" the number of loop iterations), as it roughly corresponds with
585	C<ev_prepare> and C<ev_check> calls.	624	C<ev_prepare> and C<ev_check> calls.
586		625
		626	=item unsigned int ev_loop_depth (loop)
		627
		628	Returns the number of times C<ev_loop> was entered minus the number of
		629	times C<ev_loop> was exited, in other words, the recursion depth.
		630
		631	Outside C<ev_loop>, this number is zero. In a callback, this number is
		632	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		633	in which case it is higher.
		634
		635	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		636	etc.), doesn't count as exit.
		637
587	=item unsigned int ev_backend (loop)	638	=item unsigned int ev_backend (loop)
588		639
589	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	640	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
590	use.	641	use.
591		642
…		…
605		656
606	This function is rarely useful, but when some event callback runs for a	657	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	658	very long time without entering the event loop, updating libev's idea of
608	the current time is a good idea.	659	the current time is a good idea.
609		660
610	See also "The special problem of time updates" in the C<ev_timer> section.	661	See also L<The special problem of time updates> in the C<ev_timer> section.
		662
		663	=item ev_suspend (loop)
		664
		665	=item ev_resume (loop)
		666
		667	These two functions suspend and resume a loop, for use when the loop is
		668	not used for a while and timeouts should not be processed.
		669
		670	A typical use case would be an interactive program such as a game: When
		671	the user presses C<^Z> to suspend the game and resumes it an hour later it
		672	would be best to handle timeouts as if no time had actually passed while
		673	the program was suspended. This can be achieved by calling C<ev_suspend>
		674	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		675	C<ev_resume> directly afterwards to resume timer processing.
		676
		677	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		678	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		679	will be rescheduled (that is, they will lose any events that would have
		680	occured while suspended).
		681
		682	After calling C<ev_suspend> you B<must not> call I<any> function on the
		683	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		684	without a previous call to C<ev_suspend>.
		685
		686	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		687	event loop time (see C<ev_now_update>).
611		688
612	=item ev_loop (loop, int flags)	689	=item ev_loop (loop, int flags)
613		690
614	Finally, this is it, the event handler. This function usually is called	691	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	692	after you initialised all your watchers and you want to start handling
…		…
631	the loop.	708	the loop.
632		709
633	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	710	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	711	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	712	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	713	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	714	user-registered callback will be called), and will return after one
638	iteration of the loop.	715	iteration of the loop.
639		716
640	This is useful if you are waiting for some external event in conjunction	717	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	718	with something not expressible using other libev watchers (i.e. "roll your
…		…
699		776
700	If you have a watcher you never unregister that should not keep C<ev_loop>	777	If you have a watcher you never unregister that should not keep C<ev_loop>
701	from returning, call ev_unref() after starting, and ev_ref() before	778	from returning, call ev_unref() after starting, and ev_ref() before
702	stopping it.	779	stopping it.
703		780
704	As an example, libev itself uses this for its internal signal pipe: It is	781	As an example, libev itself uses this for its internal signal pipe: It
705	not visible to the libev user and should not keep C<ev_loop> from exiting	782	is not visible to the libev user and should not keep C<ev_loop> from
706	if no event watchers registered by it are active. It is also an excellent	783	exiting if no event watchers registered by it are active. It is also an
707	way to do this for generic recurring timers or from within third-party	784	excellent way to do this for generic recurring timers or from within
708	libraries. Just remember to I<unref after start> and I<ref before stop>	785	third-party libraries. Just remember to I<unref after start> and I<ref
709	(but only if the watcher wasn't active before, or was active before,	786	before stop> (but only if the watcher wasn't active before, or was active
710	respectively).	787	before, respectively. Note also that libev might stop watchers itself
		788	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		789	in the callback).
711		790
712	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	791	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
713	running when nothing else is active.	792	running when nothing else is active.
714		793
715	ev_signal exitsig;	794	ev_signal exitsig;
…		…
744		823
745	By setting a higher I<io collect interval> you allow libev to spend more	824	By setting a higher I<io collect interval> you allow libev to spend more
746	time collecting I/O events, so you can handle more events per iteration,	825	time collecting I/O events, so you can handle more events per iteration,
747	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	826	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
748	C<ev_timer>) will be not affected. Setting this to a non-null value will	827	C<ev_timer>) will be not affected. Setting this to a non-null value will
749	introduce an additional C<ev_sleep ()> call into most loop iterations.	828	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		829	sleep time ensures that libev will not poll for I/O events more often then
		830	once per this interval, on average.
750		831
751	Likewise, by setting a higher I<timeout collect interval> you allow libev	832	Likewise, by setting a higher I<timeout collect interval> you allow libev
752	to spend more time collecting timeouts, at the expense of increased	833	to spend more time collecting timeouts, at the expense of increased
753	latency/jitter/inexactness (the watcher callback will be called	834	latency/jitter/inexactness (the watcher callback will be called
754	later). C<ev_io> watchers will not be affected. Setting this to a non-null	835	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
756		837
757	Many (busy) programs can usually benefit by setting the I/O collect	838	Many (busy) programs can usually benefit by setting the I/O collect
758	interval to a value near C<0.1> or so, which is often enough for	839	interval to a value near C<0.1> or so, which is often enough for
759	interactive servers (of course not for games), likewise for timeouts. It	840	interactive servers (of course not for games), likewise for timeouts. It
760	usually doesn't make much sense to set it to a lower value than C<0.01>,	841	usually doesn't make much sense to set it to a lower value than C<0.01>,
761	as this approaches the timing granularity of most systems.	842	as this approaches the timing granularity of most systems. Note that if
		843	you do transactions with the outside world and you can't increase the
		844	parallelity, then this setting will limit your transaction rate (if you
		845	need to poll once per transaction and the I/O collect interval is 0.01,
		846	then you can't do more than 100 transations per second).
762		847
763	Setting the I<timeout collect interval> can improve the opportunity for	848	Setting the I<timeout collect interval> can improve the opportunity for
764	saving power, as the program will "bundle" timer callback invocations that	849	saving power, as the program will "bundle" timer callback invocations that
765	are "near" in time together, by delaying some, thus reducing the number of	850	are "near" in time together, by delaying some, thus reducing the number of
766	times the process sleeps and wakes up again. Another useful technique to	851	times the process sleeps and wakes up again. Another useful technique to
767	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	852	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
768	they fire on, say, one-second boundaries only.	853	they fire on, say, one-second boundaries only.
769		854
		855	Example: we only need 0.1s timeout granularity, and we wish not to poll
		856	more often than 100 times per second:
		857
		858	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		859	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		860
		861	=item ev_invoke_pending (loop)
		862
		863	This call will simply invoke all pending watchers while resetting their
		864	pending state. Normally, C<ev_loop> does this automatically when required,
		865	but when overriding the invoke callback this call comes handy.
		866
		867	=item int ev_pending_count (loop)
		868
		869	Returns the number of pending watchers - zero indicates that no watchers
		870	are pending.
		871
		872	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		873
		874	This overrides the invoke pending functionality of the loop: Instead of
		875	invoking all pending watchers when there are any, C<ev_loop> will call
		876	this callback instead. This is useful, for example, when you want to
		877	invoke the actual watchers inside another context (another thread etc.).
		878
		879	If you want to reset the callback, use C<ev_invoke_pending> as new
		880	callback.
		881
		882	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		883
		884	Sometimes you want to share the same loop between multiple threads. This
		885	can be done relatively simply by putting mutex_lock/unlock calls around
		886	each call to a libev function.
		887
		888	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		889	wait for it to return. One way around this is to wake up the loop via
		890	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		891	and I<acquire> callbacks on the loop.
		892
		893	When set, then C<release> will be called just before the thread is
		894	suspended waiting for new events, and C<acquire> is called just
		895	afterwards.
		896
		897	Ideally, C<release> will just call your mutex_unlock function, and
		898	C<acquire> will just call the mutex_lock function again.
		899
		900	While event loop modifications are allowed between invocations of
		901	C<release> and C<acquire> (that's their only purpose after all), no
		902	modifications done will affect the event loop, i.e. adding watchers will
		903	have no effect on the set of file descriptors being watched, or the time
		904	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		905	to take note of any changes you made.
		906
		907	In theory, threads executing C<ev_loop> will be async-cancel safe between
		908	invocations of C<release> and C<acquire>.
		909
		910	See also the locking example in the C<THREADS> section later in this
		911	document.
		912
		913	=item ev_set_userdata (loop, void *data)
		914
		915	=item ev_userdata (loop)
		916
		917	Set and retrieve a single C<void *> associated with a loop. When
		918	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		919	C<0.>
		920
		921	These two functions can be used to associate arbitrary data with a loop,
		922	and are intended solely for the C<invoke_pending_cb>, C<release> and
		923	C<acquire> callbacks described above, but of course can be (ab-)used for
		924	any other purpose as well.
		925
770	=item ev_loop_verify (loop)	926	=item ev_loop_verify (loop)
771		927
772	This function only does something when C<EV_VERIFY> support has been	928	This function only does something when C<EV_VERIFY> support has been
773	compiled in. which is the default for non-minimal builds. It tries to go	929	compiled in, which is the default for non-minimal builds. It tries to go
774	through all internal structures and checks them for validity. If anything	930	through all internal structures and checks them for validity. If anything
775	is found to be inconsistent, it will print an error message to standard	931	is found to be inconsistent, it will print an error message to standard
776	error and call C<abort ()>.	932	error and call C<abort ()>.
777		933
778	This can be used to catch bugs inside libev itself: under normal	934	This can be used to catch bugs inside libev itself: under normal
…		…
782	=back	938	=back
783		939
784		940
785	=head1 ANATOMY OF A WATCHER	941	=head1 ANATOMY OF A WATCHER
786		942
		943	In the following description, uppercase C<TYPE> in names stands for the
		944	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		945	watchers and C<ev_io_start> for I/O watchers.
		946
787	A watcher is a structure that you create and register to record your	947	A watcher is a structure that you create and register to record your
788	interest in some event. For instance, if you want to wait for STDIN to	948	interest in some event. For instance, if you want to wait for STDIN to
789	become readable, you would create an C<ev_io> watcher for that:	949	become readable, you would create an C<ev_io> watcher for that:
790		950
791	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)	951	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
…		…
793	ev_io_stop (w);	953	ev_io_stop (w);
794	ev_unloop (loop, EVUNLOOP_ALL);	954	ev_unloop (loop, EVUNLOOP_ALL);
795	}	955	}
796		956
797	struct ev_loop *loop = ev_default_loop (0);	957	struct ev_loop *loop = ev_default_loop (0);
		958
798	ev_io stdin_watcher;	959	ev_io stdin_watcher;
		960
799	ev_init (&stdin_watcher, my_cb);	961	ev_init (&stdin_watcher, my_cb);
800	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	962	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
801	ev_io_start (loop, &stdin_watcher);	963	ev_io_start (loop, &stdin_watcher);
		964
802	ev_loop (loop, 0);	965	ev_loop (loop, 0);
803		966
804	As you can see, you are responsible for allocating the memory for your	967	As you can see, you are responsible for allocating the memory for your
805	watcher structures (and it is usually a bad idea to do this on the stack,	968	watcher structures (and it is I<usually> a bad idea to do this on the
806	although this can sometimes be quite valid).	969	stack).
		970
		971	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		972	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
807		973
808	Each watcher structure must be initialised by a call to C<ev_init	974	Each watcher structure must be initialised by a call to C<ev_init
809	(watcher *, callback)>, which expects a callback to be provided. This	975	(watcher *, callback)>, which expects a callback to be provided. This
810	callback gets invoked each time the event occurs (or, in the case of I/O	976	callback gets invoked each time the event occurs (or, in the case of I/O
811	watchers, each time the event loop detects that the file descriptor given	977	watchers, each time the event loop detects that the file descriptor given
812	is readable and/or writable).	978	is readable and/or writable).
813		979
814	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	980	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
815	with arguments specific to this watcher type. There is also a macro	981	macro to configure it, with arguments specific to the watcher type. There
816	to combine initialisation and setting in one call: C<< ev_<type>_init	982	is also a macro to combine initialisation and setting in one call: C<<
817	(watcher *, callback, ...) >>.	983	ev_TYPE_init (watcher *, callback, ...) >>.
818		984
819	To make the watcher actually watch out for events, you have to start it	985	To make the watcher actually watch out for events, you have to start it
820	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	986	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
821	*) >>), and you can stop watching for events at any time by calling the	987	*) >>), and you can stop watching for events at any time by calling the
822	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	988	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
823		989
824	As long as your watcher is active (has been started but not stopped) you	990	As long as your watcher is active (has been started but not stopped) you
825	must not touch the values stored in it. Most specifically you must never	991	must not touch the values stored in it. Most specifically you must never
826	reinitialise it or call its C<set> macro.	992	reinitialise it or call its C<ev_TYPE_set> macro.
827		993
828	Each and every callback receives the event loop pointer as first, the	994	Each and every callback receives the event loop pointer as first, the
829	registered watcher structure as second, and a bitset of received events as	995	registered watcher structure as second, and a bitset of received events as
830	third argument.	996	third argument.
831		997
…		…
889		1055
890	=item C<EV_ASYNC>	1056	=item C<EV_ASYNC>
891		1057
892	The given async watcher has been asynchronously notified (see C<ev_async>).	1058	The given async watcher has been asynchronously notified (see C<ev_async>).
893		1059
		1060	=item C<EV_CUSTOM>
		1061
		1062	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1063	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1064
894	=item C<EV_ERROR>	1065	=item C<EV_ERROR>
895		1066
896	An unspecified error has occurred, the watcher has been stopped. This might	1067	An unspecified error has occurred, the watcher has been stopped. This might
897	happen because the watcher could not be properly started because libev	1068	happen because the watcher could not be properly started because libev
898	ran out of memory, a file descriptor was found to be closed or any other	1069	ran out of memory, a file descriptor was found to be closed or any other
…		…
912		1083
913	=back	1084	=back
914		1085
915	=head2 GENERIC WATCHER FUNCTIONS	1086	=head2 GENERIC WATCHER FUNCTIONS
916		1087
917	In the following description, C<TYPE> stands for the watcher type,
918	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
919
920	=over 4	1088	=over 4
921		1089
922	=item C<ev_init> (ev_TYPE *watcher, callback)	1090	=item C<ev_init> (ev_TYPE *watcher, callback)
923		1091
924	This macro initialises the generic portion of a watcher. The contents	1092	This macro initialises the generic portion of a watcher. The contents
…		…
1016	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1184	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1017	(default: C<-2>). Pending watchers with higher priority will be invoked	1185	(default: C<-2>). Pending watchers with higher priority will be invoked
1018	before watchers with lower priority, but priority will not keep watchers	1186	before watchers with lower priority, but priority will not keep watchers
1019	from being executed (except for C<ev_idle> watchers).	1187	from being executed (except for C<ev_idle> watchers).
1020		1188
1021	This means that priorities are I<only> used for ordering callback
1022	invocation after new events have been received. This is useful, for
1023	example, to reduce latency after idling, or more often, to bind two
1024	watchers on the same event and make sure one is called first.
1025
1026	If you need to suppress invocation when higher priority events are pending	1189	If you need to suppress invocation when higher priority events are pending
1027	you need to look at C<ev_idle> watchers, which provide this functionality.	1190	you need to look at C<ev_idle> watchers, which provide this functionality.
1028		1191
1029	You I<must not> change the priority of a watcher as long as it is active or	1192	You I<must not> change the priority of a watcher as long as it is active or
1030	pending.	1193	pending.
1031		1194
		1195	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1196	fine, as long as you do not mind that the priority value you query might
		1197	or might not have been clamped to the valid range.
		1198
1032	The default priority used by watchers when no priority has been set is	1199	The default priority used by watchers when no priority has been set is
1033	always C<0>, which is supposed to not be too high and not be too low :).	1200	always C<0>, which is supposed to not be too high and not be too low :).
1034		1201
1035	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1202	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1036	fine, as long as you do not mind that the priority value you query might	1203	priorities.
1037	or might not have been adjusted to be within valid range.
1038		1204
1039	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1205	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1040		1206
1041	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1207	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1042	C<loop> nor C<revents> need to be valid as long as the watcher callback	1208	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1107	#include <stddef.h>	1273	#include <stddef.h>
1108		1274
1109	static void	1275	static void
1110	t1_cb (EV_P_ ev_timer *w, int revents)	1276	t1_cb (EV_P_ ev_timer *w, int revents)
1111	{	1277	{
1112	struct my_biggy big = (struct my_biggy *	1278	struct my_biggy big = (struct my_biggy *)
1113	(((char *)w) - offsetof (struct my_biggy, t1));	1279	(((char *)w) - offsetof (struct my_biggy, t1));
1114	}	1280	}
1115		1281
1116	static void	1282	static void
1117	t2_cb (EV_P_ ev_timer *w, int revents)	1283	t2_cb (EV_P_ ev_timer *w, int revents)
1118	{	1284	{
1119	struct my_biggy big = (struct my_biggy *	1285	struct my_biggy big = (struct my_biggy *)
1120	(((char *)w) - offsetof (struct my_biggy, t2));	1286	(((char *)w) - offsetof (struct my_biggy, t2));
1121	}	1287	}
		1288
		1289	=head2 WATCHER PRIORITY MODELS
		1290
		1291	Many event loops support I<watcher priorities>, which are usually small
		1292	integers that influence the ordering of event callback invocation
		1293	between watchers in some way, all else being equal.
		1294
		1295	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1296	description for the more technical details such as the actual priority
		1297	range.
		1298
		1299	There are two common ways how these these priorities are being interpreted
		1300	by event loops:
		1301
		1302	In the more common lock-out model, higher priorities "lock out" invocation
		1303	of lower priority watchers, which means as long as higher priority
		1304	watchers receive events, lower priority watchers are not being invoked.
		1305
		1306	The less common only-for-ordering model uses priorities solely to order
		1307	callback invocation within a single event loop iteration: Higher priority
		1308	watchers are invoked before lower priority ones, but they all get invoked
		1309	before polling for new events.
		1310
		1311	Libev uses the second (only-for-ordering) model for all its watchers
		1312	except for idle watchers (which use the lock-out model).
		1313
		1314	The rationale behind this is that implementing the lock-out model for
		1315	watchers is not well supported by most kernel interfaces, and most event
		1316	libraries will just poll for the same events again and again as long as
		1317	their callbacks have not been executed, which is very inefficient in the
		1318	common case of one high-priority watcher locking out a mass of lower
		1319	priority ones.
		1320
		1321	Static (ordering) priorities are most useful when you have two or more
		1322	watchers handling the same resource: a typical usage example is having an
		1323	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1324	timeouts. Under load, data might be received while the program handles
		1325	other jobs, but since timers normally get invoked first, the timeout
		1326	handler will be executed before checking for data. In that case, giving
		1327	the timer a lower priority than the I/O watcher ensures that I/O will be
		1328	handled first even under adverse conditions (which is usually, but not
		1329	always, what you want).
		1330
		1331	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1332	will only be executed when no same or higher priority watchers have
		1333	received events, they can be used to implement the "lock-out" model when
		1334	required.
		1335
		1336	For example, to emulate how many other event libraries handle priorities,
		1337	you can associate an C<ev_idle> watcher to each such watcher, and in
		1338	the normal watcher callback, you just start the idle watcher. The real
		1339	processing is done in the idle watcher callback. This causes libev to
		1340	continously poll and process kernel event data for the watcher, but when
		1341	the lock-out case is known to be rare (which in turn is rare :), this is
		1342	workable.
		1343
		1344	Usually, however, the lock-out model implemented that way will perform
		1345	miserably under the type of load it was designed to handle. In that case,
		1346	it might be preferable to stop the real watcher before starting the
		1347	idle watcher, so the kernel will not have to process the event in case
		1348	the actual processing will be delayed for considerable time.
		1349
		1350	Here is an example of an I/O watcher that should run at a strictly lower
		1351	priority than the default, and which should only process data when no
		1352	other events are pending:
		1353
		1354	ev_idle idle; // actual processing watcher
		1355	ev_io io; // actual event watcher
		1356
		1357	static void
		1358	io_cb (EV_P_ ev_io *w, int revents)
		1359	{
		1360	// stop the I/O watcher, we received the event, but
		1361	// are not yet ready to handle it.
		1362	ev_io_stop (EV_A_ w);
		1363
		1364	// start the idle watcher to ahndle the actual event.
		1365	// it will not be executed as long as other watchers
		1366	// with the default priority are receiving events.
		1367	ev_idle_start (EV_A_ &idle);
		1368	}
		1369
		1370	static void
		1371	idle_cb (EV_P_ ev_idle *w, int revents)
		1372	{
		1373	// actual processing
		1374	read (STDIN_FILENO, ...);
		1375
		1376	// have to start the I/O watcher again, as
		1377	// we have handled the event
		1378	ev_io_start (EV_P_ &io);
		1379	}
		1380
		1381	// initialisation
		1382	ev_idle_init (&idle, idle_cb);
		1383	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1384	ev_io_start (EV_DEFAULT_ &io);
		1385
		1386	In the "real" world, it might also be beneficial to start a timer, so that
		1387	low-priority connections can not be locked out forever under load. This
		1388	enables your program to keep a lower latency for important connections
		1389	during short periods of high load, while not completely locking out less
		1390	important ones.
1122		1391
1123		1392
1124	=head1 WATCHER TYPES	1393	=head1 WATCHER TYPES
1125		1394
1126	This section describes each watcher in detail, but will not repeat	1395	This section describes each watcher in detail, but will not repeat
…		…
1152	descriptors to non-blocking mode is also usually a good idea (but not	1421	descriptors to non-blocking mode is also usually a good idea (but not
1153	required if you know what you are doing).	1422	required if you know what you are doing).
1154		1423
1155	If you cannot use non-blocking mode, then force the use of a	1424	If you cannot use non-blocking mode, then force the use of a
1156	known-to-be-good backend (at the time of this writing, this includes only	1425	known-to-be-good backend (at the time of this writing, this includes only
1157	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1426	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1427	descriptors for which non-blocking operation makes no sense (such as
		1428	files) - libev doesn't guarentee any specific behaviour in that case.
1158		1429
1159	Another thing you have to watch out for is that it is quite easy to	1430	Another thing you have to watch out for is that it is quite easy to
1160	receive "spurious" readiness notifications, that is your callback might	1431	receive "spurious" readiness notifications, that is your callback might
1161	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1432	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1162	because there is no data. Not only are some backends known to create a	1433	because there is no data. Not only are some backends known to create a
…		…
1283	year, it will still time out after (roughly) one hour. "Roughly" because	1554	year, it will still time out after (roughly) one hour. "Roughly" because
1284	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1555	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1285	monotonic clock option helps a lot here).	1556	monotonic clock option helps a lot here).
1286		1557
1287	The callback is guaranteed to be invoked only I<after> its timeout has	1558	The callback is guaranteed to be invoked only I<after> its timeout has
1288	passed, but if multiple timers become ready during the same loop iteration	1559	passed (not I<at>, so on systems with very low-resolution clocks this
1289	then order of execution is undefined.	1560	might introduce a small delay). If multiple timers become ready during the
		1561	same loop iteration then the ones with earlier time-out values are invoked
		1562	before ones of the same priority with later time-out values (but this is
		1563	no longer true when a callback calls C<ev_loop> recursively).
1290		1564
1291	=head3 Be smart about timeouts	1565	=head3 Be smart about timeouts
1292		1566
1293	Many real-world problems invole some kind of time-out, usually for error	1567	Many real-world problems involve some kind of timeout, usually for error
1294	recovery. A typical example is an HTTP request - if the other side hangs,	1568	recovery. A typical example is an HTTP request - if the other side hangs,
1295	you want to raise some error after a while.	1569	you want to raise some error after a while.
1296		1570
1297	Here are some ways on how to handle this problem, from simple and	1571	What follows are some ways to handle this problem, from obvious and
1298	inefficient to very efficient.	1572	inefficient to smart and efficient.
1299		1573
1300	In the following examples a 60 second activity timeout is assumed - a	1574	In the following, a 60 second activity timeout is assumed - a timeout that
1301	timeout that gets reset to 60 seconds each time some data ("a lifesign")	1575	gets reset to 60 seconds each time there is activity (e.g. each time some
1302	was received.	1576	data or other life sign was received).
1303		1577
1304	=over 4	1578	=over 4
1305		1579
1306	=item 1. Use a timer and stop, reinitialise, start it on activity.	1580	=item 1. Use a timer and stop, reinitialise and start it on activity.
1307		1581
1308	This is the most obvious, but not the most simple way: In the beginning,	1582	This is the most obvious, but not the most simple way: In the beginning,
1309	start the watcher:	1583	start the watcher:
1310		1584
1311	ev_timer_init (timer, callback, 60., 0.);	1585	ev_timer_init (timer, callback, 60., 0.);
1312	ev_timer_start (loop, timer);	1586	ev_timer_start (loop, timer);
1313		1587
1314	Then, each time there is some activity, C<ev_timer_stop> the timer,	1588	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
1315	initialise it again, and start it:	1589	and start it again:
1316		1590
1317	ev_timer_stop (loop, timer);	1591	ev_timer_stop (loop, timer);
1318	ev_timer_set (timer, 60., 0.);	1592	ev_timer_set (timer, 60., 0.);
1319	ev_timer_start (loop, timer);	1593	ev_timer_start (loop, timer);
1320		1594
1321	This is relatively simple to implement, but means that each time there	1595	This is relatively simple to implement, but means that each time there is
1322	is some activity, libev will first have to remove the timer from it's	1596	some activity, libev will first have to remove the timer from its internal
1323	internal data strcuture and then add it again.	1597	data structure and then add it again. Libev tries to be fast, but it's
		1598	still not a constant-time operation.
1324		1599
1325	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.	1600	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
1326		1601
1327	This is the easiest way, and involves using C<ev_timer_again> instead of	1602	This is the easiest way, and involves using C<ev_timer_again> instead of
1328	C<ev_timer_start>.	1603	C<ev_timer_start>.
1329		1604
1330	For this, configure an C<ev_timer> with a C<repeat> value of C<60> and	1605	To implement this, configure an C<ev_timer> with a C<repeat> value
1331	then call C<ev_timer_again> at start and each time you successfully read	1606	of C<60> and then call C<ev_timer_again> at start and each time you
1332	or write some data. If you go into an idle state where you do not expect	1607	successfully read or write some data. If you go into an idle state where
1333	data to travel on the socket, you can C<ev_timer_stop> the timer, and	1608	you do not expect data to travel on the socket, you can C<ev_timer_stop>
1334	C<ev_timer_again> will automatically restart it if need be.	1609	the timer, and C<ev_timer_again> will automatically restart it if need be.
1335		1610
1336	That means you can ignore the C<after> value and C<ev_timer_start>	1611	That means you can ignore both the C<ev_timer_start> function and the
1337	altogether and only ever use the C<repeat> value and C<ev_timer_again>.	1612	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1613	member and C<ev_timer_again>.
1338		1614
1339	At start:	1615	At start:
1340		1616
1341	ev_timer_init (timer, callback, 0., 60.);	1617	ev_init (timer, callback);
		1618	timer->repeat = 60.;
1342	ev_timer_again (loop, timer);	1619	ev_timer_again (loop, timer);
1343		1620
1344	Each time you receive some data:	1621	Each time there is some activity:
1345		1622
1346	ev_timer_again (loop, timer);	1623	ev_timer_again (loop, timer);
1347		1624
1348	It is even possible to change the time-out on the fly:	1625	It is even possible to change the time-out on the fly, regardless of
		1626	whether the watcher is active or not:
1349		1627
1350	timer->repeat = 30.;	1628	timer->repeat = 30.;
1351	ev_timer_again (loop, timer);	1629	ev_timer_again (loop, timer);
1352		1630
1353	This is slightly more efficient then stopping/starting the timer each time	1631	This is slightly more efficient then stopping/starting the timer each time
1354	you want to modify its timeout value, as libev does not have to completely	1632	you want to modify its timeout value, as libev does not have to completely
1355	remove and re-insert the timer from/into it's internal data structure.	1633	remove and re-insert the timer from/into its internal data structure.
		1634
		1635	It is, however, even simpler than the "obvious" way to do it.
1356		1636
1357	=item 3. Let the timer time out, but then re-arm it as required.	1637	=item 3. Let the timer time out, but then re-arm it as required.
1358		1638
1359	This method is more tricky, but usually most efficient: Most timeouts are	1639	This method is more tricky, but usually most efficient: Most timeouts are
1360	relatively long compared to the loop iteration time - in our example,	1640	relatively long compared to the intervals between other activity - in
1361	within 60 seconds, there are usually many I/O events with associated	1641	our example, within 60 seconds, there are usually many I/O events with
1362	activity resets.	1642	associated activity resets.
1363		1643
1364	In this case, it would be more efficient to leave the C<ev_timer> alone,	1644	In this case, it would be more efficient to leave the C<ev_timer> alone,
1365	but remember the time of last activity, and check for a real timeout only	1645	but remember the time of last activity, and check for a real timeout only
1366	within the callback:	1646	within the callback:
1367		1647
1368	ev_tstamp last_activity; // time of last activity	1648	ev_tstamp last_activity; // time of last activity
1369		1649
1370	static void	1650	static void
1371	callback (EV_P_ ev_timer *w, int revents)	1651	callback (EV_P_ ev_timer *w, int revents)
1372	{	1652	{
1373	ev_tstamp now = ev_now (EV_A);	1653	ev_tstamp now = ev_now (EV_A);
1374	ev_tstamp timeout = last_activity + 60.;	1654	ev_tstamp timeout = last_activity + 60.;
1375		1655
1376	// if last_activity is older than now - timeout, we did time out	1656	// if last_activity + 60. is older than now, we did time out
1377	if (timeout < now)	1657	if (timeout < now)
1378	{	1658	{
1379	// timeout occured, take action	1659	// timeout occured, take action
1380	}	1660	}
1381	else	1661	else
1382	{	1662	{
1383	// callback was invoked, but there was some activity, re-arm	1663	// callback was invoked, but there was some activity, re-arm
1384	// to fire in last_activity + 60.	1664	// the watcher to fire in last_activity + 60, which is
		1665	// guaranteed to be in the future, so "again" is positive:
1385	w->again = timeout - now;	1666	w->repeat = timeout - now;
1386	ev_timer_again (EV_A_ w);	1667	ev_timer_again (EV_A_ w);
1387	}	1668	}
1388	}	1669	}
1389		1670
1390	To summarise the callback: first calculate the real time-out (defined as	1671	To summarise the callback: first calculate the real timeout (defined
1391	"60 seconds after the last activity"), then check if that time has been	1672	as "60 seconds after the last activity"), then check if that time has
1392	reached, which means there was a real timeout. Otherwise the callback was	1673	been reached, which means something I<did>, in fact, time out. Otherwise
1393	invoked too early (timeout is in the future), so re-schedule the timer to	1674	the callback was invoked too early (C<timeout> is in the future), so
1394	fire at that future time.	1675	re-schedule the timer to fire at that future time, to see if maybe we have
		1676	a timeout then.
1395		1677
1396	Note how C<ev_timer_again> is used, taking advantage of the	1678	Note how C<ev_timer_again> is used, taking advantage of the
1397	C<ev_timer_again> optimisation when the timer is already running.	1679	C<ev_timer_again> optimisation when the timer is already running.
1398		1680
1399	This scheme causes more callback invocations (about one every 60 seconds),	1681	This scheme causes more callback invocations (about one every 60 seconds
1400	but virtually no calls to libev to change the timeout.	1682	minus half the average time between activity), but virtually no calls to
		1683	libev to change the timeout.
1401		1684
1402	To start the timer, simply intiialise the watcher and C<last_activity>,	1685	To start the timer, simply initialise the watcher and set C<last_activity>
1403	then call the callback:	1686	to the current time (meaning we just have some activity :), then call the
		1687	callback, which will "do the right thing" and start the timer:
1404		1688
1405	ev_timer_init (timer, callback);	1689	ev_init (timer, callback);
1406	last_activity = ev_now (loop);	1690	last_activity = ev_now (loop);
1407	callback (loop, timer, EV_TIMEOUT);	1691	callback (loop, timer, EV_TIMEOUT);
1408		1692
1409	And when there is some activity, simply remember the time in	1693	And when there is some activity, simply store the current time in
1410	C<last_activity>:	1694	C<last_activity>, no libev calls at all:
1411		1695
1412	last_actiivty = ev_now (loop);	1696	last_actiivty = ev_now (loop);
1413		1697
1414	This technique is slightly more complex, but in most cases where the	1698	This technique is slightly more complex, but in most cases where the
1415	time-out is unlikely to be triggered, much more efficient.	1699	time-out is unlikely to be triggered, much more efficient.
1416		1700
		1701	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1702	callback :) - just change the timeout and invoke the callback, which will
		1703	fix things for you.
		1704
		1705	=item 4. Wee, just use a double-linked list for your timeouts.
		1706
		1707	If there is not one request, but many thousands (millions...), all
		1708	employing some kind of timeout with the same timeout value, then one can
		1709	do even better:
		1710
		1711	When starting the timeout, calculate the timeout value and put the timeout
		1712	at the I<end> of the list.
		1713
		1714	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1715	the list is expected to fire (for example, using the technique #3).
		1716
		1717	When there is some activity, remove the timer from the list, recalculate
		1718	the timeout, append it to the end of the list again, and make sure to
		1719	update the C<ev_timer> if it was taken from the beginning of the list.
		1720
		1721	This way, one can manage an unlimited number of timeouts in O(1) time for
		1722	starting, stopping and updating the timers, at the expense of a major
		1723	complication, and having to use a constant timeout. The constant timeout
		1724	ensures that the list stays sorted.
		1725
1417	=back	1726	=back
		1727
		1728	So which method the best?
		1729
		1730	Method #2 is a simple no-brain-required solution that is adequate in most
		1731	situations. Method #3 requires a bit more thinking, but handles many cases
		1732	better, and isn't very complicated either. In most case, choosing either
		1733	one is fine, with #3 being better in typical situations.
		1734
		1735	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1736	rather complicated, but extremely efficient, something that really pays
		1737	off after the first million or so of active timers, i.e. it's usually
		1738	overkill :)
1418		1739
1419	=head3 The special problem of time updates	1740	=head3 The special problem of time updates
1420		1741
1421	Establishing the current time is a costly operation (it usually takes at	1742	Establishing the current time is a costly operation (it usually takes at
1422	least two system calls): EV therefore updates its idea of the current	1743	least two system calls): EV therefore updates its idea of the current
…		…
1434		1755
1435	If the event loop is suspended for a long time, you can also force an	1756	If the event loop is suspended for a long time, you can also force an
1436	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1757	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1437	()>.	1758	()>.
1438		1759
		1760	=head3 The special problems of suspended animation
		1761
		1762	When you leave the server world it is quite customary to hit machines that
		1763	can suspend/hibernate - what happens to the clocks during such a suspend?
		1764
		1765	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1766	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1767	to run until the system is suspended, but they will not advance while the
		1768	system is suspended. That means, on resume, it will be as if the program
		1769	was frozen for a few seconds, but the suspend time will not be counted
		1770	towards C<ev_timer> when a monotonic clock source is used. The real time
		1771	clock advanced as expected, but if it is used as sole clocksource, then a
		1772	long suspend would be detected as a time jump by libev, and timers would
		1773	be adjusted accordingly.
		1774
		1775	I would not be surprised to see different behaviour in different between
		1776	operating systems, OS versions or even different hardware.
		1777
		1778	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1779	time jump in the monotonic clocks and the realtime clock. If the program
		1780	is suspended for a very long time, and monotonic clock sources are in use,
		1781	then you can expect C<ev_timer>s to expire as the full suspension time
		1782	will be counted towards the timers. When no monotonic clock source is in
		1783	use, then libev will again assume a timejump and adjust accordingly.
		1784
		1785	It might be beneficial for this latter case to call C<ev_suspend>
		1786	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1787	deterministic behaviour in this case (you can do nothing against
		1788	C<SIGSTOP>).
		1789
1439	=head3 Watcher-Specific Functions and Data Members	1790	=head3 Watcher-Specific Functions and Data Members
1440		1791
1441	=over 4	1792	=over 4
1442		1793
1443	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1794	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1466	If the timer is started but non-repeating, stop it (as if it timed out).	1817	If the timer is started but non-repeating, stop it (as if it timed out).
1467		1818
1468	If the timer is repeating, either start it if necessary (with the	1819	If the timer is repeating, either start it if necessary (with the
1469	C<repeat> value), or reset the running timer to the C<repeat> value.	1820	C<repeat> value), or reset the running timer to the C<repeat> value.
1470		1821
1471	This sounds a bit complicated, see "Be smart about timeouts", above, for a	1822	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1472	usage example.	1823	usage example.
1473		1824
1474	=item ev_tstamp repeat [read-write]	1825	=item ev_tstamp repeat [read-write]
1475		1826
1476	The current C<repeat> value. Will be used each time the watcher times out	1827	The current C<repeat> value. Will be used each time the watcher times out
…		…
1515	=head2 C<ev_periodic> - to cron or not to cron?	1866	=head2 C<ev_periodic> - to cron or not to cron?
1516		1867
1517	Periodic watchers are also timers of a kind, but they are very versatile	1868	Periodic watchers are also timers of a kind, but they are very versatile
1518	(and unfortunately a bit complex).	1869	(and unfortunately a bit complex).
1519		1870
1520	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1871	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1521	but on wall clock time (absolute time). You can tell a periodic watcher	1872	relative time, the physical time that passes) but on wall clock time
1522	to trigger after some specific point in time. For example, if you tell a	1873	(absolute time, the thing you can read on your calender or clock). The
1523	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1874	difference is that wall clock time can run faster or slower than real
1524	+ 10.>, that is, an absolute time not a delay) and then reset your system	1875	time, and time jumps are not uncommon (e.g. when you adjust your
1525	clock to January of the previous year, then it will take more than year	1876	wrist-watch).
1526	to trigger the event (unlike an C<ev_timer>, which would still trigger
1527	roughly 10 seconds later as it uses a relative timeout).
1528		1877
		1878	You can tell a periodic watcher to trigger after some specific point
		1879	in time: for example, if you tell a periodic watcher to trigger "in 10
		1880	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1881	not a delay) and then reset your system clock to January of the previous
		1882	year, then it will take a year or more to trigger the event (unlike an
		1883	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1884	it, as it uses a relative timeout).
		1885
1529	C<ev_periodic>s can also be used to implement vastly more complex timers,	1886	C<ev_periodic> watchers can also be used to implement vastly more complex
1530	such as triggering an event on each "midnight, local time", or other	1887	timers, such as triggering an event on each "midnight, local time", or
1531	complicated rules.	1888	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1889	those cannot react to time jumps.
1532		1890
1533	As with timers, the callback is guaranteed to be invoked only when the	1891	As with timers, the callback is guaranteed to be invoked only when the
1534	time (C<at>) has passed, but if multiple periodic timers become ready	1892	point in time where it is supposed to trigger has passed. If multiple
1535	during the same loop iteration, then order of execution is undefined.	1893	timers become ready during the same loop iteration then the ones with
		1894	earlier time-out values are invoked before ones with later time-out values
		1895	(but this is no longer true when a callback calls C<ev_loop> recursively).
1536		1896
1537	=head3 Watcher-Specific Functions and Data Members	1897	=head3 Watcher-Specific Functions and Data Members
1538		1898
1539	=over 4	1899	=over 4
1540		1900
1541	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1901	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1542		1902
1543	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1903	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1544		1904
1545	Lots of arguments, lets sort it out... There are basically three modes of	1905	Lots of arguments, let's sort it out... There are basically three modes of
1546	operation, and we will explain them from simplest to most complex:	1906	operation, and we will explain them from simplest to most complex:
1547		1907
1548	=over 4	1908	=over 4
1549		1909
1550	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1910	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1551		1911
1552	In this configuration the watcher triggers an event after the wall clock	1912	In this configuration the watcher triggers an event after the wall clock
1553	time C<at> has passed. It will not repeat and will not adjust when a time	1913	time C<offset> has passed. It will not repeat and will not adjust when a
1554	jump occurs, that is, if it is to be run at January 1st 2011 then it will	1914	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1555	only run when the system clock reaches or surpasses this time.	1915	will be stopped and invoked when the system clock reaches or surpasses
		1916	this point in time.
1556		1917
1557	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1918	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1558		1919
1559	In this mode the watcher will always be scheduled to time out at the next	1920	In this mode the watcher will always be scheduled to time out at the next
1560	C<at + N * interval> time (for some integer N, which can also be negative)	1921	C<offset + N * interval> time (for some integer N, which can also be
1561	and then repeat, regardless of any time jumps.	1922	negative) and then repeat, regardless of any time jumps. The C<offset>
		1923	argument is merely an offset into the C<interval> periods.
1562		1924
1563	This can be used to create timers that do not drift with respect to the	1925	This can be used to create timers that do not drift with respect to the
1564	system clock, for example, here is a C<ev_periodic> that triggers each	1926	system clock, for example, here is an C<ev_periodic> that triggers each
1565	hour, on the hour:	1927	hour, on the hour (with respect to UTC):
1566		1928
1567	ev_periodic_set (&periodic, 0., 3600., 0);	1929	ev_periodic_set (&periodic, 0., 3600., 0);
1568		1930
1569	This doesn't mean there will always be 3600 seconds in between triggers,	1931	This doesn't mean there will always be 3600 seconds in between triggers,
1570	but only that the callback will be called when the system time shows a	1932	but only that the callback will be called when the system time shows a
1571	full hour (UTC), or more correctly, when the system time is evenly divisible	1933	full hour (UTC), or more correctly, when the system time is evenly divisible
1572	by 3600.	1934	by 3600.
1573		1935
1574	Another way to think about it (for the mathematically inclined) is that	1936	Another way to think about it (for the mathematically inclined) is that
1575	C<ev_periodic> will try to run the callback in this mode at the next possible	1937	C<ev_periodic> will try to run the callback in this mode at the next possible
1576	time where C<time = at (mod interval)>, regardless of any time jumps.	1938	time where C<time = offset (mod interval)>, regardless of any time jumps.
1577		1939
1578	For numerical stability it is preferable that the C<at> value is near	1940	For numerical stability it is preferable that the C<offset> value is near
1579	C<ev_now ()> (the current time), but there is no range requirement for	1941	C<ev_now ()> (the current time), but there is no range requirement for
1580	this value, and in fact is often specified as zero.	1942	this value, and in fact is often specified as zero.
1581		1943
1582	Note also that there is an upper limit to how often a timer can fire (CPU	1944	Note also that there is an upper limit to how often a timer can fire (CPU
1583	speed for example), so if C<interval> is very small then timing stability	1945	speed for example), so if C<interval> is very small then timing stability
1584	will of course deteriorate. Libev itself tries to be exact to be about one	1946	will of course deteriorate. Libev itself tries to be exact to be about one
1585	millisecond (if the OS supports it and the machine is fast enough).	1947	millisecond (if the OS supports it and the machine is fast enough).
1586		1948
1587	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1949	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1588		1950
1589	In this mode the values for C<interval> and C<at> are both being	1951	In this mode the values for C<interval> and C<offset> are both being
1590	ignored. Instead, each time the periodic watcher gets scheduled, the	1952	ignored. Instead, each time the periodic watcher gets scheduled, the
1591	reschedule callback will be called with the watcher as first, and the	1953	reschedule callback will be called with the watcher as first, and the
1592	current time as second argument.	1954	current time as second argument.
1593		1955
1594	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1956	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1595	ever, or make ANY event loop modifications whatsoever>.	1957	or make ANY other event loop modifications whatsoever, unless explicitly
		1958	allowed by documentation here>.
1596		1959
1597	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1960	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1598	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1961	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1599	only event loop modification you are allowed to do).	1962	only event loop modification you are allowed to do).
1600		1963
…		…
1630	a different time than the last time it was called (e.g. in a crond like	1993	a different time than the last time it was called (e.g. in a crond like
1631	program when the crontabs have changed).	1994	program when the crontabs have changed).
1632		1995
1633	=item ev_tstamp ev_periodic_at (ev_periodic *)	1996	=item ev_tstamp ev_periodic_at (ev_periodic *)
1634		1997
1635	When active, returns the absolute time that the watcher is supposed to	1998	When active, returns the absolute time that the watcher is supposed
1636	trigger next.	1999	to trigger next. This is not the same as the C<offset> argument to
		2000	C<ev_periodic_set>, but indeed works even in interval and manual
		2001	rescheduling modes.
1637		2002
1638	=item ev_tstamp offset [read-write]	2003	=item ev_tstamp offset [read-write]
1639		2004
1640	When repeating, this contains the offset value, otherwise this is the	2005	When repeating, this contains the offset value, otherwise this is the
1641	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2006	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2007	although libev might modify this value for better numerical stability).
1642		2008
1643	Can be modified any time, but changes only take effect when the periodic	2009	Can be modified any time, but changes only take effect when the periodic
1644	timer fires or C<ev_periodic_again> is being called.	2010	timer fires or C<ev_periodic_again> is being called.
1645		2011
1646	=item ev_tstamp interval [read-write]	2012	=item ev_tstamp interval [read-write]
…		…
1755	some child status changes (most typically when a child of yours dies or	2121	some child status changes (most typically when a child of yours dies or
1756	exits). It is permissible to install a child watcher I<after> the child	2122	exits). It is permissible to install a child watcher I<after> the child
1757	has been forked (which implies it might have already exited), as long	2123	has been forked (which implies it might have already exited), as long
1758	as the event loop isn't entered (or is continued from a watcher), i.e.,	2124	as the event loop isn't entered (or is continued from a watcher), i.e.,
1759	forking and then immediately registering a watcher for the child is fine,	2125	forking and then immediately registering a watcher for the child is fine,
1760	but forking and registering a watcher a few event loop iterations later is	2126	but forking and registering a watcher a few event loop iterations later or
1761	not.	2127	in the next callback invocation is not.
1762		2128
1763	Only the default event loop is capable of handling signals, and therefore	2129	Only the default event loop is capable of handling signals, and therefore
1764	you can only register child watchers in the default event loop.	2130	you can only register child watchers in the default event loop.
		2131
		2132	Due to some design glitches inside libev, child watchers will always be
		2133	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2134	libev)
1765		2135
1766	=head3 Process Interaction	2136	=head3 Process Interaction
1767		2137
1768	Libev grabs C<SIGCHLD> as soon as the default event loop is	2138	Libev grabs C<SIGCHLD> as soon as the default event loop is
1769	initialised. This is necessary to guarantee proper behaviour even if	2139	initialised. This is necessary to guarantee proper behaviour even if
…		…
1852		2222
1853		2223
1854	=head2 C<ev_stat> - did the file attributes just change?	2224	=head2 C<ev_stat> - did the file attributes just change?
1855		2225
1856	This watches a file system path for attribute changes. That is, it calls	2226	This watches a file system path for attribute changes. That is, it calls
1857	C<stat> regularly (or when the OS says it changed) and sees if it changed	2227	C<stat> on that path in regular intervals (or when the OS says it changed)
1858	compared to the last time, invoking the callback if it did.	2228	and sees if it changed compared to the last time, invoking the callback if
		2229	it did.
1859		2230
1860	The path does not need to exist: changing from "path exists" to "path does	2231	The path does not need to exist: changing from "path exists" to "path does
1861	not exist" is a status change like any other. The condition "path does	2232	not exist" is a status change like any other. The condition "path does not
1862	not exist" is signified by the C<st_nlink> field being zero (which is	2233	exist" (or more correctly "path cannot be stat'ed") is signified by the
1863	otherwise always forced to be at least one) and all the other fields of	2234	C<st_nlink> field being zero (which is otherwise always forced to be at
1864	the stat buffer having unspecified contents.	2235	least one) and all the other fields of the stat buffer having unspecified
		2236	contents.
1865		2237
1866	The path I<should> be absolute and I<must not> end in a slash. If it is	2238	The path I<must not> end in a slash or contain special components such as
		2239	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1867	relative and your working directory changes, the behaviour is undefined.	2240	your working directory changes, then the behaviour is undefined.
1868		2241
1869	Since there is no standard kernel interface to do this, the portable	2242	Since there is no portable change notification interface available, the
1870	implementation simply calls C<stat (2)> regularly on the path to see if	2243	portable implementation simply calls C<stat(2)> regularly on the path
1871	it changed somehow. You can specify a recommended polling interval for	2244	to see if it changed somehow. You can specify a recommended polling
1872	this case. If you specify a polling interval of C<0> (highly recommended!)	2245	interval for this case. If you specify a polling interval of C<0> (highly
1873	then a I<suitable, unspecified default> value will be used (which	2246	recommended!) then a I<suitable, unspecified default> value will be used
1874	you can expect to be around five seconds, although this might change	2247	(which you can expect to be around five seconds, although this might
1875	dynamically). Libev will also impose a minimum interval which is currently	2248	change dynamically). Libev will also impose a minimum interval which is
1876	around C<0.1>, but thats usually overkill.	2249	currently around C<0.1>, but that's usually overkill.
1877		2250
1878	This watcher type is not meant for massive numbers of stat watchers,	2251	This watcher type is not meant for massive numbers of stat watchers,
1879	as even with OS-supported change notifications, this can be	2252	as even with OS-supported change notifications, this can be
1880	resource-intensive.	2253	resource-intensive.
1881		2254
1882	At the time of this writing, the only OS-specific interface implemented	2255	At the time of this writing, the only OS-specific interface implemented
1883	is the Linux inotify interface (implementing kqueue support is left as	2256	is the Linux inotify interface (implementing kqueue support is left as an
1884	an exercise for the reader. Note, however, that the author sees no way	2257	exercise for the reader. Note, however, that the author sees no way of
1885	of implementing C<ev_stat> semantics with kqueue).	2258	implementing C<ev_stat> semantics with kqueue, except as a hint).
1886		2259
1887	=head3 ABI Issues (Largefile Support)	2260	=head3 ABI Issues (Largefile Support)
1888		2261
1889	Libev by default (unless the user overrides this) uses the default	2262	Libev by default (unless the user overrides this) uses the default
1890	compilation environment, which means that on systems with large file	2263	compilation environment, which means that on systems with large file
1891	support disabled by default, you get the 32 bit version of the stat	2264	support disabled by default, you get the 32 bit version of the stat
1892	structure. When using the library from programs that change the ABI to	2265	structure. When using the library from programs that change the ABI to
1893	use 64 bit file offsets the programs will fail. In that case you have to	2266	use 64 bit file offsets the programs will fail. In that case you have to
1894	compile libev with the same flags to get binary compatibility. This is	2267	compile libev with the same flags to get binary compatibility. This is
1895	obviously the case with any flags that change the ABI, but the problem is	2268	obviously the case with any flags that change the ABI, but the problem is
1896	most noticeably disabled with ev_stat and large file support.	2269	most noticeably displayed with ev_stat and large file support.
1897		2270
1898	The solution for this is to lobby your distribution maker to make large	2271	The solution for this is to lobby your distribution maker to make large
1899	file interfaces available by default (as e.g. FreeBSD does) and not	2272	file interfaces available by default (as e.g. FreeBSD does) and not
1900	optional. Libev cannot simply switch on large file support because it has	2273	optional. Libev cannot simply switch on large file support because it has
1901	to exchange stat structures with application programs compiled using the	2274	to exchange stat structures with application programs compiled using the
1902	default compilation environment.	2275	default compilation environment.
1903		2276
1904	=head3 Inotify and Kqueue	2277	=head3 Inotify and Kqueue
1905		2278
1906	When C<inotify (7)> support has been compiled into libev (generally	2279	When C<inotify (7)> support has been compiled into libev and present at
1907	only available with Linux 2.6.25 or above due to bugs in earlier	2280	runtime, it will be used to speed up change detection where possible. The
1908	implementations) and present at runtime, it will be used to speed up	2281	inotify descriptor will be created lazily when the first C<ev_stat>
1909	change detection where possible. The inotify descriptor will be created	2282	watcher is being started.
1910	lazily when the first C<ev_stat> watcher is being started.
1911		2283
1912	Inotify presence does not change the semantics of C<ev_stat> watchers	2284	Inotify presence does not change the semantics of C<ev_stat> watchers
1913	except that changes might be detected earlier, and in some cases, to avoid	2285	except that changes might be detected earlier, and in some cases, to avoid
1914	making regular C<stat> calls. Even in the presence of inotify support	2286	making regular C<stat> calls. Even in the presence of inotify support
1915	there are many cases where libev has to resort to regular C<stat> polling,	2287	there are many cases where libev has to resort to regular C<stat> polling,
1916	but as long as the path exists, libev usually gets away without polling.	2288	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2289	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2290	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2291	xfs are fully working) libev usually gets away without polling.
1917		2292
1918	There is no support for kqueue, as apparently it cannot be used to	2293	There is no support for kqueue, as apparently it cannot be used to
1919	implement this functionality, due to the requirement of having a file	2294	implement this functionality, due to the requirement of having a file
1920	descriptor open on the object at all times, and detecting renames, unlinks	2295	descriptor open on the object at all times, and detecting renames, unlinks
1921	etc. is difficult.	2296	etc. is difficult.
1922		2297
		2298	=head3 C<stat ()> is a synchronous operation
		2299
		2300	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2301	the process. The exception are C<ev_stat> watchers - those call C<stat
		2302	()>, which is a synchronous operation.
		2303
		2304	For local paths, this usually doesn't matter: unless the system is very
		2305	busy or the intervals between stat's are large, a stat call will be fast,
		2306	as the path data is usually in memory already (except when starting the
		2307	watcher).
		2308
		2309	For networked file systems, calling C<stat ()> can block an indefinite
		2310	time due to network issues, and even under good conditions, a stat call
		2311	often takes multiple milliseconds.
		2312
		2313	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2314	paths, although this is fully supported by libev.
		2315
1923	=head3 The special problem of stat time resolution	2316	=head3 The special problem of stat time resolution
1924		2317
1925	The C<stat ()> system call only supports full-second resolution portably, and	2318	The C<stat ()> system call only supports full-second resolution portably,
1926	even on systems where the resolution is higher, most file systems still	2319	and even on systems where the resolution is higher, most file systems
1927	only support whole seconds.	2320	still only support whole seconds.
1928		2321
1929	That means that, if the time is the only thing that changes, you can	2322	That means that, if the time is the only thing that changes, you can
1930	easily miss updates: on the first update, C<ev_stat> detects a change and	2323	easily miss updates: on the first update, C<ev_stat> detects a change and
1931	calls your callback, which does something. When there is another update	2324	calls your callback, which does something. When there is another update
1932	within the same second, C<ev_stat> will be unable to detect unless the	2325	within the same second, C<ev_stat> will be unable to detect unless the
…		…
2075		2468
2076	=head3 Watcher-Specific Functions and Data Members	2469	=head3 Watcher-Specific Functions and Data Members
2077		2470
2078	=over 4	2471	=over 4
2079		2472
2080	=item ev_idle_init (ev_signal *, callback)	2473	=item ev_idle_init (ev_idle *, callback)
2081		2474
2082	Initialises and configures the idle watcher - it has no parameters of any	2475	Initialises and configures the idle watcher - it has no parameters of any
2083	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2476	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
2084	believe me.	2477	believe me.
2085		2478
…		…
2098	// no longer anything immediate to do.	2491	// no longer anything immediate to do.
2099	}	2492	}
2100		2493
2101	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2494	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2102	ev_idle_init (idle_watcher, idle_cb);	2495	ev_idle_init (idle_watcher, idle_cb);
2103	ev_idle_start (loop, idle_cb);	2496	ev_idle_start (loop, idle_watcher);
2104		2497
2105		2498
2106	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2499	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2107		2500
2108	Prepare and check watchers are usually (but not always) used in pairs:	2501	Prepare and check watchers are usually (but not always) used in pairs:
…		…
2201	struct pollfd fds [nfd];	2594	struct pollfd fds [nfd];
2202	// actual code will need to loop here and realloc etc.	2595	// actual code will need to loop here and realloc etc.
2203	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2596	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2204		2597
2205	/* the callback is illegal, but won't be called as we stop during check */	2598	/* the callback is illegal, but won't be called as we stop during check */
2206	ev_timer_init (&tw, 0, timeout * 1e-3);	2599	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2207	ev_timer_start (loop, &tw);	2600	ev_timer_start (loop, &tw);
2208		2601
2209	// create one ev_io per pollfd	2602	// create one ev_io per pollfd
2210	for (int i = 0; i < nfd; ++i)	2603	for (int i = 0; i < nfd; ++i)
2211	{	2604	{
…		…
2324	some fds have to be watched and handled very quickly (with low latency),	2717	some fds have to be watched and handled very quickly (with low latency),
2325	and even priorities and idle watchers might have too much overhead. In	2718	and even priorities and idle watchers might have too much overhead. In
2326	this case you would put all the high priority stuff in one loop and all	2719	this case you would put all the high priority stuff in one loop and all
2327	the rest in a second one, and embed the second one in the first.	2720	the rest in a second one, and embed the second one in the first.
2328		2721
2329	As long as the watcher is active, the callback will be invoked every time	2722	As long as the watcher is active, the callback will be invoked every
2330	there might be events pending in the embedded loop. The callback must then	2723	time there might be events pending in the embedded loop. The callback
2331	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2724	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2332	their callbacks (you could also start an idle watcher to give the embedded	2725	sweep and invoke their callbacks (the callback doesn't need to invoke the
2333	loop strictly lower priority for example). You can also set the callback	2726	C<ev_embed_sweep> function directly, it could also start an idle watcher
2334	to C<0>, in which case the embed watcher will automatically execute the	2727	to give the embedded loop strictly lower priority for example).
2335	embedded loop sweep.
2336		2728
2337	As long as the watcher is started it will automatically handle events. The	2729	You can also set the callback to C<0>, in which case the embed watcher
2338	callback will be invoked whenever some events have been handled. You can	2730	will automatically execute the embedded loop sweep whenever necessary.
2339	set the callback to C<0> to avoid having to specify one if you are not
2340	interested in that.
2341		2731
2342	Also, there have not currently been made special provisions for forking:	2732	Fork detection will be handled transparently while the C<ev_embed> watcher
2343	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2733	is active, i.e., the embedded loop will automatically be forked when the
2344	but you will also have to stop and restart any C<ev_embed> watchers	2734	embedding loop forks. In other cases, the user is responsible for calling
2345	yourself - but you can use a fork watcher to handle this automatically,	2735	C<ev_loop_fork> on the embedded loop.
2346	and future versions of libev might do just that.
2347		2736
2348	Unfortunately, not all backends are embeddable: only the ones returned by	2737	Unfortunately, not all backends are embeddable: only the ones returned by
2349	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2738	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2350	portable one.	2739	portable one.
2351		2740
…		…
2445	event loop blocks next and before C<ev_check> watchers are being called,	2834	event loop blocks next and before C<ev_check> watchers are being called,
2446	and only in the child after the fork. If whoever good citizen calling	2835	and only in the child after the fork. If whoever good citizen calling
2447	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2836	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2448	handlers will be invoked, too, of course.	2837	handlers will be invoked, too, of course.
2449		2838
		2839	=head3 The special problem of life after fork - how is it possible?
		2840
		2841	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2842	up/change the process environment, followed by a call to C<exec()>. This
		2843	sequence should be handled by libev without any problems.
		2844
		2845	This changes when the application actually wants to do event handling
		2846	in the child, or both parent in child, in effect "continuing" after the
		2847	fork.
		2848
		2849	The default mode of operation (for libev, with application help to detect
		2850	forks) is to duplicate all the state in the child, as would be expected
		2851	when I<either> the parent I<or> the child process continues.
		2852
		2853	When both processes want to continue using libev, then this is usually the
		2854	wrong result. In that case, usually one process (typically the parent) is
		2855	supposed to continue with all watchers in place as before, while the other
		2856	process typically wants to start fresh, i.e. without any active watchers.
		2857
		2858	The cleanest and most efficient way to achieve that with libev is to
		2859	simply create a new event loop, which of course will be "empty", and
		2860	use that for new watchers. This has the advantage of not touching more
		2861	memory than necessary, and thus avoiding the copy-on-write, and the
		2862	disadvantage of having to use multiple event loops (which do not support
		2863	signal watchers).
		2864
		2865	When this is not possible, or you want to use the default loop for
		2866	other reasons, then in the process that wants to start "fresh", call
		2867	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2868	the default loop will "orphan" (not stop) all registered watchers, so you
		2869	have to be careful not to execute code that modifies those watchers. Note
		2870	also that in that case, you have to re-register any signal watchers.
		2871
2450	=head3 Watcher-Specific Functions and Data Members	2872	=head3 Watcher-Specific Functions and Data Members
2451		2873
2452	=over 4	2874	=over 4
2453		2875
2454	=item ev_fork_init (ev_signal *, callback)	2876	=item ev_fork_init (ev_signal *, callback)
…		…
2571	=over 4	2993	=over 4
2572		2994
2573	=item ev_async_init (ev_async *, callback)	2995	=item ev_async_init (ev_async *, callback)
2574		2996
2575	Initialises and configures the async watcher - it has no parameters of any	2997	Initialises and configures the async watcher - it has no parameters of any
2576	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	2998	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2577	trust me.	2999	trust me.
2578		3000
2579	=item ev_async_send (loop, ev_async *)	3001	=item ev_async_send (loop, ev_async *)
2580		3002
2581	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3003	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2582	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3004	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2583	C<ev_feed_event>, this call is safe to do from other threads, signal or	3005	C<ev_feed_event>, this call is safe to do from other threads, signal or
2584	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3006	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2585	section below on what exactly this means).	3007	section below on what exactly this means).
2586		3008
		3009	Note that, as with other watchers in libev, multiple events might get
		3010	compressed into a single callback invocation (another way to look at this
		3011	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3012	reset when the event loop detects that).
		3013
2587	This call incurs the overhead of a system call only once per loop iteration,	3014	This call incurs the overhead of a system call only once per event loop
2588	so while the overhead might be noticeable, it doesn't apply to repeated	3015	iteration, so while the overhead might be noticeable, it doesn't apply to
2589	calls to C<ev_async_send>.	3016	repeated calls to C<ev_async_send> for the same event loop.
2590		3017
2591	=item bool = ev_async_pending (ev_async *)	3018	=item bool = ev_async_pending (ev_async *)
2592		3019
2593	Returns a non-zero value when C<ev_async_send> has been called on the	3020	Returns a non-zero value when C<ev_async_send> has been called on the
2594	watcher but the event has not yet been processed (or even noted) by the	3021	watcher but the event has not yet been processed (or even noted) by the
…		…
2597	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3024	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2598	the loop iterates next and checks for the watcher to have become active,	3025	the loop iterates next and checks for the watcher to have become active,
2599	it will reset the flag again. C<ev_async_pending> can be used to very	3026	it will reset the flag again. C<ev_async_pending> can be used to very
2600	quickly check whether invoking the loop might be a good idea.	3027	quickly check whether invoking the loop might be a good idea.
2601		3028
2602	Not that this does I<not> check whether the watcher itself is pending, only	3029	Not that this does I<not> check whether the watcher itself is pending,
2603	whether it has been requested to make this watcher pending.	3030	only whether it has been requested to make this watcher pending: there
		3031	is a time window between the event loop checking and resetting the async
		3032	notification, and the callback being invoked.
2604		3033
2605	=back	3034	=back
2606		3035
2607		3036
2608	=head1 OTHER FUNCTIONS	3037	=head1 OTHER FUNCTIONS
…		…
2787		3216
2788	myclass obj;	3217	myclass obj;
2789	ev::io iow;	3218	ev::io iow;
2790	iow.set <myclass, &myclass::io_cb> (&obj);	3219	iow.set <myclass, &myclass::io_cb> (&obj);
2791		3220
		3221	=item w->set (object *)
		3222
		3223	This is an B<experimental> feature that might go away in a future version.
		3224
		3225	This is a variation of a method callback - leaving out the method to call
		3226	will default the method to C<operator ()>, which makes it possible to use
		3227	functor objects without having to manually specify the C<operator ()> all
		3228	the time. Incidentally, you can then also leave out the template argument
		3229	list.
		3230
		3231	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3232	int revents)>.
		3233
		3234	See the method-C<set> above for more details.
		3235
		3236	Example: use a functor object as callback.
		3237
		3238	struct myfunctor
		3239	{
		3240	void operator() (ev::io &w, int revents)
		3241	{
		3242	...
		3243	}
		3244	}
		3245
		3246	myfunctor f;
		3247
		3248	ev::io w;
		3249	w.set (&f);
		3250
2792	=item w->set<function> (void *data = 0)	3251	=item w->set<function> (void *data = 0)
2793		3252
2794	Also sets a callback, but uses a static method or plain function as	3253	Also sets a callback, but uses a static method or plain function as
2795	callback. The optional C<data> argument will be stored in the watcher's	3254	callback. The optional C<data> argument will be stored in the watcher's
2796	C<data> member and is free for you to use.	3255	C<data> member and is free for you to use.
…		…
2882	L<http://software.schmorp.de/pkg/EV>.	3341	L<http://software.schmorp.de/pkg/EV>.
2883		3342
2884	=item Python	3343	=item Python
2885		3344
2886	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3345	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2887	seems to be quite complete and well-documented. Note, however, that the	3346	seems to be quite complete and well-documented.
2888	patch they require for libev is outright dangerous as it breaks the ABI
2889	for everybody else, and therefore, should never be applied in an installed
2890	libev (if python requires an incompatible ABI then it needs to embed
2891	libev).
2892		3347
2893	=item Ruby	3348	=item Ruby
2894		3349
2895	Tony Arcieri has written a ruby extension that offers access to a subset	3350	Tony Arcieri has written a ruby extension that offers access to a subset
2896	of the libev API and adds file handle abstractions, asynchronous DNS and	3351	of the libev API and adds file handle abstractions, asynchronous DNS and
2897	more on top of it. It can be found via gem servers. Its homepage is at	3352	more on top of it. It can be found via gem servers. Its homepage is at
2898	L<http://rev.rubyforge.org/>.	3353	L<http://rev.rubyforge.org/>.
2899		3354
		3355	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3356	makes rev work even on mingw.
		3357
		3358	=item Haskell
		3359
		3360	A haskell binding to libev is available at
		3361	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3362
2900	=item D	3363	=item D
2901		3364
2902	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3365	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2903	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3366	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3367
		3368	=item Ocaml
		3369
		3370	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3371	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
2904		3372
2905	=back	3373	=back
2906		3374
2907		3375
2908	=head1 MACRO MAGIC	3376	=head1 MACRO MAGIC
…		…
3009		3477
3010	#define EV_STANDALONE 1	3478	#define EV_STANDALONE 1
3011	#include "ev.h"	3479	#include "ev.h"
3012		3480
3013	Both header files and implementation files can be compiled with a C++	3481	Both header files and implementation files can be compiled with a C++
3014	compiler (at least, thats a stated goal, and breakage will be treated	3482	compiler (at least, that's a stated goal, and breakage will be treated
3015	as a bug).	3483	as a bug).
3016		3484
3017	You need the following files in your source tree, or in a directory	3485	You need the following files in your source tree, or in a directory
3018	in your include path (e.g. in libev/ when using -Ilibev):	3486	in your include path (e.g. in libev/ when using -Ilibev):
3019		3487
…		…
3075	keeps libev from including F<config.h>, and it also defines dummy	3543	keeps libev from including F<config.h>, and it also defines dummy
3076	implementations for some libevent functions (such as logging, which is not	3544	implementations for some libevent functions (such as logging, which is not
3077	supported). It will also not define any of the structs usually found in	3545	supported). It will also not define any of the structs usually found in
3078	F<event.h> that are not directly supported by the libev core alone.	3546	F<event.h> that are not directly supported by the libev core alone.
3079		3547
		3548	In stanbdalone mode, libev will still try to automatically deduce the
		3549	configuration, but has to be more conservative.
		3550
3080	=item EV_USE_MONOTONIC	3551	=item EV_USE_MONOTONIC
3081		3552
3082	If defined to be C<1>, libev will try to detect the availability of the	3553	If defined to be C<1>, libev will try to detect the availability of the
3083	monotonic clock option at both compile time and runtime. Otherwise no use	3554	monotonic clock option at both compile time and runtime. Otherwise no
3084	of the monotonic clock option will be attempted. If you enable this, you	3555	use of the monotonic clock option will be attempted. If you enable this,
3085	usually have to link against librt or something similar. Enabling it when	3556	you usually have to link against librt or something similar. Enabling it
3086	the functionality isn't available is safe, though, although you have	3557	when the functionality isn't available is safe, though, although you have
3087	to make sure you link against any libraries where the C<clock_gettime>	3558	to make sure you link against any libraries where the C<clock_gettime>
3088	function is hiding in (often F<-lrt>).	3559	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
3089		3560
3090	=item EV_USE_REALTIME	3561	=item EV_USE_REALTIME
3091		3562
3092	If defined to be C<1>, libev will try to detect the availability of the	3563	If defined to be C<1>, libev will try to detect the availability of the
3093	real-time clock option at compile time (and assume its availability at	3564	real-time clock option at compile time (and assume its availability
3094	runtime if successful). Otherwise no use of the real-time clock option will	3565	at runtime if successful). Otherwise no use of the real-time clock
3095	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3566	option will be attempted. This effectively replaces C<gettimeofday>
3096	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3567	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
3097	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3568	correctness. See the note about libraries in the description of
		3569	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3570	C<EV_USE_CLOCK_SYSCALL>.
		3571
		3572	=item EV_USE_CLOCK_SYSCALL
		3573
		3574	If defined to be C<1>, libev will try to use a direct syscall instead
		3575	of calling the system-provided C<clock_gettime> function. This option
		3576	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3577	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3578	programs needlessly. Using a direct syscall is slightly slower (in
		3579	theory), because no optimised vdso implementation can be used, but avoids
		3580	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3581	higher, as it simplifies linking (no need for C<-lrt>).
3098		3582
3099	=item EV_USE_NANOSLEEP	3583	=item EV_USE_NANOSLEEP
3100		3584
3101	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3585	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
3102	and will use it for delays. Otherwise it will use C<select ()>.	3586	and will use it for delays. Otherwise it will use C<select ()>.
…		…
3118		3602
3119	=item EV_SELECT_USE_FD_SET	3603	=item EV_SELECT_USE_FD_SET
3120		3604
3121	If defined to C<1>, then the select backend will use the system C<fd_set>	3605	If defined to C<1>, then the select backend will use the system C<fd_set>
3122	structure. This is useful if libev doesn't compile due to a missing	3606	structure. This is useful if libev doesn't compile due to a missing
3123	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3607	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
3124	exotic systems. This usually limits the range of file descriptors to some	3608	on exotic systems. This usually limits the range of file descriptors to
3125	low limit such as 1024 or might have other limitations (winsocket only	3609	some low limit such as 1024 or might have other limitations (winsocket
3126	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3610	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
3127	influence the size of the C<fd_set> used.	3611	configures the maximum size of the C<fd_set>.
3128		3612
3129	=item EV_SELECT_IS_WINSOCKET	3613	=item EV_SELECT_IS_WINSOCKET
3130		3614
3131	When defined to C<1>, the select backend will assume that	3615	When defined to C<1>, the select backend will assume that
3132	select/socket/connect etc. don't understand file descriptors but	3616	select/socket/connect etc. don't understand file descriptors but
…		…
3282	defined to be C<0>, then they are not.	3766	defined to be C<0>, then they are not.
3283		3767
3284	=item EV_MINIMAL	3768	=item EV_MINIMAL
3285		3769
3286	If you need to shave off some kilobytes of code at the expense of some	3770	If you need to shave off some kilobytes of code at the expense of some
3287	speed, define this symbol to C<1>. Currently this is used to override some	3771	speed (but with the full API), define this symbol to C<1>. Currently this
3288	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3772	is used to override some inlining decisions, saves roughly 30% code size
3289	much smaller 2-heap for timer management over the default 4-heap.	3773	on amd64. It also selects a much smaller 2-heap for timer management over
		3774	the default 4-heap.
		3775
		3776	You can save even more by disabling watcher types you do not need
		3777	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3778	(C<-DNDEBUG>) will usually reduce code size a lot.
		3779
		3780	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3781	provide a bare-bones event library. See C<ev.h> for details on what parts
		3782	of the API are still available, and do not complain if this subset changes
		3783	over time.
3290		3784
3291	=item EV_PID_HASHSIZE	3785	=item EV_PID_HASHSIZE
3292		3786
3293	C<ev_child> watchers use a small hash table to distribute workload by	3787	C<ev_child> watchers use a small hash table to distribute workload by
3294	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3788	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3480	default loop and triggering an C<ev_async> watcher from the default loop	3974	default loop and triggering an C<ev_async> watcher from the default loop
3481	watcher callback into the event loop interested in the signal.	3975	watcher callback into the event loop interested in the signal.
3482		3976
3483	=back	3977	=back
3484		3978
		3979	=head4 THREAD LOCKING EXAMPLE
		3980
		3981	Here is a fictitious example of how to run an event loop in a different
		3982	thread than where callbacks are being invoked and watchers are
		3983	created/added/removed.
		3984
		3985	For a real-world example, see the C<EV::Loop::Async> perl module,
		3986	which uses exactly this technique (which is suited for many high-level
		3987	languages).
		3988
		3989	The example uses a pthread mutex to protect the loop data, a condition
		3990	variable to wait for callback invocations, an async watcher to notify the
		3991	event loop thread and an unspecified mechanism to wake up the main thread.
		3992
		3993	First, you need to associate some data with the event loop:
		3994
		3995	typedef struct {
		3996	mutex_t lock; /* global loop lock */
		3997	ev_async async_w;
		3998	thread_t tid;
		3999	cond_t invoke_cv;
		4000	} userdata;
		4001
		4002	void prepare_loop (EV_P)
		4003	{
		4004	// for simplicity, we use a static userdata struct.
		4005	static userdata u;
		4006
		4007	ev_async_init (&u->async_w, async_cb);
		4008	ev_async_start (EV_A_ &u->async_w);
		4009
		4010	pthread_mutex_init (&u->lock, 0);
		4011	pthread_cond_init (&u->invoke_cv, 0);
		4012
		4013	// now associate this with the loop
		4014	ev_set_userdata (EV_A_ u);
		4015	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4016	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4017
		4018	// then create the thread running ev_loop
		4019	pthread_create (&u->tid, 0, l_run, EV_A);
		4020	}
		4021
		4022	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4023	solely to wake up the event loop so it takes notice of any new watchers
		4024	that might have been added:
		4025
		4026	static void
		4027	async_cb (EV_P_ ev_async *w, int revents)
		4028	{
		4029	// just used for the side effects
		4030	}
		4031
		4032	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4033	protecting the loop data, respectively.
		4034
		4035	static void
		4036	l_release (EV_P)
		4037	{
		4038	userdata *u = ev_userdata (EV_A);
		4039	pthread_mutex_unlock (&u->lock);
		4040	}
		4041
		4042	static void
		4043	l_acquire (EV_P)
		4044	{
		4045	userdata *u = ev_userdata (EV_A);
		4046	pthread_mutex_lock (&u->lock);
		4047	}
		4048
		4049	The event loop thread first acquires the mutex, and then jumps straight
		4050	into C<ev_loop>:
		4051
		4052	void *
		4053	l_run (void *thr_arg)
		4054	{
		4055	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4056
		4057	l_acquire (EV_A);
		4058	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4059	ev_loop (EV_A_ 0);
		4060	l_release (EV_A);
		4061
		4062	return 0;
		4063	}
		4064
		4065	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4066	signal the main thread via some unspecified mechanism (signals? pipe
		4067	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4068	have been called (in a while loop because a) spurious wakeups are possible
		4069	and b) skipping inter-thread-communication when there are no pending
		4070	watchers is very beneficial):
		4071
		4072	static void
		4073	l_invoke (EV_P)
		4074	{
		4075	userdata *u = ev_userdata (EV_A);
		4076
		4077	while (ev_pending_count (EV_A))
		4078	{
		4079	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4080	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4081	}
		4082	}
		4083
		4084	Now, whenever the main thread gets told to invoke pending watchers, it
		4085	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4086	thread to continue:
		4087
		4088	static void
		4089	real_invoke_pending (EV_P)
		4090	{
		4091	userdata *u = ev_userdata (EV_A);
		4092
		4093	pthread_mutex_lock (&u->lock);
		4094	ev_invoke_pending (EV_A);
		4095	pthread_cond_signal (&u->invoke_cv);
		4096	pthread_mutex_unlock (&u->lock);
		4097	}
		4098
		4099	Whenever you want to start/stop a watcher or do other modifications to an
		4100	event loop, you will now have to lock:
		4101
		4102	ev_timer timeout_watcher;
		4103	userdata *u = ev_userdata (EV_A);
		4104
		4105	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4106
		4107	pthread_mutex_lock (&u->lock);
		4108	ev_timer_start (EV_A_ &timeout_watcher);
		4109	ev_async_send (EV_A_ &u->async_w);
		4110	pthread_mutex_unlock (&u->lock);
		4111
		4112	Note that sending the C<ev_async> watcher is required because otherwise
		4113	an event loop currently blocking in the kernel will have no knowledge
		4114	about the newly added timer. By waking up the loop it will pick up any new
		4115	watchers in the next event loop iteration.
		4116
3485	=head3 COROUTINES	4117	=head3 COROUTINES
3486		4118
3487	Libev is very accommodating to coroutines ("cooperative threads"):	4119	Libev is very accommodating to coroutines ("cooperative threads"):
3488	libev fully supports nesting calls to its functions from different	4120	libev fully supports nesting calls to its functions from different
3489	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4121	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3490	different coroutines, and switch freely between both coroutines running the	4122	different coroutines, and switch freely between both coroutines running
3491	loop, as long as you don't confuse yourself). The only exception is that	4123	the loop, as long as you don't confuse yourself). The only exception is
3492	you must not do this from C<ev_periodic> reschedule callbacks.	4124	that you must not do this from C<ev_periodic> reschedule callbacks.
3493		4125
3494	Care has been taken to ensure that libev does not keep local state inside	4126	Care has been taken to ensure that libev does not keep local state inside
3495	C<ev_loop>, and other calls do not usually allow for coroutine switches as	4127	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3496	they do not clal any callbacks.	4128	they do not call any callbacks.
3497		4129
3498	=head2 COMPILER WARNINGS	4130	=head2 COMPILER WARNINGS
3499		4131
3500	Depending on your compiler and compiler settings, you might get no or a	4132	Depending on your compiler and compiler settings, you might get no or a
3501	lot of warnings when compiling libev code. Some people are apparently	4133	lot of warnings when compiling libev code. Some people are apparently
…		…
3535	==2274== definitely lost: 0 bytes in 0 blocks.	4167	==2274== definitely lost: 0 bytes in 0 blocks.
3536	==2274== possibly lost: 0 bytes in 0 blocks.	4168	==2274== possibly lost: 0 bytes in 0 blocks.
3537	==2274== still reachable: 256 bytes in 1 blocks.	4169	==2274== still reachable: 256 bytes in 1 blocks.
3538		4170
3539	Then there is no memory leak, just as memory accounted to global variables	4171	Then there is no memory leak, just as memory accounted to global variables
3540	is not a memleak - the memory is still being refernced, and didn't leak.	4172	is not a memleak - the memory is still being referenced, and didn't leak.
3541		4173
3542	Similarly, under some circumstances, valgrind might report kernel bugs	4174	Similarly, under some circumstances, valgrind might report kernel bugs
3543	as if it were a bug in libev (e.g. in realloc or in the poll backend,	4175	as if it were a bug in libev (e.g. in realloc or in the poll backend,
3544	although an acceptable workaround has been found here), or it might be	4176	although an acceptable workaround has been found here), or it might be
3545	confused.	4177	confused.
…		…
3574	way (note also that glib is the slowest event library known to man).	4206	way (note also that glib is the slowest event library known to man).
3575		4207
3576	There is no supported compilation method available on windows except	4208	There is no supported compilation method available on windows except
3577	embedding it into other applications.	4209	embedding it into other applications.
3578		4210
		4211	Sensible signal handling is officially unsupported by Microsoft - libev
		4212	tries its best, but under most conditions, signals will simply not work.
		4213
3579	Not a libev limitation but worth mentioning: windows apparently doesn't	4214	Not a libev limitation but worth mentioning: windows apparently doesn't
3580	accept large writes: instead of resulting in a partial write, windows will	4215	accept large writes: instead of resulting in a partial write, windows will
3581	either accept everything or return C<ENOBUFS> if the buffer is too large,	4216	either accept everything or return C<ENOBUFS> if the buffer is too large,
3582	so make sure you only write small amounts into your sockets (less than a	4217	so make sure you only write small amounts into your sockets (less than a
3583	megabyte seems safe, but this apparently depends on the amount of memory	4218	megabyte seems safe, but this apparently depends on the amount of memory
…		…
3587	the abysmal performance of winsockets, using a large number of sockets	4222	the abysmal performance of winsockets, using a large number of sockets
3588	is not recommended (and not reasonable). If your program needs to use	4223	is not recommended (and not reasonable). If your program needs to use
3589	more than a hundred or so sockets, then likely it needs to use a totally	4224	more than a hundred or so sockets, then likely it needs to use a totally
3590	different implementation for windows, as libev offers the POSIX readiness	4225	different implementation for windows, as libev offers the POSIX readiness
3591	notification model, which cannot be implemented efficiently on windows	4226	notification model, which cannot be implemented efficiently on windows
3592	(Microsoft monopoly games).	4227	(due to Microsoft monopoly games).
3593		4228
3594	A typical way to use libev under windows is to embed it (see the embedding	4229	A typical way to use libev under windows is to embed it (see the embedding
3595	section for details) and use the following F<evwrap.h> header file instead	4230	section for details) and use the following F<evwrap.h> header file instead
3596	of F<ev.h>:	4231	of F<ev.h>:
3597		4232
…		…
3633		4268
3634	Early versions of winsocket's select only supported waiting for a maximum	4269	Early versions of winsocket's select only supported waiting for a maximum
3635	of C<64> handles (probably owning to the fact that all windows kernels	4270	of C<64> handles (probably owning to the fact that all windows kernels
3636	can only wait for C<64> things at the same time internally; Microsoft	4271	can only wait for C<64> things at the same time internally; Microsoft
3637	recommends spawning a chain of threads and wait for 63 handles and the	4272	recommends spawning a chain of threads and wait for 63 handles and the
3638	previous thread in each. Great).	4273	previous thread in each. Sounds great!).
3639		4274
3640	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4275	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3641	to some high number (e.g. C<2048>) before compiling the winsocket select	4276	to some high number (e.g. C<2048>) before compiling the winsocket select
3642	call (which might be in libev or elsewhere, for example, perl does its own	4277	call (which might be in libev or elsewhere, for example, perl and many
3643	select emulation on windows).	4278	other interpreters do their own select emulation on windows).
3644		4279
3645	Another limit is the number of file descriptors in the Microsoft runtime	4280	Another limit is the number of file descriptors in the Microsoft runtime
3646	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4281	libraries, which by default is C<64> (there must be a hidden I<64>
3647	or something like this inside Microsoft). You can increase this by calling	4282	fetish or something like this inside Microsoft). You can increase this
3648	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4283	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3649	arbitrary limit), but is broken in many versions of the Microsoft runtime	4284	(another arbitrary limit), but is broken in many versions of the Microsoft
3650	libraries.
3651
3652	This might get you to about C<512> or C<2048> sockets (depending on	4285	runtime libraries. This might get you to about C<512> or C<2048> sockets
3653	windows version and/or the phase of the moon). To get more, you need to	4286	(depending on windows version and/or the phase of the moon). To get more,
3654	wrap all I/O functions and provide your own fd management, but the cost of	4287	you need to wrap all I/O functions and provide your own fd management, but
3655	calling select (O(n²)) will likely make this unworkable.	4288	the cost of calling select (O(n²)) will likely make this unworkable.
3656		4289
3657	=back	4290	=back
3658		4291
3659	=head2 PORTABILITY REQUIREMENTS	4292	=head2 PORTABILITY REQUIREMENTS
3660		4293
…		…
3703	=item C<double> must hold a time value in seconds with enough accuracy	4336	=item C<double> must hold a time value in seconds with enough accuracy
3704		4337
3705	The type C<double> is used to represent timestamps. It is required to	4338	The type C<double> is used to represent timestamps. It is required to
3706	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4339	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3707	enough for at least into the year 4000. This requirement is fulfilled by	4340	enough for at least into the year 4000. This requirement is fulfilled by
3708	implementations implementing IEEE 754 (basically all existing ones).	4341	implementations implementing IEEE 754, which is basically all existing
		4342	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4343	2200.
3709		4344
3710	=back	4345	=back
3711		4346
3712	If you know of other additional requirements drop me a note.	4347	If you know of other additional requirements drop me a note.
3713		4348
…		…
3781	involves iterating over all running async watchers or all signal numbers.	4416	involves iterating over all running async watchers or all signal numbers.
3782		4417
3783	=back	4418	=back
3784		4419
3785		4420
		4421	=head1 GLOSSARY
		4422
		4423	=over 4
		4424
		4425	=item active
		4426
		4427	A watcher is active as long as it has been started (has been attached to
		4428	an event loop) but not yet stopped (disassociated from the event loop).
		4429
		4430	=item application
		4431
		4432	In this document, an application is whatever is using libev.
		4433
		4434	=item callback
		4435
		4436	The address of a function that is called when some event has been
		4437	detected. Callbacks are being passed the event loop, the watcher that
		4438	received the event, and the actual event bitset.
		4439
		4440	=item callback invocation
		4441
		4442	The act of calling the callback associated with a watcher.
		4443
		4444	=item event
		4445
		4446	A change of state of some external event, such as data now being available
		4447	for reading on a file descriptor, time having passed or simply not having
		4448	any other events happening anymore.
		4449
		4450	In libev, events are represented as single bits (such as C<EV_READ> or
		4451	C<EV_TIMEOUT>).
		4452
		4453	=item event library
		4454
		4455	A software package implementing an event model and loop.
		4456
		4457	=item event loop
		4458
		4459	An entity that handles and processes external events and converts them
		4460	into callback invocations.
		4461
		4462	=item event model
		4463
		4464	The model used to describe how an event loop handles and processes
		4465	watchers and events.
		4466
		4467	=item pending
		4468
		4469	A watcher is pending as soon as the corresponding event has been detected,
		4470	and stops being pending as soon as the watcher will be invoked or its
		4471	pending status is explicitly cleared by the application.
		4472
		4473	A watcher can be pending, but not active. Stopping a watcher also clears
		4474	its pending status.
		4475
		4476	=item real time
		4477
		4478	The physical time that is observed. It is apparently strictly monotonic :)
		4479
		4480	=item wall-clock time
		4481
		4482	The time and date as shown on clocks. Unlike real time, it can actually
		4483	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4484	clock.
		4485
		4486	=item watcher
		4487
		4488	A data structure that describes interest in certain events. Watchers need
		4489	to be started (attached to an event loop) before they can receive events.
		4490
		4491	=item watcher invocation
		4492
		4493	The act of calling the callback associated with a watcher.
		4494
		4495	=back
		4496
3786	=head1 AUTHOR	4497	=head1 AUTHOR
3787		4498
3788	Marc Lehmann <libev@schmorp.de>.	4499	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3789		4500

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