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…		…
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
		14	#include <stdio.h> // for puts
		15
14	// every watcher type has its own typedef'd struct	16	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	17	// with the name ev_TYPE
16	ev_io stdin_watcher;	18	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
18		20
19	// all watcher callbacks have a similar signature	21	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	22	// this callback is called when data is readable on stdin
21	static void	23	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	25	{
24	puts ("stdin ready");	26	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	27	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	28	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	29	ev_io_stop (EV_A_ w);
…		…
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	32	ev_unloop (EV_A_ EVUNLOOP_ALL);
31	}	33	}
32		34
33	// another callback, this time for a time-out	35	// another callback, this time for a time-out
34	static void	36	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	38	{
37	puts ("timeout");	39	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	40	// this causes the innermost ev_loop to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	41	ev_unloop (EV_A_ EVUNLOOP_ONE);
40	}	42	}
…		…
60		62
61	// unloop was called, so exit	63	// unloop was called, so exit
62	return 0;	64	return 0;
63	}	65	}
64		66
65	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
66		70
67	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
70		84
71	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	87	these event sources and provide your program with events.
74		88
…		…
103	Libev is very configurable. In this manual the default (and most common)	117	Libev is very configurable. In this manual the default (and most common)
104	configuration will be described, which supports multiple event loops. For	118	configuration will be described, which supports multiple event loops. For
105	more info about various configuration options please have a look at	119	more info about various configuration options please have a look at
106	B<EMBED> section in this manual. If libev was configured without support	120	B<EMBED> section in this manual. If libev was configured without support
107	for multiple event loops, then all functions taking an initial argument of	121	for multiple event loops, then all functions taking an initial argument of
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	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
…		…
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
215	recommended ones.	229	recommended ones.
216		230
217	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
218		232
219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
220		234
221	Sets the allocation function to use (the prototype is similar - the	235	Sets the allocation function to use (the prototype is similar - the
222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	236	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
223	used to allocate and free memory (no surprises here). If it returns zero	237	used to allocate and free memory (no surprises here). If it returns zero
224	when memory needs to be allocated (C<size != 0>), the library might abort	238	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
250	}	264	}
251		265
252	...	266	...
253	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
254		268
255	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
256		270
257	Set the callback function to call on a retryable system call error (such	271	Set the callback function to call on a retryable system call error (such
258	as failed select, poll, epoll_wait). The message is a printable string	272	as failed select, poll, epoll_wait). The message is a printable string
259	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
260	callback is set, then libev will expect it to remedy the situation, no	274	callback is set, then libev will expect it to remedy the situation, no
…		…
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<struct 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, i.e.	430	watchers for a file descriptor until it has been closed, if possible,
402	keep at least one watcher active per fd at all times.	431	i.e. keep at least one watcher active per fd at all times. Stopping and
		432	starting a watcher (without re-setting it) also usually doesn't cause
		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.
403		440
404	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
405	all kernel versions tested so far.	442	all kernel versions tested so far.
406		443
407	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	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
411		448
412	Kqueue deserves special mention, as at the time of this writing, it	449	Kqueue deserves special mention, as at the time of this writing, it
413	was broken on all BSDs except NetBSD (usually it doesn't work reliably	450	was broken on all BSDs except NetBSD (usually it doesn't work reliably
414	with anything but sockets and pipes, except on Darwin, where of course	451	with anything but sockets and pipes, except on Darwin, where of course
415	it's completely useless). For this reason it's not being "auto-detected"	452	it's completely useless). Unlike epoll, however, whose brokenness
		453	is by design, these kqueue bugs can (and eventually will) be fixed
		454	without API changes to existing programs. For this reason it's not being
416	unless you explicitly specify it explicitly in the flags (i.e. using	455	"auto-detected" unless you explicitly specify it in the flags (i.e. using
417	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
418	system like NetBSD.	457	system like NetBSD.
419		458
420	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
421	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		462
424	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
425	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
426	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
427	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
428	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
429	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
430		470
431	This backend usually performs well under most conditions.	471	This backend usually performs well under most conditions.
432		472
433	While nominally embeddable in other event loops, this doesn't work	473	While nominally embeddable in other event loops, this doesn't work
434	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
435	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
436	(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
437	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	477	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
438	sockets.	478	also broken on OS X)) and, did I mention it, using it only for sockets.
439		479
440	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
441	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
442	C<NOTE_EOF>.	482	C<NOTE_EOF>.
443		483
…		…
460	While this backend scales well, it requires one system call per active	500	While this backend scales well, it requires one system call per active
461	file descriptor per loop iteration. For small and medium numbers of file	501	file descriptor per loop iteration. For small and medium numbers of file
462	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	502	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
463	might perform better.	503	might perform better.
464		504
465	On the positive side, ignoring the spurious readiness notifications, this	505	On the positive side, with the exception of the spurious readiness
466	backend actually performed to specification in all tests and is fully	506	notifications, this backend actually performed fully to specification
467	embeddable, which is a rare feat among the OS-specific backends.	507	in all tests and is fully embeddable, which is a rare feat among the
		508	OS-specific backends (I vastly prefer correctness over speed hacks).
468		509
469	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
470	C<EVBACKEND_POLL>.	511	C<EVBACKEND_POLL>.
471		512
472	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
…		…
481		522
482	If one or more of these are or'ed into the flags value, then only these	523	If one or more of these are or'ed into the flags value, then only these
483	backends will be tried (in the reverse order as listed here). If none are	524	backends will be tried (in the reverse order as listed here). If none are
484	specified, all backends in C<ev_recommended_backends ()> will be tried.	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
485		526
486	The most typical usage is like this:	527	Example: This is the most typical usage.
487		528
488	if (!ev_default_loop (0))	529	if (!ev_default_loop (0))
489	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
490		531
491	Restrict libev to the select and poll backends, and do not allow	532	Example: Restrict libev to the select and poll backends, and do not allow
492	environment settings to be taken into account:	533	environment settings to be taken into account:
493		534
494	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
495		536
496	Use whatever libev has to offer, but make sure that kqueue is used if	537	Example: Use whatever libev has to offer, but make sure that kqueue is
497	available (warning, breaks stuff, best use only with your own private	538	used if available (warning, breaks stuff, best use only with your own
498	event loop and only if you know the OS supports your types of fds):	539	private event loop and only if you know the OS supports your types of
		540	fds):
499		541
500	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
501		543
502	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
503		545
…		…
524	responsibility to either stop all watchers cleanly yourself I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
525	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
526	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
527	for example).	569	for example).
528		570
529	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
530	this function, and related watchers (such as signal and child watchers)	572	handlers), will not be freed by this function, and related watchers (such
531	would need to be stopped manually.	573	as signal and child watchers) would need to be stopped manually.
532		574
533	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
534	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
535	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
536	C<ev_loop_new> and C<ev_loop_destroy>).	578	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
561		603
562	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
563		605
564	Like C<ev_default_fork>, but acts on an event loop created by	606	Like C<ev_default_fork>, but acts on an event loop created by
565	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	607	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
566	after fork, and how you do this is entirely your own problem.	608	after fork that you want to re-use in the child, and how you do this is
		609	entirely your own problem.
567		610
568	=item int ev_is_default_loop (loop)	611	=item int ev_is_default_loop (loop)
569		612
570	Returns true when the given loop actually is the default loop, false otherwise.	613	Returns true when the given loop is, in fact, the default loop, and false
		614	otherwise.
571		615
572	=item unsigned int ev_loop_count (loop)	616	=item unsigned int ev_loop_count (loop)
573		617
574	Returns the count of loop iterations for the loop, which is identical to	618	Returns the count of loop iterations for the loop, which is identical to
575	the number of times libev did poll for new events. It starts at C<0> and	619	the number of times libev did poll for new events. It starts at C<0> and
…		…
600		644
601	This function is rarely useful, but when some event callback runs for a	645	This function is rarely useful, but when some event callback runs for a
602	very long time without entering the event loop, updating libev's idea of	646	very long time without entering the event loop, updating libev's idea of
603	the current time is a good idea.	647	the current time is a good idea.
604		648
605	See also "The special problem of time updates" in the C<ev_timer> section.	649	See also L<The special problem of time updates> in the C<ev_timer> section.
		650
		651	=item ev_suspend (loop)
		652
		653	=item ev_resume (loop)
		654
		655	These two functions suspend and resume a loop, for use when the loop is
		656	not used for a while and timeouts should not be processed.
		657
		658	A typical use case would be an interactive program such as a game: When
		659	the user presses C<^Z> to suspend the game and resumes it an hour later it
		660	would be best to handle timeouts as if no time had actually passed while
		661	the program was suspended. This can be achieved by calling C<ev_suspend>
		662	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		663	C<ev_resume> directly afterwards to resume timer processing.
		664
		665	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		666	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		667	will be rescheduled (that is, they will lose any events that would have
		668	occured while suspended).
		669
		670	After calling C<ev_suspend> you B<must not> call I<any> function on the
		671	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		672	without a previous call to C<ev_suspend>.
		673
		674	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		675	event loop time (see C<ev_now_update>).
606		676
607	=item ev_loop (loop, int flags)	677	=item ev_loop (loop, int flags)
608		678
609	Finally, this is it, the event handler. This function usually is called	679	Finally, this is it, the event handler. This function usually is called
610	after you initialised all your watchers and you want to start handling	680	after you initialised all your watchers and you want to start handling
…		…
613	If the flags argument is specified as C<0>, it will not return until	683	If the flags argument is specified as C<0>, it will not return until
614	either no event watchers are active anymore or C<ev_unloop> was called.	684	either no event watchers are active anymore or C<ev_unloop> was called.
615		685
616	Please note that an explicit C<ev_unloop> is usually better than	686	Please note that an explicit C<ev_unloop> is usually better than
617	relying on all watchers to be stopped when deciding when a program has	687	relying on all watchers to be stopped when deciding when a program has
618	finished (especially in interactive programs), but having a program that	688	finished (especially in interactive programs), but having a program
619	automatically loops as long as it has to and no longer by virtue of	689	that automatically loops as long as it has to and no longer by virtue
620	relying on its watchers stopping correctly is a thing of beauty.	690	of relying on its watchers stopping correctly, that is truly a thing of
		691	beauty.
621		692
622	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	693	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
623	those events and any outstanding ones, but will not block your process in	694	those events and any already outstanding ones, but will not block your
624	case there are no events and will return after one iteration of the loop.	695	process in case there are no events and will return after one iteration of
		696	the loop.
625		697
626	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	698	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
627	necessary) and will handle those and any outstanding ones. It will block	699	necessary) and will handle those and any already outstanding ones. It
628	your process until at least one new event arrives, and will return after	700	will block your process until at least one new event arrives (which could
629	one iteration of the loop. This is useful if you are waiting for some	701	be an event internal to libev itself, so there is no guarantee that a
630	external event in conjunction with something not expressible using other	702	user-registered callback will be called), and will return after one
		703	iteration of the loop.
		704
		705	This is useful if you are waiting for some external event in conjunction
		706	with something not expressible using other libev watchers (i.e. "roll your
631	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	707	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
632	usually a better approach for this kind of thing.	708	usually a better approach for this kind of thing.
633		709
634	Here are the gory details of what C<ev_loop> does:	710	Here are the gory details of what C<ev_loop> does:
635		711
636	- Before the first iteration, call any pending watchers.	712	- Before the first iteration, call any pending watchers.
…		…
646	any active watchers at all will result in not sleeping).	722	any active watchers at all will result in not sleeping).
647	- Sleep if the I/O and timer collect interval say so.	723	- Sleep if the I/O and timer collect interval say so.
648	- Block the process, waiting for any events.	724	- Block the process, waiting for any events.
649	- Queue all outstanding I/O (fd) events.	725	- Queue all outstanding I/O (fd) events.
650	- Update the "event loop time" (ev_now ()), and do time jump adjustments.	726	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
651	- Queue all outstanding timers.	727	- Queue all expired timers.
652	- Queue all outstanding periodics.	728	- Queue all expired periodics.
653	- Unless any events are pending now, queue all idle watchers.	729	- Unless any events are pending now, queue all idle watchers.
654	- Queue all check watchers.	730	- Queue all check watchers.
655	- Call all queued watchers in reverse order (i.e. check watchers first).	731	- Call all queued watchers in reverse order (i.e. check watchers first).
656	Signals and child watchers are implemented as I/O watchers, and will	732	Signals and child watchers are implemented as I/O watchers, and will
657	be handled here by queueing them when their watcher gets executed.	733	be handled here by queueing them when their watcher gets executed.
…		…
674	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	750	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
675	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	751	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
676		752
677	This "unloop state" will be cleared when entering C<ev_loop> again.	753	This "unloop state" will be cleared when entering C<ev_loop> again.
678		754
		755	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		756
679	=item ev_ref (loop)	757	=item ev_ref (loop)
680		758
681	=item ev_unref (loop)	759	=item ev_unref (loop)
682		760
683	Ref/unref can be used to add or remove a reference count on the event	761	Ref/unref can be used to add or remove a reference count on the event
684	loop: Every watcher keeps one reference, and as long as the reference	762	loop: Every watcher keeps one reference, and as long as the reference
685	count is nonzero, C<ev_loop> will not return on its own. If you have	763	count is nonzero, C<ev_loop> will not return on its own.
		764
686	a watcher you never unregister that should not keep C<ev_loop> from	765	If you have a watcher you never unregister that should not keep C<ev_loop>
687	returning, ev_unref() after starting, and ev_ref() before stopping it. For	766	from returning, call ev_unref() after starting, and ev_ref() before
		767	stopping it.
		768
688	example, libev itself uses this for its internal signal pipe: It is not	769	As an example, libev itself uses this for its internal signal pipe: It
689	visible to the libev user and should not keep C<ev_loop> from exiting if	770	is not visible to the libev user and should not keep C<ev_loop> from
690	no event watchers registered by it are active. It is also an excellent	771	exiting if no event watchers registered by it are active. It is also an
691	way to do this for generic recurring timers or from within third-party	772	excellent way to do this for generic recurring timers or from within
692	libraries. Just remember to I<unref after start> and I<ref before stop>	773	third-party libraries. Just remember to I<unref after start> and I<ref
693	(but only if the watcher wasn't active before, or was active before,	774	before stop> (but only if the watcher wasn't active before, or was active
694	respectively).	775	before, respectively. Note also that libev might stop watchers itself
		776	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		777	in the callback).
695		778
696	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	779	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
697	running when nothing else is active.	780	running when nothing else is active.
698		781
699	struct ev_signal exitsig;	782	ev_signal exitsig;
700	ev_signal_init (&exitsig, sig_cb, SIGINT);	783	ev_signal_init (&exitsig, sig_cb, SIGINT);
701	ev_signal_start (loop, &exitsig);	784	ev_signal_start (loop, &exitsig);
702	evf_unref (loop);	785	evf_unref (loop);
703		786
704	Example: For some weird reason, unregister the above signal handler again.	787	Example: For some weird reason, unregister the above signal handler again.
…		…
718	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	801	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
719	allows libev to delay invocation of I/O and timer/periodic callbacks	802	allows libev to delay invocation of I/O and timer/periodic callbacks
720	to increase efficiency of loop iterations (or to increase power-saving	803	to increase efficiency of loop iterations (or to increase power-saving
721	opportunities).	804	opportunities).
722		805
723	The background is that sometimes your program runs just fast enough to	806	The idea is that sometimes your program runs just fast enough to handle
724	handle one (or very few) event(s) per loop iteration. While this makes	807	one (or very few) event(s) per loop iteration. While this makes the
725	the program responsive, it also wastes a lot of CPU time to poll for new	808	program responsive, it also wastes a lot of CPU time to poll for new
726	events, especially with backends like C<select ()> which have a high	809	events, especially with backends like C<select ()> which have a high
727	overhead for the actual polling but can deliver many events at once.	810	overhead for the actual polling but can deliver many events at once.
728		811
729	By setting a higher I<io collect interval> you allow libev to spend more	812	By setting a higher I<io collect interval> you allow libev to spend more
730	time collecting I/O events, so you can handle more events per iteration,	813	time collecting I/O events, so you can handle more events per iteration,
731	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	814	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
732	C<ev_timer>) will be not affected. Setting this to a non-null value will	815	C<ev_timer>) will be not affected. Setting this to a non-null value will
733	introduce an additional C<ev_sleep ()> call into most loop iterations.	816	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		817	sleep time ensures that libev will not poll for I/O events more often then
		818	once per this interval, on average.
734		819
735	Likewise, by setting a higher I<timeout collect interval> you allow libev	820	Likewise, by setting a higher I<timeout collect interval> you allow libev
736	to spend more time collecting timeouts, at the expense of increased	821	to spend more time collecting timeouts, at the expense of increased
737	latency (the watcher callback will be called later). C<ev_io> watchers	822	latency/jitter/inexactness (the watcher callback will be called
738	will not be affected. Setting this to a non-null value will not introduce	823	later). C<ev_io> watchers will not be affected. Setting this to a non-null
739	any overhead in libev.	824	value will not introduce any overhead in libev.
740		825
741	Many (busy) programs can usually benefit by setting the I/O collect	826	Many (busy) programs can usually benefit by setting the I/O collect
742	interval to a value near C<0.1> or so, which is often enough for	827	interval to a value near C<0.1> or so, which is often enough for
743	interactive servers (of course not for games), likewise for timeouts. It	828	interactive servers (of course not for games), likewise for timeouts. It
744	usually doesn't make much sense to set it to a lower value than C<0.01>,	829	usually doesn't make much sense to set it to a lower value than C<0.01>,
745	as this approaches the timing granularity of most systems.	830	as this approaches the timing granularity of most systems. Note that if
		831	you do transactions with the outside world and you can't increase the
		832	parallelity, then this setting will limit your transaction rate (if you
		833	need to poll once per transaction and the I/O collect interval is 0.01,
		834	then you can't do more than 100 transations per second).
746		835
747	Setting the I<timeout collect interval> can improve the opportunity for	836	Setting the I<timeout collect interval> can improve the opportunity for
748	saving power, as the program will "bundle" timer callback invocations that	837	saving power, as the program will "bundle" timer callback invocations that
749	are "near" in time together, by delaying some, thus reducing the number of	838	are "near" in time together, by delaying some, thus reducing the number of
750	times the process sleeps and wakes up again. Another useful technique to	839	times the process sleeps and wakes up again. Another useful technique to
751	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	840	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
752	they fire on, say, one-second boundaries only.	841	they fire on, say, one-second boundaries only.
753		842
		843	Example: we only need 0.1s timeout granularity, and we wish not to poll
		844	more often than 100 times per second:
		845
		846	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		847	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		848
754	=item ev_loop_verify (loop)	849	=item ev_loop_verify (loop)
755		850
756	This function only does something when C<EV_VERIFY> support has been	851	This function only does something when C<EV_VERIFY> support has been
757	compiled in. It tries to go through all internal structures and checks	852	compiled in, which is the default for non-minimal builds. It tries to go
758	them for validity. If anything is found to be inconsistent, it will print	853	through all internal structures and checks them for validity. If anything
759	an error message to standard error and call C<abort ()>.	854	is found to be inconsistent, it will print an error message to standard
		855	error and call C<abort ()>.
760		856
761	This can be used to catch bugs inside libev itself: under normal	857	This can be used to catch bugs inside libev itself: under normal
762	circumstances, this function will never abort as of course libev keeps its	858	circumstances, this function will never abort as of course libev keeps its
763	data structures consistent.	859	data structures consistent.
764		860
765	=back	861	=back
766		862
767		863
768	=head1 ANATOMY OF A WATCHER	864	=head1 ANATOMY OF A WATCHER
769		865
		866	In the following description, uppercase C<TYPE> in names stands for the
		867	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		868	watchers and C<ev_io_start> for I/O watchers.
		869
770	A watcher is a structure that you create and register to record your	870	A watcher is a structure that you create and register to record your
771	interest in some event. For instance, if you want to wait for STDIN to	871	interest in some event. For instance, if you want to wait for STDIN to
772	become readable, you would create an C<ev_io> watcher for that:	872	become readable, you would create an C<ev_io> watcher for that:
773		873
774	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	874	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
775	{	875	{
776	ev_io_stop (w);	876	ev_io_stop (w);
777	ev_unloop (loop, EVUNLOOP_ALL);	877	ev_unloop (loop, EVUNLOOP_ALL);
778	}	878	}
779		879
780	struct ev_loop *loop = ev_default_loop (0);	880	struct ev_loop *loop = ev_default_loop (0);
		881
781	struct ev_io stdin_watcher;	882	ev_io stdin_watcher;
		883
782	ev_init (&stdin_watcher, my_cb);	884	ev_init (&stdin_watcher, my_cb);
783	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	885	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
784	ev_io_start (loop, &stdin_watcher);	886	ev_io_start (loop, &stdin_watcher);
		887
785	ev_loop (loop, 0);	888	ev_loop (loop, 0);
786		889
787	As you can see, you are responsible for allocating the memory for your	890	As you can see, you are responsible for allocating the memory for your
788	watcher structures (and it is usually a bad idea to do this on the stack,	891	watcher structures (and it is I<usually> a bad idea to do this on the
789	although this can sometimes be quite valid).	892	stack).
		893
		894	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		895	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
790		896
791	Each watcher structure must be initialised by a call to C<ev_init	897	Each watcher structure must be initialised by a call to C<ev_init
792	(watcher *, callback)>, which expects a callback to be provided. This	898	(watcher *, callback)>, which expects a callback to be provided. This
793	callback gets invoked each time the event occurs (or, in the case of I/O	899	callback gets invoked each time the event occurs (or, in the case of I/O
794	watchers, each time the event loop detects that the file descriptor given	900	watchers, each time the event loop detects that the file descriptor given
795	is readable and/or writable).	901	is readable and/or writable).
796		902
797	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	903	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
798	with arguments specific to this watcher type. There is also a macro	904	macro to configure it, with arguments specific to the watcher type. There
799	to combine initialisation and setting in one call: C<< ev_<type>_init	905	is also a macro to combine initialisation and setting in one call: C<<
800	(watcher *, callback, ...) >>.	906	ev_TYPE_init (watcher *, callback, ...) >>.
801		907
802	To make the watcher actually watch out for events, you have to start it	908	To make the watcher actually watch out for events, you have to start it
803	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	909	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
804	*) >>), and you can stop watching for events at any time by calling the	910	*) >>), and you can stop watching for events at any time by calling the
805	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	911	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
806		912
807	As long as your watcher is active (has been started but not stopped) you	913	As long as your watcher is active (has been started but not stopped) you
808	must not touch the values stored in it. Most specifically you must never	914	must not touch the values stored in it. Most specifically you must never
809	reinitialise it or call its C<set> macro.	915	reinitialise it or call its C<ev_TYPE_set> macro.
810		916
811	Each and every callback receives the event loop pointer as first, the	917	Each and every callback receives the event loop pointer as first, the
812	registered watcher structure as second, and a bitset of received events as	918	registered watcher structure as second, and a bitset of received events as
813	third argument.	919	third argument.
814		920
…		…
872		978
873	=item C<EV_ASYNC>	979	=item C<EV_ASYNC>
874		980
875	The given async watcher has been asynchronously notified (see C<ev_async>).	981	The given async watcher has been asynchronously notified (see C<ev_async>).
876		982
		983	=item C<EV_CUSTOM>
		984
		985	Not ever sent (or otherwise used) by libev itself, but can be freely used
		986	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		987
877	=item C<EV_ERROR>	988	=item C<EV_ERROR>
878		989
879	An unspecified error has occurred, the watcher has been stopped. This might	990	An unspecified error has occurred, the watcher has been stopped. This might
880	happen because the watcher could not be properly started because libev	991	happen because the watcher could not be properly started because libev
881	ran out of memory, a file descriptor was found to be closed or any other	992	ran out of memory, a file descriptor was found to be closed or any other
		993	problem. Libev considers these application bugs.
		994
882	problem. You best act on it by reporting the problem and somehow coping	995	You best act on it by reporting the problem and somehow coping with the
883	with the watcher being stopped.	996	watcher being stopped. Note that well-written programs should not receive
		997	an error ever, so when your watcher receives it, this usually indicates a
		998	bug in your program.
884		999
885	Libev will usually signal a few "dummy" events together with an error,	1000	Libev will usually signal a few "dummy" events together with an error, for
886	for example it might indicate that a fd is readable or writable, and if	1001	example it might indicate that a fd is readable or writable, and if your
887	your callbacks is well-written it can just attempt the operation and cope	1002	callbacks is well-written it can just attempt the operation and cope with
888	with the error from read() or write(). This will not work in multi-threaded	1003	the error from read() or write(). This will not work in multi-threaded
889	programs, though, so beware.	1004	programs, though, as the fd could already be closed and reused for another
		1005	thing, so beware.
890		1006
891	=back	1007	=back
892		1008
893	=head2 GENERIC WATCHER FUNCTIONS	1009	=head2 GENERIC WATCHER FUNCTIONS
894
895	In the following description, C<TYPE> stands for the watcher type,
896	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
897		1010
898	=over 4	1011	=over 4
899		1012
900	=item C<ev_init> (ev_TYPE *watcher, callback)	1013	=item C<ev_init> (ev_TYPE *watcher, callback)
901		1014
…		…
907	which rolls both calls into one.	1020	which rolls both calls into one.
908		1021
909	You can reinitialise a watcher at any time as long as it has been stopped	1022	You can reinitialise a watcher at any time as long as it has been stopped
910	(or never started) and there are no pending events outstanding.	1023	(or never started) and there are no pending events outstanding.
911		1024
912	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1025	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
913	int revents)>.	1026	int revents)>.
		1027
		1028	Example: Initialise an C<ev_io> watcher in two steps.
		1029
		1030	ev_io w;
		1031	ev_init (&w, my_cb);
		1032	ev_io_set (&w, STDIN_FILENO, EV_READ);
914		1033
915	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1034	=item C<ev_TYPE_set> (ev_TYPE *, [args])
916		1035
917	This macro initialises the type-specific parts of a watcher. You need to	1036	This macro initialises the type-specific parts of a watcher. You need to
918	call C<ev_init> at least once before you call this macro, but you can	1037	call C<ev_init> at least once before you call this macro, but you can
…		…
921	difference to the C<ev_init> macro).	1040	difference to the C<ev_init> macro).
922		1041
923	Although some watcher types do not have type-specific arguments	1042	Although some watcher types do not have type-specific arguments
924	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1043	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
925		1044
		1045	See C<ev_init>, above, for an example.
		1046
926	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1047	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
927		1048
928	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1049	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
929	calls into a single call. This is the most convenient method to initialise	1050	calls into a single call. This is the most convenient method to initialise
930	a watcher. The same limitations apply, of course.	1051	a watcher. The same limitations apply, of course.
931		1052
		1053	Example: Initialise and set an C<ev_io> watcher in one step.
		1054
		1055	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1056
932	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1057	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
933		1058
934	Starts (activates) the given watcher. Only active watchers will receive	1059	Starts (activates) the given watcher. Only active watchers will receive
935	events. If the watcher is already active nothing will happen.	1060	events. If the watcher is already active nothing will happen.
936		1061
		1062	Example: Start the C<ev_io> watcher that is being abused as example in this
		1063	whole section.
		1064
		1065	ev_io_start (EV_DEFAULT_UC, &w);
		1066
937	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1067	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
938		1068
939	Stops the given watcher again (if active) and clears the pending	1069	Stops the given watcher if active, and clears the pending status (whether
		1070	the watcher was active or not).
		1071
940	status. It is possible that stopped watchers are pending (for example,	1072	It is possible that stopped watchers are pending - for example,
941	non-repeating timers are being stopped when they become pending), but	1073	non-repeating timers are being stopped when they become pending - but
942	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1074	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
943	you want to free or reuse the memory used by the watcher it is therefore a	1075	pending. If you want to free or reuse the memory used by the watcher it is
944	good idea to always call its C<ev_TYPE_stop> function.	1076	therefore a good idea to always call its C<ev_TYPE_stop> function.
945		1077
946	=item bool ev_is_active (ev_TYPE *watcher)	1078	=item bool ev_is_active (ev_TYPE *watcher)
947		1079
948	Returns a true value iff the watcher is active (i.e. it has been started	1080	Returns a true value iff the watcher is active (i.e. it has been started
949	and not yet been stopped). As long as a watcher is active you must not modify	1081	and not yet been stopped). As long as a watcher is active you must not modify
…		…
975	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1107	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
976	(default: C<-2>). Pending watchers with higher priority will be invoked	1108	(default: C<-2>). Pending watchers with higher priority will be invoked
977	before watchers with lower priority, but priority will not keep watchers	1109	before watchers with lower priority, but priority will not keep watchers
978	from being executed (except for C<ev_idle> watchers).	1110	from being executed (except for C<ev_idle> watchers).
979		1111
980	This means that priorities are I<only> used for ordering callback
981	invocation after new events have been received. This is useful, for
982	example, to reduce latency after idling, or more often, to bind two
983	watchers on the same event and make sure one is called first.
984
985	If you need to suppress invocation when higher priority events are pending	1112	If you need to suppress invocation when higher priority events are pending
986	you need to look at C<ev_idle> watchers, which provide this functionality.	1113	you need to look at C<ev_idle> watchers, which provide this functionality.
987		1114
988	You I<must not> change the priority of a watcher as long as it is active or	1115	You I<must not> change the priority of a watcher as long as it is active or
989	pending.	1116	pending.
990		1117
		1118	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1119	fine, as long as you do not mind that the priority value you query might
		1120	or might not have been clamped to the valid range.
		1121
991	The default priority used by watchers when no priority has been set is	1122	The default priority used by watchers when no priority has been set is
992	always C<0>, which is supposed to not be too high and not be too low :).	1123	always C<0>, which is supposed to not be too high and not be too low :).
993		1124
994	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1125	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
995	fine, as long as you do not mind that the priority value you query might	1126	priorities.
996	or might not have been adjusted to be within valid range.
997		1127
998	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1128	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
999		1129
1000	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1130	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1001	C<loop> nor C<revents> need to be valid as long as the watcher callback	1131	C<loop> nor C<revents> need to be valid as long as the watcher callback
1002	can deal with that fact.	1132	can deal with that fact, as both are simply passed through to the
		1133	callback.
1003		1134
1004	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1135	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1005		1136
1006	If the watcher is pending, this function returns clears its pending status	1137	If the watcher is pending, this function clears its pending status and
1007	and returns its C<revents> bitset (as if its callback was invoked). If the	1138	returns its C<revents> bitset (as if its callback was invoked). If the
1008	watcher isn't pending it does nothing and returns C<0>.	1139	watcher isn't pending it does nothing and returns C<0>.
1009		1140
		1141	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1142	callback to be invoked, which can be accomplished with this function.
		1143
1010	=back	1144	=back
1011		1145
1012		1146
1013	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1147	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1014		1148
1015	Each watcher has, by default, a member C<void *data> that you can change	1149	Each watcher has, by default, a member C<void *data> that you can change
1016	and read at any time, libev will completely ignore it. This can be used	1150	and read at any time: libev will completely ignore it. This can be used
1017	to associate arbitrary data with your watcher. If you need more data and	1151	to associate arbitrary data with your watcher. If you need more data and
1018	don't want to allocate memory and store a pointer to it in that data	1152	don't want to allocate memory and store a pointer to it in that data
1019	member, you can also "subclass" the watcher type and provide your own	1153	member, you can also "subclass" the watcher type and provide your own
1020	data:	1154	data:
1021		1155
1022	struct my_io	1156	struct my_io
1023	{	1157	{
1024	struct ev_io io;	1158	ev_io io;
1025	int otherfd;	1159	int otherfd;
1026	void *somedata;	1160	void *somedata;
1027	struct whatever *mostinteresting;	1161	struct whatever *mostinteresting;
1028	};	1162	};
1029		1163
…		…
1032	ev_io_init (&w.io, my_cb, fd, EV_READ);	1166	ev_io_init (&w.io, my_cb, fd, EV_READ);
1033		1167
1034	And since your callback will be called with a pointer to the watcher, you	1168	And since your callback will be called with a pointer to the watcher, you
1035	can cast it back to your own type:	1169	can cast it back to your own type:
1036		1170
1037	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1171	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1038	{	1172	{
1039	struct my_io *w = (struct my_io *)w_;	1173	struct my_io *w = (struct my_io *)w_;
1040	...	1174	...
1041	}	1175	}
1042		1176
…		…
1053	ev_timer t2;	1187	ev_timer t2;
1054	}	1188	}
1055		1189
1056	In this case getting the pointer to C<my_biggy> is a bit more	1190	In this case getting the pointer to C<my_biggy> is a bit more
1057	complicated: Either you store the address of your C<my_biggy> struct	1191	complicated: Either you store the address of your C<my_biggy> struct
1058	in the C<data> member of the watcher, or you need to use some pointer	1192	in the C<data> member of the watcher (for woozies), or you need to use
1059	arithmetic using C<offsetof> inside your watchers:	1193	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1194	programmers):
1060		1195
1061	#include <stddef.h>	1196	#include <stddef.h>
1062		1197
1063	static void	1198	static void
1064	t1_cb (EV_P_ struct ev_timer *w, int revents)	1199	t1_cb (EV_P_ ev_timer *w, int revents)
1065	{	1200	{
1066	struct my_biggy big = (struct my_biggy *	1201	struct my_biggy big = (struct my_biggy *)
1067	(((char *)w) - offsetof (struct my_biggy, t1));	1202	(((char *)w) - offsetof (struct my_biggy, t1));
1068	}	1203	}
1069		1204
1070	static void	1205	static void
1071	t2_cb (EV_P_ struct ev_timer *w, int revents)	1206	t2_cb (EV_P_ ev_timer *w, int revents)
1072	{	1207	{
1073	struct my_biggy big = (struct my_biggy *	1208	struct my_biggy big = (struct my_biggy *)
1074	(((char *)w) - offsetof (struct my_biggy, t2));	1209	(((char *)w) - offsetof (struct my_biggy, t2));
1075	}	1210	}
		1211
		1212	=head2 WATCHER PRIORITY MODELS
		1213
		1214	Many event loops support I<watcher priorities>, which are usually small
		1215	integers that influence the ordering of event callback invocation
		1216	between watchers in some way, all else being equal.
		1217
		1218	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1219	description for the more technical details such as the actual priority
		1220	range.
		1221
		1222	There are two common ways how these these priorities are being interpreted
		1223	by event loops:
		1224
		1225	In the more common lock-out model, higher priorities "lock out" invocation
		1226	of lower priority watchers, which means as long as higher priority
		1227	watchers receive events, lower priority watchers are not being invoked.
		1228
		1229	The less common only-for-ordering model uses priorities solely to order
		1230	callback invocation within a single event loop iteration: Higher priority
		1231	watchers are invoked before lower priority ones, but they all get invoked
		1232	before polling for new events.
		1233
		1234	Libev uses the second (only-for-ordering) model for all its watchers
		1235	except for idle watchers (which use the lock-out model).
		1236
		1237	The rationale behind this is that implementing the lock-out model for
		1238	watchers is not well supported by most kernel interfaces, and most event
		1239	libraries will just poll for the same events again and again as long as
		1240	their callbacks have not been executed, which is very inefficient in the
		1241	common case of one high-priority watcher locking out a mass of lower
		1242	priority ones.
		1243
		1244	Static (ordering) priorities are most useful when you have two or more
		1245	watchers handling the same resource: a typical usage example is having an
		1246	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1247	timeouts. Under load, data might be received while the program handles
		1248	other jobs, but since timers normally get invoked first, the timeout
		1249	handler will be executed before checking for data. In that case, giving
		1250	the timer a lower priority than the I/O watcher ensures that I/O will be
		1251	handled first even under adverse conditions (which is usually, but not
		1252	always, what you want).
		1253
		1254	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1255	will only be executed when no same or higher priority watchers have
		1256	received events, they can be used to implement the "lock-out" model when
		1257	required.
		1258
		1259	For example, to emulate how many other event libraries handle priorities,
		1260	you can associate an C<ev_idle> watcher to each such watcher, and in
		1261	the normal watcher callback, you just start the idle watcher. The real
		1262	processing is done in the idle watcher callback. This causes libev to
		1263	continously poll and process kernel event data for the watcher, but when
		1264	the lock-out case is known to be rare (which in turn is rare :), this is
		1265	workable.
		1266
		1267	Usually, however, the lock-out model implemented that way will perform
		1268	miserably under the type of load it was designed to handle. In that case,
		1269	it might be preferable to stop the real watcher before starting the
		1270	idle watcher, so the kernel will not have to process the event in case
		1271	the actual processing will be delayed for considerable time.
		1272
		1273	Here is an example of an I/O watcher that should run at a strictly lower
		1274	priority than the default, and which should only process data when no
		1275	other events are pending:
		1276
		1277	ev_idle idle; // actual processing watcher
		1278	ev_io io; // actual event watcher
		1279
		1280	static void
		1281	io_cb (EV_P_ ev_io *w, int revents)
		1282	{
		1283	// stop the I/O watcher, we received the event, but
		1284	// are not yet ready to handle it.
		1285	ev_io_stop (EV_A_ w);
		1286
		1287	// start the idle watcher to ahndle the actual event.
		1288	// it will not be executed as long as other watchers
		1289	// with the default priority are receiving events.
		1290	ev_idle_start (EV_A_ &idle);
		1291	}
		1292
		1293	static void
		1294	idle_cb (EV_P_ ev_idle *w, int revents)
		1295	{
		1296	// actual processing
		1297	read (STDIN_FILENO, ...);
		1298
		1299	// have to start the I/O watcher again, as
		1300	// we have handled the event
		1301	ev_io_start (EV_P_ &io);
		1302	}
		1303
		1304	// initialisation
		1305	ev_idle_init (&idle, idle_cb);
		1306	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1307	ev_io_start (EV_DEFAULT_ &io);
		1308
		1309	In the "real" world, it might also be beneficial to start a timer, so that
		1310	low-priority connections can not be locked out forever under load. This
		1311	enables your program to keep a lower latency for important connections
		1312	during short periods of high load, while not completely locking out less
		1313	important ones.
1076		1314
1077		1315
1078	=head1 WATCHER TYPES	1316	=head1 WATCHER TYPES
1079		1317
1080	This section describes each watcher in detail, but will not repeat	1318	This section describes each watcher in detail, but will not repeat
…		…
1104	In general you can register as many read and/or write event watchers per	1342	In general you can register as many read and/or write event watchers per
1105	fd as you want (as long as you don't confuse yourself). Setting all file	1343	fd as you want (as long as you don't confuse yourself). Setting all file
1106	descriptors to non-blocking mode is also usually a good idea (but not	1344	descriptors to non-blocking mode is also usually a good idea (but not
1107	required if you know what you are doing).	1345	required if you know what you are doing).
1108		1346
1109	If you must do this, then force the use of a known-to-be-good backend	1347	If you cannot use non-blocking mode, then force the use of a
1110	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1348	known-to-be-good backend (at the time of this writing, this includes only
1111	C<EVBACKEND_POLL>).	1349	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1350	descriptors for which non-blocking operation makes no sense (such as
		1351	files) - libev doesn't guarentee any specific behaviour in that case.
1112		1352
1113	Another thing you have to watch out for is that it is quite easy to	1353	Another thing you have to watch out for is that it is quite easy to
1114	receive "spurious" readiness notifications, that is your callback might	1354	receive "spurious" readiness notifications, that is your callback might
1115	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1355	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1116	because there is no data. Not only are some backends known to create a	1356	because there is no data. Not only are some backends known to create a
1117	lot of those (for example Solaris ports), it is very easy to get into	1357	lot of those (for example Solaris ports), it is very easy to get into
1118	this situation even with a relatively standard program structure. Thus	1358	this situation even with a relatively standard program structure. Thus
1119	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1359	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1120	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1360	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1121		1361
1122	If you cannot run the fd in non-blocking mode (for example you should not	1362	If you cannot run the fd in non-blocking mode (for example you should
1123	play around with an Xlib connection), then you have to separately re-test	1363	not play around with an Xlib connection), then you have to separately
1124	whether a file descriptor is really ready with a known-to-be good interface	1364	re-test whether a file descriptor is really ready with a known-to-be good
1125	such as poll (fortunately in our Xlib example, Xlib already does this on	1365	interface such as poll (fortunately in our Xlib example, Xlib already
1126	its own, so its quite safe to use).	1366	does this on its own, so its quite safe to use). Some people additionally
		1367	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1368	indefinitely.
		1369
		1370	But really, best use non-blocking mode.
1127		1371
1128	=head3 The special problem of disappearing file descriptors	1372	=head3 The special problem of disappearing file descriptors
1129		1373
1130	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1374	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1131	descriptor (either by calling C<close> explicitly or by any other means,	1375	descriptor (either due to calling C<close> explicitly or any other means,
1132	such as C<dup>). The reason is that you register interest in some file	1376	such as C<dup2>). The reason is that you register interest in some file
1133	descriptor, but when it goes away, the operating system will silently drop	1377	descriptor, but when it goes away, the operating system will silently drop
1134	this interest. If another file descriptor with the same number then is	1378	this interest. If another file descriptor with the same number then is
1135	registered with libev, there is no efficient way to see that this is, in	1379	registered with libev, there is no efficient way to see that this is, in
1136	fact, a different file descriptor.	1380	fact, a different file descriptor.
1137		1381
…		…
1168	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1412	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1169	C<EVBACKEND_POLL>.	1413	C<EVBACKEND_POLL>.
1170		1414
1171	=head3 The special problem of SIGPIPE	1415	=head3 The special problem of SIGPIPE
1172		1416
1173	While not really specific to libev, it is easy to forget about SIGPIPE:	1417	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1174	when writing to a pipe whose other end has been closed, your program gets	1418	when writing to a pipe whose other end has been closed, your program gets
1175	send a SIGPIPE, which, by default, aborts your program. For most programs	1419	sent a SIGPIPE, which, by default, aborts your program. For most programs
1176	this is sensible behaviour, for daemons, this is usually undesirable.	1420	this is sensible behaviour, for daemons, this is usually undesirable.
1177		1421
1178	So when you encounter spurious, unexplained daemon exits, make sure you	1422	So when you encounter spurious, unexplained daemon exits, make sure you
1179	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1423	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1180	somewhere, as that would have given you a big clue).	1424	somewhere, as that would have given you a big clue).
…		…
1187	=item ev_io_init (ev_io *, callback, int fd, int events)	1431	=item ev_io_init (ev_io *, callback, int fd, int events)
1188		1432
1189	=item ev_io_set (ev_io *, int fd, int events)	1433	=item ev_io_set (ev_io *, int fd, int events)
1190		1434
1191	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1435	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1192	receive events for and events is either C<EV_READ>, C<EV_WRITE> or	1436	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1193	C<EV_READ | EV_WRITE> to receive the given events.	1437	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1194		1438
1195	=item int fd [read-only]	1439	=item int fd [read-only]
1196		1440
1197	The file descriptor being watched.	1441	The file descriptor being watched.
1198		1442
…		…
1207	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1451	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1208	readable, but only once. Since it is likely line-buffered, you could	1452	readable, but only once. Since it is likely line-buffered, you could
1209	attempt to read a whole line in the callback.	1453	attempt to read a whole line in the callback.
1210		1454
1211	static void	1455	static void
1212	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1456	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1213	{	1457	{
1214	ev_io_stop (loop, w);	1458	ev_io_stop (loop, w);
1215	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1459	.. read from stdin here (or from w->fd) and handle any I/O errors
1216	}	1460	}
1217		1461
1218	...	1462	...
1219	struct ev_loop *loop = ev_default_init (0);	1463	struct ev_loop *loop = ev_default_init (0);
1220	struct ev_io stdin_readable;	1464	ev_io stdin_readable;
1221	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1465	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1222	ev_io_start (loop, &stdin_readable);	1466	ev_io_start (loop, &stdin_readable);
1223	ev_loop (loop, 0);	1467	ev_loop (loop, 0);
1224		1468
1225		1469
…		…
1228	Timer watchers are simple relative timers that generate an event after a	1472	Timer watchers are simple relative timers that generate an event after a
1229	given time, and optionally repeating in regular intervals after that.	1473	given time, and optionally repeating in regular intervals after that.
1230		1474
1231	The timers are based on real time, that is, if you register an event that	1475	The timers are based on real time, that is, if you register an event that
1232	times out after an hour and you reset your system clock to January last	1476	times out after an hour and you reset your system clock to January last
1233	year, it will still time out after (roughly) and hour. "Roughly" because	1477	year, it will still time out after (roughly) one hour. "Roughly" because
1234	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1478	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1235	monotonic clock option helps a lot here).	1479	monotonic clock option helps a lot here).
1236		1480
1237	The callback is guaranteed to be invoked only after its timeout has passed,	1481	The callback is guaranteed to be invoked only I<after> its timeout has
1238	but if multiple timers become ready during the same loop iteration then	1482	passed (not I<at>, so on systems with very low-resolution clocks this
1239	order of execution is undefined.	1483	might introduce a small delay). If multiple timers become ready during the
		1484	same loop iteration then the ones with earlier time-out values are invoked
		1485	before ones with later time-out values (but this is no longer true when a
		1486	callback calls C<ev_loop> recursively).
		1487
		1488	=head3 Be smart about timeouts
		1489
		1490	Many real-world problems involve some kind of timeout, usually for error
		1491	recovery. A typical example is an HTTP request - if the other side hangs,
		1492	you want to raise some error after a while.
		1493
		1494	What follows are some ways to handle this problem, from obvious and
		1495	inefficient to smart and efficient.
		1496
		1497	In the following, a 60 second activity timeout is assumed - a timeout that
		1498	gets reset to 60 seconds each time there is activity (e.g. each time some
		1499	data or other life sign was received).
		1500
		1501	=over 4
		1502
		1503	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1504
		1505	This is the most obvious, but not the most simple way: In the beginning,
		1506	start the watcher:
		1507
		1508	ev_timer_init (timer, callback, 60., 0.);
		1509	ev_timer_start (loop, timer);
		1510
		1511	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1512	and start it again:
		1513
		1514	ev_timer_stop (loop, timer);
		1515	ev_timer_set (timer, 60., 0.);
		1516	ev_timer_start (loop, timer);
		1517
		1518	This is relatively simple to implement, but means that each time there is
		1519	some activity, libev will first have to remove the timer from its internal
		1520	data structure and then add it again. Libev tries to be fast, but it's
		1521	still not a constant-time operation.
		1522
		1523	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1524
		1525	This is the easiest way, and involves using C<ev_timer_again> instead of
		1526	C<ev_timer_start>.
		1527
		1528	To implement this, configure an C<ev_timer> with a C<repeat> value
		1529	of C<60> and then call C<ev_timer_again> at start and each time you
		1530	successfully read or write some data. If you go into an idle state where
		1531	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1532	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1533
		1534	That means you can ignore both the C<ev_timer_start> function and the
		1535	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1536	member and C<ev_timer_again>.
		1537
		1538	At start:
		1539
		1540	ev_init (timer, callback);
		1541	timer->repeat = 60.;
		1542	ev_timer_again (loop, timer);
		1543
		1544	Each time there is some activity:
		1545
		1546	ev_timer_again (loop, timer);
		1547
		1548	It is even possible to change the time-out on the fly, regardless of
		1549	whether the watcher is active or not:
		1550
		1551	timer->repeat = 30.;
		1552	ev_timer_again (loop, timer);
		1553
		1554	This is slightly more efficient then stopping/starting the timer each time
		1555	you want to modify its timeout value, as libev does not have to completely
		1556	remove and re-insert the timer from/into its internal data structure.
		1557
		1558	It is, however, even simpler than the "obvious" way to do it.
		1559
		1560	=item 3. Let the timer time out, but then re-arm it as required.
		1561
		1562	This method is more tricky, but usually most efficient: Most timeouts are
		1563	relatively long compared to the intervals between other activity - in
		1564	our example, within 60 seconds, there are usually many I/O events with
		1565	associated activity resets.
		1566
		1567	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1568	but remember the time of last activity, and check for a real timeout only
		1569	within the callback:
		1570
		1571	ev_tstamp last_activity; // time of last activity
		1572
		1573	static void
		1574	callback (EV_P_ ev_timer *w, int revents)
		1575	{
		1576	ev_tstamp now = ev_now (EV_A);
		1577	ev_tstamp timeout = last_activity + 60.;
		1578
		1579	// if last_activity + 60. is older than now, we did time out
		1580	if (timeout < now)
		1581	{
		1582	// timeout occured, take action
		1583	}
		1584	else
		1585	{
		1586	// callback was invoked, but there was some activity, re-arm
		1587	// the watcher to fire in last_activity + 60, which is
		1588	// guaranteed to be in the future, so "again" is positive:
		1589	w->repeat = timeout - now;
		1590	ev_timer_again (EV_A_ w);
		1591	}
		1592	}
		1593
		1594	To summarise the callback: first calculate the real timeout (defined
		1595	as "60 seconds after the last activity"), then check if that time has
		1596	been reached, which means something I<did>, in fact, time out. Otherwise
		1597	the callback was invoked too early (C<timeout> is in the future), so
		1598	re-schedule the timer to fire at that future time, to see if maybe we have
		1599	a timeout then.
		1600
		1601	Note how C<ev_timer_again> is used, taking advantage of the
		1602	C<ev_timer_again> optimisation when the timer is already running.
		1603
		1604	This scheme causes more callback invocations (about one every 60 seconds
		1605	minus half the average time between activity), but virtually no calls to
		1606	libev to change the timeout.
		1607
		1608	To start the timer, simply initialise the watcher and set C<last_activity>
		1609	to the current time (meaning we just have some activity :), then call the
		1610	callback, which will "do the right thing" and start the timer:
		1611
		1612	ev_init (timer, callback);
		1613	last_activity = ev_now (loop);
		1614	callback (loop, timer, EV_TIMEOUT);
		1615
		1616	And when there is some activity, simply store the current time in
		1617	C<last_activity>, no libev calls at all:
		1618
		1619	last_actiivty = ev_now (loop);
		1620
		1621	This technique is slightly more complex, but in most cases where the
		1622	time-out is unlikely to be triggered, much more efficient.
		1623
		1624	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1625	callback :) - just change the timeout and invoke the callback, which will
		1626	fix things for you.
		1627
		1628	=item 4. Wee, just use a double-linked list for your timeouts.
		1629
		1630	If there is not one request, but many thousands (millions...), all
		1631	employing some kind of timeout with the same timeout value, then one can
		1632	do even better:
		1633
		1634	When starting the timeout, calculate the timeout value and put the timeout
		1635	at the I<end> of the list.
		1636
		1637	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1638	the list is expected to fire (for example, using the technique #3).
		1639
		1640	When there is some activity, remove the timer from the list, recalculate
		1641	the timeout, append it to the end of the list again, and make sure to
		1642	update the C<ev_timer> if it was taken from the beginning of the list.
		1643
		1644	This way, one can manage an unlimited number of timeouts in O(1) time for
		1645	starting, stopping and updating the timers, at the expense of a major
		1646	complication, and having to use a constant timeout. The constant timeout
		1647	ensures that the list stays sorted.
		1648
		1649	=back
		1650
		1651	So which method the best?
		1652
		1653	Method #2 is a simple no-brain-required solution that is adequate in most
		1654	situations. Method #3 requires a bit more thinking, but handles many cases
		1655	better, and isn't very complicated either. In most case, choosing either
		1656	one is fine, with #3 being better in typical situations.
		1657
		1658	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1659	rather complicated, but extremely efficient, something that really pays
		1660	off after the first million or so of active timers, i.e. it's usually
		1661	overkill :)
1240		1662
1241	=head3 The special problem of time updates	1663	=head3 The special problem of time updates
1242		1664
1243	Establishing the current time is a costly operation (it usually takes at	1665	Establishing the current time is a costly operation (it usually takes at
1244	least two system calls): EV therefore updates its idea of the current	1666	least two system calls): EV therefore updates its idea of the current
1245	time only before and after C<ev_loop> polls for new events, which causes	1667	time only before and after C<ev_loop> collects new events, which causes a
1246	a growing difference between C<ev_now ()> and C<ev_time ()> when handling	1668	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1247	lots of events.	1669	lots of events in one iteration.
1248		1670
1249	The relative timeouts are calculated relative to the C<ev_now ()>	1671	The relative timeouts are calculated relative to the C<ev_now ()>
1250	time. This is usually the right thing as this timestamp refers to the time	1672	time. This is usually the right thing as this timestamp refers to the time
1251	of the event triggering whatever timeout you are modifying/starting. If	1673	of the event triggering whatever timeout you are modifying/starting. If
1252	you suspect event processing to be delayed and you I<need> to base the	1674	you suspect event processing to be delayed and you I<need> to base the
…		…
1288	If the timer is started but non-repeating, stop it (as if it timed out).	1710	If the timer is started but non-repeating, stop it (as if it timed out).
1289		1711
1290	If the timer is repeating, either start it if necessary (with the	1712	If the timer is repeating, either start it if necessary (with the
1291	C<repeat> value), or reset the running timer to the C<repeat> value.	1713	C<repeat> value), or reset the running timer to the C<repeat> value.
1292		1714
1293	This sounds a bit complicated, but here is a useful and typical	1715	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1294	example: Imagine you have a TCP connection and you want a so-called idle	1716	usage example.
1295	timeout, that is, you want to be called when there have been, say, 60
1296	seconds of inactivity on the socket. The easiest way to do this is to
1297	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1298	C<ev_timer_again> each time you successfully read or write some data. If
1299	you go into an idle state where you do not expect data to travel on the
1300	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1301	automatically restart it if need be.
1302
1303	That means you can ignore the C<after> value and C<ev_timer_start>
1304	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1305
1306	ev_timer_init (timer, callback, 0., 5.);
1307	ev_timer_again (loop, timer);
1308	...
1309	timer->again = 17.;
1310	ev_timer_again (loop, timer);
1311	...
1312	timer->again = 10.;
1313	ev_timer_again (loop, timer);
1314
1315	This is more slightly efficient then stopping/starting the timer each time
1316	you want to modify its timeout value.
1317		1717
1318	=item ev_tstamp repeat [read-write]	1718	=item ev_tstamp repeat [read-write]
1319		1719
1320	The current C<repeat> value. Will be used each time the watcher times out	1720	The current C<repeat> value. Will be used each time the watcher times out
1321	or C<ev_timer_again> is called and determines the next timeout (if any),	1721	or C<ev_timer_again> is called, and determines the next timeout (if any),
1322	which is also when any modifications are taken into account.	1722	which is also when any modifications are taken into account.
1323		1723
1324	=back	1724	=back
1325		1725
1326	=head3 Examples	1726	=head3 Examples
1327		1727
1328	Example: Create a timer that fires after 60 seconds.	1728	Example: Create a timer that fires after 60 seconds.
1329		1729
1330	static void	1730	static void
1331	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1731	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1332	{	1732	{
1333	.. one minute over, w is actually stopped right here	1733	.. one minute over, w is actually stopped right here
1334	}	1734	}
1335		1735
1336	struct ev_timer mytimer;	1736	ev_timer mytimer;
1337	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1737	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1338	ev_timer_start (loop, &mytimer);	1738	ev_timer_start (loop, &mytimer);
1339		1739
1340	Example: Create a timeout timer that times out after 10 seconds of	1740	Example: Create a timeout timer that times out after 10 seconds of
1341	inactivity.	1741	inactivity.
1342		1742
1343	static void	1743	static void
1344	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1744	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1345	{	1745	{
1346	.. ten seconds without any activity	1746	.. ten seconds without any activity
1347	}	1747	}
1348		1748
1349	struct ev_timer mytimer;	1749	ev_timer mytimer;
1350	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1750	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1351	ev_timer_again (&mytimer); /* start timer */	1751	ev_timer_again (&mytimer); /* start timer */
1352	ev_loop (loop, 0);	1752	ev_loop (loop, 0);
1353		1753
1354	// and in some piece of code that gets executed on any "activity":	1754	// and in some piece of code that gets executed on any "activity":
…		…
1359	=head2 C<ev_periodic> - to cron or not to cron?	1759	=head2 C<ev_periodic> - to cron or not to cron?
1360		1760
1361	Periodic watchers are also timers of a kind, but they are very versatile	1761	Periodic watchers are also timers of a kind, but they are very versatile
1362	(and unfortunately a bit complex).	1762	(and unfortunately a bit complex).
1363		1763
1364	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1764	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1365	but on wall clock time (absolute time). You can tell a periodic watcher	1765	relative time, the physical time that passes) but on wall clock time
1366	to trigger after some specific point in time. For example, if you tell a	1766	(absolute time, the thing you can read on your calender or clock). The
1367	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1767	difference is that wall clock time can run faster or slower than real
1368	+ 10.>, that is, an absolute time not a delay) and then reset your system	1768	time, and time jumps are not uncommon (e.g. when you adjust your
1369	clock to January of the previous year, then it will take more than year	1769	wrist-watch).
1370	to trigger the event (unlike an C<ev_timer>, which would still trigger
1371	roughly 10 seconds later as it uses a relative timeout).
1372		1770
		1771	You can tell a periodic watcher to trigger after some specific point
		1772	in time: for example, if you tell a periodic watcher to trigger "in 10
		1773	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1774	not a delay) and then reset your system clock to January of the previous
		1775	year, then it will take a year or more to trigger the event (unlike an
		1776	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1777	it, as it uses a relative timeout).
		1778
1373	C<ev_periodic>s can also be used to implement vastly more complex timers,	1779	C<ev_periodic> watchers can also be used to implement vastly more complex
1374	such as triggering an event on each "midnight, local time", or other	1780	timers, such as triggering an event on each "midnight, local time", or
1375	complicated, rules.	1781	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1782	those cannot react to time jumps.
1376		1783
1377	As with timers, the callback is guaranteed to be invoked only when the	1784	As with timers, the callback is guaranteed to be invoked only when the
1378	time (C<at>) has passed, but if multiple periodic timers become ready	1785	point in time where it is supposed to trigger has passed. If multiple
1379	during the same loop iteration then order of execution is undefined.	1786	timers become ready during the same loop iteration then the ones with
		1787	earlier time-out values are invoked before ones with later time-out values
		1788	(but this is no longer true when a callback calls C<ev_loop> recursively).
1380		1789
1381	=head3 Watcher-Specific Functions and Data Members	1790	=head3 Watcher-Specific Functions and Data Members
1382		1791
1383	=over 4	1792	=over 4
1384		1793
1385	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1794	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1386		1795
1387	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1796	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1388		1797
1389	Lots of arguments, lets sort it out... There are basically three modes of	1798	Lots of arguments, let's sort it out... There are basically three modes of
1390	operation, and we will explain them from simplest to complex:	1799	operation, and we will explain them from simplest to most complex:
1391		1800
1392	=over 4	1801	=over 4
1393		1802
1394	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1803	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1395		1804
1396	In this configuration the watcher triggers an event after the wall clock	1805	In this configuration the watcher triggers an event after the wall clock
1397	time C<at> has passed and doesn't repeat. It will not adjust when a time	1806	time C<offset> has passed. It will not repeat and will not adjust when a
1398	jump occurs, that is, if it is to be run at January 1st 2011 then it will	1807	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1399	run when the system time reaches or surpasses this time.	1808	will be stopped and invoked when the system clock reaches or surpasses
		1809	this point in time.
1400		1810
1401	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1811	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1402		1812
1403	In this mode the watcher will always be scheduled to time out at the next	1813	In this mode the watcher will always be scheduled to time out at the next
1404	C<at + N * interval> time (for some integer N, which can also be negative)	1814	C<offset + N * interval> time (for some integer N, which can also be
1405	and then repeat, regardless of any time jumps.	1815	negative) and then repeat, regardless of any time jumps. The C<offset>
		1816	argument is merely an offset into the C<interval> periods.
1406		1817
1407	This can be used to create timers that do not drift with respect to system	1818	This can be used to create timers that do not drift with respect to the
1408	time, for example, here is a C<ev_periodic> that triggers each hour, on	1819	system clock, for example, here is an C<ev_periodic> that triggers each
1409	the hour:	1820	hour, on the hour (with respect to UTC):
1410		1821
1411	ev_periodic_set (&periodic, 0., 3600., 0);	1822	ev_periodic_set (&periodic, 0., 3600., 0);
1412		1823
1413	This doesn't mean there will always be 3600 seconds in between triggers,	1824	This doesn't mean there will always be 3600 seconds in between triggers,
1414	but only that the callback will be called when the system time shows a	1825	but only that the callback will be called when the system time shows a
1415	full hour (UTC), or more correctly, when the system time is evenly divisible	1826	full hour (UTC), or more correctly, when the system time is evenly divisible
1416	by 3600.	1827	by 3600.
1417		1828
1418	Another way to think about it (for the mathematically inclined) is that	1829	Another way to think about it (for the mathematically inclined) is that
1419	C<ev_periodic> will try to run the callback in this mode at the next possible	1830	C<ev_periodic> will try to run the callback in this mode at the next possible
1420	time where C<time = at (mod interval)>, regardless of any time jumps.	1831	time where C<time = offset (mod interval)>, regardless of any time jumps.
1421		1832
1422	For numerical stability it is preferable that the C<at> value is near	1833	For numerical stability it is preferable that the C<offset> value is near
1423	C<ev_now ()> (the current time), but there is no range requirement for	1834	C<ev_now ()> (the current time), but there is no range requirement for
1424	this value, and in fact is often specified as zero.	1835	this value, and in fact is often specified as zero.
1425		1836
1426	Note also that there is an upper limit to how often a timer can fire (CPU	1837	Note also that there is an upper limit to how often a timer can fire (CPU
1427	speed for example), so if C<interval> is very small then timing stability	1838	speed for example), so if C<interval> is very small then timing stability
1428	will of course deteriorate. Libev itself tries to be exact to be about one	1839	will of course deteriorate. Libev itself tries to be exact to be about one
1429	millisecond (if the OS supports it and the machine is fast enough).	1840	millisecond (if the OS supports it and the machine is fast enough).
1430		1841
1431	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1842	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1432		1843
1433	In this mode the values for C<interval> and C<at> are both being	1844	In this mode the values for C<interval> and C<offset> are both being
1434	ignored. Instead, each time the periodic watcher gets scheduled, the	1845	ignored. Instead, each time the periodic watcher gets scheduled, the
1435	reschedule callback will be called with the watcher as first, and the	1846	reschedule callback will be called with the watcher as first, and the
1436	current time as second argument.	1847	current time as second argument.
1437		1848
1438	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1849	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1439	ever, or make ANY event loop modifications whatsoever>.	1850	or make ANY other event loop modifications whatsoever, unless explicitly
		1851	allowed by documentation here>.
1440		1852
1441	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1853	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1442	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1854	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1443	only event loop modification you are allowed to do).	1855	only event loop modification you are allowed to do).
1444		1856
1445	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	1857	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1446	*w, ev_tstamp now)>, e.g.:	1858	*w, ev_tstamp now)>, e.g.:
1447		1859
		1860	static ev_tstamp
1448	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1861	my_rescheduler (ev_periodic *w, ev_tstamp now)
1449	{	1862	{
1450	return now + 60.;	1863	return now + 60.;
1451	}	1864	}
1452		1865
1453	It must return the next time to trigger, based on the passed time value	1866	It must return the next time to trigger, based on the passed time value
…		…
1473	a different time than the last time it was called (e.g. in a crond like	1886	a different time than the last time it was called (e.g. in a crond like
1474	program when the crontabs have changed).	1887	program when the crontabs have changed).
1475		1888
1476	=item ev_tstamp ev_periodic_at (ev_periodic *)	1889	=item ev_tstamp ev_periodic_at (ev_periodic *)
1477		1890
1478	When active, returns the absolute time that the watcher is supposed to	1891	When active, returns the absolute time that the watcher is supposed
1479	trigger next.	1892	to trigger next. This is not the same as the C<offset> argument to
		1893	C<ev_periodic_set>, but indeed works even in interval and manual
		1894	rescheduling modes.
1480		1895
1481	=item ev_tstamp offset [read-write]	1896	=item ev_tstamp offset [read-write]
1482		1897
1483	When repeating, this contains the offset value, otherwise this is the	1898	When repeating, this contains the offset value, otherwise this is the
1484	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1899	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1900	although libev might modify this value for better numerical stability).
1485		1901
1486	Can be modified any time, but changes only take effect when the periodic	1902	Can be modified any time, but changes only take effect when the periodic
1487	timer fires or C<ev_periodic_again> is being called.	1903	timer fires or C<ev_periodic_again> is being called.
1488		1904
1489	=item ev_tstamp interval [read-write]	1905	=item ev_tstamp interval [read-write]
1490		1906
1491	The current interval value. Can be modified any time, but changes only	1907	The current interval value. Can be modified any time, but changes only
1492	take effect when the periodic timer fires or C<ev_periodic_again> is being	1908	take effect when the periodic timer fires or C<ev_periodic_again> is being
1493	called.	1909	called.
1494		1910
1495	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1911	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1496		1912
1497	The current reschedule callback, or C<0>, if this functionality is	1913	The current reschedule callback, or C<0>, if this functionality is
1498	switched off. Can be changed any time, but changes only take effect when	1914	switched off. Can be changed any time, but changes only take effect when
1499	the periodic timer fires or C<ev_periodic_again> is being called.	1915	the periodic timer fires or C<ev_periodic_again> is being called.
1500		1916
1501	=back	1917	=back
1502		1918
1503	=head3 Examples	1919	=head3 Examples
1504		1920
1505	Example: Call a callback every hour, or, more precisely, whenever the	1921	Example: Call a callback every hour, or, more precisely, whenever the
1506	system clock is divisible by 3600. The callback invocation times have	1922	system time is divisible by 3600. The callback invocation times have
1507	potentially a lot of jitter, but good long-term stability.	1923	potentially a lot of jitter, but good long-term stability.
1508		1924
1509	static void	1925	static void
1510	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1926	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1511	{	1927	{
1512	... its now a full hour (UTC, or TAI or whatever your clock follows)	1928	... its now a full hour (UTC, or TAI or whatever your clock follows)
1513	}	1929	}
1514		1930
1515	struct ev_periodic hourly_tick;	1931	ev_periodic hourly_tick;
1516	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1932	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1517	ev_periodic_start (loop, &hourly_tick);	1933	ev_periodic_start (loop, &hourly_tick);
1518		1934
1519	Example: The same as above, but use a reschedule callback to do it:	1935	Example: The same as above, but use a reschedule callback to do it:
1520		1936
1521	#include <math.h>	1937	#include <math.h>
1522		1938
1523	static ev_tstamp	1939	static ev_tstamp
1524	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1940	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1525	{	1941	{
1526	return fmod (now, 3600.) + 3600.;	1942	return now + (3600. - fmod (now, 3600.));
1527	}	1943	}
1528		1944
1529	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1945	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1530		1946
1531	Example: Call a callback every hour, starting now:	1947	Example: Call a callback every hour, starting now:
1532		1948
1533	struct ev_periodic hourly_tick;	1949	ev_periodic hourly_tick;
1534	ev_periodic_init (&hourly_tick, clock_cb,	1950	ev_periodic_init (&hourly_tick, clock_cb,
1535	fmod (ev_now (loop), 3600.), 3600., 0);	1951	fmod (ev_now (loop), 3600.), 3600., 0);
1536	ev_periodic_start (loop, &hourly_tick);	1952	ev_periodic_start (loop, &hourly_tick);
1537		1953
1538		1954
…		…
1541	Signal watchers will trigger an event when the process receives a specific	1957	Signal watchers will trigger an event when the process receives a specific
1542	signal one or more times. Even though signals are very asynchronous, libev	1958	signal one or more times. Even though signals are very asynchronous, libev
1543	will try it's best to deliver signals synchronously, i.e. as part of the	1959	will try it's best to deliver signals synchronously, i.e. as part of the
1544	normal event processing, like any other event.	1960	normal event processing, like any other event.
1545		1961
		1962	If you want signals asynchronously, just use C<sigaction> as you would
		1963	do without libev and forget about sharing the signal. You can even use
		1964	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1965
1546	You can configure as many watchers as you like per signal. Only when the	1966	You can configure as many watchers as you like per signal. Only when the
1547	first watcher gets started will libev actually register a signal watcher	1967	first watcher gets started will libev actually register a signal handler
1548	with the kernel (thus it coexists with your own signal handlers as long	1968	with the kernel (thus it coexists with your own signal handlers as long as
1549	as you don't register any with libev). Similarly, when the last signal	1969	you don't register any with libev for the same signal). Similarly, when
1550	watcher for a signal is stopped libev will reset the signal handler to	1970	the last signal watcher for a signal is stopped, libev will reset the
1551	SIG_DFL (regardless of what it was set to before).	1971	signal handler to SIG_DFL (regardless of what it was set to before).
1552		1972
1553	If possible and supported, libev will install its handlers with	1973	If possible and supported, libev will install its handlers with
1554	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	1974	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
1555	interrupted. If you have a problem with system calls getting interrupted by	1975	interrupted. If you have a problem with system calls getting interrupted by
1556	signals you can block all signals in an C<ev_check> watcher and unblock	1976	signals you can block all signals in an C<ev_check> watcher and unblock
…		…
1573		1993
1574	=back	1994	=back
1575		1995
1576	=head3 Examples	1996	=head3 Examples
1577		1997
1578	Example: Try to exit cleanly on SIGINT and SIGTERM.	1998	Example: Try to exit cleanly on SIGINT.
1579		1999
1580	static void	2000	static void
1581	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2001	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1582	{	2002	{
1583	ev_unloop (loop, EVUNLOOP_ALL);	2003	ev_unloop (loop, EVUNLOOP_ALL);
1584	}	2004	}
1585		2005
1586	struct ev_signal signal_watcher;	2006	ev_signal signal_watcher;
1587	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2007	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1588	ev_signal_start (loop, &sigint_cb);	2008	ev_signal_start (loop, &signal_watcher);
1589		2009
1590		2010
1591	=head2 C<ev_child> - watch out for process status changes	2011	=head2 C<ev_child> - watch out for process status changes
1592		2012
1593	Child watchers trigger when your process receives a SIGCHLD in response to	2013	Child watchers trigger when your process receives a SIGCHLD in response to
1594	some child status changes (most typically when a child of yours dies). It	2014	some child status changes (most typically when a child of yours dies or
1595	is permissible to install a child watcher I<after> the child has been	2015	exits). It is permissible to install a child watcher I<after> the child
1596	forked (which implies it might have already exited), as long as the event	2016	has been forked (which implies it might have already exited), as long
1597	loop isn't entered (or is continued from a watcher).	2017	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2018	forking and then immediately registering a watcher for the child is fine,
		2019	but forking and registering a watcher a few event loop iterations later or
		2020	in the next callback invocation is not.
1598		2021
1599	Only the default event loop is capable of handling signals, and therefore	2022	Only the default event loop is capable of handling signals, and therefore
1600	you can only register child watchers in the default event loop.	2023	you can only register child watchers in the default event loop.
1601		2024
1602	=head3 Process Interaction	2025	=head3 Process Interaction
…		…
1663	its completion.	2086	its completion.
1664		2087
1665	ev_child cw;	2088	ev_child cw;
1666		2089
1667	static void	2090	static void
1668	child_cb (EV_P_ struct ev_child *w, int revents)	2091	child_cb (EV_P_ ev_child *w, int revents)
1669	{	2092	{
1670	ev_child_stop (EV_A_ w);	2093	ev_child_stop (EV_A_ w);
1671	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2094	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1672	}	2095	}
1673		2096
…		…
1688		2111
1689		2112
1690	=head2 C<ev_stat> - did the file attributes just change?	2113	=head2 C<ev_stat> - did the file attributes just change?
1691		2114
1692	This watches a file system path for attribute changes. That is, it calls	2115	This watches a file system path for attribute changes. That is, it calls
1693	C<stat> regularly (or when the OS says it changed) and sees if it changed	2116	C<stat> on that path in regular intervals (or when the OS says it changed)
1694	compared to the last time, invoking the callback if it did.	2117	and sees if it changed compared to the last time, invoking the callback if
		2118	it did.
1695		2119
1696	The path does not need to exist: changing from "path exists" to "path does	2120	The path does not need to exist: changing from "path exists" to "path does
1697	not exist" is a status change like any other. The condition "path does	2121	not exist" is a status change like any other. The condition "path does not
1698	not exist" is signified by the C<st_nlink> field being zero (which is	2122	exist" (or more correctly "path cannot be stat'ed") is signified by the
1699	otherwise always forced to be at least one) and all the other fields of	2123	C<st_nlink> field being zero (which is otherwise always forced to be at
1700	the stat buffer having unspecified contents.	2124	least one) and all the other fields of the stat buffer having unspecified
		2125	contents.
1701		2126
1702	The path I<should> be absolute and I<must not> end in a slash. If it is	2127	The path I<must not> end in a slash or contain special components such as
		2128	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1703	relative and your working directory changes, the behaviour is undefined.	2129	your working directory changes, then the behaviour is undefined.
1704		2130
1705	Since there is no standard to do this, the portable implementation simply	2131	Since there is no portable change notification interface available, the
1706	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2132	portable implementation simply calls C<stat(2)> regularly on the path
1707	can specify a recommended polling interval for this case. If you specify	2133	to see if it changed somehow. You can specify a recommended polling
1708	a polling interval of C<0> (highly recommended!) then a I<suitable,	2134	interval for this case. If you specify a polling interval of C<0> (highly
1709	unspecified default> value will be used (which you can expect to be around	2135	recommended!) then a I<suitable, unspecified default> value will be used
1710	five seconds, although this might change dynamically). Libev will also	2136	(which you can expect to be around five seconds, although this might
1711	impose a minimum interval which is currently around C<0.1>, but thats	2137	change dynamically). Libev will also impose a minimum interval which is
1712	usually overkill.	2138	currently around C<0.1>, but that's usually overkill.
1713		2139
1714	This watcher type is not meant for massive numbers of stat watchers,	2140	This watcher type is not meant for massive numbers of stat watchers,
1715	as even with OS-supported change notifications, this can be	2141	as even with OS-supported change notifications, this can be
1716	resource-intensive.	2142	resource-intensive.
1717		2143
1718	At the time of this writing, only the Linux inotify interface is	2144	At the time of this writing, the only OS-specific interface implemented
1719	implemented (implementing kqueue support is left as an exercise for the	2145	is the Linux inotify interface (implementing kqueue support is left as an
1720	reader, note, however, that the author sees no way of implementing ev_stat	2146	exercise for the reader. Note, however, that the author sees no way of
1721	semantics with kqueue). Inotify will be used to give hints only and should	2147	implementing C<ev_stat> semantics with kqueue, except as a hint).
1722	not change the semantics of C<ev_stat> watchers, which means that libev
1723	sometimes needs to fall back to regular polling again even with inotify,
1724	but changes are usually detected immediately, and if the file exists there
1725	will be no polling.
1726		2148
1727	=head3 ABI Issues (Largefile Support)	2149	=head3 ABI Issues (Largefile Support)
1728		2150
1729	Libev by default (unless the user overrides this) uses the default	2151	Libev by default (unless the user overrides this) uses the default
1730	compilation environment, which means that on systems with large file	2152	compilation environment, which means that on systems with large file
1731	support disabled by default, you get the 32 bit version of the stat	2153	support disabled by default, you get the 32 bit version of the stat
1732	structure. When using the library from programs that change the ABI to	2154	structure. When using the library from programs that change the ABI to
1733	use 64 bit file offsets the programs will fail. In that case you have to	2155	use 64 bit file offsets the programs will fail. In that case you have to
1734	compile libev with the same flags to get binary compatibility. This is	2156	compile libev with the same flags to get binary compatibility. This is
1735	obviously the case with any flags that change the ABI, but the problem is	2157	obviously the case with any flags that change the ABI, but the problem is
1736	most noticeably disabled with ev_stat and large file support.	2158	most noticeably displayed with ev_stat and large file support.
1737		2159
1738	The solution for this is to lobby your distribution maker to make large	2160	The solution for this is to lobby your distribution maker to make large
1739	file interfaces available by default (as e.g. FreeBSD does) and not	2161	file interfaces available by default (as e.g. FreeBSD does) and not
1740	optional. Libev cannot simply switch on large file support because it has	2162	optional. Libev cannot simply switch on large file support because it has
1741	to exchange stat structures with application programs compiled using the	2163	to exchange stat structures with application programs compiled using the
1742	default compilation environment.	2164	default compilation environment.
1743		2165
1744	=head3 Inotify	2166	=head3 Inotify and Kqueue
1745		2167
1746	When C<inotify (7)> support has been compiled into libev (generally only	2168	When C<inotify (7)> support has been compiled into libev and present at
1747	available on Linux) and present at runtime, it will be used to speed up	2169	runtime, it will be used to speed up change detection where possible. The
1748	change detection where possible. The inotify descriptor will be created lazily	2170	inotify descriptor will be created lazily when the first C<ev_stat>
1749	when the first C<ev_stat> watcher is being started.	2171	watcher is being started.
1750		2172
1751	Inotify presence does not change the semantics of C<ev_stat> watchers	2173	Inotify presence does not change the semantics of C<ev_stat> watchers
1752	except that changes might be detected earlier, and in some cases, to avoid	2174	except that changes might be detected earlier, and in some cases, to avoid
1753	making regular C<stat> calls. Even in the presence of inotify support	2175	making regular C<stat> calls. Even in the presence of inotify support
1754	there are many cases where libev has to resort to regular C<stat> polling.	2176	there are many cases where libev has to resort to regular C<stat> polling,
		2177	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2178	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2179	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2180	xfs are fully working) libev usually gets away without polling.
1755		2181
1756	(There is no support for kqueue, as apparently it cannot be used to	2182	There is no support for kqueue, as apparently it cannot be used to
1757	implement this functionality, due to the requirement of having a file	2183	implement this functionality, due to the requirement of having a file
1758	descriptor open on the object at all times).	2184	descriptor open on the object at all times, and detecting renames, unlinks
		2185	etc. is difficult.
		2186
		2187	=head3 C<stat ()> is a synchronous operation
		2188
		2189	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2190	the process. The exception are C<ev_stat> watchers - those call C<stat
		2191	()>, which is a synchronous operation.
		2192
		2193	For local paths, this usually doesn't matter: unless the system is very
		2194	busy or the intervals between stat's are large, a stat call will be fast,
		2195	as the path data is usually in memory already (except when starting the
		2196	watcher).
		2197
		2198	For networked file systems, calling C<stat ()> can block an indefinite
		2199	time due to network issues, and even under good conditions, a stat call
		2200	often takes multiple milliseconds.
		2201
		2202	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2203	paths, although this is fully supported by libev.
1759		2204
1760	=head3 The special problem of stat time resolution	2205	=head3 The special problem of stat time resolution
1761		2206
1762	The C<stat ()> system call only supports full-second resolution portably, and	2207	The C<stat ()> system call only supports full-second resolution portably,
1763	even on systems where the resolution is higher, many file systems still	2208	and even on systems where the resolution is higher, most file systems
1764	only support whole seconds.	2209	still only support whole seconds.
1765		2210
1766	That means that, if the time is the only thing that changes, you can	2211	That means that, if the time is the only thing that changes, you can
1767	easily miss updates: on the first update, C<ev_stat> detects a change and	2212	easily miss updates: on the first update, C<ev_stat> detects a change and
1768	calls your callback, which does something. When there is another update	2213	calls your callback, which does something. When there is another update
1769	within the same second, C<ev_stat> will be unable to detect it as the stat	2214	within the same second, C<ev_stat> will be unable to detect unless the
1770	data does not change.	2215	stat data does change in other ways (e.g. file size).
1771		2216
1772	The solution to this is to delay acting on a change for slightly more	2217	The solution to this is to delay acting on a change for slightly more
1773	than a second (or till slightly after the next full second boundary), using	2218	than a second (or till slightly after the next full second boundary), using
1774	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);	2219	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1775	ev_timer_again (loop, w)>).	2220	ev_timer_again (loop, w)>).
…		…
1795	C<path>. The C<interval> is a hint on how quickly a change is expected to	2240	C<path>. The C<interval> is a hint on how quickly a change is expected to
1796	be detected and should normally be specified as C<0> to let libev choose	2241	be detected and should normally be specified as C<0> to let libev choose
1797	a suitable value. The memory pointed to by C<path> must point to the same	2242	a suitable value. The memory pointed to by C<path> must point to the same
1798	path for as long as the watcher is active.	2243	path for as long as the watcher is active.
1799		2244
1800	The callback will receive C<EV_STAT> when a change was detected, relative	2245	The callback will receive an C<EV_STAT> event when a change was detected,
1801	to the attributes at the time the watcher was started (or the last change	2246	relative to the attributes at the time the watcher was started (or the
1802	was detected).	2247	last change was detected).
1803		2248
1804	=item ev_stat_stat (loop, ev_stat *)	2249	=item ev_stat_stat (loop, ev_stat *)
1805		2250
1806	Updates the stat buffer immediately with new values. If you change the	2251	Updates the stat buffer immediately with new values. If you change the
1807	watched path in your callback, you could call this function to avoid	2252	watched path in your callback, you could call this function to avoid
…		…
1890		2335
1891		2336
1892	=head2 C<ev_idle> - when you've got nothing better to do...	2337	=head2 C<ev_idle> - when you've got nothing better to do...
1893		2338
1894	Idle watchers trigger events when no other events of the same or higher	2339	Idle watchers trigger events when no other events of the same or higher
1895	priority are pending (prepare, check and other idle watchers do not	2340	priority are pending (prepare, check and other idle watchers do not count
1896	count).	2341	as receiving "events").
1897		2342
1898	That is, as long as your process is busy handling sockets or timeouts	2343	That is, as long as your process is busy handling sockets or timeouts
1899	(or even signals, imagine) of the same or higher priority it will not be	2344	(or even signals, imagine) of the same or higher priority it will not be
1900	triggered. But when your process is idle (or only lower-priority watchers	2345	triggered. But when your process is idle (or only lower-priority watchers
1901	are pending), the idle watchers are being called once per event loop	2346	are pending), the idle watchers are being called once per event loop
…		…
1912		2357
1913	=head3 Watcher-Specific Functions and Data Members	2358	=head3 Watcher-Specific Functions and Data Members
1914		2359
1915	=over 4	2360	=over 4
1916		2361
1917	=item ev_idle_init (ev_signal *, callback)	2362	=item ev_idle_init (ev_idle *, callback)
1918		2363
1919	Initialises and configures the idle watcher - it has no parameters of any	2364	Initialises and configures the idle watcher - it has no parameters of any
1920	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2365	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1921	believe me.	2366	believe me.
1922		2367
…		…
1926		2371
1927	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2372	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1928	callback, free it. Also, use no error checking, as usual.	2373	callback, free it. Also, use no error checking, as usual.
1929		2374
1930	static void	2375	static void
1931	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2376	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1932	{	2377	{
1933	free (w);	2378	free (w);
1934	// now do something you wanted to do when the program has	2379	// now do something you wanted to do when the program has
1935	// no longer anything immediate to do.	2380	// no longer anything immediate to do.
1936	}	2381	}
1937		2382
1938	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2383	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1939	ev_idle_init (idle_watcher, idle_cb);	2384	ev_idle_init (idle_watcher, idle_cb);
1940	ev_idle_start (loop, idle_cb);	2385	ev_idle_start (loop, idle_watcher);
1941		2386
1942		2387
1943	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2388	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1944		2389
1945	Prepare and check watchers are usually (but not always) used in tandem:	2390	Prepare and check watchers are usually (but not always) used in pairs:
1946	prepare watchers get invoked before the process blocks and check watchers	2391	prepare watchers get invoked before the process blocks and check watchers
1947	afterwards.	2392	afterwards.
1948		2393
1949	You I<must not> call C<ev_loop> or similar functions that enter	2394	You I<must not> call C<ev_loop> or similar functions that enter
1950	the current event loop from either C<ev_prepare> or C<ev_check>	2395	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1953	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2398	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1954	C<ev_check> so if you have one watcher of each kind they will always be	2399	C<ev_check> so if you have one watcher of each kind they will always be
1955	called in pairs bracketing the blocking call.	2400	called in pairs bracketing the blocking call.
1956		2401
1957	Their main purpose is to integrate other event mechanisms into libev and	2402	Their main purpose is to integrate other event mechanisms into libev and
1958	their use is somewhat advanced. This could be used, for example, to track	2403	their use is somewhat advanced. They could be used, for example, to track
1959	variable changes, implement your own watchers, integrate net-snmp or a	2404	variable changes, implement your own watchers, integrate net-snmp or a
1960	coroutine library and lots more. They are also occasionally useful if	2405	coroutine library and lots more. They are also occasionally useful if
1961	you cache some data and want to flush it before blocking (for example,	2406	you cache some data and want to flush it before blocking (for example,
1962	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2407	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1963	watcher).	2408	watcher).
1964		2409
1965	This is done by examining in each prepare call which file descriptors need	2410	This is done by examining in each prepare call which file descriptors
1966	to be watched by the other library, registering C<ev_io> watchers for	2411	need to be watched by the other library, registering C<ev_io> watchers
1967	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2412	for them and starting an C<ev_timer> watcher for any timeouts (many
1968	provide just this functionality). Then, in the check watcher you check for	2413	libraries provide exactly this functionality). Then, in the check watcher,
1969	any events that occurred (by checking the pending status of all watchers	2414	you check for any events that occurred (by checking the pending status
1970	and stopping them) and call back into the library. The I/O and timer	2415	of all watchers and stopping them) and call back into the library. The
1971	callbacks will never actually be called (but must be valid nevertheless,	2416	I/O and timer callbacks will never actually be called (but must be valid
1972	because you never know, you know?).	2417	nevertheless, because you never know, you know?).
1973		2418
1974	As another example, the Perl Coro module uses these hooks to integrate	2419	As another example, the Perl Coro module uses these hooks to integrate
1975	coroutines into libev programs, by yielding to other active coroutines	2420	coroutines into libev programs, by yielding to other active coroutines
1976	during each prepare and only letting the process block if no coroutines	2421	during each prepare and only letting the process block if no coroutines
1977	are ready to run (it's actually more complicated: it only runs coroutines	2422	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1980	loop from blocking if lower-priority coroutines are active, thus mapping	2425	loop from blocking if lower-priority coroutines are active, thus mapping
1981	low-priority coroutines to idle/background tasks).	2426	low-priority coroutines to idle/background tasks).
1982		2427
1983	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2428	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1984	priority, to ensure that they are being run before any other watchers	2429	priority, to ensure that they are being run before any other watchers
		2430	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2431
1985	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2432	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1986	too) should not activate ("feed") events into libev. While libev fully	2433	activate ("feed") events into libev. While libev fully supports this, they
1987	supports this, they might get executed before other C<ev_check> watchers	2434	might get executed before other C<ev_check> watchers did their job. As
1988	did their job. As C<ev_check> watchers are often used to embed other	2435	C<ev_check> watchers are often used to embed other (non-libev) event
1989	(non-libev) event loops those other event loops might be in an unusable	2436	loops those other event loops might be in an unusable state until their
1990	state until their C<ev_check> watcher ran (always remind yourself to	2437	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1991	coexist peacefully with others).	2438	others).
1992		2439
1993	=head3 Watcher-Specific Functions and Data Members	2440	=head3 Watcher-Specific Functions and Data Members
1994		2441
1995	=over 4	2442	=over 4
1996		2443
…		…
1998		2445
1999	=item ev_check_init (ev_check *, callback)	2446	=item ev_check_init (ev_check *, callback)
2000		2447
2001	Initialises and configures the prepare or check watcher - they have no	2448	Initialises and configures the prepare or check watcher - they have no
2002	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2449	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
2003	macros, but using them is utterly, utterly and completely pointless.	2450	macros, but using them is utterly, utterly, utterly and completely
		2451	pointless.
2004		2452
2005	=back	2453	=back
2006		2454
2007	=head3 Examples	2455	=head3 Examples
2008		2456
…		…
2021		2469
2022	static ev_io iow [nfd];	2470	static ev_io iow [nfd];
2023	static ev_timer tw;	2471	static ev_timer tw;
2024		2472
2025	static void	2473	static void
2026	io_cb (ev_loop *loop, ev_io *w, int revents)	2474	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2027	{	2475	{
2028	}	2476	}
2029		2477
2030	// create io watchers for each fd and a timer before blocking	2478	// create io watchers for each fd and a timer before blocking
2031	static void	2479	static void
2032	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2480	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2033	{	2481	{
2034	int timeout = 3600000;	2482	int timeout = 3600000;
2035	struct pollfd fds [nfd];	2483	struct pollfd fds [nfd];
2036	// actual code will need to loop here and realloc etc.	2484	// actual code will need to loop here and realloc etc.
2037	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2485	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2038		2486
2039	/* the callback is illegal, but won't be called as we stop during check */	2487	/* the callback is illegal, but won't be called as we stop during check */
2040	ev_timer_init (&tw, 0, timeout * 1e-3);	2488	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2041	ev_timer_start (loop, &tw);	2489	ev_timer_start (loop, &tw);
2042		2490
2043	// create one ev_io per pollfd	2491	// create one ev_io per pollfd
2044	for (int i = 0; i < nfd; ++i)	2492	for (int i = 0; i < nfd; ++i)
2045	{	2493	{
…		…
2052	}	2500	}
2053	}	2501	}
2054		2502
2055	// stop all watchers after blocking	2503	// stop all watchers after blocking
2056	static void	2504	static void
2057	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2505	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2058	{	2506	{
2059	ev_timer_stop (loop, &tw);	2507	ev_timer_stop (loop, &tw);
2060		2508
2061	for (int i = 0; i < nfd; ++i)	2509	for (int i = 0; i < nfd; ++i)
2062	{	2510	{
…		…
2101	}	2549	}
2102		2550
2103	// do not ever call adns_afterpoll	2551	// do not ever call adns_afterpoll
2104		2552
2105	Method 4: Do not use a prepare or check watcher because the module you	2553	Method 4: Do not use a prepare or check watcher because the module you
2106	want to embed is too inflexible to support it. Instead, you can override	2554	want to embed is not flexible enough to support it. Instead, you can
2107	their poll function. The drawback with this solution is that the main	2555	override their poll function. The drawback with this solution is that the
2108	loop is now no longer controllable by EV. The C<Glib::EV> module does	2556	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2109	this.	2557	this approach, effectively embedding EV as a client into the horrible
		2558	libglib event loop.
2110		2559
2111	static gint	2560	static gint
2112	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2561	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2113	{	2562	{
2114	int got_events = 0;	2563	int got_events = 0;
…		…
2145	prioritise I/O.	2594	prioritise I/O.
2146		2595
2147	As an example for a bug workaround, the kqueue backend might only support	2596	As an example for a bug workaround, the kqueue backend might only support
2148	sockets on some platform, so it is unusable as generic backend, but you	2597	sockets on some platform, so it is unusable as generic backend, but you
2149	still want to make use of it because you have many sockets and it scales	2598	still want to make use of it because you have many sockets and it scales
2150	so nicely. In this case, you would create a kqueue-based loop and embed it	2599	so nicely. In this case, you would create a kqueue-based loop and embed
2151	into your default loop (which might use e.g. poll). Overall operation will	2600	it into your default loop (which might use e.g. poll). Overall operation
2152	be a bit slower because first libev has to poll and then call kevent, but	2601	will be a bit slower because first libev has to call C<poll> and then
2153	at least you can use both at what they are best.	2602	C<kevent>, but at least you can use both mechanisms for what they are
		2603	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2154		2604
2155	As for prioritising I/O: rarely you have the case where some fds have	2605	As for prioritising I/O: under rare circumstances you have the case where
2156	to be watched and handled very quickly (with low latency), and even	2606	some fds have to be watched and handled very quickly (with low latency),
2157	priorities and idle watchers might have too much overhead. In this case	2607	and even priorities and idle watchers might have too much overhead. In
2158	you would put all the high priority stuff in one loop and all the rest in	2608	this case you would put all the high priority stuff in one loop and all
2159	a second one, and embed the second one in the first.	2609	the rest in a second one, and embed the second one in the first.
2160		2610
2161	As long as the watcher is active, the callback will be invoked every time	2611	As long as the watcher is active, the callback will be invoked every
2162	there might be events pending in the embedded loop. The callback must then	2612	time there might be events pending in the embedded loop. The callback
2163	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2613	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2164	their callbacks (you could also start an idle watcher to give the embedded	2614	sweep and invoke their callbacks (the callback doesn't need to invoke the
2165	loop strictly lower priority for example). You can also set the callback	2615	C<ev_embed_sweep> function directly, it could also start an idle watcher
2166	to C<0>, in which case the embed watcher will automatically execute the	2616	to give the embedded loop strictly lower priority for example).
2167	embedded loop sweep.
2168		2617
2169	As long as the watcher is started it will automatically handle events. The	2618	You can also set the callback to C<0>, in which case the embed watcher
2170	callback will be invoked whenever some events have been handled. You can	2619	will automatically execute the embedded loop sweep whenever necessary.
2171	set the callback to C<0> to avoid having to specify one if you are not
2172	interested in that.
2173		2620
2174	Also, there have not currently been made special provisions for forking:	2621	Fork detection will be handled transparently while the C<ev_embed> watcher
2175	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2622	is active, i.e., the embedded loop will automatically be forked when the
2176	but you will also have to stop and restart any C<ev_embed> watchers	2623	embedding loop forks. In other cases, the user is responsible for calling
2177	yourself.	2624	C<ev_loop_fork> on the embedded loop.
2178		2625
2179	Unfortunately, not all backends are embeddable, only the ones returned by	2626	Unfortunately, not all backends are embeddable: only the ones returned by
2180	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2627	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2181	portable one.	2628	portable one.
2182		2629
2183	So when you want to use this feature you will always have to be prepared	2630	So when you want to use this feature you will always have to be prepared
2184	that you cannot get an embeddable loop. The recommended way to get around	2631	that you cannot get an embeddable loop. The recommended way to get around
2185	this is to have a separate variables for your embeddable loop, try to	2632	this is to have a separate variables for your embeddable loop, try to
2186	create it, and if that fails, use the normal loop for everything.	2633	create it, and if that fails, use the normal loop for everything.
		2634
		2635	=head3 C<ev_embed> and fork
		2636
		2637	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2638	automatically be applied to the embedded loop as well, so no special
		2639	fork handling is required in that case. When the watcher is not running,
		2640	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2641	as applicable.
2187		2642
2188	=head3 Watcher-Specific Functions and Data Members	2643	=head3 Watcher-Specific Functions and Data Members
2189		2644
2190	=over 4	2645	=over 4
2191		2646
…		…
2219	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2674	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2220	used).	2675	used).
2221		2676
2222	struct ev_loop *loop_hi = ev_default_init (0);	2677	struct ev_loop *loop_hi = ev_default_init (0);
2223	struct ev_loop *loop_lo = 0;	2678	struct ev_loop *loop_lo = 0;
2224	struct ev_embed embed;	2679	ev_embed embed;
2225		2680
2226	// see if there is a chance of getting one that works	2681	// see if there is a chance of getting one that works
2227	// (remember that a flags value of 0 means autodetection)	2682	// (remember that a flags value of 0 means autodetection)
2228	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2683	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2229	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2684	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2243	kqueue implementation). Store the kqueue/socket-only event loop in	2698	kqueue implementation). Store the kqueue/socket-only event loop in
2244	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2699	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2245		2700
2246	struct ev_loop *loop = ev_default_init (0);	2701	struct ev_loop *loop = ev_default_init (0);
2247	struct ev_loop *loop_socket = 0;	2702	struct ev_loop *loop_socket = 0;
2248	struct ev_embed embed;	2703	ev_embed embed;
2249		2704
2250	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2705	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2251	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2706	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2252	{	2707	{
2253	ev_embed_init (&embed, 0, loop_socket);	2708	ev_embed_init (&embed, 0, loop_socket);
…		…
2268	event loop blocks next and before C<ev_check> watchers are being called,	2723	event loop blocks next and before C<ev_check> watchers are being called,
2269	and only in the child after the fork. If whoever good citizen calling	2724	and only in the child after the fork. If whoever good citizen calling
2270	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2725	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2271	handlers will be invoked, too, of course.	2726	handlers will be invoked, too, of course.
2272		2727
		2728	=head3 The special problem of life after fork - how is it possible?
		2729
		2730	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2731	up/change the process environment, followed by a call to C<exec()>. This
		2732	sequence should be handled by libev without any problems.
		2733
		2734	This changes when the application actually wants to do event handling
		2735	in the child, or both parent in child, in effect "continuing" after the
		2736	fork.
		2737
		2738	The default mode of operation (for libev, with application help to detect
		2739	forks) is to duplicate all the state in the child, as would be expected
		2740	when I<either> the parent I<or> the child process continues.
		2741
		2742	When both processes want to continue using libev, then this is usually the
		2743	wrong result. In that case, usually one process (typically the parent) is
		2744	supposed to continue with all watchers in place as before, while the other
		2745	process typically wants to start fresh, i.e. without any active watchers.
		2746
		2747	The cleanest and most efficient way to achieve that with libev is to
		2748	simply create a new event loop, which of course will be "empty", and
		2749	use that for new watchers. This has the advantage of not touching more
		2750	memory than necessary, and thus avoiding the copy-on-write, and the
		2751	disadvantage of having to use multiple event loops (which do not support
		2752	signal watchers).
		2753
		2754	When this is not possible, or you want to use the default loop for
		2755	other reasons, then in the process that wants to start "fresh", call
		2756	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2757	the default loop will "orphan" (not stop) all registered watchers, so you
		2758	have to be careful not to execute code that modifies those watchers. Note
		2759	also that in that case, you have to re-register any signal watchers.
		2760
2273	=head3 Watcher-Specific Functions and Data Members	2761	=head3 Watcher-Specific Functions and Data Members
2274		2762
2275	=over 4	2763	=over 4
2276		2764
2277	=item ev_fork_init (ev_signal *, callback)	2765	=item ev_fork_init (ev_signal *, callback)
…		…
2309	is that the author does not know of a simple (or any) algorithm for a	2797	is that the author does not know of a simple (or any) algorithm for a
2310	multiple-writer-single-reader queue that works in all cases and doesn't	2798	multiple-writer-single-reader queue that works in all cases and doesn't
2311	need elaborate support such as pthreads.	2799	need elaborate support such as pthreads.
2312		2800
2313	That means that if you want to queue data, you have to provide your own	2801	That means that if you want to queue data, you have to provide your own
2314	queue. But at least I can tell you would implement locking around your	2802	queue. But at least I can tell you how to implement locking around your
2315	queue:	2803	queue:
2316		2804
2317	=over 4	2805	=over 4
2318		2806
2319	=item queueing from a signal handler context	2807	=item queueing from a signal handler context
2320		2808
2321	To implement race-free queueing, you simply add to the queue in the signal	2809	To implement race-free queueing, you simply add to the queue in the signal
2322	handler but you block the signal handler in the watcher callback. Here is an example that does that for	2810	handler but you block the signal handler in the watcher callback. Here is
2323	some fictitious SIGUSR1 handler:	2811	an example that does that for some fictitious SIGUSR1 handler:
2324		2812
2325	static ev_async mysig;	2813	static ev_async mysig;
2326		2814
2327	static void	2815	static void
2328	sigusr1_handler (void)	2816	sigusr1_handler (void)
…		…
2394	=over 4	2882	=over 4
2395		2883
2396	=item ev_async_init (ev_async *, callback)	2884	=item ev_async_init (ev_async *, callback)
2397		2885
2398	Initialises and configures the async watcher - it has no parameters of any	2886	Initialises and configures the async watcher - it has no parameters of any
2399	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	2887	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2400	believe me.	2888	trust me.
2401		2889
2402	=item ev_async_send (loop, ev_async *)	2890	=item ev_async_send (loop, ev_async *)
2403		2891
2404	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	2892	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2405	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	2893	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2406	C<ev_feed_event>, this call is safe to do in other threads, signal or	2894	C<ev_feed_event>, this call is safe to do from other threads, signal or
2407	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	2895	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2408	section below on what exactly this means).	2896	section below on what exactly this means).
2409		2897
		2898	Note that, as with other watchers in libev, multiple events might get
		2899	compressed into a single callback invocation (another way to look at this
		2900	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2901	reset when the event loop detects that).
		2902
2410	This call incurs the overhead of a system call only once per loop iteration,	2903	This call incurs the overhead of a system call only once per event loop
2411	so while the overhead might be noticeable, it doesn't apply to repeated	2904	iteration, so while the overhead might be noticeable, it doesn't apply to
2412	calls to C<ev_async_send>.	2905	repeated calls to C<ev_async_send> for the same event loop.
2413		2906
2414	=item bool = ev_async_pending (ev_async *)	2907	=item bool = ev_async_pending (ev_async *)
2415		2908
2416	Returns a non-zero value when C<ev_async_send> has been called on the	2909	Returns a non-zero value when C<ev_async_send> has been called on the
2417	watcher but the event has not yet been processed (or even noted) by the	2910	watcher but the event has not yet been processed (or even noted) by the
…		…
2420	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	2913	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2421	the loop iterates next and checks for the watcher to have become active,	2914	the loop iterates next and checks for the watcher to have become active,
2422	it will reset the flag again. C<ev_async_pending> can be used to very	2915	it will reset the flag again. C<ev_async_pending> can be used to very
2423	quickly check whether invoking the loop might be a good idea.	2916	quickly check whether invoking the loop might be a good idea.
2424		2917
2425	Not that this does I<not> check whether the watcher itself is pending, only	2918	Not that this does I<not> check whether the watcher itself is pending,
2426	whether it has been requested to make this watcher pending.	2919	only whether it has been requested to make this watcher pending: there
		2920	is a time window between the event loop checking and resetting the async
		2921	notification, and the callback being invoked.
2427		2922
2428	=back	2923	=back
2429		2924
2430		2925
2431	=head1 OTHER FUNCTIONS	2926	=head1 OTHER FUNCTIONS
…		…
2435	=over 4	2930	=over 4
2436		2931
2437	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2932	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2438		2933
2439	This function combines a simple timer and an I/O watcher, calls your	2934	This function combines a simple timer and an I/O watcher, calls your
2440	callback on whichever event happens first and automatically stop both	2935	callback on whichever event happens first and automatically stops both
2441	watchers. This is useful if you want to wait for a single event on an fd	2936	watchers. This is useful if you want to wait for a single event on an fd
2442	or timeout without having to allocate/configure/start/stop/free one or	2937	or timeout without having to allocate/configure/start/stop/free one or
2443	more watchers yourself.	2938	more watchers yourself.
2444		2939
2445	If C<fd> is less than 0, then no I/O watcher will be started and events	2940	If C<fd> is less than 0, then no I/O watcher will be started and the
2446	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2941	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2447	C<events> set will be created and started.	2942	the given C<fd> and C<events> set will be created and started.
2448		2943
2449	If C<timeout> is less than 0, then no timeout watcher will be	2944	If C<timeout> is less than 0, then no timeout watcher will be
2450	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2945	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2451	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2946	repeat = 0) will be started. C<0> is a valid timeout.
2452	dubious value.
2453		2947
2454	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2948	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
2455	passed an C<revents> set like normal event callbacks (a combination of	2949	passed an C<revents> set like normal event callbacks (a combination of
2456	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2950	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2457	value passed to C<ev_once>:	2951	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2952	a timeout and an io event at the same time - you probably should give io
		2953	events precedence.
		2954
		2955	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2458		2956
2459	static void stdin_ready (int revents, void *arg)	2957	static void stdin_ready (int revents, void *arg)
2460	{	2958	{
		2959	if (revents & EV_READ)
		2960	/* stdin might have data for us, joy! */;
2461	if (revents & EV_TIMEOUT)	2961	else if (revents & EV_TIMEOUT)
2462	/* doh, nothing entered */;	2962	/* doh, nothing entered */;
2463	else if (revents & EV_READ)
2464	/* stdin might have data for us, joy! */;
2465	}	2963	}
2466		2964
2467	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2965	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2468		2966
2469	=item ev_feed_event (ev_loop *, watcher *, int revents)	2967	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2470		2968
2471	Feeds the given event set into the event loop, as if the specified event	2969	Feeds the given event set into the event loop, as if the specified event
2472	had happened for the specified watcher (which must be a pointer to an	2970	had happened for the specified watcher (which must be a pointer to an
2473	initialised but not necessarily started event watcher).	2971	initialised but not necessarily started event watcher).
2474		2972
2475	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2973	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2476		2974
2477	Feed an event on the given fd, as if a file descriptor backend detected	2975	Feed an event on the given fd, as if a file descriptor backend detected
2478	the given events it.	2976	the given events it.
2479		2977
2480	=item ev_feed_signal_event (ev_loop *loop, int signum)	2978	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2481		2979
2482	Feed an event as if the given signal occurred (C<loop> must be the default	2980	Feed an event as if the given signal occurred (C<loop> must be the default
2483	loop!).	2981	loop!).
2484		2982
2485	=back	2983	=back
…		…
2607		3105
2608	myclass obj;	3106	myclass obj;
2609	ev::io iow;	3107	ev::io iow;
2610	iow.set <myclass, &myclass::io_cb> (&obj);	3108	iow.set <myclass, &myclass::io_cb> (&obj);
2611		3109
		3110	=item w->set (object *)
		3111
		3112	This is an B<experimental> feature that might go away in a future version.
		3113
		3114	This is a variation of a method callback - leaving out the method to call
		3115	will default the method to C<operator ()>, which makes it possible to use
		3116	functor objects without having to manually specify the C<operator ()> all
		3117	the time. Incidentally, you can then also leave out the template argument
		3118	list.
		3119
		3120	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3121	int revents)>.
		3122
		3123	See the method-C<set> above for more details.
		3124
		3125	Example: use a functor object as callback.
		3126
		3127	struct myfunctor
		3128	{
		3129	void operator() (ev::io &w, int revents)
		3130	{
		3131	...
		3132	}
		3133	}
		3134
		3135	myfunctor f;
		3136
		3137	ev::io w;
		3138	w.set (&f);
		3139
2612	=item w->set<function> (void *data = 0)	3140	=item w->set<function> (void *data = 0)
2613		3141
2614	Also sets a callback, but uses a static method or plain function as	3142	Also sets a callback, but uses a static method or plain function as
2615	callback. The optional C<data> argument will be stored in the watcher's	3143	callback. The optional C<data> argument will be stored in the watcher's
2616	C<data> member and is free for you to use.	3144	C<data> member and is free for you to use.
2617		3145
2618	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3146	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2619		3147
2620	See the method-C<set> above for more details.	3148	See the method-C<set> above for more details.
2621		3149
2622	Example:	3150	Example: Use a plain function as callback.
2623		3151
2624	static void io_cb (ev::io &w, int revents) { }	3152	static void io_cb (ev::io &w, int revents) { }
2625	iow.set <io_cb> ();	3153	iow.set <io_cb> ();
2626		3154
2627	=item w->set (struct ev_loop *)	3155	=item w->set (struct ev_loop *)
…		…
2665	Example: Define a class with an IO and idle watcher, start one of them in	3193	Example: Define a class with an IO and idle watcher, start one of them in
2666	the constructor.	3194	the constructor.
2667		3195
2668	class myclass	3196	class myclass
2669	{	3197	{
2670	ev::io io; void io_cb (ev::io &w, int revents);	3198	ev::io io ; void io_cb (ev::io &w, int revents);
2671	ev:idle idle void idle_cb (ev::idle &w, int revents);	3199	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2672		3200
2673	myclass (int fd)	3201	myclass (int fd)
2674	{	3202	{
2675	io .set <myclass, &myclass::io_cb > (this);	3203	io .set <myclass, &myclass::io_cb > (this);
2676	idle.set <myclass, &myclass::idle_cb> (this);	3204	idle.set <myclass, &myclass::idle_cb> (this);
…		…
2692	=item Perl	3220	=item Perl
2693		3221
2694	The EV module implements the full libev API and is actually used to test	3222	The EV module implements the full libev API and is actually used to test
2695	libev. EV is developed together with libev. Apart from the EV core module,	3223	libev. EV is developed together with libev. Apart from the EV core module,
2696	there are additional modules that implement libev-compatible interfaces	3224	there are additional modules that implement libev-compatible interfaces
2697	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3225	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2698	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3226	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3227	and C<EV::Glib>).
2699		3228
2700	It can be found and installed via CPAN, its homepage is at	3229	It can be found and installed via CPAN, its homepage is at
2701	L<http://software.schmorp.de/pkg/EV>.	3230	L<http://software.schmorp.de/pkg/EV>.
2702		3231
2703	=item Python	3232	=item Python
2704		3233
2705	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3234	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2706	seems to be quite complete and well-documented. Note, however, that the	3235	seems to be quite complete and well-documented.
2707	patch they require for libev is outright dangerous as it breaks the ABI
2708	for everybody else, and therefore, should never be applied in an installed
2709	libev (if python requires an incompatible ABI then it needs to embed
2710	libev).
2711		3236
2712	=item Ruby	3237	=item Ruby
2713		3238
2714	Tony Arcieri has written a ruby extension that offers access to a subset	3239	Tony Arcieri has written a ruby extension that offers access to a subset
2715	of the libev API and adds file handle abstractions, asynchronous DNS and	3240	of the libev API and adds file handle abstractions, asynchronous DNS and
2716	more on top of it. It can be found via gem servers. Its homepage is at	3241	more on top of it. It can be found via gem servers. Its homepage is at
2717	L<http://rev.rubyforge.org/>.	3242	L<http://rev.rubyforge.org/>.
2718		3243
		3244	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3245	makes rev work even on mingw.
		3246
		3247	=item Haskell
		3248
		3249	A haskell binding to libev is available at
		3250	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3251
2719	=item D	3252	=item D
2720		3253
2721	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3254	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2722	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3255	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3256
		3257	=item Ocaml
		3258
		3259	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3260	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
2723		3261
2724	=back	3262	=back
2725		3263
2726		3264
2727	=head1 MACRO MAGIC	3265	=head1 MACRO MAGIC
…		…
2828		3366
2829	#define EV_STANDALONE 1	3367	#define EV_STANDALONE 1
2830	#include "ev.h"	3368	#include "ev.h"
2831		3369
2832	Both header files and implementation files can be compiled with a C++	3370	Both header files and implementation files can be compiled with a C++
2833	compiler (at least, thats a stated goal, and breakage will be treated	3371	compiler (at least, that's a stated goal, and breakage will be treated
2834	as a bug).	3372	as a bug).
2835		3373
2836	You need the following files in your source tree, or in a directory	3374	You need the following files in your source tree, or in a directory
2837	in your include path (e.g. in libev/ when using -Ilibev):	3375	in your include path (e.g. in libev/ when using -Ilibev):
2838		3376
…		…
2882		3420
2883	=head2 PREPROCESSOR SYMBOLS/MACROS	3421	=head2 PREPROCESSOR SYMBOLS/MACROS
2884		3422
2885	Libev can be configured via a variety of preprocessor symbols you have to	3423	Libev can be configured via a variety of preprocessor symbols you have to
2886	define before including any of its files. The default in the absence of	3424	define before including any of its files. The default in the absence of
2887	autoconf is noted for every option.	3425	autoconf is documented for every option.
2888		3426
2889	=over 4	3427	=over 4
2890		3428
2891	=item EV_STANDALONE	3429	=item EV_STANDALONE
2892		3430
…		…
2894	keeps libev from including F<config.h>, and it also defines dummy	3432	keeps libev from including F<config.h>, and it also defines dummy
2895	implementations for some libevent functions (such as logging, which is not	3433	implementations for some libevent functions (such as logging, which is not
2896	supported). It will also not define any of the structs usually found in	3434	supported). It will also not define any of the structs usually found in
2897	F<event.h> that are not directly supported by the libev core alone.	3435	F<event.h> that are not directly supported by the libev core alone.
2898		3436
		3437	In stanbdalone mode, libev will still try to automatically deduce the
		3438	configuration, but has to be more conservative.
		3439
2899	=item EV_USE_MONOTONIC	3440	=item EV_USE_MONOTONIC
2900		3441
2901	If defined to be C<1>, libev will try to detect the availability of the	3442	If defined to be C<1>, libev will try to detect the availability of the
2902	monotonic clock option at both compile time and runtime. Otherwise no use	3443	monotonic clock option at both compile time and runtime. Otherwise no
2903	of the monotonic clock option will be attempted. If you enable this, you	3444	use of the monotonic clock option will be attempted. If you enable this,
2904	usually have to link against librt or something similar. Enabling it when	3445	you usually have to link against librt or something similar. Enabling it
2905	the functionality isn't available is safe, though, although you have	3446	when the functionality isn't available is safe, though, although you have
2906	to make sure you link against any libraries where the C<clock_gettime>	3447	to make sure you link against any libraries where the C<clock_gettime>
2907	function is hiding in (often F<-lrt>).	3448	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2908		3449
2909	=item EV_USE_REALTIME	3450	=item EV_USE_REALTIME
2910		3451
2911	If defined to be C<1>, libev will try to detect the availability of the	3452	If defined to be C<1>, libev will try to detect the availability of the
2912	real-time clock option at compile time (and assume its availability at	3453	real-time clock option at compile time (and assume its availability
2913	runtime if successful). Otherwise no use of the real-time clock option will	3454	at runtime if successful). Otherwise no use of the real-time clock
2914	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3455	option will be attempted. This effectively replaces C<gettimeofday>
2915	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3456	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2916	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3457	correctness. See the note about libraries in the description of
		3458	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3459	C<EV_USE_CLOCK_SYSCALL>.
		3460
		3461	=item EV_USE_CLOCK_SYSCALL
		3462
		3463	If defined to be C<1>, libev will try to use a direct syscall instead
		3464	of calling the system-provided C<clock_gettime> function. This option
		3465	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3466	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3467	programs needlessly. Using a direct syscall is slightly slower (in
		3468	theory), because no optimised vdso implementation can be used, but avoids
		3469	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3470	higher, as it simplifies linking (no need for C<-lrt>).
2917		3471
2918	=item EV_USE_NANOSLEEP	3472	=item EV_USE_NANOSLEEP
2919		3473
2920	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3474	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2921	and will use it for delays. Otherwise it will use C<select ()>.	3475	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2937		3491
2938	=item EV_SELECT_USE_FD_SET	3492	=item EV_SELECT_USE_FD_SET
2939		3493
2940	If defined to C<1>, then the select backend will use the system C<fd_set>	3494	If defined to C<1>, then the select backend will use the system C<fd_set>
2941	structure. This is useful if libev doesn't compile due to a missing	3495	structure. This is useful if libev doesn't compile due to a missing
2942	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3496	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2943	exotic systems. This usually limits the range of file descriptors to some	3497	on exotic systems. This usually limits the range of file descriptors to
2944	low limit such as 1024 or might have other limitations (winsocket only	3498	some low limit such as 1024 or might have other limitations (winsocket
2945	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3499	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2946	influence the size of the C<fd_set> used.	3500	configures the maximum size of the C<fd_set>.
2947		3501
2948	=item EV_SELECT_IS_WINSOCKET	3502	=item EV_SELECT_IS_WINSOCKET
2949		3503
2950	When defined to C<1>, the select backend will assume that	3504	When defined to C<1>, the select backend will assume that
2951	select/socket/connect etc. don't understand file descriptors but	3505	select/socket/connect etc. don't understand file descriptors but
…		…
3062	When doing priority-based operations, libev usually has to linearly search	3616	When doing priority-based operations, libev usually has to linearly search
3063	all the priorities, so having many of them (hundreds) uses a lot of space	3617	all the priorities, so having many of them (hundreds) uses a lot of space
3064	and time, so using the defaults of five priorities (-2 .. +2) is usually	3618	and time, so using the defaults of five priorities (-2 .. +2) is usually
3065	fine.	3619	fine.
3066		3620
3067	If your embedding application does not need any priorities, defining these both to	3621	If your embedding application does not need any priorities, defining these
3068	C<0> will save some memory and CPU.	3622	both to C<0> will save some memory and CPU.
3069		3623
3070	=item EV_PERIODIC_ENABLE	3624	=item EV_PERIODIC_ENABLE
3071		3625
3072	If undefined or defined to be C<1>, then periodic timers are supported. If	3626	If undefined or defined to be C<1>, then periodic timers are supported. If
3073	defined to be C<0>, then they are not. Disabling them saves a few kB of	3627	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
3080	code.	3634	code.
3081		3635
3082	=item EV_EMBED_ENABLE	3636	=item EV_EMBED_ENABLE
3083		3637
3084	If undefined or defined to be C<1>, then embed watchers are supported. If	3638	If undefined or defined to be C<1>, then embed watchers are supported. If
3085	defined to be C<0>, then they are not.	3639	defined to be C<0>, then they are not. Embed watchers rely on most other
		3640	watcher types, which therefore must not be disabled.
3086		3641
3087	=item EV_STAT_ENABLE	3642	=item EV_STAT_ENABLE
3088		3643
3089	If undefined or defined to be C<1>, then stat watchers are supported. If	3644	If undefined or defined to be C<1>, then stat watchers are supported. If
3090	defined to be C<0>, then they are not.	3645	defined to be C<0>, then they are not.
…		…
3122	two).	3677	two).
3123		3678
3124	=item EV_USE_4HEAP	3679	=item EV_USE_4HEAP
3125		3680
3126	Heaps are not very cache-efficient. To improve the cache-efficiency of the	3681	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3127	timer and periodics heap, libev uses a 4-heap when this symbol is defined	3682	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3128	to C<1>. The 4-heap uses more complicated (longer) code but has	3683	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3129	noticeably faster performance with many (thousands) of watchers.	3684	faster performance with many (thousands) of watchers.
3130		3685
3131	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	3686	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
3132	(disabled).	3687	(disabled).
3133		3688
3134	=item EV_HEAP_CACHE_AT	3689	=item EV_HEAP_CACHE_AT
3135		3690
3136	Heaps are not very cache-efficient. To improve the cache-efficiency of the	3691	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3137	timer and periodics heap, libev can cache the timestamp (I<at>) within	3692	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3138	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	3693	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3139	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	3694	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3140	but avoids random read accesses on heap changes. This improves performance	3695	but avoids random read accesses on heap changes. This improves performance
3141	noticeably with with many (hundreds) of watchers.	3696	noticeably with many (hundreds) of watchers.
3142		3697
3143	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	3698	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
3144	(disabled).	3699	(disabled).
3145		3700
3146	=item EV_VERIFY	3701	=item EV_VERIFY
…		…
3152	called once per loop, which can slow down libev. If set to C<3>, then the	3707	called once per loop, which can slow down libev. If set to C<3>, then the
3153	verification code will be called very frequently, which will slow down	3708	verification code will be called very frequently, which will slow down
3154	libev considerably.	3709	libev considerably.
3155		3710
3156	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	3711	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
3157	C<0.>	3712	C<0>.
3158		3713
3159	=item EV_COMMON	3714	=item EV_COMMON
3160		3715
3161	By default, all watchers have a C<void *data> member. By redefining	3716	By default, all watchers have a C<void *data> member. By redefining
3162	this macro to a something else you can include more and other types of	3717	this macro to a something else you can include more and other types of
…		…
3179	and the way callbacks are invoked and set. Must expand to a struct member	3734	and the way callbacks are invoked and set. Must expand to a struct member
3180	definition and a statement, respectively. See the F<ev.h> header file for	3735	definition and a statement, respectively. See the F<ev.h> header file for
3181	their default definitions. One possible use for overriding these is to	3736	their default definitions. One possible use for overriding these is to
3182	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3737	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3183	method calls instead of plain function calls in C++.	3738	method calls instead of plain function calls in C++.
		3739
		3740	=back
3184		3741
3185	=head2 EXPORTED API SYMBOLS	3742	=head2 EXPORTED API SYMBOLS
3186		3743
3187	If you need to re-export the API (e.g. via a DLL) and you need a list of	3744	If you need to re-export the API (e.g. via a DLL) and you need a list of
3188	exported symbols, you can use the provided F<Symbol.*> files which list	3745	exported symbols, you can use the provided F<Symbol.*> files which list
…		…
3235	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3792	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3236		3793
3237	#include "ev_cpp.h"	3794	#include "ev_cpp.h"
3238	#include "ev.c"	3795	#include "ev.c"
3239		3796
		3797	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3240		3798
3241	=head1 THREADS AND COROUTINES	3799	=head2 THREADS AND COROUTINES
3242		3800
3243	=head2 THREADS	3801	=head3 THREADS
3244		3802
3245	Libev itself is thread-safe (unless the opposite is specifically	3803	All libev functions are reentrant and thread-safe unless explicitly
3246	documented for a function), but it uses no locking itself. This means that	3804	documented otherwise, but libev implements no locking itself. This means
3247	you can use as many loops as you want in parallel, as long as only one	3805	that you can use as many loops as you want in parallel, as long as there
3248	thread ever calls into one libev function with the same loop parameter:	3806	are no concurrent calls into any libev function with the same loop
		3807	parameter (C<ev_default_*> calls have an implicit default loop parameter,
3249	libev guarentees that different event loops share no data structures that	3808	of course): libev guarantees that different event loops share no data
3250	need locking.	3809	structures that need any locking.
3251		3810
3252	Or to put it differently: calls with different loop parameters can be done	3811	Or to put it differently: calls with different loop parameters can be done
3253	concurrently from multiple threads, calls with the same loop parameter	3812	concurrently from multiple threads, calls with the same loop parameter
3254	must be done serially (but can be done from different threads, as long as	3813	must be done serially (but can be done from different threads, as long as
3255	only one thread ever is inside a call at any point in time, e.g. by using	3814	only one thread ever is inside a call at any point in time, e.g. by using
3256	a mutex per loop).	3815	a mutex per loop).
3257		3816
3258	Specifically to support threads (and signal handlers), libev implements	3817	Specifically to support threads (and signal handlers), libev implements
3259	so-called C<ev_async> watchers, which allow some limited form of	3818	so-called C<ev_async> watchers, which allow some limited form of
3260	concurrency on the same event loop.	3819	concurrency on the same event loop, namely waking it up "from the
		3820	outside".
3261		3821
3262	If you want to know which design (one loop, locking, or multiple loops	3822	If you want to know which design (one loop, locking, or multiple loops
3263	without or something else still) is best for your problem, then I cannot	3823	without or something else still) is best for your problem, then I cannot
3264	help you. I can give some generic advice however:	3824	help you, but here is some generic advice:
3265		3825
3266	=over 4	3826	=over 4
3267		3827
3268	=item * most applications have a main thread: use the default libev loop	3828	=item * most applications have a main thread: use the default libev loop
3269	in that thread, or create a separate thread running only the default loop.	3829	in that thread, or create a separate thread running only the default loop.
…		…
3281		3841
3282	Choosing a model is hard - look around, learn, know that usually you can do	3842	Choosing a model is hard - look around, learn, know that usually you can do
3283	better than you currently do :-)	3843	better than you currently do :-)
3284		3844
3285	=item * often you need to talk to some other thread which blocks in the	3845	=item * often you need to talk to some other thread which blocks in the
		3846	event loop.
		3847
3286	event loop - C<ev_async> watchers can be used to wake them up from other	3848	C<ev_async> watchers can be used to wake them up from other threads safely
3287	threads safely (or from signal contexts...).	3849	(or from signal contexts...).
3288		3850
3289	=item * some watcher types are only supported in the default loop - use	3851	An example use would be to communicate signals or other events that only
3290	C<ev_async> watchers to tell your other loops about any such events.	3852	work in the default loop by registering the signal watcher with the
		3853	default loop and triggering an C<ev_async> watcher from the default loop
		3854	watcher callback into the event loop interested in the signal.
3291		3855
3292	=back	3856	=back
3293		3857
3294	=head2 COROUTINES	3858	=head3 COROUTINES
3295		3859
3296	Libev is much more accommodating to coroutines ("cooperative threads"):	3860	Libev is very accommodating to coroutines ("cooperative threads"):
3297	libev fully supports nesting calls to it's functions from different	3861	libev fully supports nesting calls to its functions from different
3298	coroutines (e.g. you can call C<ev_loop> on the same loop from two	3862	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3299	different coroutines and switch freely between both coroutines running the	3863	different coroutines, and switch freely between both coroutines running the
3300	loop, as long as you don't confuse yourself). The only exception is that	3864	loop, as long as you don't confuse yourself). The only exception is that
3301	you must not do this from C<ev_periodic> reschedule callbacks.	3865	you must not do this from C<ev_periodic> reschedule callbacks.
3302		3866
3303	Care has been taken to ensure that libev does not keep local state inside	3867	Care has been taken to ensure that libev does not keep local state inside
3304	C<ev_loop>, and other calls do not usually allow coroutine switches.	3868	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3869	they do not call any callbacks.
3305		3870
		3871	=head2 COMPILER WARNINGS
3306		3872
3307	=head1 COMPLEXITIES	3873	Depending on your compiler and compiler settings, you might get no or a
		3874	lot of warnings when compiling libev code. Some people are apparently
		3875	scared by this.
3308		3876
3309	In this section the complexities of (many of) the algorithms used inside	3877	However, these are unavoidable for many reasons. For one, each compiler
3310	libev will be explained. For complexity discussions about backends see the	3878	has different warnings, and each user has different tastes regarding
3311	documentation for C<ev_default_init>.	3879	warning options. "Warn-free" code therefore cannot be a goal except when
		3880	targeting a specific compiler and compiler-version.
3312		3881
3313	All of the following are about amortised time: If an array needs to be	3882	Another reason is that some compiler warnings require elaborate
3314	extended, libev needs to realloc and move the whole array, but this	3883	workarounds, or other changes to the code that make it less clear and less
3315	happens asymptotically never with higher number of elements, so O(1) might	3884	maintainable.
3316	mean it might do a lengthy realloc operation in rare cases, but on average
3317	it is much faster and asymptotically approaches constant time.
3318		3885
3319	=over 4	3886	And of course, some compiler warnings are just plain stupid, or simply
		3887	wrong (because they don't actually warn about the condition their message
		3888	seems to warn about). For example, certain older gcc versions had some
		3889	warnings that resulted an extreme number of false positives. These have
		3890	been fixed, but some people still insist on making code warn-free with
		3891	such buggy versions.
3320		3892
3321	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3893	While libev is written to generate as few warnings as possible,
		3894	"warn-free" code is not a goal, and it is recommended not to build libev
		3895	with any compiler warnings enabled unless you are prepared to cope with
		3896	them (e.g. by ignoring them). Remember that warnings are just that:
		3897	warnings, not errors, or proof of bugs.
3322		3898
3323	This means that, when you have a watcher that triggers in one hour and
3324	there are 100 watchers that would trigger before that then inserting will
3325	have to skip roughly seven (C<ld 100>) of these watchers.
3326		3899
3327	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	3900	=head2 VALGRIND
3328		3901
3329	That means that changing a timer costs less than removing/adding them	3902	Valgrind has a special section here because it is a popular tool that is
3330	as only the relative motion in the event queue has to be paid for.	3903	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3331		3904
3332	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	3905	If you think you found a bug (memory leak, uninitialised data access etc.)
		3906	in libev, then check twice: If valgrind reports something like:
3333		3907
3334	These just add the watcher into an array or at the head of a list.	3908	==2274== definitely lost: 0 bytes in 0 blocks.
		3909	==2274== possibly lost: 0 bytes in 0 blocks.
		3910	==2274== still reachable: 256 bytes in 1 blocks.
3335		3911
3336	=item Stopping check/prepare/idle/fork/async watchers: O(1)	3912	Then there is no memory leak, just as memory accounted to global variables
		3913	is not a memleak - the memory is still being referenced, and didn't leak.
3337		3914
3338	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3915	Similarly, under some circumstances, valgrind might report kernel bugs
		3916	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3917	although an acceptable workaround has been found here), or it might be
		3918	confused.
3339		3919
3340	These watchers are stored in lists then need to be walked to find the	3920	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3341	correct watcher to remove. The lists are usually short (you don't usually	3921	make it into some kind of religion.
3342	have many watchers waiting for the same fd or signal).
3343		3922
3344	=item Finding the next timer in each loop iteration: O(1)	3923	If you are unsure about something, feel free to contact the mailing list
		3924	with the full valgrind report and an explanation on why you think this
		3925	is a bug in libev (best check the archives, too :). However, don't be
		3926	annoyed when you get a brisk "this is no bug" answer and take the chance
		3927	of learning how to interpret valgrind properly.
3345		3928
3346	By virtue of using a binary or 4-heap, the next timer is always found at a	3929	If you need, for some reason, empty reports from valgrind for your project
3347	fixed position in the storage array.	3930	I suggest using suppression lists.
3348		3931
3349	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3350		3932
3351	A change means an I/O watcher gets started or stopped, which requires	3933	=head1 PORTABILITY NOTES
3352	libev to recalculate its status (and possibly tell the kernel, depending
3353	on backend and whether C<ev_io_set> was used).
3354		3934
3355	=item Activating one watcher (putting it into the pending state): O(1)
3356
3357	=item Priority handling: O(number_of_priorities)
3358
3359	Priorities are implemented by allocating some space for each
3360	priority. When doing priority-based operations, libev usually has to
3361	linearly search all the priorities, but starting/stopping and activating
3362	watchers becomes O(1) w.r.t. priority handling.
3363
3364	=item Sending an ev_async: O(1)
3365
3366	=item Processing ev_async_send: O(number_of_async_watchers)
3367
3368	=item Processing signals: O(max_signal_number)
3369
3370	Sending involves a system call I<iff> there were no other C<ev_async_send>
3371	calls in the current loop iteration. Checking for async and signal events
3372	involves iterating over all running async watchers or all signal numbers.
3373
3374	=back
3375
3376
3377	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	3935	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3378		3936
3379	Win32 doesn't support any of the standards (e.g. POSIX) that libev	3937	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3380	requires, and its I/O model is fundamentally incompatible with the POSIX	3938	requires, and its I/O model is fundamentally incompatible with the POSIX
3381	model. Libev still offers limited functionality on this platform in	3939	model. Libev still offers limited functionality on this platform in
3382	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3940	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
…		…
3389	way (note also that glib is the slowest event library known to man).	3947	way (note also that glib is the slowest event library known to man).
3390		3948
3391	There is no supported compilation method available on windows except	3949	There is no supported compilation method available on windows except
3392	embedding it into other applications.	3950	embedding it into other applications.
3393		3951
		3952	Sensible signal handling is officially unsupported by Microsoft - libev
		3953	tries its best, but under most conditions, signals will simply not work.
		3954
3394	Not a libev limitation but worth mentioning: windows apparently doesn't	3955	Not a libev limitation but worth mentioning: windows apparently doesn't
3395	accept large writes: instead of resulting in a partial write, windows will	3956	accept large writes: instead of resulting in a partial write, windows will
3396	either accept everything or return C<ENOBUFS> if the buffer is too large,	3957	either accept everything or return C<ENOBUFS> if the buffer is too large,
3397	so make sure you only write small amounts into your sockets (less than a	3958	so make sure you only write small amounts into your sockets (less than a
3398	megabyte seems safe, but thsi apparently depends on the amount of memory	3959	megabyte seems safe, but this apparently depends on the amount of memory
3399	available).	3960	available).
3400		3961
3401	Due to the many, low, and arbitrary limits on the win32 platform and	3962	Due to the many, low, and arbitrary limits on the win32 platform and
3402	the abysmal performance of winsockets, using a large number of sockets	3963	the abysmal performance of winsockets, using a large number of sockets
3403	is not recommended (and not reasonable). If your program needs to use	3964	is not recommended (and not reasonable). If your program needs to use
3404	more than a hundred or so sockets, then likely it needs to use a totally	3965	more than a hundred or so sockets, then likely it needs to use a totally
3405	different implementation for windows, as libev offers the POSIX readiness	3966	different implementation for windows, as libev offers the POSIX readiness
3406	notification model, which cannot be implemented efficiently on windows	3967	notification model, which cannot be implemented efficiently on windows
3407	(Microsoft monopoly games).	3968	(due to Microsoft monopoly games).
3408		3969
3409	A typical way to use libev under windows is to embed it (see the embedding	3970	A typical way to use libev under windows is to embed it (see the embedding
3410	section for details) and use the following F<evwrap.h> header file instead	3971	section for details) and use the following F<evwrap.h> header file instead
3411	of F<ev.h>:	3972	of F<ev.h>:
3412		3973
…		…
3414	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	3975	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3415		3976
3416	#include "ev.h"	3977	#include "ev.h"
3417		3978
3418	And compile the following F<evwrap.c> file into your project (make sure	3979	And compile the following F<evwrap.c> file into your project (make sure
3419	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	3980	you do I<not> compile the F<ev.c> or any other embedded source files!):
3420		3981
3421	#include "evwrap.h"	3982	#include "evwrap.h"
3422	#include "ev.c"	3983	#include "ev.c"
3423		3984
3424	=over 4	3985	=over 4
…		…
3448		4009
3449	Early versions of winsocket's select only supported waiting for a maximum	4010	Early versions of winsocket's select only supported waiting for a maximum
3450	of C<64> handles (probably owning to the fact that all windows kernels	4011	of C<64> handles (probably owning to the fact that all windows kernels
3451	can only wait for C<64> things at the same time internally; Microsoft	4012	can only wait for C<64> things at the same time internally; Microsoft
3452	recommends spawning a chain of threads and wait for 63 handles and the	4013	recommends spawning a chain of threads and wait for 63 handles and the
3453	previous thread in each. Great).	4014	previous thread in each. Sounds great!).
3454		4015
3455	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4016	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3456	to some high number (e.g. C<2048>) before compiling the winsocket select	4017	to some high number (e.g. C<2048>) before compiling the winsocket select
3457	call (which might be in libev or elsewhere, for example, perl does its own	4018	call (which might be in libev or elsewhere, for example, perl and many
3458	select emulation on windows).	4019	other interpreters do their own select emulation on windows).
3459		4020
3460	Another limit is the number of file descriptors in the Microsoft runtime	4021	Another limit is the number of file descriptors in the Microsoft runtime
3461	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4022	libraries, which by default is C<64> (there must be a hidden I<64>
3462	or something like this inside Microsoft). You can increase this by calling	4023	fetish or something like this inside Microsoft). You can increase this
3463	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4024	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3464	arbitrary limit), but is broken in many versions of the Microsoft runtime	4025	(another arbitrary limit), but is broken in many versions of the Microsoft
3465	libraries.
3466
3467	This might get you to about C<512> or C<2048> sockets (depending on	4026	runtime libraries. This might get you to about C<512> or C<2048> sockets
3468	windows version and/or the phase of the moon). To get more, you need to	4027	(depending on windows version and/or the phase of the moon). To get more,
3469	wrap all I/O functions and provide your own fd management, but the cost of	4028	you need to wrap all I/O functions and provide your own fd management, but
3470	calling select (O(n²)) will likely make this unworkable.	4029	the cost of calling select (O(n²)) will likely make this unworkable.
3471		4030
3472	=back	4031	=back
3473		4032
3474
3475	=head1 PORTABILITY REQUIREMENTS	4033	=head2 PORTABILITY REQUIREMENTS
3476		4034
3477	In addition to a working ISO-C implementation, libev relies on a few	4035	In addition to a working ISO-C implementation and of course the
3478	additional extensions:	4036	backend-specific APIs, libev relies on a few additional extensions:
3479		4037
3480	=over 4	4038	=over 4
3481		4039
3482	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	4040	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3483	calling conventions regardless of C<ev_watcher_type *>.	4041	calling conventions regardless of C<ev_watcher_type *>.
…		…
3489	calls them using an C<ev_watcher *> internally.	4047	calls them using an C<ev_watcher *> internally.
3490		4048
3491	=item C<sig_atomic_t volatile> must be thread-atomic as well	4049	=item C<sig_atomic_t volatile> must be thread-atomic as well
3492		4050
3493	The type C<sig_atomic_t volatile> (or whatever is defined as	4051	The type C<sig_atomic_t volatile> (or whatever is defined as
3494	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4052	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3495	threads. This is not part of the specification for C<sig_atomic_t>, but is	4053	threads. This is not part of the specification for C<sig_atomic_t>, but is
3496	believed to be sufficiently portable.	4054	believed to be sufficiently portable.
3497		4055
3498	=item C<sigprocmask> must work in a threaded environment	4056	=item C<sigprocmask> must work in a threaded environment
3499		4057
…		…
3508	except the initial one, and run the default loop in the initial thread as	4066	except the initial one, and run the default loop in the initial thread as
3509	well.	4067	well.
3510		4068
3511	=item C<long> must be large enough for common memory allocation sizes	4069	=item C<long> must be large enough for common memory allocation sizes
3512		4070
3513	To improve portability and simplify using libev, libev uses C<long>	4071	To improve portability and simplify its API, libev uses C<long> internally
3514	internally instead of C<size_t> when allocating its data structures. On	4072	instead of C<size_t> when allocating its data structures. On non-POSIX
3515	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	4073	systems (Microsoft...) this might be unexpectedly low, but is still at
3516	is still at least 31 bits everywhere, which is enough for hundreds of	4074	least 31 bits everywhere, which is enough for hundreds of millions of
3517	millions of watchers.	4075	watchers.
3518		4076
3519	=item C<double> must hold a time value in seconds with enough accuracy	4077	=item C<double> must hold a time value in seconds with enough accuracy
3520		4078
3521	The type C<double> is used to represent timestamps. It is required to	4079	The type C<double> is used to represent timestamps. It is required to
3522	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4080	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3523	enough for at least into the year 4000. This requirement is fulfilled by	4081	enough for at least into the year 4000. This requirement is fulfilled by
3524	implementations implementing IEEE 754 (basically all existing ones).	4082	implementations implementing IEEE 754, which is basically all existing
		4083	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4084	2200.
3525		4085
3526	=back	4086	=back
3527		4087
3528	If you know of other additional requirements drop me a note.	4088	If you know of other additional requirements drop me a note.
3529		4089
3530		4090
3531	=head1 COMPILER WARNINGS	4091	=head1 ALGORITHMIC COMPLEXITIES
3532		4092
3533	Depending on your compiler and compiler settings, you might get no or a	4093	In this section the complexities of (many of) the algorithms used inside
3534	lot of warnings when compiling libev code. Some people are apparently	4094	libev will be documented. For complexity discussions about backends see
3535	scared by this.	4095	the documentation for C<ev_default_init>.
3536		4096
3537	However, these are unavoidable for many reasons. For one, each compiler	4097	All of the following are about amortised time: If an array needs to be
3538	has different warnings, and each user has different tastes regarding	4098	extended, libev needs to realloc and move the whole array, but this
3539	warning options. "Warn-free" code therefore cannot be a goal except when	4099	happens asymptotically rarer with higher number of elements, so O(1) might
3540	targeting a specific compiler and compiler-version.	4100	mean that libev does a lengthy realloc operation in rare cases, but on
		4101	average it is much faster and asymptotically approaches constant time.
3541		4102
3542	Another reason is that some compiler warnings require elaborate	4103	=over 4
3543	workarounds, or other changes to the code that make it less clear and less
3544	maintainable.
3545		4104
3546	And of course, some compiler warnings are just plain stupid, or simply	4105	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3547	wrong (because they don't actually warn about the condition their message
3548	seems to warn about).
3549		4106
3550	While libev is written to generate as few warnings as possible,	4107	This means that, when you have a watcher that triggers in one hour and
3551	"warn-free" code is not a goal, and it is recommended not to build libev	4108	there are 100 watchers that would trigger before that, then inserting will
3552	with any compiler warnings enabled unless you are prepared to cope with	4109	have to skip roughly seven (C<ld 100>) of these watchers.
3553	them (e.g. by ignoring them). Remember that warnings are just that:
3554	warnings, not errors, or proof of bugs.
3555		4110
		4111	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3556		4112
3557	=head1 VALGRIND	4113	That means that changing a timer costs less than removing/adding them,
		4114	as only the relative motion in the event queue has to be paid for.
3558		4115
3559	Valgrind has a special section here because it is a popular tool that is	4116	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3560	highly useful, but valgrind reports are very hard to interpret.
3561		4117
3562	If you think you found a bug (memory leak, uninitialised data access etc.)	4118	These just add the watcher into an array or at the head of a list.
3563	in libev, then check twice: If valgrind reports something like:
3564		4119
3565	==2274== definitely lost: 0 bytes in 0 blocks.	4120	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3566	==2274== possibly lost: 0 bytes in 0 blocks.
3567	==2274== still reachable: 256 bytes in 1 blocks.
3568		4121
3569	Then there is no memory leak. Similarly, under some circumstances,	4122	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3570	valgrind might report kernel bugs as if it were a bug in libev, or it
3571	might be confused (it is a very good tool, but only a tool).
3572		4123
3573	If you are unsure about something, feel free to contact the mailing list	4124	These watchers are stored in lists, so they need to be walked to find the
3574	with the full valgrind report and an explanation on why you think this is	4125	correct watcher to remove. The lists are usually short (you don't usually
3575	a bug in libev. However, don't be annoyed when you get a brisk "this is	4126	have many watchers waiting for the same fd or signal: one is typical, two
3576	no bug" answer and take the chance of learning how to interpret valgrind	4127	is rare).
3577	properly.
3578		4128
3579	If you need, for some reason, empty reports from valgrind for your project	4129	=item Finding the next timer in each loop iteration: O(1)
3580	I suggest using suppression lists.
3581		4130
		4131	By virtue of using a binary or 4-heap, the next timer is always found at a
		4132	fixed position in the storage array.
		4133
		4134	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4135
		4136	A change means an I/O watcher gets started or stopped, which requires
		4137	libev to recalculate its status (and possibly tell the kernel, depending
		4138	on backend and whether C<ev_io_set> was used).
		4139
		4140	=item Activating one watcher (putting it into the pending state): O(1)
		4141
		4142	=item Priority handling: O(number_of_priorities)
		4143
		4144	Priorities are implemented by allocating some space for each
		4145	priority. When doing priority-based operations, libev usually has to
		4146	linearly search all the priorities, but starting/stopping and activating
		4147	watchers becomes O(1) with respect to priority handling.
		4148
		4149	=item Sending an ev_async: O(1)
		4150
		4151	=item Processing ev_async_send: O(number_of_async_watchers)
		4152
		4153	=item Processing signals: O(max_signal_number)
		4154
		4155	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4156	calls in the current loop iteration. Checking for async and signal events
		4157	involves iterating over all running async watchers or all signal numbers.
		4158
		4159	=back
		4160
		4161
		4162	=head1 GLOSSARY
		4163
		4164	=over 4
		4165
		4166	=item active
		4167
		4168	A watcher is active as long as it has been started (has been attached to
		4169	an event loop) but not yet stopped (disassociated from the event loop).
		4170
		4171	=item application
		4172
		4173	In this document, an application is whatever is using libev.
		4174
		4175	=item callback
		4176
		4177	The address of a function that is called when some event has been
		4178	detected. Callbacks are being passed the event loop, the watcher that
		4179	received the event, and the actual event bitset.
		4180
		4181	=item callback invocation
		4182
		4183	The act of calling the callback associated with a watcher.
		4184
		4185	=item event
		4186
		4187	A change of state of some external event, such as data now being available
		4188	for reading on a file descriptor, time having passed or simply not having
		4189	any other events happening anymore.
		4190
		4191	In libev, events are represented as single bits (such as C<EV_READ> or
		4192	C<EV_TIMEOUT>).
		4193
		4194	=item event library
		4195
		4196	A software package implementing an event model and loop.
		4197
		4198	=item event loop
		4199
		4200	An entity that handles and processes external events and converts them
		4201	into callback invocations.
		4202
		4203	=item event model
		4204
		4205	The model used to describe how an event loop handles and processes
		4206	watchers and events.
		4207
		4208	=item pending
		4209
		4210	A watcher is pending as soon as the corresponding event has been detected,
		4211	and stops being pending as soon as the watcher will be invoked or its
		4212	pending status is explicitly cleared by the application.
		4213
		4214	A watcher can be pending, but not active. Stopping a watcher also clears
		4215	its pending status.
		4216
		4217	=item real time
		4218
		4219	The physical time that is observed. It is apparently strictly monotonic :)
		4220
		4221	=item wall-clock time
		4222
		4223	The time and date as shown on clocks. Unlike real time, it can actually
		4224	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4225	clock.
		4226
		4227	=item watcher
		4228
		4229	A data structure that describes interest in certain events. Watchers need
		4230	to be started (attached to an event loop) before they can receive events.
		4231
		4232	=item watcher invocation
		4233
		4234	The act of calling the callback associated with a watcher.
		4235
		4236	=back
3582		4237
3583	=head1 AUTHOR	4238	=head1 AUTHOR
3584		4239
3585	Marc Lehmann <libev@schmorp.de>.	4240	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3586		4241

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