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…		…
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
		14	#include <stdio.h> // for puts
		15
14	// every watcher type has its own typedef'd struct	16	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	17	// with the name ev_TYPE
16	ev_io stdin_watcher;	18	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
18		20
19	// all watcher callbacks have a similar signature	21	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	22	// this callback is called when data is readable on stdin
21	static void	23	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	25	{
24	puts ("stdin ready");	26	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	27	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	28	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	29	ev_io_stop (EV_A_ w);
…		…
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	32	ev_unloop (EV_A_ EVUNLOOP_ALL);
31	}	33	}
32		34
33	// another callback, this time for a time-out	35	// another callback, this time for a time-out
34	static void	36	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	38	{
37	puts ("timeout");	39	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	40	// this causes the innermost ev_loop to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	41	ev_unloop (EV_A_ EVUNLOOP_ONE);
40	}	42	}
…		…
60		62
61	// unloop was called, so exit	63	// unloop was called, so exit
62	return 0;	64	return 0;
63	}	65	}
64		66
65	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
66		70
67	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
70		84
71	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	87	these event sources and provide your program with events.
74		88
…		…
84	=head2 FEATURES	98	=head2 FEATURES
85		99
86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
91	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
94	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
96		111
97	It also is quite fast (see this	112	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	114	for example).
100		115
…		…
103	Libev is very configurable. In this manual the default (and most common)	118	Libev is very configurable. In this manual the default (and most common)
104	configuration will be described, which supports multiple event loops. For	119	configuration will be described, which supports multiple event loops. For
105	more info about various configuration options please have a look at	120	more info about various configuration options please have a look at
106	B<EMBED> section in this manual. If libev was configured without support	121	B<EMBED> section in this manual. If libev was configured without support
107	for multiple event loops, then all functions taking an initial argument of	122	for multiple event loops, then all functions taking an initial argument of
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	123	name C<loop> (which is always of type C<ev_loop *>) will not have
109	this argument.	124	this argument.
110		125
111	=head2 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
112		127
113	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
115	the beginning of 1970, details are complicated, don't ask). This type is	130	near the beginning of 1970, details are complicated, don't ask). This
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	type is called C<ev_tstamp>, which is what you should use too. It usually
117	to the C<double> type in C, and when you need to do any calculations on	132	aliases to the C<double> type in C. When you need to do any calculations
118	it, you should treat it as some floating point value. Unlike the name	133	on it, you should treat it as some floating point value. Unlike the name
119	component C<stamp> might indicate, it is also used for time differences	134	component C<stamp> might indicate, it is also used for time differences
120	throughout libev.	135	throughout libev.
121		136
122	=head1 ERROR HANDLING	137	=head1 ERROR HANDLING
123		138
…		…
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	229	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
215	recommended ones.	230	recommended ones.
216		231
217	See the description of C<ev_embed> watchers for more info.	232	See the description of C<ev_embed> watchers for more info.
218		233
219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	234	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
220		235
221	Sets the allocation function to use (the prototype is similar - the	236	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	237	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	238	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	239	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
250	}	265	}
251		266
252	...	267	...
253	ev_set_allocator (persistent_realloc);	268	ev_set_allocator (persistent_realloc);
254		269
255	=item ev_set_syserr_cb (void (*cb)(const char *msg));	270	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
256		271
257	Set the callback function to call on a retryable system call error (such	272	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	273	as failed select, poll, epoll_wait). The message is a printable string
259	indicating the system call or subsystem causing the problem. If this	274	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	275	callback is set, then libev will expect it to remedy the situation, no
…		…
276		291
277	=back	292	=back
278		293
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	294	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280		295
281	An event loop is described by a C<struct ev_loop *>. The library knows two	296	An event loop is described by a C<struct ev_loop *> (the C<struct>
282	types of such loops, the I<default> loop, which supports signals and child	297	is I<not> optional in this case, as there is also an C<ev_loop>
283	events, and dynamically created loops which do not.	298	I<function>).
		299
		300	The library knows two types of such loops, the I<default> loop, which
		301	supports signals and child events, and dynamically created loops which do
		302	not.
284		303
285	=over 4	304	=over 4
286		305
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	306	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		307
…		…
294	If you don't know what event loop to use, use the one returned from this	313	If you don't know what event loop to use, use the one returned from this
295	function.	314	function.
296		315
297	Note that this function is I<not> thread-safe, so if you want to use it	316	Note that this function is I<not> thread-safe, so if you want to use it
298	from multiple threads, you have to lock (note also that this is unlikely,	317	from multiple threads, you have to lock (note also that this is unlikely,
299	as loops cannot bes hared easily between threads anyway).	318	as loops cannot be shared easily between threads anyway).
300		319
301	The default loop is the only loop that can handle C<ev_signal> and	320	The default loop is the only loop that can handle C<ev_signal> and
302	C<ev_child> watchers, and to do this, it always registers a handler	321	C<ev_child> watchers, and to do this, it always registers a handler
303	for C<SIGCHLD>. If this is a problem for your application you can either	322	for C<SIGCHLD>. If this is a problem for your application you can either
304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	323	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
344	flag.	363	flag.
345		364
346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
347	environment variable.	366	environment variable.
348		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_NOSIGFD>
		376
		377	When this flag is specified, then libev will not attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		379	probably only useful to work around any bugs in libev. Consequently, this
		380	flag might go away once the signalfd functionality is considered stable,
		381	so it's useful mostly in environment variables and not in program code.
		382
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	383	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		384
351	This is your standard select(2) backend. Not I<completely> standard, as	385	This is your standard select(2) backend. Not I<completely> standard, as
352	libev tries to roll its own fd_set with no limits on the number of fds,	386	libev tries to roll its own fd_set with no limits on the number of fds,
353	but if that fails, expect a fairly low limit on the number of fds when	387	but if that fails, expect a fairly low limit on the number of fds when
…		…
377	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and	411	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
378	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	412	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
379		413
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	414	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		415
		416	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		417	kernels).
		418
382	For few fds, this backend is a bit little slower than poll and select,	419	For few fds, this backend is a bit little slower than poll and select,
383	but it scales phenomenally better. While poll and select usually scale	420	but it scales phenomenally better. While poll and select usually scale
384	like O(total_fds) where n is the total number of fds (or the highest fd),	421	like O(total_fds) where n is the total number of fds (or the highest fd),
385	epoll scales either O(1) or O(active_fds). The epoll design has a number	422	epoll scales either O(1) or O(active_fds).
386	of shortcomings, such as silently dropping events in some hard-to-detect	423
387	cases and requiring a system call per fd change, no fork support and bad	424	The epoll mechanism deserves honorable mention as the most misdesigned
388	support for dup.	425	of the more advanced event mechanisms: mere annoyances include silently
		426	dropping file descriptors, requiring a system call per change per file
		427	descriptor (and unnecessary guessing of parameters), problems with dup and
		428	so on. The biggest issue is fork races, however - if a program forks then
		429	I<both> parent and child process have to recreate the epoll set, which can
		430	take considerable time (one syscall per file descriptor) and is of course
		431	hard to detect.
		432
		433	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		434	of course I<doesn't>, and epoll just loves to report events for totally
		435	I<different> file descriptors (even already closed ones, so one cannot
		436	even remove them from the set) than registered in the set (especially
		437	on SMP systems). Libev tries to counter these spurious notifications by
		438	employing an additional generation counter and comparing that against the
		439	events to filter out spurious ones, recreating the set when required.
389		440
390	While stopping, setting and starting an I/O watcher in the same iteration	441	While stopping, setting and starting an I/O watcher in the same iteration
391	will result in some caching, there is still a system call per such incident	442	will result in some caching, there is still a system call per such
392	(because the fd could point to a different file description now), so its	443	incident (because the same I<file descriptor> could point to a different
393	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	444	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
394	very well if you register events for both fds.	445	file descriptors might not work very well if you register events for both
395		446	file descriptors.
396	Please note that epoll sometimes generates spurious notifications, so you
397	need to use non-blocking I/O or other means to avoid blocking when no data
398	(or space) is available.
399		447
400	Best performance from this backend is achieved by not unregistering all	448	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible, i.e.	449	watchers for a file descriptor until it has been closed, if possible,
402	keep at least one watcher active per fd at all times.	450	i.e. keep at least one watcher active per fd at all times. Stopping and
		451	starting a watcher (without re-setting it) also usually doesn't cause
		452	extra overhead. A fork can both result in spurious notifications as well
		453	as in libev having to destroy and recreate the epoll object, which can
		454	take considerable time and thus should be avoided.
		455
		456	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		457	faster than epoll for maybe up to a hundred file descriptors, depending on
		458	the usage. So sad.
403		459
404	While nominally embeddable in other event loops, this feature is broken in	460	While nominally embeddable in other event loops, this feature is broken in
405	all kernel versions tested so far.	461	all kernel versions tested so far.
406		462
407	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	463	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
…		…
410	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	466	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
411		467
412	Kqueue deserves special mention, as at the time of this writing, it	468	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	469	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	470	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"	471	it's completely useless). Unlike epoll, however, whose brokenness
		472	is by design, these kqueue bugs can (and eventually will) be fixed
		473	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	474	"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)	475	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
418	system like NetBSD.	476	system like NetBSD.
419		477
420	You still can embed kqueue into a normal poll or select backend and use it	478	You still can embed kqueue into a normal poll or select backend and use it
421	only for sockets (after having made sure that sockets work with kqueue on	479	only for sockets (after having made sure that sockets work with kqueue on
…		…
423		481
424	It scales in the same way as the epoll backend, but the interface to the	482	It scales in the same way as the epoll backend, but the interface to the
425	kernel is more efficient (which says nothing about its actual speed, of	483	kernel is more efficient (which says nothing about its actual speed, of
426	course). While stopping, setting and starting an I/O watcher does never	484	course). While stopping, setting and starting an I/O watcher does never
427	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	485	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
428	two event changes per incident, support for C<fork ()> is very bad and it	486	two event changes per incident. Support for C<fork ()> is very bad (but
429	drops fds silently in similarly hard-to-detect cases.	487	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		488	cases
430		489
431	This backend usually performs well under most conditions.	490	This backend usually performs well under most conditions.
432		491
433	While nominally embeddable in other event loops, this doesn't work	492	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	493	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	494	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	495	(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	496	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
438	sockets.	497	also broken on OS X)) and, did I mention it, using it only for sockets.
439		498
440	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with	499	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
441	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with	500	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
442	C<NOTE_EOF>.	501	C<NOTE_EOF>.
443		502
…		…
460	While this backend scales well, it requires one system call per active	519	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	520	file descriptor per loop iteration. For small and medium numbers of file
462	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	521	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
463	might perform better.	522	might perform better.
464		523
465	On the positive side, ignoring the spurious readiness notifications, this	524	On the positive side, with the exception of the spurious readiness
466	backend actually performed to specification in all tests and is fully	525	notifications, this backend actually performed fully to specification
467	embeddable, which is a rare feat among the OS-specific backends.	526	in all tests and is fully embeddable, which is a rare feat among the
		527	OS-specific backends (I vastly prefer correctness over speed hacks).
468		528
469	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	529	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
470	C<EVBACKEND_POLL>.	530	C<EVBACKEND_POLL>.
471		531
472	=item C<EVBACKEND_ALL>	532	=item C<EVBACKEND_ALL>
…		…
477		537
478	It is definitely not recommended to use this flag.	538	It is definitely not recommended to use this flag.
479		539
480	=back	540	=back
481		541
482	If one or more of these are or'ed into the flags value, then only these	542	If one or more of the backend flags are or'ed into the flags value,
483	backends will be tried (in the reverse order as listed here). If none are	543	then only these backends will be tried (in the reverse order as listed
484	specified, all backends in C<ev_recommended_backends ()> will be tried.	544	here). If none are specified, all backends in C<ev_recommended_backends
		545	()> will be tried.
485		546
486	The most typical usage is like this:	547	Example: This is the most typical usage.
487		548
488	if (!ev_default_loop (0))	549	if (!ev_default_loop (0))
489	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	550	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
490		551
491	Restrict libev to the select and poll backends, and do not allow	552	Example: Restrict libev to the select and poll backends, and do not allow
492	environment settings to be taken into account:	553	environment settings to be taken into account:
493		554
494	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	555	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
495		556
496	Use whatever libev has to offer, but make sure that kqueue is used if	557	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	558	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):	559	private event loop and only if you know the OS supports your types of
		560	fds):
499		561
500	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	562	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
501		563
502	=item struct ev_loop *ev_loop_new (unsigned int flags)	564	=item struct ev_loop *ev_loop_new (unsigned int flags)
503		565
…		…
524	responsibility to either stop all watchers cleanly yourself I<before>	586	responsibility to either stop all watchers cleanly yourself I<before>
525	calling this function, or cope with the fact afterwards (which is usually	587	calling this function, or cope with the fact afterwards (which is usually
526	the easiest thing, you can just ignore the watchers and/or C<free ()> them	588	the easiest thing, you can just ignore the watchers and/or C<free ()> them
527	for example).	589	for example).
528		590
529	Note that certain global state, such as signal state, will not be freed by	591	Note that certain global state, such as signal state (and installed signal
530	this function, and related watchers (such as signal and child watchers)	592	handlers), will not be freed by this function, and related watchers (such
531	would need to be stopped manually.	593	as signal and child watchers) would need to be stopped manually.
532		594
533	In general it is not advisable to call this function except in the	595	In general it is not advisable to call this function except in the
534	rare occasion where you really need to free e.g. the signal handling	596	rare occasion where you really need to free e.g. the signal handling
535	pipe fds. If you need dynamically allocated loops it is better to use	597	pipe fds. If you need dynamically allocated loops it is better to use
536	C<ev_loop_new> and C<ev_loop_destroy>).	598	C<ev_loop_new> and C<ev_loop_destroy>.
537		599
538	=item ev_loop_destroy (loop)	600	=item ev_loop_destroy (loop)
539		601
540	Like C<ev_default_destroy>, but destroys an event loop created by an	602	Like C<ev_default_destroy>, but destroys an event loop created by an
541	earlier call to C<ev_loop_new>.	603	earlier call to C<ev_loop_new>.
…		…
561		623
562	=item ev_loop_fork (loop)	624	=item ev_loop_fork (loop)
563		625
564	Like C<ev_default_fork>, but acts on an event loop created by	626	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	627	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.	628	after fork that you want to re-use in the child, and how you do this is
		629	entirely your own problem.
567		630
568	=item int ev_is_default_loop (loop)	631	=item int ev_is_default_loop (loop)
569		632
570	Returns true when the given loop actually is the default loop, false otherwise.	633	Returns true when the given loop is, in fact, the default loop, and false
		634	otherwise.
571		635
572	=item unsigned int ev_loop_count (loop)	636	=item unsigned int ev_loop_count (loop)
573		637
574	Returns the count of loop iterations for the loop, which is identical to	638	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	639	the number of times libev did poll for new events. It starts at C<0> and
576	happily wraps around with enough iterations.	640	happily wraps around with enough iterations.
577		641
578	This value can sometimes be useful as a generation counter of sorts (it	642	This value can sometimes be useful as a generation counter of sorts (it
579	"ticks" the number of loop iterations), as it roughly corresponds with	643	"ticks" the number of loop iterations), as it roughly corresponds with
580	C<ev_prepare> and C<ev_check> calls.	644	C<ev_prepare> and C<ev_check> calls.
		645
		646	=item unsigned int ev_loop_depth (loop)
		647
		648	Returns the number of times C<ev_loop> was entered minus the number of
		649	times C<ev_loop> was exited, in other words, the recursion depth.
		650
		651	Outside C<ev_loop>, this number is zero. In a callback, this number is
		652	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		653	in which case it is higher.
		654
		655	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		656	etc.), doesn't count as exit.
581		657
582	=item unsigned int ev_backend (loop)	658	=item unsigned int ev_backend (loop)
583		659
584	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	660	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
585	use.	661	use.
…		…
600		676
601	This function is rarely useful, but when some event callback runs for a	677	This function is rarely useful, but when some event callback runs for a
602	very long time without entering the event loop, updating libev's idea of	678	very long time without entering the event loop, updating libev's idea of
603	the current time is a good idea.	679	the current time is a good idea.
604		680
605	See also "The special problem of time updates" in the C<ev_timer> section.	681	See also L<The special problem of time updates> in the C<ev_timer> section.
		682
		683	=item ev_suspend (loop)
		684
		685	=item ev_resume (loop)
		686
		687	These two functions suspend and resume a loop, for use when the loop is
		688	not used for a while and timeouts should not be processed.
		689
		690	A typical use case would be an interactive program such as a game: When
		691	the user presses C<^Z> to suspend the game and resumes it an hour later it
		692	would be best to handle timeouts as if no time had actually passed while
		693	the program was suspended. This can be achieved by calling C<ev_suspend>
		694	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		695	C<ev_resume> directly afterwards to resume timer processing.
		696
		697	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		698	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		699	will be rescheduled (that is, they will lose any events that would have
		700	occured while suspended).
		701
		702	After calling C<ev_suspend> you B<must not> call I<any> function on the
		703	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		704	without a previous call to C<ev_suspend>.
		705
		706	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		707	event loop time (see C<ev_now_update>).
606		708
607	=item ev_loop (loop, int flags)	709	=item ev_loop (loop, int flags)
608		710
609	Finally, this is it, the event handler. This function usually is called	711	Finally, this is it, the event handler. This function usually is called
610	after you initialised all your watchers and you want to start handling	712	after you have initialised all your watchers and you want to start
611	events.	713	handling events.
612		714
613	If the flags argument is specified as C<0>, it will not return until	715	If the flags argument is specified as C<0>, it will not return until
614	either no event watchers are active anymore or C<ev_unloop> was called.	716	either no event watchers are active anymore or C<ev_unloop> was called.
615		717
616	Please note that an explicit C<ev_unloop> is usually better than	718	Please note that an explicit C<ev_unloop> is usually better than
617	relying on all watchers to be stopped when deciding when a program has	719	relying on all watchers to be stopped when deciding when a program has
618	finished (especially in interactive programs), but having a program that	720	finished (especially in interactive programs), but having a program
619	automatically loops as long as it has to and no longer by virtue of	721	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.	722	of relying on its watchers stopping correctly, that is truly a thing of
		723	beauty.
621		724
622	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	725	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	726	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.	727	process in case there are no events and will return after one iteration of
		728	the loop.
625		729
626	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	730	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
627	necessary) and will handle those and any outstanding ones. It will block	731	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	732	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	733	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	734	user-registered callback will be called), and will return after one
		735	iteration of the loop.
		736
		737	This is useful if you are waiting for some external event in conjunction
		738	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	739	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.	740	usually a better approach for this kind of thing.
633		741
634	Here are the gory details of what C<ev_loop> does:	742	Here are the gory details of what C<ev_loop> does:
635		743
636	- Before the first iteration, call any pending watchers.	744	- Before the first iteration, call any pending watchers.
…		…
646	any active watchers at all will result in not sleeping).	754	any active watchers at all will result in not sleeping).
647	- Sleep if the I/O and timer collect interval say so.	755	- Sleep if the I/O and timer collect interval say so.
648	- Block the process, waiting for any events.	756	- Block the process, waiting for any events.
649	- Queue all outstanding I/O (fd) events.	757	- Queue all outstanding I/O (fd) events.
650	- Update the "event loop time" (ev_now ()), and do time jump adjustments.	758	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
651	- Queue all outstanding timers.	759	- Queue all expired timers.
652	- Queue all outstanding periodics.	760	- Queue all expired periodics.
653	- Unless any events are pending now, queue all idle watchers.	761	- Unless any events are pending now, queue all idle watchers.
654	- Queue all check watchers.	762	- Queue all check watchers.
655	- Call all queued watchers in reverse order (i.e. check watchers first).	763	- 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	764	Signals and child watchers are implemented as I/O watchers, and will
657	be handled here by queueing them when their watcher gets executed.	765	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	782	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.	783	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
676		784
677	This "unloop state" will be cleared when entering C<ev_loop> again.	785	This "unloop state" will be cleared when entering C<ev_loop> again.
678		786
		787	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		788
679	=item ev_ref (loop)	789	=item ev_ref (loop)
680		790
681	=item ev_unref (loop)	791	=item ev_unref (loop)
682		792
683	Ref/unref can be used to add or remove a reference count on the event	793	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	794	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	795	count is nonzero, C<ev_loop> will not return on its own.
		796
686	a watcher you never unregister that should not keep C<ev_loop> from	797	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	798	from returning, call ev_unref() after starting, and ev_ref() before
		799	stopping it.
		800
688	example, libev itself uses this for its internal signal pipe: It is not	801	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	802	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	803	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	804	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>	805	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,	806	before stop> (but only if the watcher wasn't active before, or was active
694	respectively).	807	before, respectively. Note also that libev might stop watchers itself
		808	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		809	in the callback).
695		810
696	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	811	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
697	running when nothing else is active.	812	running when nothing else is active.
698		813
699	struct ev_signal exitsig;	814	ev_signal exitsig;
700	ev_signal_init (&exitsig, sig_cb, SIGINT);	815	ev_signal_init (&exitsig, sig_cb, SIGINT);
701	ev_signal_start (loop, &exitsig);	816	ev_signal_start (loop, &exitsig);
702	evf_unref (loop);	817	evf_unref (loop);
703		818
704	Example: For some weird reason, unregister the above signal handler again.	819	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>)	833	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	834	allows libev to delay invocation of I/O and timer/periodic callbacks
720	to increase efficiency of loop iterations (or to increase power-saving	835	to increase efficiency of loop iterations (or to increase power-saving
721	opportunities).	836	opportunities).
722		837
723	The background is that sometimes your program runs just fast enough to	838	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	839	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	840	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	841	events, especially with backends like C<select ()> which have a high
727	overhead for the actual polling but can deliver many events at once.	842	overhead for the actual polling but can deliver many events at once.
728		843
729	By setting a higher I<io collect interval> you allow libev to spend more	844	By setting a higher I<io collect interval> you allow libev to spend more
730	time collecting I/O events, so you can handle more events per iteration,	845	time collecting I/O events, so you can handle more events per iteration,
731	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	846	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
732	C<ev_timer>) will be not affected. Setting this to a non-null value will	847	C<ev_timer>) will be not affected. Setting this to a non-null value will
733	introduce an additional C<ev_sleep ()> call into most loop iterations.	848	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		849	sleep time ensures that libev will not poll for I/O events more often then
		850	once per this interval, on average.
734		851
735	Likewise, by setting a higher I<timeout collect interval> you allow libev	852	Likewise, by setting a higher I<timeout collect interval> you allow libev
736	to spend more time collecting timeouts, at the expense of increased	853	to spend more time collecting timeouts, at the expense of increased
737	latency (the watcher callback will be called later). C<ev_io> watchers	854	latency/jitter/inexactness (the watcher callback will be called
738	will not be affected. Setting this to a non-null value will not introduce	855	later). C<ev_io> watchers will not be affected. Setting this to a non-null
739	any overhead in libev.	856	value will not introduce any overhead in libev.
740		857
741	Many (busy) programs can usually benefit by setting the I/O collect	858	Many (busy) programs can usually benefit by setting the I/O collect
742	interval to a value near C<0.1> or so, which is often enough for	859	interval to a value near C<0.1> or so, which is often enough for
743	interactive servers (of course not for games), likewise for timeouts. It	860	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>,	861	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.	862	as this approaches the timing granularity of most systems. Note that if
		863	you do transactions with the outside world and you can't increase the
		864	parallelity, then this setting will limit your transaction rate (if you
		865	need to poll once per transaction and the I/O collect interval is 0.01,
		866	then you can't do more than 100 transations per second).
746		867
747	Setting the I<timeout collect interval> can improve the opportunity for	868	Setting the I<timeout collect interval> can improve the opportunity for
748	saving power, as the program will "bundle" timer callback invocations that	869	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	870	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	871	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	872	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
752	they fire on, say, one-second boundaries only.	873	they fire on, say, one-second boundaries only.
753		874
		875	Example: we only need 0.1s timeout granularity, and we wish not to poll
		876	more often than 100 times per second:
		877
		878	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		879	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		880
		881	=item ev_invoke_pending (loop)
		882
		883	This call will simply invoke all pending watchers while resetting their
		884	pending state. Normally, C<ev_loop> does this automatically when required,
		885	but when overriding the invoke callback this call comes handy.
		886
		887	=item int ev_pending_count (loop)
		888
		889	Returns the number of pending watchers - zero indicates that no watchers
		890	are pending.
		891
		892	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		893
		894	This overrides the invoke pending functionality of the loop: Instead of
		895	invoking all pending watchers when there are any, C<ev_loop> will call
		896	this callback instead. This is useful, for example, when you want to
		897	invoke the actual watchers inside another context (another thread etc.).
		898
		899	If you want to reset the callback, use C<ev_invoke_pending> as new
		900	callback.
		901
		902	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		903
		904	Sometimes you want to share the same loop between multiple threads. This
		905	can be done relatively simply by putting mutex_lock/unlock calls around
		906	each call to a libev function.
		907
		908	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		909	wait for it to return. One way around this is to wake up the loop via
		910	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		911	and I<acquire> callbacks on the loop.
		912
		913	When set, then C<release> will be called just before the thread is
		914	suspended waiting for new events, and C<acquire> is called just
		915	afterwards.
		916
		917	Ideally, C<release> will just call your mutex_unlock function, and
		918	C<acquire> will just call the mutex_lock function again.
		919
		920	While event loop modifications are allowed between invocations of
		921	C<release> and C<acquire> (that's their only purpose after all), no
		922	modifications done will affect the event loop, i.e. adding watchers will
		923	have no effect on the set of file descriptors being watched, or the time
		924	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		925	to take note of any changes you made.
		926
		927	In theory, threads executing C<ev_loop> will be async-cancel safe between
		928	invocations of C<release> and C<acquire>.
		929
		930	See also the locking example in the C<THREADS> section later in this
		931	document.
		932
		933	=item ev_set_userdata (loop, void *data)
		934
		935	=item ev_userdata (loop)
		936
		937	Set and retrieve a single C<void *> associated with a loop. When
		938	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		939	C<0.>
		940
		941	These two functions can be used to associate arbitrary data with a loop,
		942	and are intended solely for the C<invoke_pending_cb>, C<release> and
		943	C<acquire> callbacks described above, but of course can be (ab-)used for
		944	any other purpose as well.
		945
754	=item ev_loop_verify (loop)	946	=item ev_loop_verify (loop)
755		947
756	This function only does something when C<EV_VERIFY> support has been	948	This function only does something when C<EV_VERIFY> support has been
757	compiled in. It tries to go through all internal structures and checks	949	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	950	through all internal structures and checks them for validity. If anything
759	an error message to standard error and call C<abort ()>.	951	is found to be inconsistent, it will print an error message to standard
		952	error and call C<abort ()>.
760		953
761	This can be used to catch bugs inside libev itself: under normal	954	This can be used to catch bugs inside libev itself: under normal
762	circumstances, this function will never abort as of course libev keeps its	955	circumstances, this function will never abort as of course libev keeps its
763	data structures consistent.	956	data structures consistent.
764		957
765	=back	958	=back
766		959
767		960
768	=head1 ANATOMY OF A WATCHER	961	=head1 ANATOMY OF A WATCHER
769		962
		963	In the following description, uppercase C<TYPE> in names stands for the
		964	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		965	watchers and C<ev_io_start> for I/O watchers.
		966
770	A watcher is a structure that you create and register to record your	967	A watcher is a structure that you create and register to record your
771	interest in some event. For instance, if you want to wait for STDIN to	968	interest in some event. For instance, if you want to wait for STDIN to
772	become readable, you would create an C<ev_io> watcher for that:	969	become readable, you would create an C<ev_io> watcher for that:
773		970
774	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	971	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
775	{	972	{
776	ev_io_stop (w);	973	ev_io_stop (w);
777	ev_unloop (loop, EVUNLOOP_ALL);	974	ev_unloop (loop, EVUNLOOP_ALL);
778	}	975	}
779		976
780	struct ev_loop *loop = ev_default_loop (0);	977	struct ev_loop *loop = ev_default_loop (0);
		978
781	struct ev_io stdin_watcher;	979	ev_io stdin_watcher;
		980
782	ev_init (&stdin_watcher, my_cb);	981	ev_init (&stdin_watcher, my_cb);
783	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	982	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
784	ev_io_start (loop, &stdin_watcher);	983	ev_io_start (loop, &stdin_watcher);
		984
785	ev_loop (loop, 0);	985	ev_loop (loop, 0);
786		986
787	As you can see, you are responsible for allocating the memory for your	987	As you can see, you are responsible for allocating the memory for your
788	watcher structures (and it is usually a bad idea to do this on the stack,	988	watcher structures (and it is I<usually> a bad idea to do this on the
789	although this can sometimes be quite valid).	989	stack).
		990
		991	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		992	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
790		993
791	Each watcher structure must be initialised by a call to C<ev_init	994	Each watcher structure must be initialised by a call to C<ev_init
792	(watcher *, callback)>, which expects a callback to be provided. This	995	(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	996	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	997	watchers, each time the event loop detects that the file descriptor given
795	is readable and/or writable).	998	is readable and/or writable).
796		999
797	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1000	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
798	with arguments specific to this watcher type. There is also a macro	1001	macro to configure it, with arguments specific to the watcher type. There
799	to combine initialisation and setting in one call: C<< ev_<type>_init	1002	is also a macro to combine initialisation and setting in one call: C<<
800	(watcher *, callback, ...) >>.	1003	ev_TYPE_init (watcher *, callback, ...) >>.
801		1004
802	To make the watcher actually watch out for events, you have to start it	1005	To make the watcher actually watch out for events, you have to start it
803	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1006	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
804	*) >>), and you can stop watching for events at any time by calling the	1007	*) >>), and you can stop watching for events at any time by calling the
805	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1008	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
806		1009
807	As long as your watcher is active (has been started but not stopped) you	1010	As long as your watcher is active (has been started but not stopped) you
808	must not touch the values stored in it. Most specifically you must never	1011	must not touch the values stored in it. Most specifically you must never
809	reinitialise it or call its C<set> macro.	1012	reinitialise it or call its C<ev_TYPE_set> macro.
810		1013
811	Each and every callback receives the event loop pointer as first, the	1014	Each and every callback receives the event loop pointer as first, the
812	registered watcher structure as second, and a bitset of received events as	1015	registered watcher structure as second, and a bitset of received events as
813	third argument.	1016	third argument.
814		1017
…		…
872		1075
873	=item C<EV_ASYNC>	1076	=item C<EV_ASYNC>
874		1077
875	The given async watcher has been asynchronously notified (see C<ev_async>).	1078	The given async watcher has been asynchronously notified (see C<ev_async>).
876		1079
		1080	=item C<EV_CUSTOM>
		1081
		1082	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1083	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1084
877	=item C<EV_ERROR>	1085	=item C<EV_ERROR>
878		1086
879	An unspecified error has occurred, the watcher has been stopped. This might	1087	An unspecified error has occurred, the watcher has been stopped. This might
880	happen because the watcher could not be properly started because libev	1088	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	1089	ran out of memory, a file descriptor was found to be closed or any other
		1090	problem. Libev considers these application bugs.
		1091
882	problem. You best act on it by reporting the problem and somehow coping	1092	You best act on it by reporting the problem and somehow coping with the
883	with the watcher being stopped.	1093	watcher being stopped. Note that well-written programs should not receive
		1094	an error ever, so when your watcher receives it, this usually indicates a
		1095	bug in your program.
884		1096
885	Libev will usually signal a few "dummy" events together with an error,	1097	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	1098	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	1099	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	1100	the error from read() or write(). This will not work in multi-threaded
889	programs, though, so beware.	1101	programs, though, as the fd could already be closed and reused for another
		1102	thing, so beware.
890		1103
891	=back	1104	=back
892		1105
893	=head2 GENERIC WATCHER FUNCTIONS	1106	=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		1107
898	=over 4	1108	=over 4
899		1109
900	=item C<ev_init> (ev_TYPE *watcher, callback)	1110	=item C<ev_init> (ev_TYPE *watcher, callback)
901		1111
…		…
907	which rolls both calls into one.	1117	which rolls both calls into one.
908		1118
909	You can reinitialise a watcher at any time as long as it has been stopped	1119	You can reinitialise a watcher at any time as long as it has been stopped
910	(or never started) and there are no pending events outstanding.	1120	(or never started) and there are no pending events outstanding.
911		1121
912	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1122	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
913	int revents)>.	1123	int revents)>.
		1124
		1125	Example: Initialise an C<ev_io> watcher in two steps.
		1126
		1127	ev_io w;
		1128	ev_init (&w, my_cb);
		1129	ev_io_set (&w, STDIN_FILENO, EV_READ);
914		1130
915	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1131	=item C<ev_TYPE_set> (ev_TYPE *, [args])
916		1132
917	This macro initialises the type-specific parts of a watcher. You need to	1133	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	1134	call C<ev_init> at least once before you call this macro, but you can
…		…
921	difference to the C<ev_init> macro).	1137	difference to the C<ev_init> macro).
922		1138
923	Although some watcher types do not have type-specific arguments	1139	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.	1140	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
925		1141
		1142	See C<ev_init>, above, for an example.
		1143
926	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1144	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
927		1145
928	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1146	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	1147	calls into a single call. This is the most convenient method to initialise
930	a watcher. The same limitations apply, of course.	1148	a watcher. The same limitations apply, of course.
931		1149
		1150	Example: Initialise and set an C<ev_io> watcher in one step.
		1151
		1152	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1153
932	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1154	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
933		1155
934	Starts (activates) the given watcher. Only active watchers will receive	1156	Starts (activates) the given watcher. Only active watchers will receive
935	events. If the watcher is already active nothing will happen.	1157	events. If the watcher is already active nothing will happen.
936		1158
		1159	Example: Start the C<ev_io> watcher that is being abused as example in this
		1160	whole section.
		1161
		1162	ev_io_start (EV_DEFAULT_UC, &w);
		1163
937	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1164	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
938		1165
939	Stops the given watcher again (if active) and clears the pending	1166	Stops the given watcher if active, and clears the pending status (whether
		1167	the watcher was active or not).
		1168
940	status. It is possible that stopped watchers are pending (for example,	1169	It is possible that stopped watchers are pending - for example,
941	non-repeating timers are being stopped when they become pending), but	1170	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	1171	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	1172	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.	1173	therefore a good idea to always call its C<ev_TYPE_stop> function.
945		1174
946	=item bool ev_is_active (ev_TYPE *watcher)	1175	=item bool ev_is_active (ev_TYPE *watcher)
947		1176
948	Returns a true value iff the watcher is active (i.e. it has been started	1177	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	1178	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>	1204	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
976	(default: C<-2>). Pending watchers with higher priority will be invoked	1205	(default: C<-2>). Pending watchers with higher priority will be invoked
977	before watchers with lower priority, but priority will not keep watchers	1206	before watchers with lower priority, but priority will not keep watchers
978	from being executed (except for C<ev_idle> watchers).	1207	from being executed (except for C<ev_idle> watchers).
979		1208
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	1209	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.	1210	you need to look at C<ev_idle> watchers, which provide this functionality.
987		1211
988	You I<must not> change the priority of a watcher as long as it is active or	1212	You I<must not> change the priority of a watcher as long as it is active or
989	pending.	1213	pending.
990		1214
		1215	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1216	fine, as long as you do not mind that the priority value you query might
		1217	or might not have been clamped to the valid range.
		1218
991	The default priority used by watchers when no priority has been set is	1219	The default priority used by watchers when no priority has been set is
992	always C<0>, which is supposed to not be too high and not be too low :).	1220	always C<0>, which is supposed to not be too high and not be too low :).
993		1221
994	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1222	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
995	fine, as long as you do not mind that the priority value you query might	1223	priorities.
996	or might not have been adjusted to be within valid range.
997		1224
998	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1225	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
999		1226
1000	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1227	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1001	C<loop> nor C<revents> need to be valid as long as the watcher callback	1228	C<loop> nor C<revents> need to be valid as long as the watcher callback
1002	can deal with that fact.	1229	can deal with that fact, as both are simply passed through to the
		1230	callback.
1003		1231
1004	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1232	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1005		1233
1006	If the watcher is pending, this function returns clears its pending status	1234	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	1235	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>.	1236	watcher isn't pending it does nothing and returns C<0>.
1009		1237
		1238	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1239	callback to be invoked, which can be accomplished with this function.
		1240
1010	=back	1241	=back
1011		1242
1012		1243
1013	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1244	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1014		1245
1015	Each watcher has, by default, a member C<void *data> that you can change	1246	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	1247	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	1248	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	1249	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	1250	member, you can also "subclass" the watcher type and provide your own
1020	data:	1251	data:
1021		1252
1022	struct my_io	1253	struct my_io
1023	{	1254	{
1024	struct ev_io io;	1255	ev_io io;
1025	int otherfd;	1256	int otherfd;
1026	void *somedata;	1257	void *somedata;
1027	struct whatever *mostinteresting;	1258	struct whatever *mostinteresting;
1028	};	1259	};
1029		1260
…		…
1032	ev_io_init (&w.io, my_cb, fd, EV_READ);	1263	ev_io_init (&w.io, my_cb, fd, EV_READ);
1033		1264
1034	And since your callback will be called with a pointer to the watcher, you	1265	And since your callback will be called with a pointer to the watcher, you
1035	can cast it back to your own type:	1266	can cast it back to your own type:
1036		1267
1037	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1268	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1038	{	1269	{
1039	struct my_io *w = (struct my_io *)w_;	1270	struct my_io *w = (struct my_io *)w_;
1040	...	1271	...
1041	}	1272	}
1042		1273
…		…
1053	ev_timer t2;	1284	ev_timer t2;
1054	}	1285	}
1055		1286
1056	In this case getting the pointer to C<my_biggy> is a bit more	1287	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	1288	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	1289	in the C<data> member of the watcher (for woozies), or you need to use
1059	arithmetic using C<offsetof> inside your watchers:	1290	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1291	programmers):
1060		1292
1061	#include <stddef.h>	1293	#include <stddef.h>
1062		1294
1063	static void	1295	static void
1064	t1_cb (EV_P_ struct ev_timer *w, int revents)	1296	t1_cb (EV_P_ ev_timer *w, int revents)
1065	{	1297	{
1066	struct my_biggy big = (struct my_biggy *	1298	struct my_biggy big = (struct my_biggy *)
1067	(((char *)w) - offsetof (struct my_biggy, t1));	1299	(((char *)w) - offsetof (struct my_biggy, t1));
1068	}	1300	}
1069		1301
1070	static void	1302	static void
1071	t2_cb (EV_P_ struct ev_timer *w, int revents)	1303	t2_cb (EV_P_ ev_timer *w, int revents)
1072	{	1304	{
1073	struct my_biggy big = (struct my_biggy *	1305	struct my_biggy big = (struct my_biggy *)
1074	(((char *)w) - offsetof (struct my_biggy, t2));	1306	(((char *)w) - offsetof (struct my_biggy, t2));
1075	}	1307	}
		1308
		1309	=head2 WATCHER PRIORITY MODELS
		1310
		1311	Many event loops support I<watcher priorities>, which are usually small
		1312	integers that influence the ordering of event callback invocation
		1313	between watchers in some way, all else being equal.
		1314
		1315	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1316	description for the more technical details such as the actual priority
		1317	range.
		1318
		1319	There are two common ways how these these priorities are being interpreted
		1320	by event loops:
		1321
		1322	In the more common lock-out model, higher priorities "lock out" invocation
		1323	of lower priority watchers, which means as long as higher priority
		1324	watchers receive events, lower priority watchers are not being invoked.
		1325
		1326	The less common only-for-ordering model uses priorities solely to order
		1327	callback invocation within a single event loop iteration: Higher priority
		1328	watchers are invoked before lower priority ones, but they all get invoked
		1329	before polling for new events.
		1330
		1331	Libev uses the second (only-for-ordering) model for all its watchers
		1332	except for idle watchers (which use the lock-out model).
		1333
		1334	The rationale behind this is that implementing the lock-out model for
		1335	watchers is not well supported by most kernel interfaces, and most event
		1336	libraries will just poll for the same events again and again as long as
		1337	their callbacks have not been executed, which is very inefficient in the
		1338	common case of one high-priority watcher locking out a mass of lower
		1339	priority ones.
		1340
		1341	Static (ordering) priorities are most useful when you have two or more
		1342	watchers handling the same resource: a typical usage example is having an
		1343	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1344	timeouts. Under load, data might be received while the program handles
		1345	other jobs, but since timers normally get invoked first, the timeout
		1346	handler will be executed before checking for data. In that case, giving
		1347	the timer a lower priority than the I/O watcher ensures that I/O will be
		1348	handled first even under adverse conditions (which is usually, but not
		1349	always, what you want).
		1350
		1351	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1352	will only be executed when no same or higher priority watchers have
		1353	received events, they can be used to implement the "lock-out" model when
		1354	required.
		1355
		1356	For example, to emulate how many other event libraries handle priorities,
		1357	you can associate an C<ev_idle> watcher to each such watcher, and in
		1358	the normal watcher callback, you just start the idle watcher. The real
		1359	processing is done in the idle watcher callback. This causes libev to
		1360	continously poll and process kernel event data for the watcher, but when
		1361	the lock-out case is known to be rare (which in turn is rare :), this is
		1362	workable.
		1363
		1364	Usually, however, the lock-out model implemented that way will perform
		1365	miserably under the type of load it was designed to handle. In that case,
		1366	it might be preferable to stop the real watcher before starting the
		1367	idle watcher, so the kernel will not have to process the event in case
		1368	the actual processing will be delayed for considerable time.
		1369
		1370	Here is an example of an I/O watcher that should run at a strictly lower
		1371	priority than the default, and which should only process data when no
		1372	other events are pending:
		1373
		1374	ev_idle idle; // actual processing watcher
		1375	ev_io io; // actual event watcher
		1376
		1377	static void
		1378	io_cb (EV_P_ ev_io *w, int revents)
		1379	{
		1380	// stop the I/O watcher, we received the event, but
		1381	// are not yet ready to handle it.
		1382	ev_io_stop (EV_A_ w);
		1383
		1384	// start the idle watcher to ahndle the actual event.
		1385	// it will not be executed as long as other watchers
		1386	// with the default priority are receiving events.
		1387	ev_idle_start (EV_A_ &idle);
		1388	}
		1389
		1390	static void
		1391	idle_cb (EV_P_ ev_idle *w, int revents)
		1392	{
		1393	// actual processing
		1394	read (STDIN_FILENO, ...);
		1395
		1396	// have to start the I/O watcher again, as
		1397	// we have handled the event
		1398	ev_io_start (EV_P_ &io);
		1399	}
		1400
		1401	// initialisation
		1402	ev_idle_init (&idle, idle_cb);
		1403	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1404	ev_io_start (EV_DEFAULT_ &io);
		1405
		1406	In the "real" world, it might also be beneficial to start a timer, so that
		1407	low-priority connections can not be locked out forever under load. This
		1408	enables your program to keep a lower latency for important connections
		1409	during short periods of high load, while not completely locking out less
		1410	important ones.
1076		1411
1077		1412
1078	=head1 WATCHER TYPES	1413	=head1 WATCHER TYPES
1079		1414
1080	This section describes each watcher in detail, but will not repeat	1415	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	1439	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	1440	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	1441	descriptors to non-blocking mode is also usually a good idea (but not
1107	required if you know what you are doing).	1442	required if you know what you are doing).
1108		1443
1109	If you must do this, then force the use of a known-to-be-good backend	1444	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	1445	known-to-be-good backend (at the time of this writing, this includes only
1111	C<EVBACKEND_POLL>).	1446	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1447	descriptors for which non-blocking operation makes no sense (such as
		1448	files) - libev doesn't guarentee any specific behaviour in that case.
1112		1449
1113	Another thing you have to watch out for is that it is quite easy to	1450	Another thing you have to watch out for is that it is quite easy to
1114	receive "spurious" readiness notifications, that is your callback might	1451	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	1452	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	1453	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	1454	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	1455	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	1456	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.	1457	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1121		1458
1122	If you cannot run the fd in non-blocking mode (for example you should not	1459	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	1460	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	1461	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	1462	interface such as poll (fortunately in our Xlib example, Xlib already
1126	its own, so its quite safe to use).	1463	does this on its own, so its quite safe to use). Some people additionally
		1464	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1465	indefinitely.
		1466
		1467	But really, best use non-blocking mode.
1127		1468
1128	=head3 The special problem of disappearing file descriptors	1469	=head3 The special problem of disappearing file descriptors
1129		1470
1130	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1471	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,	1472	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	1473	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	1474	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	1475	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	1476	registered with libev, there is no efficient way to see that this is, in
1136	fact, a different file descriptor.	1477	fact, a different file descriptor.
1137		1478
…		…
1168	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1509	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1169	C<EVBACKEND_POLL>.	1510	C<EVBACKEND_POLL>.
1170		1511
1171	=head3 The special problem of SIGPIPE	1512	=head3 The special problem of SIGPIPE
1172		1513
1173	While not really specific to libev, it is easy to forget about SIGPIPE:	1514	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	1515	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	1516	sent a SIGPIPE, which, by default, aborts your program. For most programs
1176	this is sensible behaviour, for daemons, this is usually undesirable.	1517	this is sensible behaviour, for daemons, this is usually undesirable.
1177		1518
1178	So when you encounter spurious, unexplained daemon exits, make sure you	1519	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	1520	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).	1521	somewhere, as that would have given you a big clue).
…		…
1187	=item ev_io_init (ev_io *, callback, int fd, int events)	1528	=item ev_io_init (ev_io *, callback, int fd, int events)
1188		1529
1189	=item ev_io_set (ev_io *, int fd, int events)	1530	=item ev_io_set (ev_io *, int fd, int events)
1190		1531
1191	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1532	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	1533	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.	1534	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1194		1535
1195	=item int fd [read-only]	1536	=item int fd [read-only]
1196		1537
1197	The file descriptor being watched.	1538	The file descriptor being watched.
1198		1539
…		…
1207	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1548	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1208	readable, but only once. Since it is likely line-buffered, you could	1549	readable, but only once. Since it is likely line-buffered, you could
1209	attempt to read a whole line in the callback.	1550	attempt to read a whole line in the callback.
1210		1551
1211	static void	1552	static void
1212	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1553	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1213	{	1554	{
1214	ev_io_stop (loop, w);	1555	ev_io_stop (loop, w);
1215	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1556	.. read from stdin here (or from w->fd) and handle any I/O errors
1216	}	1557	}
1217		1558
1218	...	1559	...
1219	struct ev_loop *loop = ev_default_init (0);	1560	struct ev_loop *loop = ev_default_init (0);
1220	struct ev_io stdin_readable;	1561	ev_io stdin_readable;
1221	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1562	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1222	ev_io_start (loop, &stdin_readable);	1563	ev_io_start (loop, &stdin_readable);
1223	ev_loop (loop, 0);	1564	ev_loop (loop, 0);
1224		1565
1225		1566
…		…
1228	Timer watchers are simple relative timers that generate an event after a	1569	Timer watchers are simple relative timers that generate an event after a
1229	given time, and optionally repeating in regular intervals after that.	1570	given time, and optionally repeating in regular intervals after that.
1230		1571
1231	The timers are based on real time, that is, if you register an event that	1572	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	1573	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	1574	year, it will still time out after (roughly) one hour. "Roughly" because
1234	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1575	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1235	monotonic clock option helps a lot here).	1576	monotonic clock option helps a lot here).
1236		1577
1237	The callback is guaranteed to be invoked only after its timeout has passed,	1578	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	1579	passed (not I<at>, so on systems with very low-resolution clocks this
1239	order of execution is undefined.	1580	might introduce a small delay). If multiple timers become ready during the
		1581	same loop iteration then the ones with earlier time-out values are invoked
		1582	before ones of the same priority with later time-out values (but this is
		1583	no longer true when a callback calls C<ev_loop> recursively).
		1584
		1585	=head3 Be smart about timeouts
		1586
		1587	Many real-world problems involve some kind of timeout, usually for error
		1588	recovery. A typical example is an HTTP request - if the other side hangs,
		1589	you want to raise some error after a while.
		1590
		1591	What follows are some ways to handle this problem, from obvious and
		1592	inefficient to smart and efficient.
		1593
		1594	In the following, a 60 second activity timeout is assumed - a timeout that
		1595	gets reset to 60 seconds each time there is activity (e.g. each time some
		1596	data or other life sign was received).
		1597
		1598	=over 4
		1599
		1600	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1601
		1602	This is the most obvious, but not the most simple way: In the beginning,
		1603	start the watcher:
		1604
		1605	ev_timer_init (timer, callback, 60., 0.);
		1606	ev_timer_start (loop, timer);
		1607
		1608	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1609	and start it again:
		1610
		1611	ev_timer_stop (loop, timer);
		1612	ev_timer_set (timer, 60., 0.);
		1613	ev_timer_start (loop, timer);
		1614
		1615	This is relatively simple to implement, but means that each time there is
		1616	some activity, libev will first have to remove the timer from its internal
		1617	data structure and then add it again. Libev tries to be fast, but it's
		1618	still not a constant-time operation.
		1619
		1620	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1621
		1622	This is the easiest way, and involves using C<ev_timer_again> instead of
		1623	C<ev_timer_start>.
		1624
		1625	To implement this, configure an C<ev_timer> with a C<repeat> value
		1626	of C<60> and then call C<ev_timer_again> at start and each time you
		1627	successfully read or write some data. If you go into an idle state where
		1628	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1629	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1630
		1631	That means you can ignore both the C<ev_timer_start> function and the
		1632	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1633	member and C<ev_timer_again>.
		1634
		1635	At start:
		1636
		1637	ev_init (timer, callback);
		1638	timer->repeat = 60.;
		1639	ev_timer_again (loop, timer);
		1640
		1641	Each time there is some activity:
		1642
		1643	ev_timer_again (loop, timer);
		1644
		1645	It is even possible to change the time-out on the fly, regardless of
		1646	whether the watcher is active or not:
		1647
		1648	timer->repeat = 30.;
		1649	ev_timer_again (loop, timer);
		1650
		1651	This is slightly more efficient then stopping/starting the timer each time
		1652	you want to modify its timeout value, as libev does not have to completely
		1653	remove and re-insert the timer from/into its internal data structure.
		1654
		1655	It is, however, even simpler than the "obvious" way to do it.
		1656
		1657	=item 3. Let the timer time out, but then re-arm it as required.
		1658
		1659	This method is more tricky, but usually most efficient: Most timeouts are
		1660	relatively long compared to the intervals between other activity - in
		1661	our example, within 60 seconds, there are usually many I/O events with
		1662	associated activity resets.
		1663
		1664	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1665	but remember the time of last activity, and check for a real timeout only
		1666	within the callback:
		1667
		1668	ev_tstamp last_activity; // time of last activity
		1669
		1670	static void
		1671	callback (EV_P_ ev_timer *w, int revents)
		1672	{
		1673	ev_tstamp now = ev_now (EV_A);
		1674	ev_tstamp timeout = last_activity + 60.;
		1675
		1676	// if last_activity + 60. is older than now, we did time out
		1677	if (timeout < now)
		1678	{
		1679	// timeout occured, take action
		1680	}
		1681	else
		1682	{
		1683	// callback was invoked, but there was some activity, re-arm
		1684	// the watcher to fire in last_activity + 60, which is
		1685	// guaranteed to be in the future, so "again" is positive:
		1686	w->repeat = timeout - now;
		1687	ev_timer_again (EV_A_ w);
		1688	}
		1689	}
		1690
		1691	To summarise the callback: first calculate the real timeout (defined
		1692	as "60 seconds after the last activity"), then check if that time has
		1693	been reached, which means something I<did>, in fact, time out. Otherwise
		1694	the callback was invoked too early (C<timeout> is in the future), so
		1695	re-schedule the timer to fire at that future time, to see if maybe we have
		1696	a timeout then.
		1697
		1698	Note how C<ev_timer_again> is used, taking advantage of the
		1699	C<ev_timer_again> optimisation when the timer is already running.
		1700
		1701	This scheme causes more callback invocations (about one every 60 seconds
		1702	minus half the average time between activity), but virtually no calls to
		1703	libev to change the timeout.
		1704
		1705	To start the timer, simply initialise the watcher and set C<last_activity>
		1706	to the current time (meaning we just have some activity :), then call the
		1707	callback, which will "do the right thing" and start the timer:
		1708
		1709	ev_init (timer, callback);
		1710	last_activity = ev_now (loop);
		1711	callback (loop, timer, EV_TIMEOUT);
		1712
		1713	And when there is some activity, simply store the current time in
		1714	C<last_activity>, no libev calls at all:
		1715
		1716	last_actiivty = ev_now (loop);
		1717
		1718	This technique is slightly more complex, but in most cases where the
		1719	time-out is unlikely to be triggered, much more efficient.
		1720
		1721	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1722	callback :) - just change the timeout and invoke the callback, which will
		1723	fix things for you.
		1724
		1725	=item 4. Wee, just use a double-linked list for your timeouts.
		1726
		1727	If there is not one request, but many thousands (millions...), all
		1728	employing some kind of timeout with the same timeout value, then one can
		1729	do even better:
		1730
		1731	When starting the timeout, calculate the timeout value and put the timeout
		1732	at the I<end> of the list.
		1733
		1734	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1735	the list is expected to fire (for example, using the technique #3).
		1736
		1737	When there is some activity, remove the timer from the list, recalculate
		1738	the timeout, append it to the end of the list again, and make sure to
		1739	update the C<ev_timer> if it was taken from the beginning of the list.
		1740
		1741	This way, one can manage an unlimited number of timeouts in O(1) time for
		1742	starting, stopping and updating the timers, at the expense of a major
		1743	complication, and having to use a constant timeout. The constant timeout
		1744	ensures that the list stays sorted.
		1745
		1746	=back
		1747
		1748	So which method the best?
		1749
		1750	Method #2 is a simple no-brain-required solution that is adequate in most
		1751	situations. Method #3 requires a bit more thinking, but handles many cases
		1752	better, and isn't very complicated either. In most case, choosing either
		1753	one is fine, with #3 being better in typical situations.
		1754
		1755	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1756	rather complicated, but extremely efficient, something that really pays
		1757	off after the first million or so of active timers, i.e. it's usually
		1758	overkill :)
1240		1759
1241	=head3 The special problem of time updates	1760	=head3 The special problem of time updates
1242		1761
1243	Establishing the current time is a costly operation (it usually takes at	1762	Establishing the current time is a costly operation (it usually takes at
1244	least two system calls): EV therefore updates its idea of the current	1763	least two system calls): EV therefore updates its idea of the current
1245	time only before and after C<ev_loop> polls for new events, which causes	1764	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	1765	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1247	lots of events.	1766	lots of events in one iteration.
1248		1767
1249	The relative timeouts are calculated relative to the C<ev_now ()>	1768	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	1769	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	1770	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	1771	you suspect event processing to be delayed and you I<need> to base the
…		…
1256		1775
1257	If the event loop is suspended for a long time, you can also force an	1776	If the event loop is suspended for a long time, you can also force an
1258	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1777	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1259	()>.	1778	()>.
1260		1779
		1780	=head3 The special problems of suspended animation
		1781
		1782	When you leave the server world it is quite customary to hit machines that
		1783	can suspend/hibernate - what happens to the clocks during such a suspend?
		1784
		1785	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1786	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1787	to run until the system is suspended, but they will not advance while the
		1788	system is suspended. That means, on resume, it will be as if the program
		1789	was frozen for a few seconds, but the suspend time will not be counted
		1790	towards C<ev_timer> when a monotonic clock source is used. The real time
		1791	clock advanced as expected, but if it is used as sole clocksource, then a
		1792	long suspend would be detected as a time jump by libev, and timers would
		1793	be adjusted accordingly.
		1794
		1795	I would not be surprised to see different behaviour in different between
		1796	operating systems, OS versions or even different hardware.
		1797
		1798	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1799	time jump in the monotonic clocks and the realtime clock. If the program
		1800	is suspended for a very long time, and monotonic clock sources are in use,
		1801	then you can expect C<ev_timer>s to expire as the full suspension time
		1802	will be counted towards the timers. When no monotonic clock source is in
		1803	use, then libev will again assume a timejump and adjust accordingly.
		1804
		1805	It might be beneficial for this latter case to call C<ev_suspend>
		1806	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1807	deterministic behaviour in this case (you can do nothing against
		1808	C<SIGSTOP>).
		1809
1261	=head3 Watcher-Specific Functions and Data Members	1810	=head3 Watcher-Specific Functions and Data Members
1262		1811
1263	=over 4	1812	=over 4
1264		1813
1265	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1814	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1288	If the timer is started but non-repeating, stop it (as if it timed out).	1837	If the timer is started but non-repeating, stop it (as if it timed out).
1289		1838
1290	If the timer is repeating, either start it if necessary (with the	1839	If the timer is repeating, either start it if necessary (with the
1291	C<repeat> value), or reset the running timer to the C<repeat> value.	1840	C<repeat> value), or reset the running timer to the C<repeat> value.
1292		1841
1293	This sounds a bit complicated, but here is a useful and typical	1842	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1294	example: Imagine you have a TCP connection and you want a so-called idle	1843	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		1844
1303	That means you can ignore the C<after> value and C<ev_timer_start>	1845	=item ev_timer_remaining (loop, ev_timer *)
1304	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1305		1846
1306	ev_timer_init (timer, callback, 0., 5.);	1847	Returns the remaining time until a timer fires. If the timer is active,
1307	ev_timer_again (loop, timer);	1848	then this time is relative to the current event loop time, otherwise it's
1308	...	1849	the timeout value currently configured.
1309	timer->again = 17.;
1310	ev_timer_again (loop, timer);
1311	...
1312	timer->again = 10.;
1313	ev_timer_again (loop, timer);
1314		1850
1315	This is more slightly efficient then stopping/starting the timer each time	1851	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1316	you want to modify its timeout value.	1852	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1853	will return C<4>. When the timer expires and is restarted, it will return
		1854	roughly C<7> (likely slightly less as callback invocation takes some time,
		1855	too), and so on.
1317		1856
1318	=item ev_tstamp repeat [read-write]	1857	=item ev_tstamp repeat [read-write]
1319		1858
1320	The current C<repeat> value. Will be used each time the watcher times out	1859	The current C<repeat> value. Will be used each time the watcher times out
1321	or C<ev_timer_again> is called and determines the next timeout (if any),	1860	or C<ev_timer_again> is called, and determines the next timeout (if any),
1322	which is also when any modifications are taken into account.	1861	which is also when any modifications are taken into account.
1323		1862
1324	=back	1863	=back
1325		1864
1326	=head3 Examples	1865	=head3 Examples
1327		1866
1328	Example: Create a timer that fires after 60 seconds.	1867	Example: Create a timer that fires after 60 seconds.
1329		1868
1330	static void	1869	static void
1331	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1870	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1332	{	1871	{
1333	.. one minute over, w is actually stopped right here	1872	.. one minute over, w is actually stopped right here
1334	}	1873	}
1335		1874
1336	struct ev_timer mytimer;	1875	ev_timer mytimer;
1337	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1876	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1338	ev_timer_start (loop, &mytimer);	1877	ev_timer_start (loop, &mytimer);
1339		1878
1340	Example: Create a timeout timer that times out after 10 seconds of	1879	Example: Create a timeout timer that times out after 10 seconds of
1341	inactivity.	1880	inactivity.
1342		1881
1343	static void	1882	static void
1344	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1883	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1345	{	1884	{
1346	.. ten seconds without any activity	1885	.. ten seconds without any activity
1347	}	1886	}
1348		1887
1349	struct ev_timer mytimer;	1888	ev_timer mytimer;
1350	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1889	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1351	ev_timer_again (&mytimer); /* start timer */	1890	ev_timer_again (&mytimer); /* start timer */
1352	ev_loop (loop, 0);	1891	ev_loop (loop, 0);
1353		1892
1354	// and in some piece of code that gets executed on any "activity":	1893	// and in some piece of code that gets executed on any "activity":
…		…
1359	=head2 C<ev_periodic> - to cron or not to cron?	1898	=head2 C<ev_periodic> - to cron or not to cron?
1360		1899
1361	Periodic watchers are also timers of a kind, but they are very versatile	1900	Periodic watchers are also timers of a kind, but they are very versatile
1362	(and unfortunately a bit complex).	1901	(and unfortunately a bit complex).
1363		1902
1364	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1903	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1365	but on wall clock time (absolute time). You can tell a periodic watcher	1904	relative time, the physical time that passes) but on wall clock time
1366	to trigger after some specific point in time. For example, if you tell a	1905	(absolute time, the thing you can read on your calender or clock). The
1367	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1906	difference is that wall clock time can run faster or slower than real
1368	+ 10.>, that is, an absolute time not a delay) and then reset your system	1907	time, and time jumps are not uncommon (e.g. when you adjust your
1369	clock to January of the previous year, then it will take more than year	1908	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		1909
		1910	You can tell a periodic watcher to trigger after some specific point
		1911	in time: for example, if you tell a periodic watcher to trigger "in 10
		1912	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1913	not a delay) and then reset your system clock to January of the previous
		1914	year, then it will take a year or more to trigger the event (unlike an
		1915	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1916	it, as it uses a relative timeout).
		1917
1373	C<ev_periodic>s can also be used to implement vastly more complex timers,	1918	C<ev_periodic> watchers can also be used to implement vastly more complex
1374	such as triggering an event on each "midnight, local time", or other	1919	timers, such as triggering an event on each "midnight, local time", or
1375	complicated, rules.	1920	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1921	those cannot react to time jumps.
1376		1922
1377	As with timers, the callback is guaranteed to be invoked only when the	1923	As with timers, the callback is guaranteed to be invoked only when the
1378	time (C<at>) has passed, but if multiple periodic timers become ready	1924	point in time where it is supposed to trigger has passed. If multiple
1379	during the same loop iteration then order of execution is undefined.	1925	timers become ready during the same loop iteration then the ones with
		1926	earlier time-out values are invoked before ones with later time-out values
		1927	(but this is no longer true when a callback calls C<ev_loop> recursively).
1380		1928
1381	=head3 Watcher-Specific Functions and Data Members	1929	=head3 Watcher-Specific Functions and Data Members
1382		1930
1383	=over 4	1931	=over 4
1384		1932
1385	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1933	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1386		1934
1387	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1935	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1388		1936
1389	Lots of arguments, lets sort it out... There are basically three modes of	1937	Lots of arguments, let's sort it out... There are basically three modes of
1390	operation, and we will explain them from simplest to complex:	1938	operation, and we will explain them from simplest to most complex:
1391		1939
1392	=over 4	1940	=over 4
1393		1941
1394	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1942	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1395		1943
1396	In this configuration the watcher triggers an event after the wall clock	1944	In this configuration the watcher triggers an event after the wall clock
1397	time C<at> has passed and doesn't repeat. It will not adjust when a time	1945	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	1946	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.	1947	will be stopped and invoked when the system clock reaches or surpasses
		1948	this point in time.
1400		1949
1401	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1950	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1402		1951
1403	In this mode the watcher will always be scheduled to time out at the next	1952	In this mode the watcher will always be scheduled to time out at the next
1404	C<at + N * interval> time (for some integer N, which can also be negative)	1953	C<offset + N * interval> time (for some integer N, which can also be
1405	and then repeat, regardless of any time jumps.	1954	negative) and then repeat, regardless of any time jumps. The C<offset>
		1955	argument is merely an offset into the C<interval> periods.
1406		1956
1407	This can be used to create timers that do not drift with respect to system	1957	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	1958	system clock, for example, here is an C<ev_periodic> that triggers each
1409	the hour:	1959	hour, on the hour (with respect to UTC):
1410		1960
1411	ev_periodic_set (&periodic, 0., 3600., 0);	1961	ev_periodic_set (&periodic, 0., 3600., 0);
1412		1962
1413	This doesn't mean there will always be 3600 seconds in between triggers,	1963	This doesn't mean there will always be 3600 seconds in between triggers,
1414	but only that the callback will be called when the system time shows a	1964	but only that the callback will be called when the system time shows a
1415	full hour (UTC), or more correctly, when the system time is evenly divisible	1965	full hour (UTC), or more correctly, when the system time is evenly divisible
1416	by 3600.	1966	by 3600.
1417		1967
1418	Another way to think about it (for the mathematically inclined) is that	1968	Another way to think about it (for the mathematically inclined) is that
1419	C<ev_periodic> will try to run the callback in this mode at the next possible	1969	C<ev_periodic> will try to run the callback in this mode at the next possible
1420	time where C<time = at (mod interval)>, regardless of any time jumps.	1970	time where C<time = offset (mod interval)>, regardless of any time jumps.
1421		1971
1422	For numerical stability it is preferable that the C<at> value is near	1972	For numerical stability it is preferable that the C<offset> value is near
1423	C<ev_now ()> (the current time), but there is no range requirement for	1973	C<ev_now ()> (the current time), but there is no range requirement for
1424	this value, and in fact is often specified as zero.	1974	this value, and in fact is often specified as zero.
1425		1975
1426	Note also that there is an upper limit to how often a timer can fire (CPU	1976	Note also that there is an upper limit to how often a timer can fire (CPU
1427	speed for example), so if C<interval> is very small then timing stability	1977	speed for example), so if C<interval> is very small then timing stability
1428	will of course deteriorate. Libev itself tries to be exact to be about one	1978	will of course deteriorate. Libev itself tries to be exact to be about one
1429	millisecond (if the OS supports it and the machine is fast enough).	1979	millisecond (if the OS supports it and the machine is fast enough).
1430		1980
1431	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1981	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1432		1982
1433	In this mode the values for C<interval> and C<at> are both being	1983	In this mode the values for C<interval> and C<offset> are both being
1434	ignored. Instead, each time the periodic watcher gets scheduled, the	1984	ignored. Instead, each time the periodic watcher gets scheduled, the
1435	reschedule callback will be called with the watcher as first, and the	1985	reschedule callback will be called with the watcher as first, and the
1436	current time as second argument.	1986	current time as second argument.
1437		1987
1438	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1988	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1439	ever, or make ANY event loop modifications whatsoever>.	1989	or make ANY other event loop modifications whatsoever, unless explicitly
		1990	allowed by documentation here>.
1440		1991
1441	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1992	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1442	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1993	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1443	only event loop modification you are allowed to do).	1994	only event loop modification you are allowed to do).
1444		1995
1445	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	1996	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1446	*w, ev_tstamp now)>, e.g.:	1997	*w, ev_tstamp now)>, e.g.:
1447		1998
		1999	static ev_tstamp
1448	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2000	my_rescheduler (ev_periodic *w, ev_tstamp now)
1449	{	2001	{
1450	return now + 60.;	2002	return now + 60.;
1451	}	2003	}
1452		2004
1453	It must return the next time to trigger, based on the passed time value	2005	It must return the next time to trigger, based on the passed time value
…		…
1473	a different time than the last time it was called (e.g. in a crond like	2025	a different time than the last time it was called (e.g. in a crond like
1474	program when the crontabs have changed).	2026	program when the crontabs have changed).
1475		2027
1476	=item ev_tstamp ev_periodic_at (ev_periodic *)	2028	=item ev_tstamp ev_periodic_at (ev_periodic *)
1477		2029
1478	When active, returns the absolute time that the watcher is supposed to	2030	When active, returns the absolute time that the watcher is supposed
1479	trigger next.	2031	to trigger next. This is not the same as the C<offset> argument to
		2032	C<ev_periodic_set>, but indeed works even in interval and manual
		2033	rescheduling modes.
1480		2034
1481	=item ev_tstamp offset [read-write]	2035	=item ev_tstamp offset [read-write]
1482		2036
1483	When repeating, this contains the offset value, otherwise this is the	2037	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>).	2038	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2039	although libev might modify this value for better numerical stability).
1485		2040
1486	Can be modified any time, but changes only take effect when the periodic	2041	Can be modified any time, but changes only take effect when the periodic
1487	timer fires or C<ev_periodic_again> is being called.	2042	timer fires or C<ev_periodic_again> is being called.
1488		2043
1489	=item ev_tstamp interval [read-write]	2044	=item ev_tstamp interval [read-write]
1490		2045
1491	The current interval value. Can be modified any time, but changes only	2046	The current interval value. Can be modified any time, but changes only
1492	take effect when the periodic timer fires or C<ev_periodic_again> is being	2047	take effect when the periodic timer fires or C<ev_periodic_again> is being
1493	called.	2048	called.
1494		2049
1495	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2050	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1496		2051
1497	The current reschedule callback, or C<0>, if this functionality is	2052	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	2053	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.	2054	the periodic timer fires or C<ev_periodic_again> is being called.
1500		2055
1501	=back	2056	=back
1502		2057
1503	=head3 Examples	2058	=head3 Examples
1504		2059
1505	Example: Call a callback every hour, or, more precisely, whenever the	2060	Example: Call a callback every hour, or, more precisely, whenever the
1506	system clock is divisible by 3600. The callback invocation times have	2061	system time is divisible by 3600. The callback invocation times have
1507	potentially a lot of jitter, but good long-term stability.	2062	potentially a lot of jitter, but good long-term stability.
1508		2063
1509	static void	2064	static void
1510	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2065	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1511	{	2066	{
1512	... its now a full hour (UTC, or TAI or whatever your clock follows)	2067	... its now a full hour (UTC, or TAI or whatever your clock follows)
1513	}	2068	}
1514		2069
1515	struct ev_periodic hourly_tick;	2070	ev_periodic hourly_tick;
1516	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2071	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1517	ev_periodic_start (loop, &hourly_tick);	2072	ev_periodic_start (loop, &hourly_tick);
1518		2073
1519	Example: The same as above, but use a reschedule callback to do it:	2074	Example: The same as above, but use a reschedule callback to do it:
1520		2075
1521	#include <math.h>	2076	#include <math.h>
1522		2077
1523	static ev_tstamp	2078	static ev_tstamp
1524	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2079	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1525	{	2080	{
1526	return fmod (now, 3600.) + 3600.;	2081	return now + (3600. - fmod (now, 3600.));
1527	}	2082	}
1528		2083
1529	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2084	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1530		2085
1531	Example: Call a callback every hour, starting now:	2086	Example: Call a callback every hour, starting now:
1532		2087
1533	struct ev_periodic hourly_tick;	2088	ev_periodic hourly_tick;
1534	ev_periodic_init (&hourly_tick, clock_cb,	2089	ev_periodic_init (&hourly_tick, clock_cb,
1535	fmod (ev_now (loop), 3600.), 3600., 0);	2090	fmod (ev_now (loop), 3600.), 3600., 0);
1536	ev_periodic_start (loop, &hourly_tick);	2091	ev_periodic_start (loop, &hourly_tick);
1537		2092
1538		2093
…		…
1541	Signal watchers will trigger an event when the process receives a specific	2096	Signal watchers will trigger an event when the process receives a specific
1542	signal one or more times. Even though signals are very asynchronous, libev	2097	signal one or more times. Even though signals are very asynchronous, libev
1543	will try it's best to deliver signals synchronously, i.e. as part of the	2098	will try it's best to deliver signals synchronously, i.e. as part of the
1544	normal event processing, like any other event.	2099	normal event processing, like any other event.
1545		2100
		2101	If you want signals to be delivered truly asynchronously, just use
		2102	C<sigaction> as you would do without libev and forget about sharing
		2103	the signal. You can even use C<ev_async> from a signal handler to
		2104	synchronously wake up an event loop.
		2105
1546	You can configure as many watchers as you like per signal. Only when the	2106	You can configure as many watchers as you like for the same signal, but
		2107	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2108	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2109	C<SIGINT> in both the default loop and another loop at the same time. At
		2110	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2111
1547	first watcher gets started will libev actually register a signal watcher	2112	When the first watcher gets started will libev actually register something
1548	with the kernel (thus it coexists with your own signal handlers as long	2113	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	2114	you don't register any with libev for the same signal).
1550	watcher for a signal is stopped libev will reset the signal handler to
1551	SIG_DFL (regardless of what it was set to before).
1552		2115
1553	If possible and supported, libev will install its handlers with	2116	If possible and supported, libev will install its handlers with
1554	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2117	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1555	interrupted. If you have a problem with system calls getting interrupted by	2118	not be unduly interrupted. If you have a problem with system calls getting
1556	signals you can block all signals in an C<ev_check> watcher and unblock	2119	interrupted by signals you can block all signals in an C<ev_check> watcher
1557	them in an C<ev_prepare> watcher.	2120	and unblock them in an C<ev_prepare> watcher.
		2121
		2122	=head3 The special problem of inheritance over execve
		2123
		2124	Both the signal mask (C<sigprocmask>) and the signal disposition
		2125	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2126	stopping it again), that is, libev might or might not block the signal,
		2127	and might or might not set or restore the installed signal handler.
		2128
		2129	While this does not matter for the signal disposition (libev never
		2130	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2131	C<execve>), this matters for the signal mask: many programs do not expect
		2132	certain signals to be blocked.
		2133
		2134	This means that before calling C<exec> (from the child) you should reset
		2135	the signal mask to whatever "default" you expect (all clear is a good
		2136	choice usually).
		2137
		2138	The simplest way to ensure that the signal mask is reset in the child is
		2139	to install a fork handler with C<pthread_atfork> that resets it. That will
		2140	catch fork calls done by libraries (such as the libc) as well.
		2141
		2142	In current versions of libev, you can also ensure that the signal mask is
		2143	not blocking any signals (except temporarily, so thread users watch out)
		2144	by specifying the C<EVFLAG_NOSIGFD> when creating the event loop. This
		2145	is not guaranteed for future versions, however.
1558		2146
1559	=head3 Watcher-Specific Functions and Data Members	2147	=head3 Watcher-Specific Functions and Data Members
1560		2148
1561	=over 4	2149	=over 4
1562		2150
…		…
1573		2161
1574	=back	2162	=back
1575		2163
1576	=head3 Examples	2164	=head3 Examples
1577		2165
1578	Example: Try to exit cleanly on SIGINT and SIGTERM.	2166	Example: Try to exit cleanly on SIGINT.
1579		2167
1580	static void	2168	static void
1581	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2169	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1582	{	2170	{
1583	ev_unloop (loop, EVUNLOOP_ALL);	2171	ev_unloop (loop, EVUNLOOP_ALL);
1584	}	2172	}
1585		2173
1586	struct ev_signal signal_watcher;	2174	ev_signal signal_watcher;
1587	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2175	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1588	ev_signal_start (loop, &sigint_cb);	2176	ev_signal_start (loop, &signal_watcher);
1589		2177
1590		2178
1591	=head2 C<ev_child> - watch out for process status changes	2179	=head2 C<ev_child> - watch out for process status changes
1592		2180
1593	Child watchers trigger when your process receives a SIGCHLD in response to	2181	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	2182	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	2183	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	2184	has been forked (which implies it might have already exited), as long
1597	loop isn't entered (or is continued from a watcher).	2185	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2186	forking and then immediately registering a watcher for the child is fine,
		2187	but forking and registering a watcher a few event loop iterations later or
		2188	in the next callback invocation is not.
1598		2189
1599	Only the default event loop is capable of handling signals, and therefore	2190	Only the default event loop is capable of handling signals, and therefore
1600	you can only register child watchers in the default event loop.	2191	you can only register child watchers in the default event loop.
1601		2192
		2193	Due to some design glitches inside libev, child watchers will always be
		2194	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2195	libev)
		2196
1602	=head3 Process Interaction	2197	=head3 Process Interaction
1603		2198
1604	Libev grabs C<SIGCHLD> as soon as the default event loop is	2199	Libev grabs C<SIGCHLD> as soon as the default event loop is
1605	initialised. This is necessary to guarantee proper behaviour even if	2200	initialised. This is necessary to guarantee proper behaviour even if the
1606	the first child watcher is started after the child exits. The occurrence	2201	first child watcher is started after the child exits. The occurrence
1607	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2202	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1608	synchronously as part of the event loop processing. Libev always reaps all	2203	synchronously as part of the event loop processing. Libev always reaps all
1609	children, even ones not watched.	2204	children, even ones not watched.
1610		2205
1611	=head3 Overriding the Built-In Processing	2206	=head3 Overriding the Built-In Processing
…		…
1621	=head3 Stopping the Child Watcher	2216	=head3 Stopping the Child Watcher
1622		2217
1623	Currently, the child watcher never gets stopped, even when the	2218	Currently, the child watcher never gets stopped, even when the
1624	child terminates, so normally one needs to stop the watcher in the	2219	child terminates, so normally one needs to stop the watcher in the
1625	callback. Future versions of libev might stop the watcher automatically	2220	callback. Future versions of libev might stop the watcher automatically
1626	when a child exit is detected.	2221	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2222	problem).
1627		2223
1628	=head3 Watcher-Specific Functions and Data Members	2224	=head3 Watcher-Specific Functions and Data Members
1629		2225
1630	=over 4	2226	=over 4
1631		2227
…		…
1663	its completion.	2259	its completion.
1664		2260
1665	ev_child cw;	2261	ev_child cw;
1666		2262
1667	static void	2263	static void
1668	child_cb (EV_P_ struct ev_child *w, int revents)	2264	child_cb (EV_P_ ev_child *w, int revents)
1669	{	2265	{
1670	ev_child_stop (EV_A_ w);	2266	ev_child_stop (EV_A_ w);
1671	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2267	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1672	}	2268	}
1673		2269
…		…
1688		2284
1689		2285
1690	=head2 C<ev_stat> - did the file attributes just change?	2286	=head2 C<ev_stat> - did the file attributes just change?
1691		2287
1692	This watches a file system path for attribute changes. That is, it calls	2288	This watches a file system path for attribute changes. That is, it calls
1693	C<stat> regularly (or when the OS says it changed) and sees if it changed	2289	C<stat> on that path in regular intervals (or when the OS says it changed)
1694	compared to the last time, invoking the callback if it did.	2290	and sees if it changed compared to the last time, invoking the callback if
		2291	it did.
1695		2292
1696	The path does not need to exist: changing from "path exists" to "path does	2293	The path does not need to exist: changing from "path exists" to "path does
1697	not exist" is a status change like any other. The condition "path does	2294	not exist" is a status change like any other. The condition "path does not
1698	not exist" is signified by the C<st_nlink> field being zero (which is	2295	exist" (or more correctly "path cannot be stat'ed") is signified by the
1699	otherwise always forced to be at least one) and all the other fields of	2296	C<st_nlink> field being zero (which is otherwise always forced to be at
1700	the stat buffer having unspecified contents.	2297	least one) and all the other fields of the stat buffer having unspecified
		2298	contents.
1701		2299
1702	The path I<should> be absolute and I<must not> end in a slash. If it is	2300	The path I<must not> end in a slash or contain special components such as
		2301	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1703	relative and your working directory changes, the behaviour is undefined.	2302	your working directory changes, then the behaviour is undefined.
1704		2303
1705	Since there is no standard to do this, the portable implementation simply	2304	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	2305	portable implementation simply calls C<stat(2)> regularly on the path
1707	can specify a recommended polling interval for this case. If you specify	2306	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,	2307	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	2308	recommended!) then a I<suitable, unspecified default> value will be used
1710	five seconds, although this might change dynamically). Libev will also	2309	(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	2310	change dynamically). Libev will also impose a minimum interval which is
1712	usually overkill.	2311	currently around C<0.1>, but that's usually overkill.
1713		2312
1714	This watcher type is not meant for massive numbers of stat watchers,	2313	This watcher type is not meant for massive numbers of stat watchers,
1715	as even with OS-supported change notifications, this can be	2314	as even with OS-supported change notifications, this can be
1716	resource-intensive.	2315	resource-intensive.
1717		2316
1718	At the time of this writing, only the Linux inotify interface is	2317	At the time of this writing, the only OS-specific interface implemented
1719	implemented (implementing kqueue support is left as an exercise for the	2318	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	2319	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	2320	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		2321
1727	=head3 ABI Issues (Largefile Support)	2322	=head3 ABI Issues (Largefile Support)
1728		2323
1729	Libev by default (unless the user overrides this) uses the default	2324	Libev by default (unless the user overrides this) uses the default
1730	compilation environment, which means that on systems with large file	2325	compilation environment, which means that on systems with large file
1731	support disabled by default, you get the 32 bit version of the stat	2326	support disabled by default, you get the 32 bit version of the stat
1732	structure. When using the library from programs that change the ABI to	2327	structure. When using the library from programs that change the ABI to
1733	use 64 bit file offsets the programs will fail. In that case you have to	2328	use 64 bit file offsets the programs will fail. In that case you have to
1734	compile libev with the same flags to get binary compatibility. This is	2329	compile libev with the same flags to get binary compatibility. This is
1735	obviously the case with any flags that change the ABI, but the problem is	2330	obviously the case with any flags that change the ABI, but the problem is
1736	most noticeably disabled with ev_stat and large file support.	2331	most noticeably displayed with ev_stat and large file support.
1737		2332
1738	The solution for this is to lobby your distribution maker to make large	2333	The solution for this is to lobby your distribution maker to make large
1739	file interfaces available by default (as e.g. FreeBSD does) and not	2334	file interfaces available by default (as e.g. FreeBSD does) and not
1740	optional. Libev cannot simply switch on large file support because it has	2335	optional. Libev cannot simply switch on large file support because it has
1741	to exchange stat structures with application programs compiled using the	2336	to exchange stat structures with application programs compiled using the
1742	default compilation environment.	2337	default compilation environment.
1743		2338
1744	=head3 Inotify	2339	=head3 Inotify and Kqueue
1745		2340
1746	When C<inotify (7)> support has been compiled into libev (generally only	2341	When C<inotify (7)> support has been compiled into libev and present at
1747	available on Linux) and present at runtime, it will be used to speed up	2342	runtime, it will be used to speed up change detection where possible. The
1748	change detection where possible. The inotify descriptor will be created lazily	2343	inotify descriptor will be created lazily when the first C<ev_stat>
1749	when the first C<ev_stat> watcher is being started.	2344	watcher is being started.
1750		2345
1751	Inotify presence does not change the semantics of C<ev_stat> watchers	2346	Inotify presence does not change the semantics of C<ev_stat> watchers
1752	except that changes might be detected earlier, and in some cases, to avoid	2347	except that changes might be detected earlier, and in some cases, to avoid
1753	making regular C<stat> calls. Even in the presence of inotify support	2348	making regular C<stat> calls. Even in the presence of inotify support
1754	there are many cases where libev has to resort to regular C<stat> polling.	2349	there are many cases where libev has to resort to regular C<stat> polling,
		2350	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2351	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2352	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2353	xfs are fully working) libev usually gets away without polling.
1755		2354
1756	(There is no support for kqueue, as apparently it cannot be used to	2355	There is no support for kqueue, as apparently it cannot be used to
1757	implement this functionality, due to the requirement of having a file	2356	implement this functionality, due to the requirement of having a file
1758	descriptor open on the object at all times).	2357	descriptor open on the object at all times, and detecting renames, unlinks
		2358	etc. is difficult.
		2359
		2360	=head3 C<stat ()> is a synchronous operation
		2361
		2362	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2363	the process. The exception are C<ev_stat> watchers - those call C<stat
		2364	()>, which is a synchronous operation.
		2365
		2366	For local paths, this usually doesn't matter: unless the system is very
		2367	busy or the intervals between stat's are large, a stat call will be fast,
		2368	as the path data is usually in memory already (except when starting the
		2369	watcher).
		2370
		2371	For networked file systems, calling C<stat ()> can block an indefinite
		2372	time due to network issues, and even under good conditions, a stat call
		2373	often takes multiple milliseconds.
		2374
		2375	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2376	paths, although this is fully supported by libev.
1759		2377
1760	=head3 The special problem of stat time resolution	2378	=head3 The special problem of stat time resolution
1761		2379
1762	The C<stat ()> system call only supports full-second resolution portably, and	2380	The C<stat ()> system call only supports full-second resolution portably,
1763	even on systems where the resolution is higher, many file systems still	2381	and even on systems where the resolution is higher, most file systems
1764	only support whole seconds.	2382	still only support whole seconds.
1765		2383
1766	That means that, if the time is the only thing that changes, you can	2384	That means that, if the time is the only thing that changes, you can
1767	easily miss updates: on the first update, C<ev_stat> detects a change and	2385	easily miss updates: on the first update, C<ev_stat> detects a change and
1768	calls your callback, which does something. When there is another update	2386	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	2387	within the same second, C<ev_stat> will be unable to detect unless the
1770	data does not change.	2388	stat data does change in other ways (e.g. file size).
1771		2389
1772	The solution to this is to delay acting on a change for slightly more	2390	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	2391	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);	2392	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1775	ev_timer_again (loop, w)>).	2393	ev_timer_again (loop, w)>).
…		…
1795	C<path>. The C<interval> is a hint on how quickly a change is expected to	2413	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	2414	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	2415	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.	2416	path for as long as the watcher is active.
1799		2417
1800	The callback will receive C<EV_STAT> when a change was detected, relative	2418	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	2419	relative to the attributes at the time the watcher was started (or the
1802	was detected).	2420	last change was detected).
1803		2421
1804	=item ev_stat_stat (loop, ev_stat *)	2422	=item ev_stat_stat (loop, ev_stat *)
1805		2423
1806	Updates the stat buffer immediately with new values. If you change the	2424	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	2425	watched path in your callback, you could call this function to avoid
…		…
1890		2508
1891		2509
1892	=head2 C<ev_idle> - when you've got nothing better to do...	2510	=head2 C<ev_idle> - when you've got nothing better to do...
1893		2511
1894	Idle watchers trigger events when no other events of the same or higher	2512	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	2513	priority are pending (prepare, check and other idle watchers do not count
1896	count).	2514	as receiving "events").
1897		2515
1898	That is, as long as your process is busy handling sockets or timeouts	2516	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	2517	(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	2518	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	2519	are pending), the idle watchers are being called once per event loop
…		…
1912		2530
1913	=head3 Watcher-Specific Functions and Data Members	2531	=head3 Watcher-Specific Functions and Data Members
1914		2532
1915	=over 4	2533	=over 4
1916		2534
1917	=item ev_idle_init (ev_signal *, callback)	2535	=item ev_idle_init (ev_idle *, callback)
1918		2536
1919	Initialises and configures the idle watcher - it has no parameters of any	2537	Initialises and configures the idle watcher - it has no parameters of any
1920	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2538	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1921	believe me.	2539	believe me.
1922		2540
…		…
1926		2544
1927	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2545	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1928	callback, free it. Also, use no error checking, as usual.	2546	callback, free it. Also, use no error checking, as usual.
1929		2547
1930	static void	2548	static void
1931	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2549	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1932	{	2550	{
1933	free (w);	2551	free (w);
1934	// now do something you wanted to do when the program has	2552	// now do something you wanted to do when the program has
1935	// no longer anything immediate to do.	2553	// no longer anything immediate to do.
1936	}	2554	}
1937		2555
1938	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2556	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1939	ev_idle_init (idle_watcher, idle_cb);	2557	ev_idle_init (idle_watcher, idle_cb);
1940	ev_idle_start (loop, idle_cb);	2558	ev_idle_start (loop, idle_watcher);
1941		2559
1942		2560
1943	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2561	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1944		2562
1945	Prepare and check watchers are usually (but not always) used in tandem:	2563	Prepare and check watchers are usually (but not always) used in pairs:
1946	prepare watchers get invoked before the process blocks and check watchers	2564	prepare watchers get invoked before the process blocks and check watchers
1947	afterwards.	2565	afterwards.
1948		2566
1949	You I<must not> call C<ev_loop> or similar functions that enter	2567	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>	2568	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,	2571	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	2572	C<ev_check> so if you have one watcher of each kind they will always be
1955	called in pairs bracketing the blocking call.	2573	called in pairs bracketing the blocking call.
1956		2574
1957	Their main purpose is to integrate other event mechanisms into libev and	2575	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	2576	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	2577	variable changes, implement your own watchers, integrate net-snmp or a
1960	coroutine library and lots more. They are also occasionally useful if	2578	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,	2579	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>	2580	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1963	watcher).	2581	watcher).
1964		2582
1965	This is done by examining in each prepare call which file descriptors need	2583	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	2584	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	2585	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	2586	libraries provide exactly this functionality). Then, in the check watcher,
1969	any events that occurred (by checking the pending status of all watchers	2587	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	2588	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,	2589	I/O and timer callbacks will never actually be called (but must be valid
1972	because you never know, you know?).	2590	nevertheless, because you never know, you know?).
1973		2591
1974	As another example, the Perl Coro module uses these hooks to integrate	2592	As another example, the Perl Coro module uses these hooks to integrate
1975	coroutines into libev programs, by yielding to other active coroutines	2593	coroutines into libev programs, by yielding to other active coroutines
1976	during each prepare and only letting the process block if no coroutines	2594	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	2595	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	2598	loop from blocking if lower-priority coroutines are active, thus mapping
1981	low-priority coroutines to idle/background tasks).	2599	low-priority coroutines to idle/background tasks).
1982		2600
1983	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2601	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	2602	priority, to ensure that they are being run before any other watchers
		2603	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2604
1985	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2605	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	2606	activate ("feed") events into libev. While libev fully supports this, they
1987	supports this, they might get executed before other C<ev_check> watchers	2607	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	2608	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	2609	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	2610	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1991	coexist peacefully with others).	2611	others).
1992		2612
1993	=head3 Watcher-Specific Functions and Data Members	2613	=head3 Watcher-Specific Functions and Data Members
1994		2614
1995	=over 4	2615	=over 4
1996		2616
…		…
1998		2618
1999	=item ev_check_init (ev_check *, callback)	2619	=item ev_check_init (ev_check *, callback)
2000		2620
2001	Initialises and configures the prepare or check watcher - they have no	2621	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>	2622	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.	2623	macros, but using them is utterly, utterly, utterly and completely
		2624	pointless.
2004		2625
2005	=back	2626	=back
2006		2627
2007	=head3 Examples	2628	=head3 Examples
2008		2629
…		…
2021		2642
2022	static ev_io iow [nfd];	2643	static ev_io iow [nfd];
2023	static ev_timer tw;	2644	static ev_timer tw;
2024		2645
2025	static void	2646	static void
2026	io_cb (ev_loop *loop, ev_io *w, int revents)	2647	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2027	{	2648	{
2028	}	2649	}
2029		2650
2030	// create io watchers for each fd and a timer before blocking	2651	// create io watchers for each fd and a timer before blocking
2031	static void	2652	static void
2032	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2653	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2033	{	2654	{
2034	int timeout = 3600000;	2655	int timeout = 3600000;
2035	struct pollfd fds [nfd];	2656	struct pollfd fds [nfd];
2036	// actual code will need to loop here and realloc etc.	2657	// actual code will need to loop here and realloc etc.
2037	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2658	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2038		2659
2039	/* the callback is illegal, but won't be called as we stop during check */	2660	/* the callback is illegal, but won't be called as we stop during check */
2040	ev_timer_init (&tw, 0, timeout * 1e-3);	2661	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2041	ev_timer_start (loop, &tw);	2662	ev_timer_start (loop, &tw);
2042		2663
2043	// create one ev_io per pollfd	2664	// create one ev_io per pollfd
2044	for (int i = 0; i < nfd; ++i)	2665	for (int i = 0; i < nfd; ++i)
2045	{	2666	{
…		…
2052	}	2673	}
2053	}	2674	}
2054		2675
2055	// stop all watchers after blocking	2676	// stop all watchers after blocking
2056	static void	2677	static void
2057	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2678	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2058	{	2679	{
2059	ev_timer_stop (loop, &tw);	2680	ev_timer_stop (loop, &tw);
2060		2681
2061	for (int i = 0; i < nfd; ++i)	2682	for (int i = 0; i < nfd; ++i)
2062	{	2683	{
…		…
2101	}	2722	}
2102		2723
2103	// do not ever call adns_afterpoll	2724	// do not ever call adns_afterpoll
2104		2725
2105	Method 4: Do not use a prepare or check watcher because the module you	2726	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	2727	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	2728	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	2729	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2109	this.	2730	this approach, effectively embedding EV as a client into the horrible
		2731	libglib event loop.
2110		2732
2111	static gint	2733	static gint
2112	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2734	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2113	{	2735	{
2114	int got_events = 0;	2736	int got_events = 0;
…		…
2145	prioritise I/O.	2767	prioritise I/O.
2146		2768
2147	As an example for a bug workaround, the kqueue backend might only support	2769	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	2770	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	2771	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	2772	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	2773	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	2774	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.	2775	C<kevent>, but at least you can use both mechanisms for what they are
		2776	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2154		2777
2155	As for prioritising I/O: rarely you have the case where some fds have	2778	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	2779	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	2780	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	2781	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.	2782	the rest in a second one, and embed the second one in the first.
2160		2783
2161	As long as the watcher is active, the callback will be invoked every time	2784	As long as the watcher is active, the callback will be invoked every
2162	there might be events pending in the embedded loop. The callback must then	2785	time there might be events pending in the embedded loop. The callback
2163	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2786	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2164	their callbacks (you could also start an idle watcher to give the embedded	2787	sweep and invoke their callbacks (the callback doesn't need to invoke the
2165	loop strictly lower priority for example). You can also set the callback	2788	C<ev_embed_sweep> function directly, it could also start an idle watcher
2166	to C<0>, in which case the embed watcher will automatically execute the	2789	to give the embedded loop strictly lower priority for example).
2167	embedded loop sweep.
2168		2790
2169	As long as the watcher is started it will automatically handle events. The	2791	You can also set the callback to C<0>, in which case the embed watcher
2170	callback will be invoked whenever some events have been handled. You can	2792	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		2793
2174	Also, there have not currently been made special provisions for forking:	2794	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,	2795	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	2796	embedding loop forks. In other cases, the user is responsible for calling
2177	yourself.	2797	C<ev_loop_fork> on the embedded loop.
2178		2798
2179	Unfortunately, not all backends are embeddable, only the ones returned by	2799	Unfortunately, not all backends are embeddable: only the ones returned by
2180	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2800	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2181	portable one.	2801	portable one.
2182		2802
2183	So when you want to use this feature you will always have to be prepared	2803	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	2804	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	2805	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.	2806	create it, and if that fails, use the normal loop for everything.
		2807
		2808	=head3 C<ev_embed> and fork
		2809
		2810	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2811	automatically be applied to the embedded loop as well, so no special
		2812	fork handling is required in that case. When the watcher is not running,
		2813	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2814	as applicable.
2187		2815
2188	=head3 Watcher-Specific Functions and Data Members	2816	=head3 Watcher-Specific Functions and Data Members
2189		2817
2190	=over 4	2818	=over 4
2191		2819
…		…
2219	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2847	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2220	used).	2848	used).
2221		2849
2222	struct ev_loop *loop_hi = ev_default_init (0);	2850	struct ev_loop *loop_hi = ev_default_init (0);
2223	struct ev_loop *loop_lo = 0;	2851	struct ev_loop *loop_lo = 0;
2224	struct ev_embed embed;	2852	ev_embed embed;
2225		2853
2226	// see if there is a chance of getting one that works	2854	// see if there is a chance of getting one that works
2227	// (remember that a flags value of 0 means autodetection)	2855	// (remember that a flags value of 0 means autodetection)
2228	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2856	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2229	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2857	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2243	kqueue implementation). Store the kqueue/socket-only event loop in	2871	kqueue implementation). Store the kqueue/socket-only event loop in
2244	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2872	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2245		2873
2246	struct ev_loop *loop = ev_default_init (0);	2874	struct ev_loop *loop = ev_default_init (0);
2247	struct ev_loop *loop_socket = 0;	2875	struct ev_loop *loop_socket = 0;
2248	struct ev_embed embed;	2876	ev_embed embed;
2249		2877
2250	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2878	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2251	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2879	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2252	{	2880	{
2253	ev_embed_init (&embed, 0, loop_socket);	2881	ev_embed_init (&embed, 0, loop_socket);
…		…
2268	event loop blocks next and before C<ev_check> watchers are being called,	2896	event loop blocks next and before C<ev_check> watchers are being called,
2269	and only in the child after the fork. If whoever good citizen calling	2897	and only in the child after the fork. If whoever good citizen calling
2270	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2898	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2271	handlers will be invoked, too, of course.	2899	handlers will be invoked, too, of course.
2272		2900
		2901	=head3 The special problem of life after fork - how is it possible?
		2902
		2903	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2904	up/change the process environment, followed by a call to C<exec()>. This
		2905	sequence should be handled by libev without any problems.
		2906
		2907	This changes when the application actually wants to do event handling
		2908	in the child, or both parent in child, in effect "continuing" after the
		2909	fork.
		2910
		2911	The default mode of operation (for libev, with application help to detect
		2912	forks) is to duplicate all the state in the child, as would be expected
		2913	when I<either> the parent I<or> the child process continues.
		2914
		2915	When both processes want to continue using libev, then this is usually the
		2916	wrong result. In that case, usually one process (typically the parent) is
		2917	supposed to continue with all watchers in place as before, while the other
		2918	process typically wants to start fresh, i.e. without any active watchers.
		2919
		2920	The cleanest and most efficient way to achieve that with libev is to
		2921	simply create a new event loop, which of course will be "empty", and
		2922	use that for new watchers. This has the advantage of not touching more
		2923	memory than necessary, and thus avoiding the copy-on-write, and the
		2924	disadvantage of having to use multiple event loops (which do not support
		2925	signal watchers).
		2926
		2927	When this is not possible, or you want to use the default loop for
		2928	other reasons, then in the process that wants to start "fresh", call
		2929	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2930	the default loop will "orphan" (not stop) all registered watchers, so you
		2931	have to be careful not to execute code that modifies those watchers. Note
		2932	also that in that case, you have to re-register any signal watchers.
		2933
2273	=head3 Watcher-Specific Functions and Data Members	2934	=head3 Watcher-Specific Functions and Data Members
2274		2935
2275	=over 4	2936	=over 4
2276		2937
2277	=item ev_fork_init (ev_signal *, callback)	2938	=item ev_fork_init (ev_signal *, callback)
…		…
2309	is that the author does not know of a simple (or any) algorithm for a	2970	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	2971	multiple-writer-single-reader queue that works in all cases and doesn't
2311	need elaborate support such as pthreads.	2972	need elaborate support such as pthreads.
2312		2973
2313	That means that if you want to queue data, you have to provide your own	2974	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	2975	queue. But at least I can tell you how to implement locking around your
2315	queue:	2976	queue:
2316		2977
2317	=over 4	2978	=over 4
2318		2979
2319	=item queueing from a signal handler context	2980	=item queueing from a signal handler context
2320		2981
2321	To implement race-free queueing, you simply add to the queue in the signal	2982	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	2983	handler but you block the signal handler in the watcher callback. Here is
2323	some fictitious SIGUSR1 handler:	2984	an example that does that for some fictitious SIGUSR1 handler:
2324		2985
2325	static ev_async mysig;	2986	static ev_async mysig;
2326		2987
2327	static void	2988	static void
2328	sigusr1_handler (void)	2989	sigusr1_handler (void)
…		…
2394	=over 4	3055	=over 4
2395		3056
2396	=item ev_async_init (ev_async *, callback)	3057	=item ev_async_init (ev_async *, callback)
2397		3058
2398	Initialises and configures the async watcher - it has no parameters of any	3059	Initialises and configures the async watcher - it has no parameters of any
2399	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3060	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2400	believe me.	3061	trust me.
2401		3062
2402	=item ev_async_send (loop, ev_async *)	3063	=item ev_async_send (loop, ev_async *)
2403		3064
2404	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3065	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2405	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3066	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2406	C<ev_feed_event>, this call is safe to do in other threads, signal or	3067	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	3068	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2408	section below on what exactly this means).	3069	section below on what exactly this means).
2409		3070
		3071	Note that, as with other watchers in libev, multiple events might get
		3072	compressed into a single callback invocation (another way to look at this
		3073	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3074	reset when the event loop detects that).
		3075
2410	This call incurs the overhead of a system call only once per loop iteration,	3076	This call incurs the overhead of a system call only once per event loop
2411	so while the overhead might be noticeable, it doesn't apply to repeated	3077	iteration, so while the overhead might be noticeable, it doesn't apply to
2412	calls to C<ev_async_send>.	3078	repeated calls to C<ev_async_send> for the same event loop.
2413		3079
2414	=item bool = ev_async_pending (ev_async *)	3080	=item bool = ev_async_pending (ev_async *)
2415		3081
2416	Returns a non-zero value when C<ev_async_send> has been called on the	3082	Returns a non-zero value when C<ev_async_send> has been called on the
2417	watcher but the event has not yet been processed (or even noted) by the	3083	watcher but the event has not yet been processed (or even noted) by the
…		…
2420	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3086	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2421	the loop iterates next and checks for the watcher to have become active,	3087	the loop iterates next and checks for the watcher to have become active,
2422	it will reset the flag again. C<ev_async_pending> can be used to very	3088	it will reset the flag again. C<ev_async_pending> can be used to very
2423	quickly check whether invoking the loop might be a good idea.	3089	quickly check whether invoking the loop might be a good idea.
2424		3090
2425	Not that this does I<not> check whether the watcher itself is pending, only	3091	Not that this does I<not> check whether the watcher itself is pending,
2426	whether it has been requested to make this watcher pending.	3092	only whether it has been requested to make this watcher pending: there
		3093	is a time window between the event loop checking and resetting the async
		3094	notification, and the callback being invoked.
2427		3095
2428	=back	3096	=back
2429		3097
2430		3098
2431	=head1 OTHER FUNCTIONS	3099	=head1 OTHER FUNCTIONS
…		…
2435	=over 4	3103	=over 4
2436		3104
2437	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3105	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2438		3106
2439	This function combines a simple timer and an I/O watcher, calls your	3107	This function combines a simple timer and an I/O watcher, calls your
2440	callback on whichever event happens first and automatically stop both	3108	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	3109	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	3110	or timeout without having to allocate/configure/start/stop/free one or
2443	more watchers yourself.	3111	more watchers yourself.
2444		3112
2445	If C<fd> is less than 0, then no I/O watcher will be started and events	3113	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	3114	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2447	C<events> set will be created and started.	3115	the given C<fd> and C<events> set will be created and started.
2448		3116
2449	If C<timeout> is less than 0, then no timeout watcher will be	3117	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	3118	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	3119	repeat = 0) will be started. C<0> is a valid timeout.
2452	dubious value.
2453		3120
2454	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3121	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	3122	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>	3123	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2457	value passed to C<ev_once>:	3124	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3125	a timeout and an io event at the same time - you probably should give io
		3126	events precedence.
		3127
		3128	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2458		3129
2459	static void stdin_ready (int revents, void *arg)	3130	static void stdin_ready (int revents, void *arg)
2460	{	3131	{
		3132	if (revents & EV_READ)
		3133	/* stdin might have data for us, joy! */;
2461	if (revents & EV_TIMEOUT)	3134	else if (revents & EV_TIMEOUT)
2462	/* doh, nothing entered */;	3135	/* doh, nothing entered */;
2463	else if (revents & EV_READ)
2464	/* stdin might have data for us, joy! */;
2465	}	3136	}
2466		3137
2467	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3138	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2468		3139
2469	=item ev_feed_event (ev_loop *, watcher *, int revents)	3140	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2470		3141
2471	Feeds the given event set into the event loop, as if the specified event	3142	Feeds the given event set into the event loop, as if the specified event
2472	had happened for the specified watcher (which must be a pointer to an	3143	had happened for the specified watcher (which must be a pointer to an
2473	initialised but not necessarily started event watcher).	3144	initialised but not necessarily started event watcher).
2474		3145
2475	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3146	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2476		3147
2477	Feed an event on the given fd, as if a file descriptor backend detected	3148	Feed an event on the given fd, as if a file descriptor backend detected
2478	the given events it.	3149	the given events it.
2479		3150
2480	=item ev_feed_signal_event (ev_loop *loop, int signum)	3151	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2481		3152
2482	Feed an event as if the given signal occurred (C<loop> must be the default	3153	Feed an event as if the given signal occurred (C<loop> must be the default
2483	loop!).	3154	loop!).
2484		3155
2485	=back	3156	=back
…		…
2607		3278
2608	myclass obj;	3279	myclass obj;
2609	ev::io iow;	3280	ev::io iow;
2610	iow.set <myclass, &myclass::io_cb> (&obj);	3281	iow.set <myclass, &myclass::io_cb> (&obj);
2611		3282
		3283	=item w->set (object *)
		3284
		3285	This is an B<experimental> feature that might go away in a future version.
		3286
		3287	This is a variation of a method callback - leaving out the method to call
		3288	will default the method to C<operator ()>, which makes it possible to use
		3289	functor objects without having to manually specify the C<operator ()> all
		3290	the time. Incidentally, you can then also leave out the template argument
		3291	list.
		3292
		3293	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3294	int revents)>.
		3295
		3296	See the method-C<set> above for more details.
		3297
		3298	Example: use a functor object as callback.
		3299
		3300	struct myfunctor
		3301	{
		3302	void operator() (ev::io &w, int revents)
		3303	{
		3304	...
		3305	}
		3306	}
		3307
		3308	myfunctor f;
		3309
		3310	ev::io w;
		3311	w.set (&f);
		3312
2612	=item w->set<function> (void *data = 0)	3313	=item w->set<function> (void *data = 0)
2613		3314
2614	Also sets a callback, but uses a static method or plain function as	3315	Also sets a callback, but uses a static method or plain function as
2615	callback. The optional C<data> argument will be stored in the watcher's	3316	callback. The optional C<data> argument will be stored in the watcher's
2616	C<data> member and is free for you to use.	3317	C<data> member and is free for you to use.
2617		3318
2618	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3319	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2619		3320
2620	See the method-C<set> above for more details.	3321	See the method-C<set> above for more details.
2621		3322
2622	Example:	3323	Example: Use a plain function as callback.
2623		3324
2624	static void io_cb (ev::io &w, int revents) { }	3325	static void io_cb (ev::io &w, int revents) { }
2625	iow.set <io_cb> ();	3326	iow.set <io_cb> ();
2626		3327
2627	=item w->set (struct ev_loop *)	3328	=item w->set (struct ev_loop *)
…		…
2665	Example: Define a class with an IO and idle watcher, start one of them in	3366	Example: Define a class with an IO and idle watcher, start one of them in
2666	the constructor.	3367	the constructor.
2667		3368
2668	class myclass	3369	class myclass
2669	{	3370	{
2670	ev::io io; void io_cb (ev::io &w, int revents);	3371	ev::io io ; void io_cb (ev::io &w, int revents);
2671	ev:idle idle void idle_cb (ev::idle &w, int revents);	3372	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2672		3373
2673	myclass (int fd)	3374	myclass (int fd)
2674	{	3375	{
2675	io .set <myclass, &myclass::io_cb > (this);	3376	io .set <myclass, &myclass::io_cb > (this);
2676	idle.set <myclass, &myclass::idle_cb> (this);	3377	idle.set <myclass, &myclass::idle_cb> (this);
…		…
2692	=item Perl	3393	=item Perl
2693		3394
2694	The EV module implements the full libev API and is actually used to test	3395	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,	3396	libev. EV is developed together with libev. Apart from the EV core module,
2696	there are additional modules that implement libev-compatible interfaces	3397	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	3398	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>).	3399	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3400	and C<EV::Glib>).
2699		3401
2700	It can be found and installed via CPAN, its homepage is at	3402	It can be found and installed via CPAN, its homepage is at
2701	L<http://software.schmorp.de/pkg/EV>.	3403	L<http://software.schmorp.de/pkg/EV>.
2702		3404
2703	=item Python	3405	=item Python
2704		3406
2705	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3407	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2706	seems to be quite complete and well-documented. Note, however, that the	3408	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		3409
2712	=item Ruby	3410	=item Ruby
2713		3411
2714	Tony Arcieri has written a ruby extension that offers access to a subset	3412	Tony Arcieri has written a ruby extension that offers access to a subset
2715	of the libev API and adds file handle abstractions, asynchronous DNS and	3413	of the libev API and adds file handle abstractions, asynchronous DNS and
2716	more on top of it. It can be found via gem servers. Its homepage is at	3414	more on top of it. It can be found via gem servers. Its homepage is at
2717	L<http://rev.rubyforge.org/>.	3415	L<http://rev.rubyforge.org/>.
2718		3416
		3417	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3418	makes rev work even on mingw.
		3419
		3420	=item Haskell
		3421
		3422	A haskell binding to libev is available at
		3423	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3424
2719	=item D	3425	=item D
2720		3426
2721	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3427	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2722	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3428	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3429
		3430	=item Ocaml
		3431
		3432	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3433	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3434
		3435	=item Lua
		3436
		3437	Brian Maher has written a partial interface to libev
		3438	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3439	L<http://github.com/brimworks/lua-ev>.
2723		3440
2724	=back	3441	=back
2725		3442
2726		3443
2727	=head1 MACRO MAGIC	3444	=head1 MACRO MAGIC
…		…
2828		3545
2829	#define EV_STANDALONE 1	3546	#define EV_STANDALONE 1
2830	#include "ev.h"	3547	#include "ev.h"
2831		3548
2832	Both header files and implementation files can be compiled with a C++	3549	Both header files and implementation files can be compiled with a C++
2833	compiler (at least, thats a stated goal, and breakage will be treated	3550	compiler (at least, that's a stated goal, and breakage will be treated
2834	as a bug).	3551	as a bug).
2835		3552
2836	You need the following files in your source tree, or in a directory	3553	You need the following files in your source tree, or in a directory
2837	in your include path (e.g. in libev/ when using -Ilibev):	3554	in your include path (e.g. in libev/ when using -Ilibev):
2838		3555
…		…
2882		3599
2883	=head2 PREPROCESSOR SYMBOLS/MACROS	3600	=head2 PREPROCESSOR SYMBOLS/MACROS
2884		3601
2885	Libev can be configured via a variety of preprocessor symbols you have to	3602	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	3603	define before including any of its files. The default in the absence of
2887	autoconf is noted for every option.	3604	autoconf is documented for every option.
2888		3605
2889	=over 4	3606	=over 4
2890		3607
2891	=item EV_STANDALONE	3608	=item EV_STANDALONE
2892		3609
…		…
2894	keeps libev from including F<config.h>, and it also defines dummy	3611	keeps libev from including F<config.h>, and it also defines dummy
2895	implementations for some libevent functions (such as logging, which is not	3612	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	3613	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.	3614	F<event.h> that are not directly supported by the libev core alone.
2898		3615
		3616	In standalone mode, libev will still try to automatically deduce the
		3617	configuration, but has to be more conservative.
		3618
2899	=item EV_USE_MONOTONIC	3619	=item EV_USE_MONOTONIC
2900		3620
2901	If defined to be C<1>, libev will try to detect the availability of the	3621	If defined to be C<1>, libev will try to detect the availability of the
2902	monotonic clock option at both compile time and runtime. Otherwise no use	3622	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	3623	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	3624	you usually have to link against librt or something similar. Enabling it
2905	the functionality isn't available is safe, though, although you have	3625	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>	3626	to make sure you link against any libraries where the C<clock_gettime>
2907	function is hiding in (often F<-lrt>).	3627	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2908		3628
2909	=item EV_USE_REALTIME	3629	=item EV_USE_REALTIME
2910		3630
2911	If defined to be C<1>, libev will try to detect the availability of the	3631	If defined to be C<1>, libev will try to detect the availability of the
2912	real-time clock option at compile time (and assume its availability at	3632	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	3633	at runtime if successful). Otherwise no use of the real-time clock
2914	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3634	option will be attempted. This effectively replaces C<gettimeofday>
2915	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3635	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2916	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3636	correctness. See the note about libraries in the description of
		3637	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3638	C<EV_USE_CLOCK_SYSCALL>.
		3639
		3640	=item EV_USE_CLOCK_SYSCALL
		3641
		3642	If defined to be C<1>, libev will try to use a direct syscall instead
		3643	of calling the system-provided C<clock_gettime> function. This option
		3644	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3645	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3646	programs needlessly. Using a direct syscall is slightly slower (in
		3647	theory), because no optimised vdso implementation can be used, but avoids
		3648	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3649	higher, as it simplifies linking (no need for C<-lrt>).
2917		3650
2918	=item EV_USE_NANOSLEEP	3651	=item EV_USE_NANOSLEEP
2919		3652
2920	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3653	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2921	and will use it for delays. Otherwise it will use C<select ()>.	3654	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2937		3670
2938	=item EV_SELECT_USE_FD_SET	3671	=item EV_SELECT_USE_FD_SET
2939		3672
2940	If defined to C<1>, then the select backend will use the system C<fd_set>	3673	If defined to C<1>, then the select backend will use the system C<fd_set>
2941	structure. This is useful if libev doesn't compile due to a missing	3674	structure. This is useful if libev doesn't compile due to a missing
2942	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3675	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2943	exotic systems. This usually limits the range of file descriptors to some	3676	on exotic systems. This usually limits the range of file descriptors to
2944	low limit such as 1024 or might have other limitations (winsocket only	3677	some low limit such as 1024 or might have other limitations (winsocket
2945	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3678	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2946	influence the size of the C<fd_set> used.	3679	configures the maximum size of the C<fd_set>.
2947		3680
2948	=item EV_SELECT_IS_WINSOCKET	3681	=item EV_SELECT_IS_WINSOCKET
2949		3682
2950	When defined to C<1>, the select backend will assume that	3683	When defined to C<1>, the select backend will assume that
2951	select/socket/connect etc. don't understand file descriptors but	3684	select/socket/connect etc. don't understand file descriptors but
…		…
2953	be used is the winsock select). This means that it will call	3686	be used is the winsock select). This means that it will call
2954	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3687	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2955	it is assumed that all these functions actually work on fds, even	3688	it is assumed that all these functions actually work on fds, even
2956	on win32. Should not be defined on non-win32 platforms.	3689	on win32. Should not be defined on non-win32 platforms.
2957		3690
2958	=item EV_FD_TO_WIN32_HANDLE	3691	=item EV_FD_TO_WIN32_HANDLE(fd)
2959		3692
2960	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3693	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2961	file descriptors to socket handles. When not defining this symbol (the	3694	file descriptors to socket handles. When not defining this symbol (the
2962	default), then libev will call C<_get_osfhandle>, which is usually	3695	default), then libev will call C<_get_osfhandle>, which is usually
2963	correct. In some cases, programs use their own file descriptor management,	3696	correct. In some cases, programs use their own file descriptor management,
2964	in which case they can provide this function to map fds to socket handles.	3697	in which case they can provide this function to map fds to socket handles.
		3698
		3699	=item EV_WIN32_HANDLE_TO_FD(handle)
		3700
		3701	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3702	using the standard C<_open_osfhandle> function. For programs implementing
		3703	their own fd to handle mapping, overwriting this function makes it easier
		3704	to do so. This can be done by defining this macro to an appropriate value.
		3705
		3706	=item EV_WIN32_CLOSE_FD(fd)
		3707
		3708	If programs implement their own fd to handle mapping on win32, then this
		3709	macro can be used to override the C<close> function, useful to unregister
		3710	file descriptors again. Note that the replacement function has to close
		3711	the underlying OS handle.
2965		3712
2966	=item EV_USE_POLL	3713	=item EV_USE_POLL
2967		3714
2968	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3715	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2969	backend. Otherwise it will be enabled on non-win32 platforms. It	3716	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3062	When doing priority-based operations, libev usually has to linearly search	3809	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	3810	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	3811	and time, so using the defaults of five priorities (-2 .. +2) is usually
3065	fine.	3812	fine.
3066		3813
3067	If your embedding application does not need any priorities, defining these both to	3814	If your embedding application does not need any priorities, defining these
3068	C<0> will save some memory and CPU.	3815	both to C<0> will save some memory and CPU.
3069		3816
3070	=item EV_PERIODIC_ENABLE	3817	=item EV_PERIODIC_ENABLE
3071		3818
3072	If undefined or defined to be C<1>, then periodic timers are supported. If	3819	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	3820	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
3080	code.	3827	code.
3081		3828
3082	=item EV_EMBED_ENABLE	3829	=item EV_EMBED_ENABLE
3083		3830
3084	If undefined or defined to be C<1>, then embed watchers are supported. If	3831	If undefined or defined to be C<1>, then embed watchers are supported. If
3085	defined to be C<0>, then they are not.	3832	defined to be C<0>, then they are not. Embed watchers rely on most other
		3833	watcher types, which therefore must not be disabled.
3086		3834
3087	=item EV_STAT_ENABLE	3835	=item EV_STAT_ENABLE
3088		3836
3089	If undefined or defined to be C<1>, then stat watchers are supported. If	3837	If undefined or defined to be C<1>, then stat watchers are supported. If
3090	defined to be C<0>, then they are not.	3838	defined to be C<0>, then they are not.
…		…
3100	defined to be C<0>, then they are not.	3848	defined to be C<0>, then they are not.
3101		3849
3102	=item EV_MINIMAL	3850	=item EV_MINIMAL
3103		3851
3104	If you need to shave off some kilobytes of code at the expense of some	3852	If you need to shave off some kilobytes of code at the expense of some
3105	speed, define this symbol to C<1>. Currently this is used to override some	3853	speed (but with the full API), define this symbol to C<1>. Currently this
3106	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3854	is used to override some inlining decisions, saves roughly 30% code size
3107	much smaller 2-heap for timer management over the default 4-heap.	3855	on amd64. It also selects a much smaller 2-heap for timer management over
		3856	the default 4-heap.
		3857
		3858	You can save even more by disabling watcher types you do not need
		3859	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3860	(C<-DNDEBUG>) will usually reduce code size a lot.
		3861
		3862	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3863	provide a bare-bones event library. See C<ev.h> for details on what parts
		3864	of the API are still available, and do not complain if this subset changes
		3865	over time.
		3866
		3867	=item EV_NSIG
		3868
		3869	The highest supported signal number, +1 (or, the number of
		3870	signals): Normally, libev tries to deduce the maximum number of signals
		3871	automatically, but sometimes this fails, in which case it can be
		3872	specified. Also, using a lower number than detected (C<32> should be
		3873	good for about any system in existance) can save some memory, as libev
		3874	statically allocates some 12-24 bytes per signal number.
3108		3875
3109	=item EV_PID_HASHSIZE	3876	=item EV_PID_HASHSIZE
3110		3877
3111	C<ev_child> watchers use a small hash table to distribute workload by	3878	C<ev_child> watchers use a small hash table to distribute workload by
3112	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3879	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3122	two).	3889	two).
3123		3890
3124	=item EV_USE_4HEAP	3891	=item EV_USE_4HEAP
3125		3892
3126	Heaps are not very cache-efficient. To improve the cache-efficiency of the	3893	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	3894	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	3895	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3129	noticeably faster performance with many (thousands) of watchers.	3896	faster performance with many (thousands) of watchers.
3130		3897
3131	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	3898	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
3132	(disabled).	3899	(disabled).
3133		3900
3134	=item EV_HEAP_CACHE_AT	3901	=item EV_HEAP_CACHE_AT
3135		3902
3136	Heaps are not very cache-efficient. To improve the cache-efficiency of the	3903	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	3904	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>),	3905	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,	3906	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	3907	but avoids random read accesses on heap changes. This improves performance
3141	noticeably with with many (hundreds) of watchers.	3908	noticeably with many (hundreds) of watchers.
3142		3909
3143	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	3910	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
3144	(disabled).	3911	(disabled).
3145		3912
3146	=item EV_VERIFY	3913	=item EV_VERIFY
…		…
3152	called once per loop, which can slow down libev. If set to C<3>, then the	3919	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	3920	verification code will be called very frequently, which will slow down
3154	libev considerably.	3921	libev considerably.
3155		3922
3156	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	3923	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
3157	C<0.>	3924	C<0>.
3158		3925
3159	=item EV_COMMON	3926	=item EV_COMMON
3160		3927
3161	By default, all watchers have a C<void *data> member. By redefining	3928	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	3929	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	3946	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	3947	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	3948	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	3949	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++.	3950	method calls instead of plain function calls in C++.
		3951
		3952	=back
3184		3953
3185	=head2 EXPORTED API SYMBOLS	3954	=head2 EXPORTED API SYMBOLS
3186		3955
3187	If you need to re-export the API (e.g. via a DLL) and you need a list of	3956	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	3957	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:	4004	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3236		4005
3237	#include "ev_cpp.h"	4006	#include "ev_cpp.h"
3238	#include "ev.c"	4007	#include "ev.c"
3239		4008
		4009	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3240		4010
3241	=head1 THREADS AND COROUTINES	4011	=head2 THREADS AND COROUTINES
3242		4012
3243	=head2 THREADS	4013	=head3 THREADS
3244		4014
3245	Libev itself is completely thread-safe, but it uses no locking. This	4015	All libev functions are reentrant and thread-safe unless explicitly
		4016	documented otherwise, but libev implements no locking itself. This means
3246	means that you can use as many loops as you want in parallel, as long as	4017	that you can use as many loops as you want in parallel, as long as there
3247	only one thread ever calls into one libev function with the same loop	4018	are no concurrent calls into any libev function with the same loop
3248	parameter.	4019	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4020	of course): libev guarantees that different event loops share no data
		4021	structures that need any locking.
3249		4022
3250	Or put differently: calls with different loop parameters can be done in	4023	Or to put it differently: calls with different loop parameters can be done
3251	parallel from multiple threads, calls with the same loop parameter must be	4024	concurrently from multiple threads, calls with the same loop parameter
3252	done serially (but can be done from different threads, as long as only one	4025	must be done serially (but can be done from different threads, as long as
3253	thread ever is inside a call at any point in time, e.g. by using a mutex	4026	only one thread ever is inside a call at any point in time, e.g. by using
3254	per loop).	4027	a mutex per loop).
		4028
		4029	Specifically to support threads (and signal handlers), libev implements
		4030	so-called C<ev_async> watchers, which allow some limited form of
		4031	concurrency on the same event loop, namely waking it up "from the
		4032	outside".
3255		4033
3256	If you want to know which design (one loop, locking, or multiple loops	4034	If you want to know which design (one loop, locking, or multiple loops
3257	without or something else still) is best for your problem, then I cannot	4035	without or something else still) is best for your problem, then I cannot
3258	help you. I can give some generic advice however:	4036	help you, but here is some generic advice:
3259		4037
3260	=over 4	4038	=over 4
3261		4039
3262	=item * most applications have a main thread: use the default libev loop	4040	=item * most applications have a main thread: use the default libev loop
3263	in that thread, or create a separate thread running only the default loop.	4041	in that thread, or create a separate thread running only the default loop.
…		…
3275		4053
3276	Choosing a model is hard - look around, learn, know that usually you can do	4054	Choosing a model is hard - look around, learn, know that usually you can do
3277	better than you currently do :-)	4055	better than you currently do :-)
3278		4056
3279	=item * often you need to talk to some other thread which blocks in the	4057	=item * often you need to talk to some other thread which blocks in the
		4058	event loop.
		4059
3280	event loop - C<ev_async> watchers can be used to wake them up from other	4060	C<ev_async> watchers can be used to wake them up from other threads safely
3281	threads safely (or from signal contexts...).	4061	(or from signal contexts...).
		4062
		4063	An example use would be to communicate signals or other events that only
		4064	work in the default loop by registering the signal watcher with the
		4065	default loop and triggering an C<ev_async> watcher from the default loop
		4066	watcher callback into the event loop interested in the signal.
3282		4067
3283	=back	4068	=back
3284		4069
		4070	=head4 THREAD LOCKING EXAMPLE
		4071
		4072	Here is a fictitious example of how to run an event loop in a different
		4073	thread than where callbacks are being invoked and watchers are
		4074	created/added/removed.
		4075
		4076	For a real-world example, see the C<EV::Loop::Async> perl module,
		4077	which uses exactly this technique (which is suited for many high-level
		4078	languages).
		4079
		4080	The example uses a pthread mutex to protect the loop data, a condition
		4081	variable to wait for callback invocations, an async watcher to notify the
		4082	event loop thread and an unspecified mechanism to wake up the main thread.
		4083
		4084	First, you need to associate some data with the event loop:
		4085
		4086	typedef struct {
		4087	mutex_t lock; /* global loop lock */
		4088	ev_async async_w;
		4089	thread_t tid;
		4090	cond_t invoke_cv;
		4091	} userdata;
		4092
		4093	void prepare_loop (EV_P)
		4094	{
		4095	// for simplicity, we use a static userdata struct.
		4096	static userdata u;
		4097
		4098	ev_async_init (&u->async_w, async_cb);
		4099	ev_async_start (EV_A_ &u->async_w);
		4100
		4101	pthread_mutex_init (&u->lock, 0);
		4102	pthread_cond_init (&u->invoke_cv, 0);
		4103
		4104	// now associate this with the loop
		4105	ev_set_userdata (EV_A_ u);
		4106	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4107	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4108
		4109	// then create the thread running ev_loop
		4110	pthread_create (&u->tid, 0, l_run, EV_A);
		4111	}
		4112
		4113	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4114	solely to wake up the event loop so it takes notice of any new watchers
		4115	that might have been added:
		4116
		4117	static void
		4118	async_cb (EV_P_ ev_async *w, int revents)
		4119	{
		4120	// just used for the side effects
		4121	}
		4122
		4123	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4124	protecting the loop data, respectively.
		4125
		4126	static void
		4127	l_release (EV_P)
		4128	{
		4129	userdata *u = ev_userdata (EV_A);
		4130	pthread_mutex_unlock (&u->lock);
		4131	}
		4132
		4133	static void
		4134	l_acquire (EV_P)
		4135	{
		4136	userdata *u = ev_userdata (EV_A);
		4137	pthread_mutex_lock (&u->lock);
		4138	}
		4139
		4140	The event loop thread first acquires the mutex, and then jumps straight
		4141	into C<ev_loop>:
		4142
		4143	void *
		4144	l_run (void *thr_arg)
		4145	{
		4146	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4147
		4148	l_acquire (EV_A);
		4149	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4150	ev_loop (EV_A_ 0);
		4151	l_release (EV_A);
		4152
		4153	return 0;
		4154	}
		4155
		4156	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4157	signal the main thread via some unspecified mechanism (signals? pipe
		4158	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4159	have been called (in a while loop because a) spurious wakeups are possible
		4160	and b) skipping inter-thread-communication when there are no pending
		4161	watchers is very beneficial):
		4162
		4163	static void
		4164	l_invoke (EV_P)
		4165	{
		4166	userdata *u = ev_userdata (EV_A);
		4167
		4168	while (ev_pending_count (EV_A))
		4169	{
		4170	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4171	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4172	}
		4173	}
		4174
		4175	Now, whenever the main thread gets told to invoke pending watchers, it
		4176	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4177	thread to continue:
		4178
		4179	static void
		4180	real_invoke_pending (EV_P)
		4181	{
		4182	userdata *u = ev_userdata (EV_A);
		4183
		4184	pthread_mutex_lock (&u->lock);
		4185	ev_invoke_pending (EV_A);
		4186	pthread_cond_signal (&u->invoke_cv);
		4187	pthread_mutex_unlock (&u->lock);
		4188	}
		4189
		4190	Whenever you want to start/stop a watcher or do other modifications to an
		4191	event loop, you will now have to lock:
		4192
		4193	ev_timer timeout_watcher;
		4194	userdata *u = ev_userdata (EV_A);
		4195
		4196	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4197
		4198	pthread_mutex_lock (&u->lock);
		4199	ev_timer_start (EV_A_ &timeout_watcher);
		4200	ev_async_send (EV_A_ &u->async_w);
		4201	pthread_mutex_unlock (&u->lock);
		4202
		4203	Note that sending the C<ev_async> watcher is required because otherwise
		4204	an event loop currently blocking in the kernel will have no knowledge
		4205	about the newly added timer. By waking up the loop it will pick up any new
		4206	watchers in the next event loop iteration.
		4207
3285	=head2 COROUTINES	4208	=head3 COROUTINES
3286		4209
3287	Libev is much more accommodating to coroutines ("cooperative threads"):	4210	Libev is very accommodating to coroutines ("cooperative threads"):
3288	libev fully supports nesting calls to it's functions from different	4211	libev fully supports nesting calls to its functions from different
3289	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4212	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3290	different coroutines and switch freely between both coroutines running the	4213	different coroutines, and switch freely between both coroutines running
3291	loop, as long as you don't confuse yourself). The only exception is that	4214	the loop, as long as you don't confuse yourself). The only exception is
3292	you must not do this from C<ev_periodic> reschedule callbacks.	4215	that you must not do this from C<ev_periodic> reschedule callbacks.
3293		4216
3294	Care has been invested into making sure that libev does not keep local	4217	Care has been taken to ensure that libev does not keep local state inside
3295	state inside C<ev_loop>, and other calls do not usually allow coroutine	4218	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3296	switches.	4219	they do not call any callbacks.
3297		4220
		4221	=head2 COMPILER WARNINGS
3298		4222
3299	=head1 COMPLEXITIES	4223	Depending on your compiler and compiler settings, you might get no or a
		4224	lot of warnings when compiling libev code. Some people are apparently
		4225	scared by this.
3300		4226
3301	In this section the complexities of (many of) the algorithms used inside	4227	However, these are unavoidable for many reasons. For one, each compiler
3302	libev will be explained. For complexity discussions about backends see the	4228	has different warnings, and each user has different tastes regarding
3303	documentation for C<ev_default_init>.	4229	warning options. "Warn-free" code therefore cannot be a goal except when
		4230	targeting a specific compiler and compiler-version.
3304		4231
3305	All of the following are about amortised time: If an array needs to be	4232	Another reason is that some compiler warnings require elaborate
3306	extended, libev needs to realloc and move the whole array, but this	4233	workarounds, or other changes to the code that make it less clear and less
3307	happens asymptotically never with higher number of elements, so O(1) might	4234	maintainable.
3308	mean it might do a lengthy realloc operation in rare cases, but on average
3309	it is much faster and asymptotically approaches constant time.
3310		4235
3311	=over 4	4236	And of course, some compiler warnings are just plain stupid, or simply
		4237	wrong (because they don't actually warn about the condition their message
		4238	seems to warn about). For example, certain older gcc versions had some
		4239	warnings that resulted an extreme number of false positives. These have
		4240	been fixed, but some people still insist on making code warn-free with
		4241	such buggy versions.
3312		4242
3313	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4243	While libev is written to generate as few warnings as possible,
		4244	"warn-free" code is not a goal, and it is recommended not to build libev
		4245	with any compiler warnings enabled unless you are prepared to cope with
		4246	them (e.g. by ignoring them). Remember that warnings are just that:
		4247	warnings, not errors, or proof of bugs.
3314		4248
3315	This means that, when you have a watcher that triggers in one hour and
3316	there are 100 watchers that would trigger before that then inserting will
3317	have to skip roughly seven (C<ld 100>) of these watchers.
3318		4249
3319	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4250	=head2 VALGRIND
3320		4251
3321	That means that changing a timer costs less than removing/adding them	4252	Valgrind has a special section here because it is a popular tool that is
3322	as only the relative motion in the event queue has to be paid for.	4253	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3323		4254
3324	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4255	If you think you found a bug (memory leak, uninitialised data access etc.)
		4256	in libev, then check twice: If valgrind reports something like:
3325		4257
3326	These just add the watcher into an array or at the head of a list.	4258	==2274== definitely lost: 0 bytes in 0 blocks.
		4259	==2274== possibly lost: 0 bytes in 0 blocks.
		4260	==2274== still reachable: 256 bytes in 1 blocks.
3327		4261
3328	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4262	Then there is no memory leak, just as memory accounted to global variables
		4263	is not a memleak - the memory is still being referenced, and didn't leak.
3329		4264
3330	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4265	Similarly, under some circumstances, valgrind might report kernel bugs
		4266	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4267	although an acceptable workaround has been found here), or it might be
		4268	confused.
3331		4269
3332	These watchers are stored in lists then need to be walked to find the	4270	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3333	correct watcher to remove. The lists are usually short (you don't usually	4271	make it into some kind of religion.
3334	have many watchers waiting for the same fd or signal).
3335		4272
3336	=item Finding the next timer in each loop iteration: O(1)	4273	If you are unsure about something, feel free to contact the mailing list
		4274	with the full valgrind report and an explanation on why you think this
		4275	is a bug in libev (best check the archives, too :). However, don't be
		4276	annoyed when you get a brisk "this is no bug" answer and take the chance
		4277	of learning how to interpret valgrind properly.
3337		4278
3338	By virtue of using a binary or 4-heap, the next timer is always found at a	4279	If you need, for some reason, empty reports from valgrind for your project
3339	fixed position in the storage array.	4280	I suggest using suppression lists.
3340		4281
3341	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3342		4282
3343	A change means an I/O watcher gets started or stopped, which requires	4283	=head1 PORTABILITY NOTES
3344	libev to recalculate its status (and possibly tell the kernel, depending
3345	on backend and whether C<ev_io_set> was used).
3346		4284
3347	=item Activating one watcher (putting it into the pending state): O(1)
3348
3349	=item Priority handling: O(number_of_priorities)
3350
3351	Priorities are implemented by allocating some space for each
3352	priority. When doing priority-based operations, libev usually has to
3353	linearly search all the priorities, but starting/stopping and activating
3354	watchers becomes O(1) w.r.t. priority handling.
3355
3356	=item Sending an ev_async: O(1)
3357
3358	=item Processing ev_async_send: O(number_of_async_watchers)
3359
3360	=item Processing signals: O(max_signal_number)
3361
3362	Sending involves a system call I<iff> there were no other C<ev_async_send>
3363	calls in the current loop iteration. Checking for async and signal events
3364	involves iterating over all running async watchers or all signal numbers.
3365
3366	=back
3367
3368
3369	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	4285	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3370		4286
3371	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4287	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3372	requires, and its I/O model is fundamentally incompatible with the POSIX	4288	requires, and its I/O model is fundamentally incompatible with the POSIX
3373	model. Libev still offers limited functionality on this platform in	4289	model. Libev still offers limited functionality on this platform in
3374	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4290	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
…		…
3381	way (note also that glib is the slowest event library known to man).	4297	way (note also that glib is the slowest event library known to man).
3382		4298
3383	There is no supported compilation method available on windows except	4299	There is no supported compilation method available on windows except
3384	embedding it into other applications.	4300	embedding it into other applications.
3385		4301
		4302	Sensible signal handling is officially unsupported by Microsoft - libev
		4303	tries its best, but under most conditions, signals will simply not work.
		4304
3386	Not a libev limitation but worth mentioning: windows apparently doesn't	4305	Not a libev limitation but worth mentioning: windows apparently doesn't
3387	accept large writes: instead of resulting in a partial write, windows will	4306	accept large writes: instead of resulting in a partial write, windows will
3388	either accept everything or return C<ENOBUFS> if the buffer is too large,	4307	either accept everything or return C<ENOBUFS> if the buffer is too large,
3389	so make sure you only write small amounts into your sockets (less than a	4308	so make sure you only write small amounts into your sockets (less than a
3390	megabyte seems safe, but thsi apparently depends on the amount of memory	4309	megabyte seems safe, but this apparently depends on the amount of memory
3391	available).	4310	available).
3392		4311
3393	Due to the many, low, and arbitrary limits on the win32 platform and	4312	Due to the many, low, and arbitrary limits on the win32 platform and
3394	the abysmal performance of winsockets, using a large number of sockets	4313	the abysmal performance of winsockets, using a large number of sockets
3395	is not recommended (and not reasonable). If your program needs to use	4314	is not recommended (and not reasonable). If your program needs to use
3396	more than a hundred or so sockets, then likely it needs to use a totally	4315	more than a hundred or so sockets, then likely it needs to use a totally
3397	different implementation for windows, as libev offers the POSIX readiness	4316	different implementation for windows, as libev offers the POSIX readiness
3398	notification model, which cannot be implemented efficiently on windows	4317	notification model, which cannot be implemented efficiently on windows
3399	(Microsoft monopoly games).	4318	(due to Microsoft monopoly games).
3400		4319
3401	A typical way to use libev under windows is to embed it (see the embedding	4320	A typical way to use libev under windows is to embed it (see the embedding
3402	section for details) and use the following F<evwrap.h> header file instead	4321	section for details) and use the following F<evwrap.h> header file instead
3403	of F<ev.h>:	4322	of F<ev.h>:
3404		4323
…		…
3406	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	4325	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3407		4326
3408	#include "ev.h"	4327	#include "ev.h"
3409		4328
3410	And compile the following F<evwrap.c> file into your project (make sure	4329	And compile the following F<evwrap.c> file into your project (make sure
3411	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	4330	you do I<not> compile the F<ev.c> or any other embedded source files!):
3412		4331
3413	#include "evwrap.h"	4332	#include "evwrap.h"
3414	#include "ev.c"	4333	#include "ev.c"
3415		4334
3416	=over 4	4335	=over 4
…		…
3440		4359
3441	Early versions of winsocket's select only supported waiting for a maximum	4360	Early versions of winsocket's select only supported waiting for a maximum
3442	of C<64> handles (probably owning to the fact that all windows kernels	4361	of C<64> handles (probably owning to the fact that all windows kernels
3443	can only wait for C<64> things at the same time internally; Microsoft	4362	can only wait for C<64> things at the same time internally; Microsoft
3444	recommends spawning a chain of threads and wait for 63 handles and the	4363	recommends spawning a chain of threads and wait for 63 handles and the
3445	previous thread in each. Great).	4364	previous thread in each. Sounds great!).
3446		4365
3447	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4366	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3448	to some high number (e.g. C<2048>) before compiling the winsocket select	4367	to some high number (e.g. C<2048>) before compiling the winsocket select
3449	call (which might be in libev or elsewhere, for example, perl does its own	4368	call (which might be in libev or elsewhere, for example, perl and many
3450	select emulation on windows).	4369	other interpreters do their own select emulation on windows).
3451		4370
3452	Another limit is the number of file descriptors in the Microsoft runtime	4371	Another limit is the number of file descriptors in the Microsoft runtime
3453	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4372	libraries, which by default is C<64> (there must be a hidden I<64>
3454	or something like this inside Microsoft). You can increase this by calling	4373	fetish or something like this inside Microsoft). You can increase this
3455	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4374	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3456	arbitrary limit), but is broken in many versions of the Microsoft runtime	4375	(another arbitrary limit), but is broken in many versions of the Microsoft
3457	libraries.
3458
3459	This might get you to about C<512> or C<2048> sockets (depending on	4376	runtime libraries. This might get you to about C<512> or C<2048> sockets
3460	windows version and/or the phase of the moon). To get more, you need to	4377	(depending on windows version and/or the phase of the moon). To get more,
3461	wrap all I/O functions and provide your own fd management, but the cost of	4378	you need to wrap all I/O functions and provide your own fd management, but
3462	calling select (O(n²)) will likely make this unworkable.	4379	the cost of calling select (O(n²)) will likely make this unworkable.
3463		4380
3464	=back	4381	=back
3465		4382
3466
3467	=head1 PORTABILITY REQUIREMENTS	4383	=head2 PORTABILITY REQUIREMENTS
3468		4384
3469	In addition to a working ISO-C implementation, libev relies on a few	4385	In addition to a working ISO-C implementation and of course the
3470	additional extensions:	4386	backend-specific APIs, libev relies on a few additional extensions:
3471		4387
3472	=over 4	4388	=over 4
3473		4389
3474	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	4390	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3475	calling conventions regardless of C<ev_watcher_type *>.	4391	calling conventions regardless of C<ev_watcher_type *>.
…		…
3481	calls them using an C<ev_watcher *> internally.	4397	calls them using an C<ev_watcher *> internally.
3482		4398
3483	=item C<sig_atomic_t volatile> must be thread-atomic as well	4399	=item C<sig_atomic_t volatile> must be thread-atomic as well
3484		4400
3485	The type C<sig_atomic_t volatile> (or whatever is defined as	4401	The type C<sig_atomic_t volatile> (or whatever is defined as
3486	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4402	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3487	threads. This is not part of the specification for C<sig_atomic_t>, but is	4403	threads. This is not part of the specification for C<sig_atomic_t>, but is
3488	believed to be sufficiently portable.	4404	believed to be sufficiently portable.
3489		4405
3490	=item C<sigprocmask> must work in a threaded environment	4406	=item C<sigprocmask> must work in a threaded environment
3491		4407
…		…
3500	except the initial one, and run the default loop in the initial thread as	4416	except the initial one, and run the default loop in the initial thread as
3501	well.	4417	well.
3502		4418
3503	=item C<long> must be large enough for common memory allocation sizes	4419	=item C<long> must be large enough for common memory allocation sizes
3504		4420
3505	To improve portability and simplify using libev, libev uses C<long>	4421	To improve portability and simplify its API, libev uses C<long> internally
3506	internally instead of C<size_t> when allocating its data structures. On	4422	instead of C<size_t> when allocating its data structures. On non-POSIX
3507	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	4423	systems (Microsoft...) this might be unexpectedly low, but is still at
3508	is still at least 31 bits everywhere, which is enough for hundreds of	4424	least 31 bits everywhere, which is enough for hundreds of millions of
3509	millions of watchers.	4425	watchers.
3510		4426
3511	=item C<double> must hold a time value in seconds with enough accuracy	4427	=item C<double> must hold a time value in seconds with enough accuracy
3512		4428
3513	The type C<double> is used to represent timestamps. It is required to	4429	The type C<double> is used to represent timestamps. It is required to
3514	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4430	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3515	enough for at least into the year 4000. This requirement is fulfilled by	4431	enough for at least into the year 4000. This requirement is fulfilled by
3516	implementations implementing IEEE 754 (basically all existing ones).	4432	implementations implementing IEEE 754, which is basically all existing
		4433	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4434	2200.
3517		4435
3518	=back	4436	=back
3519		4437
3520	If you know of other additional requirements drop me a note.	4438	If you know of other additional requirements drop me a note.
3521		4439
3522		4440
3523	=head1 COMPILER WARNINGS	4441	=head1 ALGORITHMIC COMPLEXITIES
3524		4442
3525	Depending on your compiler and compiler settings, you might get no or a	4443	In this section the complexities of (many of) the algorithms used inside
3526	lot of warnings when compiling libev code. Some people are apparently	4444	libev will be documented. For complexity discussions about backends see
3527	scared by this.	4445	the documentation for C<ev_default_init>.
3528		4446
3529	However, these are unavoidable for many reasons. For one, each compiler	4447	All of the following are about amortised time: If an array needs to be
3530	has different warnings, and each user has different tastes regarding	4448	extended, libev needs to realloc and move the whole array, but this
3531	warning options. "Warn-free" code therefore cannot be a goal except when	4449	happens asymptotically rarer with higher number of elements, so O(1) might
3532	targeting a specific compiler and compiler-version.	4450	mean that libev does a lengthy realloc operation in rare cases, but on
		4451	average it is much faster and asymptotically approaches constant time.
3533		4452
3534	Another reason is that some compiler warnings require elaborate	4453	=over 4
3535	workarounds, or other changes to the code that make it less clear and less
3536	maintainable.
3537		4454
3538	And of course, some compiler warnings are just plain stupid, or simply	4455	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3539	wrong (because they don't actually warn about the condition their message
3540	seems to warn about).
3541		4456
3542	While libev is written to generate as few warnings as possible,	4457	This means that, when you have a watcher that triggers in one hour and
3543	"warn-free" code is not a goal, and it is recommended not to build libev	4458	there are 100 watchers that would trigger before that, then inserting will
3544	with any compiler warnings enabled unless you are prepared to cope with	4459	have to skip roughly seven (C<ld 100>) of these watchers.
3545	them (e.g. by ignoring them). Remember that warnings are just that:
3546	warnings, not errors, or proof of bugs.
3547		4460
		4461	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3548		4462
3549	=head1 VALGRIND	4463	That means that changing a timer costs less than removing/adding them,
		4464	as only the relative motion in the event queue has to be paid for.
3550		4465
3551	Valgrind has a special section here because it is a popular tool that is	4466	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3552	highly useful, but valgrind reports are very hard to interpret.
3553		4467
3554	If you think you found a bug (memory leak, uninitialised data access etc.)	4468	These just add the watcher into an array or at the head of a list.
3555	in libev, then check twice: If valgrind reports something like:
3556		4469
3557	==2274== definitely lost: 0 bytes in 0 blocks.	4470	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3558	==2274== possibly lost: 0 bytes in 0 blocks.
3559	==2274== still reachable: 256 bytes in 1 blocks.
3560		4471
3561	Then there is no memory leak. Similarly, under some circumstances,	4472	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3562	valgrind might report kernel bugs as if it were a bug in libev, or it
3563	might be confused (it is a very good tool, but only a tool).
3564		4473
3565	If you are unsure about something, feel free to contact the mailing list	4474	These watchers are stored in lists, so they need to be walked to find the
3566	with the full valgrind report and an explanation on why you think this is	4475	correct watcher to remove. The lists are usually short (you don't usually
3567	a bug in libev. However, don't be annoyed when you get a brisk "this is	4476	have many watchers waiting for the same fd or signal: one is typical, two
3568	no bug" answer and take the chance of learning how to interpret valgrind	4477	is rare).
3569	properly.
3570		4478
3571	If you need, for some reason, empty reports from valgrind for your project	4479	=item Finding the next timer in each loop iteration: O(1)
3572	I suggest using suppression lists.
3573		4480
		4481	By virtue of using a binary or 4-heap, the next timer is always found at a
		4482	fixed position in the storage array.
		4483
		4484	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4485
		4486	A change means an I/O watcher gets started or stopped, which requires
		4487	libev to recalculate its status (and possibly tell the kernel, depending
		4488	on backend and whether C<ev_io_set> was used).
		4489
		4490	=item Activating one watcher (putting it into the pending state): O(1)
		4491
		4492	=item Priority handling: O(number_of_priorities)
		4493
		4494	Priorities are implemented by allocating some space for each
		4495	priority. When doing priority-based operations, libev usually has to
		4496	linearly search all the priorities, but starting/stopping and activating
		4497	watchers becomes O(1) with respect to priority handling.
		4498
		4499	=item Sending an ev_async: O(1)
		4500
		4501	=item Processing ev_async_send: O(number_of_async_watchers)
		4502
		4503	=item Processing signals: O(max_signal_number)
		4504
		4505	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4506	calls in the current loop iteration. Checking for async and signal events
		4507	involves iterating over all running async watchers or all signal numbers.
		4508
		4509	=back
		4510
		4511
		4512	=head1 GLOSSARY
		4513
		4514	=over 4
		4515
		4516	=item active
		4517
		4518	A watcher is active as long as it has been started (has been attached to
		4519	an event loop) but not yet stopped (disassociated from the event loop).
		4520
		4521	=item application
		4522
		4523	In this document, an application is whatever is using libev.
		4524
		4525	=item callback
		4526
		4527	The address of a function that is called when some event has been
		4528	detected. Callbacks are being passed the event loop, the watcher that
		4529	received the event, and the actual event bitset.
		4530
		4531	=item callback invocation
		4532
		4533	The act of calling the callback associated with a watcher.
		4534
		4535	=item event
		4536
		4537	A change of state of some external event, such as data now being available
		4538	for reading on a file descriptor, time having passed or simply not having
		4539	any other events happening anymore.
		4540
		4541	In libev, events are represented as single bits (such as C<EV_READ> or
		4542	C<EV_TIMEOUT>).
		4543
		4544	=item event library
		4545
		4546	A software package implementing an event model and loop.
		4547
		4548	=item event loop
		4549
		4550	An entity that handles and processes external events and converts them
		4551	into callback invocations.
		4552
		4553	=item event model
		4554
		4555	The model used to describe how an event loop handles and processes
		4556	watchers and events.
		4557
		4558	=item pending
		4559
		4560	A watcher is pending as soon as the corresponding event has been detected,
		4561	and stops being pending as soon as the watcher will be invoked or its
		4562	pending status is explicitly cleared by the application.
		4563
		4564	A watcher can be pending, but not active. Stopping a watcher also clears
		4565	its pending status.
		4566
		4567	=item real time
		4568
		4569	The physical time that is observed. It is apparently strictly monotonic :)
		4570
		4571	=item wall-clock time
		4572
		4573	The time and date as shown on clocks. Unlike real time, it can actually
		4574	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4575	clock.
		4576
		4577	=item watcher
		4578
		4579	A data structure that describes interest in certain events. Watchers need
		4580	to be started (attached to an event loop) before they can receive events.
		4581
		4582	=item watcher invocation
		4583
		4584	The act of calling the callback associated with a watcher.
		4585
		4586	=back
3574		4587
3575	=head1 AUTHOR	4588	=head1 AUTHOR
3576		4589
3577	Marc Lehmann <libev@schmorp.de>.	4590	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3578		4591

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