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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
…		…
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
109	this argument.	124	this argument.
110		125
111	=head2 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
112		127
113	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
115	the beginning of 1970, details are complicated, don't ask). This type is	130	near the beginning of 1970, details are complicated, don't ask). This
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	type is called C<ev_tstamp>, which is what you should use too. It usually
117	to the C<double> type in C, and when you need to do any calculations on	132	aliases to the C<double> type in C. When you need to do any calculations
118	it, you should treat it as some floating point value. Unlike the name	133	on it, you should treat it as some floating point value. Unlike the name
119	component C<stamp> might indicate, it is also used for time differences	134	component C<stamp> might indicate, it is also used for time differences
120	throughout libev.	135	throughout libev.
121		136
122	=head1 ERROR HANDLING	137	=head1 ERROR HANDLING
123		138
…		…
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
…		…
359	writing a server, you should C<accept ()> in a loop to accept as many	393	writing a server, you should C<accept ()> in a loop to accept as many
360	connections as possible during one iteration. You might also want to have	394	connections as possible during one iteration. You might also want to have
361	a look at C<ev_set_io_collect_interval ()> to increase the amount of	395	a look at C<ev_set_io_collect_interval ()> to increase the amount of
362	readiness notifications you get per iteration.	396	readiness notifications you get per iteration.
363		397
		398	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		399	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		400	C<exceptfds> set on that platform).
		401
364	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	402	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
365		403
366	And this is your standard poll(2) backend. It's more complicated	404	And this is your standard poll(2) backend. It's more complicated
367	than select, but handles sparse fds better and has no artificial	405	than select, but handles sparse fds better and has no artificial
368	limit on the number of fds you can use (except it will slow down	406	limit on the number of fds you can use (except it will slow down
369	considerably with a lot of inactive fds). It scales similarly to select,	407	considerably with a lot of inactive fds). It scales similarly to select,
370	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	408	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
371	performance tips.	409	performance tips.
372		410
		411	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		412	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		413
373	=item C<EVBACKEND_EPOLL> (value 4, Linux)	414	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		415
		416	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		417	kernels).
374		418
375	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,
376	but it scales phenomenally better. While poll and select usually scale	420	but it scales phenomenally better. While poll and select usually scale
377	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),
378	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).
379	of shortcomings, such as silently dropping events in some hard-to-detect	423
380	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
381	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.
382		440
383	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
384	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
385	(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
386	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
387	very well if you register events for both fds.	445	file descriptors might not work very well if you register events for both
388		446	file descriptors.
389	Please note that epoll sometimes generates spurious notifications, so you
390	need to use non-blocking I/O or other means to avoid blocking when no data
391	(or space) is available.
392		447
393	Best performance from this backend is achieved by not unregistering all	448	Best performance from this backend is achieved by not unregistering all
394	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,
395	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.
396		459
397	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
398	all kernel versions tested so far.	461	all kernel versions tested so far.
		462
		463	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		464	C<EVBACKEND_POLL>.
399		465
400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	466	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
401		467
402	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
403	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
404	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
405	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
406	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
407	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)
408	system like NetBSD.	476	system like NetBSD.
409		477
410	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
411	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
…		…
413		481
414	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
415	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
416	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
417	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
418	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
419	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
420		489
421	This backend usually performs well under most conditions.	490	This backend usually performs well under most conditions.
422		491
423	While nominally embeddable in other event loops, this doesn't work	492	While nominally embeddable in other event loops, this doesn't work
424	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
425	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
426	(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
427	(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
428	sockets.	497	also broken on OS X)) and, did I mention it, using it only for sockets.
		498
		499	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		500	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		501	C<NOTE_EOF>.
429		502
430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	503	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
431		504
432	This is not implemented yet (and might never be, unless you send me an	505	This is not implemented yet (and might never be, unless you send me an
433	implementation). According to reports, C</dev/poll> only supports sockets	506	implementation). According to reports, C</dev/poll> only supports sockets
…		…
446	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
447	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
448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	521	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
449	might perform better.	522	might perform better.
450		523
451	On the positive side, ignoring the spurious readiness notifications, this	524	On the positive side, with the exception of the spurious readiness
452	backend actually performed to specification in all tests and is fully	525	notifications, this backend actually performed fully to specification
453	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).
		528
		529	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		530	C<EVBACKEND_POLL>.
454		531
455	=item C<EVBACKEND_ALL>	532	=item C<EVBACKEND_ALL>
456		533
457	Try all backends (even potentially broken ones that wouldn't be tried	534	Try all backends (even potentially broken ones that wouldn't be tried
458	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	535	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
…		…
460		537
461	It is definitely not recommended to use this flag.	538	It is definitely not recommended to use this flag.
462		539
463	=back	540	=back
464		541
465	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,
466	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
467	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.
468		546
469	The most typical usage is like this:	547	Example: This is the most typical usage.
470		548
471	if (!ev_default_loop (0))	549	if (!ev_default_loop (0))
472	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	550	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
473		551
474	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
475	environment settings to be taken into account:	553	environment settings to be taken into account:
476		554
477	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	555	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
478		556
479	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
480	available (warning, breaks stuff, best use only with your own private	558	used if available (warning, breaks stuff, best use only with your own
481	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):
482		561
483	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	562	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
484		563
485	=item struct ev_loop *ev_loop_new (unsigned int flags)	564	=item struct ev_loop *ev_loop_new (unsigned int flags)
486		565
…		…
507	responsibility to either stop all watchers cleanly yourself I<before>	586	responsibility to either stop all watchers cleanly yourself I<before>
508	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
509	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
510	for example).	589	for example).
511		590
512	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
513	this function, and related watchers (such as signal and child watchers)	592	handlers), will not be freed by this function, and related watchers (such
514	would need to be stopped manually.	593	as signal and child watchers) would need to be stopped manually.
515		594
516	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
517	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
518	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
519	C<ev_loop_new> and C<ev_loop_destroy>).	598	C<ev_loop_new> and C<ev_loop_destroy>.
520		599
521	=item ev_loop_destroy (loop)	600	=item ev_loop_destroy (loop)
522		601
523	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
524	earlier call to C<ev_loop_new>.	603	earlier call to C<ev_loop_new>.
…		…
544		623
545	=item ev_loop_fork (loop)	624	=item ev_loop_fork (loop)
546		625
547	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
548	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
549	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.
550		630
551	=item int ev_is_default_loop (loop)	631	=item int ev_is_default_loop (loop)
552		632
553	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.
554		635
555	=item unsigned int ev_loop_count (loop)	636	=item unsigned int ev_loop_count (loop)
556		637
557	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
558	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
559	happily wraps around with enough iterations.	640	happily wraps around with enough iterations.
560		641
561	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
562	"ticks" the number of loop iterations), as it roughly corresponds with	643	"ticks" the number of loop iterations), as it roughly corresponds with
563	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.
564		657
565	=item unsigned int ev_backend (loop)	658	=item unsigned int ev_backend (loop)
566		659
567	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
568	use.	661	use.
…		…
573	received events and started processing them. This timestamp does not	666	received events and started processing them. This timestamp does not
574	change as long as callbacks are being processed, and this is also the base	667	change as long as callbacks are being processed, and this is also the base
575	time used for relative timers. You can treat it as the timestamp of the	668	time used for relative timers. You can treat it as the timestamp of the
576	event occurring (or more correctly, libev finding out about it).	669	event occurring (or more correctly, libev finding out about it).
577		670
		671	=item ev_now_update (loop)
		672
		673	Establishes the current time by querying the kernel, updating the time
		674	returned by C<ev_now ()> in the progress. This is a costly operation and
		675	is usually done automatically within C<ev_loop ()>.
		676
		677	This function is rarely useful, but when some event callback runs for a
		678	very long time without entering the event loop, updating libev's idea of
		679	the current time is a good idea.
		680
		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>).
		708
578	=item ev_loop (loop, int flags)	709	=item ev_loop (loop, int flags)
579		710
580	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
581	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
582	events.	713	handling events.
583		714
584	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
585	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.
586		717
587	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
588	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
589	finished (especially in interactive programs), but having a program that	720	finished (especially in interactive programs), but having a program
590	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
591	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.
592		724
593	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
594	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
595	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.
596		729
597	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
598	necessary) and will handle those and any outstanding ones. It will block	731	necessary) and will handle those and any already outstanding ones. It
599	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
600	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
601	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
602	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
603	usually a better approach for this kind of thing.	740	usually a better approach for this kind of thing.
604		741
605	Here are the gory details of what C<ev_loop> does:	742	Here are the gory details of what C<ev_loop> does:
606		743
607	- Before the first iteration, call any pending watchers.	744	- Before the first iteration, call any pending watchers.
…		…
617	any active watchers at all will result in not sleeping).	754	any active watchers at all will result in not sleeping).
618	- Sleep if the I/O and timer collect interval say so.	755	- Sleep if the I/O and timer collect interval say so.
619	- Block the process, waiting for any events.	756	- Block the process, waiting for any events.
620	- Queue all outstanding I/O (fd) events.	757	- Queue all outstanding I/O (fd) events.
621	- 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.
622	- Queue all outstanding timers.	759	- Queue all expired timers.
623	- Queue all outstanding periodics.	760	- Queue all expired periodics.
624	- Unless any events are pending now, queue all idle watchers.	761	- Unless any events are pending now, queue all idle watchers.
625	- Queue all check watchers.	762	- Queue all check watchers.
626	- 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).
627	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
628	be handled here by queueing them when their watcher gets executed.	765	be handled here by queueing them when their watcher gets executed.
…		…
645	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
646	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.
647		784
648	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.
649		786
		787	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		788
650	=item ev_ref (loop)	789	=item ev_ref (loop)
651		790
652	=item ev_unref (loop)	791	=item ev_unref (loop)
653		792
654	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
655	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
656	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
657	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>
658	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
659	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
660	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
661	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
662	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
663	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
664	(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
665	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).
666		810
667	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>
668	running when nothing else is active.	812	running when nothing else is active.
669		813
670	struct ev_signal exitsig;	814	ev_signal exitsig;
671	ev_signal_init (&exitsig, sig_cb, SIGINT);	815	ev_signal_init (&exitsig, sig_cb, SIGINT);
672	ev_signal_start (loop, &exitsig);	816	ev_signal_start (loop, &exitsig);
673	evf_unref (loop);	817	evf_unref (loop);
674		818
675	Example: For some weird reason, unregister the above signal handler again.	819	Example: For some weird reason, unregister the above signal handler again.
…		…
689	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>)
690	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
691	to increase efficiency of loop iterations (or to increase power-saving	835	to increase efficiency of loop iterations (or to increase power-saving
692	opportunities).	836	opportunities).
693		837
694	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
695	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
696	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
697	events, especially with backends like C<select ()> which have a high	841	events, especially with backends like C<select ()> which have a high
698	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.
699		843
700	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
701	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,
702	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
703	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
704	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.
705		851
706	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
707	to spend more time collecting timeouts, at the expense of increased	853	to spend more time collecting timeouts, at the expense of increased
708	latency (the watcher callback will be called later). C<ev_io> watchers	854	latency/jitter/inexactness (the watcher callback will be called
709	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
710	any overhead in libev.	856	value will not introduce any overhead in libev.
711		857
712	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
713	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
714	interactive servers (of course not for games), likewise for timeouts. It	860	interactive servers (of course not for games), likewise for timeouts. It
715	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>,
716	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).
717		867
718	Setting the I<timeout collect interval> can improve the opportunity for	868	Setting the I<timeout collect interval> can improve the opportunity for
719	saving power, as the program will "bundle" timer callback invocations that	869	saving power, as the program will "bundle" timer callback invocations that
720	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
721	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
722	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
723	they fire on, say, one-second boundaries only.	873	they fire on, say, one-second boundaries only.
724		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
725	=item ev_loop_verify (loop)	946	=item ev_loop_verify (loop)
726		947
727	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
728	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
729	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
730	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 ()>.
731		953
732	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
733	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
734	data structures consistent.	956	data structures consistent.
735		957
736	=back	958	=back
737		959
738		960
739	=head1 ANATOMY OF A WATCHER	961	=head1 ANATOMY OF A WATCHER
740		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
741	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
742	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
743	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:
744		970
745	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)
746	{	972	{
747	ev_io_stop (w);	973	ev_io_stop (w);
748	ev_unloop (loop, EVUNLOOP_ALL);	974	ev_unloop (loop, EVUNLOOP_ALL);
749	}	975	}
750		976
751	struct ev_loop *loop = ev_default_loop (0);	977	struct ev_loop *loop = ev_default_loop (0);
		978
752	struct ev_io stdin_watcher;	979	ev_io stdin_watcher;
		980
753	ev_init (&stdin_watcher, my_cb);	981	ev_init (&stdin_watcher, my_cb);
754	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	982	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
755	ev_io_start (loop, &stdin_watcher);	983	ev_io_start (loop, &stdin_watcher);
		984
756	ev_loop (loop, 0);	985	ev_loop (loop, 0);
757		986
758	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
759	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
760	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).
761		993
762	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
763	(watcher *, callback)>, which expects a callback to be provided. This	995	(watcher *, callback)>, which expects a callback to be provided. This
764	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
765	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
766	is readable and/or writable).	998	is readable and/or writable).
767		999
768	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 *, ...) >>
769	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
770	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<<
771	(watcher *, callback, ...) >>.	1003	ev_TYPE_init (watcher *, callback, ...) >>.
772		1004
773	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
774	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
775	*) >>), 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
776	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1008	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
777		1009
778	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
779	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
780	reinitialise it or call its C<set> macro.	1012	reinitialise it or call its C<ev_TYPE_set> macro.
781		1013
782	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
783	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
784	third argument.	1016	third argument.
785		1017
…		…
843		1075
844	=item C<EV_ASYNC>	1076	=item C<EV_ASYNC>
845		1077
846	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>).
847		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
848	=item C<EV_ERROR>	1085	=item C<EV_ERROR>
849		1086
850	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
851	happen because the watcher could not be properly started because libev	1088	happen because the watcher could not be properly started because libev
852	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
853	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
854	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.
855		1096
856	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
857	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
858	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
859	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
860	programs, though, so beware.	1101	programs, though, as the fd could already be closed and reused for another
		1102	thing, so beware.
861		1103
862	=back	1104	=back
863		1105
864	=head2 GENERIC WATCHER FUNCTIONS	1106	=head2 GENERIC WATCHER FUNCTIONS
865
866	In the following description, C<TYPE> stands for the watcher type,
867	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
868		1107
869	=over 4	1108	=over 4
870		1109
871	=item C<ev_init> (ev_TYPE *watcher, callback)	1110	=item C<ev_init> (ev_TYPE *watcher, callback)
872		1111
…		…
878	which rolls both calls into one.	1117	which rolls both calls into one.
879		1118
880	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
881	(or never started) and there are no pending events outstanding.	1120	(or never started) and there are no pending events outstanding.
882		1121
883	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,
884	int revents)>.	1123	int revents)>.
885		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);
		1130
886	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1131	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
887		1132
888	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
889	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
890	call C<ev_TYPE_set> any number of times. You must not, however, call this	1135	call C<ev_TYPE_set> any number of times. You must not, however, call this
891	macro on a watcher that is active (it can be pending, however, which is a	1136	macro on a watcher that is active (it can be pending, however, which is a
892	difference to the C<ev_init> macro).	1137	difference to the C<ev_init> macro).
893		1138
894	Although some watcher types do not have type-specific arguments	1139	Although some watcher types do not have type-specific arguments
895	(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.
896		1141
		1142	See C<ev_init>, above, for an example.
		1143
897	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1144	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
898		1145
899	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
900	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
901	a watcher. The same limitations apply, of course.	1148	a watcher. The same limitations apply, of course.
902		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
903	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1154	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
904		1155
905	Starts (activates) the given watcher. Only active watchers will receive	1156	Starts (activates) the given watcher. Only active watchers will receive
906	events. If the watcher is already active nothing will happen.	1157	events. If the watcher is already active nothing will happen.
907		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
908	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1164	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
909		1165
910	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
911	status. It is possible that stopped watchers are pending (for example,	1169	It is possible that stopped watchers are pending - for example,
912	non-repeating timers are being stopped when they become pending), but	1170	non-repeating timers are being stopped when they become pending - but
913	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
914	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
915	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.
916		1174
917	=item bool ev_is_active (ev_TYPE *watcher)	1175	=item bool ev_is_active (ev_TYPE *watcher)
918		1176
919	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
920	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
…		…
936	=item ev_cb_set (ev_TYPE *watcher, callback)	1194	=item ev_cb_set (ev_TYPE *watcher, callback)
937		1195
938	Change the callback. You can change the callback at virtually any time	1196	Change the callback. You can change the callback at virtually any time
939	(modulo threads).	1197	(modulo threads).
940		1198
941	=item ev_set_priority (ev_TYPE *watcher, priority)	1199	=item ev_set_priority (ev_TYPE *watcher, int priority)
942		1200
943	=item int ev_priority (ev_TYPE *watcher)	1201	=item int ev_priority (ev_TYPE *watcher)
944		1202
945	Set and query the priority of the watcher. The priority is a small	1203	Set and query the priority of the watcher. The priority is a small
946	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>
947	(default: C<-2>). Pending watchers with higher priority will be invoked	1205	(default: C<-2>). Pending watchers with higher priority will be invoked
948	before watchers with lower priority, but priority will not keep watchers	1206	before watchers with lower priority, but priority will not keep watchers
949	from being executed (except for C<ev_idle> watchers).	1207	from being executed (except for C<ev_idle> watchers).
950		1208
951	This means that priorities are I<only> used for ordering callback
952	invocation after new events have been received. This is useful, for
953	example, to reduce latency after idling, or more often, to bind two
954	watchers on the same event and make sure one is called first.
955
956	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
957	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.
958		1211
959	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
960	pending.	1213	pending.
961		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
962	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
963	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 :).
964		1221
965	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
966	fine, as long as you do not mind that the priority value you query might	1223	priorities.
967	or might not have been adjusted to be within valid range.
968		1224
969	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1225	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
970		1226
971	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
972	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
973	can deal with that fact.	1229	can deal with that fact, as both are simply passed through to the
		1230	callback.
974		1231
975	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1232	=item int ev_clear_pending (loop, ev_TYPE *watcher)
976		1233
977	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
978	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
979	watcher isn't pending it does nothing and returns C<0>.	1236	watcher isn't pending it does nothing and returns C<0>.
980		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
		1241	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1242
		1243	Feeds the given event set into the event loop, as if the specified event
		1244	had happened for the specified watcher (which must be a pointer to an
		1245	initialised but not necessarily started event watcher). Obviously you must
		1246	not free the watcher as long as it has pending events.
		1247
		1248	Stopping the watcher, letting libev invoke it, or calling
		1249	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1250	not started in the first place.
		1251
		1252	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1253	functions that do not need a watcher.
		1254
981	=back	1255	=back
982		1256
983		1257
984	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1258	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
985		1259
986	Each watcher has, by default, a member C<void *data> that you can change	1260	Each watcher has, by default, a member C<void *data> that you can change
987	and read at any time, libev will completely ignore it. This can be used	1261	and read at any time: libev will completely ignore it. This can be used
988	to associate arbitrary data with your watcher. If you need more data and	1262	to associate arbitrary data with your watcher. If you need more data and
989	don't want to allocate memory and store a pointer to it in that data	1263	don't want to allocate memory and store a pointer to it in that data
990	member, you can also "subclass" the watcher type and provide your own	1264	member, you can also "subclass" the watcher type and provide your own
991	data:	1265	data:
992		1266
993	struct my_io	1267	struct my_io
994	{	1268	{
995	struct ev_io io;	1269	ev_io io;
996	int otherfd;	1270	int otherfd;
997	void *somedata;	1271	void *somedata;
998	struct whatever *mostinteresting;	1272	struct whatever *mostinteresting;
999	}	1273	};
		1274
		1275	...
		1276	struct my_io w;
		1277	ev_io_init (&w.io, my_cb, fd, EV_READ);
1000		1278
1001	And since your callback will be called with a pointer to the watcher, you	1279	And since your callback will be called with a pointer to the watcher, you
1002	can cast it back to your own type:	1280	can cast it back to your own type:
1003		1281
1004	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1282	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1005	{	1283	{
1006	struct my_io *w = (struct my_io *)w_;	1284	struct my_io *w = (struct my_io *)w_;
1007	...	1285	...
1008	}	1286	}
1009		1287
1010	More interesting and less C-conformant ways of casting your callback type	1288	More interesting and less C-conformant ways of casting your callback type
1011	instead have been omitted.	1289	instead have been omitted.
1012		1290
1013	Another common scenario is having some data structure with multiple	1291	Another common scenario is to use some data structure with multiple
1014	watchers:	1292	embedded watchers:
1015		1293
1016	struct my_biggy	1294	struct my_biggy
1017	{	1295	{
1018	int some_data;	1296	int some_data;
1019	ev_timer t1;	1297	ev_timer t1;
1020	ev_timer t2;	1298	ev_timer t2;
1021	}	1299	}
1022		1300
1023	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1301	In this case getting the pointer to C<my_biggy> is a bit more
1024	you need to use C<offsetof>:	1302	complicated: Either you store the address of your C<my_biggy> struct
		1303	in the C<data> member of the watcher (for woozies), or you need to use
		1304	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1305	programmers):
1025		1306
1026	#include <stddef.h>	1307	#include <stddef.h>
1027		1308
1028	static void	1309	static void
1029	t1_cb (EV_P_ struct ev_timer *w, int revents)	1310	t1_cb (EV_P_ ev_timer *w, int revents)
1030	{	1311	{
1031	struct my_biggy big = (struct my_biggy *	1312	struct my_biggy big = (struct my_biggy *)
1032	(((char *)w) - offsetof (struct my_biggy, t1));	1313	(((char *)w) - offsetof (struct my_biggy, t1));
1033	}	1314	}
1034		1315
1035	static void	1316	static void
1036	t2_cb (EV_P_ struct ev_timer *w, int revents)	1317	t2_cb (EV_P_ ev_timer *w, int revents)
1037	{	1318	{
1038	struct my_biggy big = (struct my_biggy *	1319	struct my_biggy big = (struct my_biggy *)
1039	(((char *)w) - offsetof (struct my_biggy, t2));	1320	(((char *)w) - offsetof (struct my_biggy, t2));
1040	}	1321	}
		1322
		1323	=head2 WATCHER PRIORITY MODELS
		1324
		1325	Many event loops support I<watcher priorities>, which are usually small
		1326	integers that influence the ordering of event callback invocation
		1327	between watchers in some way, all else being equal.
		1328
		1329	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1330	description for the more technical details such as the actual priority
		1331	range.
		1332
		1333	There are two common ways how these these priorities are being interpreted
		1334	by event loops:
		1335
		1336	In the more common lock-out model, higher priorities "lock out" invocation
		1337	of lower priority watchers, which means as long as higher priority
		1338	watchers receive events, lower priority watchers are not being invoked.
		1339
		1340	The less common only-for-ordering model uses priorities solely to order
		1341	callback invocation within a single event loop iteration: Higher priority
		1342	watchers are invoked before lower priority ones, but they all get invoked
		1343	before polling for new events.
		1344
		1345	Libev uses the second (only-for-ordering) model for all its watchers
		1346	except for idle watchers (which use the lock-out model).
		1347
		1348	The rationale behind this is that implementing the lock-out model for
		1349	watchers is not well supported by most kernel interfaces, and most event
		1350	libraries will just poll for the same events again and again as long as
		1351	their callbacks have not been executed, which is very inefficient in the
		1352	common case of one high-priority watcher locking out a mass of lower
		1353	priority ones.
		1354
		1355	Static (ordering) priorities are most useful when you have two or more
		1356	watchers handling the same resource: a typical usage example is having an
		1357	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1358	timeouts. Under load, data might be received while the program handles
		1359	other jobs, but since timers normally get invoked first, the timeout
		1360	handler will be executed before checking for data. In that case, giving
		1361	the timer a lower priority than the I/O watcher ensures that I/O will be
		1362	handled first even under adverse conditions (which is usually, but not
		1363	always, what you want).
		1364
		1365	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1366	will only be executed when no same or higher priority watchers have
		1367	received events, they can be used to implement the "lock-out" model when
		1368	required.
		1369
		1370	For example, to emulate how many other event libraries handle priorities,
		1371	you can associate an C<ev_idle> watcher to each such watcher, and in
		1372	the normal watcher callback, you just start the idle watcher. The real
		1373	processing is done in the idle watcher callback. This causes libev to
		1374	continously poll and process kernel event data for the watcher, but when
		1375	the lock-out case is known to be rare (which in turn is rare :), this is
		1376	workable.
		1377
		1378	Usually, however, the lock-out model implemented that way will perform
		1379	miserably under the type of load it was designed to handle. In that case,
		1380	it might be preferable to stop the real watcher before starting the
		1381	idle watcher, so the kernel will not have to process the event in case
		1382	the actual processing will be delayed for considerable time.
		1383
		1384	Here is an example of an I/O watcher that should run at a strictly lower
		1385	priority than the default, and which should only process data when no
		1386	other events are pending:
		1387
		1388	ev_idle idle; // actual processing watcher
		1389	ev_io io; // actual event watcher
		1390
		1391	static void
		1392	io_cb (EV_P_ ev_io *w, int revents)
		1393	{
		1394	// stop the I/O watcher, we received the event, but
		1395	// are not yet ready to handle it.
		1396	ev_io_stop (EV_A_ w);
		1397
		1398	// start the idle watcher to ahndle the actual event.
		1399	// it will not be executed as long as other watchers
		1400	// with the default priority are receiving events.
		1401	ev_idle_start (EV_A_ &idle);
		1402	}
		1403
		1404	static void
		1405	idle_cb (EV_P_ ev_idle *w, int revents)
		1406	{
		1407	// actual processing
		1408	read (STDIN_FILENO, ...);
		1409
		1410	// have to start the I/O watcher again, as
		1411	// we have handled the event
		1412	ev_io_start (EV_P_ &io);
		1413	}
		1414
		1415	// initialisation
		1416	ev_idle_init (&idle, idle_cb);
		1417	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1418	ev_io_start (EV_DEFAULT_ &io);
		1419
		1420	In the "real" world, it might also be beneficial to start a timer, so that
		1421	low-priority connections can not be locked out forever under load. This
		1422	enables your program to keep a lower latency for important connections
		1423	during short periods of high load, while not completely locking out less
		1424	important ones.
1041		1425
1042		1426
1043	=head1 WATCHER TYPES	1427	=head1 WATCHER TYPES
1044		1428
1045	This section describes each watcher in detail, but will not repeat	1429	This section describes each watcher in detail, but will not repeat
…		…
1069	In general you can register as many read and/or write event watchers per	1453	In general you can register as many read and/or write event watchers per
1070	fd as you want (as long as you don't confuse yourself). Setting all file	1454	fd as you want (as long as you don't confuse yourself). Setting all file
1071	descriptors to non-blocking mode is also usually a good idea (but not	1455	descriptors to non-blocking mode is also usually a good idea (but not
1072	required if you know what you are doing).	1456	required if you know what you are doing).
1073		1457
1074	If you must do this, then force the use of a known-to-be-good backend	1458	If you cannot use non-blocking mode, then force the use of a
1075	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1459	known-to-be-good backend (at the time of this writing, this includes only
1076	C<EVBACKEND_POLL>).	1460	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1461	descriptors for which non-blocking operation makes no sense (such as
		1462	files) - libev doesn't guarentee any specific behaviour in that case.
1077		1463
1078	Another thing you have to watch out for is that it is quite easy to	1464	Another thing you have to watch out for is that it is quite easy to
1079	receive "spurious" readiness notifications, that is your callback might	1465	receive "spurious" readiness notifications, that is your callback might
1080	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1466	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1081	because there is no data. Not only are some backends known to create a	1467	because there is no data. Not only are some backends known to create a
1082	lot of those (for example Solaris ports), it is very easy to get into	1468	lot of those (for example Solaris ports), it is very easy to get into
1083	this situation even with a relatively standard program structure. Thus	1469	this situation even with a relatively standard program structure. Thus
1084	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1470	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1085	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1471	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1086		1472
1087	If you cannot run the fd in non-blocking mode (for example you should not	1473	If you cannot run the fd in non-blocking mode (for example you should
1088	play around with an Xlib connection), then you have to separately re-test	1474	not play around with an Xlib connection), then you have to separately
1089	whether a file descriptor is really ready with a known-to-be good interface	1475	re-test whether a file descriptor is really ready with a known-to-be good
1090	such as poll (fortunately in our Xlib example, Xlib already does this on	1476	interface such as poll (fortunately in our Xlib example, Xlib already
1091	its own, so its quite safe to use).	1477	does this on its own, so its quite safe to use). Some people additionally
		1478	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1479	indefinitely.
		1480
		1481	But really, best use non-blocking mode.
1092		1482
1093	=head3 The special problem of disappearing file descriptors	1483	=head3 The special problem of disappearing file descriptors
1094		1484
1095	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1485	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1096	descriptor (either by calling C<close> explicitly or by any other means,	1486	descriptor (either due to calling C<close> explicitly or any other means,
1097	such as C<dup>). The reason is that you register interest in some file	1487	such as C<dup2>). The reason is that you register interest in some file
1098	descriptor, but when it goes away, the operating system will silently drop	1488	descriptor, but when it goes away, the operating system will silently drop
1099	this interest. If another file descriptor with the same number then is	1489	this interest. If another file descriptor with the same number then is
1100	registered with libev, there is no efficient way to see that this is, in	1490	registered with libev, there is no efficient way to see that this is, in
1101	fact, a different file descriptor.	1491	fact, a different file descriptor.
1102		1492
…		…
1133	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1523	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1134	C<EVBACKEND_POLL>.	1524	C<EVBACKEND_POLL>.
1135		1525
1136	=head3 The special problem of SIGPIPE	1526	=head3 The special problem of SIGPIPE
1137		1527
1138	While not really specific to libev, it is easy to forget about SIGPIPE:	1528	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1139	when reading from a pipe whose other end has been closed, your program	1529	when writing to a pipe whose other end has been closed, your program gets
1140	gets send a SIGPIPE, which, by default, aborts your program. For most	1530	sent a SIGPIPE, which, by default, aborts your program. For most programs
1141	programs this is sensible behaviour, for daemons, this is usually	1531	this is sensible behaviour, for daemons, this is usually undesirable.
1142	undesirable.
1143		1532
1144	So when you encounter spurious, unexplained daemon exits, make sure you	1533	So when you encounter spurious, unexplained daemon exits, make sure you
1145	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1534	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1146	somewhere, as that would have given you a big clue).	1535	somewhere, as that would have given you a big clue).
1147		1536
…		…
1153	=item ev_io_init (ev_io *, callback, int fd, int events)	1542	=item ev_io_init (ev_io *, callback, int fd, int events)
1154		1543
1155	=item ev_io_set (ev_io *, int fd, int events)	1544	=item ev_io_set (ev_io *, int fd, int events)
1156		1545
1157	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1546	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1158	receive events for and events is either C<EV_READ>, C<EV_WRITE> or	1547	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1159	C<EV_READ | EV_WRITE> to receive the given events.	1548	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1160		1549
1161	=item int fd [read-only]	1550	=item int fd [read-only]
1162		1551
1163	The file descriptor being watched.	1552	The file descriptor being watched.
1164		1553
…		…
1173	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1562	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1174	readable, but only once. Since it is likely line-buffered, you could	1563	readable, but only once. Since it is likely line-buffered, you could
1175	attempt to read a whole line in the callback.	1564	attempt to read a whole line in the callback.
1176		1565
1177	static void	1566	static void
1178	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1567	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1179	{	1568	{
1180	ev_io_stop (loop, w);	1569	ev_io_stop (loop, w);
1181	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1570	.. read from stdin here (or from w->fd) and handle any I/O errors
1182	}	1571	}
1183		1572
1184	...	1573	...
1185	struct ev_loop *loop = ev_default_init (0);	1574	struct ev_loop *loop = ev_default_init (0);
1186	struct ev_io stdin_readable;	1575	ev_io stdin_readable;
1187	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1576	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1188	ev_io_start (loop, &stdin_readable);	1577	ev_io_start (loop, &stdin_readable);
1189	ev_loop (loop, 0);	1578	ev_loop (loop, 0);
1190		1579
1191		1580
…		…
1194	Timer watchers are simple relative timers that generate an event after a	1583	Timer watchers are simple relative timers that generate an event after a
1195	given time, and optionally repeating in regular intervals after that.	1584	given time, and optionally repeating in regular intervals after that.
1196		1585
1197	The timers are based on real time, that is, if you register an event that	1586	The timers are based on real time, that is, if you register an event that
1198	times out after an hour and you reset your system clock to January last	1587	times out after an hour and you reset your system clock to January last
1199	year, it will still time out after (roughly) and hour. "Roughly" because	1588	year, it will still time out after (roughly) one hour. "Roughly" because
1200	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1589	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1201	monotonic clock option helps a lot here).	1590	monotonic clock option helps a lot here).
		1591
		1592	The callback is guaranteed to be invoked only I<after> its timeout has
		1593	passed (not I<at>, so on systems with very low-resolution clocks this
		1594	might introduce a small delay). If multiple timers become ready during the
		1595	same loop iteration then the ones with earlier time-out values are invoked
		1596	before ones of the same priority with later time-out values (but this is
		1597	no longer true when a callback calls C<ev_loop> recursively).
		1598
		1599	=head3 Be smart about timeouts
		1600
		1601	Many real-world problems involve some kind of timeout, usually for error
		1602	recovery. A typical example is an HTTP request - if the other side hangs,
		1603	you want to raise some error after a while.
		1604
		1605	What follows are some ways to handle this problem, from obvious and
		1606	inefficient to smart and efficient.
		1607
		1608	In the following, a 60 second activity timeout is assumed - a timeout that
		1609	gets reset to 60 seconds each time there is activity (e.g. each time some
		1610	data or other life sign was received).
		1611
		1612	=over 4
		1613
		1614	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1615
		1616	This is the most obvious, but not the most simple way: In the beginning,
		1617	start the watcher:
		1618
		1619	ev_timer_init (timer, callback, 60., 0.);
		1620	ev_timer_start (loop, timer);
		1621
		1622	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1623	and start it again:
		1624
		1625	ev_timer_stop (loop, timer);
		1626	ev_timer_set (timer, 60., 0.);
		1627	ev_timer_start (loop, timer);
		1628
		1629	This is relatively simple to implement, but means that each time there is
		1630	some activity, libev will first have to remove the timer from its internal
		1631	data structure and then add it again. Libev tries to be fast, but it's
		1632	still not a constant-time operation.
		1633
		1634	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1635
		1636	This is the easiest way, and involves using C<ev_timer_again> instead of
		1637	C<ev_timer_start>.
		1638
		1639	To implement this, configure an C<ev_timer> with a C<repeat> value
		1640	of C<60> and then call C<ev_timer_again> at start and each time you
		1641	successfully read or write some data. If you go into an idle state where
		1642	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1643	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1644
		1645	That means you can ignore both the C<ev_timer_start> function and the
		1646	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1647	member and C<ev_timer_again>.
		1648
		1649	At start:
		1650
		1651	ev_init (timer, callback);
		1652	timer->repeat = 60.;
		1653	ev_timer_again (loop, timer);
		1654
		1655	Each time there is some activity:
		1656
		1657	ev_timer_again (loop, timer);
		1658
		1659	It is even possible to change the time-out on the fly, regardless of
		1660	whether the watcher is active or not:
		1661
		1662	timer->repeat = 30.;
		1663	ev_timer_again (loop, timer);
		1664
		1665	This is slightly more efficient then stopping/starting the timer each time
		1666	you want to modify its timeout value, as libev does not have to completely
		1667	remove and re-insert the timer from/into its internal data structure.
		1668
		1669	It is, however, even simpler than the "obvious" way to do it.
		1670
		1671	=item 3. Let the timer time out, but then re-arm it as required.
		1672
		1673	This method is more tricky, but usually most efficient: Most timeouts are
		1674	relatively long compared to the intervals between other activity - in
		1675	our example, within 60 seconds, there are usually many I/O events with
		1676	associated activity resets.
		1677
		1678	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1679	but remember the time of last activity, and check for a real timeout only
		1680	within the callback:
		1681
		1682	ev_tstamp last_activity; // time of last activity
		1683
		1684	static void
		1685	callback (EV_P_ ev_timer *w, int revents)
		1686	{
		1687	ev_tstamp now = ev_now (EV_A);
		1688	ev_tstamp timeout = last_activity + 60.;
		1689
		1690	// if last_activity + 60. is older than now, we did time out
		1691	if (timeout < now)
		1692	{
		1693	// timeout occured, take action
		1694	}
		1695	else
		1696	{
		1697	// callback was invoked, but there was some activity, re-arm
		1698	// the watcher to fire in last_activity + 60, which is
		1699	// guaranteed to be in the future, so "again" is positive:
		1700	w->repeat = timeout - now;
		1701	ev_timer_again (EV_A_ w);
		1702	}
		1703	}
		1704
		1705	To summarise the callback: first calculate the real timeout (defined
		1706	as "60 seconds after the last activity"), then check if that time has
		1707	been reached, which means something I<did>, in fact, time out. Otherwise
		1708	the callback was invoked too early (C<timeout> is in the future), so
		1709	re-schedule the timer to fire at that future time, to see if maybe we have
		1710	a timeout then.
		1711
		1712	Note how C<ev_timer_again> is used, taking advantage of the
		1713	C<ev_timer_again> optimisation when the timer is already running.
		1714
		1715	This scheme causes more callback invocations (about one every 60 seconds
		1716	minus half the average time between activity), but virtually no calls to
		1717	libev to change the timeout.
		1718
		1719	To start the timer, simply initialise the watcher and set C<last_activity>
		1720	to the current time (meaning we just have some activity :), then call the
		1721	callback, which will "do the right thing" and start the timer:
		1722
		1723	ev_init (timer, callback);
		1724	last_activity = ev_now (loop);
		1725	callback (loop, timer, EV_TIMEOUT);
		1726
		1727	And when there is some activity, simply store the current time in
		1728	C<last_activity>, no libev calls at all:
		1729
		1730	last_actiivty = ev_now (loop);
		1731
		1732	This technique is slightly more complex, but in most cases where the
		1733	time-out is unlikely to be triggered, much more efficient.
		1734
		1735	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1736	callback :) - just change the timeout and invoke the callback, which will
		1737	fix things for you.
		1738
		1739	=item 4. Wee, just use a double-linked list for your timeouts.
		1740
		1741	If there is not one request, but many thousands (millions...), all
		1742	employing some kind of timeout with the same timeout value, then one can
		1743	do even better:
		1744
		1745	When starting the timeout, calculate the timeout value and put the timeout
		1746	at the I<end> of the list.
		1747
		1748	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1749	the list is expected to fire (for example, using the technique #3).
		1750
		1751	When there is some activity, remove the timer from the list, recalculate
		1752	the timeout, append it to the end of the list again, and make sure to
		1753	update the C<ev_timer> if it was taken from the beginning of the list.
		1754
		1755	This way, one can manage an unlimited number of timeouts in O(1) time for
		1756	starting, stopping and updating the timers, at the expense of a major
		1757	complication, and having to use a constant timeout. The constant timeout
		1758	ensures that the list stays sorted.
		1759
		1760	=back
		1761
		1762	So which method the best?
		1763
		1764	Method #2 is a simple no-brain-required solution that is adequate in most
		1765	situations. Method #3 requires a bit more thinking, but handles many cases
		1766	better, and isn't very complicated either. In most case, choosing either
		1767	one is fine, with #3 being better in typical situations.
		1768
		1769	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1770	rather complicated, but extremely efficient, something that really pays
		1771	off after the first million or so of active timers, i.e. it's usually
		1772	overkill :)
		1773
		1774	=head3 The special problem of time updates
		1775
		1776	Establishing the current time is a costly operation (it usually takes at
		1777	least two system calls): EV therefore updates its idea of the current
		1778	time only before and after C<ev_loop> collects new events, which causes a
		1779	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1780	lots of events in one iteration.
1202		1781
1203	The relative timeouts are calculated relative to the C<ev_now ()>	1782	The relative timeouts are calculated relative to the C<ev_now ()>
1204	time. This is usually the right thing as this timestamp refers to the time	1783	time. This is usually the right thing as this timestamp refers to the time
1205	of the event triggering whatever timeout you are modifying/starting. If	1784	of the event triggering whatever timeout you are modifying/starting. If
1206	you suspect event processing to be delayed and you I<need> to base the timeout	1785	you suspect event processing to be delayed and you I<need> to base the
1207	on the current time, use something like this to adjust for this:	1786	timeout on the current time, use something like this to adjust for this:
1208		1787
1209	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1788	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1210		1789
1211	The callback is guaranteed to be invoked only after its timeout has passed,	1790	If the event loop is suspended for a long time, you can also force an
1212	but if multiple timers become ready during the same loop iteration then	1791	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1213	order of execution is undefined.	1792	()>.
		1793
		1794	=head3 The special problems of suspended animation
		1795
		1796	When you leave the server world it is quite customary to hit machines that
		1797	can suspend/hibernate - what happens to the clocks during such a suspend?
		1798
		1799	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1800	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1801	to run until the system is suspended, but they will not advance while the
		1802	system is suspended. That means, on resume, it will be as if the program
		1803	was frozen for a few seconds, but the suspend time will not be counted
		1804	towards C<ev_timer> when a monotonic clock source is used. The real time
		1805	clock advanced as expected, but if it is used as sole clocksource, then a
		1806	long suspend would be detected as a time jump by libev, and timers would
		1807	be adjusted accordingly.
		1808
		1809	I would not be surprised to see different behaviour in different between
		1810	operating systems, OS versions or even different hardware.
		1811
		1812	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1813	time jump in the monotonic clocks and the realtime clock. If the program
		1814	is suspended for a very long time, and monotonic clock sources are in use,
		1815	then you can expect C<ev_timer>s to expire as the full suspension time
		1816	will be counted towards the timers. When no monotonic clock source is in
		1817	use, then libev will again assume a timejump and adjust accordingly.
		1818
		1819	It might be beneficial for this latter case to call C<ev_suspend>
		1820	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1821	deterministic behaviour in this case (you can do nothing against
		1822	C<SIGSTOP>).
1214		1823
1215	=head3 Watcher-Specific Functions and Data Members	1824	=head3 Watcher-Specific Functions and Data Members
1216		1825
1217	=over 4	1826	=over 4
1218		1827
…		…
1242	If the timer is started but non-repeating, stop it (as if it timed out).	1851	If the timer is started but non-repeating, stop it (as if it timed out).
1243		1852
1244	If the timer is repeating, either start it if necessary (with the	1853	If the timer is repeating, either start it if necessary (with the
1245	C<repeat> value), or reset the running timer to the C<repeat> value.	1854	C<repeat> value), or reset the running timer to the C<repeat> value.
1246		1855
1247	This sounds a bit complicated, but here is a useful and typical	1856	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1248	example: Imagine you have a TCP connection and you want a so-called idle	1857	usage example.
1249	timeout, that is, you want to be called when there have been, say, 60
1250	seconds of inactivity on the socket. The easiest way to do this is to
1251	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1252	C<ev_timer_again> each time you successfully read or write some data. If
1253	you go into an idle state where you do not expect data to travel on the
1254	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1255	automatically restart it if need be.
1256		1858
1257	That means you can ignore the C<after> value and C<ev_timer_start>	1859	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1258	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1259		1860
1260	ev_timer_init (timer, callback, 0., 5.);	1861	Returns the remaining time until a timer fires. If the timer is active,
1261	ev_timer_again (loop, timer);	1862	then this time is relative to the current event loop time, otherwise it's
1262	...	1863	the timeout value currently configured.
1263	timer->again = 17.;
1264	ev_timer_again (loop, timer);
1265	...
1266	timer->again = 10.;
1267	ev_timer_again (loop, timer);
1268		1864
1269	This is more slightly efficient then stopping/starting the timer each time	1865	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1270	you want to modify its timeout value.	1866	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1867	will return C<4>. When the timer expires and is restarted, it will return
		1868	roughly C<7> (likely slightly less as callback invocation takes some time,
		1869	too), and so on.
1271		1870
1272	=item ev_tstamp repeat [read-write]	1871	=item ev_tstamp repeat [read-write]
1273		1872
1274	The current C<repeat> value. Will be used each time the watcher times out	1873	The current C<repeat> value. Will be used each time the watcher times out
1275	or C<ev_timer_again> is called and determines the next timeout (if any),	1874	or C<ev_timer_again> is called, and determines the next timeout (if any),
1276	which is also when any modifications are taken into account.	1875	which is also when any modifications are taken into account.
1277		1876
1278	=back	1877	=back
1279		1878
1280	=head3 Examples	1879	=head3 Examples
1281		1880
1282	Example: Create a timer that fires after 60 seconds.	1881	Example: Create a timer that fires after 60 seconds.
1283		1882
1284	static void	1883	static void
1285	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1884	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1286	{	1885	{
1287	.. one minute over, w is actually stopped right here	1886	.. one minute over, w is actually stopped right here
1288	}	1887	}
1289		1888
1290	struct ev_timer mytimer;	1889	ev_timer mytimer;
1291	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1890	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1292	ev_timer_start (loop, &mytimer);	1891	ev_timer_start (loop, &mytimer);
1293		1892
1294	Example: Create a timeout timer that times out after 10 seconds of	1893	Example: Create a timeout timer that times out after 10 seconds of
1295	inactivity.	1894	inactivity.
1296		1895
1297	static void	1896	static void
1298	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1897	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1299	{	1898	{
1300	.. ten seconds without any activity	1899	.. ten seconds without any activity
1301	}	1900	}
1302		1901
1303	struct ev_timer mytimer;	1902	ev_timer mytimer;
1304	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1903	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1305	ev_timer_again (&mytimer); /* start timer */	1904	ev_timer_again (&mytimer); /* start timer */
1306	ev_loop (loop, 0);	1905	ev_loop (loop, 0);
1307		1906
1308	// and in some piece of code that gets executed on any "activity":	1907	// and in some piece of code that gets executed on any "activity":
…		…
1313	=head2 C<ev_periodic> - to cron or not to cron?	1912	=head2 C<ev_periodic> - to cron or not to cron?
1314		1913
1315	Periodic watchers are also timers of a kind, but they are very versatile	1914	Periodic watchers are also timers of a kind, but they are very versatile
1316	(and unfortunately a bit complex).	1915	(and unfortunately a bit complex).
1317		1916
1318	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1917	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1319	but on wall clock time (absolute time). You can tell a periodic watcher	1918	relative time, the physical time that passes) but on wall clock time
1320	to trigger after some specific point in time. For example, if you tell a	1919	(absolute time, the thing you can read on your calender or clock). The
1321	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1920	difference is that wall clock time can run faster or slower than real
1322	+ 10.>, that is, an absolute time not a delay) and then reset your system	1921	time, and time jumps are not uncommon (e.g. when you adjust your
1323	clock to January of the previous year, then it will take more than year	1922	wrist-watch).
1324	to trigger the event (unlike an C<ev_timer>, which would still trigger
1325	roughly 10 seconds later as it uses a relative timeout).
1326		1923
		1924	You can tell a periodic watcher to trigger after some specific point
		1925	in time: for example, if you tell a periodic watcher to trigger "in 10
		1926	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1927	not a delay) and then reset your system clock to January of the previous
		1928	year, then it will take a year or more to trigger the event (unlike an
		1929	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1930	it, as it uses a relative timeout).
		1931
1327	C<ev_periodic>s can also be used to implement vastly more complex timers,	1932	C<ev_periodic> watchers can also be used to implement vastly more complex
1328	such as triggering an event on each "midnight, local time", or other	1933	timers, such as triggering an event on each "midnight, local time", or
1329	complicated, rules.	1934	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1935	those cannot react to time jumps.
1330		1936
1331	As with timers, the callback is guaranteed to be invoked only when the	1937	As with timers, the callback is guaranteed to be invoked only when the
1332	time (C<at>) has passed, but if multiple periodic timers become ready	1938	point in time where it is supposed to trigger has passed. If multiple
1333	during the same loop iteration then order of execution is undefined.	1939	timers become ready during the same loop iteration then the ones with
		1940	earlier time-out values are invoked before ones with later time-out values
		1941	(but this is no longer true when a callback calls C<ev_loop> recursively).
1334		1942
1335	=head3 Watcher-Specific Functions and Data Members	1943	=head3 Watcher-Specific Functions and Data Members
1336		1944
1337	=over 4	1945	=over 4
1338		1946
1339	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1947	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1340		1948
1341	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1949	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1342		1950
1343	Lots of arguments, lets sort it out... There are basically three modes of	1951	Lots of arguments, let's sort it out... There are basically three modes of
1344	operation, and we will explain them from simplest to complex:	1952	operation, and we will explain them from simplest to most complex:
1345		1953
1346	=over 4	1954	=over 4
1347		1955
1348	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1956	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1349		1957
1350	In this configuration the watcher triggers an event after the wall clock	1958	In this configuration the watcher triggers an event after the wall clock
1351	time C<at> has passed and doesn't repeat. It will not adjust when a time	1959	time C<offset> has passed. It will not repeat and will not adjust when a
1352	jump occurs, that is, if it is to be run at January 1st 2011 then it will	1960	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1353	run when the system time reaches or surpasses this time.	1961	will be stopped and invoked when the system clock reaches or surpasses
		1962	this point in time.
1354		1963
1355	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1964	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1356		1965
1357	In this mode the watcher will always be scheduled to time out at the next	1966	In this mode the watcher will always be scheduled to time out at the next
1358	C<at + N * interval> time (for some integer N, which can also be negative)	1967	C<offset + N * interval> time (for some integer N, which can also be
1359	and then repeat, regardless of any time jumps.	1968	negative) and then repeat, regardless of any time jumps. The C<offset>
		1969	argument is merely an offset into the C<interval> periods.
1360		1970
1361	This can be used to create timers that do not drift with respect to system	1971	This can be used to create timers that do not drift with respect to the
1362	time, for example, here is a C<ev_periodic> that triggers each hour, on	1972	system clock, for example, here is an C<ev_periodic> that triggers each
1363	the hour:	1973	hour, on the hour (with respect to UTC):
1364		1974
1365	ev_periodic_set (&periodic, 0., 3600., 0);	1975	ev_periodic_set (&periodic, 0., 3600., 0);
1366		1976
1367	This doesn't mean there will always be 3600 seconds in between triggers,	1977	This doesn't mean there will always be 3600 seconds in between triggers,
1368	but only that the callback will be called when the system time shows a	1978	but only that the callback will be called when the system time shows a
1369	full hour (UTC), or more correctly, when the system time is evenly divisible	1979	full hour (UTC), or more correctly, when the system time is evenly divisible
1370	by 3600.	1980	by 3600.
1371		1981
1372	Another way to think about it (for the mathematically inclined) is that	1982	Another way to think about it (for the mathematically inclined) is that
1373	C<ev_periodic> will try to run the callback in this mode at the next possible	1983	C<ev_periodic> will try to run the callback in this mode at the next possible
1374	time where C<time = at (mod interval)>, regardless of any time jumps.	1984	time where C<time = offset (mod interval)>, regardless of any time jumps.
1375		1985
1376	For numerical stability it is preferable that the C<at> value is near	1986	For numerical stability it is preferable that the C<offset> value is near
1377	C<ev_now ()> (the current time), but there is no range requirement for	1987	C<ev_now ()> (the current time), but there is no range requirement for
1378	this value, and in fact is often specified as zero.	1988	this value, and in fact is often specified as zero.
1379		1989
1380	Note also that there is an upper limit to how often a timer can fire (CPU	1990	Note also that there is an upper limit to how often a timer can fire (CPU
1381	speed for example), so if C<interval> is very small then timing stability	1991	speed for example), so if C<interval> is very small then timing stability
1382	will of course deteriorate. Libev itself tries to be exact to be about one	1992	will of course deteriorate. Libev itself tries to be exact to be about one
1383	millisecond (if the OS supports it and the machine is fast enough).	1993	millisecond (if the OS supports it and the machine is fast enough).
1384		1994
1385	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1995	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1386		1996
1387	In this mode the values for C<interval> and C<at> are both being	1997	In this mode the values for C<interval> and C<offset> are both being
1388	ignored. Instead, each time the periodic watcher gets scheduled, the	1998	ignored. Instead, each time the periodic watcher gets scheduled, the
1389	reschedule callback will be called with the watcher as first, and the	1999	reschedule callback will be called with the watcher as first, and the
1390	current time as second argument.	2000	current time as second argument.
1391		2001
1392	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2002	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1393	ever, or make ANY event loop modifications whatsoever>.	2003	or make ANY other event loop modifications whatsoever, unless explicitly
		2004	allowed by documentation here>.
1394		2005
1395	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2006	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1396	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2007	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1397	only event loop modification you are allowed to do).	2008	only event loop modification you are allowed to do).
1398		2009
1399	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2010	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1400	*w, ev_tstamp now)>, e.g.:	2011	*w, ev_tstamp now)>, e.g.:
1401		2012
		2013	static ev_tstamp
1402	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2014	my_rescheduler (ev_periodic *w, ev_tstamp now)
1403	{	2015	{
1404	return now + 60.;	2016	return now + 60.;
1405	}	2017	}
1406		2018
1407	It must return the next time to trigger, based on the passed time value	2019	It must return the next time to trigger, based on the passed time value
…		…
1427	a different time than the last time it was called (e.g. in a crond like	2039	a different time than the last time it was called (e.g. in a crond like
1428	program when the crontabs have changed).	2040	program when the crontabs have changed).
1429		2041
1430	=item ev_tstamp ev_periodic_at (ev_periodic *)	2042	=item ev_tstamp ev_periodic_at (ev_periodic *)
1431		2043
1432	When active, returns the absolute time that the watcher is supposed to	2044	When active, returns the absolute time that the watcher is supposed
1433	trigger next.	2045	to trigger next. This is not the same as the C<offset> argument to
		2046	C<ev_periodic_set>, but indeed works even in interval and manual
		2047	rescheduling modes.
1434		2048
1435	=item ev_tstamp offset [read-write]	2049	=item ev_tstamp offset [read-write]
1436		2050
1437	When repeating, this contains the offset value, otherwise this is the	2051	When repeating, this contains the offset value, otherwise this is the
1438	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2052	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2053	although libev might modify this value for better numerical stability).
1439		2054
1440	Can be modified any time, but changes only take effect when the periodic	2055	Can be modified any time, but changes only take effect when the periodic
1441	timer fires or C<ev_periodic_again> is being called.	2056	timer fires or C<ev_periodic_again> is being called.
1442		2057
1443	=item ev_tstamp interval [read-write]	2058	=item ev_tstamp interval [read-write]
1444		2059
1445	The current interval value. Can be modified any time, but changes only	2060	The current interval value. Can be modified any time, but changes only
1446	take effect when the periodic timer fires or C<ev_periodic_again> is being	2061	take effect when the periodic timer fires or C<ev_periodic_again> is being
1447	called.	2062	called.
1448		2063
1449	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2064	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1450		2065
1451	The current reschedule callback, or C<0>, if this functionality is	2066	The current reschedule callback, or C<0>, if this functionality is
1452	switched off. Can be changed any time, but changes only take effect when	2067	switched off. Can be changed any time, but changes only take effect when
1453	the periodic timer fires or C<ev_periodic_again> is being called.	2068	the periodic timer fires or C<ev_periodic_again> is being called.
1454		2069
1455	=back	2070	=back
1456		2071
1457	=head3 Examples	2072	=head3 Examples
1458		2073
1459	Example: Call a callback every hour, or, more precisely, whenever the	2074	Example: Call a callback every hour, or, more precisely, whenever the
1460	system clock is divisible by 3600. The callback invocation times have	2075	system time is divisible by 3600. The callback invocation times have
1461	potentially a lot of jitter, but good long-term stability.	2076	potentially a lot of jitter, but good long-term stability.
1462		2077
1463	static void	2078	static void
1464	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2079	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1465	{	2080	{
1466	... its now a full hour (UTC, or TAI or whatever your clock follows)	2081	... its now a full hour (UTC, or TAI or whatever your clock follows)
1467	}	2082	}
1468		2083
1469	struct ev_periodic hourly_tick;	2084	ev_periodic hourly_tick;
1470	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2085	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1471	ev_periodic_start (loop, &hourly_tick);	2086	ev_periodic_start (loop, &hourly_tick);
1472		2087
1473	Example: The same as above, but use a reschedule callback to do it:	2088	Example: The same as above, but use a reschedule callback to do it:
1474		2089
1475	#include <math.h>	2090	#include <math.h>
1476		2091
1477	static ev_tstamp	2092	static ev_tstamp
1478	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2093	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1479	{	2094	{
1480	return fmod (now, 3600.) + 3600.;	2095	return now + (3600. - fmod (now, 3600.));
1481	}	2096	}
1482		2097
1483	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2098	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1484		2099
1485	Example: Call a callback every hour, starting now:	2100	Example: Call a callback every hour, starting now:
1486		2101
1487	struct ev_periodic hourly_tick;	2102	ev_periodic hourly_tick;
1488	ev_periodic_init (&hourly_tick, clock_cb,	2103	ev_periodic_init (&hourly_tick, clock_cb,
1489	fmod (ev_now (loop), 3600.), 3600., 0);	2104	fmod (ev_now (loop), 3600.), 3600., 0);
1490	ev_periodic_start (loop, &hourly_tick);	2105	ev_periodic_start (loop, &hourly_tick);
1491		2106
1492		2107
…		…
1495	Signal watchers will trigger an event when the process receives a specific	2110	Signal watchers will trigger an event when the process receives a specific
1496	signal one or more times. Even though signals are very asynchronous, libev	2111	signal one or more times. Even though signals are very asynchronous, libev
1497	will try it's best to deliver signals synchronously, i.e. as part of the	2112	will try it's best to deliver signals synchronously, i.e. as part of the
1498	normal event processing, like any other event.	2113	normal event processing, like any other event.
1499		2114
		2115	If you want signals to be delivered truly asynchronously, just use
		2116	C<sigaction> as you would do without libev and forget about sharing
		2117	the signal. You can even use C<ev_async> from a signal handler to
		2118	synchronously wake up an event loop.
		2119
1500	You can configure as many watchers as you like per signal. Only when the	2120	You can configure as many watchers as you like for the same signal, but
		2121	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2122	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2123	C<SIGINT> in both the default loop and another loop at the same time. At
		2124	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2125
1501	first watcher gets started will libev actually register a signal watcher	2126	When the first watcher gets started will libev actually register something
1502	with the kernel (thus it coexists with your own signal handlers as long	2127	with the kernel (thus it coexists with your own signal handlers as long as
1503	as you don't register any with libev). Similarly, when the last signal	2128	you don't register any with libev for the same signal).
1504	watcher for a signal is stopped libev will reset the signal handler to
1505	SIG_DFL (regardless of what it was set to before).
1506		2129
1507	If possible and supported, libev will install its handlers with	2130	If possible and supported, libev will install its handlers with
1508	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2131	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1509	interrupted. If you have a problem with system calls getting interrupted by	2132	not be unduly interrupted. If you have a problem with system calls getting
1510	signals you can block all signals in an C<ev_check> watcher and unblock	2133	interrupted by signals you can block all signals in an C<ev_check> watcher
1511	them in an C<ev_prepare> watcher.	2134	and unblock them in an C<ev_prepare> watcher.
		2135
		2136	=head3 The special problem of inheritance over execve
		2137
		2138	Both the signal mask (C<sigprocmask>) and the signal disposition
		2139	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2140	stopping it again), that is, libev might or might not block the signal,
		2141	and might or might not set or restore the installed signal handler.
		2142
		2143	While this does not matter for the signal disposition (libev never
		2144	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2145	C<execve>), this matters for the signal mask: many programs do not expect
		2146	certain signals to be blocked.
		2147
		2148	This means that before calling C<exec> (from the child) you should reset
		2149	the signal mask to whatever "default" you expect (all clear is a good
		2150	choice usually).
		2151
		2152	The simplest way to ensure that the signal mask is reset in the child is
		2153	to install a fork handler with C<pthread_atfork> that resets it. That will
		2154	catch fork calls done by libraries (such as the libc) as well.
		2155
		2156	In current versions of libev, you can also ensure that the signal mask is
		2157	not blocking any signals (except temporarily, so thread users watch out)
		2158	by specifying the C<EVFLAG_NOSIGFD> when creating the event loop. This
		2159	is not guaranteed for future versions, however.
1512		2160
1513	=head3 Watcher-Specific Functions and Data Members	2161	=head3 Watcher-Specific Functions and Data Members
1514		2162
1515	=over 4	2163	=over 4
1516		2164
…		…
1527		2175
1528	=back	2176	=back
1529		2177
1530	=head3 Examples	2178	=head3 Examples
1531		2179
1532	Example: Try to exit cleanly on SIGINT and SIGTERM.	2180	Example: Try to exit cleanly on SIGINT.
1533		2181
1534	static void	2182	static void
1535	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2183	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1536	{	2184	{
1537	ev_unloop (loop, EVUNLOOP_ALL);	2185	ev_unloop (loop, EVUNLOOP_ALL);
1538	}	2186	}
1539		2187
1540	struct ev_signal signal_watcher;	2188	ev_signal signal_watcher;
1541	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2189	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1542	ev_signal_start (loop, &sigint_cb);	2190	ev_signal_start (loop, &signal_watcher);
1543		2191
1544		2192
1545	=head2 C<ev_child> - watch out for process status changes	2193	=head2 C<ev_child> - watch out for process status changes
1546		2194
1547	Child watchers trigger when your process receives a SIGCHLD in response to	2195	Child watchers trigger when your process receives a SIGCHLD in response to
1548	some child status changes (most typically when a child of yours dies). It	2196	some child status changes (most typically when a child of yours dies or
1549	is permissible to install a child watcher I<after> the child has been	2197	exits). It is permissible to install a child watcher I<after> the child
1550	forked (which implies it might have already exited), as long as the event	2198	has been forked (which implies it might have already exited), as long
1551	loop isn't entered (or is continued from a watcher).	2199	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2200	forking and then immediately registering a watcher for the child is fine,
		2201	but forking and registering a watcher a few event loop iterations later or
		2202	in the next callback invocation is not.
1552		2203
1553	Only the default event loop is capable of handling signals, and therefore	2204	Only the default event loop is capable of handling signals, and therefore
1554	you can only register child watchers in the default event loop.	2205	you can only register child watchers in the default event loop.
1555		2206
		2207	Due to some design glitches inside libev, child watchers will always be
		2208	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2209	libev)
		2210
1556	=head3 Process Interaction	2211	=head3 Process Interaction
1557		2212
1558	Libev grabs C<SIGCHLD> as soon as the default event loop is	2213	Libev grabs C<SIGCHLD> as soon as the default event loop is
1559	initialised. This is necessary to guarantee proper behaviour even if	2214	initialised. This is necessary to guarantee proper behaviour even if the
1560	the first child watcher is started after the child exits. The occurrence	2215	first child watcher is started after the child exits. The occurrence
1561	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2216	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1562	synchronously as part of the event loop processing. Libev always reaps all	2217	synchronously as part of the event loop processing. Libev always reaps all
1563	children, even ones not watched.	2218	children, even ones not watched.
1564		2219
1565	=head3 Overriding the Built-In Processing	2220	=head3 Overriding the Built-In Processing
…		…
1569	handler, you can override it easily by installing your own handler for	2224	handler, you can override it easily by installing your own handler for
1570	C<SIGCHLD> after initialising the default loop, and making sure the	2225	C<SIGCHLD> after initialising the default loop, and making sure the
1571	default loop never gets destroyed. You are encouraged, however, to use an	2226	default loop never gets destroyed. You are encouraged, however, to use an
1572	event-based approach to child reaping and thus use libev's support for	2227	event-based approach to child reaping and thus use libev's support for
1573	that, so other libev users can use C<ev_child> watchers freely.	2228	that, so other libev users can use C<ev_child> watchers freely.
		2229
		2230	=head3 Stopping the Child Watcher
		2231
		2232	Currently, the child watcher never gets stopped, even when the
		2233	child terminates, so normally one needs to stop the watcher in the
		2234	callback. Future versions of libev might stop the watcher automatically
		2235	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2236	problem).
1574		2237
1575	=head3 Watcher-Specific Functions and Data Members	2238	=head3 Watcher-Specific Functions and Data Members
1576		2239
1577	=over 4	2240	=over 4
1578		2241
…		…
1610	its completion.	2273	its completion.
1611		2274
1612	ev_child cw;	2275	ev_child cw;
1613		2276
1614	static void	2277	static void
1615	child_cb (EV_P_ struct ev_child *w, int revents)	2278	child_cb (EV_P_ ev_child *w, int revents)
1616	{	2279	{
1617	ev_child_stop (EV_A_ w);	2280	ev_child_stop (EV_A_ w);
1618	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2281	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1619	}	2282	}
1620		2283
…		…
1635		2298
1636		2299
1637	=head2 C<ev_stat> - did the file attributes just change?	2300	=head2 C<ev_stat> - did the file attributes just change?
1638		2301
1639	This watches a file system path for attribute changes. That is, it calls	2302	This watches a file system path for attribute changes. That is, it calls
1640	C<stat> regularly (or when the OS says it changed) and sees if it changed	2303	C<stat> on that path in regular intervals (or when the OS says it changed)
1641	compared to the last time, invoking the callback if it did.	2304	and sees if it changed compared to the last time, invoking the callback if
		2305	it did.
1642		2306
1643	The path does not need to exist: changing from "path exists" to "path does	2307	The path does not need to exist: changing from "path exists" to "path does
1644	not exist" is a status change like any other. The condition "path does	2308	not exist" is a status change like any other. The condition "path does not
1645	not exist" is signified by the C<st_nlink> field being zero (which is	2309	exist" (or more correctly "path cannot be stat'ed") is signified by the
1646	otherwise always forced to be at least one) and all the other fields of	2310	C<st_nlink> field being zero (which is otherwise always forced to be at
1647	the stat buffer having unspecified contents.	2311	least one) and all the other fields of the stat buffer having unspecified
		2312	contents.
1648		2313
1649	The path I<should> be absolute and I<must not> end in a slash. If it is	2314	The path I<must not> end in a slash or contain special components such as
		2315	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1650	relative and your working directory changes, the behaviour is undefined.	2316	your working directory changes, then the behaviour is undefined.
1651		2317
1652	Since there is no standard to do this, the portable implementation simply	2318	Since there is no portable change notification interface available, the
1653	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2319	portable implementation simply calls C<stat(2)> regularly on the path
1654	can specify a recommended polling interval for this case. If you specify	2320	to see if it changed somehow. You can specify a recommended polling
1655	a polling interval of C<0> (highly recommended!) then a I<suitable,	2321	interval for this case. If you specify a polling interval of C<0> (highly
1656	unspecified default> value will be used (which you can expect to be around	2322	recommended!) then a I<suitable, unspecified default> value will be used
1657	five seconds, although this might change dynamically). Libev will also	2323	(which you can expect to be around five seconds, although this might
1658	impose a minimum interval which is currently around C<0.1>, but thats	2324	change dynamically). Libev will also impose a minimum interval which is
1659	usually overkill.	2325	currently around C<0.1>, but that's usually overkill.
1660		2326
1661	This watcher type is not meant for massive numbers of stat watchers,	2327	This watcher type is not meant for massive numbers of stat watchers,
1662	as even with OS-supported change notifications, this can be	2328	as even with OS-supported change notifications, this can be
1663	resource-intensive.	2329	resource-intensive.
1664		2330
1665	At the time of this writing, only the Linux inotify interface is	2331	At the time of this writing, the only OS-specific interface implemented
1666	implemented (implementing kqueue support is left as an exercise for the	2332	is the Linux inotify interface (implementing kqueue support is left as an
1667	reader, note, however, that the author sees no way of implementing ev_stat	2333	exercise for the reader. Note, however, that the author sees no way of
1668	semantics with kqueue). Inotify will be used to give hints only and should	2334	implementing C<ev_stat> semantics with kqueue, except as a hint).
1669	not change the semantics of C<ev_stat> watchers, which means that libev
1670	sometimes needs to fall back to regular polling again even with inotify,
1671	but changes are usually detected immediately, and if the file exists there
1672	will be no polling.
1673		2335
1674	=head3 ABI Issues (Largefile Support)	2336	=head3 ABI Issues (Largefile Support)
1675		2337
1676	Libev by default (unless the user overrides this) uses the default	2338	Libev by default (unless the user overrides this) uses the default
1677	compilation environment, which means that on systems with large file	2339	compilation environment, which means that on systems with large file
1678	support disabled by default, you get the 32 bit version of the stat	2340	support disabled by default, you get the 32 bit version of the stat
1679	structure. When using the library from programs that change the ABI to	2341	structure. When using the library from programs that change the ABI to
1680	use 64 bit file offsets the programs will fail. In that case you have to	2342	use 64 bit file offsets the programs will fail. In that case you have to
1681	compile libev with the same flags to get binary compatibility. This is	2343	compile libev with the same flags to get binary compatibility. This is
1682	obviously the case with any flags that change the ABI, but the problem is	2344	obviously the case with any flags that change the ABI, but the problem is
1683	most noticeably disabled with ev_stat and large file support.	2345	most noticeably displayed with ev_stat and large file support.
1684		2346
1685	The solution for this is to lobby your distribution maker to make large	2347	The solution for this is to lobby your distribution maker to make large
1686	file interfaces available by default (as e.g. FreeBSD does) and not	2348	file interfaces available by default (as e.g. FreeBSD does) and not
1687	optional. Libev cannot simply switch on large file support because it has	2349	optional. Libev cannot simply switch on large file support because it has
1688	to exchange stat structures with application programs compiled using the	2350	to exchange stat structures with application programs compiled using the
1689	default compilation environment.	2351	default compilation environment.
1690		2352
1691	=head3 Inotify	2353	=head3 Inotify and Kqueue
1692		2354
1693	When C<inotify (7)> support has been compiled into libev (generally only	2355	When C<inotify (7)> support has been compiled into libev and present at
1694	available on Linux) and present at runtime, it will be used to speed up	2356	runtime, it will be used to speed up change detection where possible. The
1695	change detection where possible. The inotify descriptor will be created lazily	2357	inotify descriptor will be created lazily when the first C<ev_stat>
1696	when the first C<ev_stat> watcher is being started.	2358	watcher is being started.
1697		2359
1698	Inotify presence does not change the semantics of C<ev_stat> watchers	2360	Inotify presence does not change the semantics of C<ev_stat> watchers
1699	except that changes might be detected earlier, and in some cases, to avoid	2361	except that changes might be detected earlier, and in some cases, to avoid
1700	making regular C<stat> calls. Even in the presence of inotify support	2362	making regular C<stat> calls. Even in the presence of inotify support
1701	there are many cases where libev has to resort to regular C<stat> polling.	2363	there are many cases where libev has to resort to regular C<stat> polling,
		2364	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2365	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2366	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2367	xfs are fully working) libev usually gets away without polling.
1702		2368
1703	(There is no support for kqueue, as apparently it cannot be used to	2369	There is no support for kqueue, as apparently it cannot be used to
1704	implement this functionality, due to the requirement of having a file	2370	implement this functionality, due to the requirement of having a file
1705	descriptor open on the object at all times).	2371	descriptor open on the object at all times, and detecting renames, unlinks
		2372	etc. is difficult.
		2373
		2374	=head3 C<stat ()> is a synchronous operation
		2375
		2376	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2377	the process. The exception are C<ev_stat> watchers - those call C<stat
		2378	()>, which is a synchronous operation.
		2379
		2380	For local paths, this usually doesn't matter: unless the system is very
		2381	busy or the intervals between stat's are large, a stat call will be fast,
		2382	as the path data is usually in memory already (except when starting the
		2383	watcher).
		2384
		2385	For networked file systems, calling C<stat ()> can block an indefinite
		2386	time due to network issues, and even under good conditions, a stat call
		2387	often takes multiple milliseconds.
		2388
		2389	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2390	paths, although this is fully supported by libev.
1706		2391
1707	=head3 The special problem of stat time resolution	2392	=head3 The special problem of stat time resolution
1708		2393
1709	The C<stat ()> system call only supports full-second resolution portably, and	2394	The C<stat ()> system call only supports full-second resolution portably,
1710	even on systems where the resolution is higher, many file systems still	2395	and even on systems where the resolution is higher, most file systems
1711	only support whole seconds.	2396	still only support whole seconds.
1712		2397
1713	That means that, if the time is the only thing that changes, you can	2398	That means that, if the time is the only thing that changes, you can
1714	easily miss updates: on the first update, C<ev_stat> detects a change and	2399	easily miss updates: on the first update, C<ev_stat> detects a change and
1715	calls your callback, which does something. When there is another update	2400	calls your callback, which does something. When there is another update
1716	within the same second, C<ev_stat> will be unable to detect it as the stat	2401	within the same second, C<ev_stat> will be unable to detect unless the
1717	data does not change.	2402	stat data does change in other ways (e.g. file size).
1718		2403
1719	The solution to this is to delay acting on a change for slightly more	2404	The solution to this is to delay acting on a change for slightly more
1720	than a second (or till slightly after the next full second boundary), using	2405	than a second (or till slightly after the next full second boundary), using
1721	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);	2406	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1722	ev_timer_again (loop, w)>).	2407	ev_timer_again (loop, w)>).
…		…
1742	C<path>. The C<interval> is a hint on how quickly a change is expected to	2427	C<path>. The C<interval> is a hint on how quickly a change is expected to
1743	be detected and should normally be specified as C<0> to let libev choose	2428	be detected and should normally be specified as C<0> to let libev choose
1744	a suitable value. The memory pointed to by C<path> must point to the same	2429	a suitable value. The memory pointed to by C<path> must point to the same
1745	path for as long as the watcher is active.	2430	path for as long as the watcher is active.
1746		2431
1747	The callback will receive C<EV_STAT> when a change was detected, relative	2432	The callback will receive an C<EV_STAT> event when a change was detected,
1748	to the attributes at the time the watcher was started (or the last change	2433	relative to the attributes at the time the watcher was started (or the
1749	was detected).	2434	last change was detected).
1750		2435
1751	=item ev_stat_stat (loop, ev_stat *)	2436	=item ev_stat_stat (loop, ev_stat *)
1752		2437
1753	Updates the stat buffer immediately with new values. If you change the	2438	Updates the stat buffer immediately with new values. If you change the
1754	watched path in your callback, you could call this function to avoid	2439	watched path in your callback, you could call this function to avoid
…		…
1837		2522
1838		2523
1839	=head2 C<ev_idle> - when you've got nothing better to do...	2524	=head2 C<ev_idle> - when you've got nothing better to do...
1840		2525
1841	Idle watchers trigger events when no other events of the same or higher	2526	Idle watchers trigger events when no other events of the same or higher
1842	priority are pending (prepare, check and other idle watchers do not	2527	priority are pending (prepare, check and other idle watchers do not count
1843	count).	2528	as receiving "events").
1844		2529
1845	That is, as long as your process is busy handling sockets or timeouts	2530	That is, as long as your process is busy handling sockets or timeouts
1846	(or even signals, imagine) of the same or higher priority it will not be	2531	(or even signals, imagine) of the same or higher priority it will not be
1847	triggered. But when your process is idle (or only lower-priority watchers	2532	triggered. But when your process is idle (or only lower-priority watchers
1848	are pending), the idle watchers are being called once per event loop	2533	are pending), the idle watchers are being called once per event loop
…		…
1859		2544
1860	=head3 Watcher-Specific Functions and Data Members	2545	=head3 Watcher-Specific Functions and Data Members
1861		2546
1862	=over 4	2547	=over 4
1863		2548
1864	=item ev_idle_init (ev_signal *, callback)	2549	=item ev_idle_init (ev_idle *, callback)
1865		2550
1866	Initialises and configures the idle watcher - it has no parameters of any	2551	Initialises and configures the idle watcher - it has no parameters of any
1867	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2552	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1868	believe me.	2553	believe me.
1869		2554
…		…
1873		2558
1874	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2559	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1875	callback, free it. Also, use no error checking, as usual.	2560	callback, free it. Also, use no error checking, as usual.
1876		2561
1877	static void	2562	static void
1878	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2563	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1879	{	2564	{
1880	free (w);	2565	free (w);
1881	// now do something you wanted to do when the program has	2566	// now do something you wanted to do when the program has
1882	// no longer anything immediate to do.	2567	// no longer anything immediate to do.
1883	}	2568	}
1884		2569
1885	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2570	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1886	ev_idle_init (idle_watcher, idle_cb);	2571	ev_idle_init (idle_watcher, idle_cb);
1887	ev_idle_start (loop, idle_cb);	2572	ev_idle_start (loop, idle_watcher);
1888		2573
1889		2574
1890	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2575	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1891		2576
1892	Prepare and check watchers are usually (but not always) used in tandem:	2577	Prepare and check watchers are usually (but not always) used in pairs:
1893	prepare watchers get invoked before the process blocks and check watchers	2578	prepare watchers get invoked before the process blocks and check watchers
1894	afterwards.	2579	afterwards.
1895		2580
1896	You I<must not> call C<ev_loop> or similar functions that enter	2581	You I<must not> call C<ev_loop> or similar functions that enter
1897	the current event loop from either C<ev_prepare> or C<ev_check>	2582	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1900	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2585	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1901	C<ev_check> so if you have one watcher of each kind they will always be	2586	C<ev_check> so if you have one watcher of each kind they will always be
1902	called in pairs bracketing the blocking call.	2587	called in pairs bracketing the blocking call.
1903		2588
1904	Their main purpose is to integrate other event mechanisms into libev and	2589	Their main purpose is to integrate other event mechanisms into libev and
1905	their use is somewhat advanced. This could be used, for example, to track	2590	their use is somewhat advanced. They could be used, for example, to track
1906	variable changes, implement your own watchers, integrate net-snmp or a	2591	variable changes, implement your own watchers, integrate net-snmp or a
1907	coroutine library and lots more. They are also occasionally useful if	2592	coroutine library and lots more. They are also occasionally useful if
1908	you cache some data and want to flush it before blocking (for example,	2593	you cache some data and want to flush it before blocking (for example,
1909	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2594	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1910	watcher).	2595	watcher).
1911		2596
1912	This is done by examining in each prepare call which file descriptors need	2597	This is done by examining in each prepare call which file descriptors
1913	to be watched by the other library, registering C<ev_io> watchers for	2598	need to be watched by the other library, registering C<ev_io> watchers
1914	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2599	for them and starting an C<ev_timer> watcher for any timeouts (many
1915	provide just this functionality). Then, in the check watcher you check for	2600	libraries provide exactly this functionality). Then, in the check watcher,
1916	any events that occurred (by checking the pending status of all watchers	2601	you check for any events that occurred (by checking the pending status
1917	and stopping them) and call back into the library. The I/O and timer	2602	of all watchers and stopping them) and call back into the library. The
1918	callbacks will never actually be called (but must be valid nevertheless,	2603	I/O and timer callbacks will never actually be called (but must be valid
1919	because you never know, you know?).	2604	nevertheless, because you never know, you know?).
1920		2605
1921	As another example, the Perl Coro module uses these hooks to integrate	2606	As another example, the Perl Coro module uses these hooks to integrate
1922	coroutines into libev programs, by yielding to other active coroutines	2607	coroutines into libev programs, by yielding to other active coroutines
1923	during each prepare and only letting the process block if no coroutines	2608	during each prepare and only letting the process block if no coroutines
1924	are ready to run (it's actually more complicated: it only runs coroutines	2609	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1927	loop from blocking if lower-priority coroutines are active, thus mapping	2612	loop from blocking if lower-priority coroutines are active, thus mapping
1928	low-priority coroutines to idle/background tasks).	2613	low-priority coroutines to idle/background tasks).
1929		2614
1930	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2615	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1931	priority, to ensure that they are being run before any other watchers	2616	priority, to ensure that they are being run before any other watchers
		2617	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2618
1932	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2619	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1933	too) should not activate ("feed") events into libev. While libev fully	2620	activate ("feed") events into libev. While libev fully supports this, they
1934	supports this, they might get executed before other C<ev_check> watchers	2621	might get executed before other C<ev_check> watchers did their job. As
1935	did their job. As C<ev_check> watchers are often used to embed other	2622	C<ev_check> watchers are often used to embed other (non-libev) event
1936	(non-libev) event loops those other event loops might be in an unusable	2623	loops those other event loops might be in an unusable state until their
1937	state until their C<ev_check> watcher ran (always remind yourself to	2624	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1938	coexist peacefully with others).	2625	others).
1939		2626
1940	=head3 Watcher-Specific Functions and Data Members	2627	=head3 Watcher-Specific Functions and Data Members
1941		2628
1942	=over 4	2629	=over 4
1943		2630
…		…
1945		2632
1946	=item ev_check_init (ev_check *, callback)	2633	=item ev_check_init (ev_check *, callback)
1947		2634
1948	Initialises and configures the prepare or check watcher - they have no	2635	Initialises and configures the prepare or check watcher - they have no
1949	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2636	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1950	macros, but using them is utterly, utterly and completely pointless.	2637	macros, but using them is utterly, utterly, utterly and completely
		2638	pointless.
1951		2639
1952	=back	2640	=back
1953		2641
1954	=head3 Examples	2642	=head3 Examples
1955		2643
…		…
1968		2656
1969	static ev_io iow [nfd];	2657	static ev_io iow [nfd];
1970	static ev_timer tw;	2658	static ev_timer tw;
1971		2659
1972	static void	2660	static void
1973	io_cb (ev_loop *loop, ev_io *w, int revents)	2661	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1974	{	2662	{
1975	}	2663	}
1976		2664
1977	// create io watchers for each fd and a timer before blocking	2665	// create io watchers for each fd and a timer before blocking
1978	static void	2666	static void
1979	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2667	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1980	{	2668	{
1981	int timeout = 3600000;	2669	int timeout = 3600000;
1982	struct pollfd fds [nfd];	2670	struct pollfd fds [nfd];
1983	// actual code will need to loop here and realloc etc.	2671	// actual code will need to loop here and realloc etc.
1984	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2672	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1985		2673
1986	/* the callback is illegal, but won't be called as we stop during check */	2674	/* the callback is illegal, but won't be called as we stop during check */
1987	ev_timer_init (&tw, 0, timeout * 1e-3);	2675	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1988	ev_timer_start (loop, &tw);	2676	ev_timer_start (loop, &tw);
1989		2677
1990	// create one ev_io per pollfd	2678	// create one ev_io per pollfd
1991	for (int i = 0; i < nfd; ++i)	2679	for (int i = 0; i < nfd; ++i)
1992	{	2680	{
…		…
1999	}	2687	}
2000	}	2688	}
2001		2689
2002	// stop all watchers after blocking	2690	// stop all watchers after blocking
2003	static void	2691	static void
2004	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2692	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2005	{	2693	{
2006	ev_timer_stop (loop, &tw);	2694	ev_timer_stop (loop, &tw);
2007		2695
2008	for (int i = 0; i < nfd; ++i)	2696	for (int i = 0; i < nfd; ++i)
2009	{	2697	{
…		…
2048	}	2736	}
2049		2737
2050	// do not ever call adns_afterpoll	2738	// do not ever call adns_afterpoll
2051		2739
2052	Method 4: Do not use a prepare or check watcher because the module you	2740	Method 4: Do not use a prepare or check watcher because the module you
2053	want to embed is too inflexible to support it. Instead, you can override	2741	want to embed is not flexible enough to support it. Instead, you can
2054	their poll function. The drawback with this solution is that the main	2742	override their poll function. The drawback with this solution is that the
2055	loop is now no longer controllable by EV. The C<Glib::EV> module does	2743	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2056	this.	2744	this approach, effectively embedding EV as a client into the horrible
		2745	libglib event loop.
2057		2746
2058	static gint	2747	static gint
2059	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2748	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2060	{	2749	{
2061	int got_events = 0;	2750	int got_events = 0;
…		…
2092	prioritise I/O.	2781	prioritise I/O.
2093		2782
2094	As an example for a bug workaround, the kqueue backend might only support	2783	As an example for a bug workaround, the kqueue backend might only support
2095	sockets on some platform, so it is unusable as generic backend, but you	2784	sockets on some platform, so it is unusable as generic backend, but you
2096	still want to make use of it because you have many sockets and it scales	2785	still want to make use of it because you have many sockets and it scales
2097	so nicely. In this case, you would create a kqueue-based loop and embed it	2786	so nicely. In this case, you would create a kqueue-based loop and embed
2098	into your default loop (which might use e.g. poll). Overall operation will	2787	it into your default loop (which might use e.g. poll). Overall operation
2099	be a bit slower because first libev has to poll and then call kevent, but	2788	will be a bit slower because first libev has to call C<poll> and then
2100	at least you can use both at what they are best.	2789	C<kevent>, but at least you can use both mechanisms for what they are
		2790	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2101		2791
2102	As for prioritising I/O: rarely you have the case where some fds have	2792	As for prioritising I/O: under rare circumstances you have the case where
2103	to be watched and handled very quickly (with low latency), and even	2793	some fds have to be watched and handled very quickly (with low latency),
2104	priorities and idle watchers might have too much overhead. In this case	2794	and even priorities and idle watchers might have too much overhead. In
2105	you would put all the high priority stuff in one loop and all the rest in	2795	this case you would put all the high priority stuff in one loop and all
2106	a second one, and embed the second one in the first.	2796	the rest in a second one, and embed the second one in the first.
2107		2797
2108	As long as the watcher is active, the callback will be invoked every time	2798	As long as the watcher is active, the callback will be invoked every
2109	there might be events pending in the embedded loop. The callback must then	2799	time there might be events pending in the embedded loop. The callback
2110	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2800	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2111	their callbacks (you could also start an idle watcher to give the embedded	2801	sweep and invoke their callbacks (the callback doesn't need to invoke the
2112	loop strictly lower priority for example). You can also set the callback	2802	C<ev_embed_sweep> function directly, it could also start an idle watcher
2113	to C<0>, in which case the embed watcher will automatically execute the	2803	to give the embedded loop strictly lower priority for example).
2114	embedded loop sweep.
2115		2804
2116	As long as the watcher is started it will automatically handle events. The	2805	You can also set the callback to C<0>, in which case the embed watcher
2117	callback will be invoked whenever some events have been handled. You can	2806	will automatically execute the embedded loop sweep whenever necessary.
2118	set the callback to C<0> to avoid having to specify one if you are not
2119	interested in that.
2120		2807
2121	Also, there have not currently been made special provisions for forking:	2808	Fork detection will be handled transparently while the C<ev_embed> watcher
2122	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2809	is active, i.e., the embedded loop will automatically be forked when the
2123	but you will also have to stop and restart any C<ev_embed> watchers	2810	embedding loop forks. In other cases, the user is responsible for calling
2124	yourself.	2811	C<ev_loop_fork> on the embedded loop.
2125		2812
2126	Unfortunately, not all backends are embeddable, only the ones returned by	2813	Unfortunately, not all backends are embeddable: only the ones returned by
2127	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2814	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2128	portable one.	2815	portable one.
2129		2816
2130	So when you want to use this feature you will always have to be prepared	2817	So when you want to use this feature you will always have to be prepared
2131	that you cannot get an embeddable loop. The recommended way to get around	2818	that you cannot get an embeddable loop. The recommended way to get around
2132	this is to have a separate variables for your embeddable loop, try to	2819	this is to have a separate variables for your embeddable loop, try to
2133	create it, and if that fails, use the normal loop for everything.	2820	create it, and if that fails, use the normal loop for everything.
		2821
		2822	=head3 C<ev_embed> and fork
		2823
		2824	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2825	automatically be applied to the embedded loop as well, so no special
		2826	fork handling is required in that case. When the watcher is not running,
		2827	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2828	as applicable.
2134		2829
2135	=head3 Watcher-Specific Functions and Data Members	2830	=head3 Watcher-Specific Functions and Data Members
2136		2831
2137	=over 4	2832	=over 4
2138		2833
…		…
2166	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2861	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2167	used).	2862	used).
2168		2863
2169	struct ev_loop *loop_hi = ev_default_init (0);	2864	struct ev_loop *loop_hi = ev_default_init (0);
2170	struct ev_loop *loop_lo = 0;	2865	struct ev_loop *loop_lo = 0;
2171	struct ev_embed embed;	2866	ev_embed embed;
2172		2867
2173	// see if there is a chance of getting one that works	2868	// see if there is a chance of getting one that works
2174	// (remember that a flags value of 0 means autodetection)	2869	// (remember that a flags value of 0 means autodetection)
2175	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2870	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2176	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2871	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2190	kqueue implementation). Store the kqueue/socket-only event loop in	2885	kqueue implementation). Store the kqueue/socket-only event loop in
2191	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2886	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2192		2887
2193	struct ev_loop *loop = ev_default_init (0);	2888	struct ev_loop *loop = ev_default_init (0);
2194	struct ev_loop *loop_socket = 0;	2889	struct ev_loop *loop_socket = 0;
2195	struct ev_embed embed;	2890	ev_embed embed;
2196		2891
2197	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2892	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2198	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2893	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2199	{	2894	{
2200	ev_embed_init (&embed, 0, loop_socket);	2895	ev_embed_init (&embed, 0, loop_socket);
…		…
2215	event loop blocks next and before C<ev_check> watchers are being called,	2910	event loop blocks next and before C<ev_check> watchers are being called,
2216	and only in the child after the fork. If whoever good citizen calling	2911	and only in the child after the fork. If whoever good citizen calling
2217	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2912	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2218	handlers will be invoked, too, of course.	2913	handlers will be invoked, too, of course.
2219		2914
		2915	=head3 The special problem of life after fork - how is it possible?
		2916
		2917	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2918	up/change the process environment, followed by a call to C<exec()>. This
		2919	sequence should be handled by libev without any problems.
		2920
		2921	This changes when the application actually wants to do event handling
		2922	in the child, or both parent in child, in effect "continuing" after the
		2923	fork.
		2924
		2925	The default mode of operation (for libev, with application help to detect
		2926	forks) is to duplicate all the state in the child, as would be expected
		2927	when I<either> the parent I<or> the child process continues.
		2928
		2929	When both processes want to continue using libev, then this is usually the
		2930	wrong result. In that case, usually one process (typically the parent) is
		2931	supposed to continue with all watchers in place as before, while the other
		2932	process typically wants to start fresh, i.e. without any active watchers.
		2933
		2934	The cleanest and most efficient way to achieve that with libev is to
		2935	simply create a new event loop, which of course will be "empty", and
		2936	use that for new watchers. This has the advantage of not touching more
		2937	memory than necessary, and thus avoiding the copy-on-write, and the
		2938	disadvantage of having to use multiple event loops (which do not support
		2939	signal watchers).
		2940
		2941	When this is not possible, or you want to use the default loop for
		2942	other reasons, then in the process that wants to start "fresh", call
		2943	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2944	the default loop will "orphan" (not stop) all registered watchers, so you
		2945	have to be careful not to execute code that modifies those watchers. Note
		2946	also that in that case, you have to re-register any signal watchers.
		2947
2220	=head3 Watcher-Specific Functions and Data Members	2948	=head3 Watcher-Specific Functions and Data Members
2221		2949
2222	=over 4	2950	=over 4
2223		2951
2224	=item ev_fork_init (ev_signal *, callback)	2952	=item ev_fork_init (ev_signal *, callback)
…		…
2253	=head3 Queueing	2981	=head3 Queueing
2254		2982
2255	C<ev_async> does not support queueing of data in any way. The reason	2983	C<ev_async> does not support queueing of data in any way. The reason
2256	is that the author does not know of a simple (or any) algorithm for a	2984	is that the author does not know of a simple (or any) algorithm for a
2257	multiple-writer-single-reader queue that works in all cases and doesn't	2985	multiple-writer-single-reader queue that works in all cases and doesn't
2258	need elaborate support such as pthreads.	2986	need elaborate support such as pthreads or unportable memory access
		2987	semantics.
2259		2988
2260	That means that if you want to queue data, you have to provide your own	2989	That means that if you want to queue data, you have to provide your own
2261	queue. But at least I can tell you would implement locking around your	2990	queue. But at least I can tell you how to implement locking around your
2262	queue:	2991	queue:
2263		2992
2264	=over 4	2993	=over 4
2265		2994
2266	=item queueing from a signal handler context	2995	=item queueing from a signal handler context
2267		2996
2268	To implement race-free queueing, you simply add to the queue in the signal	2997	To implement race-free queueing, you simply add to the queue in the signal
2269	handler but you block the signal handler in the watcher callback. Here is an example that does that for	2998	handler but you block the signal handler in the watcher callback. Here is
2270	some fictitious SIGUSR1 handler:	2999	an example that does that for some fictitious SIGUSR1 handler:
2271		3000
2272	static ev_async mysig;	3001	static ev_async mysig;
2273		3002
2274	static void	3003	static void
2275	sigusr1_handler (void)	3004	sigusr1_handler (void)
…		…
2341	=over 4	3070	=over 4
2342		3071
2343	=item ev_async_init (ev_async *, callback)	3072	=item ev_async_init (ev_async *, callback)
2344		3073
2345	Initialises and configures the async watcher - it has no parameters of any	3074	Initialises and configures the async watcher - it has no parameters of any
2346	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3075	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2347	believe me.	3076	trust me.
2348		3077
2349	=item ev_async_send (loop, ev_async *)	3078	=item ev_async_send (loop, ev_async *)
2350		3079
2351	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3080	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2352	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3081	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2353	C<ev_feed_event>, this call is safe to do in other threads, signal or	3082	C<ev_feed_event>, this call is safe to do from other threads, signal or
2354	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3083	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2355	section below on what exactly this means).	3084	section below on what exactly this means).
2356		3085
		3086	Note that, as with other watchers in libev, multiple events might get
		3087	compressed into a single callback invocation (another way to look at this
		3088	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3089	reset when the event loop detects that).
		3090
2357	This call incurs the overhead of a system call only once per loop iteration,	3091	This call incurs the overhead of a system call only once per event loop
2358	so while the overhead might be noticeable, it doesn't apply to repeated	3092	iteration, so while the overhead might be noticeable, it doesn't apply to
2359	calls to C<ev_async_send>.	3093	repeated calls to C<ev_async_send> for the same event loop.
2360		3094
2361	=item bool = ev_async_pending (ev_async *)	3095	=item bool = ev_async_pending (ev_async *)
2362		3096
2363	Returns a non-zero value when C<ev_async_send> has been called on the	3097	Returns a non-zero value when C<ev_async_send> has been called on the
2364	watcher but the event has not yet been processed (or even noted) by the	3098	watcher but the event has not yet been processed (or even noted) by the
…		…
2367	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3101	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2368	the loop iterates next and checks for the watcher to have become active,	3102	the loop iterates next and checks for the watcher to have become active,
2369	it will reset the flag again. C<ev_async_pending> can be used to very	3103	it will reset the flag again. C<ev_async_pending> can be used to very
2370	quickly check whether invoking the loop might be a good idea.	3104	quickly check whether invoking the loop might be a good idea.
2371		3105
2372	Not that this does I<not> check whether the watcher itself is pending, only	3106	Not that this does I<not> check whether the watcher itself is pending,
2373	whether it has been requested to make this watcher pending.	3107	only whether it has been requested to make this watcher pending: there
		3108	is a time window between the event loop checking and resetting the async
		3109	notification, and the callback being invoked.
2374		3110
2375	=back	3111	=back
2376		3112
2377		3113
2378	=head1 OTHER FUNCTIONS	3114	=head1 OTHER FUNCTIONS
…		…
2382	=over 4	3118	=over 4
2383		3119
2384	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3120	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2385		3121
2386	This function combines a simple timer and an I/O watcher, calls your	3122	This function combines a simple timer and an I/O watcher, calls your
2387	callback on whichever event happens first and automatically stop both	3123	callback on whichever event happens first and automatically stops both
2388	watchers. This is useful if you want to wait for a single event on an fd	3124	watchers. This is useful if you want to wait for a single event on an fd
2389	or timeout without having to allocate/configure/start/stop/free one or	3125	or timeout without having to allocate/configure/start/stop/free one or
2390	more watchers yourself.	3126	more watchers yourself.
2391		3127
2392	If C<fd> is less than 0, then no I/O watcher will be started and events	3128	If C<fd> is less than 0, then no I/O watcher will be started and the
2393	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3129	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2394	C<events> set will be created and started.	3130	the given C<fd> and C<events> set will be created and started.
2395		3131
2396	If C<timeout> is less than 0, then no timeout watcher will be	3132	If C<timeout> is less than 0, then no timeout watcher will be
2397	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3133	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2398	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3134	repeat = 0) will be started. C<0> is a valid timeout.
2399	dubious value.
2400		3135
2401	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3136	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
2402	passed an C<revents> set like normal event callbacks (a combination of	3137	passed an C<revents> set like normal event callbacks (a combination of
2403	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3138	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2404	value passed to C<ev_once>:	3139	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3140	a timeout and an io event at the same time - you probably should give io
		3141	events precedence.
		3142
		3143	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2405		3144
2406	static void stdin_ready (int revents, void *arg)	3145	static void stdin_ready (int revents, void *arg)
2407	{	3146	{
		3147	if (revents & EV_READ)
		3148	/* stdin might have data for us, joy! */;
2408	if (revents & EV_TIMEOUT)	3149	else if (revents & EV_TIMEOUT)
2409	/* doh, nothing entered */;	3150	/* doh, nothing entered */;
2410	else if (revents & EV_READ)
2411	/* stdin might have data for us, joy! */;
2412	}	3151	}
2413		3152
2414	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3153	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2415		3154
2416	=item ev_feed_event (ev_loop *, watcher *, int revents)
2417
2418	Feeds the given event set into the event loop, as if the specified event
2419	had happened for the specified watcher (which must be a pointer to an
2420	initialised but not necessarily started event watcher).
2421
2422	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3155	=item ev_feed_fd_event (loop, int fd, int revents)
2423		3156
2424	Feed an event on the given fd, as if a file descriptor backend detected	3157	Feed an event on the given fd, as if a file descriptor backend detected
2425	the given events it.	3158	the given events it.
2426		3159
2427	=item ev_feed_signal_event (ev_loop *loop, int signum)	3160	=item ev_feed_signal_event (loop, int signum)
2428		3161
2429	Feed an event as if the given signal occurred (C<loop> must be the default	3162	Feed an event as if the given signal occurred (C<loop> must be the default
2430	loop!).	3163	loop!).
2431		3164
2432	=back	3165	=back
…		…
2512		3245
2513	=over 4	3246	=over 4
2514		3247
2515	=item ev::TYPE::TYPE ()	3248	=item ev::TYPE::TYPE ()
2516		3249
2517	=item ev::TYPE::TYPE (struct ev_loop *)	3250	=item ev::TYPE::TYPE (loop)
2518		3251
2519	=item ev::TYPE::~TYPE	3252	=item ev::TYPE::~TYPE
2520		3253
2521	The constructor (optionally) takes an event loop to associate the watcher	3254	The constructor (optionally) takes an event loop to associate the watcher
2522	with. If it is omitted, it will use C<EV_DEFAULT>.	3255	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2554		3287
2555	myclass obj;	3288	myclass obj;
2556	ev::io iow;	3289	ev::io iow;
2557	iow.set <myclass, &myclass::io_cb> (&obj);	3290	iow.set <myclass, &myclass::io_cb> (&obj);
2558		3291
		3292	=item w->set (object *)
		3293
		3294	This is an B<experimental> feature that might go away in a future version.
		3295
		3296	This is a variation of a method callback - leaving out the method to call
		3297	will default the method to C<operator ()>, which makes it possible to use
		3298	functor objects without having to manually specify the C<operator ()> all
		3299	the time. Incidentally, you can then also leave out the template argument
		3300	list.
		3301
		3302	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3303	int revents)>.
		3304
		3305	See the method-C<set> above for more details.
		3306
		3307	Example: use a functor object as callback.
		3308
		3309	struct myfunctor
		3310	{
		3311	void operator() (ev::io &w, int revents)
		3312	{
		3313	...
		3314	}
		3315	}
		3316
		3317	myfunctor f;
		3318
		3319	ev::io w;
		3320	w.set (&f);
		3321
2559	=item w->set<function> (void *data = 0)	3322	=item w->set<function> (void *data = 0)
2560		3323
2561	Also sets a callback, but uses a static method or plain function as	3324	Also sets a callback, but uses a static method or plain function as
2562	callback. The optional C<data> argument will be stored in the watcher's	3325	callback. The optional C<data> argument will be stored in the watcher's
2563	C<data> member and is free for you to use.	3326	C<data> member and is free for you to use.
2564		3327
2565	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3328	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2566		3329
2567	See the method-C<set> above for more details.	3330	See the method-C<set> above for more details.
2568		3331
2569	Example:	3332	Example: Use a plain function as callback.
2570		3333
2571	static void io_cb (ev::io &w, int revents) { }	3334	static void io_cb (ev::io &w, int revents) { }
2572	iow.set <io_cb> ();	3335	iow.set <io_cb> ();
2573		3336
2574	=item w->set (struct ev_loop *)	3337	=item w->set (loop)
2575		3338
2576	Associates a different C<struct ev_loop> with this watcher. You can only	3339	Associates a different C<struct ev_loop> with this watcher. You can only
2577	do this when the watcher is inactive (and not pending either).	3340	do this when the watcher is inactive (and not pending either).
2578		3341
2579	=item w->set ([arguments])	3342	=item w->set ([arguments])
…		…
2612	Example: Define a class with an IO and idle watcher, start one of them in	3375	Example: Define a class with an IO and idle watcher, start one of them in
2613	the constructor.	3376	the constructor.
2614		3377
2615	class myclass	3378	class myclass
2616	{	3379	{
2617	ev::io io; void io_cb (ev::io &w, int revents);	3380	ev::io io ; void io_cb (ev::io &w, int revents);
2618	ev:idle idle void idle_cb (ev::idle &w, int revents);	3381	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2619		3382
2620	myclass (int fd)	3383	myclass (int fd)
2621	{	3384	{
2622	io .set <myclass, &myclass::io_cb > (this);	3385	io .set <myclass, &myclass::io_cb > (this);
2623	idle.set <myclass, &myclass::idle_cb> (this);	3386	idle.set <myclass, &myclass::idle_cb> (this);
…		…
2639	=item Perl	3402	=item Perl
2640		3403
2641	The EV module implements the full libev API and is actually used to test	3404	The EV module implements the full libev API and is actually used to test
2642	libev. EV is developed together with libev. Apart from the EV core module,	3405	libev. EV is developed together with libev. Apart from the EV core module,
2643	there are additional modules that implement libev-compatible interfaces	3406	there are additional modules that implement libev-compatible interfaces
2644	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3407	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2645	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3408	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3409	and C<EV::Glib>).
2646		3410
2647	It can be found and installed via CPAN, its homepage is at	3411	It can be found and installed via CPAN, its homepage is at
2648	L<http://software.schmorp.de/pkg/EV>.	3412	L<http://software.schmorp.de/pkg/EV>.
2649		3413
2650	=item Python	3414	=item Python
2651		3415
2652	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3416	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2653	seems to be quite complete and well-documented. Note, however, that the	3417	seems to be quite complete and well-documented.
2654	patch they require for libev is outright dangerous as it breaks the ABI
2655	for everybody else, and therefore, should never be applied in an installed
2656	libev (if python requires an incompatible ABI then it needs to embed
2657	libev).
2658		3418
2659	=item Ruby	3419	=item Ruby
2660		3420
2661	Tony Arcieri has written a ruby extension that offers access to a subset	3421	Tony Arcieri has written a ruby extension that offers access to a subset
2662	of the libev API and adds file handle abstractions, asynchronous DNS and	3422	of the libev API and adds file handle abstractions, asynchronous DNS and
2663	more on top of it. It can be found via gem servers. Its homepage is at	3423	more on top of it. It can be found via gem servers. Its homepage is at
2664	L<http://rev.rubyforge.org/>.	3424	L<http://rev.rubyforge.org/>.
2665		3425
		3426	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3427	makes rev work even on mingw.
		3428
		3429	=item Haskell
		3430
		3431	A haskell binding to libev is available at
		3432	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3433
2666	=item D	3434	=item D
2667		3435
2668	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3436	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2669	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3437	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3438
		3439	=item Ocaml
		3440
		3441	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3442	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3443
		3444	=item Lua
		3445
		3446	Brian Maher has written a partial interface to libev
		3447	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3448	L<http://github.com/brimworks/lua-ev>.
2670		3449
2671	=back	3450	=back
2672		3451
2673		3452
2674	=head1 MACRO MAGIC	3453	=head1 MACRO MAGIC
…		…
2775		3554
2776	#define EV_STANDALONE 1	3555	#define EV_STANDALONE 1
2777	#include "ev.h"	3556	#include "ev.h"
2778		3557
2779	Both header files and implementation files can be compiled with a C++	3558	Both header files and implementation files can be compiled with a C++
2780	compiler (at least, thats a stated goal, and breakage will be treated	3559	compiler (at least, that's a stated goal, and breakage will be treated
2781	as a bug).	3560	as a bug).
2782		3561
2783	You need the following files in your source tree, or in a directory	3562	You need the following files in your source tree, or in a directory
2784	in your include path (e.g. in libev/ when using -Ilibev):	3563	in your include path (e.g. in libev/ when using -Ilibev):
2785		3564
…		…
2829		3608
2830	=head2 PREPROCESSOR SYMBOLS/MACROS	3609	=head2 PREPROCESSOR SYMBOLS/MACROS
2831		3610
2832	Libev can be configured via a variety of preprocessor symbols you have to	3611	Libev can be configured via a variety of preprocessor symbols you have to
2833	define before including any of its files. The default in the absence of	3612	define before including any of its files. The default in the absence of
2834	autoconf is noted for every option.	3613	autoconf is documented for every option.
2835		3614
2836	=over 4	3615	=over 4
2837		3616
2838	=item EV_STANDALONE	3617	=item EV_STANDALONE
2839		3618
…		…
2841	keeps libev from including F<config.h>, and it also defines dummy	3620	keeps libev from including F<config.h>, and it also defines dummy
2842	implementations for some libevent functions (such as logging, which is not	3621	implementations for some libevent functions (such as logging, which is not
2843	supported). It will also not define any of the structs usually found in	3622	supported). It will also not define any of the structs usually found in
2844	F<event.h> that are not directly supported by the libev core alone.	3623	F<event.h> that are not directly supported by the libev core alone.
2845		3624
		3625	In standalone mode, libev will still try to automatically deduce the
		3626	configuration, but has to be more conservative.
		3627
2846	=item EV_USE_MONOTONIC	3628	=item EV_USE_MONOTONIC
2847		3629
2848	If defined to be C<1>, libev will try to detect the availability of the	3630	If defined to be C<1>, libev will try to detect the availability of the
2849	monotonic clock option at both compile time and runtime. Otherwise no use	3631	monotonic clock option at both compile time and runtime. Otherwise no
2850	of the monotonic clock option will be attempted. If you enable this, you	3632	use of the monotonic clock option will be attempted. If you enable this,
2851	usually have to link against librt or something similar. Enabling it when	3633	you usually have to link against librt or something similar. Enabling it
2852	the functionality isn't available is safe, though, although you have	3634	when the functionality isn't available is safe, though, although you have
2853	to make sure you link against any libraries where the C<clock_gettime>	3635	to make sure you link against any libraries where the C<clock_gettime>
2854	function is hiding in (often F<-lrt>).	3636	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2855		3637
2856	=item EV_USE_REALTIME	3638	=item EV_USE_REALTIME
2857		3639
2858	If defined to be C<1>, libev will try to detect the availability of the	3640	If defined to be C<1>, libev will try to detect the availability of the
2859	real-time clock option at compile time (and assume its availability at	3641	real-time clock option at compile time (and assume its availability
2860	runtime if successful). Otherwise no use of the real-time clock option will	3642	at runtime if successful). Otherwise no use of the real-time clock
2861	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3643	option will be attempted. This effectively replaces C<gettimeofday>
2862	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3644	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2863	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3645	correctness. See the note about libraries in the description of
		3646	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3647	C<EV_USE_CLOCK_SYSCALL>.
		3648
		3649	=item EV_USE_CLOCK_SYSCALL
		3650
		3651	If defined to be C<1>, libev will try to use a direct syscall instead
		3652	of calling the system-provided C<clock_gettime> function. This option
		3653	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3654	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3655	programs needlessly. Using a direct syscall is slightly slower (in
		3656	theory), because no optimised vdso implementation can be used, but avoids
		3657	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3658	higher, as it simplifies linking (no need for C<-lrt>).
2864		3659
2865	=item EV_USE_NANOSLEEP	3660	=item EV_USE_NANOSLEEP
2866		3661
2867	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3662	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2868	and will use it for delays. Otherwise it will use C<select ()>.	3663	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2884		3679
2885	=item EV_SELECT_USE_FD_SET	3680	=item EV_SELECT_USE_FD_SET
2886		3681
2887	If defined to C<1>, then the select backend will use the system C<fd_set>	3682	If defined to C<1>, then the select backend will use the system C<fd_set>
2888	structure. This is useful if libev doesn't compile due to a missing	3683	structure. This is useful if libev doesn't compile due to a missing
2889	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3684	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2890	exotic systems. This usually limits the range of file descriptors to some	3685	on exotic systems. This usually limits the range of file descriptors to
2891	low limit such as 1024 or might have other limitations (winsocket only	3686	some low limit such as 1024 or might have other limitations (winsocket
2892	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3687	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2893	influence the size of the C<fd_set> used.	3688	configures the maximum size of the C<fd_set>.
2894		3689
2895	=item EV_SELECT_IS_WINSOCKET	3690	=item EV_SELECT_IS_WINSOCKET
2896		3691
2897	When defined to C<1>, the select backend will assume that	3692	When defined to C<1>, the select backend will assume that
2898	select/socket/connect etc. don't understand file descriptors but	3693	select/socket/connect etc. don't understand file descriptors but
…		…
2900	be used is the winsock select). This means that it will call	3695	be used is the winsock select). This means that it will call
2901	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3696	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2902	it is assumed that all these functions actually work on fds, even	3697	it is assumed that all these functions actually work on fds, even
2903	on win32. Should not be defined on non-win32 platforms.	3698	on win32. Should not be defined on non-win32 platforms.
2904		3699
2905	=item EV_FD_TO_WIN32_HANDLE	3700	=item EV_FD_TO_WIN32_HANDLE(fd)
2906		3701
2907	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3702	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2908	file descriptors to socket handles. When not defining this symbol (the	3703	file descriptors to socket handles. When not defining this symbol (the
2909	default), then libev will call C<_get_osfhandle>, which is usually	3704	default), then libev will call C<_get_osfhandle>, which is usually
2910	correct. In some cases, programs use their own file descriptor management,	3705	correct. In some cases, programs use their own file descriptor management,
2911	in which case they can provide this function to map fds to socket handles.	3706	in which case they can provide this function to map fds to socket handles.
		3707
		3708	=item EV_WIN32_HANDLE_TO_FD(handle)
		3709
		3710	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3711	using the standard C<_open_osfhandle> function. For programs implementing
		3712	their own fd to handle mapping, overwriting this function makes it easier
		3713	to do so. This can be done by defining this macro to an appropriate value.
		3714
		3715	=item EV_WIN32_CLOSE_FD(fd)
		3716
		3717	If programs implement their own fd to handle mapping on win32, then this
		3718	macro can be used to override the C<close> function, useful to unregister
		3719	file descriptors again. Note that the replacement function has to close
		3720	the underlying OS handle.
2912		3721
2913	=item EV_USE_POLL	3722	=item EV_USE_POLL
2914		3723
2915	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3724	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2916	backend. Otherwise it will be enabled on non-win32 platforms. It	3725	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3009	When doing priority-based operations, libev usually has to linearly search	3818	When doing priority-based operations, libev usually has to linearly search
3010	all the priorities, so having many of them (hundreds) uses a lot of space	3819	all the priorities, so having many of them (hundreds) uses a lot of space
3011	and time, so using the defaults of five priorities (-2 .. +2) is usually	3820	and time, so using the defaults of five priorities (-2 .. +2) is usually
3012	fine.	3821	fine.
3013		3822
3014	If your embedding application does not need any priorities, defining these both to	3823	If your embedding application does not need any priorities, defining these
3015	C<0> will save some memory and CPU.	3824	both to C<0> will save some memory and CPU.
3016		3825
3017	=item EV_PERIODIC_ENABLE	3826	=item EV_PERIODIC_ENABLE
3018		3827
3019	If undefined or defined to be C<1>, then periodic timers are supported. If	3828	If undefined or defined to be C<1>, then periodic timers are supported. If
3020	defined to be C<0>, then they are not. Disabling them saves a few kB of	3829	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
3027	code.	3836	code.
3028		3837
3029	=item EV_EMBED_ENABLE	3838	=item EV_EMBED_ENABLE
3030		3839
3031	If undefined or defined to be C<1>, then embed watchers are supported. If	3840	If undefined or defined to be C<1>, then embed watchers are supported. If
3032	defined to be C<0>, then they are not.	3841	defined to be C<0>, then they are not. Embed watchers rely on most other
		3842	watcher types, which therefore must not be disabled.
3033		3843
3034	=item EV_STAT_ENABLE	3844	=item EV_STAT_ENABLE
3035		3845
3036	If undefined or defined to be C<1>, then stat watchers are supported. If	3846	If undefined or defined to be C<1>, then stat watchers are supported. If
3037	defined to be C<0>, then they are not.	3847	defined to be C<0>, then they are not.
…		…
3047	defined to be C<0>, then they are not.	3857	defined to be C<0>, then they are not.
3048		3858
3049	=item EV_MINIMAL	3859	=item EV_MINIMAL
3050		3860
3051	If you need to shave off some kilobytes of code at the expense of some	3861	If you need to shave off some kilobytes of code at the expense of some
3052	speed, define this symbol to C<1>. Currently this is used to override some	3862	speed (but with the full API), define this symbol to C<1>. Currently this
3053	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3863	is used to override some inlining decisions, saves roughly 30% code size
3054	much smaller 2-heap for timer management over the default 4-heap.	3864	on amd64. It also selects a much smaller 2-heap for timer management over
		3865	the default 4-heap.
		3866
		3867	You can save even more by disabling watcher types you do not need
		3868	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3869	(C<-DNDEBUG>) will usually reduce code size a lot.
		3870
		3871	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3872	provide a bare-bones event library. See C<ev.h> for details on what parts
		3873	of the API are still available, and do not complain if this subset changes
		3874	over time.
		3875
		3876	=item EV_NSIG
		3877
		3878	The highest supported signal number, +1 (or, the number of
		3879	signals): Normally, libev tries to deduce the maximum number of signals
		3880	automatically, but sometimes this fails, in which case it can be
		3881	specified. Also, using a lower number than detected (C<32> should be
		3882	good for about any system in existance) can save some memory, as libev
		3883	statically allocates some 12-24 bytes per signal number.
3055		3884
3056	=item EV_PID_HASHSIZE	3885	=item EV_PID_HASHSIZE
3057		3886
3058	C<ev_child> watchers use a small hash table to distribute workload by	3887	C<ev_child> watchers use a small hash table to distribute workload by
3059	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3888	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3069	two).	3898	two).
3070		3899
3071	=item EV_USE_4HEAP	3900	=item EV_USE_4HEAP
3072		3901
3073	Heaps are not very cache-efficient. To improve the cache-efficiency of the	3902	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3074	timer and periodics heap, libev uses a 4-heap when this symbol is defined	3903	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3075	to C<1>. The 4-heap uses more complicated (longer) code but has	3904	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3076	noticeably faster performance with many (thousands) of watchers.	3905	faster performance with many (thousands) of watchers.
3077		3906
3078	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	3907	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
3079	(disabled).	3908	(disabled).
3080		3909
3081	=item EV_HEAP_CACHE_AT	3910	=item EV_HEAP_CACHE_AT
3082		3911
3083	Heaps are not very cache-efficient. To improve the cache-efficiency of the	3912	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3084	timer and periodics heap, libev can cache the timestamp (I<at>) within	3913	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3085	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	3914	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3086	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	3915	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3087	but avoids random read accesses on heap changes. This improves performance	3916	but avoids random read accesses on heap changes. This improves performance
3088	noticeably with with many (hundreds) of watchers.	3917	noticeably with many (hundreds) of watchers.
3089		3918
3090	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	3919	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
3091	(disabled).	3920	(disabled).
3092		3921
3093	=item EV_VERIFY	3922	=item EV_VERIFY
…		…
3099	called once per loop, which can slow down libev. If set to C<3>, then the	3928	called once per loop, which can slow down libev. If set to C<3>, then the
3100	verification code will be called very frequently, which will slow down	3929	verification code will be called very frequently, which will slow down
3101	libev considerably.	3930	libev considerably.
3102		3931
3103	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	3932	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
3104	C<0.>	3933	C<0>.
3105		3934
3106	=item EV_COMMON	3935	=item EV_COMMON
3107		3936
3108	By default, all watchers have a C<void *data> member. By redefining	3937	By default, all watchers have a C<void *data> member. By redefining
3109	this macro to a something else you can include more and other types of	3938	this macro to a something else you can include more and other types of
…		…
3126	and the way callbacks are invoked and set. Must expand to a struct member	3955	and the way callbacks are invoked and set. Must expand to a struct member
3127	definition and a statement, respectively. See the F<ev.h> header file for	3956	definition and a statement, respectively. See the F<ev.h> header file for
3128	their default definitions. One possible use for overriding these is to	3957	their default definitions. One possible use for overriding these is to
3129	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3958	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3130	method calls instead of plain function calls in C++.	3959	method calls instead of plain function calls in C++.
		3960
		3961	=back
3131		3962
3132	=head2 EXPORTED API SYMBOLS	3963	=head2 EXPORTED API SYMBOLS
3133		3964
3134	If you need to re-export the API (e.g. via a DLL) and you need a list of	3965	If you need to re-export the API (e.g. via a DLL) and you need a list of
3135	exported symbols, you can use the provided F<Symbol.*> files which list	3966	exported symbols, you can use the provided F<Symbol.*> files which list
…		…
3182	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4013	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3183		4014
3184	#include "ev_cpp.h"	4015	#include "ev_cpp.h"
3185	#include "ev.c"	4016	#include "ev.c"
3186		4017
		4018	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3187		4019
3188	=head1 THREADS AND COROUTINES	4020	=head2 THREADS AND COROUTINES
3189		4021
3190	=head2 THREADS	4022	=head3 THREADS
3191		4023
3192	Libev itself is completely thread-safe, but it uses no locking. This	4024	All libev functions are reentrant and thread-safe unless explicitly
		4025	documented otherwise, but libev implements no locking itself. This means
3193	means that you can use as many loops as you want in parallel, as long as	4026	that you can use as many loops as you want in parallel, as long as there
3194	only one thread ever calls into one libev function with the same loop	4027	are no concurrent calls into any libev function with the same loop
3195	parameter.	4028	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4029	of course): libev guarantees that different event loops share no data
		4030	structures that need any locking.
3196		4031
3197	Or put differently: calls with different loop parameters can be done in	4032	Or to put it differently: calls with different loop parameters can be done
3198	parallel from multiple threads, calls with the same loop parameter must be	4033	concurrently from multiple threads, calls with the same loop parameter
3199	done serially (but can be done from different threads, as long as only one	4034	must be done serially (but can be done from different threads, as long as
3200	thread ever is inside a call at any point in time, e.g. by using a mutex	4035	only one thread ever is inside a call at any point in time, e.g. by using
3201	per loop).	4036	a mutex per loop).
		4037
		4038	Specifically to support threads (and signal handlers), libev implements
		4039	so-called C<ev_async> watchers, which allow some limited form of
		4040	concurrency on the same event loop, namely waking it up "from the
		4041	outside".
3202		4042
3203	If you want to know which design (one loop, locking, or multiple loops	4043	If you want to know which design (one loop, locking, or multiple loops
3204	without or something else still) is best for your problem, then I cannot	4044	without or something else still) is best for your problem, then I cannot
3205	help you. I can give some generic advice however:	4045	help you, but here is some generic advice:
3206		4046
3207	=over 4	4047	=over 4
3208		4048
3209	=item * most applications have a main thread: use the default libev loop	4049	=item * most applications have a main thread: use the default libev loop
3210	in that thread, or create a separate thread running only the default loop.	4050	in that thread, or create a separate thread running only the default loop.
…		…
3222		4062
3223	Choosing a model is hard - look around, learn, know that usually you can do	4063	Choosing a model is hard - look around, learn, know that usually you can do
3224	better than you currently do :-)	4064	better than you currently do :-)
3225		4065
3226	=item * often you need to talk to some other thread which blocks in the	4066	=item * often you need to talk to some other thread which blocks in the
		4067	event loop.
		4068
3227	event loop - C<ev_async> watchers can be used to wake them up from other	4069	C<ev_async> watchers can be used to wake them up from other threads safely
3228	threads safely (or from signal contexts...).	4070	(or from signal contexts...).
		4071
		4072	An example use would be to communicate signals or other events that only
		4073	work in the default loop by registering the signal watcher with the
		4074	default loop and triggering an C<ev_async> watcher from the default loop
		4075	watcher callback into the event loop interested in the signal.
3229		4076
3230	=back	4077	=back
3231		4078
		4079	=head4 THREAD LOCKING EXAMPLE
		4080
		4081	Here is a fictitious example of how to run an event loop in a different
		4082	thread than where callbacks are being invoked and watchers are
		4083	created/added/removed.
		4084
		4085	For a real-world example, see the C<EV::Loop::Async> perl module,
		4086	which uses exactly this technique (which is suited for many high-level
		4087	languages).
		4088
		4089	The example uses a pthread mutex to protect the loop data, a condition
		4090	variable to wait for callback invocations, an async watcher to notify the
		4091	event loop thread and an unspecified mechanism to wake up the main thread.
		4092
		4093	First, you need to associate some data with the event loop:
		4094
		4095	typedef struct {
		4096	mutex_t lock; /* global loop lock */
		4097	ev_async async_w;
		4098	thread_t tid;
		4099	cond_t invoke_cv;
		4100	} userdata;
		4101
		4102	void prepare_loop (EV_P)
		4103	{
		4104	// for simplicity, we use a static userdata struct.
		4105	static userdata u;
		4106
		4107	ev_async_init (&u->async_w, async_cb);
		4108	ev_async_start (EV_A_ &u->async_w);
		4109
		4110	pthread_mutex_init (&u->lock, 0);
		4111	pthread_cond_init (&u->invoke_cv, 0);
		4112
		4113	// now associate this with the loop
		4114	ev_set_userdata (EV_A_ u);
		4115	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4116	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4117
		4118	// then create the thread running ev_loop
		4119	pthread_create (&u->tid, 0, l_run, EV_A);
		4120	}
		4121
		4122	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4123	solely to wake up the event loop so it takes notice of any new watchers
		4124	that might have been added:
		4125
		4126	static void
		4127	async_cb (EV_P_ ev_async *w, int revents)
		4128	{
		4129	// just used for the side effects
		4130	}
		4131
		4132	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4133	protecting the loop data, respectively.
		4134
		4135	static void
		4136	l_release (EV_P)
		4137	{
		4138	userdata *u = ev_userdata (EV_A);
		4139	pthread_mutex_unlock (&u->lock);
		4140	}
		4141
		4142	static void
		4143	l_acquire (EV_P)
		4144	{
		4145	userdata *u = ev_userdata (EV_A);
		4146	pthread_mutex_lock (&u->lock);
		4147	}
		4148
		4149	The event loop thread first acquires the mutex, and then jumps straight
		4150	into C<ev_loop>:
		4151
		4152	void *
		4153	l_run (void *thr_arg)
		4154	{
		4155	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4156
		4157	l_acquire (EV_A);
		4158	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4159	ev_loop (EV_A_ 0);
		4160	l_release (EV_A);
		4161
		4162	return 0;
		4163	}
		4164
		4165	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4166	signal the main thread via some unspecified mechanism (signals? pipe
		4167	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4168	have been called (in a while loop because a) spurious wakeups are possible
		4169	and b) skipping inter-thread-communication when there are no pending
		4170	watchers is very beneficial):
		4171
		4172	static void
		4173	l_invoke (EV_P)
		4174	{
		4175	userdata *u = ev_userdata (EV_A);
		4176
		4177	while (ev_pending_count (EV_A))
		4178	{
		4179	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4180	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4181	}
		4182	}
		4183
		4184	Now, whenever the main thread gets told to invoke pending watchers, it
		4185	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4186	thread to continue:
		4187
		4188	static void
		4189	real_invoke_pending (EV_P)
		4190	{
		4191	userdata *u = ev_userdata (EV_A);
		4192
		4193	pthread_mutex_lock (&u->lock);
		4194	ev_invoke_pending (EV_A);
		4195	pthread_cond_signal (&u->invoke_cv);
		4196	pthread_mutex_unlock (&u->lock);
		4197	}
		4198
		4199	Whenever you want to start/stop a watcher or do other modifications to an
		4200	event loop, you will now have to lock:
		4201
		4202	ev_timer timeout_watcher;
		4203	userdata *u = ev_userdata (EV_A);
		4204
		4205	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4206
		4207	pthread_mutex_lock (&u->lock);
		4208	ev_timer_start (EV_A_ &timeout_watcher);
		4209	ev_async_send (EV_A_ &u->async_w);
		4210	pthread_mutex_unlock (&u->lock);
		4211
		4212	Note that sending the C<ev_async> watcher is required because otherwise
		4213	an event loop currently blocking in the kernel will have no knowledge
		4214	about the newly added timer. By waking up the loop it will pick up any new
		4215	watchers in the next event loop iteration.
		4216
3232	=head2 COROUTINES	4217	=head3 COROUTINES
3233		4218
3234	Libev is much more accommodating to coroutines ("cooperative threads"):	4219	Libev is very accommodating to coroutines ("cooperative threads"):
3235	libev fully supports nesting calls to it's functions from different	4220	libev fully supports nesting calls to its functions from different
3236	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4221	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3237	different coroutines and switch freely between both coroutines running the	4222	different coroutines, and switch freely between both coroutines running
3238	loop, as long as you don't confuse yourself). The only exception is that	4223	the loop, as long as you don't confuse yourself). The only exception is
3239	you must not do this from C<ev_periodic> reschedule callbacks.	4224	that you must not do this from C<ev_periodic> reschedule callbacks.
3240		4225
3241	Care has been invested into making sure that libev does not keep local	4226	Care has been taken to ensure that libev does not keep local state inside
3242	state inside C<ev_loop>, and other calls do not usually allow coroutine	4227	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3243	switches.	4228	they do not call any callbacks.
3244		4229
		4230	=head2 COMPILER WARNINGS
3245		4231
3246	=head1 COMPLEXITIES	4232	Depending on your compiler and compiler settings, you might get no or a
		4233	lot of warnings when compiling libev code. Some people are apparently
		4234	scared by this.
3247		4235
3248	In this section the complexities of (many of) the algorithms used inside	4236	However, these are unavoidable for many reasons. For one, each compiler
3249	libev will be explained. For complexity discussions about backends see the	4237	has different warnings, and each user has different tastes regarding
3250	documentation for C<ev_default_init>.	4238	warning options. "Warn-free" code therefore cannot be a goal except when
		4239	targeting a specific compiler and compiler-version.
3251		4240
3252	All of the following are about amortised time: If an array needs to be	4241	Another reason is that some compiler warnings require elaborate
3253	extended, libev needs to realloc and move the whole array, but this	4242	workarounds, or other changes to the code that make it less clear and less
3254	happens asymptotically never with higher number of elements, so O(1) might	4243	maintainable.
3255	mean it might do a lengthy realloc operation in rare cases, but on average
3256	it is much faster and asymptotically approaches constant time.
3257		4244
3258	=over 4	4245	And of course, some compiler warnings are just plain stupid, or simply
		4246	wrong (because they don't actually warn about the condition their message
		4247	seems to warn about). For example, certain older gcc versions had some
		4248	warnings that resulted an extreme number of false positives. These have
		4249	been fixed, but some people still insist on making code warn-free with
		4250	such buggy versions.
3259		4251
3260	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4252	While libev is written to generate as few warnings as possible,
		4253	"warn-free" code is not a goal, and it is recommended not to build libev
		4254	with any compiler warnings enabled unless you are prepared to cope with
		4255	them (e.g. by ignoring them). Remember that warnings are just that:
		4256	warnings, not errors, or proof of bugs.
3261		4257
3262	This means that, when you have a watcher that triggers in one hour and
3263	there are 100 watchers that would trigger before that then inserting will
3264	have to skip roughly seven (C<ld 100>) of these watchers.
3265		4258
3266	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4259	=head2 VALGRIND
3267		4260
3268	That means that changing a timer costs less than removing/adding them	4261	Valgrind has a special section here because it is a popular tool that is
3269	as only the relative motion in the event queue has to be paid for.	4262	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3270		4263
3271	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4264	If you think you found a bug (memory leak, uninitialised data access etc.)
		4265	in libev, then check twice: If valgrind reports something like:
3272		4266
3273	These just add the watcher into an array or at the head of a list.	4267	==2274== definitely lost: 0 bytes in 0 blocks.
		4268	==2274== possibly lost: 0 bytes in 0 blocks.
		4269	==2274== still reachable: 256 bytes in 1 blocks.
3274		4270
3275	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4271	Then there is no memory leak, just as memory accounted to global variables
		4272	is not a memleak - the memory is still being referenced, and didn't leak.
3276		4273
3277	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4274	Similarly, under some circumstances, valgrind might report kernel bugs
		4275	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4276	although an acceptable workaround has been found here), or it might be
		4277	confused.
3278		4278
3279	These watchers are stored in lists then need to be walked to find the	4279	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3280	correct watcher to remove. The lists are usually short (you don't usually	4280	make it into some kind of religion.
3281	have many watchers waiting for the same fd or signal).
3282		4281
3283	=item Finding the next timer in each loop iteration: O(1)	4282	If you are unsure about something, feel free to contact the mailing list
		4283	with the full valgrind report and an explanation on why you think this
		4284	is a bug in libev (best check the archives, too :). However, don't be
		4285	annoyed when you get a brisk "this is no bug" answer and take the chance
		4286	of learning how to interpret valgrind properly.
3284		4287
3285	By virtue of using a binary or 4-heap, the next timer is always found at a	4288	If you need, for some reason, empty reports from valgrind for your project
3286	fixed position in the storage array.	4289	I suggest using suppression lists.
3287		4290
3288	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3289		4291
3290	A change means an I/O watcher gets started or stopped, which requires	4292	=head1 PORTABILITY NOTES
3291	libev to recalculate its status (and possibly tell the kernel, depending
3292	on backend and whether C<ev_io_set> was used).
3293		4293
3294	=item Activating one watcher (putting it into the pending state): O(1)
3295
3296	=item Priority handling: O(number_of_priorities)
3297
3298	Priorities are implemented by allocating some space for each
3299	priority. When doing priority-based operations, libev usually has to
3300	linearly search all the priorities, but starting/stopping and activating
3301	watchers becomes O(1) w.r.t. priority handling.
3302
3303	=item Sending an ev_async: O(1)
3304
3305	=item Processing ev_async_send: O(number_of_async_watchers)
3306
3307	=item Processing signals: O(max_signal_number)
3308
3309	Sending involves a system call I<iff> there were no other C<ev_async_send>
3310	calls in the current loop iteration. Checking for async and signal events
3311	involves iterating over all running async watchers or all signal numbers.
3312
3313	=back
3314
3315
3316	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	4294	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3317		4295
3318	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4296	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3319	requires, and its I/O model is fundamentally incompatible with the POSIX	4297	requires, and its I/O model is fundamentally incompatible with the POSIX
3320	model. Libev still offers limited functionality on this platform in	4298	model. Libev still offers limited functionality on this platform in
3321	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4299	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
…		…
3328	way (note also that glib is the slowest event library known to man).	4306	way (note also that glib is the slowest event library known to man).
3329		4307
3330	There is no supported compilation method available on windows except	4308	There is no supported compilation method available on windows except
3331	embedding it into other applications.	4309	embedding it into other applications.
3332		4310
		4311	Sensible signal handling is officially unsupported by Microsoft - libev
		4312	tries its best, but under most conditions, signals will simply not work.
		4313
3333	Not a libev limitation but worth mentioning: windows apparently doesn't	4314	Not a libev limitation but worth mentioning: windows apparently doesn't
3334	accept large writes: instead of resulting in a partial write, windows will	4315	accept large writes: instead of resulting in a partial write, windows will
3335	either accept everything or return C<ENOBUFS> if the buffer is too large,	4316	either accept everything or return C<ENOBUFS> if the buffer is too large,
3336	so make sure you only write small amounts into your sockets (less than a	4317	so make sure you only write small amounts into your sockets (less than a
3337	megabyte seems safe, but thsi apparently depends on the amount of memory	4318	megabyte seems safe, but this apparently depends on the amount of memory
3338	available).	4319	available).
3339		4320
3340	Due to the many, low, and arbitrary limits on the win32 platform and	4321	Due to the many, low, and arbitrary limits on the win32 platform and
3341	the abysmal performance of winsockets, using a large number of sockets	4322	the abysmal performance of winsockets, using a large number of sockets
3342	is not recommended (and not reasonable). If your program needs to use	4323	is not recommended (and not reasonable). If your program needs to use
3343	more than a hundred or so sockets, then likely it needs to use a totally	4324	more than a hundred or so sockets, then likely it needs to use a totally
3344	different implementation for windows, as libev offers the POSIX readiness	4325	different implementation for windows, as libev offers the POSIX readiness
3345	notification model, which cannot be implemented efficiently on windows	4326	notification model, which cannot be implemented efficiently on windows
3346	(Microsoft monopoly games).	4327	(due to Microsoft monopoly games).
3347		4328
3348	A typical way to use libev under windows is to embed it (see the embedding	4329	A typical way to use libev under windows is to embed it (see the embedding
3349	section for details) and use the following F<evwrap.h> header file instead	4330	section for details) and use the following F<evwrap.h> header file instead
3350	of F<ev.h>:	4331	of F<ev.h>:
3351		4332
…		…
3353	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	4334	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3354		4335
3355	#include "ev.h"	4336	#include "ev.h"
3356		4337
3357	And compile the following F<evwrap.c> file into your project (make sure	4338	And compile the following F<evwrap.c> file into your project (make sure
3358	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	4339	you do I<not> compile the F<ev.c> or any other embedded source files!):
3359		4340
3360	#include "evwrap.h"	4341	#include "evwrap.h"
3361	#include "ev.c"	4342	#include "ev.c"
3362		4343
3363	=over 4	4344	=over 4
…		…
3387		4368
3388	Early versions of winsocket's select only supported waiting for a maximum	4369	Early versions of winsocket's select only supported waiting for a maximum
3389	of C<64> handles (probably owning to the fact that all windows kernels	4370	of C<64> handles (probably owning to the fact that all windows kernels
3390	can only wait for C<64> things at the same time internally; Microsoft	4371	can only wait for C<64> things at the same time internally; Microsoft
3391	recommends spawning a chain of threads and wait for 63 handles and the	4372	recommends spawning a chain of threads and wait for 63 handles and the
3392	previous thread in each. Great).	4373	previous thread in each. Sounds great!).
3393		4374
3394	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4375	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3395	to some high number (e.g. C<2048>) before compiling the winsocket select	4376	to some high number (e.g. C<2048>) before compiling the winsocket select
3396	call (which might be in libev or elsewhere, for example, perl does its own	4377	call (which might be in libev or elsewhere, for example, perl and many
3397	select emulation on windows).	4378	other interpreters do their own select emulation on windows).
3398		4379
3399	Another limit is the number of file descriptors in the Microsoft runtime	4380	Another limit is the number of file descriptors in the Microsoft runtime
3400	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4381	libraries, which by default is C<64> (there must be a hidden I<64>
3401	or something like this inside Microsoft). You can increase this by calling	4382	fetish or something like this inside Microsoft). You can increase this
3402	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4383	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3403	arbitrary limit), but is broken in many versions of the Microsoft runtime	4384	(another arbitrary limit), but is broken in many versions of the Microsoft
3404	libraries.
3405
3406	This might get you to about C<512> or C<2048> sockets (depending on	4385	runtime libraries. This might get you to about C<512> or C<2048> sockets
3407	windows version and/or the phase of the moon). To get more, you need to	4386	(depending on windows version and/or the phase of the moon). To get more,
3408	wrap all I/O functions and provide your own fd management, but the cost of	4387	you need to wrap all I/O functions and provide your own fd management, but
3409	calling select (O(n²)) will likely make this unworkable.	4388	the cost of calling select (O(n²)) will likely make this unworkable.
3410		4389
3411	=back	4390	=back
3412		4391
3413
3414	=head1 PORTABILITY REQUIREMENTS	4392	=head2 PORTABILITY REQUIREMENTS
3415		4393
3416	In addition to a working ISO-C implementation, libev relies on a few	4394	In addition to a working ISO-C implementation and of course the
3417	additional extensions:	4395	backend-specific APIs, libev relies on a few additional extensions:
3418		4396
3419	=over 4	4397	=over 4
3420		4398
3421	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	4399	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3422	calling conventions regardless of C<ev_watcher_type *>.	4400	calling conventions regardless of C<ev_watcher_type *>.
…		…
3428	calls them using an C<ev_watcher *> internally.	4406	calls them using an C<ev_watcher *> internally.
3429		4407
3430	=item C<sig_atomic_t volatile> must be thread-atomic as well	4408	=item C<sig_atomic_t volatile> must be thread-atomic as well
3431		4409
3432	The type C<sig_atomic_t volatile> (or whatever is defined as	4410	The type C<sig_atomic_t volatile> (or whatever is defined as
3433	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4411	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3434	threads. This is not part of the specification for C<sig_atomic_t>, but is	4412	threads. This is not part of the specification for C<sig_atomic_t>, but is
3435	believed to be sufficiently portable.	4413	believed to be sufficiently portable.
3436		4414
3437	=item C<sigprocmask> must work in a threaded environment	4415	=item C<sigprocmask> must work in a threaded environment
3438		4416
…		…
3447	except the initial one, and run the default loop in the initial thread as	4425	except the initial one, and run the default loop in the initial thread as
3448	well.	4426	well.
3449		4427
3450	=item C<long> must be large enough for common memory allocation sizes	4428	=item C<long> must be large enough for common memory allocation sizes
3451		4429
3452	To improve portability and simplify using libev, libev uses C<long>	4430	To improve portability and simplify its API, libev uses C<long> internally
3453	internally instead of C<size_t> when allocating its data structures. On	4431	instead of C<size_t> when allocating its data structures. On non-POSIX
3454	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	4432	systems (Microsoft...) this might be unexpectedly low, but is still at
3455	is still at least 31 bits everywhere, which is enough for hundreds of	4433	least 31 bits everywhere, which is enough for hundreds of millions of
3456	millions of watchers.	4434	watchers.
3457		4435
3458	=item C<double> must hold a time value in seconds with enough accuracy	4436	=item C<double> must hold a time value in seconds with enough accuracy
3459		4437
3460	The type C<double> is used to represent timestamps. It is required to	4438	The type C<double> is used to represent timestamps. It is required to
3461	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4439	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3462	enough for at least into the year 4000. This requirement is fulfilled by	4440	enough for at least into the year 4000. This requirement is fulfilled by
3463	implementations implementing IEEE 754 (basically all existing ones).	4441	implementations implementing IEEE 754, which is basically all existing
		4442	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4443	2200.
3464		4444
3465	=back	4445	=back
3466		4446
3467	If you know of other additional requirements drop me a note.	4447	If you know of other additional requirements drop me a note.
3468		4448
3469		4449
3470	=head1 COMPILER WARNINGS	4450	=head1 ALGORITHMIC COMPLEXITIES
3471		4451
3472	Depending on your compiler and compiler settings, you might get no or a	4452	In this section the complexities of (many of) the algorithms used inside
3473	lot of warnings when compiling libev code. Some people are apparently	4453	libev will be documented. For complexity discussions about backends see
3474	scared by this.	4454	the documentation for C<ev_default_init>.
3475		4455
3476	However, these are unavoidable for many reasons. For one, each compiler	4456	All of the following are about amortised time: If an array needs to be
3477	has different warnings, and each user has different tastes regarding	4457	extended, libev needs to realloc and move the whole array, but this
3478	warning options. "Warn-free" code therefore cannot be a goal except when	4458	happens asymptotically rarer with higher number of elements, so O(1) might
3479	targeting a specific compiler and compiler-version.	4459	mean that libev does a lengthy realloc operation in rare cases, but on
		4460	average it is much faster and asymptotically approaches constant time.
3480		4461
3481	Another reason is that some compiler warnings require elaborate	4462	=over 4
3482	workarounds, or other changes to the code that make it less clear and less
3483	maintainable.
3484		4463
3485	And of course, some compiler warnings are just plain stupid, or simply	4464	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3486	wrong (because they don't actually warn about the condition their message
3487	seems to warn about).
3488		4465
3489	While libev is written to generate as few warnings as possible,	4466	This means that, when you have a watcher that triggers in one hour and
3490	"warn-free" code is not a goal, and it is recommended not to build libev	4467	there are 100 watchers that would trigger before that, then inserting will
3491	with any compiler warnings enabled unless you are prepared to cope with	4468	have to skip roughly seven (C<ld 100>) of these watchers.
3492	them (e.g. by ignoring them). Remember that warnings are just that:
3493	warnings, not errors, or proof of bugs.
3494		4469
		4470	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3495		4471
3496	=head1 VALGRIND	4472	That means that changing a timer costs less than removing/adding them,
		4473	as only the relative motion in the event queue has to be paid for.
3497		4474
3498	Valgrind has a special section here because it is a popular tool that is	4475	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3499	highly useful, but valgrind reports are very hard to interpret.
3500		4476
3501	If you think you found a bug (memory leak, uninitialised data access etc.)	4477	These just add the watcher into an array or at the head of a list.
3502	in libev, then check twice: If valgrind reports something like:
3503		4478
3504	==2274== definitely lost: 0 bytes in 0 blocks.	4479	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3505	==2274== possibly lost: 0 bytes in 0 blocks.
3506	==2274== still reachable: 256 bytes in 1 blocks.
3507		4480
3508	Then there is no memory leak. Similarly, under some circumstances,	4481	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3509	valgrind might report kernel bugs as if it were a bug in libev, or it
3510	might be confused (it is a very good tool, but only a tool).
3511		4482
3512	If you are unsure about something, feel free to contact the mailing list	4483	These watchers are stored in lists, so they need to be walked to find the
3513	with the full valgrind report and an explanation on why you think this is	4484	correct watcher to remove. The lists are usually short (you don't usually
3514	a bug in libev. However, don't be annoyed when you get a brisk "this is	4485	have many watchers waiting for the same fd or signal: one is typical, two
3515	no bug" answer and take the chance of learning how to interpret valgrind	4486	is rare).
3516	properly.
3517		4487
3518	If you need, for some reason, empty reports from valgrind for your project	4488	=item Finding the next timer in each loop iteration: O(1)
3519	I suggest using suppression lists.
3520		4489
		4490	By virtue of using a binary or 4-heap, the next timer is always found at a
		4491	fixed position in the storage array.
		4492
		4493	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4494
		4495	A change means an I/O watcher gets started or stopped, which requires
		4496	libev to recalculate its status (and possibly tell the kernel, depending
		4497	on backend and whether C<ev_io_set> was used).
		4498
		4499	=item Activating one watcher (putting it into the pending state): O(1)
		4500
		4501	=item Priority handling: O(number_of_priorities)
		4502
		4503	Priorities are implemented by allocating some space for each
		4504	priority. When doing priority-based operations, libev usually has to
		4505	linearly search all the priorities, but starting/stopping and activating
		4506	watchers becomes O(1) with respect to priority handling.
		4507
		4508	=item Sending an ev_async: O(1)
		4509
		4510	=item Processing ev_async_send: O(number_of_async_watchers)
		4511
		4512	=item Processing signals: O(max_signal_number)
		4513
		4514	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4515	calls in the current loop iteration. Checking for async and signal events
		4516	involves iterating over all running async watchers or all signal numbers.
		4517
		4518	=back
		4519
		4520
		4521	=head1 GLOSSARY
		4522
		4523	=over 4
		4524
		4525	=item active
		4526
		4527	A watcher is active as long as it has been started (has been attached to
		4528	an event loop) but not yet stopped (disassociated from the event loop).
		4529
		4530	=item application
		4531
		4532	In this document, an application is whatever is using libev.
		4533
		4534	=item callback
		4535
		4536	The address of a function that is called when some event has been
		4537	detected. Callbacks are being passed the event loop, the watcher that
		4538	received the event, and the actual event bitset.
		4539
		4540	=item callback invocation
		4541
		4542	The act of calling the callback associated with a watcher.
		4543
		4544	=item event
		4545
		4546	A change of state of some external event, such as data now being available
		4547	for reading on a file descriptor, time having passed or simply not having
		4548	any other events happening anymore.
		4549
		4550	In libev, events are represented as single bits (such as C<EV_READ> or
		4551	C<EV_TIMEOUT>).
		4552
		4553	=item event library
		4554
		4555	A software package implementing an event model and loop.
		4556
		4557	=item event loop
		4558
		4559	An entity that handles and processes external events and converts them
		4560	into callback invocations.
		4561
		4562	=item event model
		4563
		4564	The model used to describe how an event loop handles and processes
		4565	watchers and events.
		4566
		4567	=item pending
		4568
		4569	A watcher is pending as soon as the corresponding event has been detected,
		4570	and stops being pending as soon as the watcher will be invoked or its
		4571	pending status is explicitly cleared by the application.
		4572
		4573	A watcher can be pending, but not active. Stopping a watcher also clears
		4574	its pending status.
		4575
		4576	=item real time
		4577
		4578	The physical time that is observed. It is apparently strictly monotonic :)
		4579
		4580	=item wall-clock time
		4581
		4582	The time and date as shown on clocks. Unlike real time, it can actually
		4583	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4584	clock.
		4585
		4586	=item watcher
		4587
		4588	A data structure that describes interest in certain events. Watchers need
		4589	to be started (attached to an event loop) before they can receive events.
		4590
		4591	=item watcher invocation
		4592
		4593	The act of calling the callback associated with a watcher.
		4594
		4595	=back
3521		4596
3522	=head1 AUTHOR	4597	=head1 AUTHOR
3523		4598
3524	Marc Lehmann <libev@schmorp.de>.	4599	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3525		4600

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