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Revision 1.163 by root, Sat May 31 23:19:23 2008 UTC vs.
Revision 1.292 by sf-exg, Mon Mar 22 09:57:01 2010 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
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);
28		30
29	// this causes all nested ev_loop's to stop iterating	31	// this causes all nested ev_loop's to stop iterating
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	}
41		43
42	int	44	int
43	main (void)	45	main (void)
44	{	46	{
45	// use the default event loop unless you have special needs	47	// use the default event loop unless you have special needs
46	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
47		49
48	// initialise an io watcher, then start it	50	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	51	// this one will watch for stdin to become readable
50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
51	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
52		54
53	// initialise a timer watcher, then start it	55	// initialise a timer watcher, then start it
54	// simple non-repeating 5.5 second timeout	56	// simple non-repeating 5.5 second timeout
55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
56	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
57		59
58	// now wait for events to arrive	60	// now wait for events to arrive
59	ev_loop (loop, 0);	61	ev_loop (loop, 0);
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
…		…
178	not a problem.	193	not a problem.
179		194
180	Example: Make sure we haven't accidentally been linked against the wrong	195	Example: Make sure we haven't accidentally been linked against the wrong
181	version.	196	version.
182		197
183	assert (("libev version mismatch",	198	assert (("libev version mismatch",
184	ev_version_major () == EV_VERSION_MAJOR	199	ev_version_major () == EV_VERSION_MAJOR
185	&& ev_version_minor () >= EV_VERSION_MINOR));	200	&& ev_version_minor () >= EV_VERSION_MINOR));
186		201
187	=item unsigned int ev_supported_backends ()	202	=item unsigned int ev_supported_backends ()
188		203
189	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	204	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
190	value) compiled into this binary of libev (independent of their	205	value) compiled into this binary of libev (independent of their
…		…
192	a description of the set values.	207	a description of the set values.
193		208
194	Example: make sure we have the epoll method, because yeah this is cool and	209	Example: make sure we have the epoll method, because yeah this is cool and
195	a must have and can we have a torrent of it please!!!11	210	a must have and can we have a torrent of it please!!!11
196		211
197	assert (("sorry, no epoll, no sex",	212	assert (("sorry, no epoll, no sex",
198	ev_supported_backends () & EVBACKEND_EPOLL));	213	ev_supported_backends () & EVBACKEND_EPOLL));
199		214
200	=item unsigned int ev_recommended_backends ()	215	=item unsigned int ev_recommended_backends ()
201		216
202	Return the set of all backends compiled into this binary of libev and also	217	Return the set of all backends compiled into this binary of libev and also
203	recommended for this platform. This set is often smaller than the one	218	recommended for this platform. This set is often smaller than the one
…		…
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
…		…
326	useful to try out specific backends to test their performance, or to work	345	useful to try out specific backends to test their performance, or to work
327	around bugs.	346	around bugs.
328		347
329	=item C<EVFLAG_FORKCHECK>	348	=item C<EVFLAG_FORKCHECK>
330		349
331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	350	Instead of calling C<ev_loop_fork> manually after a fork, you can also
332	a fork, you can also make libev check for a fork in each iteration by	351	make libev check for a fork in each iteration by enabling this flag.
333	enabling this flag.
334		352
335	This works by calling C<getpid ()> on every iteration of the loop,	353	This works by calling C<getpid ()> on every iteration of the loop,
336	and thus this might slow down your event loop if you do a lot of loop	354	and thus this might slow down your event loop if you do a lot of loop
337	iterations and little real work, but is usually not noticeable (on my	355	iterations and little real work, but is usually not noticeable (on my
338	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	356	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
…		…
344	flag.	362	flag.
345		363
346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
347	environment variable.	365	environment variable.
348		366
		367	=item C<EVFLAG_NOINOTIFY>
		368
		369	When this flag is specified, then libev will not attempt to use the
		370	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		371	testing, this flag can be useful to conserve inotify file descriptors, as
		372	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		373
		374	=item C<EVFLAG_SIGNALFD>
		375
		376	When this flag is specified, then libev will attempt to use the
		377	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		378	delivers signals synchronously, which makes it both faster and might make
		379	it possible to get the queued signal data. It can also simplify signal
		380	handling with threads, as long as you properly block signals in your
		381	threads that are not interested in handling them.
		382
		383	Signalfd will not be used by default as this changes your signal mask, and
		384	there are a lot of shoddy libraries and programs (glib's threadpool for
		385	example) that can't properly initialise their signal masks.
		386
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	387	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		388
351	This is your standard select(2) backend. Not I<completely> standard, as	389	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,	390	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	391	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	397	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	398	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	399	a look at C<ev_set_io_collect_interval ()> to increase the amount of
362	readiness notifications you get per iteration.	400	readiness notifications you get per iteration.
363		401
		402	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		403	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		404	C<exceptfds> set on that platform).
		405
364	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	406	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
365		407
366	And this is your standard poll(2) backend. It's more complicated	408	And this is your standard poll(2) backend. It's more complicated
367	than select, but handles sparse fds better and has no artificial	409	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	410	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,	411	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	412	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
371	performance tips.	413	performance tips.
372		414
		415	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		416	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		417
373	=item C<EVBACKEND_EPOLL> (value 4, Linux)	418	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		419
		420	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		421	kernels).
374		422
375	For few fds, this backend is a bit little slower than poll and select,	423	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	424	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),	425	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	426	epoll scales either O(1) or O(active_fds).
379	of shortcomings, such as silently dropping events in some hard-to-detect	427
380	cases and requiring a system call per fd change, no fork support and bad	428	The epoll mechanism deserves honorable mention as the most misdesigned
381	support for dup.	429	of the more advanced event mechanisms: mere annoyances include silently
		430	dropping file descriptors, requiring a system call per change per file
		431	descriptor (and unnecessary guessing of parameters), problems with dup and
		432	so on. The biggest issue is fork races, however - if a program forks then
		433	I<both> parent and child process have to recreate the epoll set, which can
		434	take considerable time (one syscall per file descriptor) and is of course
		435	hard to detect.
		436
		437	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		438	of course I<doesn't>, and epoll just loves to report events for totally
		439	I<different> file descriptors (even already closed ones, so one cannot
		440	even remove them from the set) than registered in the set (especially
		441	on SMP systems). Libev tries to counter these spurious notifications by
		442	employing an additional generation counter and comparing that against the
		443	events to filter out spurious ones, recreating the set when required.
382		444
383	While stopping, setting and starting an I/O watcher in the same iteration	445	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	446	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	447	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	448	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
387	very well if you register events for both fds.	449	file descriptors might not work very well if you register events for both
388		450	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		451
393	Best performance from this backend is achieved by not unregistering all	452	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.	453	watchers for a file descriptor until it has been closed, if possible,
395	keep at least one watcher active per fd at all times.	454	i.e. keep at least one watcher active per fd at all times. Stopping and
		455	starting a watcher (without re-setting it) also usually doesn't cause
		456	extra overhead. A fork can both result in spurious notifications as well
		457	as in libev having to destroy and recreate the epoll object, which can
		458	take considerable time and thus should be avoided.
		459
		460	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		461	faster than epoll for maybe up to a hundred file descriptors, depending on
		462	the usage. So sad.
396		463
397	While nominally embeddable in other event loops, this feature is broken in	464	While nominally embeddable in other event loops, this feature is broken in
398	all kernel versions tested so far.	465	all kernel versions tested so far.
		466
		467	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		468	C<EVBACKEND_POLL>.
399		469
400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	470	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
401		471
402	Kqueue deserves special mention, as at the time of this writing, it	472	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	473	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	474	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"	475	it's completely useless). Unlike epoll, however, whose brokenness
		476	is by design, these kqueue bugs can (and eventually will) be fixed
		477	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	478	"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)	479	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
408	system like NetBSD.	480	system like NetBSD.
409		481
410	You still can embed kqueue into a normal poll or select backend and use it	482	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	483	only for sockets (after having made sure that sockets work with kqueue on
…		…
413		485
414	It scales in the same way as the epoll backend, but the interface to the	486	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	487	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	488	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	489	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	490	two event changes per incident. Support for C<fork ()> is very bad (but
419	drops fds silently in similarly hard-to-detect cases.	491	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		492	cases
420		493
421	This backend usually performs well under most conditions.	494	This backend usually performs well under most conditions.
422		495
423	While nominally embeddable in other event loops, this doesn't work	496	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	497	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	498	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	499	(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	500	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
428	sockets.	501	also broken on OS X)) and, did I mention it, using it only for sockets.
		502
		503	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		504	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		505	C<NOTE_EOF>.
429		506
430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	507	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
431		508
432	This is not implemented yet (and might never be, unless you send me an	509	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	510	implementation). According to reports, C</dev/poll> only supports sockets
…		…
446	While this backend scales well, it requires one system call per active	523	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	524	file descriptor per loop iteration. For small and medium numbers of file
448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	525	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
449	might perform better.	526	might perform better.
450		527
451	On the positive side, ignoring the spurious readiness notifications, this	528	On the positive side, with the exception of the spurious readiness
452	backend actually performed to specification in all tests and is fully	529	notifications, this backend actually performed fully to specification
453	embeddable, which is a rare feat among the OS-specific backends.	530	in all tests and is fully embeddable, which is a rare feat among the
		531	OS-specific backends (I vastly prefer correctness over speed hacks).
		532
		533	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		534	C<EVBACKEND_POLL>.
454		535
455	=item C<EVBACKEND_ALL>	536	=item C<EVBACKEND_ALL>
456		537
457	Try all backends (even potentially broken ones that wouldn't be tried	538	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	539	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
…		…
460		541
461	It is definitely not recommended to use this flag.	542	It is definitely not recommended to use this flag.
462		543
463	=back	544	=back
464		545
465	If one or more of these are or'ed into the flags value, then only these	546	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	547	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.	548	here). If none are specified, all backends in C<ev_recommended_backends
		549	()> will be tried.
468		550
469	The most typical usage is like this:	551	Example: This is the most typical usage.
470		552
471	if (!ev_default_loop (0))	553	if (!ev_default_loop (0))
472	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	554	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
473		555
474	Restrict libev to the select and poll backends, and do not allow	556	Example: Restrict libev to the select and poll backends, and do not allow
475	environment settings to be taken into account:	557	environment settings to be taken into account:
476		558
477	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	559	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
478		560
479	Use whatever libev has to offer, but make sure that kqueue is used if	561	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	562	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):	563	private event loop and only if you know the OS supports your types of
		564	fds):
482		565
483	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	566	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
484		567
485	=item struct ev_loop *ev_loop_new (unsigned int flags)	568	=item struct ev_loop *ev_loop_new (unsigned int flags)
486		569
487	Similar to C<ev_default_loop>, but always creates a new event loop that is	570	Similar to C<ev_default_loop>, but always creates a new event loop that is
488	always distinct from the default loop. Unlike the default loop, it cannot	571	always distinct from the default loop.
489	handle signal and child watchers, and attempts to do so will be greeted by
490	undefined behaviour (or a failed assertion if assertions are enabled).
491		572
492	Note that this function I<is> thread-safe, and the recommended way to use	573	Note that this function I<is> thread-safe, and one common way to use
493	libev with threads is indeed to create one loop per thread, and using the	574	libev with threads is indeed to create one loop per thread, and using the
494	default loop in the "main" or "initial" thread.	575	default loop in the "main" or "initial" thread.
495		576
496	Example: Try to create a event loop that uses epoll and nothing else.	577	Example: Try to create a event loop that uses epoll and nothing else.
497		578
498	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	579	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
499	if (!epoller)	580	if (!epoller)
500	fatal ("no epoll found here, maybe it hides under your chair");	581	fatal ("no epoll found here, maybe it hides under your chair");
501		582
502	=item ev_default_destroy ()	583	=item ev_default_destroy ()
503		584
504	Destroys the default loop again (frees all memory and kernel state	585	Destroys the default loop (frees all memory and kernel state etc.). None
505	etc.). None of the active event watchers will be stopped in the normal	586	of the active event watchers will be stopped in the normal sense, so
506	sense, so e.g. C<ev_is_active> might still return true. It is your	587	e.g. C<ev_is_active> might still return true. It is your responsibility to
507	responsibility to either stop all watchers cleanly yourself I<before>	588	either stop all watchers cleanly yourself I<before> calling this function,
508	calling this function, or cope with the fact afterwards (which is usually	589	or cope with the fact afterwards (which is usually the easiest thing, you
509	the easiest thing, you can just ignore the watchers and/or C<free ()> them	590	can just ignore the watchers and/or C<free ()> them for example).
510	for example).
511		591
512	Note that certain global state, such as signal state, will not be freed by	592	Note that certain global state, such as signal state (and installed signal
513	this function, and related watchers (such as signal and child watchers)	593	handlers), will not be freed by this function, and related watchers (such
514	would need to be stopped manually.	594	as signal and child watchers) would need to be stopped manually.
515		595
516	In general it is not advisable to call this function except in the	596	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	597	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	598	pipe fds. If you need dynamically allocated loops it is better to use
519	C<ev_loop_new> and C<ev_loop_destroy>).	599	C<ev_loop_new> and C<ev_loop_destroy>.
520		600
521	=item ev_loop_destroy (loop)	601	=item ev_loop_destroy (loop)
522		602
523	Like C<ev_default_destroy>, but destroys an event loop created by an	603	Like C<ev_default_destroy>, but destroys an event loop created by an
524	earlier call to C<ev_loop_new>.	604	earlier call to C<ev_loop_new>.
…		…
530	name, you can call it anytime, but it makes most sense after forking, in	610	name, you can call it anytime, but it makes most sense after forking, in
531	the child process (or both child and parent, but that again makes little	611	the child process (or both child and parent, but that again makes little
532	sense). You I<must> call it in the child before using any of the libev	612	sense). You I<must> call it in the child before using any of the libev
533	functions, and it will only take effect at the next C<ev_loop> iteration.	613	functions, and it will only take effect at the next C<ev_loop> iteration.
534		614
		615	Again, you I<have> to call it on I<any> loop that you want to re-use after
		616	a fork, I<even if you do not plan to use the loop in the parent>. This is
		617	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		618	during fork.
		619
535	On the other hand, you only need to call this function in the child	620	On the other hand, you only need to call this function in the child
536	process if and only if you want to use the event library in the child. If	621	process if and only if you want to use the event loop in the child. If you
537	you just fork+exec, you don't have to call it at all.	622	just fork+exec or create a new loop in the child, you don't have to call
		623	it at all.
538		624
539	The function itself is quite fast and it's usually not a problem to call	625	The function itself is quite fast and it's usually not a problem to call
540	it just in case after a fork. To make this easy, the function will fit in	626	it just in case after a fork. To make this easy, the function will fit in
541	quite nicely into a call to C<pthread_atfork>:	627	quite nicely into a call to C<pthread_atfork>:
542		628
…		…
544		630
545	=item ev_loop_fork (loop)	631	=item ev_loop_fork (loop)
546		632
547	Like C<ev_default_fork>, but acts on an event loop created by	633	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	634	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.	635	after fork that you want to re-use in the child, and how you keep track of
		636	them is entirely your own problem.
550		637
551	=item int ev_is_default_loop (loop)	638	=item int ev_is_default_loop (loop)
552		639
553	Returns true when the given loop actually is the default loop, false otherwise.	640	Returns true when the given loop is, in fact, the default loop, and false
		641	otherwise.
554		642
555	=item unsigned int ev_loop_count (loop)	643	=item unsigned int ev_iteration (loop)
556		644
557	Returns the count of loop iterations for the loop, which is identical to	645	Returns the current iteration count for the loop, which is identical to
558	the number of times libev did poll for new events. It starts at C<0> and	646	the number of times libev did poll for new events. It starts at C<0> and
559	happily wraps around with enough iterations.	647	happily wraps around with enough iterations.
560		648
561	This value can sometimes be useful as a generation counter of sorts (it	649	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	650	"ticks" the number of loop iterations), as it roughly corresponds with
563	C<ev_prepare> and C<ev_check> calls.	651	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		652	prepare and check phases.
		653
		654	=item unsigned int ev_depth (loop)
		655
		656	Returns the number of times C<ev_loop> was entered minus the number of
		657	times C<ev_loop> was exited, in other words, the recursion depth.
		658
		659	Outside C<ev_loop>, this number is zero. In a callback, this number is
		660	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		661	in which case it is higher.
		662
		663	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		664	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		665	ungentleman behaviour unless it's really convenient.
564		666
565	=item unsigned int ev_backend (loop)	667	=item unsigned int ev_backend (loop)
566		668
567	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	669	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
568	use.	670	use.
…		…
573	received events and started processing them. This timestamp does not	675	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	676	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	677	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).	678	event occurring (or more correctly, libev finding out about it).
577		679
		680	=item ev_now_update (loop)
		681
		682	Establishes the current time by querying the kernel, updating the time
		683	returned by C<ev_now ()> in the progress. This is a costly operation and
		684	is usually done automatically within C<ev_loop ()>.
		685
		686	This function is rarely useful, but when some event callback runs for a
		687	very long time without entering the event loop, updating libev's idea of
		688	the current time is a good idea.
		689
		690	See also L<The special problem of time updates> in the C<ev_timer> section.
		691
		692	=item ev_suspend (loop)
		693
		694	=item ev_resume (loop)
		695
		696	These two functions suspend and resume a loop, for use when the loop is
		697	not used for a while and timeouts should not be processed.
		698
		699	A typical use case would be an interactive program such as a game: When
		700	the user presses C<^Z> to suspend the game and resumes it an hour later it
		701	would be best to handle timeouts as if no time had actually passed while
		702	the program was suspended. This can be achieved by calling C<ev_suspend>
		703	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		704	C<ev_resume> directly afterwards to resume timer processing.
		705
		706	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		707	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		708	will be rescheduled (that is, they will lose any events that would have
		709	occured while suspended).
		710
		711	After calling C<ev_suspend> you B<must not> call I<any> function on the
		712	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		713	without a previous call to C<ev_suspend>.
		714
		715	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		716	event loop time (see C<ev_now_update>).
		717
578	=item ev_loop (loop, int flags)	718	=item ev_loop (loop, int flags)
579		719
580	Finally, this is it, the event handler. This function usually is called	720	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	721	after you have initialised all your watchers and you want to start
582	events.	722	handling events.
583		723
584	If the flags argument is specified as C<0>, it will not return until	724	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.	725	either no event watchers are active anymore or C<ev_unloop> was called.
586		726
587	Please note that an explicit C<ev_unloop> is usually better than	727	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	728	relying on all watchers to be stopped when deciding when a program has
589	finished (especially in interactive programs), but having a program that	729	finished (especially in interactive programs), but having a program
590	automatically loops as long as it has to and no longer by virtue of	730	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.	731	of relying on its watchers stopping correctly, that is truly a thing of
		732	beauty.
592		733
593	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	734	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	735	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.	736	process in case there are no events and will return after one iteration of
		737	the loop.
596		738
597	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	739	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	740	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	741	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	742	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	743	user-registered callback will be called), and will return after one
		744	iteration of the loop.
		745
		746	This is useful if you are waiting for some external event in conjunction
		747	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	748	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.	749	usually a better approach for this kind of thing.
604		750
605	Here are the gory details of what C<ev_loop> does:	751	Here are the gory details of what C<ev_loop> does:
606		752
607	- Before the first iteration, call any pending watchers.	753	- Before the first iteration, call any pending watchers.
608	* If EVFLAG_FORKCHECK was used, check for a fork.	754	* If EVFLAG_FORKCHECK was used, check for a fork.
609	- If a fork was detected, queue and call all fork watchers.	755	- If a fork was detected (by any means), queue and call all fork watchers.
610	- Queue and call all prepare watchers.	756	- Queue and call all prepare watchers.
611	- If we have been forked, recreate the kernel state.	757	- If we have been forked, detach and recreate the kernel state
		758	as to not disturb the other process.
612	- Update the kernel state with all outstanding changes.	759	- Update the kernel state with all outstanding changes.
613	- Update the "event loop time".	760	- Update the "event loop time" (ev_now ()).
614	- Calculate for how long to sleep or block, if at all	761	- Calculate for how long to sleep or block, if at all
615	(active idle watchers, EVLOOP_NONBLOCK or not having	762	(active idle watchers, EVLOOP_NONBLOCK or not having
616	any active watchers at all will result in not sleeping).	763	any active watchers at all will result in not sleeping).
617	- Sleep if the I/O and timer collect interval say so.	764	- Sleep if the I/O and timer collect interval say so.
618	- Block the process, waiting for any events.	765	- Block the process, waiting for any events.
619	- Queue all outstanding I/O (fd) events.	766	- Queue all outstanding I/O (fd) events.
620	- Update the "event loop time" and do time jump handling.	767	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
621	- Queue all outstanding timers.	768	- Queue all expired timers.
622	- Queue all outstanding periodics.	769	- Queue all expired periodics.
623	- If no events are pending now, queue all idle watchers.	770	- Unless any events are pending now, queue all idle watchers.
624	- Queue all check watchers.	771	- Queue all check watchers.
625	- Call all queued watchers in reverse order (i.e. check watchers first).	772	- Call all queued watchers in reverse order (i.e. check watchers first).
626	Signals and child watchers are implemented as I/O watchers, and will	773	Signals and child watchers are implemented as I/O watchers, and will
627	be handled here by queueing them when their watcher gets executed.	774	be handled here by queueing them when their watcher gets executed.
628	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	775	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
…		…
633	anymore.	780	anymore.
634		781
635	... queue jobs here, make sure they register event watchers as long	782	... queue jobs here, make sure they register event watchers as long
636	... as they still have work to do (even an idle watcher will do..)	783	... as they still have work to do (even an idle watcher will do..)
637	ev_loop (my_loop, 0);	784	ev_loop (my_loop, 0);
638	... jobs done. yeah!	785	... jobs done or somebody called unloop. yeah!
639		786
640	=item ev_unloop (loop, how)	787	=item ev_unloop (loop, how)
641		788
642	Can be used to make a call to C<ev_loop> return early (but only after it	789	Can be used to make a call to C<ev_loop> return early (but only after it
643	has processed all outstanding events). The C<how> argument must be either	790	has processed all outstanding events). The C<how> argument must be either
644	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	791	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
645	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	792	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
646		793
647	This "unloop state" will be cleared when entering C<ev_loop> again.	794	This "unloop state" will be cleared when entering C<ev_loop> again.
648		795
		796	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		797
649	=item ev_ref (loop)	798	=item ev_ref (loop)
650		799
651	=item ev_unref (loop)	800	=item ev_unref (loop)
652		801
653	Ref/unref can be used to add or remove a reference count on the event	802	Ref/unref can be used to add or remove a reference count on the event
654	loop: Every watcher keeps one reference, and as long as the reference	803	loop: Every watcher keeps one reference, and as long as the reference
655	count is nonzero, C<ev_loop> will not return on its own. If you have	804	count is nonzero, C<ev_loop> will not return on its own.
656	a watcher you never unregister that should not keep C<ev_loop> from	805
657	returning, ev_unref() after starting, and ev_ref() before stopping it. For	806	This is useful when you have a watcher that you never intend to
		807	unregister, but that nevertheless should not keep C<ev_loop> from
		808	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		809	before stopping it.
		810
658	example, libev itself uses this for its internal signal pipe: It is not	811	As an example, libev itself uses this for its internal signal pipe: It
659	visible to the libev user and should not keep C<ev_loop> from exiting if	812	is not visible to the libev user and should not keep C<ev_loop> from
660	no event watchers registered by it are active. It is also an excellent	813	exiting if no event watchers registered by it are active. It is also an
661	way to do this for generic recurring timers or from within third-party	814	excellent way to do this for generic recurring timers or from within
662	libraries. Just remember to I<unref after start> and I<ref before stop>	815	third-party libraries. Just remember to I<unref after start> and I<ref
663	(but only if the watcher wasn't active before, or was active before,	816	before stop> (but only if the watcher wasn't active before, or was active
664	respectively).	817	before, respectively. Note also that libev might stop watchers itself
		818	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		819	in the callback).
665		820
666	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	821	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
667	running when nothing else is active.	822	running when nothing else is active.
668		823
669	struct ev_signal exitsig;	824	ev_signal exitsig;
670	ev_signal_init (&exitsig, sig_cb, SIGINT);	825	ev_signal_init (&exitsig, sig_cb, SIGINT);
671	ev_signal_start (loop, &exitsig);	826	ev_signal_start (loop, &exitsig);
672	evf_unref (loop);	827	evf_unref (loop);
673		828
674	Example: For some weird reason, unregister the above signal handler again.	829	Example: For some weird reason, unregister the above signal handler again.
675		830
676	ev_ref (loop);	831	ev_ref (loop);
677	ev_signal_stop (loop, &exitsig);	832	ev_signal_stop (loop, &exitsig);
678		833
679	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	834	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
680		835
681	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	836	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
682		837
683	These advanced functions influence the time that libev will spend waiting	838	These advanced functions influence the time that libev will spend waiting
684	for events. Both are by default C<0>, meaning that libev will try to	839	for events. Both time intervals are by default C<0>, meaning that libev
685	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	840	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		841	latency.
686		842
687	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	843	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
688	allows libev to delay invocation of I/O and timer/periodic callbacks to	844	allows libev to delay invocation of I/O and timer/periodic callbacks
689	increase efficiency of loop iterations.	845	to increase efficiency of loop iterations (or to increase power-saving
		846	opportunities).
690		847
691	The background is that sometimes your program runs just fast enough to	848	The idea is that sometimes your program runs just fast enough to handle
692	handle one (or very few) event(s) per loop iteration. While this makes	849	one (or very few) event(s) per loop iteration. While this makes the
693	the program responsive, it also wastes a lot of CPU time to poll for new	850	program responsive, it also wastes a lot of CPU time to poll for new
694	events, especially with backends like C<select ()> which have a high	851	events, especially with backends like C<select ()> which have a high
695	overhead for the actual polling but can deliver many events at once.	852	overhead for the actual polling but can deliver many events at once.
696		853
697	By setting a higher I<io collect interval> you allow libev to spend more	854	By setting a higher I<io collect interval> you allow libev to spend more
698	time collecting I/O events, so you can handle more events per iteration,	855	time collecting I/O events, so you can handle more events per iteration,
699	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	856	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
700	C<ev_timer>) will be not affected. Setting this to a non-null value will	857	C<ev_timer>) will be not affected. Setting this to a non-null value will
701	introduce an additional C<ev_sleep ()> call into most loop iterations.	858	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		859	sleep time ensures that libev will not poll for I/O events more often then
		860	once per this interval, on average.
702		861
703	Likewise, by setting a higher I<timeout collect interval> you allow libev	862	Likewise, by setting a higher I<timeout collect interval> you allow libev
704	to spend more time collecting timeouts, at the expense of increased	863	to spend more time collecting timeouts, at the expense of increased
705	latency (the watcher callback will be called later). C<ev_io> watchers	864	latency/jitter/inexactness (the watcher callback will be called
706	will not be affected. Setting this to a non-null value will not introduce	865	later). C<ev_io> watchers will not be affected. Setting this to a non-null
707	any overhead in libev.	866	value will not introduce any overhead in libev.
708		867
709	Many (busy) programs can usually benefit by setting the I/O collect	868	Many (busy) programs can usually benefit by setting the I/O collect
710	interval to a value near C<0.1> or so, which is often enough for	869	interval to a value near C<0.1> or so, which is often enough for
711	interactive servers (of course not for games), likewise for timeouts. It	870	interactive servers (of course not for games), likewise for timeouts. It
712	usually doesn't make much sense to set it to a lower value than C<0.01>,	871	usually doesn't make much sense to set it to a lower value than C<0.01>,
713	as this approaches the timing granularity of most systems.	872	as this approaches the timing granularity of most systems. Note that if
		873	you do transactions with the outside world and you can't increase the
		874	parallelity, then this setting will limit your transaction rate (if you
		875	need to poll once per transaction and the I/O collect interval is 0.01,
		876	then you can't do more than 100 transations per second).
		877
		878	Setting the I<timeout collect interval> can improve the opportunity for
		879	saving power, as the program will "bundle" timer callback invocations that
		880	are "near" in time together, by delaying some, thus reducing the number of
		881	times the process sleeps and wakes up again. Another useful technique to
		882	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		883	they fire on, say, one-second boundaries only.
		884
		885	Example: we only need 0.1s timeout granularity, and we wish not to poll
		886	more often than 100 times per second:
		887
		888	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		889	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		890
		891	=item ev_invoke_pending (loop)
		892
		893	This call will simply invoke all pending watchers while resetting their
		894	pending state. Normally, C<ev_loop> does this automatically when required,
		895	but when overriding the invoke callback this call comes handy.
		896
		897	=item int ev_pending_count (loop)
		898
		899	Returns the number of pending watchers - zero indicates that no watchers
		900	are pending.
		901
		902	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		903
		904	This overrides the invoke pending functionality of the loop: Instead of
		905	invoking all pending watchers when there are any, C<ev_loop> will call
		906	this callback instead. This is useful, for example, when you want to
		907	invoke the actual watchers inside another context (another thread etc.).
		908
		909	If you want to reset the callback, use C<ev_invoke_pending> as new
		910	callback.
		911
		912	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		913
		914	Sometimes you want to share the same loop between multiple threads. This
		915	can be done relatively simply by putting mutex_lock/unlock calls around
		916	each call to a libev function.
		917
		918	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		919	wait for it to return. One way around this is to wake up the loop via
		920	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		921	and I<acquire> callbacks on the loop.
		922
		923	When set, then C<release> will be called just before the thread is
		924	suspended waiting for new events, and C<acquire> is called just
		925	afterwards.
		926
		927	Ideally, C<release> will just call your mutex_unlock function, and
		928	C<acquire> will just call the mutex_lock function again.
		929
		930	While event loop modifications are allowed between invocations of
		931	C<release> and C<acquire> (that's their only purpose after all), no
		932	modifications done will affect the event loop, i.e. adding watchers will
		933	have no effect on the set of file descriptors being watched, or the time
		934	waited. Use an C<ev_async> watcher to wake up C<ev_loop> when you want it
		935	to take note of any changes you made.
		936
		937	In theory, threads executing C<ev_loop> will be async-cancel safe between
		938	invocations of C<release> and C<acquire>.
		939
		940	See also the locking example in the C<THREADS> section later in this
		941	document.
		942
		943	=item ev_set_userdata (loop, void *data)
		944
		945	=item ev_userdata (loop)
		946
		947	Set and retrieve a single C<void *> associated with a loop. When
		948	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		949	C<0.>
		950
		951	These two functions can be used to associate arbitrary data with a loop,
		952	and are intended solely for the C<invoke_pending_cb>, C<release> and
		953	C<acquire> callbacks described above, but of course can be (ab-)used for
		954	any other purpose as well.
714		955
715	=item ev_loop_verify (loop)	956	=item ev_loop_verify (loop)
716		957
717	This function only does something when C<EV_VERIFY> support has been	958	This function only does something when C<EV_VERIFY> support has been
718	compiled in. It tries to go through all internal structures and checks	959	compiled in, which is the default for non-minimal builds. It tries to go
719	them for validity. If anything is found to be inconsistent, it will print	960	through all internal structures and checks them for validity. If anything
720	an error message to standard error and call C<abort ()>.	961	is found to be inconsistent, it will print an error message to standard
		962	error and call C<abort ()>.
721		963
722	This can be used to catch bugs inside libev itself: under normal	964	This can be used to catch bugs inside libev itself: under normal
723	circumstances, this function will never abort as of course libev keeps its	965	circumstances, this function will never abort as of course libev keeps its
724	data structures consistent.	966	data structures consistent.
725		967
726	=back	968	=back
727		969
728		970
729	=head1 ANATOMY OF A WATCHER	971	=head1 ANATOMY OF A WATCHER
730		972
		973	In the following description, uppercase C<TYPE> in names stands for the
		974	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		975	watchers and C<ev_io_start> for I/O watchers.
		976
731	A watcher is a structure that you create and register to record your	977	A watcher is a structure that you create and register to record your
732	interest in some event. For instance, if you want to wait for STDIN to	978	interest in some event. For instance, if you want to wait for STDIN to
733	become readable, you would create an C<ev_io> watcher for that:	979	become readable, you would create an C<ev_io> watcher for that:
734		980
735	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	981	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
736	{	982	{
737	ev_io_stop (w);	983	ev_io_stop (w);
738	ev_unloop (loop, EVUNLOOP_ALL);	984	ev_unloop (loop, EVUNLOOP_ALL);
739	}	985	}
740		986
741	struct ev_loop *loop = ev_default_loop (0);	987	struct ev_loop *loop = ev_default_loop (0);
		988
742	struct ev_io stdin_watcher;	989	ev_io stdin_watcher;
		990
743	ev_init (&stdin_watcher, my_cb);	991	ev_init (&stdin_watcher, my_cb);
744	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	992	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
745	ev_io_start (loop, &stdin_watcher);	993	ev_io_start (loop, &stdin_watcher);
		994
746	ev_loop (loop, 0);	995	ev_loop (loop, 0);
747		996
748	As you can see, you are responsible for allocating the memory for your	997	As you can see, you are responsible for allocating the memory for your
749	watcher structures (and it is usually a bad idea to do this on the stack,	998	watcher structures (and it is I<usually> a bad idea to do this on the
750	although this can sometimes be quite valid).	999	stack).
		1000
		1001	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1002	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
751		1003
752	Each watcher structure must be initialised by a call to C<ev_init	1004	Each watcher structure must be initialised by a call to C<ev_init
753	(watcher *, callback)>, which expects a callback to be provided. This	1005	(watcher *, callback)>, which expects a callback to be provided. This
754	callback gets invoked each time the event occurs (or, in the case of I/O	1006	callback gets invoked each time the event occurs (or, in the case of I/O
755	watchers, each time the event loop detects that the file descriptor given	1007	watchers, each time the event loop detects that the file descriptor given
756	is readable and/or writable).	1008	is readable and/or writable).
757		1009
758	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1010	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
759	with arguments specific to this watcher type. There is also a macro	1011	macro to configure it, with arguments specific to the watcher type. There
760	to combine initialisation and setting in one call: C<< ev_<type>_init	1012	is also a macro to combine initialisation and setting in one call: C<<
761	(watcher *, callback, ...) >>.	1013	ev_TYPE_init (watcher *, callback, ...) >>.
762		1014
763	To make the watcher actually watch out for events, you have to start it	1015	To make the watcher actually watch out for events, you have to start it
764	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1016	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
765	*) >>), and you can stop watching for events at any time by calling the	1017	*) >>), and you can stop watching for events at any time by calling the
766	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1018	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
767		1019
768	As long as your watcher is active (has been started but not stopped) you	1020	As long as your watcher is active (has been started but not stopped) you
769	must not touch the values stored in it. Most specifically you must never	1021	must not touch the values stored in it. Most specifically you must never
770	reinitialise it or call its C<set> macro.	1022	reinitialise it or call its C<ev_TYPE_set> macro.
771		1023
772	Each and every callback receives the event loop pointer as first, the	1024	Each and every callback receives the event loop pointer as first, the
773	registered watcher structure as second, and a bitset of received events as	1025	registered watcher structure as second, and a bitset of received events as
774	third argument.	1026	third argument.
775		1027
…		…
784	=item C<EV_WRITE>	1036	=item C<EV_WRITE>
785		1037
786	The file descriptor in the C<ev_io> watcher has become readable and/or	1038	The file descriptor in the C<ev_io> watcher has become readable and/or
787	writable.	1039	writable.
788		1040
789	=item C<EV_TIMEOUT>	1041	=item C<EV_TIMER>
790		1042
791	The C<ev_timer> watcher has timed out.	1043	The C<ev_timer> watcher has timed out.
792		1044
793	=item C<EV_PERIODIC>	1045	=item C<EV_PERIODIC>
794		1046
…		…
833		1085
834	=item C<EV_ASYNC>	1086	=item C<EV_ASYNC>
835		1087
836	The given async watcher has been asynchronously notified (see C<ev_async>).	1088	The given async watcher has been asynchronously notified (see C<ev_async>).
837		1089
		1090	=item C<EV_CUSTOM>
		1091
		1092	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1093	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1094
838	=item C<EV_ERROR>	1095	=item C<EV_ERROR>
839		1096
840	An unspecified error has occurred, the watcher has been stopped. This might	1097	An unspecified error has occurred, the watcher has been stopped. This might
841	happen because the watcher could not be properly started because libev	1098	happen because the watcher could not be properly started because libev
842	ran out of memory, a file descriptor was found to be closed or any other	1099	ran out of memory, a file descriptor was found to be closed or any other
		1100	problem. Libev considers these application bugs.
		1101
843	problem. You best act on it by reporting the problem and somehow coping	1102	You best act on it by reporting the problem and somehow coping with the
844	with the watcher being stopped.	1103	watcher being stopped. Note that well-written programs should not receive
		1104	an error ever, so when your watcher receives it, this usually indicates a
		1105	bug in your program.
845		1106
846	Libev will usually signal a few "dummy" events together with an error,	1107	Libev will usually signal a few "dummy" events together with an error, for
847	for example it might indicate that a fd is readable or writable, and if	1108	example it might indicate that a fd is readable or writable, and if your
848	your callbacks is well-written it can just attempt the operation and cope	1109	callbacks is well-written it can just attempt the operation and cope with
849	with the error from read() or write(). This will not work in multi-threaded	1110	the error from read() or write(). This will not work in multi-threaded
850	programs, though, so beware.	1111	programs, though, as the fd could already be closed and reused for another
		1112	thing, so beware.
851		1113
852	=back	1114	=back
853		1115
854	=head2 GENERIC WATCHER FUNCTIONS	1116	=head2 GENERIC WATCHER FUNCTIONS
855
856	In the following description, C<TYPE> stands for the watcher type,
857	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
858		1117
859	=over 4	1118	=over 4
860		1119
861	=item C<ev_init> (ev_TYPE *watcher, callback)	1120	=item C<ev_init> (ev_TYPE *watcher, callback)
862		1121
…		…
868	which rolls both calls into one.	1127	which rolls both calls into one.
869		1128
870	You can reinitialise a watcher at any time as long as it has been stopped	1129	You can reinitialise a watcher at any time as long as it has been stopped
871	(or never started) and there are no pending events outstanding.	1130	(or never started) and there are no pending events outstanding.
872		1131
873	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1132	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
874	int revents)>.	1133	int revents)>.
875		1134
		1135	Example: Initialise an C<ev_io> watcher in two steps.
		1136
		1137	ev_io w;
		1138	ev_init (&w, my_cb);
		1139	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1140
876	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1141	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
877		1142
878	This macro initialises the type-specific parts of a watcher. You need to	1143	This macro initialises the type-specific parts of a watcher. You need to
879	call C<ev_init> at least once before you call this macro, but you can	1144	call C<ev_init> at least once before you call this macro, but you can
880	call C<ev_TYPE_set> any number of times. You must not, however, call this	1145	call C<ev_TYPE_set> any number of times. You must not, however, call this
881	macro on a watcher that is active (it can be pending, however, which is a	1146	macro on a watcher that is active (it can be pending, however, which is a
882	difference to the C<ev_init> macro).	1147	difference to the C<ev_init> macro).
883		1148
884	Although some watcher types do not have type-specific arguments	1149	Although some watcher types do not have type-specific arguments
885	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1150	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
886		1151
		1152	See C<ev_init>, above, for an example.
		1153
887	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1154	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
888		1155
889	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1156	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
890	calls into a single call. This is the most convenient method to initialise	1157	calls into a single call. This is the most convenient method to initialise
891	a watcher. The same limitations apply, of course.	1158	a watcher. The same limitations apply, of course.
892		1159
		1160	Example: Initialise and set an C<ev_io> watcher in one step.
		1161
		1162	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1163
893	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1164	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
894		1165
895	Starts (activates) the given watcher. Only active watchers will receive	1166	Starts (activates) the given watcher. Only active watchers will receive
896	events. If the watcher is already active nothing will happen.	1167	events. If the watcher is already active nothing will happen.
897		1168
		1169	Example: Start the C<ev_io> watcher that is being abused as example in this
		1170	whole section.
		1171
		1172	ev_io_start (EV_DEFAULT_UC, &w);
		1173
898	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1174	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
899		1175
900	Stops the given watcher again (if active) and clears the pending	1176	Stops the given watcher if active, and clears the pending status (whether
		1177	the watcher was active or not).
		1178
901	status. It is possible that stopped watchers are pending (for example,	1179	It is possible that stopped watchers are pending - for example,
902	non-repeating timers are being stopped when they become pending), but	1180	non-repeating timers are being stopped when they become pending - but
903	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1181	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
904	you want to free or reuse the memory used by the watcher it is therefore a	1182	pending. If you want to free or reuse the memory used by the watcher it is
905	good idea to always call its C<ev_TYPE_stop> function.	1183	therefore a good idea to always call its C<ev_TYPE_stop> function.
906		1184
907	=item bool ev_is_active (ev_TYPE *watcher)	1185	=item bool ev_is_active (ev_TYPE *watcher)
908		1186
909	Returns a true value iff the watcher is active (i.e. it has been started	1187	Returns a true value iff the watcher is active (i.e. it has been started
910	and not yet been stopped). As long as a watcher is active you must not modify	1188	and not yet been stopped). As long as a watcher is active you must not modify
…		…
926	=item ev_cb_set (ev_TYPE *watcher, callback)	1204	=item ev_cb_set (ev_TYPE *watcher, callback)
927		1205
928	Change the callback. You can change the callback at virtually any time	1206	Change the callback. You can change the callback at virtually any time
929	(modulo threads).	1207	(modulo threads).
930		1208
931	=item ev_set_priority (ev_TYPE *watcher, priority)	1209	=item ev_set_priority (ev_TYPE *watcher, int priority)
932		1210
933	=item int ev_priority (ev_TYPE *watcher)	1211	=item int ev_priority (ev_TYPE *watcher)
934		1212
935	Set and query the priority of the watcher. The priority is a small	1213	Set and query the priority of the watcher. The priority is a small
936	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1214	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
937	(default: C<-2>). Pending watchers with higher priority will be invoked	1215	(default: C<-2>). Pending watchers with higher priority will be invoked
938	before watchers with lower priority, but priority will not keep watchers	1216	before watchers with lower priority, but priority will not keep watchers
939	from being executed (except for C<ev_idle> watchers).	1217	from being executed (except for C<ev_idle> watchers).
940		1218
941	This means that priorities are I<only> used for ordering callback
942	invocation after new events have been received. This is useful, for
943	example, to reduce latency after idling, or more often, to bind two
944	watchers on the same event and make sure one is called first.
945
946	If you need to suppress invocation when higher priority events are pending	1219	If you need to suppress invocation when higher priority events are pending
947	you need to look at C<ev_idle> watchers, which provide this functionality.	1220	you need to look at C<ev_idle> watchers, which provide this functionality.
948		1221
949	You I<must not> change the priority of a watcher as long as it is active or	1222	You I<must not> change the priority of a watcher as long as it is active or
950	pending.	1223	pending.
951		1224
		1225	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1226	fine, as long as you do not mind that the priority value you query might
		1227	or might not have been clamped to the valid range.
		1228
952	The default priority used by watchers when no priority has been set is	1229	The default priority used by watchers when no priority has been set is
953	always C<0>, which is supposed to not be too high and not be too low :).	1230	always C<0>, which is supposed to not be too high and not be too low :).
954		1231
955	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1232	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
956	fine, as long as you do not mind that the priority value you query might	1233	priorities.
957	or might not have been adjusted to be within valid range.
958		1234
959	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1235	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
960		1236
961	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1237	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
962	C<loop> nor C<revents> need to be valid as long as the watcher callback	1238	C<loop> nor C<revents> need to be valid as long as the watcher callback
963	can deal with that fact.	1239	can deal with that fact, as both are simply passed through to the
		1240	callback.
964		1241
965	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1242	=item int ev_clear_pending (loop, ev_TYPE *watcher)
966		1243
967	If the watcher is pending, this function returns clears its pending status	1244	If the watcher is pending, this function clears its pending status and
968	and returns its C<revents> bitset (as if its callback was invoked). If the	1245	returns its C<revents> bitset (as if its callback was invoked). If the
969	watcher isn't pending it does nothing and returns C<0>.	1246	watcher isn't pending it does nothing and returns C<0>.
970		1247
		1248	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1249	callback to be invoked, which can be accomplished with this function.
		1250
		1251	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1252
		1253	Feeds the given event set into the event loop, as if the specified event
		1254	had happened for the specified watcher (which must be a pointer to an
		1255	initialised but not necessarily started event watcher). Obviously you must
		1256	not free the watcher as long as it has pending events.
		1257
		1258	Stopping the watcher, letting libev invoke it, or calling
		1259	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1260	not started in the first place.
		1261
		1262	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1263	functions that do not need a watcher.
		1264
971	=back	1265	=back
972		1266
973		1267
974	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1268	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
975		1269
976	Each watcher has, by default, a member C<void *data> that you can change	1270	Each watcher has, by default, a member C<void *data> that you can change
977	and read at any time, libev will completely ignore it. This can be used	1271	and read at any time: libev will completely ignore it. This can be used
978	to associate arbitrary data with your watcher. If you need more data and	1272	to associate arbitrary data with your watcher. If you need more data and
979	don't want to allocate memory and store a pointer to it in that data	1273	don't want to allocate memory and store a pointer to it in that data
980	member, you can also "subclass" the watcher type and provide your own	1274	member, you can also "subclass" the watcher type and provide your own
981	data:	1275	data:
982		1276
983	struct my_io	1277	struct my_io
984	{	1278	{
985	struct ev_io io;	1279	ev_io io;
986	int otherfd;	1280	int otherfd;
987	void *somedata;	1281	void *somedata;
988	struct whatever *mostinteresting;	1282	struct whatever *mostinteresting;
989	}	1283	};
		1284
		1285	...
		1286	struct my_io w;
		1287	ev_io_init (&w.io, my_cb, fd, EV_READ);
990		1288
991	And since your callback will be called with a pointer to the watcher, you	1289	And since your callback will be called with a pointer to the watcher, you
992	can cast it back to your own type:	1290	can cast it back to your own type:
993		1291
994	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1292	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
995	{	1293	{
996	struct my_io *w = (struct my_io *)w_;	1294	struct my_io *w = (struct my_io *)w_;
997	...	1295	...
998	}	1296	}
999		1297
1000	More interesting and less C-conformant ways of casting your callback type	1298	More interesting and less C-conformant ways of casting your callback type
1001	instead have been omitted.	1299	instead have been omitted.
1002		1300
1003	Another common scenario is having some data structure with multiple	1301	Another common scenario is to use some data structure with multiple
1004	watchers:	1302	embedded watchers:
1005		1303
1006	struct my_biggy	1304	struct my_biggy
1007	{	1305	{
1008	int some_data;	1306	int some_data;
1009	ev_timer t1;	1307	ev_timer t1;
1010	ev_timer t2;	1308	ev_timer t2;
1011	}	1309	}
1012		1310
1013	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1311	In this case getting the pointer to C<my_biggy> is a bit more
1014	you need to use C<offsetof>:	1312	complicated: Either you store the address of your C<my_biggy> struct
		1313	in the C<data> member of the watcher (for woozies), or you need to use
		1314	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1315	programmers):
1015		1316
1016	#include <stddef.h>	1317	#include <stddef.h>
1017		1318
1018	static void	1319	static void
1019	t1_cb (EV_P_ struct ev_timer *w, int revents)	1320	t1_cb (EV_P_ ev_timer *w, int revents)
1020	{	1321	{
1021	struct my_biggy big = (struct my_biggy *	1322	struct my_biggy big = (struct my_biggy *)
1022	(((char *)w) - offsetof (struct my_biggy, t1));	1323	(((char *)w) - offsetof (struct my_biggy, t1));
1023	}	1324	}
1024		1325
1025	static void	1326	static void
1026	t2_cb (EV_P_ struct ev_timer *w, int revents)	1327	t2_cb (EV_P_ ev_timer *w, int revents)
1027	{	1328	{
1028	struct my_biggy big = (struct my_biggy *	1329	struct my_biggy big = (struct my_biggy *)
1029	(((char *)w) - offsetof (struct my_biggy, t2));	1330	(((char *)w) - offsetof (struct my_biggy, t2));
1030	}	1331	}
		1332
		1333	=head2 WATCHER PRIORITY MODELS
		1334
		1335	Many event loops support I<watcher priorities>, which are usually small
		1336	integers that influence the ordering of event callback invocation
		1337	between watchers in some way, all else being equal.
		1338
		1339	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1340	description for the more technical details such as the actual priority
		1341	range.
		1342
		1343	There are two common ways how these these priorities are being interpreted
		1344	by event loops:
		1345
		1346	In the more common lock-out model, higher priorities "lock out" invocation
		1347	of lower priority watchers, which means as long as higher priority
		1348	watchers receive events, lower priority watchers are not being invoked.
		1349
		1350	The less common only-for-ordering model uses priorities solely to order
		1351	callback invocation within a single event loop iteration: Higher priority
		1352	watchers are invoked before lower priority ones, but they all get invoked
		1353	before polling for new events.
		1354
		1355	Libev uses the second (only-for-ordering) model for all its watchers
		1356	except for idle watchers (which use the lock-out model).
		1357
		1358	The rationale behind this is that implementing the lock-out model for
		1359	watchers is not well supported by most kernel interfaces, and most event
		1360	libraries will just poll for the same events again and again as long as
		1361	their callbacks have not been executed, which is very inefficient in the
		1362	common case of one high-priority watcher locking out a mass of lower
		1363	priority ones.
		1364
		1365	Static (ordering) priorities are most useful when you have two or more
		1366	watchers handling the same resource: a typical usage example is having an
		1367	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1368	timeouts. Under load, data might be received while the program handles
		1369	other jobs, but since timers normally get invoked first, the timeout
		1370	handler will be executed before checking for data. In that case, giving
		1371	the timer a lower priority than the I/O watcher ensures that I/O will be
		1372	handled first even under adverse conditions (which is usually, but not
		1373	always, what you want).
		1374
		1375	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1376	will only be executed when no same or higher priority watchers have
		1377	received events, they can be used to implement the "lock-out" model when
		1378	required.
		1379
		1380	For example, to emulate how many other event libraries handle priorities,
		1381	you can associate an C<ev_idle> watcher to each such watcher, and in
		1382	the normal watcher callback, you just start the idle watcher. The real
		1383	processing is done in the idle watcher callback. This causes libev to
		1384	continously poll and process kernel event data for the watcher, but when
		1385	the lock-out case is known to be rare (which in turn is rare :), this is
		1386	workable.
		1387
		1388	Usually, however, the lock-out model implemented that way will perform
		1389	miserably under the type of load it was designed to handle. In that case,
		1390	it might be preferable to stop the real watcher before starting the
		1391	idle watcher, so the kernel will not have to process the event in case
		1392	the actual processing will be delayed for considerable time.
		1393
		1394	Here is an example of an I/O watcher that should run at a strictly lower
		1395	priority than the default, and which should only process data when no
		1396	other events are pending:
		1397
		1398	ev_idle idle; // actual processing watcher
		1399	ev_io io; // actual event watcher
		1400
		1401	static void
		1402	io_cb (EV_P_ ev_io *w, int revents)
		1403	{
		1404	// stop the I/O watcher, we received the event, but
		1405	// are not yet ready to handle it.
		1406	ev_io_stop (EV_A_ w);
		1407
		1408	// start the idle watcher to ahndle the actual event.
		1409	// it will not be executed as long as other watchers
		1410	// with the default priority are receiving events.
		1411	ev_idle_start (EV_A_ &idle);
		1412	}
		1413
		1414	static void
		1415	idle_cb (EV_P_ ev_idle *w, int revents)
		1416	{
		1417	// actual processing
		1418	read (STDIN_FILENO, ...);
		1419
		1420	// have to start the I/O watcher again, as
		1421	// we have handled the event
		1422	ev_io_start (EV_P_ &io);
		1423	}
		1424
		1425	// initialisation
		1426	ev_idle_init (&idle, idle_cb);
		1427	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1428	ev_io_start (EV_DEFAULT_ &io);
		1429
		1430	In the "real" world, it might also be beneficial to start a timer, so that
		1431	low-priority connections can not be locked out forever under load. This
		1432	enables your program to keep a lower latency for important connections
		1433	during short periods of high load, while not completely locking out less
		1434	important ones.
1031		1435
1032		1436
1033	=head1 WATCHER TYPES	1437	=head1 WATCHER TYPES
1034		1438
1035	This section describes each watcher in detail, but will not repeat	1439	This section describes each watcher in detail, but will not repeat
…		…
1059	In general you can register as many read and/or write event watchers per	1463	In general you can register as many read and/or write event watchers per
1060	fd as you want (as long as you don't confuse yourself). Setting all file	1464	fd as you want (as long as you don't confuse yourself). Setting all file
1061	descriptors to non-blocking mode is also usually a good idea (but not	1465	descriptors to non-blocking mode is also usually a good idea (but not
1062	required if you know what you are doing).	1466	required if you know what you are doing).
1063		1467
1064	If you must do this, then force the use of a known-to-be-good backend	1468	If you cannot use non-blocking mode, then force the use of a
1065	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1469	known-to-be-good backend (at the time of this writing, this includes only
1066	C<EVBACKEND_POLL>).	1470	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1471	descriptors for which non-blocking operation makes no sense (such as
		1472	files) - libev doesn't guarentee any specific behaviour in that case.
1067		1473
1068	Another thing you have to watch out for is that it is quite easy to	1474	Another thing you have to watch out for is that it is quite easy to
1069	receive "spurious" readiness notifications, that is your callback might	1475	receive "spurious" readiness notifications, that is your callback might
1070	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1476	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1071	because there is no data. Not only are some backends known to create a	1477	because there is no data. Not only are some backends known to create a
1072	lot of those (for example Solaris ports), it is very easy to get into	1478	lot of those (for example Solaris ports), it is very easy to get into
1073	this situation even with a relatively standard program structure. Thus	1479	this situation even with a relatively standard program structure. Thus
1074	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1480	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1075	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1481	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1076		1482
1077	If you cannot run the fd in non-blocking mode (for example you should not	1483	If you cannot run the fd in non-blocking mode (for example you should
1078	play around with an Xlib connection), then you have to separately re-test	1484	not play around with an Xlib connection), then you have to separately
1079	whether a file descriptor is really ready with a known-to-be good interface	1485	re-test whether a file descriptor is really ready with a known-to-be good
1080	such as poll (fortunately in our Xlib example, Xlib already does this on	1486	interface such as poll (fortunately in our Xlib example, Xlib already
1081	its own, so its quite safe to use).	1487	does this on its own, so its quite safe to use). Some people additionally
		1488	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1489	indefinitely.
		1490
		1491	But really, best use non-blocking mode.
1082		1492
1083	=head3 The special problem of disappearing file descriptors	1493	=head3 The special problem of disappearing file descriptors
1084		1494
1085	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1495	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1086	descriptor (either by calling C<close> explicitly or by any other means,	1496	descriptor (either due to calling C<close> explicitly or any other means,
1087	such as C<dup>). The reason is that you register interest in some file	1497	such as C<dup2>). The reason is that you register interest in some file
1088	descriptor, but when it goes away, the operating system will silently drop	1498	descriptor, but when it goes away, the operating system will silently drop
1089	this interest. If another file descriptor with the same number then is	1499	this interest. If another file descriptor with the same number then is
1090	registered with libev, there is no efficient way to see that this is, in	1500	registered with libev, there is no efficient way to see that this is, in
1091	fact, a different file descriptor.	1501	fact, a different file descriptor.
1092		1502
…		…
1123	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1533	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1124	C<EVBACKEND_POLL>.	1534	C<EVBACKEND_POLL>.
1125		1535
1126	=head3 The special problem of SIGPIPE	1536	=head3 The special problem of SIGPIPE
1127		1537
1128	While not really specific to libev, it is easy to forget about SIGPIPE:	1538	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1129	when reading from a pipe whose other end has been closed, your program	1539	when writing to a pipe whose other end has been closed, your program gets
1130	gets send a SIGPIPE, which, by default, aborts your program. For most	1540	sent a SIGPIPE, which, by default, aborts your program. For most programs
1131	programs this is sensible behaviour, for daemons, this is usually	1541	this is sensible behaviour, for daemons, this is usually undesirable.
1132	undesirable.
1133		1542
1134	So when you encounter spurious, unexplained daemon exits, make sure you	1543	So when you encounter spurious, unexplained daemon exits, make sure you
1135	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1544	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1136	somewhere, as that would have given you a big clue).	1545	somewhere, as that would have given you a big clue).
1137		1546
		1547	=head3 The special problem of accept()ing when you can't
		1548
		1549	Many implementations of the POSIX C<accept> function (for example,
		1550	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1551	connection from the pending queue in all error cases.
		1552
		1553	For example, larger servers often run out of file descriptors (because
		1554	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1555	rejecting the connection, leading to libev signalling readiness on
		1556	the next iteration again (the connection still exists after all), and
		1557	typically causing the program to loop at 100% CPU usage.
		1558
		1559	Unfortunately, the set of errors that cause this issue differs between
		1560	operating systems, there is usually little the app can do to remedy the
		1561	situation, and no known thread-safe method of removing the connection to
		1562	cope with overload is known (to me).
		1563
		1564	One of the easiest ways to handle this situation is to just ignore it
		1565	- when the program encounters an overload, it will just loop until the
		1566	situation is over. While this is a form of busy waiting, no OS offers an
		1567	event-based way to handle this situation, so it's the best one can do.
		1568
		1569	A better way to handle the situation is to log any errors other than
		1570	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1571	messages, and continue as usual, which at least gives the user an idea of
		1572	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1573	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1574	usage.
		1575
		1576	If your program is single-threaded, then you could also keep a dummy file
		1577	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1578	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1579	close that fd, and create a new dummy fd. This will gracefully refuse
		1580	clients under typical overload conditions.
		1581
		1582	The last way to handle it is to simply log the error and C<exit>, as
		1583	is often done with C<malloc> failures, but this results in an easy
		1584	opportunity for a DoS attack.
1138		1585
1139	=head3 Watcher-Specific Functions	1586	=head3 Watcher-Specific Functions
1140		1587
1141	=over 4	1588	=over 4
1142		1589
1143	=item ev_io_init (ev_io *, callback, int fd, int events)	1590	=item ev_io_init (ev_io *, callback, int fd, int events)
1144		1591
1145	=item ev_io_set (ev_io *, int fd, int events)	1592	=item ev_io_set (ev_io *, int fd, int events)
1146		1593
1147	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1594	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1148	receive events for and events is either C<EV_READ>, C<EV_WRITE> or	1595	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1149	C<EV_READ | EV_WRITE> to receive the given events.	1596	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1150		1597
1151	=item int fd [read-only]	1598	=item int fd [read-only]
1152		1599
1153	The file descriptor being watched.	1600	The file descriptor being watched.
1154		1601
…		…
1162		1609
1163	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1610	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1164	readable, but only once. Since it is likely line-buffered, you could	1611	readable, but only once. Since it is likely line-buffered, you could
1165	attempt to read a whole line in the callback.	1612	attempt to read a whole line in the callback.
1166		1613
1167	static void	1614	static void
1168	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1615	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1169	{	1616	{
1170	ev_io_stop (loop, w);	1617	ev_io_stop (loop, w);
1171	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1618	.. read from stdin here (or from w->fd) and handle any I/O errors
1172	}	1619	}
1173		1620
1174	...	1621	...
1175	struct ev_loop *loop = ev_default_init (0);	1622	struct ev_loop *loop = ev_default_init (0);
1176	struct ev_io stdin_readable;	1623	ev_io stdin_readable;
1177	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1624	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1178	ev_io_start (loop, &stdin_readable);	1625	ev_io_start (loop, &stdin_readable);
1179	ev_loop (loop, 0);	1626	ev_loop (loop, 0);
1180		1627
1181		1628
1182	=head2 C<ev_timer> - relative and optionally repeating timeouts	1629	=head2 C<ev_timer> - relative and optionally repeating timeouts
1183		1630
1184	Timer watchers are simple relative timers that generate an event after a	1631	Timer watchers are simple relative timers that generate an event after a
1185	given time, and optionally repeating in regular intervals after that.	1632	given time, and optionally repeating in regular intervals after that.
1186		1633
1187	The timers are based on real time, that is, if you register an event that	1634	The timers are based on real time, that is, if you register an event that
1188	times out after an hour and you reset your system clock to January last	1635	times out after an hour and you reset your system clock to January last
1189	year, it will still time out after (roughly) and hour. "Roughly" because	1636	year, it will still time out after (roughly) one hour. "Roughly" because
1190	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1637	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1191	monotonic clock option helps a lot here).	1638	monotonic clock option helps a lot here).
		1639
		1640	The callback is guaranteed to be invoked only I<after> its timeout has
		1641	passed (not I<at>, so on systems with very low-resolution clocks this
		1642	might introduce a small delay). If multiple timers become ready during the
		1643	same loop iteration then the ones with earlier time-out values are invoked
		1644	before ones of the same priority with later time-out values (but this is
		1645	no longer true when a callback calls C<ev_loop> recursively).
		1646
		1647	=head3 Be smart about timeouts
		1648
		1649	Many real-world problems involve some kind of timeout, usually for error
		1650	recovery. A typical example is an HTTP request - if the other side hangs,
		1651	you want to raise some error after a while.
		1652
		1653	What follows are some ways to handle this problem, from obvious and
		1654	inefficient to smart and efficient.
		1655
		1656	In the following, a 60 second activity timeout is assumed - a timeout that
		1657	gets reset to 60 seconds each time there is activity (e.g. each time some
		1658	data or other life sign was received).
		1659
		1660	=over 4
		1661
		1662	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1663
		1664	This is the most obvious, but not the most simple way: In the beginning,
		1665	start the watcher:
		1666
		1667	ev_timer_init (timer, callback, 60., 0.);
		1668	ev_timer_start (loop, timer);
		1669
		1670	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1671	and start it again:
		1672
		1673	ev_timer_stop (loop, timer);
		1674	ev_timer_set (timer, 60., 0.);
		1675	ev_timer_start (loop, timer);
		1676
		1677	This is relatively simple to implement, but means that each time there is
		1678	some activity, libev will first have to remove the timer from its internal
		1679	data structure and then add it again. Libev tries to be fast, but it's
		1680	still not a constant-time operation.
		1681
		1682	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1683
		1684	This is the easiest way, and involves using C<ev_timer_again> instead of
		1685	C<ev_timer_start>.
		1686
		1687	To implement this, configure an C<ev_timer> with a C<repeat> value
		1688	of C<60> and then call C<ev_timer_again> at start and each time you
		1689	successfully read or write some data. If you go into an idle state where
		1690	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1691	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1692
		1693	That means you can ignore both the C<ev_timer_start> function and the
		1694	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1695	member and C<ev_timer_again>.
		1696
		1697	At start:
		1698
		1699	ev_init (timer, callback);
		1700	timer->repeat = 60.;
		1701	ev_timer_again (loop, timer);
		1702
		1703	Each time there is some activity:
		1704
		1705	ev_timer_again (loop, timer);
		1706
		1707	It is even possible to change the time-out on the fly, regardless of
		1708	whether the watcher is active or not:
		1709
		1710	timer->repeat = 30.;
		1711	ev_timer_again (loop, timer);
		1712
		1713	This is slightly more efficient then stopping/starting the timer each time
		1714	you want to modify its timeout value, as libev does not have to completely
		1715	remove and re-insert the timer from/into its internal data structure.
		1716
		1717	It is, however, even simpler than the "obvious" way to do it.
		1718
		1719	=item 3. Let the timer time out, but then re-arm it as required.
		1720
		1721	This method is more tricky, but usually most efficient: Most timeouts are
		1722	relatively long compared to the intervals between other activity - in
		1723	our example, within 60 seconds, there are usually many I/O events with
		1724	associated activity resets.
		1725
		1726	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1727	but remember the time of last activity, and check for a real timeout only
		1728	within the callback:
		1729
		1730	ev_tstamp last_activity; // time of last activity
		1731
		1732	static void
		1733	callback (EV_P_ ev_timer *w, int revents)
		1734	{
		1735	ev_tstamp now = ev_now (EV_A);
		1736	ev_tstamp timeout = last_activity + 60.;
		1737
		1738	// if last_activity + 60. is older than now, we did time out
		1739	if (timeout < now)
		1740	{
		1741	// timeout occured, take action
		1742	}
		1743	else
		1744	{
		1745	// callback was invoked, but there was some activity, re-arm
		1746	// the watcher to fire in last_activity + 60, which is
		1747	// guaranteed to be in the future, so "again" is positive:
		1748	w->repeat = timeout - now;
		1749	ev_timer_again (EV_A_ w);
		1750	}
		1751	}
		1752
		1753	To summarise the callback: first calculate the real timeout (defined
		1754	as "60 seconds after the last activity"), then check if that time has
		1755	been reached, which means something I<did>, in fact, time out. Otherwise
		1756	the callback was invoked too early (C<timeout> is in the future), so
		1757	re-schedule the timer to fire at that future time, to see if maybe we have
		1758	a timeout then.
		1759
		1760	Note how C<ev_timer_again> is used, taking advantage of the
		1761	C<ev_timer_again> optimisation when the timer is already running.
		1762
		1763	This scheme causes more callback invocations (about one every 60 seconds
		1764	minus half the average time between activity), but virtually no calls to
		1765	libev to change the timeout.
		1766
		1767	To start the timer, simply initialise the watcher and set C<last_activity>
		1768	to the current time (meaning we just have some activity :), then call the
		1769	callback, which will "do the right thing" and start the timer:
		1770
		1771	ev_init (timer, callback);
		1772	last_activity = ev_now (loop);
		1773	callback (loop, timer, EV_TIMER);
		1774
		1775	And when there is some activity, simply store the current time in
		1776	C<last_activity>, no libev calls at all:
		1777
		1778	last_actiivty = ev_now (loop);
		1779
		1780	This technique is slightly more complex, but in most cases where the
		1781	time-out is unlikely to be triggered, much more efficient.
		1782
		1783	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1784	callback :) - just change the timeout and invoke the callback, which will
		1785	fix things for you.
		1786
		1787	=item 4. Wee, just use a double-linked list for your timeouts.
		1788
		1789	If there is not one request, but many thousands (millions...), all
		1790	employing some kind of timeout with the same timeout value, then one can
		1791	do even better:
		1792
		1793	When starting the timeout, calculate the timeout value and put the timeout
		1794	at the I<end> of the list.
		1795
		1796	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1797	the list is expected to fire (for example, using the technique #3).
		1798
		1799	When there is some activity, remove the timer from the list, recalculate
		1800	the timeout, append it to the end of the list again, and make sure to
		1801	update the C<ev_timer> if it was taken from the beginning of the list.
		1802
		1803	This way, one can manage an unlimited number of timeouts in O(1) time for
		1804	starting, stopping and updating the timers, at the expense of a major
		1805	complication, and having to use a constant timeout. The constant timeout
		1806	ensures that the list stays sorted.
		1807
		1808	=back
		1809
		1810	So which method the best?
		1811
		1812	Method #2 is a simple no-brain-required solution that is adequate in most
		1813	situations. Method #3 requires a bit more thinking, but handles many cases
		1814	better, and isn't very complicated either. In most case, choosing either
		1815	one is fine, with #3 being better in typical situations.
		1816
		1817	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1818	rather complicated, but extremely efficient, something that really pays
		1819	off after the first million or so of active timers, i.e. it's usually
		1820	overkill :)
		1821
		1822	=head3 The special problem of time updates
		1823
		1824	Establishing the current time is a costly operation (it usually takes at
		1825	least two system calls): EV therefore updates its idea of the current
		1826	time only before and after C<ev_loop> collects new events, which causes a
		1827	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1828	lots of events in one iteration.
1192		1829
1193	The relative timeouts are calculated relative to the C<ev_now ()>	1830	The relative timeouts are calculated relative to the C<ev_now ()>
1194	time. This is usually the right thing as this timestamp refers to the time	1831	time. This is usually the right thing as this timestamp refers to the time
1195	of the event triggering whatever timeout you are modifying/starting. If	1832	of the event triggering whatever timeout you are modifying/starting. If
1196	you suspect event processing to be delayed and you I<need> to base the timeout	1833	you suspect event processing to be delayed and you I<need> to base the
1197	on the current time, use something like this to adjust for this:	1834	timeout on the current time, use something like this to adjust for this:
1198		1835
1199	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1836	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1200		1837
1201	The callback is guaranteed to be invoked only after its timeout has passed,	1838	If the event loop is suspended for a long time, you can also force an
1202	but if multiple timers become ready during the same loop iteration then	1839	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1203	order of execution is undefined.	1840	()>.
		1841
		1842	=head3 The special problems of suspended animation
		1843
		1844	When you leave the server world it is quite customary to hit machines that
		1845	can suspend/hibernate - what happens to the clocks during such a suspend?
		1846
		1847	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1848	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1849	to run until the system is suspended, but they will not advance while the
		1850	system is suspended. That means, on resume, it will be as if the program
		1851	was frozen for a few seconds, but the suspend time will not be counted
		1852	towards C<ev_timer> when a monotonic clock source is used. The real time
		1853	clock advanced as expected, but if it is used as sole clocksource, then a
		1854	long suspend would be detected as a time jump by libev, and timers would
		1855	be adjusted accordingly.
		1856
		1857	I would not be surprised to see different behaviour in different between
		1858	operating systems, OS versions or even different hardware.
		1859
		1860	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1861	time jump in the monotonic clocks and the realtime clock. If the program
		1862	is suspended for a very long time, and monotonic clock sources are in use,
		1863	then you can expect C<ev_timer>s to expire as the full suspension time
		1864	will be counted towards the timers. When no monotonic clock source is in
		1865	use, then libev will again assume a timejump and adjust accordingly.
		1866
		1867	It might be beneficial for this latter case to call C<ev_suspend>
		1868	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1869	deterministic behaviour in this case (you can do nothing against
		1870	C<SIGSTOP>).
1204		1871
1205	=head3 Watcher-Specific Functions and Data Members	1872	=head3 Watcher-Specific Functions and Data Members
1206		1873
1207	=over 4	1874	=over 4
1208		1875
…		…
1232	If the timer is started but non-repeating, stop it (as if it timed out).	1899	If the timer is started but non-repeating, stop it (as if it timed out).
1233		1900
1234	If the timer is repeating, either start it if necessary (with the	1901	If the timer is repeating, either start it if necessary (with the
1235	C<repeat> value), or reset the running timer to the C<repeat> value.	1902	C<repeat> value), or reset the running timer to the C<repeat> value.
1236		1903
1237	This sounds a bit complicated, but here is a useful and typical	1904	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1238	example: Imagine you have a TCP connection and you want a so-called idle	1905	usage example.
1239	timeout, that is, you want to be called when there have been, say, 60
1240	seconds of inactivity on the socket. The easiest way to do this is to
1241	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1242	C<ev_timer_again> each time you successfully read or write some data. If
1243	you go into an idle state where you do not expect data to travel on the
1244	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1245	automatically restart it if need be.
1246		1906
1247	That means you can ignore the C<after> value and C<ev_timer_start>	1907	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1248	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1249		1908
1250	ev_timer_init (timer, callback, 0., 5.);	1909	Returns the remaining time until a timer fires. If the timer is active,
1251	ev_timer_again (loop, timer);	1910	then this time is relative to the current event loop time, otherwise it's
1252	...	1911	the timeout value currently configured.
1253	timer->again = 17.;
1254	ev_timer_again (loop, timer);
1255	...
1256	timer->again = 10.;
1257	ev_timer_again (loop, timer);
1258		1912
1259	This is more slightly efficient then stopping/starting the timer each time	1913	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1260	you want to modify its timeout value.	1914	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		1915	will return C<4>. When the timer expires and is restarted, it will return
		1916	roughly C<7> (likely slightly less as callback invocation takes some time,
		1917	too), and so on.
1261		1918
1262	=item ev_tstamp repeat [read-write]	1919	=item ev_tstamp repeat [read-write]
1263		1920
1264	The current C<repeat> value. Will be used each time the watcher times out	1921	The current C<repeat> value. Will be used each time the watcher times out
1265	or C<ev_timer_again> is called and determines the next timeout (if any),	1922	or C<ev_timer_again> is called, and determines the next timeout (if any),
1266	which is also when any modifications are taken into account.	1923	which is also when any modifications are taken into account.
1267		1924
1268	=back	1925	=back
1269		1926
1270	=head3 Examples	1927	=head3 Examples
1271		1928
1272	Example: Create a timer that fires after 60 seconds.	1929	Example: Create a timer that fires after 60 seconds.
1273		1930
1274	static void	1931	static void
1275	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1932	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1276	{	1933	{
1277	.. one minute over, w is actually stopped right here	1934	.. one minute over, w is actually stopped right here
1278	}	1935	}
1279		1936
1280	struct ev_timer mytimer;	1937	ev_timer mytimer;
1281	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1938	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1282	ev_timer_start (loop, &mytimer);	1939	ev_timer_start (loop, &mytimer);
1283		1940
1284	Example: Create a timeout timer that times out after 10 seconds of	1941	Example: Create a timeout timer that times out after 10 seconds of
1285	inactivity.	1942	inactivity.
1286		1943
1287	static void	1944	static void
1288	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1945	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1289	{	1946	{
1290	.. ten seconds without any activity	1947	.. ten seconds without any activity
1291	}	1948	}
1292		1949
1293	struct ev_timer mytimer;	1950	ev_timer mytimer;
1294	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1951	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1295	ev_timer_again (&mytimer); /* start timer */	1952	ev_timer_again (&mytimer); /* start timer */
1296	ev_loop (loop, 0);	1953	ev_loop (loop, 0);
1297		1954
1298	// and in some piece of code that gets executed on any "activity":	1955	// and in some piece of code that gets executed on any "activity":
1299	// reset the timeout to start ticking again at 10 seconds	1956	// reset the timeout to start ticking again at 10 seconds
1300	ev_timer_again (&mytimer);	1957	ev_timer_again (&mytimer);
1301		1958
1302		1959
1303	=head2 C<ev_periodic> - to cron or not to cron?	1960	=head2 C<ev_periodic> - to cron or not to cron?
1304		1961
1305	Periodic watchers are also timers of a kind, but they are very versatile	1962	Periodic watchers are also timers of a kind, but they are very versatile
1306	(and unfortunately a bit complex).	1963	(and unfortunately a bit complex).
1307		1964
1308	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1965	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1309	but on wall clock time (absolute time). You can tell a periodic watcher	1966	relative time, the physical time that passes) but on wall clock time
1310	to trigger after some specific point in time. For example, if you tell a	1967	(absolute time, the thing you can read on your calender or clock). The
1311	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1968	difference is that wall clock time can run faster or slower than real
1312	+ 10.>, that is, an absolute time not a delay) and then reset your system	1969	time, and time jumps are not uncommon (e.g. when you adjust your
1313	clock to January of the previous year, then it will take more than year	1970	wrist-watch).
1314	to trigger the event (unlike an C<ev_timer>, which would still trigger
1315	roughly 10 seconds later as it uses a relative timeout).
1316		1971
		1972	You can tell a periodic watcher to trigger after some specific point
		1973	in time: for example, if you tell a periodic watcher to trigger "in 10
		1974	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1975	not a delay) and then reset your system clock to January of the previous
		1976	year, then it will take a year or more to trigger the event (unlike an
		1977	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1978	it, as it uses a relative timeout).
		1979
1317	C<ev_periodic>s can also be used to implement vastly more complex timers,	1980	C<ev_periodic> watchers can also be used to implement vastly more complex
1318	such as triggering an event on each "midnight, local time", or other	1981	timers, such as triggering an event on each "midnight, local time", or
1319	complicated, rules.	1982	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1983	those cannot react to time jumps.
1320		1984
1321	As with timers, the callback is guaranteed to be invoked only when the	1985	As with timers, the callback is guaranteed to be invoked only when the
1322	time (C<at>) has passed, but if multiple periodic timers become ready	1986	point in time where it is supposed to trigger has passed. If multiple
1323	during the same loop iteration then order of execution is undefined.	1987	timers become ready during the same loop iteration then the ones with
		1988	earlier time-out values are invoked before ones with later time-out values
		1989	(but this is no longer true when a callback calls C<ev_loop> recursively).
1324		1990
1325	=head3 Watcher-Specific Functions and Data Members	1991	=head3 Watcher-Specific Functions and Data Members
1326		1992
1327	=over 4	1993	=over 4
1328		1994
1329	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1995	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1330		1996
1331	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1997	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1332		1998
1333	Lots of arguments, lets sort it out... There are basically three modes of	1999	Lots of arguments, let's sort it out... There are basically three modes of
1334	operation, and we will explain them from simplest to complex:	2000	operation, and we will explain them from simplest to most complex:
1335		2001
1336	=over 4	2002	=over 4
1337		2003
1338	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2004	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1339		2005
1340	In this configuration the watcher triggers an event after the wall clock	2006	In this configuration the watcher triggers an event after the wall clock
1341	time C<at> has passed and doesn't repeat. It will not adjust when a time	2007	time C<offset> has passed. It will not repeat and will not adjust when a
1342	jump occurs, that is, if it is to be run at January 1st 2011 then it will	2008	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1343	run when the system time reaches or surpasses this time.	2009	will be stopped and invoked when the system clock reaches or surpasses
		2010	this point in time.
1344		2011
1345	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2012	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1346		2013
1347	In this mode the watcher will always be scheduled to time out at the next	2014	In this mode the watcher will always be scheduled to time out at the next
1348	C<at + N * interval> time (for some integer N, which can also be negative)	2015	C<offset + N * interval> time (for some integer N, which can also be
1349	and then repeat, regardless of any time jumps.	2016	negative) and then repeat, regardless of any time jumps. The C<offset>
		2017	argument is merely an offset into the C<interval> periods.
1350		2018
1351	This can be used to create timers that do not drift with respect to system	2019	This can be used to create timers that do not drift with respect to the
1352	time, for example, here is a C<ev_periodic> that triggers each hour, on	2020	system clock, for example, here is an C<ev_periodic> that triggers each
1353	the hour:	2021	hour, on the hour (with respect to UTC):
1354		2022
1355	ev_periodic_set (&periodic, 0., 3600., 0);	2023	ev_periodic_set (&periodic, 0., 3600., 0);
1356		2024
1357	This doesn't mean there will always be 3600 seconds in between triggers,	2025	This doesn't mean there will always be 3600 seconds in between triggers,
1358	but only that the callback will be called when the system time shows a	2026	but only that the callback will be called when the system time shows a
1359	full hour (UTC), or more correctly, when the system time is evenly divisible	2027	full hour (UTC), or more correctly, when the system time is evenly divisible
1360	by 3600.	2028	by 3600.
1361		2029
1362	Another way to think about it (for the mathematically inclined) is that	2030	Another way to think about it (for the mathematically inclined) is that
1363	C<ev_periodic> will try to run the callback in this mode at the next possible	2031	C<ev_periodic> will try to run the callback in this mode at the next possible
1364	time where C<time = at (mod interval)>, regardless of any time jumps.	2032	time where C<time = offset (mod interval)>, regardless of any time jumps.
1365		2033
1366	For numerical stability it is preferable that the C<at> value is near	2034	For numerical stability it is preferable that the C<offset> value is near
1367	C<ev_now ()> (the current time), but there is no range requirement for	2035	C<ev_now ()> (the current time), but there is no range requirement for
1368	this value, and in fact is often specified as zero.	2036	this value, and in fact is often specified as zero.
1369		2037
1370	Note also that there is an upper limit to how often a timer can fire (CPU	2038	Note also that there is an upper limit to how often a timer can fire (CPU
1371	speed for example), so if C<interval> is very small then timing stability	2039	speed for example), so if C<interval> is very small then timing stability
1372	will of course deteriorate. Libev itself tries to be exact to be about one	2040	will of course deteriorate. Libev itself tries to be exact to be about one
1373	millisecond (if the OS supports it and the machine is fast enough).	2041	millisecond (if the OS supports it and the machine is fast enough).
1374		2042
1375	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2043	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1376		2044
1377	In this mode the values for C<interval> and C<at> are both being	2045	In this mode the values for C<interval> and C<offset> are both being
1378	ignored. Instead, each time the periodic watcher gets scheduled, the	2046	ignored. Instead, each time the periodic watcher gets scheduled, the
1379	reschedule callback will be called with the watcher as first, and the	2047	reschedule callback will be called with the watcher as first, and the
1380	current time as second argument.	2048	current time as second argument.
1381		2049
1382	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2050	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1383	ever, or make ANY event loop modifications whatsoever>.	2051	or make ANY other event loop modifications whatsoever, unless explicitly
		2052	allowed by documentation here>.
1384		2053
1385	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2054	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1386	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2055	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1387	only event loop modification you are allowed to do).	2056	only event loop modification you are allowed to do).
1388		2057
1389	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2058	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1390	*w, ev_tstamp now)>, e.g.:	2059	*w, ev_tstamp now)>, e.g.:
1391		2060
		2061	static ev_tstamp
1392	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2062	my_rescheduler (ev_periodic *w, ev_tstamp now)
1393	{	2063	{
1394	return now + 60.;	2064	return now + 60.;
1395	}	2065	}
1396		2066
1397	It must return the next time to trigger, based on the passed time value	2067	It must return the next time to trigger, based on the passed time value
…		…
1417	a different time than the last time it was called (e.g. in a crond like	2087	a different time than the last time it was called (e.g. in a crond like
1418	program when the crontabs have changed).	2088	program when the crontabs have changed).
1419		2089
1420	=item ev_tstamp ev_periodic_at (ev_periodic *)	2090	=item ev_tstamp ev_periodic_at (ev_periodic *)
1421		2091
1422	When active, returns the absolute time that the watcher is supposed to	2092	When active, returns the absolute time that the watcher is supposed
1423	trigger next.	2093	to trigger next. This is not the same as the C<offset> argument to
		2094	C<ev_periodic_set>, but indeed works even in interval and manual
		2095	rescheduling modes.
1424		2096
1425	=item ev_tstamp offset [read-write]	2097	=item ev_tstamp offset [read-write]
1426		2098
1427	When repeating, this contains the offset value, otherwise this is the	2099	When repeating, this contains the offset value, otherwise this is the
1428	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2100	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2101	although libev might modify this value for better numerical stability).
1429		2102
1430	Can be modified any time, but changes only take effect when the periodic	2103	Can be modified any time, but changes only take effect when the periodic
1431	timer fires or C<ev_periodic_again> is being called.	2104	timer fires or C<ev_periodic_again> is being called.
1432		2105
1433	=item ev_tstamp interval [read-write]	2106	=item ev_tstamp interval [read-write]
1434		2107
1435	The current interval value. Can be modified any time, but changes only	2108	The current interval value. Can be modified any time, but changes only
1436	take effect when the periodic timer fires or C<ev_periodic_again> is being	2109	take effect when the periodic timer fires or C<ev_periodic_again> is being
1437	called.	2110	called.
1438		2111
1439	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2112	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1440		2113
1441	The current reschedule callback, or C<0>, if this functionality is	2114	The current reschedule callback, or C<0>, if this functionality is
1442	switched off. Can be changed any time, but changes only take effect when	2115	switched off. Can be changed any time, but changes only take effect when
1443	the periodic timer fires or C<ev_periodic_again> is being called.	2116	the periodic timer fires or C<ev_periodic_again> is being called.
1444		2117
1445	=back	2118	=back
1446		2119
1447	=head3 Examples	2120	=head3 Examples
1448		2121
1449	Example: Call a callback every hour, or, more precisely, whenever the	2122	Example: Call a callback every hour, or, more precisely, whenever the
1450	system clock is divisible by 3600. The callback invocation times have	2123	system time is divisible by 3600. The callback invocation times have
1451	potentially a lot of jitter, but good long-term stability.	2124	potentially a lot of jitter, but good long-term stability.
1452		2125
1453	static void	2126	static void
1454	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2127	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1455	{	2128	{
1456	... its now a full hour (UTC, or TAI or whatever your clock follows)	2129	... its now a full hour (UTC, or TAI or whatever your clock follows)
1457	}	2130	}
1458		2131
1459	struct ev_periodic hourly_tick;	2132	ev_periodic hourly_tick;
1460	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2133	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1461	ev_periodic_start (loop, &hourly_tick);	2134	ev_periodic_start (loop, &hourly_tick);
1462		2135
1463	Example: The same as above, but use a reschedule callback to do it:	2136	Example: The same as above, but use a reschedule callback to do it:
1464		2137
1465	#include <math.h>	2138	#include <math.h>
1466		2139
1467	static ev_tstamp	2140	static ev_tstamp
1468	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2141	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1469	{	2142	{
1470	return fmod (now, 3600.) + 3600.;	2143	return now + (3600. - fmod (now, 3600.));
1471	}	2144	}
1472		2145
1473	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2146	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1474		2147
1475	Example: Call a callback every hour, starting now:	2148	Example: Call a callback every hour, starting now:
1476		2149
1477	struct ev_periodic hourly_tick;	2150	ev_periodic hourly_tick;
1478	ev_periodic_init (&hourly_tick, clock_cb,	2151	ev_periodic_init (&hourly_tick, clock_cb,
1479	fmod (ev_now (loop), 3600.), 3600., 0);	2152	fmod (ev_now (loop), 3600.), 3600., 0);
1480	ev_periodic_start (loop, &hourly_tick);	2153	ev_periodic_start (loop, &hourly_tick);
1481		2154
1482		2155
1483	=head2 C<ev_signal> - signal me when a signal gets signalled!	2156	=head2 C<ev_signal> - signal me when a signal gets signalled!
1484		2157
1485	Signal watchers will trigger an event when the process receives a specific	2158	Signal watchers will trigger an event when the process receives a specific
1486	signal one or more times. Even though signals are very asynchronous, libev	2159	signal one or more times. Even though signals are very asynchronous, libev
1487	will try it's best to deliver signals synchronously, i.e. as part of the	2160	will try it's best to deliver signals synchronously, i.e. as part of the
1488	normal event processing, like any other event.	2161	normal event processing, like any other event.
1489		2162
		2163	If you want signals to be delivered truly asynchronously, just use
		2164	C<sigaction> as you would do without libev and forget about sharing
		2165	the signal. You can even use C<ev_async> from a signal handler to
		2166	synchronously wake up an event loop.
		2167
1490	You can configure as many watchers as you like per signal. Only when the	2168	You can configure as many watchers as you like for the same signal, but
		2169	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2170	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2171	C<SIGINT> in both the default loop and another loop at the same time. At
		2172	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2173
1491	first watcher gets started will libev actually register a signal watcher	2174	When the first watcher gets started will libev actually register something
1492	with the kernel (thus it coexists with your own signal handlers as long	2175	with the kernel (thus it coexists with your own signal handlers as long as
1493	as you don't register any with libev). Similarly, when the last signal	2176	you don't register any with libev for the same signal).
1494	watcher for a signal is stopped libev will reset the signal handler to
1495	SIG_DFL (regardless of what it was set to before).
1496		2177
1497	If possible and supported, libev will install its handlers with	2178	If possible and supported, libev will install its handlers with
1498	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2179	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1499	interrupted. If you have a problem with system calls getting interrupted by	2180	not be unduly interrupted. If you have a problem with system calls getting
1500	signals you can block all signals in an C<ev_check> watcher and unblock	2181	interrupted by signals you can block all signals in an C<ev_check> watcher
1501	them in an C<ev_prepare> watcher.	2182	and unblock them in an C<ev_prepare> watcher.
		2183
		2184	=head3 The special problem of inheritance over fork/execve/pthread_create
		2185
		2186	Both the signal mask (C<sigprocmask>) and the signal disposition
		2187	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2188	stopping it again), that is, libev might or might not block the signal,
		2189	and might or might not set or restore the installed signal handler.
		2190
		2191	While this does not matter for the signal disposition (libev never
		2192	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2193	C<execve>), this matters for the signal mask: many programs do not expect
		2194	certain signals to be blocked.
		2195
		2196	This means that before calling C<exec> (from the child) you should reset
		2197	the signal mask to whatever "default" you expect (all clear is a good
		2198	choice usually).
		2199
		2200	The simplest way to ensure that the signal mask is reset in the child is
		2201	to install a fork handler with C<pthread_atfork> that resets it. That will
		2202	catch fork calls done by libraries (such as the libc) as well.
		2203
		2204	In current versions of libev, the signal will not be blocked indefinitely
		2205	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2206	the window of opportunity for problems, it will not go away, as libev
		2207	I<has> to modify the signal mask, at least temporarily.
		2208
		2209	So I can't stress this enough: I<If you do not reset your signal mask when
		2210	you expect it to be empty, you have a race condition in your code>. This
		2211	is not a libev-specific thing, this is true for most event libraries.
1502		2212
1503	=head3 Watcher-Specific Functions and Data Members	2213	=head3 Watcher-Specific Functions and Data Members
1504		2214
1505	=over 4	2215	=over 4
1506		2216
…		…
1517		2227
1518	=back	2228	=back
1519		2229
1520	=head3 Examples	2230	=head3 Examples
1521		2231
1522	Example: Try to exit cleanly on SIGINT and SIGTERM.	2232	Example: Try to exit cleanly on SIGINT.
1523		2233
1524	static void	2234	static void
1525	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2235	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1526	{	2236	{
1527	ev_unloop (loop, EVUNLOOP_ALL);	2237	ev_unloop (loop, EVUNLOOP_ALL);
1528	}	2238	}
1529		2239
1530	struct ev_signal signal_watcher;	2240	ev_signal signal_watcher;
1531	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2241	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1532	ev_signal_start (loop, &sigint_cb);	2242	ev_signal_start (loop, &signal_watcher);
1533		2243
1534		2244
1535	=head2 C<ev_child> - watch out for process status changes	2245	=head2 C<ev_child> - watch out for process status changes
1536		2246
1537	Child watchers trigger when your process receives a SIGCHLD in response to	2247	Child watchers trigger when your process receives a SIGCHLD in response to
1538	some child status changes (most typically when a child of yours dies). It	2248	some child status changes (most typically when a child of yours dies or
1539	is permissible to install a child watcher I<after> the child has been	2249	exits). It is permissible to install a child watcher I<after> the child
1540	forked (which implies it might have already exited), as long as the event	2250	has been forked (which implies it might have already exited), as long
1541	loop isn't entered (or is continued from a watcher).	2251	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2252	forking and then immediately registering a watcher for the child is fine,
		2253	but forking and registering a watcher a few event loop iterations later or
		2254	in the next callback invocation is not.
1542		2255
1543	Only the default event loop is capable of handling signals, and therefore	2256	Only the default event loop is capable of handling signals, and therefore
1544	you can only register child watchers in the default event loop.	2257	you can only register child watchers in the default event loop.
1545		2258
		2259	Due to some design glitches inside libev, child watchers will always be
		2260	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2261	libev)
		2262
1546	=head3 Process Interaction	2263	=head3 Process Interaction
1547		2264
1548	Libev grabs C<SIGCHLD> as soon as the default event loop is	2265	Libev grabs C<SIGCHLD> as soon as the default event loop is
1549	initialised. This is necessary to guarantee proper behaviour even if	2266	initialised. This is necessary to guarantee proper behaviour even if the
1550	the first child watcher is started after the child exits. The occurrence	2267	first child watcher is started after the child exits. The occurrence
1551	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2268	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1552	synchronously as part of the event loop processing. Libev always reaps all	2269	synchronously as part of the event loop processing. Libev always reaps all
1553	children, even ones not watched.	2270	children, even ones not watched.
1554		2271
1555	=head3 Overriding the Built-In Processing	2272	=head3 Overriding the Built-In Processing
…		…
1559	handler, you can override it easily by installing your own handler for	2276	handler, you can override it easily by installing your own handler for
1560	C<SIGCHLD> after initialising the default loop, and making sure the	2277	C<SIGCHLD> after initialising the default loop, and making sure the
1561	default loop never gets destroyed. You are encouraged, however, to use an	2278	default loop never gets destroyed. You are encouraged, however, to use an
1562	event-based approach to child reaping and thus use libev's support for	2279	event-based approach to child reaping and thus use libev's support for
1563	that, so other libev users can use C<ev_child> watchers freely.	2280	that, so other libev users can use C<ev_child> watchers freely.
		2281
		2282	=head3 Stopping the Child Watcher
		2283
		2284	Currently, the child watcher never gets stopped, even when the
		2285	child terminates, so normally one needs to stop the watcher in the
		2286	callback. Future versions of libev might stop the watcher automatically
		2287	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2288	problem).
1564		2289
1565	=head3 Watcher-Specific Functions and Data Members	2290	=head3 Watcher-Specific Functions and Data Members
1566		2291
1567	=over 4	2292	=over 4
1568		2293
…		…
1597	=head3 Examples	2322	=head3 Examples
1598		2323
1599	Example: C<fork()> a new process and install a child handler to wait for	2324	Example: C<fork()> a new process and install a child handler to wait for
1600	its completion.	2325	its completion.
1601		2326
1602	ev_child cw;	2327	ev_child cw;
1603		2328
1604	static void	2329	static void
1605	child_cb (EV_P_ struct ev_child *w, int revents)	2330	child_cb (EV_P_ ev_child *w, int revents)
1606	{	2331	{
1607	ev_child_stop (EV_A_ w);	2332	ev_child_stop (EV_A_ w);
1608	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2333	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1609	}	2334	}
1610		2335
1611	pid_t pid = fork ();	2336	pid_t pid = fork ();
1612		2337
1613	if (pid < 0)	2338	if (pid < 0)
1614	// error	2339	// error
1615	else if (pid == 0)	2340	else if (pid == 0)
1616	{	2341	{
1617	// the forked child executes here	2342	// the forked child executes here
1618	exit (1);	2343	exit (1);
1619	}	2344	}
1620	else	2345	else
1621	{	2346	{
1622	ev_child_init (&cw, child_cb, pid, 0);	2347	ev_child_init (&cw, child_cb, pid, 0);
1623	ev_child_start (EV_DEFAULT_ &cw);	2348	ev_child_start (EV_DEFAULT_ &cw);
1624	}	2349	}
1625		2350
1626		2351
1627	=head2 C<ev_stat> - did the file attributes just change?	2352	=head2 C<ev_stat> - did the file attributes just change?
1628		2353
1629	This watches a file system path for attribute changes. That is, it calls	2354	This watches a file system path for attribute changes. That is, it calls
1630	C<stat> regularly (or when the OS says it changed) and sees if it changed	2355	C<stat> on that path in regular intervals (or when the OS says it changed)
1631	compared to the last time, invoking the callback if it did.	2356	and sees if it changed compared to the last time, invoking the callback if
		2357	it did.
1632		2358
1633	The path does not need to exist: changing from "path exists" to "path does	2359	The path does not need to exist: changing from "path exists" to "path does
1634	not exist" is a status change like any other. The condition "path does	2360	not exist" is a status change like any other. The condition "path does not
1635	not exist" is signified by the C<st_nlink> field being zero (which is	2361	exist" (or more correctly "path cannot be stat'ed") is signified by the
1636	otherwise always forced to be at least one) and all the other fields of	2362	C<st_nlink> field being zero (which is otherwise always forced to be at
1637	the stat buffer having unspecified contents.	2363	least one) and all the other fields of the stat buffer having unspecified
		2364	contents.
1638		2365
1639	The path I<should> be absolute and I<must not> end in a slash. If it is	2366	The path I<must not> end in a slash or contain special components such as
		2367	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1640	relative and your working directory changes, the behaviour is undefined.	2368	your working directory changes, then the behaviour is undefined.
1641		2369
1642	Since there is no standard to do this, the portable implementation simply	2370	Since there is no portable change notification interface available, the
1643	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2371	portable implementation simply calls C<stat(2)> regularly on the path
1644	can specify a recommended polling interval for this case. If you specify	2372	to see if it changed somehow. You can specify a recommended polling
1645	a polling interval of C<0> (highly recommended!) then a I<suitable,	2373	interval for this case. If you specify a polling interval of C<0> (highly
1646	unspecified default> value will be used (which you can expect to be around	2374	recommended!) then a I<suitable, unspecified default> value will be used
1647	five seconds, although this might change dynamically). Libev will also	2375	(which you can expect to be around five seconds, although this might
1648	impose a minimum interval which is currently around C<0.1>, but thats	2376	change dynamically). Libev will also impose a minimum interval which is
1649	usually overkill.	2377	currently around C<0.1>, but that's usually overkill.
1650		2378
1651	This watcher type is not meant for massive numbers of stat watchers,	2379	This watcher type is not meant for massive numbers of stat watchers,
1652	as even with OS-supported change notifications, this can be	2380	as even with OS-supported change notifications, this can be
1653	resource-intensive.	2381	resource-intensive.
1654		2382
1655	At the time of this writing, only the Linux inotify interface is	2383	At the time of this writing, the only OS-specific interface implemented
1656	implemented (implementing kqueue support is left as an exercise for the	2384	is the Linux inotify interface (implementing kqueue support is left as an
1657	reader, note, however, that the author sees no way of implementing ev_stat	2385	exercise for the reader. Note, however, that the author sees no way of
1658	semantics with kqueue). Inotify will be used to give hints only and should	2386	implementing C<ev_stat> semantics with kqueue, except as a hint).
1659	not change the semantics of C<ev_stat> watchers, which means that libev
1660	sometimes needs to fall back to regular polling again even with inotify,
1661	but changes are usually detected immediately, and if the file exists there
1662	will be no polling.
1663		2387
1664	=head3 ABI Issues (Largefile Support)	2388	=head3 ABI Issues (Largefile Support)
1665		2389
1666	Libev by default (unless the user overrides this) uses the default	2390	Libev by default (unless the user overrides this) uses the default
1667	compilation environment, which means that on systems with optionally	2391	compilation environment, which means that on systems with large file
1668	disabled large file support, you get the 32 bit version of the stat	2392	support disabled by default, you get the 32 bit version of the stat
1669	structure. When using the library from programs that change the ABI to	2393	structure. When using the library from programs that change the ABI to
1670	use 64 bit file offsets the programs will fail. In that case you have to	2394	use 64 bit file offsets the programs will fail. In that case you have to
1671	compile libev with the same flags to get binary compatibility. This is	2395	compile libev with the same flags to get binary compatibility. This is
1672	obviously the case with any flags that change the ABI, but the problem is	2396	obviously the case with any flags that change the ABI, but the problem is
1673	most noticeably with ev_stat and large file support.	2397	most noticeably displayed with ev_stat and large file support.
1674		2398
1675	=head3 Inotify	2399	The solution for this is to lobby your distribution maker to make large
		2400	file interfaces available by default (as e.g. FreeBSD does) and not
		2401	optional. Libev cannot simply switch on large file support because it has
		2402	to exchange stat structures with application programs compiled using the
		2403	default compilation environment.
1676		2404
		2405	=head3 Inotify and Kqueue
		2406
1677	When C<inotify (7)> support has been compiled into libev (generally only	2407	When C<inotify (7)> support has been compiled into libev and present at
1678	available on Linux) and present at runtime, it will be used to speed up	2408	runtime, it will be used to speed up change detection where possible. The
1679	change detection where possible. The inotify descriptor will be created lazily	2409	inotify descriptor will be created lazily when the first C<ev_stat>
1680	when the first C<ev_stat> watcher is being started.	2410	watcher is being started.
1681		2411
1682	Inotify presence does not change the semantics of C<ev_stat> watchers	2412	Inotify presence does not change the semantics of C<ev_stat> watchers
1683	except that changes might be detected earlier, and in some cases, to avoid	2413	except that changes might be detected earlier, and in some cases, to avoid
1684	making regular C<stat> calls. Even in the presence of inotify support	2414	making regular C<stat> calls. Even in the presence of inotify support
1685	there are many cases where libev has to resort to regular C<stat> polling.	2415	there are many cases where libev has to resort to regular C<stat> polling,
		2416	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2417	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2418	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2419	xfs are fully working) libev usually gets away without polling.
1686		2420
1687	(There is no support for kqueue, as apparently it cannot be used to	2421	There is no support for kqueue, as apparently it cannot be used to
1688	implement this functionality, due to the requirement of having a file	2422	implement this functionality, due to the requirement of having a file
1689	descriptor open on the object at all times).	2423	descriptor open on the object at all times, and detecting renames, unlinks
		2424	etc. is difficult.
		2425
		2426	=head3 C<stat ()> is a synchronous operation
		2427
		2428	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2429	the process. The exception are C<ev_stat> watchers - those call C<stat
		2430	()>, which is a synchronous operation.
		2431
		2432	For local paths, this usually doesn't matter: unless the system is very
		2433	busy or the intervals between stat's are large, a stat call will be fast,
		2434	as the path data is usually in memory already (except when starting the
		2435	watcher).
		2436
		2437	For networked file systems, calling C<stat ()> can block an indefinite
		2438	time due to network issues, and even under good conditions, a stat call
		2439	often takes multiple milliseconds.
		2440
		2441	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2442	paths, although this is fully supported by libev.
1690		2443
1691	=head3 The special problem of stat time resolution	2444	=head3 The special problem of stat time resolution
1692		2445
1693	The C<stat ()> system call only supports full-second resolution portably, and	2446	The C<stat ()> system call only supports full-second resolution portably,
1694	even on systems where the resolution is higher, many file systems still	2447	and even on systems where the resolution is higher, most file systems
1695	only support whole seconds.	2448	still only support whole seconds.
1696		2449
1697	That means that, if the time is the only thing that changes, you can	2450	That means that, if the time is the only thing that changes, you can
1698	easily miss updates: on the first update, C<ev_stat> detects a change and	2451	easily miss updates: on the first update, C<ev_stat> detects a change and
1699	calls your callback, which does something. When there is another update	2452	calls your callback, which does something. When there is another update
1700	within the same second, C<ev_stat> will be unable to detect it as the stat	2453	within the same second, C<ev_stat> will be unable to detect unless the
1701	data does not change.	2454	stat data does change in other ways (e.g. file size).
1702		2455
1703	The solution to this is to delay acting on a change for slightly more	2456	The solution to this is to delay acting on a change for slightly more
1704	than a second (or till slightly after the next full second boundary), using	2457	than a second (or till slightly after the next full second boundary), using
1705	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);	2458	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1706	ev_timer_again (loop, w)>).	2459	ev_timer_again (loop, w)>).
…		…
1726	C<path>. The C<interval> is a hint on how quickly a change is expected to	2479	C<path>. The C<interval> is a hint on how quickly a change is expected to
1727	be detected and should normally be specified as C<0> to let libev choose	2480	be detected and should normally be specified as C<0> to let libev choose
1728	a suitable value. The memory pointed to by C<path> must point to the same	2481	a suitable value. The memory pointed to by C<path> must point to the same
1729	path for as long as the watcher is active.	2482	path for as long as the watcher is active.
1730		2483
1731	The callback will receive C<EV_STAT> when a change was detected, relative	2484	The callback will receive an C<EV_STAT> event when a change was detected,
1732	to the attributes at the time the watcher was started (or the last change	2485	relative to the attributes at the time the watcher was started (or the
1733	was detected).	2486	last change was detected).
1734		2487
1735	=item ev_stat_stat (loop, ev_stat *)	2488	=item ev_stat_stat (loop, ev_stat *)
1736		2489
1737	Updates the stat buffer immediately with new values. If you change the	2490	Updates the stat buffer immediately with new values. If you change the
1738	watched path in your callback, you could call this function to avoid	2491	watched path in your callback, you could call this function to avoid
…		…
1767		2520
1768	=head3 Examples	2521	=head3 Examples
1769		2522
1770	Example: Watch C</etc/passwd> for attribute changes.	2523	Example: Watch C</etc/passwd> for attribute changes.
1771		2524
1772	static void	2525	static void
1773	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2526	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1774	{	2527	{
1775	/* /etc/passwd changed in some way */	2528	/* /etc/passwd changed in some way */
1776	if (w->attr.st_nlink)	2529	if (w->attr.st_nlink)
1777	{	2530	{
1778	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2531	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1779	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2532	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1780	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2533	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1781	}	2534	}
1782	else	2535	else
1783	/* you shalt not abuse printf for puts */	2536	/* you shalt not abuse printf for puts */
1784	puts ("wow, /etc/passwd is not there, expect problems. "	2537	puts ("wow, /etc/passwd is not there, expect problems. "
1785	"if this is windows, they already arrived\n");	2538	"if this is windows, they already arrived\n");
1786	}	2539	}
1787		2540
1788	...	2541	...
1789	ev_stat passwd;	2542	ev_stat passwd;
1790		2543
1791	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2544	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1792	ev_stat_start (loop, &passwd);	2545	ev_stat_start (loop, &passwd);
1793		2546
1794	Example: Like above, but additionally use a one-second delay so we do not	2547	Example: Like above, but additionally use a one-second delay so we do not
1795	miss updates (however, frequent updates will delay processing, too, so	2548	miss updates (however, frequent updates will delay processing, too, so
1796	one might do the work both on C<ev_stat> callback invocation I<and> on	2549	one might do the work both on C<ev_stat> callback invocation I<and> on
1797	C<ev_timer> callback invocation).	2550	C<ev_timer> callback invocation).
1798		2551
1799	static ev_stat passwd;	2552	static ev_stat passwd;
1800	static ev_timer timer;	2553	static ev_timer timer;
1801		2554
1802	static void	2555	static void
1803	timer_cb (EV_P_ ev_timer *w, int revents)	2556	timer_cb (EV_P_ ev_timer *w, int revents)
1804	{	2557	{
1805	ev_timer_stop (EV_A_ w);	2558	ev_timer_stop (EV_A_ w);
1806		2559
1807	/* now it's one second after the most recent passwd change */	2560	/* now it's one second after the most recent passwd change */
1808	}	2561	}
1809		2562
1810	static void	2563	static void
1811	stat_cb (EV_P_ ev_stat *w, int revents)	2564	stat_cb (EV_P_ ev_stat *w, int revents)
1812	{	2565	{
1813	/* reset the one-second timer */	2566	/* reset the one-second timer */
1814	ev_timer_again (EV_A_ &timer);	2567	ev_timer_again (EV_A_ &timer);
1815	}	2568	}
1816		2569
1817	...	2570	...
1818	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2571	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1819	ev_stat_start (loop, &passwd);	2572	ev_stat_start (loop, &passwd);
1820	ev_timer_init (&timer, timer_cb, 0., 1.02);	2573	ev_timer_init (&timer, timer_cb, 0., 1.02);
1821		2574
1822		2575
1823	=head2 C<ev_idle> - when you've got nothing better to do...	2576	=head2 C<ev_idle> - when you've got nothing better to do...
1824		2577
1825	Idle watchers trigger events when no other events of the same or higher	2578	Idle watchers trigger events when no other events of the same or higher
1826	priority are pending (prepare, check and other idle watchers do not	2579	priority are pending (prepare, check and other idle watchers do not count
1827	count).	2580	as receiving "events").
1828		2581
1829	That is, as long as your process is busy handling sockets or timeouts	2582	That is, as long as your process is busy handling sockets or timeouts
1830	(or even signals, imagine) of the same or higher priority it will not be	2583	(or even signals, imagine) of the same or higher priority it will not be
1831	triggered. But when your process is idle (or only lower-priority watchers	2584	triggered. But when your process is idle (or only lower-priority watchers
1832	are pending), the idle watchers are being called once per event loop	2585	are pending), the idle watchers are being called once per event loop
…		…
1843		2596
1844	=head3 Watcher-Specific Functions and Data Members	2597	=head3 Watcher-Specific Functions and Data Members
1845		2598
1846	=over 4	2599	=over 4
1847		2600
1848	=item ev_idle_init (ev_signal *, callback)	2601	=item ev_idle_init (ev_idle *, callback)
1849		2602
1850	Initialises and configures the idle watcher - it has no parameters of any	2603	Initialises and configures the idle watcher - it has no parameters of any
1851	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2604	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1852	believe me.	2605	believe me.
1853		2606
…		…
1856	=head3 Examples	2609	=head3 Examples
1857		2610
1858	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2611	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1859	callback, free it. Also, use no error checking, as usual.	2612	callback, free it. Also, use no error checking, as usual.
1860		2613
1861	static void	2614	static void
1862	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2615	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1863	{	2616	{
1864	free (w);	2617	free (w);
1865	// now do something you wanted to do when the program has	2618	// now do something you wanted to do when the program has
1866	// no longer anything immediate to do.	2619	// no longer anything immediate to do.
1867	}	2620	}
1868		2621
1869	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2622	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1870	ev_idle_init (idle_watcher, idle_cb);	2623	ev_idle_init (idle_watcher, idle_cb);
1871	ev_idle_start (loop, idle_cb);	2624	ev_idle_start (loop, idle_watcher);
1872		2625
1873		2626
1874	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2627	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1875		2628
1876	Prepare and check watchers are usually (but not always) used in tandem:	2629	Prepare and check watchers are usually (but not always) used in pairs:
1877	prepare watchers get invoked before the process blocks and check watchers	2630	prepare watchers get invoked before the process blocks and check watchers
1878	afterwards.	2631	afterwards.
1879		2632
1880	You I<must not> call C<ev_loop> or similar functions that enter	2633	You I<must not> call C<ev_loop> or similar functions that enter
1881	the current event loop from either C<ev_prepare> or C<ev_check>	2634	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1884	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2637	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1885	C<ev_check> so if you have one watcher of each kind they will always be	2638	C<ev_check> so if you have one watcher of each kind they will always be
1886	called in pairs bracketing the blocking call.	2639	called in pairs bracketing the blocking call.
1887		2640
1888	Their main purpose is to integrate other event mechanisms into libev and	2641	Their main purpose is to integrate other event mechanisms into libev and
1889	their use is somewhat advanced. This could be used, for example, to track	2642	their use is somewhat advanced. They could be used, for example, to track
1890	variable changes, implement your own watchers, integrate net-snmp or a	2643	variable changes, implement your own watchers, integrate net-snmp or a
1891	coroutine library and lots more. They are also occasionally useful if	2644	coroutine library and lots more. They are also occasionally useful if
1892	you cache some data and want to flush it before blocking (for example,	2645	you cache some data and want to flush it before blocking (for example,
1893	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2646	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1894	watcher).	2647	watcher).
1895		2648
1896	This is done by examining in each prepare call which file descriptors need	2649	This is done by examining in each prepare call which file descriptors
1897	to be watched by the other library, registering C<ev_io> watchers for	2650	need to be watched by the other library, registering C<ev_io> watchers
1898	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2651	for them and starting an C<ev_timer> watcher for any timeouts (many
1899	provide just this functionality). Then, in the check watcher you check for	2652	libraries provide exactly this functionality). Then, in the check watcher,
1900	any events that occurred (by checking the pending status of all watchers	2653	you check for any events that occurred (by checking the pending status
1901	and stopping them) and call back into the library. The I/O and timer	2654	of all watchers and stopping them) and call back into the library. The
1902	callbacks will never actually be called (but must be valid nevertheless,	2655	I/O and timer callbacks will never actually be called (but must be valid
1903	because you never know, you know?).	2656	nevertheless, because you never know, you know?).
1904		2657
1905	As another example, the Perl Coro module uses these hooks to integrate	2658	As another example, the Perl Coro module uses these hooks to integrate
1906	coroutines into libev programs, by yielding to other active coroutines	2659	coroutines into libev programs, by yielding to other active coroutines
1907	during each prepare and only letting the process block if no coroutines	2660	during each prepare and only letting the process block if no coroutines
1908	are ready to run (it's actually more complicated: it only runs coroutines	2661	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1911	loop from blocking if lower-priority coroutines are active, thus mapping	2664	loop from blocking if lower-priority coroutines are active, thus mapping
1912	low-priority coroutines to idle/background tasks).	2665	low-priority coroutines to idle/background tasks).
1913		2666
1914	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2667	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1915	priority, to ensure that they are being run before any other watchers	2668	priority, to ensure that they are being run before any other watchers
		2669	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2670
1916	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2671	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1917	too) should not activate ("feed") events into libev. While libev fully	2672	activate ("feed") events into libev. While libev fully supports this, they
1918	supports this, they might get executed before other C<ev_check> watchers	2673	might get executed before other C<ev_check> watchers did their job. As
1919	did their job. As C<ev_check> watchers are often used to embed other	2674	C<ev_check> watchers are often used to embed other (non-libev) event
1920	(non-libev) event loops those other event loops might be in an unusable	2675	loops those other event loops might be in an unusable state until their
1921	state until their C<ev_check> watcher ran (always remind yourself to	2676	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1922	coexist peacefully with others).	2677	others).
1923		2678
1924	=head3 Watcher-Specific Functions and Data Members	2679	=head3 Watcher-Specific Functions and Data Members
1925		2680
1926	=over 4	2681	=over 4
1927		2682
…		…
1929		2684
1930	=item ev_check_init (ev_check *, callback)	2685	=item ev_check_init (ev_check *, callback)
1931		2686
1932	Initialises and configures the prepare or check watcher - they have no	2687	Initialises and configures the prepare or check watcher - they have no
1933	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2688	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1934	macros, but using them is utterly, utterly and completely pointless.	2689	macros, but using them is utterly, utterly, utterly and completely
		2690	pointless.
1935		2691
1936	=back	2692	=back
1937		2693
1938	=head3 Examples	2694	=head3 Examples
1939		2695
…		…
1948	and in a check watcher, destroy them and call into libadns. What follows	2704	and in a check watcher, destroy them and call into libadns. What follows
1949	is pseudo-code only of course. This requires you to either use a low	2705	is pseudo-code only of course. This requires you to either use a low
1950	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2706	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1951	the callbacks for the IO/timeout watchers might not have been called yet.	2707	the callbacks for the IO/timeout watchers might not have been called yet.
1952		2708
1953	static ev_io iow [nfd];	2709	static ev_io iow [nfd];
1954	static ev_timer tw;	2710	static ev_timer tw;
1955		2711
1956	static void	2712	static void
1957	io_cb (ev_loop *loop, ev_io *w, int revents)	2713	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1958	{	2714	{
1959	}	2715	}
1960		2716
1961	// create io watchers for each fd and a timer before blocking	2717	// create io watchers for each fd and a timer before blocking
1962	static void	2718	static void
1963	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2719	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1964	{	2720	{
1965	int timeout = 3600000;	2721	int timeout = 3600000;
1966	struct pollfd fds [nfd];	2722	struct pollfd fds [nfd];
1967	// actual code will need to loop here and realloc etc.	2723	// actual code will need to loop here and realloc etc.
1968	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2724	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1969		2725
1970	/* the callback is illegal, but won't be called as we stop during check */	2726	/* the callback is illegal, but won't be called as we stop during check */
1971	ev_timer_init (&tw, 0, timeout * 1e-3);	2727	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1972	ev_timer_start (loop, &tw);	2728	ev_timer_start (loop, &tw);
1973		2729
1974	// create one ev_io per pollfd	2730	// create one ev_io per pollfd
1975	for (int i = 0; i < nfd; ++i)	2731	for (int i = 0; i < nfd; ++i)
1976	{	2732	{
1977	ev_io_init (iow + i, io_cb, fds [i].fd,	2733	ev_io_init (iow + i, io_cb, fds [i].fd,
1978	((fds [i].events & POLLIN ? EV_READ : 0)	2734	((fds [i].events & POLLIN ? EV_READ : 0)
1979	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2735	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1980		2736
1981	fds [i].revents = 0;	2737	fds [i].revents = 0;
1982	ev_io_start (loop, iow + i);	2738	ev_io_start (loop, iow + i);
1983	}	2739	}
1984	}	2740	}
1985		2741
1986	// stop all watchers after blocking	2742	// stop all watchers after blocking
1987	static void	2743	static void
1988	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2744	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1989	{	2745	{
1990	ev_timer_stop (loop, &tw);	2746	ev_timer_stop (loop, &tw);
1991		2747
1992	for (int i = 0; i < nfd; ++i)	2748	for (int i = 0; i < nfd; ++i)
1993	{	2749	{
1994	// set the relevant poll flags	2750	// set the relevant poll flags
1995	// could also call adns_processreadable etc. here	2751	// could also call adns_processreadable etc. here
1996	struct pollfd *fd = fds + i;	2752	struct pollfd *fd = fds + i;
1997	int revents = ev_clear_pending (iow + i);	2753	int revents = ev_clear_pending (iow + i);
1998	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2754	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1999	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2755	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
2000		2756
2001	// now stop the watcher	2757	// now stop the watcher
2002	ev_io_stop (loop, iow + i);	2758	ev_io_stop (loop, iow + i);
2003	}	2759	}
2004		2760
2005	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2761	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2006	}	2762	}
2007		2763
2008	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2764	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
2009	in the prepare watcher and would dispose of the check watcher.	2765	in the prepare watcher and would dispose of the check watcher.
2010		2766
2011	Method 3: If the module to be embedded supports explicit event	2767	Method 3: If the module to be embedded supports explicit event
2012	notification (libadns does), you can also make use of the actual watcher	2768	notification (libadns does), you can also make use of the actual watcher
2013	callbacks, and only destroy/create the watchers in the prepare watcher.	2769	callbacks, and only destroy/create the watchers in the prepare watcher.
2014		2770
2015	static void	2771	static void
2016	timer_cb (EV_P_ ev_timer *w, int revents)	2772	timer_cb (EV_P_ ev_timer *w, int revents)
2017	{	2773	{
2018	adns_state ads = (adns_state)w->data;	2774	adns_state ads = (adns_state)w->data;
2019	update_now (EV_A);	2775	update_now (EV_A);
2020		2776
2021	adns_processtimeouts (ads, &tv_now);	2777	adns_processtimeouts (ads, &tv_now);
2022	}	2778	}
2023		2779
2024	static void	2780	static void
2025	io_cb (EV_P_ ev_io *w, int revents)	2781	io_cb (EV_P_ ev_io *w, int revents)
2026	{	2782	{
2027	adns_state ads = (adns_state)w->data;	2783	adns_state ads = (adns_state)w->data;
2028	update_now (EV_A);	2784	update_now (EV_A);
2029		2785
2030	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2786	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
2031	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2787	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
2032	}	2788	}
2033		2789
2034	// do not ever call adns_afterpoll	2790	// do not ever call adns_afterpoll
2035		2791
2036	Method 4: Do not use a prepare or check watcher because the module you	2792	Method 4: Do not use a prepare or check watcher because the module you
2037	want to embed is too inflexible to support it. Instead, you can override	2793	want to embed is not flexible enough to support it. Instead, you can
2038	their poll function. The drawback with this solution is that the main	2794	override their poll function. The drawback with this solution is that the
2039	loop is now no longer controllable by EV. The C<Glib::EV> module does	2795	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2040	this.	2796	this approach, effectively embedding EV as a client into the horrible
		2797	libglib event loop.
2041		2798
2042	static gint	2799	static gint
2043	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2800	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2044	{	2801	{
2045	int got_events = 0;	2802	int got_events = 0;
2046		2803
2047	for (n = 0; n < nfds; ++n)	2804	for (n = 0; n < nfds; ++n)
2048	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2805	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2049		2806
2050	if (timeout >= 0)	2807	if (timeout >= 0)
2051	// create/start timer	2808	// create/start timer
2052		2809
2053	// poll	2810	// poll
2054	ev_loop (EV_A_ 0);	2811	ev_loop (EV_A_ 0);
2055		2812
2056	// stop timer again	2813	// stop timer again
2057	if (timeout >= 0)	2814	if (timeout >= 0)
2058	ev_timer_stop (EV_A_ &to);	2815	ev_timer_stop (EV_A_ &to);
2059		2816
2060	// stop io watchers again - their callbacks should have set	2817	// stop io watchers again - their callbacks should have set
2061	for (n = 0; n < nfds; ++n)	2818	for (n = 0; n < nfds; ++n)
2062	ev_io_stop (EV_A_ iow [n]);	2819	ev_io_stop (EV_A_ iow [n]);
2063		2820
2064	return got_events;	2821	return got_events;
2065	}	2822	}
2066		2823
2067		2824
2068	=head2 C<ev_embed> - when one backend isn't enough...	2825	=head2 C<ev_embed> - when one backend isn't enough...
2069		2826
2070	This is a rather advanced watcher type that lets you embed one event loop	2827	This is a rather advanced watcher type that lets you embed one event loop
…		…
2076	prioritise I/O.	2833	prioritise I/O.
2077		2834
2078	As an example for a bug workaround, the kqueue backend might only support	2835	As an example for a bug workaround, the kqueue backend might only support
2079	sockets on some platform, so it is unusable as generic backend, but you	2836	sockets on some platform, so it is unusable as generic backend, but you
2080	still want to make use of it because you have many sockets and it scales	2837	still want to make use of it because you have many sockets and it scales
2081	so nicely. In this case, you would create a kqueue-based loop and embed it	2838	so nicely. In this case, you would create a kqueue-based loop and embed
2082	into your default loop (which might use e.g. poll). Overall operation will	2839	it into your default loop (which might use e.g. poll). Overall operation
2083	be a bit slower because first libev has to poll and then call kevent, but	2840	will be a bit slower because first libev has to call C<poll> and then
2084	at least you can use both at what they are best.	2841	C<kevent>, but at least you can use both mechanisms for what they are
		2842	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2085		2843
2086	As for prioritising I/O: rarely you have the case where some fds have	2844	As for prioritising I/O: under rare circumstances you have the case where
2087	to be watched and handled very quickly (with low latency), and even	2845	some fds have to be watched and handled very quickly (with low latency),
2088	priorities and idle watchers might have too much overhead. In this case	2846	and even priorities and idle watchers might have too much overhead. In
2089	you would put all the high priority stuff in one loop and all the rest in	2847	this case you would put all the high priority stuff in one loop and all
2090	a second one, and embed the second one in the first.	2848	the rest in a second one, and embed the second one in the first.
2091		2849
2092	As long as the watcher is active, the callback will be invoked every time	2850	As long as the watcher is active, the callback will be invoked every
2093	there might be events pending in the embedded loop. The callback must then	2851	time there might be events pending in the embedded loop. The callback
2094	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2852	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2095	their callbacks (you could also start an idle watcher to give the embedded	2853	sweep and invoke their callbacks (the callback doesn't need to invoke the
2096	loop strictly lower priority for example). You can also set the callback	2854	C<ev_embed_sweep> function directly, it could also start an idle watcher
2097	to C<0>, in which case the embed watcher will automatically execute the	2855	to give the embedded loop strictly lower priority for example).
2098	embedded loop sweep.
2099		2856
2100	As long as the watcher is started it will automatically handle events. The	2857	You can also set the callback to C<0>, in which case the embed watcher
2101	callback will be invoked whenever some events have been handled. You can	2858	will automatically execute the embedded loop sweep whenever necessary.
2102	set the callback to C<0> to avoid having to specify one if you are not
2103	interested in that.
2104		2859
2105	Also, there have not currently been made special provisions for forking:	2860	Fork detection will be handled transparently while the C<ev_embed> watcher
2106	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2861	is active, i.e., the embedded loop will automatically be forked when the
2107	but you will also have to stop and restart any C<ev_embed> watchers	2862	embedding loop forks. In other cases, the user is responsible for calling
2108	yourself.	2863	C<ev_loop_fork> on the embedded loop.
2109		2864
2110	Unfortunately, not all backends are embeddable, only the ones returned by	2865	Unfortunately, not all backends are embeddable: only the ones returned by
2111	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2866	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2112	portable one.	2867	portable one.
2113		2868
2114	So when you want to use this feature you will always have to be prepared	2869	So when you want to use this feature you will always have to be prepared
2115	that you cannot get an embeddable loop. The recommended way to get around	2870	that you cannot get an embeddable loop. The recommended way to get around
2116	this is to have a separate variables for your embeddable loop, try to	2871	this is to have a separate variables for your embeddable loop, try to
2117	create it, and if that fails, use the normal loop for everything.	2872	create it, and if that fails, use the normal loop for everything.
		2873
		2874	=head3 C<ev_embed> and fork
		2875
		2876	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2877	automatically be applied to the embedded loop as well, so no special
		2878	fork handling is required in that case. When the watcher is not running,
		2879	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2880	as applicable.
2118		2881
2119	=head3 Watcher-Specific Functions and Data Members	2882	=head3 Watcher-Specific Functions and Data Members
2120		2883
2121	=over 4	2884	=over 4
2122		2885
…		…
2148	event loop. If that is not possible, use the default loop. The default	2911	event loop. If that is not possible, use the default loop. The default
2149	loop is stored in C<loop_hi>, while the embeddable loop is stored in	2912	loop is stored in C<loop_hi>, while the embeddable loop is stored in
2150	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2913	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2151	used).	2914	used).
2152		2915
2153	struct ev_loop *loop_hi = ev_default_init (0);	2916	struct ev_loop *loop_hi = ev_default_init (0);
2154	struct ev_loop *loop_lo = 0;	2917	struct ev_loop *loop_lo = 0;
2155	struct ev_embed embed;	2918	ev_embed embed;
2156		2919
2157	// see if there is a chance of getting one that works	2920	// see if there is a chance of getting one that works
2158	// (remember that a flags value of 0 means autodetection)	2921	// (remember that a flags value of 0 means autodetection)
2159	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2922	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2160	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2923	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2161	: 0;	2924	: 0;
2162		2925
2163	// if we got one, then embed it, otherwise default to loop_hi	2926	// if we got one, then embed it, otherwise default to loop_hi
2164	if (loop_lo)	2927	if (loop_lo)
2165	{	2928	{
2166	ev_embed_init (&embed, 0, loop_lo);	2929	ev_embed_init (&embed, 0, loop_lo);
2167	ev_embed_start (loop_hi, &embed);	2930	ev_embed_start (loop_hi, &embed);
2168	}	2931	}
2169	else	2932	else
2170	loop_lo = loop_hi;	2933	loop_lo = loop_hi;
2171		2934
2172	Example: Check if kqueue is available but not recommended and create	2935	Example: Check if kqueue is available but not recommended and create
2173	a kqueue backend for use with sockets (which usually work with any	2936	a kqueue backend for use with sockets (which usually work with any
2174	kqueue implementation). Store the kqueue/socket-only event loop in	2937	kqueue implementation). Store the kqueue/socket-only event loop in
2175	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2938	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2176		2939
2177	struct ev_loop *loop = ev_default_init (0);	2940	struct ev_loop *loop = ev_default_init (0);
2178	struct ev_loop *loop_socket = 0;	2941	struct ev_loop *loop_socket = 0;
2179	struct ev_embed embed;	2942	ev_embed embed;
2180		2943
2181	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2944	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2182	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2945	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2183	{	2946	{
2184	ev_embed_init (&embed, 0, loop_socket);	2947	ev_embed_init (&embed, 0, loop_socket);
2185	ev_embed_start (loop, &embed);	2948	ev_embed_start (loop, &embed);
2186	}	2949	}
2187		2950
2188	if (!loop_socket)	2951	if (!loop_socket)
2189	loop_socket = loop;	2952	loop_socket = loop;
2190		2953
2191	// now use loop_socket for all sockets, and loop for everything else	2954	// now use loop_socket for all sockets, and loop for everything else
2192		2955
2193		2956
2194	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2957	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2195		2958
2196	Fork watchers are called when a C<fork ()> was detected (usually because	2959	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2199	event loop blocks next and before C<ev_check> watchers are being called,	2962	event loop blocks next and before C<ev_check> watchers are being called,
2200	and only in the child after the fork. If whoever good citizen calling	2963	and only in the child after the fork. If whoever good citizen calling
2201	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2964	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2202	handlers will be invoked, too, of course.	2965	handlers will be invoked, too, of course.
2203		2966
		2967	=head3 The special problem of life after fork - how is it possible?
		2968
		2969	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2970	up/change the process environment, followed by a call to C<exec()>. This
		2971	sequence should be handled by libev without any problems.
		2972
		2973	This changes when the application actually wants to do event handling
		2974	in the child, or both parent in child, in effect "continuing" after the
		2975	fork.
		2976
		2977	The default mode of operation (for libev, with application help to detect
		2978	forks) is to duplicate all the state in the child, as would be expected
		2979	when I<either> the parent I<or> the child process continues.
		2980
		2981	When both processes want to continue using libev, then this is usually the
		2982	wrong result. In that case, usually one process (typically the parent) is
		2983	supposed to continue with all watchers in place as before, while the other
		2984	process typically wants to start fresh, i.e. without any active watchers.
		2985
		2986	The cleanest and most efficient way to achieve that with libev is to
		2987	simply create a new event loop, which of course will be "empty", and
		2988	use that for new watchers. This has the advantage of not touching more
		2989	memory than necessary, and thus avoiding the copy-on-write, and the
		2990	disadvantage of having to use multiple event loops (which do not support
		2991	signal watchers).
		2992
		2993	When this is not possible, or you want to use the default loop for
		2994	other reasons, then in the process that wants to start "fresh", call
		2995	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2996	the default loop will "orphan" (not stop) all registered watchers, so you
		2997	have to be careful not to execute code that modifies those watchers. Note
		2998	also that in that case, you have to re-register any signal watchers.
		2999
2204	=head3 Watcher-Specific Functions and Data Members	3000	=head3 Watcher-Specific Functions and Data Members
2205		3001
2206	=over 4	3002	=over 4
2207		3003
2208	=item ev_fork_init (ev_signal *, callback)	3004	=item ev_fork_init (ev_signal *, callback)
…		…
2237	=head3 Queueing	3033	=head3 Queueing
2238		3034
2239	C<ev_async> does not support queueing of data in any way. The reason	3035	C<ev_async> does not support queueing of data in any way. The reason
2240	is that the author does not know of a simple (or any) algorithm for a	3036	is that the author does not know of a simple (or any) algorithm for a
2241	multiple-writer-single-reader queue that works in all cases and doesn't	3037	multiple-writer-single-reader queue that works in all cases and doesn't
2242	need elaborate support such as pthreads.	3038	need elaborate support such as pthreads or unportable memory access
		3039	semantics.
2243		3040
2244	That means that if you want to queue data, you have to provide your own	3041	That means that if you want to queue data, you have to provide your own
2245	queue. But at least I can tell you would implement locking around your	3042	queue. But at least I can tell you how to implement locking around your
2246	queue:	3043	queue:
2247		3044
2248	=over 4	3045	=over 4
2249		3046
2250	=item queueing from a signal handler context	3047	=item queueing from a signal handler context
2251		3048
2252	To implement race-free queueing, you simply add to the queue in the signal	3049	To implement race-free queueing, you simply add to the queue in the signal
2253	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3050	handler but you block the signal handler in the watcher callback. Here is
2254	some fictitious SIGUSR1 handler:	3051	an example that does that for some fictitious SIGUSR1 handler:
2255		3052
2256	static ev_async mysig;	3053	static ev_async mysig;
2257		3054
2258	static void	3055	static void
2259	sigusr1_handler (void)	3056	sigusr1_handler (void)
…		…
2325	=over 4	3122	=over 4
2326		3123
2327	=item ev_async_init (ev_async *, callback)	3124	=item ev_async_init (ev_async *, callback)
2328		3125
2329	Initialises and configures the async watcher - it has no parameters of any	3126	Initialises and configures the async watcher - it has no parameters of any
2330	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3127	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2331	believe me.	3128	trust me.
2332		3129
2333	=item ev_async_send (loop, ev_async *)	3130	=item ev_async_send (loop, ev_async *)
2334		3131
2335	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3132	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2336	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3133	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2337	C<ev_feed_event>, this call is safe to do in other threads, signal or	3134	C<ev_feed_event>, this call is safe to do from other threads, signal or
2338	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3135	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2339	section below on what exactly this means).	3136	section below on what exactly this means).
2340		3137
		3138	Note that, as with other watchers in libev, multiple events might get
		3139	compressed into a single callback invocation (another way to look at this
		3140	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3141	reset when the event loop detects that).
		3142
2341	This call incurs the overhead of a system call only once per loop iteration,	3143	This call incurs the overhead of a system call only once per event loop
2342	so while the overhead might be noticeable, it doesn't apply to repeated	3144	iteration, so while the overhead might be noticeable, it doesn't apply to
2343	calls to C<ev_async_send>.	3145	repeated calls to C<ev_async_send> for the same event loop.
2344		3146
2345	=item bool = ev_async_pending (ev_async *)	3147	=item bool = ev_async_pending (ev_async *)
2346		3148
2347	Returns a non-zero value when C<ev_async_send> has been called on the	3149	Returns a non-zero value when C<ev_async_send> has been called on the
2348	watcher but the event has not yet been processed (or even noted) by the	3150	watcher but the event has not yet been processed (or even noted) by the
…		…
2351	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3153	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2352	the loop iterates next and checks for the watcher to have become active,	3154	the loop iterates next and checks for the watcher to have become active,
2353	it will reset the flag again. C<ev_async_pending> can be used to very	3155	it will reset the flag again. C<ev_async_pending> can be used to very
2354	quickly check whether invoking the loop might be a good idea.	3156	quickly check whether invoking the loop might be a good idea.
2355		3157
2356	Not that this does I<not> check whether the watcher itself is pending, only	3158	Not that this does I<not> check whether the watcher itself is pending,
2357	whether it has been requested to make this watcher pending.	3159	only whether it has been requested to make this watcher pending: there
		3160	is a time window between the event loop checking and resetting the async
		3161	notification, and the callback being invoked.
2358		3162
2359	=back	3163	=back
2360		3164
2361		3165
2362	=head1 OTHER FUNCTIONS	3166	=head1 OTHER FUNCTIONS
…		…
2366	=over 4	3170	=over 4
2367		3171
2368	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3172	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2369		3173
2370	This function combines a simple timer and an I/O watcher, calls your	3174	This function combines a simple timer and an I/O watcher, calls your
2371	callback on whichever event happens first and automatically stop both	3175	callback on whichever event happens first and automatically stops both
2372	watchers. This is useful if you want to wait for a single event on an fd	3176	watchers. This is useful if you want to wait for a single event on an fd
2373	or timeout without having to allocate/configure/start/stop/free one or	3177	or timeout without having to allocate/configure/start/stop/free one or
2374	more watchers yourself.	3178	more watchers yourself.
2375		3179
2376	If C<fd> is less than 0, then no I/O watcher will be started and events	3180	If C<fd> is less than 0, then no I/O watcher will be started and the
2377	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3181	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2378	C<events> set will be created and started.	3182	the given C<fd> and C<events> set will be created and started.
2379		3183
2380	If C<timeout> is less than 0, then no timeout watcher will be	3184	If C<timeout> is less than 0, then no timeout watcher will be
2381	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3185	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2382	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3186	repeat = 0) will be started. C<0> is a valid timeout.
2383	dubious value.
2384		3187
2385	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3188	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2386	passed an C<revents> set like normal event callbacks (a combination of	3189	passed an C<revents> set like normal event callbacks (a combination of
2387	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3190	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2388	value passed to C<ev_once>:	3191	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3192	a timeout and an io event at the same time - you probably should give io
		3193	events precedence.
2389		3194
		3195	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3196
2390	static void stdin_ready (int revents, void *arg)	3197	static void stdin_ready (int revents, void *arg)
2391	{	3198	{
2392	if (revents & EV_TIMEOUT)
2393	/* doh, nothing entered */;
2394	else if (revents & EV_READ)	3199	if (revents & EV_READ)
2395	/* stdin might have data for us, joy! */;	3200	/* stdin might have data for us, joy! */;
		3201	else if (revents & EV_TIMER)
		3202	/* doh, nothing entered */;
2396	}	3203	}
2397		3204
2398	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3205	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2399		3206
2400	=item ev_feed_event (ev_loop *, watcher *, int revents)
2401
2402	Feeds the given event set into the event loop, as if the specified event
2403	had happened for the specified watcher (which must be a pointer to an
2404	initialised but not necessarily started event watcher).
2405
2406	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3207	=item ev_feed_fd_event (loop, int fd, int revents)
2407		3208
2408	Feed an event on the given fd, as if a file descriptor backend detected	3209	Feed an event on the given fd, as if a file descriptor backend detected
2409	the given events it.	3210	the given events it.
2410		3211
2411	=item ev_feed_signal_event (ev_loop *loop, int signum)	3212	=item ev_feed_signal_event (loop, int signum)
2412		3213
2413	Feed an event as if the given signal occurred (C<loop> must be the default	3214	Feed an event as if the given signal occurred (C<loop> must be the default
2414	loop!).	3215	loop!).
2415		3216
2416	=back	3217	=back
…		…
2452	you to use some convenience methods to start/stop watchers and also change	3253	you to use some convenience methods to start/stop watchers and also change
2453	the callback model to a model using method callbacks on objects.	3254	the callback model to a model using method callbacks on objects.
2454		3255
2455	To use it,	3256	To use it,
2456		3257
2457	#include <ev++.h>	3258	#include <ev++.h>
2458		3259
2459	This automatically includes F<ev.h> and puts all of its definitions (many	3260	This automatically includes F<ev.h> and puts all of its definitions (many
2460	of them macros) into the global namespace. All C++ specific things are	3261	of them macros) into the global namespace. All C++ specific things are
2461	put into the C<ev> namespace. It should support all the same embedding	3262	put into the C<ev> namespace. It should support all the same embedding
2462	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3263	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2496		3297
2497	=over 4	3298	=over 4
2498		3299
2499	=item ev::TYPE::TYPE ()	3300	=item ev::TYPE::TYPE ()
2500		3301
2501	=item ev::TYPE::TYPE (struct ev_loop *)	3302	=item ev::TYPE::TYPE (loop)
2502		3303
2503	=item ev::TYPE::~TYPE	3304	=item ev::TYPE::~TYPE
2504		3305
2505	The constructor (optionally) takes an event loop to associate the watcher	3306	The constructor (optionally) takes an event loop to associate the watcher
2506	with. If it is omitted, it will use C<EV_DEFAULT>.	3307	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2529	your compiler is good :), then the method will be fully inlined into the	3330	your compiler is good :), then the method will be fully inlined into the
2530	thunking function, making it as fast as a direct C callback.	3331	thunking function, making it as fast as a direct C callback.
2531		3332
2532	Example: simple class declaration and watcher initialisation	3333	Example: simple class declaration and watcher initialisation
2533		3334
2534	struct myclass	3335	struct myclass
2535	{	3336	{
2536	void io_cb (ev::io &w, int revents) { }	3337	void io_cb (ev::io &w, int revents) { }
2537	}	3338	}
2538		3339
2539	myclass obj;	3340	myclass obj;
2540	ev::io iow;	3341	ev::io iow;
2541	iow.set <myclass, &myclass::io_cb> (&obj);	3342	iow.set <myclass, &myclass::io_cb> (&obj);
		3343
		3344	=item w->set (object *)
		3345
		3346	This is an B<experimental> feature that might go away in a future version.
		3347
		3348	This is a variation of a method callback - leaving out the method to call
		3349	will default the method to C<operator ()>, which makes it possible to use
		3350	functor objects without having to manually specify the C<operator ()> all
		3351	the time. Incidentally, you can then also leave out the template argument
		3352	list.
		3353
		3354	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3355	int revents)>.
		3356
		3357	See the method-C<set> above for more details.
		3358
		3359	Example: use a functor object as callback.
		3360
		3361	struct myfunctor
		3362	{
		3363	void operator() (ev::io &w, int revents)
		3364	{
		3365	...
		3366	}
		3367	}
		3368
		3369	myfunctor f;
		3370
		3371	ev::io w;
		3372	w.set (&f);
2542		3373
2543	=item w->set<function> (void *data = 0)	3374	=item w->set<function> (void *data = 0)
2544		3375
2545	Also sets a callback, but uses a static method or plain function as	3376	Also sets a callback, but uses a static method or plain function as
2546	callback. The optional C<data> argument will be stored in the watcher's	3377	callback. The optional C<data> argument will be stored in the watcher's
…		…
2548		3379
2549	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3380	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2550		3381
2551	See the method-C<set> above for more details.	3382	See the method-C<set> above for more details.
2552		3383
2553	Example:	3384	Example: Use a plain function as callback.
2554		3385
2555	static void io_cb (ev::io &w, int revents) { }	3386	static void io_cb (ev::io &w, int revents) { }
2556	iow.set <io_cb> ();	3387	iow.set <io_cb> ();
2557		3388
2558	=item w->set (struct ev_loop *)	3389	=item w->set (loop)
2559		3390
2560	Associates a different C<struct ev_loop> with this watcher. You can only	3391	Associates a different C<struct ev_loop> with this watcher. You can only
2561	do this when the watcher is inactive (and not pending either).	3392	do this when the watcher is inactive (and not pending either).
2562		3393
2563	=item w->set ([arguments])	3394	=item w->set ([arguments])
…		…
2594	=back	3425	=back
2595		3426
2596	Example: Define a class with an IO and idle watcher, start one of them in	3427	Example: Define a class with an IO and idle watcher, start one of them in
2597	the constructor.	3428	the constructor.
2598		3429
2599	class myclass	3430	class myclass
2600	{	3431	{
2601	ev::io io; void io_cb (ev::io &w, int revents);	3432	ev::io io ; void io_cb (ev::io &w, int revents);
2602	ev:idle idle void idle_cb (ev::idle &w, int revents);	3433	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2603		3434
2604	myclass (int fd)	3435	myclass (int fd)
2605	{	3436	{
2606	io .set <myclass, &myclass::io_cb > (this);	3437	io .set <myclass, &myclass::io_cb > (this);
2607	idle.set <myclass, &myclass::idle_cb> (this);	3438	idle.set <myclass, &myclass::idle_cb> (this);
2608		3439
2609	io.start (fd, ev::READ);	3440	io.start (fd, ev::READ);
2610	}	3441	}
2611	};	3442	};
2612		3443
2613		3444
2614	=head1 OTHER LANGUAGE BINDINGS	3445	=head1 OTHER LANGUAGE BINDINGS
2615		3446
2616	Libev does not offer other language bindings itself, but bindings for a	3447	Libev does not offer other language bindings itself, but bindings for a
…		…
2623	=item Perl	3454	=item Perl
2624		3455
2625	The EV module implements the full libev API and is actually used to test	3456	The EV module implements the full libev API and is actually used to test
2626	libev. EV is developed together with libev. Apart from the EV core module,	3457	libev. EV is developed together with libev. Apart from the EV core module,
2627	there are additional modules that implement libev-compatible interfaces	3458	there are additional modules that implement libev-compatible interfaces
2628	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3459	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2629	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3460	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3461	and C<EV::Glib>).
2630		3462
2631	It can be found and installed via CPAN, its homepage is found at	3463	It can be found and installed via CPAN, its homepage is at
2632	L<http://software.schmorp.de/pkg/EV>.	3464	L<http://software.schmorp.de/pkg/EV>.
		3465
		3466	=item Python
		3467
		3468	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3469	seems to be quite complete and well-documented.
2633		3470
2634	=item Ruby	3471	=item Ruby
2635		3472
2636	Tony Arcieri has written a ruby extension that offers access to a subset	3473	Tony Arcieri has written a ruby extension that offers access to a subset
2637	of the libev API and adds file handle abstractions, asynchronous DNS and	3474	of the libev API and adds file handle abstractions, asynchronous DNS and
2638	more on top of it. It can be found via gem servers. Its homepage is at	3475	more on top of it. It can be found via gem servers. Its homepage is at
2639	L<http://rev.rubyforge.org/>.	3476	L<http://rev.rubyforge.org/>.
2640		3477
		3478	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3479	makes rev work even on mingw.
		3480
		3481	=item Haskell
		3482
		3483	A haskell binding to libev is available at
		3484	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3485
2641	=item D	3486	=item D
2642		3487
2643	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3488	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2644	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.	3489	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3490
		3491	=item Ocaml
		3492
		3493	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3494	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3495
		3496	=item Lua
		3497
		3498	Brian Maher has written a partial interface to libev for lua (at the
		3499	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3500	L<http://github.com/brimworks/lua-ev>.
2645		3501
2646	=back	3502	=back
2647		3503
2648		3504
2649	=head1 MACRO MAGIC	3505	=head1 MACRO MAGIC
…		…
2661		3517
2662	This provides the loop I<argument> for functions, if one is required ("ev	3518	This provides the loop I<argument> for functions, if one is required ("ev
2663	loop argument"). The C<EV_A> form is used when this is the sole argument,	3519	loop argument"). The C<EV_A> form is used when this is the sole argument,
2664	C<EV_A_> is used when other arguments are following. Example:	3520	C<EV_A_> is used when other arguments are following. Example:
2665		3521
2666	ev_unref (EV_A);	3522	ev_unref (EV_A);
2667	ev_timer_add (EV_A_ watcher);	3523	ev_timer_add (EV_A_ watcher);
2668	ev_loop (EV_A_ 0);	3524	ev_loop (EV_A_ 0);
2669		3525
2670	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3526	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2671	which is often provided by the following macro.	3527	which is often provided by the following macro.
2672		3528
2673	=item C<EV_P>, C<EV_P_>	3529	=item C<EV_P>, C<EV_P_>
2674		3530
2675	This provides the loop I<parameter> for functions, if one is required ("ev	3531	This provides the loop I<parameter> for functions, if one is required ("ev
2676	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3532	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2677	C<EV_P_> is used when other parameters are following. Example:	3533	C<EV_P_> is used when other parameters are following. Example:
2678		3534
2679	// this is how ev_unref is being declared	3535	// this is how ev_unref is being declared
2680	static void ev_unref (EV_P);	3536	static void ev_unref (EV_P);
2681		3537
2682	// this is how you can declare your typical callback	3538	// this is how you can declare your typical callback
2683	static void cb (EV_P_ ev_timer *w, int revents)	3539	static void cb (EV_P_ ev_timer *w, int revents)
2684		3540
2685	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3541	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2686	suitable for use with C<EV_A>.	3542	suitable for use with C<EV_A>.
2687		3543
2688	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3544	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
…		…
2704		3560
2705	Example: Declare and initialise a check watcher, utilising the above	3561	Example: Declare and initialise a check watcher, utilising the above
2706	macros so it will work regardless of whether multiple loops are supported	3562	macros so it will work regardless of whether multiple loops are supported
2707	or not.	3563	or not.
2708		3564
2709	static void	3565	static void
2710	check_cb (EV_P_ ev_timer *w, int revents)	3566	check_cb (EV_P_ ev_timer *w, int revents)
2711	{	3567	{
2712	ev_check_stop (EV_A_ w);	3568	ev_check_stop (EV_A_ w);
2713	}	3569	}
2714		3570
2715	ev_check check;	3571	ev_check check;
2716	ev_check_init (&check, check_cb);	3572	ev_check_init (&check, check_cb);
2717	ev_check_start (EV_DEFAULT_ &check);	3573	ev_check_start (EV_DEFAULT_ &check);
2718	ev_loop (EV_DEFAULT_ 0);	3574	ev_loop (EV_DEFAULT_ 0);
2719		3575
2720	=head1 EMBEDDING	3576	=head1 EMBEDDING
2721		3577
2722	Libev can (and often is) directly embedded into host	3578	Libev can (and often is) directly embedded into host
2723	applications. Examples of applications that embed it include the Deliantra	3579	applications. Examples of applications that embed it include the Deliantra
…		…
2737	=head3 CORE EVENT LOOP	3593	=head3 CORE EVENT LOOP
2738		3594
2739	To include only the libev core (all the C<ev_*> functions), with manual	3595	To include only the libev core (all the C<ev_*> functions), with manual
2740	configuration (no autoconf):	3596	configuration (no autoconf):
2741		3597
2742	#define EV_STANDALONE 1	3598	#define EV_STANDALONE 1
2743	#include "ev.c"	3599	#include "ev.c"
2744		3600
2745	This will automatically include F<ev.h>, too, and should be done in a	3601	This will automatically include F<ev.h>, too, and should be done in a
2746	single C source file only to provide the function implementations. To use	3602	single C source file only to provide the function implementations. To use
2747	it, do the same for F<ev.h> in all files wishing to use this API (best	3603	it, do the same for F<ev.h> in all files wishing to use this API (best
2748	done by writing a wrapper around F<ev.h> that you can include instead and	3604	done by writing a wrapper around F<ev.h> that you can include instead and
2749	where you can put other configuration options):	3605	where you can put other configuration options):
2750		3606
2751	#define EV_STANDALONE 1	3607	#define EV_STANDALONE 1
2752	#include "ev.h"	3608	#include "ev.h"
2753		3609
2754	Both header files and implementation files can be compiled with a C++	3610	Both header files and implementation files can be compiled with a C++
2755	compiler (at least, thats a stated goal, and breakage will be treated	3611	compiler (at least, that's a stated goal, and breakage will be treated
2756	as a bug).	3612	as a bug).
2757		3613
2758	You need the following files in your source tree, or in a directory	3614	You need the following files in your source tree, or in a directory
2759	in your include path (e.g. in libev/ when using -Ilibev):	3615	in your include path (e.g. in libev/ when using -Ilibev):
2760		3616
2761	ev.h	3617	ev.h
2762	ev.c	3618	ev.c
2763	ev_vars.h	3619	ev_vars.h
2764	ev_wrap.h	3620	ev_wrap.h
2765		3621
2766	ev_win32.c required on win32 platforms only	3622	ev_win32.c required on win32 platforms only
2767		3623
2768	ev_select.c only when select backend is enabled (which is enabled by default)	3624	ev_select.c only when select backend is enabled (which is enabled by default)
2769	ev_poll.c only when poll backend is enabled (disabled by default)	3625	ev_poll.c only when poll backend is enabled (disabled by default)
2770	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3626	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2771	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3627	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2772	ev_port.c only when the solaris port backend is enabled (disabled by default)	3628	ev_port.c only when the solaris port backend is enabled (disabled by default)
2773		3629
2774	F<ev.c> includes the backend files directly when enabled, so you only need	3630	F<ev.c> includes the backend files directly when enabled, so you only need
2775	to compile this single file.	3631	to compile this single file.
2776		3632
2777	=head3 LIBEVENT COMPATIBILITY API	3633	=head3 LIBEVENT COMPATIBILITY API
2778		3634
2779	To include the libevent compatibility API, also include:	3635	To include the libevent compatibility API, also include:
2780		3636
2781	#include "event.c"	3637	#include "event.c"
2782		3638
2783	in the file including F<ev.c>, and:	3639	in the file including F<ev.c>, and:
2784		3640
2785	#include "event.h"	3641	#include "event.h"
2786		3642
2787	in the files that want to use the libevent API. This also includes F<ev.h>.	3643	in the files that want to use the libevent API. This also includes F<ev.h>.
2788		3644
2789	You need the following additional files for this:	3645	You need the following additional files for this:
2790		3646
2791	event.h	3647	event.h
2792	event.c	3648	event.c
2793		3649
2794	=head3 AUTOCONF SUPPORT	3650	=head3 AUTOCONF SUPPORT
2795		3651
2796	Instead of using C<EV_STANDALONE=1> and providing your configuration in	3652	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2797	whatever way you want, you can also C<m4_include([libev.m4])> in your	3653	whatever way you want, you can also C<m4_include([libev.m4])> in your
2798	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3654	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2799	include F<config.h> and configure itself accordingly.	3655	include F<config.h> and configure itself accordingly.
2800		3656
2801	For this of course you need the m4 file:	3657	For this of course you need the m4 file:
2802		3658
2803	libev.m4	3659	libev.m4
2804		3660
2805	=head2 PREPROCESSOR SYMBOLS/MACROS	3661	=head2 PREPROCESSOR SYMBOLS/MACROS
2806		3662
2807	Libev can be configured via a variety of preprocessor symbols you have to	3663	Libev can be configured via a variety of preprocessor symbols you have to
2808	define before including any of its files. The default in the absence of	3664	define before including (or compiling) any of its files. The default in
2809	autoconf is noted for every option.	3665	the absence of autoconf is documented for every option.
		3666
		3667	Symbols marked with "(h)" do not change the ABI, and can have different
		3668	values when compiling libev vs. including F<ev.h>, so it is permissible
		3669	to redefine them before including F<ev.h> without breaking compatibility
		3670	to a compiled library. All other symbols change the ABI, which means all
		3671	users of libev and the libev code itself must be compiled with compatible
		3672	settings.
2810		3673
2811	=over 4	3674	=over 4
2812		3675
2813	=item EV_STANDALONE	3676	=item EV_STANDALONE (h)
2814		3677
2815	Must always be C<1> if you do not use autoconf configuration, which	3678	Must always be C<1> if you do not use autoconf configuration, which
2816	keeps libev from including F<config.h>, and it also defines dummy	3679	keeps libev from including F<config.h>, and it also defines dummy
2817	implementations for some libevent functions (such as logging, which is not	3680	implementations for some libevent functions (such as logging, which is not
2818	supported). It will also not define any of the structs usually found in	3681	supported). It will also not define any of the structs usually found in
2819	F<event.h> that are not directly supported by the libev core alone.	3682	F<event.h> that are not directly supported by the libev core alone.
2820		3683
		3684	In standalone mode, libev will still try to automatically deduce the
		3685	configuration, but has to be more conservative.
		3686
2821	=item EV_USE_MONOTONIC	3687	=item EV_USE_MONOTONIC
2822		3688
2823	If defined to be C<1>, libev will try to detect the availability of the	3689	If defined to be C<1>, libev will try to detect the availability of the
2824	monotonic clock option at both compile time and runtime. Otherwise no use	3690	monotonic clock option at both compile time and runtime. Otherwise no
2825	of the monotonic clock option will be attempted. If you enable this, you	3691	use of the monotonic clock option will be attempted. If you enable this,
2826	usually have to link against librt or something similar. Enabling it when	3692	you usually have to link against librt or something similar. Enabling it
2827	the functionality isn't available is safe, though, although you have	3693	when the functionality isn't available is safe, though, although you have
2828	to make sure you link against any libraries where the C<clock_gettime>	3694	to make sure you link against any libraries where the C<clock_gettime>
2829	function is hiding in (often F<-lrt>).	3695	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2830		3696
2831	=item EV_USE_REALTIME	3697	=item EV_USE_REALTIME
2832		3698
2833	If defined to be C<1>, libev will try to detect the availability of the	3699	If defined to be C<1>, libev will try to detect the availability of the
2834	real-time clock option at compile time (and assume its availability at	3700	real-time clock option at compile time (and assume its availability
2835	runtime if successful). Otherwise no use of the real-time clock option will	3701	at runtime if successful). Otherwise no use of the real-time clock
2836	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3702	option will be attempted. This effectively replaces C<gettimeofday>
2837	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3703	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2838	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3704	correctness. See the note about libraries in the description of
		3705	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3706	C<EV_USE_CLOCK_SYSCALL>.
		3707
		3708	=item EV_USE_CLOCK_SYSCALL
		3709
		3710	If defined to be C<1>, libev will try to use a direct syscall instead
		3711	of calling the system-provided C<clock_gettime> function. This option
		3712	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3713	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3714	programs needlessly. Using a direct syscall is slightly slower (in
		3715	theory), because no optimised vdso implementation can be used, but avoids
		3716	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3717	higher, as it simplifies linking (no need for C<-lrt>).
2839		3718
2840	=item EV_USE_NANOSLEEP	3719	=item EV_USE_NANOSLEEP
2841		3720
2842	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3721	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2843	and will use it for delays. Otherwise it will use C<select ()>.	3722	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2859		3738
2860	=item EV_SELECT_USE_FD_SET	3739	=item EV_SELECT_USE_FD_SET
2861		3740
2862	If defined to C<1>, then the select backend will use the system C<fd_set>	3741	If defined to C<1>, then the select backend will use the system C<fd_set>
2863	structure. This is useful if libev doesn't compile due to a missing	3742	structure. This is useful if libev doesn't compile due to a missing
2864	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3743	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2865	exotic systems. This usually limits the range of file descriptors to some	3744	on exotic systems. This usually limits the range of file descriptors to
2866	low limit such as 1024 or might have other limitations (winsocket only	3745	some low limit such as 1024 or might have other limitations (winsocket
2867	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3746	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2868	influence the size of the C<fd_set> used.	3747	configures the maximum size of the C<fd_set>.
2869		3748
2870	=item EV_SELECT_IS_WINSOCKET	3749	=item EV_SELECT_IS_WINSOCKET
2871		3750
2872	When defined to C<1>, the select backend will assume that	3751	When defined to C<1>, the select backend will assume that
2873	select/socket/connect etc. don't understand file descriptors but	3752	select/socket/connect etc. don't understand file descriptors but
…		…
2875	be used is the winsock select). This means that it will call	3754	be used is the winsock select). This means that it will call
2876	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3755	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2877	it is assumed that all these functions actually work on fds, even	3756	it is assumed that all these functions actually work on fds, even
2878	on win32. Should not be defined on non-win32 platforms.	3757	on win32. Should not be defined on non-win32 platforms.
2879		3758
2880	=item EV_FD_TO_WIN32_HANDLE	3759	=item EV_FD_TO_WIN32_HANDLE(fd)
2881		3760
2882	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3761	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2883	file descriptors to socket handles. When not defining this symbol (the	3762	file descriptors to socket handles. When not defining this symbol (the
2884	default), then libev will call C<_get_osfhandle>, which is usually	3763	default), then libev will call C<_get_osfhandle>, which is usually
2885	correct. In some cases, programs use their own file descriptor management,	3764	correct. In some cases, programs use their own file descriptor management,
2886	in which case they can provide this function to map fds to socket handles.	3765	in which case they can provide this function to map fds to socket handles.
		3766
		3767	=item EV_WIN32_HANDLE_TO_FD(handle)
		3768
		3769	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3770	using the standard C<_open_osfhandle> function. For programs implementing
		3771	their own fd to handle mapping, overwriting this function makes it easier
		3772	to do so. This can be done by defining this macro to an appropriate value.
		3773
		3774	=item EV_WIN32_CLOSE_FD(fd)
		3775
		3776	If programs implement their own fd to handle mapping on win32, then this
		3777	macro can be used to override the C<close> function, useful to unregister
		3778	file descriptors again. Note that the replacement function has to close
		3779	the underlying OS handle.
2887		3780
2888	=item EV_USE_POLL	3781	=item EV_USE_POLL
2889		3782
2890	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3783	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2891	backend. Otherwise it will be enabled on non-win32 platforms. It	3784	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
2938	as well as for signal and thread safety in C<ev_async> watchers.	3831	as well as for signal and thread safety in C<ev_async> watchers.
2939		3832
2940	In the absence of this define, libev will use C<sig_atomic_t volatile>	3833	In the absence of this define, libev will use C<sig_atomic_t volatile>
2941	(from F<signal.h>), which is usually good enough on most platforms.	3834	(from F<signal.h>), which is usually good enough on most platforms.
2942		3835
2943	=item EV_H	3836	=item EV_H (h)
2944		3837
2945	The name of the F<ev.h> header file used to include it. The default if	3838	The name of the F<ev.h> header file used to include it. The default if
2946	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	3839	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2947	used to virtually rename the F<ev.h> header file in case of conflicts.	3840	used to virtually rename the F<ev.h> header file in case of conflicts.
2948		3841
2949	=item EV_CONFIG_H	3842	=item EV_CONFIG_H (h)
2950		3843
2951	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3844	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2952	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3845	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2953	C<EV_H>, above.	3846	C<EV_H>, above.
2954		3847
2955	=item EV_EVENT_H	3848	=item EV_EVENT_H (h)
2956		3849
2957	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3850	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2958	of how the F<event.h> header can be found, the default is C<"event.h">.	3851	of how the F<event.h> header can be found, the default is C<"event.h">.
2959		3852
2960	=item EV_PROTOTYPES	3853	=item EV_PROTOTYPES (h)
2961		3854
2962	If defined to be C<0>, then F<ev.h> will not define any function	3855	If defined to be C<0>, then F<ev.h> will not define any function
2963	prototypes, but still define all the structs and other symbols. This is	3856	prototypes, but still define all the structs and other symbols. This is
2964	occasionally useful if you want to provide your own wrapper functions	3857	occasionally useful if you want to provide your own wrapper functions
2965	around libev functions.	3858	around libev functions.
…		…
2984	When doing priority-based operations, libev usually has to linearly search	3877	When doing priority-based operations, libev usually has to linearly search
2985	all the priorities, so having many of them (hundreds) uses a lot of space	3878	all the priorities, so having many of them (hundreds) uses a lot of space
2986	and time, so using the defaults of five priorities (-2 .. +2) is usually	3879	and time, so using the defaults of five priorities (-2 .. +2) is usually
2987	fine.	3880	fine.
2988		3881
2989	If your embedding application does not need any priorities, defining these both to	3882	If your embedding application does not need any priorities, defining these
2990	C<0> will save some memory and CPU.	3883	both to C<0> will save some memory and CPU.
2991		3884
2992	=item EV_PERIODIC_ENABLE	3885	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		3886	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		3887	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2993		3888
2994	If undefined or defined to be C<1>, then periodic timers are supported. If	3889	If undefined or defined to be C<1> (and the platform supports it), then
2995	defined to be C<0>, then they are not. Disabling them saves a few kB of	3890	the respective watcher type is supported. If defined to be C<0>, then it
2996	code.	3891	is not. Disabling watcher types mainly saves codesize.
2997		3892
2998	=item EV_IDLE_ENABLE	3893	=item EV_FEATURES
2999
3000	If undefined or defined to be C<1>, then idle watchers are supported. If
3001	defined to be C<0>, then they are not. Disabling them saves a few kB of
3002	code.
3003
3004	=item EV_EMBED_ENABLE
3005
3006	If undefined or defined to be C<1>, then embed watchers are supported. If
3007	defined to be C<0>, then they are not.
3008
3009	=item EV_STAT_ENABLE
3010
3011	If undefined or defined to be C<1>, then stat watchers are supported. If
3012	defined to be C<0>, then they are not.
3013
3014	=item EV_FORK_ENABLE
3015
3016	If undefined or defined to be C<1>, then fork watchers are supported. If
3017	defined to be C<0>, then they are not.
3018
3019	=item EV_ASYNC_ENABLE
3020
3021	If undefined or defined to be C<1>, then async watchers are supported. If
3022	defined to be C<0>, then they are not.
3023
3024	=item EV_MINIMAL
3025		3894
3026	If you need to shave off some kilobytes of code at the expense of some	3895	If you need to shave off some kilobytes of code at the expense of some
3027	speed, define this symbol to C<1>. Currently this is used to override some	3896	speed (but with the full API), you can define this symbol to request
3028	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3897	certain subsets of functionality. The default is to enable all features
3029	much smaller 2-heap for timer management over the default 4-heap.	3898	that can be enabled on the platform.
		3899
		3900	A typical way to use this symbol is to define it to C<0> (or to a bitset
		3901	with some broad features you want) and then selectively re-enable
		3902	additional parts you want, for example if you want everything minimal,
		3903	but multiple event loop support, async and child watchers and the poll
		3904	backend, use this:
		3905
		3906	#define EV_FEATURES 0
		3907	#define EV_MULTIPLICITY 1
		3908	#define EV_USE_POLL 1
		3909	#define EV_CHILD_ENABLE 1
		3910	#define EV_ASYNC_ENABLE 1
		3911
		3912	The actual value is a bitset, it can be a combination of the following
		3913	values:
		3914
		3915	=over 4
		3916
		3917	=item C<1> - faster/larger code
		3918
		3919	Use larger code to speed up some operations.
		3920
		3921	Currently this is used to override some inlining decisions (enlarging the roughly
		3922	30% code size on amd64.
		3923
		3924	When optimising for size, use of compiler flags such as C<-Os> with
		3925	gcc recommended, as well as C<-DNDEBUG>, as libev contains a number of
		3926	assertions.
		3927
		3928	=item C<2> - faster/larger data structures
		3929
		3930	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		3931	hash table sizes and so on. This will usually further increase codesize
		3932	and can additionally have an effect on the size of data structures at
		3933	runtime.
		3934
		3935	=item C<4> - full API configuration
		3936
		3937	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		3938	enables multiplicity (C<EV_MULTIPLICITY>=1).
		3939
		3940	=item C<8> - full API
		3941
		3942	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		3943	details on which parts of the API are still available without this
		3944	feature, and do not complain if this subset changes over time.
		3945
		3946	=item C<16> - enable all optional watcher types
		3947
		3948	Enables all optional watcher types. If you want to selectively enable
		3949	only some watcher types other than I/O and timers (e.g. prepare,
		3950	embed, async, child...) you can enable them manually by defining
		3951	C<EV_watchertype_ENABLE> to C<1> instead.
		3952
		3953	=item C<32> - enable all backends
		3954
		3955	This enables all backends - without this feature, you need to enable at
		3956	least one backend manually (C<EV_USE_SELECT> is a good choice).
		3957
		3958	=item C<64> - enable OS-specific "helper" APIs
		3959
		3960	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		3961	default.
		3962
		3963	=back
		3964
		3965	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		3966	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		3967	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		3968	watchers, timers and monotonic clock support.
		3969
		3970	With an intelligent-enough linker (gcc+binutils are intelligent enough
		3971	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		3972	your program might be left out as well - a binary starting a timer and an
		3973	I/O watcher then might come out at only 5Kb.
		3974
		3975	=item EV_AVOID_STDIO
		3976
		3977	If this is set to C<1> at compiletime, then libev will avoid using stdio
		3978	functions (printf, scanf, perror etc.). This will increase the codesize
		3979	somewhat, but if your program doesn't otherwise depend on stdio and your
		3980	libc allows it, this avoids linking in the stdio library which is quite
		3981	big.
		3982
		3983	Note that error messages might become less precise when this option is
		3984	enabled.
		3985
		3986	=item EV_NSIG
		3987
		3988	The highest supported signal number, +1 (or, the number of
		3989	signals): Normally, libev tries to deduce the maximum number of signals
		3990	automatically, but sometimes this fails, in which case it can be
		3991	specified. Also, using a lower number than detected (C<32> should be
		3992	good for about any system in existance) can save some memory, as libev
		3993	statically allocates some 12-24 bytes per signal number.
3030		3994
3031	=item EV_PID_HASHSIZE	3995	=item EV_PID_HASHSIZE
3032		3996
3033	C<ev_child> watchers use a small hash table to distribute workload by	3997	C<ev_child> watchers use a small hash table to distribute workload by
3034	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3998	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
3035	than enough. If you need to manage thousands of children you might want to	3999	usually more than enough. If you need to manage thousands of children you
3036	increase this value (I<must> be a power of two).	4000	might want to increase this value (I<must> be a power of two).
3037		4001
3038	=item EV_INOTIFY_HASHSIZE	4002	=item EV_INOTIFY_HASHSIZE
3039		4003
3040	C<ev_stat> watchers use a small hash table to distribute workload by	4004	C<ev_stat> watchers use a small hash table to distribute workload by
3041	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4005	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
3042	usually more than enough. If you need to manage thousands of C<ev_stat>	4006	disabled), usually more than enough. If you need to manage thousands of
3043	watchers you might want to increase this value (I<must> be a power of	4007	C<ev_stat> watchers you might want to increase this value (I<must> be a
3044	two).	4008	power of two).
3045		4009
3046	=item EV_USE_4HEAP	4010	=item EV_USE_4HEAP
3047		4011
3048	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4012	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3049	timer and periodics heap, libev uses a 4-heap when this symbol is defined	4013	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3050	to C<1>. The 4-heap uses more complicated (longer) code but has	4014	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3051	noticeably faster performance with many (thousands) of watchers.	4015	faster performance with many (thousands) of watchers.
3052		4016
3053	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4017	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3054	(disabled).	4018	will be C<0>.
3055		4019
3056	=item EV_HEAP_CACHE_AT	4020	=item EV_HEAP_CACHE_AT
3057		4021
3058	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4022	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3059	timer and periodics heap, libev can cache the timestamp (I<at>) within	4023	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3060	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	4024	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3061	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	4025	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3062	but avoids random read accesses on heap changes. This improves performance	4026	but avoids random read accesses on heap changes. This improves performance
3063	noticeably with with many (hundreds) of watchers.	4027	noticeably with many (hundreds) of watchers.
3064		4028
3065	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4029	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3066	(disabled).	4030	will be C<0>.
3067		4031
3068	=item EV_VERIFY	4032	=item EV_VERIFY
3069		4033
3070	Controls how much internal verification (see C<ev_loop_verify ()>) will	4034	Controls how much internal verification (see C<ev_loop_verify ()>) will
3071	be done: If set to C<0>, no internal verification code will be compiled	4035	be done: If set to C<0>, no internal verification code will be compiled
…		…
3073	called. If set to C<2>, then the internal verification code will be	4037	called. If set to C<2>, then the internal verification code will be
3074	called once per loop, which can slow down libev. If set to C<3>, then the	4038	called once per loop, which can slow down libev. If set to C<3>, then the
3075	verification code will be called very frequently, which will slow down	4039	verification code will be called very frequently, which will slow down
3076	libev considerably.	4040	libev considerably.
3077		4041
3078	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	4042	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3079	C<0.>	4043	will be C<0>.
3080		4044
3081	=item EV_COMMON	4045	=item EV_COMMON
3082		4046
3083	By default, all watchers have a C<void *data> member. By redefining	4047	By default, all watchers have a C<void *data> member. By redefining
3084	this macro to a something else you can include more and other types of	4048	this macro to a something else you can include more and other types of
3085	members. You have to define it each time you include one of the files,	4049	members. You have to define it each time you include one of the files,
3086	though, and it must be identical each time.	4050	though, and it must be identical each time.
3087		4051
3088	For example, the perl EV module uses something like this:	4052	For example, the perl EV module uses something like this:
3089		4053
3090	#define EV_COMMON \	4054	#define EV_COMMON \
3091	SV *self; /* contains this struct */ \	4055	SV *self; /* contains this struct */ \
3092	SV *cb_sv, *fh /* note no trailing ";" */	4056	SV *cb_sv, *fh /* note no trailing ";" */
3093		4057
3094	=item EV_CB_DECLARE (type)	4058	=item EV_CB_DECLARE (type)
3095		4059
3096	=item EV_CB_INVOKE (watcher, revents)	4060	=item EV_CB_INVOKE (watcher, revents)
3097		4061
…		…
3102	definition and a statement, respectively. See the F<ev.h> header file for	4066	definition and a statement, respectively. See the F<ev.h> header file for
3103	their default definitions. One possible use for overriding these is to	4067	their default definitions. One possible use for overriding these is to
3104	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4068	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3105	method calls instead of plain function calls in C++.	4069	method calls instead of plain function calls in C++.
3106		4070
		4071	=back
		4072
3107	=head2 EXPORTED API SYMBOLS	4073	=head2 EXPORTED API SYMBOLS
3108		4074
3109	If you need to re-export the API (e.g. via a DLL) and you need a list of	4075	If you need to re-export the API (e.g. via a DLL) and you need a list of
3110	exported symbols, you can use the provided F<Symbol.*> files which list	4076	exported symbols, you can use the provided F<Symbol.*> files which list
3111	all public symbols, one per line:	4077	all public symbols, one per line:
3112		4078
3113	Symbols.ev for libev proper	4079	Symbols.ev for libev proper
3114	Symbols.event for the libevent emulation	4080	Symbols.event for the libevent emulation
3115		4081
3116	This can also be used to rename all public symbols to avoid clashes with	4082	This can also be used to rename all public symbols to avoid clashes with
3117	multiple versions of libev linked together (which is obviously bad in	4083	multiple versions of libev linked together (which is obviously bad in
3118	itself, but sometimes it is inconvenient to avoid this).	4084	itself, but sometimes it is inconvenient to avoid this).
3119		4085
…		…
3140	file.	4106	file.
3141		4107
3142	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4108	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3143	that everybody includes and which overrides some configure choices:	4109	that everybody includes and which overrides some configure choices:
3144		4110
3145	#define EV_MINIMAL 1	4111	#define EV_FEATURES 8
3146	#define EV_USE_POLL 0	4112	#define EV_USE_SELECT 1
3147	#define EV_MULTIPLICITY 0
3148	#define EV_PERIODIC_ENABLE 0	4113	#define EV_PREPARE_ENABLE 1
		4114	#define EV_IDLE_ENABLE 1
3149	#define EV_STAT_ENABLE 0	4115	#define EV_SIGNAL_ENABLE 1
3150	#define EV_FORK_ENABLE 0	4116	#define EV_CHILD_ENABLE 1
		4117	#define EV_USE_STDEXCEPT 0
3151	#define EV_CONFIG_H <config.h>	4118	#define EV_CONFIG_H <config.h>
3152	#define EV_MINPRI 0
3153	#define EV_MAXPRI 0
3154		4119
3155	#include "ev++.h"	4120	#include "ev++.h"
3156		4121
3157	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4122	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3158		4123
3159	#include "ev_cpp.h"	4124	#include "ev_cpp.h"
3160	#include "ev.c"	4125	#include "ev.c"
3161		4126
		4127	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3162		4128
3163	=head1 THREADS AND COROUTINES	4129	=head2 THREADS AND COROUTINES
3164		4130
3165	=head2 THREADS	4131	=head3 THREADS
3166		4132
3167	Libev itself is completely thread-safe, but it uses no locking. This	4133	All libev functions are reentrant and thread-safe unless explicitly
		4134	documented otherwise, but libev implements no locking itself. This means
3168	means that you can use as many loops as you want in parallel, as long as	4135	that you can use as many loops as you want in parallel, as long as there
3169	only one thread ever calls into one libev function with the same loop	4136	are no concurrent calls into any libev function with the same loop
3170	parameter.	4137	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4138	of course): libev guarantees that different event loops share no data
		4139	structures that need any locking.
3171		4140
3172	Or put differently: calls with different loop parameters can be done in	4141	Or to put it differently: calls with different loop parameters can be done
3173	parallel from multiple threads, calls with the same loop parameter must be	4142	concurrently from multiple threads, calls with the same loop parameter
3174	done serially (but can be done from different threads, as long as only one	4143	must be done serially (but can be done from different threads, as long as
3175	thread ever is inside a call at any point in time, e.g. by using a mutex	4144	only one thread ever is inside a call at any point in time, e.g. by using
3176	per loop).	4145	a mutex per loop).
3177		4146
3178	If you want to know which design is best for your problem, then I cannot	4147	Specifically to support threads (and signal handlers), libev implements
		4148	so-called C<ev_async> watchers, which allow some limited form of
		4149	concurrency on the same event loop, namely waking it up "from the
		4150	outside".
		4151
		4152	If you want to know which design (one loop, locking, or multiple loops
		4153	without or something else still) is best for your problem, then I cannot
3179	help you but by giving some generic advice:	4154	help you, but here is some generic advice:
3180		4155
3181	=over 4	4156	=over 4
3182		4157
3183	=item * most applications have a main thread: use the default libev loop	4158	=item * most applications have a main thread: use the default libev loop
3184	in that thread, or create a separate thread running only the default loop.	4159	in that thread, or create a separate thread running only the default loop.
…		…
3196		4171
3197	Choosing a model is hard - look around, learn, know that usually you can do	4172	Choosing a model is hard - look around, learn, know that usually you can do
3198	better than you currently do :-)	4173	better than you currently do :-)
3199		4174
3200	=item * often you need to talk to some other thread which blocks in the	4175	=item * often you need to talk to some other thread which blocks in the
		4176	event loop.
		4177
3201	event loop - C<ev_async> watchers can be used to wake them up from other	4178	C<ev_async> watchers can be used to wake them up from other threads safely
3202	threads safely (or from signal contexts...).	4179	(or from signal contexts...).
		4180
		4181	An example use would be to communicate signals or other events that only
		4182	work in the default loop by registering the signal watcher with the
		4183	default loop and triggering an C<ev_async> watcher from the default loop
		4184	watcher callback into the event loop interested in the signal.
3203		4185
3204	=back	4186	=back
3205		4187
		4188	=head4 THREAD LOCKING EXAMPLE
		4189
		4190	Here is a fictitious example of how to run an event loop in a different
		4191	thread than where callbacks are being invoked and watchers are
		4192	created/added/removed.
		4193
		4194	For a real-world example, see the C<EV::Loop::Async> perl module,
		4195	which uses exactly this technique (which is suited for many high-level
		4196	languages).
		4197
		4198	The example uses a pthread mutex to protect the loop data, a condition
		4199	variable to wait for callback invocations, an async watcher to notify the
		4200	event loop thread and an unspecified mechanism to wake up the main thread.
		4201
		4202	First, you need to associate some data with the event loop:
		4203
		4204	typedef struct {
		4205	mutex_t lock; /* global loop lock */
		4206	ev_async async_w;
		4207	thread_t tid;
		4208	cond_t invoke_cv;
		4209	} userdata;
		4210
		4211	void prepare_loop (EV_P)
		4212	{
		4213	// for simplicity, we use a static userdata struct.
		4214	static userdata u;
		4215
		4216	ev_async_init (&u->async_w, async_cb);
		4217	ev_async_start (EV_A_ &u->async_w);
		4218
		4219	pthread_mutex_init (&u->lock, 0);
		4220	pthread_cond_init (&u->invoke_cv, 0);
		4221
		4222	// now associate this with the loop
		4223	ev_set_userdata (EV_A_ u);
		4224	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4225	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4226
		4227	// then create the thread running ev_loop
		4228	pthread_create (&u->tid, 0, l_run, EV_A);
		4229	}
		4230
		4231	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4232	solely to wake up the event loop so it takes notice of any new watchers
		4233	that might have been added:
		4234
		4235	static void
		4236	async_cb (EV_P_ ev_async *w, int revents)
		4237	{
		4238	// just used for the side effects
		4239	}
		4240
		4241	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4242	protecting the loop data, respectively.
		4243
		4244	static void
		4245	l_release (EV_P)
		4246	{
		4247	userdata *u = ev_userdata (EV_A);
		4248	pthread_mutex_unlock (&u->lock);
		4249	}
		4250
		4251	static void
		4252	l_acquire (EV_P)
		4253	{
		4254	userdata *u = ev_userdata (EV_A);
		4255	pthread_mutex_lock (&u->lock);
		4256	}
		4257
		4258	The event loop thread first acquires the mutex, and then jumps straight
		4259	into C<ev_loop>:
		4260
		4261	void *
		4262	l_run (void *thr_arg)
		4263	{
		4264	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4265
		4266	l_acquire (EV_A);
		4267	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4268	ev_loop (EV_A_ 0);
		4269	l_release (EV_A);
		4270
		4271	return 0;
		4272	}
		4273
		4274	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4275	signal the main thread via some unspecified mechanism (signals? pipe
		4276	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4277	have been called (in a while loop because a) spurious wakeups are possible
		4278	and b) skipping inter-thread-communication when there are no pending
		4279	watchers is very beneficial):
		4280
		4281	static void
		4282	l_invoke (EV_P)
		4283	{
		4284	userdata *u = ev_userdata (EV_A);
		4285
		4286	while (ev_pending_count (EV_A))
		4287	{
		4288	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4289	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4290	}
		4291	}
		4292
		4293	Now, whenever the main thread gets told to invoke pending watchers, it
		4294	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4295	thread to continue:
		4296
		4297	static void
		4298	real_invoke_pending (EV_P)
		4299	{
		4300	userdata *u = ev_userdata (EV_A);
		4301
		4302	pthread_mutex_lock (&u->lock);
		4303	ev_invoke_pending (EV_A);
		4304	pthread_cond_signal (&u->invoke_cv);
		4305	pthread_mutex_unlock (&u->lock);
		4306	}
		4307
		4308	Whenever you want to start/stop a watcher or do other modifications to an
		4309	event loop, you will now have to lock:
		4310
		4311	ev_timer timeout_watcher;
		4312	userdata *u = ev_userdata (EV_A);
		4313
		4314	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4315
		4316	pthread_mutex_lock (&u->lock);
		4317	ev_timer_start (EV_A_ &timeout_watcher);
		4318	ev_async_send (EV_A_ &u->async_w);
		4319	pthread_mutex_unlock (&u->lock);
		4320
		4321	Note that sending the C<ev_async> watcher is required because otherwise
		4322	an event loop currently blocking in the kernel will have no knowledge
		4323	about the newly added timer. By waking up the loop it will pick up any new
		4324	watchers in the next event loop iteration.
		4325
3206	=head2 COROUTINES	4326	=head3 COROUTINES
3207		4327
3208	Libev is much more accommodating to coroutines ("cooperative threads"):	4328	Libev is very accommodating to coroutines ("cooperative threads"):
3209	libev fully supports nesting calls to it's functions from different	4329	libev fully supports nesting calls to its functions from different
3210	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4330	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3211	different coroutines and switch freely between both coroutines running the	4331	different coroutines, and switch freely between both coroutines running
3212	loop, as long as you don't confuse yourself). The only exception is that	4332	the loop, as long as you don't confuse yourself). The only exception is
3213	you must not do this from C<ev_periodic> reschedule callbacks.	4333	that you must not do this from C<ev_periodic> reschedule callbacks.
3214		4334
3215	Care has been invested into making sure that libev does not keep local	4335	Care has been taken to ensure that libev does not keep local state inside
3216	state inside C<ev_loop>, and other calls do not usually allow coroutine	4336	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3217	switches.	4337	they do not call any callbacks.
3218		4338
		4339	=head2 COMPILER WARNINGS
3219		4340
3220	=head1 COMPLEXITIES	4341	Depending on your compiler and compiler settings, you might get no or a
		4342	lot of warnings when compiling libev code. Some people are apparently
		4343	scared by this.
3221		4344
3222	In this section the complexities of (many of) the algorithms used inside	4345	However, these are unavoidable for many reasons. For one, each compiler
3223	libev will be explained. For complexity discussions about backends see the	4346	has different warnings, and each user has different tastes regarding
3224	documentation for C<ev_default_init>.	4347	warning options. "Warn-free" code therefore cannot be a goal except when
		4348	targeting a specific compiler and compiler-version.
3225		4349
3226	All of the following are about amortised time: If an array needs to be	4350	Another reason is that some compiler warnings require elaborate
3227	extended, libev needs to realloc and move the whole array, but this	4351	workarounds, or other changes to the code that make it less clear and less
3228	happens asymptotically never with higher number of elements, so O(1) might	4352	maintainable.
3229	mean it might do a lengthy realloc operation in rare cases, but on average
3230	it is much faster and asymptotically approaches constant time.
3231		4353
3232	=over 4	4354	And of course, some compiler warnings are just plain stupid, or simply
		4355	wrong (because they don't actually warn about the condition their message
		4356	seems to warn about). For example, certain older gcc versions had some
		4357	warnings that resulted an extreme number of false positives. These have
		4358	been fixed, but some people still insist on making code warn-free with
		4359	such buggy versions.
3233		4360
3234	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4361	While libev is written to generate as few warnings as possible,
		4362	"warn-free" code is not a goal, and it is recommended not to build libev
		4363	with any compiler warnings enabled unless you are prepared to cope with
		4364	them (e.g. by ignoring them). Remember that warnings are just that:
		4365	warnings, not errors, or proof of bugs.
3235		4366
3236	This means that, when you have a watcher that triggers in one hour and
3237	there are 100 watchers that would trigger before that then inserting will
3238	have to skip roughly seven (C<ld 100>) of these watchers.
3239		4367
3240	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4368	=head2 VALGRIND
3241		4369
3242	That means that changing a timer costs less than removing/adding them	4370	Valgrind has a special section here because it is a popular tool that is
3243	as only the relative motion in the event queue has to be paid for.	4371	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3244		4372
3245	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4373	If you think you found a bug (memory leak, uninitialised data access etc.)
		4374	in libev, then check twice: If valgrind reports something like:
3246		4375
3247	These just add the watcher into an array or at the head of a list.	4376	==2274== definitely lost: 0 bytes in 0 blocks.
		4377	==2274== possibly lost: 0 bytes in 0 blocks.
		4378	==2274== still reachable: 256 bytes in 1 blocks.
3248		4379
3249	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4380	Then there is no memory leak, just as memory accounted to global variables
		4381	is not a memleak - the memory is still being referenced, and didn't leak.
3250		4382
3251	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4383	Similarly, under some circumstances, valgrind might report kernel bugs
		4384	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4385	although an acceptable workaround has been found here), or it might be
		4386	confused.
3252		4387
3253	These watchers are stored in lists then need to be walked to find the	4388	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3254	correct watcher to remove. The lists are usually short (you don't usually	4389	make it into some kind of religion.
3255	have many watchers waiting for the same fd or signal).
3256		4390
3257	=item Finding the next timer in each loop iteration: O(1)	4391	If you are unsure about something, feel free to contact the mailing list
		4392	with the full valgrind report and an explanation on why you think this
		4393	is a bug in libev (best check the archives, too :). However, don't be
		4394	annoyed when you get a brisk "this is no bug" answer and take the chance
		4395	of learning how to interpret valgrind properly.
3258		4396
3259	By virtue of using a binary or 4-heap, the next timer is always found at a	4397	If you need, for some reason, empty reports from valgrind for your project
3260	fixed position in the storage array.	4398	I suggest using suppression lists.
3261		4399
3262	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3263		4400
3264	A change means an I/O watcher gets started or stopped, which requires	4401	=head1 PORTABILITY NOTES
3265	libev to recalculate its status (and possibly tell the kernel, depending
3266	on backend and whether C<ev_io_set> was used).
3267		4402
3268	=item Activating one watcher (putting it into the pending state): O(1)
3269
3270	=item Priority handling: O(number_of_priorities)
3271
3272	Priorities are implemented by allocating some space for each
3273	priority. When doing priority-based operations, libev usually has to
3274	linearly search all the priorities, but starting/stopping and activating
3275	watchers becomes O(1) w.r.t. priority handling.
3276
3277	=item Sending an ev_async: O(1)
3278
3279	=item Processing ev_async_send: O(number_of_async_watchers)
3280
3281	=item Processing signals: O(max_signal_number)
3282
3283	Sending involves a system call I<iff> there were no other C<ev_async_send>
3284	calls in the current loop iteration. Checking for async and signal events
3285	involves iterating over all running async watchers or all signal numbers.
3286
3287	=back
3288
3289
3290	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	4403	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3291		4404
3292	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4405	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3293	requires, and its I/O model is fundamentally incompatible with the POSIX	4406	requires, and its I/O model is fundamentally incompatible with the POSIX
3294	model. Libev still offers limited functionality on this platform in	4407	model. Libev still offers limited functionality on this platform in
3295	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4408	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
…		…
3302	way (note also that glib is the slowest event library known to man).	4415	way (note also that glib is the slowest event library known to man).
3303		4416
3304	There is no supported compilation method available on windows except	4417	There is no supported compilation method available on windows except
3305	embedding it into other applications.	4418	embedding it into other applications.
3306		4419
		4420	Sensible signal handling is officially unsupported by Microsoft - libev
		4421	tries its best, but under most conditions, signals will simply not work.
		4422
3307	Not a libev limitation but worth mentioning: windows apparently doesn't	4423	Not a libev limitation but worth mentioning: windows apparently doesn't
3308	accept large writes: instead of resulting in a partial write, windows will	4424	accept large writes: instead of resulting in a partial write, windows will
3309	either accept everything or return C<ENOBUFS> if the buffer is too large,	4425	either accept everything or return C<ENOBUFS> if the buffer is too large,
3310	so make sure you only write small amounts into your sockets (less than a	4426	so make sure you only write small amounts into your sockets (less than a
3311	megabyte seems safe, but thsi apparently depends on the amount of memory	4427	megabyte seems safe, but this apparently depends on the amount of memory
3312	available).	4428	available).
3313		4429
3314	Due to the many, low, and arbitrary limits on the win32 platform and	4430	Due to the many, low, and arbitrary limits on the win32 platform and
3315	the abysmal performance of winsockets, using a large number of sockets	4431	the abysmal performance of winsockets, using a large number of sockets
3316	is not recommended (and not reasonable). If your program needs to use	4432	is not recommended (and not reasonable). If your program needs to use
3317	more than a hundred or so sockets, then likely it needs to use a totally	4433	more than a hundred or so sockets, then likely it needs to use a totally
3318	different implementation for windows, as libev offers the POSIX readiness	4434	different implementation for windows, as libev offers the POSIX readiness
3319	notification model, which cannot be implemented efficiently on windows	4435	notification model, which cannot be implemented efficiently on windows
3320	(Microsoft monopoly games).	4436	(due to Microsoft monopoly games).
		4437
		4438	A typical way to use libev under windows is to embed it (see the embedding
		4439	section for details) and use the following F<evwrap.h> header file instead
		4440	of F<ev.h>:
		4441
		4442	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4443	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4444
		4445	#include "ev.h"
		4446
		4447	And compile the following F<evwrap.c> file into your project (make sure
		4448	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4449
		4450	#include "evwrap.h"
		4451	#include "ev.c"
3321		4452
3322	=over 4	4453	=over 4
3323		4454
3324	=item The winsocket select function	4455	=item The winsocket select function
3325		4456
3326	The winsocket C<select> function doesn't follow POSIX in that it	4457	The winsocket C<select> function doesn't follow POSIX in that it
3327	requires socket I<handles> and not socket I<file descriptors> (it is	4458	requires socket I<handles> and not socket I<file descriptors> (it is
3328	also extremely buggy). This makes select very inefficient, and also	4459	also extremely buggy). This makes select very inefficient, and also
3329	requires a mapping from file descriptors to socket handles. See the	4460	requires a mapping from file descriptors to socket handles (the Microsoft
		4461	C runtime provides the function C<_open_osfhandle> for this). See the
3330	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and	4462	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
3331	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.	4463	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
3332		4464
3333	The configuration for a "naked" win32 using the Microsoft runtime	4465	The configuration for a "naked" win32 using the Microsoft runtime
3334	libraries and raw winsocket select is:	4466	libraries and raw winsocket select is:
3335		4467
3336	#define EV_USE_SELECT 1	4468	#define EV_USE_SELECT 1
3337	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4469	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3338		4470
3339	Note that winsockets handling of fd sets is O(n), so you can easily get a	4471	Note that winsockets handling of fd sets is O(n), so you can easily get a
3340	complexity in the O(n²) range when using win32.	4472	complexity in the O(n²) range when using win32.
3341		4473
3342	=item Limited number of file descriptors	4474	=item Limited number of file descriptors
…		…
3345		4477
3346	Early versions of winsocket's select only supported waiting for a maximum	4478	Early versions of winsocket's select only supported waiting for a maximum
3347	of C<64> handles (probably owning to the fact that all windows kernels	4479	of C<64> handles (probably owning to the fact that all windows kernels
3348	can only wait for C<64> things at the same time internally; Microsoft	4480	can only wait for C<64> things at the same time internally; Microsoft
3349	recommends spawning a chain of threads and wait for 63 handles and the	4481	recommends spawning a chain of threads and wait for 63 handles and the
3350	previous thread in each. Great).	4482	previous thread in each. Sounds great!).
3351		4483
3352	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4484	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3353	to some high number (e.g. C<2048>) before compiling the winsocket select	4485	to some high number (e.g. C<2048>) before compiling the winsocket select
3354	call (which might be in libev or elsewhere, for example, perl does its own	4486	call (which might be in libev or elsewhere, for example, perl and many
3355	select emulation on windows).	4487	other interpreters do their own select emulation on windows).
3356		4488
3357	Another limit is the number of file descriptors in the Microsoft runtime	4489	Another limit is the number of file descriptors in the Microsoft runtime
3358	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4490	libraries, which by default is C<64> (there must be a hidden I<64>
3359	or something like this inside Microsoft). You can increase this by calling	4491	fetish or something like this inside Microsoft). You can increase this
3360	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4492	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3361	arbitrary limit), but is broken in many versions of the Microsoft runtime	4493	(another arbitrary limit), but is broken in many versions of the Microsoft
3362	libraries.
3363
3364	This might get you to about C<512> or C<2048> sockets (depending on	4494	runtime libraries. This might get you to about C<512> or C<2048> sockets
3365	windows version and/or the phase of the moon). To get more, you need to	4495	(depending on windows version and/or the phase of the moon). To get more,
3366	wrap all I/O functions and provide your own fd management, but the cost of	4496	you need to wrap all I/O functions and provide your own fd management, but
3367	calling select (O(n²)) will likely make this unworkable.	4497	the cost of calling select (O(n²)) will likely make this unworkable.
3368		4498
3369	=back	4499	=back
3370		4500
3371
3372	=head1 PORTABILITY REQUIREMENTS	4501	=head2 PORTABILITY REQUIREMENTS
3373		4502
3374	In addition to a working ISO-C implementation, libev relies on a few	4503	In addition to a working ISO-C implementation and of course the
3375	additional extensions:	4504	backend-specific APIs, libev relies on a few additional extensions:
3376		4505
3377	=over 4	4506	=over 4
3378		4507
		4508	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4509	calling conventions regardless of C<ev_watcher_type *>.
		4510
		4511	Libev assumes not only that all watcher pointers have the same internal
		4512	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4513	assumes that the same (machine) code can be used to call any watcher
		4514	callback: The watcher callbacks have different type signatures, but libev
		4515	calls them using an C<ev_watcher *> internally.
		4516
3379	=item C<sig_atomic_t volatile> must be thread-atomic as well	4517	=item C<sig_atomic_t volatile> must be thread-atomic as well
3380		4518
3381	The type C<sig_atomic_t volatile> (or whatever is defined as	4519	The type C<sig_atomic_t volatile> (or whatever is defined as
3382	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4520	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3383	threads. This is not part of the specification for C<sig_atomic_t>, but is	4521	threads. This is not part of the specification for C<sig_atomic_t>, but is
3384	believed to be sufficiently portable.	4522	believed to be sufficiently portable.
3385		4523
3386	=item C<sigprocmask> must work in a threaded environment	4524	=item C<sigprocmask> must work in a threaded environment
3387		4525
…		…
3396	except the initial one, and run the default loop in the initial thread as	4534	except the initial one, and run the default loop in the initial thread as
3397	well.	4535	well.
3398		4536
3399	=item C<long> must be large enough for common memory allocation sizes	4537	=item C<long> must be large enough for common memory allocation sizes
3400		4538
3401	To improve portability and simplify using libev, libev uses C<long>	4539	To improve portability and simplify its API, libev uses C<long> internally
3402	internally instead of C<size_t> when allocating its data structures. On	4540	instead of C<size_t> when allocating its data structures. On non-POSIX
3403	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	4541	systems (Microsoft...) this might be unexpectedly low, but is still at
3404	is still at least 31 bits everywhere, which is enough for hundreds of	4542	least 31 bits everywhere, which is enough for hundreds of millions of
3405	millions of watchers.	4543	watchers.
3406		4544
3407	=item C<double> must hold a time value in seconds with enough accuracy	4545	=item C<double> must hold a time value in seconds with enough accuracy
3408		4546
3409	The type C<double> is used to represent timestamps. It is required to	4547	The type C<double> is used to represent timestamps. It is required to
3410	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4548	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3411	enough for at least into the year 4000. This requirement is fulfilled by	4549	enough for at least into the year 4000. This requirement is fulfilled by
3412	implementations implementing IEEE 754 (basically all existing ones).	4550	implementations implementing IEEE 754, which is basically all existing
		4551	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4552	2200.
3413		4553
3414	=back	4554	=back
3415		4555
3416	If you know of other additional requirements drop me a note.	4556	If you know of other additional requirements drop me a note.
3417		4557
3418		4558
3419	=head1 COMPILER WARNINGS	4559	=head1 ALGORITHMIC COMPLEXITIES
3420		4560
3421	Depending on your compiler and compiler settings, you might get no or a	4561	In this section the complexities of (many of) the algorithms used inside
3422	lot of warnings when compiling libev code. Some people are apparently	4562	libev will be documented. For complexity discussions about backends see
3423	scared by this.	4563	the documentation for C<ev_default_init>.
3424		4564
3425	However, these are unavoidable for many reasons. For one, each compiler	4565	All of the following are about amortised time: If an array needs to be
3426	has different warnings, and each user has different tastes regarding	4566	extended, libev needs to realloc and move the whole array, but this
3427	warning options. "Warn-free" code therefore cannot be a goal except when	4567	happens asymptotically rarer with higher number of elements, so O(1) might
3428	targeting a specific compiler and compiler-version.	4568	mean that libev does a lengthy realloc operation in rare cases, but on
		4569	average it is much faster and asymptotically approaches constant time.
3429		4570
3430	Another reason is that some compiler warnings require elaborate	4571	=over 4
3431	workarounds, or other changes to the code that make it less clear and less
3432	maintainable.
3433		4572
3434	And of course, some compiler warnings are just plain stupid, or simply	4573	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3435	wrong (because they don't actually warn about the condition their message
3436	seems to warn about).
3437		4574
3438	While libev is written to generate as few warnings as possible,	4575	This means that, when you have a watcher that triggers in one hour and
3439	"warn-free" code is not a goal, and it is recommended not to build libev	4576	there are 100 watchers that would trigger before that, then inserting will
3440	with any compiler warnings enabled unless you are prepared to cope with	4577	have to skip roughly seven (C<ld 100>) of these watchers.
3441	them (e.g. by ignoring them). Remember that warnings are just that:
3442	warnings, not errors, or proof of bugs.
3443		4578
		4579	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3444		4580
3445	=head1 VALGRIND	4581	That means that changing a timer costs less than removing/adding them,
		4582	as only the relative motion in the event queue has to be paid for.
3446		4583
3447	Valgrind has a special section here because it is a popular tool that is	4584	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3448	highly useful, but valgrind reports are very hard to interpret.
3449		4585
3450	If you think you found a bug (memory leak, uninitialised data access etc.)	4586	These just add the watcher into an array or at the head of a list.
3451	in libev, then check twice: If valgrind reports something like:
3452		4587
3453	==2274== definitely lost: 0 bytes in 0 blocks.	4588	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3454	==2274== possibly lost: 0 bytes in 0 blocks.
3455	==2274== still reachable: 256 bytes in 1 blocks.
3456		4589
3457	Then there is no memory leak. Similarly, under some circumstances,	4590	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3458	valgrind might report kernel bugs as if it were a bug in libev, or it
3459	might be confused (it is a very good tool, but only a tool).
3460		4591
3461	If you are unsure about something, feel free to contact the mailing list	4592	These watchers are stored in lists, so they need to be walked to find the
3462	with the full valgrind report and an explanation on why you think this is	4593	correct watcher to remove. The lists are usually short (you don't usually
3463	a bug in libev. However, don't be annoyed when you get a brisk "this is	4594	have many watchers waiting for the same fd or signal: one is typical, two
3464	no bug" answer and take the chance of learning how to interpret valgrind	4595	is rare).
3465	properly.
3466		4596
3467	If you need, for some reason, empty reports from valgrind for your project	4597	=item Finding the next timer in each loop iteration: O(1)
3468	I suggest using suppression lists.
3469		4598
		4599	By virtue of using a binary or 4-heap, the next timer is always found at a
		4600	fixed position in the storage array.
		4601
		4602	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4603
		4604	A change means an I/O watcher gets started or stopped, which requires
		4605	libev to recalculate its status (and possibly tell the kernel, depending
		4606	on backend and whether C<ev_io_set> was used).
		4607
		4608	=item Activating one watcher (putting it into the pending state): O(1)
		4609
		4610	=item Priority handling: O(number_of_priorities)
		4611
		4612	Priorities are implemented by allocating some space for each
		4613	priority. When doing priority-based operations, libev usually has to
		4614	linearly search all the priorities, but starting/stopping and activating
		4615	watchers becomes O(1) with respect to priority handling.
		4616
		4617	=item Sending an ev_async: O(1)
		4618
		4619	=item Processing ev_async_send: O(number_of_async_watchers)
		4620
		4621	=item Processing signals: O(max_signal_number)
		4622
		4623	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4624	calls in the current loop iteration. Checking for async and signal events
		4625	involves iterating over all running async watchers or all signal numbers.
		4626
		4627	=back
		4628
		4629
		4630	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4631
		4632	The major version 4 introduced some minor incompatible changes to the API.
		4633
		4634	At the moment, the C<ev.h> header file tries to implement superficial
		4635	compatibility, so most programs should still compile. Those might be
		4636	removed in later versions of libev, so better update early than late.
		4637
		4638	=over 4
		4639
		4640	=item C<ev_loop_count> renamed to C<ev_iteration>
		4641
		4642	=item C<ev_loop_depth> renamed to C<ev_depth>
		4643
		4644	=item C<ev_loop_verify> renamed to C<ev_verify>
		4645
		4646	Most functions working on C<struct ev_loop> objects don't have an
		4647	C<ev_loop_> prefix, so it was removed. Note that C<ev_loop_fork> is
		4648	still called C<ev_loop_fork> because it would otherwise clash with the
		4649	C<ev_fork> typedef.
		4650
		4651	=item C<EV_TIMEOUT> renamed to C<EV_TIMER> in C<revents>
		4652
		4653	This is a simple rename - all other watcher types use their name
		4654	as revents flag, and now C<ev_timer> does, too.
		4655
		4656	Both C<EV_TIMER> and C<EV_TIMEOUT> symbols were present in 3.x versions
		4657	and continue to be present for the forseeable future, so this is mostly a
		4658	documentation change.
		4659
		4660	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4661
		4662	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4663	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4664	and work, but the library code will of course be larger.
		4665
		4666	=back
		4667
		4668
		4669	=head1 GLOSSARY
		4670
		4671	=over 4
		4672
		4673	=item active
		4674
		4675	A watcher is active as long as it has been started (has been attached to
		4676	an event loop) but not yet stopped (disassociated from the event loop).
		4677
		4678	=item application
		4679
		4680	In this document, an application is whatever is using libev.
		4681
		4682	=item callback
		4683
		4684	The address of a function that is called when some event has been
		4685	detected. Callbacks are being passed the event loop, the watcher that
		4686	received the event, and the actual event bitset.
		4687
		4688	=item callback invocation
		4689
		4690	The act of calling the callback associated with a watcher.
		4691
		4692	=item event
		4693
		4694	A change of state of some external event, such as data now being available
		4695	for reading on a file descriptor, time having passed or simply not having
		4696	any other events happening anymore.
		4697
		4698	In libev, events are represented as single bits (such as C<EV_READ> or
		4699	C<EV_TIMER>).
		4700
		4701	=item event library
		4702
		4703	A software package implementing an event model and loop.
		4704
		4705	=item event loop
		4706
		4707	An entity that handles and processes external events and converts them
		4708	into callback invocations.
		4709
		4710	=item event model
		4711
		4712	The model used to describe how an event loop handles and processes
		4713	watchers and events.
		4714
		4715	=item pending
		4716
		4717	A watcher is pending as soon as the corresponding event has been detected,
		4718	and stops being pending as soon as the watcher will be invoked or its
		4719	pending status is explicitly cleared by the application.
		4720
		4721	A watcher can be pending, but not active. Stopping a watcher also clears
		4722	its pending status.
		4723
		4724	=item real time
		4725
		4726	The physical time that is observed. It is apparently strictly monotonic :)
		4727
		4728	=item wall-clock time
		4729
		4730	The time and date as shown on clocks. Unlike real time, it can actually
		4731	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4732	clock.
		4733
		4734	=item watcher
		4735
		4736	A data structure that describes interest in certain events. Watchers need
		4737	to be started (attached to an event loop) before they can receive events.
		4738
		4739	=item watcher invocation
		4740
		4741	The act of calling the callback associated with a watcher.
		4742
		4743	=back
3470		4744
3471	=head1 AUTHOR	4745	=head1 AUTHOR
3472		4746
3473	Marc Lehmann <libev@schmorp.de>.	4747	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3474		4748

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