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Revision 1.161 by root, Sat May 24 03:08:03 2008 UTC vs.
Revision 1.306 by root, Mon Oct 18 07:36:05 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	Familiarity 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 (in practise
115	the beginning of 1970, details are complicated, don't ask). This type is	130	somewhere near the beginning of 1970, details are complicated, don't
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	ask). This type is called C<ev_tstamp>, which is what you should use
117	to the C<double> type in C, and when you need to do any calculations on	132	too. It usually aliases to the C<double> type in C. When you need to do
118	it, you should treat it as some floating point value. Unlike the name	133	any calculations on it, you should treat it as some floating point value.
		134
119	component C<stamp> might indicate, it is also used for time differences	135	Unlike the name component C<stamp> might indicate, it is also used for
120	throughout libev.	136	time differences (e.g. delays) throughout libev.
121		137
122	=head1 ERROR HANDLING	138	=head1 ERROR HANDLING
123		139
124	Libev knows three classes of errors: operating system errors, usage errors	140	Libev knows three classes of errors: operating system errors, usage errors
125	and internal errors (bugs).	141	and internal errors (bugs).
…		…
176	as this indicates an incompatible change. Minor versions are usually	192	as this indicates an incompatible change. Minor versions are usually
177	compatible to older versions, so a larger minor version alone is usually	193	compatible to older versions, so a larger minor version alone is usually
178	not a problem.	194	not a problem.
179		195
180	Example: Make sure we haven't accidentally been linked against the wrong	196	Example: Make sure we haven't accidentally been linked against the wrong
181	version.	197	version (note, however, that this will not detect ABI mismatches :).
182		198
183	assert (("libev version mismatch",	199	assert (("libev version mismatch",
184	ev_version_major () == EV_VERSION_MAJOR	200	ev_version_major () == EV_VERSION_MAJOR
185	&& ev_version_minor () >= EV_VERSION_MINOR));	201	&& ev_version_minor () >= EV_VERSION_MINOR));
186		202
187	=item unsigned int ev_supported_backends ()	203	=item unsigned int ev_supported_backends ()
188		204
189	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	205	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
190	value) compiled into this binary of libev (independent of their	206	value) compiled into this binary of libev (independent of their
…		…
192	a description of the set values.	208	a description of the set values.
193		209
194	Example: make sure we have the epoll method, because yeah this is cool and	210	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	211	a must have and can we have a torrent of it please!!!11
196		212
197	assert (("sorry, no epoll, no sex",	213	assert (("sorry, no epoll, no sex",
198	ev_supported_backends () & EVBACKEND_EPOLL));	214	ev_supported_backends () & EVBACKEND_EPOLL));
199		215
200	=item unsigned int ev_recommended_backends ()	216	=item unsigned int ev_recommended_backends ()
201		217
202	Return the set of all backends compiled into this binary of libev and also	218	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	219	recommended for this platform. This set is often smaller than the one
…		…
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	230	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
215	recommended ones.	231	recommended ones.
216		232
217	See the description of C<ev_embed> watchers for more info.	233	See the description of C<ev_embed> watchers for more info.
218		234
219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	235	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
220		236
221	Sets the allocation function to use (the prototype is similar - the	237	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	238	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	239	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	240	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
250	}	266	}
251		267
252	...	268	...
253	ev_set_allocator (persistent_realloc);	269	ev_set_allocator (persistent_realloc);
254		270
255	=item ev_set_syserr_cb (void (*cb)(const char *msg));	271	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
256		272
257	Set the callback function to call on a retryable system call error (such	273	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	274	as failed select, poll, epoll_wait). The message is a printable string
259	indicating the system call or subsystem causing the problem. If this	275	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	276	callback is set, then libev will expect it to remedy the situation, no
…		…
276		292
277	=back	293	=back
278		294
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	295	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280		296
281	An event loop is described by a C<struct ev_loop *>. The library knows two	297	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	298	is I<not> optional in this case, as there is also an C<ev_loop>
283	events, and dynamically created loops which do not.	299	I<function>).
		300
		301	The library knows two types of such loops, the I<default> loop, which
		302	supports signals and child events, and dynamically created loops which do
		303	not.
284		304
285	=over 4	305	=over 4
286		306
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	307	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		308
…		…
294	If you don't know what event loop to use, use the one returned from this	314	If you don't know what event loop to use, use the one returned from this
295	function.	315	function.
296		316
297	Note that this function is I<not> thread-safe, so if you want to use it	317	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,	318	from multiple threads, you have to lock (note also that this is unlikely,
299	as loops cannot bes hared easily between threads anyway).	319	as loops cannot be shared easily between threads anyway).
300		320
301	The default loop is the only loop that can handle C<ev_signal> and	321	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	322	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	323	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	324	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	346	useful to try out specific backends to test their performance, or to work
327	around bugs.	347	around bugs.
328		348
329	=item C<EVFLAG_FORKCHECK>	349	=item C<EVFLAG_FORKCHECK>
330		350
331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	351	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	352	make libev check for a fork in each iteration by enabling this flag.
333	enabling this flag.
334		353
335	This works by calling C<getpid ()> on every iteration of the loop,	354	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	355	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	356	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	357	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
…		…
344	flag.	363	flag.
345		364
346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
347	environment variable.	366	environment variable.
348		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_SIGNALFD>
		376
		377	When this flag is specified, then libev will attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		379	delivers signals synchronously, which makes it both faster and might make
		380	it possible to get the queued signal data. It can also simplify signal
		381	handling with threads, as long as you properly block signals in your
		382	threads that are not interested in handling them.
		383
		384	Signalfd will not be used by default as this changes your signal mask, and
		385	there are a lot of shoddy libraries and programs (glib's threadpool for
		386	example) that can't properly initialise their signal masks.
		387
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		389
351	This is your standard select(2) backend. Not I<completely> standard, as	390	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,	391	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	392	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	398	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	399	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	400	a look at C<ev_set_io_collect_interval ()> to increase the amount of
362	readiness notifications you get per iteration.	401	readiness notifications you get per iteration.
363		402
		403	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		404	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		405	C<exceptfds> set on that platform).
		406
364	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	407	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
365		408
366	And this is your standard poll(2) backend. It's more complicated	409	And this is your standard poll(2) backend. It's more complicated
367	than select, but handles sparse fds better and has no artificial	410	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	411	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,	412	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	413	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
371	performance tips.	414	performance tips.
372		415
		416	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		417	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		418
373	=item C<EVBACKEND_EPOLL> (value 4, Linux)	419	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		420
		421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		422	kernels).
374		423
375	For few fds, this backend is a bit little slower than poll and select,	424	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	425	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),	426	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	427	epoll scales either O(1) or O(active_fds).
379	of shortcomings, such as silently dropping events in some hard-to-detect	428
380	cases and requiring a system call per fd change, no fork support and bad	429	The epoll mechanism deserves honorable mention as the most misdesigned
381	support for dup.	430	of the more advanced event mechanisms: mere annoyances include silently
		431	dropping file descriptors, requiring a system call per change per file
		432	descriptor (and unnecessary guessing of parameters), problems with dup and
		433	so on. The biggest issue is fork races, however - if a program forks then
		434	I<both> parent and child process have to recreate the epoll set, which can
		435	take considerable time (one syscall per file descriptor) and is of course
		436	hard to detect.
		437
		438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		439	of course I<doesn't>, and epoll just loves to report events for totally
		440	I<different> file descriptors (even already closed ones, so one cannot
		441	even remove them from the set) than registered in the set (especially
		442	on SMP systems). Libev tries to counter these spurious notifications by
		443	employing an additional generation counter and comparing that against the
		444	events to filter out spurious ones, recreating the set when required. Last
		445	not least, it also refuses to work with some file descriptors which work
		446	perfectly fine with C<select> (files, many character devices...).
382		447
383	While stopping, setting and starting an I/O watcher in the same iteration	448	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	449	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	450	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	451	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
387	very well if you register events for both fds.	452	file descriptors might not work very well if you register events for both
388		453	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		454
393	Best performance from this backend is achieved by not unregistering all	455	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.	456	watchers for a file descriptor until it has been closed, if possible,
395	keep at least one watcher active per fd at all times.	457	i.e. keep at least one watcher active per fd at all times. Stopping and
		458	starting a watcher (without re-setting it) also usually doesn't cause
		459	extra overhead. A fork can both result in spurious notifications as well
		460	as in libev having to destroy and recreate the epoll object, which can
		461	take considerable time and thus should be avoided.
		462
		463	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		464	faster than epoll for maybe up to a hundred file descriptors, depending on
		465	the usage. So sad.
396		466
397	While nominally embeddable in other event loops, this feature is broken in	467	While nominally embeddable in other event loops, this feature is broken in
398	all kernel versions tested so far.	468	all kernel versions tested so far.
		469
		470	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		471	C<EVBACKEND_POLL>.
399		472
400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	473	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
401		474
402	Kqueue deserves special mention, as at the time of this writing, it	475	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	476	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	477	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"	478	it's completely useless). Unlike epoll, however, whose brokenness
		479	is by design, these kqueue bugs can (and eventually will) be fixed
		480	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	481	"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)	482	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
408	system like NetBSD.	483	system like NetBSD.
409		484
410	You still can embed kqueue into a normal poll or select backend and use it	485	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	486	only for sockets (after having made sure that sockets work with kqueue on
…		…
413		488
414	It scales in the same way as the epoll backend, but the interface to the	489	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	490	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	491	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	492	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	493	two event changes per incident. Support for C<fork ()> is very bad (but
419	drops fds silently in similarly hard-to-detect cases.	494	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		495	cases
420		496
421	This backend usually performs well under most conditions.	497	This backend usually performs well under most conditions.
422		498
423	While nominally embeddable in other event loops, this doesn't work	499	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	500	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	501	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	502	(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	503	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
428	sockets.	504	also broken on OS X)) and, did I mention it, using it only for sockets.
		505
		506	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		507	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		508	C<NOTE_EOF>.
429		509
430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	510	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
431		511
432	This is not implemented yet (and might never be, unless you send me an	512	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	513	implementation). According to reports, C</dev/poll> only supports sockets
…		…
446	While this backend scales well, it requires one system call per active	526	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	527	file descriptor per loop iteration. For small and medium numbers of file
448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	528	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
449	might perform better.	529	might perform better.
450		530
451	On the positive side, ignoring the spurious readiness notifications, this	531	On the positive side, with the exception of the spurious readiness
452	backend actually performed to specification in all tests and is fully	532	notifications, this backend actually performed fully to specification
453	embeddable, which is a rare feat among the OS-specific backends.	533	in all tests and is fully embeddable, which is a rare feat among the
		534	OS-specific backends (I vastly prefer correctness over speed hacks).
		535
		536	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		537	C<EVBACKEND_POLL>.
454		538
455	=item C<EVBACKEND_ALL>	539	=item C<EVBACKEND_ALL>
456		540
457	Try all backends (even potentially broken ones that wouldn't be tried	541	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	542	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
…		…
460		544
461	It is definitely not recommended to use this flag.	545	It is definitely not recommended to use this flag.
462		546
463	=back	547	=back
464		548
465	If one or more of these are or'ed into the flags value, then only these	549	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	550	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.	551	here). If none are specified, all backends in C<ev_recommended_backends
		552	()> will be tried.
468		553
469	The most typical usage is like this:	554	Example: This is the most typical usage.
470		555
471	if (!ev_default_loop (0))	556	if (!ev_default_loop (0))
472	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	557	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
473		558
474	Restrict libev to the select and poll backends, and do not allow	559	Example: Restrict libev to the select and poll backends, and do not allow
475	environment settings to be taken into account:	560	environment settings to be taken into account:
476		561
477	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	562	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
478		563
479	Use whatever libev has to offer, but make sure that kqueue is used if	564	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	565	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):	566	private event loop and only if you know the OS supports your types of
		567	fds):
482		568
483	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	569	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
484		570
485	=item struct ev_loop *ev_loop_new (unsigned int flags)	571	=item struct ev_loop *ev_loop_new (unsigned int flags)
486		572
487	Similar to C<ev_default_loop>, but always creates a new event loop that is	573	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	574	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		575
492	Note that this function I<is> thread-safe, and the recommended way to use	576	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	577	libev with threads is indeed to create one loop per thread, and using the
494	default loop in the "main" or "initial" thread.	578	default loop in the "main" or "initial" thread.
495		579
496	Example: Try to create a event loop that uses epoll and nothing else.	580	Example: Try to create a event loop that uses epoll and nothing else.
497		581
498	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	582	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
499	if (!epoller)	583	if (!epoller)
500	fatal ("no epoll found here, maybe it hides under your chair");	584	fatal ("no epoll found here, maybe it hides under your chair");
501		585
502	=item ev_default_destroy ()	586	=item ev_default_destroy ()
503		587
504	Destroys the default loop again (frees all memory and kernel state	588	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	589	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	590	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>	591	either stop all watchers cleanly yourself I<before> calling this function,
508	calling this function, or cope with the fact afterwards (which is usually	592	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	593	can just ignore the watchers and/or C<free ()> them for example).
510	for example).
511		594
512	Note that certain global state, such as signal state, will not be freed by	595	Note that certain global state, such as signal state (and installed signal
513	this function, and related watchers (such as signal and child watchers)	596	handlers), will not be freed by this function, and related watchers (such
514	would need to be stopped manually.	597	as signal and child watchers) would need to be stopped manually.
515		598
516	In general it is not advisable to call this function except in the	599	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	600	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	601	pipe fds. If you need dynamically allocated loops it is better to use
519	C<ev_loop_new> and C<ev_loop_destroy>).	602	C<ev_loop_new> and C<ev_loop_destroy>.
520		603
521	=item ev_loop_destroy (loop)	604	=item ev_loop_destroy (loop)
522		605
523	Like C<ev_default_destroy>, but destroys an event loop created by an	606	Like C<ev_default_destroy>, but destroys an event loop created by an
524	earlier call to C<ev_loop_new>.	607	earlier call to C<ev_loop_new>.
…		…
530	name, you can call it anytime, but it makes most sense after forking, in	613	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	614	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	615	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.	616	functions, and it will only take effect at the next C<ev_loop> iteration.
534		617
		618	Again, you I<have> to call it on I<any> loop that you want to re-use after
		619	a fork, I<even if you do not plan to use the loop in the parent>. This is
		620	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		621	during fork.
		622
535	On the other hand, you only need to call this function in the child	623	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	624	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.	625	just fork+exec or create a new loop in the child, you don't have to call
		626	it at all.
538		627
539	The function itself is quite fast and it's usually not a problem to call	628	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	629	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>:	630	quite nicely into a call to C<pthread_atfork>:
542		631
…		…
544		633
545	=item ev_loop_fork (loop)	634	=item ev_loop_fork (loop)
546		635
547	Like C<ev_default_fork>, but acts on an event loop created by	636	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	637	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.	638	after fork that you want to re-use in the child, and how you keep track of
		639	them is entirely your own problem.
550		640
551	=item int ev_is_default_loop (loop)	641	=item int ev_is_default_loop (loop)
552		642
553	Returns true when the given loop actually is the default loop, false otherwise.	643	Returns true when the given loop is, in fact, the default loop, and false
		644	otherwise.
554		645
555	=item unsigned int ev_loop_count (loop)	646	=item unsigned int ev_iteration (loop)
556		647
557	Returns the count of loop iterations for the loop, which is identical to	648	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	649	the number of times libev did poll for new events. It starts at C<0> and
559	happily wraps around with enough iterations.	650	happily wraps around with enough iterations.
560		651
561	This value can sometimes be useful as a generation counter of sorts (it	652	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	653	"ticks" the number of loop iterations), as it roughly corresponds with
563	C<ev_prepare> and C<ev_check> calls.	654	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		655	prepare and check phases.
		656
		657	=item unsigned int ev_depth (loop)
		658
		659	Returns the number of times C<ev_loop> was entered minus the number of
		660	times C<ev_loop> was exited, in other words, the recursion depth.
		661
		662	Outside C<ev_loop>, this number is zero. In a callback, this number is
		663	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		664	in which case it is higher.
		665
		666	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		667	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		668	ungentleman behaviour unless it's really convenient.
564		669
565	=item unsigned int ev_backend (loop)	670	=item unsigned int ev_backend (loop)
566		671
567	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	672	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
568	use.	673	use.
…		…
573	received events and started processing them. This timestamp does not	678	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	679	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	680	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).	681	event occurring (or more correctly, libev finding out about it).
577		682
		683	=item ev_now_update (loop)
		684
		685	Establishes the current time by querying the kernel, updating the time
		686	returned by C<ev_now ()> in the progress. This is a costly operation and
		687	is usually done automatically within C<ev_loop ()>.
		688
		689	This function is rarely useful, but when some event callback runs for a
		690	very long time without entering the event loop, updating libev's idea of
		691	the current time is a good idea.
		692
		693	See also L<The special problem of time updates> in the C<ev_timer> section.
		694
		695	=item ev_suspend (loop)
		696
		697	=item ev_resume (loop)
		698
		699	These two functions suspend and resume a loop, for use when the loop is
		700	not used for a while and timeouts should not be processed.
		701
		702	A typical use case would be an interactive program such as a game: When
		703	the user presses C<^Z> to suspend the game and resumes it an hour later it
		704	would be best to handle timeouts as if no time had actually passed while
		705	the program was suspended. This can be achieved by calling C<ev_suspend>
		706	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		707	C<ev_resume> directly afterwards to resume timer processing.
		708
		709	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		710	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		711	will be rescheduled (that is, they will lose any events that would have
		712	occurred while suspended).
		713
		714	After calling C<ev_suspend> you B<must not> call I<any> function on the
		715	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		716	without a previous call to C<ev_suspend>.
		717
		718	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		719	event loop time (see C<ev_now_update>).
		720
578	=item ev_loop (loop, int flags)	721	=item ev_loop (loop, int flags)
579		722
580	Finally, this is it, the event handler. This function usually is called	723	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	724	after you have initialised all your watchers and you want to start
582	events.	725	handling events.
583		726
584	If the flags argument is specified as C<0>, it will not return until	727	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.	728	either no event watchers are active anymore or C<ev_unloop> was called.
586		729
587	Please note that an explicit C<ev_unloop> is usually better than	730	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	731	relying on all watchers to be stopped when deciding when a program has
589	finished (especially in interactive programs), but having a program that	732	finished (especially in interactive programs), but having a program
590	automatically loops as long as it has to and no longer by virtue of	733	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.	734	of relying on its watchers stopping correctly, that is truly a thing of
		735	beauty.
592		736
593	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	737	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	738	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.	739	process in case there are no events and will return after one iteration of
		740	the loop.
596		741
597	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	742	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	743	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	744	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	745	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	746	user-registered callback will be called), and will return after one
		747	iteration of the loop.
		748
		749	This is useful if you are waiting for some external event in conjunction
		750	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	751	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.	752	usually a better approach for this kind of thing.
604		753
605	Here are the gory details of what C<ev_loop> does:	754	Here are the gory details of what C<ev_loop> does:
606		755
607	- Before the first iteration, call any pending watchers.	756	- Before the first iteration, call any pending watchers.
608	* If EVFLAG_FORKCHECK was used, check for a fork.	757	* If EVFLAG_FORKCHECK was used, check for a fork.
609	- If a fork was detected, queue and call all fork watchers.	758	- If a fork was detected (by any means), queue and call all fork watchers.
610	- Queue and call all prepare watchers.	759	- Queue and call all prepare watchers.
611	- If we have been forked, recreate the kernel state.	760	- If we have been forked, detach and recreate the kernel state
		761	as to not disturb the other process.
612	- Update the kernel state with all outstanding changes.	762	- Update the kernel state with all outstanding changes.
613	- Update the "event loop time".	763	- Update the "event loop time" (ev_now ()).
614	- Calculate for how long to sleep or block, if at all	764	- Calculate for how long to sleep or block, if at all
615	(active idle watchers, EVLOOP_NONBLOCK or not having	765	(active idle watchers, EVLOOP_NONBLOCK or not having
616	any active watchers at all will result in not sleeping).	766	any active watchers at all will result in not sleeping).
617	- Sleep if the I/O and timer collect interval say so.	767	- Sleep if the I/O and timer collect interval say so.
618	- Block the process, waiting for any events.	768	- Block the process, waiting for any events.
619	- Queue all outstanding I/O (fd) events.	769	- Queue all outstanding I/O (fd) events.
620	- Update the "event loop time" and do time jump handling.	770	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
621	- Queue all outstanding timers.	771	- Queue all expired timers.
622	- Queue all outstanding periodics.	772	- Queue all expired periodics.
623	- If no events are pending now, queue all idle watchers.	773	- Unless any events are pending now, queue all idle watchers.
624	- Queue all check watchers.	774	- Queue all check watchers.
625	- Call all queued watchers in reverse order (i.e. check watchers first).	775	- 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	776	Signals and child watchers are implemented as I/O watchers, and will
627	be handled here by queueing them when their watcher gets executed.	777	be handled here by queueing them when their watcher gets executed.
628	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	778	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
…		…
633	anymore.	783	anymore.
634		784
635	... queue jobs here, make sure they register event watchers as long	785	... 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..)	786	... as they still have work to do (even an idle watcher will do..)
637	ev_loop (my_loop, 0);	787	ev_loop (my_loop, 0);
638	... jobs done. yeah!	788	... jobs done or somebody called unloop. yeah!
639		789
640	=item ev_unloop (loop, how)	790	=item ev_unloop (loop, how)
641		791
642	Can be used to make a call to C<ev_loop> return early (but only after it	792	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	793	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	794	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.	795	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
646		796
647	This "unloop state" will be cleared when entering C<ev_loop> again.	797	This "unloop state" will be cleared when entering C<ev_loop> again.
648		798
		799	It is safe to call C<ev_unloop> from outside any C<ev_loop> calls.
		800
649	=item ev_ref (loop)	801	=item ev_ref (loop)
650		802
651	=item ev_unref (loop)	803	=item ev_unref (loop)
652		804
653	Ref/unref can be used to add or remove a reference count on the event	805	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	806	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	807	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	808
657	returning, ev_unref() after starting, and ev_ref() before stopping it. For	809	This is useful when you have a watcher that you never intend to
		810	unregister, but that nevertheless should not keep C<ev_loop> from
		811	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		812	before stopping it.
		813
658	example, libev itself uses this for its internal signal pipe: It is not	814	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	815	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	816	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	817	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>	818	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,	819	before stop> (but only if the watcher wasn't active before, or was active
664	respectively).	820	before, respectively. Note also that libev might stop watchers itself
		821	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		822	in the callback).
665		823
666	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	824	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
667	running when nothing else is active.	825	running when nothing else is active.
668		826
669	struct ev_signal exitsig;	827	ev_signal exitsig;
670	ev_signal_init (&exitsig, sig_cb, SIGINT);	828	ev_signal_init (&exitsig, sig_cb, SIGINT);
671	ev_signal_start (loop, &exitsig);	829	ev_signal_start (loop, &exitsig);
672	evf_unref (loop);	830	evf_unref (loop);
673		831
674	Example: For some weird reason, unregister the above signal handler again.	832	Example: For some weird reason, unregister the above signal handler again.
675		833
676	ev_ref (loop);	834	ev_ref (loop);
677	ev_signal_stop (loop, &exitsig);	835	ev_signal_stop (loop, &exitsig);
678		836
679	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	837	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
680		838
681	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	839	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
682		840
683	These advanced functions influence the time that libev will spend waiting	841	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	842	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.	843	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		844	latency.
686		845
687	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	846	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	847	allows libev to delay invocation of I/O and timer/periodic callbacks
689	increase efficiency of loop iterations.	848	to increase efficiency of loop iterations (or to increase power-saving
		849	opportunities).
690		850
691	The background is that sometimes your program runs just fast enough to	851	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	852	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	853	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	854	events, especially with backends like C<select ()> which have a high
695	overhead for the actual polling but can deliver many events at once.	855	overhead for the actual polling but can deliver many events at once.
696		856
697	By setting a higher I<io collect interval> you allow libev to spend more	857	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,	858	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	859	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	860	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.	861	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		862	sleep time ensures that libev will not poll for I/O events more often then
		863	once per this interval, on average.
702		864
703	Likewise, by setting a higher I<timeout collect interval> you allow libev	865	Likewise, by setting a higher I<timeout collect interval> you allow libev
704	to spend more time collecting timeouts, at the expense of increased	866	to spend more time collecting timeouts, at the expense of increased
705	latency (the watcher callback will be called later). C<ev_io> watchers	867	latency/jitter/inexactness (the watcher callback will be called
706	will not be affected. Setting this to a non-null value will not introduce	868	later). C<ev_io> watchers will not be affected. Setting this to a non-null
707	any overhead in libev.	869	value will not introduce any overhead in libev.
708		870
709	Many (busy) programs can usually benefit by setting the I/O collect	871	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	872	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	873	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>,	874	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.	875	as this approaches the timing granularity of most systems. Note that if
		876	you do transactions with the outside world and you can't increase the
		877	parallelity, then this setting will limit your transaction rate (if you
		878	need to poll once per transaction and the I/O collect interval is 0.01,
		879	then you can't do more than 100 transactions per second).
		880
		881	Setting the I<timeout collect interval> can improve the opportunity for
		882	saving power, as the program will "bundle" timer callback invocations that
		883	are "near" in time together, by delaying some, thus reducing the number of
		884	times the process sleeps and wakes up again. Another useful technique to
		885	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		886	they fire on, say, one-second boundaries only.
		887
		888	Example: we only need 0.1s timeout granularity, and we wish not to poll
		889	more often than 100 times per second:
		890
		891	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		892	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		893
		894	=item ev_invoke_pending (loop)
		895
		896	This call will simply invoke all pending watchers while resetting their
		897	pending state. Normally, C<ev_loop> does this automatically when required,
		898	but when overriding the invoke callback this call comes handy.
		899
		900	=item int ev_pending_count (loop)
		901
		902	Returns the number of pending watchers - zero indicates that no watchers
		903	are pending.
		904
		905	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		906
		907	This overrides the invoke pending functionality of the loop: Instead of
		908	invoking all pending watchers when there are any, C<ev_loop> will call
		909	this callback instead. This is useful, for example, when you want to
		910	invoke the actual watchers inside another context (another thread etc.).
		911
		912	If you want to reset the callback, use C<ev_invoke_pending> as new
		913	callback.
		914
		915	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		916
		917	Sometimes you want to share the same loop between multiple threads. This
		918	can be done relatively simply by putting mutex_lock/unlock calls around
		919	each call to a libev function.
		920
		921	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		922	wait for it to return. One way around this is to wake up the loop via
		923	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		924	and I<acquire> callbacks on the loop.
		925
		926	When set, then C<release> will be called just before the thread is
		927	suspended waiting for new events, and C<acquire> is called just
		928	afterwards.
		929
		930	Ideally, C<release> will just call your mutex_unlock function, and
		931	C<acquire> will just call the mutex_lock function again.
		932
		933	While event loop modifications are allowed between invocations of
		934	C<release> and C<acquire> (that's their only purpose after all), no
		935	modifications done will affect the event loop, i.e. adding watchers will
		936	have no effect on the set of file descriptors being watched, or the time
		937	waited. Use an C<ev_async> watcher to wake up C<ev_loop> when you want it
		938	to take note of any changes you made.
		939
		940	In theory, threads executing C<ev_loop> will be async-cancel safe between
		941	invocations of C<release> and C<acquire>.
		942
		943	See also the locking example in the C<THREADS> section later in this
		944	document.
		945
		946	=item ev_set_userdata (loop, void *data)
		947
		948	=item ev_userdata (loop)
		949
		950	Set and retrieve a single C<void *> associated with a loop. When
		951	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		952	C<0.>
		953
		954	These two functions can be used to associate arbitrary data with a loop,
		955	and are intended solely for the C<invoke_pending_cb>, C<release> and
		956	C<acquire> callbacks described above, but of course can be (ab-)used for
		957	any other purpose as well.
714		958
715	=item ev_loop_verify (loop)	959	=item ev_loop_verify (loop)
716		960
717	This function only does something when C<EV_VERIFY> support has been	961	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	962	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	963	through all internal structures and checks them for validity. If anything
720	an error message to standard error and call C<abort ()>.	964	is found to be inconsistent, it will print an error message to standard
		965	error and call C<abort ()>.
721		966
722	This can be used to catch bugs inside libev itself: under normal	967	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	968	circumstances, this function will never abort as of course libev keeps its
724	data structures consistent.	969	data structures consistent.
725		970
726	=back	971	=back
727		972
728		973
729	=head1 ANATOMY OF A WATCHER	974	=head1 ANATOMY OF A WATCHER
730		975
		976	In the following description, uppercase C<TYPE> in names stands for the
		977	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		978	watchers and C<ev_io_start> for I/O watchers.
		979
731	A watcher is a structure that you create and register to record your	980	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	981	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:	982	become readable, you would create an C<ev_io> watcher for that:
734		983
735	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	984	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
736	{	985	{
737	ev_io_stop (w);	986	ev_io_stop (w);
738	ev_unloop (loop, EVUNLOOP_ALL);	987	ev_unloop (loop, EVUNLOOP_ALL);
739	}	988	}
740		989
741	struct ev_loop *loop = ev_default_loop (0);	990	struct ev_loop *loop = ev_default_loop (0);
		991
742	struct ev_io stdin_watcher;	992	ev_io stdin_watcher;
		993
743	ev_init (&stdin_watcher, my_cb);	994	ev_init (&stdin_watcher, my_cb);
744	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	995	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
745	ev_io_start (loop, &stdin_watcher);	996	ev_io_start (loop, &stdin_watcher);
		997
746	ev_loop (loop, 0);	998	ev_loop (loop, 0);
747		999
748	As you can see, you are responsible for allocating the memory for your	1000	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,	1001	watcher structures (and it is I<usually> a bad idea to do this on the
750	although this can sometimes be quite valid).	1002	stack).
		1003
		1004	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1005	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
751		1006
752	Each watcher structure must be initialised by a call to C<ev_init	1007	Each watcher structure must be initialised by a call to C<ev_init
753	(watcher *, callback)>, which expects a callback to be provided. This	1008	(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	1009	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	1010	watchers, each time the event loop detects that the file descriptor given
756	is readable and/or writable).	1011	is readable and/or writable).
757		1012
758	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1013	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	1014	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	1015	is also a macro to combine initialisation and setting in one call: C<<
761	(watcher *, callback, ...) >>.	1016	ev_TYPE_init (watcher *, callback, ...) >>.
762		1017
763	To make the watcher actually watch out for events, you have to start it	1018	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	1019	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	1020	*) >>), and you can stop watching for events at any time by calling the
766	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1021	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
767		1022
768	As long as your watcher is active (has been started but not stopped) you	1023	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	1024	must not touch the values stored in it. Most specifically you must never
770	reinitialise it or call its C<set> macro.	1025	reinitialise it or call its C<ev_TYPE_set> macro.
771		1026
772	Each and every callback receives the event loop pointer as first, the	1027	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	1028	registered watcher structure as second, and a bitset of received events as
774	third argument.	1029	third argument.
775		1030
…		…
784	=item C<EV_WRITE>	1039	=item C<EV_WRITE>
785		1040
786	The file descriptor in the C<ev_io> watcher has become readable and/or	1041	The file descriptor in the C<ev_io> watcher has become readable and/or
787	writable.	1042	writable.
788		1043
789	=item C<EV_TIMEOUT>	1044	=item C<EV_TIMER>
790		1045
791	The C<ev_timer> watcher has timed out.	1046	The C<ev_timer> watcher has timed out.
792		1047
793	=item C<EV_PERIODIC>	1048	=item C<EV_PERIODIC>
794		1049
…		…
833		1088
834	=item C<EV_ASYNC>	1089	=item C<EV_ASYNC>
835		1090
836	The given async watcher has been asynchronously notified (see C<ev_async>).	1091	The given async watcher has been asynchronously notified (see C<ev_async>).
837		1092
		1093	=item C<EV_CUSTOM>
		1094
		1095	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1096	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1097
838	=item C<EV_ERROR>	1098	=item C<EV_ERROR>
839		1099
840	An unspecified error has occurred, the watcher has been stopped. This might	1100	An unspecified error has occurred, the watcher has been stopped. This might
841	happen because the watcher could not be properly started because libev	1101	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	1102	ran out of memory, a file descriptor was found to be closed or any other
		1103	problem. Libev considers these application bugs.
		1104
843	problem. You best act on it by reporting the problem and somehow coping	1105	You best act on it by reporting the problem and somehow coping with the
844	with the watcher being stopped.	1106	watcher being stopped. Note that well-written programs should not receive
		1107	an error ever, so when your watcher receives it, this usually indicates a
		1108	bug in your program.
845		1109
846	Libev will usually signal a few "dummy" events together with an error,	1110	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	1111	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	1112	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	1113	the error from read() or write(). This will not work in multi-threaded
850	programs, though, so beware.	1114	programs, though, as the fd could already be closed and reused for another
		1115	thing, so beware.
851		1116
852	=back	1117	=back
853		1118
854	=head2 GENERIC WATCHER FUNCTIONS	1119	=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		1120
859	=over 4	1121	=over 4
860		1122
861	=item C<ev_init> (ev_TYPE *watcher, callback)	1123	=item C<ev_init> (ev_TYPE *watcher, callback)
862		1124
…		…
868	which rolls both calls into one.	1130	which rolls both calls into one.
869		1131
870	You can reinitialise a watcher at any time as long as it has been stopped	1132	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.	1133	(or never started) and there are no pending events outstanding.
872		1134
873	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1135	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
874	int revents)>.	1136	int revents)>.
875		1137
		1138	Example: Initialise an C<ev_io> watcher in two steps.
		1139
		1140	ev_io w;
		1141	ev_init (&w, my_cb);
		1142	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1143
876	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1144	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
877		1145
878	This macro initialises the type-specific parts of a watcher. You need to	1146	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	1147	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	1148	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	1149	macro on a watcher that is active (it can be pending, however, which is a
882	difference to the C<ev_init> macro).	1150	difference to the C<ev_init> macro).
883		1151
884	Although some watcher types do not have type-specific arguments	1152	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.	1153	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
886		1154
		1155	See C<ev_init>, above, for an example.
		1156
887	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1157	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
888		1158
889	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1159	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	1160	calls into a single call. This is the most convenient method to initialise
891	a watcher. The same limitations apply, of course.	1161	a watcher. The same limitations apply, of course.
892		1162
		1163	Example: Initialise and set an C<ev_io> watcher in one step.
		1164
		1165	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1166
893	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1167	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
894		1168
895	Starts (activates) the given watcher. Only active watchers will receive	1169	Starts (activates) the given watcher. Only active watchers will receive
896	events. If the watcher is already active nothing will happen.	1170	events. If the watcher is already active nothing will happen.
897		1171
		1172	Example: Start the C<ev_io> watcher that is being abused as example in this
		1173	whole section.
		1174
		1175	ev_io_start (EV_DEFAULT_UC, &w);
		1176
898	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1177	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
899		1178
900	Stops the given watcher again (if active) and clears the pending	1179	Stops the given watcher if active, and clears the pending status (whether
		1180	the watcher was active or not).
		1181
901	status. It is possible that stopped watchers are pending (for example,	1182	It is possible that stopped watchers are pending - for example,
902	non-repeating timers are being stopped when they become pending), but	1183	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	1184	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	1185	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.	1186	therefore a good idea to always call its C<ev_TYPE_stop> function.
906		1187
907	=item bool ev_is_active (ev_TYPE *watcher)	1188	=item bool ev_is_active (ev_TYPE *watcher)
908		1189
909	Returns a true value iff the watcher is active (i.e. it has been started	1190	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	1191	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)	1207	=item ev_cb_set (ev_TYPE *watcher, callback)
927		1208
928	Change the callback. You can change the callback at virtually any time	1209	Change the callback. You can change the callback at virtually any time
929	(modulo threads).	1210	(modulo threads).
930		1211
931	=item ev_set_priority (ev_TYPE *watcher, priority)	1212	=item ev_set_priority (ev_TYPE *watcher, int priority)
932		1213
933	=item int ev_priority (ev_TYPE *watcher)	1214	=item int ev_priority (ev_TYPE *watcher)
934		1215
935	Set and query the priority of the watcher. The priority is a small	1216	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>	1217	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
937	(default: C<-2>). Pending watchers with higher priority will be invoked	1218	(default: C<-2>). Pending watchers with higher priority will be invoked
938	before watchers with lower priority, but priority will not keep watchers	1219	before watchers with lower priority, but priority will not keep watchers
939	from being executed (except for C<ev_idle> watchers).	1220	from being executed (except for C<ev_idle> watchers).
940		1221
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	1222	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.	1223	you need to look at C<ev_idle> watchers, which provide this functionality.
948		1224
949	You I<must not> change the priority of a watcher as long as it is active or	1225	You I<must not> change the priority of a watcher as long as it is active or
950	pending.	1226	pending.
951		1227
		1228	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1229	fine, as long as you do not mind that the priority value you query might
		1230	or might not have been clamped to the valid range.
		1231
952	The default priority used by watchers when no priority has been set is	1232	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 :).	1233	always C<0>, which is supposed to not be too high and not be too low :).
954		1234
955	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1235	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	1236	priorities.
957	or might not have been adjusted to be within valid range.
958		1237
959	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1238	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
960		1239
961	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1240	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	1241	C<loop> nor C<revents> need to be valid as long as the watcher callback
963	can deal with that fact.	1242	can deal with that fact, as both are simply passed through to the
		1243	callback.
964		1244
965	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1245	=item int ev_clear_pending (loop, ev_TYPE *watcher)
966		1246
967	If the watcher is pending, this function returns clears its pending status	1247	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	1248	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>.	1249	watcher isn't pending it does nothing and returns C<0>.
970		1250
		1251	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1252	callback to be invoked, which can be accomplished with this function.
		1253
		1254	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1255
		1256	Feeds the given event set into the event loop, as if the specified event
		1257	had happened for the specified watcher (which must be a pointer to an
		1258	initialised but not necessarily started event watcher). Obviously you must
		1259	not free the watcher as long as it has pending events.
		1260
		1261	Stopping the watcher, letting libev invoke it, or calling
		1262	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1263	not started in the first place.
		1264
		1265	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1266	functions that do not need a watcher.
		1267
971	=back	1268	=back
972		1269
973		1270
974	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1271	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
975		1272
976	Each watcher has, by default, a member C<void *data> that you can change	1273	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	1274	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	1275	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	1276	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	1277	member, you can also "subclass" the watcher type and provide your own
981	data:	1278	data:
982		1279
983	struct my_io	1280	struct my_io
984	{	1281	{
985	struct ev_io io;	1282	ev_io io;
986	int otherfd;	1283	int otherfd;
987	void *somedata;	1284	void *somedata;
988	struct whatever *mostinteresting;	1285	struct whatever *mostinteresting;
989	}	1286	};
		1287
		1288	...
		1289	struct my_io w;
		1290	ev_io_init (&w.io, my_cb, fd, EV_READ);
990		1291
991	And since your callback will be called with a pointer to the watcher, you	1292	And since your callback will be called with a pointer to the watcher, you
992	can cast it back to your own type:	1293	can cast it back to your own type:
993		1294
994	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1295	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
995	{	1296	{
996	struct my_io *w = (struct my_io *)w_;	1297	struct my_io *w = (struct my_io *)w_;
997	...	1298	...
998	}	1299	}
999		1300
1000	More interesting and less C-conformant ways of casting your callback type	1301	More interesting and less C-conformant ways of casting your callback type
1001	instead have been omitted.	1302	instead have been omitted.
1002		1303
1003	Another common scenario is having some data structure with multiple	1304	Another common scenario is to use some data structure with multiple
1004	watchers:	1305	embedded watchers:
1005		1306
1006	struct my_biggy	1307	struct my_biggy
1007	{	1308	{
1008	int some_data;	1309	int some_data;
1009	ev_timer t1;	1310	ev_timer t1;
1010	ev_timer t2;	1311	ev_timer t2;
1011	}	1312	}
1012		1313
1013	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1314	In this case getting the pointer to C<my_biggy> is a bit more
1014	you need to use C<offsetof>:	1315	complicated: Either you store the address of your C<my_biggy> struct
		1316	in the C<data> member of the watcher (for woozies), or you need to use
		1317	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1318	programmers):
1015		1319
1016	#include <stddef.h>	1320	#include <stddef.h>
1017		1321
1018	static void	1322	static void
1019	t1_cb (EV_P_ struct ev_timer *w, int revents)	1323	t1_cb (EV_P_ ev_timer *w, int revents)
1020	{	1324	{
1021	struct my_biggy big = (struct my_biggy *	1325	struct my_biggy big = (struct my_biggy *)
1022	(((char *)w) - offsetof (struct my_biggy, t1));	1326	(((char *)w) - offsetof (struct my_biggy, t1));
1023	}	1327	}
1024		1328
1025	static void	1329	static void
1026	t2_cb (EV_P_ struct ev_timer *w, int revents)	1330	t2_cb (EV_P_ ev_timer *w, int revents)
1027	{	1331	{
1028	struct my_biggy big = (struct my_biggy *	1332	struct my_biggy big = (struct my_biggy *)
1029	(((char *)w) - offsetof (struct my_biggy, t2));	1333	(((char *)w) - offsetof (struct my_biggy, t2));
1030	}	1334	}
		1335
		1336	=head2 WATCHER PRIORITY MODELS
		1337
		1338	Many event loops support I<watcher priorities>, which are usually small
		1339	integers that influence the ordering of event callback invocation
		1340	between watchers in some way, all else being equal.
		1341
		1342	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1343	description for the more technical details such as the actual priority
		1344	range.
		1345
		1346	There are two common ways how these these priorities are being interpreted
		1347	by event loops:
		1348
		1349	In the more common lock-out model, higher priorities "lock out" invocation
		1350	of lower priority watchers, which means as long as higher priority
		1351	watchers receive events, lower priority watchers are not being invoked.
		1352
		1353	The less common only-for-ordering model uses priorities solely to order
		1354	callback invocation within a single event loop iteration: Higher priority
		1355	watchers are invoked before lower priority ones, but they all get invoked
		1356	before polling for new events.
		1357
		1358	Libev uses the second (only-for-ordering) model for all its watchers
		1359	except for idle watchers (which use the lock-out model).
		1360
		1361	The rationale behind this is that implementing the lock-out model for
		1362	watchers is not well supported by most kernel interfaces, and most event
		1363	libraries will just poll for the same events again and again as long as
		1364	their callbacks have not been executed, which is very inefficient in the
		1365	common case of one high-priority watcher locking out a mass of lower
		1366	priority ones.
		1367
		1368	Static (ordering) priorities are most useful when you have two or more
		1369	watchers handling the same resource: a typical usage example is having an
		1370	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1371	timeouts. Under load, data might be received while the program handles
		1372	other jobs, but since timers normally get invoked first, the timeout
		1373	handler will be executed before checking for data. In that case, giving
		1374	the timer a lower priority than the I/O watcher ensures that I/O will be
		1375	handled first even under adverse conditions (which is usually, but not
		1376	always, what you want).
		1377
		1378	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1379	will only be executed when no same or higher priority watchers have
		1380	received events, they can be used to implement the "lock-out" model when
		1381	required.
		1382
		1383	For example, to emulate how many other event libraries handle priorities,
		1384	you can associate an C<ev_idle> watcher to each such watcher, and in
		1385	the normal watcher callback, you just start the idle watcher. The real
		1386	processing is done in the idle watcher callback. This causes libev to
		1387	continuously poll and process kernel event data for the watcher, but when
		1388	the lock-out case is known to be rare (which in turn is rare :), this is
		1389	workable.
		1390
		1391	Usually, however, the lock-out model implemented that way will perform
		1392	miserably under the type of load it was designed to handle. In that case,
		1393	it might be preferable to stop the real watcher before starting the
		1394	idle watcher, so the kernel will not have to process the event in case
		1395	the actual processing will be delayed for considerable time.
		1396
		1397	Here is an example of an I/O watcher that should run at a strictly lower
		1398	priority than the default, and which should only process data when no
		1399	other events are pending:
		1400
		1401	ev_idle idle; // actual processing watcher
		1402	ev_io io; // actual event watcher
		1403
		1404	static void
		1405	io_cb (EV_P_ ev_io *w, int revents)
		1406	{
		1407	// stop the I/O watcher, we received the event, but
		1408	// are not yet ready to handle it.
		1409	ev_io_stop (EV_A_ w);
		1410
		1411	// start the idle watcher to handle the actual event.
		1412	// it will not be executed as long as other watchers
		1413	// with the default priority are receiving events.
		1414	ev_idle_start (EV_A_ &idle);
		1415	}
		1416
		1417	static void
		1418	idle_cb (EV_P_ ev_idle *w, int revents)
		1419	{
		1420	// actual processing
		1421	read (STDIN_FILENO, ...);
		1422
		1423	// have to start the I/O watcher again, as
		1424	// we have handled the event
		1425	ev_io_start (EV_P_ &io);
		1426	}
		1427
		1428	// initialisation
		1429	ev_idle_init (&idle, idle_cb);
		1430	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1431	ev_io_start (EV_DEFAULT_ &io);
		1432
		1433	In the "real" world, it might also be beneficial to start a timer, so that
		1434	low-priority connections can not be locked out forever under load. This
		1435	enables your program to keep a lower latency for important connections
		1436	during short periods of high load, while not completely locking out less
		1437	important ones.
1031		1438
1032		1439
1033	=head1 WATCHER TYPES	1440	=head1 WATCHER TYPES
1034		1441
1035	This section describes each watcher in detail, but will not repeat	1442	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	1466	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	1467	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	1468	descriptors to non-blocking mode is also usually a good idea (but not
1062	required if you know what you are doing).	1469	required if you know what you are doing).
1063		1470
1064	If you must do this, then force the use of a known-to-be-good backend	1471	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	1472	known-to-be-good backend (at the time of this writing, this includes only
1066	C<EVBACKEND_POLL>).	1473	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1474	descriptors for which non-blocking operation makes no sense (such as
		1475	files) - libev doesn't guarantee any specific behaviour in that case.
1067		1476
1068	Another thing you have to watch out for is that it is quite easy to	1477	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	1478	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	1479	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	1480	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	1481	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	1482	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	1483	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.	1484	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1076		1485
1077	If you cannot run the fd in non-blocking mode (for example you should not	1486	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	1487	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	1488	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	1489	interface such as poll (fortunately in our Xlib example, Xlib already
1081	its own, so its quite safe to use).	1490	does this on its own, so its quite safe to use). Some people additionally
		1491	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1492	indefinitely.
		1493
		1494	But really, best use non-blocking mode.
1082		1495
1083	=head3 The special problem of disappearing file descriptors	1496	=head3 The special problem of disappearing file descriptors
1084		1497
1085	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1498	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,	1499	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	1500	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	1501	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	1502	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	1503	registered with libev, there is no efficient way to see that this is, in
1091	fact, a different file descriptor.	1504	fact, a different file descriptor.
1092		1505
…		…
1123	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1536	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1124	C<EVBACKEND_POLL>.	1537	C<EVBACKEND_POLL>.
1125		1538
1126	=head3 The special problem of SIGPIPE	1539	=head3 The special problem of SIGPIPE
1127		1540
1128	While not really specific to libev, it is easy to forget about SIGPIPE:	1541	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	1542	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	1543	sent a SIGPIPE, which, by default, aborts your program. For most programs
1131	programs this is sensible behaviour, for daemons, this is usually	1544	this is sensible behaviour, for daemons, this is usually undesirable.
1132	undesirable.
1133		1545
1134	So when you encounter spurious, unexplained daemon exits, make sure you	1546	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	1547	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).	1548	somewhere, as that would have given you a big clue).
1137		1549
		1550	=head3 The special problem of accept()ing when you can't
		1551
		1552	Many implementations of the POSIX C<accept> function (for example,
		1553	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1554	connection from the pending queue in all error cases.
		1555
		1556	For example, larger servers often run out of file descriptors (because
		1557	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1558	rejecting the connection, leading to libev signalling readiness on
		1559	the next iteration again (the connection still exists after all), and
		1560	typically causing the program to loop at 100% CPU usage.
		1561
		1562	Unfortunately, the set of errors that cause this issue differs between
		1563	operating systems, there is usually little the app can do to remedy the
		1564	situation, and no known thread-safe method of removing the connection to
		1565	cope with overload is known (to me).
		1566
		1567	One of the easiest ways to handle this situation is to just ignore it
		1568	- when the program encounters an overload, it will just loop until the
		1569	situation is over. While this is a form of busy waiting, no OS offers an
		1570	event-based way to handle this situation, so it's the best one can do.
		1571
		1572	A better way to handle the situation is to log any errors other than
		1573	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1574	messages, and continue as usual, which at least gives the user an idea of
		1575	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1576	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1577	usage.
		1578
		1579	If your program is single-threaded, then you could also keep a dummy file
		1580	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1581	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1582	close that fd, and create a new dummy fd. This will gracefully refuse
		1583	clients under typical overload conditions.
		1584
		1585	The last way to handle it is to simply log the error and C<exit>, as
		1586	is often done with C<malloc> failures, but this results in an easy
		1587	opportunity for a DoS attack.
1138		1588
1139	=head3 Watcher-Specific Functions	1589	=head3 Watcher-Specific Functions
1140		1590
1141	=over 4	1591	=over 4
1142		1592
1143	=item ev_io_init (ev_io *, callback, int fd, int events)	1593	=item ev_io_init (ev_io *, callback, int fd, int events)
1144		1594
1145	=item ev_io_set (ev_io *, int fd, int events)	1595	=item ev_io_set (ev_io *, int fd, int events)
1146		1596
1147	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1597	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	1598	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.	1599	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1150		1600
1151	=item int fd [read-only]	1601	=item int fd [read-only]
1152		1602
1153	The file descriptor being watched.	1603	The file descriptor being watched.
1154		1604
…		…
1162		1612
1163	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1613	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	1614	readable, but only once. Since it is likely line-buffered, you could
1165	attempt to read a whole line in the callback.	1615	attempt to read a whole line in the callback.
1166		1616
1167	static void	1617	static void
1168	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1618	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1169	{	1619	{
1170	ev_io_stop (loop, w);	1620	ev_io_stop (loop, w);
1171	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1621	.. read from stdin here (or from w->fd) and handle any I/O errors
1172	}	1622	}
1173		1623
1174	...	1624	...
1175	struct ev_loop *loop = ev_default_init (0);	1625	struct ev_loop *loop = ev_default_init (0);
1176	struct ev_io stdin_readable;	1626	ev_io stdin_readable;
1177	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1627	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1178	ev_io_start (loop, &stdin_readable);	1628	ev_io_start (loop, &stdin_readable);
1179	ev_loop (loop, 0);	1629	ev_loop (loop, 0);
1180		1630
1181		1631
1182	=head2 C<ev_timer> - relative and optionally repeating timeouts	1632	=head2 C<ev_timer> - relative and optionally repeating timeouts
1183		1633
1184	Timer watchers are simple relative timers that generate an event after a	1634	Timer watchers are simple relative timers that generate an event after a
1185	given time, and optionally repeating in regular intervals after that.	1635	given time, and optionally repeating in regular intervals after that.
1186		1636
1187	The timers are based on real time, that is, if you register an event that	1637	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	1638	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	1639	year, it will still time out after (roughly) one hour. "Roughly" because
1190	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1640	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1191	monotonic clock option helps a lot here).	1641	monotonic clock option helps a lot here).
		1642
		1643	The callback is guaranteed to be invoked only I<after> its timeout has
		1644	passed (not I<at>, so on systems with very low-resolution clocks this
		1645	might introduce a small delay). If multiple timers become ready during the
		1646	same loop iteration then the ones with earlier time-out values are invoked
		1647	before ones of the same priority with later time-out values (but this is
		1648	no longer true when a callback calls C<ev_loop> recursively).
		1649
		1650	=head3 Be smart about timeouts
		1651
		1652	Many real-world problems involve some kind of timeout, usually for error
		1653	recovery. A typical example is an HTTP request - if the other side hangs,
		1654	you want to raise some error after a while.
		1655
		1656	What follows are some ways to handle this problem, from obvious and
		1657	inefficient to smart and efficient.
		1658
		1659	In the following, a 60 second activity timeout is assumed - a timeout that
		1660	gets reset to 60 seconds each time there is activity (e.g. each time some
		1661	data or other life sign was received).
		1662
		1663	=over 4
		1664
		1665	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1666
		1667	This is the most obvious, but not the most simple way: In the beginning,
		1668	start the watcher:
		1669
		1670	ev_timer_init (timer, callback, 60., 0.);
		1671	ev_timer_start (loop, timer);
		1672
		1673	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1674	and start it again:
		1675
		1676	ev_timer_stop (loop, timer);
		1677	ev_timer_set (timer, 60., 0.);
		1678	ev_timer_start (loop, timer);
		1679
		1680	This is relatively simple to implement, but means that each time there is
		1681	some activity, libev will first have to remove the timer from its internal
		1682	data structure and then add it again. Libev tries to be fast, but it's
		1683	still not a constant-time operation.
		1684
		1685	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1686
		1687	This is the easiest way, and involves using C<ev_timer_again> instead of
		1688	C<ev_timer_start>.
		1689
		1690	To implement this, configure an C<ev_timer> with a C<repeat> value
		1691	of C<60> and then call C<ev_timer_again> at start and each time you
		1692	successfully read or write some data. If you go into an idle state where
		1693	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1694	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1695
		1696	That means you can ignore both the C<ev_timer_start> function and the
		1697	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1698	member and C<ev_timer_again>.
		1699
		1700	At start:
		1701
		1702	ev_init (timer, callback);
		1703	timer->repeat = 60.;
		1704	ev_timer_again (loop, timer);
		1705
		1706	Each time there is some activity:
		1707
		1708	ev_timer_again (loop, timer);
		1709
		1710	It is even possible to change the time-out on the fly, regardless of
		1711	whether the watcher is active or not:
		1712
		1713	timer->repeat = 30.;
		1714	ev_timer_again (loop, timer);
		1715
		1716	This is slightly more efficient then stopping/starting the timer each time
		1717	you want to modify its timeout value, as libev does not have to completely
		1718	remove and re-insert the timer from/into its internal data structure.
		1719
		1720	It is, however, even simpler than the "obvious" way to do it.
		1721
		1722	=item 3. Let the timer time out, but then re-arm it as required.
		1723
		1724	This method is more tricky, but usually most efficient: Most timeouts are
		1725	relatively long compared to the intervals between other activity - in
		1726	our example, within 60 seconds, there are usually many I/O events with
		1727	associated activity resets.
		1728
		1729	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1730	but remember the time of last activity, and check for a real timeout only
		1731	within the callback:
		1732
		1733	ev_tstamp last_activity; // time of last activity
		1734
		1735	static void
		1736	callback (EV_P_ ev_timer *w, int revents)
		1737	{
		1738	ev_tstamp now = ev_now (EV_A);
		1739	ev_tstamp timeout = last_activity + 60.;
		1740
		1741	// if last_activity + 60. is older than now, we did time out
		1742	if (timeout < now)
		1743	{
		1744	// timeout occurred, take action
		1745	}
		1746	else
		1747	{
		1748	// callback was invoked, but there was some activity, re-arm
		1749	// the watcher to fire in last_activity + 60, which is
		1750	// guaranteed to be in the future, so "again" is positive:
		1751	w->repeat = timeout - now;
		1752	ev_timer_again (EV_A_ w);
		1753	}
		1754	}
		1755
		1756	To summarise the callback: first calculate the real timeout (defined
		1757	as "60 seconds after the last activity"), then check if that time has
		1758	been reached, which means something I<did>, in fact, time out. Otherwise
		1759	the callback was invoked too early (C<timeout> is in the future), so
		1760	re-schedule the timer to fire at that future time, to see if maybe we have
		1761	a timeout then.
		1762
		1763	Note how C<ev_timer_again> is used, taking advantage of the
		1764	C<ev_timer_again> optimisation when the timer is already running.
		1765
		1766	This scheme causes more callback invocations (about one every 60 seconds
		1767	minus half the average time between activity), but virtually no calls to
		1768	libev to change the timeout.
		1769
		1770	To start the timer, simply initialise the watcher and set C<last_activity>
		1771	to the current time (meaning we just have some activity :), then call the
		1772	callback, which will "do the right thing" and start the timer:
		1773
		1774	ev_init (timer, callback);
		1775	last_activity = ev_now (loop);
		1776	callback (loop, timer, EV_TIMER);
		1777
		1778	And when there is some activity, simply store the current time in
		1779	C<last_activity>, no libev calls at all:
		1780
		1781	last_activity = ev_now (loop);
		1782
		1783	This technique is slightly more complex, but in most cases where the
		1784	time-out is unlikely to be triggered, much more efficient.
		1785
		1786	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1787	callback :) - just change the timeout and invoke the callback, which will
		1788	fix things for you.
		1789
		1790	=item 4. Wee, just use a double-linked list for your timeouts.
		1791
		1792	If there is not one request, but many thousands (millions...), all
		1793	employing some kind of timeout with the same timeout value, then one can
		1794	do even better:
		1795
		1796	When starting the timeout, calculate the timeout value and put the timeout
		1797	at the I<end> of the list.
		1798
		1799	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1800	the list is expected to fire (for example, using the technique #3).
		1801
		1802	When there is some activity, remove the timer from the list, recalculate
		1803	the timeout, append it to the end of the list again, and make sure to
		1804	update the C<ev_timer> if it was taken from the beginning of the list.
		1805
		1806	This way, one can manage an unlimited number of timeouts in O(1) time for
		1807	starting, stopping and updating the timers, at the expense of a major
		1808	complication, and having to use a constant timeout. The constant timeout
		1809	ensures that the list stays sorted.
		1810
		1811	=back
		1812
		1813	So which method the best?
		1814
		1815	Method #2 is a simple no-brain-required solution that is adequate in most
		1816	situations. Method #3 requires a bit more thinking, but handles many cases
		1817	better, and isn't very complicated either. In most case, choosing either
		1818	one is fine, with #3 being better in typical situations.
		1819
		1820	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1821	rather complicated, but extremely efficient, something that really pays
		1822	off after the first million or so of active timers, i.e. it's usually
		1823	overkill :)
		1824
		1825	=head3 The special problem of time updates
		1826
		1827	Establishing the current time is a costly operation (it usually takes at
		1828	least two system calls): EV therefore updates its idea of the current
		1829	time only before and after C<ev_loop> collects new events, which causes a
		1830	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1831	lots of events in one iteration.
1192		1832
1193	The relative timeouts are calculated relative to the C<ev_now ()>	1833	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	1834	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	1835	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	1836	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:	1837	timeout on the current time, use something like this to adjust for this:
1198		1838
1199	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1839	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1200		1840
1201	The callback is guaranteed to be invoked only after its timeout has passed,	1841	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	1842	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1203	order of execution is undefined.	1843	()>.
		1844
		1845	=head3 The special problems of suspended animation
		1846
		1847	When you leave the server world it is quite customary to hit machines that
		1848	can suspend/hibernate - what happens to the clocks during such a suspend?
		1849
		1850	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1851	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1852	to run until the system is suspended, but they will not advance while the
		1853	system is suspended. That means, on resume, it will be as if the program
		1854	was frozen for a few seconds, but the suspend time will not be counted
		1855	towards C<ev_timer> when a monotonic clock source is used. The real time
		1856	clock advanced as expected, but if it is used as sole clocksource, then a
		1857	long suspend would be detected as a time jump by libev, and timers would
		1858	be adjusted accordingly.
		1859
		1860	I would not be surprised to see different behaviour in different between
		1861	operating systems, OS versions or even different hardware.
		1862
		1863	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1864	time jump in the monotonic clocks and the realtime clock. If the program
		1865	is suspended for a very long time, and monotonic clock sources are in use,
		1866	then you can expect C<ev_timer>s to expire as the full suspension time
		1867	will be counted towards the timers. When no monotonic clock source is in
		1868	use, then libev will again assume a timejump and adjust accordingly.
		1869
		1870	It might be beneficial for this latter case to call C<ev_suspend>
		1871	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1872	deterministic behaviour in this case (you can do nothing against
		1873	C<SIGSTOP>).
1204		1874
1205	=head3 Watcher-Specific Functions and Data Members	1875	=head3 Watcher-Specific Functions and Data Members
1206		1876
1207	=over 4	1877	=over 4
1208		1878
…		…
1232	If the timer is started but non-repeating, stop it (as if it timed out).	1902	If the timer is started but non-repeating, stop it (as if it timed out).
1233		1903
1234	If the timer is repeating, either start it if necessary (with the	1904	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.	1905	C<repeat> value), or reset the running timer to the C<repeat> value.
1236		1906
1237	This sounds a bit complicated, but here is a useful and typical	1907	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	1908	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		1909
1247	That means you can ignore the C<after> value and C<ev_timer_start>	1910	=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		1911
1250	ev_timer_init (timer, callback, 0., 5.);	1912	Returns the remaining time until a timer fires. If the timer is active,
1251	ev_timer_again (loop, timer);	1913	then this time is relative to the current event loop time, otherwise it's
1252	...	1914	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		1915
1259	This is more slightly efficient then stopping/starting the timer each time	1916	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1260	you want to modify its timeout value.	1917	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		1918	will return C<4>. When the timer expires and is restarted, it will return
		1919	roughly C<7> (likely slightly less as callback invocation takes some time,
		1920	too), and so on.
1261		1921
1262	=item ev_tstamp repeat [read-write]	1922	=item ev_tstamp repeat [read-write]
1263		1923
1264	The current C<repeat> value. Will be used each time the watcher times out	1924	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),	1925	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.	1926	which is also when any modifications are taken into account.
1267		1927
1268	=back	1928	=back
1269		1929
1270	=head3 Examples	1930	=head3 Examples
1271		1931
1272	Example: Create a timer that fires after 60 seconds.	1932	Example: Create a timer that fires after 60 seconds.
1273		1933
1274	static void	1934	static void
1275	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1935	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1276	{	1936	{
1277	.. one minute over, w is actually stopped right here	1937	.. one minute over, w is actually stopped right here
1278	}	1938	}
1279		1939
1280	struct ev_timer mytimer;	1940	ev_timer mytimer;
1281	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1941	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1282	ev_timer_start (loop, &mytimer);	1942	ev_timer_start (loop, &mytimer);
1283		1943
1284	Example: Create a timeout timer that times out after 10 seconds of	1944	Example: Create a timeout timer that times out after 10 seconds of
1285	inactivity.	1945	inactivity.
1286		1946
1287	static void	1947	static void
1288	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1948	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1289	{	1949	{
1290	.. ten seconds without any activity	1950	.. ten seconds without any activity
1291	}	1951	}
1292		1952
1293	struct ev_timer mytimer;	1953	ev_timer mytimer;
1294	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1954	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1295	ev_timer_again (&mytimer); /* start timer */	1955	ev_timer_again (&mytimer); /* start timer */
1296	ev_loop (loop, 0);	1956	ev_loop (loop, 0);
1297		1957
1298	// and in some piece of code that gets executed on any "activity":	1958	// and in some piece of code that gets executed on any "activity":
1299	// reset the timeout to start ticking again at 10 seconds	1959	// reset the timeout to start ticking again at 10 seconds
1300	ev_timer_again (&mytimer);	1960	ev_timer_again (&mytimer);
1301		1961
1302		1962
1303	=head2 C<ev_periodic> - to cron or not to cron?	1963	=head2 C<ev_periodic> - to cron or not to cron?
1304		1964
1305	Periodic watchers are also timers of a kind, but they are very versatile	1965	Periodic watchers are also timers of a kind, but they are very versatile
1306	(and unfortunately a bit complex).	1966	(and unfortunately a bit complex).
1307		1967
1308	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1968	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	1969	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	1970	(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 ()	1971	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	1972	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	1973	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		1974
		1975	You can tell a periodic watcher to trigger after some specific point
		1976	in time: for example, if you tell a periodic watcher to trigger "in 10
		1977	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1978	not a delay) and then reset your system clock to January of the previous
		1979	year, then it will take a year or more to trigger the event (unlike an
		1980	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1981	it, as it uses a relative timeout).
		1982
1317	C<ev_periodic>s can also be used to implement vastly more complex timers,	1983	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	1984	timers, such as triggering an event on each "midnight, local time", or
1319	complicated, rules.	1985	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1986	those cannot react to time jumps.
1320		1987
1321	As with timers, the callback is guaranteed to be invoked only when the	1988	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	1989	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.	1990	timers become ready during the same loop iteration then the ones with
		1991	earlier time-out values are invoked before ones with later time-out values
		1992	(but this is no longer true when a callback calls C<ev_loop> recursively).
1324		1993
1325	=head3 Watcher-Specific Functions and Data Members	1994	=head3 Watcher-Specific Functions and Data Members
1326		1995
1327	=over 4	1996	=over 4
1328		1997
1329	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1998	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1330		1999
1331	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2000	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1332		2001
1333	Lots of arguments, lets sort it out... There are basically three modes of	2002	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:	2003	operation, and we will explain them from simplest to most complex:
1335		2004
1336	=over 4	2005	=over 4
1337		2006
1338	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2007	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1339		2008
1340	In this configuration the watcher triggers an event after the wall clock	2009	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	2010	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	2011	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.	2012	will be stopped and invoked when the system clock reaches or surpasses
		2013	this point in time.
1344		2014
1345	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2015	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1346		2016
1347	In this mode the watcher will always be scheduled to time out at the next	2017	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)	2018	C<offset + N * interval> time (for some integer N, which can also be
1349	and then repeat, regardless of any time jumps.	2019	negative) and then repeat, regardless of any time jumps. The C<offset>
		2020	argument is merely an offset into the C<interval> periods.
1350		2021
1351	This can be used to create timers that do not drift with respect to system	2022	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	2023	system clock, for example, here is an C<ev_periodic> that triggers each
1353	the hour:	2024	hour, on the hour (with respect to UTC):
1354		2025
1355	ev_periodic_set (&periodic, 0., 3600., 0);	2026	ev_periodic_set (&periodic, 0., 3600., 0);
1356		2027
1357	This doesn't mean there will always be 3600 seconds in between triggers,	2028	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	2029	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	2030	full hour (UTC), or more correctly, when the system time is evenly divisible
1360	by 3600.	2031	by 3600.
1361		2032
1362	Another way to think about it (for the mathematically inclined) is that	2033	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	2034	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.	2035	time where C<time = offset (mod interval)>, regardless of any time jumps.
1365		2036
1366	For numerical stability it is preferable that the C<at> value is near	2037	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	2038	C<ev_now ()> (the current time), but there is no range requirement for
1368	this value, and in fact is often specified as zero.	2039	this value, and in fact is often specified as zero.
1369		2040
1370	Note also that there is an upper limit to how often a timer can fire (CPU	2041	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	2042	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	2043	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).	2044	millisecond (if the OS supports it and the machine is fast enough).
1374		2045
1375	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2046	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1376		2047
1377	In this mode the values for C<interval> and C<at> are both being	2048	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	2049	ignored. Instead, each time the periodic watcher gets scheduled, the
1379	reschedule callback will be called with the watcher as first, and the	2050	reschedule callback will be called with the watcher as first, and the
1380	current time as second argument.	2051	current time as second argument.
1381		2052
1382	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2053	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1383	ever, or make ANY event loop modifications whatsoever>.	2054	or make ANY other event loop modifications whatsoever, unless explicitly
		2055	allowed by documentation here>.
1384		2056
1385	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2057	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	2058	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1387	only event loop modification you are allowed to do).	2059	only event loop modification you are allowed to do).
1388		2060
1389	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2061	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1390	*w, ev_tstamp now)>, e.g.:	2062	*w, ev_tstamp now)>, e.g.:
1391		2063
		2064	static ev_tstamp
1392	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2065	my_rescheduler (ev_periodic *w, ev_tstamp now)
1393	{	2066	{
1394	return now + 60.;	2067	return now + 60.;
1395	}	2068	}
1396		2069
1397	It must return the next time to trigger, based on the passed time value	2070	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	2090	a different time than the last time it was called (e.g. in a crond like
1418	program when the crontabs have changed).	2091	program when the crontabs have changed).
1419		2092
1420	=item ev_tstamp ev_periodic_at (ev_periodic *)	2093	=item ev_tstamp ev_periodic_at (ev_periodic *)
1421		2094
1422	When active, returns the absolute time that the watcher is supposed to	2095	When active, returns the absolute time that the watcher is supposed
1423	trigger next.	2096	to trigger next. This is not the same as the C<offset> argument to
		2097	C<ev_periodic_set>, but indeed works even in interval and manual
		2098	rescheduling modes.
1424		2099
1425	=item ev_tstamp offset [read-write]	2100	=item ev_tstamp offset [read-write]
1426		2101
1427	When repeating, this contains the offset value, otherwise this is the	2102	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>).	2103	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2104	although libev might modify this value for better numerical stability).
1429		2105
1430	Can be modified any time, but changes only take effect when the periodic	2106	Can be modified any time, but changes only take effect when the periodic
1431	timer fires or C<ev_periodic_again> is being called.	2107	timer fires or C<ev_periodic_again> is being called.
1432		2108
1433	=item ev_tstamp interval [read-write]	2109	=item ev_tstamp interval [read-write]
1434		2110
1435	The current interval value. Can be modified any time, but changes only	2111	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	2112	take effect when the periodic timer fires or C<ev_periodic_again> is being
1437	called.	2113	called.
1438		2114
1439	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2115	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1440		2116
1441	The current reschedule callback, or C<0>, if this functionality is	2117	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	2118	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.	2119	the periodic timer fires or C<ev_periodic_again> is being called.
1444		2120
1445	=back	2121	=back
1446		2122
1447	=head3 Examples	2123	=head3 Examples
1448		2124
1449	Example: Call a callback every hour, or, more precisely, whenever the	2125	Example: Call a callback every hour, or, more precisely, whenever the
1450	system clock is divisible by 3600. The callback invocation times have	2126	system time is divisible by 3600. The callback invocation times have
1451	potentially a lot of jitter, but good long-term stability.	2127	potentially a lot of jitter, but good long-term stability.
1452		2128
1453	static void	2129	static void
1454	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2130	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1455	{	2131	{
1456	... its now a full hour (UTC, or TAI or whatever your clock follows)	2132	... its now a full hour (UTC, or TAI or whatever your clock follows)
1457	}	2133	}
1458		2134
1459	struct ev_periodic hourly_tick;	2135	ev_periodic hourly_tick;
1460	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2136	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1461	ev_periodic_start (loop, &hourly_tick);	2137	ev_periodic_start (loop, &hourly_tick);
1462		2138
1463	Example: The same as above, but use a reschedule callback to do it:	2139	Example: The same as above, but use a reschedule callback to do it:
1464		2140
1465	#include <math.h>	2141	#include <math.h>
1466		2142
1467	static ev_tstamp	2143	static ev_tstamp
1468	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2144	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1469	{	2145	{
1470	return fmod (now, 3600.) + 3600.;	2146	return now + (3600. - fmod (now, 3600.));
1471	}	2147	}
1472		2148
1473	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2149	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1474		2150
1475	Example: Call a callback every hour, starting now:	2151	Example: Call a callback every hour, starting now:
1476		2152
1477	struct ev_periodic hourly_tick;	2153	ev_periodic hourly_tick;
1478	ev_periodic_init (&hourly_tick, clock_cb,	2154	ev_periodic_init (&hourly_tick, clock_cb,
1479	fmod (ev_now (loop), 3600.), 3600., 0);	2155	fmod (ev_now (loop), 3600.), 3600., 0);
1480	ev_periodic_start (loop, &hourly_tick);	2156	ev_periodic_start (loop, &hourly_tick);
1481		2157
1482		2158
1483	=head2 C<ev_signal> - signal me when a signal gets signalled!	2159	=head2 C<ev_signal> - signal me when a signal gets signalled!
1484		2160
1485	Signal watchers will trigger an event when the process receives a specific	2161	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	2162	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	2163	will try it's best to deliver signals synchronously, i.e. as part of the
1488	normal event processing, like any other event.	2164	normal event processing, like any other event.
1489		2165
		2166	If you want signals to be delivered truly asynchronously, just use
		2167	C<sigaction> as you would do without libev and forget about sharing
		2168	the signal. You can even use C<ev_async> from a signal handler to
		2169	synchronously wake up an event loop.
		2170
1490	You can configure as many watchers as you like per signal. Only when the	2171	You can configure as many watchers as you like for the same signal, but
		2172	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2173	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2174	C<SIGINT> in both the default loop and another loop at the same time. At
		2175	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2176
1491	first watcher gets started will libev actually register a signal watcher	2177	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	2178	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	2179	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		2180
1497	If possible and supported, libev will install its handlers with	2181	If possible and supported, libev will install its handlers with
1498	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2182	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1499	interrupted. If you have a problem with system calls getting interrupted by	2183	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	2184	interrupted by signals you can block all signals in an C<ev_check> watcher
1501	them in an C<ev_prepare> watcher.	2185	and unblock them in an C<ev_prepare> watcher.
		2186
		2187	=head3 The special problem of inheritance over fork/execve/pthread_create
		2188
		2189	Both the signal mask (C<sigprocmask>) and the signal disposition
		2190	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2191	stopping it again), that is, libev might or might not block the signal,
		2192	and might or might not set or restore the installed signal handler.
		2193
		2194	While this does not matter for the signal disposition (libev never
		2195	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2196	C<execve>), this matters for the signal mask: many programs do not expect
		2197	certain signals to be blocked.
		2198
		2199	This means that before calling C<exec> (from the child) you should reset
		2200	the signal mask to whatever "default" you expect (all clear is a good
		2201	choice usually).
		2202
		2203	The simplest way to ensure that the signal mask is reset in the child is
		2204	to install a fork handler with C<pthread_atfork> that resets it. That will
		2205	catch fork calls done by libraries (such as the libc) as well.
		2206
		2207	In current versions of libev, the signal will not be blocked indefinitely
		2208	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2209	the window of opportunity for problems, it will not go away, as libev
		2210	I<has> to modify the signal mask, at least temporarily.
		2211
		2212	So I can't stress this enough: I<If you do not reset your signal mask when
		2213	you expect it to be empty, you have a race condition in your code>. This
		2214	is not a libev-specific thing, this is true for most event libraries.
1502		2215
1503	=head3 Watcher-Specific Functions and Data Members	2216	=head3 Watcher-Specific Functions and Data Members
1504		2217
1505	=over 4	2218	=over 4
1506		2219
…		…
1517		2230
1518	=back	2231	=back
1519		2232
1520	=head3 Examples	2233	=head3 Examples
1521		2234
1522	Example: Try to exit cleanly on SIGINT and SIGTERM.	2235	Example: Try to exit cleanly on SIGINT.
1523		2236
1524	static void	2237	static void
1525	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2238	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1526	{	2239	{
1527	ev_unloop (loop, EVUNLOOP_ALL);	2240	ev_unloop (loop, EVUNLOOP_ALL);
1528	}	2241	}
1529		2242
1530	struct ev_signal signal_watcher;	2243	ev_signal signal_watcher;
1531	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2244	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1532	ev_signal_start (loop, &sigint_cb);	2245	ev_signal_start (loop, &signal_watcher);
1533		2246
1534		2247
1535	=head2 C<ev_child> - watch out for process status changes	2248	=head2 C<ev_child> - watch out for process status changes
1536		2249
1537	Child watchers trigger when your process receives a SIGCHLD in response to	2250	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	2251	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	2252	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	2253	has been forked (which implies it might have already exited), as long
1541	loop isn't entered (or is continued from a watcher).	2254	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2255	forking and then immediately registering a watcher for the child is fine,
		2256	but forking and registering a watcher a few event loop iterations later or
		2257	in the next callback invocation is not.
1542		2258
1543	Only the default event loop is capable of handling signals, and therefore	2259	Only the default event loop is capable of handling signals, and therefore
1544	you can only register child watchers in the default event loop.	2260	you can only register child watchers in the default event loop.
1545		2261
		2262	Due to some design glitches inside libev, child watchers will always be
		2263	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2264	libev)
		2265
1546	=head3 Process Interaction	2266	=head3 Process Interaction
1547		2267
1548	Libev grabs C<SIGCHLD> as soon as the default event loop is	2268	Libev grabs C<SIGCHLD> as soon as the default event loop is
1549	initialised. This is necessary to guarantee proper behaviour even if	2269	initialised. This is necessary to guarantee proper behaviour even if the
1550	the first child watcher is started after the child exits. The occurrence	2270	first child watcher is started after the child exits. The occurrence
1551	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2271	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1552	synchronously as part of the event loop processing. Libev always reaps all	2272	synchronously as part of the event loop processing. Libev always reaps all
1553	children, even ones not watched.	2273	children, even ones not watched.
1554		2274
1555	=head3 Overriding the Built-In Processing	2275	=head3 Overriding the Built-In Processing
…		…
1559	handler, you can override it easily by installing your own handler for	2279	handler, you can override it easily by installing your own handler for
1560	C<SIGCHLD> after initialising the default loop, and making sure the	2280	C<SIGCHLD> after initialising the default loop, and making sure the
1561	default loop never gets destroyed. You are encouraged, however, to use an	2281	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	2282	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.	2283	that, so other libev users can use C<ev_child> watchers freely.
		2284
		2285	=head3 Stopping the Child Watcher
		2286
		2287	Currently, the child watcher never gets stopped, even when the
		2288	child terminates, so normally one needs to stop the watcher in the
		2289	callback. Future versions of libev might stop the watcher automatically
		2290	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2291	problem).
1564		2292
1565	=head3 Watcher-Specific Functions and Data Members	2293	=head3 Watcher-Specific Functions and Data Members
1566		2294
1567	=over 4	2295	=over 4
1568		2296
…		…
1597	=head3 Examples	2325	=head3 Examples
1598		2326
1599	Example: C<fork()> a new process and install a child handler to wait for	2327	Example: C<fork()> a new process and install a child handler to wait for
1600	its completion.	2328	its completion.
1601		2329
1602	ev_child cw;	2330	ev_child cw;
1603		2331
1604	static void	2332	static void
1605	child_cb (EV_P_ struct ev_child *w, int revents)	2333	child_cb (EV_P_ ev_child *w, int revents)
1606	{	2334	{
1607	ev_child_stop (EV_A_ w);	2335	ev_child_stop (EV_A_ w);
1608	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2336	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1609	}	2337	}
1610		2338
1611	pid_t pid = fork ();	2339	pid_t pid = fork ();
1612		2340
1613	if (pid < 0)	2341	if (pid < 0)
1614	// error	2342	// error
1615	else if (pid == 0)	2343	else if (pid == 0)
1616	{	2344	{
1617	// the forked child executes here	2345	// the forked child executes here
1618	exit (1);	2346	exit (1);
1619	}	2347	}
1620	else	2348	else
1621	{	2349	{
1622	ev_child_init (&cw, child_cb, pid, 0);	2350	ev_child_init (&cw, child_cb, pid, 0);
1623	ev_child_start (EV_DEFAULT_ &cw);	2351	ev_child_start (EV_DEFAULT_ &cw);
1624	}	2352	}
1625		2353
1626		2354
1627	=head2 C<ev_stat> - did the file attributes just change?	2355	=head2 C<ev_stat> - did the file attributes just change?
1628		2356
1629	This watches a file system path for attribute changes. That is, it calls	2357	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	2358	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.	2359	and sees if it changed compared to the last time, invoking the callback if
		2360	it did.
1632		2361
1633	The path does not need to exist: changing from "path exists" to "path does	2362	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	2363	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	2364	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	2365	C<st_nlink> field being zero (which is otherwise always forced to be at
1637	the stat buffer having unspecified contents.	2366	least one) and all the other fields of the stat buffer having unspecified
		2367	contents.
1638		2368
1639	The path I<should> be absolute and I<must not> end in a slash. If it is	2369	The path I<must not> end in a slash or contain special components such as
		2370	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.	2371	your working directory changes, then the behaviour is undefined.
1641		2372
1642	Since there is no standard to do this, the portable implementation simply	2373	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	2374	portable implementation simply calls C<stat(2)> regularly on the path
1644	can specify a recommended polling interval for this case. If you specify	2375	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,	2376	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	2377	recommended!) then a I<suitable, unspecified default> value will be used
1647	five seconds, although this might change dynamically). Libev will also	2378	(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	2379	change dynamically). Libev will also impose a minimum interval which is
1649	usually overkill.	2380	currently around C<0.1>, but that's usually overkill.
1650		2381
1651	This watcher type is not meant for massive numbers of stat watchers,	2382	This watcher type is not meant for massive numbers of stat watchers,
1652	as even with OS-supported change notifications, this can be	2383	as even with OS-supported change notifications, this can be
1653	resource-intensive.	2384	resource-intensive.
1654		2385
1655	At the time of this writing, only the Linux inotify interface is	2386	At the time of this writing, the only OS-specific interface implemented
1656	implemented (implementing kqueue support is left as an exercise for the	2387	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	2388	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	2389	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		2390
1664	=head3 ABI Issues (Largefile Support)	2391	=head3 ABI Issues (Largefile Support)
1665		2392
1666	Libev by default (unless the user overrides this) uses the default	2393	Libev by default (unless the user overrides this) uses the default
1667	compilation environment, which means that on systems with optionally	2394	compilation environment, which means that on systems with large file
1668	disabled large file support, you get the 32 bit version of the stat	2395	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	2396	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	2397	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	2398	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	2399	obviously the case with any flags that change the ABI, but the problem is
1673	most noticeably with ev_stat and large file support.	2400	most noticeably displayed with ev_stat and large file support.
1674		2401
1675	=head3 Inotify	2402	The solution for this is to lobby your distribution maker to make large
		2403	file interfaces available by default (as e.g. FreeBSD does) and not
		2404	optional. Libev cannot simply switch on large file support because it has
		2405	to exchange stat structures with application programs compiled using the
		2406	default compilation environment.
1676		2407
		2408	=head3 Inotify and Kqueue
		2409
1677	When C<inotify (7)> support has been compiled into libev (generally only	2410	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	2411	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	2412	inotify descriptor will be created lazily when the first C<ev_stat>
1680	when the first C<ev_stat> watcher is being started.	2413	watcher is being started.
1681		2414
1682	Inotify presence does not change the semantics of C<ev_stat> watchers	2415	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	2416	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	2417	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.	2418	there are many cases where libev has to resort to regular C<stat> polling,
		2419	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2420	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2421	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2422	xfs are fully working) libev usually gets away without polling.
1686		2423
1687	(There is no support for kqueue, as apparently it cannot be used to	2424	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	2425	implement this functionality, due to the requirement of having a file
1689	descriptor open on the object at all times).	2426	descriptor open on the object at all times, and detecting renames, unlinks
		2427	etc. is difficult.
		2428
		2429	=head3 C<stat ()> is a synchronous operation
		2430
		2431	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2432	the process. The exception are C<ev_stat> watchers - those call C<stat
		2433	()>, which is a synchronous operation.
		2434
		2435	For local paths, this usually doesn't matter: unless the system is very
		2436	busy or the intervals between stat's are large, a stat call will be fast,
		2437	as the path data is usually in memory already (except when starting the
		2438	watcher).
		2439
		2440	For networked file systems, calling C<stat ()> can block an indefinite
		2441	time due to network issues, and even under good conditions, a stat call
		2442	often takes multiple milliseconds.
		2443
		2444	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2445	paths, although this is fully supported by libev.
1690		2446
1691	=head3 The special problem of stat time resolution	2447	=head3 The special problem of stat time resolution
1692		2448
1693	The C<stat ()> system call only supports full-second resolution portably, and	2449	The C<stat ()> system call only supports full-second resolution portably,
1694	even on systems where the resolution is higher, many file systems still	2450	and even on systems where the resolution is higher, most file systems
1695	only support whole seconds.	2451	still only support whole seconds.
1696		2452
1697	That means that, if the time is the only thing that changes, you can	2453	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	2454	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	2455	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	2456	within the same second, C<ev_stat> will be unable to detect unless the
1701	data does not change.	2457	stat data does change in other ways (e.g. file size).
1702		2458
1703	The solution to this is to delay acting on a change for slightly more	2459	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	2460	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);	2461	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1706	ev_timer_again (loop, w)>).	2462	ev_timer_again (loop, w)>).
…		…
1726	C<path>. The C<interval> is a hint on how quickly a change is expected to	2482	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	2483	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	2484	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.	2485	path for as long as the watcher is active.
1730		2486
1731	The callback will receive C<EV_STAT> when a change was detected, relative	2487	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	2488	relative to the attributes at the time the watcher was started (or the
1733	was detected).	2489	last change was detected).
1734		2490
1735	=item ev_stat_stat (loop, ev_stat *)	2491	=item ev_stat_stat (loop, ev_stat *)
1736		2492
1737	Updates the stat buffer immediately with new values. If you change the	2493	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	2494	watched path in your callback, you could call this function to avoid
…		…
1767		2523
1768	=head3 Examples	2524	=head3 Examples
1769		2525
1770	Example: Watch C</etc/passwd> for attribute changes.	2526	Example: Watch C</etc/passwd> for attribute changes.
1771		2527
1772	static void	2528	static void
1773	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2529	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1774	{	2530	{
1775	/* /etc/passwd changed in some way */	2531	/* /etc/passwd changed in some way */
1776	if (w->attr.st_nlink)	2532	if (w->attr.st_nlink)
1777	{	2533	{
1778	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2534	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1779	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2535	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1780	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2536	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1781	}	2537	}
1782	else	2538	else
1783	/* you shalt not abuse printf for puts */	2539	/* you shalt not abuse printf for puts */
1784	puts ("wow, /etc/passwd is not there, expect problems. "	2540	puts ("wow, /etc/passwd is not there, expect problems. "
1785	"if this is windows, they already arrived\n");	2541	"if this is windows, they already arrived\n");
1786	}	2542	}
1787		2543
1788	...	2544	...
1789	ev_stat passwd;	2545	ev_stat passwd;
1790		2546
1791	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2547	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1792	ev_stat_start (loop, &passwd);	2548	ev_stat_start (loop, &passwd);
1793		2549
1794	Example: Like above, but additionally use a one-second delay so we do not	2550	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	2551	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	2552	one might do the work both on C<ev_stat> callback invocation I<and> on
1797	C<ev_timer> callback invocation).	2553	C<ev_timer> callback invocation).
1798		2554
1799	static ev_stat passwd;	2555	static ev_stat passwd;
1800	static ev_timer timer;	2556	static ev_timer timer;
1801		2557
1802	static void	2558	static void
1803	timer_cb (EV_P_ ev_timer *w, int revents)	2559	timer_cb (EV_P_ ev_timer *w, int revents)
1804	{	2560	{
1805	ev_timer_stop (EV_A_ w);	2561	ev_timer_stop (EV_A_ w);
1806		2562
1807	/* now it's one second after the most recent passwd change */	2563	/* now it's one second after the most recent passwd change */
1808	}	2564	}
1809		2565
1810	static void	2566	static void
1811	stat_cb (EV_P_ ev_stat *w, int revents)	2567	stat_cb (EV_P_ ev_stat *w, int revents)
1812	{	2568	{
1813	/* reset the one-second timer */	2569	/* reset the one-second timer */
1814	ev_timer_again (EV_A_ &timer);	2570	ev_timer_again (EV_A_ &timer);
1815	}	2571	}
1816		2572
1817	...	2573	...
1818	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2574	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1819	ev_stat_start (loop, &passwd);	2575	ev_stat_start (loop, &passwd);
1820	ev_timer_init (&timer, timer_cb, 0., 1.02);	2576	ev_timer_init (&timer, timer_cb, 0., 1.02);
1821		2577
1822		2578
1823	=head2 C<ev_idle> - when you've got nothing better to do...	2579	=head2 C<ev_idle> - when you've got nothing better to do...
1824		2580
1825	Idle watchers trigger events when no other events of the same or higher	2581	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	2582	priority are pending (prepare, check and other idle watchers do not count
1827	count).	2583	as receiving "events").
1828		2584
1829	That is, as long as your process is busy handling sockets or timeouts	2585	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	2586	(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	2587	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	2588	are pending), the idle watchers are being called once per event loop
…		…
1843		2599
1844	=head3 Watcher-Specific Functions and Data Members	2600	=head3 Watcher-Specific Functions and Data Members
1845		2601
1846	=over 4	2602	=over 4
1847		2603
1848	=item ev_idle_init (ev_signal *, callback)	2604	=item ev_idle_init (ev_idle *, callback)
1849		2605
1850	Initialises and configures the idle watcher - it has no parameters of any	2606	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,	2607	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1852	believe me.	2608	believe me.
1853		2609
…		…
1856	=head3 Examples	2612	=head3 Examples
1857		2613
1858	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2614	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1859	callback, free it. Also, use no error checking, as usual.	2615	callback, free it. Also, use no error checking, as usual.
1860		2616
1861	static void	2617	static void
1862	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2618	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1863	{	2619	{
1864	free (w);	2620	free (w);
1865	// now do something you wanted to do when the program has	2621	// now do something you wanted to do when the program has
1866	// no longer anything immediate to do.	2622	// no longer anything immediate to do.
1867	}	2623	}
1868		2624
1869	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2625	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1870	ev_idle_init (idle_watcher, idle_cb);	2626	ev_idle_init (idle_watcher, idle_cb);
1871	ev_idle_start (loop, idle_cb);	2627	ev_idle_start (loop, idle_watcher);
1872		2628
1873		2629
1874	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2630	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1875		2631
1876	Prepare and check watchers are usually (but not always) used in tandem:	2632	Prepare and check watchers are usually (but not always) used in pairs:
1877	prepare watchers get invoked before the process blocks and check watchers	2633	prepare watchers get invoked before the process blocks and check watchers
1878	afterwards.	2634	afterwards.
1879		2635
1880	You I<must not> call C<ev_loop> or similar functions that enter	2636	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>	2637	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,	2640	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	2641	C<ev_check> so if you have one watcher of each kind they will always be
1886	called in pairs bracketing the blocking call.	2642	called in pairs bracketing the blocking call.
1887		2643
1888	Their main purpose is to integrate other event mechanisms into libev and	2644	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	2645	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	2646	variable changes, implement your own watchers, integrate net-snmp or a
1891	coroutine library and lots more. They are also occasionally useful if	2647	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,	2648	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>	2649	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1894	watcher).	2650	watcher).
1895		2651
1896	This is done by examining in each prepare call which file descriptors need	2652	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	2653	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	2654	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	2655	libraries provide exactly this functionality). Then, in the check watcher,
1900	any events that occurred (by checking the pending status of all watchers	2656	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	2657	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,	2658	I/O and timer callbacks will never actually be called (but must be valid
1903	because you never know, you know?).	2659	nevertheless, because you never know, you know?).
1904		2660
1905	As another example, the Perl Coro module uses these hooks to integrate	2661	As another example, the Perl Coro module uses these hooks to integrate
1906	coroutines into libev programs, by yielding to other active coroutines	2662	coroutines into libev programs, by yielding to other active coroutines
1907	during each prepare and only letting the process block if no coroutines	2663	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	2664	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	2667	loop from blocking if lower-priority coroutines are active, thus mapping
1912	low-priority coroutines to idle/background tasks).	2668	low-priority coroutines to idle/background tasks).
1913		2669
1914	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2670	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	2671	priority, to ensure that they are being run before any other watchers
		2672	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2673
1916	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2674	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	2675	activate ("feed") events into libev. While libev fully supports this, they
1918	supports this, they might get executed before other C<ev_check> watchers	2676	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	2677	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	2678	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	2679	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1922	coexist peacefully with others).	2680	others).
1923		2681
1924	=head3 Watcher-Specific Functions and Data Members	2682	=head3 Watcher-Specific Functions and Data Members
1925		2683
1926	=over 4	2684	=over 4
1927		2685
…		…
1929		2687
1930	=item ev_check_init (ev_check *, callback)	2688	=item ev_check_init (ev_check *, callback)
1931		2689
1932	Initialises and configures the prepare or check watcher - they have no	2690	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>	2691	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.	2692	macros, but using them is utterly, utterly, utterly and completely
		2693	pointless.
1935		2694
1936	=back	2695	=back
1937		2696
1938	=head3 Examples	2697	=head3 Examples
1939		2698
…		…
1948	and in a check watcher, destroy them and call into libadns. What follows	2707	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	2708	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	2709	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.	2710	the callbacks for the IO/timeout watchers might not have been called yet.
1952		2711
1953	static ev_io iow [nfd];	2712	static ev_io iow [nfd];
1954	static ev_timer tw;	2713	static ev_timer tw;
1955		2714
1956	static void	2715	static void
1957	io_cb (ev_loop *loop, ev_io *w, int revents)	2716	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1958	{	2717	{
1959	}	2718	}
1960		2719
1961	// create io watchers for each fd and a timer before blocking	2720	// create io watchers for each fd and a timer before blocking
1962	static void	2721	static void
1963	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2722	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1964	{	2723	{
1965	int timeout = 3600000;	2724	int timeout = 3600000;
1966	struct pollfd fds [nfd];	2725	struct pollfd fds [nfd];
1967	// actual code will need to loop here and realloc etc.	2726	// actual code will need to loop here and realloc etc.
1968	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2727	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1969		2728
1970	/* the callback is illegal, but won't be called as we stop during check */	2729	/* the callback is illegal, but won't be called as we stop during check */
1971	ev_timer_init (&tw, 0, timeout * 1e-3);	2730	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1972	ev_timer_start (loop, &tw);	2731	ev_timer_start (loop, &tw);
1973		2732
1974	// create one ev_io per pollfd	2733	// create one ev_io per pollfd
1975	for (int i = 0; i < nfd; ++i)	2734	for (int i = 0; i < nfd; ++i)
1976	{	2735	{
1977	ev_io_init (iow + i, io_cb, fds [i].fd,	2736	ev_io_init (iow + i, io_cb, fds [i].fd,
1978	((fds [i].events & POLLIN ? EV_READ : 0)	2737	((fds [i].events & POLLIN ? EV_READ : 0)
1979	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2738	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1980		2739
1981	fds [i].revents = 0;	2740	fds [i].revents = 0;
1982	ev_io_start (loop, iow + i);	2741	ev_io_start (loop, iow + i);
1983	}	2742	}
1984	}	2743	}
1985		2744
1986	// stop all watchers after blocking	2745	// stop all watchers after blocking
1987	static void	2746	static void
1988	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2747	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1989	{	2748	{
1990	ev_timer_stop (loop, &tw);	2749	ev_timer_stop (loop, &tw);
1991		2750
1992	for (int i = 0; i < nfd; ++i)	2751	for (int i = 0; i < nfd; ++i)
1993	{	2752	{
1994	// set the relevant poll flags	2753	// set the relevant poll flags
1995	// could also call adns_processreadable etc. here	2754	// could also call adns_processreadable etc. here
1996	struct pollfd *fd = fds + i;	2755	struct pollfd *fd = fds + i;
1997	int revents = ev_clear_pending (iow + i);	2756	int revents = ev_clear_pending (iow + i);
1998	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2757	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1999	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2758	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
2000		2759
2001	// now stop the watcher	2760	// now stop the watcher
2002	ev_io_stop (loop, iow + i);	2761	ev_io_stop (loop, iow + i);
2003	}	2762	}
2004		2763
2005	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2764	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2006	}	2765	}
2007		2766
2008	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2767	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.	2768	in the prepare watcher and would dispose of the check watcher.
2010		2769
2011	Method 3: If the module to be embedded supports explicit event	2770	Method 3: If the module to be embedded supports explicit event
2012	notification (libadns does), you can also make use of the actual watcher	2771	notification (libadns does), you can also make use of the actual watcher
2013	callbacks, and only destroy/create the watchers in the prepare watcher.	2772	callbacks, and only destroy/create the watchers in the prepare watcher.
2014		2773
2015	static void	2774	static void
2016	timer_cb (EV_P_ ev_timer *w, int revents)	2775	timer_cb (EV_P_ ev_timer *w, int revents)
2017	{	2776	{
2018	adns_state ads = (adns_state)w->data;	2777	adns_state ads = (adns_state)w->data;
2019	update_now (EV_A);	2778	update_now (EV_A);
2020		2779
2021	adns_processtimeouts (ads, &tv_now);	2780	adns_processtimeouts (ads, &tv_now);
2022	}	2781	}
2023		2782
2024	static void	2783	static void
2025	io_cb (EV_P_ ev_io *w, int revents)	2784	io_cb (EV_P_ ev_io *w, int revents)
2026	{	2785	{
2027	adns_state ads = (adns_state)w->data;	2786	adns_state ads = (adns_state)w->data;
2028	update_now (EV_A);	2787	update_now (EV_A);
2029		2788
2030	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2789	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
2031	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2790	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
2032	}	2791	}
2033		2792
2034	// do not ever call adns_afterpoll	2793	// do not ever call adns_afterpoll
2035		2794
2036	Method 4: Do not use a prepare or check watcher because the module you	2795	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	2796	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	2797	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	2798	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2040	this.	2799	this approach, effectively embedding EV as a client into the horrible
		2800	libglib event loop.
2041		2801
2042	static gint	2802	static gint
2043	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2803	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2044	{	2804	{
2045	int got_events = 0;	2805	int got_events = 0;
2046		2806
2047	for (n = 0; n < nfds; ++n)	2807	for (n = 0; n < nfds; ++n)
2048	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2808	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2049		2809
2050	if (timeout >= 0)	2810	if (timeout >= 0)
2051	// create/start timer	2811	// create/start timer
2052		2812
2053	// poll	2813	// poll
2054	ev_loop (EV_A_ 0);	2814	ev_loop (EV_A_ 0);
2055		2815
2056	// stop timer again	2816	// stop timer again
2057	if (timeout >= 0)	2817	if (timeout >= 0)
2058	ev_timer_stop (EV_A_ &to);	2818	ev_timer_stop (EV_A_ &to);
2059		2819
2060	// stop io watchers again - their callbacks should have set	2820	// stop io watchers again - their callbacks should have set
2061	for (n = 0; n < nfds; ++n)	2821	for (n = 0; n < nfds; ++n)
2062	ev_io_stop (EV_A_ iow [n]);	2822	ev_io_stop (EV_A_ iow [n]);
2063		2823
2064	return got_events;	2824	return got_events;
2065	}	2825	}
2066		2826
2067		2827
2068	=head2 C<ev_embed> - when one backend isn't enough...	2828	=head2 C<ev_embed> - when one backend isn't enough...
2069		2829
2070	This is a rather advanced watcher type that lets you embed one event loop	2830	This is a rather advanced watcher type that lets you embed one event loop
…		…
2076	prioritise I/O.	2836	prioritise I/O.
2077		2837
2078	As an example for a bug workaround, the kqueue backend might only support	2838	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	2839	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	2840	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	2841	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	2842	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	2843	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.	2844	C<kevent>, but at least you can use both mechanisms for what they are
		2845	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2085		2846
2086	As for prioritising I/O: rarely you have the case where some fds have	2847	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	2848	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	2849	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	2850	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.	2851	the rest in a second one, and embed the second one in the first.
2091		2852
2092	As long as the watcher is active, the callback will be invoked every time	2853	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	2854	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	2855	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	2856	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	2857	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	2858	to give the embedded loop strictly lower priority for example).
2098	embedded loop sweep.
2099		2859
2100	As long as the watcher is started it will automatically handle events. The	2860	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	2861	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		2862
2105	Also, there have not currently been made special provisions for forking:	2863	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,	2864	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	2865	embedding loop forks. In other cases, the user is responsible for calling
2108	yourself.	2866	C<ev_loop_fork> on the embedded loop.
2109		2867
2110	Unfortunately, not all backends are embeddable, only the ones returned by	2868	Unfortunately, not all backends are embeddable: only the ones returned by
2111	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2869	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2112	portable one.	2870	portable one.
2113		2871
2114	So when you want to use this feature you will always have to be prepared	2872	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	2873	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	2874	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.	2875	create it, and if that fails, use the normal loop for everything.
		2876
		2877	=head3 C<ev_embed> and fork
		2878
		2879	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2880	automatically be applied to the embedded loop as well, so no special
		2881	fork handling is required in that case. When the watcher is not running,
		2882	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2883	as applicable.
2118		2884
2119	=head3 Watcher-Specific Functions and Data Members	2885	=head3 Watcher-Specific Functions and Data Members
2120		2886
2121	=over 4	2887	=over 4
2122		2888
…		…
2148	event loop. If that is not possible, use the default loop. The default	2914	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	2915	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	2916	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2151	used).	2917	used).
2152		2918
2153	struct ev_loop *loop_hi = ev_default_init (0);	2919	struct ev_loop *loop_hi = ev_default_init (0);
2154	struct ev_loop *loop_lo = 0;	2920	struct ev_loop *loop_lo = 0;
2155	struct ev_embed embed;	2921	ev_embed embed;
2156		2922
2157	// see if there is a chance of getting one that works	2923	// see if there is a chance of getting one that works
2158	// (remember that a flags value of 0 means autodetection)	2924	// (remember that a flags value of 0 means autodetection)
2159	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2925	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2160	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2926	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2161	: 0;	2927	: 0;
2162		2928
2163	// if we got one, then embed it, otherwise default to loop_hi	2929	// if we got one, then embed it, otherwise default to loop_hi
2164	if (loop_lo)	2930	if (loop_lo)
2165	{	2931	{
2166	ev_embed_init (&embed, 0, loop_lo);	2932	ev_embed_init (&embed, 0, loop_lo);
2167	ev_embed_start (loop_hi, &embed);	2933	ev_embed_start (loop_hi, &embed);
2168	}	2934	}
2169	else	2935	else
2170	loop_lo = loop_hi;	2936	loop_lo = loop_hi;
2171		2937
2172	Example: Check if kqueue is available but not recommended and create	2938	Example: Check if kqueue is available but not recommended and create
2173	a kqueue backend for use with sockets (which usually work with any	2939	a kqueue backend for use with sockets (which usually work with any
2174	kqueue implementation). Store the kqueue/socket-only event loop in	2940	kqueue implementation). Store the kqueue/socket-only event loop in
2175	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2941	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2176		2942
2177	struct ev_loop *loop = ev_default_init (0);	2943	struct ev_loop *loop = ev_default_init (0);
2178	struct ev_loop *loop_socket = 0;	2944	struct ev_loop *loop_socket = 0;
2179	struct ev_embed embed;	2945	ev_embed embed;
2180		2946
2181	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2947	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2182	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2948	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2183	{	2949	{
2184	ev_embed_init (&embed, 0, loop_socket);	2950	ev_embed_init (&embed, 0, loop_socket);
2185	ev_embed_start (loop, &embed);	2951	ev_embed_start (loop, &embed);
2186	}	2952	}
2187		2953
2188	if (!loop_socket)	2954	if (!loop_socket)
2189	loop_socket = loop;	2955	loop_socket = loop;
2190		2956
2191	// now use loop_socket for all sockets, and loop for everything else	2957	// now use loop_socket for all sockets, and loop for everything else
2192		2958
2193		2959
2194	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2960	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2195		2961
2196	Fork watchers are called when a C<fork ()> was detected (usually because	2962	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,	2965	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	2966	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	2967	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2202	handlers will be invoked, too, of course.	2968	handlers will be invoked, too, of course.
2203		2969
		2970	=head3 The special problem of life after fork - how is it possible?
		2971
		2972	Most uses of C<fork()> consist of forking, then some simple calls to set
		2973	up/change the process environment, followed by a call to C<exec()>. This
		2974	sequence should be handled by libev without any problems.
		2975
		2976	This changes when the application actually wants to do event handling
		2977	in the child, or both parent in child, in effect "continuing" after the
		2978	fork.
		2979
		2980	The default mode of operation (for libev, with application help to detect
		2981	forks) is to duplicate all the state in the child, as would be expected
		2982	when I<either> the parent I<or> the child process continues.
		2983
		2984	When both processes want to continue using libev, then this is usually the
		2985	wrong result. In that case, usually one process (typically the parent) is
		2986	supposed to continue with all watchers in place as before, while the other
		2987	process typically wants to start fresh, i.e. without any active watchers.
		2988
		2989	The cleanest and most efficient way to achieve that with libev is to
		2990	simply create a new event loop, which of course will be "empty", and
		2991	use that for new watchers. This has the advantage of not touching more
		2992	memory than necessary, and thus avoiding the copy-on-write, and the
		2993	disadvantage of having to use multiple event loops (which do not support
		2994	signal watchers).
		2995
		2996	When this is not possible, or you want to use the default loop for
		2997	other reasons, then in the process that wants to start "fresh", call
		2998	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2999	the default loop will "orphan" (not stop) all registered watchers, so you
		3000	have to be careful not to execute code that modifies those watchers. Note
		3001	also that in that case, you have to re-register any signal watchers.
		3002
2204	=head3 Watcher-Specific Functions and Data Members	3003	=head3 Watcher-Specific Functions and Data Members
2205		3004
2206	=over 4	3005	=over 4
2207		3006
2208	=item ev_fork_init (ev_signal *, callback)	3007	=item ev_fork_init (ev_signal *, callback)
…		…
2212	believe me.	3011	believe me.
2213		3012
2214	=back	3013	=back
2215		3014
2216		3015
2217	=head2 C<ev_async> - how to wake up another event loop	3016	=head2 C<ev_async> - how to wake up an event loop
2218		3017
2219	In general, you cannot use an C<ev_loop> from multiple threads or other	3018	In general, you cannot use an C<ev_loop> from multiple threads or other
2220	asynchronous sources such as signal handlers (as opposed to multiple event	3019	asynchronous sources such as signal handlers (as opposed to multiple event
2221	loops - those are of course safe to use in different threads).	3020	loops - those are of course safe to use in different threads).
2222		3021
2223	Sometimes, however, you need to wake up another event loop you do not	3022	Sometimes, however, you need to wake up an event loop you do not control,
2224	control, for example because it belongs to another thread. This is what	3023	for example because it belongs to another thread. This is what C<ev_async>
2225	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3024	watchers do: as long as the C<ev_async> watcher is active, you can signal
2226	can signal it by calling C<ev_async_send>, which is thread- and signal	3025	it by calling C<ev_async_send>, which is thread- and signal safe.
2227	safe.
2228		3026
2229	This functionality is very similar to C<ev_signal> watchers, as signals,	3027	This functionality is very similar to C<ev_signal> watchers, as signals,
2230	too, are asynchronous in nature, and signals, too, will be compressed	3028	too, are asynchronous in nature, and signals, too, will be compressed
2231	(i.e. the number of callback invocations may be less than the number of	3029	(i.e. the number of callback invocations may be less than the number of
2232	C<ev_async_sent> calls).	3030	C<ev_async_sent> calls).
…		…
2237	=head3 Queueing	3035	=head3 Queueing
2238		3036
2239	C<ev_async> does not support queueing of data in any way. The reason	3037	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	3038	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	3039	multiple-writer-single-reader queue that works in all cases and doesn't
2242	need elaborate support such as pthreads.	3040	need elaborate support such as pthreads or unportable memory access
		3041	semantics.
2243		3042
2244	That means that if you want to queue data, you have to provide your own	3043	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	3044	queue. But at least I can tell you how to implement locking around your
2246	queue:	3045	queue:
2247		3046
2248	=over 4	3047	=over 4
2249		3048
2250	=item queueing from a signal handler context	3049	=item queueing from a signal handler context
2251		3050
2252	To implement race-free queueing, you simply add to the queue in the signal	3051	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	3052	handler but you block the signal handler in the watcher callback. Here is
2254	some fictitious SIGUSR1 handler:	3053	an example that does that for some fictitious SIGUSR1 handler:
2255		3054
2256	static ev_async mysig;	3055	static ev_async mysig;
2257		3056
2258	static void	3057	static void
2259	sigusr1_handler (void)	3058	sigusr1_handler (void)
…		…
2325	=over 4	3124	=over 4
2326		3125
2327	=item ev_async_init (ev_async *, callback)	3126	=item ev_async_init (ev_async *, callback)
2328		3127
2329	Initialises and configures the async watcher - it has no parameters of any	3128	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,	3129	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2331	believe me.	3130	trust me.
2332		3131
2333	=item ev_async_send (loop, ev_async *)	3132	=item ev_async_send (loop, ev_async *)
2334		3133
2335	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3134	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	3135	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	3136	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	3137	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2339	section below on what exactly this means).	3138	section below on what exactly this means).
2340		3139
		3140	Note that, as with other watchers in libev, multiple events might get
		3141	compressed into a single callback invocation (another way to look at this
		3142	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3143	reset when the event loop detects that).
		3144
2341	This call incurs the overhead of a system call only once per loop iteration,	3145	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	3146	iteration, so while the overhead might be noticeable, it doesn't apply to
2343	calls to C<ev_async_send>.	3147	repeated calls to C<ev_async_send> for the same event loop.
2344		3148
2345	=item bool = ev_async_pending (ev_async *)	3149	=item bool = ev_async_pending (ev_async *)
2346		3150
2347	Returns a non-zero value when C<ev_async_send> has been called on the	3151	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	3152	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	3155	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,	3156	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	3157	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.	3158	quickly check whether invoking the loop might be a good idea.
2355		3159
2356	Not that this does I<not> check whether the watcher itself is pending, only	3160	Not that this does I<not> check whether the watcher itself is pending,
2357	whether it has been requested to make this watcher pending.	3161	only whether it has been requested to make this watcher pending: there
		3162	is a time window between the event loop checking and resetting the async
		3163	notification, and the callback being invoked.
2358		3164
2359	=back	3165	=back
2360		3166
2361		3167
2362	=head1 OTHER FUNCTIONS	3168	=head1 OTHER FUNCTIONS
…		…
2366	=over 4	3172	=over 4
2367		3173
2368	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3174	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2369		3175
2370	This function combines a simple timer and an I/O watcher, calls your	3176	This function combines a simple timer and an I/O watcher, calls your
2371	callback on whichever event happens first and automatically stop both	3177	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	3178	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	3179	or timeout without having to allocate/configure/start/stop/free one or
2374	more watchers yourself.	3180	more watchers yourself.
2375		3181
2376	If C<fd> is less than 0, then no I/O watcher will be started and events	3182	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	3183	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2378	C<events> set will be created and started.	3184	the given C<fd> and C<events> set will be created and started.
2379		3185
2380	If C<timeout> is less than 0, then no timeout watcher will be	3186	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	3187	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	3188	repeat = 0) will be started. C<0> is a valid timeout.
2383	dubious value.
2384		3189
2385	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3190	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	3191	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>	3192	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2388	value passed to C<ev_once>:	3193	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3194	a timeout and an io event at the same time - you probably should give io
		3195	events precedence.
2389		3196
		3197	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3198
2390	static void stdin_ready (int revents, void *arg)	3199	static void stdin_ready (int revents, void *arg)
2391	{	3200	{
2392	if (revents & EV_TIMEOUT)
2393	/* doh, nothing entered */;
2394	else if (revents & EV_READ)	3201	if (revents & EV_READ)
2395	/* stdin might have data for us, joy! */;	3202	/* stdin might have data for us, joy! */;
		3203	else if (revents & EV_TIMER)
		3204	/* doh, nothing entered */;
2396	}	3205	}
2397		3206
2398	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3207	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2399		3208
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)	3209	=item ev_feed_fd_event (loop, int fd, int revents)
2407		3210
2408	Feed an event on the given fd, as if a file descriptor backend detected	3211	Feed an event on the given fd, as if a file descriptor backend detected
2409	the given events it.	3212	the given events it.
2410		3213
2411	=item ev_feed_signal_event (ev_loop *loop, int signum)	3214	=item ev_feed_signal_event (loop, int signum)
2412		3215
2413	Feed an event as if the given signal occurred (C<loop> must be the default	3216	Feed an event as if the given signal occurred (C<loop> must be the default
2414	loop!).	3217	loop!).
2415		3218
2416	=back	3219	=back
…		…
2452	you to use some convenience methods to start/stop watchers and also change	3255	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.	3256	the callback model to a model using method callbacks on objects.
2454		3257
2455	To use it,	3258	To use it,
2456		3259
2457	#include <ev++.h>	3260	#include <ev++.h>
2458		3261
2459	This automatically includes F<ev.h> and puts all of its definitions (many	3262	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	3263	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	3264	put into the C<ev> namespace. It should support all the same embedding
2462	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3265	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2496		3299
2497	=over 4	3300	=over 4
2498		3301
2499	=item ev::TYPE::TYPE ()	3302	=item ev::TYPE::TYPE ()
2500		3303
2501	=item ev::TYPE::TYPE (struct ev_loop *)	3304	=item ev::TYPE::TYPE (loop)
2502		3305
2503	=item ev::TYPE::~TYPE	3306	=item ev::TYPE::~TYPE
2504		3307
2505	The constructor (optionally) takes an event loop to associate the watcher	3308	The constructor (optionally) takes an event loop to associate the watcher
2506	with. If it is omitted, it will use C<EV_DEFAULT>.	3309	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	3332	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.	3333	thunking function, making it as fast as a direct C callback.
2531		3334
2532	Example: simple class declaration and watcher initialisation	3335	Example: simple class declaration and watcher initialisation
2533		3336
2534	struct myclass	3337	struct myclass
2535	{	3338	{
2536	void io_cb (ev::io &w, int revents) { }	3339	void io_cb (ev::io &w, int revents) { }
2537	}	3340	}
2538		3341
2539	myclass obj;	3342	myclass obj;
2540	ev::io iow;	3343	ev::io iow;
2541	iow.set <myclass, &myclass::io_cb> (&obj);	3344	iow.set <myclass, &myclass::io_cb> (&obj);
		3345
		3346	=item w->set (object *)
		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 code size.
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
		3922	code size by roughly 30% on amd64).
		3923
		3924	When optimising for size, use of compiler flags such as C<-Os> with
		3925	gcc is 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 code size
		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 code size
		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 existence) 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 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 in 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)	4403	=head2 GNU/LINUX 32 BIT LIMITATIONS
3269		4404
3270	=item Priority handling: O(number_of_priorities)	4405	GNU/Linux is the only common platform that supports 64 bit file/large file
		4406	interfaces but I<disables> them by default.
3271		4407
3272	Priorities are implemented by allocating some space for each	4408	That means that libev compiled in the default environment doesn't support
3273	priority. When doing priority-based operations, libev usually has to	4409	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
3274	linearly search all the priorities, but starting/stopping and activating
3275	watchers becomes O(1) w.r.t. priority handling.
3276		4410
3277	=item Sending an ev_async: O(1)	4411	Unfortunately, many programs try to work around this GNU/Linux issue
		4412	by enabling the large file API, which makes them incompatible with the
		4413	standard libev compiled for their system.
3278		4414
3279	=item Processing ev_async_send: O(number_of_async_watchers)	4415	Likewise, libev cannot enable the large file API itself as this would
		4416	suddenly make it incompatible to the default compile time environment,
		4417	i.e. all programs not using special compile switches.
3280		4418
3281	=item Processing signals: O(max_signal_number)	4419	=head2 OS/X AND DARWIN BUGS
3282		4420
3283	Sending involves a system call I<iff> there were no other C<ev_async_send>	4421	The whole thing is a bug if you ask me - basically any system interface
3284	calls in the current loop iteration. Checking for async and signal events	4422	you touch is broken, whether it is locales, poll, kqueue or even the
3285	involves iterating over all running async watchers or all signal numbers.	4423	OpenGL drivers.
3286		4424
3287	=back	4425	=head3 C<kqueue> is buggy
3288		4426
		4427	The kqueue syscall is broken in all known versions - most versions support
		4428	only sockets, many support pipes.
3289		4429
3290	=head1 Win32 platform limitations and workarounds	4430	Libev tries to work around this by not using C<kqueue> by default on
		4431	this rotten platform, but of course you can still ask for it when creating
		4432	a loop.
		4433
		4434	=head3 C<poll> is buggy
		4435
		4436	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4437	implementation by something calling C<kqueue> internally around the 10.5.6
		4438	release, so now C<kqueue> I<and> C<poll> are broken.
		4439
		4440	Libev tries to work around this by not using C<poll> by default on
		4441	this rotten platform, but of course you can still ask for it when creating
		4442	a loop.
		4443
		4444	=head3 C<select> is buggy
		4445
		4446	All that's left is C<select>, and of course Apple found a way to fuck this
		4447	one up as well: On OS/X, C<select> actively limits the number of file
		4448	descriptors you can pass in to 1024 - your program suddenly crashes when
		4449	you use more.
		4450
		4451	There is an undocumented "workaround" for this - defining
		4452	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4453	work on OS/X.
		4454
		4455	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4456
		4457	=head3 C<errno> reentrancy
		4458
		4459	The default compile environment on Solaris is unfortunately so
		4460	thread-unsafe that you can't even use components/libraries compiled
		4461	without C<-D_REENTRANT> (as long as they use C<errno>), which, of course,
		4462	isn't defined by default.
		4463
		4464	If you want to use libev in threaded environments you have to make sure
		4465	it's compiled with C<_REENTRANT> defined.
		4466
		4467	=head3 Event port backend
		4468
		4469	The scalable event interface for Solaris is called "event ports". Unfortunately,
		4470	this mechanism is very buggy. If you run into high CPU usage, your program
		4471	freezes or you get a large number of spurious wakeups, make sure you have
		4472	all the relevant and latest kernel patches applied. No, I don't know which
		4473	ones, but there are multiple ones.
		4474
		4475	If you can't get it to work, you can try running the program by setting
		4476	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4477	C<select> backends.
		4478
		4479	=head2 AIX POLL BUG
		4480
		4481	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4482	this by trying to avoid the poll backend altogether (i.e. it's not even
		4483	compiled in), which normally isn't a big problem as C<select> works fine
		4484	with large bitsets, and AIX is dead anyway.
		4485
		4486	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4487
		4488	=head3 General issues
3291		4489
3292	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4490	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	4491	requires, and its I/O model is fundamentally incompatible with the POSIX
3294	model. Libev still offers limited functionality on this platform in	4492	model. Libev still offers limited functionality on this platform in
3295	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4493	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3296	descriptors. This only applies when using Win32 natively, not when using	4494	descriptors. This only applies when using Win32 natively, not when using
3297	e.g. cygwin.	4495	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4496	as every compielr comes with a slightly differently broken/incompatible
		4497	environment.
3298		4498
3299	Lifting these limitations would basically require the full	4499	Lifting these limitations would basically require the full
3300	re-implementation of the I/O system. If you are into these kinds of	4500	re-implementation of the I/O system. If you are into this kind of thing,
3301	things, then note that glib does exactly that for you in a very portable	4501	then note that glib does exactly that for you in a very portable way (note
3302	way (note also that glib is the slowest event library known to man).	4502	also that glib is the slowest event library known to man).
3303		4503
3304	There is no supported compilation method available on windows except	4504	There is no supported compilation method available on windows except
3305	embedding it into other applications.	4505	embedding it into other applications.
		4506
		4507	Sensible signal handling is officially unsupported by Microsoft - libev
		4508	tries its best, but under most conditions, signals will simply not work.
		4509
		4510	Not a libev limitation but worth mentioning: windows apparently doesn't
		4511	accept large writes: instead of resulting in a partial write, windows will
		4512	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4513	so make sure you only write small amounts into your sockets (less than a
		4514	megabyte seems safe, but this apparently depends on the amount of memory
		4515	available).
3306		4516
3307	Due to the many, low, and arbitrary limits on the win32 platform and	4517	Due to the many, low, and arbitrary limits on the win32 platform and
3308	the abysmal performance of winsockets, using a large number of sockets	4518	the abysmal performance of winsockets, using a large number of sockets
3309	is not recommended (and not reasonable). If your program needs to use	4519	is not recommended (and not reasonable). If your program needs to use
3310	more than a hundred or so sockets, then likely it needs to use a totally	4520	more than a hundred or so sockets, then likely it needs to use a totally
3311	different implementation for windows, as libev offers the POSIX readiness	4521	different implementation for windows, as libev offers the POSIX readiness
3312	notification model, which cannot be implemented efficiently on windows	4522	notification model, which cannot be implemented efficiently on windows
3313	(Microsoft monopoly games).	4523	(due to Microsoft monopoly games).
3314		4524
3315	=over 4	4525	A typical way to use libev under windows is to embed it (see the embedding
		4526	section for details) and use the following F<evwrap.h> header file instead
		4527	of F<ev.h>:
3316		4528
		4529	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4530	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4531
		4532	#include "ev.h"
		4533
		4534	And compile the following F<evwrap.c> file into your project (make sure
		4535	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4536
		4537	#include "evwrap.h"
		4538	#include "ev.c"
		4539
3317	=item The winsocket select function	4540	=head3 The winsocket C<select> function
3318		4541
3319	The winsocket C<select> function doesn't follow POSIX in that it	4542	The winsocket C<select> function doesn't follow POSIX in that it
3320	requires socket I<handles> and not socket I<file descriptors> (it is	4543	requires socket I<handles> and not socket I<file descriptors> (it is
3321	also extremely buggy). This makes select very inefficient, and also	4544	also extremely buggy). This makes select very inefficient, and also
3322	requires a mapping from file descriptors to socket handles. See the	4545	requires a mapping from file descriptors to socket handles (the Microsoft
		4546	C runtime provides the function C<_open_osfhandle> for this). See the
3323	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and	4547	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
3324	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.	4548	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
3325		4549
3326	The configuration for a "naked" win32 using the Microsoft runtime	4550	The configuration for a "naked" win32 using the Microsoft runtime
3327	libraries and raw winsocket select is:	4551	libraries and raw winsocket select is:
3328		4552
3329	#define EV_USE_SELECT 1	4553	#define EV_USE_SELECT 1
3330	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4554	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3331		4555
3332	Note that winsockets handling of fd sets is O(n), so you can easily get a	4556	Note that winsockets handling of fd sets is O(n), so you can easily get a
3333	complexity in the O(n²) range when using win32.	4557	complexity in the O(n²) range when using win32.
3334		4558
3335	=item Limited number of file descriptors	4559	=head3 Limited number of file descriptors
3336		4560
3337	Windows has numerous arbitrary (and low) limits on things.	4561	Windows has numerous arbitrary (and low) limits on things.
3338		4562
3339	Early versions of winsocket's select only supported waiting for a maximum	4563	Early versions of winsocket's select only supported waiting for a maximum
3340	of C<64> handles (probably owning to the fact that all windows kernels	4564	of C<64> handles (probably owning to the fact that all windows kernels
3341	can only wait for C<64> things at the same time internally; Microsoft	4565	can only wait for C<64> things at the same time internally; Microsoft
3342	recommends spawning a chain of threads and wait for 63 handles and the	4566	recommends spawning a chain of threads and wait for 63 handles and the
3343	previous thread in each. Great).	4567	previous thread in each. Sounds great!).
3344		4568
3345	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4569	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3346	to some high number (e.g. C<2048>) before compiling the winsocket select	4570	to some high number (e.g. C<2048>) before compiling the winsocket select
3347	call (which might be in libev or elsewhere, for example, perl does its own	4571	call (which might be in libev or elsewhere, for example, perl and many
3348	select emulation on windows).	4572	other interpreters do their own select emulation on windows).
3349		4573
3350	Another limit is the number of file descriptors in the Microsoft runtime	4574	Another limit is the number of file descriptors in the Microsoft runtime
3351	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4575	libraries, which by default is C<64> (there must be a hidden I<64>
3352	or something like this inside Microsoft). You can increase this by calling	4576	fetish or something like this inside Microsoft). You can increase this
3353	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4577	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3354	arbitrary limit), but is broken in many versions of the Microsoft runtime	4578	(another arbitrary limit), but is broken in many versions of the Microsoft
3355	libraries.
3356
3357	This might get you to about C<512> or C<2048> sockets (depending on	4579	runtime libraries. This might get you to about C<512> or C<2048> sockets
3358	windows version and/or the phase of the moon). To get more, you need to	4580	(depending on windows version and/or the phase of the moon). To get more,
3359	wrap all I/O functions and provide your own fd management, but the cost of	4581	you need to wrap all I/O functions and provide your own fd management, but
3360	calling select (O(n²)) will likely make this unworkable.	4582	the cost of calling select (O(n²)) will likely make this unworkable.
3361		4583
3362	=back
3363
3364
3365	=head1 PORTABILITY REQUIREMENTS	4584	=head2 PORTABILITY REQUIREMENTS
3366		4585
3367	In addition to a working ISO-C implementation, libev relies on a few	4586	In addition to a working ISO-C implementation and of course the
3368	additional extensions:	4587	backend-specific APIs, libev relies on a few additional extensions:
3369		4588
3370	=over 4	4589	=over 4
3371		4590
		4591	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4592	calling conventions regardless of C<ev_watcher_type *>.
		4593
		4594	Libev assumes not only that all watcher pointers have the same internal
		4595	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4596	assumes that the same (machine) code can be used to call any watcher
		4597	callback: The watcher callbacks have different type signatures, but libev
		4598	calls them using an C<ev_watcher *> internally.
		4599
3372	=item C<sig_atomic_t volatile> must be thread-atomic as well	4600	=item C<sig_atomic_t volatile> must be thread-atomic as well
3373		4601
3374	The type C<sig_atomic_t volatile> (or whatever is defined as	4602	The type C<sig_atomic_t volatile> (or whatever is defined as
3375	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4603	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3376	threads. This is not part of the specification for C<sig_atomic_t>, but is	4604	threads. This is not part of the specification for C<sig_atomic_t>, but is
3377	believed to be sufficiently portable.	4605	believed to be sufficiently portable.
3378		4606
3379	=item C<sigprocmask> must work in a threaded environment	4607	=item C<sigprocmask> must work in a threaded environment
3380		4608
…		…
3389	except the initial one, and run the default loop in the initial thread as	4617	except the initial one, and run the default loop in the initial thread as
3390	well.	4618	well.
3391		4619
3392	=item C<long> must be large enough for common memory allocation sizes	4620	=item C<long> must be large enough for common memory allocation sizes
3393		4621
3394	To improve portability and simplify using libev, libev uses C<long>	4622	To improve portability and simplify its API, libev uses C<long> internally
3395	internally instead of C<size_t> when allocating its data structures. On	4623	instead of C<size_t> when allocating its data structures. On non-POSIX
3396	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	4624	systems (Microsoft...) this might be unexpectedly low, but is still at
3397	is still at least 31 bits everywhere, which is enough for hundreds of	4625	least 31 bits everywhere, which is enough for hundreds of millions of
3398	millions of watchers.	4626	watchers.
3399		4627
3400	=item C<double> must hold a time value in seconds with enough accuracy	4628	=item C<double> must hold a time value in seconds with enough accuracy
3401		4629
3402	The type C<double> is used to represent timestamps. It is required to	4630	The type C<double> is used to represent timestamps. It is required to
3403	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4631	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3404	enough for at least into the year 4000. This requirement is fulfilled by	4632	enough for at least into the year 4000. This requirement is fulfilled by
3405	implementations implementing IEEE 754 (basically all existing ones).	4633	implementations implementing IEEE 754, which is basically all existing
		4634	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4635	2200.
3406		4636
3407	=back	4637	=back
3408		4638
3409	If you know of other additional requirements drop me a note.	4639	If you know of other additional requirements drop me a note.
3410		4640
3411		4641
3412	=head1 COMPILER WARNINGS	4642	=head1 ALGORITHMIC COMPLEXITIES
3413		4643
3414	Depending on your compiler and compiler settings, you might get no or a	4644	In this section the complexities of (many of) the algorithms used inside
3415	lot of warnings when compiling libev code. Some people are apparently	4645	libev will be documented. For complexity discussions about backends see
3416	scared by this.	4646	the documentation for C<ev_default_init>.
3417		4647
3418	However, these are unavoidable for many reasons. For one, each compiler	4648	All of the following are about amortised time: If an array needs to be
3419	has different warnings, and each user has different tastes regarding	4649	extended, libev needs to realloc and move the whole array, but this
3420	warning options. "Warn-free" code therefore cannot be a goal except when	4650	happens asymptotically rarer with higher number of elements, so O(1) might
3421	targeting a specific compiler and compiler-version.	4651	mean that libev does a lengthy realloc operation in rare cases, but on
		4652	average it is much faster and asymptotically approaches constant time.
3422		4653
3423	Another reason is that some compiler warnings require elaborate	4654	=over 4
3424	workarounds, or other changes to the code that make it less clear and less
3425	maintainable.
3426		4655
3427	And of course, some compiler warnings are just plain stupid, or simply	4656	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3428	wrong (because they don't actually warn about the condition their message
3429	seems to warn about).
3430		4657
3431	While libev is written to generate as few warnings as possible,	4658	This means that, when you have a watcher that triggers in one hour and
3432	"warn-free" code is not a goal, and it is recommended not to build libev	4659	there are 100 watchers that would trigger before that, then inserting will
3433	with any compiler warnings enabled unless you are prepared to cope with	4660	have to skip roughly seven (C<ld 100>) of these watchers.
3434	them (e.g. by ignoring them). Remember that warnings are just that:
3435	warnings, not errors, or proof of bugs.
3436		4661
		4662	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3437		4663
3438	=head1 VALGRIND	4664	That means that changing a timer costs less than removing/adding them,
		4665	as only the relative motion in the event queue has to be paid for.
3439		4666
3440	Valgrind has a special section here because it is a popular tool that is	4667	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3441	highly useful, but valgrind reports are very hard to interpret.
3442		4668
3443	If you think you found a bug (memory leak, uninitialised data access etc.)	4669	These just add the watcher into an array or at the head of a list.
3444	in libev, then check twice: If valgrind reports something like:
3445		4670
3446	==2274== definitely lost: 0 bytes in 0 blocks.	4671	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3447	==2274== possibly lost: 0 bytes in 0 blocks.
3448	==2274== still reachable: 256 bytes in 1 blocks.
3449		4672
3450	Then there is no memory leak. Similarly, under some circumstances,	4673	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3451	valgrind might report kernel bugs as if it were a bug in libev, or it
3452	might be confused (it is a very good tool, but only a tool).
3453		4674
3454	If you are unsure about something, feel free to contact the mailing list	4675	These watchers are stored in lists, so they need to be walked to find the
3455	with the full valgrind report and an explanation on why you think this is	4676	correct watcher to remove. The lists are usually short (you don't usually
3456	a bug in libev. However, don't be annoyed when you get a brisk "this is	4677	have many watchers waiting for the same fd or signal: one is typical, two
3457	no bug" answer and take the chance of learning how to interpret valgrind	4678	is rare).
3458	properly.
3459		4679
3460	If you need, for some reason, empty reports from valgrind for your project	4680	=item Finding the next timer in each loop iteration: O(1)
3461	I suggest using suppression lists.
3462		4681
		4682	By virtue of using a binary or 4-heap, the next timer is always found at a
		4683	fixed position in the storage array.
		4684
		4685	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4686
		4687	A change means an I/O watcher gets started or stopped, which requires
		4688	libev to recalculate its status (and possibly tell the kernel, depending
		4689	on backend and whether C<ev_io_set> was used).
		4690
		4691	=item Activating one watcher (putting it into the pending state): O(1)
		4692
		4693	=item Priority handling: O(number_of_priorities)
		4694
		4695	Priorities are implemented by allocating some space for each
		4696	priority. When doing priority-based operations, libev usually has to
		4697	linearly search all the priorities, but starting/stopping and activating
		4698	watchers becomes O(1) with respect to priority handling.
		4699
		4700	=item Sending an ev_async: O(1)
		4701
		4702	=item Processing ev_async_send: O(number_of_async_watchers)
		4703
		4704	=item Processing signals: O(max_signal_number)
		4705
		4706	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4707	calls in the current loop iteration. Checking for async and signal events
		4708	involves iterating over all running async watchers or all signal numbers.
		4709
		4710	=back
		4711
		4712
		4713	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4714
		4715	The major version 4 introduced some minor incompatible changes to the API.
		4716
		4717	At the moment, the C<ev.h> header file tries to implement superficial
		4718	compatibility, so most programs should still compile. Those might be
		4719	removed in later versions of libev, so better update early than late.
		4720
		4721	=over 4
		4722
		4723	=item C<ev_loop_count> renamed to C<ev_iteration>
		4724
		4725	=item C<ev_loop_depth> renamed to C<ev_depth>
		4726
		4727	=item C<ev_loop_verify> renamed to C<ev_verify>
		4728
		4729	Most functions working on C<struct ev_loop> objects don't have an
		4730	C<ev_loop_> prefix, so it was removed. Note that C<ev_loop_fork> is
		4731	still called C<ev_loop_fork> because it would otherwise clash with the
		4732	C<ev_fork> typedef.
		4733
		4734	=item C<EV_TIMEOUT> renamed to C<EV_TIMER> in C<revents>
		4735
		4736	This is a simple rename - all other watcher types use their name
		4737	as revents flag, and now C<ev_timer> does, too.
		4738
		4739	Both C<EV_TIMER> and C<EV_TIMEOUT> symbols were present in 3.x versions
		4740	and continue to be present for the foreseeable future, so this is mostly a
		4741	documentation change.
		4742
		4743	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4744
		4745	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4746	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4747	and work, but the library code will of course be larger.
		4748
		4749	=back
		4750
		4751
		4752	=head1 GLOSSARY
		4753
		4754	=over 4
		4755
		4756	=item active
		4757
		4758	A watcher is active as long as it has been started (has been attached to
		4759	an event loop) but not yet stopped (disassociated from the event loop).
		4760
		4761	=item application
		4762
		4763	In this document, an application is whatever is using libev.
		4764
		4765	=item callback
		4766
		4767	The address of a function that is called when some event has been
		4768	detected. Callbacks are being passed the event loop, the watcher that
		4769	received the event, and the actual event bitset.
		4770
		4771	=item callback invocation
		4772
		4773	The act of calling the callback associated with a watcher.
		4774
		4775	=item event
		4776
		4777	A change of state of some external event, such as data now being available
		4778	for reading on a file descriptor, time having passed or simply not having
		4779	any other events happening anymore.
		4780
		4781	In libev, events are represented as single bits (such as C<EV_READ> or
		4782	C<EV_TIMER>).
		4783
		4784	=item event library
		4785
		4786	A software package implementing an event model and loop.
		4787
		4788	=item event loop
		4789
		4790	An entity that handles and processes external events and converts them
		4791	into callback invocations.
		4792
		4793	=item event model
		4794
		4795	The model used to describe how an event loop handles and processes
		4796	watchers and events.
		4797
		4798	=item pending
		4799
		4800	A watcher is pending as soon as the corresponding event has been detected,
		4801	and stops being pending as soon as the watcher will be invoked or its
		4802	pending status is explicitly cleared by the application.
		4803
		4804	A watcher can be pending, but not active. Stopping a watcher also clears
		4805	its pending status.
		4806
		4807	=item real time
		4808
		4809	The physical time that is observed. It is apparently strictly monotonic :)
		4810
		4811	=item wall-clock time
		4812
		4813	The time and date as shown on clocks. Unlike real time, it can actually
		4814	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4815	clock.
		4816
		4817	=item watcher
		4818
		4819	A data structure that describes interest in certain events. Watchers need
		4820	to be started (attached to an event loop) before they can receive events.
		4821
		4822	=item watcher invocation
		4823
		4824	The act of calling the callback associated with a watcher.
		4825
		4826	=back
3463		4827
3464	=head1 AUTHOR	4828	=head1 AUTHOR
3465		4829
3466	Marc Lehmann <libev@schmorp.de>.	4830	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3467		4831

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