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…		…
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
		14	#include <stdio.h> // for puts
		15
14	// every watcher type has its own typedef'd struct	16	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	17	// with the name ev_TYPE
16	ev_io stdin_watcher;	18	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
18		20
19	// all watcher callbacks have a similar signature	21	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	22	// this callback is called when data is readable on stdin
21	static void	23	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	25	{
24	puts ("stdin ready");	26	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	27	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	28	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	29	ev_io_stop (EV_A_ w);
28		30
29	// this causes all nested ev_loop's to stop iterating	31	// this causes all nested ev_run's to stop iterating
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	32	ev_break (EV_A_ EVBREAK_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_run to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	41	ev_break (EV_A_ EVBREAK_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;
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);
…		…
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_run (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 practice
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).
…		…
149		165
150	=item ev_tstamp ev_time ()	166	=item ev_tstamp ev_time ()
151		167
152	Returns the current time as libev would use it. Please note that the	168	Returns the current time as libev would use it. Please note that the
153	C<ev_now> function is usually faster and also often returns the timestamp	169	C<ev_now> function is usually faster and also often returns the timestamp
154	you actually want to know.	170	you actually want to know. Also interesting is the combination of
		171	C<ev_update_now> and C<ev_now>.
155		172
156	=item ev_sleep (ev_tstamp interval)	173	=item ev_sleep (ev_tstamp interval)
157		174
158	Sleep for the given interval: The current thread will be blocked until	175	Sleep for the given interval: The current thread will be blocked until
159	either it is interrupted or the given time interval has passed. Basically	176	either it is interrupted or the given time interval has passed. Basically
…		…
176	as this indicates an incompatible change. Minor versions are usually	193	as this indicates an incompatible change. Minor versions are usually
177	compatible to older versions, so a larger minor version alone is usually	194	compatible to older versions, so a larger minor version alone is usually
178	not a problem.	195	not a problem.
179		196
180	Example: Make sure we haven't accidentally been linked against the wrong	197	Example: Make sure we haven't accidentally been linked against the wrong
181	version.	198	version (note, however, that this will not detect other ABI mismatches,
		199	such as LFS or reentrancy).
182		200
183	assert (("libev version mismatch",	201	assert (("libev version mismatch",
184	ev_version_major () == EV_VERSION_MAJOR	202	ev_version_major () == EV_VERSION_MAJOR
185	&& ev_version_minor () >= EV_VERSION_MINOR));	203	&& ev_version_minor () >= EV_VERSION_MINOR));
186		204
…		…
197	assert (("sorry, no epoll, no sex",	215	assert (("sorry, no epoll, no sex",
198	ev_supported_backends () & EVBACKEND_EPOLL));	216	ev_supported_backends () & EVBACKEND_EPOLL));
199		217
200	=item unsigned int ev_recommended_backends ()	218	=item unsigned int ev_recommended_backends ()
201		219
202	Return the set of all backends compiled into this binary of libev and also	220	Return the set of all backends compiled into this binary of libev and
203	recommended for this platform. This set is often smaller than the one	221	also recommended for this platform, meaning it will work for most file
		222	descriptor types. This set is often smaller than the one returned by
204	returned by C<ev_supported_backends>, as for example kqueue is broken on	223	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
205	most BSDs and will not be auto-detected unless you explicitly request it	224	and will not be auto-detected unless you explicitly request it (assuming
206	(assuming you know what you are doing). This is the set of backends that	225	you know what you are doing). This is the set of backends that libev will
207	libev will probe for if you specify no backends explicitly.	226	probe for if you specify no backends explicitly.
208		227
209	=item unsigned int ev_embeddable_backends ()	228	=item unsigned int ev_embeddable_backends ()
210		229
211	Returns the set of backends that are embeddable in other event loops. This	230	Returns the set of backends that are embeddable in other event loops. This
212	is the theoretical, all-platform, value. To find which backends	231	value is platform-specific but can include backends not available on the
213	might be supported on the current system, you would need to look at	232	current system. To find which embeddable backends might be supported on
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	233	the current system, you would need to look at C<ev_embeddable_backends ()
215	recommended ones.	234	& ev_supported_backends ()>, likewise for recommended ones.
216		235
217	See the description of C<ev_embed> watchers for more info.	236	See the description of C<ev_embed> watchers for more info.
218		237
219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	238	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
220		239
221	Sets the allocation function to use (the prototype is similar - the	240	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	241	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	242	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	243	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
250	}	269	}
251		270
252	...	271	...
253	ev_set_allocator (persistent_realloc);	272	ev_set_allocator (persistent_realloc);
254		273
255	=item ev_set_syserr_cb (void (*cb)(const char *msg));	274	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
256		275
257	Set the callback function to call on a retryable system call error (such	276	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	277	as failed select, poll, epoll_wait). The message is a printable string
259	indicating the system call or subsystem causing the problem. If this	278	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	279	callback is set, then libev will expect it to remedy the situation, no
…		…
274	...	293	...
275	ev_set_syserr_cb (fatal_error);	294	ev_set_syserr_cb (fatal_error);
276		295
277	=back	296	=back
278		297
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	298	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
280		299
281	An event loop is described by a C<struct ev_loop *>. The library knows two	300	An event loop is described by a C<struct ev_loop *> (the C<struct> is
282	types of such loops, the I<default> loop, which supports signals and child	301	I<not> optional in this case unless libev 3 compatibility is disabled, as
283	events, and dynamically created loops which do not.	302	libev 3 had an C<ev_loop> function colliding with the struct name).
		303
		304	The library knows two types of such loops, the I<default> loop, which
		305	supports signals and child events, and dynamically created event loops
		306	which do not.
284		307
285	=over 4	308	=over 4
286		309
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	310	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		311
289	This will initialise the default event loop if it hasn't been initialised	312	This returns the "default" event loop object, which is what you should
290	yet and return it. If the default loop could not be initialised, returns	313	normally use when you just need "the event loop". Event loop objects and
291	false. If it already was initialised it simply returns it (and ignores the	314	the C<flags> parameter are described in more detail in the entry for
292	flags. If that is troubling you, check C<ev_backend ()> afterwards).	315	C<ev_loop_new>.
		316
		317	If the default loop is already initialised then this function simply
		318	returns it (and ignores the flags. If that is troubling you, check
		319	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		320	flags, which should almost always be C<0>, unless the caller is also the
		321	one calling C<ev_run> or otherwise qualifies as "the main program".
293		322
294	If you don't know what event loop to use, use the one returned from this	323	If you don't know what event loop to use, use the one returned from this
295	function.	324	function (or via the C<EV_DEFAULT> macro).
296		325
297	Note that this function is I<not> thread-safe, so if you want to use it	326	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,	327	from multiple threads, you have to employ some kind of mutex (note also
299	as loops cannot bes hared easily between threads anyway).	328	that this case is unlikely, as loops cannot be shared easily between
		329	threads anyway).
300		330
301	The default loop is the only loop that can handle C<ev_signal> and	331	The default loop is the only loop that can handle C<ev_child> watchers,
302	C<ev_child> watchers, and to do this, it always registers a handler	332	and to do this, it always registers a handler for C<SIGCHLD>. If this is
303	for C<SIGCHLD>. If this is a problem for your application you can either	333	a problem for your application you can either create a dynamic loop with
304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	334	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
305	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	335	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
306	C<ev_default_init>.	336
		337	Example: This is the most typical usage.
		338
		339	if (!ev_default_loop (0))
		340	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		341
		342	Example: Restrict libev to the select and poll backends, and do not allow
		343	environment settings to be taken into account:
		344
		345	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		346
		347	=item struct ev_loop *ev_loop_new (unsigned int flags)
		348
		349	This will create and initialise a new event loop object. If the loop
		350	could not be initialised, returns false.
		351
		352	Note that this function I<is> thread-safe, and one common way to use
		353	libev with threads is indeed to create one loop per thread, and using the
		354	default loop in the "main" or "initial" thread.
307		355
308	The flags argument can be used to specify special behaviour or specific	356	The flags argument can be used to specify special behaviour or specific
309	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	357	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
310		358
311	The following flags are supported:	359	The following flags are supported:
…		…
326	useful to try out specific backends to test their performance, or to work	374	useful to try out specific backends to test their performance, or to work
327	around bugs.	375	around bugs.
328		376
329	=item C<EVFLAG_FORKCHECK>	377	=item C<EVFLAG_FORKCHECK>
330		378
331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	379	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	380	make libev check for a fork in each iteration by enabling this flag.
333	enabling this flag.
334		381
335	This works by calling C<getpid ()> on every iteration of the loop,	382	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	383	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	384	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	385	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
…		…
344	flag.	391	flag.
345		392
346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	393	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
347	environment variable.	394	environment variable.
348		395
		396	=item C<EVFLAG_NOINOTIFY>
		397
		398	When this flag is specified, then libev will not attempt to use the
		399	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		400	testing, this flag can be useful to conserve inotify file descriptors, as
		401	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		402
		403	=item C<EVFLAG_SIGNALFD>
		404
		405	When this flag is specified, then libev will attempt to use the
		406	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		407	delivers signals synchronously, which makes it both faster and might make
		408	it possible to get the queued signal data. It can also simplify signal
		409	handling with threads, as long as you properly block signals in your
		410	threads that are not interested in handling them.
		411
		412	Signalfd will not be used by default as this changes your signal mask, and
		413	there are a lot of shoddy libraries and programs (glib's threadpool for
		414	example) that can't properly initialise their signal masks.
		415
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	416	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		417
351	This is your standard select(2) backend. Not I<completely> standard, as	418	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,	419	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	420	but if that fails, expect a fairly low limit on the number of fds when
…		…
377	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and	444	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
378	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	445	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
379		446
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	447	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		448
		449	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		450	kernels).
		451
382	For few fds, this backend is a bit little slower than poll and select,	452	For few fds, this backend is a bit little slower than poll and select,
383	but it scales phenomenally better. While poll and select usually scale	453	but it scales phenomenally better. While poll and select usually scale
384	like O(total_fds) where n is the total number of fds (or the highest fd),	454	like O(total_fds) where n is the total number of fds (or the highest fd),
385	epoll scales either O(1) or O(active_fds). The epoll design has a number	455	epoll scales either O(1) or O(active_fds).
386	of shortcomings, such as silently dropping events in some hard-to-detect	456
387	cases and requiring a system call per fd change, no fork support and bad	457	The epoll mechanism deserves honorable mention as the most misdesigned
388	support for dup.	458	of the more advanced event mechanisms: mere annoyances include silently
		459	dropping file descriptors, requiring a system call per change per file
		460	descriptor (and unnecessary guessing of parameters), problems with dup and
		461	so on. The biggest issue is fork races, however - if a program forks then
		462	I<both> parent and child process have to recreate the epoll set, which can
		463	take considerable time (one syscall per file descriptor) and is of course
		464	hard to detect.
		465
		466	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		467	of course I<doesn't>, and epoll just loves to report events for totally
		468	I<different> file descriptors (even already closed ones, so one cannot
		469	even remove them from the set) than registered in the set (especially
		470	on SMP systems). Libev tries to counter these spurious notifications by
		471	employing an additional generation counter and comparing that against the
		472	events to filter out spurious ones, recreating the set when required. Last
		473	not least, it also refuses to work with some file descriptors which work
		474	perfectly fine with C<select> (files, many character devices...).
389		475
390	While stopping, setting and starting an I/O watcher in the same iteration	476	While stopping, setting and starting an I/O watcher in the same iteration
391	will result in some caching, there is still a system call per such incident	477	will result in some caching, there is still a system call per such
392	(because the fd could point to a different file description now), so its	478	incident (because the same I<file descriptor> could point to a different
393	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	479	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
394	very well if you register events for both fds.	480	file descriptors might not work very well if you register events for both
395		481	file descriptors.
396	Please note that epoll sometimes generates spurious notifications, so you
397	need to use non-blocking I/O or other means to avoid blocking when no data
398	(or space) is available.
399		482
400	Best performance from this backend is achieved by not unregistering all	483	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible, i.e.	484	watchers for a file descriptor until it has been closed, if possible,
402	keep at least one watcher active per fd at all times.	485	i.e. keep at least one watcher active per fd at all times. Stopping and
		486	starting a watcher (without re-setting it) also usually doesn't cause
		487	extra overhead. A fork can both result in spurious notifications as well
		488	as in libev having to destroy and recreate the epoll object, which can
		489	take considerable time and thus should be avoided.
		490
		491	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		492	faster than epoll for maybe up to a hundred file descriptors, depending on
		493	the usage. So sad.
403		494
404	While nominally embeddable in other event loops, this feature is broken in	495	While nominally embeddable in other event loops, this feature is broken in
405	all kernel versions tested so far.	496	all kernel versions tested so far.
406		497
407	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	498	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
…		…
410	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	501	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
411		502
412	Kqueue deserves special mention, as at the time of this writing, it	503	Kqueue deserves special mention, as at the time of this writing, it
413	was broken on all BSDs except NetBSD (usually it doesn't work reliably	504	was broken on all BSDs except NetBSD (usually it doesn't work reliably
414	with anything but sockets and pipes, except on Darwin, where of course	505	with anything but sockets and pipes, except on Darwin, where of course
415	it's completely useless). For this reason it's not being "auto-detected"	506	it's completely useless). Unlike epoll, however, whose brokenness
		507	is by design, these kqueue bugs can (and eventually will) be fixed
		508	without API changes to existing programs. For this reason it's not being
416	unless you explicitly specify it explicitly in the flags (i.e. using	509	"auto-detected" unless you explicitly specify it in the flags (i.e. using
417	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	510	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
418	system like NetBSD.	511	system like NetBSD.
419		512
420	You still can embed kqueue into a normal poll or select backend and use it	513	You still can embed kqueue into a normal poll or select backend and use it
421	only for sockets (after having made sure that sockets work with kqueue on	514	only for sockets (after having made sure that sockets work with kqueue on
…		…
423		516
424	It scales in the same way as the epoll backend, but the interface to the	517	It scales in the same way as the epoll backend, but the interface to the
425	kernel is more efficient (which says nothing about its actual speed, of	518	kernel is more efficient (which says nothing about its actual speed, of
426	course). While stopping, setting and starting an I/O watcher does never	519	course). While stopping, setting and starting an I/O watcher does never
427	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	520	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
428	two event changes per incident, support for C<fork ()> is very bad and it	521	two event changes per incident. Support for C<fork ()> is very bad (but
429	drops fds silently in similarly hard-to-detect cases.	522	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		523	cases
430		524
431	This backend usually performs well under most conditions.	525	This backend usually performs well under most conditions.
432		526
433	While nominally embeddable in other event loops, this doesn't work	527	While nominally embeddable in other event loops, this doesn't work
434	everywhere, so you might need to test for this. And since it is broken	528	everywhere, so you might need to test for this. And since it is broken
435	almost everywhere, you should only use it when you have a lot of sockets	529	almost everywhere, you should only use it when you have a lot of sockets
436	(for which it usually works), by embedding it into another event loop	530	(for which it usually works), by embedding it into another event loop
437	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	531	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
438	sockets.	532	also broken on OS X)) and, did I mention it, using it only for sockets.
439		533
440	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with	534	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
441	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with	535	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
442	C<NOTE_EOF>.	536	C<NOTE_EOF>.
443		537
…		…
460	While this backend scales well, it requires one system call per active	554	While this backend scales well, it requires one system call per active
461	file descriptor per loop iteration. For small and medium numbers of file	555	file descriptor per loop iteration. For small and medium numbers of file
462	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	556	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
463	might perform better.	557	might perform better.
464		558
465	On the positive side, ignoring the spurious readiness notifications, this	559	On the positive side, with the exception of the spurious readiness
466	backend actually performed to specification in all tests and is fully	560	notifications, this backend actually performed fully to specification
467	embeddable, which is a rare feat among the OS-specific backends.	561	in all tests and is fully embeddable, which is a rare feat among the
		562	OS-specific backends (I vastly prefer correctness over speed hacks).
468		563
469	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	564	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
470	C<EVBACKEND_POLL>.	565	C<EVBACKEND_POLL>.
471		566
472	=item C<EVBACKEND_ALL>	567	=item C<EVBACKEND_ALL>
…		…
477		572
478	It is definitely not recommended to use this flag.	573	It is definitely not recommended to use this flag.
479		574
480	=back	575	=back
481		576
482	If one or more of these are or'ed into the flags value, then only these	577	If one or more of the backend flags are or'ed into the flags value,
483	backends will be tried (in the reverse order as listed here). If none are	578	then only these backends will be tried (in the reverse order as listed
484	specified, all backends in C<ev_recommended_backends ()> will be tried.	579	here). If none are specified, all backends in C<ev_recommended_backends
485		580	()> will be tried.
486	The most typical usage is like this:
487
488	if (!ev_default_loop (0))
489	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
490
491	Restrict libev to the select and poll backends, and do not allow
492	environment settings to be taken into account:
493
494	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
495
496	Use whatever libev has to offer, but make sure that kqueue is used if
497	available (warning, breaks stuff, best use only with your own private
498	event loop and only if you know the OS supports your types of fds):
499
500	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
501
502	=item struct ev_loop *ev_loop_new (unsigned int flags)
503
504	Similar to C<ev_default_loop>, but always creates a new event loop that is
505	always distinct from the default loop. Unlike the default loop, it cannot
506	handle signal and child watchers, and attempts to do so will be greeted by
507	undefined behaviour (or a failed assertion if assertions are enabled).
508
509	Note that this function I<is> thread-safe, and the recommended way to use
510	libev with threads is indeed to create one loop per thread, and using the
511	default loop in the "main" or "initial" thread.
512		581
513	Example: Try to create a event loop that uses epoll and nothing else.	582	Example: Try to create a event loop that uses epoll and nothing else.
514		583
515	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	584	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
516	if (!epoller)	585	if (!epoller)
517	fatal ("no epoll found here, maybe it hides under your chair");	586	fatal ("no epoll found here, maybe it hides under your chair");
518		587
		588	Example: Use whatever libev has to offer, but make sure that kqueue is
		589	used if available.
		590
		591	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		592
519	=item ev_default_destroy ()	593	=item ev_loop_destroy (loop)
520		594
521	Destroys the default loop again (frees all memory and kernel state	595	Destroys an event loop object (frees all memory and kernel state
522	etc.). None of the active event watchers will be stopped in the normal	596	etc.). None of the active event watchers will be stopped in the normal
523	sense, so e.g. C<ev_is_active> might still return true. It is your	597	sense, so e.g. C<ev_is_active> might still return true. It is your
524	responsibility to either stop all watchers cleanly yourself I<before>	598	responsibility to either stop all watchers cleanly yourself I<before>
525	calling this function, or cope with the fact afterwards (which is usually	599	calling this function, or cope with the fact afterwards (which is usually
526	the easiest thing, you can just ignore the watchers and/or C<free ()> them	600	the easiest thing, you can just ignore the watchers and/or C<free ()> them
527	for example).	601	for example).
528		602
529	Note that certain global state, such as signal state, will not be freed by	603	Note that certain global state, such as signal state (and installed signal
530	this function, and related watchers (such as signal and child watchers)	604	handlers), will not be freed by this function, and related watchers (such
531	would need to be stopped manually.	605	as signal and child watchers) would need to be stopped manually.
532		606
533	In general it is not advisable to call this function except in the	607	This function is normally used on loop objects allocated by
534	rare occasion where you really need to free e.g. the signal handling	608	C<ev_loop_new>, but it can also be used on the default loop returned by
		609	C<ev_default_loop>, in which case it is not thread-safe.
		610
		611	Note that it is not advisable to call this function on the default loop
		612	except in the rare occasion where you really need to free it's resources.
535	pipe fds. If you need dynamically allocated loops it is better to use	613	If you need dynamically allocated loops it is better to use C<ev_loop_new>
536	C<ev_loop_new> and C<ev_loop_destroy>).	614	and C<ev_loop_destroy>.
537		615
538	=item ev_loop_destroy (loop)	616	=item ev_loop_fork (loop)
539		617
540	Like C<ev_default_destroy>, but destroys an event loop created by an
541	earlier call to C<ev_loop_new>.
542
543	=item ev_default_fork ()
544
545	This function sets a flag that causes subsequent C<ev_loop> iterations	618	This function sets a flag that causes subsequent C<ev_run> iterations to
546	to reinitialise the kernel state for backends that have one. Despite the	619	reinitialise the kernel state for backends that have one. Despite the
547	name, you can call it anytime, but it makes most sense after forking, in	620	name, you can call it anytime, but it makes most sense after forking, in
548	the child process (or both child and parent, but that again makes little	621	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
549	sense). You I<must> call it in the child before using any of the libev	622	child before resuming or calling C<ev_run>.
550	functions, and it will only take effect at the next C<ev_loop> iteration.	623
		624	Again, you I<have> to call it on I<any> loop that you want to re-use after
		625	a fork, I<even if you do not plan to use the loop in the parent>. This is
		626	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		627	during fork.
551		628
552	On the other hand, you only need to call this function in the child	629	On the other hand, you only need to call this function in the child
553	process if and only if you want to use the event library in the child. If	630	process if and only if you want to use the event loop in the child. If
554	you just fork+exec, you don't have to call it at all.	631	you just fork+exec or create a new loop in the child, you don't have to
		632	call it at all (in fact, C<epoll> is so badly broken that it makes a
		633	difference, but libev will usually detect this case on its own and do a
		634	costly reset of the backend).
555		635
556	The function itself is quite fast and it's usually not a problem to call	636	The function itself is quite fast and it's usually not a problem to call
557	it just in case after a fork. To make this easy, the function will fit in	637	it just in case after a fork.
558	quite nicely into a call to C<pthread_atfork>:
559		638
		639	Example: Automate calling C<ev_loop_fork> on the default loop when
		640	using pthreads.
		641
		642	static void
		643	post_fork_child (void)
		644	{
		645	ev_loop_fork (EV_DEFAULT);
		646	}
		647
		648	...
560	pthread_atfork (0, 0, ev_default_fork);	649	pthread_atfork (0, 0, post_fork_child);
561
562	=item ev_loop_fork (loop)
563
564	Like C<ev_default_fork>, but acts on an event loop created by
565	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
566	after fork, and how you do this is entirely your own problem.
567		650
568	=item int ev_is_default_loop (loop)	651	=item int ev_is_default_loop (loop)
569		652
570	Returns true when the given loop actually is the default loop, false otherwise.	653	Returns true when the given loop is, in fact, the default loop, and false
		654	otherwise.
571		655
572	=item unsigned int ev_loop_count (loop)	656	=item unsigned int ev_iteration (loop)
573		657
574	Returns the count of loop iterations for the loop, which is identical to	658	Returns the current iteration count for the event loop, which is identical
575	the number of times libev did poll for new events. It starts at C<0> and	659	to the number of times libev did poll for new events. It starts at C<0>
576	happily wraps around with enough iterations.	660	and happily wraps around with enough iterations.
577		661
578	This value can sometimes be useful as a generation counter of sorts (it	662	This value can sometimes be useful as a generation counter of sorts (it
579	"ticks" the number of loop iterations), as it roughly corresponds with	663	"ticks" the number of loop iterations), as it roughly corresponds with
580	C<ev_prepare> and C<ev_check> calls.	664	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		665	prepare and check phases.
		666
		667	=item unsigned int ev_depth (loop)
		668
		669	Returns the number of times C<ev_run> was entered minus the number of
		670	times C<ev_run> was exited, in other words, the recursion depth.
		671
		672	Outside C<ev_run>, this number is zero. In a callback, this number is
		673	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		674	in which case it is higher.
		675
		676	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread
		677	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		678	ungentleman-like behaviour unless it's really convenient.
581		679
582	=item unsigned int ev_backend (loop)	680	=item unsigned int ev_backend (loop)
583		681
584	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	682	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
585	use.	683	use.
…		…
594		692
595	=item ev_now_update (loop)	693	=item ev_now_update (loop)
596		694
597	Establishes the current time by querying the kernel, updating the time	695	Establishes the current time by querying the kernel, updating the time
598	returned by C<ev_now ()> in the progress. This is a costly operation and	696	returned by C<ev_now ()> in the progress. This is a costly operation and
599	is usually done automatically within C<ev_loop ()>.	697	is usually done automatically within C<ev_run ()>.
600		698
601	This function is rarely useful, but when some event callback runs for a	699	This function is rarely useful, but when some event callback runs for a
602	very long time without entering the event loop, updating libev's idea of	700	very long time without entering the event loop, updating libev's idea of
603	the current time is a good idea.	701	the current time is a good idea.
604		702
605	See also "The special problem of time updates" in the C<ev_timer> section.	703	See also L<The special problem of time updates> in the C<ev_timer> section.
606		704
		705	=item ev_suspend (loop)
		706
		707	=item ev_resume (loop)
		708
		709	These two functions suspend and resume an event loop, for use when the
		710	loop is not used for a while and timeouts should not be processed.
		711
		712	A typical use case would be an interactive program such as a game: When
		713	the user presses C<^Z> to suspend the game and resumes it an hour later it
		714	would be best to handle timeouts as if no time had actually passed while
		715	the program was suspended. This can be achieved by calling C<ev_suspend>
		716	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		717	C<ev_resume> directly afterwards to resume timer processing.
		718
		719	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		720	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		721	will be rescheduled (that is, they will lose any events that would have
		722	occurred while suspended).
		723
		724	After calling C<ev_suspend> you B<must not> call I<any> function on the
		725	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		726	without a previous call to C<ev_suspend>.
		727
		728	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		729	event loop time (see C<ev_now_update>).
		730
607	=item ev_loop (loop, int flags)	731	=item ev_run (loop, int flags)
608		732
609	Finally, this is it, the event handler. This function usually is called	733	Finally, this is it, the event handler. This function usually is called
610	after you initialised all your watchers and you want to start handling	734	after you have initialised all your watchers and you want to start
611	events.	735	handling events. It will ask the operating system for any new events, call
		736	the watcher callbacks, an then repeat the whole process indefinitely: This
		737	is why event loops are called I<loops>.
612		738
613	If the flags argument is specified as C<0>, it will not return until	739	If the flags argument is specified as C<0>, it will keep handling events
614	either no event watchers are active anymore or C<ev_unloop> was called.	740	until either no event watchers are active anymore or C<ev_break> was
		741	called.
615		742
616	Please note that an explicit C<ev_unloop> is usually better than	743	Please note that an explicit C<ev_break> is usually better than
617	relying on all watchers to be stopped when deciding when a program has	744	relying on all watchers to be stopped when deciding when a program has
618	finished (especially in interactive programs), but having a program that	745	finished (especially in interactive programs), but having a program
619	automatically loops as long as it has to and no longer by virtue of	746	that automatically loops as long as it has to and no longer by virtue
620	relying on its watchers stopping correctly is a thing of beauty.	747	of relying on its watchers stopping correctly, that is truly a thing of
		748	beauty.
621		749
622	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	750	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
623	those events and any outstanding ones, but will not block your process in	751	those events and any already outstanding ones, but will not wait and
624	case there are no events and will return after one iteration of the loop.	752	block your process in case there are no events and will return after one
		753	iteration of the loop. This is sometimes useful to poll and handle new
		754	events while doing lengthy calculations, to keep the program responsive.
625		755
626	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	756	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
627	necessary) and will handle those and any outstanding ones. It will block	757	necessary) and will handle those and any already outstanding ones. It
628	your process until at least one new event arrives, and will return after	758	will block your process until at least one new event arrives (which could
629	one iteration of the loop. This is useful if you are waiting for some	759	be an event internal to libev itself, so there is no guarantee that a
630	external event in conjunction with something not expressible using other	760	user-registered callback will be called), and will return after one
		761	iteration of the loop.
		762
		763	This is useful if you are waiting for some external event in conjunction
		764	with something not expressible using other libev watchers (i.e. "roll your
631	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	765	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
632	usually a better approach for this kind of thing.	766	usually a better approach for this kind of thing.
633		767
634	Here are the gory details of what C<ev_loop> does:	768	Here are the gory details of what C<ev_run> does:
635		769
		770	- Increment loop depth.
		771	- Reset the ev_break status.
636	- Before the first iteration, call any pending watchers.	772	- Before the first iteration, call any pending watchers.
		773	LOOP:
637	* If EVFLAG_FORKCHECK was used, check for a fork.	774	- If EVFLAG_FORKCHECK was used, check for a fork.
638	- If a fork was detected (by any means), queue and call all fork watchers.	775	- If a fork was detected (by any means), queue and call all fork watchers.
639	- Queue and call all prepare watchers.	776	- Queue and call all prepare watchers.
		777	- If ev_break was called, goto FINISH.
640	- If we have been forked, detach and recreate the kernel state	778	- If we have been forked, detach and recreate the kernel state
641	as to not disturb the other process.	779	as to not disturb the other process.
642	- Update the kernel state with all outstanding changes.	780	- Update the kernel state with all outstanding changes.
643	- Update the "event loop time" (ev_now ()).	781	- Update the "event loop time" (ev_now ()).
644	- Calculate for how long to sleep or block, if at all	782	- Calculate for how long to sleep or block, if at all
645	(active idle watchers, EVLOOP_NONBLOCK or not having	783	(active idle watchers, EVRUN_NOWAIT or not having
646	any active watchers at all will result in not sleeping).	784	any active watchers at all will result in not sleeping).
647	- Sleep if the I/O and timer collect interval say so.	785	- Sleep if the I/O and timer collect interval say so.
		786	- Increment loop iteration counter.
648	- Block the process, waiting for any events.	787	- Block the process, waiting for any events.
649	- Queue all outstanding I/O (fd) events.	788	- Queue all outstanding I/O (fd) events.
650	- Update the "event loop time" (ev_now ()), and do time jump adjustments.	789	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
651	- Queue all outstanding timers.	790	- Queue all expired timers.
652	- Queue all outstanding periodics.	791	- Queue all expired periodics.
653	- Unless any events are pending now, queue all idle watchers.	792	- Queue all idle watchers with priority higher than that of pending events.
654	- Queue all check watchers.	793	- Queue all check watchers.
655	- Call all queued watchers in reverse order (i.e. check watchers first).	794	- Call all queued watchers in reverse order (i.e. check watchers first).
656	Signals and child watchers are implemented as I/O watchers, and will	795	Signals and child watchers are implemented as I/O watchers, and will
657	be handled here by queueing them when their watcher gets executed.	796	be handled here by queueing them when their watcher gets executed.
658	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	797	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
659	were used, or there are no active watchers, return, otherwise	798	were used, or there are no active watchers, goto FINISH, otherwise
660	continue with step *.	799	continue with step LOOP.
		800	FINISH:
		801	- Reset the ev_break status iff it was EVBREAK_ONE.
		802	- Decrement the loop depth.
		803	- Return.
661		804
662	Example: Queue some jobs and then loop until no events are outstanding	805	Example: Queue some jobs and then loop until no events are outstanding
663	anymore.	806	anymore.
664		807
665	... queue jobs here, make sure they register event watchers as long	808	... queue jobs here, make sure they register event watchers as long
666	... as they still have work to do (even an idle watcher will do..)	809	... as they still have work to do (even an idle watcher will do..)
667	ev_loop (my_loop, 0);	810	ev_run (my_loop, 0);
668	... jobs done or somebody called unloop. yeah!	811	... jobs done or somebody called unloop. yeah!
669		812
670	=item ev_unloop (loop, how)	813	=item ev_break (loop, how)
671		814
672	Can be used to make a call to C<ev_loop> return early (but only after it	815	Can be used to make a call to C<ev_run> return early (but only after it
673	has processed all outstanding events). The C<how> argument must be either	816	has processed all outstanding events). The C<how> argument must be either
674	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	817	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
675	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	818	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
676		819
677	This "unloop state" will be cleared when entering C<ev_loop> again.	820	This "unloop state" will be cleared when entering C<ev_run> again.
		821
		822	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##
678		823
679	=item ev_ref (loop)	824	=item ev_ref (loop)
680		825
681	=item ev_unref (loop)	826	=item ev_unref (loop)
682		827
683	Ref/unref can be used to add or remove a reference count on the event	828	Ref/unref can be used to add or remove a reference count on the event
684	loop: Every watcher keeps one reference, and as long as the reference	829	loop: Every watcher keeps one reference, and as long as the reference
685	count is nonzero, C<ev_loop> will not return on its own. If you have	830	count is nonzero, C<ev_run> will not return on its own.
686	a watcher you never unregister that should not keep C<ev_loop> from	831
687	returning, ev_unref() after starting, and ev_ref() before stopping it. For	832	This is useful when you have a watcher that you never intend to
		833	unregister, but that nevertheless should not keep C<ev_run> from
		834	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		835	before stopping it.
		836
688	example, libev itself uses this for its internal signal pipe: It is not	837	As an example, libev itself uses this for its internal signal pipe: It
689	visible to the libev user and should not keep C<ev_loop> from exiting if	838	is not visible to the libev user and should not keep C<ev_run> from
690	no event watchers registered by it are active. It is also an excellent	839	exiting if no event watchers registered by it are active. It is also an
691	way to do this for generic recurring timers or from within third-party	840	excellent way to do this for generic recurring timers or from within
692	libraries. Just remember to I<unref after start> and I<ref before stop>	841	third-party libraries. Just remember to I<unref after start> and I<ref
693	(but only if the watcher wasn't active before, or was active before,	842	before stop> (but only if the watcher wasn't active before, or was active
694	respectively).	843	before, respectively. Note also that libev might stop watchers itself
		844	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		845	in the callback).
695		846
696	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	847	Example: Create a signal watcher, but keep it from keeping C<ev_run>
697	running when nothing else is active.	848	running when nothing else is active.
698		849
699	struct ev_signal exitsig;	850	ev_signal exitsig;
700	ev_signal_init (&exitsig, sig_cb, SIGINT);	851	ev_signal_init (&exitsig, sig_cb, SIGINT);
701	ev_signal_start (loop, &exitsig);	852	ev_signal_start (loop, &exitsig);
702	evf_unref (loop);	853	evf_unref (loop);
703		854
704	Example: For some weird reason, unregister the above signal handler again.	855	Example: For some weird reason, unregister the above signal handler again.
…		…
718	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	869	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
719	allows libev to delay invocation of I/O and timer/periodic callbacks	870	allows libev to delay invocation of I/O and timer/periodic callbacks
720	to increase efficiency of loop iterations (or to increase power-saving	871	to increase efficiency of loop iterations (or to increase power-saving
721	opportunities).	872	opportunities).
722		873
723	The background is that sometimes your program runs just fast enough to	874	The idea is that sometimes your program runs just fast enough to handle
724	handle one (or very few) event(s) per loop iteration. While this makes	875	one (or very few) event(s) per loop iteration. While this makes the
725	the program responsive, it also wastes a lot of CPU time to poll for new	876	program responsive, it also wastes a lot of CPU time to poll for new
726	events, especially with backends like C<select ()> which have a high	877	events, especially with backends like C<select ()> which have a high
727	overhead for the actual polling but can deliver many events at once.	878	overhead for the actual polling but can deliver many events at once.
728		879
729	By setting a higher I<io collect interval> you allow libev to spend more	880	By setting a higher I<io collect interval> you allow libev to spend more
730	time collecting I/O events, so you can handle more events per iteration,	881	time collecting I/O events, so you can handle more events per iteration,
731	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	882	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
732	C<ev_timer>) will be not affected. Setting this to a non-null value will	883	C<ev_timer>) will be not affected. Setting this to a non-null value will
733	introduce an additional C<ev_sleep ()> call into most loop iterations.	884	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		885	sleep time ensures that libev will not poll for I/O events more often then
		886	once per this interval, on average.
734		887
735	Likewise, by setting a higher I<timeout collect interval> you allow libev	888	Likewise, by setting a higher I<timeout collect interval> you allow libev
736	to spend more time collecting timeouts, at the expense of increased	889	to spend more time collecting timeouts, at the expense of increased
737	latency (the watcher callback will be called later). C<ev_io> watchers	890	latency/jitter/inexactness (the watcher callback will be called
738	will not be affected. Setting this to a non-null value will not introduce	891	later). C<ev_io> watchers will not be affected. Setting this to a non-null
739	any overhead in libev.	892	value will not introduce any overhead in libev.
740		893
741	Many (busy) programs can usually benefit by setting the I/O collect	894	Many (busy) programs can usually benefit by setting the I/O collect
742	interval to a value near C<0.1> or so, which is often enough for	895	interval to a value near C<0.1> or so, which is often enough for
743	interactive servers (of course not for games), likewise for timeouts. It	896	interactive servers (of course not for games), likewise for timeouts. It
744	usually doesn't make much sense to set it to a lower value than C<0.01>,	897	usually doesn't make much sense to set it to a lower value than C<0.01>,
745	as this approaches the timing granularity of most systems.	898	as this approaches the timing granularity of most systems. Note that if
		899	you do transactions with the outside world and you can't increase the
		900	parallelity, then this setting will limit your transaction rate (if you
		901	need to poll once per transaction and the I/O collect interval is 0.01,
		902	then you can't do more than 100 transactions per second).
746		903
747	Setting the I<timeout collect interval> can improve the opportunity for	904	Setting the I<timeout collect interval> can improve the opportunity for
748	saving power, as the program will "bundle" timer callback invocations that	905	saving power, as the program will "bundle" timer callback invocations that
749	are "near" in time together, by delaying some, thus reducing the number of	906	are "near" in time together, by delaying some, thus reducing the number of
750	times the process sleeps and wakes up again. Another useful technique to	907	times the process sleeps and wakes up again. Another useful technique to
751	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	908	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
752	they fire on, say, one-second boundaries only.	909	they fire on, say, one-second boundaries only.
753		910
		911	Example: we only need 0.1s timeout granularity, and we wish not to poll
		912	more often than 100 times per second:
		913
		914	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		915	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		916
		917	=item ev_invoke_pending (loop)
		918
		919	This call will simply invoke all pending watchers while resetting their
		920	pending state. Normally, C<ev_run> does this automatically when required,
		921	but when overriding the invoke callback this call comes handy. This
		922	function can be invoked from a watcher - this can be useful for example
		923	when you want to do some lengthy calculation and want to pass further
		924	event handling to another thread (you still have to make sure only one
		925	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		926
		927	=item int ev_pending_count (loop)
		928
		929	Returns the number of pending watchers - zero indicates that no watchers
		930	are pending.
		931
		932	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		933
		934	This overrides the invoke pending functionality of the loop: Instead of
		935	invoking all pending watchers when there are any, C<ev_run> will call
		936	this callback instead. This is useful, for example, when you want to
		937	invoke the actual watchers inside another context (another thread etc.).
		938
		939	If you want to reset the callback, use C<ev_invoke_pending> as new
		940	callback.
		941
		942	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		943
		944	Sometimes you want to share the same loop between multiple threads. This
		945	can be done relatively simply by putting mutex_lock/unlock calls around
		946	each call to a libev function.
		947
		948	However, C<ev_run> can run an indefinite time, so it is not feasible
		949	to wait for it to return. One way around this is to wake up the event
		950	loop via C<ev_break> and C<av_async_send>, another way is to set these
		951	I<release> and I<acquire> callbacks on the loop.
		952
		953	When set, then C<release> will be called just before the thread is
		954	suspended waiting for new events, and C<acquire> is called just
		955	afterwards.
		956
		957	Ideally, C<release> will just call your mutex_unlock function, and
		958	C<acquire> will just call the mutex_lock function again.
		959
		960	While event loop modifications are allowed between invocations of
		961	C<release> and C<acquire> (that's their only purpose after all), no
		962	modifications done will affect the event loop, i.e. adding watchers will
		963	have no effect on the set of file descriptors being watched, or the time
		964	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		965	to take note of any changes you made.
		966
		967	In theory, threads executing C<ev_run> will be async-cancel safe between
		968	invocations of C<release> and C<acquire>.
		969
		970	See also the locking example in the C<THREADS> section later in this
		971	document.
		972
		973	=item ev_set_userdata (loop, void *data)
		974
		975	=item ev_userdata (loop)
		976
		977	Set and retrieve a single C<void *> associated with a loop. When
		978	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		979	C<0.>
		980
		981	These two functions can be used to associate arbitrary data with a loop,
		982	and are intended solely for the C<invoke_pending_cb>, C<release> and
		983	C<acquire> callbacks described above, but of course can be (ab-)used for
		984	any other purpose as well.
		985
754	=item ev_loop_verify (loop)	986	=item ev_verify (loop)
755		987
756	This function only does something when C<EV_VERIFY> support has been	988	This function only does something when C<EV_VERIFY> support has been
757	compiled in. It tries to go through all internal structures and checks	989	compiled in, which is the default for non-minimal builds. It tries to go
758	them for validity. If anything is found to be inconsistent, it will print	990	through all internal structures and checks them for validity. If anything
759	an error message to standard error and call C<abort ()>.	991	is found to be inconsistent, it will print an error message to standard
		992	error and call C<abort ()>.
760		993
761	This can be used to catch bugs inside libev itself: under normal	994	This can be used to catch bugs inside libev itself: under normal
762	circumstances, this function will never abort as of course libev keeps its	995	circumstances, this function will never abort as of course libev keeps its
763	data structures consistent.	996	data structures consistent.
764		997
765	=back	998	=back
766		999
767		1000
768	=head1 ANATOMY OF A WATCHER	1001	=head1 ANATOMY OF A WATCHER
769		1002
		1003	In the following description, uppercase C<TYPE> in names stands for the
		1004	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1005	watchers and C<ev_io_start> for I/O watchers.
		1006
770	A watcher is a structure that you create and register to record your	1007	A watcher is an opaque structure that you allocate and register to record
771	interest in some event. For instance, if you want to wait for STDIN to	1008	your interest in some event. To make a concrete example, imagine you want
772	become readable, you would create an C<ev_io> watcher for that:	1009	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1010	for that:
773		1011
774	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1012	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
775	{	1013	{
776	ev_io_stop (w);	1014	ev_io_stop (w);
777	ev_unloop (loop, EVUNLOOP_ALL);	1015	ev_break (loop, EVBREAK_ALL);
778	}	1016	}
779		1017
780	struct ev_loop *loop = ev_default_loop (0);	1018	struct ev_loop *loop = ev_default_loop (0);
		1019
781	struct ev_io stdin_watcher;	1020	ev_io stdin_watcher;
		1021
782	ev_init (&stdin_watcher, my_cb);	1022	ev_init (&stdin_watcher, my_cb);
783	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1023	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
784	ev_io_start (loop, &stdin_watcher);	1024	ev_io_start (loop, &stdin_watcher);
		1025
785	ev_loop (loop, 0);	1026	ev_run (loop, 0);
786		1027
787	As you can see, you are responsible for allocating the memory for your	1028	As you can see, you are responsible for allocating the memory for your
788	watcher structures (and it is usually a bad idea to do this on the stack,	1029	watcher structures (and it is I<usually> a bad idea to do this on the
789	although this can sometimes be quite valid).	1030	stack).
790		1031
		1032	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1033	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1034
791	Each watcher structure must be initialised by a call to C<ev_init	1035	Each watcher structure must be initialised by a call to C<ev_init (watcher
792	(watcher *, callback)>, which expects a callback to be provided. This	1036	*, callback)>, which expects a callback to be provided. This callback is
793	callback gets invoked each time the event occurs (or, in the case of I/O	1037	invoked each time the event occurs (or, in the case of I/O watchers, each
794	watchers, each time the event loop detects that the file descriptor given	1038	time the event loop detects that the file descriptor given is readable
795	is readable and/or writable).	1039	and/or writable).
796		1040
797	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1041	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
798	with arguments specific to this watcher type. There is also a macro	1042	macro to configure it, with arguments specific to the watcher type. There
799	to combine initialisation and setting in one call: C<< ev_<type>_init	1043	is also a macro to combine initialisation and setting in one call: C<<
800	(watcher *, callback, ...) >>.	1044	ev_TYPE_init (watcher *, callback, ...) >>.
801		1045
802	To make the watcher actually watch out for events, you have to start it	1046	To make the watcher actually watch out for events, you have to start it
803	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1047	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
804	*) >>), and you can stop watching for events at any time by calling the	1048	*) >>), and you can stop watching for events at any time by calling the
805	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1049	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
806		1050
807	As long as your watcher is active (has been started but not stopped) you	1051	As long as your watcher is active (has been started but not stopped) you
808	must not touch the values stored in it. Most specifically you must never	1052	must not touch the values stored in it. Most specifically you must never
809	reinitialise it or call its C<set> macro.	1053	reinitialise it or call its C<ev_TYPE_set> macro.
810		1054
811	Each and every callback receives the event loop pointer as first, the	1055	Each and every callback receives the event loop pointer as first, the
812	registered watcher structure as second, and a bitset of received events as	1056	registered watcher structure as second, and a bitset of received events as
813	third argument.	1057	third argument.
814		1058
…		…
823	=item C<EV_WRITE>	1067	=item C<EV_WRITE>
824		1068
825	The file descriptor in the C<ev_io> watcher has become readable and/or	1069	The file descriptor in the C<ev_io> watcher has become readable and/or
826	writable.	1070	writable.
827		1071
828	=item C<EV_TIMEOUT>	1072	=item C<EV_TIMER>
829		1073
830	The C<ev_timer> watcher has timed out.	1074	The C<ev_timer> watcher has timed out.
831		1075
832	=item C<EV_PERIODIC>	1076	=item C<EV_PERIODIC>
833		1077
…		…
851		1095
852	=item C<EV_PREPARE>	1096	=item C<EV_PREPARE>
853		1097
854	=item C<EV_CHECK>	1098	=item C<EV_CHECK>
855		1099
856	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1100	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
857	to gather new events, and all C<ev_check> watchers are invoked just after	1101	to gather new events, and all C<ev_check> watchers are invoked just after
858	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1102	C<ev_run> has gathered them, but before it invokes any callbacks for any
859	received events. Callbacks of both watcher types can start and stop as	1103	received events. Callbacks of both watcher types can start and stop as
860	many watchers as they want, and all of them will be taken into account	1104	many watchers as they want, and all of them will be taken into account
861	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1105	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
862	C<ev_loop> from blocking).	1106	C<ev_run> from blocking).
863		1107
864	=item C<EV_EMBED>	1108	=item C<EV_EMBED>
865		1109
866	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1110	The embedded event loop specified in the C<ev_embed> watcher needs attention.
867		1111
…		…
871	C<ev_fork>).	1115	C<ev_fork>).
872		1116
873	=item C<EV_ASYNC>	1117	=item C<EV_ASYNC>
874		1118
875	The given async watcher has been asynchronously notified (see C<ev_async>).	1119	The given async watcher has been asynchronously notified (see C<ev_async>).
		1120
		1121	=item C<EV_CUSTOM>
		1122
		1123	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1124	by libev users to signal watchers (e.g. via C<ev_feed_event>).
876		1125
877	=item C<EV_ERROR>	1126	=item C<EV_ERROR>
878		1127
879	An unspecified error has occurred, the watcher has been stopped. This might	1128	An unspecified error has occurred, the watcher has been stopped. This might
880	happen because the watcher could not be properly started because libev	1129	happen because the watcher could not be properly started because libev
881	ran out of memory, a file descriptor was found to be closed or any other	1130	ran out of memory, a file descriptor was found to be closed or any other
		1131	problem. Libev considers these application bugs.
		1132
882	problem. You best act on it by reporting the problem and somehow coping	1133	You best act on it by reporting the problem and somehow coping with the
883	with the watcher being stopped.	1134	watcher being stopped. Note that well-written programs should not receive
		1135	an error ever, so when your watcher receives it, this usually indicates a
		1136	bug in your program.
884		1137
885	Libev will usually signal a few "dummy" events together with an error,	1138	Libev will usually signal a few "dummy" events together with an error, for
886	for example it might indicate that a fd is readable or writable, and if	1139	example it might indicate that a fd is readable or writable, and if your
887	your callbacks is well-written it can just attempt the operation and cope	1140	callbacks is well-written it can just attempt the operation and cope with
888	with the error from read() or write(). This will not work in multi-threaded	1141	the error from read() or write(). This will not work in multi-threaded
889	programs, though, so beware.	1142	programs, though, as the fd could already be closed and reused for another
		1143	thing, so beware.
890		1144
891	=back	1145	=back
892		1146
		1147	=head2 WATCHER STATES
		1148
		1149	There are various watcher states mentioned throughout this manual -
		1150	active, pending and so on. In this section these states and the rules to
		1151	transition between them will be described in more detail - and while these
		1152	rules might look complicated, they usually do "the right thing".
		1153
		1154	=over 4
		1155
		1156	=item initialiased
		1157
		1158	Before a watcher can be registered with the event looop it has to be
		1159	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1160	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1161
		1162	In this state it is simply some block of memory that is suitable for use
		1163	in an event loop. It can be moved around, freed, reused etc. at will.
		1164
		1165	=item started/running/active
		1166
		1167	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1168	property of the event loop, and is actively waiting for events. While in
		1169	this state it cannot be accessed (except in a few documented ways), moved,
		1170	freed or anything else - the only legal thing is to keep a pointer to it,
		1171	and call libev functions on it that are documented to work on active watchers.
		1172
		1173	=item pending
		1174
		1175	If a watcher is active and libev determines that an event it is interested
		1176	in has occurred (such as a timer expiring), it will become pending. It will
		1177	stay in this pending state until either it is stopped or its callback is
		1178	about to be invoked, so it is not normally pending inside the watcher
		1179	callback.
		1180
		1181	The watcher might or might not be active while it is pending (for example,
		1182	an expired non-repeating timer can be pending but no longer active). If it
		1183	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1184	but it is still property of the event loop at this time, so cannot be
		1185	moved, freed or reused. And if it is active the rules described in the
		1186	previous item still apply.
		1187
		1188	It is also possible to feed an event on a watcher that is not active (e.g.
		1189	via C<ev_feed_event>), in which case it becomes pending without being
		1190	active.
		1191
		1192	=item stopped
		1193
		1194	A watcher can be stopped implicitly by libev (in which case it might still
		1195	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1196	latter will clear any pending state the watcher might be in, regardless
		1197	of whether it was active or not, so stopping a watcher explicitly before
		1198	freeing it is often a good idea.
		1199
		1200	While stopped (and not pending) the watcher is essentially in the
		1201	initialised state, that is it can be reused, moved, modified in any way
		1202	you wish.
		1203
		1204	=back
		1205
893	=head2 GENERIC WATCHER FUNCTIONS	1206	=head2 GENERIC WATCHER FUNCTIONS
894
895	In the following description, C<TYPE> stands for the watcher type,
896	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
897		1207
898	=over 4	1208	=over 4
899		1209
900	=item C<ev_init> (ev_TYPE *watcher, callback)	1210	=item C<ev_init> (ev_TYPE *watcher, callback)
901		1211
…		…
907	which rolls both calls into one.	1217	which rolls both calls into one.
908		1218
909	You can reinitialise a watcher at any time as long as it has been stopped	1219	You can reinitialise a watcher at any time as long as it has been stopped
910	(or never started) and there are no pending events outstanding.	1220	(or never started) and there are no pending events outstanding.
911		1221
912	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1222	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
913	int revents)>.	1223	int revents)>.
914		1224
		1225	Example: Initialise an C<ev_io> watcher in two steps.
		1226
		1227	ev_io w;
		1228	ev_init (&w, my_cb);
		1229	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1230
915	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1231	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
916		1232
917	This macro initialises the type-specific parts of a watcher. You need to	1233	This macro initialises the type-specific parts of a watcher. You need to
918	call C<ev_init> at least once before you call this macro, but you can	1234	call C<ev_init> at least once before you call this macro, but you can
919	call C<ev_TYPE_set> any number of times. You must not, however, call this	1235	call C<ev_TYPE_set> any number of times. You must not, however, call this
920	macro on a watcher that is active (it can be pending, however, which is a	1236	macro on a watcher that is active (it can be pending, however, which is a
921	difference to the C<ev_init> macro).	1237	difference to the C<ev_init> macro).
922		1238
923	Although some watcher types do not have type-specific arguments	1239	Although some watcher types do not have type-specific arguments
924	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1240	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
925		1241
		1242	See C<ev_init>, above, for an example.
		1243
926	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1244	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
927		1245
928	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1246	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
929	calls into a single call. This is the most convenient method to initialise	1247	calls into a single call. This is the most convenient method to initialise
930	a watcher. The same limitations apply, of course.	1248	a watcher. The same limitations apply, of course.
931		1249
		1250	Example: Initialise and set an C<ev_io> watcher in one step.
		1251
		1252	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1253
932	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1254	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
933		1255
934	Starts (activates) the given watcher. Only active watchers will receive	1256	Starts (activates) the given watcher. Only active watchers will receive
935	events. If the watcher is already active nothing will happen.	1257	events. If the watcher is already active nothing will happen.
936		1258
		1259	Example: Start the C<ev_io> watcher that is being abused as example in this
		1260	whole section.
		1261
		1262	ev_io_start (EV_DEFAULT_UC, &w);
		1263
937	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1264	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
938		1265
939	Stops the given watcher again (if active) and clears the pending	1266	Stops the given watcher if active, and clears the pending status (whether
		1267	the watcher was active or not).
		1268
940	status. It is possible that stopped watchers are pending (for example,	1269	It is possible that stopped watchers are pending - for example,
941	non-repeating timers are being stopped when they become pending), but	1270	non-repeating timers are being stopped when they become pending - but
942	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1271	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
943	you want to free or reuse the memory used by the watcher it is therefore a	1272	pending. If you want to free or reuse the memory used by the watcher it is
944	good idea to always call its C<ev_TYPE_stop> function.	1273	therefore a good idea to always call its C<ev_TYPE_stop> function.
945		1274
946	=item bool ev_is_active (ev_TYPE *watcher)	1275	=item bool ev_is_active (ev_TYPE *watcher)
947		1276
948	Returns a true value iff the watcher is active (i.e. it has been started	1277	Returns a true value iff the watcher is active (i.e. it has been started
949	and not yet been stopped). As long as a watcher is active you must not modify	1278	and not yet been stopped). As long as a watcher is active you must not modify
…		…
965	=item ev_cb_set (ev_TYPE *watcher, callback)	1294	=item ev_cb_set (ev_TYPE *watcher, callback)
966		1295
967	Change the callback. You can change the callback at virtually any time	1296	Change the callback. You can change the callback at virtually any time
968	(modulo threads).	1297	(modulo threads).
969		1298
970	=item ev_set_priority (ev_TYPE *watcher, priority)	1299	=item ev_set_priority (ev_TYPE *watcher, int priority)
971		1300
972	=item int ev_priority (ev_TYPE *watcher)	1301	=item int ev_priority (ev_TYPE *watcher)
973		1302
974	Set and query the priority of the watcher. The priority is a small	1303	Set and query the priority of the watcher. The priority is a small
975	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1304	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
976	(default: C<-2>). Pending watchers with higher priority will be invoked	1305	(default: C<-2>). Pending watchers with higher priority will be invoked
977	before watchers with lower priority, but priority will not keep watchers	1306	before watchers with lower priority, but priority will not keep watchers
978	from being executed (except for C<ev_idle> watchers).	1307	from being executed (except for C<ev_idle> watchers).
979		1308
980	This means that priorities are I<only> used for ordering callback
981	invocation after new events have been received. This is useful, for
982	example, to reduce latency after idling, or more often, to bind two
983	watchers on the same event and make sure one is called first.
984
985	If you need to suppress invocation when higher priority events are pending	1309	If you need to suppress invocation when higher priority events are pending
986	you need to look at C<ev_idle> watchers, which provide this functionality.	1310	you need to look at C<ev_idle> watchers, which provide this functionality.
987		1311
988	You I<must not> change the priority of a watcher as long as it is active or	1312	You I<must not> change the priority of a watcher as long as it is active or
989	pending.	1313	pending.
990		1314
		1315	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1316	fine, as long as you do not mind that the priority value you query might
		1317	or might not have been clamped to the valid range.
		1318
991	The default priority used by watchers when no priority has been set is	1319	The default priority used by watchers when no priority has been set is
992	always C<0>, which is supposed to not be too high and not be too low :).	1320	always C<0>, which is supposed to not be too high and not be too low :).
993		1321
994	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1322	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
995	fine, as long as you do not mind that the priority value you query might	1323	priorities.
996	or might not have been adjusted to be within valid range.
997		1324
998	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1325	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
999		1326
1000	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1327	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1001	C<loop> nor C<revents> need to be valid as long as the watcher callback	1328	C<loop> nor C<revents> need to be valid as long as the watcher callback
1002	can deal with that fact.	1329	can deal with that fact, as both are simply passed through to the
		1330	callback.
1003		1331
1004	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1332	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1005		1333
1006	If the watcher is pending, this function returns clears its pending status	1334	If the watcher is pending, this function clears its pending status and
1007	and returns its C<revents> bitset (as if its callback was invoked). If the	1335	returns its C<revents> bitset (as if its callback was invoked). If the
1008	watcher isn't pending it does nothing and returns C<0>.	1336	watcher isn't pending it does nothing and returns C<0>.
1009		1337
		1338	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1339	callback to be invoked, which can be accomplished with this function.
		1340
		1341	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1342
		1343	Feeds the given event set into the event loop, as if the specified event
		1344	had happened for the specified watcher (which must be a pointer to an
		1345	initialised but not necessarily started event watcher). Obviously you must
		1346	not free the watcher as long as it has pending events.
		1347
		1348	Stopping the watcher, letting libev invoke it, or calling
		1349	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1350	not started in the first place.
		1351
		1352	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1353	functions that do not need a watcher.
		1354
1010	=back	1355	=back
1011		1356
1012		1357
1013	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1358	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1014		1359
1015	Each watcher has, by default, a member C<void *data> that you can change	1360	Each watcher has, by default, a member C<void *data> that you can change
1016	and read at any time, libev will completely ignore it. This can be used	1361	and read at any time: libev will completely ignore it. This can be used
1017	to associate arbitrary data with your watcher. If you need more data and	1362	to associate arbitrary data with your watcher. If you need more data and
1018	don't want to allocate memory and store a pointer to it in that data	1363	don't want to allocate memory and store a pointer to it in that data
1019	member, you can also "subclass" the watcher type and provide your own	1364	member, you can also "subclass" the watcher type and provide your own
1020	data:	1365	data:
1021		1366
1022	struct my_io	1367	struct my_io
1023	{	1368	{
1024	struct ev_io io;	1369	ev_io io;
1025	int otherfd;	1370	int otherfd;
1026	void *somedata;	1371	void *somedata;
1027	struct whatever *mostinteresting;	1372	struct whatever *mostinteresting;
1028	};	1373	};
1029		1374
…		…
1032	ev_io_init (&w.io, my_cb, fd, EV_READ);	1377	ev_io_init (&w.io, my_cb, fd, EV_READ);
1033		1378
1034	And since your callback will be called with a pointer to the watcher, you	1379	And since your callback will be called with a pointer to the watcher, you
1035	can cast it back to your own type:	1380	can cast it back to your own type:
1036		1381
1037	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1382	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1038	{	1383	{
1039	struct my_io *w = (struct my_io *)w_;	1384	struct my_io *w = (struct my_io *)w_;
1040	...	1385	...
1041	}	1386	}
1042		1387
…		…
1053	ev_timer t2;	1398	ev_timer t2;
1054	}	1399	}
1055		1400
1056	In this case getting the pointer to C<my_biggy> is a bit more	1401	In this case getting the pointer to C<my_biggy> is a bit more
1057	complicated: Either you store the address of your C<my_biggy> struct	1402	complicated: Either you store the address of your C<my_biggy> struct
1058	in the C<data> member of the watcher, or you need to use some pointer	1403	in the C<data> member of the watcher (for woozies), or you need to use
1059	arithmetic using C<offsetof> inside your watchers:	1404	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1405	programmers):
1060		1406
1061	#include <stddef.h>	1407	#include <stddef.h>
1062		1408
1063	static void	1409	static void
1064	t1_cb (EV_P_ struct ev_timer *w, int revents)	1410	t1_cb (EV_P_ ev_timer *w, int revents)
1065	{	1411	{
1066	struct my_biggy big = (struct my_biggy *	1412	struct my_biggy big = (struct my_biggy *)
1067	(((char *)w) - offsetof (struct my_biggy, t1));	1413	(((char *)w) - offsetof (struct my_biggy, t1));
1068	}	1414	}
1069		1415
1070	static void	1416	static void
1071	t2_cb (EV_P_ struct ev_timer *w, int revents)	1417	t2_cb (EV_P_ ev_timer *w, int revents)
1072	{	1418	{
1073	struct my_biggy big = (struct my_biggy *	1419	struct my_biggy big = (struct my_biggy *)
1074	(((char *)w) - offsetof (struct my_biggy, t2));	1420	(((char *)w) - offsetof (struct my_biggy, t2));
1075	}	1421	}
		1422
		1423	=head2 WATCHER PRIORITY MODELS
		1424
		1425	Many event loops support I<watcher priorities>, which are usually small
		1426	integers that influence the ordering of event callback invocation
		1427	between watchers in some way, all else being equal.
		1428
		1429	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1430	description for the more technical details such as the actual priority
		1431	range.
		1432
		1433	There are two common ways how these these priorities are being interpreted
		1434	by event loops:
		1435
		1436	In the more common lock-out model, higher priorities "lock out" invocation
		1437	of lower priority watchers, which means as long as higher priority
		1438	watchers receive events, lower priority watchers are not being invoked.
		1439
		1440	The less common only-for-ordering model uses priorities solely to order
		1441	callback invocation within a single event loop iteration: Higher priority
		1442	watchers are invoked before lower priority ones, but they all get invoked
		1443	before polling for new events.
		1444
		1445	Libev uses the second (only-for-ordering) model for all its watchers
		1446	except for idle watchers (which use the lock-out model).
		1447
		1448	The rationale behind this is that implementing the lock-out model for
		1449	watchers is not well supported by most kernel interfaces, and most event
		1450	libraries will just poll for the same events again and again as long as
		1451	their callbacks have not been executed, which is very inefficient in the
		1452	common case of one high-priority watcher locking out a mass of lower
		1453	priority ones.
		1454
		1455	Static (ordering) priorities are most useful when you have two or more
		1456	watchers handling the same resource: a typical usage example is having an
		1457	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1458	timeouts. Under load, data might be received while the program handles
		1459	other jobs, but since timers normally get invoked first, the timeout
		1460	handler will be executed before checking for data. In that case, giving
		1461	the timer a lower priority than the I/O watcher ensures that I/O will be
		1462	handled first even under adverse conditions (which is usually, but not
		1463	always, what you want).
		1464
		1465	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1466	will only be executed when no same or higher priority watchers have
		1467	received events, they can be used to implement the "lock-out" model when
		1468	required.
		1469
		1470	For example, to emulate how many other event libraries handle priorities,
		1471	you can associate an C<ev_idle> watcher to each such watcher, and in
		1472	the normal watcher callback, you just start the idle watcher. The real
		1473	processing is done in the idle watcher callback. This causes libev to
		1474	continuously poll and process kernel event data for the watcher, but when
		1475	the lock-out case is known to be rare (which in turn is rare :), this is
		1476	workable.
		1477
		1478	Usually, however, the lock-out model implemented that way will perform
		1479	miserably under the type of load it was designed to handle. In that case,
		1480	it might be preferable to stop the real watcher before starting the
		1481	idle watcher, so the kernel will not have to process the event in case
		1482	the actual processing will be delayed for considerable time.
		1483
		1484	Here is an example of an I/O watcher that should run at a strictly lower
		1485	priority than the default, and which should only process data when no
		1486	other events are pending:
		1487
		1488	ev_idle idle; // actual processing watcher
		1489	ev_io io; // actual event watcher
		1490
		1491	static void
		1492	io_cb (EV_P_ ev_io *w, int revents)
		1493	{
		1494	// stop the I/O watcher, we received the event, but
		1495	// are not yet ready to handle it.
		1496	ev_io_stop (EV_A_ w);
		1497
		1498	// start the idle watcher to handle the actual event.
		1499	// it will not be executed as long as other watchers
		1500	// with the default priority are receiving events.
		1501	ev_idle_start (EV_A_ &idle);
		1502	}
		1503
		1504	static void
		1505	idle_cb (EV_P_ ev_idle *w, int revents)
		1506	{
		1507	// actual processing
		1508	read (STDIN_FILENO, ...);
		1509
		1510	// have to start the I/O watcher again, as
		1511	// we have handled the event
		1512	ev_io_start (EV_P_ &io);
		1513	}
		1514
		1515	// initialisation
		1516	ev_idle_init (&idle, idle_cb);
		1517	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1518	ev_io_start (EV_DEFAULT_ &io);
		1519
		1520	In the "real" world, it might also be beneficial to start a timer, so that
		1521	low-priority connections can not be locked out forever under load. This
		1522	enables your program to keep a lower latency for important connections
		1523	during short periods of high load, while not completely locking out less
		1524	important ones.
1076		1525
1077		1526
1078	=head1 WATCHER TYPES	1527	=head1 WATCHER TYPES
1079		1528
1080	This section describes each watcher in detail, but will not repeat	1529	This section describes each watcher in detail, but will not repeat
…		…
1104	In general you can register as many read and/or write event watchers per	1553	In general you can register as many read and/or write event watchers per
1105	fd as you want (as long as you don't confuse yourself). Setting all file	1554	fd as you want (as long as you don't confuse yourself). Setting all file
1106	descriptors to non-blocking mode is also usually a good idea (but not	1555	descriptors to non-blocking mode is also usually a good idea (but not
1107	required if you know what you are doing).	1556	required if you know what you are doing).
1108		1557
1109	If you must do this, then force the use of a known-to-be-good backend	1558	If you cannot use non-blocking mode, then force the use of a
1110	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1559	known-to-be-good backend (at the time of this writing, this includes only
1111	C<EVBACKEND_POLL>).	1560	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1561	descriptors for which non-blocking operation makes no sense (such as
		1562	files) - libev doesn't guarantee any specific behaviour in that case.
1112		1563
1113	Another thing you have to watch out for is that it is quite easy to	1564	Another thing you have to watch out for is that it is quite easy to
1114	receive "spurious" readiness notifications, that is your callback might	1565	receive "spurious" readiness notifications, that is your callback might
1115	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1566	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1116	because there is no data. Not only are some backends known to create a	1567	because there is no data. Not only are some backends known to create a
1117	lot of those (for example Solaris ports), it is very easy to get into	1568	lot of those (for example Solaris ports), it is very easy to get into
1118	this situation even with a relatively standard program structure. Thus	1569	this situation even with a relatively standard program structure. Thus
1119	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1570	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1120	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1571	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1121		1572
1122	If you cannot run the fd in non-blocking mode (for example you should not	1573	If you cannot run the fd in non-blocking mode (for example you should
1123	play around with an Xlib connection), then you have to separately re-test	1574	not play around with an Xlib connection), then you have to separately
1124	whether a file descriptor is really ready with a known-to-be good interface	1575	re-test whether a file descriptor is really ready with a known-to-be good
1125	such as poll (fortunately in our Xlib example, Xlib already does this on	1576	interface such as poll (fortunately in our Xlib example, Xlib already
1126	its own, so its quite safe to use).	1577	does this on its own, so its quite safe to use). Some people additionally
		1578	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1579	indefinitely.
		1580
		1581	But really, best use non-blocking mode.
1127		1582
1128	=head3 The special problem of disappearing file descriptors	1583	=head3 The special problem of disappearing file descriptors
1129		1584
1130	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1585	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1131	descriptor (either by calling C<close> explicitly or by any other means,	1586	descriptor (either due to calling C<close> explicitly or any other means,
1132	such as C<dup>). The reason is that you register interest in some file	1587	such as C<dup2>). The reason is that you register interest in some file
1133	descriptor, but when it goes away, the operating system will silently drop	1588	descriptor, but when it goes away, the operating system will silently drop
1134	this interest. If another file descriptor with the same number then is	1589	this interest. If another file descriptor with the same number then is
1135	registered with libev, there is no efficient way to see that this is, in	1590	registered with libev, there is no efficient way to see that this is, in
1136	fact, a different file descriptor.	1591	fact, a different file descriptor.
1137		1592
…		…
1168	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1623	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1169	C<EVBACKEND_POLL>.	1624	C<EVBACKEND_POLL>.
1170		1625
1171	=head3 The special problem of SIGPIPE	1626	=head3 The special problem of SIGPIPE
1172		1627
1173	While not really specific to libev, it is easy to forget about SIGPIPE:	1628	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1174	when writing to a pipe whose other end has been closed, your program gets	1629	when writing to a pipe whose other end has been closed, your program gets
1175	send a SIGPIPE, which, by default, aborts your program. For most programs	1630	sent a SIGPIPE, which, by default, aborts your program. For most programs
1176	this is sensible behaviour, for daemons, this is usually undesirable.	1631	this is sensible behaviour, for daemons, this is usually undesirable.
1177		1632
1178	So when you encounter spurious, unexplained daemon exits, make sure you	1633	So when you encounter spurious, unexplained daemon exits, make sure you
1179	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1634	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1180	somewhere, as that would have given you a big clue).	1635	somewhere, as that would have given you a big clue).
1181		1636
		1637	=head3 The special problem of accept()ing when you can't
		1638
		1639	Many implementations of the POSIX C<accept> function (for example,
		1640	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1641	connection from the pending queue in all error cases.
		1642
		1643	For example, larger servers often run out of file descriptors (because
		1644	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1645	rejecting the connection, leading to libev signalling readiness on
		1646	the next iteration again (the connection still exists after all), and
		1647	typically causing the program to loop at 100% CPU usage.
		1648
		1649	Unfortunately, the set of errors that cause this issue differs between
		1650	operating systems, there is usually little the app can do to remedy the
		1651	situation, and no known thread-safe method of removing the connection to
		1652	cope with overload is known (to me).
		1653
		1654	One of the easiest ways to handle this situation is to just ignore it
		1655	- when the program encounters an overload, it will just loop until the
		1656	situation is over. While this is a form of busy waiting, no OS offers an
		1657	event-based way to handle this situation, so it's the best one can do.
		1658
		1659	A better way to handle the situation is to log any errors other than
		1660	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1661	messages, and continue as usual, which at least gives the user an idea of
		1662	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1663	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1664	usage.
		1665
		1666	If your program is single-threaded, then you could also keep a dummy file
		1667	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1668	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1669	close that fd, and create a new dummy fd. This will gracefully refuse
		1670	clients under typical overload conditions.
		1671
		1672	The last way to handle it is to simply log the error and C<exit>, as
		1673	is often done with C<malloc> failures, but this results in an easy
		1674	opportunity for a DoS attack.
1182		1675
1183	=head3 Watcher-Specific Functions	1676	=head3 Watcher-Specific Functions
1184		1677
1185	=over 4	1678	=over 4
1186		1679
1187	=item ev_io_init (ev_io *, callback, int fd, int events)	1680	=item ev_io_init (ev_io *, callback, int fd, int events)
1188		1681
1189	=item ev_io_set (ev_io *, int fd, int events)	1682	=item ev_io_set (ev_io *, int fd, int events)
1190		1683
1191	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1684	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1192	receive events for and events is either C<EV_READ>, C<EV_WRITE> or	1685	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1193	C<EV_READ | EV_WRITE> to receive the given events.	1686	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1194		1687
1195	=item int fd [read-only]	1688	=item int fd [read-only]
1196		1689
1197	The file descriptor being watched.	1690	The file descriptor being watched.
1198		1691
…		…
1207	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1700	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1208	readable, but only once. Since it is likely line-buffered, you could	1701	readable, but only once. Since it is likely line-buffered, you could
1209	attempt to read a whole line in the callback.	1702	attempt to read a whole line in the callback.
1210		1703
1211	static void	1704	static void
1212	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1705	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1213	{	1706	{
1214	ev_io_stop (loop, w);	1707	ev_io_stop (loop, w);
1215	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1708	.. read from stdin here (or from w->fd) and handle any I/O errors
1216	}	1709	}
1217		1710
1218	...	1711	...
1219	struct ev_loop *loop = ev_default_init (0);	1712	struct ev_loop *loop = ev_default_init (0);
1220	struct ev_io stdin_readable;	1713	ev_io stdin_readable;
1221	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1714	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1222	ev_io_start (loop, &stdin_readable);	1715	ev_io_start (loop, &stdin_readable);
1223	ev_loop (loop, 0);	1716	ev_run (loop, 0);
1224		1717
1225		1718
1226	=head2 C<ev_timer> - relative and optionally repeating timeouts	1719	=head2 C<ev_timer> - relative and optionally repeating timeouts
1227		1720
1228	Timer watchers are simple relative timers that generate an event after a	1721	Timer watchers are simple relative timers that generate an event after a
1229	given time, and optionally repeating in regular intervals after that.	1722	given time, and optionally repeating in regular intervals after that.
1230		1723
1231	The timers are based on real time, that is, if you register an event that	1724	The timers are based on real time, that is, if you register an event that
1232	times out after an hour and you reset your system clock to January last	1725	times out after an hour and you reset your system clock to January last
1233	year, it will still time out after (roughly) and hour. "Roughly" because	1726	year, it will still time out after (roughly) one hour. "Roughly" because
1234	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1727	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1235	monotonic clock option helps a lot here).	1728	monotonic clock option helps a lot here).
1236		1729
1237	The callback is guaranteed to be invoked only after its timeout has passed,	1730	The callback is guaranteed to be invoked only I<after> its timeout has
1238	but if multiple timers become ready during the same loop iteration then	1731	passed (not I<at>, so on systems with very low-resolution clocks this
1239	order of execution is undefined.	1732	might introduce a small delay). If multiple timers become ready during the
		1733	same loop iteration then the ones with earlier time-out values are invoked
		1734	before ones of the same priority with later time-out values (but this is
		1735	no longer true when a callback calls C<ev_run> recursively).
		1736
		1737	=head3 Be smart about timeouts
		1738
		1739	Many real-world problems involve some kind of timeout, usually for error
		1740	recovery. A typical example is an HTTP request - if the other side hangs,
		1741	you want to raise some error after a while.
		1742
		1743	What follows are some ways to handle this problem, from obvious and
		1744	inefficient to smart and efficient.
		1745
		1746	In the following, a 60 second activity timeout is assumed - a timeout that
		1747	gets reset to 60 seconds each time there is activity (e.g. each time some
		1748	data or other life sign was received).
		1749
		1750	=over 4
		1751
		1752	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1753
		1754	This is the most obvious, but not the most simple way: In the beginning,
		1755	start the watcher:
		1756
		1757	ev_timer_init (timer, callback, 60., 0.);
		1758	ev_timer_start (loop, timer);
		1759
		1760	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1761	and start it again:
		1762
		1763	ev_timer_stop (loop, timer);
		1764	ev_timer_set (timer, 60., 0.);
		1765	ev_timer_start (loop, timer);
		1766
		1767	This is relatively simple to implement, but means that each time there is
		1768	some activity, libev will first have to remove the timer from its internal
		1769	data structure and then add it again. Libev tries to be fast, but it's
		1770	still not a constant-time operation.
		1771
		1772	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1773
		1774	This is the easiest way, and involves using C<ev_timer_again> instead of
		1775	C<ev_timer_start>.
		1776
		1777	To implement this, configure an C<ev_timer> with a C<repeat> value
		1778	of C<60> and then call C<ev_timer_again> at start and each time you
		1779	successfully read or write some data. If you go into an idle state where
		1780	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1781	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1782
		1783	That means you can ignore both the C<ev_timer_start> function and the
		1784	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1785	member and C<ev_timer_again>.
		1786
		1787	At start:
		1788
		1789	ev_init (timer, callback);
		1790	timer->repeat = 60.;
		1791	ev_timer_again (loop, timer);
		1792
		1793	Each time there is some activity:
		1794
		1795	ev_timer_again (loop, timer);
		1796
		1797	It is even possible to change the time-out on the fly, regardless of
		1798	whether the watcher is active or not:
		1799
		1800	timer->repeat = 30.;
		1801	ev_timer_again (loop, timer);
		1802
		1803	This is slightly more efficient then stopping/starting the timer each time
		1804	you want to modify its timeout value, as libev does not have to completely
		1805	remove and re-insert the timer from/into its internal data structure.
		1806
		1807	It is, however, even simpler than the "obvious" way to do it.
		1808
		1809	=item 3. Let the timer time out, but then re-arm it as required.
		1810
		1811	This method is more tricky, but usually most efficient: Most timeouts are
		1812	relatively long compared to the intervals between other activity - in
		1813	our example, within 60 seconds, there are usually many I/O events with
		1814	associated activity resets.
		1815
		1816	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1817	but remember the time of last activity, and check for a real timeout only
		1818	within the callback:
		1819
		1820	ev_tstamp last_activity; // time of last activity
		1821
		1822	static void
		1823	callback (EV_P_ ev_timer *w, int revents)
		1824	{
		1825	ev_tstamp now = ev_now (EV_A);
		1826	ev_tstamp timeout = last_activity + 60.;
		1827
		1828	// if last_activity + 60. is older than now, we did time out
		1829	if (timeout < now)
		1830	{
		1831	// timeout occurred, take action
		1832	}
		1833	else
		1834	{
		1835	// callback was invoked, but there was some activity, re-arm
		1836	// the watcher to fire in last_activity + 60, which is
		1837	// guaranteed to be in the future, so "again" is positive:
		1838	w->repeat = timeout - now;
		1839	ev_timer_again (EV_A_ w);
		1840	}
		1841	}
		1842
		1843	To summarise the callback: first calculate the real timeout (defined
		1844	as "60 seconds after the last activity"), then check if that time has
		1845	been reached, which means something I<did>, in fact, time out. Otherwise
		1846	the callback was invoked too early (C<timeout> is in the future), so
		1847	re-schedule the timer to fire at that future time, to see if maybe we have
		1848	a timeout then.
		1849
		1850	Note how C<ev_timer_again> is used, taking advantage of the
		1851	C<ev_timer_again> optimisation when the timer is already running.
		1852
		1853	This scheme causes more callback invocations (about one every 60 seconds
		1854	minus half the average time between activity), but virtually no calls to
		1855	libev to change the timeout.
		1856
		1857	To start the timer, simply initialise the watcher and set C<last_activity>
		1858	to the current time (meaning we just have some activity :), then call the
		1859	callback, which will "do the right thing" and start the timer:
		1860
		1861	ev_init (timer, callback);
		1862	last_activity = ev_now (loop);
		1863	callback (loop, timer, EV_TIMER);
		1864
		1865	And when there is some activity, simply store the current time in
		1866	C<last_activity>, no libev calls at all:
		1867
		1868	last_activity = ev_now (loop);
		1869
		1870	This technique is slightly more complex, but in most cases where the
		1871	time-out is unlikely to be triggered, much more efficient.
		1872
		1873	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1874	callback :) - just change the timeout and invoke the callback, which will
		1875	fix things for you.
		1876
		1877	=item 4. Wee, just use a double-linked list for your timeouts.
		1878
		1879	If there is not one request, but many thousands (millions...), all
		1880	employing some kind of timeout with the same timeout value, then one can
		1881	do even better:
		1882
		1883	When starting the timeout, calculate the timeout value and put the timeout
		1884	at the I<end> of the list.
		1885
		1886	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1887	the list is expected to fire (for example, using the technique #3).
		1888
		1889	When there is some activity, remove the timer from the list, recalculate
		1890	the timeout, append it to the end of the list again, and make sure to
		1891	update the C<ev_timer> if it was taken from the beginning of the list.
		1892
		1893	This way, one can manage an unlimited number of timeouts in O(1) time for
		1894	starting, stopping and updating the timers, at the expense of a major
		1895	complication, and having to use a constant timeout. The constant timeout
		1896	ensures that the list stays sorted.
		1897
		1898	=back
		1899
		1900	So which method the best?
		1901
		1902	Method #2 is a simple no-brain-required solution that is adequate in most
		1903	situations. Method #3 requires a bit more thinking, but handles many cases
		1904	better, and isn't very complicated either. In most case, choosing either
		1905	one is fine, with #3 being better in typical situations.
		1906
		1907	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1908	rather complicated, but extremely efficient, something that really pays
		1909	off after the first million or so of active timers, i.e. it's usually
		1910	overkill :)
1240		1911
1241	=head3 The special problem of time updates	1912	=head3 The special problem of time updates
1242		1913
1243	Establishing the current time is a costly operation (it usually takes at	1914	Establishing the current time is a costly operation (it usually takes at
1244	least two system calls): EV therefore updates its idea of the current	1915	least two system calls): EV therefore updates its idea of the current
1245	time only before and after C<ev_loop> polls for new events, which causes	1916	time only before and after C<ev_run> collects new events, which causes a
1246	a growing difference between C<ev_now ()> and C<ev_time ()> when handling	1917	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1247	lots of events.	1918	lots of events in one iteration.
1248		1919
1249	The relative timeouts are calculated relative to the C<ev_now ()>	1920	The relative timeouts are calculated relative to the C<ev_now ()>
1250	time. This is usually the right thing as this timestamp refers to the time	1921	time. This is usually the right thing as this timestamp refers to the time
1251	of the event triggering whatever timeout you are modifying/starting. If	1922	of the event triggering whatever timeout you are modifying/starting. If
1252	you suspect event processing to be delayed and you I<need> to base the	1923	you suspect event processing to be delayed and you I<need> to base the
…		…
1256		1927
1257	If the event loop is suspended for a long time, you can also force an	1928	If the event loop is suspended for a long time, you can also force an
1258	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1929	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1259	()>.	1930	()>.
1260		1931
		1932	=head3 The special problems of suspended animation
		1933
		1934	When you leave the server world it is quite customary to hit machines that
		1935	can suspend/hibernate - what happens to the clocks during such a suspend?
		1936
		1937	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1938	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1939	to run until the system is suspended, but they will not advance while the
		1940	system is suspended. That means, on resume, it will be as if the program
		1941	was frozen for a few seconds, but the suspend time will not be counted
		1942	towards C<ev_timer> when a monotonic clock source is used. The real time
		1943	clock advanced as expected, but if it is used as sole clocksource, then a
		1944	long suspend would be detected as a time jump by libev, and timers would
		1945	be adjusted accordingly.
		1946
		1947	I would not be surprised to see different behaviour in different between
		1948	operating systems, OS versions or even different hardware.
		1949
		1950	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1951	time jump in the monotonic clocks and the realtime clock. If the program
		1952	is suspended for a very long time, and monotonic clock sources are in use,
		1953	then you can expect C<ev_timer>s to expire as the full suspension time
		1954	will be counted towards the timers. When no monotonic clock source is in
		1955	use, then libev will again assume a timejump and adjust accordingly.
		1956
		1957	It might be beneficial for this latter case to call C<ev_suspend>
		1958	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1959	deterministic behaviour in this case (you can do nothing against
		1960	C<SIGSTOP>).
		1961
1261	=head3 Watcher-Specific Functions and Data Members	1962	=head3 Watcher-Specific Functions and Data Members
1262		1963
1263	=over 4	1964	=over 4
1264		1965
1265	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1966	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1288	If the timer is started but non-repeating, stop it (as if it timed out).	1989	If the timer is started but non-repeating, stop it (as if it timed out).
1289		1990
1290	If the timer is repeating, either start it if necessary (with the	1991	If the timer is repeating, either start it if necessary (with the
1291	C<repeat> value), or reset the running timer to the C<repeat> value.	1992	C<repeat> value), or reset the running timer to the C<repeat> value.
1292		1993
1293	This sounds a bit complicated, but here is a useful and typical	1994	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1294	example: Imagine you have a TCP connection and you want a so-called idle	1995	usage example.
1295	timeout, that is, you want to be called when there have been, say, 60
1296	seconds of inactivity on the socket. The easiest way to do this is to
1297	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1298	C<ev_timer_again> each time you successfully read or write some data. If
1299	you go into an idle state where you do not expect data to travel on the
1300	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1301	automatically restart it if need be.
1302		1996
1303	That means you can ignore the C<after> value and C<ev_timer_start>	1997	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1304	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1305		1998
1306	ev_timer_init (timer, callback, 0., 5.);	1999	Returns the remaining time until a timer fires. If the timer is active,
1307	ev_timer_again (loop, timer);	2000	then this time is relative to the current event loop time, otherwise it's
1308	...	2001	the timeout value currently configured.
1309	timer->again = 17.;
1310	ev_timer_again (loop, timer);
1311	...
1312	timer->again = 10.;
1313	ev_timer_again (loop, timer);
1314		2002
1315	This is more slightly efficient then stopping/starting the timer each time	2003	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1316	you want to modify its timeout value.	2004	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2005	will return C<4>. When the timer expires and is restarted, it will return
		2006	roughly C<7> (likely slightly less as callback invocation takes some time,
		2007	too), and so on.
1317		2008
1318	=item ev_tstamp repeat [read-write]	2009	=item ev_tstamp repeat [read-write]
1319		2010
1320	The current C<repeat> value. Will be used each time the watcher times out	2011	The current C<repeat> value. Will be used each time the watcher times out
1321	or C<ev_timer_again> is called and determines the next timeout (if any),	2012	or C<ev_timer_again> is called, and determines the next timeout (if any),
1322	which is also when any modifications are taken into account.	2013	which is also when any modifications are taken into account.
1323		2014
1324	=back	2015	=back
1325		2016
1326	=head3 Examples	2017	=head3 Examples
1327		2018
1328	Example: Create a timer that fires after 60 seconds.	2019	Example: Create a timer that fires after 60 seconds.
1329		2020
1330	static void	2021	static void
1331	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2022	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1332	{	2023	{
1333	.. one minute over, w is actually stopped right here	2024	.. one minute over, w is actually stopped right here
1334	}	2025	}
1335		2026
1336	struct ev_timer mytimer;	2027	ev_timer mytimer;
1337	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2028	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1338	ev_timer_start (loop, &mytimer);	2029	ev_timer_start (loop, &mytimer);
1339		2030
1340	Example: Create a timeout timer that times out after 10 seconds of	2031	Example: Create a timeout timer that times out after 10 seconds of
1341	inactivity.	2032	inactivity.
1342		2033
1343	static void	2034	static void
1344	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2035	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1345	{	2036	{
1346	.. ten seconds without any activity	2037	.. ten seconds without any activity
1347	}	2038	}
1348		2039
1349	struct ev_timer mytimer;	2040	ev_timer mytimer;
1350	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2041	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1351	ev_timer_again (&mytimer); /* start timer */	2042	ev_timer_again (&mytimer); /* start timer */
1352	ev_loop (loop, 0);	2043	ev_run (loop, 0);
1353		2044
1354	// and in some piece of code that gets executed on any "activity":	2045	// and in some piece of code that gets executed on any "activity":
1355	// reset the timeout to start ticking again at 10 seconds	2046	// reset the timeout to start ticking again at 10 seconds
1356	ev_timer_again (&mytimer);	2047	ev_timer_again (&mytimer);
1357		2048
…		…
1359	=head2 C<ev_periodic> - to cron or not to cron?	2050	=head2 C<ev_periodic> - to cron or not to cron?
1360		2051
1361	Periodic watchers are also timers of a kind, but they are very versatile	2052	Periodic watchers are also timers of a kind, but they are very versatile
1362	(and unfortunately a bit complex).	2053	(and unfortunately a bit complex).
1363		2054
1364	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2055	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1365	but on wall clock time (absolute time). You can tell a periodic watcher	2056	relative time, the physical time that passes) but on wall clock time
1366	to trigger after some specific point in time. For example, if you tell a	2057	(absolute time, the thing you can read on your calender or clock). The
1367	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	2058	difference is that wall clock time can run faster or slower than real
1368	+ 10.>, that is, an absolute time not a delay) and then reset your system	2059	time, and time jumps are not uncommon (e.g. when you adjust your
1369	clock to January of the previous year, then it will take more than year	2060	wrist-watch).
1370	to trigger the event (unlike an C<ev_timer>, which would still trigger
1371	roughly 10 seconds later as it uses a relative timeout).
1372		2061
		2062	You can tell a periodic watcher to trigger after some specific point
		2063	in time: for example, if you tell a periodic watcher to trigger "in 10
		2064	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2065	not a delay) and then reset your system clock to January of the previous
		2066	year, then it will take a year or more to trigger the event (unlike an
		2067	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2068	it, as it uses a relative timeout).
		2069
1373	C<ev_periodic>s can also be used to implement vastly more complex timers,	2070	C<ev_periodic> watchers can also be used to implement vastly more complex
1374	such as triggering an event on each "midnight, local time", or other	2071	timers, such as triggering an event on each "midnight, local time", or
1375	complicated, rules.	2072	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2073	those cannot react to time jumps.
1376		2074
1377	As with timers, the callback is guaranteed to be invoked only when the	2075	As with timers, the callback is guaranteed to be invoked only when the
1378	time (C<at>) has passed, but if multiple periodic timers become ready	2076	point in time where it is supposed to trigger has passed. If multiple
1379	during the same loop iteration then order of execution is undefined.	2077	timers become ready during the same loop iteration then the ones with
		2078	earlier time-out values are invoked before ones with later time-out values
		2079	(but this is no longer true when a callback calls C<ev_run> recursively).
1380		2080
1381	=head3 Watcher-Specific Functions and Data Members	2081	=head3 Watcher-Specific Functions and Data Members
1382		2082
1383	=over 4	2083	=over 4
1384		2084
1385	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2085	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1386		2086
1387	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2087	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1388		2088
1389	Lots of arguments, lets sort it out... There are basically three modes of	2089	Lots of arguments, let's sort it out... There are basically three modes of
1390	operation, and we will explain them from simplest to complex:	2090	operation, and we will explain them from simplest to most complex:
1391		2091
1392	=over 4	2092	=over 4
1393		2093
1394	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2094	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1395		2095
1396	In this configuration the watcher triggers an event after the wall clock	2096	In this configuration the watcher triggers an event after the wall clock
1397	time C<at> has passed and doesn't repeat. It will not adjust when a time	2097	time C<offset> has passed. It will not repeat and will not adjust when a
1398	jump occurs, that is, if it is to be run at January 1st 2011 then it will	2098	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1399	run when the system time reaches or surpasses this time.	2099	will be stopped and invoked when the system clock reaches or surpasses
		2100	this point in time.
1400		2101
1401	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2102	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1402		2103
1403	In this mode the watcher will always be scheduled to time out at the next	2104	In this mode the watcher will always be scheduled to time out at the next
1404	C<at + N * interval> time (for some integer N, which can also be negative)	2105	C<offset + N * interval> time (for some integer N, which can also be
1405	and then repeat, regardless of any time jumps.	2106	negative) and then repeat, regardless of any time jumps. The C<offset>
		2107	argument is merely an offset into the C<interval> periods.
1406		2108
1407	This can be used to create timers that do not drift with respect to system	2109	This can be used to create timers that do not drift with respect to the
1408	time, for example, here is a C<ev_periodic> that triggers each hour, on	2110	system clock, for example, here is an C<ev_periodic> that triggers each
1409	the hour:	2111	hour, on the hour (with respect to UTC):
1410		2112
1411	ev_periodic_set (&periodic, 0., 3600., 0);	2113	ev_periodic_set (&periodic, 0., 3600., 0);
1412		2114
1413	This doesn't mean there will always be 3600 seconds in between triggers,	2115	This doesn't mean there will always be 3600 seconds in between triggers,
1414	but only that the callback will be called when the system time shows a	2116	but only that the callback will be called when the system time shows a
1415	full hour (UTC), or more correctly, when the system time is evenly divisible	2117	full hour (UTC), or more correctly, when the system time is evenly divisible
1416	by 3600.	2118	by 3600.
1417		2119
1418	Another way to think about it (for the mathematically inclined) is that	2120	Another way to think about it (for the mathematically inclined) is that
1419	C<ev_periodic> will try to run the callback in this mode at the next possible	2121	C<ev_periodic> will try to run the callback in this mode at the next possible
1420	time where C<time = at (mod interval)>, regardless of any time jumps.	2122	time where C<time = offset (mod interval)>, regardless of any time jumps.
1421		2123
1422	For numerical stability it is preferable that the C<at> value is near	2124	For numerical stability it is preferable that the C<offset> value is near
1423	C<ev_now ()> (the current time), but there is no range requirement for	2125	C<ev_now ()> (the current time), but there is no range requirement for
1424	this value, and in fact is often specified as zero.	2126	this value, and in fact is often specified as zero.
1425		2127
1426	Note also that there is an upper limit to how often a timer can fire (CPU	2128	Note also that there is an upper limit to how often a timer can fire (CPU
1427	speed for example), so if C<interval> is very small then timing stability	2129	speed for example), so if C<interval> is very small then timing stability
1428	will of course deteriorate. Libev itself tries to be exact to be about one	2130	will of course deteriorate. Libev itself tries to be exact to be about one
1429	millisecond (if the OS supports it and the machine is fast enough).	2131	millisecond (if the OS supports it and the machine is fast enough).
1430		2132
1431	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2133	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1432		2134
1433	In this mode the values for C<interval> and C<at> are both being	2135	In this mode the values for C<interval> and C<offset> are both being
1434	ignored. Instead, each time the periodic watcher gets scheduled, the	2136	ignored. Instead, each time the periodic watcher gets scheduled, the
1435	reschedule callback will be called with the watcher as first, and the	2137	reschedule callback will be called with the watcher as first, and the
1436	current time as second argument.	2138	current time as second argument.
1437		2139
1438	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2140	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1439	ever, or make ANY event loop modifications whatsoever>.	2141	or make ANY other event loop modifications whatsoever, unless explicitly
		2142	allowed by documentation here>.
1440		2143
1441	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2144	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1442	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2145	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1443	only event loop modification you are allowed to do).	2146	only event loop modification you are allowed to do).
1444		2147
1445	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2148	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1446	*w, ev_tstamp now)>, e.g.:	2149	*w, ev_tstamp now)>, e.g.:
1447		2150
		2151	static ev_tstamp
1448	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2152	my_rescheduler (ev_periodic *w, ev_tstamp now)
1449	{	2153	{
1450	return now + 60.;	2154	return now + 60.;
1451	}	2155	}
1452		2156
1453	It must return the next time to trigger, based on the passed time value	2157	It must return the next time to trigger, based on the passed time value
…		…
1473	a different time than the last time it was called (e.g. in a crond like	2177	a different time than the last time it was called (e.g. in a crond like
1474	program when the crontabs have changed).	2178	program when the crontabs have changed).
1475		2179
1476	=item ev_tstamp ev_periodic_at (ev_periodic *)	2180	=item ev_tstamp ev_periodic_at (ev_periodic *)
1477		2181
1478	When active, returns the absolute time that the watcher is supposed to	2182	When active, returns the absolute time that the watcher is supposed
1479	trigger next.	2183	to trigger next. This is not the same as the C<offset> argument to
		2184	C<ev_periodic_set>, but indeed works even in interval and manual
		2185	rescheduling modes.
1480		2186
1481	=item ev_tstamp offset [read-write]	2187	=item ev_tstamp offset [read-write]
1482		2188
1483	When repeating, this contains the offset value, otherwise this is the	2189	When repeating, this contains the offset value, otherwise this is the
1484	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2190	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2191	although libev might modify this value for better numerical stability).
1485		2192
1486	Can be modified any time, but changes only take effect when the periodic	2193	Can be modified any time, but changes only take effect when the periodic
1487	timer fires or C<ev_periodic_again> is being called.	2194	timer fires or C<ev_periodic_again> is being called.
1488		2195
1489	=item ev_tstamp interval [read-write]	2196	=item ev_tstamp interval [read-write]
1490		2197
1491	The current interval value. Can be modified any time, but changes only	2198	The current interval value. Can be modified any time, but changes only
1492	take effect when the periodic timer fires or C<ev_periodic_again> is being	2199	take effect when the periodic timer fires or C<ev_periodic_again> is being
1493	called.	2200	called.
1494		2201
1495	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2202	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1496		2203
1497	The current reschedule callback, or C<0>, if this functionality is	2204	The current reschedule callback, or C<0>, if this functionality is
1498	switched off. Can be changed any time, but changes only take effect when	2205	switched off. Can be changed any time, but changes only take effect when
1499	the periodic timer fires or C<ev_periodic_again> is being called.	2206	the periodic timer fires or C<ev_periodic_again> is being called.
1500		2207
1501	=back	2208	=back
1502		2209
1503	=head3 Examples	2210	=head3 Examples
1504		2211
1505	Example: Call a callback every hour, or, more precisely, whenever the	2212	Example: Call a callback every hour, or, more precisely, whenever the
1506	system clock is divisible by 3600. The callback invocation times have	2213	system time is divisible by 3600. The callback invocation times have
1507	potentially a lot of jitter, but good long-term stability.	2214	potentially a lot of jitter, but good long-term stability.
1508		2215
1509	static void	2216	static void
1510	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2217	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1511	{	2218	{
1512	... its now a full hour (UTC, or TAI or whatever your clock follows)	2219	... its now a full hour (UTC, or TAI or whatever your clock follows)
1513	}	2220	}
1514		2221
1515	struct ev_periodic hourly_tick;	2222	ev_periodic hourly_tick;
1516	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2223	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1517	ev_periodic_start (loop, &hourly_tick);	2224	ev_periodic_start (loop, &hourly_tick);
1518		2225
1519	Example: The same as above, but use a reschedule callback to do it:	2226	Example: The same as above, but use a reschedule callback to do it:
1520		2227
1521	#include <math.h>	2228	#include <math.h>
1522		2229
1523	static ev_tstamp	2230	static ev_tstamp
1524	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2231	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1525	{	2232	{
1526	return fmod (now, 3600.) + 3600.;	2233	return now + (3600. - fmod (now, 3600.));
1527	}	2234	}
1528		2235
1529	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2236	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1530		2237
1531	Example: Call a callback every hour, starting now:	2238	Example: Call a callback every hour, starting now:
1532		2239
1533	struct ev_periodic hourly_tick;	2240	ev_periodic hourly_tick;
1534	ev_periodic_init (&hourly_tick, clock_cb,	2241	ev_periodic_init (&hourly_tick, clock_cb,
1535	fmod (ev_now (loop), 3600.), 3600., 0);	2242	fmod (ev_now (loop), 3600.), 3600., 0);
1536	ev_periodic_start (loop, &hourly_tick);	2243	ev_periodic_start (loop, &hourly_tick);
1537		2244
1538		2245
…		…
1541	Signal watchers will trigger an event when the process receives a specific	2248	Signal watchers will trigger an event when the process receives a specific
1542	signal one or more times. Even though signals are very asynchronous, libev	2249	signal one or more times. Even though signals are very asynchronous, libev
1543	will try it's best to deliver signals synchronously, i.e. as part of the	2250	will try it's best to deliver signals synchronously, i.e. as part of the
1544	normal event processing, like any other event.	2251	normal event processing, like any other event.
1545		2252
		2253	If you want signals to be delivered truly asynchronously, just use
		2254	C<sigaction> as you would do without libev and forget about sharing
		2255	the signal. You can even use C<ev_async> from a signal handler to
		2256	synchronously wake up an event loop.
		2257
1546	You can configure as many watchers as you like per signal. Only when the	2258	You can configure as many watchers as you like for the same signal, but
		2259	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2260	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2261	C<SIGINT> in both the default loop and another loop at the same time. At
		2262	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2263
1547	first watcher gets started will libev actually register a signal watcher	2264	When the first watcher gets started will libev actually register something
1548	with the kernel (thus it coexists with your own signal handlers as long	2265	with the kernel (thus it coexists with your own signal handlers as long as
1549	as you don't register any with libev). Similarly, when the last signal	2266	you don't register any with libev for the same signal).
1550	watcher for a signal is stopped libev will reset the signal handler to
1551	SIG_DFL (regardless of what it was set to before).
1552		2267
1553	If possible and supported, libev will install its handlers with	2268	If possible and supported, libev will install its handlers with
1554	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2269	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1555	interrupted. If you have a problem with system calls getting interrupted by	2270	not be unduly interrupted. If you have a problem with system calls getting
1556	signals you can block all signals in an C<ev_check> watcher and unblock	2271	interrupted by signals you can block all signals in an C<ev_check> watcher
1557	them in an C<ev_prepare> watcher.	2272	and unblock them in an C<ev_prepare> watcher.
		2273
		2274	=head3 The special problem of inheritance over fork/execve/pthread_create
		2275
		2276	Both the signal mask (C<sigprocmask>) and the signal disposition
		2277	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2278	stopping it again), that is, libev might or might not block the signal,
		2279	and might or might not set or restore the installed signal handler.
		2280
		2281	While this does not matter for the signal disposition (libev never
		2282	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2283	C<execve>), this matters for the signal mask: many programs do not expect
		2284	certain signals to be blocked.
		2285
		2286	This means that before calling C<exec> (from the child) you should reset
		2287	the signal mask to whatever "default" you expect (all clear is a good
		2288	choice usually).
		2289
		2290	The simplest way to ensure that the signal mask is reset in the child is
		2291	to install a fork handler with C<pthread_atfork> that resets it. That will
		2292	catch fork calls done by libraries (such as the libc) as well.
		2293
		2294	In current versions of libev, the signal will not be blocked indefinitely
		2295	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2296	the window of opportunity for problems, it will not go away, as libev
		2297	I<has> to modify the signal mask, at least temporarily.
		2298
		2299	So I can't stress this enough: I<If you do not reset your signal mask when
		2300	you expect it to be empty, you have a race condition in your code>. This
		2301	is not a libev-specific thing, this is true for most event libraries.
1558		2302
1559	=head3 Watcher-Specific Functions and Data Members	2303	=head3 Watcher-Specific Functions and Data Members
1560		2304
1561	=over 4	2305	=over 4
1562		2306
…		…
1573		2317
1574	=back	2318	=back
1575		2319
1576	=head3 Examples	2320	=head3 Examples
1577		2321
1578	Example: Try to exit cleanly on SIGINT and SIGTERM.	2322	Example: Try to exit cleanly on SIGINT.
1579		2323
1580	static void	2324	static void
1581	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2325	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1582	{	2326	{
1583	ev_unloop (loop, EVUNLOOP_ALL);	2327	ev_break (loop, EVBREAK_ALL);
1584	}	2328	}
1585		2329
1586	struct ev_signal signal_watcher;	2330	ev_signal signal_watcher;
1587	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2331	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1588	ev_signal_start (loop, &sigint_cb);	2332	ev_signal_start (loop, &signal_watcher);
1589		2333
1590		2334
1591	=head2 C<ev_child> - watch out for process status changes	2335	=head2 C<ev_child> - watch out for process status changes
1592		2336
1593	Child watchers trigger when your process receives a SIGCHLD in response to	2337	Child watchers trigger when your process receives a SIGCHLD in response to
1594	some child status changes (most typically when a child of yours dies). It	2338	some child status changes (most typically when a child of yours dies or
1595	is permissible to install a child watcher I<after> the child has been	2339	exits). It is permissible to install a child watcher I<after> the child
1596	forked (which implies it might have already exited), as long as the event	2340	has been forked (which implies it might have already exited), as long
1597	loop isn't entered (or is continued from a watcher).	2341	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2342	forking and then immediately registering a watcher for the child is fine,
		2343	but forking and registering a watcher a few event loop iterations later or
		2344	in the next callback invocation is not.
1598		2345
1599	Only the default event loop is capable of handling signals, and therefore	2346	Only the default event loop is capable of handling signals, and therefore
1600	you can only register child watchers in the default event loop.	2347	you can only register child watchers in the default event loop.
1601		2348
		2349	Due to some design glitches inside libev, child watchers will always be
		2350	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2351	libev)
		2352
1602	=head3 Process Interaction	2353	=head3 Process Interaction
1603		2354
1604	Libev grabs C<SIGCHLD> as soon as the default event loop is	2355	Libev grabs C<SIGCHLD> as soon as the default event loop is
1605	initialised. This is necessary to guarantee proper behaviour even if	2356	initialised. This is necessary to guarantee proper behaviour even if the
1606	the first child watcher is started after the child exits. The occurrence	2357	first child watcher is started after the child exits. The occurrence
1607	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2358	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1608	synchronously as part of the event loop processing. Libev always reaps all	2359	synchronously as part of the event loop processing. Libev always reaps all
1609	children, even ones not watched.	2360	children, even ones not watched.
1610		2361
1611	=head3 Overriding the Built-In Processing	2362	=head3 Overriding the Built-In Processing
…		…
1621	=head3 Stopping the Child Watcher	2372	=head3 Stopping the Child Watcher
1622		2373
1623	Currently, the child watcher never gets stopped, even when the	2374	Currently, the child watcher never gets stopped, even when the
1624	child terminates, so normally one needs to stop the watcher in the	2375	child terminates, so normally one needs to stop the watcher in the
1625	callback. Future versions of libev might stop the watcher automatically	2376	callback. Future versions of libev might stop the watcher automatically
1626	when a child exit is detected.	2377	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2378	problem).
1627		2379
1628	=head3 Watcher-Specific Functions and Data Members	2380	=head3 Watcher-Specific Functions and Data Members
1629		2381
1630	=over 4	2382	=over 4
1631		2383
…		…
1663	its completion.	2415	its completion.
1664		2416
1665	ev_child cw;	2417	ev_child cw;
1666		2418
1667	static void	2419	static void
1668	child_cb (EV_P_ struct ev_child *w, int revents)	2420	child_cb (EV_P_ ev_child *w, int revents)
1669	{	2421	{
1670	ev_child_stop (EV_A_ w);	2422	ev_child_stop (EV_A_ w);
1671	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2423	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1672	}	2424	}
1673		2425
…		…
1688		2440
1689		2441
1690	=head2 C<ev_stat> - did the file attributes just change?	2442	=head2 C<ev_stat> - did the file attributes just change?
1691		2443
1692	This watches a file system path for attribute changes. That is, it calls	2444	This watches a file system path for attribute changes. That is, it calls
1693	C<stat> regularly (or when the OS says it changed) and sees if it changed	2445	C<stat> on that path in regular intervals (or when the OS says it changed)
1694	compared to the last time, invoking the callback if it did.	2446	and sees if it changed compared to the last time, invoking the callback if
		2447	it did.
1695		2448
1696	The path does not need to exist: changing from "path exists" to "path does	2449	The path does not need to exist: changing from "path exists" to "path does
1697	not exist" is a status change like any other. The condition "path does	2450	not exist" is a status change like any other. The condition "path does not
1698	not exist" is signified by the C<st_nlink> field being zero (which is	2451	exist" (or more correctly "path cannot be stat'ed") is signified by the
1699	otherwise always forced to be at least one) and all the other fields of	2452	C<st_nlink> field being zero (which is otherwise always forced to be at
1700	the stat buffer having unspecified contents.	2453	least one) and all the other fields of the stat buffer having unspecified
		2454	contents.
1701		2455
1702	The path I<should> be absolute and I<must not> end in a slash. If it is	2456	The path I<must not> end in a slash or contain special components such as
		2457	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1703	relative and your working directory changes, the behaviour is undefined.	2458	your working directory changes, then the behaviour is undefined.
1704		2459
1705	Since there is no standard to do this, the portable implementation simply	2460	Since there is no portable change notification interface available, the
1706	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2461	portable implementation simply calls C<stat(2)> regularly on the path
1707	can specify a recommended polling interval for this case. If you specify	2462	to see if it changed somehow. You can specify a recommended polling
1708	a polling interval of C<0> (highly recommended!) then a I<suitable,	2463	interval for this case. If you specify a polling interval of C<0> (highly
1709	unspecified default> value will be used (which you can expect to be around	2464	recommended!) then a I<suitable, unspecified default> value will be used
1710	five seconds, although this might change dynamically). Libev will also	2465	(which you can expect to be around five seconds, although this might
1711	impose a minimum interval which is currently around C<0.1>, but thats	2466	change dynamically). Libev will also impose a minimum interval which is
1712	usually overkill.	2467	currently around C<0.1>, but that's usually overkill.
1713		2468
1714	This watcher type is not meant for massive numbers of stat watchers,	2469	This watcher type is not meant for massive numbers of stat watchers,
1715	as even with OS-supported change notifications, this can be	2470	as even with OS-supported change notifications, this can be
1716	resource-intensive.	2471	resource-intensive.
1717		2472
1718	At the time of this writing, only the Linux inotify interface is	2473	At the time of this writing, the only OS-specific interface implemented
1719	implemented (implementing kqueue support is left as an exercise for the	2474	is the Linux inotify interface (implementing kqueue support is left as an
1720	reader, note, however, that the author sees no way of implementing ev_stat	2475	exercise for the reader. Note, however, that the author sees no way of
1721	semantics with kqueue). Inotify will be used to give hints only and should	2476	implementing C<ev_stat> semantics with kqueue, except as a hint).
1722	not change the semantics of C<ev_stat> watchers, which means that libev
1723	sometimes needs to fall back to regular polling again even with inotify,
1724	but changes are usually detected immediately, and if the file exists there
1725	will be no polling.
1726		2477
1727	=head3 ABI Issues (Largefile Support)	2478	=head3 ABI Issues (Largefile Support)
1728		2479
1729	Libev by default (unless the user overrides this) uses the default	2480	Libev by default (unless the user overrides this) uses the default
1730	compilation environment, which means that on systems with large file	2481	compilation environment, which means that on systems with large file
1731	support disabled by default, you get the 32 bit version of the stat	2482	support disabled by default, you get the 32 bit version of the stat
1732	structure. When using the library from programs that change the ABI to	2483	structure. When using the library from programs that change the ABI to
1733	use 64 bit file offsets the programs will fail. In that case you have to	2484	use 64 bit file offsets the programs will fail. In that case you have to
1734	compile libev with the same flags to get binary compatibility. This is	2485	compile libev with the same flags to get binary compatibility. This is
1735	obviously the case with any flags that change the ABI, but the problem is	2486	obviously the case with any flags that change the ABI, but the problem is
1736	most noticeably disabled with ev_stat and large file support.	2487	most noticeably displayed with ev_stat and large file support.
1737		2488
1738	The solution for this is to lobby your distribution maker to make large	2489	The solution for this is to lobby your distribution maker to make large
1739	file interfaces available by default (as e.g. FreeBSD does) and not	2490	file interfaces available by default (as e.g. FreeBSD does) and not
1740	optional. Libev cannot simply switch on large file support because it has	2491	optional. Libev cannot simply switch on large file support because it has
1741	to exchange stat structures with application programs compiled using the	2492	to exchange stat structures with application programs compiled using the
1742	default compilation environment.	2493	default compilation environment.
1743		2494
1744	=head3 Inotify	2495	=head3 Inotify and Kqueue
1745		2496
1746	When C<inotify (7)> support has been compiled into libev (generally only	2497	When C<inotify (7)> support has been compiled into libev and present at
1747	available on Linux) and present at runtime, it will be used to speed up	2498	runtime, it will be used to speed up change detection where possible. The
1748	change detection where possible. The inotify descriptor will be created lazily	2499	inotify descriptor will be created lazily when the first C<ev_stat>
1749	when the first C<ev_stat> watcher is being started.	2500	watcher is being started.
1750		2501
1751	Inotify presence does not change the semantics of C<ev_stat> watchers	2502	Inotify presence does not change the semantics of C<ev_stat> watchers
1752	except that changes might be detected earlier, and in some cases, to avoid	2503	except that changes might be detected earlier, and in some cases, to avoid
1753	making regular C<stat> calls. Even in the presence of inotify support	2504	making regular C<stat> calls. Even in the presence of inotify support
1754	there are many cases where libev has to resort to regular C<stat> polling.	2505	there are many cases where libev has to resort to regular C<stat> polling,
		2506	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2507	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2508	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2509	xfs are fully working) libev usually gets away without polling.
1755		2510
1756	(There is no support for kqueue, as apparently it cannot be used to	2511	There is no support for kqueue, as apparently it cannot be used to
1757	implement this functionality, due to the requirement of having a file	2512	implement this functionality, due to the requirement of having a file
1758	descriptor open on the object at all times).	2513	descriptor open on the object at all times, and detecting renames, unlinks
		2514	etc. is difficult.
		2515
		2516	=head3 C<stat ()> is a synchronous operation
		2517
		2518	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2519	the process. The exception are C<ev_stat> watchers - those call C<stat
		2520	()>, which is a synchronous operation.
		2521
		2522	For local paths, this usually doesn't matter: unless the system is very
		2523	busy or the intervals between stat's are large, a stat call will be fast,
		2524	as the path data is usually in memory already (except when starting the
		2525	watcher).
		2526
		2527	For networked file systems, calling C<stat ()> can block an indefinite
		2528	time due to network issues, and even under good conditions, a stat call
		2529	often takes multiple milliseconds.
		2530
		2531	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2532	paths, although this is fully supported by libev.
1759		2533
1760	=head3 The special problem of stat time resolution	2534	=head3 The special problem of stat time resolution
1761		2535
1762	The C<stat ()> system call only supports full-second resolution portably, and	2536	The C<stat ()> system call only supports full-second resolution portably,
1763	even on systems where the resolution is higher, many file systems still	2537	and even on systems where the resolution is higher, most file systems
1764	only support whole seconds.	2538	still only support whole seconds.
1765		2539
1766	That means that, if the time is the only thing that changes, you can	2540	That means that, if the time is the only thing that changes, you can
1767	easily miss updates: on the first update, C<ev_stat> detects a change and	2541	easily miss updates: on the first update, C<ev_stat> detects a change and
1768	calls your callback, which does something. When there is another update	2542	calls your callback, which does something. When there is another update
1769	within the same second, C<ev_stat> will be unable to detect it as the stat	2543	within the same second, C<ev_stat> will be unable to detect unless the
1770	data does not change.	2544	stat data does change in other ways (e.g. file size).
1771		2545
1772	The solution to this is to delay acting on a change for slightly more	2546	The solution to this is to delay acting on a change for slightly more
1773	than a second (or till slightly after the next full second boundary), using	2547	than a second (or till slightly after the next full second boundary), using
1774	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);	2548	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1775	ev_timer_again (loop, w)>).	2549	ev_timer_again (loop, w)>).
…		…
1795	C<path>. The C<interval> is a hint on how quickly a change is expected to	2569	C<path>. The C<interval> is a hint on how quickly a change is expected to
1796	be detected and should normally be specified as C<0> to let libev choose	2570	be detected and should normally be specified as C<0> to let libev choose
1797	a suitable value. The memory pointed to by C<path> must point to the same	2571	a suitable value. The memory pointed to by C<path> must point to the same
1798	path for as long as the watcher is active.	2572	path for as long as the watcher is active.
1799		2573
1800	The callback will receive C<EV_STAT> when a change was detected, relative	2574	The callback will receive an C<EV_STAT> event when a change was detected,
1801	to the attributes at the time the watcher was started (or the last change	2575	relative to the attributes at the time the watcher was started (or the
1802	was detected).	2576	last change was detected).
1803		2577
1804	=item ev_stat_stat (loop, ev_stat *)	2578	=item ev_stat_stat (loop, ev_stat *)
1805		2579
1806	Updates the stat buffer immediately with new values. If you change the	2580	Updates the stat buffer immediately with new values. If you change the
1807	watched path in your callback, you could call this function to avoid	2581	watched path in your callback, you could call this function to avoid
…		…
1890		2664
1891		2665
1892	=head2 C<ev_idle> - when you've got nothing better to do...	2666	=head2 C<ev_idle> - when you've got nothing better to do...
1893		2667
1894	Idle watchers trigger events when no other events of the same or higher	2668	Idle watchers trigger events when no other events of the same or higher
1895	priority are pending (prepare, check and other idle watchers do not	2669	priority are pending (prepare, check and other idle watchers do not count
1896	count).	2670	as receiving "events").
1897		2671
1898	That is, as long as your process is busy handling sockets or timeouts	2672	That is, as long as your process is busy handling sockets or timeouts
1899	(or even signals, imagine) of the same or higher priority it will not be	2673	(or even signals, imagine) of the same or higher priority it will not be
1900	triggered. But when your process is idle (or only lower-priority watchers	2674	triggered. But when your process is idle (or only lower-priority watchers
1901	are pending), the idle watchers are being called once per event loop	2675	are pending), the idle watchers are being called once per event loop
…		…
1912		2686
1913	=head3 Watcher-Specific Functions and Data Members	2687	=head3 Watcher-Specific Functions and Data Members
1914		2688
1915	=over 4	2689	=over 4
1916		2690
1917	=item ev_idle_init (ev_signal *, callback)	2691	=item ev_idle_init (ev_idle *, callback)
1918		2692
1919	Initialises and configures the idle watcher - it has no parameters of any	2693	Initialises and configures the idle watcher - it has no parameters of any
1920	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2694	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1921	believe me.	2695	believe me.
1922		2696
…		…
1926		2700
1927	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2701	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1928	callback, free it. Also, use no error checking, as usual.	2702	callback, free it. Also, use no error checking, as usual.
1929		2703
1930	static void	2704	static void
1931	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2705	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1932	{	2706	{
1933	free (w);	2707	free (w);
1934	// now do something you wanted to do when the program has	2708	// now do something you wanted to do when the program has
1935	// no longer anything immediate to do.	2709	// no longer anything immediate to do.
1936	}	2710	}
1937		2711
1938	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2712	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1939	ev_idle_init (idle_watcher, idle_cb);	2713	ev_idle_init (idle_watcher, idle_cb);
1940	ev_idle_start (loop, idle_cb);	2714	ev_idle_start (loop, idle_watcher);
1941		2715
1942		2716
1943	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2717	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1944		2718
1945	Prepare and check watchers are usually (but not always) used in tandem:	2719	Prepare and check watchers are usually (but not always) used in pairs:
1946	prepare watchers get invoked before the process blocks and check watchers	2720	prepare watchers get invoked before the process blocks and check watchers
1947	afterwards.	2721	afterwards.
1948		2722
1949	You I<must not> call C<ev_loop> or similar functions that enter	2723	You I<must not> call C<ev_run> or similar functions that enter
1950	the current event loop from either C<ev_prepare> or C<ev_check>	2724	the current event loop from either C<ev_prepare> or C<ev_check>
1951	watchers. Other loops than the current one are fine, however. The	2725	watchers. Other loops than the current one are fine, however. The
1952	rationale behind this is that you do not need to check for recursion in	2726	rationale behind this is that you do not need to check for recursion in
1953	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2727	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1954	C<ev_check> so if you have one watcher of each kind they will always be	2728	C<ev_check> so if you have one watcher of each kind they will always be
1955	called in pairs bracketing the blocking call.	2729	called in pairs bracketing the blocking call.
1956		2730
1957	Their main purpose is to integrate other event mechanisms into libev and	2731	Their main purpose is to integrate other event mechanisms into libev and
1958	their use is somewhat advanced. This could be used, for example, to track	2732	their use is somewhat advanced. They could be used, for example, to track
1959	variable changes, implement your own watchers, integrate net-snmp or a	2733	variable changes, implement your own watchers, integrate net-snmp or a
1960	coroutine library and lots more. They are also occasionally useful if	2734	coroutine library and lots more. They are also occasionally useful if
1961	you cache some data and want to flush it before blocking (for example,	2735	you cache some data and want to flush it before blocking (for example,
1962	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2736	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1963	watcher).	2737	watcher).
1964		2738
1965	This is done by examining in each prepare call which file descriptors need	2739	This is done by examining in each prepare call which file descriptors
1966	to be watched by the other library, registering C<ev_io> watchers for	2740	need to be watched by the other library, registering C<ev_io> watchers
1967	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2741	for them and starting an C<ev_timer> watcher for any timeouts (many
1968	provide just this functionality). Then, in the check watcher you check for	2742	libraries provide exactly this functionality). Then, in the check watcher,
1969	any events that occurred (by checking the pending status of all watchers	2743	you check for any events that occurred (by checking the pending status
1970	and stopping them) and call back into the library. The I/O and timer	2744	of all watchers and stopping them) and call back into the library. The
1971	callbacks will never actually be called (but must be valid nevertheless,	2745	I/O and timer callbacks will never actually be called (but must be valid
1972	because you never know, you know?).	2746	nevertheless, because you never know, you know?).
1973		2747
1974	As another example, the Perl Coro module uses these hooks to integrate	2748	As another example, the Perl Coro module uses these hooks to integrate
1975	coroutines into libev programs, by yielding to other active coroutines	2749	coroutines into libev programs, by yielding to other active coroutines
1976	during each prepare and only letting the process block if no coroutines	2750	during each prepare and only letting the process block if no coroutines
1977	are ready to run (it's actually more complicated: it only runs coroutines	2751	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1980	loop from blocking if lower-priority coroutines are active, thus mapping	2754	loop from blocking if lower-priority coroutines are active, thus mapping
1981	low-priority coroutines to idle/background tasks).	2755	low-priority coroutines to idle/background tasks).
1982		2756
1983	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2757	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1984	priority, to ensure that they are being run before any other watchers	2758	priority, to ensure that they are being run before any other watchers
		2759	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2760
1985	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2761	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1986	too) should not activate ("feed") events into libev. While libev fully	2762	activate ("feed") events into libev. While libev fully supports this, they
1987	supports this, they might get executed before other C<ev_check> watchers	2763	might get executed before other C<ev_check> watchers did their job. As
1988	did their job. As C<ev_check> watchers are often used to embed other	2764	C<ev_check> watchers are often used to embed other (non-libev) event
1989	(non-libev) event loops those other event loops might be in an unusable	2765	loops those other event loops might be in an unusable state until their
1990	state until their C<ev_check> watcher ran (always remind yourself to	2766	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1991	coexist peacefully with others).	2767	others).
1992		2768
1993	=head3 Watcher-Specific Functions and Data Members	2769	=head3 Watcher-Specific Functions and Data Members
1994		2770
1995	=over 4	2771	=over 4
1996		2772
…		…
1998		2774
1999	=item ev_check_init (ev_check *, callback)	2775	=item ev_check_init (ev_check *, callback)
2000		2776
2001	Initialises and configures the prepare or check watcher - they have no	2777	Initialises and configures the prepare or check watcher - they have no
2002	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2778	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
2003	macros, but using them is utterly, utterly and completely pointless.	2779	macros, but using them is utterly, utterly, utterly and completely
		2780	pointless.
2004		2781
2005	=back	2782	=back
2006		2783
2007	=head3 Examples	2784	=head3 Examples
2008		2785
…		…
2021		2798
2022	static ev_io iow [nfd];	2799	static ev_io iow [nfd];
2023	static ev_timer tw;	2800	static ev_timer tw;
2024		2801
2025	static void	2802	static void
2026	io_cb (ev_loop *loop, ev_io *w, int revents)	2803	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2027	{	2804	{
2028	}	2805	}
2029		2806
2030	// create io watchers for each fd and a timer before blocking	2807	// create io watchers for each fd and a timer before blocking
2031	static void	2808	static void
2032	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2809	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2033	{	2810	{
2034	int timeout = 3600000;	2811	int timeout = 3600000;
2035	struct pollfd fds [nfd];	2812	struct pollfd fds [nfd];
2036	// actual code will need to loop here and realloc etc.	2813	// actual code will need to loop here and realloc etc.
2037	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2814	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2038		2815
2039	/* the callback is illegal, but won't be called as we stop during check */	2816	/* the callback is illegal, but won't be called as we stop during check */
2040	ev_timer_init (&tw, 0, timeout * 1e-3);	2817	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2041	ev_timer_start (loop, &tw);	2818	ev_timer_start (loop, &tw);
2042		2819
2043	// create one ev_io per pollfd	2820	// create one ev_io per pollfd
2044	for (int i = 0; i < nfd; ++i)	2821	for (int i = 0; i < nfd; ++i)
2045	{	2822	{
…		…
2052	}	2829	}
2053	}	2830	}
2054		2831
2055	// stop all watchers after blocking	2832	// stop all watchers after blocking
2056	static void	2833	static void
2057	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2834	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2058	{	2835	{
2059	ev_timer_stop (loop, &tw);	2836	ev_timer_stop (loop, &tw);
2060		2837
2061	for (int i = 0; i < nfd; ++i)	2838	for (int i = 0; i < nfd; ++i)
2062	{	2839	{
…		…
2101	}	2878	}
2102		2879
2103	// do not ever call adns_afterpoll	2880	// do not ever call adns_afterpoll
2104		2881
2105	Method 4: Do not use a prepare or check watcher because the module you	2882	Method 4: Do not use a prepare or check watcher because the module you
2106	want to embed is too inflexible to support it. Instead, you can override	2883	want to embed is not flexible enough to support it. Instead, you can
2107	their poll function. The drawback with this solution is that the main	2884	override their poll function. The drawback with this solution is that the
2108	loop is now no longer controllable by EV. The C<Glib::EV> module does	2885	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2109	this.	2886	this approach, effectively embedding EV as a client into the horrible
		2887	libglib event loop.
2110		2888
2111	static gint	2889	static gint
2112	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2890	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2113	{	2891	{
2114	int got_events = 0;	2892	int got_events = 0;
…		…
2118		2896
2119	if (timeout >= 0)	2897	if (timeout >= 0)
2120	// create/start timer	2898	// create/start timer
2121		2899
2122	// poll	2900	// poll
2123	ev_loop (EV_A_ 0);	2901	ev_run (EV_A_ 0);
2124		2902
2125	// stop timer again	2903	// stop timer again
2126	if (timeout >= 0)	2904	if (timeout >= 0)
2127	ev_timer_stop (EV_A_ &to);	2905	ev_timer_stop (EV_A_ &to);
2128		2906
…		…
2145	prioritise I/O.	2923	prioritise I/O.
2146		2924
2147	As an example for a bug workaround, the kqueue backend might only support	2925	As an example for a bug workaround, the kqueue backend might only support
2148	sockets on some platform, so it is unusable as generic backend, but you	2926	sockets on some platform, so it is unusable as generic backend, but you
2149	still want to make use of it because you have many sockets and it scales	2927	still want to make use of it because you have many sockets and it scales
2150	so nicely. In this case, you would create a kqueue-based loop and embed it	2928	so nicely. In this case, you would create a kqueue-based loop and embed
2151	into your default loop (which might use e.g. poll). Overall operation will	2929	it into your default loop (which might use e.g. poll). Overall operation
2152	be a bit slower because first libev has to poll and then call kevent, but	2930	will be a bit slower because first libev has to call C<poll> and then
2153	at least you can use both at what they are best.	2931	C<kevent>, but at least you can use both mechanisms for what they are
		2932	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2154		2933
2155	As for prioritising I/O: rarely you have the case where some fds have	2934	As for prioritising I/O: under rare circumstances you have the case where
2156	to be watched and handled very quickly (with low latency), and even	2935	some fds have to be watched and handled very quickly (with low latency),
2157	priorities and idle watchers might have too much overhead. In this case	2936	and even priorities and idle watchers might have too much overhead. In
2158	you would put all the high priority stuff in one loop and all the rest in	2937	this case you would put all the high priority stuff in one loop and all
2159	a second one, and embed the second one in the first.	2938	the rest in a second one, and embed the second one in the first.
2160		2939
2161	As long as the watcher is active, the callback will be invoked every time	2940	As long as the watcher is active, the callback will be invoked every
2162	there might be events pending in the embedded loop. The callback must then	2941	time there might be events pending in the embedded loop. The callback
2163	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2942	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2164	their callbacks (you could also start an idle watcher to give the embedded	2943	sweep and invoke their callbacks (the callback doesn't need to invoke the
2165	loop strictly lower priority for example). You can also set the callback	2944	C<ev_embed_sweep> function directly, it could also start an idle watcher
2166	to C<0>, in which case the embed watcher will automatically execute the	2945	to give the embedded loop strictly lower priority for example).
2167	embedded loop sweep.
2168		2946
2169	As long as the watcher is started it will automatically handle events. The	2947	You can also set the callback to C<0>, in which case the embed watcher
2170	callback will be invoked whenever some events have been handled. You can	2948	will automatically execute the embedded loop sweep whenever necessary.
2171	set the callback to C<0> to avoid having to specify one if you are not
2172	interested in that.
2173		2949
2174	Also, there have not currently been made special provisions for forking:	2950	Fork detection will be handled transparently while the C<ev_embed> watcher
2175	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2951	is active, i.e., the embedded loop will automatically be forked when the
2176	but you will also have to stop and restart any C<ev_embed> watchers	2952	embedding loop forks. In other cases, the user is responsible for calling
2177	yourself.	2953	C<ev_loop_fork> on the embedded loop.
2178		2954
2179	Unfortunately, not all backends are embeddable, only the ones returned by	2955	Unfortunately, not all backends are embeddable: only the ones returned by
2180	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2956	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2181	portable one.	2957	portable one.
2182		2958
2183	So when you want to use this feature you will always have to be prepared	2959	So when you want to use this feature you will always have to be prepared
2184	that you cannot get an embeddable loop. The recommended way to get around	2960	that you cannot get an embeddable loop. The recommended way to get around
2185	this is to have a separate variables for your embeddable loop, try to	2961	this is to have a separate variables for your embeddable loop, try to
2186	create it, and if that fails, use the normal loop for everything.	2962	create it, and if that fails, use the normal loop for everything.
		2963
		2964	=head3 C<ev_embed> and fork
		2965
		2966	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2967	automatically be applied to the embedded loop as well, so no special
		2968	fork handling is required in that case. When the watcher is not running,
		2969	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2970	as applicable.
2187		2971
2188	=head3 Watcher-Specific Functions and Data Members	2972	=head3 Watcher-Specific Functions and Data Members
2189		2973
2190	=over 4	2974	=over 4
2191		2975
…		…
2200	if you do not want that, you need to temporarily stop the embed watcher).	2984	if you do not want that, you need to temporarily stop the embed watcher).
2201		2985
2202	=item ev_embed_sweep (loop, ev_embed *)	2986	=item ev_embed_sweep (loop, ev_embed *)
2203		2987
2204	Make a single, non-blocking sweep over the embedded loop. This works	2988	Make a single, non-blocking sweep over the embedded loop. This works
2205	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2989	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2206	appropriate way for embedded loops.	2990	appropriate way for embedded loops.
2207		2991
2208	=item struct ev_loop *other [read-only]	2992	=item struct ev_loop *other [read-only]
2209		2993
2210	The embedded event loop.	2994	The embedded event loop.
…		…
2219	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	3003	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2220	used).	3004	used).
2221		3005
2222	struct ev_loop *loop_hi = ev_default_init (0);	3006	struct ev_loop *loop_hi = ev_default_init (0);
2223	struct ev_loop *loop_lo = 0;	3007	struct ev_loop *loop_lo = 0;
2224	struct ev_embed embed;	3008	ev_embed embed;
2225		3009
2226	// see if there is a chance of getting one that works	3010	// see if there is a chance of getting one that works
2227	// (remember that a flags value of 0 means autodetection)	3011	// (remember that a flags value of 0 means autodetection)
2228	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3012	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2229	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3013	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2243	kqueue implementation). Store the kqueue/socket-only event loop in	3027	kqueue implementation). Store the kqueue/socket-only event loop in
2244	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3028	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2245		3029
2246	struct ev_loop *loop = ev_default_init (0);	3030	struct ev_loop *loop = ev_default_init (0);
2247	struct ev_loop *loop_socket = 0;	3031	struct ev_loop *loop_socket = 0;
2248	struct ev_embed embed;	3032	ev_embed embed;
2249		3033
2250	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3034	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2251	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3035	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2252	{	3036	{
2253	ev_embed_init (&embed, 0, loop_socket);	3037	ev_embed_init (&embed, 0, loop_socket);
…		…
2268	event loop blocks next and before C<ev_check> watchers are being called,	3052	event loop blocks next and before C<ev_check> watchers are being called,
2269	and only in the child after the fork. If whoever good citizen calling	3053	and only in the child after the fork. If whoever good citizen calling
2270	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3054	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2271	handlers will be invoked, too, of course.	3055	handlers will be invoked, too, of course.
2272		3056
		3057	=head3 The special problem of life after fork - how is it possible?
		3058
		3059	Most uses of C<fork()> consist of forking, then some simple calls to set
		3060	up/change the process environment, followed by a call to C<exec()>. This
		3061	sequence should be handled by libev without any problems.
		3062
		3063	This changes when the application actually wants to do event handling
		3064	in the child, or both parent in child, in effect "continuing" after the
		3065	fork.
		3066
		3067	The default mode of operation (for libev, with application help to detect
		3068	forks) is to duplicate all the state in the child, as would be expected
		3069	when I<either> the parent I<or> the child process continues.
		3070
		3071	When both processes want to continue using libev, then this is usually the
		3072	wrong result. In that case, usually one process (typically the parent) is
		3073	supposed to continue with all watchers in place as before, while the other
		3074	process typically wants to start fresh, i.e. without any active watchers.
		3075
		3076	The cleanest and most efficient way to achieve that with libev is to
		3077	simply create a new event loop, which of course will be "empty", and
		3078	use that for new watchers. This has the advantage of not touching more
		3079	memory than necessary, and thus avoiding the copy-on-write, and the
		3080	disadvantage of having to use multiple event loops (which do not support
		3081	signal watchers).
		3082
		3083	When this is not possible, or you want to use the default loop for
		3084	other reasons, then in the process that wants to start "fresh", call
		3085	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3086	Destroying the default loop will "orphan" (not stop) all registered
		3087	watchers, so you have to be careful not to execute code that modifies
		3088	those watchers. Note also that in that case, you have to re-register any
		3089	signal watchers.
		3090
2273	=head3 Watcher-Specific Functions and Data Members	3091	=head3 Watcher-Specific Functions and Data Members
2274		3092
2275	=over 4	3093	=over 4
2276		3094
2277	=item ev_fork_init (ev_signal *, callback)	3095	=item ev_fork_init (ev_signal *, callback)
…		…
2281	believe me.	3099	believe me.
2282		3100
2283	=back	3101	=back
2284		3102
2285		3103
2286	=head2 C<ev_async> - how to wake up another event loop	3104	=head2 C<ev_async> - how to wake up an event loop
2287		3105
2288	In general, you cannot use an C<ev_loop> from multiple threads or other	3106	In general, you cannot use an C<ev_run> from multiple threads or other
2289	asynchronous sources such as signal handlers (as opposed to multiple event	3107	asynchronous sources such as signal handlers (as opposed to multiple event
2290	loops - those are of course safe to use in different threads).	3108	loops - those are of course safe to use in different threads).
2291		3109
2292	Sometimes, however, you need to wake up another event loop you do not	3110	Sometimes, however, you need to wake up an event loop you do not control,
2293	control, for example because it belongs to another thread. This is what	3111	for example because it belongs to another thread. This is what C<ev_async>
2294	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3112	watchers do: as long as the C<ev_async> watcher is active, you can signal
2295	can signal it by calling C<ev_async_send>, which is thread- and signal	3113	it by calling C<ev_async_send>, which is thread- and signal safe.
2296	safe.
2297		3114
2298	This functionality is very similar to C<ev_signal> watchers, as signals,	3115	This functionality is very similar to C<ev_signal> watchers, as signals,
2299	too, are asynchronous in nature, and signals, too, will be compressed	3116	too, are asynchronous in nature, and signals, too, will be compressed
2300	(i.e. the number of callback invocations may be less than the number of	3117	(i.e. the number of callback invocations may be less than the number of
2301	C<ev_async_sent> calls).	3118	C<ev_async_sent> calls).
…		…
2306	=head3 Queueing	3123	=head3 Queueing
2307		3124
2308	C<ev_async> does not support queueing of data in any way. The reason	3125	C<ev_async> does not support queueing of data in any way. The reason
2309	is that the author does not know of a simple (or any) algorithm for a	3126	is that the author does not know of a simple (or any) algorithm for a
2310	multiple-writer-single-reader queue that works in all cases and doesn't	3127	multiple-writer-single-reader queue that works in all cases and doesn't
2311	need elaborate support such as pthreads.	3128	need elaborate support such as pthreads or unportable memory access
		3129	semantics.
2312		3130
2313	That means that if you want to queue data, you have to provide your own	3131	That means that if you want to queue data, you have to provide your own
2314	queue. But at least I can tell you would implement locking around your	3132	queue. But at least I can tell you how to implement locking around your
2315	queue:	3133	queue:
2316		3134
2317	=over 4	3135	=over 4
2318		3136
2319	=item queueing from a signal handler context	3137	=item queueing from a signal handler context
2320		3138
2321	To implement race-free queueing, you simply add to the queue in the signal	3139	To implement race-free queueing, you simply add to the queue in the signal
2322	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3140	handler but you block the signal handler in the watcher callback. Here is
2323	some fictitious SIGUSR1 handler:	3141	an example that does that for some fictitious SIGUSR1 handler:
2324		3142
2325	static ev_async mysig;	3143	static ev_async mysig;
2326		3144
2327	static void	3145	static void
2328	sigusr1_handler (void)	3146	sigusr1_handler (void)
…		…
2394	=over 4	3212	=over 4
2395		3213
2396	=item ev_async_init (ev_async *, callback)	3214	=item ev_async_init (ev_async *, callback)
2397		3215
2398	Initialises and configures the async watcher - it has no parameters of any	3216	Initialises and configures the async watcher - it has no parameters of any
2399	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3217	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2400	believe me.	3218	trust me.
2401		3219
2402	=item ev_async_send (loop, ev_async *)	3220	=item ev_async_send (loop, ev_async *)
2403		3221
2404	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3222	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2405	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3223	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2406	C<ev_feed_event>, this call is safe to do in other threads, signal or	3224	C<ev_feed_event>, this call is safe to do from other threads, signal or
2407	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3225	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2408	section below on what exactly this means).	3226	section below on what exactly this means).
2409		3227
		3228	Note that, as with other watchers in libev, multiple events might get
		3229	compressed into a single callback invocation (another way to look at this
		3230	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3231	reset when the event loop detects that).
		3232
2410	This call incurs the overhead of a system call only once per loop iteration,	3233	This call incurs the overhead of a system call only once per event loop
2411	so while the overhead might be noticeable, it doesn't apply to repeated	3234	iteration, so while the overhead might be noticeable, it doesn't apply to
2412	calls to C<ev_async_send>.	3235	repeated calls to C<ev_async_send> for the same event loop.
2413		3236
2414	=item bool = ev_async_pending (ev_async *)	3237	=item bool = ev_async_pending (ev_async *)
2415		3238
2416	Returns a non-zero value when C<ev_async_send> has been called on the	3239	Returns a non-zero value when C<ev_async_send> has been called on the
2417	watcher but the event has not yet been processed (or even noted) by the	3240	watcher but the event has not yet been processed (or even noted) by the
…		…
2420	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3243	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2421	the loop iterates next and checks for the watcher to have become active,	3244	the loop iterates next and checks for the watcher to have become active,
2422	it will reset the flag again. C<ev_async_pending> can be used to very	3245	it will reset the flag again. C<ev_async_pending> can be used to very
2423	quickly check whether invoking the loop might be a good idea.	3246	quickly check whether invoking the loop might be a good idea.
2424		3247
2425	Not that this does I<not> check whether the watcher itself is pending, only	3248	Not that this does I<not> check whether the watcher itself is pending,
2426	whether it has been requested to make this watcher pending.	3249	only whether it has been requested to make this watcher pending: there
		3250	is a time window between the event loop checking and resetting the async
		3251	notification, and the callback being invoked.
2427		3252
2428	=back	3253	=back
2429		3254
2430		3255
2431	=head1 OTHER FUNCTIONS	3256	=head1 OTHER FUNCTIONS
…		…
2435	=over 4	3260	=over 4
2436		3261
2437	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3262	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2438		3263
2439	This function combines a simple timer and an I/O watcher, calls your	3264	This function combines a simple timer and an I/O watcher, calls your
2440	callback on whichever event happens first and automatically stop both	3265	callback on whichever event happens first and automatically stops both
2441	watchers. This is useful if you want to wait for a single event on an fd	3266	watchers. This is useful if you want to wait for a single event on an fd
2442	or timeout without having to allocate/configure/start/stop/free one or	3267	or timeout without having to allocate/configure/start/stop/free one or
2443	more watchers yourself.	3268	more watchers yourself.
2444		3269
2445	If C<fd> is less than 0, then no I/O watcher will be started and events	3270	If C<fd> is less than 0, then no I/O watcher will be started and the
2446	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3271	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2447	C<events> set will be created and started.	3272	the given C<fd> and C<events> set will be created and started.
2448		3273
2449	If C<timeout> is less than 0, then no timeout watcher will be	3274	If C<timeout> is less than 0, then no timeout watcher will be
2450	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3275	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2451	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3276	repeat = 0) will be started. C<0> is a valid timeout.
2452	dubious value.
2453		3277
2454	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3278	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2455	passed an C<revents> set like normal event callbacks (a combination of	3279	passed an C<revents> set like normal event callbacks (a combination of
2456	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3280	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2457	value passed to C<ev_once>:	3281	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3282	a timeout and an io event at the same time - you probably should give io
		3283	events precedence.
		3284
		3285	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2458		3286
2459	static void stdin_ready (int revents, void *arg)	3287	static void stdin_ready (int revents, void *arg)
2460	{	3288	{
		3289	if (revents & EV_READ)
		3290	/* stdin might have data for us, joy! */;
2461	if (revents & EV_TIMEOUT)	3291	else if (revents & EV_TIMER)
2462	/* doh, nothing entered */;	3292	/* doh, nothing entered */;
2463	else if (revents & EV_READ)
2464	/* stdin might have data for us, joy! */;
2465	}	3293	}
2466		3294
2467	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3295	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2468		3296
2469	=item ev_feed_event (ev_loop *, watcher *, int revents)
2470
2471	Feeds the given event set into the event loop, as if the specified event
2472	had happened for the specified watcher (which must be a pointer to an
2473	initialised but not necessarily started event watcher).
2474
2475	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3297	=item ev_feed_fd_event (loop, int fd, int revents)
2476		3298
2477	Feed an event on the given fd, as if a file descriptor backend detected	3299	Feed an event on the given fd, as if a file descriptor backend detected
2478	the given events it.	3300	the given events it.
2479		3301
2480	=item ev_feed_signal_event (ev_loop *loop, int signum)	3302	=item ev_feed_signal_event (loop, int signum)
2481		3303
2482	Feed an event as if the given signal occurred (C<loop> must be the default	3304	Feed an event as if the given signal occurred (C<loop> must be the default
2483	loop!).	3305	loop!).
2484		3306
2485	=back	3307	=back
…		…
2565		3387
2566	=over 4	3388	=over 4
2567		3389
2568	=item ev::TYPE::TYPE ()	3390	=item ev::TYPE::TYPE ()
2569		3391
2570	=item ev::TYPE::TYPE (struct ev_loop *)	3392	=item ev::TYPE::TYPE (loop)
2571		3393
2572	=item ev::TYPE::~TYPE	3394	=item ev::TYPE::~TYPE
2573		3395
2574	The constructor (optionally) takes an event loop to associate the watcher	3396	The constructor (optionally) takes an event loop to associate the watcher
2575	with. If it is omitted, it will use C<EV_DEFAULT>.	3397	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2607		3429
2608	myclass obj;	3430	myclass obj;
2609	ev::io iow;	3431	ev::io iow;
2610	iow.set <myclass, &myclass::io_cb> (&obj);	3432	iow.set <myclass, &myclass::io_cb> (&obj);
2611		3433
		3434	=item w->set (object *)
		3435
		3436	This is a variation of a method callback - leaving out the method to call
		3437	will default the method to C<operator ()>, which makes it possible to use
		3438	functor objects without having to manually specify the C<operator ()> all
		3439	the time. Incidentally, you can then also leave out the template argument
		3440	list.
		3441
		3442	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3443	int revents)>.
		3444
		3445	See the method-C<set> above for more details.
		3446
		3447	Example: use a functor object as callback.
		3448
		3449	struct myfunctor
		3450	{
		3451	void operator() (ev::io &w, int revents)
		3452	{
		3453	...
		3454	}
		3455	}
		3456
		3457	myfunctor f;
		3458
		3459	ev::io w;
		3460	w.set (&f);
		3461
2612	=item w->set<function> (void *data = 0)	3462	=item w->set<function> (void *data = 0)
2613		3463
2614	Also sets a callback, but uses a static method or plain function as	3464	Also sets a callback, but uses a static method or plain function as
2615	callback. The optional C<data> argument will be stored in the watcher's	3465	callback. The optional C<data> argument will be stored in the watcher's
2616	C<data> member and is free for you to use.	3466	C<data> member and is free for you to use.
2617		3467
2618	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3468	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2619		3469
2620	See the method-C<set> above for more details.	3470	See the method-C<set> above for more details.
2621		3471
2622	Example:	3472	Example: Use a plain function as callback.
2623		3473
2624	static void io_cb (ev::io &w, int revents) { }	3474	static void io_cb (ev::io &w, int revents) { }
2625	iow.set <io_cb> ();	3475	iow.set <io_cb> ();
2626		3476
2627	=item w->set (struct ev_loop *)	3477	=item w->set (loop)
2628		3478
2629	Associates a different C<struct ev_loop> with this watcher. You can only	3479	Associates a different C<struct ev_loop> with this watcher. You can only
2630	do this when the watcher is inactive (and not pending either).	3480	do this when the watcher is inactive (and not pending either).
2631		3481
2632	=item w->set ([arguments])	3482	=item w->set ([arguments])
2633		3483
2634	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be	3484	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2635	called at least once. Unlike the C counterpart, an active watcher gets	3485	method or a suitable start method must be called at least once. Unlike the
2636	automatically stopped and restarted when reconfiguring it with this	3486	C counterpart, an active watcher gets automatically stopped and restarted
2637	method.	3487	when reconfiguring it with this method.
2638		3488
2639	=item w->start ()	3489	=item w->start ()
2640		3490
2641	Starts the watcher. Note that there is no C<loop> argument, as the	3491	Starts the watcher. Note that there is no C<loop> argument, as the
2642	constructor already stores the event loop.	3492	constructor already stores the event loop.
2643		3493
		3494	=item w->start ([arguments])
		3495
		3496	Instead of calling C<set> and C<start> methods separately, it is often
		3497	convenient to wrap them in one call. Uses the same type of arguments as
		3498	the configure C<set> method of the watcher.
		3499
2644	=item w->stop ()	3500	=item w->stop ()
2645		3501
2646	Stops the watcher if it is active. Again, no C<loop> argument.	3502	Stops the watcher if it is active. Again, no C<loop> argument.
2647		3503
2648	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3504	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2660		3516
2661	=back	3517	=back
2662		3518
2663	=back	3519	=back
2664		3520
2665	Example: Define a class with an IO and idle watcher, start one of them in	3521	Example: Define a class with two I/O and idle watchers, start the I/O
2666	the constructor.	3522	watchers in the constructor.
2667		3523
2668	class myclass	3524	class myclass
2669	{	3525	{
2670	ev::io io; void io_cb (ev::io &w, int revents);	3526	ev::io io ; void io_cb (ev::io &w, int revents);
		3527	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2671	ev:idle idle void idle_cb (ev::idle &w, int revents);	3528	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2672		3529
2673	myclass (int fd)	3530	myclass (int fd)
2674	{	3531	{
2675	io .set <myclass, &myclass::io_cb > (this);	3532	io .set <myclass, &myclass::io_cb > (this);
		3533	io2 .set <myclass, &myclass::io2_cb > (this);
2676	idle.set <myclass, &myclass::idle_cb> (this);	3534	idle.set <myclass, &myclass::idle_cb> (this);
2677		3535
2678	io.start (fd, ev::READ);	3536	io.set (fd, ev::WRITE); // configure the watcher
		3537	io.start (); // start it whenever convenient
		3538
		3539	io2.start (fd, ev::READ); // set + start in one call
2679	}	3540	}
2680	};	3541	};
2681		3542
2682		3543
2683	=head1 OTHER LANGUAGE BINDINGS	3544	=head1 OTHER LANGUAGE BINDINGS
…		…
2692	=item Perl	3553	=item Perl
2693		3554
2694	The EV module implements the full libev API and is actually used to test	3555	The EV module implements the full libev API and is actually used to test
2695	libev. EV is developed together with libev. Apart from the EV core module,	3556	libev. EV is developed together with libev. Apart from the EV core module,
2696	there are additional modules that implement libev-compatible interfaces	3557	there are additional modules that implement libev-compatible interfaces
2697	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3558	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2698	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3559	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3560	and C<EV::Glib>).
2699		3561
2700	It can be found and installed via CPAN, its homepage is at	3562	It can be found and installed via CPAN, its homepage is at
2701	L<http://software.schmorp.de/pkg/EV>.	3563	L<http://software.schmorp.de/pkg/EV>.
2702		3564
2703	=item Python	3565	=item Python
2704		3566
2705	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3567	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2706	seems to be quite complete and well-documented. Note, however, that the	3568	seems to be quite complete and well-documented.
2707	patch they require for libev is outright dangerous as it breaks the ABI
2708	for everybody else, and therefore, should never be applied in an installed
2709	libev (if python requires an incompatible ABI then it needs to embed
2710	libev).
2711		3569
2712	=item Ruby	3570	=item Ruby
2713		3571
2714	Tony Arcieri has written a ruby extension that offers access to a subset	3572	Tony Arcieri has written a ruby extension that offers access to a subset
2715	of the libev API and adds file handle abstractions, asynchronous DNS and	3573	of the libev API and adds file handle abstractions, asynchronous DNS and
2716	more on top of it. It can be found via gem servers. Its homepage is at	3574	more on top of it. It can be found via gem servers. Its homepage is at
2717	L<http://rev.rubyforge.org/>.	3575	L<http://rev.rubyforge.org/>.
2718		3576
		3577	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3578	makes rev work even on mingw.
		3579
		3580	=item Haskell
		3581
		3582	A haskell binding to libev is available at
		3583	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3584
2719	=item D	3585	=item D
2720		3586
2721	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3587	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2722	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3588	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3589
		3590	=item Ocaml
		3591
		3592	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3593	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3594
		3595	=item Lua
		3596
		3597	Brian Maher has written a partial interface to libev for lua (at the
		3598	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3599	L<http://github.com/brimworks/lua-ev>.
2723		3600
2724	=back	3601	=back
2725		3602
2726		3603
2727	=head1 MACRO MAGIC	3604	=head1 MACRO MAGIC
…		…
2741	loop argument"). The C<EV_A> form is used when this is the sole argument,	3618	loop argument"). The C<EV_A> form is used when this is the sole argument,
2742	C<EV_A_> is used when other arguments are following. Example:	3619	C<EV_A_> is used when other arguments are following. Example:
2743		3620
2744	ev_unref (EV_A);	3621	ev_unref (EV_A);
2745	ev_timer_add (EV_A_ watcher);	3622	ev_timer_add (EV_A_ watcher);
2746	ev_loop (EV_A_ 0);	3623	ev_run (EV_A_ 0);
2747		3624
2748	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3625	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2749	which is often provided by the following macro.	3626	which is often provided by the following macro.
2750		3627
2751	=item C<EV_P>, C<EV_P_>	3628	=item C<EV_P>, C<EV_P_>
…		…
2791	}	3668	}
2792		3669
2793	ev_check check;	3670	ev_check check;
2794	ev_check_init (&check, check_cb);	3671	ev_check_init (&check, check_cb);
2795	ev_check_start (EV_DEFAULT_ &check);	3672	ev_check_start (EV_DEFAULT_ &check);
2796	ev_loop (EV_DEFAULT_ 0);	3673	ev_run (EV_DEFAULT_ 0);
2797		3674
2798	=head1 EMBEDDING	3675	=head1 EMBEDDING
2799		3676
2800	Libev can (and often is) directly embedded into host	3677	Libev can (and often is) directly embedded into host
2801	applications. Examples of applications that embed it include the Deliantra	3678	applications. Examples of applications that embed it include the Deliantra
…		…
2828		3705
2829	#define EV_STANDALONE 1	3706	#define EV_STANDALONE 1
2830	#include "ev.h"	3707	#include "ev.h"
2831		3708
2832	Both header files and implementation files can be compiled with a C++	3709	Both header files and implementation files can be compiled with a C++
2833	compiler (at least, thats a stated goal, and breakage will be treated	3710	compiler (at least, that's a stated goal, and breakage will be treated
2834	as a bug).	3711	as a bug).
2835		3712
2836	You need the following files in your source tree, or in a directory	3713	You need the following files in your source tree, or in a directory
2837	in your include path (e.g. in libev/ when using -Ilibev):	3714	in your include path (e.g. in libev/ when using -Ilibev):
2838		3715
…		…
2881	libev.m4	3758	libev.m4
2882		3759
2883	=head2 PREPROCESSOR SYMBOLS/MACROS	3760	=head2 PREPROCESSOR SYMBOLS/MACROS
2884		3761
2885	Libev can be configured via a variety of preprocessor symbols you have to	3762	Libev can be configured via a variety of preprocessor symbols you have to
2886	define before including any of its files. The default in the absence of	3763	define before including (or compiling) any of its files. The default in
2887	autoconf is noted for every option.	3764	the absence of autoconf is documented for every option.
		3765
		3766	Symbols marked with "(h)" do not change the ABI, and can have different
		3767	values when compiling libev vs. including F<ev.h>, so it is permissible
		3768	to redefine them before including F<ev.h> without breaking compatibility
		3769	to a compiled library. All other symbols change the ABI, which means all
		3770	users of libev and the libev code itself must be compiled with compatible
		3771	settings.
2888		3772
2889	=over 4	3773	=over 4
2890		3774
		3775	=item EV_COMPAT3 (h)
		3776
		3777	Backwards compatibility is a major concern for libev. This is why this
		3778	release of libev comes with wrappers for the functions and symbols that
		3779	have been renamed between libev version 3 and 4.
		3780
		3781	You can disable these wrappers (to test compatibility with future
		3782	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3783	sources. This has the additional advantage that you can drop the C<struct>
		3784	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3785	typedef in that case.
		3786
		3787	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3788	and in some even more future version the compatibility code will be
		3789	removed completely.
		3790
2891	=item EV_STANDALONE	3791	=item EV_STANDALONE (h)
2892		3792
2893	Must always be C<1> if you do not use autoconf configuration, which	3793	Must always be C<1> if you do not use autoconf configuration, which
2894	keeps libev from including F<config.h>, and it also defines dummy	3794	keeps libev from including F<config.h>, and it also defines dummy
2895	implementations for some libevent functions (such as logging, which is not	3795	implementations for some libevent functions (such as logging, which is not
2896	supported). It will also not define any of the structs usually found in	3796	supported). It will also not define any of the structs usually found in
2897	F<event.h> that are not directly supported by the libev core alone.	3797	F<event.h> that are not directly supported by the libev core alone.
2898		3798
		3799	In standalone mode, libev will still try to automatically deduce the
		3800	configuration, but has to be more conservative.
		3801
2899	=item EV_USE_MONOTONIC	3802	=item EV_USE_MONOTONIC
2900		3803
2901	If defined to be C<1>, libev will try to detect the availability of the	3804	If defined to be C<1>, libev will try to detect the availability of the
2902	monotonic clock option at both compile time and runtime. Otherwise no use	3805	monotonic clock option at both compile time and runtime. Otherwise no
2903	of the monotonic clock option will be attempted. If you enable this, you	3806	use of the monotonic clock option will be attempted. If you enable this,
2904	usually have to link against librt or something similar. Enabling it when	3807	you usually have to link against librt or something similar. Enabling it
2905	the functionality isn't available is safe, though, although you have	3808	when the functionality isn't available is safe, though, although you have
2906	to make sure you link against any libraries where the C<clock_gettime>	3809	to make sure you link against any libraries where the C<clock_gettime>
2907	function is hiding in (often F<-lrt>).	3810	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2908		3811
2909	=item EV_USE_REALTIME	3812	=item EV_USE_REALTIME
2910		3813
2911	If defined to be C<1>, libev will try to detect the availability of the	3814	If defined to be C<1>, libev will try to detect the availability of the
2912	real-time clock option at compile time (and assume its availability at	3815	real-time clock option at compile time (and assume its availability
2913	runtime if successful). Otherwise no use of the real-time clock option will	3816	at runtime if successful). Otherwise no use of the real-time clock
2914	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3817	option will be attempted. This effectively replaces C<gettimeofday>
2915	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3818	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2916	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3819	correctness. See the note about libraries in the description of
		3820	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3821	C<EV_USE_CLOCK_SYSCALL>.
		3822
		3823	=item EV_USE_CLOCK_SYSCALL
		3824
		3825	If defined to be C<1>, libev will try to use a direct syscall instead
		3826	of calling the system-provided C<clock_gettime> function. This option
		3827	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3828	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3829	programs needlessly. Using a direct syscall is slightly slower (in
		3830	theory), because no optimised vdso implementation can be used, but avoids
		3831	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3832	higher, as it simplifies linking (no need for C<-lrt>).
2917		3833
2918	=item EV_USE_NANOSLEEP	3834	=item EV_USE_NANOSLEEP
2919		3835
2920	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3836	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2921	and will use it for delays. Otherwise it will use C<select ()>.	3837	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2937		3853
2938	=item EV_SELECT_USE_FD_SET	3854	=item EV_SELECT_USE_FD_SET
2939		3855
2940	If defined to C<1>, then the select backend will use the system C<fd_set>	3856	If defined to C<1>, then the select backend will use the system C<fd_set>
2941	structure. This is useful if libev doesn't compile due to a missing	3857	structure. This is useful if libev doesn't compile due to a missing
2942	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3858	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2943	exotic systems. This usually limits the range of file descriptors to some	3859	on exotic systems. This usually limits the range of file descriptors to
2944	low limit such as 1024 or might have other limitations (winsocket only	3860	some low limit such as 1024 or might have other limitations (winsocket
2945	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3861	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2946	influence the size of the C<fd_set> used.	3862	configures the maximum size of the C<fd_set>.
2947		3863
2948	=item EV_SELECT_IS_WINSOCKET	3864	=item EV_SELECT_IS_WINSOCKET
2949		3865
2950	When defined to C<1>, the select backend will assume that	3866	When defined to C<1>, the select backend will assume that
2951	select/socket/connect etc. don't understand file descriptors but	3867	select/socket/connect etc. don't understand file descriptors but
…		…
2953	be used is the winsock select). This means that it will call	3869	be used is the winsock select). This means that it will call
2954	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3870	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2955	it is assumed that all these functions actually work on fds, even	3871	it is assumed that all these functions actually work on fds, even
2956	on win32. Should not be defined on non-win32 platforms.	3872	on win32. Should not be defined on non-win32 platforms.
2957		3873
2958	=item EV_FD_TO_WIN32_HANDLE	3874	=item EV_FD_TO_WIN32_HANDLE(fd)
2959		3875
2960	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3876	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2961	file descriptors to socket handles. When not defining this symbol (the	3877	file descriptors to socket handles. When not defining this symbol (the
2962	default), then libev will call C<_get_osfhandle>, which is usually	3878	default), then libev will call C<_get_osfhandle>, which is usually
2963	correct. In some cases, programs use their own file descriptor management,	3879	correct. In some cases, programs use their own file descriptor management,
2964	in which case they can provide this function to map fds to socket handles.	3880	in which case they can provide this function to map fds to socket handles.
		3881
		3882	=item EV_WIN32_HANDLE_TO_FD(handle)
		3883
		3884	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3885	using the standard C<_open_osfhandle> function. For programs implementing
		3886	their own fd to handle mapping, overwriting this function makes it easier
		3887	to do so. This can be done by defining this macro to an appropriate value.
		3888
		3889	=item EV_WIN32_CLOSE_FD(fd)
		3890
		3891	If programs implement their own fd to handle mapping on win32, then this
		3892	macro can be used to override the C<close> function, useful to unregister
		3893	file descriptors again. Note that the replacement function has to close
		3894	the underlying OS handle.
2965		3895
2966	=item EV_USE_POLL	3896	=item EV_USE_POLL
2967		3897
2968	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3898	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2969	backend. Otherwise it will be enabled on non-win32 platforms. It	3899	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3016	as well as for signal and thread safety in C<ev_async> watchers.	3946	as well as for signal and thread safety in C<ev_async> watchers.
3017		3947
3018	In the absence of this define, libev will use C<sig_atomic_t volatile>	3948	In the absence of this define, libev will use C<sig_atomic_t volatile>
3019	(from F<signal.h>), which is usually good enough on most platforms.	3949	(from F<signal.h>), which is usually good enough on most platforms.
3020		3950
3021	=item EV_H	3951	=item EV_H (h)
3022		3952
3023	The name of the F<ev.h> header file used to include it. The default if	3953	The name of the F<ev.h> header file used to include it. The default if
3024	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	3954	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
3025	used to virtually rename the F<ev.h> header file in case of conflicts.	3955	used to virtually rename the F<ev.h> header file in case of conflicts.
3026		3956
3027	=item EV_CONFIG_H	3957	=item EV_CONFIG_H (h)
3028		3958
3029	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3959	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
3030	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3960	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
3031	C<EV_H>, above.	3961	C<EV_H>, above.
3032		3962
3033	=item EV_EVENT_H	3963	=item EV_EVENT_H (h)
3034		3964
3035	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3965	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
3036	of how the F<event.h> header can be found, the default is C<"event.h">.	3966	of how the F<event.h> header can be found, the default is C<"event.h">.
3037		3967
3038	=item EV_PROTOTYPES	3968	=item EV_PROTOTYPES (h)
3039		3969
3040	If defined to be C<0>, then F<ev.h> will not define any function	3970	If defined to be C<0>, then F<ev.h> will not define any function
3041	prototypes, but still define all the structs and other symbols. This is	3971	prototypes, but still define all the structs and other symbols. This is
3042	occasionally useful if you want to provide your own wrapper functions	3972	occasionally useful if you want to provide your own wrapper functions
3043	around libev functions.	3973	around libev functions.
…		…
3062	When doing priority-based operations, libev usually has to linearly search	3992	When doing priority-based operations, libev usually has to linearly search
3063	all the priorities, so having many of them (hundreds) uses a lot of space	3993	all the priorities, so having many of them (hundreds) uses a lot of space
3064	and time, so using the defaults of five priorities (-2 .. +2) is usually	3994	and time, so using the defaults of five priorities (-2 .. +2) is usually
3065	fine.	3995	fine.
3066		3996
3067	If your embedding application does not need any priorities, defining these both to	3997	If your embedding application does not need any priorities, defining these
3068	C<0> will save some memory and CPU.	3998	both to C<0> will save some memory and CPU.
3069		3999
3070	=item EV_PERIODIC_ENABLE	4000	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4001	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4002	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
3071		4003
3072	If undefined or defined to be C<1>, then periodic timers are supported. If	4004	If undefined or defined to be C<1> (and the platform supports it), then
3073	defined to be C<0>, then they are not. Disabling them saves a few kB of	4005	the respective watcher type is supported. If defined to be C<0>, then it
3074	code.	4006	is not. Disabling watcher types mainly saves code size.
3075		4007
3076	=item EV_IDLE_ENABLE	4008	=item EV_FEATURES
3077
3078	If undefined or defined to be C<1>, then idle watchers are supported. If
3079	defined to be C<0>, then they are not. Disabling them saves a few kB of
3080	code.
3081
3082	=item EV_EMBED_ENABLE
3083
3084	If undefined or defined to be C<1>, then embed watchers are supported. If
3085	defined to be C<0>, then they are not.
3086
3087	=item EV_STAT_ENABLE
3088
3089	If undefined or defined to be C<1>, then stat watchers are supported. If
3090	defined to be C<0>, then they are not.
3091
3092	=item EV_FORK_ENABLE
3093
3094	If undefined or defined to be C<1>, then fork watchers are supported. If
3095	defined to be C<0>, then they are not.
3096
3097	=item EV_ASYNC_ENABLE
3098
3099	If undefined or defined to be C<1>, then async watchers are supported. If
3100	defined to be C<0>, then they are not.
3101
3102	=item EV_MINIMAL
3103		4009
3104	If you need to shave off some kilobytes of code at the expense of some	4010	If you need to shave off some kilobytes of code at the expense of some
3105	speed, define this symbol to C<1>. Currently this is used to override some	4011	speed (but with the full API), you can define this symbol to request
3106	inlining decisions, saves roughly 30% code size on amd64. It also selects a	4012	certain subsets of functionality. The default is to enable all features
3107	much smaller 2-heap for timer management over the default 4-heap.	4013	that can be enabled on the platform.
		4014
		4015	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4016	with some broad features you want) and then selectively re-enable
		4017	additional parts you want, for example if you want everything minimal,
		4018	but multiple event loop support, async and child watchers and the poll
		4019	backend, use this:
		4020
		4021	#define EV_FEATURES 0
		4022	#define EV_MULTIPLICITY 1
		4023	#define EV_USE_POLL 1
		4024	#define EV_CHILD_ENABLE 1
		4025	#define EV_ASYNC_ENABLE 1
		4026
		4027	The actual value is a bitset, it can be a combination of the following
		4028	values:
		4029
		4030	=over 4
		4031
		4032	=item C<1> - faster/larger code
		4033
		4034	Use larger code to speed up some operations.
		4035
		4036	Currently this is used to override some inlining decisions (enlarging the
		4037	code size by roughly 30% on amd64).
		4038
		4039	When optimising for size, use of compiler flags such as C<-Os> with
		4040	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4041	assertions.
		4042
		4043	=item C<2> - faster/larger data structures
		4044
		4045	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4046	hash table sizes and so on. This will usually further increase code size
		4047	and can additionally have an effect on the size of data structures at
		4048	runtime.
		4049
		4050	=item C<4> - full API configuration
		4051
		4052	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4053	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4054
		4055	=item C<8> - full API
		4056
		4057	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4058	details on which parts of the API are still available without this
		4059	feature, and do not complain if this subset changes over time.
		4060
		4061	=item C<16> - enable all optional watcher types
		4062
		4063	Enables all optional watcher types. If you want to selectively enable
		4064	only some watcher types other than I/O and timers (e.g. prepare,
		4065	embed, async, child...) you can enable them manually by defining
		4066	C<EV_watchertype_ENABLE> to C<1> instead.
		4067
		4068	=item C<32> - enable all backends
		4069
		4070	This enables all backends - without this feature, you need to enable at
		4071	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4072
		4073	=item C<64> - enable OS-specific "helper" APIs
		4074
		4075	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4076	default.
		4077
		4078	=back
		4079
		4080	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4081	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4082	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4083	watchers, timers and monotonic clock support.
		4084
		4085	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4086	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4087	your program might be left out as well - a binary starting a timer and an
		4088	I/O watcher then might come out at only 5Kb.
		4089
		4090	=item EV_AVOID_STDIO
		4091
		4092	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4093	functions (printf, scanf, perror etc.). This will increase the code size
		4094	somewhat, but if your program doesn't otherwise depend on stdio and your
		4095	libc allows it, this avoids linking in the stdio library which is quite
		4096	big.
		4097
		4098	Note that error messages might become less precise when this option is
		4099	enabled.
		4100
		4101	=item EV_NSIG
		4102
		4103	The highest supported signal number, +1 (or, the number of
		4104	signals): Normally, libev tries to deduce the maximum number of signals
		4105	automatically, but sometimes this fails, in which case it can be
		4106	specified. Also, using a lower number than detected (C<32> should be
		4107	good for about any system in existence) can save some memory, as libev
		4108	statically allocates some 12-24 bytes per signal number.
3108		4109
3109	=item EV_PID_HASHSIZE	4110	=item EV_PID_HASHSIZE
3110		4111
3111	C<ev_child> watchers use a small hash table to distribute workload by	4112	C<ev_child> watchers use a small hash table to distribute workload by
3112	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4113	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
3113	than enough. If you need to manage thousands of children you might want to	4114	usually more than enough. If you need to manage thousands of children you
3114	increase this value (I<must> be a power of two).	4115	might want to increase this value (I<must> be a power of two).
3115		4116
3116	=item EV_INOTIFY_HASHSIZE	4117	=item EV_INOTIFY_HASHSIZE
3117		4118
3118	C<ev_stat> watchers use a small hash table to distribute workload by	4119	C<ev_stat> watchers use a small hash table to distribute workload by
3119	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4120	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
3120	usually more than enough. If you need to manage thousands of C<ev_stat>	4121	disabled), usually more than enough. If you need to manage thousands of
3121	watchers you might want to increase this value (I<must> be a power of	4122	C<ev_stat> watchers you might want to increase this value (I<must> be a
3122	two).	4123	power of two).
3123		4124
3124	=item EV_USE_4HEAP	4125	=item EV_USE_4HEAP
3125		4126
3126	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4127	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3127	timer and periodics heap, libev uses a 4-heap when this symbol is defined	4128	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3128	to C<1>. The 4-heap uses more complicated (longer) code but has	4129	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3129	noticeably faster performance with many (thousands) of watchers.	4130	faster performance with many (thousands) of watchers.
3130		4131
3131	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4132	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3132	(disabled).	4133	will be C<0>.
3133		4134
3134	=item EV_HEAP_CACHE_AT	4135	=item EV_HEAP_CACHE_AT
3135		4136
3136	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4137	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3137	timer and periodics heap, libev can cache the timestamp (I<at>) within	4138	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3138	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	4139	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3139	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	4140	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3140	but avoids random read accesses on heap changes. This improves performance	4141	but avoids random read accesses on heap changes. This improves performance
3141	noticeably with with many (hundreds) of watchers.	4142	noticeably with many (hundreds) of watchers.
3142		4143
3143	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4144	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3144	(disabled).	4145	will be C<0>.
3145		4146
3146	=item EV_VERIFY	4147	=item EV_VERIFY
3147		4148
3148	Controls how much internal verification (see C<ev_loop_verify ()>) will	4149	Controls how much internal verification (see C<ev_verify ()>) will
3149	be done: If set to C<0>, no internal verification code will be compiled	4150	be done: If set to C<0>, no internal verification code will be compiled
3150	in. If set to C<1>, then verification code will be compiled in, but not	4151	in. If set to C<1>, then verification code will be compiled in, but not
3151	called. If set to C<2>, then the internal verification code will be	4152	called. If set to C<2>, then the internal verification code will be
3152	called once per loop, which can slow down libev. If set to C<3>, then the	4153	called once per loop, which can slow down libev. If set to C<3>, then the
3153	verification code will be called very frequently, which will slow down	4154	verification code will be called very frequently, which will slow down
3154	libev considerably.	4155	libev considerably.
3155		4156
3156	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	4157	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3157	C<0.>	4158	will be C<0>.
3158		4159
3159	=item EV_COMMON	4160	=item EV_COMMON
3160		4161
3161	By default, all watchers have a C<void *data> member. By redefining	4162	By default, all watchers have a C<void *data> member. By redefining
3162	this macro to a something else you can include more and other types of	4163	this macro to something else you can include more and other types of
3163	members. You have to define it each time you include one of the files,	4164	members. You have to define it each time you include one of the files,
3164	though, and it must be identical each time.	4165	though, and it must be identical each time.
3165		4166
3166	For example, the perl EV module uses something like this:	4167	For example, the perl EV module uses something like this:
3167		4168
…		…
3179	and the way callbacks are invoked and set. Must expand to a struct member	4180	and the way callbacks are invoked and set. Must expand to a struct member
3180	definition and a statement, respectively. See the F<ev.h> header file for	4181	definition and a statement, respectively. See the F<ev.h> header file for
3181	their default definitions. One possible use for overriding these is to	4182	their default definitions. One possible use for overriding these is to
3182	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4183	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3183	method calls instead of plain function calls in C++.	4184	method calls instead of plain function calls in C++.
		4185
		4186	=back
3184		4187
3185	=head2 EXPORTED API SYMBOLS	4188	=head2 EXPORTED API SYMBOLS
3186		4189
3187	If you need to re-export the API (e.g. via a DLL) and you need a list of	4190	If you need to re-export the API (e.g. via a DLL) and you need a list of
3188	exported symbols, you can use the provided F<Symbol.*> files which list	4191	exported symbols, you can use the provided F<Symbol.*> files which list
…		…
3218	file.	4221	file.
3219		4222
3220	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4223	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3221	that everybody includes and which overrides some configure choices:	4224	that everybody includes and which overrides some configure choices:
3222		4225
3223	#define EV_MINIMAL 1	4226	#define EV_FEATURES 8
3224	#define EV_USE_POLL 0	4227	#define EV_USE_SELECT 1
3225	#define EV_MULTIPLICITY 0
3226	#define EV_PERIODIC_ENABLE 0	4228	#define EV_PREPARE_ENABLE 1
		4229	#define EV_IDLE_ENABLE 1
3227	#define EV_STAT_ENABLE 0	4230	#define EV_SIGNAL_ENABLE 1
3228	#define EV_FORK_ENABLE 0	4231	#define EV_CHILD_ENABLE 1
		4232	#define EV_USE_STDEXCEPT 0
3229	#define EV_CONFIG_H <config.h>	4233	#define EV_CONFIG_H <config.h>
3230	#define EV_MINPRI 0
3231	#define EV_MAXPRI 0
3232		4234
3233	#include "ev++.h"	4235	#include "ev++.h"
3234		4236
3235	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4237	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3236		4238
3237	#include "ev_cpp.h"	4239	#include "ev_cpp.h"
3238	#include "ev.c"	4240	#include "ev.c"
3239		4241
		4242	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3240		4243
3241	=head1 THREADS AND COROUTINES	4244	=head2 THREADS AND COROUTINES
3242		4245
3243	=head2 THREADS	4246	=head3 THREADS
3244		4247
3245	Libev itself is thread-safe (unless the opposite is specifically	4248	All libev functions are reentrant and thread-safe unless explicitly
3246	documented for a function), but it uses no locking itself. This means that	4249	documented otherwise, but libev implements no locking itself. This means
3247	you can use as many loops as you want in parallel, as long as only one	4250	that you can use as many loops as you want in parallel, as long as there
3248	thread ever calls into one libev function with the same loop parameter:	4251	are no concurrent calls into any libev function with the same loop
		4252	parameter (C<ev_default_*> calls have an implicit default loop parameter,
3249	libev guarentees that different event loops share no data structures that	4253	of course): libev guarantees that different event loops share no data
3250	need locking.	4254	structures that need any locking.
3251		4255
3252	Or to put it differently: calls with different loop parameters can be done	4256	Or to put it differently: calls with different loop parameters can be done
3253	concurrently from multiple threads, calls with the same loop parameter	4257	concurrently from multiple threads, calls with the same loop parameter
3254	must be done serially (but can be done from different threads, as long as	4258	must be done serially (but can be done from different threads, as long as
3255	only one thread ever is inside a call at any point in time, e.g. by using	4259	only one thread ever is inside a call at any point in time, e.g. by using
3256	a mutex per loop).	4260	a mutex per loop).
3257		4261
3258	Specifically to support threads (and signal handlers), libev implements	4262	Specifically to support threads (and signal handlers), libev implements
3259	so-called C<ev_async> watchers, which allow some limited form of	4263	so-called C<ev_async> watchers, which allow some limited form of
3260	concurrency on the same event loop.	4264	concurrency on the same event loop, namely waking it up "from the
		4265	outside".
3261		4266
3262	If you want to know which design (one loop, locking, or multiple loops	4267	If you want to know which design (one loop, locking, or multiple loops
3263	without or something else still) is best for your problem, then I cannot	4268	without or something else still) is best for your problem, then I cannot
3264	help you. I can give some generic advice however:	4269	help you, but here is some generic advice:
3265		4270
3266	=over 4	4271	=over 4
3267		4272
3268	=item * most applications have a main thread: use the default libev loop	4273	=item * most applications have a main thread: use the default libev loop
3269	in that thread, or create a separate thread running only the default loop.	4274	in that thread, or create a separate thread running only the default loop.
…		…
3293	default loop and triggering an C<ev_async> watcher from the default loop	4298	default loop and triggering an C<ev_async> watcher from the default loop
3294	watcher callback into the event loop interested in the signal.	4299	watcher callback into the event loop interested in the signal.
3295		4300
3296	=back	4301	=back
3297		4302
		4303	=head4 THREAD LOCKING EXAMPLE
		4304
		4305	Here is a fictitious example of how to run an event loop in a different
		4306	thread than where callbacks are being invoked and watchers are
		4307	created/added/removed.
		4308
		4309	For a real-world example, see the C<EV::Loop::Async> perl module,
		4310	which uses exactly this technique (which is suited for many high-level
		4311	languages).
		4312
		4313	The example uses a pthread mutex to protect the loop data, a condition
		4314	variable to wait for callback invocations, an async watcher to notify the
		4315	event loop thread and an unspecified mechanism to wake up the main thread.
		4316
		4317	First, you need to associate some data with the event loop:
		4318
		4319	typedef struct {
		4320	mutex_t lock; /* global loop lock */
		4321	ev_async async_w;
		4322	thread_t tid;
		4323	cond_t invoke_cv;
		4324	} userdata;
		4325
		4326	void prepare_loop (EV_P)
		4327	{
		4328	// for simplicity, we use a static userdata struct.
		4329	static userdata u;
		4330
		4331	ev_async_init (&u->async_w, async_cb);
		4332	ev_async_start (EV_A_ &u->async_w);
		4333
		4334	pthread_mutex_init (&u->lock, 0);
		4335	pthread_cond_init (&u->invoke_cv, 0);
		4336
		4337	// now associate this with the loop
		4338	ev_set_userdata (EV_A_ u);
		4339	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4340	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4341
		4342	// then create the thread running ev_loop
		4343	pthread_create (&u->tid, 0, l_run, EV_A);
		4344	}
		4345
		4346	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4347	solely to wake up the event loop so it takes notice of any new watchers
		4348	that might have been added:
		4349
		4350	static void
		4351	async_cb (EV_P_ ev_async *w, int revents)
		4352	{
		4353	// just used for the side effects
		4354	}
		4355
		4356	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4357	protecting the loop data, respectively.
		4358
		4359	static void
		4360	l_release (EV_P)
		4361	{
		4362	userdata *u = ev_userdata (EV_A);
		4363	pthread_mutex_unlock (&u->lock);
		4364	}
		4365
		4366	static void
		4367	l_acquire (EV_P)
		4368	{
		4369	userdata *u = ev_userdata (EV_A);
		4370	pthread_mutex_lock (&u->lock);
		4371	}
		4372
		4373	The event loop thread first acquires the mutex, and then jumps straight
		4374	into C<ev_run>:
		4375
		4376	void *
		4377	l_run (void *thr_arg)
		4378	{
		4379	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4380
		4381	l_acquire (EV_A);
		4382	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4383	ev_run (EV_A_ 0);
		4384	l_release (EV_A);
		4385
		4386	return 0;
		4387	}
		4388
		4389	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4390	signal the main thread via some unspecified mechanism (signals? pipe
		4391	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4392	have been called (in a while loop because a) spurious wakeups are possible
		4393	and b) skipping inter-thread-communication when there are no pending
		4394	watchers is very beneficial):
		4395
		4396	static void
		4397	l_invoke (EV_P)
		4398	{
		4399	userdata *u = ev_userdata (EV_A);
		4400
		4401	while (ev_pending_count (EV_A))
		4402	{
		4403	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4404	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4405	}
		4406	}
		4407
		4408	Now, whenever the main thread gets told to invoke pending watchers, it
		4409	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4410	thread to continue:
		4411
		4412	static void
		4413	real_invoke_pending (EV_P)
		4414	{
		4415	userdata *u = ev_userdata (EV_A);
		4416
		4417	pthread_mutex_lock (&u->lock);
		4418	ev_invoke_pending (EV_A);
		4419	pthread_cond_signal (&u->invoke_cv);
		4420	pthread_mutex_unlock (&u->lock);
		4421	}
		4422
		4423	Whenever you want to start/stop a watcher or do other modifications to an
		4424	event loop, you will now have to lock:
		4425
		4426	ev_timer timeout_watcher;
		4427	userdata *u = ev_userdata (EV_A);
		4428
		4429	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4430
		4431	pthread_mutex_lock (&u->lock);
		4432	ev_timer_start (EV_A_ &timeout_watcher);
		4433	ev_async_send (EV_A_ &u->async_w);
		4434	pthread_mutex_unlock (&u->lock);
		4435
		4436	Note that sending the C<ev_async> watcher is required because otherwise
		4437	an event loop currently blocking in the kernel will have no knowledge
		4438	about the newly added timer. By waking up the loop it will pick up any new
		4439	watchers in the next event loop iteration.
		4440
3298	=head2 COROUTINES	4441	=head3 COROUTINES
3299		4442
3300	Libev is much more accommodating to coroutines ("cooperative threads"):	4443	Libev is very accommodating to coroutines ("cooperative threads"):
3301	libev fully supports nesting calls to it's functions from different	4444	libev fully supports nesting calls to its functions from different
3302	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4445	coroutines (e.g. you can call C<ev_run> on the same loop from two
3303	different coroutines and switch freely between both coroutines running the	4446	different coroutines, and switch freely between both coroutines running
3304	loop, as long as you don't confuse yourself). The only exception is that	4447	the loop, as long as you don't confuse yourself). The only exception is
3305	you must not do this from C<ev_periodic> reschedule callbacks.	4448	that you must not do this from C<ev_periodic> reschedule callbacks.
3306		4449
3307	Care has been taken to ensure that libev does not keep local state inside	4450	Care has been taken to ensure that libev does not keep local state inside
3308	C<ev_loop>, and other calls do not usually allow coroutine switches.	4451	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4452	they do not call any callbacks.
3309		4453
		4454	=head2 COMPILER WARNINGS
3310		4455
3311	=head1 COMPLEXITIES	4456	Depending on your compiler and compiler settings, you might get no or a
		4457	lot of warnings when compiling libev code. Some people are apparently
		4458	scared by this.
3312		4459
3313	In this section the complexities of (many of) the algorithms used inside	4460	However, these are unavoidable for many reasons. For one, each compiler
3314	libev will be explained. For complexity discussions about backends see the	4461	has different warnings, and each user has different tastes regarding
3315	documentation for C<ev_default_init>.	4462	warning options. "Warn-free" code therefore cannot be a goal except when
		4463	targeting a specific compiler and compiler-version.
3316		4464
3317	All of the following are about amortised time: If an array needs to be	4465	Another reason is that some compiler warnings require elaborate
3318	extended, libev needs to realloc and move the whole array, but this	4466	workarounds, or other changes to the code that make it less clear and less
3319	happens asymptotically never with higher number of elements, so O(1) might	4467	maintainable.
3320	mean it might do a lengthy realloc operation in rare cases, but on average
3321	it is much faster and asymptotically approaches constant time.
3322		4468
3323	=over 4	4469	And of course, some compiler warnings are just plain stupid, or simply
		4470	wrong (because they don't actually warn about the condition their message
		4471	seems to warn about). For example, certain older gcc versions had some
		4472	warnings that resulted in an extreme number of false positives. These have
		4473	been fixed, but some people still insist on making code warn-free with
		4474	such buggy versions.
3324		4475
3325	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4476	While libev is written to generate as few warnings as possible,
		4477	"warn-free" code is not a goal, and it is recommended not to build libev
		4478	with any compiler warnings enabled unless you are prepared to cope with
		4479	them (e.g. by ignoring them). Remember that warnings are just that:
		4480	warnings, not errors, or proof of bugs.
3326		4481
3327	This means that, when you have a watcher that triggers in one hour and
3328	there are 100 watchers that would trigger before that then inserting will
3329	have to skip roughly seven (C<ld 100>) of these watchers.
3330		4482
3331	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4483	=head2 VALGRIND
3332		4484
3333	That means that changing a timer costs less than removing/adding them	4485	Valgrind has a special section here because it is a popular tool that is
3334	as only the relative motion in the event queue has to be paid for.	4486	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3335		4487
3336	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4488	If you think you found a bug (memory leak, uninitialised data access etc.)
		4489	in libev, then check twice: If valgrind reports something like:
3337		4490
3338	These just add the watcher into an array or at the head of a list.	4491	==2274== definitely lost: 0 bytes in 0 blocks.
		4492	==2274== possibly lost: 0 bytes in 0 blocks.
		4493	==2274== still reachable: 256 bytes in 1 blocks.
3339		4494
3340	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4495	Then there is no memory leak, just as memory accounted to global variables
		4496	is not a memleak - the memory is still being referenced, and didn't leak.
3341		4497
3342	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4498	Similarly, under some circumstances, valgrind might report kernel bugs
		4499	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4500	although an acceptable workaround has been found here), or it might be
		4501	confused.
3343		4502
3344	These watchers are stored in lists then need to be walked to find the	4503	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3345	correct watcher to remove. The lists are usually short (you don't usually	4504	make it into some kind of religion.
3346	have many watchers waiting for the same fd or signal).
3347		4505
3348	=item Finding the next timer in each loop iteration: O(1)	4506	If you are unsure about something, feel free to contact the mailing list
		4507	with the full valgrind report and an explanation on why you think this
		4508	is a bug in libev (best check the archives, too :). However, don't be
		4509	annoyed when you get a brisk "this is no bug" answer and take the chance
		4510	of learning how to interpret valgrind properly.
3349		4511
3350	By virtue of using a binary or 4-heap, the next timer is always found at a	4512	If you need, for some reason, empty reports from valgrind for your project
3351	fixed position in the storage array.	4513	I suggest using suppression lists.
3352		4514
3353	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3354		4515
3355	A change means an I/O watcher gets started or stopped, which requires	4516	=head1 PORTABILITY NOTES
3356	libev to recalculate its status (and possibly tell the kernel, depending
3357	on backend and whether C<ev_io_set> was used).
3358		4517
3359	=item Activating one watcher (putting it into the pending state): O(1)	4518	=head2 GNU/LINUX 32 BIT LIMITATIONS
3360		4519
3361	=item Priority handling: O(number_of_priorities)	4520	GNU/Linux is the only common platform that supports 64 bit file/large file
		4521	interfaces but I<disables> them by default.
3362		4522
3363	Priorities are implemented by allocating some space for each	4523	That means that libev compiled in the default environment doesn't support
3364	priority. When doing priority-based operations, libev usually has to	4524	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
3365	linearly search all the priorities, but starting/stopping and activating
3366	watchers becomes O(1) w.r.t. priority handling.
3367		4525
3368	=item Sending an ev_async: O(1)	4526	Unfortunately, many programs try to work around this GNU/Linux issue
		4527	by enabling the large file API, which makes them incompatible with the
		4528	standard libev compiled for their system.
3369		4529
3370	=item Processing ev_async_send: O(number_of_async_watchers)	4530	Likewise, libev cannot enable the large file API itself as this would
		4531	suddenly make it incompatible to the default compile time environment,
		4532	i.e. all programs not using special compile switches.
3371		4533
3372	=item Processing signals: O(max_signal_number)	4534	=head2 OS/X AND DARWIN BUGS
3373		4535
3374	Sending involves a system call I<iff> there were no other C<ev_async_send>	4536	The whole thing is a bug if you ask me - basically any system interface
3375	calls in the current loop iteration. Checking for async and signal events	4537	you touch is broken, whether it is locales, poll, kqueue or even the
3376	involves iterating over all running async watchers or all signal numbers.	4538	OpenGL drivers.
3377		4539
3378	=back	4540	=head3 C<kqueue> is buggy
3379		4541
		4542	The kqueue syscall is broken in all known versions - most versions support
		4543	only sockets, many support pipes.
3380		4544
		4545	Libev tries to work around this by not using C<kqueue> by default on this
		4546	rotten platform, but of course you can still ask for it when creating a
		4547	loop - embedding a socket-only kqueue loop into a select-based one is
		4548	probably going to work well.
		4549
		4550	=head3 C<poll> is buggy
		4551
		4552	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4553	implementation by something calling C<kqueue> internally around the 10.5.6
		4554	release, so now C<kqueue> I<and> C<poll> are broken.
		4555
		4556	Libev tries to work around this by not using C<poll> by default on
		4557	this rotten platform, but of course you can still ask for it when creating
		4558	a loop.
		4559
		4560	=head3 C<select> is buggy
		4561
		4562	All that's left is C<select>, and of course Apple found a way to fuck this
		4563	one up as well: On OS/X, C<select> actively limits the number of file
		4564	descriptors you can pass in to 1024 - your program suddenly crashes when
		4565	you use more.
		4566
		4567	There is an undocumented "workaround" for this - defining
		4568	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4569	work on OS/X.
		4570
		4571	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4572
		4573	=head3 C<errno> reentrancy
		4574
		4575	The default compile environment on Solaris is unfortunately so
		4576	thread-unsafe that you can't even use components/libraries compiled
		4577	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4578	defined by default. A valid, if stupid, implementation choice.
		4579
		4580	If you want to use libev in threaded environments you have to make sure
		4581	it's compiled with C<_REENTRANT> defined.
		4582
		4583	=head3 Event port backend
		4584
		4585	The scalable event interface for Solaris is called "event
		4586	ports". Unfortunately, this mechanism is very buggy in all major
		4587	releases. If you run into high CPU usage, your program freezes or you get
		4588	a large number of spurious wakeups, make sure you have all the relevant
		4589	and latest kernel patches applied. No, I don't know which ones, but there
		4590	are multiple ones to apply, and afterwards, event ports actually work
		4591	great.
		4592
		4593	If you can't get it to work, you can try running the program by setting
		4594	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4595	C<select> backends.
		4596
		4597	=head2 AIX POLL BUG
		4598
		4599	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4600	this by trying to avoid the poll backend altogether (i.e. it's not even
		4601	compiled in), which normally isn't a big problem as C<select> works fine
		4602	with large bitsets on AIX, and AIX is dead anyway.
		4603
3381	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	4604	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4605
		4606	=head3 General issues
3382		4607
3383	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4608	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3384	requires, and its I/O model is fundamentally incompatible with the POSIX	4609	requires, and its I/O model is fundamentally incompatible with the POSIX
3385	model. Libev still offers limited functionality on this platform in	4610	model. Libev still offers limited functionality on this platform in
3386	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4611	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3387	descriptors. This only applies when using Win32 natively, not when using	4612	descriptors. This only applies when using Win32 natively, not when using
3388	e.g. cygwin.	4613	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4614	as every compielr comes with a slightly differently broken/incompatible
		4615	environment.
3389		4616
3390	Lifting these limitations would basically require the full	4617	Lifting these limitations would basically require the full
3391	re-implementation of the I/O system. If you are into these kinds of	4618	re-implementation of the I/O system. If you are into this kind of thing,
3392	things, then note that glib does exactly that for you in a very portable	4619	then note that glib does exactly that for you in a very portable way (note
3393	way (note also that glib is the slowest event library known to man).	4620	also that glib is the slowest event library known to man).
3394		4621
3395	There is no supported compilation method available on windows except	4622	There is no supported compilation method available on windows except
3396	embedding it into other applications.	4623	embedding it into other applications.
		4624
		4625	Sensible signal handling is officially unsupported by Microsoft - libev
		4626	tries its best, but under most conditions, signals will simply not work.
3397		4627
3398	Not a libev limitation but worth mentioning: windows apparently doesn't	4628	Not a libev limitation but worth mentioning: windows apparently doesn't
3399	accept large writes: instead of resulting in a partial write, windows will	4629	accept large writes: instead of resulting in a partial write, windows will
3400	either accept everything or return C<ENOBUFS> if the buffer is too large,	4630	either accept everything or return C<ENOBUFS> if the buffer is too large,
3401	so make sure you only write small amounts into your sockets (less than a	4631	so make sure you only write small amounts into your sockets (less than a
3402	megabyte seems safe, but thsi apparently depends on the amount of memory	4632	megabyte seems safe, but this apparently depends on the amount of memory
3403	available).	4633	available).
3404		4634
3405	Due to the many, low, and arbitrary limits on the win32 platform and	4635	Due to the many, low, and arbitrary limits on the win32 platform and
3406	the abysmal performance of winsockets, using a large number of sockets	4636	the abysmal performance of winsockets, using a large number of sockets
3407	is not recommended (and not reasonable). If your program needs to use	4637	is not recommended (and not reasonable). If your program needs to use
3408	more than a hundred or so sockets, then likely it needs to use a totally	4638	more than a hundred or so sockets, then likely it needs to use a totally
3409	different implementation for windows, as libev offers the POSIX readiness	4639	different implementation for windows, as libev offers the POSIX readiness
3410	notification model, which cannot be implemented efficiently on windows	4640	notification model, which cannot be implemented efficiently on windows
3411	(Microsoft monopoly games).	4641	(due to Microsoft monopoly games).
3412		4642
3413	A typical way to use libev under windows is to embed it (see the embedding	4643	A typical way to use libev under windows is to embed it (see the embedding
3414	section for details) and use the following F<evwrap.h> header file instead	4644	section for details) and use the following F<evwrap.h> header file instead
3415	of F<ev.h>:	4645	of F<ev.h>:
3416		4646
…		…
3418	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	4648	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3419		4649
3420	#include "ev.h"	4650	#include "ev.h"
3421		4651
3422	And compile the following F<evwrap.c> file into your project (make sure	4652	And compile the following F<evwrap.c> file into your project (make sure
3423	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	4653	you do I<not> compile the F<ev.c> or any other embedded source files!):
3424		4654
3425	#include "evwrap.h"	4655	#include "evwrap.h"
3426	#include "ev.c"	4656	#include "ev.c"
3427		4657
3428	=over 4
3429
3430	=item The winsocket select function	4658	=head3 The winsocket C<select> function
3431		4659
3432	The winsocket C<select> function doesn't follow POSIX in that it	4660	The winsocket C<select> function doesn't follow POSIX in that it
3433	requires socket I<handles> and not socket I<file descriptors> (it is	4661	requires socket I<handles> and not socket I<file descriptors> (it is
3434	also extremely buggy). This makes select very inefficient, and also	4662	also extremely buggy). This makes select very inefficient, and also
3435	requires a mapping from file descriptors to socket handles (the Microsoft	4663	requires a mapping from file descriptors to socket handles (the Microsoft
…		…
3444	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4672	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3445		4673
3446	Note that winsockets handling of fd sets is O(n), so you can easily get a	4674	Note that winsockets handling of fd sets is O(n), so you can easily get a
3447	complexity in the O(n²) range when using win32.	4675	complexity in the O(n²) range when using win32.
3448		4676
3449	=item Limited number of file descriptors	4677	=head3 Limited number of file descriptors
3450		4678
3451	Windows has numerous arbitrary (and low) limits on things.	4679	Windows has numerous arbitrary (and low) limits on things.
3452		4680
3453	Early versions of winsocket's select only supported waiting for a maximum	4681	Early versions of winsocket's select only supported waiting for a maximum
3454	of C<64> handles (probably owning to the fact that all windows kernels	4682	of C<64> handles (probably owning to the fact that all windows kernels
3455	can only wait for C<64> things at the same time internally; Microsoft	4683	can only wait for C<64> things at the same time internally; Microsoft
3456	recommends spawning a chain of threads and wait for 63 handles and the	4684	recommends spawning a chain of threads and wait for 63 handles and the
3457	previous thread in each. Great).	4685	previous thread in each. Sounds great!).
3458		4686
3459	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4687	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3460	to some high number (e.g. C<2048>) before compiling the winsocket select	4688	to some high number (e.g. C<2048>) before compiling the winsocket select
3461	call (which might be in libev or elsewhere, for example, perl does its own	4689	call (which might be in libev or elsewhere, for example, perl and many
3462	select emulation on windows).	4690	other interpreters do their own select emulation on windows).
3463		4691
3464	Another limit is the number of file descriptors in the Microsoft runtime	4692	Another limit is the number of file descriptors in the Microsoft runtime
3465	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4693	libraries, which by default is C<64> (there must be a hidden I<64>
3466	or something like this inside Microsoft). You can increase this by calling	4694	fetish or something like this inside Microsoft). You can increase this
3467	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4695	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3468	arbitrary limit), but is broken in many versions of the Microsoft runtime	4696	(another arbitrary limit), but is broken in many versions of the Microsoft
3469	libraries.
3470
3471	This might get you to about C<512> or C<2048> sockets (depending on	4697	runtime libraries. This might get you to about C<512> or C<2048> sockets
3472	windows version and/or the phase of the moon). To get more, you need to	4698	(depending on windows version and/or the phase of the moon). To get more,
3473	wrap all I/O functions and provide your own fd management, but the cost of	4699	you need to wrap all I/O functions and provide your own fd management, but
3474	calling select (O(n²)) will likely make this unworkable.	4700	the cost of calling select (O(n²)) will likely make this unworkable.
3475		4701
3476	=back
3477
3478
3479	=head1 PORTABILITY REQUIREMENTS	4702	=head2 PORTABILITY REQUIREMENTS
3480		4703
3481	In addition to a working ISO-C implementation, libev relies on a few	4704	In addition to a working ISO-C implementation and of course the
3482	additional extensions:	4705	backend-specific APIs, libev relies on a few additional extensions:
3483		4706
3484	=over 4	4707	=over 4
3485		4708
3486	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	4709	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3487	calling conventions regardless of C<ev_watcher_type *>.	4710	calling conventions regardless of C<ev_watcher_type *>.
…		…
3493	calls them using an C<ev_watcher *> internally.	4716	calls them using an C<ev_watcher *> internally.
3494		4717
3495	=item C<sig_atomic_t volatile> must be thread-atomic as well	4718	=item C<sig_atomic_t volatile> must be thread-atomic as well
3496		4719
3497	The type C<sig_atomic_t volatile> (or whatever is defined as	4720	The type C<sig_atomic_t volatile> (or whatever is defined as
3498	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4721	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3499	threads. This is not part of the specification for C<sig_atomic_t>, but is	4722	threads. This is not part of the specification for C<sig_atomic_t>, but is
3500	believed to be sufficiently portable.	4723	believed to be sufficiently portable.
3501		4724
3502	=item C<sigprocmask> must work in a threaded environment	4725	=item C<sigprocmask> must work in a threaded environment
3503		4726
…		…
3512	except the initial one, and run the default loop in the initial thread as	4735	except the initial one, and run the default loop in the initial thread as
3513	well.	4736	well.
3514		4737
3515	=item C<long> must be large enough for common memory allocation sizes	4738	=item C<long> must be large enough for common memory allocation sizes
3516		4739
3517	To improve portability and simplify using libev, libev uses C<long>	4740	To improve portability and simplify its API, libev uses C<long> internally
3518	internally instead of C<size_t> when allocating its data structures. On	4741	instead of C<size_t> when allocating its data structures. On non-POSIX
3519	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	4742	systems (Microsoft...) this might be unexpectedly low, but is still at
3520	is still at least 31 bits everywhere, which is enough for hundreds of	4743	least 31 bits everywhere, which is enough for hundreds of millions of
3521	millions of watchers.	4744	watchers.
3522		4745
3523	=item C<double> must hold a time value in seconds with enough accuracy	4746	=item C<double> must hold a time value in seconds with enough accuracy
3524		4747
3525	The type C<double> is used to represent timestamps. It is required to	4748	The type C<double> is used to represent timestamps. It is required to
3526	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4749	have at least 51 bits of mantissa (and 9 bits of exponent), which is
3527	enough for at least into the year 4000. This requirement is fulfilled by	4750	good enough for at least into the year 4000 with millisecond accuracy
		4751	(the design goal for libev). This requirement is overfulfilled by
3528	implementations implementing IEEE 754 (basically all existing ones).	4752	implementations using IEEE 754, which is basically all existing ones. With
		4753	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
3529		4754
3530	=back	4755	=back
3531		4756
3532	If you know of other additional requirements drop me a note.	4757	If you know of other additional requirements drop me a note.
3533		4758
3534		4759
3535	=head1 COMPILER WARNINGS	4760	=head1 ALGORITHMIC COMPLEXITIES
3536		4761
3537	Depending on your compiler and compiler settings, you might get no or a	4762	In this section the complexities of (many of) the algorithms used inside
3538	lot of warnings when compiling libev code. Some people are apparently	4763	libev will be documented. For complexity discussions about backends see
3539	scared by this.	4764	the documentation for C<ev_default_init>.
3540		4765
3541	However, these are unavoidable for many reasons. For one, each compiler	4766	All of the following are about amortised time: If an array needs to be
3542	has different warnings, and each user has different tastes regarding	4767	extended, libev needs to realloc and move the whole array, but this
3543	warning options. "Warn-free" code therefore cannot be a goal except when	4768	happens asymptotically rarer with higher number of elements, so O(1) might
3544	targeting a specific compiler and compiler-version.	4769	mean that libev does a lengthy realloc operation in rare cases, but on
		4770	average it is much faster and asymptotically approaches constant time.
3545		4771
3546	Another reason is that some compiler warnings require elaborate	4772	=over 4
3547	workarounds, or other changes to the code that make it less clear and less
3548	maintainable.
3549		4773
3550	And of course, some compiler warnings are just plain stupid, or simply	4774	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3551	wrong (because they don't actually warn about the condition their message
3552	seems to warn about).
3553		4775
3554	While libev is written to generate as few warnings as possible,	4776	This means that, when you have a watcher that triggers in one hour and
3555	"warn-free" code is not a goal, and it is recommended not to build libev	4777	there are 100 watchers that would trigger before that, then inserting will
3556	with any compiler warnings enabled unless you are prepared to cope with	4778	have to skip roughly seven (C<ld 100>) of these watchers.
3557	them (e.g. by ignoring them). Remember that warnings are just that:
3558	warnings, not errors, or proof of bugs.
3559		4779
		4780	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3560		4781
3561	=head1 VALGRIND	4782	That means that changing a timer costs less than removing/adding them,
		4783	as only the relative motion in the event queue has to be paid for.
3562		4784
3563	Valgrind has a special section here because it is a popular tool that is	4785	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3564	highly useful, but valgrind reports are very hard to interpret.
3565		4786
3566	If you think you found a bug (memory leak, uninitialised data access etc.)	4787	These just add the watcher into an array or at the head of a list.
3567	in libev, then check twice: If valgrind reports something like:
3568		4788
3569	==2274== definitely lost: 0 bytes in 0 blocks.	4789	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3570	==2274== possibly lost: 0 bytes in 0 blocks.
3571	==2274== still reachable: 256 bytes in 1 blocks.
3572		4790
3573	Then there is no memory leak. Similarly, under some circumstances,	4791	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3574	valgrind might report kernel bugs as if it were a bug in libev, or it
3575	might be confused (it is a very good tool, but only a tool).
3576		4792
3577	If you are unsure about something, feel free to contact the mailing list	4793	These watchers are stored in lists, so they need to be walked to find the
3578	with the full valgrind report and an explanation on why you think this is	4794	correct watcher to remove. The lists are usually short (you don't usually
3579	a bug in libev. However, don't be annoyed when you get a brisk "this is	4795	have many watchers waiting for the same fd or signal: one is typical, two
3580	no bug" answer and take the chance of learning how to interpret valgrind	4796	is rare).
3581	properly.
3582		4797
3583	If you need, for some reason, empty reports from valgrind for your project	4798	=item Finding the next timer in each loop iteration: O(1)
3584	I suggest using suppression lists.
3585		4799
		4800	By virtue of using a binary or 4-heap, the next timer is always found at a
		4801	fixed position in the storage array.
		4802
		4803	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4804
		4805	A change means an I/O watcher gets started or stopped, which requires
		4806	libev to recalculate its status (and possibly tell the kernel, depending
		4807	on backend and whether C<ev_io_set> was used).
		4808
		4809	=item Activating one watcher (putting it into the pending state): O(1)
		4810
		4811	=item Priority handling: O(number_of_priorities)
		4812
		4813	Priorities are implemented by allocating some space for each
		4814	priority. When doing priority-based operations, libev usually has to
		4815	linearly search all the priorities, but starting/stopping and activating
		4816	watchers becomes O(1) with respect to priority handling.
		4817
		4818	=item Sending an ev_async: O(1)
		4819
		4820	=item Processing ev_async_send: O(number_of_async_watchers)
		4821
		4822	=item Processing signals: O(max_signal_number)
		4823
		4824	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4825	calls in the current loop iteration. Checking for async and signal events
		4826	involves iterating over all running async watchers or all signal numbers.
		4827
		4828	=back
		4829
		4830
		4831	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4832
		4833	The major version 4 introduced some minor incompatible changes to the API.
		4834
		4835	At the moment, the C<ev.h> header file tries to implement superficial
		4836	compatibility, so most programs should still compile. Those might be
		4837	removed in later versions of libev, so better update early than late.
		4838
		4839	=over 4
		4840
		4841	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		4842
		4843	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		4844
		4845	ev_loop_destroy (EV_DEFAULT);
		4846	ev_loop_fork (EV_DEFAULT);
		4847
		4848	=item function/symbol renames
		4849
		4850	A number of functions and symbols have been renamed:
		4851
		4852	ev_loop => ev_run
		4853	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		4854	EVLOOP_ONESHOT => EVRUN_ONCE
		4855
		4856	ev_unloop => ev_break
		4857	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		4858	EVUNLOOP_ONE => EVBREAK_ONE
		4859	EVUNLOOP_ALL => EVBREAK_ALL
		4860
		4861	EV_TIMEOUT => EV_TIMER
		4862
		4863	ev_loop_count => ev_iteration
		4864	ev_loop_depth => ev_depth
		4865	ev_loop_verify => ev_verify
		4866
		4867	Most functions working on C<struct ev_loop> objects don't have an
		4868	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		4869	associated constants have been renamed to not collide with the C<struct
		4870	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		4871	as all other watcher types. Note that C<ev_loop_fork> is still called
		4872	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		4873	typedef.
		4874
		4875	=item C<EV_COMPAT3> backwards compatibility mechanism
		4876
		4877	The backward compatibility mechanism can be controlled by
		4878	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		4879	section.
		4880
		4881	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4882
		4883	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4884	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4885	and work, but the library code will of course be larger.
		4886
		4887	=back
		4888
		4889
		4890	=head1 GLOSSARY
		4891
		4892	=over 4
		4893
		4894	=item active
		4895
		4896	A watcher is active as long as it has been started and not yet stopped.
		4897	See L<WATCHER STATES> for details.
		4898
		4899	=item application
		4900
		4901	In this document, an application is whatever is using libev.
		4902
		4903	=item backend
		4904
		4905	The part of the code dealing with the operating system interfaces.
		4906
		4907	=item callback
		4908
		4909	The address of a function that is called when some event has been
		4910	detected. Callbacks are being passed the event loop, the watcher that
		4911	received the event, and the actual event bitset.
		4912
		4913	=item callback/watcher invocation
		4914
		4915	The act of calling the callback associated with a watcher.
		4916
		4917	=item event
		4918
		4919	A change of state of some external event, such as data now being available
		4920	for reading on a file descriptor, time having passed or simply not having
		4921	any other events happening anymore.
		4922
		4923	In libev, events are represented as single bits (such as C<EV_READ> or
		4924	C<EV_TIMER>).
		4925
		4926	=item event library
		4927
		4928	A software package implementing an event model and loop.
		4929
		4930	=item event loop
		4931
		4932	An entity that handles and processes external events and converts them
		4933	into callback invocations.
		4934
		4935	=item event model
		4936
		4937	The model used to describe how an event loop handles and processes
		4938	watchers and events.
		4939
		4940	=item pending
		4941
		4942	A watcher is pending as soon as the corresponding event has been
		4943	detected. See L<WATCHER STATES> for details.
		4944
		4945	=item real time
		4946
		4947	The physical time that is observed. It is apparently strictly monotonic :)
		4948
		4949	=item wall-clock time
		4950
		4951	The time and date as shown on clocks. Unlike real time, it can actually
		4952	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4953	clock.
		4954
		4955	=item watcher
		4956
		4957	A data structure that describes interest in certain events. Watchers need
		4958	to be started (attached to an event loop) before they can receive events.
		4959
		4960	=back
3586		4961
3587	=head1 AUTHOR	4962	=head1 AUTHOR
3588		4963
3589	Marc Lehmann <libev@schmorp.de>.	4964	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3590		4965

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