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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
868	=item C<EV_FORK>	1112	=item C<EV_FORK>
869		1113
870	The event loop has been resumed in the child process after fork (see	1114	The event loop has been resumed in the child process after fork (see
871	C<ev_fork>).	1115	C<ev_fork>).
872		1116
		1117	=item C<EV_CLEANUP>
		1118
		1119	The event loop is abotu to be destroyed (see C<ev_cleanup>).
		1120
873	=item C<EV_ASYNC>	1121	=item C<EV_ASYNC>
874		1122
875	The given async watcher has been asynchronously notified (see C<ev_async>).	1123	The given async watcher has been asynchronously notified (see C<ev_async>).
		1124
		1125	=item C<EV_CUSTOM>
		1126
		1127	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1128	by libev users to signal watchers (e.g. via C<ev_feed_event>).
876		1129
877	=item C<EV_ERROR>	1130	=item C<EV_ERROR>
878		1131
879	An unspecified error has occurred, the watcher has been stopped. This might	1132	An unspecified error has occurred, the watcher has been stopped. This might
880	happen because the watcher could not be properly started because libev	1133	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	1134	ran out of memory, a file descriptor was found to be closed or any other
		1135	problem. Libev considers these application bugs.
		1136
882	problem. You best act on it by reporting the problem and somehow coping	1137	You best act on it by reporting the problem and somehow coping with the
883	with the watcher being stopped.	1138	watcher being stopped. Note that well-written programs should not receive
		1139	an error ever, so when your watcher receives it, this usually indicates a
		1140	bug in your program.
884		1141
885	Libev will usually signal a few "dummy" events together with an error,	1142	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	1143	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	1144	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	1145	the error from read() or write(). This will not work in multi-threaded
889	programs, though, so beware.	1146	programs, though, as the fd could already be closed and reused for another
		1147	thing, so beware.
890		1148
891	=back	1149	=back
892		1150
		1151	=head2 WATCHER STATES
		1152
		1153	There are various watcher states mentioned throughout this manual -
		1154	active, pending and so on. In this section these states and the rules to
		1155	transition between them will be described in more detail - and while these
		1156	rules might look complicated, they usually do "the right thing".
		1157
		1158	=over 4
		1159
		1160	=item initialiased
		1161
		1162	Before a watcher can be registered with the event looop it has to be
		1163	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1164	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1165
		1166	In this state it is simply some block of memory that is suitable for use
		1167	in an event loop. It can be moved around, freed, reused etc. at will.
		1168
		1169	=item started/running/active
		1170
		1171	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1172	property of the event loop, and is actively waiting for events. While in
		1173	this state it cannot be accessed (except in a few documented ways), moved,
		1174	freed or anything else - the only legal thing is to keep a pointer to it,
		1175	and call libev functions on it that are documented to work on active watchers.
		1176
		1177	=item pending
		1178
		1179	If a watcher is active and libev determines that an event it is interested
		1180	in has occurred (such as a timer expiring), it will become pending. It will
		1181	stay in this pending state until either it is stopped or its callback is
		1182	about to be invoked, so it is not normally pending inside the watcher
		1183	callback.
		1184
		1185	The watcher might or might not be active while it is pending (for example,
		1186	an expired non-repeating timer can be pending but no longer active). If it
		1187	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1188	but it is still property of the event loop at this time, so cannot be
		1189	moved, freed or reused. And if it is active the rules described in the
		1190	previous item still apply.
		1191
		1192	It is also possible to feed an event on a watcher that is not active (e.g.
		1193	via C<ev_feed_event>), in which case it becomes pending without being
		1194	active.
		1195
		1196	=item stopped
		1197
		1198	A watcher can be stopped implicitly by libev (in which case it might still
		1199	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1200	latter will clear any pending state the watcher might be in, regardless
		1201	of whether it was active or not, so stopping a watcher explicitly before
		1202	freeing it is often a good idea.
		1203
		1204	While stopped (and not pending) the watcher is essentially in the
		1205	initialised state, that is it can be reused, moved, modified in any way
		1206	you wish.
		1207
		1208	=back
		1209
893	=head2 GENERIC WATCHER FUNCTIONS	1210	=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		1211
898	=over 4	1212	=over 4
899		1213
900	=item C<ev_init> (ev_TYPE *watcher, callback)	1214	=item C<ev_init> (ev_TYPE *watcher, callback)
901		1215
…		…
907	which rolls both calls into one.	1221	which rolls both calls into one.
908		1222
909	You can reinitialise a watcher at any time as long as it has been stopped	1223	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.	1224	(or never started) and there are no pending events outstanding.
911		1225
912	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1226	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
913	int revents)>.	1227	int revents)>.
914		1228
		1229	Example: Initialise an C<ev_io> watcher in two steps.
		1230
		1231	ev_io w;
		1232	ev_init (&w, my_cb);
		1233	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1234
915	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1235	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
916		1236
917	This macro initialises the type-specific parts of a watcher. You need to	1237	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	1238	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	1239	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	1240	macro on a watcher that is active (it can be pending, however, which is a
921	difference to the C<ev_init> macro).	1241	difference to the C<ev_init> macro).
922		1242
923	Although some watcher types do not have type-specific arguments	1243	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.	1244	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
925		1245
		1246	See C<ev_init>, above, for an example.
		1247
926	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1248	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
927		1249
928	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1250	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	1251	calls into a single call. This is the most convenient method to initialise
930	a watcher. The same limitations apply, of course.	1252	a watcher. The same limitations apply, of course.
931		1253
		1254	Example: Initialise and set an C<ev_io> watcher in one step.
		1255
		1256	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1257
932	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1258	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
933		1259
934	Starts (activates) the given watcher. Only active watchers will receive	1260	Starts (activates) the given watcher. Only active watchers will receive
935	events. If the watcher is already active nothing will happen.	1261	events. If the watcher is already active nothing will happen.
936		1262
		1263	Example: Start the C<ev_io> watcher that is being abused as example in this
		1264	whole section.
		1265
		1266	ev_io_start (EV_DEFAULT_UC, &w);
		1267
937	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1268	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
938		1269
939	Stops the given watcher again (if active) and clears the pending	1270	Stops the given watcher if active, and clears the pending status (whether
		1271	the watcher was active or not).
		1272
940	status. It is possible that stopped watchers are pending (for example,	1273	It is possible that stopped watchers are pending - for example,
941	non-repeating timers are being stopped when they become pending), but	1274	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	1275	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	1276	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.	1277	therefore a good idea to always call its C<ev_TYPE_stop> function.
945		1278
946	=item bool ev_is_active (ev_TYPE *watcher)	1279	=item bool ev_is_active (ev_TYPE *watcher)
947		1280
948	Returns a true value iff the watcher is active (i.e. it has been started	1281	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	1282	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)	1298	=item ev_cb_set (ev_TYPE *watcher, callback)
966		1299
967	Change the callback. You can change the callback at virtually any time	1300	Change the callback. You can change the callback at virtually any time
968	(modulo threads).	1301	(modulo threads).
969		1302
970	=item ev_set_priority (ev_TYPE *watcher, priority)	1303	=item ev_set_priority (ev_TYPE *watcher, int priority)
971		1304
972	=item int ev_priority (ev_TYPE *watcher)	1305	=item int ev_priority (ev_TYPE *watcher)
973		1306
974	Set and query the priority of the watcher. The priority is a small	1307	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>	1308	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
976	(default: C<-2>). Pending watchers with higher priority will be invoked	1309	(default: C<-2>). Pending watchers with higher priority will be invoked
977	before watchers with lower priority, but priority will not keep watchers	1310	before watchers with lower priority, but priority will not keep watchers
978	from being executed (except for C<ev_idle> watchers).	1311	from being executed (except for C<ev_idle> watchers).
979		1312
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	1313	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.	1314	you need to look at C<ev_idle> watchers, which provide this functionality.
987		1315
988	You I<must not> change the priority of a watcher as long as it is active or	1316	You I<must not> change the priority of a watcher as long as it is active or
989	pending.	1317	pending.
990		1318
		1319	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1320	fine, as long as you do not mind that the priority value you query might
		1321	or might not have been clamped to the valid range.
		1322
991	The default priority used by watchers when no priority has been set is	1323	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 :).	1324	always C<0>, which is supposed to not be too high and not be too low :).
993		1325
994	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1326	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	1327	priorities.
996	or might not have been adjusted to be within valid range.
997		1328
998	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1329	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
999		1330
1000	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1331	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	1332	C<loop> nor C<revents> need to be valid as long as the watcher callback
1002	can deal with that fact.	1333	can deal with that fact, as both are simply passed through to the
		1334	callback.
1003		1335
1004	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1336	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1005		1337
1006	If the watcher is pending, this function returns clears its pending status	1338	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	1339	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>.	1340	watcher isn't pending it does nothing and returns C<0>.
1009		1341
		1342	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1343	callback to be invoked, which can be accomplished with this function.
		1344
		1345	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1346
		1347	Feeds the given event set into the event loop, as if the specified event
		1348	had happened for the specified watcher (which must be a pointer to an
		1349	initialised but not necessarily started event watcher). Obviously you must
		1350	not free the watcher as long as it has pending events.
		1351
		1352	Stopping the watcher, letting libev invoke it, or calling
		1353	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1354	not started in the first place.
		1355
		1356	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1357	functions that do not need a watcher.
		1358
1010	=back	1359	=back
1011		1360
1012		1361
1013	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1362	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1014		1363
1015	Each watcher has, by default, a member C<void *data> that you can change	1364	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	1365	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	1366	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	1367	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	1368	member, you can also "subclass" the watcher type and provide your own
1020	data:	1369	data:
1021		1370
1022	struct my_io	1371	struct my_io
1023	{	1372	{
1024	struct ev_io io;	1373	ev_io io;
1025	int otherfd;	1374	int otherfd;
1026	void *somedata;	1375	void *somedata;
1027	struct whatever *mostinteresting;	1376	struct whatever *mostinteresting;
1028	};	1377	};
1029		1378
…		…
1032	ev_io_init (&w.io, my_cb, fd, EV_READ);	1381	ev_io_init (&w.io, my_cb, fd, EV_READ);
1033		1382
1034	And since your callback will be called with a pointer to the watcher, you	1383	And since your callback will be called with a pointer to the watcher, you
1035	can cast it back to your own type:	1384	can cast it back to your own type:
1036		1385
1037	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1386	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1038	{	1387	{
1039	struct my_io *w = (struct my_io *)w_;	1388	struct my_io *w = (struct my_io *)w_;
1040	...	1389	...
1041	}	1390	}
1042		1391
…		…
1053	ev_timer t2;	1402	ev_timer t2;
1054	}	1403	}
1055		1404
1056	In this case getting the pointer to C<my_biggy> is a bit more	1405	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	1406	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	1407	in the C<data> member of the watcher (for woozies), or you need to use
1059	arithmetic using C<offsetof> inside your watchers:	1408	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1409	programmers):
1060		1410
1061	#include <stddef.h>	1411	#include <stddef.h>
1062		1412
1063	static void	1413	static void
1064	t1_cb (EV_P_ struct ev_timer *w, int revents)	1414	t1_cb (EV_P_ ev_timer *w, int revents)
1065	{	1415	{
1066	struct my_biggy big = (struct my_biggy *	1416	struct my_biggy big = (struct my_biggy *)
1067	(((char *)w) - offsetof (struct my_biggy, t1));	1417	(((char *)w) - offsetof (struct my_biggy, t1));
1068	}	1418	}
1069		1419
1070	static void	1420	static void
1071	t2_cb (EV_P_ struct ev_timer *w, int revents)	1421	t2_cb (EV_P_ ev_timer *w, int revents)
1072	{	1422	{
1073	struct my_biggy big = (struct my_biggy *	1423	struct my_biggy big = (struct my_biggy *)
1074	(((char *)w) - offsetof (struct my_biggy, t2));	1424	(((char *)w) - offsetof (struct my_biggy, t2));
1075	}	1425	}
		1426
		1427	=head2 WATCHER PRIORITY MODELS
		1428
		1429	Many event loops support I<watcher priorities>, which are usually small
		1430	integers that influence the ordering of event callback invocation
		1431	between watchers in some way, all else being equal.
		1432
		1433	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1434	description for the more technical details such as the actual priority
		1435	range.
		1436
		1437	There are two common ways how these these priorities are being interpreted
		1438	by event loops:
		1439
		1440	In the more common lock-out model, higher priorities "lock out" invocation
		1441	of lower priority watchers, which means as long as higher priority
		1442	watchers receive events, lower priority watchers are not being invoked.
		1443
		1444	The less common only-for-ordering model uses priorities solely to order
		1445	callback invocation within a single event loop iteration: Higher priority
		1446	watchers are invoked before lower priority ones, but they all get invoked
		1447	before polling for new events.
		1448
		1449	Libev uses the second (only-for-ordering) model for all its watchers
		1450	except for idle watchers (which use the lock-out model).
		1451
		1452	The rationale behind this is that implementing the lock-out model for
		1453	watchers is not well supported by most kernel interfaces, and most event
		1454	libraries will just poll for the same events again and again as long as
		1455	their callbacks have not been executed, which is very inefficient in the
		1456	common case of one high-priority watcher locking out a mass of lower
		1457	priority ones.
		1458
		1459	Static (ordering) priorities are most useful when you have two or more
		1460	watchers handling the same resource: a typical usage example is having an
		1461	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1462	timeouts. Under load, data might be received while the program handles
		1463	other jobs, but since timers normally get invoked first, the timeout
		1464	handler will be executed before checking for data. In that case, giving
		1465	the timer a lower priority than the I/O watcher ensures that I/O will be
		1466	handled first even under adverse conditions (which is usually, but not
		1467	always, what you want).
		1468
		1469	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1470	will only be executed when no same or higher priority watchers have
		1471	received events, they can be used to implement the "lock-out" model when
		1472	required.
		1473
		1474	For example, to emulate how many other event libraries handle priorities,
		1475	you can associate an C<ev_idle> watcher to each such watcher, and in
		1476	the normal watcher callback, you just start the idle watcher. The real
		1477	processing is done in the idle watcher callback. This causes libev to
		1478	continuously poll and process kernel event data for the watcher, but when
		1479	the lock-out case is known to be rare (which in turn is rare :), this is
		1480	workable.
		1481
		1482	Usually, however, the lock-out model implemented that way will perform
		1483	miserably under the type of load it was designed to handle. In that case,
		1484	it might be preferable to stop the real watcher before starting the
		1485	idle watcher, so the kernel will not have to process the event in case
		1486	the actual processing will be delayed for considerable time.
		1487
		1488	Here is an example of an I/O watcher that should run at a strictly lower
		1489	priority than the default, and which should only process data when no
		1490	other events are pending:
		1491
		1492	ev_idle idle; // actual processing watcher
		1493	ev_io io; // actual event watcher
		1494
		1495	static void
		1496	io_cb (EV_P_ ev_io *w, int revents)
		1497	{
		1498	// stop the I/O watcher, we received the event, but
		1499	// are not yet ready to handle it.
		1500	ev_io_stop (EV_A_ w);
		1501
		1502	// start the idle watcher to handle the actual event.
		1503	// it will not be executed as long as other watchers
		1504	// with the default priority are receiving events.
		1505	ev_idle_start (EV_A_ &idle);
		1506	}
		1507
		1508	static void
		1509	idle_cb (EV_P_ ev_idle *w, int revents)
		1510	{
		1511	// actual processing
		1512	read (STDIN_FILENO, ...);
		1513
		1514	// have to start the I/O watcher again, as
		1515	// we have handled the event
		1516	ev_io_start (EV_P_ &io);
		1517	}
		1518
		1519	// initialisation
		1520	ev_idle_init (&idle, idle_cb);
		1521	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1522	ev_io_start (EV_DEFAULT_ &io);
		1523
		1524	In the "real" world, it might also be beneficial to start a timer, so that
		1525	low-priority connections can not be locked out forever under load. This
		1526	enables your program to keep a lower latency for important connections
		1527	during short periods of high load, while not completely locking out less
		1528	important ones.
1076		1529
1077		1530
1078	=head1 WATCHER TYPES	1531	=head1 WATCHER TYPES
1079		1532
1080	This section describes each watcher in detail, but will not repeat	1533	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	1557	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	1558	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	1559	descriptors to non-blocking mode is also usually a good idea (but not
1107	required if you know what you are doing).	1560	required if you know what you are doing).
1108		1561
1109	If you must do this, then force the use of a known-to-be-good backend	1562	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	1563	known-to-be-good backend (at the time of this writing, this includes only
1111	C<EVBACKEND_POLL>).	1564	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1565	descriptors for which non-blocking operation makes no sense (such as
		1566	files) - libev doesn't guarantee any specific behaviour in that case.
1112		1567
1113	Another thing you have to watch out for is that it is quite easy to	1568	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	1569	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	1570	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	1571	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	1572	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	1573	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	1574	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.	1575	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1121		1576
1122	If you cannot run the fd in non-blocking mode (for example you should not	1577	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	1578	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	1579	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	1580	interface such as poll (fortunately in our Xlib example, Xlib already
1126	its own, so its quite safe to use).	1581	does this on its own, so its quite safe to use). Some people additionally
		1582	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1583	indefinitely.
		1584
		1585	But really, best use non-blocking mode.
1127		1586
1128	=head3 The special problem of disappearing file descriptors	1587	=head3 The special problem of disappearing file descriptors
1129		1588
1130	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1589	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,	1590	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	1591	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	1592	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	1593	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	1594	registered with libev, there is no efficient way to see that this is, in
1136	fact, a different file descriptor.	1595	fact, a different file descriptor.
1137		1596
…		…
1168	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1627	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1169	C<EVBACKEND_POLL>.	1628	C<EVBACKEND_POLL>.
1170		1629
1171	=head3 The special problem of SIGPIPE	1630	=head3 The special problem of SIGPIPE
1172		1631
1173	While not really specific to libev, it is easy to forget about SIGPIPE:	1632	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	1633	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	1634	sent a SIGPIPE, which, by default, aborts your program. For most programs
1176	this is sensible behaviour, for daemons, this is usually undesirable.	1635	this is sensible behaviour, for daemons, this is usually undesirable.
1177		1636
1178	So when you encounter spurious, unexplained daemon exits, make sure you	1637	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	1638	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).	1639	somewhere, as that would have given you a big clue).
1181		1640
		1641	=head3 The special problem of accept()ing when you can't
		1642
		1643	Many implementations of the POSIX C<accept> function (for example,
		1644	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1645	connection from the pending queue in all error cases.
		1646
		1647	For example, larger servers often run out of file descriptors (because
		1648	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1649	rejecting the connection, leading to libev signalling readiness on
		1650	the next iteration again (the connection still exists after all), and
		1651	typically causing the program to loop at 100% CPU usage.
		1652
		1653	Unfortunately, the set of errors that cause this issue differs between
		1654	operating systems, there is usually little the app can do to remedy the
		1655	situation, and no known thread-safe method of removing the connection to
		1656	cope with overload is known (to me).
		1657
		1658	One of the easiest ways to handle this situation is to just ignore it
		1659	- when the program encounters an overload, it will just loop until the
		1660	situation is over. While this is a form of busy waiting, no OS offers an
		1661	event-based way to handle this situation, so it's the best one can do.
		1662
		1663	A better way to handle the situation is to log any errors other than
		1664	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1665	messages, and continue as usual, which at least gives the user an idea of
		1666	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1667	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1668	usage.
		1669
		1670	If your program is single-threaded, then you could also keep a dummy file
		1671	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1672	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1673	close that fd, and create a new dummy fd. This will gracefully refuse
		1674	clients under typical overload conditions.
		1675
		1676	The last way to handle it is to simply log the error and C<exit>, as
		1677	is often done with C<malloc> failures, but this results in an easy
		1678	opportunity for a DoS attack.
1182		1679
1183	=head3 Watcher-Specific Functions	1680	=head3 Watcher-Specific Functions
1184		1681
1185	=over 4	1682	=over 4
1186		1683
1187	=item ev_io_init (ev_io *, callback, int fd, int events)	1684	=item ev_io_init (ev_io *, callback, int fd, int events)
1188		1685
1189	=item ev_io_set (ev_io *, int fd, int events)	1686	=item ev_io_set (ev_io *, int fd, int events)
1190		1687
1191	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1688	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	1689	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.	1690	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1194		1691
1195	=item int fd [read-only]	1692	=item int fd [read-only]
1196		1693
1197	The file descriptor being watched.	1694	The file descriptor being watched.
1198		1695
…		…
1207	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1704	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	1705	readable, but only once. Since it is likely line-buffered, you could
1209	attempt to read a whole line in the callback.	1706	attempt to read a whole line in the callback.
1210		1707
1211	static void	1708	static void
1212	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1709	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1213	{	1710	{
1214	ev_io_stop (loop, w);	1711	ev_io_stop (loop, w);
1215	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1712	.. read from stdin here (or from w->fd) and handle any I/O errors
1216	}	1713	}
1217		1714
1218	...	1715	...
1219	struct ev_loop *loop = ev_default_init (0);	1716	struct ev_loop *loop = ev_default_init (0);
1220	struct ev_io stdin_readable;	1717	ev_io stdin_readable;
1221	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1718	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1222	ev_io_start (loop, &stdin_readable);	1719	ev_io_start (loop, &stdin_readable);
1223	ev_loop (loop, 0);	1720	ev_run (loop, 0);
1224		1721
1225		1722
1226	=head2 C<ev_timer> - relative and optionally repeating timeouts	1723	=head2 C<ev_timer> - relative and optionally repeating timeouts
1227		1724
1228	Timer watchers are simple relative timers that generate an event after a	1725	Timer watchers are simple relative timers that generate an event after a
1229	given time, and optionally repeating in regular intervals after that.	1726	given time, and optionally repeating in regular intervals after that.
1230		1727
1231	The timers are based on real time, that is, if you register an event that	1728	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	1729	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	1730	year, it will still time out after (roughly) one hour. "Roughly" because
1234	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1731	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1235	monotonic clock option helps a lot here).	1732	monotonic clock option helps a lot here).
1236		1733
1237	The callback is guaranteed to be invoked only after its timeout has passed,	1734	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	1735	passed (not I<at>, so on systems with very low-resolution clocks this
1239	order of execution is undefined.	1736	might introduce a small delay). If multiple timers become ready during the
		1737	same loop iteration then the ones with earlier time-out values are invoked
		1738	before ones of the same priority with later time-out values (but this is
		1739	no longer true when a callback calls C<ev_run> recursively).
		1740
		1741	=head3 Be smart about timeouts
		1742
		1743	Many real-world problems involve some kind of timeout, usually for error
		1744	recovery. A typical example is an HTTP request - if the other side hangs,
		1745	you want to raise some error after a while.
		1746
		1747	What follows are some ways to handle this problem, from obvious and
		1748	inefficient to smart and efficient.
		1749
		1750	In the following, a 60 second activity timeout is assumed - a timeout that
		1751	gets reset to 60 seconds each time there is activity (e.g. each time some
		1752	data or other life sign was received).
		1753
		1754	=over 4
		1755
		1756	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1757
		1758	This is the most obvious, but not the most simple way: In the beginning,
		1759	start the watcher:
		1760
		1761	ev_timer_init (timer, callback, 60., 0.);
		1762	ev_timer_start (loop, timer);
		1763
		1764	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1765	and start it again:
		1766
		1767	ev_timer_stop (loop, timer);
		1768	ev_timer_set (timer, 60., 0.);
		1769	ev_timer_start (loop, timer);
		1770
		1771	This is relatively simple to implement, but means that each time there is
		1772	some activity, libev will first have to remove the timer from its internal
		1773	data structure and then add it again. Libev tries to be fast, but it's
		1774	still not a constant-time operation.
		1775
		1776	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1777
		1778	This is the easiest way, and involves using C<ev_timer_again> instead of
		1779	C<ev_timer_start>.
		1780
		1781	To implement this, configure an C<ev_timer> with a C<repeat> value
		1782	of C<60> and then call C<ev_timer_again> at start and each time you
		1783	successfully read or write some data. If you go into an idle state where
		1784	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1785	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1786
		1787	That means you can ignore both the C<ev_timer_start> function and the
		1788	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1789	member and C<ev_timer_again>.
		1790
		1791	At start:
		1792
		1793	ev_init (timer, callback);
		1794	timer->repeat = 60.;
		1795	ev_timer_again (loop, timer);
		1796
		1797	Each time there is some activity:
		1798
		1799	ev_timer_again (loop, timer);
		1800
		1801	It is even possible to change the time-out on the fly, regardless of
		1802	whether the watcher is active or not:
		1803
		1804	timer->repeat = 30.;
		1805	ev_timer_again (loop, timer);
		1806
		1807	This is slightly more efficient then stopping/starting the timer each time
		1808	you want to modify its timeout value, as libev does not have to completely
		1809	remove and re-insert the timer from/into its internal data structure.
		1810
		1811	It is, however, even simpler than the "obvious" way to do it.
		1812
		1813	=item 3. Let the timer time out, but then re-arm it as required.
		1814
		1815	This method is more tricky, but usually most efficient: Most timeouts are
		1816	relatively long compared to the intervals between other activity - in
		1817	our example, within 60 seconds, there are usually many I/O events with
		1818	associated activity resets.
		1819
		1820	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1821	but remember the time of last activity, and check for a real timeout only
		1822	within the callback:
		1823
		1824	ev_tstamp last_activity; // time of last activity
		1825
		1826	static void
		1827	callback (EV_P_ ev_timer *w, int revents)
		1828	{
		1829	ev_tstamp now = ev_now (EV_A);
		1830	ev_tstamp timeout = last_activity + 60.;
		1831
		1832	// if last_activity + 60. is older than now, we did time out
		1833	if (timeout < now)
		1834	{
		1835	// timeout occurred, take action
		1836	}
		1837	else
		1838	{
		1839	// callback was invoked, but there was some activity, re-arm
		1840	// the watcher to fire in last_activity + 60, which is
		1841	// guaranteed to be in the future, so "again" is positive:
		1842	w->repeat = timeout - now;
		1843	ev_timer_again (EV_A_ w);
		1844	}
		1845	}
		1846
		1847	To summarise the callback: first calculate the real timeout (defined
		1848	as "60 seconds after the last activity"), then check if that time has
		1849	been reached, which means something I<did>, in fact, time out. Otherwise
		1850	the callback was invoked too early (C<timeout> is in the future), so
		1851	re-schedule the timer to fire at that future time, to see if maybe we have
		1852	a timeout then.
		1853
		1854	Note how C<ev_timer_again> is used, taking advantage of the
		1855	C<ev_timer_again> optimisation when the timer is already running.
		1856
		1857	This scheme causes more callback invocations (about one every 60 seconds
		1858	minus half the average time between activity), but virtually no calls to
		1859	libev to change the timeout.
		1860
		1861	To start the timer, simply initialise the watcher and set C<last_activity>
		1862	to the current time (meaning we just have some activity :), then call the
		1863	callback, which will "do the right thing" and start the timer:
		1864
		1865	ev_init (timer, callback);
		1866	last_activity = ev_now (loop);
		1867	callback (loop, timer, EV_TIMER);
		1868
		1869	And when there is some activity, simply store the current time in
		1870	C<last_activity>, no libev calls at all:
		1871
		1872	last_activity = ev_now (loop);
		1873
		1874	This technique is slightly more complex, but in most cases where the
		1875	time-out is unlikely to be triggered, much more efficient.
		1876
		1877	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1878	callback :) - just change the timeout and invoke the callback, which will
		1879	fix things for you.
		1880
		1881	=item 4. Wee, just use a double-linked list for your timeouts.
		1882
		1883	If there is not one request, but many thousands (millions...), all
		1884	employing some kind of timeout with the same timeout value, then one can
		1885	do even better:
		1886
		1887	When starting the timeout, calculate the timeout value and put the timeout
		1888	at the I<end> of the list.
		1889
		1890	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1891	the list is expected to fire (for example, using the technique #3).
		1892
		1893	When there is some activity, remove the timer from the list, recalculate
		1894	the timeout, append it to the end of the list again, and make sure to
		1895	update the C<ev_timer> if it was taken from the beginning of the list.
		1896
		1897	This way, one can manage an unlimited number of timeouts in O(1) time for
		1898	starting, stopping and updating the timers, at the expense of a major
		1899	complication, and having to use a constant timeout. The constant timeout
		1900	ensures that the list stays sorted.
		1901
		1902	=back
		1903
		1904	So which method the best?
		1905
		1906	Method #2 is a simple no-brain-required solution that is adequate in most
		1907	situations. Method #3 requires a bit more thinking, but handles many cases
		1908	better, and isn't very complicated either. In most case, choosing either
		1909	one is fine, with #3 being better in typical situations.
		1910
		1911	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1912	rather complicated, but extremely efficient, something that really pays
		1913	off after the first million or so of active timers, i.e. it's usually
		1914	overkill :)
1240		1915
1241	=head3 The special problem of time updates	1916	=head3 The special problem of time updates
1242		1917
1243	Establishing the current time is a costly operation (it usually takes at	1918	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	1919	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	1920	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	1921	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1247	lots of events.	1922	lots of events in one iteration.
1248		1923
1249	The relative timeouts are calculated relative to the C<ev_now ()>	1924	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	1925	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	1926	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	1927	you suspect event processing to be delayed and you I<need> to base the
…		…
1256		1931
1257	If the event loop is suspended for a long time, you can also force an	1932	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	1933	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1259	()>.	1934	()>.
1260		1935
		1936	=head3 The special problems of suspended animation
		1937
		1938	When you leave the server world it is quite customary to hit machines that
		1939	can suspend/hibernate - what happens to the clocks during such a suspend?
		1940
		1941	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1942	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1943	to run until the system is suspended, but they will not advance while the
		1944	system is suspended. That means, on resume, it will be as if the program
		1945	was frozen for a few seconds, but the suspend time will not be counted
		1946	towards C<ev_timer> when a monotonic clock source is used. The real time
		1947	clock advanced as expected, but if it is used as sole clocksource, then a
		1948	long suspend would be detected as a time jump by libev, and timers would
		1949	be adjusted accordingly.
		1950
		1951	I would not be surprised to see different behaviour in different between
		1952	operating systems, OS versions or even different hardware.
		1953
		1954	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1955	time jump in the monotonic clocks and the realtime clock. If the program
		1956	is suspended for a very long time, and monotonic clock sources are in use,
		1957	then you can expect C<ev_timer>s to expire as the full suspension time
		1958	will be counted towards the timers. When no monotonic clock source is in
		1959	use, then libev will again assume a timejump and adjust accordingly.
		1960
		1961	It might be beneficial for this latter case to call C<ev_suspend>
		1962	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1963	deterministic behaviour in this case (you can do nothing against
		1964	C<SIGSTOP>).
		1965
1261	=head3 Watcher-Specific Functions and Data Members	1966	=head3 Watcher-Specific Functions and Data Members
1262		1967
1263	=over 4	1968	=over 4
1264		1969
1265	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1970	=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).	1993	If the timer is started but non-repeating, stop it (as if it timed out).
1289		1994
1290	If the timer is repeating, either start it if necessary (with the	1995	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.	1996	C<repeat> value), or reset the running timer to the C<repeat> value.
1292		1997
1293	This sounds a bit complicated, but here is a useful and typical	1998	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	1999	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		2000
1303	That means you can ignore the C<after> value and C<ev_timer_start>	2001	=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		2002
1306	ev_timer_init (timer, callback, 0., 5.);	2003	Returns the remaining time until a timer fires. If the timer is active,
1307	ev_timer_again (loop, timer);	2004	then this time is relative to the current event loop time, otherwise it's
1308	...	2005	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		2006
1315	This is more slightly efficient then stopping/starting the timer each time	2007	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1316	you want to modify its timeout value.	2008	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2009	will return C<4>. When the timer expires and is restarted, it will return
		2010	roughly C<7> (likely slightly less as callback invocation takes some time,
		2011	too), and so on.
1317		2012
1318	=item ev_tstamp repeat [read-write]	2013	=item ev_tstamp repeat [read-write]
1319		2014
1320	The current C<repeat> value. Will be used each time the watcher times out	2015	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),	2016	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.	2017	which is also when any modifications are taken into account.
1323		2018
1324	=back	2019	=back
1325		2020
1326	=head3 Examples	2021	=head3 Examples
1327		2022
1328	Example: Create a timer that fires after 60 seconds.	2023	Example: Create a timer that fires after 60 seconds.
1329		2024
1330	static void	2025	static void
1331	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2026	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1332	{	2027	{
1333	.. one minute over, w is actually stopped right here	2028	.. one minute over, w is actually stopped right here
1334	}	2029	}
1335		2030
1336	struct ev_timer mytimer;	2031	ev_timer mytimer;
1337	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2032	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1338	ev_timer_start (loop, &mytimer);	2033	ev_timer_start (loop, &mytimer);
1339		2034
1340	Example: Create a timeout timer that times out after 10 seconds of	2035	Example: Create a timeout timer that times out after 10 seconds of
1341	inactivity.	2036	inactivity.
1342		2037
1343	static void	2038	static void
1344	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2039	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1345	{	2040	{
1346	.. ten seconds without any activity	2041	.. ten seconds without any activity
1347	}	2042	}
1348		2043
1349	struct ev_timer mytimer;	2044	ev_timer mytimer;
1350	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2045	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1351	ev_timer_again (&mytimer); /* start timer */	2046	ev_timer_again (&mytimer); /* start timer */
1352	ev_loop (loop, 0);	2047	ev_run (loop, 0);
1353		2048
1354	// and in some piece of code that gets executed on any "activity":	2049	// and in some piece of code that gets executed on any "activity":
1355	// reset the timeout to start ticking again at 10 seconds	2050	// reset the timeout to start ticking again at 10 seconds
1356	ev_timer_again (&mytimer);	2051	ev_timer_again (&mytimer);
1357		2052
…		…
1359	=head2 C<ev_periodic> - to cron or not to cron?	2054	=head2 C<ev_periodic> - to cron or not to cron?
1360		2055
1361	Periodic watchers are also timers of a kind, but they are very versatile	2056	Periodic watchers are also timers of a kind, but they are very versatile
1362	(and unfortunately a bit complex).	2057	(and unfortunately a bit complex).
1363		2058
1364	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2059	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	2060	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	2061	(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 ()	2062	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	2063	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	2064	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		2065
		2066	You can tell a periodic watcher to trigger after some specific point
		2067	in time: for example, if you tell a periodic watcher to trigger "in 10
		2068	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2069	not a delay) and then reset your system clock to January of the previous
		2070	year, then it will take a year or more to trigger the event (unlike an
		2071	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2072	it, as it uses a relative timeout).
		2073
1373	C<ev_periodic>s can also be used to implement vastly more complex timers,	2074	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	2075	timers, such as triggering an event on each "midnight, local time", or
1375	complicated, rules.	2076	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2077	those cannot react to time jumps.
1376		2078
1377	As with timers, the callback is guaranteed to be invoked only when the	2079	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	2080	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.	2081	timers become ready during the same loop iteration then the ones with
		2082	earlier time-out values are invoked before ones with later time-out values
		2083	(but this is no longer true when a callback calls C<ev_run> recursively).
1380		2084
1381	=head3 Watcher-Specific Functions and Data Members	2085	=head3 Watcher-Specific Functions and Data Members
1382		2086
1383	=over 4	2087	=over 4
1384		2088
1385	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2089	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1386		2090
1387	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2091	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1388		2092
1389	Lots of arguments, lets sort it out... There are basically three modes of	2093	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:	2094	operation, and we will explain them from simplest to most complex:
1391		2095
1392	=over 4	2096	=over 4
1393		2097
1394	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2098	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1395		2099
1396	In this configuration the watcher triggers an event after the wall clock	2100	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	2101	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	2102	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.	2103	will be stopped and invoked when the system clock reaches or surpasses
		2104	this point in time.
1400		2105
1401	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2106	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1402		2107
1403	In this mode the watcher will always be scheduled to time out at the next	2108	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)	2109	C<offset + N * interval> time (for some integer N, which can also be
1405	and then repeat, regardless of any time jumps.	2110	negative) and then repeat, regardless of any time jumps. The C<offset>
		2111	argument is merely an offset into the C<interval> periods.
1406		2112
1407	This can be used to create timers that do not drift with respect to system	2113	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	2114	system clock, for example, here is an C<ev_periodic> that triggers each
1409	the hour:	2115	hour, on the hour (with respect to UTC):
1410		2116
1411	ev_periodic_set (&periodic, 0., 3600., 0);	2117	ev_periodic_set (&periodic, 0., 3600., 0);
1412		2118
1413	This doesn't mean there will always be 3600 seconds in between triggers,	2119	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	2120	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	2121	full hour (UTC), or more correctly, when the system time is evenly divisible
1416	by 3600.	2122	by 3600.
1417		2123
1418	Another way to think about it (for the mathematically inclined) is that	2124	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	2125	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.	2126	time where C<time = offset (mod interval)>, regardless of any time jumps.
1421		2127
1422	For numerical stability it is preferable that the C<at> value is near	2128	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	2129	C<ev_now ()> (the current time), but there is no range requirement for
1424	this value, and in fact is often specified as zero.	2130	this value, and in fact is often specified as zero.
1425		2131
1426	Note also that there is an upper limit to how often a timer can fire (CPU	2132	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	2133	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	2134	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).	2135	millisecond (if the OS supports it and the machine is fast enough).
1430		2136
1431	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2137	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1432		2138
1433	In this mode the values for C<interval> and C<at> are both being	2139	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	2140	ignored. Instead, each time the periodic watcher gets scheduled, the
1435	reschedule callback will be called with the watcher as first, and the	2141	reschedule callback will be called with the watcher as first, and the
1436	current time as second argument.	2142	current time as second argument.
1437		2143
1438	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2144	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1439	ever, or make ANY event loop modifications whatsoever>.	2145	or make ANY other event loop modifications whatsoever, unless explicitly
		2146	allowed by documentation here>.
1440		2147
1441	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2148	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	2149	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1443	only event loop modification you are allowed to do).	2150	only event loop modification you are allowed to do).
1444		2151
1445	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2152	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1446	*w, ev_tstamp now)>, e.g.:	2153	*w, ev_tstamp now)>, e.g.:
1447		2154
		2155	static ev_tstamp
1448	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2156	my_rescheduler (ev_periodic *w, ev_tstamp now)
1449	{	2157	{
1450	return now + 60.;	2158	return now + 60.;
1451	}	2159	}
1452		2160
1453	It must return the next time to trigger, based on the passed time value	2161	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	2181	a different time than the last time it was called (e.g. in a crond like
1474	program when the crontabs have changed).	2182	program when the crontabs have changed).
1475		2183
1476	=item ev_tstamp ev_periodic_at (ev_periodic *)	2184	=item ev_tstamp ev_periodic_at (ev_periodic *)
1477		2185
1478	When active, returns the absolute time that the watcher is supposed to	2186	When active, returns the absolute time that the watcher is supposed
1479	trigger next.	2187	to trigger next. This is not the same as the C<offset> argument to
		2188	C<ev_periodic_set>, but indeed works even in interval and manual
		2189	rescheduling modes.
1480		2190
1481	=item ev_tstamp offset [read-write]	2191	=item ev_tstamp offset [read-write]
1482		2192
1483	When repeating, this contains the offset value, otherwise this is the	2193	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>).	2194	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2195	although libev might modify this value for better numerical stability).
1485		2196
1486	Can be modified any time, but changes only take effect when the periodic	2197	Can be modified any time, but changes only take effect when the periodic
1487	timer fires or C<ev_periodic_again> is being called.	2198	timer fires or C<ev_periodic_again> is being called.
1488		2199
1489	=item ev_tstamp interval [read-write]	2200	=item ev_tstamp interval [read-write]
1490		2201
1491	The current interval value. Can be modified any time, but changes only	2202	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	2203	take effect when the periodic timer fires or C<ev_periodic_again> is being
1493	called.	2204	called.
1494		2205
1495	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2206	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1496		2207
1497	The current reschedule callback, or C<0>, if this functionality is	2208	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	2209	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.	2210	the periodic timer fires or C<ev_periodic_again> is being called.
1500		2211
1501	=back	2212	=back
1502		2213
1503	=head3 Examples	2214	=head3 Examples
1504		2215
1505	Example: Call a callback every hour, or, more precisely, whenever the	2216	Example: Call a callback every hour, or, more precisely, whenever the
1506	system clock is divisible by 3600. The callback invocation times have	2217	system time is divisible by 3600. The callback invocation times have
1507	potentially a lot of jitter, but good long-term stability.	2218	potentially a lot of jitter, but good long-term stability.
1508		2219
1509	static void	2220	static void
1510	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2221	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1511	{	2222	{
1512	... its now a full hour (UTC, or TAI or whatever your clock follows)	2223	... its now a full hour (UTC, or TAI or whatever your clock follows)
1513	}	2224	}
1514		2225
1515	struct ev_periodic hourly_tick;	2226	ev_periodic hourly_tick;
1516	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2227	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1517	ev_periodic_start (loop, &hourly_tick);	2228	ev_periodic_start (loop, &hourly_tick);
1518		2229
1519	Example: The same as above, but use a reschedule callback to do it:	2230	Example: The same as above, but use a reschedule callback to do it:
1520		2231
1521	#include <math.h>	2232	#include <math.h>
1522		2233
1523	static ev_tstamp	2234	static ev_tstamp
1524	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2235	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1525	{	2236	{
1526	return fmod (now, 3600.) + 3600.;	2237	return now + (3600. - fmod (now, 3600.));
1527	}	2238	}
1528		2239
1529	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2240	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1530		2241
1531	Example: Call a callback every hour, starting now:	2242	Example: Call a callback every hour, starting now:
1532		2243
1533	struct ev_periodic hourly_tick;	2244	ev_periodic hourly_tick;
1534	ev_periodic_init (&hourly_tick, clock_cb,	2245	ev_periodic_init (&hourly_tick, clock_cb,
1535	fmod (ev_now (loop), 3600.), 3600., 0);	2246	fmod (ev_now (loop), 3600.), 3600., 0);
1536	ev_periodic_start (loop, &hourly_tick);	2247	ev_periodic_start (loop, &hourly_tick);
1537		2248
1538		2249
…		…
1541	Signal watchers will trigger an event when the process receives a specific	2252	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	2253	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	2254	will try it's best to deliver signals synchronously, i.e. as part of the
1544	normal event processing, like any other event.	2255	normal event processing, like any other event.
1545		2256
		2257	If you want signals to be delivered truly asynchronously, just use
		2258	C<sigaction> as you would do without libev and forget about sharing
		2259	the signal. You can even use C<ev_async> from a signal handler to
		2260	synchronously wake up an event loop.
		2261
1546	You can configure as many watchers as you like per signal. Only when the	2262	You can configure as many watchers as you like for the same signal, but
		2263	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2264	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2265	C<SIGINT> in both the default loop and another loop at the same time. At
		2266	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2267
1547	first watcher gets started will libev actually register a signal watcher	2268	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	2269	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	2270	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		2271
1553	If possible and supported, libev will install its handlers with	2272	If possible and supported, libev will install its handlers with
1554	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2273	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1555	interrupted. If you have a problem with system calls getting interrupted by	2274	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	2275	interrupted by signals you can block all signals in an C<ev_check> watcher
1557	them in an C<ev_prepare> watcher.	2276	and unblock them in an C<ev_prepare> watcher.
		2277
		2278	=head3 The special problem of inheritance over fork/execve/pthread_create
		2279
		2280	Both the signal mask (C<sigprocmask>) and the signal disposition
		2281	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2282	stopping it again), that is, libev might or might not block the signal,
		2283	and might or might not set or restore the installed signal handler.
		2284
		2285	While this does not matter for the signal disposition (libev never
		2286	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2287	C<execve>), this matters for the signal mask: many programs do not expect
		2288	certain signals to be blocked.
		2289
		2290	This means that before calling C<exec> (from the child) you should reset
		2291	the signal mask to whatever "default" you expect (all clear is a good
		2292	choice usually).
		2293
		2294	The simplest way to ensure that the signal mask is reset in the child is
		2295	to install a fork handler with C<pthread_atfork> that resets it. That will
		2296	catch fork calls done by libraries (such as the libc) as well.
		2297
		2298	In current versions of libev, the signal will not be blocked indefinitely
		2299	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2300	the window of opportunity for problems, it will not go away, as libev
		2301	I<has> to modify the signal mask, at least temporarily.
		2302
		2303	So I can't stress this enough: I<If you do not reset your signal mask when
		2304	you expect it to be empty, you have a race condition in your code>. This
		2305	is not a libev-specific thing, this is true for most event libraries.
1558		2306
1559	=head3 Watcher-Specific Functions and Data Members	2307	=head3 Watcher-Specific Functions and Data Members
1560		2308
1561	=over 4	2309	=over 4
1562		2310
…		…
1573		2321
1574	=back	2322	=back
1575		2323
1576	=head3 Examples	2324	=head3 Examples
1577		2325
1578	Example: Try to exit cleanly on SIGINT and SIGTERM.	2326	Example: Try to exit cleanly on SIGINT.
1579		2327
1580	static void	2328	static void
1581	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2329	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1582	{	2330	{
1583	ev_unloop (loop, EVUNLOOP_ALL);	2331	ev_break (loop, EVBREAK_ALL);
1584	}	2332	}
1585		2333
1586	struct ev_signal signal_watcher;	2334	ev_signal signal_watcher;
1587	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2335	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1588	ev_signal_start (loop, &sigint_cb);	2336	ev_signal_start (loop, &signal_watcher);
1589		2337
1590		2338
1591	=head2 C<ev_child> - watch out for process status changes	2339	=head2 C<ev_child> - watch out for process status changes
1592		2340
1593	Child watchers trigger when your process receives a SIGCHLD in response to	2341	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	2342	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	2343	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	2344	has been forked (which implies it might have already exited), as long
1597	loop isn't entered (or is continued from a watcher).	2345	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2346	forking and then immediately registering a watcher for the child is fine,
		2347	but forking and registering a watcher a few event loop iterations later or
		2348	in the next callback invocation is not.
1598		2349
1599	Only the default event loop is capable of handling signals, and therefore	2350	Only the default event loop is capable of handling signals, and therefore
1600	you can only register child watchers in the default event loop.	2351	you can only register child watchers in the default event loop.
1601		2352
		2353	Due to some design glitches inside libev, child watchers will always be
		2354	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2355	libev)
		2356
1602	=head3 Process Interaction	2357	=head3 Process Interaction
1603		2358
1604	Libev grabs C<SIGCHLD> as soon as the default event loop is	2359	Libev grabs C<SIGCHLD> as soon as the default event loop is
1605	initialised. This is necessary to guarantee proper behaviour even if	2360	initialised. This is necessary to guarantee proper behaviour even if the
1606	the first child watcher is started after the child exits. The occurrence	2361	first child watcher is started after the child exits. The occurrence
1607	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2362	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1608	synchronously as part of the event loop processing. Libev always reaps all	2363	synchronously as part of the event loop processing. Libev always reaps all
1609	children, even ones not watched.	2364	children, even ones not watched.
1610		2365
1611	=head3 Overriding the Built-In Processing	2366	=head3 Overriding the Built-In Processing
…		…
1621	=head3 Stopping the Child Watcher	2376	=head3 Stopping the Child Watcher
1622		2377
1623	Currently, the child watcher never gets stopped, even when the	2378	Currently, the child watcher never gets stopped, even when the
1624	child terminates, so normally one needs to stop the watcher in the	2379	child terminates, so normally one needs to stop the watcher in the
1625	callback. Future versions of libev might stop the watcher automatically	2380	callback. Future versions of libev might stop the watcher automatically
1626	when a child exit is detected.	2381	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2382	problem).
1627		2383
1628	=head3 Watcher-Specific Functions and Data Members	2384	=head3 Watcher-Specific Functions and Data Members
1629		2385
1630	=over 4	2386	=over 4
1631		2387
…		…
1663	its completion.	2419	its completion.
1664		2420
1665	ev_child cw;	2421	ev_child cw;
1666		2422
1667	static void	2423	static void
1668	child_cb (EV_P_ struct ev_child *w, int revents)	2424	child_cb (EV_P_ ev_child *w, int revents)
1669	{	2425	{
1670	ev_child_stop (EV_A_ w);	2426	ev_child_stop (EV_A_ w);
1671	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2427	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1672	}	2428	}
1673		2429
…		…
1688		2444
1689		2445
1690	=head2 C<ev_stat> - did the file attributes just change?	2446	=head2 C<ev_stat> - did the file attributes just change?
1691		2447
1692	This watches a file system path for attribute changes. That is, it calls	2448	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	2449	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.	2450	and sees if it changed compared to the last time, invoking the callback if
		2451	it did.
1695		2452
1696	The path does not need to exist: changing from "path exists" to "path does	2453	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	2454	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	2455	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	2456	C<st_nlink> field being zero (which is otherwise always forced to be at
1700	the stat buffer having unspecified contents.	2457	least one) and all the other fields of the stat buffer having unspecified
		2458	contents.
1701		2459
1702	The path I<should> be absolute and I<must not> end in a slash. If it is	2460	The path I<must not> end in a slash or contain special components such as
		2461	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.	2462	your working directory changes, then the behaviour is undefined.
1704		2463
1705	Since there is no standard to do this, the portable implementation simply	2464	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	2465	portable implementation simply calls C<stat(2)> regularly on the path
1707	can specify a recommended polling interval for this case. If you specify	2466	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,	2467	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	2468	recommended!) then a I<suitable, unspecified default> value will be used
1710	five seconds, although this might change dynamically). Libev will also	2469	(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	2470	change dynamically). Libev will also impose a minimum interval which is
1712	usually overkill.	2471	currently around C<0.1>, but that's usually overkill.
1713		2472
1714	This watcher type is not meant for massive numbers of stat watchers,	2473	This watcher type is not meant for massive numbers of stat watchers,
1715	as even with OS-supported change notifications, this can be	2474	as even with OS-supported change notifications, this can be
1716	resource-intensive.	2475	resource-intensive.
1717		2476
1718	At the time of this writing, only the Linux inotify interface is	2477	At the time of this writing, the only OS-specific interface implemented
1719	implemented (implementing kqueue support is left as an exercise for the	2478	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	2479	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	2480	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		2481
1727	=head3 ABI Issues (Largefile Support)	2482	=head3 ABI Issues (Largefile Support)
1728		2483
1729	Libev by default (unless the user overrides this) uses the default	2484	Libev by default (unless the user overrides this) uses the default
1730	compilation environment, which means that on systems with large file	2485	compilation environment, which means that on systems with large file
1731	support disabled by default, you get the 32 bit version of the stat	2486	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	2487	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	2488	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	2489	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	2490	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.	2491	most noticeably displayed with ev_stat and large file support.
1737		2492
1738	The solution for this is to lobby your distribution maker to make large	2493	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	2494	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	2495	optional. Libev cannot simply switch on large file support because it has
1741	to exchange stat structures with application programs compiled using the	2496	to exchange stat structures with application programs compiled using the
1742	default compilation environment.	2497	default compilation environment.
1743		2498
1744	=head3 Inotify	2499	=head3 Inotify and Kqueue
1745		2500
1746	When C<inotify (7)> support has been compiled into libev (generally only	2501	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	2502	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	2503	inotify descriptor will be created lazily when the first C<ev_stat>
1749	when the first C<ev_stat> watcher is being started.	2504	watcher is being started.
1750		2505
1751	Inotify presence does not change the semantics of C<ev_stat> watchers	2506	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	2507	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	2508	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.	2509	there are many cases where libev has to resort to regular C<stat> polling,
		2510	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2511	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2512	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2513	xfs are fully working) libev usually gets away without polling.
1755		2514
1756	(There is no support for kqueue, as apparently it cannot be used to	2515	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	2516	implement this functionality, due to the requirement of having a file
1758	descriptor open on the object at all times).	2517	descriptor open on the object at all times, and detecting renames, unlinks
		2518	etc. is difficult.
		2519
		2520	=head3 C<stat ()> is a synchronous operation
		2521
		2522	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2523	the process. The exception are C<ev_stat> watchers - those call C<stat
		2524	()>, which is a synchronous operation.
		2525
		2526	For local paths, this usually doesn't matter: unless the system is very
		2527	busy or the intervals between stat's are large, a stat call will be fast,
		2528	as the path data is usually in memory already (except when starting the
		2529	watcher).
		2530
		2531	For networked file systems, calling C<stat ()> can block an indefinite
		2532	time due to network issues, and even under good conditions, a stat call
		2533	often takes multiple milliseconds.
		2534
		2535	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2536	paths, although this is fully supported by libev.
1759		2537
1760	=head3 The special problem of stat time resolution	2538	=head3 The special problem of stat time resolution
1761		2539
1762	The C<stat ()> system call only supports full-second resolution portably, and	2540	The C<stat ()> system call only supports full-second resolution portably,
1763	even on systems where the resolution is higher, many file systems still	2541	and even on systems where the resolution is higher, most file systems
1764	only support whole seconds.	2542	still only support whole seconds.
1765		2543
1766	That means that, if the time is the only thing that changes, you can	2544	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	2545	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	2546	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	2547	within the same second, C<ev_stat> will be unable to detect unless the
1770	data does not change.	2548	stat data does change in other ways (e.g. file size).
1771		2549
1772	The solution to this is to delay acting on a change for slightly more	2550	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	2551	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);	2552	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1775	ev_timer_again (loop, w)>).	2553	ev_timer_again (loop, w)>).
…		…
1795	C<path>. The C<interval> is a hint on how quickly a change is expected to	2573	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	2574	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	2575	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.	2576	path for as long as the watcher is active.
1799		2577
1800	The callback will receive C<EV_STAT> when a change was detected, relative	2578	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	2579	relative to the attributes at the time the watcher was started (or the
1802	was detected).	2580	last change was detected).
1803		2581
1804	=item ev_stat_stat (loop, ev_stat *)	2582	=item ev_stat_stat (loop, ev_stat *)
1805		2583
1806	Updates the stat buffer immediately with new values. If you change the	2584	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	2585	watched path in your callback, you could call this function to avoid
…		…
1890		2668
1891		2669
1892	=head2 C<ev_idle> - when you've got nothing better to do...	2670	=head2 C<ev_idle> - when you've got nothing better to do...
1893		2671
1894	Idle watchers trigger events when no other events of the same or higher	2672	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	2673	priority are pending (prepare, check and other idle watchers do not count
1896	count).	2674	as receiving "events").
1897		2675
1898	That is, as long as your process is busy handling sockets or timeouts	2676	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	2677	(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	2678	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	2679	are pending), the idle watchers are being called once per event loop
…		…
1912		2690
1913	=head3 Watcher-Specific Functions and Data Members	2691	=head3 Watcher-Specific Functions and Data Members
1914		2692
1915	=over 4	2693	=over 4
1916		2694
1917	=item ev_idle_init (ev_signal *, callback)	2695	=item ev_idle_init (ev_idle *, callback)
1918		2696
1919	Initialises and configures the idle watcher - it has no parameters of any	2697	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,	2698	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1921	believe me.	2699	believe me.
1922		2700
…		…
1926		2704
1927	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2705	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1928	callback, free it. Also, use no error checking, as usual.	2706	callback, free it. Also, use no error checking, as usual.
1929		2707
1930	static void	2708	static void
1931	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2709	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1932	{	2710	{
1933	free (w);	2711	free (w);
1934	// now do something you wanted to do when the program has	2712	// now do something you wanted to do when the program has
1935	// no longer anything immediate to do.	2713	// no longer anything immediate to do.
1936	}	2714	}
1937		2715
1938	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2716	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1939	ev_idle_init (idle_watcher, idle_cb);	2717	ev_idle_init (idle_watcher, idle_cb);
1940	ev_idle_start (loop, idle_cb);	2718	ev_idle_start (loop, idle_watcher);
1941		2719
1942		2720
1943	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2721	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1944		2722
1945	Prepare and check watchers are usually (but not always) used in tandem:	2723	Prepare and check watchers are usually (but not always) used in pairs:
1946	prepare watchers get invoked before the process blocks and check watchers	2724	prepare watchers get invoked before the process blocks and check watchers
1947	afterwards.	2725	afterwards.
1948		2726
1949	You I<must not> call C<ev_loop> or similar functions that enter	2727	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>	2728	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	2729	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	2730	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,	2731	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	2732	C<ev_check> so if you have one watcher of each kind they will always be
1955	called in pairs bracketing the blocking call.	2733	called in pairs bracketing the blocking call.
1956		2734
1957	Their main purpose is to integrate other event mechanisms into libev and	2735	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	2736	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	2737	variable changes, implement your own watchers, integrate net-snmp or a
1960	coroutine library and lots more. They are also occasionally useful if	2738	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,	2739	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>	2740	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1963	watcher).	2741	watcher).
1964		2742
1965	This is done by examining in each prepare call which file descriptors need	2743	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	2744	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	2745	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	2746	libraries provide exactly this functionality). Then, in the check watcher,
1969	any events that occurred (by checking the pending status of all watchers	2747	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	2748	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,	2749	I/O and timer callbacks will never actually be called (but must be valid
1972	because you never know, you know?).	2750	nevertheless, because you never know, you know?).
1973		2751
1974	As another example, the Perl Coro module uses these hooks to integrate	2752	As another example, the Perl Coro module uses these hooks to integrate
1975	coroutines into libev programs, by yielding to other active coroutines	2753	coroutines into libev programs, by yielding to other active coroutines
1976	during each prepare and only letting the process block if no coroutines	2754	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	2755	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	2758	loop from blocking if lower-priority coroutines are active, thus mapping
1981	low-priority coroutines to idle/background tasks).	2759	low-priority coroutines to idle/background tasks).
1982		2760
1983	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2761	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	2762	priority, to ensure that they are being run before any other watchers
		2763	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2764
1985	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2765	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	2766	activate ("feed") events into libev. While libev fully supports this, they
1987	supports this, they might get executed before other C<ev_check> watchers	2767	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	2768	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	2769	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	2770	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1991	coexist peacefully with others).	2771	others).
1992		2772
1993	=head3 Watcher-Specific Functions and Data Members	2773	=head3 Watcher-Specific Functions and Data Members
1994		2774
1995	=over 4	2775	=over 4
1996		2776
…		…
1998		2778
1999	=item ev_check_init (ev_check *, callback)	2779	=item ev_check_init (ev_check *, callback)
2000		2780
2001	Initialises and configures the prepare or check watcher - they have no	2781	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>	2782	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.	2783	macros, but using them is utterly, utterly, utterly and completely
		2784	pointless.
2004		2785
2005	=back	2786	=back
2006		2787
2007	=head3 Examples	2788	=head3 Examples
2008		2789
…		…
2021		2802
2022	static ev_io iow [nfd];	2803	static ev_io iow [nfd];
2023	static ev_timer tw;	2804	static ev_timer tw;
2024		2805
2025	static void	2806	static void
2026	io_cb (ev_loop *loop, ev_io *w, int revents)	2807	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2027	{	2808	{
2028	}	2809	}
2029		2810
2030	// create io watchers for each fd and a timer before blocking	2811	// create io watchers for each fd and a timer before blocking
2031	static void	2812	static void
2032	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2813	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2033	{	2814	{
2034	int timeout = 3600000;	2815	int timeout = 3600000;
2035	struct pollfd fds [nfd];	2816	struct pollfd fds [nfd];
2036	// actual code will need to loop here and realloc etc.	2817	// actual code will need to loop here and realloc etc.
2037	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2818	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2038		2819
2039	/* the callback is illegal, but won't be called as we stop during check */	2820	/* the callback is illegal, but won't be called as we stop during check */
2040	ev_timer_init (&tw, 0, timeout * 1e-3);	2821	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2041	ev_timer_start (loop, &tw);	2822	ev_timer_start (loop, &tw);
2042		2823
2043	// create one ev_io per pollfd	2824	// create one ev_io per pollfd
2044	for (int i = 0; i < nfd; ++i)	2825	for (int i = 0; i < nfd; ++i)
2045	{	2826	{
…		…
2052	}	2833	}
2053	}	2834	}
2054		2835
2055	// stop all watchers after blocking	2836	// stop all watchers after blocking
2056	static void	2837	static void
2057	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2838	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2058	{	2839	{
2059	ev_timer_stop (loop, &tw);	2840	ev_timer_stop (loop, &tw);
2060		2841
2061	for (int i = 0; i < nfd; ++i)	2842	for (int i = 0; i < nfd; ++i)
2062	{	2843	{
…		…
2101	}	2882	}
2102		2883
2103	// do not ever call adns_afterpoll	2884	// do not ever call adns_afterpoll
2104		2885
2105	Method 4: Do not use a prepare or check watcher because the module you	2886	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	2887	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	2888	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	2889	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2109	this.	2890	this approach, effectively embedding EV as a client into the horrible
		2891	libglib event loop.
2110		2892
2111	static gint	2893	static gint
2112	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2894	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2113	{	2895	{
2114	int got_events = 0;	2896	int got_events = 0;
…		…
2118		2900
2119	if (timeout >= 0)	2901	if (timeout >= 0)
2120	// create/start timer	2902	// create/start timer
2121		2903
2122	// poll	2904	// poll
2123	ev_loop (EV_A_ 0);	2905	ev_run (EV_A_ 0);
2124		2906
2125	// stop timer again	2907	// stop timer again
2126	if (timeout >= 0)	2908	if (timeout >= 0)
2127	ev_timer_stop (EV_A_ &to);	2909	ev_timer_stop (EV_A_ &to);
2128		2910
…		…
2145	prioritise I/O.	2927	prioritise I/O.
2146		2928
2147	As an example for a bug workaround, the kqueue backend might only support	2929	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	2930	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	2931	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	2932	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	2933	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	2934	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.	2935	C<kevent>, but at least you can use both mechanisms for what they are
		2936	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2154		2937
2155	As for prioritising I/O: rarely you have the case where some fds have	2938	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	2939	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	2940	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	2941	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.	2942	the rest in a second one, and embed the second one in the first.
2160		2943
2161	As long as the watcher is active, the callback will be invoked every time	2944	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	2945	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	2946	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	2947	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	2948	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	2949	to give the embedded loop strictly lower priority for example).
2167	embedded loop sweep.
2168		2950
2169	As long as the watcher is started it will automatically handle events. The	2951	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	2952	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		2953
2174	Also, there have not currently been made special provisions for forking:	2954	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,	2955	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	2956	embedding loop forks. In other cases, the user is responsible for calling
2177	yourself.	2957	C<ev_loop_fork> on the embedded loop.
2178		2958
2179	Unfortunately, not all backends are embeddable, only the ones returned by	2959	Unfortunately, not all backends are embeddable: only the ones returned by
2180	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2960	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2181	portable one.	2961	portable one.
2182		2962
2183	So when you want to use this feature you will always have to be prepared	2963	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	2964	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	2965	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.	2966	create it, and if that fails, use the normal loop for everything.
		2967
		2968	=head3 C<ev_embed> and fork
		2969
		2970	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2971	automatically be applied to the embedded loop as well, so no special
		2972	fork handling is required in that case. When the watcher is not running,
		2973	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2974	as applicable.
2187		2975
2188	=head3 Watcher-Specific Functions and Data Members	2976	=head3 Watcher-Specific Functions and Data Members
2189		2977
2190	=over 4	2978	=over 4
2191		2979
…		…
2200	if you do not want that, you need to temporarily stop the embed watcher).	2988	if you do not want that, you need to temporarily stop the embed watcher).
2201		2989
2202	=item ev_embed_sweep (loop, ev_embed *)	2990	=item ev_embed_sweep (loop, ev_embed *)
2203		2991
2204	Make a single, non-blocking sweep over the embedded loop. This works	2992	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	2993	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2206	appropriate way for embedded loops.	2994	appropriate way for embedded loops.
2207		2995
2208	=item struct ev_loop *other [read-only]	2996	=item struct ev_loop *other [read-only]
2209		2997
2210	The embedded event loop.	2998	The embedded event loop.
…		…
2219	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	3007	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2220	used).	3008	used).
2221		3009
2222	struct ev_loop *loop_hi = ev_default_init (0);	3010	struct ev_loop *loop_hi = ev_default_init (0);
2223	struct ev_loop *loop_lo = 0;	3011	struct ev_loop *loop_lo = 0;
2224	struct ev_embed embed;	3012	ev_embed embed;
2225		3013
2226	// see if there is a chance of getting one that works	3014	// see if there is a chance of getting one that works
2227	// (remember that a flags value of 0 means autodetection)	3015	// (remember that a flags value of 0 means autodetection)
2228	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3016	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2229	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3017	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2243	kqueue implementation). Store the kqueue/socket-only event loop in	3031	kqueue implementation). Store the kqueue/socket-only event loop in
2244	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3032	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2245		3033
2246	struct ev_loop *loop = ev_default_init (0);	3034	struct ev_loop *loop = ev_default_init (0);
2247	struct ev_loop *loop_socket = 0;	3035	struct ev_loop *loop_socket = 0;
2248	struct ev_embed embed;	3036	ev_embed embed;
2249		3037
2250	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3038	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2251	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3039	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2252	{	3040	{
2253	ev_embed_init (&embed, 0, loop_socket);	3041	ev_embed_init (&embed, 0, loop_socket);
…		…
2268	event loop blocks next and before C<ev_check> watchers are being called,	3056	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	3057	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	3058	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2271	handlers will be invoked, too, of course.	3059	handlers will be invoked, too, of course.
2272		3060
		3061	=head3 The special problem of life after fork - how is it possible?
		3062
		3063	Most uses of C<fork()> consist of forking, then some simple calls to set
		3064	up/change the process environment, followed by a call to C<exec()>. This
		3065	sequence should be handled by libev without any problems.
		3066
		3067	This changes when the application actually wants to do event handling
		3068	in the child, or both parent in child, in effect "continuing" after the
		3069	fork.
		3070
		3071	The default mode of operation (for libev, with application help to detect
		3072	forks) is to duplicate all the state in the child, as would be expected
		3073	when I<either> the parent I<or> the child process continues.
		3074
		3075	When both processes want to continue using libev, then this is usually the
		3076	wrong result. In that case, usually one process (typically the parent) is
		3077	supposed to continue with all watchers in place as before, while the other
		3078	process typically wants to start fresh, i.e. without any active watchers.
		3079
		3080	The cleanest and most efficient way to achieve that with libev is to
		3081	simply create a new event loop, which of course will be "empty", and
		3082	use that for new watchers. This has the advantage of not touching more
		3083	memory than necessary, and thus avoiding the copy-on-write, and the
		3084	disadvantage of having to use multiple event loops (which do not support
		3085	signal watchers).
		3086
		3087	When this is not possible, or you want to use the default loop for
		3088	other reasons, then in the process that wants to start "fresh", call
		3089	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3090	Destroying the default loop will "orphan" (not stop) all registered
		3091	watchers, so you have to be careful not to execute code that modifies
		3092	those watchers. Note also that in that case, you have to re-register any
		3093	signal watchers.
		3094
2273	=head3 Watcher-Specific Functions and Data Members	3095	=head3 Watcher-Specific Functions and Data Members
2274		3096
2275	=over 4	3097	=over 4
2276		3098
2277	=item ev_fork_init (ev_signal *, callback)	3099	=item ev_fork_init (ev_fork *, callback)
2278		3100
2279	Initialises and configures the fork watcher - it has no parameters of any	3101	Initialises and configures the fork watcher - it has no parameters of any
2280	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3102	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2281	believe me.	3103	believe me.
2282		3104
2283	=back	3105	=back
2284		3106
2285		3107
		3108	=head2 C<ev_cleanup> - even the best things end
		3109
		3110	Cleanup watchers are called just before the event loop they are registered
		3111	with is being destroyed.
		3112
		3113	While there is no guarantee that the event loop gets destroyed, cleanup
		3114	watchers provide a convenient method to install cleanup hooks for your
		3115	program, worker threads and so on - you just to make sure to destroy the
		3116	loop when you want them to be invoked.
		3117
		3118	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3119	all other watchers, they do not keep a reference to the event loop (which
		3120	makes a lot of sense if you think about it). Like all other watchers, you
		3121	can call libev functions in the callback, except C<ev_cleanup_start>.
		3122
		3123	=head3 Watcher-Specific Functions and Data Members
		3124
		3125	=over 4
		3126
		3127	=item ev_cleanup_init (ev_cleanup *, callback)
		3128
		3129	Initialises and configures the cleanup watcher - it has no parameters of
		3130	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3131	pointless, believe me.
		3132
		3133	=back
		3134
		3135	Example: Register an atexit handler to destroy the default loop, so any
		3136	cleanup functions are called.
		3137
		3138	static void
		3139	program_exits (void)
		3140	{
		3141	ev_loop_destroy (EV_DEFAULT_UC);
		3142	}
		3143
		3144	...
		3145	atexit (program_exits);
		3146
		3147
2286	=head2 C<ev_async> - how to wake up another event loop	3148	=head2 C<ev_async> - how to wake up an event loop
2287		3149
2288	In general, you cannot use an C<ev_loop> from multiple threads or other	3150	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	3151	asynchronous sources such as signal handlers (as opposed to multiple event
2290	loops - those are of course safe to use in different threads).	3152	loops - those are of course safe to use in different threads).
2291		3153
2292	Sometimes, however, you need to wake up another event loop you do not	3154	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	3155	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	3156	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	3157	it by calling C<ev_async_send>, which is thread- and signal safe.
2296	safe.
2297		3158
2298	This functionality is very similar to C<ev_signal> watchers, as signals,	3159	This functionality is very similar to C<ev_signal> watchers, as signals,
2299	too, are asynchronous in nature, and signals, too, will be compressed	3160	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	3161	(i.e. the number of callback invocations may be less than the number of
2301	C<ev_async_sent> calls).	3162	C<ev_async_sent> calls).
…		…
2306	=head3 Queueing	3167	=head3 Queueing
2307		3168
2308	C<ev_async> does not support queueing of data in any way. The reason	3169	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	3170	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	3171	multiple-writer-single-reader queue that works in all cases and doesn't
2311	need elaborate support such as pthreads.	3172	need elaborate support such as pthreads or unportable memory access
		3173	semantics.
2312		3174
2313	That means that if you want to queue data, you have to provide your own	3175	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	3176	queue. But at least I can tell you how to implement locking around your
2315	queue:	3177	queue:
2316		3178
2317	=over 4	3179	=over 4
2318		3180
2319	=item queueing from a signal handler context	3181	=item queueing from a signal handler context
2320		3182
2321	To implement race-free queueing, you simply add to the queue in the signal	3183	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	3184	handler but you block the signal handler in the watcher callback. Here is
2323	some fictitious SIGUSR1 handler:	3185	an example that does that for some fictitious SIGUSR1 handler:
2324		3186
2325	static ev_async mysig;	3187	static ev_async mysig;
2326		3188
2327	static void	3189	static void
2328	sigusr1_handler (void)	3190	sigusr1_handler (void)
…		…
2394	=over 4	3256	=over 4
2395		3257
2396	=item ev_async_init (ev_async *, callback)	3258	=item ev_async_init (ev_async *, callback)
2397		3259
2398	Initialises and configures the async watcher - it has no parameters of any	3260	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,	3261	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2400	believe me.	3262	trust me.
2401		3263
2402	=item ev_async_send (loop, ev_async *)	3264	=item ev_async_send (loop, ev_async *)
2403		3265
2404	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3266	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	3267	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	3268	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	3269	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2408	section below on what exactly this means).	3270	section below on what exactly this means).
2409		3271
		3272	Note that, as with other watchers in libev, multiple events might get
		3273	compressed into a single callback invocation (another way to look at this
		3274	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3275	reset when the event loop detects that).
		3276
2410	This call incurs the overhead of a system call only once per loop iteration,	3277	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	3278	iteration, so while the overhead might be noticeable, it doesn't apply to
2412	calls to C<ev_async_send>.	3279	repeated calls to C<ev_async_send> for the same event loop.
2413		3280
2414	=item bool = ev_async_pending (ev_async *)	3281	=item bool = ev_async_pending (ev_async *)
2415		3282
2416	Returns a non-zero value when C<ev_async_send> has been called on the	3283	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	3284	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	3287	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,	3288	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	3289	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.	3290	quickly check whether invoking the loop might be a good idea.
2424		3291
2425	Not that this does I<not> check whether the watcher itself is pending, only	3292	Not that this does I<not> check whether the watcher itself is pending,
2426	whether it has been requested to make this watcher pending.	3293	only whether it has been requested to make this watcher pending: there
		3294	is a time window between the event loop checking and resetting the async
		3295	notification, and the callback being invoked.
2427		3296
2428	=back	3297	=back
2429		3298
2430		3299
2431	=head1 OTHER FUNCTIONS	3300	=head1 OTHER FUNCTIONS
…		…
2435	=over 4	3304	=over 4
2436		3305
2437	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3306	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2438		3307
2439	This function combines a simple timer and an I/O watcher, calls your	3308	This function combines a simple timer and an I/O watcher, calls your
2440	callback on whichever event happens first and automatically stop both	3309	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	3310	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	3311	or timeout without having to allocate/configure/start/stop/free one or
2443	more watchers yourself.	3312	more watchers yourself.
2444		3313
2445	If C<fd> is less than 0, then no I/O watcher will be started and events	3314	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	3315	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2447	C<events> set will be created and started.	3316	the given C<fd> and C<events> set will be created and started.
2448		3317
2449	If C<timeout> is less than 0, then no timeout watcher will be	3318	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	3319	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	3320	repeat = 0) will be started. C<0> is a valid timeout.
2452	dubious value.
2453		3321
2454	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3322	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	3323	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>	3324	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2457	value passed to C<ev_once>:	3325	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3326	a timeout and an io event at the same time - you probably should give io
		3327	events precedence.
		3328
		3329	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2458		3330
2459	static void stdin_ready (int revents, void *arg)	3331	static void stdin_ready (int revents, void *arg)
2460	{	3332	{
		3333	if (revents & EV_READ)
		3334	/* stdin might have data for us, joy! */;
2461	if (revents & EV_TIMEOUT)	3335	else if (revents & EV_TIMER)
2462	/* doh, nothing entered */;	3336	/* doh, nothing entered */;
2463	else if (revents & EV_READ)
2464	/* stdin might have data for us, joy! */;
2465	}	3337	}
2466		3338
2467	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3339	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2468		3340
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)	3341	=item ev_feed_fd_event (loop, int fd, int revents)
2476		3342
2477	Feed an event on the given fd, as if a file descriptor backend detected	3343	Feed an event on the given fd, as if a file descriptor backend detected
2478	the given events it.	3344	the given events it.
2479		3345
2480	=item ev_feed_signal_event (ev_loop *loop, int signum)	3346	=item ev_feed_signal_event (loop, int signum)
2481		3347
2482	Feed an event as if the given signal occurred (C<loop> must be the default	3348	Feed an event as if the given signal occurred (C<loop> must be the default
2483	loop!).	3349	loop!).
2484		3350
2485	=back	3351	=back
…		…
2565		3431
2566	=over 4	3432	=over 4
2567		3433
2568	=item ev::TYPE::TYPE ()	3434	=item ev::TYPE::TYPE ()
2569		3435
2570	=item ev::TYPE::TYPE (struct ev_loop *)	3436	=item ev::TYPE::TYPE (loop)
2571		3437
2572	=item ev::TYPE::~TYPE	3438	=item ev::TYPE::~TYPE
2573		3439
2574	The constructor (optionally) takes an event loop to associate the watcher	3440	The constructor (optionally) takes an event loop to associate the watcher
2575	with. If it is omitted, it will use C<EV_DEFAULT>.	3441	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2607		3473
2608	myclass obj;	3474	myclass obj;
2609	ev::io iow;	3475	ev::io iow;
2610	iow.set <myclass, &myclass::io_cb> (&obj);	3476	iow.set <myclass, &myclass::io_cb> (&obj);
2611		3477
		3478	=item w->set (object *)
		3479
		3480	This is a variation of a method callback - leaving out the method to call
		3481	will default the method to C<operator ()>, which makes it possible to use
		3482	functor objects without having to manually specify the C<operator ()> all
		3483	the time. Incidentally, you can then also leave out the template argument
		3484	list.
		3485
		3486	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3487	int revents)>.
		3488
		3489	See the method-C<set> above for more details.
		3490
		3491	Example: use a functor object as callback.
		3492
		3493	struct myfunctor
		3494	{
		3495	void operator() (ev::io &w, int revents)
		3496	{
		3497	...
		3498	}
		3499	}
		3500
		3501	myfunctor f;
		3502
		3503	ev::io w;
		3504	w.set (&f);
		3505
2612	=item w->set<function> (void *data = 0)	3506	=item w->set<function> (void *data = 0)
2613		3507
2614	Also sets a callback, but uses a static method or plain function as	3508	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	3509	callback. The optional C<data> argument will be stored in the watcher's
2616	C<data> member and is free for you to use.	3510	C<data> member and is free for you to use.
2617		3511
2618	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3512	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2619		3513
2620	See the method-C<set> above for more details.	3514	See the method-C<set> above for more details.
2621		3515
2622	Example:	3516	Example: Use a plain function as callback.
2623		3517
2624	static void io_cb (ev::io &w, int revents) { }	3518	static void io_cb (ev::io &w, int revents) { }
2625	iow.set <io_cb> ();	3519	iow.set <io_cb> ();
2626		3520
2627	=item w->set (struct ev_loop *)	3521	=item w->set (loop)
2628		3522
2629	Associates a different C<struct ev_loop> with this watcher. You can only	3523	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).	3524	do this when the watcher is inactive (and not pending either).
2631		3525
2632	=item w->set ([arguments])	3526	=item w->set ([arguments])
2633		3527
2634	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be	3528	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	3529	method or a suitable start method must be called at least once. Unlike the
2636	automatically stopped and restarted when reconfiguring it with this	3530	C counterpart, an active watcher gets automatically stopped and restarted
2637	method.	3531	when reconfiguring it with this method.
2638		3532
2639	=item w->start ()	3533	=item w->start ()
2640		3534
2641	Starts the watcher. Note that there is no C<loop> argument, as the	3535	Starts the watcher. Note that there is no C<loop> argument, as the
2642	constructor already stores the event loop.	3536	constructor already stores the event loop.
2643		3537
		3538	=item w->start ([arguments])
		3539
		3540	Instead of calling C<set> and C<start> methods separately, it is often
		3541	convenient to wrap them in one call. Uses the same type of arguments as
		3542	the configure C<set> method of the watcher.
		3543
2644	=item w->stop ()	3544	=item w->stop ()
2645		3545
2646	Stops the watcher if it is active. Again, no C<loop> argument.	3546	Stops the watcher if it is active. Again, no C<loop> argument.
2647		3547
2648	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3548	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2660		3560
2661	=back	3561	=back
2662		3562
2663	=back	3563	=back
2664		3564
2665	Example: Define a class with an IO and idle watcher, start one of them in	3565	Example: Define a class with two I/O and idle watchers, start the I/O
2666	the constructor.	3566	watchers in the constructor.
2667		3567
2668	class myclass	3568	class myclass
2669	{	3569	{
2670	ev::io io; void io_cb (ev::io &w, int revents);	3570	ev::io io ; void io_cb (ev::io &w, int revents);
		3571	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2671	ev:idle idle void idle_cb (ev::idle &w, int revents);	3572	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2672		3573
2673	myclass (int fd)	3574	myclass (int fd)
2674	{	3575	{
2675	io .set <myclass, &myclass::io_cb > (this);	3576	io .set <myclass, &myclass::io_cb > (this);
		3577	io2 .set <myclass, &myclass::io2_cb > (this);
2676	idle.set <myclass, &myclass::idle_cb> (this);	3578	idle.set <myclass, &myclass::idle_cb> (this);
2677		3579
2678	io.start (fd, ev::READ);	3580	io.set (fd, ev::WRITE); // configure the watcher
		3581	io.start (); // start it whenever convenient
		3582
		3583	io2.start (fd, ev::READ); // set + start in one call
2679	}	3584	}
2680	};	3585	};
2681		3586
2682		3587
2683	=head1 OTHER LANGUAGE BINDINGS	3588	=head1 OTHER LANGUAGE BINDINGS
…		…
2692	=item Perl	3597	=item Perl
2693		3598
2694	The EV module implements the full libev API and is actually used to test	3599	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,	3600	libev. EV is developed together with libev. Apart from the EV core module,
2696	there are additional modules that implement libev-compatible interfaces	3601	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	3602	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>).	3603	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3604	and C<EV::Glib>).
2699		3605
2700	It can be found and installed via CPAN, its homepage is at	3606	It can be found and installed via CPAN, its homepage is at
2701	L<http://software.schmorp.de/pkg/EV>.	3607	L<http://software.schmorp.de/pkg/EV>.
2702		3608
2703	=item Python	3609	=item Python
2704		3610
2705	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3611	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	3612	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		3613
2712	=item Ruby	3614	=item Ruby
2713		3615
2714	Tony Arcieri has written a ruby extension that offers access to a subset	3616	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	3617	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	3618	more on top of it. It can be found via gem servers. Its homepage is at
2717	L<http://rev.rubyforge.org/>.	3619	L<http://rev.rubyforge.org/>.
2718		3620
		3621	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3622	makes rev work even on mingw.
		3623
		3624	=item Haskell
		3625
		3626	A haskell binding to libev is available at
		3627	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3628
2719	=item D	3629	=item D
2720		3630
2721	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3631	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>.	3632	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3633
		3634	=item Ocaml
		3635
		3636	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3637	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3638
		3639	=item Lua
		3640
		3641	Brian Maher has written a partial interface to libev for lua (at the
		3642	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3643	L<http://github.com/brimworks/lua-ev>.
2723		3644
2724	=back	3645	=back
2725		3646
2726		3647
2727	=head1 MACRO MAGIC	3648	=head1 MACRO MAGIC
…		…
2741	loop argument"). The C<EV_A> form is used when this is the sole argument,	3662	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:	3663	C<EV_A_> is used when other arguments are following. Example:
2743		3664
2744	ev_unref (EV_A);	3665	ev_unref (EV_A);
2745	ev_timer_add (EV_A_ watcher);	3666	ev_timer_add (EV_A_ watcher);
2746	ev_loop (EV_A_ 0);	3667	ev_run (EV_A_ 0);
2747		3668
2748	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3669	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2749	which is often provided by the following macro.	3670	which is often provided by the following macro.
2750		3671
2751	=item C<EV_P>, C<EV_P_>	3672	=item C<EV_P>, C<EV_P_>
…		…
2791	}	3712	}
2792		3713
2793	ev_check check;	3714	ev_check check;
2794	ev_check_init (&check, check_cb);	3715	ev_check_init (&check, check_cb);
2795	ev_check_start (EV_DEFAULT_ &check);	3716	ev_check_start (EV_DEFAULT_ &check);
2796	ev_loop (EV_DEFAULT_ 0);	3717	ev_run (EV_DEFAULT_ 0);
2797		3718
2798	=head1 EMBEDDING	3719	=head1 EMBEDDING
2799		3720
2800	Libev can (and often is) directly embedded into host	3721	Libev can (and often is) directly embedded into host
2801	applications. Examples of applications that embed it include the Deliantra	3722	applications. Examples of applications that embed it include the Deliantra
…		…
2828		3749
2829	#define EV_STANDALONE 1	3750	#define EV_STANDALONE 1
2830	#include "ev.h"	3751	#include "ev.h"
2831		3752
2832	Both header files and implementation files can be compiled with a C++	3753	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	3754	compiler (at least, that's a stated goal, and breakage will be treated
2834	as a bug).	3755	as a bug).
2835		3756
2836	You need the following files in your source tree, or in a directory	3757	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):	3758	in your include path (e.g. in libev/ when using -Ilibev):
2838		3759
…		…
2881	libev.m4	3802	libev.m4
2882		3803
2883	=head2 PREPROCESSOR SYMBOLS/MACROS	3804	=head2 PREPROCESSOR SYMBOLS/MACROS
2884		3805
2885	Libev can be configured via a variety of preprocessor symbols you have to	3806	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	3807	define before including (or compiling) any of its files. The default in
2887	autoconf is noted for every option.	3808	the absence of autoconf is documented for every option.
		3809
		3810	Symbols marked with "(h)" do not change the ABI, and can have different
		3811	values when compiling libev vs. including F<ev.h>, so it is permissible
		3812	to redefine them before including F<ev.h> without breaking compatibility
		3813	to a compiled library. All other symbols change the ABI, which means all
		3814	users of libev and the libev code itself must be compiled with compatible
		3815	settings.
2888		3816
2889	=over 4	3817	=over 4
2890		3818
		3819	=item EV_COMPAT3 (h)
		3820
		3821	Backwards compatibility is a major concern for libev. This is why this
		3822	release of libev comes with wrappers for the functions and symbols that
		3823	have been renamed between libev version 3 and 4.
		3824
		3825	You can disable these wrappers (to test compatibility with future
		3826	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3827	sources. This has the additional advantage that you can drop the C<struct>
		3828	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3829	typedef in that case.
		3830
		3831	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3832	and in some even more future version the compatibility code will be
		3833	removed completely.
		3834
2891	=item EV_STANDALONE	3835	=item EV_STANDALONE (h)
2892		3836
2893	Must always be C<1> if you do not use autoconf configuration, which	3837	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	3838	keeps libev from including F<config.h>, and it also defines dummy
2895	implementations for some libevent functions (such as logging, which is not	3839	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	3840	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.	3841	F<event.h> that are not directly supported by the libev core alone.
2898		3842
		3843	In standalone mode, libev will still try to automatically deduce the
		3844	configuration, but has to be more conservative.
		3845
2899	=item EV_USE_MONOTONIC	3846	=item EV_USE_MONOTONIC
2900		3847
2901	If defined to be C<1>, libev will try to detect the availability of the	3848	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	3849	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	3850	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	3851	you usually have to link against librt or something similar. Enabling it
2905	the functionality isn't available is safe, though, although you have	3852	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>	3853	to make sure you link against any libraries where the C<clock_gettime>
2907	function is hiding in (often F<-lrt>).	3854	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2908		3855
2909	=item EV_USE_REALTIME	3856	=item EV_USE_REALTIME
2910		3857
2911	If defined to be C<1>, libev will try to detect the availability of the	3858	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	3859	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	3860	at runtime if successful). Otherwise no use of the real-time clock
2914	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3861	option will be attempted. This effectively replaces C<gettimeofday>
2915	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3862	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2916	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3863	correctness. See the note about libraries in the description of
		3864	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3865	C<EV_USE_CLOCK_SYSCALL>.
		3866
		3867	=item EV_USE_CLOCK_SYSCALL
		3868
		3869	If defined to be C<1>, libev will try to use a direct syscall instead
		3870	of calling the system-provided C<clock_gettime> function. This option
		3871	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3872	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3873	programs needlessly. Using a direct syscall is slightly slower (in
		3874	theory), because no optimised vdso implementation can be used, but avoids
		3875	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3876	higher, as it simplifies linking (no need for C<-lrt>).
2917		3877
2918	=item EV_USE_NANOSLEEP	3878	=item EV_USE_NANOSLEEP
2919		3879
2920	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3880	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 ()>.	3881	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2937		3897
2938	=item EV_SELECT_USE_FD_SET	3898	=item EV_SELECT_USE_FD_SET
2939		3899
2940	If defined to C<1>, then the select backend will use the system C<fd_set>	3900	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	3901	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	3902	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	3903	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	3904	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	3905	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2946	influence the size of the C<fd_set> used.	3906	configures the maximum size of the C<fd_set>.
2947		3907
2948	=item EV_SELECT_IS_WINSOCKET	3908	=item EV_SELECT_IS_WINSOCKET
2949		3909
2950	When defined to C<1>, the select backend will assume that	3910	When defined to C<1>, the select backend will assume that
2951	select/socket/connect etc. don't understand file descriptors but	3911	select/socket/connect etc. don't understand file descriptors but
…		…
2953	be used is the winsock select). This means that it will call	3913	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,	3914	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	3915	it is assumed that all these functions actually work on fds, even
2956	on win32. Should not be defined on non-win32 platforms.	3916	on win32. Should not be defined on non-win32 platforms.
2957		3917
2958	=item EV_FD_TO_WIN32_HANDLE	3918	=item EV_FD_TO_WIN32_HANDLE(fd)
2959		3919
2960	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3920	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	3921	file descriptors to socket handles. When not defining this symbol (the
2962	default), then libev will call C<_get_osfhandle>, which is usually	3922	default), then libev will call C<_get_osfhandle>, which is usually
2963	correct. In some cases, programs use their own file descriptor management,	3923	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.	3924	in which case they can provide this function to map fds to socket handles.
		3925
		3926	=item EV_WIN32_HANDLE_TO_FD(handle)
		3927
		3928	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3929	using the standard C<_open_osfhandle> function. For programs implementing
		3930	their own fd to handle mapping, overwriting this function makes it easier
		3931	to do so. This can be done by defining this macro to an appropriate value.
		3932
		3933	=item EV_WIN32_CLOSE_FD(fd)
		3934
		3935	If programs implement their own fd to handle mapping on win32, then this
		3936	macro can be used to override the C<close> function, useful to unregister
		3937	file descriptors again. Note that the replacement function has to close
		3938	the underlying OS handle.
2965		3939
2966	=item EV_USE_POLL	3940	=item EV_USE_POLL
2967		3941
2968	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3942	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	3943	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.	3990	as well as for signal and thread safety in C<ev_async> watchers.
3017		3991
3018	In the absence of this define, libev will use C<sig_atomic_t volatile>	3992	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.	3993	(from F<signal.h>), which is usually good enough on most platforms.
3020		3994
3021	=item EV_H	3995	=item EV_H (h)
3022		3996
3023	The name of the F<ev.h> header file used to include it. The default if	3997	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	3998	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.	3999	used to virtually rename the F<ev.h> header file in case of conflicts.
3026		4000
3027	=item EV_CONFIG_H	4001	=item EV_CONFIG_H (h)
3028		4002
3029	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4003	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	4004	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
3031	C<EV_H>, above.	4005	C<EV_H>, above.
3032		4006
3033	=item EV_EVENT_H	4007	=item EV_EVENT_H (h)
3034		4008
3035	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4009	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">.	4010	of how the F<event.h> header can be found, the default is C<"event.h">.
3037		4011
3038	=item EV_PROTOTYPES	4012	=item EV_PROTOTYPES (h)
3039		4013
3040	If defined to be C<0>, then F<ev.h> will not define any function	4014	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	4015	prototypes, but still define all the structs and other symbols. This is
3042	occasionally useful if you want to provide your own wrapper functions	4016	occasionally useful if you want to provide your own wrapper functions
3043	around libev functions.	4017	around libev functions.
…		…
3062	When doing priority-based operations, libev usually has to linearly search	4036	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	4037	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	4038	and time, so using the defaults of five priorities (-2 .. +2) is usually
3065	fine.	4039	fine.
3066		4040
3067	If your embedding application does not need any priorities, defining these both to	4041	If your embedding application does not need any priorities, defining these
3068	C<0> will save some memory and CPU.	4042	both to C<0> will save some memory and CPU.
3069		4043
3070	=item EV_PERIODIC_ENABLE	4044	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4045	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4046	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
3071		4047
3072	If undefined or defined to be C<1>, then periodic timers are supported. If	4048	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	4049	the respective watcher type is supported. If defined to be C<0>, then it
3074	code.	4050	is not. Disabling watcher types mainly saves code size.
3075		4051
3076	=item EV_IDLE_ENABLE	4052	=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		4053
3104	If you need to shave off some kilobytes of code at the expense of some	4054	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	4055	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	4056	certain subsets of functionality. The default is to enable all features
3107	much smaller 2-heap for timer management over the default 4-heap.	4057	that can be enabled on the platform.
		4058
		4059	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4060	with some broad features you want) and then selectively re-enable
		4061	additional parts you want, for example if you want everything minimal,
		4062	but multiple event loop support, async and child watchers and the poll
		4063	backend, use this:
		4064
		4065	#define EV_FEATURES 0
		4066	#define EV_MULTIPLICITY 1
		4067	#define EV_USE_POLL 1
		4068	#define EV_CHILD_ENABLE 1
		4069	#define EV_ASYNC_ENABLE 1
		4070
		4071	The actual value is a bitset, it can be a combination of the following
		4072	values:
		4073
		4074	=over 4
		4075
		4076	=item C<1> - faster/larger code
		4077
		4078	Use larger code to speed up some operations.
		4079
		4080	Currently this is used to override some inlining decisions (enlarging the
		4081	code size by roughly 30% on amd64).
		4082
		4083	When optimising for size, use of compiler flags such as C<-Os> with
		4084	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4085	assertions.
		4086
		4087	=item C<2> - faster/larger data structures
		4088
		4089	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4090	hash table sizes and so on. This will usually further increase code size
		4091	and can additionally have an effect on the size of data structures at
		4092	runtime.
		4093
		4094	=item C<4> - full API configuration
		4095
		4096	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4097	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4098
		4099	=item C<8> - full API
		4100
		4101	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4102	details on which parts of the API are still available without this
		4103	feature, and do not complain if this subset changes over time.
		4104
		4105	=item C<16> - enable all optional watcher types
		4106
		4107	Enables all optional watcher types. If you want to selectively enable
		4108	only some watcher types other than I/O and timers (e.g. prepare,
		4109	embed, async, child...) you can enable them manually by defining
		4110	C<EV_watchertype_ENABLE> to C<1> instead.
		4111
		4112	=item C<32> - enable all backends
		4113
		4114	This enables all backends - without this feature, you need to enable at
		4115	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4116
		4117	=item C<64> - enable OS-specific "helper" APIs
		4118
		4119	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4120	default.
		4121
		4122	=back
		4123
		4124	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4125	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4126	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4127	watchers, timers and monotonic clock support.
		4128
		4129	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4130	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4131	your program might be left out as well - a binary starting a timer and an
		4132	I/O watcher then might come out at only 5Kb.
		4133
		4134	=item EV_AVOID_STDIO
		4135
		4136	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4137	functions (printf, scanf, perror etc.). This will increase the code size
		4138	somewhat, but if your program doesn't otherwise depend on stdio and your
		4139	libc allows it, this avoids linking in the stdio library which is quite
		4140	big.
		4141
		4142	Note that error messages might become less precise when this option is
		4143	enabled.
		4144
		4145	=item EV_NSIG
		4146
		4147	The highest supported signal number, +1 (or, the number of
		4148	signals): Normally, libev tries to deduce the maximum number of signals
		4149	automatically, but sometimes this fails, in which case it can be
		4150	specified. Also, using a lower number than detected (C<32> should be
		4151	good for about any system in existence) can save some memory, as libev
		4152	statically allocates some 12-24 bytes per signal number.
3108		4153
3109	=item EV_PID_HASHSIZE	4154	=item EV_PID_HASHSIZE
3110		4155
3111	C<ev_child> watchers use a small hash table to distribute workload by	4156	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	4157	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	4158	usually more than enough. If you need to manage thousands of children you
3114	increase this value (I<must> be a power of two).	4159	might want to increase this value (I<must> be a power of two).
3115		4160
3116	=item EV_INOTIFY_HASHSIZE	4161	=item EV_INOTIFY_HASHSIZE
3117		4162
3118	C<ev_stat> watchers use a small hash table to distribute workload by	4163	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>),	4164	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>	4165	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	4166	C<ev_stat> watchers you might want to increase this value (I<must> be a
3122	two).	4167	power of two).
3123		4168
3124	=item EV_USE_4HEAP	4169	=item EV_USE_4HEAP
3125		4170
3126	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4171	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	4172	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	4173	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3129	noticeably faster performance with many (thousands) of watchers.	4174	faster performance with many (thousands) of watchers.
3130		4175
3131	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4176	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3132	(disabled).	4177	will be C<0>.
3133		4178
3134	=item EV_HEAP_CACHE_AT	4179	=item EV_HEAP_CACHE_AT
3135		4180
3136	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4181	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	4182	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>),	4183	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,	4184	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	4185	but avoids random read accesses on heap changes. This improves performance
3141	noticeably with with many (hundreds) of watchers.	4186	noticeably with many (hundreds) of watchers.
3142		4187
3143	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4188	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3144	(disabled).	4189	will be C<0>.
3145		4190
3146	=item EV_VERIFY	4191	=item EV_VERIFY
3147		4192
3148	Controls how much internal verification (see C<ev_loop_verify ()>) will	4193	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	4194	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	4195	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	4196	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	4197	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	4198	verification code will be called very frequently, which will slow down
3154	libev considerably.	4199	libev considerably.
3155		4200
3156	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	4201	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3157	C<0.>	4202	will be C<0>.
3158		4203
3159	=item EV_COMMON	4204	=item EV_COMMON
3160		4205
3161	By default, all watchers have a C<void *data> member. By redefining	4206	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	4207	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,	4208	members. You have to define it each time you include one of the files,
3164	though, and it must be identical each time.	4209	though, and it must be identical each time.
3165		4210
3166	For example, the perl EV module uses something like this:	4211	For example, the perl EV module uses something like this:
3167		4212
…		…
3179	and the way callbacks are invoked and set. Must expand to a struct member	4224	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	4225	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	4226	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	4227	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++.	4228	method calls instead of plain function calls in C++.
		4229
		4230	=back
3184		4231
3185	=head2 EXPORTED API SYMBOLS	4232	=head2 EXPORTED API SYMBOLS
3186		4233
3187	If you need to re-export the API (e.g. via a DLL) and you need a list of	4234	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	4235	exported symbols, you can use the provided F<Symbol.*> files which list
…		…
3218	file.	4265	file.
3219		4266
3220	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4267	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:	4268	that everybody includes and which overrides some configure choices:
3222		4269
3223	#define EV_MINIMAL 1	4270	#define EV_FEATURES 8
3224	#define EV_USE_POLL 0	4271	#define EV_USE_SELECT 1
3225	#define EV_MULTIPLICITY 0
3226	#define EV_PERIODIC_ENABLE 0	4272	#define EV_PREPARE_ENABLE 1
		4273	#define EV_IDLE_ENABLE 1
3227	#define EV_STAT_ENABLE 0	4274	#define EV_SIGNAL_ENABLE 1
3228	#define EV_FORK_ENABLE 0	4275	#define EV_CHILD_ENABLE 1
		4276	#define EV_USE_STDEXCEPT 0
3229	#define EV_CONFIG_H <config.h>	4277	#define EV_CONFIG_H <config.h>
3230	#define EV_MINPRI 0
3231	#define EV_MAXPRI 0
3232		4278
3233	#include "ev++.h"	4279	#include "ev++.h"
3234		4280
3235	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4281	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3236		4282
3237	#include "ev_cpp.h"	4283	#include "ev_cpp.h"
3238	#include "ev.c"	4284	#include "ev.c"
3239		4285
		4286	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3240		4287
3241	=head1 THREADS AND COROUTINES	4288	=head2 THREADS AND COROUTINES
3242		4289
3243	=head2 THREADS	4290	=head3 THREADS
3244		4291
3245	Libev itself is thread-safe (unless the opposite is specifically	4292	All libev functions are reentrant and thread-safe unless explicitly
3246	documented for a function), but it uses no locking itself. This means that	4293	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	4294	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:	4295	are no concurrent calls into any libev function with the same loop
		4296	parameter (C<ev_default_*> calls have an implicit default loop parameter,
3249	libev guarentees that different event loops share no data structures that	4297	of course): libev guarantees that different event loops share no data
3250	need locking.	4298	structures that need any locking.
3251		4299
3252	Or to put it differently: calls with different loop parameters can be done	4300	Or to put it differently: calls with different loop parameters can be done
3253	concurrently from multiple threads, calls with the same loop parameter	4301	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	4302	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	4303	only one thread ever is inside a call at any point in time, e.g. by using
3256	a mutex per loop).	4304	a mutex per loop).
3257		4305
3258	Specifically to support threads (and signal handlers), libev implements	4306	Specifically to support threads (and signal handlers), libev implements
3259	so-called C<ev_async> watchers, which allow some limited form of	4307	so-called C<ev_async> watchers, which allow some limited form of
3260	concurrency on the same event loop.	4308	concurrency on the same event loop, namely waking it up "from the
		4309	outside".
3261		4310
3262	If you want to know which design (one loop, locking, or multiple loops	4311	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	4312	without or something else still) is best for your problem, then I cannot
3264	help you. I can give some generic advice however:	4313	help you, but here is some generic advice:
3265		4314
3266	=over 4	4315	=over 4
3267		4316
3268	=item * most applications have a main thread: use the default libev loop	4317	=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.	4318	in that thread, or create a separate thread running only the default loop.
…		…
3281		4330
3282	Choosing a model is hard - look around, learn, know that usually you can do	4331	Choosing a model is hard - look around, learn, know that usually you can do
3283	better than you currently do :-)	4332	better than you currently do :-)
3284		4333
3285	=item * often you need to talk to some other thread which blocks in the	4334	=item * often you need to talk to some other thread which blocks in the
		4335	event loop.
		4336
3286	event loop - C<ev_async> watchers can be used to wake them up from other	4337	C<ev_async> watchers can be used to wake them up from other threads safely
3287	threads safely (or from signal contexts...).	4338	(or from signal contexts...).
3288		4339
3289	=item * some watcher types are only supported in the default loop - use	4340	An example use would be to communicate signals or other events that only
3290	C<ev_async> watchers to tell your other loops about any such events.	4341	work in the default loop by registering the signal watcher with the
		4342	default loop and triggering an C<ev_async> watcher from the default loop
		4343	watcher callback into the event loop interested in the signal.
3291		4344
3292	=back	4345	=back
3293		4346
		4347	=head4 THREAD LOCKING EXAMPLE
		4348
		4349	Here is a fictitious example of how to run an event loop in a different
		4350	thread than where callbacks are being invoked and watchers are
		4351	created/added/removed.
		4352
		4353	For a real-world example, see the C<EV::Loop::Async> perl module,
		4354	which uses exactly this technique (which is suited for many high-level
		4355	languages).
		4356
		4357	The example uses a pthread mutex to protect the loop data, a condition
		4358	variable to wait for callback invocations, an async watcher to notify the
		4359	event loop thread and an unspecified mechanism to wake up the main thread.
		4360
		4361	First, you need to associate some data with the event loop:
		4362
		4363	typedef struct {
		4364	mutex_t lock; /* global loop lock */
		4365	ev_async async_w;
		4366	thread_t tid;
		4367	cond_t invoke_cv;
		4368	} userdata;
		4369
		4370	void prepare_loop (EV_P)
		4371	{
		4372	// for simplicity, we use a static userdata struct.
		4373	static userdata u;
		4374
		4375	ev_async_init (&u->async_w, async_cb);
		4376	ev_async_start (EV_A_ &u->async_w);
		4377
		4378	pthread_mutex_init (&u->lock, 0);
		4379	pthread_cond_init (&u->invoke_cv, 0);
		4380
		4381	// now associate this with the loop
		4382	ev_set_userdata (EV_A_ u);
		4383	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4384	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4385
		4386	// then create the thread running ev_loop
		4387	pthread_create (&u->tid, 0, l_run, EV_A);
		4388	}
		4389
		4390	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4391	solely to wake up the event loop so it takes notice of any new watchers
		4392	that might have been added:
		4393
		4394	static void
		4395	async_cb (EV_P_ ev_async *w, int revents)
		4396	{
		4397	// just used for the side effects
		4398	}
		4399
		4400	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4401	protecting the loop data, respectively.
		4402
		4403	static void
		4404	l_release (EV_P)
		4405	{
		4406	userdata *u = ev_userdata (EV_A);
		4407	pthread_mutex_unlock (&u->lock);
		4408	}
		4409
		4410	static void
		4411	l_acquire (EV_P)
		4412	{
		4413	userdata *u = ev_userdata (EV_A);
		4414	pthread_mutex_lock (&u->lock);
		4415	}
		4416
		4417	The event loop thread first acquires the mutex, and then jumps straight
		4418	into C<ev_run>:
		4419
		4420	void *
		4421	l_run (void *thr_arg)
		4422	{
		4423	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4424
		4425	l_acquire (EV_A);
		4426	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4427	ev_run (EV_A_ 0);
		4428	l_release (EV_A);
		4429
		4430	return 0;
		4431	}
		4432
		4433	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4434	signal the main thread via some unspecified mechanism (signals? pipe
		4435	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4436	have been called (in a while loop because a) spurious wakeups are possible
		4437	and b) skipping inter-thread-communication when there are no pending
		4438	watchers is very beneficial):
		4439
		4440	static void
		4441	l_invoke (EV_P)
		4442	{
		4443	userdata *u = ev_userdata (EV_A);
		4444
		4445	while (ev_pending_count (EV_A))
		4446	{
		4447	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4448	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4449	}
		4450	}
		4451
		4452	Now, whenever the main thread gets told to invoke pending watchers, it
		4453	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4454	thread to continue:
		4455
		4456	static void
		4457	real_invoke_pending (EV_P)
		4458	{
		4459	userdata *u = ev_userdata (EV_A);
		4460
		4461	pthread_mutex_lock (&u->lock);
		4462	ev_invoke_pending (EV_A);
		4463	pthread_cond_signal (&u->invoke_cv);
		4464	pthread_mutex_unlock (&u->lock);
		4465	}
		4466
		4467	Whenever you want to start/stop a watcher or do other modifications to an
		4468	event loop, you will now have to lock:
		4469
		4470	ev_timer timeout_watcher;
		4471	userdata *u = ev_userdata (EV_A);
		4472
		4473	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4474
		4475	pthread_mutex_lock (&u->lock);
		4476	ev_timer_start (EV_A_ &timeout_watcher);
		4477	ev_async_send (EV_A_ &u->async_w);
		4478	pthread_mutex_unlock (&u->lock);
		4479
		4480	Note that sending the C<ev_async> watcher is required because otherwise
		4481	an event loop currently blocking in the kernel will have no knowledge
		4482	about the newly added timer. By waking up the loop it will pick up any new
		4483	watchers in the next event loop iteration.
		4484
3294	=head2 COROUTINES	4485	=head3 COROUTINES
3295		4486
3296	Libev is much more accommodating to coroutines ("cooperative threads"):	4487	Libev is very accommodating to coroutines ("cooperative threads"):
3297	libev fully supports nesting calls to it's functions from different	4488	libev fully supports nesting calls to its functions from different
3298	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4489	coroutines (e.g. you can call C<ev_run> on the same loop from two
3299	different coroutines and switch freely between both coroutines running the	4490	different coroutines, and switch freely between both coroutines running
3300	loop, as long as you don't confuse yourself). The only exception is that	4491	the loop, as long as you don't confuse yourself). The only exception is
3301	you must not do this from C<ev_periodic> reschedule callbacks.	4492	that you must not do this from C<ev_periodic> reschedule callbacks.
3302		4493
3303	Care has been taken to ensure that libev does not keep local state inside	4494	Care has been taken to ensure that libev does not keep local state inside
3304	C<ev_loop>, and other calls do not usually allow coroutine switches.	4495	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4496	they do not call any callbacks.
3305		4497
		4498	=head2 COMPILER WARNINGS
3306		4499
3307	=head1 COMPLEXITIES	4500	Depending on your compiler and compiler settings, you might get no or a
		4501	lot of warnings when compiling libev code. Some people are apparently
		4502	scared by this.
3308		4503
3309	In this section the complexities of (many of) the algorithms used inside	4504	However, these are unavoidable for many reasons. For one, each compiler
3310	libev will be explained. For complexity discussions about backends see the	4505	has different warnings, and each user has different tastes regarding
3311	documentation for C<ev_default_init>.	4506	warning options. "Warn-free" code therefore cannot be a goal except when
		4507	targeting a specific compiler and compiler-version.
3312		4508
3313	All of the following are about amortised time: If an array needs to be	4509	Another reason is that some compiler warnings require elaborate
3314	extended, libev needs to realloc and move the whole array, but this	4510	workarounds, or other changes to the code that make it less clear and less
3315	happens asymptotically never with higher number of elements, so O(1) might	4511	maintainable.
3316	mean it might do a lengthy realloc operation in rare cases, but on average
3317	it is much faster and asymptotically approaches constant time.
3318		4512
3319	=over 4	4513	And of course, some compiler warnings are just plain stupid, or simply
		4514	wrong (because they don't actually warn about the condition their message
		4515	seems to warn about). For example, certain older gcc versions had some
		4516	warnings that resulted in an extreme number of false positives. These have
		4517	been fixed, but some people still insist on making code warn-free with
		4518	such buggy versions.
3320		4519
3321	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4520	While libev is written to generate as few warnings as possible,
		4521	"warn-free" code is not a goal, and it is recommended not to build libev
		4522	with any compiler warnings enabled unless you are prepared to cope with
		4523	them (e.g. by ignoring them). Remember that warnings are just that:
		4524	warnings, not errors, or proof of bugs.
3322		4525
3323	This means that, when you have a watcher that triggers in one hour and
3324	there are 100 watchers that would trigger before that then inserting will
3325	have to skip roughly seven (C<ld 100>) of these watchers.
3326		4526
3327	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4527	=head2 VALGRIND
3328		4528
3329	That means that changing a timer costs less than removing/adding them	4529	Valgrind has a special section here because it is a popular tool that is
3330	as only the relative motion in the event queue has to be paid for.	4530	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3331		4531
3332	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4532	If you think you found a bug (memory leak, uninitialised data access etc.)
		4533	in libev, then check twice: If valgrind reports something like:
3333		4534
3334	These just add the watcher into an array or at the head of a list.	4535	==2274== definitely lost: 0 bytes in 0 blocks.
		4536	==2274== possibly lost: 0 bytes in 0 blocks.
		4537	==2274== still reachable: 256 bytes in 1 blocks.
3335		4538
3336	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4539	Then there is no memory leak, just as memory accounted to global variables
		4540	is not a memleak - the memory is still being referenced, and didn't leak.
3337		4541
3338	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4542	Similarly, under some circumstances, valgrind might report kernel bugs
		4543	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4544	although an acceptable workaround has been found here), or it might be
		4545	confused.
3339		4546
3340	These watchers are stored in lists then need to be walked to find the	4547	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3341	correct watcher to remove. The lists are usually short (you don't usually	4548	make it into some kind of religion.
3342	have many watchers waiting for the same fd or signal).
3343		4549
3344	=item Finding the next timer in each loop iteration: O(1)	4550	If you are unsure about something, feel free to contact the mailing list
		4551	with the full valgrind report and an explanation on why you think this
		4552	is a bug in libev (best check the archives, too :). However, don't be
		4553	annoyed when you get a brisk "this is no bug" answer and take the chance
		4554	of learning how to interpret valgrind properly.
3345		4555
3346	By virtue of using a binary or 4-heap, the next timer is always found at a	4556	If you need, for some reason, empty reports from valgrind for your project
3347	fixed position in the storage array.	4557	I suggest using suppression lists.
3348		4558
3349	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3350		4559
3351	A change means an I/O watcher gets started or stopped, which requires	4560	=head1 PORTABILITY NOTES
3352	libev to recalculate its status (and possibly tell the kernel, depending
3353	on backend and whether C<ev_io_set> was used).
3354		4561
3355	=item Activating one watcher (putting it into the pending state): O(1)	4562	=head2 GNU/LINUX 32 BIT LIMITATIONS
3356		4563
3357	=item Priority handling: O(number_of_priorities)	4564	GNU/Linux is the only common platform that supports 64 bit file/large file
		4565	interfaces but I<disables> them by default.
3358		4566
3359	Priorities are implemented by allocating some space for each	4567	That means that libev compiled in the default environment doesn't support
3360	priority. When doing priority-based operations, libev usually has to	4568	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
3361	linearly search all the priorities, but starting/stopping and activating
3362	watchers becomes O(1) w.r.t. priority handling.
3363		4569
3364	=item Sending an ev_async: O(1)	4570	Unfortunately, many programs try to work around this GNU/Linux issue
		4571	by enabling the large file API, which makes them incompatible with the
		4572	standard libev compiled for their system.
3365		4573
3366	=item Processing ev_async_send: O(number_of_async_watchers)	4574	Likewise, libev cannot enable the large file API itself as this would
		4575	suddenly make it incompatible to the default compile time environment,
		4576	i.e. all programs not using special compile switches.
3367		4577
3368	=item Processing signals: O(max_signal_number)	4578	=head2 OS/X AND DARWIN BUGS
3369		4579
3370	Sending involves a system call I<iff> there were no other C<ev_async_send>	4580	The whole thing is a bug if you ask me - basically any system interface
3371	calls in the current loop iteration. Checking for async and signal events	4581	you touch is broken, whether it is locales, poll, kqueue or even the
3372	involves iterating over all running async watchers or all signal numbers.	4582	OpenGL drivers.
3373		4583
3374	=back	4584	=head3 C<kqueue> is buggy
3375		4585
		4586	The kqueue syscall is broken in all known versions - most versions support
		4587	only sockets, many support pipes.
3376		4588
		4589	Libev tries to work around this by not using C<kqueue> by default on this
		4590	rotten platform, but of course you can still ask for it when creating a
		4591	loop - embedding a socket-only kqueue loop into a select-based one is
		4592	probably going to work well.
		4593
		4594	=head3 C<poll> is buggy
		4595
		4596	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4597	implementation by something calling C<kqueue> internally around the 10.5.6
		4598	release, so now C<kqueue> I<and> C<poll> are broken.
		4599
		4600	Libev tries to work around this by not using C<poll> by default on
		4601	this rotten platform, but of course you can still ask for it when creating
		4602	a loop.
		4603
		4604	=head3 C<select> is buggy
		4605
		4606	All that's left is C<select>, and of course Apple found a way to fuck this
		4607	one up as well: On OS/X, C<select> actively limits the number of file
		4608	descriptors you can pass in to 1024 - your program suddenly crashes when
		4609	you use more.
		4610
		4611	There is an undocumented "workaround" for this - defining
		4612	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4613	work on OS/X.
		4614
		4615	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4616
		4617	=head3 C<errno> reentrancy
		4618
		4619	The default compile environment on Solaris is unfortunately so
		4620	thread-unsafe that you can't even use components/libraries compiled
		4621	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4622	defined by default. A valid, if stupid, implementation choice.
		4623
		4624	If you want to use libev in threaded environments you have to make sure
		4625	it's compiled with C<_REENTRANT> defined.
		4626
		4627	=head3 Event port backend
		4628
		4629	The scalable event interface for Solaris is called "event
		4630	ports". Unfortunately, this mechanism is very buggy in all major
		4631	releases. If you run into high CPU usage, your program freezes or you get
		4632	a large number of spurious wakeups, make sure you have all the relevant
		4633	and latest kernel patches applied. No, I don't know which ones, but there
		4634	are multiple ones to apply, and afterwards, event ports actually work
		4635	great.
		4636
		4637	If you can't get it to work, you can try running the program by setting
		4638	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4639	C<select> backends.
		4640
		4641	=head2 AIX POLL BUG
		4642
		4643	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4644	this by trying to avoid the poll backend altogether (i.e. it's not even
		4645	compiled in), which normally isn't a big problem as C<select> works fine
		4646	with large bitsets on AIX, and AIX is dead anyway.
		4647
3377	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	4648	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4649
		4650	=head3 General issues
3378		4651
3379	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4652	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3380	requires, and its I/O model is fundamentally incompatible with the POSIX	4653	requires, and its I/O model is fundamentally incompatible with the POSIX
3381	model. Libev still offers limited functionality on this platform in	4654	model. Libev still offers limited functionality on this platform in
3382	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4655	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3383	descriptors. This only applies when using Win32 natively, not when using	4656	descriptors. This only applies when using Win32 natively, not when using
3384	e.g. cygwin.	4657	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4658	as every compielr comes with a slightly differently broken/incompatible
		4659	environment.
3385		4660
3386	Lifting these limitations would basically require the full	4661	Lifting these limitations would basically require the full
3387	re-implementation of the I/O system. If you are into these kinds of	4662	re-implementation of the I/O system. If you are into this kind of thing,
3388	things, then note that glib does exactly that for you in a very portable	4663	then note that glib does exactly that for you in a very portable way (note
3389	way (note also that glib is the slowest event library known to man).	4664	also that glib is the slowest event library known to man).
3390		4665
3391	There is no supported compilation method available on windows except	4666	There is no supported compilation method available on windows except
3392	embedding it into other applications.	4667	embedding it into other applications.
		4668
		4669	Sensible signal handling is officially unsupported by Microsoft - libev
		4670	tries its best, but under most conditions, signals will simply not work.
3393		4671
3394	Not a libev limitation but worth mentioning: windows apparently doesn't	4672	Not a libev limitation but worth mentioning: windows apparently doesn't
3395	accept large writes: instead of resulting in a partial write, windows will	4673	accept large writes: instead of resulting in a partial write, windows will
3396	either accept everything or return C<ENOBUFS> if the buffer is too large,	4674	either accept everything or return C<ENOBUFS> if the buffer is too large,
3397	so make sure you only write small amounts into your sockets (less than a	4675	so make sure you only write small amounts into your sockets (less than a
3398	megabyte seems safe, but thsi apparently depends on the amount of memory	4676	megabyte seems safe, but this apparently depends on the amount of memory
3399	available).	4677	available).
3400		4678
3401	Due to the many, low, and arbitrary limits on the win32 platform and	4679	Due to the many, low, and arbitrary limits on the win32 platform and
3402	the abysmal performance of winsockets, using a large number of sockets	4680	the abysmal performance of winsockets, using a large number of sockets
3403	is not recommended (and not reasonable). If your program needs to use	4681	is not recommended (and not reasonable). If your program needs to use
3404	more than a hundred or so sockets, then likely it needs to use a totally	4682	more than a hundred or so sockets, then likely it needs to use a totally
3405	different implementation for windows, as libev offers the POSIX readiness	4683	different implementation for windows, as libev offers the POSIX readiness
3406	notification model, which cannot be implemented efficiently on windows	4684	notification model, which cannot be implemented efficiently on windows
3407	(Microsoft monopoly games).	4685	(due to Microsoft monopoly games).
3408		4686
3409	A typical way to use libev under windows is to embed it (see the embedding	4687	A typical way to use libev under windows is to embed it (see the embedding
3410	section for details) and use the following F<evwrap.h> header file instead	4688	section for details) and use the following F<evwrap.h> header file instead
3411	of F<ev.h>:	4689	of F<ev.h>:
3412		4690
…		…
3414	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	4692	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3415		4693
3416	#include "ev.h"	4694	#include "ev.h"
3417		4695
3418	And compile the following F<evwrap.c> file into your project (make sure	4696	And compile the following F<evwrap.c> file into your project (make sure
3419	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	4697	you do I<not> compile the F<ev.c> or any other embedded source files!):
3420		4698
3421	#include "evwrap.h"	4699	#include "evwrap.h"
3422	#include "ev.c"	4700	#include "ev.c"
3423		4701
3424	=over 4
3425
3426	=item The winsocket select function	4702	=head3 The winsocket C<select> function
3427		4703
3428	The winsocket C<select> function doesn't follow POSIX in that it	4704	The winsocket C<select> function doesn't follow POSIX in that it
3429	requires socket I<handles> and not socket I<file descriptors> (it is	4705	requires socket I<handles> and not socket I<file descriptors> (it is
3430	also extremely buggy). This makes select very inefficient, and also	4706	also extremely buggy). This makes select very inefficient, and also
3431	requires a mapping from file descriptors to socket handles (the Microsoft	4707	requires a mapping from file descriptors to socket handles (the Microsoft
…		…
3440	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4716	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3441		4717
3442	Note that winsockets handling of fd sets is O(n), so you can easily get a	4718	Note that winsockets handling of fd sets is O(n), so you can easily get a
3443	complexity in the O(n²) range when using win32.	4719	complexity in the O(n²) range when using win32.
3444		4720
3445	=item Limited number of file descriptors	4721	=head3 Limited number of file descriptors
3446		4722
3447	Windows has numerous arbitrary (and low) limits on things.	4723	Windows has numerous arbitrary (and low) limits on things.
3448		4724
3449	Early versions of winsocket's select only supported waiting for a maximum	4725	Early versions of winsocket's select only supported waiting for a maximum
3450	of C<64> handles (probably owning to the fact that all windows kernels	4726	of C<64> handles (probably owning to the fact that all windows kernels
3451	can only wait for C<64> things at the same time internally; Microsoft	4727	can only wait for C<64> things at the same time internally; Microsoft
3452	recommends spawning a chain of threads and wait for 63 handles and the	4728	recommends spawning a chain of threads and wait for 63 handles and the
3453	previous thread in each. Great).	4729	previous thread in each. Sounds great!).
3454		4730
3455	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4731	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3456	to some high number (e.g. C<2048>) before compiling the winsocket select	4732	to some high number (e.g. C<2048>) before compiling the winsocket select
3457	call (which might be in libev or elsewhere, for example, perl does its own	4733	call (which might be in libev or elsewhere, for example, perl and many
3458	select emulation on windows).	4734	other interpreters do their own select emulation on windows).
3459		4735
3460	Another limit is the number of file descriptors in the Microsoft runtime	4736	Another limit is the number of file descriptors in the Microsoft runtime
3461	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4737	libraries, which by default is C<64> (there must be a hidden I<64>
3462	or something like this inside Microsoft). You can increase this by calling	4738	fetish or something like this inside Microsoft). You can increase this
3463	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4739	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3464	arbitrary limit), but is broken in many versions of the Microsoft runtime	4740	(another arbitrary limit), but is broken in many versions of the Microsoft
3465	libraries.
3466
3467	This might get you to about C<512> or C<2048> sockets (depending on	4741	runtime libraries. This might get you to about C<512> or C<2048> sockets
3468	windows version and/or the phase of the moon). To get more, you need to	4742	(depending on windows version and/or the phase of the moon). To get more,
3469	wrap all I/O functions and provide your own fd management, but the cost of	4743	you need to wrap all I/O functions and provide your own fd management, but
3470	calling select (O(n²)) will likely make this unworkable.	4744	the cost of calling select (O(n²)) will likely make this unworkable.
3471		4745
3472	=back
3473
3474
3475	=head1 PORTABILITY REQUIREMENTS	4746	=head2 PORTABILITY REQUIREMENTS
3476		4747
3477	In addition to a working ISO-C implementation, libev relies on a few	4748	In addition to a working ISO-C implementation and of course the
3478	additional extensions:	4749	backend-specific APIs, libev relies on a few additional extensions:
3479		4750
3480	=over 4	4751	=over 4
3481		4752
3482	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	4753	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3483	calling conventions regardless of C<ev_watcher_type *>.	4754	calling conventions regardless of C<ev_watcher_type *>.
…		…
3489	calls them using an C<ev_watcher *> internally.	4760	calls them using an C<ev_watcher *> internally.
3490		4761
3491	=item C<sig_atomic_t volatile> must be thread-atomic as well	4762	=item C<sig_atomic_t volatile> must be thread-atomic as well
3492		4763
3493	The type C<sig_atomic_t volatile> (or whatever is defined as	4764	The type C<sig_atomic_t volatile> (or whatever is defined as
3494	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4765	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3495	threads. This is not part of the specification for C<sig_atomic_t>, but is	4766	threads. This is not part of the specification for C<sig_atomic_t>, but is
3496	believed to be sufficiently portable.	4767	believed to be sufficiently portable.
3497		4768
3498	=item C<sigprocmask> must work in a threaded environment	4769	=item C<sigprocmask> must work in a threaded environment
3499		4770
…		…
3508	except the initial one, and run the default loop in the initial thread as	4779	except the initial one, and run the default loop in the initial thread as
3509	well.	4780	well.
3510		4781
3511	=item C<long> must be large enough for common memory allocation sizes	4782	=item C<long> must be large enough for common memory allocation sizes
3512		4783
3513	To improve portability and simplify using libev, libev uses C<long>	4784	To improve portability and simplify its API, libev uses C<long> internally
3514	internally instead of C<size_t> when allocating its data structures. On	4785	instead of C<size_t> when allocating its data structures. On non-POSIX
3515	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	4786	systems (Microsoft...) this might be unexpectedly low, but is still at
3516	is still at least 31 bits everywhere, which is enough for hundreds of	4787	least 31 bits everywhere, which is enough for hundreds of millions of
3517	millions of watchers.	4788	watchers.
3518		4789
3519	=item C<double> must hold a time value in seconds with enough accuracy	4790	=item C<double> must hold a time value in seconds with enough accuracy
3520		4791
3521	The type C<double> is used to represent timestamps. It is required to	4792	The type C<double> is used to represent timestamps. It is required to
3522	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4793	have at least 51 bits of mantissa (and 9 bits of exponent), which is
3523	enough for at least into the year 4000. This requirement is fulfilled by	4794	good enough for at least into the year 4000 with millisecond accuracy
		4795	(the design goal for libev). This requirement is overfulfilled by
3524	implementations implementing IEEE 754 (basically all existing ones).	4796	implementations using IEEE 754, which is basically all existing ones. With
		4797	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
3525		4798
3526	=back	4799	=back
3527		4800
3528	If you know of other additional requirements drop me a note.	4801	If you know of other additional requirements drop me a note.
3529		4802
3530		4803
3531	=head1 COMPILER WARNINGS	4804	=head1 ALGORITHMIC COMPLEXITIES
3532		4805
3533	Depending on your compiler and compiler settings, you might get no or a	4806	In this section the complexities of (many of) the algorithms used inside
3534	lot of warnings when compiling libev code. Some people are apparently	4807	libev will be documented. For complexity discussions about backends see
3535	scared by this.	4808	the documentation for C<ev_default_init>.
3536		4809
3537	However, these are unavoidable for many reasons. For one, each compiler	4810	All of the following are about amortised time: If an array needs to be
3538	has different warnings, and each user has different tastes regarding	4811	extended, libev needs to realloc and move the whole array, but this
3539	warning options. "Warn-free" code therefore cannot be a goal except when	4812	happens asymptotically rarer with higher number of elements, so O(1) might
3540	targeting a specific compiler and compiler-version.	4813	mean that libev does a lengthy realloc operation in rare cases, but on
		4814	average it is much faster and asymptotically approaches constant time.
3541		4815
3542	Another reason is that some compiler warnings require elaborate	4816	=over 4
3543	workarounds, or other changes to the code that make it less clear and less
3544	maintainable.
3545		4817
3546	And of course, some compiler warnings are just plain stupid, or simply	4818	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3547	wrong (because they don't actually warn about the condition their message
3548	seems to warn about).
3549		4819
3550	While libev is written to generate as few warnings as possible,	4820	This means that, when you have a watcher that triggers in one hour and
3551	"warn-free" code is not a goal, and it is recommended not to build libev	4821	there are 100 watchers that would trigger before that, then inserting will
3552	with any compiler warnings enabled unless you are prepared to cope with	4822	have to skip roughly seven (C<ld 100>) of these watchers.
3553	them (e.g. by ignoring them). Remember that warnings are just that:
3554	warnings, not errors, or proof of bugs.
3555		4823
		4824	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3556		4825
3557	=head1 VALGRIND	4826	That means that changing a timer costs less than removing/adding them,
		4827	as only the relative motion in the event queue has to be paid for.
3558		4828
3559	Valgrind has a special section here because it is a popular tool that is	4829	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3560	highly useful, but valgrind reports are very hard to interpret.
3561		4830
3562	If you think you found a bug (memory leak, uninitialised data access etc.)	4831	These just add the watcher into an array or at the head of a list.
3563	in libev, then check twice: If valgrind reports something like:
3564		4832
3565	==2274== definitely lost: 0 bytes in 0 blocks.	4833	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3566	==2274== possibly lost: 0 bytes in 0 blocks.
3567	==2274== still reachable: 256 bytes in 1 blocks.
3568		4834
3569	Then there is no memory leak. Similarly, under some circumstances,	4835	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3570	valgrind might report kernel bugs as if it were a bug in libev, or it
3571	might be confused (it is a very good tool, but only a tool).
3572		4836
3573	If you are unsure about something, feel free to contact the mailing list	4837	These watchers are stored in lists, so they need to be walked to find the
3574	with the full valgrind report and an explanation on why you think this is	4838	correct watcher to remove. The lists are usually short (you don't usually
3575	a bug in libev. However, don't be annoyed when you get a brisk "this is	4839	have many watchers waiting for the same fd or signal: one is typical, two
3576	no bug" answer and take the chance of learning how to interpret valgrind	4840	is rare).
3577	properly.
3578		4841
3579	If you need, for some reason, empty reports from valgrind for your project	4842	=item Finding the next timer in each loop iteration: O(1)
3580	I suggest using suppression lists.
3581		4843
		4844	By virtue of using a binary or 4-heap, the next timer is always found at a
		4845	fixed position in the storage array.
		4846
		4847	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4848
		4849	A change means an I/O watcher gets started or stopped, which requires
		4850	libev to recalculate its status (and possibly tell the kernel, depending
		4851	on backend and whether C<ev_io_set> was used).
		4852
		4853	=item Activating one watcher (putting it into the pending state): O(1)
		4854
		4855	=item Priority handling: O(number_of_priorities)
		4856
		4857	Priorities are implemented by allocating some space for each
		4858	priority. When doing priority-based operations, libev usually has to
		4859	linearly search all the priorities, but starting/stopping and activating
		4860	watchers becomes O(1) with respect to priority handling.
		4861
		4862	=item Sending an ev_async: O(1)
		4863
		4864	=item Processing ev_async_send: O(number_of_async_watchers)
		4865
		4866	=item Processing signals: O(max_signal_number)
		4867
		4868	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4869	calls in the current loop iteration. Checking for async and signal events
		4870	involves iterating over all running async watchers or all signal numbers.
		4871
		4872	=back
		4873
		4874
		4875	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4876
		4877	The major version 4 introduced some minor incompatible changes to the API.
		4878
		4879	At the moment, the C<ev.h> header file tries to implement superficial
		4880	compatibility, so most programs should still compile. Those might be
		4881	removed in later versions of libev, so better update early than late.
		4882
		4883	=over 4
		4884
		4885	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		4886
		4887	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		4888
		4889	ev_loop_destroy (EV_DEFAULT_UC);
		4890	ev_loop_fork (EV_DEFAULT);
		4891
		4892	=item function/symbol renames
		4893
		4894	A number of functions and symbols have been renamed:
		4895
		4896	ev_loop => ev_run
		4897	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		4898	EVLOOP_ONESHOT => EVRUN_ONCE
		4899
		4900	ev_unloop => ev_break
		4901	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		4902	EVUNLOOP_ONE => EVBREAK_ONE
		4903	EVUNLOOP_ALL => EVBREAK_ALL
		4904
		4905	EV_TIMEOUT => EV_TIMER
		4906
		4907	ev_loop_count => ev_iteration
		4908	ev_loop_depth => ev_depth
		4909	ev_loop_verify => ev_verify
		4910
		4911	Most functions working on C<struct ev_loop> objects don't have an
		4912	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		4913	associated constants have been renamed to not collide with the C<struct
		4914	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		4915	as all other watcher types. Note that C<ev_loop_fork> is still called
		4916	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		4917	typedef.
		4918
		4919	=item C<EV_COMPAT3> backwards compatibility mechanism
		4920
		4921	The backward compatibility mechanism can be controlled by
		4922	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		4923	section.
		4924
		4925	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4926
		4927	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4928	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4929	and work, but the library code will of course be larger.
		4930
		4931	=back
		4932
		4933
		4934	=head1 GLOSSARY
		4935
		4936	=over 4
		4937
		4938	=item active
		4939
		4940	A watcher is active as long as it has been started and not yet stopped.
		4941	See L<WATCHER STATES> for details.
		4942
		4943	=item application
		4944
		4945	In this document, an application is whatever is using libev.
		4946
		4947	=item backend
		4948
		4949	The part of the code dealing with the operating system interfaces.
		4950
		4951	=item callback
		4952
		4953	The address of a function that is called when some event has been
		4954	detected. Callbacks are being passed the event loop, the watcher that
		4955	received the event, and the actual event bitset.
		4956
		4957	=item callback/watcher invocation
		4958
		4959	The act of calling the callback associated with a watcher.
		4960
		4961	=item event
		4962
		4963	A change of state of some external event, such as data now being available
		4964	for reading on a file descriptor, time having passed or simply not having
		4965	any other events happening anymore.
		4966
		4967	In libev, events are represented as single bits (such as C<EV_READ> or
		4968	C<EV_TIMER>).
		4969
		4970	=item event library
		4971
		4972	A software package implementing an event model and loop.
		4973
		4974	=item event loop
		4975
		4976	An entity that handles and processes external events and converts them
		4977	into callback invocations.
		4978
		4979	=item event model
		4980
		4981	The model used to describe how an event loop handles and processes
		4982	watchers and events.
		4983
		4984	=item pending
		4985
		4986	A watcher is pending as soon as the corresponding event has been
		4987	detected. See L<WATCHER STATES> for details.
		4988
		4989	=item real time
		4990
		4991	The physical time that is observed. It is apparently strictly monotonic :)
		4992
		4993	=item wall-clock time
		4994
		4995	The time and date as shown on clocks. Unlike real time, it can actually
		4996	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4997	clock.
		4998
		4999	=item watcher
		5000
		5001	A data structure that describes interest in certain events. Watchers need
		5002	to be started (attached to an event loop) before they can receive events.
		5003
		5004	=back
3582		5005
3583	=head1 AUTHOR	5006	=head1 AUTHOR
3584		5007
3585	Marc Lehmann <libev@schmorp.de>.	5008	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3586		5009

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