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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 WHAT TO READ WHEN IN A HURRY
		84
		85	This manual tries to be very detailed, but unfortunately, this also makes
		86	it very long. If you just want to know the basics of libev, I suggest
		87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
		88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
		89	C<ev_timer> sections in L<WATCHER TYPES>.
		90
		91	=head1 ABOUT LIBEV
70		92
71	Libev is an event loop: you register interest in certain events (such as a	93	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	94	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	95	these event sources and provide your program with events.
74		96
…		…
84	=head2 FEATURES	106	=head2 FEATURES
85		107
86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	112	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	113	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	114	(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	115	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	116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	117	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		118	limited support for fork events (C<ev_fork>).
96		119
97	It also is quite fast (see this	120	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	121	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	122	for example).
100		123
…		…
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	131	name C<loop> (which is always of type C<struct ev_loop *>) will not have
109	this argument.	132	this argument.
110		133
111	=head2 TIME REPRESENTATION	134	=head2 TIME REPRESENTATION
112		135
113	Libev represents time as a single floating point number, representing the	136	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	137	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	138	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	139	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	140	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	141	any calculations on it, you should treat it as some floating point value.
		142
119	component C<stamp> might indicate, it is also used for time differences	143	Unlike the name component C<stamp> might indicate, it is also used for
120	throughout libev.	144	time differences (e.g. delays) throughout libev.
121		145
122	=head1 ERROR HANDLING	146	=head1 ERROR HANDLING
123		147
124	Libev knows three classes of errors: operating system errors, usage errors	148	Libev knows three classes of errors: operating system errors, usage errors
125	and internal errors (bugs).	149	and internal errors (bugs).
…		…
149		173
150	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
151		175
152	Returns the current time as libev would use it. Please note that the	176	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	177	C<ev_now> function is usually faster and also often returns the timestamp
154	you actually want to know.	178	you actually want to know. Also interesting is the combination of
		179	C<ev_update_now> and C<ev_now>.
155		180
156	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
157		182
158	Sleep for the given interval: The current thread will be blocked until	183	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	184	either it is interrupted or the given time interval has passed. Basically
…		…
176	as this indicates an incompatible change. Minor versions are usually	201	as this indicates an incompatible change. Minor versions are usually
177	compatible to older versions, so a larger minor version alone is usually	202	compatible to older versions, so a larger minor version alone is usually
178	not a problem.	203	not a problem.
179		204
180	Example: Make sure we haven't accidentally been linked against the wrong	205	Example: Make sure we haven't accidentally been linked against the wrong
181	version.	206	version (note, however, that this will not detect other ABI mismatches,
		207	such as LFS or reentrancy).
182		208
183	assert (("libev version mismatch",	209	assert (("libev version mismatch",
184	ev_version_major () == EV_VERSION_MAJOR	210	ev_version_major () == EV_VERSION_MAJOR
185	&& ev_version_minor () >= EV_VERSION_MINOR));	211	&& ev_version_minor () >= EV_VERSION_MINOR));
186		212
…		…
197	assert (("sorry, no epoll, no sex",	223	assert (("sorry, no epoll, no sex",
198	ev_supported_backends () & EVBACKEND_EPOLL));	224	ev_supported_backends () & EVBACKEND_EPOLL));
199		225
200	=item unsigned int ev_recommended_backends ()	226	=item unsigned int ev_recommended_backends ()
201		227
202	Return the set of all backends compiled into this binary of libev and also	228	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	229	also recommended for this platform, meaning it will work for most file
		230	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	231	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	232	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	233	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.	234	probe for if you specify no backends explicitly.
208		235
209	=item unsigned int ev_embeddable_backends ()	236	=item unsigned int ev_embeddable_backends ()
210		237
211	Returns the set of backends that are embeddable in other event loops. This	238	Returns the set of backends that are embeddable in other event loops. This
212	is the theoretical, all-platform, value. To find which backends	239	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	240	current system. To find which embeddable backends might be supported on
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	241	the current system, you would need to look at C<ev_embeddable_backends ()
215	recommended ones.	242	& ev_supported_backends ()>, likewise for recommended ones.
216		243
217	See the description of C<ev_embed> watchers for more info.	244	See the description of C<ev_embed> watchers for more info.
218		245
219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
220		247
…		…
250	}	277	}
251		278
252	...	279	...
253	ev_set_allocator (persistent_realloc);	280	ev_set_allocator (persistent_realloc);
254		281
255	=item ev_set_syserr_cb (void (*cb)(const char *msg));	282	=item ev_set_syserr_cb (void (*cb)(const char *msg))
256		283
257	Set the callback function to call on a retryable system call error (such	284	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	285	as failed select, poll, epoll_wait). The message is a printable string
259	indicating the system call or subsystem causing the problem. If this	286	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	287	callback is set, then libev will expect it to remedy the situation, no
…		…
272	}	299	}
273		300
274	...	301	...
275	ev_set_syserr_cb (fatal_error);	302	ev_set_syserr_cb (fatal_error);
276		303
		304	=item ev_feed_signal (int signum)
		305
		306	This function can be used to "simulate" a signal receive. It is completely
		307	safe to call this function at any time, from any context, including signal
		308	handlers or random threads.
		309
		310	Its main use is to customise signal handling in your process, especially
		311	in the presence of threads. For example, you could block signals
		312	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		313	creating any loops), and in one thread, use C<sigwait> or any other
		314	mechanism to wait for signals, then "deliver" them to libev by calling
		315	C<ev_feed_signal>.
		316
277	=back	317	=back
278		318
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	319	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
280		320
281	An event loop is described by a C<struct ev_loop *>. The library knows two	321	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	322	I<not> optional in this case unless libev 3 compatibility is disabled, as
283	events, and dynamically created loops which do not.	323	libev 3 had an C<ev_loop> function colliding with the struct name).
		324
		325	The library knows two types of such loops, the I<default> loop, which
		326	supports child process events, and dynamically created event loops which
		327	do not.
284		328
285	=over 4	329	=over 4
286		330
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	331	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		332
289	This will initialise the default event loop if it hasn't been initialised	333	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	334	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	335	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).	336	C<ev_loop_new>.
		337
		338	If the default loop is already initialised then this function simply
		339	returns it (and ignores the flags. If that is troubling you, check
		340	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		341	flags, which should almost always be C<0>, unless the caller is also the
		342	one calling C<ev_run> or otherwise qualifies as "the main program".
293		343
294	If you don't know what event loop to use, use the one returned from this	344	If you don't know what event loop to use, use the one returned from this
295	function.	345	function (or via the C<EV_DEFAULT> macro).
296		346
297	Note that this function is I<not> thread-safe, so if you want to use it	347	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,	348	from multiple threads, you have to employ some kind of mutex (note also
299	as loops cannot bes hared easily between threads anyway).	349	that this case is unlikely, as loops cannot be shared easily between
		350	threads anyway).
300		351
301	The default loop is the only loop that can handle C<ev_signal> and	352	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	353	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	354	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	355	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	356	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
306	C<ev_default_init>.	357
		358	Example: This is the most typical usage.
		359
		360	if (!ev_default_loop (0))
		361	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		362
		363	Example: Restrict libev to the select and poll backends, and do not allow
		364	environment settings to be taken into account:
		365
		366	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		367
		368	=item struct ev_loop *ev_loop_new (unsigned int flags)
		369
		370	This will create and initialise a new event loop object. If the loop
		371	could not be initialised, returns false.
		372
		373	This function is thread-safe, and one common way to use libev with
		374	threads is indeed to create one loop per thread, and using the default
		375	loop in the "main" or "initial" thread.
307		376
308	The flags argument can be used to specify special behaviour or specific	377	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>).	378	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
310		379
311	The following flags are supported:	380	The following flags are supported:
…		…
326	useful to try out specific backends to test their performance, or to work	395	useful to try out specific backends to test their performance, or to work
327	around bugs.	396	around bugs.
328		397
329	=item C<EVFLAG_FORKCHECK>	398	=item C<EVFLAG_FORKCHECK>
330		399
331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	400	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	401	make libev check for a fork in each iteration by enabling this flag.
333	enabling this flag.
334		402
335	This works by calling C<getpid ()> on every iteration of the loop,	403	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	404	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	405	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	406	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
…		…
344	flag.	412	flag.
345		413
346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	414	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
347	environment variable.	415	environment variable.
348		416
		417	=item C<EVFLAG_NOINOTIFY>
		418
		419	When this flag is specified, then libev will not attempt to use the
		420	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		421	testing, this flag can be useful to conserve inotify file descriptors, as
		422	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		423
		424	=item C<EVFLAG_SIGNALFD>
		425
		426	When this flag is specified, then libev will attempt to use the
		427	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		428	delivers signals synchronously, which makes it both faster and might make
		429	it possible to get the queued signal data. It can also simplify signal
		430	handling with threads, as long as you properly block signals in your
		431	threads that are not interested in handling them.
		432
		433	Signalfd will not be used by default as this changes your signal mask, and
		434	there are a lot of shoddy libraries and programs (glib's threadpool for
		435	example) that can't properly initialise their signal masks.
		436
		437	=item C<EVFLAG_NOSIGMASK>
		438
		439	When this flag is specified, then libev will avoid to modify the signal
		440	mask. Specifically, this means you ahve to make sure signals are unblocked
		441	when you want to receive them.
		442
		443	This behaviour is useful when you want to do your own signal handling, or
		444	want to handle signals only in specific threads and want to avoid libev
		445	unblocking the signals.
		446
		447	It's also required by POSIX in a threaded program, as libev calls
		448	C<sigprocmask>, whose behaviour is officially unspecified.
		449
		450	This flag's behaviour will become the default in future versions of libev.
		451
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	452	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		453
351	This is your standard select(2) backend. Not I<completely> standard, as	454	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,	455	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	456	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	480	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
378	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	481	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
379		482
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	483	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		484
		485	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		486	kernels).
		487
382	For few fds, this backend is a bit little slower than poll and select,	488	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	489	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),	490	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	491	epoll scales either O(1) or O(active_fds).
386	of shortcomings, such as silently dropping events in some hard-to-detect	492
387	cases and requiring a system call per fd change, no fork support and bad	493	The epoll mechanism deserves honorable mention as the most misdesigned
388	support for dup.	494	of the more advanced event mechanisms: mere annoyances include silently
		495	dropping file descriptors, requiring a system call per change per file
		496	descriptor (and unnecessary guessing of parameters), problems with dup,
		497	returning before the timeout value, resulting in additional iterations
		498	(and only giving 5ms accuracy while select on the same platform gives
		499	0.1ms) and so on. The biggest issue is fork races, however - if a program
		500	forks then I<both> parent and child process have to recreate the epoll
		501	set, which can take considerable time (one syscall per file descriptor)
		502	and is of course hard to detect.
		503
		504	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		505	of course I<doesn't>, and epoll just loves to report events for totally
		506	I<different> file descriptors (even already closed ones, so one cannot
		507	even remove them from the set) than registered in the set (especially
		508	on SMP systems). Libev tries to counter these spurious notifications by
		509	employing an additional generation counter and comparing that against the
		510	events to filter out spurious ones, recreating the set when required. Last
		511	not least, it also refuses to work with some file descriptors which work
		512	perfectly fine with C<select> (files, many character devices...).
		513
		514	Epoll is truly the train wreck analog among event poll mechanisms,
		515	a frankenpoll, cobbled together in a hurry, no thought to design or
		516	interaction with others.
389		517
390	While stopping, setting and starting an I/O watcher in the same iteration	518	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	519	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	520	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	521	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
394	very well if you register events for both fds.	522	file descriptors might not work very well if you register events for both
395		523	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		524
400	Best performance from this backend is achieved by not unregistering all	525	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.	526	watchers for a file descriptor until it has been closed, if possible,
402	keep at least one watcher active per fd at all times.	527	i.e. keep at least one watcher active per fd at all times. Stopping and
		528	starting a watcher (without re-setting it) also usually doesn't cause
		529	extra overhead. A fork can both result in spurious notifications as well
		530	as in libev having to destroy and recreate the epoll object, which can
		531	take considerable time and thus should be avoided.
		532
		533	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		534	faster than epoll for maybe up to a hundred file descriptors, depending on
		535	the usage. So sad.
403		536
404	While nominally embeddable in other event loops, this feature is broken in	537	While nominally embeddable in other event loops, this feature is broken in
405	all kernel versions tested so far.	538	all kernel versions tested so far.
406		539
407	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	540	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)	543	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
411		544
412	Kqueue deserves special mention, as at the time of this writing, it	545	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	546	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	547	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"	548	it's completely useless). Unlike epoll, however, whose brokenness
		549	is by design, these kqueue bugs can (and eventually will) be fixed
		550	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	551	"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)	552	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
418	system like NetBSD.	553	system like NetBSD.
419		554
420	You still can embed kqueue into a normal poll or select backend and use it	555	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	556	only for sockets (after having made sure that sockets work with kqueue on
…		…
423		558
424	It scales in the same way as the epoll backend, but the interface to the	559	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	560	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	561	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	562	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	563	two event changes per incident. Support for C<fork ()> is very bad (but
429	drops fds silently in similarly hard-to-detect cases.	564	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		565	cases
430		566
431	This backend usually performs well under most conditions.	567	This backend usually performs well under most conditions.
432		568
433	While nominally embeddable in other event loops, this doesn't work	569	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	570	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	571	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	572	(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	573	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
438	sockets.	574	also broken on OS X)) and, did I mention it, using it only for sockets.
439		575
440	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with	576	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	577	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
442	C<NOTE_EOF>.	578	C<NOTE_EOF>.
443		579
…		…
451	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	587	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
452		588
453	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	589	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
454	it's really slow, but it still scales very well (O(active_fds)).	590	it's really slow, but it still scales very well (O(active_fds)).
455		591
456	Please note that Solaris event ports can deliver a lot of spurious
457	notifications, so you need to use non-blocking I/O or other means to avoid
458	blocking when no data (or space) is available.
459
460	While this backend scales well, it requires one system call per active	592	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	593	file descriptor per loop iteration. For small and medium numbers of file
462	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	594	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
463	might perform better.	595	might perform better.
464		596
465	On the positive side, ignoring the spurious readiness notifications, this	597	On the positive side, this backend actually performed fully to
466	backend actually performed to specification in all tests and is fully	598	specification in all tests and is fully embeddable, which is a rare feat
467	embeddable, which is a rare feat among the OS-specific backends.	599	among the OS-specific backends (I vastly prefer correctness over speed
		600	hacks).
		601
		602	On the negative side, the interface is I<bizarre> - so bizarre that
		603	even sun itself gets it wrong in their code examples: The event polling
		604	function sometimes returning events to the caller even though an error
		605	occurred, but with no indication whether it has done so or not (yes, it's
		606	even documented that way) - deadly for edge-triggered interfaces where
		607	you absolutely have to know whether an event occurred or not because you
		608	have to re-arm the watcher.
		609
		610	Fortunately libev seems to be able to work around these idiocies.
468		611
469	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	612	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
470	C<EVBACKEND_POLL>.	613	C<EVBACKEND_POLL>.
471		614
472	=item C<EVBACKEND_ALL>	615	=item C<EVBACKEND_ALL>
473		616
474	Try all backends (even potentially broken ones that wouldn't be tried	617	Try all backends (even potentially broken ones that wouldn't be tried
475	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	618	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
476	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	619	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
477		620
478	It is definitely not recommended to use this flag.	621	It is definitely not recommended to use this flag, use whatever
		622	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		623	at all.
		624
		625	=item C<EVBACKEND_MASK>
		626
		627	Not a backend at all, but a mask to select all backend bits from a
		628	C<flags> value, in case you want to mask out any backends from a flags
		629	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
479		630
480	=back	631	=back
481		632
482	If one or more of these are or'ed into the flags value, then only these	633	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	634	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.	635	here). If none are specified, all backends in C<ev_recommended_backends
485		636	()> 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		637
513	Example: Try to create a event loop that uses epoll and nothing else.	638	Example: Try to create a event loop that uses epoll and nothing else.
514		639
515	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	640	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
516	if (!epoller)	641	if (!epoller)
517	fatal ("no epoll found here, maybe it hides under your chair");	642	fatal ("no epoll found here, maybe it hides under your chair");
518		643
		644	Example: Use whatever libev has to offer, but make sure that kqueue is
		645	used if available.
		646
		647	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		648
519	=item ev_default_destroy ()	649	=item ev_loop_destroy (loop)
520		650
521	Destroys the default loop again (frees all memory and kernel state	651	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	652	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	653	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>	654	responsibility to either stop all watchers cleanly yourself I<before>
525	calling this function, or cope with the fact afterwards (which is usually	655	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	656	the easiest thing, you can just ignore the watchers and/or C<free ()> them
527	for example).	657	for example).
528		658
529	Note that certain global state, such as signal state, will not be freed by	659	Note that certain global state, such as signal state (and installed signal
530	this function, and related watchers (such as signal and child watchers)	660	handlers), will not be freed by this function, and related watchers (such
531	would need to be stopped manually.	661	as signal and child watchers) would need to be stopped manually.
532		662
533	In general it is not advisable to call this function except in the	663	This function is normally used on loop objects allocated by
534	rare occasion where you really need to free e.g. the signal handling	664	C<ev_loop_new>, but it can also be used on the default loop returned by
		665	C<ev_default_loop>, in which case it is not thread-safe.
		666
		667	Note that it is not advisable to call this function on the default loop
		668	except in the rare occasion where you really need to free its resources.
535	pipe fds. If you need dynamically allocated loops it is better to use	669	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>).	670	and C<ev_loop_destroy>.
537		671
538	=item ev_loop_destroy (loop)	672	=item ev_loop_fork (loop)
539		673
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	674	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	675	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	676	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	677	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	678	child before resuming or calling C<ev_run>.
550	functions, and it will only take effect at the next C<ev_loop> iteration.	679
		680	Again, you I<have> to call it on I<any> loop that you want to re-use after
		681	a fork, I<even if you do not plan to use the loop in the parent>. This is
		682	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		683	during fork.
551		684
552	On the other hand, you only need to call this function in the child	685	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	686	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.	687	you just fork+exec or create a new loop in the child, you don't have to
		688	call it at all (in fact, C<epoll> is so badly broken that it makes a
		689	difference, but libev will usually detect this case on its own and do a
		690	costly reset of the backend).
555		691
556	The function itself is quite fast and it's usually not a problem to call	692	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	693	it just in case after a fork.
558	quite nicely into a call to C<pthread_atfork>:
559		694
		695	Example: Automate calling C<ev_loop_fork> on the default loop when
		696	using pthreads.
		697
		698	static void
		699	post_fork_child (void)
		700	{
		701	ev_loop_fork (EV_DEFAULT);
		702	}
		703
		704	...
560	pthread_atfork (0, 0, ev_default_fork);	705	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		706
568	=item int ev_is_default_loop (loop)	707	=item int ev_is_default_loop (loop)
569		708
570	Returns true when the given loop actually is the default loop, false otherwise.	709	Returns true when the given loop is, in fact, the default loop, and false
		710	otherwise.
571		711
572	=item unsigned int ev_loop_count (loop)	712	=item unsigned int ev_iteration (loop)
573		713
574	Returns the count of loop iterations for the loop, which is identical to	714	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	715	to the number of times libev did poll for new events. It starts at C<0>
576	happily wraps around with enough iterations.	716	and happily wraps around with enough iterations.
577		717
578	This value can sometimes be useful as a generation counter of sorts (it	718	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	719	"ticks" the number of loop iterations), as it roughly corresponds with
580	C<ev_prepare> and C<ev_check> calls.	720	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		721	prepare and check phases.
		722
		723	=item unsigned int ev_depth (loop)
		724
		725	Returns the number of times C<ev_run> was entered minus the number of
		726	times C<ev_run> was exited normally, in other words, the recursion depth.
		727
		728	Outside C<ev_run>, this number is zero. In a callback, this number is
		729	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		730	in which case it is higher.
		731
		732	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		733	throwing an exception etc.), doesn't count as "exit" - consider this
		734	as a hint to avoid such ungentleman-like behaviour unless it's really
		735	convenient, in which case it is fully supported.
581		736
582	=item unsigned int ev_backend (loop)	737	=item unsigned int ev_backend (loop)
583		738
584	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	739	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
585	use.	740	use.
…		…
594		749
595	=item ev_now_update (loop)	750	=item ev_now_update (loop)
596		751
597	Establishes the current time by querying the kernel, updating the time	752	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	753	returned by C<ev_now ()> in the progress. This is a costly operation and
599	is usually done automatically within C<ev_loop ()>.	754	is usually done automatically within C<ev_run ()>.
600		755
601	This function is rarely useful, but when some event callback runs for a	756	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	757	very long time without entering the event loop, updating libev's idea of
603	the current time is a good idea.	758	the current time is a good idea.
604		759
605	See also "The special problem of time updates" in the C<ev_timer> section.	760	See also L<The special problem of time updates> in the C<ev_timer> section.
606		761
		762	=item ev_suspend (loop)
		763
		764	=item ev_resume (loop)
		765
		766	These two functions suspend and resume an event loop, for use when the
		767	loop is not used for a while and timeouts should not be processed.
		768
		769	A typical use case would be an interactive program such as a game: When
		770	the user presses C<^Z> to suspend the game and resumes it an hour later it
		771	would be best to handle timeouts as if no time had actually passed while
		772	the program was suspended. This can be achieved by calling C<ev_suspend>
		773	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		774	C<ev_resume> directly afterwards to resume timer processing.
		775
		776	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		777	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		778	will be rescheduled (that is, they will lose any events that would have
		779	occurred while suspended).
		780
		781	After calling C<ev_suspend> you B<must not> call I<any> function on the
		782	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		783	without a previous call to C<ev_suspend>.
		784
		785	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		786	event loop time (see C<ev_now_update>).
		787
607	=item ev_loop (loop, int flags)	788	=item ev_run (loop, int flags)
608		789
609	Finally, this is it, the event handler. This function usually is called	790	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	791	after you have initialised all your watchers and you want to start
611	events.	792	handling events. It will ask the operating system for any new events, call
		793	the watcher callbacks, an then repeat the whole process indefinitely: This
		794	is why event loops are called I<loops>.
612		795
613	If the flags argument is specified as C<0>, it will not return until	796	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.	797	until either no event watchers are active anymore or C<ev_break> was
		798	called.
615		799
616	Please note that an explicit C<ev_unloop> is usually better than	800	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	801	relying on all watchers to be stopped when deciding when a program has
618	finished (especially in interactive programs), but having a program that	802	finished (especially in interactive programs), but having a program
619	automatically loops as long as it has to and no longer by virtue of	803	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.	804	of relying on its watchers stopping correctly, that is truly a thing of
		805	beauty.
621		806
		807	This function is also I<mostly> exception-safe - you can break out of
		808	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		809	exception and so on. This does not decrement the C<ev_depth> value, nor
		810	will it clear any outstanding C<EVBREAK_ONE> breaks.
		811
622	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	812	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	813	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.	814	block your process in case there are no events and will return after one
		815	iteration of the loop. This is sometimes useful to poll and handle new
		816	events while doing lengthy calculations, to keep the program responsive.
625		817
626	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	818	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	819	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	820	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	821	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	822	user-registered callback will be called), and will return after one
		823	iteration of the loop.
		824
		825	This is useful if you are waiting for some external event in conjunction
		826	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	827	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.	828	usually a better approach for this kind of thing.
633		829
634	Here are the gory details of what C<ev_loop> does:	830	Here are the gory details of what C<ev_run> does:
635		831
		832	- Increment loop depth.
		833	- Reset the ev_break status.
636	- Before the first iteration, call any pending watchers.	834	- Before the first iteration, call any pending watchers.
		835	LOOP:
637	* If EVFLAG_FORKCHECK was used, check for a fork.	836	- If EVFLAG_FORKCHECK was used, check for a fork.
638	- If a fork was detected (by any means), queue and call all fork watchers.	837	- If a fork was detected (by any means), queue and call all fork watchers.
639	- Queue and call all prepare watchers.	838	- Queue and call all prepare watchers.
		839	- If ev_break was called, goto FINISH.
640	- If we have been forked, detach and recreate the kernel state	840	- If we have been forked, detach and recreate the kernel state
641	as to not disturb the other process.	841	as to not disturb the other process.
642	- Update the kernel state with all outstanding changes.	842	- Update the kernel state with all outstanding changes.
643	- Update the "event loop time" (ev_now ()).	843	- Update the "event loop time" (ev_now ()).
644	- Calculate for how long to sleep or block, if at all	844	- Calculate for how long to sleep or block, if at all
645	(active idle watchers, EVLOOP_NONBLOCK or not having	845	(active idle watchers, EVRUN_NOWAIT or not having
646	any active watchers at all will result in not sleeping).	846	any active watchers at all will result in not sleeping).
647	- Sleep if the I/O and timer collect interval say so.	847	- Sleep if the I/O and timer collect interval say so.
		848	- Increment loop iteration counter.
648	- Block the process, waiting for any events.	849	- Block the process, waiting for any events.
649	- Queue all outstanding I/O (fd) events.	850	- Queue all outstanding I/O (fd) events.
650	- Update the "event loop time" (ev_now ()), and do time jump adjustments.	851	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
651	- Queue all outstanding timers.	852	- Queue all expired timers.
652	- Queue all outstanding periodics.	853	- Queue all expired periodics.
653	- Unless any events are pending now, queue all idle watchers.	854	- Queue all idle watchers with priority higher than that of pending events.
654	- Queue all check watchers.	855	- Queue all check watchers.
655	- Call all queued watchers in reverse order (i.e. check watchers first).	856	- 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	857	Signals and child watchers are implemented as I/O watchers, and will
657	be handled here by queueing them when their watcher gets executed.	858	be handled here by queueing them when their watcher gets executed.
658	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	859	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
659	were used, or there are no active watchers, return, otherwise	860	were used, or there are no active watchers, goto FINISH, otherwise
660	continue with step *.	861	continue with step LOOP.
		862	FINISH:
		863	- Reset the ev_break status iff it was EVBREAK_ONE.
		864	- Decrement the loop depth.
		865	- Return.
661		866
662	Example: Queue some jobs and then loop until no events are outstanding	867	Example: Queue some jobs and then loop until no events are outstanding
663	anymore.	868	anymore.
664		869
665	... queue jobs here, make sure they register event watchers as long	870	... 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..)	871	... as they still have work to do (even an idle watcher will do..)
667	ev_loop (my_loop, 0);	872	ev_run (my_loop, 0);
668	... jobs done or somebody called unloop. yeah!	873	... jobs done or somebody called unloop. yeah!
669		874
670	=item ev_unloop (loop, how)	875	=item ev_break (loop, how)
671		876
672	Can be used to make a call to C<ev_loop> return early (but only after it	877	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	878	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	879	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.	880	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
676		881
677	This "unloop state" will be cleared when entering C<ev_loop> again.	882	This "break state" will be cleared on the next call to C<ev_run>.
		883
		884	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		885	which case it will have no effect.
678		886
679	=item ev_ref (loop)	887	=item ev_ref (loop)
680		888
681	=item ev_unref (loop)	889	=item ev_unref (loop)
682		890
683	Ref/unref can be used to add or remove a reference count on the event	891	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	892	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	893	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	894
687	returning, ev_unref() after starting, and ev_ref() before stopping it. For	895	This is useful when you have a watcher that you never intend to
		896	unregister, but that nevertheless should not keep C<ev_run> from
		897	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		898	before stopping it.
		899
688	example, libev itself uses this for its internal signal pipe: It is not	900	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	901	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	902	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	903	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>	904	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,	905	before stop> (but only if the watcher wasn't active before, or was active
694	respectively).	906	before, respectively. Note also that libev might stop watchers itself
		907	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		908	in the callback).
695		909
696	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	910	Example: Create a signal watcher, but keep it from keeping C<ev_run>
697	running when nothing else is active.	911	running when nothing else is active.
698		912
699	struct ev_signal exitsig;	913	ev_signal exitsig;
700	ev_signal_init (&exitsig, sig_cb, SIGINT);	914	ev_signal_init (&exitsig, sig_cb, SIGINT);
701	ev_signal_start (loop, &exitsig);	915	ev_signal_start (loop, &exitsig);
702	evf_unref (loop);	916	ev_unref (loop);
703		917
704	Example: For some weird reason, unregister the above signal handler again.	918	Example: For some weird reason, unregister the above signal handler again.
705		919
706	ev_ref (loop);	920	ev_ref (loop);
707	ev_signal_stop (loop, &exitsig);	921	ev_signal_stop (loop, &exitsig);
…		…
718	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	932	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	933	allows libev to delay invocation of I/O and timer/periodic callbacks
720	to increase efficiency of loop iterations (or to increase power-saving	934	to increase efficiency of loop iterations (or to increase power-saving
721	opportunities).	935	opportunities).
722		936
723	The background is that sometimes your program runs just fast enough to	937	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	938	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	939	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	940	events, especially with backends like C<select ()> which have a high
727	overhead for the actual polling but can deliver many events at once.	941	overhead for the actual polling but can deliver many events at once.
728		942
729	By setting a higher I<io collect interval> you allow libev to spend more	943	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,	944	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	945	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	946	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.	947	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		948	sleep time ensures that libev will not poll for I/O events more often then
		949	once per this interval, on average.
734		950
735	Likewise, by setting a higher I<timeout collect interval> you allow libev	951	Likewise, by setting a higher I<timeout collect interval> you allow libev
736	to spend more time collecting timeouts, at the expense of increased	952	to spend more time collecting timeouts, at the expense of increased
737	latency (the watcher callback will be called later). C<ev_io> watchers	953	latency/jitter/inexactness (the watcher callback will be called
738	will not be affected. Setting this to a non-null value will not introduce	954	later). C<ev_io> watchers will not be affected. Setting this to a non-null
739	any overhead in libev.	955	value will not introduce any overhead in libev.
740		956
741	Many (busy) programs can usually benefit by setting the I/O collect	957	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	958	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	959	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>,	960	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.	961	as this approaches the timing granularity of most systems. Note that if
		962	you do transactions with the outside world and you can't increase the
		963	parallelity, then this setting will limit your transaction rate (if you
		964	need to poll once per transaction and the I/O collect interval is 0.01,
		965	then you can't do more than 100 transactions per second).
746		966
747	Setting the I<timeout collect interval> can improve the opportunity for	967	Setting the I<timeout collect interval> can improve the opportunity for
748	saving power, as the program will "bundle" timer callback invocations that	968	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	969	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	970	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	971	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
752	they fire on, say, one-second boundaries only.	972	they fire on, say, one-second boundaries only.
753		973
		974	Example: we only need 0.1s timeout granularity, and we wish not to poll
		975	more often than 100 times per second:
		976
		977	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		978	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		979
		980	=item ev_invoke_pending (loop)
		981
		982	This call will simply invoke all pending watchers while resetting their
		983	pending state. Normally, C<ev_run> does this automatically when required,
		984	but when overriding the invoke callback this call comes handy. This
		985	function can be invoked from a watcher - this can be useful for example
		986	when you want to do some lengthy calculation and want to pass further
		987	event handling to another thread (you still have to make sure only one
		988	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		989
		990	=item int ev_pending_count (loop)
		991
		992	Returns the number of pending watchers - zero indicates that no watchers
		993	are pending.
		994
		995	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		996
		997	This overrides the invoke pending functionality of the loop: Instead of
		998	invoking all pending watchers when there are any, C<ev_run> will call
		999	this callback instead. This is useful, for example, when you want to
		1000	invoke the actual watchers inside another context (another thread etc.).
		1001
		1002	If you want to reset the callback, use C<ev_invoke_pending> as new
		1003	callback.
		1004
		1005	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		1006
		1007	Sometimes you want to share the same loop between multiple threads. This
		1008	can be done relatively simply by putting mutex_lock/unlock calls around
		1009	each call to a libev function.
		1010
		1011	However, C<ev_run> can run an indefinite time, so it is not feasible
		1012	to wait for it to return. One way around this is to wake up the event
		1013	loop via C<ev_break> and C<av_async_send>, another way is to set these
		1014	I<release> and I<acquire> callbacks on the loop.
		1015
		1016	When set, then C<release> will be called just before the thread is
		1017	suspended waiting for new events, and C<acquire> is called just
		1018	afterwards.
		1019
		1020	Ideally, C<release> will just call your mutex_unlock function, and
		1021	C<acquire> will just call the mutex_lock function again.
		1022
		1023	While event loop modifications are allowed between invocations of
		1024	C<release> and C<acquire> (that's their only purpose after all), no
		1025	modifications done will affect the event loop, i.e. adding watchers will
		1026	have no effect on the set of file descriptors being watched, or the time
		1027	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1028	to take note of any changes you made.
		1029
		1030	In theory, threads executing C<ev_run> will be async-cancel safe between
		1031	invocations of C<release> and C<acquire>.
		1032
		1033	See also the locking example in the C<THREADS> section later in this
		1034	document.
		1035
		1036	=item ev_set_userdata (loop, void *data)
		1037
		1038	=item void *ev_userdata (loop)
		1039
		1040	Set and retrieve a single C<void *> associated with a loop. When
		1041	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1042	C<0>.
		1043
		1044	These two functions can be used to associate arbitrary data with a loop,
		1045	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1046	C<acquire> callbacks described above, but of course can be (ab-)used for
		1047	any other purpose as well.
		1048
754	=item ev_loop_verify (loop)	1049	=item ev_verify (loop)
755		1050
756	This function only does something when C<EV_VERIFY> support has been	1051	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	1052	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	1053	through all internal structures and checks them for validity. If anything
759	an error message to standard error and call C<abort ()>.	1054	is found to be inconsistent, it will print an error message to standard
		1055	error and call C<abort ()>.
760		1056
761	This can be used to catch bugs inside libev itself: under normal	1057	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	1058	circumstances, this function will never abort as of course libev keeps its
763	data structures consistent.	1059	data structures consistent.
764		1060
765	=back	1061	=back
766		1062
767		1063
768	=head1 ANATOMY OF A WATCHER	1064	=head1 ANATOMY OF A WATCHER
769		1065
		1066	In the following description, uppercase C<TYPE> in names stands for the
		1067	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1068	watchers and C<ev_io_start> for I/O watchers.
		1069
770	A watcher is a structure that you create and register to record your	1070	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	1071	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:	1072	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1073	for that:
773		1074
774	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1075	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
775	{	1076	{
776	ev_io_stop (w);	1077	ev_io_stop (w);
777	ev_unloop (loop, EVUNLOOP_ALL);	1078	ev_break (loop, EVBREAK_ALL);
778	}	1079	}
779		1080
780	struct ev_loop *loop = ev_default_loop (0);	1081	struct ev_loop *loop = ev_default_loop (0);
		1082
781	struct ev_io stdin_watcher;	1083	ev_io stdin_watcher;
		1084
782	ev_init (&stdin_watcher, my_cb);	1085	ev_init (&stdin_watcher, my_cb);
783	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1086	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
784	ev_io_start (loop, &stdin_watcher);	1087	ev_io_start (loop, &stdin_watcher);
		1088
785	ev_loop (loop, 0);	1089	ev_run (loop, 0);
786		1090
787	As you can see, you are responsible for allocating the memory for your	1091	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,	1092	watcher structures (and it is I<usually> a bad idea to do this on the
789	although this can sometimes be quite valid).	1093	stack).
790		1094
		1095	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1096	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1097
791	Each watcher structure must be initialised by a call to C<ev_init	1098	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	1099	*, 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	1100	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	1101	time the event loop detects that the file descriptor given is readable
795	is readable and/or writable).	1102	and/or writable).
796		1103
797	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1104	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	1105	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	1106	is also a macro to combine initialisation and setting in one call: C<<
800	(watcher *, callback, ...) >>.	1107	ev_TYPE_init (watcher *, callback, ...) >>.
801		1108
802	To make the watcher actually watch out for events, you have to start it	1109	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	1110	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	1111	*) >>), and you can stop watching for events at any time by calling the
805	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1112	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
806		1113
807	As long as your watcher is active (has been started but not stopped) you	1114	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	1115	must not touch the values stored in it. Most specifically you must never
809	reinitialise it or call its C<set> macro.	1116	reinitialise it or call its C<ev_TYPE_set> macro.
810		1117
811	Each and every callback receives the event loop pointer as first, the	1118	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	1119	registered watcher structure as second, and a bitset of received events as
813	third argument.	1120	third argument.
814		1121
…		…
823	=item C<EV_WRITE>	1130	=item C<EV_WRITE>
824		1131
825	The file descriptor in the C<ev_io> watcher has become readable and/or	1132	The file descriptor in the C<ev_io> watcher has become readable and/or
826	writable.	1133	writable.
827		1134
828	=item C<EV_TIMEOUT>	1135	=item C<EV_TIMER>
829		1136
830	The C<ev_timer> watcher has timed out.	1137	The C<ev_timer> watcher has timed out.
831		1138
832	=item C<EV_PERIODIC>	1139	=item C<EV_PERIODIC>
833		1140
…		…
851		1158
852	=item C<EV_PREPARE>	1159	=item C<EV_PREPARE>
853		1160
854	=item C<EV_CHECK>	1161	=item C<EV_CHECK>
855		1162
856	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1163	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	1164	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	1165	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	1166	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	1167	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	1168	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
862	C<ev_loop> from blocking).	1169	C<ev_run> from blocking).
863		1170
864	=item C<EV_EMBED>	1171	=item C<EV_EMBED>
865		1172
866	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1173	The embedded event loop specified in the C<ev_embed> watcher needs attention.
867		1174
868	=item C<EV_FORK>	1175	=item C<EV_FORK>
869		1176
870	The event loop has been resumed in the child process after fork (see	1177	The event loop has been resumed in the child process after fork (see
871	C<ev_fork>).	1178	C<ev_fork>).
872		1179
		1180	=item C<EV_CLEANUP>
		1181
		1182	The event loop is about to be destroyed (see C<ev_cleanup>).
		1183
873	=item C<EV_ASYNC>	1184	=item C<EV_ASYNC>
874		1185
875	The given async watcher has been asynchronously notified (see C<ev_async>).	1186	The given async watcher has been asynchronously notified (see C<ev_async>).
		1187
		1188	=item C<EV_CUSTOM>
		1189
		1190	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1191	by libev users to signal watchers (e.g. via C<ev_feed_event>).
876		1192
877	=item C<EV_ERROR>	1193	=item C<EV_ERROR>
878		1194
879	An unspecified error has occurred, the watcher has been stopped. This might	1195	An unspecified error has occurred, the watcher has been stopped. This might
880	happen because the watcher could not be properly started because libev	1196	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	1197	ran out of memory, a file descriptor was found to be closed or any other
		1198	problem. Libev considers these application bugs.
		1199
882	problem. You best act on it by reporting the problem and somehow coping	1200	You best act on it by reporting the problem and somehow coping with the
883	with the watcher being stopped.	1201	watcher being stopped. Note that well-written programs should not receive
		1202	an error ever, so when your watcher receives it, this usually indicates a
		1203	bug in your program.
884		1204
885	Libev will usually signal a few "dummy" events together with an error,	1205	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	1206	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	1207	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	1208	the error from read() or write(). This will not work in multi-threaded
889	programs, though, so beware.	1209	programs, though, as the fd could already be closed and reused for another
		1210	thing, so beware.
890		1211
891	=back	1212	=back
892		1213
893	=head2 GENERIC WATCHER FUNCTIONS	1214	=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		1215
898	=over 4	1216	=over 4
899		1217
900	=item C<ev_init> (ev_TYPE *watcher, callback)	1218	=item C<ev_init> (ev_TYPE *watcher, callback)
901		1219
…		…
907	which rolls both calls into one.	1225	which rolls both calls into one.
908		1226
909	You can reinitialise a watcher at any time as long as it has been stopped	1227	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.	1228	(or never started) and there are no pending events outstanding.
911		1229
912	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1230	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
913	int revents)>.	1231	int revents)>.
914		1232
		1233	Example: Initialise an C<ev_io> watcher in two steps.
		1234
		1235	ev_io w;
		1236	ev_init (&w, my_cb);
		1237	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1238
915	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1239	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
916		1240
917	This macro initialises the type-specific parts of a watcher. You need to	1241	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	1242	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	1243	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	1244	macro on a watcher that is active (it can be pending, however, which is a
921	difference to the C<ev_init> macro).	1245	difference to the C<ev_init> macro).
922		1246
923	Although some watcher types do not have type-specific arguments	1247	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.	1248	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
925		1249
		1250	See C<ev_init>, above, for an example.
		1251
926	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1252	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
927		1253
928	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1254	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	1255	calls into a single call. This is the most convenient method to initialise
930	a watcher. The same limitations apply, of course.	1256	a watcher. The same limitations apply, of course.
931		1257
		1258	Example: Initialise and set an C<ev_io> watcher in one step.
		1259
		1260	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1261
932	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1262	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
933		1263
934	Starts (activates) the given watcher. Only active watchers will receive	1264	Starts (activates) the given watcher. Only active watchers will receive
935	events. If the watcher is already active nothing will happen.	1265	events. If the watcher is already active nothing will happen.
936		1266
		1267	Example: Start the C<ev_io> watcher that is being abused as example in this
		1268	whole section.
		1269
		1270	ev_io_start (EV_DEFAULT_UC, &w);
		1271
937	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1272	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
938		1273
939	Stops the given watcher again (if active) and clears the pending	1274	Stops the given watcher if active, and clears the pending status (whether
		1275	the watcher was active or not).
		1276
940	status. It is possible that stopped watchers are pending (for example,	1277	It is possible that stopped watchers are pending - for example,
941	non-repeating timers are being stopped when they become pending), but	1278	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	1279	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	1280	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.	1281	therefore a good idea to always call its C<ev_TYPE_stop> function.
945		1282
946	=item bool ev_is_active (ev_TYPE *watcher)	1283	=item bool ev_is_active (ev_TYPE *watcher)
947		1284
948	Returns a true value iff the watcher is active (i.e. it has been started	1285	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	1286	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)	1302	=item ev_cb_set (ev_TYPE *watcher, callback)
966		1303
967	Change the callback. You can change the callback at virtually any time	1304	Change the callback. You can change the callback at virtually any time
968	(modulo threads).	1305	(modulo threads).
969		1306
970	=item ev_set_priority (ev_TYPE *watcher, priority)	1307	=item ev_set_priority (ev_TYPE *watcher, int priority)
971		1308
972	=item int ev_priority (ev_TYPE *watcher)	1309	=item int ev_priority (ev_TYPE *watcher)
973		1310
974	Set and query the priority of the watcher. The priority is a small	1311	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>	1312	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
976	(default: C<-2>). Pending watchers with higher priority will be invoked	1313	(default: C<-2>). Pending watchers with higher priority will be invoked
977	before watchers with lower priority, but priority will not keep watchers	1314	before watchers with lower priority, but priority will not keep watchers
978	from being executed (except for C<ev_idle> watchers).	1315	from being executed (except for C<ev_idle> watchers).
979		1316
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	1317	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.	1318	you need to look at C<ev_idle> watchers, which provide this functionality.
987		1319
988	You I<must not> change the priority of a watcher as long as it is active or	1320	You I<must not> change the priority of a watcher as long as it is active or
989	pending.	1321	pending.
990		1322
		1323	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1324	fine, as long as you do not mind that the priority value you query might
		1325	or might not have been clamped to the valid range.
		1326
991	The default priority used by watchers when no priority has been set is	1327	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 :).	1328	always C<0>, which is supposed to not be too high and not be too low :).
993		1329
994	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1330	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	1331	priorities.
996	or might not have been adjusted to be within valid range.
997		1332
998	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1333	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
999		1334
1000	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1335	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	1336	C<loop> nor C<revents> need to be valid as long as the watcher callback
1002	can deal with that fact.	1337	can deal with that fact, as both are simply passed through to the
		1338	callback.
1003		1339
1004	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1340	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1005		1341
1006	If the watcher is pending, this function returns clears its pending status	1342	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	1343	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>.	1344	watcher isn't pending it does nothing and returns C<0>.
1009		1345
		1346	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1347	callback to be invoked, which can be accomplished with this function.
		1348
		1349	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1350
		1351	Feeds the given event set into the event loop, as if the specified event
		1352	had happened for the specified watcher (which must be a pointer to an
		1353	initialised but not necessarily started event watcher). Obviously you must
		1354	not free the watcher as long as it has pending events.
		1355
		1356	Stopping the watcher, letting libev invoke it, or calling
		1357	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1358	not started in the first place.
		1359
		1360	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1361	functions that do not need a watcher.
		1362
1010	=back	1363	=back
1011		1364
		1365	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1366	OWN COMPOSITE WATCHERS> idioms.
1012		1367
1013	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1368	=head2 WATCHER STATES
1014		1369
1015	Each watcher has, by default, a member C<void *data> that you can change	1370	There are various watcher states mentioned throughout this manual -
1016	and read at any time, libev will completely ignore it. This can be used	1371	active, pending and so on. In this section these states and the rules to
1017	to associate arbitrary data with your watcher. If you need more data and	1372	transition between them will be described in more detail - and while these
1018	don't want to allocate memory and store a pointer to it in that data	1373	rules might look complicated, they usually do "the right thing".
1019	member, you can also "subclass" the watcher type and provide your own
1020	data:
1021		1374
1022	struct my_io	1375	=over 4
		1376
		1377	=item initialiased
		1378
		1379	Before a watcher can be registered with the event looop it has to be
		1380	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1381	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1382
		1383	In this state it is simply some block of memory that is suitable for use
		1384	in an event loop. It can be moved around, freed, reused etc. at will.
		1385
		1386	=item started/running/active
		1387
		1388	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1389	property of the event loop, and is actively waiting for events. While in
		1390	this state it cannot be accessed (except in a few documented ways), moved,
		1391	freed or anything else - the only legal thing is to keep a pointer to it,
		1392	and call libev functions on it that are documented to work on active watchers.
		1393
		1394	=item pending
		1395
		1396	If a watcher is active and libev determines that an event it is interested
		1397	in has occurred (such as a timer expiring), it will become pending. It will
		1398	stay in this pending state until either it is stopped or its callback is
		1399	about to be invoked, so it is not normally pending inside the watcher
		1400	callback.
		1401
		1402	The watcher might or might not be active while it is pending (for example,
		1403	an expired non-repeating timer can be pending but no longer active). If it
		1404	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1405	but it is still property of the event loop at this time, so cannot be
		1406	moved, freed or reused. And if it is active the rules described in the
		1407	previous item still apply.
		1408
		1409	It is also possible to feed an event on a watcher that is not active (e.g.
		1410	via C<ev_feed_event>), in which case it becomes pending without being
		1411	active.
		1412
		1413	=item stopped
		1414
		1415	A watcher can be stopped implicitly by libev (in which case it might still
		1416	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1417	latter will clear any pending state the watcher might be in, regardless
		1418	of whether it was active or not, so stopping a watcher explicitly before
		1419	freeing it is often a good idea.
		1420
		1421	While stopped (and not pending) the watcher is essentially in the
		1422	initialised state, that is it can be reused, moved, modified in any way
		1423	you wish.
		1424
		1425	=back
		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)
1023	{	1497	{
1024	struct ev_io io;	1498	// stop the I/O watcher, we received the event, but
1025	int otherfd;	1499	// are not yet ready to handle it.
1026	void *somedata;	1500	ev_io_stop (EV_A_ w);
1027	struct whatever *mostinteresting;	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);
1028	};	1506	}
1029		1507
1030	...	1508	static void
1031	struct my_io w;	1509	idle_cb (EV_P_ ev_idle *w, int revents)
1032	ev_io_init (&w.io, my_cb, fd, EV_READ);
1033
1034	And since your callback will be called with a pointer to the watcher, you
1035	can cast it back to your own type:
1036
1037	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
1038	{	1510	{
1039	struct my_io *w = (struct my_io *)w_;	1511	// actual processing
1040	...	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);
1041	}	1517	}
1042		1518
1043	More interesting and less C-conformant ways of casting your callback type	1519	// initialisation
1044	instead have been omitted.	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);
1045		1523
1046	Another common scenario is to use some data structure with multiple	1524	In the "real" world, it might also be beneficial to start a timer, so that
1047	embedded watchers:	1525	low-priority connections can not be locked out forever under load. This
1048		1526	enables your program to keep a lower latency for important connections
1049	struct my_biggy	1527	during short periods of high load, while not completely locking out less
1050	{	1528	important ones.
1051	int some_data;
1052	ev_timer t1;
1053	ev_timer t2;
1054	}
1055
1056	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
1058	in the C<data> member of the watcher, or you need to use some pointer
1059	arithmetic using C<offsetof> inside your watchers:
1060
1061	#include <stddef.h>
1062
1063	static void
1064	t1_cb (EV_P_ struct ev_timer *w, int revents)
1065	{
1066	struct my_biggy big = (struct my_biggy *
1067	(((char *)w) - offsetof (struct my_biggy, t1));
1068	}
1069
1070	static void
1071	t2_cb (EV_P_ struct ev_timer *w, int revents)
1072	{
1073	struct my_biggy big = (struct my_biggy *
1074	(((char *)w) - offsetof (struct my_biggy, t2));
1075	}
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
1110	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1111	C<EVBACKEND_POLL>).
1112
1113	Another thing you have to watch out for is that it is quite easy to	1562	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	1563	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	1564	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	1565	because there is no data. It is very easy to get into this situation even
1117	lot of those (for example Solaris ports), it is very easy to get into	1566	with a relatively standard program structure. Thus it is best to always
1118	this situation even with a relatively standard program structure. Thus	1567	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1119	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.	1568	preferable to a program hanging until some data arrives.
1121		1569
1122	If you cannot run the fd in non-blocking mode (for example you should not	1570	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	1571	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	1572	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	1573	interface such as poll (fortunately in the case of Xlib, it already does
1126	its own, so its quite safe to use).	1574	this on its own, so its quite safe to use). Some people additionally
		1575	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1576	indefinitely.
		1577
		1578	But really, best use non-blocking mode.
1127		1579
1128	=head3 The special problem of disappearing file descriptors	1580	=head3 The special problem of disappearing file descriptors
1129		1581
1130	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1582	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,	1583	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	1584	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	1585	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	1586	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	1587	registered with libev, there is no efficient way to see that this is, in
1136	fact, a different file descriptor.	1588	fact, a different file descriptor.
1137		1589
…		…
1155		1607
1156	There is no workaround possible except not registering events	1608	There is no workaround possible except not registering events
1157	for potentially C<dup ()>'ed file descriptors, or to resort to	1609	for potentially C<dup ()>'ed file descriptors, or to resort to
1158	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1610	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1159		1611
		1612	=head3 The special problem of files
		1613
		1614	Many people try to use C<select> (or libev) on file descriptors
		1615	representing files, and expect it to become ready when their program
		1616	doesn't block on disk accesses (which can take a long time on their own).
		1617
		1618	However, this cannot ever work in the "expected" way - you get a readiness
		1619	notification as soon as the kernel knows whether and how much data is
		1620	there, and in the case of open files, that's always the case, so you
		1621	always get a readiness notification instantly, and your read (or possibly
		1622	write) will still block on the disk I/O.
		1623
		1624	Another way to view it is that in the case of sockets, pipes, character
		1625	devices and so on, there is another party (the sender) that delivers data
		1626	on its own, but in the case of files, there is no such thing: the disk
		1627	will not send data on its own, simply because it doesn't know what you
		1628	wish to read - you would first have to request some data.
		1629
		1630	Since files are typically not-so-well supported by advanced notification
		1631	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1632	to files, even though you should not use it. The reason for this is
		1633	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1634	usually a tty, often a pipe, but also sometimes files or special devices
		1635	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1636	F</dev/urandom>), and even though the file might better be served with
		1637	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1638	it "just works" instead of freezing.
		1639
		1640	So avoid file descriptors pointing to files when you know it (e.g. use
		1641	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1642	when you rarely read from a file instead of from a socket, and want to
		1643	reuse the same code path.
		1644
1160	=head3 The special problem of fork	1645	=head3 The special problem of fork
1161		1646
1162	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1647	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1163	useless behaviour. Libev fully supports fork, but needs to be told about	1648	useless behaviour. Libev fully supports fork, but needs to be told about
1164	it in the child.	1649	it in the child if you want to continue to use it in the child.
1165		1650
1166	To support fork in your programs, you either have to call	1651	To support fork in your child processes, you have to call C<ev_loop_fork
1167	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1652	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1168	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1653	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1169	C<EVBACKEND_POLL>.
1170		1654
1171	=head3 The special problem of SIGPIPE	1655	=head3 The special problem of SIGPIPE
1172		1656
1173	While not really specific to libev, it is easy to forget about SIGPIPE:	1657	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	1658	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	1659	sent a SIGPIPE, which, by default, aborts your program. For most programs
1176	this is sensible behaviour, for daemons, this is usually undesirable.	1660	this is sensible behaviour, for daemons, this is usually undesirable.
1177		1661
1178	So when you encounter spurious, unexplained daemon exits, make sure you	1662	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	1663	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).	1664	somewhere, as that would have given you a big clue).
1181		1665
		1666	=head3 The special problem of accept()ing when you can't
		1667
		1668	Many implementations of the POSIX C<accept> function (for example,
		1669	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1670	connection from the pending queue in all error cases.
		1671
		1672	For example, larger servers often run out of file descriptors (because
		1673	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1674	rejecting the connection, leading to libev signalling readiness on
		1675	the next iteration again (the connection still exists after all), and
		1676	typically causing the program to loop at 100% CPU usage.
		1677
		1678	Unfortunately, the set of errors that cause this issue differs between
		1679	operating systems, there is usually little the app can do to remedy the
		1680	situation, and no known thread-safe method of removing the connection to
		1681	cope with overload is known (to me).
		1682
		1683	One of the easiest ways to handle this situation is to just ignore it
		1684	- when the program encounters an overload, it will just loop until the
		1685	situation is over. While this is a form of busy waiting, no OS offers an
		1686	event-based way to handle this situation, so it's the best one can do.
		1687
		1688	A better way to handle the situation is to log any errors other than
		1689	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1690	messages, and continue as usual, which at least gives the user an idea of
		1691	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1692	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1693	usage.
		1694
		1695	If your program is single-threaded, then you could also keep a dummy file
		1696	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1697	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1698	close that fd, and create a new dummy fd. This will gracefully refuse
		1699	clients under typical overload conditions.
		1700
		1701	The last way to handle it is to simply log the error and C<exit>, as
		1702	is often done with C<malloc> failures, but this results in an easy
		1703	opportunity for a DoS attack.
1182		1704
1183	=head3 Watcher-Specific Functions	1705	=head3 Watcher-Specific Functions
1184		1706
1185	=over 4	1707	=over 4
1186		1708
1187	=item ev_io_init (ev_io *, callback, int fd, int events)	1709	=item ev_io_init (ev_io *, callback, int fd, int events)
1188		1710
1189	=item ev_io_set (ev_io *, int fd, int events)	1711	=item ev_io_set (ev_io *, int fd, int events)
1190		1712
1191	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1713	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	1714	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.	1715	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1194		1716
1195	=item int fd [read-only]	1717	=item int fd [read-only]
1196		1718
1197	The file descriptor being watched.	1719	The file descriptor being watched.
1198		1720
…		…
1207	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1729	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	1730	readable, but only once. Since it is likely line-buffered, you could
1209	attempt to read a whole line in the callback.	1731	attempt to read a whole line in the callback.
1210		1732
1211	static void	1733	static void
1212	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1734	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1213	{	1735	{
1214	ev_io_stop (loop, w);	1736	ev_io_stop (loop, w);
1215	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1737	.. read from stdin here (or from w->fd) and handle any I/O errors
1216	}	1738	}
1217		1739
1218	...	1740	...
1219	struct ev_loop *loop = ev_default_init (0);	1741	struct ev_loop *loop = ev_default_init (0);
1220	struct ev_io stdin_readable;	1742	ev_io stdin_readable;
1221	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1743	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1222	ev_io_start (loop, &stdin_readable);	1744	ev_io_start (loop, &stdin_readable);
1223	ev_loop (loop, 0);	1745	ev_run (loop, 0);
1224		1746
1225		1747
1226	=head2 C<ev_timer> - relative and optionally repeating timeouts	1748	=head2 C<ev_timer> - relative and optionally repeating timeouts
1227		1749
1228	Timer watchers are simple relative timers that generate an event after a	1750	Timer watchers are simple relative timers that generate an event after a
1229	given time, and optionally repeating in regular intervals after that.	1751	given time, and optionally repeating in regular intervals after that.
1230		1752
1231	The timers are based on real time, that is, if you register an event that	1753	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	1754	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	1755	year, it will still time out after (roughly) one hour. "Roughly" because
1234	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1756	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1235	monotonic clock option helps a lot here).	1757	monotonic clock option helps a lot here).
1236		1758
1237	The callback is guaranteed to be invoked only after its timeout has passed,	1759	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	1760	passed (not I<at>, so on systems with very low-resolution clocks this
1239	order of execution is undefined.	1761	might introduce a small delay). If multiple timers become ready during the
		1762	same loop iteration then the ones with earlier time-out values are invoked
		1763	before ones of the same priority with later time-out values (but this is
		1764	no longer true when a callback calls C<ev_run> recursively).
		1765
		1766	=head3 Be smart about timeouts
		1767
		1768	Many real-world problems involve some kind of timeout, usually for error
		1769	recovery. A typical example is an HTTP request - if the other side hangs,
		1770	you want to raise some error after a while.
		1771
		1772	What follows are some ways to handle this problem, from obvious and
		1773	inefficient to smart and efficient.
		1774
		1775	In the following, a 60 second activity timeout is assumed - a timeout that
		1776	gets reset to 60 seconds each time there is activity (e.g. each time some
		1777	data or other life sign was received).
		1778
		1779	=over 4
		1780
		1781	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1782
		1783	This is the most obvious, but not the most simple way: In the beginning,
		1784	start the watcher:
		1785
		1786	ev_timer_init (timer, callback, 60., 0.);
		1787	ev_timer_start (loop, timer);
		1788
		1789	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1790	and start it again:
		1791
		1792	ev_timer_stop (loop, timer);
		1793	ev_timer_set (timer, 60., 0.);
		1794	ev_timer_start (loop, timer);
		1795
		1796	This is relatively simple to implement, but means that each time there is
		1797	some activity, libev will first have to remove the timer from its internal
		1798	data structure and then add it again. Libev tries to be fast, but it's
		1799	still not a constant-time operation.
		1800
		1801	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1802
		1803	This is the easiest way, and involves using C<ev_timer_again> instead of
		1804	C<ev_timer_start>.
		1805
		1806	To implement this, configure an C<ev_timer> with a C<repeat> value
		1807	of C<60> and then call C<ev_timer_again> at start and each time you
		1808	successfully read or write some data. If you go into an idle state where
		1809	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1810	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1811
		1812	That means you can ignore both the C<ev_timer_start> function and the
		1813	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1814	member and C<ev_timer_again>.
		1815
		1816	At start:
		1817
		1818	ev_init (timer, callback);
		1819	timer->repeat = 60.;
		1820	ev_timer_again (loop, timer);
		1821
		1822	Each time there is some activity:
		1823
		1824	ev_timer_again (loop, timer);
		1825
		1826	It is even possible to change the time-out on the fly, regardless of
		1827	whether the watcher is active or not:
		1828
		1829	timer->repeat = 30.;
		1830	ev_timer_again (loop, timer);
		1831
		1832	This is slightly more efficient then stopping/starting the timer each time
		1833	you want to modify its timeout value, as libev does not have to completely
		1834	remove and re-insert the timer from/into its internal data structure.
		1835
		1836	It is, however, even simpler than the "obvious" way to do it.
		1837
		1838	=item 3. Let the timer time out, but then re-arm it as required.
		1839
		1840	This method is more tricky, but usually most efficient: Most timeouts are
		1841	relatively long compared to the intervals between other activity - in
		1842	our example, within 60 seconds, there are usually many I/O events with
		1843	associated activity resets.
		1844
		1845	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1846	but remember the time of last activity, and check for a real timeout only
		1847	within the callback:
		1848
		1849	ev_tstamp last_activity; // time of last activity
		1850
		1851	static void
		1852	callback (EV_P_ ev_timer *w, int revents)
		1853	{
		1854	ev_tstamp now = ev_now (EV_A);
		1855	ev_tstamp timeout = last_activity + 60.;
		1856
		1857	// if last_activity + 60. is older than now, we did time out
		1858	if (timeout < now)
		1859	{
		1860	// timeout occurred, take action
		1861	}
		1862	else
		1863	{
		1864	// callback was invoked, but there was some activity, re-arm
		1865	// the watcher to fire in last_activity + 60, which is
		1866	// guaranteed to be in the future, so "again" is positive:
		1867	w->repeat = timeout - now;
		1868	ev_timer_again (EV_A_ w);
		1869	}
		1870	}
		1871
		1872	To summarise the callback: first calculate the real timeout (defined
		1873	as "60 seconds after the last activity"), then check if that time has
		1874	been reached, which means something I<did>, in fact, time out. Otherwise
		1875	the callback was invoked too early (C<timeout> is in the future), so
		1876	re-schedule the timer to fire at that future time, to see if maybe we have
		1877	a timeout then.
		1878
		1879	Note how C<ev_timer_again> is used, taking advantage of the
		1880	C<ev_timer_again> optimisation when the timer is already running.
		1881
		1882	This scheme causes more callback invocations (about one every 60 seconds
		1883	minus half the average time between activity), but virtually no calls to
		1884	libev to change the timeout.
		1885
		1886	To start the timer, simply initialise the watcher and set C<last_activity>
		1887	to the current time (meaning we just have some activity :), then call the
		1888	callback, which will "do the right thing" and start the timer:
		1889
		1890	ev_init (timer, callback);
		1891	last_activity = ev_now (loop);
		1892	callback (loop, timer, EV_TIMER);
		1893
		1894	And when there is some activity, simply store the current time in
		1895	C<last_activity>, no libev calls at all:
		1896
		1897	last_activity = ev_now (loop);
		1898
		1899	This technique is slightly more complex, but in most cases where the
		1900	time-out is unlikely to be triggered, much more efficient.
		1901
		1902	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1903	callback :) - just change the timeout and invoke the callback, which will
		1904	fix things for you.
		1905
		1906	=item 4. Wee, just use a double-linked list for your timeouts.
		1907
		1908	If there is not one request, but many thousands (millions...), all
		1909	employing some kind of timeout with the same timeout value, then one can
		1910	do even better:
		1911
		1912	When starting the timeout, calculate the timeout value and put the timeout
		1913	at the I<end> of the list.
		1914
		1915	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1916	the list is expected to fire (for example, using the technique #3).
		1917
		1918	When there is some activity, remove the timer from the list, recalculate
		1919	the timeout, append it to the end of the list again, and make sure to
		1920	update the C<ev_timer> if it was taken from the beginning of the list.
		1921
		1922	This way, one can manage an unlimited number of timeouts in O(1) time for
		1923	starting, stopping and updating the timers, at the expense of a major
		1924	complication, and having to use a constant timeout. The constant timeout
		1925	ensures that the list stays sorted.
		1926
		1927	=back
		1928
		1929	So which method the best?
		1930
		1931	Method #2 is a simple no-brain-required solution that is adequate in most
		1932	situations. Method #3 requires a bit more thinking, but handles many cases
		1933	better, and isn't very complicated either. In most case, choosing either
		1934	one is fine, with #3 being better in typical situations.
		1935
		1936	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1937	rather complicated, but extremely efficient, something that really pays
		1938	off after the first million or so of active timers, i.e. it's usually
		1939	overkill :)
1240		1940
1241	=head3 The special problem of time updates	1941	=head3 The special problem of time updates
1242		1942
1243	Establishing the current time is a costly operation (it usually takes at	1943	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	1944	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	1945	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	1946	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1247	lots of events.	1947	lots of events in one iteration.
1248		1948
1249	The relative timeouts are calculated relative to the C<ev_now ()>	1949	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	1950	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	1951	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	1952	you suspect event processing to be delayed and you I<need> to base the
…		…
1256		1956
1257	If the event loop is suspended for a long time, you can also force an	1957	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	1958	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1259	()>.	1959	()>.
1260		1960
		1961	=head3 The special problems of suspended animation
		1962
		1963	When you leave the server world it is quite customary to hit machines that
		1964	can suspend/hibernate - what happens to the clocks during such a suspend?
		1965
		1966	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1967	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1968	to run until the system is suspended, but they will not advance while the
		1969	system is suspended. That means, on resume, it will be as if the program
		1970	was frozen for a few seconds, but the suspend time will not be counted
		1971	towards C<ev_timer> when a monotonic clock source is used. The real time
		1972	clock advanced as expected, but if it is used as sole clocksource, then a
		1973	long suspend would be detected as a time jump by libev, and timers would
		1974	be adjusted accordingly.
		1975
		1976	I would not be surprised to see different behaviour in different between
		1977	operating systems, OS versions or even different hardware.
		1978
		1979	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1980	time jump in the monotonic clocks and the realtime clock. If the program
		1981	is suspended for a very long time, and monotonic clock sources are in use,
		1982	then you can expect C<ev_timer>s to expire as the full suspension time
		1983	will be counted towards the timers. When no monotonic clock source is in
		1984	use, then libev will again assume a timejump and adjust accordingly.
		1985
		1986	It might be beneficial for this latter case to call C<ev_suspend>
		1987	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1988	deterministic behaviour in this case (you can do nothing against
		1989	C<SIGSTOP>).
		1990
1261	=head3 Watcher-Specific Functions and Data Members	1991	=head3 Watcher-Specific Functions and Data Members
1262		1992
1263	=over 4	1993	=over 4
1264		1994
1265	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1995	=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).	2018	If the timer is started but non-repeating, stop it (as if it timed out).
1289		2019
1290	If the timer is repeating, either start it if necessary (with the	2020	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.	2021	C<repeat> value), or reset the running timer to the C<repeat> value.
1292		2022
1293	This sounds a bit complicated, but here is a useful and typical	2023	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	2024	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		2025
1303	That means you can ignore the C<after> value and C<ev_timer_start>	2026	=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		2027
1306	ev_timer_init (timer, callback, 0., 5.);	2028	Returns the remaining time until a timer fires. If the timer is active,
1307	ev_timer_again (loop, timer);	2029	then this time is relative to the current event loop time, otherwise it's
1308	...	2030	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		2031
1315	This is more slightly efficient then stopping/starting the timer each time	2032	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1316	you want to modify its timeout value.	2033	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2034	will return C<4>. When the timer expires and is restarted, it will return
		2035	roughly C<7> (likely slightly less as callback invocation takes some time,
		2036	too), and so on.
1317		2037
1318	=item ev_tstamp repeat [read-write]	2038	=item ev_tstamp repeat [read-write]
1319		2039
1320	The current C<repeat> value. Will be used each time the watcher times out	2040	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),	2041	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.	2042	which is also when any modifications are taken into account.
1323		2043
1324	=back	2044	=back
1325		2045
1326	=head3 Examples	2046	=head3 Examples
1327		2047
1328	Example: Create a timer that fires after 60 seconds.	2048	Example: Create a timer that fires after 60 seconds.
1329		2049
1330	static void	2050	static void
1331	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2051	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1332	{	2052	{
1333	.. one minute over, w is actually stopped right here	2053	.. one minute over, w is actually stopped right here
1334	}	2054	}
1335		2055
1336	struct ev_timer mytimer;	2056	ev_timer mytimer;
1337	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2057	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1338	ev_timer_start (loop, &mytimer);	2058	ev_timer_start (loop, &mytimer);
1339		2059
1340	Example: Create a timeout timer that times out after 10 seconds of	2060	Example: Create a timeout timer that times out after 10 seconds of
1341	inactivity.	2061	inactivity.
1342		2062
1343	static void	2063	static void
1344	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2064	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1345	{	2065	{
1346	.. ten seconds without any activity	2066	.. ten seconds without any activity
1347	}	2067	}
1348		2068
1349	struct ev_timer mytimer;	2069	ev_timer mytimer;
1350	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2070	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1351	ev_timer_again (&mytimer); /* start timer */	2071	ev_timer_again (&mytimer); /* start timer */
1352	ev_loop (loop, 0);	2072	ev_run (loop, 0);
1353		2073
1354	// and in some piece of code that gets executed on any "activity":	2074	// and in some piece of code that gets executed on any "activity":
1355	// reset the timeout to start ticking again at 10 seconds	2075	// reset the timeout to start ticking again at 10 seconds
1356	ev_timer_again (&mytimer);	2076	ev_timer_again (&mytimer);
1357		2077
…		…
1359	=head2 C<ev_periodic> - to cron or not to cron?	2079	=head2 C<ev_periodic> - to cron or not to cron?
1360		2080
1361	Periodic watchers are also timers of a kind, but they are very versatile	2081	Periodic watchers are also timers of a kind, but they are very versatile
1362	(and unfortunately a bit complex).	2082	(and unfortunately a bit complex).
1363		2083
1364	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2084	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	2085	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	2086	(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 ()	2087	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	2088	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	2089	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		2090
		2091	You can tell a periodic watcher to trigger after some specific point
		2092	in time: for example, if you tell a periodic watcher to trigger "in 10
		2093	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2094	not a delay) and then reset your system clock to January of the previous
		2095	year, then it will take a year or more to trigger the event (unlike an
		2096	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2097	it, as it uses a relative timeout).
		2098
1373	C<ev_periodic>s can also be used to implement vastly more complex timers,	2099	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	2100	timers, such as triggering an event on each "midnight, local time", or
1375	complicated, rules.	2101	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2102	those cannot react to time jumps.
1376		2103
1377	As with timers, the callback is guaranteed to be invoked only when the	2104	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	2105	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.	2106	timers become ready during the same loop iteration then the ones with
		2107	earlier time-out values are invoked before ones with later time-out values
		2108	(but this is no longer true when a callback calls C<ev_run> recursively).
1380		2109
1381	=head3 Watcher-Specific Functions and Data Members	2110	=head3 Watcher-Specific Functions and Data Members
1382		2111
1383	=over 4	2112	=over 4
1384		2113
1385	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2114	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1386		2115
1387	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2116	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1388		2117
1389	Lots of arguments, lets sort it out... There are basically three modes of	2118	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:	2119	operation, and we will explain them from simplest to most complex:
1391		2120
1392	=over 4	2121	=over 4
1393		2122
1394	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2123	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1395		2124
1396	In this configuration the watcher triggers an event after the wall clock	2125	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	2126	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	2127	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.	2128	will be stopped and invoked when the system clock reaches or surpasses
		2129	this point in time.
1400		2130
1401	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2131	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1402		2132
1403	In this mode the watcher will always be scheduled to time out at the next	2133	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)	2134	C<offset + N * interval> time (for some integer N, which can also be
1405	and then repeat, regardless of any time jumps.	2135	negative) and then repeat, regardless of any time jumps. The C<offset>
		2136	argument is merely an offset into the C<interval> periods.
1406		2137
1407	This can be used to create timers that do not drift with respect to system	2138	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	2139	system clock, for example, here is an C<ev_periodic> that triggers each
1409	the hour:	2140	hour, on the hour (with respect to UTC):
1410		2141
1411	ev_periodic_set (&periodic, 0., 3600., 0);	2142	ev_periodic_set (&periodic, 0., 3600., 0);
1412		2143
1413	This doesn't mean there will always be 3600 seconds in between triggers,	2144	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	2145	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	2146	full hour (UTC), or more correctly, when the system time is evenly divisible
1416	by 3600.	2147	by 3600.
1417		2148
1418	Another way to think about it (for the mathematically inclined) is that	2149	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	2150	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.	2151	time where C<time = offset (mod interval)>, regardless of any time jumps.
1421		2152
1422	For numerical stability it is preferable that the C<at> value is near	2153	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	2154	C<ev_now ()> (the current time), but there is no range requirement for
1424	this value, and in fact is often specified as zero.	2155	this value, and in fact is often specified as zero.
1425		2156
1426	Note also that there is an upper limit to how often a timer can fire (CPU	2157	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	2158	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	2159	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).	2160	millisecond (if the OS supports it and the machine is fast enough).
1430		2161
1431	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2162	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1432		2163
1433	In this mode the values for C<interval> and C<at> are both being	2164	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	2165	ignored. Instead, each time the periodic watcher gets scheduled, the
1435	reschedule callback will be called with the watcher as first, and the	2166	reschedule callback will be called with the watcher as first, and the
1436	current time as second argument.	2167	current time as second argument.
1437		2168
1438	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2169	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1439	ever, or make ANY event loop modifications whatsoever>.	2170	or make ANY other event loop modifications whatsoever, unless explicitly
		2171	allowed by documentation here>.
1440		2172
1441	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2173	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	2174	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1443	only event loop modification you are allowed to do).	2175	only event loop modification you are allowed to do).
1444		2176
1445	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2177	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1446	*w, ev_tstamp now)>, e.g.:	2178	*w, ev_tstamp now)>, e.g.:
1447		2179
		2180	static ev_tstamp
1448	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2181	my_rescheduler (ev_periodic *w, ev_tstamp now)
1449	{	2182	{
1450	return now + 60.;	2183	return now + 60.;
1451	}	2184	}
1452		2185
1453	It must return the next time to trigger, based on the passed time value	2186	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	2206	a different time than the last time it was called (e.g. in a crond like
1474	program when the crontabs have changed).	2207	program when the crontabs have changed).
1475		2208
1476	=item ev_tstamp ev_periodic_at (ev_periodic *)	2209	=item ev_tstamp ev_periodic_at (ev_periodic *)
1477		2210
1478	When active, returns the absolute time that the watcher is supposed to	2211	When active, returns the absolute time that the watcher is supposed
1479	trigger next.	2212	to trigger next. This is not the same as the C<offset> argument to
		2213	C<ev_periodic_set>, but indeed works even in interval and manual
		2214	rescheduling modes.
1480		2215
1481	=item ev_tstamp offset [read-write]	2216	=item ev_tstamp offset [read-write]
1482		2217
1483	When repeating, this contains the offset value, otherwise this is the	2218	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>).	2219	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2220	although libev might modify this value for better numerical stability).
1485		2221
1486	Can be modified any time, but changes only take effect when the periodic	2222	Can be modified any time, but changes only take effect when the periodic
1487	timer fires or C<ev_periodic_again> is being called.	2223	timer fires or C<ev_periodic_again> is being called.
1488		2224
1489	=item ev_tstamp interval [read-write]	2225	=item ev_tstamp interval [read-write]
1490		2226
1491	The current interval value. Can be modified any time, but changes only	2227	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	2228	take effect when the periodic timer fires or C<ev_periodic_again> is being
1493	called.	2229	called.
1494		2230
1495	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2231	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1496		2232
1497	The current reschedule callback, or C<0>, if this functionality is	2233	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	2234	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.	2235	the periodic timer fires or C<ev_periodic_again> is being called.
1500		2236
1501	=back	2237	=back
1502		2238
1503	=head3 Examples	2239	=head3 Examples
1504		2240
1505	Example: Call a callback every hour, or, more precisely, whenever the	2241	Example: Call a callback every hour, or, more precisely, whenever the
1506	system clock is divisible by 3600. The callback invocation times have	2242	system time is divisible by 3600. The callback invocation times have
1507	potentially a lot of jitter, but good long-term stability.	2243	potentially a lot of jitter, but good long-term stability.
1508		2244
1509	static void	2245	static void
1510	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2246	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1511	{	2247	{
1512	... its now a full hour (UTC, or TAI or whatever your clock follows)	2248	... its now a full hour (UTC, or TAI or whatever your clock follows)
1513	}	2249	}
1514		2250
1515	struct ev_periodic hourly_tick;	2251	ev_periodic hourly_tick;
1516	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2252	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1517	ev_periodic_start (loop, &hourly_tick);	2253	ev_periodic_start (loop, &hourly_tick);
1518		2254
1519	Example: The same as above, but use a reschedule callback to do it:	2255	Example: The same as above, but use a reschedule callback to do it:
1520		2256
1521	#include <math.h>	2257	#include <math.h>
1522		2258
1523	static ev_tstamp	2259	static ev_tstamp
1524	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2260	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1525	{	2261	{
1526	return fmod (now, 3600.) + 3600.;	2262	return now + (3600. - fmod (now, 3600.));
1527	}	2263	}
1528		2264
1529	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2265	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1530		2266
1531	Example: Call a callback every hour, starting now:	2267	Example: Call a callback every hour, starting now:
1532		2268
1533	struct ev_periodic hourly_tick;	2269	ev_periodic hourly_tick;
1534	ev_periodic_init (&hourly_tick, clock_cb,	2270	ev_periodic_init (&hourly_tick, clock_cb,
1535	fmod (ev_now (loop), 3600.), 3600., 0);	2271	fmod (ev_now (loop), 3600.), 3600., 0);
1536	ev_periodic_start (loop, &hourly_tick);	2272	ev_periodic_start (loop, &hourly_tick);
1537		2273
1538		2274
1539	=head2 C<ev_signal> - signal me when a signal gets signalled!	2275	=head2 C<ev_signal> - signal me when a signal gets signalled!
1540		2276
1541	Signal watchers will trigger an event when the process receives a specific	2277	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	2278	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	2279	will try its best to deliver signals synchronously, i.e. as part of the
1544	normal event processing, like any other event.	2280	normal event processing, like any other event.
1545		2281
		2282	If you want signals to be delivered truly asynchronously, just use
		2283	C<sigaction> as you would do without libev and forget about sharing
		2284	the signal. You can even use C<ev_async> from a signal handler to
		2285	synchronously wake up an event loop.
		2286
1546	You can configure as many watchers as you like per signal. Only when the	2287	You can configure as many watchers as you like for the same signal, but
		2288	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2289	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2290	C<SIGINT> in both the default loop and another loop at the same time. At
		2291	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2292
1547	first watcher gets started will libev actually register a signal watcher	2293	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	2294	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	2295	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		2296
1553	If possible and supported, libev will install its handlers with	2297	If possible and supported, libev will install its handlers with
1554	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2298	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1555	interrupted. If you have a problem with system calls getting interrupted by	2299	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	2300	interrupted by signals you can block all signals in an C<ev_check> watcher
1557	them in an C<ev_prepare> watcher.	2301	and unblock them in an C<ev_prepare> watcher.
		2302
		2303	=head3 The special problem of inheritance over fork/execve/pthread_create
		2304
		2305	Both the signal mask (C<sigprocmask>) and the signal disposition
		2306	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2307	stopping it again), that is, libev might or might not block the signal,
		2308	and might or might not set or restore the installed signal handler (but
		2309	see C<EVFLAG_NOSIGMASK>).
		2310
		2311	While this does not matter for the signal disposition (libev never
		2312	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2313	C<execve>), this matters for the signal mask: many programs do not expect
		2314	certain signals to be blocked.
		2315
		2316	This means that before calling C<exec> (from the child) you should reset
		2317	the signal mask to whatever "default" you expect (all clear is a good
		2318	choice usually).
		2319
		2320	The simplest way to ensure that the signal mask is reset in the child is
		2321	to install a fork handler with C<pthread_atfork> that resets it. That will
		2322	catch fork calls done by libraries (such as the libc) as well.
		2323
		2324	In current versions of libev, the signal will not be blocked indefinitely
		2325	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2326	the window of opportunity for problems, it will not go away, as libev
		2327	I<has> to modify the signal mask, at least temporarily.
		2328
		2329	So I can't stress this enough: I<If you do not reset your signal mask when
		2330	you expect it to be empty, you have a race condition in your code>. This
		2331	is not a libev-specific thing, this is true for most event libraries.
		2332
		2333	=head3 The special problem of threads signal handling
		2334
		2335	POSIX threads has problematic signal handling semantics, specifically,
		2336	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2337	threads in a process block signals, which is hard to achieve.
		2338
		2339	When you want to use sigwait (or mix libev signal handling with your own
		2340	for the same signals), you can tackle this problem by globally blocking
		2341	all signals before creating any threads (or creating them with a fully set
		2342	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2343	loops. Then designate one thread as "signal receiver thread" which handles
		2344	these signals. You can pass on any signals that libev might be interested
		2345	in by calling C<ev_feed_signal>.
1558		2346
1559	=head3 Watcher-Specific Functions and Data Members	2347	=head3 Watcher-Specific Functions and Data Members
1560		2348
1561	=over 4	2349	=over 4
1562		2350
…		…
1573		2361
1574	=back	2362	=back
1575		2363
1576	=head3 Examples	2364	=head3 Examples
1577		2365
1578	Example: Try to exit cleanly on SIGINT and SIGTERM.	2366	Example: Try to exit cleanly on SIGINT.
1579		2367
1580	static void	2368	static void
1581	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2369	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1582	{	2370	{
1583	ev_unloop (loop, EVUNLOOP_ALL);	2371	ev_break (loop, EVBREAK_ALL);
1584	}	2372	}
1585		2373
1586	struct ev_signal signal_watcher;	2374	ev_signal signal_watcher;
1587	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2375	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1588	ev_signal_start (loop, &sigint_cb);	2376	ev_signal_start (loop, &signal_watcher);
1589		2377
1590		2378
1591	=head2 C<ev_child> - watch out for process status changes	2379	=head2 C<ev_child> - watch out for process status changes
1592		2380
1593	Child watchers trigger when your process receives a SIGCHLD in response to	2381	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	2382	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	2383	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	2384	has been forked (which implies it might have already exited), as long
1597	loop isn't entered (or is continued from a watcher).	2385	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2386	forking and then immediately registering a watcher for the child is fine,
		2387	but forking and registering a watcher a few event loop iterations later or
		2388	in the next callback invocation is not.
1598		2389
1599	Only the default event loop is capable of handling signals, and therefore	2390	Only the default event loop is capable of handling signals, and therefore
1600	you can only register child watchers in the default event loop.	2391	you can only register child watchers in the default event loop.
1601		2392
		2393	Due to some design glitches inside libev, child watchers will always be
		2394	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2395	libev)
		2396
1602	=head3 Process Interaction	2397	=head3 Process Interaction
1603		2398
1604	Libev grabs C<SIGCHLD> as soon as the default event loop is	2399	Libev grabs C<SIGCHLD> as soon as the default event loop is
1605	initialised. This is necessary to guarantee proper behaviour even if	2400	initialised. This is necessary to guarantee proper behaviour even if the
1606	the first child watcher is started after the child exits. The occurrence	2401	first child watcher is started after the child exits. The occurrence
1607	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2402	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1608	synchronously as part of the event loop processing. Libev always reaps all	2403	synchronously as part of the event loop processing. Libev always reaps all
1609	children, even ones not watched.	2404	children, even ones not watched.
1610		2405
1611	=head3 Overriding the Built-In Processing	2406	=head3 Overriding the Built-In Processing
…		…
1621	=head3 Stopping the Child Watcher	2416	=head3 Stopping the Child Watcher
1622		2417
1623	Currently, the child watcher never gets stopped, even when the	2418	Currently, the child watcher never gets stopped, even when the
1624	child terminates, so normally one needs to stop the watcher in the	2419	child terminates, so normally one needs to stop the watcher in the
1625	callback. Future versions of libev might stop the watcher automatically	2420	callback. Future versions of libev might stop the watcher automatically
1626	when a child exit is detected.	2421	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2422	problem).
1627		2423
1628	=head3 Watcher-Specific Functions and Data Members	2424	=head3 Watcher-Specific Functions and Data Members
1629		2425
1630	=over 4	2426	=over 4
1631		2427
…		…
1663	its completion.	2459	its completion.
1664		2460
1665	ev_child cw;	2461	ev_child cw;
1666		2462
1667	static void	2463	static void
1668	child_cb (EV_P_ struct ev_child *w, int revents)	2464	child_cb (EV_P_ ev_child *w, int revents)
1669	{	2465	{
1670	ev_child_stop (EV_A_ w);	2466	ev_child_stop (EV_A_ w);
1671	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2467	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1672	}	2468	}
1673		2469
…		…
1688		2484
1689		2485
1690	=head2 C<ev_stat> - did the file attributes just change?	2486	=head2 C<ev_stat> - did the file attributes just change?
1691		2487
1692	This watches a file system path for attribute changes. That is, it calls	2488	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	2489	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.	2490	and sees if it changed compared to the last time, invoking the callback if
		2491	it did.
1695		2492
1696	The path does not need to exist: changing from "path exists" to "path does	2493	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	2494	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	2495	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	2496	C<st_nlink> field being zero (which is otherwise always forced to be at
1700	the stat buffer having unspecified contents.	2497	least one) and all the other fields of the stat buffer having unspecified
		2498	contents.
1701		2499
1702	The path I<should> be absolute and I<must not> end in a slash. If it is	2500	The path I<must not> end in a slash or contain special components such as
		2501	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.	2502	your working directory changes, then the behaviour is undefined.
1704		2503
1705	Since there is no standard to do this, the portable implementation simply	2504	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	2505	portable implementation simply calls C<stat(2)> regularly on the path
1707	can specify a recommended polling interval for this case. If you specify	2506	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,	2507	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	2508	recommended!) then a I<suitable, unspecified default> value will be used
1710	five seconds, although this might change dynamically). Libev will also	2509	(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	2510	change dynamically). Libev will also impose a minimum interval which is
1712	usually overkill.	2511	currently around C<0.1>, but that's usually overkill.
1713		2512
1714	This watcher type is not meant for massive numbers of stat watchers,	2513	This watcher type is not meant for massive numbers of stat watchers,
1715	as even with OS-supported change notifications, this can be	2514	as even with OS-supported change notifications, this can be
1716	resource-intensive.	2515	resource-intensive.
1717		2516
1718	At the time of this writing, only the Linux inotify interface is	2517	At the time of this writing, the only OS-specific interface implemented
1719	implemented (implementing kqueue support is left as an exercise for the	2518	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	2519	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	2520	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		2521
1727	=head3 ABI Issues (Largefile Support)	2522	=head3 ABI Issues (Largefile Support)
1728		2523
1729	Libev by default (unless the user overrides this) uses the default	2524	Libev by default (unless the user overrides this) uses the default
1730	compilation environment, which means that on systems with large file	2525	compilation environment, which means that on systems with large file
1731	support disabled by default, you get the 32 bit version of the stat	2526	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	2527	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	2528	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	2529	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	2530	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.	2531	most noticeably displayed with ev_stat and large file support.
1737		2532
1738	The solution for this is to lobby your distribution maker to make large	2533	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	2534	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	2535	optional. Libev cannot simply switch on large file support because it has
1741	to exchange stat structures with application programs compiled using the	2536	to exchange stat structures with application programs compiled using the
1742	default compilation environment.	2537	default compilation environment.
1743		2538
1744	=head3 Inotify	2539	=head3 Inotify and Kqueue
1745		2540
1746	When C<inotify (7)> support has been compiled into libev (generally only	2541	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	2542	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	2543	inotify descriptor will be created lazily when the first C<ev_stat>
1749	when the first C<ev_stat> watcher is being started.	2544	watcher is being started.
1750		2545
1751	Inotify presence does not change the semantics of C<ev_stat> watchers	2546	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	2547	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	2548	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.	2549	there are many cases where libev has to resort to regular C<stat> polling,
		2550	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2551	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2552	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2553	xfs are fully working) libev usually gets away without polling.
1755		2554
1756	(There is no support for kqueue, as apparently it cannot be used to	2555	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	2556	implement this functionality, due to the requirement of having a file
1758	descriptor open on the object at all times).	2557	descriptor open on the object at all times, and detecting renames, unlinks
		2558	etc. is difficult.
		2559
		2560	=head3 C<stat ()> is a synchronous operation
		2561
		2562	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2563	the process. The exception are C<ev_stat> watchers - those call C<stat
		2564	()>, which is a synchronous operation.
		2565
		2566	For local paths, this usually doesn't matter: unless the system is very
		2567	busy or the intervals between stat's are large, a stat call will be fast,
		2568	as the path data is usually in memory already (except when starting the
		2569	watcher).
		2570
		2571	For networked file systems, calling C<stat ()> can block an indefinite
		2572	time due to network issues, and even under good conditions, a stat call
		2573	often takes multiple milliseconds.
		2574
		2575	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2576	paths, although this is fully supported by libev.
1759		2577
1760	=head3 The special problem of stat time resolution	2578	=head3 The special problem of stat time resolution
1761		2579
1762	The C<stat ()> system call only supports full-second resolution portably, and	2580	The C<stat ()> system call only supports full-second resolution portably,
1763	even on systems where the resolution is higher, many file systems still	2581	and even on systems where the resolution is higher, most file systems
1764	only support whole seconds.	2582	still only support whole seconds.
1765		2583
1766	That means that, if the time is the only thing that changes, you can	2584	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	2585	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	2586	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	2587	within the same second, C<ev_stat> will be unable to detect unless the
1770	data does not change.	2588	stat data does change in other ways (e.g. file size).
1771		2589
1772	The solution to this is to delay acting on a change for slightly more	2590	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	2591	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);	2592	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1775	ev_timer_again (loop, w)>).	2593	ev_timer_again (loop, w)>).
…		…
1795	C<path>. The C<interval> is a hint on how quickly a change is expected to	2613	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	2614	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	2615	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.	2616	path for as long as the watcher is active.
1799		2617
1800	The callback will receive C<EV_STAT> when a change was detected, relative	2618	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	2619	relative to the attributes at the time the watcher was started (or the
1802	was detected).	2620	last change was detected).
1803		2621
1804	=item ev_stat_stat (loop, ev_stat *)	2622	=item ev_stat_stat (loop, ev_stat *)
1805		2623
1806	Updates the stat buffer immediately with new values. If you change the	2624	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	2625	watched path in your callback, you could call this function to avoid
…		…
1890		2708
1891		2709
1892	=head2 C<ev_idle> - when you've got nothing better to do...	2710	=head2 C<ev_idle> - when you've got nothing better to do...
1893		2711
1894	Idle watchers trigger events when no other events of the same or higher	2712	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	2713	priority are pending (prepare, check and other idle watchers do not count
1896	count).	2714	as receiving "events").
1897		2715
1898	That is, as long as your process is busy handling sockets or timeouts	2716	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	2717	(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	2718	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	2719	are pending), the idle watchers are being called once per event loop
…		…
1912		2730
1913	=head3 Watcher-Specific Functions and Data Members	2731	=head3 Watcher-Specific Functions and Data Members
1914		2732
1915	=over 4	2733	=over 4
1916		2734
1917	=item ev_idle_init (ev_signal *, callback)	2735	=item ev_idle_init (ev_idle *, callback)
1918		2736
1919	Initialises and configures the idle watcher - it has no parameters of any	2737	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,	2738	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1921	believe me.	2739	believe me.
1922		2740
…		…
1926		2744
1927	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2745	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1928	callback, free it. Also, use no error checking, as usual.	2746	callback, free it. Also, use no error checking, as usual.
1929		2747
1930	static void	2748	static void
1931	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2749	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1932	{	2750	{
1933	free (w);	2751	free (w);
1934	// now do something you wanted to do when the program has	2752	// now do something you wanted to do when the program has
1935	// no longer anything immediate to do.	2753	// no longer anything immediate to do.
1936	}	2754	}
1937		2755
1938	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2756	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1939	ev_idle_init (idle_watcher, idle_cb);	2757	ev_idle_init (idle_watcher, idle_cb);
1940	ev_idle_start (loop, idle_cb);	2758	ev_idle_start (loop, idle_watcher);
1941		2759
1942		2760
1943	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2761	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1944		2762
1945	Prepare and check watchers are usually (but not always) used in tandem:	2763	Prepare and check watchers are usually (but not always) used in pairs:
1946	prepare watchers get invoked before the process blocks and check watchers	2764	prepare watchers get invoked before the process blocks and check watchers
1947	afterwards.	2765	afterwards.
1948		2766
1949	You I<must not> call C<ev_loop> or similar functions that enter	2767	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>	2768	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	2769	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	2770	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,	2771	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	2772	C<ev_check> so if you have one watcher of each kind they will always be
1955	called in pairs bracketing the blocking call.	2773	called in pairs bracketing the blocking call.
1956		2774
1957	Their main purpose is to integrate other event mechanisms into libev and	2775	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	2776	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	2777	variable changes, implement your own watchers, integrate net-snmp or a
1960	coroutine library and lots more. They are also occasionally useful if	2778	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,	2779	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>	2780	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1963	watcher).	2781	watcher).
1964		2782
1965	This is done by examining in each prepare call which file descriptors need	2783	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	2784	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	2785	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	2786	libraries provide exactly this functionality). Then, in the check watcher,
1969	any events that occurred (by checking the pending status of all watchers	2787	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	2788	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,	2789	I/O and timer callbacks will never actually be called (but must be valid
1972	because you never know, you know?).	2790	nevertheless, because you never know, you know?).
1973		2791
1974	As another example, the Perl Coro module uses these hooks to integrate	2792	As another example, the Perl Coro module uses these hooks to integrate
1975	coroutines into libev programs, by yielding to other active coroutines	2793	coroutines into libev programs, by yielding to other active coroutines
1976	during each prepare and only letting the process block if no coroutines	2794	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	2795	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	2798	loop from blocking if lower-priority coroutines are active, thus mapping
1981	low-priority coroutines to idle/background tasks).	2799	low-priority coroutines to idle/background tasks).
1982		2800
1983	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2801	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	2802	priority, to ensure that they are being run before any other watchers
		2803	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2804
1985	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2805	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	2806	activate ("feed") events into libev. While libev fully supports this, they
1987	supports this, they might get executed before other C<ev_check> watchers	2807	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	2808	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	2809	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	2810	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1991	coexist peacefully with others).	2811	others).
1992		2812
1993	=head3 Watcher-Specific Functions and Data Members	2813	=head3 Watcher-Specific Functions and Data Members
1994		2814
1995	=over 4	2815	=over 4
1996		2816
…		…
1998		2818
1999	=item ev_check_init (ev_check *, callback)	2819	=item ev_check_init (ev_check *, callback)
2000		2820
2001	Initialises and configures the prepare or check watcher - they have no	2821	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>	2822	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.	2823	macros, but using them is utterly, utterly, utterly and completely
		2824	pointless.
2004		2825
2005	=back	2826	=back
2006		2827
2007	=head3 Examples	2828	=head3 Examples
2008		2829
…		…
2021		2842
2022	static ev_io iow [nfd];	2843	static ev_io iow [nfd];
2023	static ev_timer tw;	2844	static ev_timer tw;
2024		2845
2025	static void	2846	static void
2026	io_cb (ev_loop *loop, ev_io *w, int revents)	2847	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2027	{	2848	{
2028	}	2849	}
2029		2850
2030	// create io watchers for each fd and a timer before blocking	2851	// create io watchers for each fd and a timer before blocking
2031	static void	2852	static void
2032	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2853	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2033	{	2854	{
2034	int timeout = 3600000;	2855	int timeout = 3600000;
2035	struct pollfd fds [nfd];	2856	struct pollfd fds [nfd];
2036	// actual code will need to loop here and realloc etc.	2857	// actual code will need to loop here and realloc etc.
2037	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2858	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2038		2859
2039	/* the callback is illegal, but won't be called as we stop during check */	2860	/* the callback is illegal, but won't be called as we stop during check */
2040	ev_timer_init (&tw, 0, timeout * 1e-3);	2861	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2041	ev_timer_start (loop, &tw);	2862	ev_timer_start (loop, &tw);
2042		2863
2043	// create one ev_io per pollfd	2864	// create one ev_io per pollfd
2044	for (int i = 0; i < nfd; ++i)	2865	for (int i = 0; i < nfd; ++i)
2045	{	2866	{
…		…
2052	}	2873	}
2053	}	2874	}
2054		2875
2055	// stop all watchers after blocking	2876	// stop all watchers after blocking
2056	static void	2877	static void
2057	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2878	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2058	{	2879	{
2059	ev_timer_stop (loop, &tw);	2880	ev_timer_stop (loop, &tw);
2060		2881
2061	for (int i = 0; i < nfd; ++i)	2882	for (int i = 0; i < nfd; ++i)
2062	{	2883	{
…		…
2101	}	2922	}
2102		2923
2103	// do not ever call adns_afterpoll	2924	// do not ever call adns_afterpoll
2104		2925
2105	Method 4: Do not use a prepare or check watcher because the module you	2926	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	2927	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	2928	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	2929	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2109	this.	2930	this approach, effectively embedding EV as a client into the horrible
		2931	libglib event loop.
2110		2932
2111	static gint	2933	static gint
2112	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2934	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2113	{	2935	{
2114	int got_events = 0;	2936	int got_events = 0;
…		…
2118		2940
2119	if (timeout >= 0)	2941	if (timeout >= 0)
2120	// create/start timer	2942	// create/start timer
2121		2943
2122	// poll	2944	// poll
2123	ev_loop (EV_A_ 0);	2945	ev_run (EV_A_ 0);
2124		2946
2125	// stop timer again	2947	// stop timer again
2126	if (timeout >= 0)	2948	if (timeout >= 0)
2127	ev_timer_stop (EV_A_ &to);	2949	ev_timer_stop (EV_A_ &to);
2128		2950
…		…
2145	prioritise I/O.	2967	prioritise I/O.
2146		2968
2147	As an example for a bug workaround, the kqueue backend might only support	2969	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	2970	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	2971	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	2972	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	2973	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	2974	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.	2975	C<kevent>, but at least you can use both mechanisms for what they are
		2976	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2154		2977
2155	As for prioritising I/O: rarely you have the case where some fds have	2978	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	2979	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	2980	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	2981	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.	2982	the rest in a second one, and embed the second one in the first.
2160		2983
2161	As long as the watcher is active, the callback will be invoked every time	2984	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	2985	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	2986	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	2987	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	2988	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	2989	to give the embedded loop strictly lower priority for example).
2167	embedded loop sweep.
2168		2990
2169	As long as the watcher is started it will automatically handle events. The	2991	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	2992	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		2993
2174	Also, there have not currently been made special provisions for forking:	2994	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,	2995	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	2996	embedding loop forks. In other cases, the user is responsible for calling
2177	yourself.	2997	C<ev_loop_fork> on the embedded loop.
2178		2998
2179	Unfortunately, not all backends are embeddable, only the ones returned by	2999	Unfortunately, not all backends are embeddable: only the ones returned by
2180	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3000	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2181	portable one.	3001	portable one.
2182		3002
2183	So when you want to use this feature you will always have to be prepared	3003	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	3004	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	3005	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.	3006	create it, and if that fails, use the normal loop for everything.
		3007
		3008	=head3 C<ev_embed> and fork
		3009
		3010	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3011	automatically be applied to the embedded loop as well, so no special
		3012	fork handling is required in that case. When the watcher is not running,
		3013	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3014	as applicable.
2187		3015
2188	=head3 Watcher-Specific Functions and Data Members	3016	=head3 Watcher-Specific Functions and Data Members
2189		3017
2190	=over 4	3018	=over 4
2191		3019
…		…
2200	if you do not want that, you need to temporarily stop the embed watcher).	3028	if you do not want that, you need to temporarily stop the embed watcher).
2201		3029
2202	=item ev_embed_sweep (loop, ev_embed *)	3030	=item ev_embed_sweep (loop, ev_embed *)
2203		3031
2204	Make a single, non-blocking sweep over the embedded loop. This works	3032	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	3033	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2206	appropriate way for embedded loops.	3034	appropriate way for embedded loops.
2207		3035
2208	=item struct ev_loop *other [read-only]	3036	=item struct ev_loop *other [read-only]
2209		3037
2210	The embedded event loop.	3038	The embedded event loop.
…		…
2219	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	3047	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2220	used).	3048	used).
2221		3049
2222	struct ev_loop *loop_hi = ev_default_init (0);	3050	struct ev_loop *loop_hi = ev_default_init (0);
2223	struct ev_loop *loop_lo = 0;	3051	struct ev_loop *loop_lo = 0;
2224	struct ev_embed embed;	3052	ev_embed embed;
2225		3053
2226	// see if there is a chance of getting one that works	3054	// see if there is a chance of getting one that works
2227	// (remember that a flags value of 0 means autodetection)	3055	// (remember that a flags value of 0 means autodetection)
2228	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3056	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2229	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3057	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2243	kqueue implementation). Store the kqueue/socket-only event loop in	3071	kqueue implementation). Store the kqueue/socket-only event loop in
2244	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3072	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2245		3073
2246	struct ev_loop *loop = ev_default_init (0);	3074	struct ev_loop *loop = ev_default_init (0);
2247	struct ev_loop *loop_socket = 0;	3075	struct ev_loop *loop_socket = 0;
2248	struct ev_embed embed;	3076	ev_embed embed;
2249		3077
2250	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3078	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2251	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3079	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2252	{	3080	{
2253	ev_embed_init (&embed, 0, loop_socket);	3081	ev_embed_init (&embed, 0, loop_socket);
…		…
2268	event loop blocks next and before C<ev_check> watchers are being called,	3096	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	3097	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	3098	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2271	handlers will be invoked, too, of course.	3099	handlers will be invoked, too, of course.
2272		3100
		3101	=head3 The special problem of life after fork - how is it possible?
		3102
		3103	Most uses of C<fork()> consist of forking, then some simple calls to set
		3104	up/change the process environment, followed by a call to C<exec()>. This
		3105	sequence should be handled by libev without any problems.
		3106
		3107	This changes when the application actually wants to do event handling
		3108	in the child, or both parent in child, in effect "continuing" after the
		3109	fork.
		3110
		3111	The default mode of operation (for libev, with application help to detect
		3112	forks) is to duplicate all the state in the child, as would be expected
		3113	when I<either> the parent I<or> the child process continues.
		3114
		3115	When both processes want to continue using libev, then this is usually the
		3116	wrong result. In that case, usually one process (typically the parent) is
		3117	supposed to continue with all watchers in place as before, while the other
		3118	process typically wants to start fresh, i.e. without any active watchers.
		3119
		3120	The cleanest and most efficient way to achieve that with libev is to
		3121	simply create a new event loop, which of course will be "empty", and
		3122	use that for new watchers. This has the advantage of not touching more
		3123	memory than necessary, and thus avoiding the copy-on-write, and the
		3124	disadvantage of having to use multiple event loops (which do not support
		3125	signal watchers).
		3126
		3127	When this is not possible, or you want to use the default loop for
		3128	other reasons, then in the process that wants to start "fresh", call
		3129	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3130	Destroying the default loop will "orphan" (not stop) all registered
		3131	watchers, so you have to be careful not to execute code that modifies
		3132	those watchers. Note also that in that case, you have to re-register any
		3133	signal watchers.
		3134
2273	=head3 Watcher-Specific Functions and Data Members	3135	=head3 Watcher-Specific Functions and Data Members
2274		3136
2275	=over 4	3137	=over 4
2276		3138
2277	=item ev_fork_init (ev_signal *, callback)	3139	=item ev_fork_init (ev_fork *, callback)
2278		3140
2279	Initialises and configures the fork watcher - it has no parameters of any	3141	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,	3142	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2281	believe me.	3143	really.
2282		3144
2283	=back	3145	=back
2284		3146
2285		3147
		3148	=head2 C<ev_cleanup> - even the best things end
		3149
		3150	Cleanup watchers are called just before the event loop is being destroyed
		3151	by a call to C<ev_loop_destroy>.
		3152
		3153	While there is no guarantee that the event loop gets destroyed, cleanup
		3154	watchers provide a convenient method to install cleanup hooks for your
		3155	program, worker threads and so on - you just to make sure to destroy the
		3156	loop when you want them to be invoked.
		3157
		3158	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3159	all other watchers, they do not keep a reference to the event loop (which
		3160	makes a lot of sense if you think about it). Like all other watchers, you
		3161	can call libev functions in the callback, except C<ev_cleanup_start>.
		3162
		3163	=head3 Watcher-Specific Functions and Data Members
		3164
		3165	=over 4
		3166
		3167	=item ev_cleanup_init (ev_cleanup *, callback)
		3168
		3169	Initialises and configures the cleanup watcher - it has no parameters of
		3170	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3171	pointless, I assure you.
		3172
		3173	=back
		3174
		3175	Example: Register an atexit handler to destroy the default loop, so any
		3176	cleanup functions are called.
		3177
		3178	static void
		3179	program_exits (void)
		3180	{
		3181	ev_loop_destroy (EV_DEFAULT_UC);
		3182	}
		3183
		3184	...
		3185	atexit (program_exits);
		3186
		3187
2286	=head2 C<ev_async> - how to wake up another event loop	3188	=head2 C<ev_async> - how to wake up an event loop
2287		3189
2288	In general, you cannot use an C<ev_loop> from multiple threads or other	3190	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	3191	asynchronous sources such as signal handlers (as opposed to multiple event
2290	loops - those are of course safe to use in different threads).	3192	loops - those are of course safe to use in different threads).
2291		3193
2292	Sometimes, however, you need to wake up another event loop you do not	3194	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	3195	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	3196	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	3197	it by calling C<ev_async_send>, which is thread- and signal safe.
2296	safe.
2297		3198
2298	This functionality is very similar to C<ev_signal> watchers, as signals,	3199	This functionality is very similar to C<ev_signal> watchers, as signals,
2299	too, are asynchronous in nature, and signals, too, will be compressed	3200	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	3201	(i.e. the number of callback invocations may be less than the number of
2301	C<ev_async_sent> calls).	3202	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3203	of "global async watchers" by using a watcher on an otherwise unused
		3204	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3205	even without knowing which loop owns the signal.
2302		3206
2303	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3207	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
2304	just the default loop.	3208	just the default loop.
2305		3209
2306	=head3 Queueing	3210	=head3 Queueing
2307		3211
2308	C<ev_async> does not support queueing of data in any way. The reason	3212	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	3213	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	3214	multiple-writer-single-reader queue that works in all cases and doesn't
2311	need elaborate support such as pthreads.	3215	need elaborate support such as pthreads or unportable memory access
		3216	semantics.
2312		3217
2313	That means that if you want to queue data, you have to provide your own	3218	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	3219	queue. But at least I can tell you how to implement locking around your
2315	queue:	3220	queue:
2316		3221
2317	=over 4	3222	=over 4
2318		3223
2319	=item queueing from a signal handler context	3224	=item queueing from a signal handler context
2320		3225
2321	To implement race-free queueing, you simply add to the queue in the signal	3226	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	3227	handler but you block the signal handler in the watcher callback. Here is
2323	some fictitious SIGUSR1 handler:	3228	an example that does that for some fictitious SIGUSR1 handler:
2324		3229
2325	static ev_async mysig;	3230	static ev_async mysig;
2326		3231
2327	static void	3232	static void
2328	sigusr1_handler (void)	3233	sigusr1_handler (void)
…		…
2394	=over 4	3299	=over 4
2395		3300
2396	=item ev_async_init (ev_async *, callback)	3301	=item ev_async_init (ev_async *, callback)
2397		3302
2398	Initialises and configures the async watcher - it has no parameters of any	3303	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,	3304	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2400	believe me.	3305	trust me.
2401		3306
2402	=item ev_async_send (loop, ev_async *)	3307	=item ev_async_send (loop, ev_async *)
2403		3308
2404	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3309	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	3310	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	3311	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	3312	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2408	section below on what exactly this means).	3313	section below on what exactly this means).
2409		3314
		3315	Note that, as with other watchers in libev, multiple events might get
		3316	compressed into a single callback invocation (another way to look at this
		3317	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3318	reset when the event loop detects that).
		3319
2410	This call incurs the overhead of a system call only once per loop iteration,	3320	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	3321	iteration, so while the overhead might be noticeable, it doesn't apply to
2412	calls to C<ev_async_send>.	3322	repeated calls to C<ev_async_send> for the same event loop.
2413		3323
2414	=item bool = ev_async_pending (ev_async *)	3324	=item bool = ev_async_pending (ev_async *)
2415		3325
2416	Returns a non-zero value when C<ev_async_send> has been called on the	3326	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	3327	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	3330	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,	3331	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	3332	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.	3333	quickly check whether invoking the loop might be a good idea.
2424		3334
2425	Not that this does I<not> check whether the watcher itself is pending, only	3335	Not that this does I<not> check whether the watcher itself is pending,
2426	whether it has been requested to make this watcher pending.	3336	only whether it has been requested to make this watcher pending: there
		3337	is a time window between the event loop checking and resetting the async
		3338	notification, and the callback being invoked.
2427		3339
2428	=back	3340	=back
2429		3341
2430		3342
2431	=head1 OTHER FUNCTIONS	3343	=head1 OTHER FUNCTIONS
…		…
2435	=over 4	3347	=over 4
2436		3348
2437	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3349	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2438		3350
2439	This function combines a simple timer and an I/O watcher, calls your	3351	This function combines a simple timer and an I/O watcher, calls your
2440	callback on whichever event happens first and automatically stop both	3352	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	3353	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	3354	or timeout without having to allocate/configure/start/stop/free one or
2443	more watchers yourself.	3355	more watchers yourself.
2444		3356
2445	If C<fd> is less than 0, then no I/O watcher will be started and events	3357	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	3358	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2447	C<events> set will be created and started.	3359	the given C<fd> and C<events> set will be created and started.
2448		3360
2449	If C<timeout> is less than 0, then no timeout watcher will be	3361	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	3362	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	3363	repeat = 0) will be started. C<0> is a valid timeout.
2452	dubious value.
2453		3364
2454	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3365	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	3366	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>	3367	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2457	value passed to C<ev_once>:	3368	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3369	a timeout and an io event at the same time - you probably should give io
		3370	events precedence.
		3371
		3372	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2458		3373
2459	static void stdin_ready (int revents, void *arg)	3374	static void stdin_ready (int revents, void *arg)
2460	{	3375	{
		3376	if (revents & EV_READ)
		3377	/* stdin might have data for us, joy! */;
2461	if (revents & EV_TIMEOUT)	3378	else if (revents & EV_TIMER)
2462	/* doh, nothing entered */;	3379	/* doh, nothing entered */;
2463	else if (revents & EV_READ)
2464	/* stdin might have data for us, joy! */;
2465	}	3380	}
2466		3381
2467	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3382	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2468		3383
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)	3384	=item ev_feed_fd_event (loop, int fd, int revents)
2476		3385
2477	Feed an event on the given fd, as if a file descriptor backend detected	3386	Feed an event on the given fd, as if a file descriptor backend detected
2478	the given events it.	3387	the given events it.
2479		3388
2480	=item ev_feed_signal_event (ev_loop *loop, int signum)	3389	=item ev_feed_signal_event (loop, int signum)
2481		3390
2482	Feed an event as if the given signal occurred (C<loop> must be the default	3391	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
2483	loop!).	3392	which is async-safe.
2484		3393
2485	=back	3394	=back
		3395
		3396
		3397	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3398
		3399	This section explains some common idioms that are not immediately
		3400	obvious. Note that examples are sprinkled over the whole manual, and this
		3401	section only contains stuff that wouldn't fit anywhere else.
		3402
		3403	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3404
		3405	Each watcher has, by default, a C<void *data> member that you can read
		3406	or modify at any time: libev will completely ignore it. This can be used
		3407	to associate arbitrary data with your watcher. If you need more data and
		3408	don't want to allocate memory separately and store a pointer to it in that
		3409	data member, you can also "subclass" the watcher type and provide your own
		3410	data:
		3411
		3412	struct my_io
		3413	{
		3414	ev_io io;
		3415	int otherfd;
		3416	void *somedata;
		3417	struct whatever *mostinteresting;
		3418	};
		3419
		3420	...
		3421	struct my_io w;
		3422	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3423
		3424	And since your callback will be called with a pointer to the watcher, you
		3425	can cast it back to your own type:
		3426
		3427	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3428	{
		3429	struct my_io *w = (struct my_io *)w_;
		3430	...
		3431	}
		3432
		3433	More interesting and less C-conformant ways of casting your callback
		3434	function type instead have been omitted.
		3435
		3436	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3437
		3438	Another common scenario is to use some data structure with multiple
		3439	embedded watchers, in effect creating your own watcher that combines
		3440	multiple libev event sources into one "super-watcher":
		3441
		3442	struct my_biggy
		3443	{
		3444	int some_data;
		3445	ev_timer t1;
		3446	ev_timer t2;
		3447	}
		3448
		3449	In this case getting the pointer to C<my_biggy> is a bit more
		3450	complicated: Either you store the address of your C<my_biggy> struct in
		3451	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3452	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3453	real programmers):
		3454
		3455	#include <stddef.h>
		3456
		3457	static void
		3458	t1_cb (EV_P_ ev_timer *w, int revents)
		3459	{
		3460	struct my_biggy big = (struct my_biggy *)
		3461	(((char *)w) - offsetof (struct my_biggy, t1));
		3462	}
		3463
		3464	static void
		3465	t2_cb (EV_P_ ev_timer *w, int revents)
		3466	{
		3467	struct my_biggy big = (struct my_biggy *)
		3468	(((char *)w) - offsetof (struct my_biggy, t2));
		3469	}
		3470
		3471	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3472
		3473	Often (especially in GUI toolkits) there are places where you have
		3474	I<modal> interaction, which is most easily implemented by recursively
		3475	invoking C<ev_run>.
		3476
		3477	This brings the problem of exiting - a callback might want to finish the
		3478	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3479	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3480	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3481	other combination: In these cases, C<ev_break> will not work alone.
		3482
		3483	The solution is to maintain "break this loop" variable for each C<ev_run>
		3484	invocation, and use a loop around C<ev_run> until the condition is
		3485	triggered, using C<EVRUN_ONCE>:
		3486
		3487	// main loop
		3488	int exit_main_loop = 0;
		3489
		3490	while (!exit_main_loop)
		3491	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3492
		3493	// in a model watcher
		3494	int exit_nested_loop = 0;
		3495
		3496	while (!exit_nested_loop)
		3497	ev_run (EV_A_ EVRUN_ONCE);
		3498
		3499	To exit from any of these loops, just set the corresponding exit variable:
		3500
		3501	// exit modal loop
		3502	exit_nested_loop = 1;
		3503
		3504	// exit main program, after modal loop is finished
		3505	exit_main_loop = 1;
		3506
		3507	// exit both
		3508	exit_main_loop = exit_nested_loop = 1;
		3509
		3510	=head2 THREAD LOCKING EXAMPLE
		3511
		3512	Here is a fictitious example of how to run an event loop in a different
		3513	thread from where callbacks are being invoked and watchers are
		3514	created/added/removed.
		3515
		3516	For a real-world example, see the C<EV::Loop::Async> perl module,
		3517	which uses exactly this technique (which is suited for many high-level
		3518	languages).
		3519
		3520	The example uses a pthread mutex to protect the loop data, a condition
		3521	variable to wait for callback invocations, an async watcher to notify the
		3522	event loop thread and an unspecified mechanism to wake up the main thread.
		3523
		3524	First, you need to associate some data with the event loop:
		3525
		3526	typedef struct {
		3527	mutex_t lock; /* global loop lock */
		3528	ev_async async_w;
		3529	thread_t tid;
		3530	cond_t invoke_cv;
		3531	} userdata;
		3532
		3533	void prepare_loop (EV_P)
		3534	{
		3535	// for simplicity, we use a static userdata struct.
		3536	static userdata u;
		3537
		3538	ev_async_init (&u->async_w, async_cb);
		3539	ev_async_start (EV_A_ &u->async_w);
		3540
		3541	pthread_mutex_init (&u->lock, 0);
		3542	pthread_cond_init (&u->invoke_cv, 0);
		3543
		3544	// now associate this with the loop
		3545	ev_set_userdata (EV_A_ u);
		3546	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3547	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3548
		3549	// then create the thread running ev_loop
		3550	pthread_create (&u->tid, 0, l_run, EV_A);
		3551	}
		3552
		3553	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3554	solely to wake up the event loop so it takes notice of any new watchers
		3555	that might have been added:
		3556
		3557	static void
		3558	async_cb (EV_P_ ev_async *w, int revents)
		3559	{
		3560	// just used for the side effects
		3561	}
		3562
		3563	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3564	protecting the loop data, respectively.
		3565
		3566	static void
		3567	l_release (EV_P)
		3568	{
		3569	userdata *u = ev_userdata (EV_A);
		3570	pthread_mutex_unlock (&u->lock);
		3571	}
		3572
		3573	static void
		3574	l_acquire (EV_P)
		3575	{
		3576	userdata *u = ev_userdata (EV_A);
		3577	pthread_mutex_lock (&u->lock);
		3578	}
		3579
		3580	The event loop thread first acquires the mutex, and then jumps straight
		3581	into C<ev_run>:
		3582
		3583	void *
		3584	l_run (void *thr_arg)
		3585	{
		3586	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3587
		3588	l_acquire (EV_A);
		3589	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3590	ev_run (EV_A_ 0);
		3591	l_release (EV_A);
		3592
		3593	return 0;
		3594	}
		3595
		3596	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3597	signal the main thread via some unspecified mechanism (signals? pipe
		3598	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3599	have been called (in a while loop because a) spurious wakeups are possible
		3600	and b) skipping inter-thread-communication when there are no pending
		3601	watchers is very beneficial):
		3602
		3603	static void
		3604	l_invoke (EV_P)
		3605	{
		3606	userdata *u = ev_userdata (EV_A);
		3607
		3608	while (ev_pending_count (EV_A))
		3609	{
		3610	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3611	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3612	}
		3613	}
		3614
		3615	Now, whenever the main thread gets told to invoke pending watchers, it
		3616	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3617	thread to continue:
		3618
		3619	static void
		3620	real_invoke_pending (EV_P)
		3621	{
		3622	userdata *u = ev_userdata (EV_A);
		3623
		3624	pthread_mutex_lock (&u->lock);
		3625	ev_invoke_pending (EV_A);
		3626	pthread_cond_signal (&u->invoke_cv);
		3627	pthread_mutex_unlock (&u->lock);
		3628	}
		3629
		3630	Whenever you want to start/stop a watcher or do other modifications to an
		3631	event loop, you will now have to lock:
		3632
		3633	ev_timer timeout_watcher;
		3634	userdata *u = ev_userdata (EV_A);
		3635
		3636	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3637
		3638	pthread_mutex_lock (&u->lock);
		3639	ev_timer_start (EV_A_ &timeout_watcher);
		3640	ev_async_send (EV_A_ &u->async_w);
		3641	pthread_mutex_unlock (&u->lock);
		3642
		3643	Note that sending the C<ev_async> watcher is required because otherwise
		3644	an event loop currently blocking in the kernel will have no knowledge
		3645	about the newly added timer. By waking up the loop it will pick up any new
		3646	watchers in the next event loop iteration.
		3647
		3648	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3649
		3650	While the overhead of a callback that e.g. schedules a thread is small, it
		3651	is still an overhead. If you embed libev, and your main usage is with some
		3652	kind of threads or coroutines, you might want to customise libev so that
		3653	doesn't need callbacks anymore.
		3654
		3655	Imagine you have coroutines that you can switch to using a function
		3656	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3657	and that due to some magic, the currently active coroutine is stored in a
		3658	global called C<current_coro>. Then you can build your own "wait for libev
		3659	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3660	the differing C<;> conventions):
		3661
		3662	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3663	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3664
		3665	That means instead of having a C callback function, you store the
		3666	coroutine to switch to in each watcher, and instead of having libev call
		3667	your callback, you instead have it switch to that coroutine.
		3668
		3669	A coroutine might now wait for an event with a function called
		3670	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3671	matter when, or whether the watcher is active or not when this function is
		3672	called):
		3673
		3674	void
		3675	wait_for_event (ev_watcher *w)
		3676	{
		3677	ev_cb_set (w) = current_coro;
		3678	switch_to (libev_coro);
		3679	}
		3680
		3681	That basically suspends the coroutine inside C<wait_for_event> and
		3682	continues the libev coroutine, which, when appropriate, switches back to
		3683	this or any other coroutine. I am sure if you sue this your own :)
		3684
		3685	You can do similar tricks if you have, say, threads with an event queue -
		3686	instead of storing a coroutine, you store the queue object and instead of
		3687	switching to a coroutine, you push the watcher onto the queue and notify
		3688	any waiters.
		3689
		3690	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3691	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3692
		3693	// my_ev.h
		3694	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3695	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3696	#include "../libev/ev.h"
		3697
		3698	// my_ev.c
		3699	#define EV_H "my_ev.h"
		3700	#include "../libev/ev.c"
		3701
		3702	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3703	F<my_ev.c> into your project. When properly specifying include paths, you
		3704	can even use F<ev.h> as header file name directly.
2486		3705
2487		3706
2488	=head1 LIBEVENT EMULATION	3707	=head1 LIBEVENT EMULATION
2489		3708
2490	Libev offers a compatibility emulation layer for libevent. It cannot	3709	Libev offers a compatibility emulation layer for libevent. It cannot
2491	emulate the internals of libevent, so here are some usage hints:	3710	emulate the internals of libevent, so here are some usage hints:
2492		3711
2493	=over 4	3712	=over 4
		3713
		3714	=item * Only the libevent-1.4.1-beta API is being emulated.
		3715
		3716	This was the newest libevent version available when libev was implemented,
		3717	and is still mostly unchanged in 2010.
2494		3718
2495	=item * Use it by including <event.h>, as usual.	3719	=item * Use it by including <event.h>, as usual.
2496		3720
2497	=item * The following members are fully supported: ev_base, ev_callback,	3721	=item * The following members are fully supported: ev_base, ev_callback,
2498	ev_arg, ev_fd, ev_res, ev_events.	3722	ev_arg, ev_fd, ev_res, ev_events.
…		…
2504	=item * Priorities are not currently supported. Initialising priorities	3728	=item * Priorities are not currently supported. Initialising priorities
2505	will fail and all watchers will have the same priority, even though there	3729	will fail and all watchers will have the same priority, even though there
2506	is an ev_pri field.	3730	is an ev_pri field.
2507		3731
2508	=item * In libevent, the last base created gets the signals, in libev, the	3732	=item * In libevent, the last base created gets the signals, in libev, the
2509	first base created (== the default loop) gets the signals.	3733	base that registered the signal gets the signals.
2510		3734
2511	=item * Other members are not supported.	3735	=item * Other members are not supported.
2512		3736
2513	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3737	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2514	to use the libev header file and library.	3738	to use the libev header file and library.
…		…
2533	Care has been taken to keep the overhead low. The only data member the C++	3757	Care has been taken to keep the overhead low. The only data member the C++
2534	classes add (compared to plain C-style watchers) is the event loop pointer	3758	classes add (compared to plain C-style watchers) is the event loop pointer
2535	that the watcher is associated with (or no additional members at all if	3759	that the watcher is associated with (or no additional members at all if
2536	you disable C<EV_MULTIPLICITY> when embedding libev).	3760	you disable C<EV_MULTIPLICITY> when embedding libev).
2537		3761
2538	Currently, functions, and static and non-static member functions can be	3762	Currently, functions, static and non-static member functions and classes
2539	used as callbacks. Other types should be easy to add as long as they only	3763	with C<operator ()> can be used as callbacks. Other types should be easy
2540	need one additional pointer for context. If you need support for other	3764	to add as long as they only need one additional pointer for context. If
2541	types of functors please contact the author (preferably after implementing	3765	you need support for other types of functors please contact the author
2542	it).	3766	(preferably after implementing it).
2543		3767
2544	Here is a list of things available in the C<ev> namespace:	3768	Here is a list of things available in the C<ev> namespace:
2545		3769
2546	=over 4	3770	=over 4
2547		3771
…		…
2565		3789
2566	=over 4	3790	=over 4
2567		3791
2568	=item ev::TYPE::TYPE ()	3792	=item ev::TYPE::TYPE ()
2569		3793
2570	=item ev::TYPE::TYPE (struct ev_loop *)	3794	=item ev::TYPE::TYPE (loop)
2571		3795
2572	=item ev::TYPE::~TYPE	3796	=item ev::TYPE::~TYPE
2573		3797
2574	The constructor (optionally) takes an event loop to associate the watcher	3798	The constructor (optionally) takes an event loop to associate the watcher
2575	with. If it is omitted, it will use C<EV_DEFAULT>.	3799	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2607		3831
2608	myclass obj;	3832	myclass obj;
2609	ev::io iow;	3833	ev::io iow;
2610	iow.set <myclass, &myclass::io_cb> (&obj);	3834	iow.set <myclass, &myclass::io_cb> (&obj);
2611		3835
		3836	=item w->set (object *)
		3837
		3838	This is a variation of a method callback - leaving out the method to call
		3839	will default the method to C<operator ()>, which makes it possible to use
		3840	functor objects without having to manually specify the C<operator ()> all
		3841	the time. Incidentally, you can then also leave out the template argument
		3842	list.
		3843
		3844	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3845	int revents)>.
		3846
		3847	See the method-C<set> above for more details.
		3848
		3849	Example: use a functor object as callback.
		3850
		3851	struct myfunctor
		3852	{
		3853	void operator() (ev::io &w, int revents)
		3854	{
		3855	...
		3856	}
		3857	}
		3858
		3859	myfunctor f;
		3860
		3861	ev::io w;
		3862	w.set (&f);
		3863
2612	=item w->set<function> (void *data = 0)	3864	=item w->set<function> (void *data = 0)
2613		3865
2614	Also sets a callback, but uses a static method or plain function as	3866	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	3867	callback. The optional C<data> argument will be stored in the watcher's
2616	C<data> member and is free for you to use.	3868	C<data> member and is free for you to use.
2617		3869
2618	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3870	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2619		3871
2620	See the method-C<set> above for more details.	3872	See the method-C<set> above for more details.
2621		3873
2622	Example:	3874	Example: Use a plain function as callback.
2623		3875
2624	static void io_cb (ev::io &w, int revents) { }	3876	static void io_cb (ev::io &w, int revents) { }
2625	iow.set <io_cb> ();	3877	iow.set <io_cb> ();
2626		3878
2627	=item w->set (struct ev_loop *)	3879	=item w->set (loop)
2628		3880
2629	Associates a different C<struct ev_loop> with this watcher. You can only	3881	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).	3882	do this when the watcher is inactive (and not pending either).
2631		3883
2632	=item w->set ([arguments])	3884	=item w->set ([arguments])
2633		3885
2634	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be	3886	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	3887	method or a suitable start method must be called at least once. Unlike the
2636	automatically stopped and restarted when reconfiguring it with this	3888	C counterpart, an active watcher gets automatically stopped and restarted
2637	method.	3889	when reconfiguring it with this method.
2638		3890
2639	=item w->start ()	3891	=item w->start ()
2640		3892
2641	Starts the watcher. Note that there is no C<loop> argument, as the	3893	Starts the watcher. Note that there is no C<loop> argument, as the
2642	constructor already stores the event loop.	3894	constructor already stores the event loop.
2643		3895
		3896	=item w->start ([arguments])
		3897
		3898	Instead of calling C<set> and C<start> methods separately, it is often
		3899	convenient to wrap them in one call. Uses the same type of arguments as
		3900	the configure C<set> method of the watcher.
		3901
2644	=item w->stop ()	3902	=item w->stop ()
2645		3903
2646	Stops the watcher if it is active. Again, no C<loop> argument.	3904	Stops the watcher if it is active. Again, no C<loop> argument.
2647		3905
2648	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3906	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2660		3918
2661	=back	3919	=back
2662		3920
2663	=back	3921	=back
2664		3922
2665	Example: Define a class with an IO and idle watcher, start one of them in	3923	Example: Define a class with two I/O and idle watchers, start the I/O
2666	the constructor.	3924	watchers in the constructor.
2667		3925
2668	class myclass	3926	class myclass
2669	{	3927	{
2670	ev::io io; void io_cb (ev::io &w, int revents);	3928	ev::io io ; void io_cb (ev::io &w, int revents);
		3929	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2671	ev:idle idle void idle_cb (ev::idle &w, int revents);	3930	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2672		3931
2673	myclass (int fd)	3932	myclass (int fd)
2674	{	3933	{
2675	io .set <myclass, &myclass::io_cb > (this);	3934	io .set <myclass, &myclass::io_cb > (this);
		3935	io2 .set <myclass, &myclass::io2_cb > (this);
2676	idle.set <myclass, &myclass::idle_cb> (this);	3936	idle.set <myclass, &myclass::idle_cb> (this);
2677		3937
2678	io.start (fd, ev::READ);	3938	io.set (fd, ev::WRITE); // configure the watcher
		3939	io.start (); // start it whenever convenient
		3940
		3941	io2.start (fd, ev::READ); // set + start in one call
2679	}	3942	}
2680	};	3943	};
2681		3944
2682		3945
2683	=head1 OTHER LANGUAGE BINDINGS	3946	=head1 OTHER LANGUAGE BINDINGS
…		…
2692	=item Perl	3955	=item Perl
2693		3956
2694	The EV module implements the full libev API and is actually used to test	3957	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,	3958	libev. EV is developed together with libev. Apart from the EV core module,
2696	there are additional modules that implement libev-compatible interfaces	3959	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	3960	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>).	3961	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3962	and C<EV::Glib>).
2699		3963
2700	It can be found and installed via CPAN, its homepage is at	3964	It can be found and installed via CPAN, its homepage is at
2701	L<http://software.schmorp.de/pkg/EV>.	3965	L<http://software.schmorp.de/pkg/EV>.
2702		3966
2703	=item Python	3967	=item Python
2704		3968
2705	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3969	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	3970	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		3971
2712	=item Ruby	3972	=item Ruby
2713		3973
2714	Tony Arcieri has written a ruby extension that offers access to a subset	3974	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	3975	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	3976	more on top of it. It can be found via gem servers. Its homepage is at
2717	L<http://rev.rubyforge.org/>.	3977	L<http://rev.rubyforge.org/>.
2718		3978
		3979	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3980	makes rev work even on mingw.
		3981
		3982	=item Haskell
		3983
		3984	A haskell binding to libev is available at
		3985	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3986
2719	=item D	3987	=item D
2720		3988
2721	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3989	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>.	3990	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3991
		3992	=item Ocaml
		3993
		3994	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3995	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3996
		3997	=item Lua
		3998
		3999	Brian Maher has written a partial interface to libev for lua (at the
		4000	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4001	L<http://github.com/brimworks/lua-ev>.
2723		4002
2724	=back	4003	=back
2725		4004
2726		4005
2727	=head1 MACRO MAGIC	4006	=head1 MACRO MAGIC
…		…
2741	loop argument"). The C<EV_A> form is used when this is the sole argument,	4020	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:	4021	C<EV_A_> is used when other arguments are following. Example:
2743		4022
2744	ev_unref (EV_A);	4023	ev_unref (EV_A);
2745	ev_timer_add (EV_A_ watcher);	4024	ev_timer_add (EV_A_ watcher);
2746	ev_loop (EV_A_ 0);	4025	ev_run (EV_A_ 0);
2747		4026
2748	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4027	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2749	which is often provided by the following macro.	4028	which is often provided by the following macro.
2750		4029
2751	=item C<EV_P>, C<EV_P_>	4030	=item C<EV_P>, C<EV_P_>
…		…
2791	}	4070	}
2792		4071
2793	ev_check check;	4072	ev_check check;
2794	ev_check_init (&check, check_cb);	4073	ev_check_init (&check, check_cb);
2795	ev_check_start (EV_DEFAULT_ &check);	4074	ev_check_start (EV_DEFAULT_ &check);
2796	ev_loop (EV_DEFAULT_ 0);	4075	ev_run (EV_DEFAULT_ 0);
2797		4076
2798	=head1 EMBEDDING	4077	=head1 EMBEDDING
2799		4078
2800	Libev can (and often is) directly embedded into host	4079	Libev can (and often is) directly embedded into host
2801	applications. Examples of applications that embed it include the Deliantra	4080	applications. Examples of applications that embed it include the Deliantra
…		…
2828		4107
2829	#define EV_STANDALONE 1	4108	#define EV_STANDALONE 1
2830	#include "ev.h"	4109	#include "ev.h"
2831		4110
2832	Both header files and implementation files can be compiled with a C++	4111	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	4112	compiler (at least, that's a stated goal, and breakage will be treated
2834	as a bug).	4113	as a bug).
2835		4114
2836	You need the following files in your source tree, or in a directory	4115	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):	4116	in your include path (e.g. in libev/ when using -Ilibev):
2838		4117
…		…
2881	libev.m4	4160	libev.m4
2882		4161
2883	=head2 PREPROCESSOR SYMBOLS/MACROS	4162	=head2 PREPROCESSOR SYMBOLS/MACROS
2884		4163
2885	Libev can be configured via a variety of preprocessor symbols you have to	4164	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	4165	define before including (or compiling) any of its files. The default in
2887	autoconf is noted for every option.	4166	the absence of autoconf is documented for every option.
		4167
		4168	Symbols marked with "(h)" do not change the ABI, and can have different
		4169	values when compiling libev vs. including F<ev.h>, so it is permissible
		4170	to redefine them before including F<ev.h> without breaking compatibility
		4171	to a compiled library. All other symbols change the ABI, which means all
		4172	users of libev and the libev code itself must be compiled with compatible
		4173	settings.
2888		4174
2889	=over 4	4175	=over 4
2890		4176
		4177	=item EV_COMPAT3 (h)
		4178
		4179	Backwards compatibility is a major concern for libev. This is why this
		4180	release of libev comes with wrappers for the functions and symbols that
		4181	have been renamed between libev version 3 and 4.
		4182
		4183	You can disable these wrappers (to test compatibility with future
		4184	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4185	sources. This has the additional advantage that you can drop the C<struct>
		4186	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4187	typedef in that case.
		4188
		4189	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4190	and in some even more future version the compatibility code will be
		4191	removed completely.
		4192
2891	=item EV_STANDALONE	4193	=item EV_STANDALONE (h)
2892		4194
2893	Must always be C<1> if you do not use autoconf configuration, which	4195	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	4196	keeps libev from including F<config.h>, and it also defines dummy
2895	implementations for some libevent functions (such as logging, which is not	4197	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	4198	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.	4199	F<event.h> that are not directly supported by the libev core alone.
2898		4200
		4201	In standalone mode, libev will still try to automatically deduce the
		4202	configuration, but has to be more conservative.
		4203
2899	=item EV_USE_MONOTONIC	4204	=item EV_USE_MONOTONIC
2900		4205
2901	If defined to be C<1>, libev will try to detect the availability of the	4206	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	4207	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	4208	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	4209	you usually have to link against librt or something similar. Enabling it
2905	the functionality isn't available is safe, though, although you have	4210	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>	4211	to make sure you link against any libraries where the C<clock_gettime>
2907	function is hiding in (often F<-lrt>).	4212	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2908		4213
2909	=item EV_USE_REALTIME	4214	=item EV_USE_REALTIME
2910		4215
2911	If defined to be C<1>, libev will try to detect the availability of the	4216	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	4217	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	4218	at runtime if successful). Otherwise no use of the real-time clock
2914	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4219	option will be attempted. This effectively replaces C<gettimeofday>
2915	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4220	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2916	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4221	correctness. See the note about libraries in the description of
		4222	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4223	C<EV_USE_CLOCK_SYSCALL>.
		4224
		4225	=item EV_USE_CLOCK_SYSCALL
		4226
		4227	If defined to be C<1>, libev will try to use a direct syscall instead
		4228	of calling the system-provided C<clock_gettime> function. This option
		4229	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4230	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4231	programs needlessly. Using a direct syscall is slightly slower (in
		4232	theory), because no optimised vdso implementation can be used, but avoids
		4233	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4234	higher, as it simplifies linking (no need for C<-lrt>).
2917		4235
2918	=item EV_USE_NANOSLEEP	4236	=item EV_USE_NANOSLEEP
2919		4237
2920	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4238	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 ()>.	4239	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2937		4255
2938	=item EV_SELECT_USE_FD_SET	4256	=item EV_SELECT_USE_FD_SET
2939		4257
2940	If defined to C<1>, then the select backend will use the system C<fd_set>	4258	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	4259	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	4260	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	4261	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	4262	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	4263	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2946	influence the size of the C<fd_set> used.	4264	configures the maximum size of the C<fd_set>.
2947		4265
2948	=item EV_SELECT_IS_WINSOCKET	4266	=item EV_SELECT_IS_WINSOCKET
2949		4267
2950	When defined to C<1>, the select backend will assume that	4268	When defined to C<1>, the select backend will assume that
2951	select/socket/connect etc. don't understand file descriptors but	4269	select/socket/connect etc. don't understand file descriptors but
…		…
2953	be used is the winsock select). This means that it will call	4271	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,	4272	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	4273	it is assumed that all these functions actually work on fds, even
2956	on win32. Should not be defined on non-win32 platforms.	4274	on win32. Should not be defined on non-win32 platforms.
2957		4275
2958	=item EV_FD_TO_WIN32_HANDLE	4276	=item EV_FD_TO_WIN32_HANDLE(fd)
2959		4277
2960	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4278	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	4279	file descriptors to socket handles. When not defining this symbol (the
2962	default), then libev will call C<_get_osfhandle>, which is usually	4280	default), then libev will call C<_get_osfhandle>, which is usually
2963	correct. In some cases, programs use their own file descriptor management,	4281	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.	4282	in which case they can provide this function to map fds to socket handles.
		4283
		4284	=item EV_WIN32_HANDLE_TO_FD(handle)
		4285
		4286	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4287	using the standard C<_open_osfhandle> function. For programs implementing
		4288	their own fd to handle mapping, overwriting this function makes it easier
		4289	to do so. This can be done by defining this macro to an appropriate value.
		4290
		4291	=item EV_WIN32_CLOSE_FD(fd)
		4292
		4293	If programs implement their own fd to handle mapping on win32, then this
		4294	macro can be used to override the C<close> function, useful to unregister
		4295	file descriptors again. Note that the replacement function has to close
		4296	the underlying OS handle.
2965		4297
2966	=item EV_USE_POLL	4298	=item EV_USE_POLL
2967		4299
2968	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4300	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	4301	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.	4348	as well as for signal and thread safety in C<ev_async> watchers.
3017		4349
3018	In the absence of this define, libev will use C<sig_atomic_t volatile>	4350	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.	4351	(from F<signal.h>), which is usually good enough on most platforms.
3020		4352
3021	=item EV_H	4353	=item EV_H (h)
3022		4354
3023	The name of the F<ev.h> header file used to include it. The default if	4355	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	4356	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.	4357	used to virtually rename the F<ev.h> header file in case of conflicts.
3026		4358
3027	=item EV_CONFIG_H	4359	=item EV_CONFIG_H (h)
3028		4360
3029	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4361	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	4362	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
3031	C<EV_H>, above.	4363	C<EV_H>, above.
3032		4364
3033	=item EV_EVENT_H	4365	=item EV_EVENT_H (h)
3034		4366
3035	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4367	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">.	4368	of how the F<event.h> header can be found, the default is C<"event.h">.
3037		4369
3038	=item EV_PROTOTYPES	4370	=item EV_PROTOTYPES (h)
3039		4371
3040	If defined to be C<0>, then F<ev.h> will not define any function	4372	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	4373	prototypes, but still define all the structs and other symbols. This is
3042	occasionally useful if you want to provide your own wrapper functions	4374	occasionally useful if you want to provide your own wrapper functions
3043	around libev functions.	4375	around libev functions.
…		…
3062	When doing priority-based operations, libev usually has to linearly search	4394	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	4395	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	4396	and time, so using the defaults of five priorities (-2 .. +2) is usually
3065	fine.	4397	fine.
3066		4398
3067	If your embedding application does not need any priorities, defining these both to	4399	If your embedding application does not need any priorities, defining these
3068	C<0> will save some memory and CPU.	4400	both to C<0> will save some memory and CPU.
3069		4401
3070	=item EV_PERIODIC_ENABLE	4402	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4403	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4404	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
3071		4405
3072	If undefined or defined to be C<1>, then periodic timers are supported. If	4406	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	4407	the respective watcher type is supported. If defined to be C<0>, then it
3074	code.	4408	is not. Disabling watcher types mainly saves code size.
3075		4409
3076	=item EV_IDLE_ENABLE	4410	=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		4411
3104	If you need to shave off some kilobytes of code at the expense of some	4412	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	4413	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	4414	certain subsets of functionality. The default is to enable all features
3107	much smaller 2-heap for timer management over the default 4-heap.	4415	that can be enabled on the platform.
		4416
		4417	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4418	with some broad features you want) and then selectively re-enable
		4419	additional parts you want, for example if you want everything minimal,
		4420	but multiple event loop support, async and child watchers and the poll
		4421	backend, use this:
		4422
		4423	#define EV_FEATURES 0
		4424	#define EV_MULTIPLICITY 1
		4425	#define EV_USE_POLL 1
		4426	#define EV_CHILD_ENABLE 1
		4427	#define EV_ASYNC_ENABLE 1
		4428
		4429	The actual value is a bitset, it can be a combination of the following
		4430	values:
		4431
		4432	=over 4
		4433
		4434	=item C<1> - faster/larger code
		4435
		4436	Use larger code to speed up some operations.
		4437
		4438	Currently this is used to override some inlining decisions (enlarging the
		4439	code size by roughly 30% on amd64).
		4440
		4441	When optimising for size, use of compiler flags such as C<-Os> with
		4442	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4443	assertions.
		4444
		4445	=item C<2> - faster/larger data structures
		4446
		4447	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4448	hash table sizes and so on. This will usually further increase code size
		4449	and can additionally have an effect on the size of data structures at
		4450	runtime.
		4451
		4452	=item C<4> - full API configuration
		4453
		4454	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4455	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4456
		4457	=item C<8> - full API
		4458
		4459	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4460	details on which parts of the API are still available without this
		4461	feature, and do not complain if this subset changes over time.
		4462
		4463	=item C<16> - enable all optional watcher types
		4464
		4465	Enables all optional watcher types. If you want to selectively enable
		4466	only some watcher types other than I/O and timers (e.g. prepare,
		4467	embed, async, child...) you can enable them manually by defining
		4468	C<EV_watchertype_ENABLE> to C<1> instead.
		4469
		4470	=item C<32> - enable all backends
		4471
		4472	This enables all backends - without this feature, you need to enable at
		4473	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4474
		4475	=item C<64> - enable OS-specific "helper" APIs
		4476
		4477	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4478	default.
		4479
		4480	=back
		4481
		4482	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4483	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4484	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4485	watchers, timers and monotonic clock support.
		4486
		4487	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4488	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4489	your program might be left out as well - a binary starting a timer and an
		4490	I/O watcher then might come out at only 5Kb.
		4491
		4492	=item EV_AVOID_STDIO
		4493
		4494	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4495	functions (printf, scanf, perror etc.). This will increase the code size
		4496	somewhat, but if your program doesn't otherwise depend on stdio and your
		4497	libc allows it, this avoids linking in the stdio library which is quite
		4498	big.
		4499
		4500	Note that error messages might become less precise when this option is
		4501	enabled.
		4502
		4503	=item EV_NSIG
		4504
		4505	The highest supported signal number, +1 (or, the number of
		4506	signals): Normally, libev tries to deduce the maximum number of signals
		4507	automatically, but sometimes this fails, in which case it can be
		4508	specified. Also, using a lower number than detected (C<32> should be
		4509	good for about any system in existence) can save some memory, as libev
		4510	statically allocates some 12-24 bytes per signal number.
3108		4511
3109	=item EV_PID_HASHSIZE	4512	=item EV_PID_HASHSIZE
3110		4513
3111	C<ev_child> watchers use a small hash table to distribute workload by	4514	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	4515	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	4516	usually more than enough. If you need to manage thousands of children you
3114	increase this value (I<must> be a power of two).	4517	might want to increase this value (I<must> be a power of two).
3115		4518
3116	=item EV_INOTIFY_HASHSIZE	4519	=item EV_INOTIFY_HASHSIZE
3117		4520
3118	C<ev_stat> watchers use a small hash table to distribute workload by	4521	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>),	4522	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>	4523	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	4524	C<ev_stat> watchers you might want to increase this value (I<must> be a
3122	two).	4525	power of two).
3123		4526
3124	=item EV_USE_4HEAP	4527	=item EV_USE_4HEAP
3125		4528
3126	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4529	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	4530	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	4531	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3129	noticeably faster performance with many (thousands) of watchers.	4532	faster performance with many (thousands) of watchers.
3130		4533
3131	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4534	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3132	(disabled).	4535	will be C<0>.
3133		4536
3134	=item EV_HEAP_CACHE_AT	4537	=item EV_HEAP_CACHE_AT
3135		4538
3136	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4539	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	4540	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>),	4541	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,	4542	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	4543	but avoids random read accesses on heap changes. This improves performance
3141	noticeably with with many (hundreds) of watchers.	4544	noticeably with many (hundreds) of watchers.
3142		4545
3143	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4546	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3144	(disabled).	4547	will be C<0>.
3145		4548
3146	=item EV_VERIFY	4549	=item EV_VERIFY
3147		4550
3148	Controls how much internal verification (see C<ev_loop_verify ()>) will	4551	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	4552	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	4553	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	4554	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	4555	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	4556	verification code will be called very frequently, which will slow down
3154	libev considerably.	4557	libev considerably.
3155		4558
3156	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	4559	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3157	C<0.>	4560	will be C<0>.
3158		4561
3159	=item EV_COMMON	4562	=item EV_COMMON
3160		4563
3161	By default, all watchers have a C<void *data> member. By redefining	4564	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	4565	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,	4566	members. You have to define it each time you include one of the files,
3164	though, and it must be identical each time.	4567	though, and it must be identical each time.
3165		4568
3166	For example, the perl EV module uses something like this:	4569	For example, the perl EV module uses something like this:
3167		4570
…		…
3179	and the way callbacks are invoked and set. Must expand to a struct member	4582	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	4583	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	4584	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	4585	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++.	4586	method calls instead of plain function calls in C++.
		4587
		4588	=back
3184		4589
3185	=head2 EXPORTED API SYMBOLS	4590	=head2 EXPORTED API SYMBOLS
3186		4591
3187	If you need to re-export the API (e.g. via a DLL) and you need a list of	4592	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	4593	exported symbols, you can use the provided F<Symbol.*> files which list
…		…
3218	file.	4623	file.
3219		4624
3220	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4625	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:	4626	that everybody includes and which overrides some configure choices:
3222		4627
3223	#define EV_MINIMAL 1	4628	#define EV_FEATURES 8
3224	#define EV_USE_POLL 0	4629	#define EV_USE_SELECT 1
3225	#define EV_MULTIPLICITY 0
3226	#define EV_PERIODIC_ENABLE 0	4630	#define EV_PREPARE_ENABLE 1
		4631	#define EV_IDLE_ENABLE 1
3227	#define EV_STAT_ENABLE 0	4632	#define EV_SIGNAL_ENABLE 1
3228	#define EV_FORK_ENABLE 0	4633	#define EV_CHILD_ENABLE 1
		4634	#define EV_USE_STDEXCEPT 0
3229	#define EV_CONFIG_H <config.h>	4635	#define EV_CONFIG_H <config.h>
3230	#define EV_MINPRI 0
3231	#define EV_MAXPRI 0
3232		4636
3233	#include "ev++.h"	4637	#include "ev++.h"
3234		4638
3235	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4639	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3236		4640
3237	#include "ev_cpp.h"	4641	#include "ev_cpp.h"
3238	#include "ev.c"	4642	#include "ev.c"
3239		4643
		4644	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
3240		4645
3241	=head1 THREADS AND COROUTINES	4646	=head2 THREADS AND COROUTINES
3242		4647
3243	=head2 THREADS	4648	=head3 THREADS
3244		4649
3245	Libev itself is thread-safe (unless the opposite is specifically	4650	All libev functions are reentrant and thread-safe unless explicitly
3246	documented for a function), but it uses no locking itself. This means that	4651	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	4652	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:	4653	are no concurrent calls into any libev function with the same loop
		4654	parameter (C<ev_default_*> calls have an implicit default loop parameter,
3249	libev guarentees that different event loops share no data structures that	4655	of course): libev guarantees that different event loops share no data
3250	need locking.	4656	structures that need any locking.
3251		4657
3252	Or to put it differently: calls with different loop parameters can be done	4658	Or to put it differently: calls with different loop parameters can be done
3253	concurrently from multiple threads, calls with the same loop parameter	4659	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	4660	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	4661	only one thread ever is inside a call at any point in time, e.g. by using
3256	a mutex per loop).	4662	a mutex per loop).
3257		4663
3258	Specifically to support threads (and signal handlers), libev implements	4664	Specifically to support threads (and signal handlers), libev implements
3259	so-called C<ev_async> watchers, which allow some limited form of	4665	so-called C<ev_async> watchers, which allow some limited form of
3260	concurrency on the same event loop.	4666	concurrency on the same event loop, namely waking it up "from the
		4667	outside".
3261		4668
3262	If you want to know which design (one loop, locking, or multiple loops	4669	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	4670	without or something else still) is best for your problem, then I cannot
3264	help you. I can give some generic advice however:	4671	help you, but here is some generic advice:
3265		4672
3266	=over 4	4673	=over 4
3267		4674
3268	=item * most applications have a main thread: use the default libev loop	4675	=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.	4676	in that thread, or create a separate thread running only the default loop.
…		…
3293	default loop and triggering an C<ev_async> watcher from the default loop	4700	default loop and triggering an C<ev_async> watcher from the default loop
3294	watcher callback into the event loop interested in the signal.	4701	watcher callback into the event loop interested in the signal.
3295		4702
3296	=back	4703	=back
3297		4704
		4705	See also L<THREAD LOCKING EXAMPLE>.
		4706
3298	=head2 COROUTINES	4707	=head3 COROUTINES
3299		4708
3300	Libev is much more accommodating to coroutines ("cooperative threads"):	4709	Libev is very accommodating to coroutines ("cooperative threads"):
3301	libev fully supports nesting calls to it's functions from different	4710	libev fully supports nesting calls to its functions from different
3302	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4711	coroutines (e.g. you can call C<ev_run> on the same loop from two
3303	different coroutines and switch freely between both coroutines running the	4712	different coroutines, and switch freely between both coroutines running
3304	loop, as long as you don't confuse yourself). The only exception is that	4713	the loop, as long as you don't confuse yourself). The only exception is
3305	you must not do this from C<ev_periodic> reschedule callbacks.	4714	that you must not do this from C<ev_periodic> reschedule callbacks.
3306		4715
3307	Care has been taken to ensure that libev does not keep local state inside	4716	Care has been taken to ensure that libev does not keep local state inside
3308	C<ev_loop>, and other calls do not usually allow coroutine switches.	4717	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4718	they do not call any callbacks.
3309		4719
		4720	=head2 COMPILER WARNINGS
3310		4721
3311	=head1 COMPLEXITIES	4722	Depending on your compiler and compiler settings, you might get no or a
		4723	lot of warnings when compiling libev code. Some people are apparently
		4724	scared by this.
3312		4725
3313	In this section the complexities of (many of) the algorithms used inside	4726	However, these are unavoidable for many reasons. For one, each compiler
3314	libev will be explained. For complexity discussions about backends see the	4727	has different warnings, and each user has different tastes regarding
3315	documentation for C<ev_default_init>.	4728	warning options. "Warn-free" code therefore cannot be a goal except when
		4729	targeting a specific compiler and compiler-version.
3316		4730
3317	All of the following are about amortised time: If an array needs to be	4731	Another reason is that some compiler warnings require elaborate
3318	extended, libev needs to realloc and move the whole array, but this	4732	workarounds, or other changes to the code that make it less clear and less
3319	happens asymptotically never with higher number of elements, so O(1) might	4733	maintainable.
3320	mean it might do a lengthy realloc operation in rare cases, but on average
3321	it is much faster and asymptotically approaches constant time.
3322		4734
3323	=over 4	4735	And of course, some compiler warnings are just plain stupid, or simply
		4736	wrong (because they don't actually warn about the condition their message
		4737	seems to warn about). For example, certain older gcc versions had some
		4738	warnings that resulted in an extreme number of false positives. These have
		4739	been fixed, but some people still insist on making code warn-free with
		4740	such buggy versions.
3324		4741
3325	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4742	While libev is written to generate as few warnings as possible,
		4743	"warn-free" code is not a goal, and it is recommended not to build libev
		4744	with any compiler warnings enabled unless you are prepared to cope with
		4745	them (e.g. by ignoring them). Remember that warnings are just that:
		4746	warnings, not errors, or proof of bugs.
3326		4747
3327	This means that, when you have a watcher that triggers in one hour and
3328	there are 100 watchers that would trigger before that then inserting will
3329	have to skip roughly seven (C<ld 100>) of these watchers.
3330		4748
3331	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4749	=head2 VALGRIND
3332		4750
3333	That means that changing a timer costs less than removing/adding them	4751	Valgrind has a special section here because it is a popular tool that is
3334	as only the relative motion in the event queue has to be paid for.	4752	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3335		4753
3336	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4754	If you think you found a bug (memory leak, uninitialised data access etc.)
		4755	in libev, then check twice: If valgrind reports something like:
3337		4756
3338	These just add the watcher into an array or at the head of a list.	4757	==2274== definitely lost: 0 bytes in 0 blocks.
		4758	==2274== possibly lost: 0 bytes in 0 blocks.
		4759	==2274== still reachable: 256 bytes in 1 blocks.
3339		4760
3340	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4761	Then there is no memory leak, just as memory accounted to global variables
		4762	is not a memleak - the memory is still being referenced, and didn't leak.
3341		4763
3342	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4764	Similarly, under some circumstances, valgrind might report kernel bugs
		4765	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4766	although an acceptable workaround has been found here), or it might be
		4767	confused.
3343		4768
3344	These watchers are stored in lists then need to be walked to find the	4769	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3345	correct watcher to remove. The lists are usually short (you don't usually	4770	make it into some kind of religion.
3346	have many watchers waiting for the same fd or signal).
3347		4771
3348	=item Finding the next timer in each loop iteration: O(1)	4772	If you are unsure about something, feel free to contact the mailing list
		4773	with the full valgrind report and an explanation on why you think this
		4774	is a bug in libev (best check the archives, too :). However, don't be
		4775	annoyed when you get a brisk "this is no bug" answer and take the chance
		4776	of learning how to interpret valgrind properly.
3349		4777
3350	By virtue of using a binary or 4-heap, the next timer is always found at a	4778	If you need, for some reason, empty reports from valgrind for your project
3351	fixed position in the storage array.	4779	I suggest using suppression lists.
3352		4780
3353	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3354		4781
3355	A change means an I/O watcher gets started or stopped, which requires	4782	=head1 PORTABILITY NOTES
3356	libev to recalculate its status (and possibly tell the kernel, depending
3357	on backend and whether C<ev_io_set> was used).
3358		4783
3359	=item Activating one watcher (putting it into the pending state): O(1)	4784	=head2 GNU/LINUX 32 BIT LIMITATIONS
3360		4785
3361	=item Priority handling: O(number_of_priorities)	4786	GNU/Linux is the only common platform that supports 64 bit file/large file
		4787	interfaces but I<disables> them by default.
3362		4788
3363	Priorities are implemented by allocating some space for each	4789	That means that libev compiled in the default environment doesn't support
3364	priority. When doing priority-based operations, libev usually has to	4790	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
3365	linearly search all the priorities, but starting/stopping and activating
3366	watchers becomes O(1) w.r.t. priority handling.
3367		4791
3368	=item Sending an ev_async: O(1)	4792	Unfortunately, many programs try to work around this GNU/Linux issue
		4793	by enabling the large file API, which makes them incompatible with the
		4794	standard libev compiled for their system.
3369		4795
3370	=item Processing ev_async_send: O(number_of_async_watchers)	4796	Likewise, libev cannot enable the large file API itself as this would
		4797	suddenly make it incompatible to the default compile time environment,
		4798	i.e. all programs not using special compile switches.
3371		4799
3372	=item Processing signals: O(max_signal_number)	4800	=head2 OS/X AND DARWIN BUGS
3373		4801
3374	Sending involves a system call I<iff> there were no other C<ev_async_send>	4802	The whole thing is a bug if you ask me - basically any system interface
3375	calls in the current loop iteration. Checking for async and signal events	4803	you touch is broken, whether it is locales, poll, kqueue or even the
3376	involves iterating over all running async watchers or all signal numbers.	4804	OpenGL drivers.
3377		4805
3378	=back	4806	=head3 C<kqueue> is buggy
3379		4807
		4808	The kqueue syscall is broken in all known versions - most versions support
		4809	only sockets, many support pipes.
3380		4810
		4811	Libev tries to work around this by not using C<kqueue> by default on this
		4812	rotten platform, but of course you can still ask for it when creating a
		4813	loop - embedding a socket-only kqueue loop into a select-based one is
		4814	probably going to work well.
		4815
		4816	=head3 C<poll> is buggy
		4817
		4818	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4819	implementation by something calling C<kqueue> internally around the 10.5.6
		4820	release, so now C<kqueue> I<and> C<poll> are broken.
		4821
		4822	Libev tries to work around this by not using C<poll> by default on
		4823	this rotten platform, but of course you can still ask for it when creating
		4824	a loop.
		4825
		4826	=head3 C<select> is buggy
		4827
		4828	All that's left is C<select>, and of course Apple found a way to fuck this
		4829	one up as well: On OS/X, C<select> actively limits the number of file
		4830	descriptors you can pass in to 1024 - your program suddenly crashes when
		4831	you use more.
		4832
		4833	There is an undocumented "workaround" for this - defining
		4834	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4835	work on OS/X.
		4836
		4837	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4838
		4839	=head3 C<errno> reentrancy
		4840
		4841	The default compile environment on Solaris is unfortunately so
		4842	thread-unsafe that you can't even use components/libraries compiled
		4843	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4844	defined by default. A valid, if stupid, implementation choice.
		4845
		4846	If you want to use libev in threaded environments you have to make sure
		4847	it's compiled with C<_REENTRANT> defined.
		4848
		4849	=head3 Event port backend
		4850
		4851	The scalable event interface for Solaris is called "event
		4852	ports". Unfortunately, this mechanism is very buggy in all major
		4853	releases. If you run into high CPU usage, your program freezes or you get
		4854	a large number of spurious wakeups, make sure you have all the relevant
		4855	and latest kernel patches applied. No, I don't know which ones, but there
		4856	are multiple ones to apply, and afterwards, event ports actually work
		4857	great.
		4858
		4859	If you can't get it to work, you can try running the program by setting
		4860	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4861	C<select> backends.
		4862
		4863	=head2 AIX POLL BUG
		4864
		4865	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4866	this by trying to avoid the poll backend altogether (i.e. it's not even
		4867	compiled in), which normally isn't a big problem as C<select> works fine
		4868	with large bitsets on AIX, and AIX is dead anyway.
		4869
3381	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	4870	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4871
		4872	=head3 General issues
3382		4873
3383	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4874	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3384	requires, and its I/O model is fundamentally incompatible with the POSIX	4875	requires, and its I/O model is fundamentally incompatible with the POSIX
3385	model. Libev still offers limited functionality on this platform in	4876	model. Libev still offers limited functionality on this platform in
3386	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4877	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3387	descriptors. This only applies when using Win32 natively, not when using	4878	descriptors. This only applies when using Win32 natively, not when using
3388	e.g. cygwin.	4879	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4880	as every compielr comes with a slightly differently broken/incompatible
		4881	environment.
3389		4882
3390	Lifting these limitations would basically require the full	4883	Lifting these limitations would basically require the full
3391	re-implementation of the I/O system. If you are into these kinds of	4884	re-implementation of the I/O system. If you are into this kind of thing,
3392	things, then note that glib does exactly that for you in a very portable	4885	then note that glib does exactly that for you in a very portable way (note
3393	way (note also that glib is the slowest event library known to man).	4886	also that glib is the slowest event library known to man).
3394		4887
3395	There is no supported compilation method available on windows except	4888	There is no supported compilation method available on windows except
3396	embedding it into other applications.	4889	embedding it into other applications.
		4890
		4891	Sensible signal handling is officially unsupported by Microsoft - libev
		4892	tries its best, but under most conditions, signals will simply not work.
3397		4893
3398	Not a libev limitation but worth mentioning: windows apparently doesn't	4894	Not a libev limitation but worth mentioning: windows apparently doesn't
3399	accept large writes: instead of resulting in a partial write, windows will	4895	accept large writes: instead of resulting in a partial write, windows will
3400	either accept everything or return C<ENOBUFS> if the buffer is too large,	4896	either accept everything or return C<ENOBUFS> if the buffer is too large,
3401	so make sure you only write small amounts into your sockets (less than a	4897	so make sure you only write small amounts into your sockets (less than a
3402	megabyte seems safe, but thsi apparently depends on the amount of memory	4898	megabyte seems safe, but this apparently depends on the amount of memory
3403	available).	4899	available).
3404		4900
3405	Due to the many, low, and arbitrary limits on the win32 platform and	4901	Due to the many, low, and arbitrary limits on the win32 platform and
3406	the abysmal performance of winsockets, using a large number of sockets	4902	the abysmal performance of winsockets, using a large number of sockets
3407	is not recommended (and not reasonable). If your program needs to use	4903	is not recommended (and not reasonable). If your program needs to use
3408	more than a hundred or so sockets, then likely it needs to use a totally	4904	more than a hundred or so sockets, then likely it needs to use a totally
3409	different implementation for windows, as libev offers the POSIX readiness	4905	different implementation for windows, as libev offers the POSIX readiness
3410	notification model, which cannot be implemented efficiently on windows	4906	notification model, which cannot be implemented efficiently on windows
3411	(Microsoft monopoly games).	4907	(due to Microsoft monopoly games).
3412		4908
3413	A typical way to use libev under windows is to embed it (see the embedding	4909	A typical way to use libev under windows is to embed it (see the embedding
3414	section for details) and use the following F<evwrap.h> header file instead	4910	section for details) and use the following F<evwrap.h> header file instead
3415	of F<ev.h>:	4911	of F<ev.h>:
3416		4912
…		…
3418	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	4914	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3419		4915
3420	#include "ev.h"	4916	#include "ev.h"
3421		4917
3422	And compile the following F<evwrap.c> file into your project (make sure	4918	And compile the following F<evwrap.c> file into your project (make sure
3423	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	4919	you do I<not> compile the F<ev.c> or any other embedded source files!):
3424		4920
3425	#include "evwrap.h"	4921	#include "evwrap.h"
3426	#include "ev.c"	4922	#include "ev.c"
3427		4923
3428	=over 4
3429
3430	=item The winsocket select function	4924	=head3 The winsocket C<select> function
3431		4925
3432	The winsocket C<select> function doesn't follow POSIX in that it	4926	The winsocket C<select> function doesn't follow POSIX in that it
3433	requires socket I<handles> and not socket I<file descriptors> (it is	4927	requires socket I<handles> and not socket I<file descriptors> (it is
3434	also extremely buggy). This makes select very inefficient, and also	4928	also extremely buggy). This makes select very inefficient, and also
3435	requires a mapping from file descriptors to socket handles (the Microsoft	4929	requires a mapping from file descriptors to socket handles (the Microsoft
…		…
3444	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4938	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3445		4939
3446	Note that winsockets handling of fd sets is O(n), so you can easily get a	4940	Note that winsockets handling of fd sets is O(n), so you can easily get a
3447	complexity in the O(n²) range when using win32.	4941	complexity in the O(n²) range when using win32.
3448		4942
3449	=item Limited number of file descriptors	4943	=head3 Limited number of file descriptors
3450		4944
3451	Windows has numerous arbitrary (and low) limits on things.	4945	Windows has numerous arbitrary (and low) limits on things.
3452		4946
3453	Early versions of winsocket's select only supported waiting for a maximum	4947	Early versions of winsocket's select only supported waiting for a maximum
3454	of C<64> handles (probably owning to the fact that all windows kernels	4948	of C<64> handles (probably owning to the fact that all windows kernels
3455	can only wait for C<64> things at the same time internally; Microsoft	4949	can only wait for C<64> things at the same time internally; Microsoft
3456	recommends spawning a chain of threads and wait for 63 handles and the	4950	recommends spawning a chain of threads and wait for 63 handles and the
3457	previous thread in each. Great).	4951	previous thread in each. Sounds great!).
3458		4952
3459	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4953	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3460	to some high number (e.g. C<2048>) before compiling the winsocket select	4954	to some high number (e.g. C<2048>) before compiling the winsocket select
3461	call (which might be in libev or elsewhere, for example, perl does its own	4955	call (which might be in libev or elsewhere, for example, perl and many
3462	select emulation on windows).	4956	other interpreters do their own select emulation on windows).
3463		4957
3464	Another limit is the number of file descriptors in the Microsoft runtime	4958	Another limit is the number of file descriptors in the Microsoft runtime
3465	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4959	libraries, which by default is C<64> (there must be a hidden I<64>
3466	or something like this inside Microsoft). You can increase this by calling	4960	fetish or something like this inside Microsoft). You can increase this
3467	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4961	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3468	arbitrary limit), but is broken in many versions of the Microsoft runtime	4962	(another arbitrary limit), but is broken in many versions of the Microsoft
3469	libraries.
3470
3471	This might get you to about C<512> or C<2048> sockets (depending on	4963	runtime libraries. This might get you to about C<512> or C<2048> sockets
3472	windows version and/or the phase of the moon). To get more, you need to	4964	(depending on windows version and/or the phase of the moon). To get more,
3473	wrap all I/O functions and provide your own fd management, but the cost of	4965	you need to wrap all I/O functions and provide your own fd management, but
3474	calling select (O(n²)) will likely make this unworkable.	4966	the cost of calling select (O(n²)) will likely make this unworkable.
3475		4967
3476	=back
3477
3478
3479	=head1 PORTABILITY REQUIREMENTS	4968	=head2 PORTABILITY REQUIREMENTS
3480		4969
3481	In addition to a working ISO-C implementation, libev relies on a few	4970	In addition to a working ISO-C implementation and of course the
3482	additional extensions:	4971	backend-specific APIs, libev relies on a few additional extensions:
3483		4972
3484	=over 4	4973	=over 4
3485		4974
3486	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	4975	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3487	calling conventions regardless of C<ev_watcher_type *>.	4976	calling conventions regardless of C<ev_watcher_type *>.
…		…
3490	structure (guaranteed by POSIX but not by ISO C for example), but it also	4979	structure (guaranteed by POSIX but not by ISO C for example), but it also
3491	assumes that the same (machine) code can be used to call any watcher	4980	assumes that the same (machine) code can be used to call any watcher
3492	callback: The watcher callbacks have different type signatures, but libev	4981	callback: The watcher callbacks have different type signatures, but libev
3493	calls them using an C<ev_watcher *> internally.	4982	calls them using an C<ev_watcher *> internally.
3494		4983
		4984	=item pointer accesses must be thread-atomic
		4985
		4986	Accessing a pointer value must be atomic, it must both be readable and
		4987	writable in one piece - this is the case on all current architectures.
		4988
3495	=item C<sig_atomic_t volatile> must be thread-atomic as well	4989	=item C<sig_atomic_t volatile> must be thread-atomic as well
3496		4990
3497	The type C<sig_atomic_t volatile> (or whatever is defined as	4991	The type C<sig_atomic_t volatile> (or whatever is defined as
3498	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4992	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3499	threads. This is not part of the specification for C<sig_atomic_t>, but is	4993	threads. This is not part of the specification for C<sig_atomic_t>, but is
3500	believed to be sufficiently portable.	4994	believed to be sufficiently portable.
3501		4995
3502	=item C<sigprocmask> must work in a threaded environment	4996	=item C<sigprocmask> must work in a threaded environment
3503		4997
…		…
3512	except the initial one, and run the default loop in the initial thread as	5006	except the initial one, and run the default loop in the initial thread as
3513	well.	5007	well.
3514		5008
3515	=item C<long> must be large enough for common memory allocation sizes	5009	=item C<long> must be large enough for common memory allocation sizes
3516		5010
3517	To improve portability and simplify using libev, libev uses C<long>	5011	To improve portability and simplify its API, libev uses C<long> internally
3518	internally instead of C<size_t> when allocating its data structures. On	5012	instead of C<size_t> when allocating its data structures. On non-POSIX
3519	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	5013	systems (Microsoft...) this might be unexpectedly low, but is still at
3520	is still at least 31 bits everywhere, which is enough for hundreds of	5014	least 31 bits everywhere, which is enough for hundreds of millions of
3521	millions of watchers.	5015	watchers.
3522		5016
3523	=item C<double> must hold a time value in seconds with enough accuracy	5017	=item C<double> must hold a time value in seconds with enough accuracy
3524		5018
3525	The type C<double> is used to represent timestamps. It is required to	5019	The type C<double> is used to represent timestamps. It is required to
3526	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	5020	have at least 51 bits of mantissa (and 9 bits of exponent), which is
3527	enough for at least into the year 4000. This requirement is fulfilled by	5021	good enough for at least into the year 4000 with millisecond accuracy
		5022	(the design goal for libev). This requirement is overfulfilled by
3528	implementations implementing IEEE 754 (basically all existing ones).	5023	implementations using IEEE 754, which is basically all existing ones. With
		5024	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
3529		5025
3530	=back	5026	=back
3531		5027
3532	If you know of other additional requirements drop me a note.	5028	If you know of other additional requirements drop me a note.
3533		5029
3534		5030
3535	=head1 COMPILER WARNINGS	5031	=head1 ALGORITHMIC COMPLEXITIES
3536		5032
3537	Depending on your compiler and compiler settings, you might get no or a	5033	In this section the complexities of (many of) the algorithms used inside
3538	lot of warnings when compiling libev code. Some people are apparently	5034	libev will be documented. For complexity discussions about backends see
3539	scared by this.	5035	the documentation for C<ev_default_init>.
3540		5036
3541	However, these are unavoidable for many reasons. For one, each compiler	5037	All of the following are about amortised time: If an array needs to be
3542	has different warnings, and each user has different tastes regarding	5038	extended, libev needs to realloc and move the whole array, but this
3543	warning options. "Warn-free" code therefore cannot be a goal except when	5039	happens asymptotically rarer with higher number of elements, so O(1) might
3544	targeting a specific compiler and compiler-version.	5040	mean that libev does a lengthy realloc operation in rare cases, but on
		5041	average it is much faster and asymptotically approaches constant time.
3545		5042
3546	Another reason is that some compiler warnings require elaborate	5043	=over 4
3547	workarounds, or other changes to the code that make it less clear and less
3548	maintainable.
3549		5044
3550	And of course, some compiler warnings are just plain stupid, or simply	5045	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3551	wrong (because they don't actually warn about the condition their message
3552	seems to warn about).
3553		5046
3554	While libev is written to generate as few warnings as possible,	5047	This means that, when you have a watcher that triggers in one hour and
3555	"warn-free" code is not a goal, and it is recommended not to build libev	5048	there are 100 watchers that would trigger before that, then inserting will
3556	with any compiler warnings enabled unless you are prepared to cope with	5049	have to skip roughly seven (C<ld 100>) of these watchers.
3557	them (e.g. by ignoring them). Remember that warnings are just that:
3558	warnings, not errors, or proof of bugs.
3559		5050
		5051	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3560		5052
3561	=head1 VALGRIND	5053	That means that changing a timer costs less than removing/adding them,
		5054	as only the relative motion in the event queue has to be paid for.
3562		5055
3563	Valgrind has a special section here because it is a popular tool that is	5056	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3564	highly useful, but valgrind reports are very hard to interpret.
3565		5057
3566	If you think you found a bug (memory leak, uninitialised data access etc.)	5058	These just add the watcher into an array or at the head of a list.
3567	in libev, then check twice: If valgrind reports something like:
3568		5059
3569	==2274== definitely lost: 0 bytes in 0 blocks.	5060	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3570	==2274== possibly lost: 0 bytes in 0 blocks.
3571	==2274== still reachable: 256 bytes in 1 blocks.
3572		5061
3573	Then there is no memory leak. Similarly, under some circumstances,	5062	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3574	valgrind might report kernel bugs as if it were a bug in libev, or it
3575	might be confused (it is a very good tool, but only a tool).
3576		5063
3577	If you are unsure about something, feel free to contact the mailing list	5064	These watchers are stored in lists, so they need to be walked to find the
3578	with the full valgrind report and an explanation on why you think this is	5065	correct watcher to remove. The lists are usually short (you don't usually
3579	a bug in libev. However, don't be annoyed when you get a brisk "this is	5066	have many watchers waiting for the same fd or signal: one is typical, two
3580	no bug" answer and take the chance of learning how to interpret valgrind	5067	is rare).
3581	properly.
3582		5068
3583	If you need, for some reason, empty reports from valgrind for your project	5069	=item Finding the next timer in each loop iteration: O(1)
3584	I suggest using suppression lists.
3585		5070
		5071	By virtue of using a binary or 4-heap, the next timer is always found at a
		5072	fixed position in the storage array.
		5073
		5074	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5075
		5076	A change means an I/O watcher gets started or stopped, which requires
		5077	libev to recalculate its status (and possibly tell the kernel, depending
		5078	on backend and whether C<ev_io_set> was used).
		5079
		5080	=item Activating one watcher (putting it into the pending state): O(1)
		5081
		5082	=item Priority handling: O(number_of_priorities)
		5083
		5084	Priorities are implemented by allocating some space for each
		5085	priority. When doing priority-based operations, libev usually has to
		5086	linearly search all the priorities, but starting/stopping and activating
		5087	watchers becomes O(1) with respect to priority handling.
		5088
		5089	=item Sending an ev_async: O(1)
		5090
		5091	=item Processing ev_async_send: O(number_of_async_watchers)
		5092
		5093	=item Processing signals: O(max_signal_number)
		5094
		5095	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5096	calls in the current loop iteration. Checking for async and signal events
		5097	involves iterating over all running async watchers or all signal numbers.
		5098
		5099	=back
		5100
		5101
		5102	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5103
		5104	The major version 4 introduced some incompatible changes to the API.
		5105
		5106	At the moment, the C<ev.h> header file provides compatibility definitions
		5107	for all changes, so most programs should still compile. The compatibility
		5108	layer might be removed in later versions of libev, so better update to the
		5109	new API early than late.
		5110
		5111	=over 4
		5112
		5113	=item C<EV_COMPAT3> backwards compatibility mechanism
		5114
		5115	The backward compatibility mechanism can be controlled by
		5116	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5117	section.
		5118
		5119	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5120
		5121	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5122
		5123	ev_loop_destroy (EV_DEFAULT_UC);
		5124	ev_loop_fork (EV_DEFAULT);
		5125
		5126	=item function/symbol renames
		5127
		5128	A number of functions and symbols have been renamed:
		5129
		5130	ev_loop => ev_run
		5131	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5132	EVLOOP_ONESHOT => EVRUN_ONCE
		5133
		5134	ev_unloop => ev_break
		5135	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5136	EVUNLOOP_ONE => EVBREAK_ONE
		5137	EVUNLOOP_ALL => EVBREAK_ALL
		5138
		5139	EV_TIMEOUT => EV_TIMER
		5140
		5141	ev_loop_count => ev_iteration
		5142	ev_loop_depth => ev_depth
		5143	ev_loop_verify => ev_verify
		5144
		5145	Most functions working on C<struct ev_loop> objects don't have an
		5146	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5147	associated constants have been renamed to not collide with the C<struct
		5148	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5149	as all other watcher types. Note that C<ev_loop_fork> is still called
		5150	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5151	typedef.
		5152
		5153	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5154
		5155	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5156	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5157	and work, but the library code will of course be larger.
		5158
		5159	=back
		5160
		5161
		5162	=head1 GLOSSARY
		5163
		5164	=over 4
		5165
		5166	=item active
		5167
		5168	A watcher is active as long as it has been started and not yet stopped.
		5169	See L<WATCHER STATES> for details.
		5170
		5171	=item application
		5172
		5173	In this document, an application is whatever is using libev.
		5174
		5175	=item backend
		5176
		5177	The part of the code dealing with the operating system interfaces.
		5178
		5179	=item callback
		5180
		5181	The address of a function that is called when some event has been
		5182	detected. Callbacks are being passed the event loop, the watcher that
		5183	received the event, and the actual event bitset.
		5184
		5185	=item callback/watcher invocation
		5186
		5187	The act of calling the callback associated with a watcher.
		5188
		5189	=item event
		5190
		5191	A change of state of some external event, such as data now being available
		5192	for reading on a file descriptor, time having passed or simply not having
		5193	any other events happening anymore.
		5194
		5195	In libev, events are represented as single bits (such as C<EV_READ> or
		5196	C<EV_TIMER>).
		5197
		5198	=item event library
		5199
		5200	A software package implementing an event model and loop.
		5201
		5202	=item event loop
		5203
		5204	An entity that handles and processes external events and converts them
		5205	into callback invocations.
		5206
		5207	=item event model
		5208
		5209	The model used to describe how an event loop handles and processes
		5210	watchers and events.
		5211
		5212	=item pending
		5213
		5214	A watcher is pending as soon as the corresponding event has been
		5215	detected. See L<WATCHER STATES> for details.
		5216
		5217	=item real time
		5218
		5219	The physical time that is observed. It is apparently strictly monotonic :)
		5220
		5221	=item wall-clock time
		5222
		5223	The time and date as shown on clocks. Unlike real time, it can actually
		5224	be wrong and jump forwards and backwards, e.g. when the you adjust your
		5225	clock.
		5226
		5227	=item watcher
		5228
		5229	A data structure that describes interest in certain events. Watchers need
		5230	to be started (attached to an event loop) before they can receive events.
		5231
		5232	=back
3586		5233
3587	=head1 AUTHOR	5234	=head1 AUTHOR
3588		5235
3589	Marc Lehmann <libev@schmorp.de>.	5236	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5237	Magnusson and Emanuele Giaquinta.
3590		5238

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