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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
…		…
9	=head2 EXAMPLE PROGRAM	11	=head2 EXAMPLE PROGRAM
10		12
11	// a single header file is required	13	// a single header file is required
12	#include <ev.h>	14	#include <ev.h>
13		15
		16	#include <stdio.h> // for puts
		17
14	// every watcher type has its own typedef'd struct	18	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	19	// with the name ev_TYPE
16	ev_io stdin_watcher;	20	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	21	ev_timer timeout_watcher;
18		22
19	// all watcher callbacks have a similar signature	23	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	24	// this callback is called when data is readable on stdin
21	static void	25	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	26	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	27	{
24	puts ("stdin ready");	28	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	29	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	30	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	31	ev_io_stop (EV_A_ w);
28		32
29	// this causes all nested ev_loop's to stop iterating	33	// this causes all nested ev_run's to stop iterating
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	34	ev_break (EV_A_ EVBREAK_ALL);
31	}	35	}
32		36
33	// another callback, this time for a time-out	37	// another callback, this time for a time-out
34	static void	38	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	39	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	40	{
37	puts ("timeout");	41	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	42	// this causes the innermost ev_run to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	43	ev_break (EV_A_ EVBREAK_ONE);
40	}	44	}
41		45
42	int	46	int
43	main (void)	47	main (void)
44	{	48	{
45	// use the default event loop unless you have special needs	49	// use the default event loop unless you have special needs
46	struct ev_loop *loop = ev_default_loop (0);	50	struct ev_loop *loop = EV_DEFAULT;
47		51
48	// initialise an io watcher, then start it	52	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	53	// this one will watch for stdin to become readable
50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	54	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
51	ev_io_start (loop, &stdin_watcher);	55	ev_io_start (loop, &stdin_watcher);
…		…
54	// simple non-repeating 5.5 second timeout	58	// simple non-repeating 5.5 second timeout
55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	59	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
56	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
57		61
58	// now wait for events to arrive	62	// now wait for events to arrive
59	ev_loop (loop, 0);	63	ev_run (loop, 0);
60		64
61	// unloop was called, so exit	65	// break was called, so exit
62	return 0;	66	return 0;
63	}	67	}
64		68
65	=head1 DESCRIPTION	69	=head1 ABOUT THIS DOCUMENT
		70
		71	This document documents the libev software package.
66		72
67	The newest version of this document is also available as an html-formatted	73	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	74	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>.	75	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		76
		77	While this document tries to be as complete as possible in documenting
		78	libev, its usage and the rationale behind its design, it is not a tutorial
		79	on event-based programming, nor will it introduce event-based programming
		80	with libev.
		81
		82	Familiarity with event based programming techniques in general is assumed
		83	throughout this document.
		84
		85	=head1 WHAT TO READ WHEN IN A HURRY
		86
		87	This manual tries to be very detailed, but unfortunately, this also makes
		88	it very long. If you just want to know the basics of libev, I suggest
		89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		91	C<ev_timer> sections in L</WATCHER TYPES>.
		92
		93	=head1 ABOUT LIBEV
70		94
71	Libev is an event loop: you register interest in certain events (such as a	95	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	96	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	97	these event sources and provide your program with events.
74		98
…		…
84	=head2 FEATURES	108	=head2 FEATURES
85		109
86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	110	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	113	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	114	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	115	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	116	(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	117	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	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	119	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		120	limited support for fork events (C<ev_fork>).
96		121
97	It also is quite fast (see this	122	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	123	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	124	for example).
100		125
…		…
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	133	name C<loop> (which is always of type C<struct ev_loop *>) will not have
109	this argument.	134	this argument.
110		135
111	=head2 TIME REPRESENTATION	136	=head2 TIME REPRESENTATION
112		137
113	Libev represents time as a single floating point number, representing the	138	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	139	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	140	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	141	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	142	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	143	any calculations on it, you should treat it as some floating point value.
		144
119	component C<stamp> might indicate, it is also used for time differences	145	Unlike the name component C<stamp> might indicate, it is also used for
120	throughout libev.	146	time differences (e.g. delays) throughout libev.
121		147
122	=head1 ERROR HANDLING	148	=head1 ERROR HANDLING
123		149
124	Libev knows three classes of errors: operating system errors, usage errors	150	Libev knows three classes of errors: operating system errors, usage errors
125	and internal errors (bugs).	151	and internal errors (bugs).
…		…
149		175
150	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
151		177
152	Returns the current time as libev would use it. Please note that the	178	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	179	C<ev_now> function is usually faster and also often returns the timestamp
154	you actually want to know.	180	you actually want to know. Also interesting is the combination of
		181	C<ev_now_update> and C<ev_now>.
155		182
156	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
157		184
158	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
159	either it is interrupted or the given time interval has passed. Basically	186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
160	this is a sub-second-resolution C<sleep ()>.	190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
161		194
162	=item int ev_version_major ()	195	=item int ev_version_major ()
163		196
164	=item int ev_version_minor ()	197	=item int ev_version_minor ()
165		198
…		…
176	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
177	compatible to older versions, so a larger minor version alone is usually	210	compatible to older versions, so a larger minor version alone is usually
178	not a problem.	211	not a problem.
179		212
180	Example: Make sure we haven't accidentally been linked against the wrong	213	Example: Make sure we haven't accidentally been linked against the wrong
181	version.	214	version (note, however, that this will not detect other ABI mismatches,
		215	such as LFS or reentrancy).
182		216
183	assert (("libev version mismatch",	217	assert (("libev version mismatch",
184	ev_version_major () == EV_VERSION_MAJOR	218	ev_version_major () == EV_VERSION_MAJOR
185	&& ev_version_minor () >= EV_VERSION_MINOR));	219	&& ev_version_minor () >= EV_VERSION_MINOR));
186		220
…		…
197	assert (("sorry, no epoll, no sex",	231	assert (("sorry, no epoll, no sex",
198	ev_supported_backends () & EVBACKEND_EPOLL));	232	ev_supported_backends () & EVBACKEND_EPOLL));
199		233
200	=item unsigned int ev_recommended_backends ()	234	=item unsigned int ev_recommended_backends ()
201		235
202	Return the set of all backends compiled into this binary of libev and also	236	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	237	also recommended for this platform, meaning it will work for most file
		238	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	239	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	240	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	241	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.	242	probe for if you specify no backends explicitly.
208		243
209	=item unsigned int ev_embeddable_backends ()	244	=item unsigned int ev_embeddable_backends ()
210		245
211	Returns the set of backends that are embeddable in other event loops. This	246	Returns the set of backends that are embeddable in other event loops. This
212	is the theoretical, all-platform, value. To find which backends	247	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	248	current system. To find which embeddable backends might be supported on
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	249	the current system, you would need to look at C<ev_embeddable_backends ()
215	recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
216		251
217	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
218		253
219	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
220		255
221	Sets the allocation function to use (the prototype is similar - the	256	Sets the allocation function to use (the prototype is similar - the
222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	257	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
223	used to allocate and free memory (no surprises here). If it returns zero	258	used to allocate and free memory (no surprises here). If it returns zero
224	when memory needs to be allocated (C<size != 0>), the library might abort	259	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
250	}	285	}
251		286
252	...	287	...
253	ev_set_allocator (persistent_realloc);	288	ev_set_allocator (persistent_realloc);
254		289
255	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	290	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
256		291
257	Set the callback function to call on a retryable system call error (such	292	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	293	as failed select, poll, epoll_wait). The message is a printable string
259	indicating the system call or subsystem causing the problem. If this	294	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	295	callback is set, then libev will expect it to remedy the situation, no
…		…
272	}	307	}
273		308
274	...	309	...
275	ev_set_syserr_cb (fatal_error);	310	ev_set_syserr_cb (fatal_error);
276		311
		312	=item ev_feed_signal (int signum)
		313
		314	This function can be used to "simulate" a signal receive. It is completely
		315	safe to call this function at any time, from any context, including signal
		316	handlers or random threads.
		317
		318	Its main use is to customise signal handling in your process, especially
		319	in the presence of threads. For example, you could block signals
		320	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		321	creating any loops), and in one thread, use C<sigwait> or any other
		322	mechanism to wait for signals, then "deliver" them to libev by calling
		323	C<ev_feed_signal>.
		324
277	=back	325	=back
278		326
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	327	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
280		328
281	An event loop is described by a C<struct ev_loop *>. The library knows two	329	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	330	I<not> optional in this case unless libev 3 compatibility is disabled, as
283	events, and dynamically created loops which do not.	331	libev 3 had an C<ev_loop> function colliding with the struct name).
		332
		333	The library knows two types of such loops, the I<default> loop, which
		334	supports child process events, and dynamically created event loops which
		335	do not.
284		336
285	=over 4	337	=over 4
286		338
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	339	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		340
289	This will initialise the default event loop if it hasn't been initialised	341	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	342	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	343	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).	344	C<ev_loop_new>.
		345
		346	If the default loop is already initialised then this function simply
		347	returns it (and ignores the flags. If that is troubling you, check
		348	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		349	flags, which should almost always be C<0>, unless the caller is also the
		350	one calling C<ev_run> or otherwise qualifies as "the main program".
293		351
294	If you don't know what event loop to use, use the one returned from this	352	If you don't know what event loop to use, use the one returned from this
295	function.	353	function (or via the C<EV_DEFAULT> macro).
296		354
297	Note that this function is I<not> thread-safe, so if you want to use it	355	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,	356	from multiple threads, you have to employ some kind of mutex (note also
299	as loops cannot bes hared easily between threads anyway).	357	that this case is unlikely, as loops cannot be shared easily between
		358	threads anyway).
300		359
301	The default loop is the only loop that can handle C<ev_signal> and	360	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	361	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	362	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	363	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	364	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
306	C<ev_default_init>.	365
		366	Example: This is the most typical usage.
		367
		368	if (!ev_default_loop (0))
		369	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		370
		371	Example: Restrict libev to the select and poll backends, and do not allow
		372	environment settings to be taken into account:
		373
		374	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		375
		376	=item struct ev_loop *ev_loop_new (unsigned int flags)
		377
		378	This will create and initialise a new event loop object. If the loop
		379	could not be initialised, returns false.
		380
		381	This function is thread-safe, and one common way to use libev with
		382	threads is indeed to create one loop per thread, and using the default
		383	loop in the "main" or "initial" thread.
307		384
308	The flags argument can be used to specify special behaviour or specific	385	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>).	386	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
310		387
311	The following flags are supported:	388	The following flags are supported:
…		…
321		398
322	If this flag bit is or'ed into the flag value (or the program runs setuid	399	If this flag bit is or'ed into the flag value (or the program runs setuid
323	or setgid) then libev will I<not> look at the environment variable	400	or setgid) then libev will I<not> look at the environment variable
324	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	401	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
325	override the flags completely if it is found in the environment. This is	402	override the flags completely if it is found in the environment. This is
326	useful to try out specific backends to test their performance, or to work	403	useful to try out specific backends to test their performance, to work
327	around bugs.	404	around bugs, or to make libev threadsafe (accessing environment variables
		405	cannot be done in a threadsafe way, but usually it works if no other
		406	thread modifies them).
328		407
329	=item C<EVFLAG_FORKCHECK>	408	=item C<EVFLAG_FORKCHECK>
330		409
331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	410	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	411	make libev check for a fork in each iteration by enabling this flag.
333	enabling this flag.
334		412
335	This works by calling C<getpid ()> on every iteration of the loop,	413	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	414	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	415	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	416	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
…		…
344	flag.	422	flag.
345		423
346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	424	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
347	environment variable.	425	environment variable.
348		426
		427	=item C<EVFLAG_NOINOTIFY>
		428
		429	When this flag is specified, then libev will not attempt to use the
		430	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		431	testing, this flag can be useful to conserve inotify file descriptors, as
		432	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		433
		434	=item C<EVFLAG_SIGNALFD>
		435
		436	When this flag is specified, then libev will attempt to use the
		437	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		438	delivers signals synchronously, which makes it both faster and might make
		439	it possible to get the queued signal data. It can also simplify signal
		440	handling with threads, as long as you properly block signals in your
		441	threads that are not interested in handling them.
		442
		443	Signalfd will not be used by default as this changes your signal mask, and
		444	there are a lot of shoddy libraries and programs (glib's threadpool for
		445	example) that can't properly initialise their signal masks.
		446
		447	=item C<EVFLAG_NOSIGMASK>
		448
		449	When this flag is specified, then libev will avoid to modify the signal
		450	mask. Specifically, this means you have to make sure signals are unblocked
		451	when you want to receive them.
		452
		453	This behaviour is useful when you want to do your own signal handling, or
		454	want to handle signals only in specific threads and want to avoid libev
		455	unblocking the signals.
		456
		457	It's also required by POSIX in a threaded program, as libev calls
		458	C<sigprocmask>, whose behaviour is officially unspecified.
		459
		460	This flag's behaviour will become the default in future versions of libev.
		461
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	462	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		463
351	This is your standard select(2) backend. Not I<completely> standard, as	464	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,	465	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	466	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	490	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
378	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	491	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
379		492
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	493	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		494
		495	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		496	kernels).
		497
382	For few fds, this backend is a bit little slower than poll and select,	498	For few fds, this backend is a bit little slower than poll and select, but
383	but it scales phenomenally better. While poll and select usually scale	499	it scales phenomenally better. While poll and select usually scale like
384	like O(total_fds) where n is the total number of fds (or the highest fd),	500	O(total_fds) where total_fds is the total number of fds (or the highest
385	epoll scales either O(1) or O(active_fds). The epoll design has a number	501	fd), epoll scales either O(1) or O(active_fds).
386	of shortcomings, such as silently dropping events in some hard-to-detect	502
387	cases and requiring a system call per fd change, no fork support and bad	503	The epoll mechanism deserves honorable mention as the most misdesigned
388	support for dup.	504	of the more advanced event mechanisms: mere annoyances include silently
		505	dropping file descriptors, requiring a system call per change per file
		506	descriptor (and unnecessary guessing of parameters), problems with dup,
		507	returning before the timeout value, resulting in additional iterations
		508	(and only giving 5ms accuracy while select on the same platform gives
		509	0.1ms) and so on. The biggest issue is fork races, however - if a program
		510	forks then I<both> parent and child process have to recreate the epoll
		511	set, which can take considerable time (one syscall per file descriptor)
		512	and is of course hard to detect.
		513
		514	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		515	but of course I<doesn't>, and epoll just loves to report events for
		516	totally I<different> file descriptors (even already closed ones, so
		517	one cannot even remove them from the set) than registered in the set
		518	(especially on SMP systems). Libev tries to counter these spurious
		519	notifications by employing an additional generation counter and comparing
		520	that against the events to filter out spurious ones, recreating the set
		521	when required. Epoll also erroneously rounds down timeouts, but gives you
		522	no way to know when and by how much, so sometimes you have to busy-wait
		523	because epoll returns immediately despite a nonzero timeout. And last
		524	not least, it also refuses to work with some file descriptors which work
		525	perfectly fine with C<select> (files, many character devices...).
		526
		527	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		528	cobbled together in a hurry, no thought to design or interaction with
		529	others. Oh, the pain, will it ever stop...
389		530
390	While stopping, setting and starting an I/O watcher in the same iteration	531	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	532	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	533	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	534	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
394	very well if you register events for both fds.	535	file descriptors might not work very well if you register events for both
395		536	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		537
400	Best performance from this backend is achieved by not unregistering all	538	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible,	539	watchers for a file descriptor until it has been closed, if possible,
402	i.e. keep at least one watcher active per fd at all times. Stopping and	540	i.e. keep at least one watcher active per fd at all times. Stopping and
403	starting a watcher (without re-setting it) also usually doesn't cause	541	starting a watcher (without re-setting it) also usually doesn't cause
404	extra overhead.	542	extra overhead. A fork can both result in spurious notifications as well
		543	as in libev having to destroy and recreate the epoll object, which can
		544	take considerable time and thus should be avoided.
		545
		546	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		547	faster than epoll for maybe up to a hundred file descriptors, depending on
		548	the usage. So sad.
405		549
406	While nominally embeddable in other event loops, this feature is broken in	550	While nominally embeddable in other event loops, this feature is broken in
407	all kernel versions tested so far.	551	all kernel versions tested so far.
408		552
409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	553	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
410	C<EVBACKEND_POLL>.	554	C<EVBACKEND_POLL>.
411		555
412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	556	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
413		557
414	Kqueue deserves special mention, as at the time of this writing, it was	558	Kqueue deserves special mention, as at the time of this writing, it
415	broken on all BSDs except NetBSD (usually it doesn't work reliably with	559	was broken on all BSDs except NetBSD (usually it doesn't work reliably
416	anything but sockets and pipes, except on Darwin, where of course it's	560	with anything but sockets and pipes, except on Darwin, where of course
417	completely useless). For this reason it's not being "auto-detected" unless	561	it's completely useless). Unlike epoll, however, whose brokenness
418	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or	562	is by design, these kqueue bugs can (and eventually will) be fixed
419	libev was compiled on a known-to-be-good (-enough) system like NetBSD.	563	without API changes to existing programs. For this reason it's not being
		564	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		565	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		566	system like NetBSD.
420		567
421	You still can embed kqueue into a normal poll or select backend and use it	568	You still can embed kqueue into a normal poll or select backend and use it
422	only for sockets (after having made sure that sockets work with kqueue on	569	only for sockets (after having made sure that sockets work with kqueue on
423	the target platform). See C<ev_embed> watchers for more info.	570	the target platform). See C<ev_embed> watchers for more info.
424		571
425	It scales in the same way as the epoll backend, but the interface to the	572	It scales in the same way as the epoll backend, but the interface to the
426	kernel is more efficient (which says nothing about its actual speed, of	573	kernel is more efficient (which says nothing about its actual speed, of
427	course). While stopping, setting and starting an I/O watcher does never	574	course). While stopping, setting and starting an I/O watcher does never
428	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	575	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
429	two event changes per incident. Support for C<fork ()> is very bad and it	576	two event changes per incident. Support for C<fork ()> is very bad (you
		577	might have to leak fd's on fork, but it's more sane than epoll) and it
430	drops fds silently in similarly hard-to-detect cases.	578	drops fds silently in similarly hard-to-detect cases.
431		579
432	This backend usually performs well under most conditions.	580	This backend usually performs well under most conditions.
433		581
434	While nominally embeddable in other event loops, this doesn't work	582	While nominally embeddable in other event loops, this doesn't work
435	everywhere, so you might need to test for this. And since it is broken	583	everywhere, so you might need to test for this. And since it is broken
436	almost everywhere, you should only use it when you have a lot of sockets	584	almost everywhere, you should only use it when you have a lot of sockets
437	(for which it usually works), by embedding it into another event loop	585	(for which it usually works), by embedding it into another event loop
438	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,	586	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
439	using it only for sockets.	587	also broken on OS X)) and, did I mention it, using it only for sockets.
440		588
441	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with	589	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
442	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with	590	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
443	C<NOTE_EOF>.	591	C<NOTE_EOF>.
444		592
…		…
452	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	600	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
453		601
454	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	602	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
455	it's really slow, but it still scales very well (O(active_fds)).	603	it's really slow, but it still scales very well (O(active_fds)).
456		604
457	Please note that Solaris event ports can deliver a lot of spurious
458	notifications, so you need to use non-blocking I/O or other means to avoid
459	blocking when no data (or space) is available.
460
461	While this backend scales well, it requires one system call per active	605	While this backend scales well, it requires one system call per active
462	file descriptor per loop iteration. For small and medium numbers of file	606	file descriptor per loop iteration. For small and medium numbers of file
463	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	607	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
464	might perform better.	608	might perform better.
465		609
466	On the positive side, with the exception of the spurious readiness	610	On the positive side, this backend actually performed fully to
467	notifications, this backend actually performed fully to specification
468	in all tests and is fully embeddable, which is a rare feat among the	611	specification in all tests and is fully embeddable, which is a rare feat
469	OS-specific backends.	612	among the OS-specific backends (I vastly prefer correctness over speed
		613	hacks).
		614
		615	On the negative side, the interface is I<bizarre> - so bizarre that
		616	even sun itself gets it wrong in their code examples: The event polling
		617	function sometimes returns events to the caller even though an error
		618	occurred, but with no indication whether it has done so or not (yes, it's
		619	even documented that way) - deadly for edge-triggered interfaces where you
		620	absolutely have to know whether an event occurred or not because you have
		621	to re-arm the watcher.
		622
		623	Fortunately libev seems to be able to work around these idiocies.
470		624
471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	625	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
472	C<EVBACKEND_POLL>.	626	C<EVBACKEND_POLL>.
473		627
474	=item C<EVBACKEND_ALL>	628	=item C<EVBACKEND_ALL>
475		629
476	Try all backends (even potentially broken ones that wouldn't be tried	630	Try all backends (even potentially broken ones that wouldn't be tried
477	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	631	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
478	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	632	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
479		633
480	It is definitely not recommended to use this flag.	634	It is definitely not recommended to use this flag, use whatever
		635	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		636	at all.
		637
		638	=item C<EVBACKEND_MASK>
		639
		640	Not a backend at all, but a mask to select all backend bits from a
		641	C<flags> value, in case you want to mask out any backends from a flags
		642	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
481		643
482	=back	644	=back
483		645
484	If one or more of these are or'ed into the flags value, then only these	646	If one or more of the backend flags are or'ed into the flags value,
485	backends will be tried (in the reverse order as listed here). If none are	647	then only these backends will be tried (in the reverse order as listed
486	specified, all backends in C<ev_recommended_backends ()> will be tried.	648	here). If none are specified, all backends in C<ev_recommended_backends
487		649	()> will be tried.
488	Example: This is the most typical usage.
489
490	if (!ev_default_loop (0))
491	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
492
493	Example: Restrict libev to the select and poll backends, and do not allow
494	environment settings to be taken into account:
495
496	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
497
498	Example: Use whatever libev has to offer, but make sure that kqueue is
499	used if available (warning, breaks stuff, best use only with your own
500	private event loop and only if you know the OS supports your types of
501	fds):
502
503	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
504
505	=item struct ev_loop *ev_loop_new (unsigned int flags)
506
507	Similar to C<ev_default_loop>, but always creates a new event loop that is
508	always distinct from the default loop. Unlike the default loop, it cannot
509	handle signal and child watchers, and attempts to do so will be greeted by
510	undefined behaviour (or a failed assertion if assertions are enabled).
511
512	Note that this function I<is> thread-safe, and the recommended way to use
513	libev with threads is indeed to create one loop per thread, and using the
514	default loop in the "main" or "initial" thread.
515		650
516	Example: Try to create a event loop that uses epoll and nothing else.	651	Example: Try to create a event loop that uses epoll and nothing else.
517		652
518	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	653	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
519	if (!epoller)	654	if (!epoller)
520	fatal ("no epoll found here, maybe it hides under your chair");	655	fatal ("no epoll found here, maybe it hides under your chair");
521		656
		657	Example: Use whatever libev has to offer, but make sure that kqueue is
		658	used if available.
		659
		660	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		661
522	=item ev_default_destroy ()	662	=item ev_loop_destroy (loop)
523		663
524	Destroys the default loop again (frees all memory and kernel state	664	Destroys an event loop object (frees all memory and kernel state
525	etc.). None of the active event watchers will be stopped in the normal	665	etc.). None of the active event watchers will be stopped in the normal
526	sense, so e.g. C<ev_is_active> might still return true. It is your	666	sense, so e.g. C<ev_is_active> might still return true. It is your
527	responsibility to either stop all watchers cleanly yourself I<before>	667	responsibility to either stop all watchers cleanly yourself I<before>
528	calling this function, or cope with the fact afterwards (which is usually	668	calling this function, or cope with the fact afterwards (which is usually
529	the easiest thing, you can just ignore the watchers and/or C<free ()> them	669	the easiest thing, you can just ignore the watchers and/or C<free ()> them
530	for example).	670	for example).
531		671
532	Note that certain global state, such as signal state, will not be freed by	672	Note that certain global state, such as signal state (and installed signal
533	this function, and related watchers (such as signal and child watchers)	673	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	674	as signal and child watchers) would need to be stopped manually.
535		675
536	In general it is not advisable to call this function except in the	676	This function is normally used on loop objects allocated by
537	rare occasion where you really need to free e.g. the signal handling	677	C<ev_loop_new>, but it can also be used on the default loop returned by
		678	C<ev_default_loop>, in which case it is not thread-safe.
		679
		680	Note that it is not advisable to call this function on the default loop
		681	except in the rare occasion where you really need to free its resources.
538	pipe fds. If you need dynamically allocated loops it is better to use	682	If you need dynamically allocated loops it is better to use C<ev_loop_new>
539	C<ev_loop_new> and C<ev_loop_destroy>).	683	and C<ev_loop_destroy>.
540		684
541	=item ev_loop_destroy (loop)	685	=item ev_loop_fork (loop)
542		686
543	Like C<ev_default_destroy>, but destroys an event loop created by an
544	earlier call to C<ev_loop_new>.
545
546	=item ev_default_fork ()
547
548	This function sets a flag that causes subsequent C<ev_loop> iterations	687	This function sets a flag that causes subsequent C<ev_run> iterations
549	to reinitialise the kernel state for backends that have one. Despite the	688	to reinitialise the kernel state for backends that have one. Despite
550	name, you can call it anytime, but it makes most sense after forking, in	689	the name, you can call it anytime you are allowed to start or stop
551	the child process (or both child and parent, but that again makes little	690	watchers (except inside an C<ev_prepare> callback), but it makes most
552	sense). You I<must> call it in the child before using any of the libev	691	sense after forking, in the child process. You I<must> call it (or use
553	functions, and it will only take effect at the next C<ev_loop> iteration.	692	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
		693
		694	Again, you I<have> to call it on I<any> loop that you want to re-use after
		695	a fork, I<even if you do not plan to use the loop in the parent>. This is
		696	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		697	during fork.
554		698
555	On the other hand, you only need to call this function in the child	699	On the other hand, you only need to call this function in the child
556	process if and only if you want to use the event library in the child. If	700	process if and only if you want to use the event loop in the child. If
557	you just fork+exec, you don't have to call it at all.	701	you just fork+exec or create a new loop in the child, you don't have to
		702	call it at all (in fact, C<epoll> is so badly broken that it makes a
		703	difference, but libev will usually detect this case on its own and do a
		704	costly reset of the backend).
558		705
559	The function itself is quite fast and it's usually not a problem to call	706	The function itself is quite fast and it's usually not a problem to call
560	it just in case after a fork. To make this easy, the function will fit in	707	it just in case after a fork.
561	quite nicely into a call to C<pthread_atfork>:
562		708
		709	Example: Automate calling C<ev_loop_fork> on the default loop when
		710	using pthreads.
		711
		712	static void
		713	post_fork_child (void)
		714	{
		715	ev_loop_fork (EV_DEFAULT);
		716	}
		717
		718	...
563	pthread_atfork (0, 0, ev_default_fork);	719	pthread_atfork (0, 0, post_fork_child);
564
565	=item ev_loop_fork (loop)
566
567	Like C<ev_default_fork>, but acts on an event loop created by
568	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
569	after fork that you want to re-use in the child, and how you do this is
570	entirely your own problem.
571		720
572	=item int ev_is_default_loop (loop)	721	=item int ev_is_default_loop (loop)
573		722
574	Returns true when the given loop is, in fact, the default loop, and false	723	Returns true when the given loop is, in fact, the default loop, and false
575	otherwise.	724	otherwise.
576		725
577	=item unsigned int ev_loop_count (loop)	726	=item unsigned int ev_iteration (loop)
578		727
579	Returns the count of loop iterations for the loop, which is identical to	728	Returns the current iteration count for the event loop, which is identical
580	the number of times libev did poll for new events. It starts at C<0> and	729	to the number of times libev did poll for new events. It starts at C<0>
581	happily wraps around with enough iterations.	730	and happily wraps around with enough iterations.
582		731
583	This value can sometimes be useful as a generation counter of sorts (it	732	This value can sometimes be useful as a generation counter of sorts (it
584	"ticks" the number of loop iterations), as it roughly corresponds with	733	"ticks" the number of loop iterations), as it roughly corresponds with
585	C<ev_prepare> and C<ev_check> calls.	734	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		735	prepare and check phases.
		736
		737	=item unsigned int ev_depth (loop)
		738
		739	Returns the number of times C<ev_run> was entered minus the number of
		740	times C<ev_run> was exited normally, in other words, the recursion depth.
		741
		742	Outside C<ev_run>, this number is zero. In a callback, this number is
		743	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		744	in which case it is higher.
		745
		746	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		747	throwing an exception etc.), doesn't count as "exit" - consider this
		748	as a hint to avoid such ungentleman-like behaviour unless it's really
		749	convenient, in which case it is fully supported.
586		750
587	=item unsigned int ev_backend (loop)	751	=item unsigned int ev_backend (loop)
588		752
589	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	753	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
590	use.	754	use.
…		…
599		763
600	=item ev_now_update (loop)	764	=item ev_now_update (loop)
601		765
602	Establishes the current time by querying the kernel, updating the time	766	Establishes the current time by querying the kernel, updating the time
603	returned by C<ev_now ()> in the progress. This is a costly operation and	767	returned by C<ev_now ()> in the progress. This is a costly operation and
604	is usually done automatically within C<ev_loop ()>.	768	is usually done automatically within C<ev_run ()>.
605		769
606	This function is rarely useful, but when some event callback runs for a	770	This function is rarely useful, but when some event callback runs for a
607	very long time without entering the event loop, updating libev's idea of	771	very long time without entering the event loop, updating libev's idea of
608	the current time is a good idea.	772	the current time is a good idea.
609		773
610	See also "The special problem of time updates" in the C<ev_timer> section.	774	See also L</The special problem of time updates> in the C<ev_timer> section.
611		775
		776	=item ev_suspend (loop)
		777
		778	=item ev_resume (loop)
		779
		780	These two functions suspend and resume an event loop, for use when the
		781	loop is not used for a while and timeouts should not be processed.
		782
		783	A typical use case would be an interactive program such as a game: When
		784	the user presses C<^Z> to suspend the game and resumes it an hour later it
		785	would be best to handle timeouts as if no time had actually passed while
		786	the program was suspended. This can be achieved by calling C<ev_suspend>
		787	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		788	C<ev_resume> directly afterwards to resume timer processing.
		789
		790	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		791	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		792	will be rescheduled (that is, they will lose any events that would have
		793	occurred while suspended).
		794
		795	After calling C<ev_suspend> you B<must not> call I<any> function on the
		796	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		797	without a previous call to C<ev_suspend>.
		798
		799	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		800	event loop time (see C<ev_now_update>).
		801
612	=item ev_loop (loop, int flags)	802	=item bool ev_run (loop, int flags)
613		803
614	Finally, this is it, the event handler. This function usually is called	804	Finally, this is it, the event handler. This function usually is called
615	after you initialised all your watchers and you want to start handling	805	after you have initialised all your watchers and you want to start
616	events.	806	handling events. It will ask the operating system for any new events, call
		807	the watcher callbacks, and then repeat the whole process indefinitely: This
		808	is why event loops are called I<loops>.
617		809
618	If the flags argument is specified as C<0>, it will not return until	810	If the flags argument is specified as C<0>, it will keep handling events
619	either no event watchers are active anymore or C<ev_unloop> was called.	811	until either no event watchers are active anymore or C<ev_break> was
		812	called.
620		813
		814	The return value is false if there are no more active watchers (which
		815	usually means "all jobs done" or "deadlock"), and true in all other cases
		816	(which usually means " you should call C<ev_run> again").
		817
621	Please note that an explicit C<ev_unloop> is usually better than	818	Please note that an explicit C<ev_break> is usually better than
622	relying on all watchers to be stopped when deciding when a program has	819	relying on all watchers to be stopped when deciding when a program has
623	finished (especially in interactive programs), but having a program	820	finished (especially in interactive programs), but having a program
624	that automatically loops as long as it has to and no longer by virtue	821	that automatically loops as long as it has to and no longer by virtue
625	of relying on its watchers stopping correctly, that is truly a thing of	822	of relying on its watchers stopping correctly, that is truly a thing of
626	beauty.	823	beauty.
627		824
		825	This function is I<mostly> exception-safe - you can break out of a
		826	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		827	exception and so on. This does not decrement the C<ev_depth> value, nor
		828	will it clear any outstanding C<EVBREAK_ONE> breaks.
		829
628	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	830	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
629	those events and any already outstanding ones, but will not block your	831	those events and any already outstanding ones, but will not wait and
630	process in case there are no events and will return after one iteration of	832	block your process in case there are no events and will return after one
631	the loop.	833	iteration of the loop. This is sometimes useful to poll and handle new
		834	events while doing lengthy calculations, to keep the program responsive.
632		835
633	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	836	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
634	necessary) and will handle those and any already outstanding ones. It	837	necessary) and will handle those and any already outstanding ones. It
635	will block your process until at least one new event arrives (which could	838	will block your process until at least one new event arrives (which could
636	be an event internal to libev itself, so there is no guarentee that a	839	be an event internal to libev itself, so there is no guarantee that a
637	user-registered callback will be called), and will return after one	840	user-registered callback will be called), and will return after one
638	iteration of the loop.	841	iteration of the loop.
639		842
640	This is useful if you are waiting for some external event in conjunction	843	This is useful if you are waiting for some external event in conjunction
641	with something not expressible using other libev watchers (i.e. "roll your	844	with something not expressible using other libev watchers (i.e. "roll your
642	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	845	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
643	usually a better approach for this kind of thing.	846	usually a better approach for this kind of thing.
644		847
645	Here are the gory details of what C<ev_loop> does:	848	Here are the gory details of what C<ev_run> does (this is for your
		849	understanding, not a guarantee that things will work exactly like this in
		850	future versions):
646		851
		852	- Increment loop depth.
		853	- Reset the ev_break status.
647	- Before the first iteration, call any pending watchers.	854	- Before the first iteration, call any pending watchers.
		855	LOOP:
648	* If EVFLAG_FORKCHECK was used, check for a fork.	856	- If EVFLAG_FORKCHECK was used, check for a fork.
649	- If a fork was detected (by any means), queue and call all fork watchers.	857	- If a fork was detected (by any means), queue and call all fork watchers.
650	- Queue and call all prepare watchers.	858	- Queue and call all prepare watchers.
		859	- If ev_break was called, goto FINISH.
651	- If we have been forked, detach and recreate the kernel state	860	- If we have been forked, detach and recreate the kernel state
652	as to not disturb the other process.	861	as to not disturb the other process.
653	- Update the kernel state with all outstanding changes.	862	- Update the kernel state with all outstanding changes.
654	- Update the "event loop time" (ev_now ()).	863	- Update the "event loop time" (ev_now ()).
655	- Calculate for how long to sleep or block, if at all	864	- Calculate for how long to sleep or block, if at all
656	(active idle watchers, EVLOOP_NONBLOCK or not having	865	(active idle watchers, EVRUN_NOWAIT or not having
657	any active watchers at all will result in not sleeping).	866	any active watchers at all will result in not sleeping).
658	- Sleep if the I/O and timer collect interval say so.	867	- Sleep if the I/O and timer collect interval say so.
		868	- Increment loop iteration counter.
659	- Block the process, waiting for any events.	869	- Block the process, waiting for any events.
660	- Queue all outstanding I/O (fd) events.	870	- Queue all outstanding I/O (fd) events.
661	- Update the "event loop time" (ev_now ()), and do time jump adjustments.	871	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
662	- Queue all expired timers.	872	- Queue all expired timers.
663	- Queue all expired periodics.	873	- Queue all expired periodics.
664	- Unless any events are pending now, queue all idle watchers.	874	- Queue all idle watchers with priority higher than that of pending events.
665	- Queue all check watchers.	875	- Queue all check watchers.
666	- Call all queued watchers in reverse order (i.e. check watchers first).	876	- Call all queued watchers in reverse order (i.e. check watchers first).
667	Signals and child watchers are implemented as I/O watchers, and will	877	Signals and child watchers are implemented as I/O watchers, and will
668	be handled here by queueing them when their watcher gets executed.	878	be handled here by queueing them when their watcher gets executed.
669	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	879	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
670	were used, or there are no active watchers, return, otherwise	880	were used, or there are no active watchers, goto FINISH, otherwise
671	continue with step *.	881	continue with step LOOP.
		882	FINISH:
		883	- Reset the ev_break status iff it was EVBREAK_ONE.
		884	- Decrement the loop depth.
		885	- Return.
672		886
673	Example: Queue some jobs and then loop until no events are outstanding	887	Example: Queue some jobs and then loop until no events are outstanding
674	anymore.	888	anymore.
675		889
676	... queue jobs here, make sure they register event watchers as long	890	... queue jobs here, make sure they register event watchers as long
677	... as they still have work to do (even an idle watcher will do..)	891	... as they still have work to do (even an idle watcher will do..)
678	ev_loop (my_loop, 0);	892	ev_run (my_loop, 0);
679	... jobs done or somebody called unloop. yeah!	893	... jobs done or somebody called break. yeah!
680		894
681	=item ev_unloop (loop, how)	895	=item ev_break (loop, how)
682		896
683	Can be used to make a call to C<ev_loop> return early (but only after it	897	Can be used to make a call to C<ev_run> return early (but only after it
684	has processed all outstanding events). The C<how> argument must be either	898	has processed all outstanding events). The C<how> argument must be either
685	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	899	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
686	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	900	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
687		901
688	This "unloop state" will be cleared when entering C<ev_loop> again.	902	This "break state" will be cleared on the next call to C<ev_run>.
		903
		904	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		905	which case it will have no effect.
689		906
690	=item ev_ref (loop)	907	=item ev_ref (loop)
691		908
692	=item ev_unref (loop)	909	=item ev_unref (loop)
693		910
694	Ref/unref can be used to add or remove a reference count on the event	911	Ref/unref can be used to add or remove a reference count on the event
695	loop: Every watcher keeps one reference, and as long as the reference	912	loop: Every watcher keeps one reference, and as long as the reference
696	count is nonzero, C<ev_loop> will not return on its own.	913	count is nonzero, C<ev_run> will not return on its own.
697		914
698	If you have a watcher you never unregister that should not keep C<ev_loop>	915	This is useful when you have a watcher that you never intend to
699	from returning, call ev_unref() after starting, and ev_ref() before	916	unregister, but that nevertheless should not keep C<ev_run> from
		917	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
700	stopping it.	918	before stopping it.
701		919
702	As an example, libev itself uses this for its internal signal pipe: It is	920	As an example, libev itself uses this for its internal signal pipe: It
703	not visible to the libev user and should not keep C<ev_loop> from exiting	921	is not visible to the libev user and should not keep C<ev_run> from
704	if no event watchers registered by it are active. It is also an excellent	922	exiting if no event watchers registered by it are active. It is also an
705	way to do this for generic recurring timers or from within third-party	923	excellent way to do this for generic recurring timers or from within
706	libraries. Just remember to I<unref after start> and I<ref before stop>	924	third-party libraries. Just remember to I<unref after start> and I<ref
707	(but only if the watcher wasn't active before, or was active before,	925	before stop> (but only if the watcher wasn't active before, or was active
708	respectively).	926	before, respectively. Note also that libev might stop watchers itself
		927	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		928	in the callback).
709		929
710	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	930	Example: Create a signal watcher, but keep it from keeping C<ev_run>
711	running when nothing else is active.	931	running when nothing else is active.
712		932
713	struct ev_signal exitsig;	933	ev_signal exitsig;
714	ev_signal_init (&exitsig, sig_cb, SIGINT);	934	ev_signal_init (&exitsig, sig_cb, SIGINT);
715	ev_signal_start (loop, &exitsig);	935	ev_signal_start (loop, &exitsig);
716	evf_unref (loop);	936	ev_unref (loop);
717		937
718	Example: For some weird reason, unregister the above signal handler again.	938	Example: For some weird reason, unregister the above signal handler again.
719		939
720	ev_ref (loop);	940	ev_ref (loop);
721	ev_signal_stop (loop, &exitsig);	941	ev_signal_stop (loop, &exitsig);
…		…
741	overhead for the actual polling but can deliver many events at once.	961	overhead for the actual polling but can deliver many events at once.
742		962
743	By setting a higher I<io collect interval> you allow libev to spend more	963	By setting a higher I<io collect interval> you allow libev to spend more
744	time collecting I/O events, so you can handle more events per iteration,	964	time collecting I/O events, so you can handle more events per iteration,
745	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	965	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
746	C<ev_timer>) will be not affected. Setting this to a non-null value will	966	C<ev_timer>) will not be affected. Setting this to a non-null value will
747	introduce an additional C<ev_sleep ()> call into most loop iterations.	967	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		968	sleep time ensures that libev will not poll for I/O events more often then
		969	once per this interval, on average (as long as the host time resolution is
		970	good enough).
748		971
749	Likewise, by setting a higher I<timeout collect interval> you allow libev	972	Likewise, by setting a higher I<timeout collect interval> you allow libev
750	to spend more time collecting timeouts, at the expense of increased	973	to spend more time collecting timeouts, at the expense of increased
751	latency/jitter/inexactness (the watcher callback will be called	974	latency/jitter/inexactness (the watcher callback will be called
752	later). C<ev_io> watchers will not be affected. Setting this to a non-null	975	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
754		977
755	Many (busy) programs can usually benefit by setting the I/O collect	978	Many (busy) programs can usually benefit by setting the I/O collect
756	interval to a value near C<0.1> or so, which is often enough for	979	interval to a value near C<0.1> or so, which is often enough for
757	interactive servers (of course not for games), likewise for timeouts. It	980	interactive servers (of course not for games), likewise for timeouts. It
758	usually doesn't make much sense to set it to a lower value than C<0.01>,	981	usually doesn't make much sense to set it to a lower value than C<0.01>,
759	as this approaches the timing granularity of most systems.	982	as this approaches the timing granularity of most systems. Note that if
		983	you do transactions with the outside world and you can't increase the
		984	parallelity, then this setting will limit your transaction rate (if you
		985	need to poll once per transaction and the I/O collect interval is 0.01,
		986	then you can't do more than 100 transactions per second).
760		987
761	Setting the I<timeout collect interval> can improve the opportunity for	988	Setting the I<timeout collect interval> can improve the opportunity for
762	saving power, as the program will "bundle" timer callback invocations that	989	saving power, as the program will "bundle" timer callback invocations that
763	are "near" in time together, by delaying some, thus reducing the number of	990	are "near" in time together, by delaying some, thus reducing the number of
764	times the process sleeps and wakes up again. Another useful technique to	991	times the process sleeps and wakes up again. Another useful technique to
765	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	992	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
766	they fire on, say, one-second boundaries only.	993	they fire on, say, one-second boundaries only.
767		994
		995	Example: we only need 0.1s timeout granularity, and we wish not to poll
		996	more often than 100 times per second:
		997
		998	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		999	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		1000
		1001	=item ev_invoke_pending (loop)
		1002
		1003	This call will simply invoke all pending watchers while resetting their
		1004	pending state. Normally, C<ev_run> does this automatically when required,
		1005	but when overriding the invoke callback this call comes handy. This
		1006	function can be invoked from a watcher - this can be useful for example
		1007	when you want to do some lengthy calculation and want to pass further
		1008	event handling to another thread (you still have to make sure only one
		1009	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1010
		1011	=item int ev_pending_count (loop)
		1012
		1013	Returns the number of pending watchers - zero indicates that no watchers
		1014	are pending.
		1015
		1016	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1017
		1018	This overrides the invoke pending functionality of the loop: Instead of
		1019	invoking all pending watchers when there are any, C<ev_run> will call
		1020	this callback instead. This is useful, for example, when you want to
		1021	invoke the actual watchers inside another context (another thread etc.).
		1022
		1023	If you want to reset the callback, use C<ev_invoke_pending> as new
		1024	callback.
		1025
		1026	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1027
		1028	Sometimes you want to share the same loop between multiple threads. This
		1029	can be done relatively simply by putting mutex_lock/unlock calls around
		1030	each call to a libev function.
		1031
		1032	However, C<ev_run> can run an indefinite time, so it is not feasible
		1033	to wait for it to return. One way around this is to wake up the event
		1034	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1035	I<release> and I<acquire> callbacks on the loop.
		1036
		1037	When set, then C<release> will be called just before the thread is
		1038	suspended waiting for new events, and C<acquire> is called just
		1039	afterwards.
		1040
		1041	Ideally, C<release> will just call your mutex_unlock function, and
		1042	C<acquire> will just call the mutex_lock function again.
		1043
		1044	While event loop modifications are allowed between invocations of
		1045	C<release> and C<acquire> (that's their only purpose after all), no
		1046	modifications done will affect the event loop, i.e. adding watchers will
		1047	have no effect on the set of file descriptors being watched, or the time
		1048	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1049	to take note of any changes you made.
		1050
		1051	In theory, threads executing C<ev_run> will be async-cancel safe between
		1052	invocations of C<release> and C<acquire>.
		1053
		1054	See also the locking example in the C<THREADS> section later in this
		1055	document.
		1056
		1057	=item ev_set_userdata (loop, void *data)
		1058
		1059	=item void *ev_userdata (loop)
		1060
		1061	Set and retrieve a single C<void *> associated with a loop. When
		1062	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1063	C<0>.
		1064
		1065	These two functions can be used to associate arbitrary data with a loop,
		1066	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1067	C<acquire> callbacks described above, but of course can be (ab-)used for
		1068	any other purpose as well.
		1069
768	=item ev_loop_verify (loop)	1070	=item ev_verify (loop)
769		1071
770	This function only does something when C<EV_VERIFY> support has been	1072	This function only does something when C<EV_VERIFY> support has been
771	compiled in. which is the default for non-minimal builds. It tries to go	1073	compiled in, which is the default for non-minimal builds. It tries to go
772	through all internal structures and checks them for validity. If anything	1074	through all internal structures and checks them for validity. If anything
773	is found to be inconsistent, it will print an error message to standard	1075	is found to be inconsistent, it will print an error message to standard
774	error and call C<abort ()>.	1076	error and call C<abort ()>.
775		1077
776	This can be used to catch bugs inside libev itself: under normal	1078	This can be used to catch bugs inside libev itself: under normal
…		…
780	=back	1082	=back
781		1083
782		1084
783	=head1 ANATOMY OF A WATCHER	1085	=head1 ANATOMY OF A WATCHER
784		1086
		1087	In the following description, uppercase C<TYPE> in names stands for the
		1088	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1089	watchers and C<ev_io_start> for I/O watchers.
		1090
785	A watcher is a structure that you create and register to record your	1091	A watcher is an opaque structure that you allocate and register to record
786	interest in some event. For instance, if you want to wait for STDIN to	1092	your interest in some event. To make a concrete example, imagine you want
787	become readable, you would create an C<ev_io> watcher for that:	1093	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1094	for that:
788		1095
789	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1096	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
790	{	1097	{
791	ev_io_stop (w);	1098	ev_io_stop (w);
792	ev_unloop (loop, EVUNLOOP_ALL);	1099	ev_break (loop, EVBREAK_ALL);
793	}	1100	}
794		1101
795	struct ev_loop *loop = ev_default_loop (0);	1102	struct ev_loop *loop = ev_default_loop (0);
		1103
796	struct ev_io stdin_watcher;	1104	ev_io stdin_watcher;
		1105
797	ev_init (&stdin_watcher, my_cb);	1106	ev_init (&stdin_watcher, my_cb);
798	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1107	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
799	ev_io_start (loop, &stdin_watcher);	1108	ev_io_start (loop, &stdin_watcher);
		1109
800	ev_loop (loop, 0);	1110	ev_run (loop, 0);
801		1111
802	As you can see, you are responsible for allocating the memory for your	1112	As you can see, you are responsible for allocating the memory for your
803	watcher structures (and it is usually a bad idea to do this on the stack,	1113	watcher structures (and it is I<usually> a bad idea to do this on the
804	although this can sometimes be quite valid).	1114	stack).
805		1115
		1116	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1117	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1118
806	Each watcher structure must be initialised by a call to C<ev_init	1119	Each watcher structure must be initialised by a call to C<ev_init (watcher
807	(watcher *, callback)>, which expects a callback to be provided. This	1120	*, callback)>, which expects a callback to be provided. This callback is
808	callback gets invoked each time the event occurs (or, in the case of I/O	1121	invoked each time the event occurs (or, in the case of I/O watchers, each
809	watchers, each time the event loop detects that the file descriptor given	1122	time the event loop detects that the file descriptor given is readable
810	is readable and/or writable).	1123	and/or writable).
811		1124
812	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1125	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
813	with arguments specific to this watcher type. There is also a macro	1126	macro to configure it, with arguments specific to the watcher type. There
814	to combine initialisation and setting in one call: C<< ev_<type>_init	1127	is also a macro to combine initialisation and setting in one call: C<<
815	(watcher *, callback, ...) >>.	1128	ev_TYPE_init (watcher *, callback, ...) >>.
816		1129
817	To make the watcher actually watch out for events, you have to start it	1130	To make the watcher actually watch out for events, you have to start it
818	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1131	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
819	*) >>), and you can stop watching for events at any time by calling the	1132	*) >>), and you can stop watching for events at any time by calling the
820	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1133	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
821		1134
822	As long as your watcher is active (has been started but not stopped) you	1135	As long as your watcher is active (has been started but not stopped) you
823	must not touch the values stored in it. Most specifically you must never	1136	must not touch the values stored in it. Most specifically you must never
824	reinitialise it or call its C<set> macro.	1137	reinitialise it or call its C<ev_TYPE_set> macro.
825		1138
826	Each and every callback receives the event loop pointer as first, the	1139	Each and every callback receives the event loop pointer as first, the
827	registered watcher structure as second, and a bitset of received events as	1140	registered watcher structure as second, and a bitset of received events as
828	third argument.	1141	third argument.
829		1142
…		…
838	=item C<EV_WRITE>	1151	=item C<EV_WRITE>
839		1152
840	The file descriptor in the C<ev_io> watcher has become readable and/or	1153	The file descriptor in the C<ev_io> watcher has become readable and/or
841	writable.	1154	writable.
842		1155
843	=item C<EV_TIMEOUT>	1156	=item C<EV_TIMER>
844		1157
845	The C<ev_timer> watcher has timed out.	1158	The C<ev_timer> watcher has timed out.
846		1159
847	=item C<EV_PERIODIC>	1160	=item C<EV_PERIODIC>
848		1161
…		…
866		1179
867	=item C<EV_PREPARE>	1180	=item C<EV_PREPARE>
868		1181
869	=item C<EV_CHECK>	1182	=item C<EV_CHECK>
870		1183
871	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1184	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
872	to gather new events, and all C<ev_check> watchers are invoked just after	1185	gather new events, and all C<ev_check> watchers are queued (not invoked)
873	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1186	just after C<ev_run> has gathered them, but before it queues any callbacks
		1187	for any received events. That means C<ev_prepare> watchers are the last
		1188	watchers invoked before the event loop sleeps or polls for new events, and
		1189	C<ev_check> watchers will be invoked before any other watchers of the same
		1190	or lower priority within an event loop iteration.
		1191
874	received events. Callbacks of both watcher types can start and stop as	1192	Callbacks of both watcher types can start and stop as many watchers as
875	many watchers as they want, and all of them will be taken into account	1193	they want, and all of them will be taken into account (for example, a
876	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1194	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
877	C<ev_loop> from blocking).	1195	blocking).
878		1196
879	=item C<EV_EMBED>	1197	=item C<EV_EMBED>
880		1198
881	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1199	The embedded event loop specified in the C<ev_embed> watcher needs attention.
882		1200
883	=item C<EV_FORK>	1201	=item C<EV_FORK>
884		1202
885	The event loop has been resumed in the child process after fork (see	1203	The event loop has been resumed in the child process after fork (see
886	C<ev_fork>).	1204	C<ev_fork>).
887		1205
		1206	=item C<EV_CLEANUP>
		1207
		1208	The event loop is about to be destroyed (see C<ev_cleanup>).
		1209
888	=item C<EV_ASYNC>	1210	=item C<EV_ASYNC>
889		1211
890	The given async watcher has been asynchronously notified (see C<ev_async>).	1212	The given async watcher has been asynchronously notified (see C<ev_async>).
		1213
		1214	=item C<EV_CUSTOM>
		1215
		1216	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1217	by libev users to signal watchers (e.g. via C<ev_feed_event>).
891		1218
892	=item C<EV_ERROR>	1219	=item C<EV_ERROR>
893		1220
894	An unspecified error has occurred, the watcher has been stopped. This might	1221	An unspecified error has occurred, the watcher has been stopped. This might
895	happen because the watcher could not be properly started because libev	1222	happen because the watcher could not be properly started because libev
896	ran out of memory, a file descriptor was found to be closed or any other	1223	ran out of memory, a file descriptor was found to be closed or any other
		1224	problem. Libev considers these application bugs.
		1225
897	problem. You best act on it by reporting the problem and somehow coping	1226	You best act on it by reporting the problem and somehow coping with the
898	with the watcher being stopped.	1227	watcher being stopped. Note that well-written programs should not receive
		1228	an error ever, so when your watcher receives it, this usually indicates a
		1229	bug in your program.
899		1230
900	Libev will usually signal a few "dummy" events together with an error, for	1231	Libev will usually signal a few "dummy" events together with an error, for
901	example it might indicate that a fd is readable or writable, and if your	1232	example it might indicate that a fd is readable or writable, and if your
902	callbacks is well-written it can just attempt the operation and cope with	1233	callbacks is well-written it can just attempt the operation and cope with
903	the error from read() or write(). This will not work in multi-threaded	1234	the error from read() or write(). This will not work in multi-threaded
…		…
906		1237
907	=back	1238	=back
908		1239
909	=head2 GENERIC WATCHER FUNCTIONS	1240	=head2 GENERIC WATCHER FUNCTIONS
910		1241
911	In the following description, C<TYPE> stands for the watcher type,
912	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
913
914	=over 4	1242	=over 4
915		1243
916	=item C<ev_init> (ev_TYPE *watcher, callback)	1244	=item C<ev_init> (ev_TYPE *watcher, callback)
917		1245
918	This macro initialises the generic portion of a watcher. The contents	1246	This macro initialises the generic portion of a watcher. The contents
…		…
923	which rolls both calls into one.	1251	which rolls both calls into one.
924		1252
925	You can reinitialise a watcher at any time as long as it has been stopped	1253	You can reinitialise a watcher at any time as long as it has been stopped
926	(or never started) and there are no pending events outstanding.	1254	(or never started) and there are no pending events outstanding.
927		1255
928	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1256	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
929	int revents)>.	1257	int revents)>.
930		1258
931	Example: Initialise an C<ev_io> watcher in two steps.	1259	Example: Initialise an C<ev_io> watcher in two steps.
932		1260
933	ev_io w;	1261	ev_io w;
934	ev_init (&w, my_cb);	1262	ev_init (&w, my_cb);
935	ev_io_set (&w, STDIN_FILENO, EV_READ);	1263	ev_io_set (&w, STDIN_FILENO, EV_READ);
936		1264
937	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1265	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
938		1266
939	This macro initialises the type-specific parts of a watcher. You need to	1267	This macro initialises the type-specific parts of a watcher. You need to
940	call C<ev_init> at least once before you call this macro, but you can	1268	call C<ev_init> at least once before you call this macro, but you can
941	call C<ev_TYPE_set> any number of times. You must not, however, call this	1269	call C<ev_TYPE_set> any number of times. You must not, however, call this
942	macro on a watcher that is active (it can be pending, however, which is a	1270	macro on a watcher that is active (it can be pending, however, which is a
…		…
955		1283
956	Example: Initialise and set an C<ev_io> watcher in one step.	1284	Example: Initialise and set an C<ev_io> watcher in one step.
957		1285
958	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);	1286	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
959		1287
960	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1288	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
961		1289
962	Starts (activates) the given watcher. Only active watchers will receive	1290	Starts (activates) the given watcher. Only active watchers will receive
963	events. If the watcher is already active nothing will happen.	1291	events. If the watcher is already active nothing will happen.
964		1292
965	Example: Start the C<ev_io> watcher that is being abused as example in this	1293	Example: Start the C<ev_io> watcher that is being abused as example in this
966	whole section.	1294	whole section.
967		1295
968	ev_io_start (EV_DEFAULT_UC, &w);	1296	ev_io_start (EV_DEFAULT_UC, &w);
969		1297
970	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1298	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
971		1299
972	Stops the given watcher again (if active) and clears the pending	1300	Stops the given watcher if active, and clears the pending status (whether
		1301	the watcher was active or not).
		1302
973	status. It is possible that stopped watchers are pending (for example,	1303	It is possible that stopped watchers are pending - for example,
974	non-repeating timers are being stopped when they become pending), but	1304	non-repeating timers are being stopped when they become pending - but
975	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1305	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
976	you want to free or reuse the memory used by the watcher it is therefore a	1306	pending. If you want to free or reuse the memory used by the watcher it is
977	good idea to always call its C<ev_TYPE_stop> function.	1307	therefore a good idea to always call its C<ev_TYPE_stop> function.
978		1308
979	=item bool ev_is_active (ev_TYPE *watcher)	1309	=item bool ev_is_active (ev_TYPE *watcher)
980		1310
981	Returns a true value iff the watcher is active (i.e. it has been started	1311	Returns a true value iff the watcher is active (i.e. it has been started
982	and not yet been stopped). As long as a watcher is active you must not modify	1312	and not yet been stopped). As long as a watcher is active you must not modify
…		…
993		1323
994	=item callback ev_cb (ev_TYPE *watcher)	1324	=item callback ev_cb (ev_TYPE *watcher)
995		1325
996	Returns the callback currently set on the watcher.	1326	Returns the callback currently set on the watcher.
997		1327
998	=item ev_cb_set (ev_TYPE *watcher, callback)	1328	=item ev_set_cb (ev_TYPE *watcher, callback)
999		1329
1000	Change the callback. You can change the callback at virtually any time	1330	Change the callback. You can change the callback at virtually any time
1001	(modulo threads).	1331	(modulo threads).
1002		1332
1003	=item ev_set_priority (ev_TYPE *watcher, priority)	1333	=item ev_set_priority (ev_TYPE *watcher, int priority)
1004		1334
1005	=item int ev_priority (ev_TYPE *watcher)	1335	=item int ev_priority (ev_TYPE *watcher)
1006		1336
1007	Set and query the priority of the watcher. The priority is a small	1337	Set and query the priority of the watcher. The priority is a small
1008	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1338	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1009	(default: C<-2>). Pending watchers with higher priority will be invoked	1339	(default: C<-2>). Pending watchers with higher priority will be invoked
1010	before watchers with lower priority, but priority will not keep watchers	1340	before watchers with lower priority, but priority will not keep watchers
1011	from being executed (except for C<ev_idle> watchers).	1341	from being executed (except for C<ev_idle> watchers).
1012		1342
1013	This means that priorities are I<only> used for ordering callback
1014	invocation after new events have been received. This is useful, for
1015	example, to reduce latency after idling, or more often, to bind two
1016	watchers on the same event and make sure one is called first.
1017
1018	If you need to suppress invocation when higher priority events are pending	1343	If you need to suppress invocation when higher priority events are pending
1019	you need to look at C<ev_idle> watchers, which provide this functionality.	1344	you need to look at C<ev_idle> watchers, which provide this functionality.
1020		1345
1021	You I<must not> change the priority of a watcher as long as it is active or	1346	You I<must not> change the priority of a watcher as long as it is active or
1022	pending.	1347	pending.
1023		1348
		1349	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1350	fine, as long as you do not mind that the priority value you query might
		1351	or might not have been clamped to the valid range.
		1352
1024	The default priority used by watchers when no priority has been set is	1353	The default priority used by watchers when no priority has been set is
1025	always C<0>, which is supposed to not be too high and not be too low :).	1354	always C<0>, which is supposed to not be too high and not be too low :).
1026		1355
1027	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1356	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1028	fine, as long as you do not mind that the priority value you query might	1357	priorities.
1029	or might not have been adjusted to be within valid range.
1030		1358
1031	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1359	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1032		1360
1033	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1361	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1034	C<loop> nor C<revents> need to be valid as long as the watcher callback	1362	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1042	watcher isn't pending it does nothing and returns C<0>.	1370	watcher isn't pending it does nothing and returns C<0>.
1043		1371
1044	Sometimes it can be useful to "poll" a watcher instead of waiting for its	1372	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1045	callback to be invoked, which can be accomplished with this function.	1373	callback to be invoked, which can be accomplished with this function.
1046		1374
		1375	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1376
		1377	Feeds the given event set into the event loop, as if the specified event
		1378	had happened for the specified watcher (which must be a pointer to an
		1379	initialised but not necessarily started event watcher). Obviously you must
		1380	not free the watcher as long as it has pending events.
		1381
		1382	Stopping the watcher, letting libev invoke it, or calling
		1383	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1384	not started in the first place.
		1385
		1386	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1387	functions that do not need a watcher.
		1388
1047	=back	1389	=back
1048		1390
		1391	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1392	OWN COMPOSITE WATCHERS> idioms.
1049		1393
1050	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1394	=head2 WATCHER STATES
1051		1395
1052	Each watcher has, by default, a member C<void *data> that you can change	1396	There are various watcher states mentioned throughout this manual -
1053	and read at any time: libev will completely ignore it. This can be used	1397	active, pending and so on. In this section these states and the rules to
1054	to associate arbitrary data with your watcher. If you need more data and	1398	transition between them will be described in more detail - and while these
1055	don't want to allocate memory and store a pointer to it in that data	1399	rules might look complicated, they usually do "the right thing".
1056	member, you can also "subclass" the watcher type and provide your own
1057	data:
1058		1400
1059	struct my_io	1401	=over 4
		1402
		1403	=item initialised
		1404
		1405	Before a watcher can be registered with the event loop it has to be
		1406	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1407	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1408
		1409	In this state it is simply some block of memory that is suitable for
		1410	use in an event loop. It can be moved around, freed, reused etc. at
		1411	will - as long as you either keep the memory contents intact, or call
		1412	C<ev_TYPE_init> again.
		1413
		1414	=item started/running/active
		1415
		1416	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1417	property of the event loop, and is actively waiting for events. While in
		1418	this state it cannot be accessed (except in a few documented ways), moved,
		1419	freed or anything else - the only legal thing is to keep a pointer to it,
		1420	and call libev functions on it that are documented to work on active watchers.
		1421
		1422	=item pending
		1423
		1424	If a watcher is active and libev determines that an event it is interested
		1425	in has occurred (such as a timer expiring), it will become pending. It will
		1426	stay in this pending state until either it is stopped or its callback is
		1427	about to be invoked, so it is not normally pending inside the watcher
		1428	callback.
		1429
		1430	The watcher might or might not be active while it is pending (for example,
		1431	an expired non-repeating timer can be pending but no longer active). If it
		1432	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1433	but it is still property of the event loop at this time, so cannot be
		1434	moved, freed or reused. And if it is active the rules described in the
		1435	previous item still apply.
		1436
		1437	It is also possible to feed an event on a watcher that is not active (e.g.
		1438	via C<ev_feed_event>), in which case it becomes pending without being
		1439	active.
		1440
		1441	=item stopped
		1442
		1443	A watcher can be stopped implicitly by libev (in which case it might still
		1444	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1445	latter will clear any pending state the watcher might be in, regardless
		1446	of whether it was active or not, so stopping a watcher explicitly before
		1447	freeing it is often a good idea.
		1448
		1449	While stopped (and not pending) the watcher is essentially in the
		1450	initialised state, that is, it can be reused, moved, modified in any way
		1451	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1452	it again).
		1453
		1454	=back
		1455
		1456	=head2 WATCHER PRIORITY MODELS
		1457
		1458	Many event loops support I<watcher priorities>, which are usually small
		1459	integers that influence the ordering of event callback invocation
		1460	between watchers in some way, all else being equal.
		1461
		1462	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1463	description for the more technical details such as the actual priority
		1464	range.
		1465
		1466	There are two common ways how these these priorities are being interpreted
		1467	by event loops:
		1468
		1469	In the more common lock-out model, higher priorities "lock out" invocation
		1470	of lower priority watchers, which means as long as higher priority
		1471	watchers receive events, lower priority watchers are not being invoked.
		1472
		1473	The less common only-for-ordering model uses priorities solely to order
		1474	callback invocation within a single event loop iteration: Higher priority
		1475	watchers are invoked before lower priority ones, but they all get invoked
		1476	before polling for new events.
		1477
		1478	Libev uses the second (only-for-ordering) model for all its watchers
		1479	except for idle watchers (which use the lock-out model).
		1480
		1481	The rationale behind this is that implementing the lock-out model for
		1482	watchers is not well supported by most kernel interfaces, and most event
		1483	libraries will just poll for the same events again and again as long as
		1484	their callbacks have not been executed, which is very inefficient in the
		1485	common case of one high-priority watcher locking out a mass of lower
		1486	priority ones.
		1487
		1488	Static (ordering) priorities are most useful when you have two or more
		1489	watchers handling the same resource: a typical usage example is having an
		1490	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1491	timeouts. Under load, data might be received while the program handles
		1492	other jobs, but since timers normally get invoked first, the timeout
		1493	handler will be executed before checking for data. In that case, giving
		1494	the timer a lower priority than the I/O watcher ensures that I/O will be
		1495	handled first even under adverse conditions (which is usually, but not
		1496	always, what you want).
		1497
		1498	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1499	will only be executed when no same or higher priority watchers have
		1500	received events, they can be used to implement the "lock-out" model when
		1501	required.
		1502
		1503	For example, to emulate how many other event libraries handle priorities,
		1504	you can associate an C<ev_idle> watcher to each such watcher, and in
		1505	the normal watcher callback, you just start the idle watcher. The real
		1506	processing is done in the idle watcher callback. This causes libev to
		1507	continuously poll and process kernel event data for the watcher, but when
		1508	the lock-out case is known to be rare (which in turn is rare :), this is
		1509	workable.
		1510
		1511	Usually, however, the lock-out model implemented that way will perform
		1512	miserably under the type of load it was designed to handle. In that case,
		1513	it might be preferable to stop the real watcher before starting the
		1514	idle watcher, so the kernel will not have to process the event in case
		1515	the actual processing will be delayed for considerable time.
		1516
		1517	Here is an example of an I/O watcher that should run at a strictly lower
		1518	priority than the default, and which should only process data when no
		1519	other events are pending:
		1520
		1521	ev_idle idle; // actual processing watcher
		1522	ev_io io; // actual event watcher
		1523
		1524	static void
		1525	io_cb (EV_P_ ev_io *w, int revents)
1060	{	1526	{
1061	struct ev_io io;	1527	// stop the I/O watcher, we received the event, but
1062	int otherfd;	1528	// are not yet ready to handle it.
1063	void *somedata;	1529	ev_io_stop (EV_A_ w);
1064	struct whatever *mostinteresting;	1530
		1531	// start the idle watcher to handle the actual event.
		1532	// it will not be executed as long as other watchers
		1533	// with the default priority are receiving events.
		1534	ev_idle_start (EV_A_ &idle);
1065	};	1535	}
1066		1536
1067	...	1537	static void
1068	struct my_io w;	1538	idle_cb (EV_P_ ev_idle *w, int revents)
1069	ev_io_init (&w.io, my_cb, fd, EV_READ);
1070
1071	And since your callback will be called with a pointer to the watcher, you
1072	can cast it back to your own type:
1073
1074	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
1075	{	1539	{
1076	struct my_io *w = (struct my_io *)w_;	1540	// actual processing
1077	...	1541	read (STDIN_FILENO, ...);
		1542
		1543	// have to start the I/O watcher again, as
		1544	// we have handled the event
		1545	ev_io_start (EV_P_ &io);
1078	}	1546	}
1079		1547
1080	More interesting and less C-conformant ways of casting your callback type	1548	// initialisation
1081	instead have been omitted.	1549	ev_idle_init (&idle, idle_cb);
		1550	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1551	ev_io_start (EV_DEFAULT_ &io);
1082		1552
1083	Another common scenario is to use some data structure with multiple	1553	In the "real" world, it might also be beneficial to start a timer, so that
1084	embedded watchers:	1554	low-priority connections can not be locked out forever under load. This
1085		1555	enables your program to keep a lower latency for important connections
1086	struct my_biggy	1556	during short periods of high load, while not completely locking out less
1087	{	1557	important ones.
1088	int some_data;
1089	ev_timer t1;
1090	ev_timer t2;
1091	}
1092
1093	In this case getting the pointer to C<my_biggy> is a bit more
1094	complicated: Either you store the address of your C<my_biggy> struct
1095	in the C<data> member of the watcher (for woozies), or you need to use
1096	some pointer arithmetic using C<offsetof> inside your watchers (for real
1097	programmers):
1098
1099	#include <stddef.h>
1100
1101	static void
1102	t1_cb (EV_P_ struct ev_timer *w, int revents)
1103	{
1104	struct my_biggy big = (struct my_biggy *
1105	(((char *)w) - offsetof (struct my_biggy, t1));
1106	}
1107
1108	static void
1109	t2_cb (EV_P_ struct ev_timer *w, int revents)
1110	{
1111	struct my_biggy big = (struct my_biggy *
1112	(((char *)w) - offsetof (struct my_biggy, t2));
1113	}
1114		1558
1115		1559
1116	=head1 WATCHER TYPES	1560	=head1 WATCHER TYPES
1117		1561
1118	This section describes each watcher in detail, but will not repeat	1562	This section describes each watcher in detail, but will not repeat
…		…
1142	In general you can register as many read and/or write event watchers per	1586	In general you can register as many read and/or write event watchers per
1143	fd as you want (as long as you don't confuse yourself). Setting all file	1587	fd as you want (as long as you don't confuse yourself). Setting all file
1144	descriptors to non-blocking mode is also usually a good idea (but not	1588	descriptors to non-blocking mode is also usually a good idea (but not
1145	required if you know what you are doing).	1589	required if you know what you are doing).
1146		1590
1147	If you cannot use non-blocking mode, then force the use of a
1148	known-to-be-good backend (at the time of this writing, this includes only
1149	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
1150
1151	Another thing you have to watch out for is that it is quite easy to	1591	Another thing you have to watch out for is that it is quite easy to
1152	receive "spurious" readiness notifications, that is your callback might	1592	receive "spurious" readiness notifications, that is, your callback might
1153	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1593	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1154	because there is no data. Not only are some backends known to create a	1594	because there is no data. It is very easy to get into this situation even
1155	lot of those (for example Solaris ports), it is very easy to get into	1595	with a relatively standard program structure. Thus it is best to always
1156	this situation even with a relatively standard program structure. Thus	1596	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1157	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1158	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1597	preferable to a program hanging until some data arrives.
1159		1598
1160	If you cannot run the fd in non-blocking mode (for example you should	1599	If you cannot run the fd in non-blocking mode (for example you should
1161	not play around with an Xlib connection), then you have to separately	1600	not play around with an Xlib connection), then you have to separately
1162	re-test whether a file descriptor is really ready with a known-to-be good	1601	re-test whether a file descriptor is really ready with a known-to-be good
1163	interface such as poll (fortunately in our Xlib example, Xlib already	1602	interface such as poll (fortunately in the case of Xlib, it already does
1164	does this on its own, so its quite safe to use). Some people additionally	1603	this on its own, so its quite safe to use). Some people additionally
1165	use C<SIGALRM> and an interval timer, just to be sure you won't block	1604	use C<SIGALRM> and an interval timer, just to be sure you won't block
1166	indefinitely.	1605	indefinitely.
1167		1606
1168	But really, best use non-blocking mode.	1607	But really, best use non-blocking mode.
1169		1608
…		…
1197		1636
1198	There is no workaround possible except not registering events	1637	There is no workaround possible except not registering events
1199	for potentially C<dup ()>'ed file descriptors, or to resort to	1638	for potentially C<dup ()>'ed file descriptors, or to resort to
1200	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1639	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1201		1640
		1641	=head3 The special problem of files
		1642
		1643	Many people try to use C<select> (or libev) on file descriptors
		1644	representing files, and expect it to become ready when their program
		1645	doesn't block on disk accesses (which can take a long time on their own).
		1646
		1647	However, this cannot ever work in the "expected" way - you get a readiness
		1648	notification as soon as the kernel knows whether and how much data is
		1649	there, and in the case of open files, that's always the case, so you
		1650	always get a readiness notification instantly, and your read (or possibly
		1651	write) will still block on the disk I/O.
		1652
		1653	Another way to view it is that in the case of sockets, pipes, character
		1654	devices and so on, there is another party (the sender) that delivers data
		1655	on its own, but in the case of files, there is no such thing: the disk
		1656	will not send data on its own, simply because it doesn't know what you
		1657	wish to read - you would first have to request some data.
		1658
		1659	Since files are typically not-so-well supported by advanced notification
		1660	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1661	to files, even though you should not use it. The reason for this is
		1662	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1663	usually a tty, often a pipe, but also sometimes files or special devices
		1664	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1665	F</dev/urandom>), and even though the file might better be served with
		1666	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1667	it "just works" instead of freezing.
		1668
		1669	So avoid file descriptors pointing to files when you know it (e.g. use
		1670	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1671	when you rarely read from a file instead of from a socket, and want to
		1672	reuse the same code path.
		1673
1202	=head3 The special problem of fork	1674	=head3 The special problem of fork
1203		1675
1204	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1676	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1205	useless behaviour. Libev fully supports fork, but needs to be told about	1677	useless behaviour. Libev fully supports fork, but needs to be told about
1206	it in the child.	1678	it in the child if you want to continue to use it in the child.
1207		1679
1208	To support fork in your programs, you either have to call	1680	To support fork in your child processes, you have to call C<ev_loop_fork
1209	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1681	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1210	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1682	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1211	C<EVBACKEND_POLL>.
1212		1683
1213	=head3 The special problem of SIGPIPE	1684	=head3 The special problem of SIGPIPE
1214		1685
1215	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1686	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1216	when writing to a pipe whose other end has been closed, your program gets	1687	when writing to a pipe whose other end has been closed, your program gets
…		…
1219		1690
1220	So when you encounter spurious, unexplained daemon exits, make sure you	1691	So when you encounter spurious, unexplained daemon exits, make sure you
1221	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1692	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1222	somewhere, as that would have given you a big clue).	1693	somewhere, as that would have given you a big clue).
1223		1694
		1695	=head3 The special problem of accept()ing when you can't
		1696
		1697	Many implementations of the POSIX C<accept> function (for example,
		1698	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1699	connection from the pending queue in all error cases.
		1700
		1701	For example, larger servers often run out of file descriptors (because
		1702	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1703	rejecting the connection, leading to libev signalling readiness on
		1704	the next iteration again (the connection still exists after all), and
		1705	typically causing the program to loop at 100% CPU usage.
		1706
		1707	Unfortunately, the set of errors that cause this issue differs between
		1708	operating systems, there is usually little the app can do to remedy the
		1709	situation, and no known thread-safe method of removing the connection to
		1710	cope with overload is known (to me).
		1711
		1712	One of the easiest ways to handle this situation is to just ignore it
		1713	- when the program encounters an overload, it will just loop until the
		1714	situation is over. While this is a form of busy waiting, no OS offers an
		1715	event-based way to handle this situation, so it's the best one can do.
		1716
		1717	A better way to handle the situation is to log any errors other than
		1718	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1719	messages, and continue as usual, which at least gives the user an idea of
		1720	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1721	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1722	usage.
		1723
		1724	If your program is single-threaded, then you could also keep a dummy file
		1725	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1726	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1727	close that fd, and create a new dummy fd. This will gracefully refuse
		1728	clients under typical overload conditions.
		1729
		1730	The last way to handle it is to simply log the error and C<exit>, as
		1731	is often done with C<malloc> failures, but this results in an easy
		1732	opportunity for a DoS attack.
1224		1733
1225	=head3 Watcher-Specific Functions	1734	=head3 Watcher-Specific Functions
1226		1735
1227	=over 4	1736	=over 4
1228		1737
…		…
1249	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1758	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1250	readable, but only once. Since it is likely line-buffered, you could	1759	readable, but only once. Since it is likely line-buffered, you could
1251	attempt to read a whole line in the callback.	1760	attempt to read a whole line in the callback.
1252		1761
1253	static void	1762	static void
1254	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1763	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1255	{	1764	{
1256	ev_io_stop (loop, w);	1765	ev_io_stop (loop, w);
1257	.. read from stdin here (or from w->fd) and handle any I/O errors	1766	.. read from stdin here (or from w->fd) and handle any I/O errors
1258	}	1767	}
1259		1768
1260	...	1769	...
1261	struct ev_loop *loop = ev_default_init (0);	1770	struct ev_loop *loop = ev_default_init (0);
1262	struct ev_io stdin_readable;	1771	ev_io stdin_readable;
1263	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1772	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1264	ev_io_start (loop, &stdin_readable);	1773	ev_io_start (loop, &stdin_readable);
1265	ev_loop (loop, 0);	1774	ev_run (loop, 0);
1266		1775
1267		1776
1268	=head2 C<ev_timer> - relative and optionally repeating timeouts	1777	=head2 C<ev_timer> - relative and optionally repeating timeouts
1269		1778
1270	Timer watchers are simple relative timers that generate an event after a	1779	Timer watchers are simple relative timers that generate an event after a
…		…
1275	year, it will still time out after (roughly) one hour. "Roughly" because	1784	year, it will still time out after (roughly) one hour. "Roughly" because
1276	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1785	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1277	monotonic clock option helps a lot here).	1786	monotonic clock option helps a lot here).
1278		1787
1279	The callback is guaranteed to be invoked only I<after> its timeout has	1788	The callback is guaranteed to be invoked only I<after> its timeout has
1280	passed, but if multiple timers become ready during the same loop iteration	1789	passed (not I<at>, so on systems with very low-resolution clocks this
1281	then order of execution is undefined.	1790	might introduce a small delay, see "the special problem of being too
		1791	early", below). If multiple timers become ready during the same loop
		1792	iteration then the ones with earlier time-out values are invoked before
		1793	ones of the same priority with later time-out values (but this is no
		1794	longer true when a callback calls C<ev_run> recursively).
		1795
		1796	=head3 Be smart about timeouts
		1797
		1798	Many real-world problems involve some kind of timeout, usually for error
		1799	recovery. A typical example is an HTTP request - if the other side hangs,
		1800	you want to raise some error after a while.
		1801
		1802	What follows are some ways to handle this problem, from obvious and
		1803	inefficient to smart and efficient.
		1804
		1805	In the following, a 60 second activity timeout is assumed - a timeout that
		1806	gets reset to 60 seconds each time there is activity (e.g. each time some
		1807	data or other life sign was received).
		1808
		1809	=over 4
		1810
		1811	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1812
		1813	This is the most obvious, but not the most simple way: In the beginning,
		1814	start the watcher:
		1815
		1816	ev_timer_init (timer, callback, 60., 0.);
		1817	ev_timer_start (loop, timer);
		1818
		1819	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1820	and start it again:
		1821
		1822	ev_timer_stop (loop, timer);
		1823	ev_timer_set (timer, 60., 0.);
		1824	ev_timer_start (loop, timer);
		1825
		1826	This is relatively simple to implement, but means that each time there is
		1827	some activity, libev will first have to remove the timer from its internal
		1828	data structure and then add it again. Libev tries to be fast, but it's
		1829	still not a constant-time operation.
		1830
		1831	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1832
		1833	This is the easiest way, and involves using C<ev_timer_again> instead of
		1834	C<ev_timer_start>.
		1835
		1836	To implement this, configure an C<ev_timer> with a C<repeat> value
		1837	of C<60> and then call C<ev_timer_again> at start and each time you
		1838	successfully read or write some data. If you go into an idle state where
		1839	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1840	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1841
		1842	That means you can ignore both the C<ev_timer_start> function and the
		1843	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1844	member and C<ev_timer_again>.
		1845
		1846	At start:
		1847
		1848	ev_init (timer, callback);
		1849	timer->repeat = 60.;
		1850	ev_timer_again (loop, timer);
		1851
		1852	Each time there is some activity:
		1853
		1854	ev_timer_again (loop, timer);
		1855
		1856	It is even possible to change the time-out on the fly, regardless of
		1857	whether the watcher is active or not:
		1858
		1859	timer->repeat = 30.;
		1860	ev_timer_again (loop, timer);
		1861
		1862	This is slightly more efficient then stopping/starting the timer each time
		1863	you want to modify its timeout value, as libev does not have to completely
		1864	remove and re-insert the timer from/into its internal data structure.
		1865
		1866	It is, however, even simpler than the "obvious" way to do it.
		1867
		1868	=item 3. Let the timer time out, but then re-arm it as required.
		1869
		1870	This method is more tricky, but usually most efficient: Most timeouts are
		1871	relatively long compared to the intervals between other activity - in
		1872	our example, within 60 seconds, there are usually many I/O events with
		1873	associated activity resets.
		1874
		1875	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1876	but remember the time of last activity, and check for a real timeout only
		1877	within the callback:
		1878
		1879	ev_tstamp timeout = 60.;
		1880	ev_tstamp last_activity; // time of last activity
		1881	ev_timer timer;
		1882
		1883	static void
		1884	callback (EV_P_ ev_timer *w, int revents)
		1885	{
		1886	// calculate when the timeout would happen
		1887	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1888
		1889	// if negative, it means we the timeout already occurred
		1890	if (after < 0.)
		1891	{
		1892	// timeout occurred, take action
		1893	}
		1894	else
		1895	{
		1896	// callback was invoked, but there was some recent
		1897	// activity. simply restart the timer to time out
		1898	// after "after" seconds, which is the earliest time
		1899	// the timeout can occur.
		1900	ev_timer_set (w, after, 0.);
		1901	ev_timer_start (EV_A_ w);
		1902	}
		1903	}
		1904
		1905	To summarise the callback: first calculate in how many seconds the
		1906	timeout will occur (by calculating the absolute time when it would occur,
		1907	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1908	(EV_A)> from that).
		1909
		1910	If this value is negative, then we are already past the timeout, i.e. we
		1911	timed out, and need to do whatever is needed in this case.
		1912
		1913	Otherwise, we now the earliest time at which the timeout would trigger,
		1914	and simply start the timer with this timeout value.
		1915
		1916	In other words, each time the callback is invoked it will check whether
		1917	the timeout occurred. If not, it will simply reschedule itself to check
		1918	again at the earliest time it could time out. Rinse. Repeat.
		1919
		1920	This scheme causes more callback invocations (about one every 60 seconds
		1921	minus half the average time between activity), but virtually no calls to
		1922	libev to change the timeout.
		1923
		1924	To start the machinery, simply initialise the watcher and set
		1925	C<last_activity> to the current time (meaning there was some activity just
		1926	now), then call the callback, which will "do the right thing" and start
		1927	the timer:
		1928
		1929	last_activity = ev_now (EV_A);
		1930	ev_init (&timer, callback);
		1931	callback (EV_A_ &timer, 0);
		1932
		1933	When there is some activity, simply store the current time in
		1934	C<last_activity>, no libev calls at all:
		1935
		1936	if (activity detected)
		1937	last_activity = ev_now (EV_A);
		1938
		1939	When your timeout value changes, then the timeout can be changed by simply
		1940	providing a new value, stopping the timer and calling the callback, which
		1941	will again do the right thing (for example, time out immediately :).
		1942
		1943	timeout = new_value;
		1944	ev_timer_stop (EV_A_ &timer);
		1945	callback (EV_A_ &timer, 0);
		1946
		1947	This technique is slightly more complex, but in most cases where the
		1948	time-out is unlikely to be triggered, much more efficient.
		1949
		1950	=item 4. Wee, just use a double-linked list for your timeouts.
		1951
		1952	If there is not one request, but many thousands (millions...), all
		1953	employing some kind of timeout with the same timeout value, then one can
		1954	do even better:
		1955
		1956	When starting the timeout, calculate the timeout value and put the timeout
		1957	at the I<end> of the list.
		1958
		1959	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1960	the list is expected to fire (for example, using the technique #3).
		1961
		1962	When there is some activity, remove the timer from the list, recalculate
		1963	the timeout, append it to the end of the list again, and make sure to
		1964	update the C<ev_timer> if it was taken from the beginning of the list.
		1965
		1966	This way, one can manage an unlimited number of timeouts in O(1) time for
		1967	starting, stopping and updating the timers, at the expense of a major
		1968	complication, and having to use a constant timeout. The constant timeout
		1969	ensures that the list stays sorted.
		1970
		1971	=back
		1972
		1973	So which method the best?
		1974
		1975	Method #2 is a simple no-brain-required solution that is adequate in most
		1976	situations. Method #3 requires a bit more thinking, but handles many cases
		1977	better, and isn't very complicated either. In most case, choosing either
		1978	one is fine, with #3 being better in typical situations.
		1979
		1980	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1981	rather complicated, but extremely efficient, something that really pays
		1982	off after the first million or so of active timers, i.e. it's usually
		1983	overkill :)
		1984
		1985	=head3 The special problem of being too early
		1986
		1987	If you ask a timer to call your callback after three seconds, then
		1988	you expect it to be invoked after three seconds - but of course, this
		1989	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1990	guaranteed to any precision by libev - imagine somebody suspending the
		1991	process with a STOP signal for a few hours for example.
		1992
		1993	So, libev tries to invoke your callback as soon as possible I<after> the
		1994	delay has occurred, but cannot guarantee this.
		1995
		1996	A less obvious failure mode is calling your callback too early: many event
		1997	loops compare timestamps with a "elapsed delay >= requested delay", but
		1998	this can cause your callback to be invoked much earlier than you would
		1999	expect.
		2000
		2001	To see why, imagine a system with a clock that only offers full second
		2002	resolution (think windows if you can't come up with a broken enough OS
		2003	yourself). If you schedule a one-second timer at the time 500.9, then the
		2004	event loop will schedule your timeout to elapse at a system time of 500
		2005	(500.9 truncated to the resolution) + 1, or 501.
		2006
		2007	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2008	501" and invoke the callback 0.1s after it was started, even though a
		2009	one-second delay was requested - this is being "too early", despite best
		2010	intentions.
		2011
		2012	This is the reason why libev will never invoke the callback if the elapsed
		2013	delay equals the requested delay, but only when the elapsed delay is
		2014	larger than the requested delay. In the example above, libev would only invoke
		2015	the callback at system time 502, or 1.1s after the timer was started.
		2016
		2017	So, while libev cannot guarantee that your callback will be invoked
		2018	exactly when requested, it I<can> and I<does> guarantee that the requested
		2019	delay has actually elapsed, or in other words, it always errs on the "too
		2020	late" side of things.
1282		2021
1283	=head3 The special problem of time updates	2022	=head3 The special problem of time updates
1284		2023
1285	Establishing the current time is a costly operation (it usually takes at	2024	Establishing the current time is a costly operation (it usually takes
1286	least two system calls): EV therefore updates its idea of the current	2025	at least one system call): EV therefore updates its idea of the current
1287	time only before and after C<ev_loop> collects new events, which causes a	2026	time only before and after C<ev_run> collects new events, which causes a
1288	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2027	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1289	lots of events in one iteration.	2028	lots of events in one iteration.
1290		2029
1291	The relative timeouts are calculated relative to the C<ev_now ()>	2030	The relative timeouts are calculated relative to the C<ev_now ()>
1292	time. This is usually the right thing as this timestamp refers to the time	2031	time. This is usually the right thing as this timestamp refers to the time
…		…
1298		2037
1299	If the event loop is suspended for a long time, you can also force an	2038	If the event loop is suspended for a long time, you can also force an
1300	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2039	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1301	()>.	2040	()>.
1302		2041
		2042	=head3 The special problem of unsynchronised clocks
		2043
		2044	Modern systems have a variety of clocks - libev itself uses the normal
		2045	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2046	jumps).
		2047
		2048	Neither of these clocks is synchronised with each other or any other clock
		2049	on the system, so C<ev_time ()> might return a considerably different time
		2050	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2051	a call to C<gettimeofday> might return a second count that is one higher
		2052	than a directly following call to C<time>.
		2053
		2054	The moral of this is to only compare libev-related timestamps with
		2055	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2056	a second or so.
		2057
		2058	One more problem arises due to this lack of synchronisation: if libev uses
		2059	the system monotonic clock and you compare timestamps from C<ev_time>
		2060	or C<ev_now> from when you started your timer and when your callback is
		2061	invoked, you will find that sometimes the callback is a bit "early".
		2062
		2063	This is because C<ev_timer>s work in real time, not wall clock time, so
		2064	libev makes sure your callback is not invoked before the delay happened,
		2065	I<measured according to the real time>, not the system clock.
		2066
		2067	If your timeouts are based on a physical timescale (e.g. "time out this
		2068	connection after 100 seconds") then this shouldn't bother you as it is
		2069	exactly the right behaviour.
		2070
		2071	If you want to compare wall clock/system timestamps to your timers, then
		2072	you need to use C<ev_periodic>s, as these are based on the wall clock
		2073	time, where your comparisons will always generate correct results.
		2074
		2075	=head3 The special problems of suspended animation
		2076
		2077	When you leave the server world it is quite customary to hit machines that
		2078	can suspend/hibernate - what happens to the clocks during such a suspend?
		2079
		2080	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2081	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2082	to run until the system is suspended, but they will not advance while the
		2083	system is suspended. That means, on resume, it will be as if the program
		2084	was frozen for a few seconds, but the suspend time will not be counted
		2085	towards C<ev_timer> when a monotonic clock source is used. The real time
		2086	clock advanced as expected, but if it is used as sole clocksource, then a
		2087	long suspend would be detected as a time jump by libev, and timers would
		2088	be adjusted accordingly.
		2089
		2090	I would not be surprised to see different behaviour in different between
		2091	operating systems, OS versions or even different hardware.
		2092
		2093	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2094	time jump in the monotonic clocks and the realtime clock. If the program
		2095	is suspended for a very long time, and monotonic clock sources are in use,
		2096	then you can expect C<ev_timer>s to expire as the full suspension time
		2097	will be counted towards the timers. When no monotonic clock source is in
		2098	use, then libev will again assume a timejump and adjust accordingly.
		2099
		2100	It might be beneficial for this latter case to call C<ev_suspend>
		2101	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2102	deterministic behaviour in this case (you can do nothing against
		2103	C<SIGSTOP>).
		2104
1303	=head3 Watcher-Specific Functions and Data Members	2105	=head3 Watcher-Specific Functions and Data Members
1304		2106
1305	=over 4	2107	=over 4
1306		2108
1307	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2109	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1320	keep up with the timer (because it takes longer than those 10 seconds to	2122	keep up with the timer (because it takes longer than those 10 seconds to
1321	do stuff) the timer will not fire more than once per event loop iteration.	2123	do stuff) the timer will not fire more than once per event loop iteration.
1322		2124
1323	=item ev_timer_again (loop, ev_timer *)	2125	=item ev_timer_again (loop, ev_timer *)
1324		2126
1325	This will act as if the timer timed out and restart it again if it is	2127	This will act as if the timer timed out, and restarts it again if it is
1326	repeating. The exact semantics are:	2128	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2129	timeout to the C<repeat> value and calling C<ev_timer_start>.
1327		2130
		2131	The exact semantics are as in the following rules, all of which will be
		2132	applied to the watcher:
		2133
		2134	=over 4
		2135
1328	If the timer is pending, its pending status is cleared.	2136	=item If the timer is pending, the pending status is always cleared.
1329		2137
1330	If the timer is started but non-repeating, stop it (as if it timed out).	2138	=item If the timer is started but non-repeating, stop it (as if it timed
		2139	out, without invoking it).
1331		2140
1332	If the timer is repeating, either start it if necessary (with the	2141	=item If the timer is repeating, make the C<repeat> value the new timeout
1333	C<repeat> value), or reset the running timer to the C<repeat> value.	2142	and start the timer, if necessary.
1334		2143
1335	This sounds a bit complicated, but here is a useful and typical	2144	=back
1336	example: Imagine you have a TCP connection and you want a so-called idle
1337	timeout, that is, you want to be called when there have been, say, 60
1338	seconds of inactivity on the socket. The easiest way to do this is to
1339	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1340	C<ev_timer_again> each time you successfully read or write some data. If
1341	you go into an idle state where you do not expect data to travel on the
1342	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1343	automatically restart it if need be.
1344		2145
1345	That means you can ignore the C<after> value and C<ev_timer_start>	2146	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1346	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2147	usage example.
1347		2148
1348	ev_timer_init (timer, callback, 0., 5.);	2149	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1349	ev_timer_again (loop, timer);
1350	...
1351	timer->again = 17.;
1352	ev_timer_again (loop, timer);
1353	...
1354	timer->again = 10.;
1355	ev_timer_again (loop, timer);
1356		2150
1357	This is more slightly efficient then stopping/starting the timer each time	2151	Returns the remaining time until a timer fires. If the timer is active,
1358	you want to modify its timeout value.	2152	then this time is relative to the current event loop time, otherwise it's
		2153	the timeout value currently configured.
1359		2154
1360	Note, however, that it is often even more efficient to remember the	2155	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1361	time of the last activity and let the timer time-out naturally. In the	2156	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
1362	callback, you then check whether the time-out is real, or, if there was	2157	will return C<4>. When the timer expires and is restarted, it will return
1363	some activity, you reschedule the watcher to time-out in "last_activity +	2158	roughly C<7> (likely slightly less as callback invocation takes some time,
1364	timeout - ev_now ()" seconds.	2159	too), and so on.
1365		2160
1366	=item ev_tstamp repeat [read-write]	2161	=item ev_tstamp repeat [read-write]
1367		2162
1368	The current C<repeat> value. Will be used each time the watcher times out	2163	The current C<repeat> value. Will be used each time the watcher times out
1369	or C<ev_timer_again> is called, and determines the next timeout (if any),	2164	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1374	=head3 Examples	2169	=head3 Examples
1375		2170
1376	Example: Create a timer that fires after 60 seconds.	2171	Example: Create a timer that fires after 60 seconds.
1377		2172
1378	static void	2173	static void
1379	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2174	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1380	{	2175	{
1381	.. one minute over, w is actually stopped right here	2176	.. one minute over, w is actually stopped right here
1382	}	2177	}
1383		2178
1384	struct ev_timer mytimer;	2179	ev_timer mytimer;
1385	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2180	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1386	ev_timer_start (loop, &mytimer);	2181	ev_timer_start (loop, &mytimer);
1387		2182
1388	Example: Create a timeout timer that times out after 10 seconds of	2183	Example: Create a timeout timer that times out after 10 seconds of
1389	inactivity.	2184	inactivity.
1390		2185
1391	static void	2186	static void
1392	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2187	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1393	{	2188	{
1394	.. ten seconds without any activity	2189	.. ten seconds without any activity
1395	}	2190	}
1396		2191
1397	struct ev_timer mytimer;	2192	ev_timer mytimer;
1398	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2193	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1399	ev_timer_again (&mytimer); /* start timer */	2194	ev_timer_again (&mytimer); /* start timer */
1400	ev_loop (loop, 0);	2195	ev_run (loop, 0);
1401		2196
1402	// and in some piece of code that gets executed on any "activity":	2197	// and in some piece of code that gets executed on any "activity":
1403	// reset the timeout to start ticking again at 10 seconds	2198	// reset the timeout to start ticking again at 10 seconds
1404	ev_timer_again (&mytimer);	2199	ev_timer_again (&mytimer);
1405		2200
…		…
1407	=head2 C<ev_periodic> - to cron or not to cron?	2202	=head2 C<ev_periodic> - to cron or not to cron?
1408		2203
1409	Periodic watchers are also timers of a kind, but they are very versatile	2204	Periodic watchers are also timers of a kind, but they are very versatile
1410	(and unfortunately a bit complex).	2205	(and unfortunately a bit complex).
1411		2206
1412	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2207	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1413	but on wall clock time (absolute time). You can tell a periodic watcher	2208	relative time, the physical time that passes) but on wall clock time
1414	to trigger after some specific point in time. For example, if you tell a	2209	(absolute time, the thing you can read on your calender or clock). The
1415	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	2210	difference is that wall clock time can run faster or slower than real
1416	+ 10.>, that is, an absolute time not a delay) and then reset your system	2211	time, and time jumps are not uncommon (e.g. when you adjust your
1417	clock to January of the previous year, then it will take more than year	2212	wrist-watch).
1418	to trigger the event (unlike an C<ev_timer>, which would still trigger
1419	roughly 10 seconds later as it uses a relative timeout).
1420		2213
		2214	You can tell a periodic watcher to trigger after some specific point
		2215	in time: for example, if you tell a periodic watcher to trigger "in 10
		2216	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2217	not a delay) and then reset your system clock to January of the previous
		2218	year, then it will take a year or more to trigger the event (unlike an
		2219	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2220	it, as it uses a relative timeout).
		2221
1421	C<ev_periodic>s can also be used to implement vastly more complex timers,	2222	C<ev_periodic> watchers can also be used to implement vastly more complex
1422	such as triggering an event on each "midnight, local time", or other	2223	timers, such as triggering an event on each "midnight, local time", or
1423	complicated rules.	2224	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2225	those cannot react to time jumps.
1424		2226
1425	As with timers, the callback is guaranteed to be invoked only when the	2227	As with timers, the callback is guaranteed to be invoked only when the
1426	time (C<at>) has passed, but if multiple periodic timers become ready	2228	point in time where it is supposed to trigger has passed. If multiple
1427	during the same loop iteration, then order of execution is undefined.	2229	timers become ready during the same loop iteration then the ones with
		2230	earlier time-out values are invoked before ones with later time-out values
		2231	(but this is no longer true when a callback calls C<ev_run> recursively).
1428		2232
1429	=head3 Watcher-Specific Functions and Data Members	2233	=head3 Watcher-Specific Functions and Data Members
1430		2234
1431	=over 4	2235	=over 4
1432		2236
1433	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2237	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1434		2238
1435	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2239	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1436		2240
1437	Lots of arguments, lets sort it out... There are basically three modes of	2241	Lots of arguments, let's sort it out... There are basically three modes of
1438	operation, and we will explain them from simplest to most complex:	2242	operation, and we will explain them from simplest to most complex:
1439		2243
1440	=over 4	2244	=over 4
1441		2245
1442	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2246	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1443		2247
1444	In this configuration the watcher triggers an event after the wall clock	2248	In this configuration the watcher triggers an event after the wall clock
1445	time C<at> has passed. It will not repeat and will not adjust when a time	2249	time C<offset> has passed. It will not repeat and will not adjust when a
1446	jump occurs, that is, if it is to be run at January 1st 2011 then it will	2250	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1447	only run when the system clock reaches or surpasses this time.	2251	will be stopped and invoked when the system clock reaches or surpasses
		2252	this point in time.
1448		2253
1449	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2254	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1450		2255
1451	In this mode the watcher will always be scheduled to time out at the next	2256	In this mode the watcher will always be scheduled to time out at the next
1452	C<at + N * interval> time (for some integer N, which can also be negative)	2257	C<offset + N * interval> time (for some integer N, which can also be
1453	and then repeat, regardless of any time jumps.	2258	negative) and then repeat, regardless of any time jumps. The C<offset>
		2259	argument is merely an offset into the C<interval> periods.
1454		2260
1455	This can be used to create timers that do not drift with respect to the	2261	This can be used to create timers that do not drift with respect to the
1456	system clock, for example, here is a C<ev_periodic> that triggers each	2262	system clock, for example, here is an C<ev_periodic> that triggers each
1457	hour, on the hour:	2263	hour, on the hour (with respect to UTC):
1458		2264
1459	ev_periodic_set (&periodic, 0., 3600., 0);	2265	ev_periodic_set (&periodic, 0., 3600., 0);
1460		2266
1461	This doesn't mean there will always be 3600 seconds in between triggers,	2267	This doesn't mean there will always be 3600 seconds in between triggers,
1462	but only that the callback will be called when the system time shows a	2268	but only that the callback will be called when the system time shows a
1463	full hour (UTC), or more correctly, when the system time is evenly divisible	2269	full hour (UTC), or more correctly, when the system time is evenly divisible
1464	by 3600.	2270	by 3600.
1465		2271
1466	Another way to think about it (for the mathematically inclined) is that	2272	Another way to think about it (for the mathematically inclined) is that
1467	C<ev_periodic> will try to run the callback in this mode at the next possible	2273	C<ev_periodic> will try to run the callback in this mode at the next possible
1468	time where C<time = at (mod interval)>, regardless of any time jumps.	2274	time where C<time = offset (mod interval)>, regardless of any time jumps.
1469		2275
1470	For numerical stability it is preferable that the C<at> value is near	2276	The C<interval> I<MUST> be positive, and for numerical stability, the
1471	C<ev_now ()> (the current time), but there is no range requirement for	2277	interval value should be higher than C<1/8192> (which is around 100
1472	this value, and in fact is often specified as zero.	2278	microseconds) and C<offset> should be higher than C<0> and should have
		2279	at most a similar magnitude as the current time (say, within a factor of
		2280	ten). Typical values for offset are, in fact, C<0> or something between
		2281	C<0> and C<interval>, which is also the recommended range.
1473		2282
1474	Note also that there is an upper limit to how often a timer can fire (CPU	2283	Note also that there is an upper limit to how often a timer can fire (CPU
1475	speed for example), so if C<interval> is very small then timing stability	2284	speed for example), so if C<interval> is very small then timing stability
1476	will of course deteriorate. Libev itself tries to be exact to be about one	2285	will of course deteriorate. Libev itself tries to be exact to be about one
1477	millisecond (if the OS supports it and the machine is fast enough).	2286	millisecond (if the OS supports it and the machine is fast enough).
1478		2287
1479	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2288	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1480		2289
1481	In this mode the values for C<interval> and C<at> are both being	2290	In this mode the values for C<interval> and C<offset> are both being
1482	ignored. Instead, each time the periodic watcher gets scheduled, the	2291	ignored. Instead, each time the periodic watcher gets scheduled, the
1483	reschedule callback will be called with the watcher as first, and the	2292	reschedule callback will be called with the watcher as first, and the
1484	current time as second argument.	2293	current time as second argument.
1485		2294
1486	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2295	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1487	ever, or make ANY event loop modifications whatsoever>.	2296	or make ANY other event loop modifications whatsoever, unless explicitly
		2297	allowed by documentation here>.
1488		2298
1489	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2299	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1490	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2300	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1491	only event loop modification you are allowed to do).	2301	only event loop modification you are allowed to do).
1492		2302
1493	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2303	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1494	*w, ev_tstamp now)>, e.g.:	2304	*w, ev_tstamp now)>, e.g.:
1495		2305
		2306	static ev_tstamp
1496	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2307	my_rescheduler (ev_periodic *w, ev_tstamp now)
1497	{	2308	{
1498	return now + 60.;	2309	return now + 60.;
1499	}	2310	}
1500		2311
1501	It must return the next time to trigger, based on the passed time value	2312	It must return the next time to trigger, based on the passed time value
…		…
1521	a different time than the last time it was called (e.g. in a crond like	2332	a different time than the last time it was called (e.g. in a crond like
1522	program when the crontabs have changed).	2333	program when the crontabs have changed).
1523		2334
1524	=item ev_tstamp ev_periodic_at (ev_periodic *)	2335	=item ev_tstamp ev_periodic_at (ev_periodic *)
1525		2336
1526	When active, returns the absolute time that the watcher is supposed to	2337	When active, returns the absolute time that the watcher is supposed
1527	trigger next.	2338	to trigger next. This is not the same as the C<offset> argument to
		2339	C<ev_periodic_set>, but indeed works even in interval and manual
		2340	rescheduling modes.
1528		2341
1529	=item ev_tstamp offset [read-write]	2342	=item ev_tstamp offset [read-write]
1530		2343
1531	When repeating, this contains the offset value, otherwise this is the	2344	When repeating, this contains the offset value, otherwise this is the
1532	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2345	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2346	although libev might modify this value for better numerical stability).
1533		2347
1534	Can be modified any time, but changes only take effect when the periodic	2348	Can be modified any time, but changes only take effect when the periodic
1535	timer fires or C<ev_periodic_again> is being called.	2349	timer fires or C<ev_periodic_again> is being called.
1536		2350
1537	=item ev_tstamp interval [read-write]	2351	=item ev_tstamp interval [read-write]
1538		2352
1539	The current interval value. Can be modified any time, but changes only	2353	The current interval value. Can be modified any time, but changes only
1540	take effect when the periodic timer fires or C<ev_periodic_again> is being	2354	take effect when the periodic timer fires or C<ev_periodic_again> is being
1541	called.	2355	called.
1542		2356
1543	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2357	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1544		2358
1545	The current reschedule callback, or C<0>, if this functionality is	2359	The current reschedule callback, or C<0>, if this functionality is
1546	switched off. Can be changed any time, but changes only take effect when	2360	switched off. Can be changed any time, but changes only take effect when
1547	the periodic timer fires or C<ev_periodic_again> is being called.	2361	the periodic timer fires or C<ev_periodic_again> is being called.
1548		2362
…		…
1553	Example: Call a callback every hour, or, more precisely, whenever the	2367	Example: Call a callback every hour, or, more precisely, whenever the
1554	system time is divisible by 3600. The callback invocation times have	2368	system time is divisible by 3600. The callback invocation times have
1555	potentially a lot of jitter, but good long-term stability.	2369	potentially a lot of jitter, but good long-term stability.
1556		2370
1557	static void	2371	static void
1558	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2372	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1559	{	2373	{
1560	... its now a full hour (UTC, or TAI or whatever your clock follows)	2374	... its now a full hour (UTC, or TAI or whatever your clock follows)
1561	}	2375	}
1562		2376
1563	struct ev_periodic hourly_tick;	2377	ev_periodic hourly_tick;
1564	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2378	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1565	ev_periodic_start (loop, &hourly_tick);	2379	ev_periodic_start (loop, &hourly_tick);
1566		2380
1567	Example: The same as above, but use a reschedule callback to do it:	2381	Example: The same as above, but use a reschedule callback to do it:
1568		2382
1569	#include <math.h>	2383	#include <math.h>
1570		2384
1571	static ev_tstamp	2385	static ev_tstamp
1572	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2386	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1573	{	2387	{
1574	return now + (3600. - fmod (now, 3600.));	2388	return now + (3600. - fmod (now, 3600.));
1575	}	2389	}
1576		2390
1577	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2391	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1578		2392
1579	Example: Call a callback every hour, starting now:	2393	Example: Call a callback every hour, starting now:
1580		2394
1581	struct ev_periodic hourly_tick;	2395	ev_periodic hourly_tick;
1582	ev_periodic_init (&hourly_tick, clock_cb,	2396	ev_periodic_init (&hourly_tick, clock_cb,
1583	fmod (ev_now (loop), 3600.), 3600., 0);	2397	fmod (ev_now (loop), 3600.), 3600., 0);
1584	ev_periodic_start (loop, &hourly_tick);	2398	ev_periodic_start (loop, &hourly_tick);
1585		2399
1586		2400
1587	=head2 C<ev_signal> - signal me when a signal gets signalled!	2401	=head2 C<ev_signal> - signal me when a signal gets signalled!
1588		2402
1589	Signal watchers will trigger an event when the process receives a specific	2403	Signal watchers will trigger an event when the process receives a specific
1590	signal one or more times. Even though signals are very asynchronous, libev	2404	signal one or more times. Even though signals are very asynchronous, libev
1591	will try it's best to deliver signals synchronously, i.e. as part of the	2405	will try its best to deliver signals synchronously, i.e. as part of the
1592	normal event processing, like any other event.	2406	normal event processing, like any other event.
1593		2407
1594	If you want signals asynchronously, just use C<sigaction> as you would	2408	If you want signals to be delivered truly asynchronously, just use
1595	do without libev and forget about sharing the signal. You can even use	2409	C<sigaction> as you would do without libev and forget about sharing
1596	C<ev_async> from a signal handler to synchronously wake up an event loop.	2410	the signal. You can even use C<ev_async> from a signal handler to
		2411	synchronously wake up an event loop.
1597		2412
1598	You can configure as many watchers as you like per signal. Only when the	2413	You can configure as many watchers as you like for the same signal, but
1599	first watcher gets started will libev actually register a signal handler	2414	only within the same loop, i.e. you can watch for C<SIGINT> in your
1600	with the kernel (thus it coexists with your own signal handlers as long as	2415	default loop and for C<SIGIO> in another loop, but you cannot watch for
1601	you don't register any with libev for the same signal). Similarly, when	2416	C<SIGINT> in both the default loop and another loop at the same time. At
1602	the last signal watcher for a signal is stopped, libev will reset the	2417	the moment, C<SIGCHLD> is permanently tied to the default loop.
1603	signal handler to SIG_DFL (regardless of what it was set to before).	2418
		2419	Only after the first watcher for a signal is started will libev actually
		2420	register something with the kernel. It thus coexists with your own signal
		2421	handlers as long as you don't register any with libev for the same signal.
1604		2422
1605	If possible and supported, libev will install its handlers with	2423	If possible and supported, libev will install its handlers with
1606	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2424	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1607	interrupted. If you have a problem with system calls getting interrupted by	2425	not be unduly interrupted. If you have a problem with system calls getting
1608	signals you can block all signals in an C<ev_check> watcher and unblock	2426	interrupted by signals you can block all signals in an C<ev_check> watcher
1609	them in an C<ev_prepare> watcher.	2427	and unblock them in an C<ev_prepare> watcher.
		2428
		2429	=head3 The special problem of inheritance over fork/execve/pthread_create
		2430
		2431	Both the signal mask (C<sigprocmask>) and the signal disposition
		2432	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2433	stopping it again), that is, libev might or might not block the signal,
		2434	and might or might not set or restore the installed signal handler (but
		2435	see C<EVFLAG_NOSIGMASK>).
		2436
		2437	While this does not matter for the signal disposition (libev never
		2438	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2439	C<execve>), this matters for the signal mask: many programs do not expect
		2440	certain signals to be blocked.
		2441
		2442	This means that before calling C<exec> (from the child) you should reset
		2443	the signal mask to whatever "default" you expect (all clear is a good
		2444	choice usually).
		2445
		2446	The simplest way to ensure that the signal mask is reset in the child is
		2447	to install a fork handler with C<pthread_atfork> that resets it. That will
		2448	catch fork calls done by libraries (such as the libc) as well.
		2449
		2450	In current versions of libev, the signal will not be blocked indefinitely
		2451	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2452	the window of opportunity for problems, it will not go away, as libev
		2453	I<has> to modify the signal mask, at least temporarily.
		2454
		2455	So I can't stress this enough: I<If you do not reset your signal mask when
		2456	you expect it to be empty, you have a race condition in your code>. This
		2457	is not a libev-specific thing, this is true for most event libraries.
		2458
		2459	=head3 The special problem of threads signal handling
		2460
		2461	POSIX threads has problematic signal handling semantics, specifically,
		2462	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2463	threads in a process block signals, which is hard to achieve.
		2464
		2465	When you want to use sigwait (or mix libev signal handling with your own
		2466	for the same signals), you can tackle this problem by globally blocking
		2467	all signals before creating any threads (or creating them with a fully set
		2468	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2469	loops. Then designate one thread as "signal receiver thread" which handles
		2470	these signals. You can pass on any signals that libev might be interested
		2471	in by calling C<ev_feed_signal>.
1610		2472
1611	=head3 Watcher-Specific Functions and Data Members	2473	=head3 Watcher-Specific Functions and Data Members
1612		2474
1613	=over 4	2475	=over 4
1614		2476
…		…
1628	=head3 Examples	2490	=head3 Examples
1629		2491
1630	Example: Try to exit cleanly on SIGINT.	2492	Example: Try to exit cleanly on SIGINT.
1631		2493
1632	static void	2494	static void
1633	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2495	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1634	{	2496	{
1635	ev_unloop (loop, EVUNLOOP_ALL);	2497	ev_break (loop, EVBREAK_ALL);
1636	}	2498	}
1637		2499
1638	struct ev_signal signal_watcher;	2500	ev_signal signal_watcher;
1639	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2501	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1640	ev_signal_start (loop, &signal_watcher);	2502	ev_signal_start (loop, &signal_watcher);
1641		2503
1642		2504
1643	=head2 C<ev_child> - watch out for process status changes	2505	=head2 C<ev_child> - watch out for process status changes
…		…
1646	some child status changes (most typically when a child of yours dies or	2508	some child status changes (most typically when a child of yours dies or
1647	exits). It is permissible to install a child watcher I<after> the child	2509	exits). It is permissible to install a child watcher I<after> the child
1648	has been forked (which implies it might have already exited), as long	2510	has been forked (which implies it might have already exited), as long
1649	as the event loop isn't entered (or is continued from a watcher), i.e.,	2511	as the event loop isn't entered (or is continued from a watcher), i.e.,
1650	forking and then immediately registering a watcher for the child is fine,	2512	forking and then immediately registering a watcher for the child is fine,
1651	but forking and registering a watcher a few event loop iterations later is	2513	but forking and registering a watcher a few event loop iterations later or
1652	not.	2514	in the next callback invocation is not.
1653		2515
1654	Only the default event loop is capable of handling signals, and therefore	2516	Only the default event loop is capable of handling signals, and therefore
1655	you can only register child watchers in the default event loop.	2517	you can only register child watchers in the default event loop.
1656		2518
		2519	Due to some design glitches inside libev, child watchers will always be
		2520	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2521	libev)
		2522
1657	=head3 Process Interaction	2523	=head3 Process Interaction
1658		2524
1659	Libev grabs C<SIGCHLD> as soon as the default event loop is	2525	Libev grabs C<SIGCHLD> as soon as the default event loop is
1660	initialised. This is necessary to guarantee proper behaviour even if	2526	initialised. This is necessary to guarantee proper behaviour even if the
1661	the first child watcher is started after the child exits. The occurrence	2527	first child watcher is started after the child exits. The occurrence
1662	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2528	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1663	synchronously as part of the event loop processing. Libev always reaps all	2529	synchronously as part of the event loop processing. Libev always reaps all
1664	children, even ones not watched.	2530	children, even ones not watched.
1665		2531
1666	=head3 Overriding the Built-In Processing	2532	=head3 Overriding the Built-In Processing
…		…
1676	=head3 Stopping the Child Watcher	2542	=head3 Stopping the Child Watcher
1677		2543
1678	Currently, the child watcher never gets stopped, even when the	2544	Currently, the child watcher never gets stopped, even when the
1679	child terminates, so normally one needs to stop the watcher in the	2545	child terminates, so normally one needs to stop the watcher in the
1680	callback. Future versions of libev might stop the watcher automatically	2546	callback. Future versions of libev might stop the watcher automatically
1681	when a child exit is detected.	2547	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2548	problem).
1682		2549
1683	=head3 Watcher-Specific Functions and Data Members	2550	=head3 Watcher-Specific Functions and Data Members
1684		2551
1685	=over 4	2552	=over 4
1686		2553
…		…
1718	its completion.	2585	its completion.
1719		2586
1720	ev_child cw;	2587	ev_child cw;
1721		2588
1722	static void	2589	static void
1723	child_cb (EV_P_ struct ev_child *w, int revents)	2590	child_cb (EV_P_ ev_child *w, int revents)
1724	{	2591	{
1725	ev_child_stop (EV_A_ w);	2592	ev_child_stop (EV_A_ w);
1726	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2593	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1727	}	2594	}
1728		2595
…		…
1743		2610
1744		2611
1745	=head2 C<ev_stat> - did the file attributes just change?	2612	=head2 C<ev_stat> - did the file attributes just change?
1746		2613
1747	This watches a file system path for attribute changes. That is, it calls	2614	This watches a file system path for attribute changes. That is, it calls
1748	C<stat> regularly (or when the OS says it changed) and sees if it changed	2615	C<stat> on that path in regular intervals (or when the OS says it changed)
1749	compared to the last time, invoking the callback if it did.	2616	and sees if it changed compared to the last time, invoking the callback
		2617	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2618	happen after the watcher has been started will be reported.
1750		2619
1751	The path does not need to exist: changing from "path exists" to "path does	2620	The path does not need to exist: changing from "path exists" to "path does
1752	not exist" is a status change like any other. The condition "path does	2621	not exist" is a status change like any other. The condition "path does not
1753	not exist" is signified by the C<st_nlink> field being zero (which is	2622	exist" (or more correctly "path cannot be stat'ed") is signified by the
1754	otherwise always forced to be at least one) and all the other fields of	2623	C<st_nlink> field being zero (which is otherwise always forced to be at
1755	the stat buffer having unspecified contents.	2624	least one) and all the other fields of the stat buffer having unspecified
		2625	contents.
1756		2626
1757	The path I<should> be absolute and I<must not> end in a slash. If it is	2627	The path I<must not> end in a slash or contain special components such as
		2628	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1758	relative and your working directory changes, the behaviour is undefined.	2629	your working directory changes, then the behaviour is undefined.
1759		2630
1760	Since there is no standard kernel interface to do this, the portable	2631	Since there is no portable change notification interface available, the
1761	implementation simply calls C<stat (2)> regularly on the path to see if	2632	portable implementation simply calls C<stat(2)> regularly on the path
1762	it changed somehow. You can specify a recommended polling interval for	2633	to see if it changed somehow. You can specify a recommended polling
1763	this case. If you specify a polling interval of C<0> (highly recommended!)	2634	interval for this case. If you specify a polling interval of C<0> (highly
1764	then a I<suitable, unspecified default> value will be used (which	2635	recommended!) then a I<suitable, unspecified default> value will be used
1765	you can expect to be around five seconds, although this might change	2636	(which you can expect to be around five seconds, although this might
1766	dynamically). Libev will also impose a minimum interval which is currently	2637	change dynamically). Libev will also impose a minimum interval which is
1767	around C<0.1>, but thats usually overkill.	2638	currently around C<0.1>, but that's usually overkill.
1768		2639
1769	This watcher type is not meant for massive numbers of stat watchers,	2640	This watcher type is not meant for massive numbers of stat watchers,
1770	as even with OS-supported change notifications, this can be	2641	as even with OS-supported change notifications, this can be
1771	resource-intensive.	2642	resource-intensive.
1772		2643
1773	At the time of this writing, the only OS-specific interface implemented	2644	At the time of this writing, the only OS-specific interface implemented
1774	is the Linux inotify interface (implementing kqueue support is left as	2645	is the Linux inotify interface (implementing kqueue support is left as an
1775	an exercise for the reader. Note, however, that the author sees no way	2646	exercise for the reader. Note, however, that the author sees no way of
1776	of implementing C<ev_stat> semantics with kqueue).	2647	implementing C<ev_stat> semantics with kqueue, except as a hint).
1777		2648
1778	=head3 ABI Issues (Largefile Support)	2649	=head3 ABI Issues (Largefile Support)
1779		2650
1780	Libev by default (unless the user overrides this) uses the default	2651	Libev by default (unless the user overrides this) uses the default
1781	compilation environment, which means that on systems with large file	2652	compilation environment, which means that on systems with large file
1782	support disabled by default, you get the 32 bit version of the stat	2653	support disabled by default, you get the 32 bit version of the stat
1783	structure. When using the library from programs that change the ABI to	2654	structure. When using the library from programs that change the ABI to
1784	use 64 bit file offsets the programs will fail. In that case you have to	2655	use 64 bit file offsets the programs will fail. In that case you have to
1785	compile libev with the same flags to get binary compatibility. This is	2656	compile libev with the same flags to get binary compatibility. This is
1786	obviously the case with any flags that change the ABI, but the problem is	2657	obviously the case with any flags that change the ABI, but the problem is
1787	most noticeably disabled with ev_stat and large file support.	2658	most noticeably displayed with ev_stat and large file support.
1788		2659
1789	The solution for this is to lobby your distribution maker to make large	2660	The solution for this is to lobby your distribution maker to make large
1790	file interfaces available by default (as e.g. FreeBSD does) and not	2661	file interfaces available by default (as e.g. FreeBSD does) and not
1791	optional. Libev cannot simply switch on large file support because it has	2662	optional. Libev cannot simply switch on large file support because it has
1792	to exchange stat structures with application programs compiled using the	2663	to exchange stat structures with application programs compiled using the
1793	default compilation environment.	2664	default compilation environment.
1794		2665
1795	=head3 Inotify and Kqueue	2666	=head3 Inotify and Kqueue
1796		2667
1797	When C<inotify (7)> support has been compiled into libev (generally only	2668	When C<inotify (7)> support has been compiled into libev and present at
1798	available with Linux) and present at runtime, it will be used to speed up	2669	runtime, it will be used to speed up change detection where possible. The
1799	change detection where possible. The inotify descriptor will be created lazily	2670	inotify descriptor will be created lazily when the first C<ev_stat>
1800	when the first C<ev_stat> watcher is being started.	2671	watcher is being started.
1801		2672
1802	Inotify presence does not change the semantics of C<ev_stat> watchers	2673	Inotify presence does not change the semantics of C<ev_stat> watchers
1803	except that changes might be detected earlier, and in some cases, to avoid	2674	except that changes might be detected earlier, and in some cases, to avoid
1804	making regular C<stat> calls. Even in the presence of inotify support	2675	making regular C<stat> calls. Even in the presence of inotify support
1805	there are many cases where libev has to resort to regular C<stat> polling,	2676	there are many cases where libev has to resort to regular C<stat> polling,
1806	but as long as the path exists, libev usually gets away without polling.	2677	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2678	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2679	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2680	xfs are fully working) libev usually gets away without polling.
1807		2681
1808	There is no support for kqueue, as apparently it cannot be used to	2682	There is no support for kqueue, as apparently it cannot be used to
1809	implement this functionality, due to the requirement of having a file	2683	implement this functionality, due to the requirement of having a file
1810	descriptor open on the object at all times, and detecting renames, unlinks	2684	descriptor open on the object at all times, and detecting renames, unlinks
1811	etc. is difficult.	2685	etc. is difficult.
1812		2686
		2687	=head3 C<stat ()> is a synchronous operation
		2688
		2689	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2690	the process. The exception are C<ev_stat> watchers - those call C<stat
		2691	()>, which is a synchronous operation.
		2692
		2693	For local paths, this usually doesn't matter: unless the system is very
		2694	busy or the intervals between stat's are large, a stat call will be fast,
		2695	as the path data is usually in memory already (except when starting the
		2696	watcher).
		2697
		2698	For networked file systems, calling C<stat ()> can block an indefinite
		2699	time due to network issues, and even under good conditions, a stat call
		2700	often takes multiple milliseconds.
		2701
		2702	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2703	paths, although this is fully supported by libev.
		2704
1813	=head3 The special problem of stat time resolution	2705	=head3 The special problem of stat time resolution
1814		2706
1815	The C<stat ()> system call only supports full-second resolution portably, and	2707	The C<stat ()> system call only supports full-second resolution portably,
1816	even on systems where the resolution is higher, most file systems still	2708	and even on systems where the resolution is higher, most file systems
1817	only support whole seconds.	2709	still only support whole seconds.
1818		2710
1819	That means that, if the time is the only thing that changes, you can	2711	That means that, if the time is the only thing that changes, you can
1820	easily miss updates: on the first update, C<ev_stat> detects a change and	2712	easily miss updates: on the first update, C<ev_stat> detects a change and
1821	calls your callback, which does something. When there is another update	2713	calls your callback, which does something. When there is another update
1822	within the same second, C<ev_stat> will be unable to detect unless the	2714	within the same second, C<ev_stat> will be unable to detect unless the
…		…
1961	Apart from keeping your process non-blocking (which is a useful	2853	Apart from keeping your process non-blocking (which is a useful
1962	effect on its own sometimes), idle watchers are a good place to do	2854	effect on its own sometimes), idle watchers are a good place to do
1963	"pseudo-background processing", or delay processing stuff to after the	2855	"pseudo-background processing", or delay processing stuff to after the
1964	event loop has handled all outstanding events.	2856	event loop has handled all outstanding events.
1965		2857
		2858	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2859
		2860	As long as there is at least one active idle watcher, libev will never
		2861	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2862	For this to work, the idle watcher doesn't need to be invoked at all - the
		2863	lowest priority will do.
		2864
		2865	This mode of operation can be useful together with an C<ev_check> watcher,
		2866	to do something on each event loop iteration - for example to balance load
		2867	between different connections.
		2868
		2869	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2870	example.
		2871
1966	=head3 Watcher-Specific Functions and Data Members	2872	=head3 Watcher-Specific Functions and Data Members
1967		2873
1968	=over 4	2874	=over 4
1969		2875
1970	=item ev_idle_init (ev_signal *, callback)	2876	=item ev_idle_init (ev_idle *, callback)
1971		2877
1972	Initialises and configures the idle watcher - it has no parameters of any	2878	Initialises and configures the idle watcher - it has no parameters of any
1973	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2879	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1974	believe me.	2880	believe me.
1975		2881
…		…
1979		2885
1980	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2886	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1981	callback, free it. Also, use no error checking, as usual.	2887	callback, free it. Also, use no error checking, as usual.
1982		2888
1983	static void	2889	static void
1984	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2890	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1985	{	2891	{
		2892	// stop the watcher
		2893	ev_idle_stop (loop, w);
		2894
		2895	// now we can free it
1986	free (w);	2896	free (w);
		2897
1987	// now do something you wanted to do when the program has	2898	// now do something you wanted to do when the program has
1988	// no longer anything immediate to do.	2899	// no longer anything immediate to do.
1989	}	2900	}
1990		2901
1991	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2902	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1992	ev_idle_init (idle_watcher, idle_cb);	2903	ev_idle_init (idle_watcher, idle_cb);
1993	ev_idle_start (loop, idle_cb);	2904	ev_idle_start (loop, idle_watcher);
1994		2905
1995		2906
1996	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2907	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1997		2908
1998	Prepare and check watchers are usually (but not always) used in pairs:	2909	Prepare and check watchers are often (but not always) used in pairs:
1999	prepare watchers get invoked before the process blocks and check watchers	2910	prepare watchers get invoked before the process blocks and check watchers
2000	afterwards.	2911	afterwards.
2001		2912
2002	You I<must not> call C<ev_loop> or similar functions that enter	2913	You I<must not> call C<ev_run> (or similar functions that enter the
2003	the current event loop from either C<ev_prepare> or C<ev_check>	2914	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2004	watchers. Other loops than the current one are fine, however. The	2915	C<ev_check> watchers. Other loops than the current one are fine,
2005	rationale behind this is that you do not need to check for recursion in	2916	however. The rationale behind this is that you do not need to check
2006	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2917	for recursion in those watchers, i.e. the sequence will always be
2007	C<ev_check> so if you have one watcher of each kind they will always be	2918	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2008	called in pairs bracketing the blocking call.	2919	kind they will always be called in pairs bracketing the blocking call.
2009		2920
2010	Their main purpose is to integrate other event mechanisms into libev and	2921	Their main purpose is to integrate other event mechanisms into libev and
2011	their use is somewhat advanced. They could be used, for example, to track	2922	their use is somewhat advanced. They could be used, for example, to track
2012	variable changes, implement your own watchers, integrate net-snmp or a	2923	variable changes, implement your own watchers, integrate net-snmp or a
2013	coroutine library and lots more. They are also occasionally useful if	2924	coroutine library and lots more. They are also occasionally useful if
…		…
2031	with priority higher than or equal to the event loop and one coroutine	2942	with priority higher than or equal to the event loop and one coroutine
2032	of lower priority, but only once, using idle watchers to keep the event	2943	of lower priority, but only once, using idle watchers to keep the event
2033	loop from blocking if lower-priority coroutines are active, thus mapping	2944	loop from blocking if lower-priority coroutines are active, thus mapping
2034	low-priority coroutines to idle/background tasks).	2945	low-priority coroutines to idle/background tasks).
2035		2946
2036	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2947	When used for this purpose, it is recommended to give C<ev_check> watchers
2037	priority, to ensure that they are being run before any other watchers	2948	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2038	after the poll (this doesn't matter for C<ev_prepare> watchers).	2949	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2950	watchers).
2039		2951
2040	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	2952	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2041	activate ("feed") events into libev. While libev fully supports this, they	2953	activate ("feed") events into libev. While libev fully supports this, they
2042	might get executed before other C<ev_check> watchers did their job. As	2954	might get executed before other C<ev_check> watchers did their job. As
2043	C<ev_check> watchers are often used to embed other (non-libev) event	2955	C<ev_check> watchers are often used to embed other (non-libev) event
2044	loops those other event loops might be in an unusable state until their	2956	loops those other event loops might be in an unusable state until their
2045	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2957	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2046	others).	2958	others).
2047		2959
		2960	=head3 Abusing an C<ev_check> watcher for its side-effect
		2961
		2962	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2963	useful because they are called once per event loop iteration. For
		2964	example, if you want to handle a large number of connections fairly, you
		2965	normally only do a bit of work for each active connection, and if there
		2966	is more work to do, you wait for the next event loop iteration, so other
		2967	connections have a chance of making progress.
		2968
		2969	Using an C<ev_check> watcher is almost enough: it will be called on the
		2970	next event loop iteration. However, that isn't as soon as possible -
		2971	without external events, your C<ev_check> watcher will not be invoked.
		2972
		2973	This is where C<ev_idle> watchers come in handy - all you need is a
		2974	single global idle watcher that is active as long as you have one active
		2975	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2976	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2977	invoked. Neither watcher alone can do that.
		2978
2048	=head3 Watcher-Specific Functions and Data Members	2979	=head3 Watcher-Specific Functions and Data Members
2049		2980
2050	=over 4	2981	=over 4
2051		2982
2052	=item ev_prepare_init (ev_prepare *, callback)	2983	=item ev_prepare_init (ev_prepare *, callback)
…		…
2077		3008
2078	static ev_io iow [nfd];	3009	static ev_io iow [nfd];
2079	static ev_timer tw;	3010	static ev_timer tw;
2080		3011
2081	static void	3012	static void
2082	io_cb (ev_loop *loop, ev_io *w, int revents)	3013	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2083	{	3014	{
2084	}	3015	}
2085		3016
2086	// create io watchers for each fd and a timer before blocking	3017	// create io watchers for each fd and a timer before blocking
2087	static void	3018	static void
2088	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3019	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2089	{	3020	{
2090	int timeout = 3600000;	3021	int timeout = 3600000;
2091	struct pollfd fds [nfd];	3022	struct pollfd fds [nfd];
2092	// actual code will need to loop here and realloc etc.	3023	// actual code will need to loop here and realloc etc.
2093	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3024	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2094		3025
2095	/* the callback is illegal, but won't be called as we stop during check */	3026	/* the callback is illegal, but won't be called as we stop during check */
2096	ev_timer_init (&tw, 0, timeout * 1e-3);	3027	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2097	ev_timer_start (loop, &tw);	3028	ev_timer_start (loop, &tw);
2098		3029
2099	// create one ev_io per pollfd	3030	// create one ev_io per pollfd
2100	for (int i = 0; i < nfd; ++i)	3031	for (int i = 0; i < nfd; ++i)
2101	{	3032	{
…		…
2108	}	3039	}
2109	}	3040	}
2110		3041
2111	// stop all watchers after blocking	3042	// stop all watchers after blocking
2112	static void	3043	static void
2113	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3044	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2114	{	3045	{
2115	ev_timer_stop (loop, &tw);	3046	ev_timer_stop (loop, &tw);
2116		3047
2117	for (int i = 0; i < nfd; ++i)	3048	for (int i = 0; i < nfd; ++i)
2118	{	3049	{
…		…
2175		3106
2176	if (timeout >= 0)	3107	if (timeout >= 0)
2177	// create/start timer	3108	// create/start timer
2178		3109
2179	// poll	3110	// poll
2180	ev_loop (EV_A_ 0);	3111	ev_run (EV_A_ 0);
2181		3112
2182	// stop timer again	3113	// stop timer again
2183	if (timeout >= 0)	3114	if (timeout >= 0)
2184	ev_timer_stop (EV_A_ &to);	3115	ev_timer_stop (EV_A_ &to);
2185		3116
…		…
2214	some fds have to be watched and handled very quickly (with low latency),	3145	some fds have to be watched and handled very quickly (with low latency),
2215	and even priorities and idle watchers might have too much overhead. In	3146	and even priorities and idle watchers might have too much overhead. In
2216	this case you would put all the high priority stuff in one loop and all	3147	this case you would put all the high priority stuff in one loop and all
2217	the rest in a second one, and embed the second one in the first.	3148	the rest in a second one, and embed the second one in the first.
2218		3149
2219	As long as the watcher is active, the callback will be invoked every time	3150	As long as the watcher is active, the callback will be invoked every
2220	there might be events pending in the embedded loop. The callback must then	3151	time there might be events pending in the embedded loop. The callback
2221	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3152	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2222	their callbacks (you could also start an idle watcher to give the embedded	3153	sweep and invoke their callbacks (the callback doesn't need to invoke the
2223	loop strictly lower priority for example). You can also set the callback	3154	C<ev_embed_sweep> function directly, it could also start an idle watcher
2224	to C<0>, in which case the embed watcher will automatically execute the	3155	to give the embedded loop strictly lower priority for example).
2225	embedded loop sweep.
2226		3156
2227	As long as the watcher is started it will automatically handle events. The	3157	You can also set the callback to C<0>, in which case the embed watcher
2228	callback will be invoked whenever some events have been handled. You can	3158	will automatically execute the embedded loop sweep whenever necessary.
2229	set the callback to C<0> to avoid having to specify one if you are not
2230	interested in that.
2231		3159
2232	Also, there have not currently been made special provisions for forking:	3160	Fork detection will be handled transparently while the C<ev_embed> watcher
2233	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3161	is active, i.e., the embedded loop will automatically be forked when the
2234	but you will also have to stop and restart any C<ev_embed> watchers	3162	embedding loop forks. In other cases, the user is responsible for calling
2235	yourself - but you can use a fork watcher to handle this automatically,	3163	C<ev_loop_fork> on the embedded loop.
2236	and future versions of libev might do just that.
2237		3164
2238	Unfortunately, not all backends are embeddable: only the ones returned by	3165	Unfortunately, not all backends are embeddable: only the ones returned by
2239	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3166	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2240	portable one.	3167	portable one.
2241		3168
…		…
2256		3183
2257	=over 4	3184	=over 4
2258		3185
2259	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3186	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2260		3187
2261	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3188	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2262		3189
2263	Configures the watcher to embed the given loop, which must be	3190	Configures the watcher to embed the given loop, which must be
2264	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3191	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2265	invoked automatically, otherwise it is the responsibility of the callback	3192	invoked automatically, otherwise it is the responsibility of the callback
2266	to invoke it (it will continue to be called until the sweep has been done,	3193	to invoke it (it will continue to be called until the sweep has been done,
2267	if you do not want that, you need to temporarily stop the embed watcher).	3194	if you do not want that, you need to temporarily stop the embed watcher).
2268		3195
2269	=item ev_embed_sweep (loop, ev_embed *)	3196	=item ev_embed_sweep (loop, ev_embed *)
2270		3197
2271	Make a single, non-blocking sweep over the embedded loop. This works	3198	Make a single, non-blocking sweep over the embedded loop. This works
2272	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3199	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2273	appropriate way for embedded loops.	3200	appropriate way for embedded loops.
2274		3201
2275	=item struct ev_loop *other [read-only]	3202	=item struct ev_loop *other [read-only]
2276		3203
2277	The embedded event loop.	3204	The embedded event loop.
…		…
2286	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	3213	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2287	used).	3214	used).
2288		3215
2289	struct ev_loop *loop_hi = ev_default_init (0);	3216	struct ev_loop *loop_hi = ev_default_init (0);
2290	struct ev_loop *loop_lo = 0;	3217	struct ev_loop *loop_lo = 0;
2291	struct ev_embed embed;	3218	ev_embed embed;
2292		3219
2293	// see if there is a chance of getting one that works	3220	// see if there is a chance of getting one that works
2294	// (remember that a flags value of 0 means autodetection)	3221	// (remember that a flags value of 0 means autodetection)
2295	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3222	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2296	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3223	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2297	: 0;	3224	: 0;
…		…
2310	kqueue implementation). Store the kqueue/socket-only event loop in	3237	kqueue implementation). Store the kqueue/socket-only event loop in
2311	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3238	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2312		3239
2313	struct ev_loop *loop = ev_default_init (0);	3240	struct ev_loop *loop = ev_default_init (0);
2314	struct ev_loop *loop_socket = 0;	3241	struct ev_loop *loop_socket = 0;
2315	struct ev_embed embed;	3242	ev_embed embed;
2316		3243
2317	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3244	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2318	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3245	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2319	{	3246	{
2320	ev_embed_init (&embed, 0, loop_socket);	3247	ev_embed_init (&embed, 0, loop_socket);
2321	ev_embed_start (loop, &embed);	3248	ev_embed_start (loop, &embed);
…		…
2329		3256
2330	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3257	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2331		3258
2332	Fork watchers are called when a C<fork ()> was detected (usually because	3259	Fork watchers are called when a C<fork ()> was detected (usually because
2333	whoever is a good citizen cared to tell libev about it by calling	3260	whoever is a good citizen cared to tell libev about it by calling
2334	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3261	C<ev_loop_fork>). The invocation is done before the event loop blocks next
2335	event loop blocks next and before C<ev_check> watchers are being called,	3262	and before C<ev_check> watchers are being called, and only in the child
2336	and only in the child after the fork. If whoever good citizen calling	3263	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
2337	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3264	and calls it in the wrong process, the fork handlers will be invoked, too,
2338	handlers will be invoked, too, of course.	3265	of course.
		3266
		3267	=head3 The special problem of life after fork - how is it possible?
		3268
		3269	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3270	up/change the process environment, followed by a call to C<exec()>. This
		3271	sequence should be handled by libev without any problems.
		3272
		3273	This changes when the application actually wants to do event handling
		3274	in the child, or both parent in child, in effect "continuing" after the
		3275	fork.
		3276
		3277	The default mode of operation (for libev, with application help to detect
		3278	forks) is to duplicate all the state in the child, as would be expected
		3279	when I<either> the parent I<or> the child process continues.
		3280
		3281	When both processes want to continue using libev, then this is usually the
		3282	wrong result. In that case, usually one process (typically the parent) is
		3283	supposed to continue with all watchers in place as before, while the other
		3284	process typically wants to start fresh, i.e. without any active watchers.
		3285
		3286	The cleanest and most efficient way to achieve that with libev is to
		3287	simply create a new event loop, which of course will be "empty", and
		3288	use that for new watchers. This has the advantage of not touching more
		3289	memory than necessary, and thus avoiding the copy-on-write, and the
		3290	disadvantage of having to use multiple event loops (which do not support
		3291	signal watchers).
		3292
		3293	When this is not possible, or you want to use the default loop for
		3294	other reasons, then in the process that wants to start "fresh", call
		3295	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3296	Destroying the default loop will "orphan" (not stop) all registered
		3297	watchers, so you have to be careful not to execute code that modifies
		3298	those watchers. Note also that in that case, you have to re-register any
		3299	signal watchers.
2339		3300
2340	=head3 Watcher-Specific Functions and Data Members	3301	=head3 Watcher-Specific Functions and Data Members
2341		3302
2342	=over 4	3303	=over 4
2343		3304
2344	=item ev_fork_init (ev_signal *, callback)	3305	=item ev_fork_init (ev_fork *, callback)
2345		3306
2346	Initialises and configures the fork watcher - it has no parameters of any	3307	Initialises and configures the fork watcher - it has no parameters of any
2347	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3308	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2348	believe me.	3309	really.
2349		3310
2350	=back	3311	=back
2351		3312
2352		3313
		3314	=head2 C<ev_cleanup> - even the best things end
		3315
		3316	Cleanup watchers are called just before the event loop is being destroyed
		3317	by a call to C<ev_loop_destroy>.
		3318
		3319	While there is no guarantee that the event loop gets destroyed, cleanup
		3320	watchers provide a convenient method to install cleanup hooks for your
		3321	program, worker threads and so on - you just to make sure to destroy the
		3322	loop when you want them to be invoked.
		3323
		3324	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3325	all other watchers, they do not keep a reference to the event loop (which
		3326	makes a lot of sense if you think about it). Like all other watchers, you
		3327	can call libev functions in the callback, except C<ev_cleanup_start>.
		3328
		3329	=head3 Watcher-Specific Functions and Data Members
		3330
		3331	=over 4
		3332
		3333	=item ev_cleanup_init (ev_cleanup *, callback)
		3334
		3335	Initialises and configures the cleanup watcher - it has no parameters of
		3336	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3337	pointless, I assure you.
		3338
		3339	=back
		3340
		3341	Example: Register an atexit handler to destroy the default loop, so any
		3342	cleanup functions are called.
		3343
		3344	static void
		3345	program_exits (void)
		3346	{
		3347	ev_loop_destroy (EV_DEFAULT_UC);
		3348	}
		3349
		3350	...
		3351	atexit (program_exits);
		3352
		3353
2353	=head2 C<ev_async> - how to wake up another event loop	3354	=head2 C<ev_async> - how to wake up an event loop
2354		3355
2355	In general, you cannot use an C<ev_loop> from multiple threads or other	3356	In general, you cannot use an C<ev_loop> from multiple threads or other
2356	asynchronous sources such as signal handlers (as opposed to multiple event	3357	asynchronous sources such as signal handlers (as opposed to multiple event
2357	loops - those are of course safe to use in different threads).	3358	loops - those are of course safe to use in different threads).
2358		3359
2359	Sometimes, however, you need to wake up another event loop you do not	3360	Sometimes, however, you need to wake up an event loop you do not control,
2360	control, for example because it belongs to another thread. This is what	3361	for example because it belongs to another thread. This is what C<ev_async>
2361	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3362	watchers do: as long as the C<ev_async> watcher is active, you can signal
2362	can signal it by calling C<ev_async_send>, which is thread- and signal	3363	it by calling C<ev_async_send>, which is thread- and signal safe.
2363	safe.
2364		3364
2365	This functionality is very similar to C<ev_signal> watchers, as signals,	3365	This functionality is very similar to C<ev_signal> watchers, as signals,
2366	too, are asynchronous in nature, and signals, too, will be compressed	3366	too, are asynchronous in nature, and signals, too, will be compressed
2367	(i.e. the number of callback invocations may be less than the number of	3367	(i.e. the number of callback invocations may be less than the number of
2368	C<ev_async_sent> calls).	3368	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
2369		3369	of "global async watchers" by using a watcher on an otherwise unused
2370	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3370	signal, and C<ev_feed_signal> to signal this watcher from another thread,
2371	just the default loop.	3371	even without knowing which loop owns the signal.
2372		3372
2373	=head3 Queueing	3373	=head3 Queueing
2374		3374
2375	C<ev_async> does not support queueing of data in any way. The reason	3375	C<ev_async> does not support queueing of data in any way. The reason
2376	is that the author does not know of a simple (or any) algorithm for a	3376	is that the author does not know of a simple (or any) algorithm for a
2377	multiple-writer-single-reader queue that works in all cases and doesn't	3377	multiple-writer-single-reader queue that works in all cases and doesn't
2378	need elaborate support such as pthreads.	3378	need elaborate support such as pthreads or unportable memory access
		3379	semantics.
2379		3380
2380	That means that if you want to queue data, you have to provide your own	3381	That means that if you want to queue data, you have to provide your own
2381	queue. But at least I can tell you how to implement locking around your	3382	queue. But at least I can tell you how to implement locking around your
2382	queue:	3383	queue:
2383		3384
…		…
2461	=over 4	3462	=over 4
2462		3463
2463	=item ev_async_init (ev_async *, callback)	3464	=item ev_async_init (ev_async *, callback)
2464		3465
2465	Initialises and configures the async watcher - it has no parameters of any	3466	Initialises and configures the async watcher - it has no parameters of any
2466	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3467	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2467	trust me.	3468	trust me.
2468		3469
2469	=item ev_async_send (loop, ev_async *)	3470	=item ev_async_send (loop, ev_async *)
2470		3471
2471	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3472	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2472	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3473	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3474	returns.
		3475
2473	C<ev_feed_event>, this call is safe to do from other threads, signal or	3476	Unlike C<ev_feed_event>, this call is safe to do from other threads,
2474	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3477	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
2475	section below on what exactly this means).	3478	embedding section below on what exactly this means).
2476		3479
2477	This call incurs the overhead of a system call only once per loop iteration,	3480	Note that, as with other watchers in libev, multiple events might get
2478	so while the overhead might be noticeable, it doesn't apply to repeated	3481	compressed into a single callback invocation (another way to look at
2479	calls to C<ev_async_send>.	3482	this is that C<ev_async> watchers are level-triggered: they are set on
		3483	C<ev_async_send>, reset when the event loop detects that).
		3484
		3485	This call incurs the overhead of at most one extra system call per event
		3486	loop iteration, if the event loop is blocked, and no syscall at all if
		3487	the event loop (or your program) is processing events. That means that
		3488	repeated calls are basically free (there is no need to avoid calls for
		3489	performance reasons) and that the overhead becomes smaller (typically
		3490	zero) under load.
2480		3491
2481	=item bool = ev_async_pending (ev_async *)	3492	=item bool = ev_async_pending (ev_async *)
2482		3493
2483	Returns a non-zero value when C<ev_async_send> has been called on the	3494	Returns a non-zero value when C<ev_async_send> has been called on the
2484	watcher but the event has not yet been processed (or even noted) by the	3495	watcher but the event has not yet been processed (or even noted) by the
…		…
2487	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3498	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2488	the loop iterates next and checks for the watcher to have become active,	3499	the loop iterates next and checks for the watcher to have become active,
2489	it will reset the flag again. C<ev_async_pending> can be used to very	3500	it will reset the flag again. C<ev_async_pending> can be used to very
2490	quickly check whether invoking the loop might be a good idea.	3501	quickly check whether invoking the loop might be a good idea.
2491		3502
2492	Not that this does I<not> check whether the watcher itself is pending, only	3503	Not that this does I<not> check whether the watcher itself is pending,
2493	whether it has been requested to make this watcher pending.	3504	only whether it has been requested to make this watcher pending: there
		3505	is a time window between the event loop checking and resetting the async
		3506	notification, and the callback being invoked.
2494		3507
2495	=back	3508	=back
2496		3509
2497		3510
2498	=head1 OTHER FUNCTIONS	3511	=head1 OTHER FUNCTIONS
…		…
2513	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for	3526	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2514	the given C<fd> and C<events> set will be created and started.	3527	the given C<fd> and C<events> set will be created and started.
2515		3528
2516	If C<timeout> is less than 0, then no timeout watcher will be	3529	If C<timeout> is less than 0, then no timeout watcher will be
2517	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3530	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2518	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3531	repeat = 0) will be started. C<0> is a valid timeout.
2519	dubious value.
2520		3532
2521	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3533	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2522	passed an C<revents> set like normal event callbacks (a combination of	3534	passed an C<revents> set like normal event callbacks (a combination of
2523	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3535	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2524	value passed to C<ev_once>:	3536	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3537	a timeout and an io event at the same time - you probably should give io
		3538	events precedence.
		3539
		3540	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2525		3541
2526	static void stdin_ready (int revents, void *arg)	3542	static void stdin_ready (int revents, void *arg)
2527	{	3543	{
		3544	if (revents & EV_READ)
		3545	/* stdin might have data for us, joy! */;
2528	if (revents & EV_TIMEOUT)	3546	else if (revents & EV_TIMER)
2529	/* doh, nothing entered */;	3547	/* doh, nothing entered */;
2530	else if (revents & EV_READ)
2531	/* stdin might have data for us, joy! */;
2532	}	3548	}
2533		3549
2534	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3550	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2535		3551
2536	=item ev_feed_event (ev_loop *, watcher *, int revents)
2537
2538	Feeds the given event set into the event loop, as if the specified event
2539	had happened for the specified watcher (which must be a pointer to an
2540	initialised but not necessarily started event watcher).
2541
2542	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3552	=item ev_feed_fd_event (loop, int fd, int revents)
2543		3553
2544	Feed an event on the given fd, as if a file descriptor backend detected	3554	Feed an event on the given fd, as if a file descriptor backend detected
2545	the given events it.	3555	the given events.
2546		3556
2547	=item ev_feed_signal_event (ev_loop *loop, int signum)	3557	=item ev_feed_signal_event (loop, int signum)
2548		3558
2549	Feed an event as if the given signal occurred (C<loop> must be the default	3559	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
2550	loop!).	3560	which is async-safe.
2551		3561
2552	=back	3562	=back
		3563
		3564
		3565	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3566
		3567	This section explains some common idioms that are not immediately
		3568	obvious. Note that examples are sprinkled over the whole manual, and this
		3569	section only contains stuff that wouldn't fit anywhere else.
		3570
		3571	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3572
		3573	Each watcher has, by default, a C<void *data> member that you can read
		3574	or modify at any time: libev will completely ignore it. This can be used
		3575	to associate arbitrary data with your watcher. If you need more data and
		3576	don't want to allocate memory separately and store a pointer to it in that
		3577	data member, you can also "subclass" the watcher type and provide your own
		3578	data:
		3579
		3580	struct my_io
		3581	{
		3582	ev_io io;
		3583	int otherfd;
		3584	void *somedata;
		3585	struct whatever *mostinteresting;
		3586	};
		3587
		3588	...
		3589	struct my_io w;
		3590	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3591
		3592	And since your callback will be called with a pointer to the watcher, you
		3593	can cast it back to your own type:
		3594
		3595	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3596	{
		3597	struct my_io *w = (struct my_io *)w_;
		3598	...
		3599	}
		3600
		3601	More interesting and less C-conformant ways of casting your callback
		3602	function type instead have been omitted.
		3603
		3604	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3605
		3606	Another common scenario is to use some data structure with multiple
		3607	embedded watchers, in effect creating your own watcher that combines
		3608	multiple libev event sources into one "super-watcher":
		3609
		3610	struct my_biggy
		3611	{
		3612	int some_data;
		3613	ev_timer t1;
		3614	ev_timer t2;
		3615	}
		3616
		3617	In this case getting the pointer to C<my_biggy> is a bit more
		3618	complicated: Either you store the address of your C<my_biggy> struct in
		3619	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3620	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3621	real programmers):
		3622
		3623	#include <stddef.h>
		3624
		3625	static void
		3626	t1_cb (EV_P_ ev_timer *w, int revents)
		3627	{
		3628	struct my_biggy big = (struct my_biggy *)
		3629	(((char *)w) - offsetof (struct my_biggy, t1));
		3630	}
		3631
		3632	static void
		3633	t2_cb (EV_P_ ev_timer *w, int revents)
		3634	{
		3635	struct my_biggy big = (struct my_biggy *)
		3636	(((char *)w) - offsetof (struct my_biggy, t2));
		3637	}
		3638
		3639	=head2 AVOIDING FINISHING BEFORE RETURNING
		3640
		3641	Often you have structures like this in event-based programs:
		3642
		3643	callback ()
		3644	{
		3645	free (request);
		3646	}
		3647
		3648	request = start_new_request (..., callback);
		3649
		3650	The intent is to start some "lengthy" operation. The C<request> could be
		3651	used to cancel the operation, or do other things with it.
		3652
		3653	It's not uncommon to have code paths in C<start_new_request> that
		3654	immediately invoke the callback, for example, to report errors. Or you add
		3655	some caching layer that finds that it can skip the lengthy aspects of the
		3656	operation and simply invoke the callback with the result.
		3657
		3658	The problem here is that this will happen I<before> C<start_new_request>
		3659	has returned, so C<request> is not set.
		3660
		3661	Even if you pass the request by some safer means to the callback, you
		3662	might want to do something to the request after starting it, such as
		3663	canceling it, which probably isn't working so well when the callback has
		3664	already been invoked.
		3665
		3666	A common way around all these issues is to make sure that
		3667	C<start_new_request> I<always> returns before the callback is invoked. If
		3668	C<start_new_request> immediately knows the result, it can artificially
		3669	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3670	example, or more sneakily, by reusing an existing (stopped) watcher and
		3671	pushing it into the pending queue:
		3672
		3673	ev_set_cb (watcher, callback);
		3674	ev_feed_event (EV_A_ watcher, 0);
		3675
		3676	This way, C<start_new_request> can safely return before the callback is
		3677	invoked, while not delaying callback invocation too much.
		3678
		3679	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3680
		3681	Often (especially in GUI toolkits) there are places where you have
		3682	I<modal> interaction, which is most easily implemented by recursively
		3683	invoking C<ev_run>.
		3684
		3685	This brings the problem of exiting - a callback might want to finish the
		3686	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3687	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3688	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3689	other combination: In these cases, a simple C<ev_break> will not work.
		3690
		3691	The solution is to maintain "break this loop" variable for each C<ev_run>
		3692	invocation, and use a loop around C<ev_run> until the condition is
		3693	triggered, using C<EVRUN_ONCE>:
		3694
		3695	// main loop
		3696	int exit_main_loop = 0;
		3697
		3698	while (!exit_main_loop)
		3699	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3700
		3701	// in a modal watcher
		3702	int exit_nested_loop = 0;
		3703
		3704	while (!exit_nested_loop)
		3705	ev_run (EV_A_ EVRUN_ONCE);
		3706
		3707	To exit from any of these loops, just set the corresponding exit variable:
		3708
		3709	// exit modal loop
		3710	exit_nested_loop = 1;
		3711
		3712	// exit main program, after modal loop is finished
		3713	exit_main_loop = 1;
		3714
		3715	// exit both
		3716	exit_main_loop = exit_nested_loop = 1;
		3717
		3718	=head2 THREAD LOCKING EXAMPLE
		3719
		3720	Here is a fictitious example of how to run an event loop in a different
		3721	thread from where callbacks are being invoked and watchers are
		3722	created/added/removed.
		3723
		3724	For a real-world example, see the C<EV::Loop::Async> perl module,
		3725	which uses exactly this technique (which is suited for many high-level
		3726	languages).
		3727
		3728	The example uses a pthread mutex to protect the loop data, a condition
		3729	variable to wait for callback invocations, an async watcher to notify the
		3730	event loop thread and an unspecified mechanism to wake up the main thread.
		3731
		3732	First, you need to associate some data with the event loop:
		3733
		3734	typedef struct {
		3735	mutex_t lock; /* global loop lock */
		3736	ev_async async_w;
		3737	thread_t tid;
		3738	cond_t invoke_cv;
		3739	} userdata;
		3740
		3741	void prepare_loop (EV_P)
		3742	{
		3743	// for simplicity, we use a static userdata struct.
		3744	static userdata u;
		3745
		3746	ev_async_init (&u->async_w, async_cb);
		3747	ev_async_start (EV_A_ &u->async_w);
		3748
		3749	pthread_mutex_init (&u->lock, 0);
		3750	pthread_cond_init (&u->invoke_cv, 0);
		3751
		3752	// now associate this with the loop
		3753	ev_set_userdata (EV_A_ u);
		3754	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3755	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3756
		3757	// then create the thread running ev_run
		3758	pthread_create (&u->tid, 0, l_run, EV_A);
		3759	}
		3760
		3761	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3762	solely to wake up the event loop so it takes notice of any new watchers
		3763	that might have been added:
		3764
		3765	static void
		3766	async_cb (EV_P_ ev_async *w, int revents)
		3767	{
		3768	// just used for the side effects
		3769	}
		3770
		3771	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3772	protecting the loop data, respectively.
		3773
		3774	static void
		3775	l_release (EV_P)
		3776	{
		3777	userdata *u = ev_userdata (EV_A);
		3778	pthread_mutex_unlock (&u->lock);
		3779	}
		3780
		3781	static void
		3782	l_acquire (EV_P)
		3783	{
		3784	userdata *u = ev_userdata (EV_A);
		3785	pthread_mutex_lock (&u->lock);
		3786	}
		3787
		3788	The event loop thread first acquires the mutex, and then jumps straight
		3789	into C<ev_run>:
		3790
		3791	void *
		3792	l_run (void *thr_arg)
		3793	{
		3794	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3795
		3796	l_acquire (EV_A);
		3797	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3798	ev_run (EV_A_ 0);
		3799	l_release (EV_A);
		3800
		3801	return 0;
		3802	}
		3803
		3804	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3805	signal the main thread via some unspecified mechanism (signals? pipe
		3806	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3807	have been called (in a while loop because a) spurious wakeups are possible
		3808	and b) skipping inter-thread-communication when there are no pending
		3809	watchers is very beneficial):
		3810
		3811	static void
		3812	l_invoke (EV_P)
		3813	{
		3814	userdata *u = ev_userdata (EV_A);
		3815
		3816	while (ev_pending_count (EV_A))
		3817	{
		3818	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3819	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3820	}
		3821	}
		3822
		3823	Now, whenever the main thread gets told to invoke pending watchers, it
		3824	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3825	thread to continue:
		3826
		3827	static void
		3828	real_invoke_pending (EV_P)
		3829	{
		3830	userdata *u = ev_userdata (EV_A);
		3831
		3832	pthread_mutex_lock (&u->lock);
		3833	ev_invoke_pending (EV_A);
		3834	pthread_cond_signal (&u->invoke_cv);
		3835	pthread_mutex_unlock (&u->lock);
		3836	}
		3837
		3838	Whenever you want to start/stop a watcher or do other modifications to an
		3839	event loop, you will now have to lock:
		3840
		3841	ev_timer timeout_watcher;
		3842	userdata *u = ev_userdata (EV_A);
		3843
		3844	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3845
		3846	pthread_mutex_lock (&u->lock);
		3847	ev_timer_start (EV_A_ &timeout_watcher);
		3848	ev_async_send (EV_A_ &u->async_w);
		3849	pthread_mutex_unlock (&u->lock);
		3850
		3851	Note that sending the C<ev_async> watcher is required because otherwise
		3852	an event loop currently blocking in the kernel will have no knowledge
		3853	about the newly added timer. By waking up the loop it will pick up any new
		3854	watchers in the next event loop iteration.
		3855
		3856	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3857
		3858	While the overhead of a callback that e.g. schedules a thread is small, it
		3859	is still an overhead. If you embed libev, and your main usage is with some
		3860	kind of threads or coroutines, you might want to customise libev so that
		3861	doesn't need callbacks anymore.
		3862
		3863	Imagine you have coroutines that you can switch to using a function
		3864	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3865	and that due to some magic, the currently active coroutine is stored in a
		3866	global called C<current_coro>. Then you can build your own "wait for libev
		3867	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3868	the differing C<;> conventions):
		3869
		3870	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3871	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3872
		3873	That means instead of having a C callback function, you store the
		3874	coroutine to switch to in each watcher, and instead of having libev call
		3875	your callback, you instead have it switch to that coroutine.
		3876
		3877	A coroutine might now wait for an event with a function called
		3878	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3879	matter when, or whether the watcher is active or not when this function is
		3880	called):
		3881
		3882	void
		3883	wait_for_event (ev_watcher *w)
		3884	{
		3885	ev_set_cb (w, current_coro);
		3886	switch_to (libev_coro);
		3887	}
		3888
		3889	That basically suspends the coroutine inside C<wait_for_event> and
		3890	continues the libev coroutine, which, when appropriate, switches back to
		3891	this or any other coroutine.
		3892
		3893	You can do similar tricks if you have, say, threads with an event queue -
		3894	instead of storing a coroutine, you store the queue object and instead of
		3895	switching to a coroutine, you push the watcher onto the queue and notify
		3896	any waiters.
		3897
		3898	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3899	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3900
		3901	// my_ev.h
		3902	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3903	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3904	#include "../libev/ev.h"
		3905
		3906	// my_ev.c
		3907	#define EV_H "my_ev.h"
		3908	#include "../libev/ev.c"
		3909
		3910	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3911	F<my_ev.c> into your project. When properly specifying include paths, you
		3912	can even use F<ev.h> as header file name directly.
2553		3913
2554		3914
2555	=head1 LIBEVENT EMULATION	3915	=head1 LIBEVENT EMULATION
2556		3916
2557	Libev offers a compatibility emulation layer for libevent. It cannot	3917	Libev offers a compatibility emulation layer for libevent. It cannot
2558	emulate the internals of libevent, so here are some usage hints:	3918	emulate the internals of libevent, so here are some usage hints:
2559		3919
2560	=over 4	3920	=over 4
		3921
		3922	=item * Only the libevent-1.4.1-beta API is being emulated.
		3923
		3924	This was the newest libevent version available when libev was implemented,
		3925	and is still mostly unchanged in 2010.
2561		3926
2562	=item * Use it by including <event.h>, as usual.	3927	=item * Use it by including <event.h>, as usual.
2563		3928
2564	=item * The following members are fully supported: ev_base, ev_callback,	3929	=item * The following members are fully supported: ev_base, ev_callback,
2565	ev_arg, ev_fd, ev_res, ev_events.	3930	ev_arg, ev_fd, ev_res, ev_events.
…		…
2571	=item * Priorities are not currently supported. Initialising priorities	3936	=item * Priorities are not currently supported. Initialising priorities
2572	will fail and all watchers will have the same priority, even though there	3937	will fail and all watchers will have the same priority, even though there
2573	is an ev_pri field.	3938	is an ev_pri field.
2574		3939
2575	=item * In libevent, the last base created gets the signals, in libev, the	3940	=item * In libevent, the last base created gets the signals, in libev, the
2576	first base created (== the default loop) gets the signals.	3941	base that registered the signal gets the signals.
2577		3942
2578	=item * Other members are not supported.	3943	=item * Other members are not supported.
2579		3944
2580	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3945	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2581	to use the libev header file and library.	3946	to use the libev header file and library.
2582		3947
2583	=back	3948	=back
2584		3949
2585	=head1 C++ SUPPORT	3950	=head1 C++ SUPPORT
		3951
		3952	=head2 C API
		3953
		3954	The normal C API should work fine when used from C++: both ev.h and the
		3955	libev sources can be compiled as C++. Therefore, code that uses the C API
		3956	will work fine.
		3957
		3958	Proper exception specifications might have to be added to callbacks passed
		3959	to libev: exceptions may be thrown only from watcher callbacks, all
		3960	other callbacks (allocator, syserr, loop acquire/release and periodic
		3961	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3962	()> specification. If you have code that needs to be compiled as both C
		3963	and C++ you can use the C<EV_THROW> macro for this:
		3964
		3965	static void
		3966	fatal_error (const char *msg) EV_THROW
		3967	{
		3968	perror (msg);
		3969	abort ();
		3970	}
		3971
		3972	...
		3973	ev_set_syserr_cb (fatal_error);
		3974
		3975	The only API functions that can currently throw exceptions are C<ev_run>,
		3976	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3977	because it runs cleanup watchers).
		3978
		3979	Throwing exceptions in watcher callbacks is only supported if libev itself
		3980	is compiled with a C++ compiler or your C and C++ environments allow
		3981	throwing exceptions through C libraries (most do).
		3982
		3983	=head2 C++ API
2586		3984
2587	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3985	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2588	you to use some convenience methods to start/stop watchers and also change	3986	you to use some convenience methods to start/stop watchers and also change
2589	the callback model to a model using method callbacks on objects.	3987	the callback model to a model using method callbacks on objects.
2590		3988
2591	To use it,	3989	To use it,
2592		3990
2593	#include <ev++.h>	3991	#include <ev++.h>
2594		3992
2595	This automatically includes F<ev.h> and puts all of its definitions (many	3993	This automatically includes F<ev.h> and puts all of its definitions (many
2596	of them macros) into the global namespace. All C++ specific things are	3994	of them macros) into the global namespace. All C++ specific things are
2597	put into the C<ev> namespace. It should support all the same embedding	3995	put into the C<ev> namespace. It should support all the same embedding
…		…
2600	Care has been taken to keep the overhead low. The only data member the C++	3998	Care has been taken to keep the overhead low. The only data member the C++
2601	classes add (compared to plain C-style watchers) is the event loop pointer	3999	classes add (compared to plain C-style watchers) is the event loop pointer
2602	that the watcher is associated with (or no additional members at all if	4000	that the watcher is associated with (or no additional members at all if
2603	you disable C<EV_MULTIPLICITY> when embedding libev).	4001	you disable C<EV_MULTIPLICITY> when embedding libev).
2604		4002
2605	Currently, functions, and static and non-static member functions can be	4003	Currently, functions, static and non-static member functions and classes
2606	used as callbacks. Other types should be easy to add as long as they only	4004	with C<operator ()> can be used as callbacks. Other types should be easy
2607	need one additional pointer for context. If you need support for other	4005	to add as long as they only need one additional pointer for context. If
2608	types of functors please contact the author (preferably after implementing	4006	you need support for other types of functors please contact the author
2609	it).	4007	(preferably after implementing it).
		4008
		4009	For all this to work, your C++ compiler either has to use the same calling
		4010	conventions as your C compiler (for static member functions), or you have
		4011	to embed libev and compile libev itself as C++.
2610		4012
2611	Here is a list of things available in the C<ev> namespace:	4013	Here is a list of things available in the C<ev> namespace:
2612		4014
2613	=over 4	4015	=over 4
2614		4016
…		…
2624	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4026	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
2625		4027
2626	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4028	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
2627	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4029	the same name in the C<ev> namespace, with the exception of C<ev_signal>
2628	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4030	which is called C<ev::sig> to avoid clashes with the C<signal> macro
2629	defines by many implementations.	4031	defined by many implementations.
2630		4032
2631	All of those classes have these methods:	4033	All of those classes have these methods:
2632		4034
2633	=over 4	4035	=over 4
2634		4036
2635	=item ev::TYPE::TYPE ()	4037	=item ev::TYPE::TYPE ()
2636		4038
2637	=item ev::TYPE::TYPE (struct ev_loop *)	4039	=item ev::TYPE::TYPE (loop)
2638		4040
2639	=item ev::TYPE::~TYPE	4041	=item ev::TYPE::~TYPE
2640		4042
2641	The constructor (optionally) takes an event loop to associate the watcher	4043	The constructor (optionally) takes an event loop to associate the watcher
2642	with. If it is omitted, it will use C<EV_DEFAULT>.	4044	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2674		4076
2675	myclass obj;	4077	myclass obj;
2676	ev::io iow;	4078	ev::io iow;
2677	iow.set <myclass, &myclass::io_cb> (&obj);	4079	iow.set <myclass, &myclass::io_cb> (&obj);
2678		4080
		4081	=item w->set (object *)
		4082
		4083	This is a variation of a method callback - leaving out the method to call
		4084	will default the method to C<operator ()>, which makes it possible to use
		4085	functor objects without having to manually specify the C<operator ()> all
		4086	the time. Incidentally, you can then also leave out the template argument
		4087	list.
		4088
		4089	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4090	int revents)>.
		4091
		4092	See the method-C<set> above for more details.
		4093
		4094	Example: use a functor object as callback.
		4095
		4096	struct myfunctor
		4097	{
		4098	void operator() (ev::io &w, int revents)
		4099	{
		4100	...
		4101	}
		4102	}
		4103
		4104	myfunctor f;
		4105
		4106	ev::io w;
		4107	w.set (&f);
		4108
2679	=item w->set<function> (void *data = 0)	4109	=item w->set<function> (void *data = 0)
2680		4110
2681	Also sets a callback, but uses a static method or plain function as	4111	Also sets a callback, but uses a static method or plain function as
2682	callback. The optional C<data> argument will be stored in the watcher's	4112	callback. The optional C<data> argument will be stored in the watcher's
2683	C<data> member and is free for you to use.	4113	C<data> member and is free for you to use.
…		…
2689	Example: Use a plain function as callback.	4119	Example: Use a plain function as callback.
2690		4120
2691	static void io_cb (ev::io &w, int revents) { }	4121	static void io_cb (ev::io &w, int revents) { }
2692	iow.set <io_cb> ();	4122	iow.set <io_cb> ();
2693		4123
2694	=item w->set (struct ev_loop *)	4124	=item w->set (loop)
2695		4125
2696	Associates a different C<struct ev_loop> with this watcher. You can only	4126	Associates a different C<struct ev_loop> with this watcher. You can only
2697	do this when the watcher is inactive (and not pending either).	4127	do this when the watcher is inactive (and not pending either).
2698		4128
2699	=item w->set ([arguments])	4129	=item w->set ([arguments])
2700		4130
2701	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be	4131	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4132	with the same arguments. Either this method or a suitable start method
2702	called at least once. Unlike the C counterpart, an active watcher gets	4133	must be called at least once. Unlike the C counterpart, an active watcher
2703	automatically stopped and restarted when reconfiguring it with this	4134	gets automatically stopped and restarted when reconfiguring it with this
2704	method.	4135	method.
		4136
		4137	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4138	clashing with the C<set (loop)> method.
2705		4139
2706	=item w->start ()	4140	=item w->start ()
2707		4141
2708	Starts the watcher. Note that there is no C<loop> argument, as the	4142	Starts the watcher. Note that there is no C<loop> argument, as the
2709	constructor already stores the event loop.	4143	constructor already stores the event loop.
2710		4144
		4145	=item w->start ([arguments])
		4146
		4147	Instead of calling C<set> and C<start> methods separately, it is often
		4148	convenient to wrap them in one call. Uses the same type of arguments as
		4149	the configure C<set> method of the watcher.
		4150
2711	=item w->stop ()	4151	=item w->stop ()
2712		4152
2713	Stops the watcher if it is active. Again, no C<loop> argument.	4153	Stops the watcher if it is active. Again, no C<loop> argument.
2714		4154
2715	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4155	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2727		4167
2728	=back	4168	=back
2729		4169
2730	=back	4170	=back
2731		4171
2732	Example: Define a class with an IO and idle watcher, start one of them in	4172	Example: Define a class with two I/O and idle watchers, start the I/O
2733	the constructor.	4173	watchers in the constructor.
2734		4174
2735	class myclass	4175	class myclass
2736	{	4176	{
2737	ev::io io ; void io_cb (ev::io &w, int revents);	4177	ev::io io ; void io_cb (ev::io &w, int revents);
		4178	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2738	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4179	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2739		4180
2740	myclass (int fd)	4181	myclass (int fd)
2741	{	4182	{
2742	io .set <myclass, &myclass::io_cb > (this);	4183	io .set <myclass, &myclass::io_cb > (this);
		4184	io2 .set <myclass, &myclass::io2_cb > (this);
2743	idle.set <myclass, &myclass::idle_cb> (this);	4185	idle.set <myclass, &myclass::idle_cb> (this);
2744		4186
2745	io.start (fd, ev::READ);	4187	io.set (fd, ev::WRITE); // configure the watcher
		4188	io.start (); // start it whenever convenient
		4189
		4190	io2.start (fd, ev::READ); // set + start in one call
2746	}	4191	}
2747	};	4192	};
2748		4193
2749		4194
2750	=head1 OTHER LANGUAGE BINDINGS	4195	=head1 OTHER LANGUAGE BINDINGS
…		…
2769	L<http://software.schmorp.de/pkg/EV>.	4214	L<http://software.schmorp.de/pkg/EV>.
2770		4215
2771	=item Python	4216	=item Python
2772		4217
2773	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	4218	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2774	seems to be quite complete and well-documented. Note, however, that the	4219	seems to be quite complete and well-documented.
2775	patch they require for libev is outright dangerous as it breaks the ABI
2776	for everybody else, and therefore, should never be applied in an installed
2777	libev (if python requires an incompatible ABI then it needs to embed
2778	libev).
2779		4220
2780	=item Ruby	4221	=item Ruby
2781		4222
2782	Tony Arcieri has written a ruby extension that offers access to a subset	4223	Tony Arcieri has written a ruby extension that offers access to a subset
2783	of the libev API and adds file handle abstractions, asynchronous DNS and	4224	of the libev API and adds file handle abstractions, asynchronous DNS and
2784	more on top of it. It can be found via gem servers. Its homepage is at	4225	more on top of it. It can be found via gem servers. Its homepage is at
2785	L<http://rev.rubyforge.org/>.	4226	L<http://rev.rubyforge.org/>.
2786		4227
		4228	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4229	makes rev work even on mingw.
		4230
		4231	=item Haskell
		4232
		4233	A haskell binding to libev is available at
		4234	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4235
2787	=item D	4236	=item D
2788		4237
2789	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4238	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2790	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4239	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4240
		4241	=item Ocaml
		4242
		4243	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4244	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4245
		4246	=item Lua
		4247
		4248	Brian Maher has written a partial interface to libev for lua (at the
		4249	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4250	L<http://github.com/brimworks/lua-ev>.
		4251
		4252	=item Javascript
		4253
		4254	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4255
		4256	=item Others
		4257
		4258	There are others, and I stopped counting.
2791		4259
2792	=back	4260	=back
2793		4261
2794		4262
2795	=head1 MACRO MAGIC	4263	=head1 MACRO MAGIC
…		…
2809	loop argument"). The C<EV_A> form is used when this is the sole argument,	4277	loop argument"). The C<EV_A> form is used when this is the sole argument,
2810	C<EV_A_> is used when other arguments are following. Example:	4278	C<EV_A_> is used when other arguments are following. Example:
2811		4279
2812	ev_unref (EV_A);	4280	ev_unref (EV_A);
2813	ev_timer_add (EV_A_ watcher);	4281	ev_timer_add (EV_A_ watcher);
2814	ev_loop (EV_A_ 0);	4282	ev_run (EV_A_ 0);
2815		4283
2816	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4284	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2817	which is often provided by the following macro.	4285	which is often provided by the following macro.
2818		4286
2819	=item C<EV_P>, C<EV_P_>	4287	=item C<EV_P>, C<EV_P_>
…		…
2832	suitable for use with C<EV_A>.	4300	suitable for use with C<EV_A>.
2833		4301
2834	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4302	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2835		4303
2836	Similar to the other two macros, this gives you the value of the default	4304	Similar to the other two macros, this gives you the value of the default
2837	loop, if multiple loops are supported ("ev loop default").	4305	loop, if multiple loops are supported ("ev loop default"). The default loop
		4306	will be initialised if it isn't already initialised.
		4307
		4308	For non-multiplicity builds, these macros do nothing, so you always have
		4309	to initialise the loop somewhere.
2838		4310
2839	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4311	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
2840		4312
2841	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4313	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
2842	default loop has been initialised (C<UC> == unchecked). Their behaviour	4314	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
2859	}	4331	}
2860		4332
2861	ev_check check;	4333	ev_check check;
2862	ev_check_init (&check, check_cb);	4334	ev_check_init (&check, check_cb);
2863	ev_check_start (EV_DEFAULT_ &check);	4335	ev_check_start (EV_DEFAULT_ &check);
2864	ev_loop (EV_DEFAULT_ 0);	4336	ev_run (EV_DEFAULT_ 0);
2865		4337
2866	=head1 EMBEDDING	4338	=head1 EMBEDDING
2867		4339
2868	Libev can (and often is) directly embedded into host	4340	Libev can (and often is) directly embedded into host
2869	applications. Examples of applications that embed it include the Deliantra	4341	applications. Examples of applications that embed it include the Deliantra
…		…
2896		4368
2897	#define EV_STANDALONE 1	4369	#define EV_STANDALONE 1
2898	#include "ev.h"	4370	#include "ev.h"
2899		4371
2900	Both header files and implementation files can be compiled with a C++	4372	Both header files and implementation files can be compiled with a C++
2901	compiler (at least, thats a stated goal, and breakage will be treated	4373	compiler (at least, that's a stated goal, and breakage will be treated
2902	as a bug).	4374	as a bug).
2903		4375
2904	You need the following files in your source tree, or in a directory	4376	You need the following files in your source tree, or in a directory
2905	in your include path (e.g. in libev/ when using -Ilibev):	4377	in your include path (e.g. in libev/ when using -Ilibev):
2906		4378
…		…
2949	libev.m4	4421	libev.m4
2950		4422
2951	=head2 PREPROCESSOR SYMBOLS/MACROS	4423	=head2 PREPROCESSOR SYMBOLS/MACROS
2952		4424
2953	Libev can be configured via a variety of preprocessor symbols you have to	4425	Libev can be configured via a variety of preprocessor symbols you have to
2954	define before including any of its files. The default in the absence of	4426	define before including (or compiling) any of its files. The default in
2955	autoconf is documented for every option.	4427	the absence of autoconf is documented for every option.
		4428
		4429	Symbols marked with "(h)" do not change the ABI, and can have different
		4430	values when compiling libev vs. including F<ev.h>, so it is permissible
		4431	to redefine them before including F<ev.h> without breaking compatibility
		4432	to a compiled library. All other symbols change the ABI, which means all
		4433	users of libev and the libev code itself must be compiled with compatible
		4434	settings.
2956		4435
2957	=over 4	4436	=over 4
2958		4437
		4438	=item EV_COMPAT3 (h)
		4439
		4440	Backwards compatibility is a major concern for libev. This is why this
		4441	release of libev comes with wrappers for the functions and symbols that
		4442	have been renamed between libev version 3 and 4.
		4443
		4444	You can disable these wrappers (to test compatibility with future
		4445	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4446	sources. This has the additional advantage that you can drop the C<struct>
		4447	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4448	typedef in that case.
		4449
		4450	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4451	and in some even more future version the compatibility code will be
		4452	removed completely.
		4453
2959	=item EV_STANDALONE	4454	=item EV_STANDALONE (h)
2960		4455
2961	Must always be C<1> if you do not use autoconf configuration, which	4456	Must always be C<1> if you do not use autoconf configuration, which
2962	keeps libev from including F<config.h>, and it also defines dummy	4457	keeps libev from including F<config.h>, and it also defines dummy
2963	implementations for some libevent functions (such as logging, which is not	4458	implementations for some libevent functions (such as logging, which is not
2964	supported). It will also not define any of the structs usually found in	4459	supported). It will also not define any of the structs usually found in
2965	F<event.h> that are not directly supported by the libev core alone.	4460	F<event.h> that are not directly supported by the libev core alone.
2966		4461
		4462	In standalone mode, libev will still try to automatically deduce the
		4463	configuration, but has to be more conservative.
		4464
		4465	=item EV_USE_FLOOR
		4466
		4467	If defined to be C<1>, libev will use the C<floor ()> function for its
		4468	periodic reschedule calculations, otherwise libev will fall back on a
		4469	portable (slower) implementation. If you enable this, you usually have to
		4470	link against libm or something equivalent. Enabling this when the C<floor>
		4471	function is not available will fail, so the safe default is to not enable
		4472	this.
		4473
2967	=item EV_USE_MONOTONIC	4474	=item EV_USE_MONOTONIC
2968		4475
2969	If defined to be C<1>, libev will try to detect the availability of the	4476	If defined to be C<1>, libev will try to detect the availability of the
2970	monotonic clock option at both compile time and runtime. Otherwise no use	4477	monotonic clock option at both compile time and runtime. Otherwise no
2971	of the monotonic clock option will be attempted. If you enable this, you	4478	use of the monotonic clock option will be attempted. If you enable this,
2972	usually have to link against librt or something similar. Enabling it when	4479	you usually have to link against librt or something similar. Enabling it
2973	the functionality isn't available is safe, though, although you have	4480	when the functionality isn't available is safe, though, although you have
2974	to make sure you link against any libraries where the C<clock_gettime>	4481	to make sure you link against any libraries where the C<clock_gettime>
2975	function is hiding in (often F<-lrt>).	4482	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2976		4483
2977	=item EV_USE_REALTIME	4484	=item EV_USE_REALTIME
2978		4485
2979	If defined to be C<1>, libev will try to detect the availability of the	4486	If defined to be C<1>, libev will try to detect the availability of the
2980	real-time clock option at compile time (and assume its availability at	4487	real-time clock option at compile time (and assume its availability
2981	runtime if successful). Otherwise no use of the real-time clock option will	4488	at runtime if successful). Otherwise no use of the real-time clock
2982	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4489	option will be attempted. This effectively replaces C<gettimeofday>
2983	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4490	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2984	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4491	correctness. See the note about libraries in the description of
		4492	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4493	C<EV_USE_CLOCK_SYSCALL>.
		4494
		4495	=item EV_USE_CLOCK_SYSCALL
		4496
		4497	If defined to be C<1>, libev will try to use a direct syscall instead
		4498	of calling the system-provided C<clock_gettime> function. This option
		4499	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4500	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4501	programs needlessly. Using a direct syscall is slightly slower (in
		4502	theory), because no optimised vdso implementation can be used, but avoids
		4503	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4504	higher, as it simplifies linking (no need for C<-lrt>).
2985		4505
2986	=item EV_USE_NANOSLEEP	4506	=item EV_USE_NANOSLEEP
2987		4507
2988	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4508	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2989	and will use it for delays. Otherwise it will use C<select ()>.	4509	and will use it for delays. Otherwise it will use C<select ()>.
…		…
3005		4525
3006	=item EV_SELECT_USE_FD_SET	4526	=item EV_SELECT_USE_FD_SET
3007		4527
3008	If defined to C<1>, then the select backend will use the system C<fd_set>	4528	If defined to C<1>, then the select backend will use the system C<fd_set>
3009	structure. This is useful if libev doesn't compile due to a missing	4529	structure. This is useful if libev doesn't compile due to a missing
3010	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	4530	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
3011	exotic systems. This usually limits the range of file descriptors to some	4531	on exotic systems. This usually limits the range of file descriptors to
3012	low limit such as 1024 or might have other limitations (winsocket only	4532	some low limit such as 1024 or might have other limitations (winsocket
3013	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4533	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
3014	influence the size of the C<fd_set> used.	4534	configures the maximum size of the C<fd_set>.
3015		4535
3016	=item EV_SELECT_IS_WINSOCKET	4536	=item EV_SELECT_IS_WINSOCKET
3017		4537
3018	When defined to C<1>, the select backend will assume that	4538	When defined to C<1>, the select backend will assume that
3019	select/socket/connect etc. don't understand file descriptors but	4539	select/socket/connect etc. don't understand file descriptors but
…		…
3021	be used is the winsock select). This means that it will call	4541	be used is the winsock select). This means that it will call
3022	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4542	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
3023	it is assumed that all these functions actually work on fds, even	4543	it is assumed that all these functions actually work on fds, even
3024	on win32. Should not be defined on non-win32 platforms.	4544	on win32. Should not be defined on non-win32 platforms.
3025		4545
3026	=item EV_FD_TO_WIN32_HANDLE	4546	=item EV_FD_TO_WIN32_HANDLE(fd)
3027		4547
3028	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4548	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
3029	file descriptors to socket handles. When not defining this symbol (the	4549	file descriptors to socket handles. When not defining this symbol (the
3030	default), then libev will call C<_get_osfhandle>, which is usually	4550	default), then libev will call C<_get_osfhandle>, which is usually
3031	correct. In some cases, programs use their own file descriptor management,	4551	correct. In some cases, programs use their own file descriptor management,
3032	in which case they can provide this function to map fds to socket handles.	4552	in which case they can provide this function to map fds to socket handles.
		4553
		4554	=item EV_WIN32_HANDLE_TO_FD(handle)
		4555
		4556	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4557	using the standard C<_open_osfhandle> function. For programs implementing
		4558	their own fd to handle mapping, overwriting this function makes it easier
		4559	to do so. This can be done by defining this macro to an appropriate value.
		4560
		4561	=item EV_WIN32_CLOSE_FD(fd)
		4562
		4563	If programs implement their own fd to handle mapping on win32, then this
		4564	macro can be used to override the C<close> function, useful to unregister
		4565	file descriptors again. Note that the replacement function has to close
		4566	the underlying OS handle.
		4567
		4568	=item EV_USE_WSASOCKET
		4569
		4570	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4571	communication socket, which works better in some environments. Otherwise,
		4572	the normal C<socket> function will be used, which works better in other
		4573	environments.
3033		4574
3034	=item EV_USE_POLL	4575	=item EV_USE_POLL
3035		4576
3036	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4577	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3037	backend. Otherwise it will be enabled on non-win32 platforms. It	4578	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3073	If defined to be C<1>, libev will compile in support for the Linux inotify	4614	If defined to be C<1>, libev will compile in support for the Linux inotify
3074	interface to speed up C<ev_stat> watchers. Its actual availability will	4615	interface to speed up C<ev_stat> watchers. Its actual availability will
3075	be detected at runtime. If undefined, it will be enabled if the headers	4616	be detected at runtime. If undefined, it will be enabled if the headers
3076	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4617	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3077		4618
		4619	=item EV_NO_SMP
		4620
		4621	If defined to be C<1>, libev will assume that memory is always coherent
		4622	between threads, that is, threads can be used, but threads never run on
		4623	different cpus (or different cpu cores). This reduces dependencies
		4624	and makes libev faster.
		4625
		4626	=item EV_NO_THREADS
		4627
		4628	If defined to be C<1>, libev will assume that it will never be called from
		4629	different threads (that includes signal handlers), which is a stronger
		4630	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4631	libev faster.
		4632
3078	=item EV_ATOMIC_T	4633	=item EV_ATOMIC_T
3079		4634
3080	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4635	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3081	access is atomic with respect to other threads or signal contexts. No such	4636	access is atomic with respect to other threads or signal contexts. No
3082	type is easily found in the C language, so you can provide your own type	4637	such type is easily found in the C language, so you can provide your own
3083	that you know is safe for your purposes. It is used both for signal handler "locking"	4638	type that you know is safe for your purposes. It is used both for signal
3084	as well as for signal and thread safety in C<ev_async> watchers.	4639	handler "locking" as well as for signal and thread safety in C<ev_async>
		4640	watchers.
3085		4641
3086	In the absence of this define, libev will use C<sig_atomic_t volatile>	4642	In the absence of this define, libev will use C<sig_atomic_t volatile>
3087	(from F<signal.h>), which is usually good enough on most platforms.	4643	(from F<signal.h>), which is usually good enough on most platforms.
3088		4644
3089	=item EV_H	4645	=item EV_H (h)
3090		4646
3091	The name of the F<ev.h> header file used to include it. The default if	4647	The name of the F<ev.h> header file used to include it. The default if
3092	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4648	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
3093	used to virtually rename the F<ev.h> header file in case of conflicts.	4649	used to virtually rename the F<ev.h> header file in case of conflicts.
3094		4650
3095	=item EV_CONFIG_H	4651	=item EV_CONFIG_H (h)
3096		4652
3097	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4653	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
3098	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4654	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
3099	C<EV_H>, above.	4655	C<EV_H>, above.
3100		4656
3101	=item EV_EVENT_H	4657	=item EV_EVENT_H (h)
3102		4658
3103	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4659	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
3104	of how the F<event.h> header can be found, the default is C<"event.h">.	4660	of how the F<event.h> header can be found, the default is C<"event.h">.
3105		4661
3106	=item EV_PROTOTYPES	4662	=item EV_PROTOTYPES (h)
3107		4663
3108	If defined to be C<0>, then F<ev.h> will not define any function	4664	If defined to be C<0>, then F<ev.h> will not define any function
3109	prototypes, but still define all the structs and other symbols. This is	4665	prototypes, but still define all the structs and other symbols. This is
3110	occasionally useful if you want to provide your own wrapper functions	4666	occasionally useful if you want to provide your own wrapper functions
3111	around libev functions.	4667	around libev functions.
…		…
3116	will have the C<struct ev_loop *> as first argument, and you can create	4672	will have the C<struct ev_loop *> as first argument, and you can create
3117	additional independent event loops. Otherwise there will be no support	4673	additional independent event loops. Otherwise there will be no support
3118	for multiple event loops and there is no first event loop pointer	4674	for multiple event loops and there is no first event loop pointer
3119	argument. Instead, all functions act on the single default loop.	4675	argument. Instead, all functions act on the single default loop.
3120		4676
		4677	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4678	default loop when multiplicity is switched off - you always have to
		4679	initialise the loop manually in this case.
		4680
3121	=item EV_MINPRI	4681	=item EV_MINPRI
3122		4682
3123	=item EV_MAXPRI	4683	=item EV_MAXPRI
3124		4684
3125	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4685	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
3133	fine.	4693	fine.
3134		4694
3135	If your embedding application does not need any priorities, defining these	4695	If your embedding application does not need any priorities, defining these
3136	both to C<0> will save some memory and CPU.	4696	both to C<0> will save some memory and CPU.
3137		4697
3138	=item EV_PERIODIC_ENABLE	4698	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4699	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4700	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
3139		4701
3140	If undefined or defined to be C<1>, then periodic timers are supported. If	4702	If undefined or defined to be C<1> (and the platform supports it), then
3141	defined to be C<0>, then they are not. Disabling them saves a few kB of	4703	the respective watcher type is supported. If defined to be C<0>, then it
3142	code.	4704	is not. Disabling watcher types mainly saves code size.
3143		4705
3144	=item EV_IDLE_ENABLE	4706	=item EV_FEATURES
3145
3146	If undefined or defined to be C<1>, then idle watchers are supported. If
3147	defined to be C<0>, then they are not. Disabling them saves a few kB of
3148	code.
3149
3150	=item EV_EMBED_ENABLE
3151
3152	If undefined or defined to be C<1>, then embed watchers are supported. If
3153	defined to be C<0>, then they are not. Embed watchers rely on most other
3154	watcher types, which therefore must not be disabled.
3155
3156	=item EV_STAT_ENABLE
3157
3158	If undefined or defined to be C<1>, then stat watchers are supported. If
3159	defined to be C<0>, then they are not.
3160
3161	=item EV_FORK_ENABLE
3162
3163	If undefined or defined to be C<1>, then fork watchers are supported. If
3164	defined to be C<0>, then they are not.
3165
3166	=item EV_ASYNC_ENABLE
3167
3168	If undefined or defined to be C<1>, then async watchers are supported. If
3169	defined to be C<0>, then they are not.
3170
3171	=item EV_MINIMAL
3172		4707
3173	If you need to shave off some kilobytes of code at the expense of some	4708	If you need to shave off some kilobytes of code at the expense of some
3174	speed, define this symbol to C<1>. Currently this is used to override some	4709	speed (but with the full API), you can define this symbol to request
3175	inlining decisions, saves roughly 30% code size on amd64. It also selects a	4710	certain subsets of functionality. The default is to enable all features
3176	much smaller 2-heap for timer management over the default 4-heap.	4711	that can be enabled on the platform.
		4712
		4713	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4714	with some broad features you want) and then selectively re-enable
		4715	additional parts you want, for example if you want everything minimal,
		4716	but multiple event loop support, async and child watchers and the poll
		4717	backend, use this:
		4718
		4719	#define EV_FEATURES 0
		4720	#define EV_MULTIPLICITY 1
		4721	#define EV_USE_POLL 1
		4722	#define EV_CHILD_ENABLE 1
		4723	#define EV_ASYNC_ENABLE 1
		4724
		4725	The actual value is a bitset, it can be a combination of the following
		4726	values (by default, all of these are enabled):
		4727
		4728	=over 4
		4729
		4730	=item C<1> - faster/larger code
		4731
		4732	Use larger code to speed up some operations.
		4733
		4734	Currently this is used to override some inlining decisions (enlarging the
		4735	code size by roughly 30% on amd64).
		4736
		4737	When optimising for size, use of compiler flags such as C<-Os> with
		4738	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4739	assertions.
		4740
		4741	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4742	(e.g. gcc with C<-Os>).
		4743
		4744	=item C<2> - faster/larger data structures
		4745
		4746	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4747	hash table sizes and so on. This will usually further increase code size
		4748	and can additionally have an effect on the size of data structures at
		4749	runtime.
		4750
		4751	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4752	(e.g. gcc with C<-Os>).
		4753
		4754	=item C<4> - full API configuration
		4755
		4756	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4757	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4758
		4759	=item C<8> - full API
		4760
		4761	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4762	details on which parts of the API are still available without this
		4763	feature, and do not complain if this subset changes over time.
		4764
		4765	=item C<16> - enable all optional watcher types
		4766
		4767	Enables all optional watcher types. If you want to selectively enable
		4768	only some watcher types other than I/O and timers (e.g. prepare,
		4769	embed, async, child...) you can enable them manually by defining
		4770	C<EV_watchertype_ENABLE> to C<1> instead.
		4771
		4772	=item C<32> - enable all backends
		4773
		4774	This enables all backends - without this feature, you need to enable at
		4775	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4776
		4777	=item C<64> - enable OS-specific "helper" APIs
		4778
		4779	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4780	default.
		4781
		4782	=back
		4783
		4784	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4785	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4786	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4787	watchers, timers and monotonic clock support.
		4788
		4789	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4790	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4791	your program might be left out as well - a binary starting a timer and an
		4792	I/O watcher then might come out at only 5Kb.
		4793
		4794	=item EV_API_STATIC
		4795
		4796	If this symbol is defined (by default it is not), then all identifiers
		4797	will have static linkage. This means that libev will not export any
		4798	identifiers, and you cannot link against libev anymore. This can be useful
		4799	when you embed libev, only want to use libev functions in a single file,
		4800	and do not want its identifiers to be visible.
		4801
		4802	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4803	wants to use libev.
		4804
		4805	This option only works when libev is compiled with a C compiler, as C++
		4806	doesn't support the required declaration syntax.
		4807
		4808	=item EV_AVOID_STDIO
		4809
		4810	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4811	functions (printf, scanf, perror etc.). This will increase the code size
		4812	somewhat, but if your program doesn't otherwise depend on stdio and your
		4813	libc allows it, this avoids linking in the stdio library which is quite
		4814	big.
		4815
		4816	Note that error messages might become less precise when this option is
		4817	enabled.
		4818
		4819	=item EV_NSIG
		4820
		4821	The highest supported signal number, +1 (or, the number of
		4822	signals): Normally, libev tries to deduce the maximum number of signals
		4823	automatically, but sometimes this fails, in which case it can be
		4824	specified. Also, using a lower number than detected (C<32> should be
		4825	good for about any system in existence) can save some memory, as libev
		4826	statically allocates some 12-24 bytes per signal number.
3177		4827
3178	=item EV_PID_HASHSIZE	4828	=item EV_PID_HASHSIZE
3179		4829
3180	C<ev_child> watchers use a small hash table to distribute workload by	4830	C<ev_child> watchers use a small hash table to distribute workload by
3181	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4831	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
3182	than enough. If you need to manage thousands of children you might want to	4832	usually more than enough. If you need to manage thousands of children you
3183	increase this value (I<must> be a power of two).	4833	might want to increase this value (I<must> be a power of two).
3184		4834
3185	=item EV_INOTIFY_HASHSIZE	4835	=item EV_INOTIFY_HASHSIZE
3186		4836
3187	C<ev_stat> watchers use a small hash table to distribute workload by	4837	C<ev_stat> watchers use a small hash table to distribute workload by
3188	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4838	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
3189	usually more than enough. If you need to manage thousands of C<ev_stat>	4839	disabled), usually more than enough. If you need to manage thousands of
3190	watchers you might want to increase this value (I<must> be a power of	4840	C<ev_stat> watchers you might want to increase this value (I<must> be a
3191	two).	4841	power of two).
3192		4842
3193	=item EV_USE_4HEAP	4843	=item EV_USE_4HEAP
3194		4844
3195	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4845	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3196	timer and periodics heaps, libev uses a 4-heap when this symbol is defined	4846	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3197	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably	4847	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3198	faster performance with many (thousands) of watchers.	4848	faster performance with many (thousands) of watchers.
3199		4849
3200	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4850	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3201	(disabled).	4851	will be C<0>.
3202		4852
3203	=item EV_HEAP_CACHE_AT	4853	=item EV_HEAP_CACHE_AT
3204		4854
3205	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4855	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3206	timer and periodics heaps, libev can cache the timestamp (I<at>) within	4856	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3207	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	4857	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3208	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	4858	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3209	but avoids random read accesses on heap changes. This improves performance	4859	but avoids random read accesses on heap changes. This improves performance
3210	noticeably with many (hundreds) of watchers.	4860	noticeably with many (hundreds) of watchers.
3211		4861
3212	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4862	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3213	(disabled).	4863	will be C<0>.
3214		4864
3215	=item EV_VERIFY	4865	=item EV_VERIFY
3216		4866
3217	Controls how much internal verification (see C<ev_loop_verify ()>) will	4867	Controls how much internal verification (see C<ev_verify ()>) will
3218	be done: If set to C<0>, no internal verification code will be compiled	4868	be done: If set to C<0>, no internal verification code will be compiled
3219	in. If set to C<1>, then verification code will be compiled in, but not	4869	in. If set to C<1>, then verification code will be compiled in, but not
3220	called. If set to C<2>, then the internal verification code will be	4870	called. If set to C<2>, then the internal verification code will be
3221	called once per loop, which can slow down libev. If set to C<3>, then the	4871	called once per loop, which can slow down libev. If set to C<3>, then the
3222	verification code will be called very frequently, which will slow down	4872	verification code will be called very frequently, which will slow down
3223	libev considerably.	4873	libev considerably.
3224		4874
3225	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	4875	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3226	C<0>.	4876	will be C<0>.
3227		4877
3228	=item EV_COMMON	4878	=item EV_COMMON
3229		4879
3230	By default, all watchers have a C<void *data> member. By redefining	4880	By default, all watchers have a C<void *data> member. By redefining
3231	this macro to a something else you can include more and other types of	4881	this macro to something else you can include more and other types of
3232	members. You have to define it each time you include one of the files,	4882	members. You have to define it each time you include one of the files,
3233	though, and it must be identical each time.	4883	though, and it must be identical each time.
3234		4884
3235	For example, the perl EV module uses something like this:	4885	For example, the perl EV module uses something like this:
3236		4886
…		…
3289	file.	4939	file.
3290		4940
3291	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4941	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3292	that everybody includes and which overrides some configure choices:	4942	that everybody includes and which overrides some configure choices:
3293		4943
3294	#define EV_MINIMAL 1	4944	#define EV_FEATURES 8
3295	#define EV_USE_POLL 0	4945	#define EV_USE_SELECT 1
3296	#define EV_MULTIPLICITY 0
3297	#define EV_PERIODIC_ENABLE 0	4946	#define EV_PREPARE_ENABLE 1
		4947	#define EV_IDLE_ENABLE 1
3298	#define EV_STAT_ENABLE 0	4948	#define EV_SIGNAL_ENABLE 1
3299	#define EV_FORK_ENABLE 0	4949	#define EV_CHILD_ENABLE 1
		4950	#define EV_USE_STDEXCEPT 0
3300	#define EV_CONFIG_H <config.h>	4951	#define EV_CONFIG_H <config.h>
3301	#define EV_MINPRI 0
3302	#define EV_MAXPRI 0
3303		4952
3304	#include "ev++.h"	4953	#include "ev++.h"
3305		4954
3306	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4955	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3307		4956
3308	#include "ev_cpp.h"	4957	#include "ev_cpp.h"
3309	#include "ev.c"	4958	#include "ev.c"
3310		4959
3311	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4960	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
3312		4961
3313	=head2 THREADS AND COROUTINES	4962	=head2 THREADS AND COROUTINES
3314		4963
3315	=head3 THREADS	4964	=head3 THREADS
3316		4965
…		…
3367	default loop and triggering an C<ev_async> watcher from the default loop	5016	default loop and triggering an C<ev_async> watcher from the default loop
3368	watcher callback into the event loop interested in the signal.	5017	watcher callback into the event loop interested in the signal.
3369		5018
3370	=back	5019	=back
3371		5020
		5021	See also L</THREAD LOCKING EXAMPLE>.
		5022
3372	=head3 COROUTINES	5023	=head3 COROUTINES
3373		5024
3374	Libev is very accommodating to coroutines ("cooperative threads"):	5025	Libev is very accommodating to coroutines ("cooperative threads"):
3375	libev fully supports nesting calls to its functions from different	5026	libev fully supports nesting calls to its functions from different
3376	coroutines (e.g. you can call C<ev_loop> on the same loop from two	5027	coroutines (e.g. you can call C<ev_run> on the same loop from two
3377	different coroutines, and switch freely between both coroutines running the	5028	different coroutines, and switch freely between both coroutines running
3378	loop, as long as you don't confuse yourself). The only exception is that	5029	the loop, as long as you don't confuse yourself). The only exception is
3379	you must not do this from C<ev_periodic> reschedule callbacks.	5030	that you must not do this from C<ev_periodic> reschedule callbacks.
3380		5031
3381	Care has been taken to ensure that libev does not keep local state inside	5032	Care has been taken to ensure that libev does not keep local state inside
3382	C<ev_loop>, and other calls do not usually allow for coroutine switches as	5033	C<ev_run>, and other calls do not usually allow for coroutine switches as
3383	they do not clal any callbacks.	5034	they do not call any callbacks.
3384		5035
3385	=head2 COMPILER WARNINGS	5036	=head2 COMPILER WARNINGS
3386		5037
3387	Depending on your compiler and compiler settings, you might get no or a	5038	Depending on your compiler and compiler settings, you might get no or a
3388	lot of warnings when compiling libev code. Some people are apparently	5039	lot of warnings when compiling libev code. Some people are apparently
…		…
3398	maintainable.	5049	maintainable.
3399		5050
3400	And of course, some compiler warnings are just plain stupid, or simply	5051	And of course, some compiler warnings are just plain stupid, or simply
3401	wrong (because they don't actually warn about the condition their message	5052	wrong (because they don't actually warn about the condition their message
3402	seems to warn about). For example, certain older gcc versions had some	5053	seems to warn about). For example, certain older gcc versions had some
3403	warnings that resulted an extreme number of false positives. These have	5054	warnings that resulted in an extreme number of false positives. These have
3404	been fixed, but some people still insist on making code warn-free with	5055	been fixed, but some people still insist on making code warn-free with
3405	such buggy versions.	5056	such buggy versions.
3406		5057
3407	While libev is written to generate as few warnings as possible,	5058	While libev is written to generate as few warnings as possible,
3408	"warn-free" code is not a goal, and it is recommended not to build libev	5059	"warn-free" code is not a goal, and it is recommended not to build libev
…		…
3422	==2274== definitely lost: 0 bytes in 0 blocks.	5073	==2274== definitely lost: 0 bytes in 0 blocks.
3423	==2274== possibly lost: 0 bytes in 0 blocks.	5074	==2274== possibly lost: 0 bytes in 0 blocks.
3424	==2274== still reachable: 256 bytes in 1 blocks.	5075	==2274== still reachable: 256 bytes in 1 blocks.
3425		5076
3426	Then there is no memory leak, just as memory accounted to global variables	5077	Then there is no memory leak, just as memory accounted to global variables
3427	is not a memleak - the memory is still being refernced, and didn't leak.	5078	is not a memleak - the memory is still being referenced, and didn't leak.
3428		5079
3429	Similarly, under some circumstances, valgrind might report kernel bugs	5080	Similarly, under some circumstances, valgrind might report kernel bugs
3430	as if it were a bug in libev (e.g. in realloc or in the poll backend,	5081	as if it were a bug in libev (e.g. in realloc or in the poll backend,
3431	although an acceptable workaround has been found here), or it might be	5082	although an acceptable workaround has been found here), or it might be
3432	confused.	5083	confused.
…		…
3444	I suggest using suppression lists.	5095	I suggest using suppression lists.
3445		5096
3446		5097
3447	=head1 PORTABILITY NOTES	5098	=head1 PORTABILITY NOTES
3448		5099
		5100	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5101
		5102	GNU/Linux is the only common platform that supports 64 bit file/large file
		5103	interfaces but I<disables> them by default.
		5104
		5105	That means that libev compiled in the default environment doesn't support
		5106	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5107
		5108	Unfortunately, many programs try to work around this GNU/Linux issue
		5109	by enabling the large file API, which makes them incompatible with the
		5110	standard libev compiled for their system.
		5111
		5112	Likewise, libev cannot enable the large file API itself as this would
		5113	suddenly make it incompatible to the default compile time environment,
		5114	i.e. all programs not using special compile switches.
		5115
		5116	=head2 OS/X AND DARWIN BUGS
		5117
		5118	The whole thing is a bug if you ask me - basically any system interface
		5119	you touch is broken, whether it is locales, poll, kqueue or even the
		5120	OpenGL drivers.
		5121
		5122	=head3 C<kqueue> is buggy
		5123
		5124	The kqueue syscall is broken in all known versions - most versions support
		5125	only sockets, many support pipes.
		5126
		5127	Libev tries to work around this by not using C<kqueue> by default on this
		5128	rotten platform, but of course you can still ask for it when creating a
		5129	loop - embedding a socket-only kqueue loop into a select-based one is
		5130	probably going to work well.
		5131
		5132	=head3 C<poll> is buggy
		5133
		5134	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5135	implementation by something calling C<kqueue> internally around the 10.5.6
		5136	release, so now C<kqueue> I<and> C<poll> are broken.
		5137
		5138	Libev tries to work around this by not using C<poll> by default on
		5139	this rotten platform, but of course you can still ask for it when creating
		5140	a loop.
		5141
		5142	=head3 C<select> is buggy
		5143
		5144	All that's left is C<select>, and of course Apple found a way to fuck this
		5145	one up as well: On OS/X, C<select> actively limits the number of file
		5146	descriptors you can pass in to 1024 - your program suddenly crashes when
		5147	you use more.
		5148
		5149	There is an undocumented "workaround" for this - defining
		5150	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5151	work on OS/X.
		5152
		5153	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5154
		5155	=head3 C<errno> reentrancy
		5156
		5157	The default compile environment on Solaris is unfortunately so
		5158	thread-unsafe that you can't even use components/libraries compiled
		5159	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5160	defined by default. A valid, if stupid, implementation choice.
		5161
		5162	If you want to use libev in threaded environments you have to make sure
		5163	it's compiled with C<_REENTRANT> defined.
		5164
		5165	=head3 Event port backend
		5166
		5167	The scalable event interface for Solaris is called "event
		5168	ports". Unfortunately, this mechanism is very buggy in all major
		5169	releases. If you run into high CPU usage, your program freezes or you get
		5170	a large number of spurious wakeups, make sure you have all the relevant
		5171	and latest kernel patches applied. No, I don't know which ones, but there
		5172	are multiple ones to apply, and afterwards, event ports actually work
		5173	great.
		5174
		5175	If you can't get it to work, you can try running the program by setting
		5176	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5177	C<select> backends.
		5178
		5179	=head2 AIX POLL BUG
		5180
		5181	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5182	this by trying to avoid the poll backend altogether (i.e. it's not even
		5183	compiled in), which normally isn't a big problem as C<select> works fine
		5184	with large bitsets on AIX, and AIX is dead anyway.
		5185
3449	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	5186	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5187
		5188	=head3 General issues
3450		5189
3451	Win32 doesn't support any of the standards (e.g. POSIX) that libev	5190	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3452	requires, and its I/O model is fundamentally incompatible with the POSIX	5191	requires, and its I/O model is fundamentally incompatible with the POSIX
3453	model. Libev still offers limited functionality on this platform in	5192	model. Libev still offers limited functionality on this platform in
3454	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5193	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3455	descriptors. This only applies when using Win32 natively, not when using	5194	descriptors. This only applies when using Win32 natively, not when using
3456	e.g. cygwin.	5195	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5196	as every compiler comes with a slightly differently broken/incompatible
		5197	environment.
3457		5198
3458	Lifting these limitations would basically require the full	5199	Lifting these limitations would basically require the full
3459	re-implementation of the I/O system. If you are into these kinds of	5200	re-implementation of the I/O system. If you are into this kind of thing,
3460	things, then note that glib does exactly that for you in a very portable	5201	then note that glib does exactly that for you in a very portable way (note
3461	way (note also that glib is the slowest event library known to man).	5202	also that glib is the slowest event library known to man).
3462		5203
3463	There is no supported compilation method available on windows except	5204	There is no supported compilation method available on windows except
3464	embedding it into other applications.	5205	embedding it into other applications.
		5206
		5207	Sensible signal handling is officially unsupported by Microsoft - libev
		5208	tries its best, but under most conditions, signals will simply not work.
3465		5209
3466	Not a libev limitation but worth mentioning: windows apparently doesn't	5210	Not a libev limitation but worth mentioning: windows apparently doesn't
3467	accept large writes: instead of resulting in a partial write, windows will	5211	accept large writes: instead of resulting in a partial write, windows will
3468	either accept everything or return C<ENOBUFS> if the buffer is too large,	5212	either accept everything or return C<ENOBUFS> if the buffer is too large,
3469	so make sure you only write small amounts into your sockets (less than a	5213	so make sure you only write small amounts into your sockets (less than a
…		…
3474	the abysmal performance of winsockets, using a large number of sockets	5218	the abysmal performance of winsockets, using a large number of sockets
3475	is not recommended (and not reasonable). If your program needs to use	5219	is not recommended (and not reasonable). If your program needs to use
3476	more than a hundred or so sockets, then likely it needs to use a totally	5220	more than a hundred or so sockets, then likely it needs to use a totally
3477	different implementation for windows, as libev offers the POSIX readiness	5221	different implementation for windows, as libev offers the POSIX readiness
3478	notification model, which cannot be implemented efficiently on windows	5222	notification model, which cannot be implemented efficiently on windows
3479	(Microsoft monopoly games).	5223	(due to Microsoft monopoly games).
3480		5224
3481	A typical way to use libev under windows is to embed it (see the embedding	5225	A typical way to use libev under windows is to embed it (see the embedding
3482	section for details) and use the following F<evwrap.h> header file instead	5226	section for details) and use the following F<evwrap.h> header file instead
3483	of F<ev.h>:	5227	of F<ev.h>:
3484		5228
…		…
3491	you do I<not> compile the F<ev.c> or any other embedded source files!):	5235	you do I<not> compile the F<ev.c> or any other embedded source files!):
3492		5236
3493	#include "evwrap.h"	5237	#include "evwrap.h"
3494	#include "ev.c"	5238	#include "ev.c"
3495		5239
3496	=over 4
3497
3498	=item The winsocket select function	5240	=head3 The winsocket C<select> function
3499		5241
3500	The winsocket C<select> function doesn't follow POSIX in that it	5242	The winsocket C<select> function doesn't follow POSIX in that it
3501	requires socket I<handles> and not socket I<file descriptors> (it is	5243	requires socket I<handles> and not socket I<file descriptors> (it is
3502	also extremely buggy). This makes select very inefficient, and also	5244	also extremely buggy). This makes select very inefficient, and also
3503	requires a mapping from file descriptors to socket handles (the Microsoft	5245	requires a mapping from file descriptors to socket handles (the Microsoft
…		…
3512	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	5254	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3513		5255
3514	Note that winsockets handling of fd sets is O(n), so you can easily get a	5256	Note that winsockets handling of fd sets is O(n), so you can easily get a
3515	complexity in the O(n²) range when using win32.	5257	complexity in the O(n²) range when using win32.
3516		5258
3517	=item Limited number of file descriptors	5259	=head3 Limited number of file descriptors
3518		5260
3519	Windows has numerous arbitrary (and low) limits on things.	5261	Windows has numerous arbitrary (and low) limits on things.
3520		5262
3521	Early versions of winsocket's select only supported waiting for a maximum	5263	Early versions of winsocket's select only supported waiting for a maximum
3522	of C<64> handles (probably owning to the fact that all windows kernels	5264	of C<64> handles (probably owning to the fact that all windows kernels
3523	can only wait for C<64> things at the same time internally; Microsoft	5265	can only wait for C<64> things at the same time internally; Microsoft
3524	recommends spawning a chain of threads and wait for 63 handles and the	5266	recommends spawning a chain of threads and wait for 63 handles and the
3525	previous thread in each. Great).	5267	previous thread in each. Sounds great!).
3526		5268
3527	Newer versions support more handles, but you need to define C<FD_SETSIZE>	5269	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3528	to some high number (e.g. C<2048>) before compiling the winsocket select	5270	to some high number (e.g. C<2048>) before compiling the winsocket select
3529	call (which might be in libev or elsewhere, for example, perl does its own	5271	call (which might be in libev or elsewhere, for example, perl and many
3530	select emulation on windows).	5272	other interpreters do their own select emulation on windows).
3531		5273
3532	Another limit is the number of file descriptors in the Microsoft runtime	5274	Another limit is the number of file descriptors in the Microsoft runtime
3533	libraries, which by default is C<64> (there must be a hidden I<64> fetish	5275	libraries, which by default is C<64> (there must be a hidden I<64>
3534	or something like this inside Microsoft). You can increase this by calling	5276	fetish or something like this inside Microsoft). You can increase this
3535	C<_setmaxstdio>, which can increase this limit to C<2048> (another	5277	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3536	arbitrary limit), but is broken in many versions of the Microsoft runtime	5278	(another arbitrary limit), but is broken in many versions of the Microsoft
3537	libraries.
3538
3539	This might get you to about C<512> or C<2048> sockets (depending on	5279	runtime libraries. This might get you to about C<512> or C<2048> sockets
3540	windows version and/or the phase of the moon). To get more, you need to	5280	(depending on windows version and/or the phase of the moon). To get more,
3541	wrap all I/O functions and provide your own fd management, but the cost of	5281	you need to wrap all I/O functions and provide your own fd management, but
3542	calling select (O(n²)) will likely make this unworkable.	5282	the cost of calling select (O(n²)) will likely make this unworkable.
3543
3544	=back
3545		5283
3546	=head2 PORTABILITY REQUIREMENTS	5284	=head2 PORTABILITY REQUIREMENTS
3547		5285
3548	In addition to a working ISO-C implementation and of course the	5286	In addition to a working ISO-C implementation and of course the
3549	backend-specific APIs, libev relies on a few additional extensions:	5287	backend-specific APIs, libev relies on a few additional extensions:
…		…
3556	Libev assumes not only that all watcher pointers have the same internal	5294	Libev assumes not only that all watcher pointers have the same internal
3557	structure (guaranteed by POSIX but not by ISO C for example), but it also	5295	structure (guaranteed by POSIX but not by ISO C for example), but it also
3558	assumes that the same (machine) code can be used to call any watcher	5296	assumes that the same (machine) code can be used to call any watcher
3559	callback: The watcher callbacks have different type signatures, but libev	5297	callback: The watcher callbacks have different type signatures, but libev
3560	calls them using an C<ev_watcher *> internally.	5298	calls them using an C<ev_watcher *> internally.
		5299
		5300	=item pointer accesses must be thread-atomic
		5301
		5302	Accessing a pointer value must be atomic, it must both be readable and
		5303	writable in one piece - this is the case on all current architectures.
3561		5304
3562	=item C<sig_atomic_t volatile> must be thread-atomic as well	5305	=item C<sig_atomic_t volatile> must be thread-atomic as well
3563		5306
3564	The type C<sig_atomic_t volatile> (or whatever is defined as	5307	The type C<sig_atomic_t volatile> (or whatever is defined as
3565	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5308	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
…		…
3574	thread" or will block signals process-wide, both behaviours would	5317	thread" or will block signals process-wide, both behaviours would
3575	be compatible with libev. Interaction between C<sigprocmask> and	5318	be compatible with libev. Interaction between C<sigprocmask> and
3576	C<pthread_sigmask> could complicate things, however.	5319	C<pthread_sigmask> could complicate things, however.
3577		5320
3578	The most portable way to handle signals is to block signals in all threads	5321	The most portable way to handle signals is to block signals in all threads
3579	except the initial one, and run the default loop in the initial thread as	5322	except the initial one, and run the signal handling loop in the initial
3580	well.	5323	thread as well.
3581		5324
3582	=item C<long> must be large enough for common memory allocation sizes	5325	=item C<long> must be large enough for common memory allocation sizes
3583		5326
3584	To improve portability and simplify its API, libev uses C<long> internally	5327	To improve portability and simplify its API, libev uses C<long> internally
3585	instead of C<size_t> when allocating its data structures. On non-POSIX	5328	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
3588	watchers.	5331	watchers.
3589		5332
3590	=item C<double> must hold a time value in seconds with enough accuracy	5333	=item C<double> must hold a time value in seconds with enough accuracy
3591		5334
3592	The type C<double> is used to represent timestamps. It is required to	5335	The type C<double> is used to represent timestamps. It is required to
3593	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	5336	have at least 51 bits of mantissa (and 9 bits of exponent), which is
3594	enough for at least into the year 4000. This requirement is fulfilled by	5337	good enough for at least into the year 4000 with millisecond accuracy
		5338	(the design goal for libev). This requirement is overfulfilled by
3595	implementations implementing IEEE 754 (basically all existing ones).	5339	implementations using IEEE 754, which is basically all existing ones.
		5340
		5341	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5342	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5343	is either obsolete or somebody patched it to use C<long double> or
		5344	something like that, just kidding).
3596		5345
3597	=back	5346	=back
3598		5347
3599	If you know of other additional requirements drop me a note.	5348	If you know of other additional requirements drop me a note.
3600		5349
…		…
3662	=item Processing ev_async_send: O(number_of_async_watchers)	5411	=item Processing ev_async_send: O(number_of_async_watchers)
3663		5412
3664	=item Processing signals: O(max_signal_number)	5413	=item Processing signals: O(max_signal_number)
3665		5414
3666	Sending involves a system call I<iff> there were no other C<ev_async_send>	5415	Sending involves a system call I<iff> there were no other C<ev_async_send>
3667	calls in the current loop iteration. Checking for async and signal events	5416	calls in the current loop iteration and the loop is currently
		5417	blocked. Checking for async and signal events involves iterating over all
3668	involves iterating over all running async watchers or all signal numbers.	5418	running async watchers or all signal numbers.
3669		5419
3670	=back	5420	=back
3671		5421
3672		5422
		5423	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5424
		5425	The major version 4 introduced some incompatible changes to the API.
		5426
		5427	At the moment, the C<ev.h> header file provides compatibility definitions
		5428	for all changes, so most programs should still compile. The compatibility
		5429	layer might be removed in later versions of libev, so better update to the
		5430	new API early than late.
		5431
		5432	=over 4
		5433
		5434	=item C<EV_COMPAT3> backwards compatibility mechanism
		5435
		5436	The backward compatibility mechanism can be controlled by
		5437	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5438	section.
		5439
		5440	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5441
		5442	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5443
		5444	ev_loop_destroy (EV_DEFAULT_UC);
		5445	ev_loop_fork (EV_DEFAULT);
		5446
		5447	=item function/symbol renames
		5448
		5449	A number of functions and symbols have been renamed:
		5450
		5451	ev_loop => ev_run
		5452	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5453	EVLOOP_ONESHOT => EVRUN_ONCE
		5454
		5455	ev_unloop => ev_break
		5456	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5457	EVUNLOOP_ONE => EVBREAK_ONE
		5458	EVUNLOOP_ALL => EVBREAK_ALL
		5459
		5460	EV_TIMEOUT => EV_TIMER
		5461
		5462	ev_loop_count => ev_iteration
		5463	ev_loop_depth => ev_depth
		5464	ev_loop_verify => ev_verify
		5465
		5466	Most functions working on C<struct ev_loop> objects don't have an
		5467	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5468	associated constants have been renamed to not collide with the C<struct
		5469	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5470	as all other watcher types. Note that C<ev_loop_fork> is still called
		5471	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5472	typedef.
		5473
		5474	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5475
		5476	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5477	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5478	and work, but the library code will of course be larger.
		5479
		5480	=back
		5481
		5482
		5483	=head1 GLOSSARY
		5484
		5485	=over 4
		5486
		5487	=item active
		5488
		5489	A watcher is active as long as it has been started and not yet stopped.
		5490	See L</WATCHER STATES> for details.
		5491
		5492	=item application
		5493
		5494	In this document, an application is whatever is using libev.
		5495
		5496	=item backend
		5497
		5498	The part of the code dealing with the operating system interfaces.
		5499
		5500	=item callback
		5501
		5502	The address of a function that is called when some event has been
		5503	detected. Callbacks are being passed the event loop, the watcher that
		5504	received the event, and the actual event bitset.
		5505
		5506	=item callback/watcher invocation
		5507
		5508	The act of calling the callback associated with a watcher.
		5509
		5510	=item event
		5511
		5512	A change of state of some external event, such as data now being available
		5513	for reading on a file descriptor, time having passed or simply not having
		5514	any other events happening anymore.
		5515
		5516	In libev, events are represented as single bits (such as C<EV_READ> or
		5517	C<EV_TIMER>).
		5518
		5519	=item event library
		5520
		5521	A software package implementing an event model and loop.
		5522
		5523	=item event loop
		5524
		5525	An entity that handles and processes external events and converts them
		5526	into callback invocations.
		5527
		5528	=item event model
		5529
		5530	The model used to describe how an event loop handles and processes
		5531	watchers and events.
		5532
		5533	=item pending
		5534
		5535	A watcher is pending as soon as the corresponding event has been
		5536	detected. See L</WATCHER STATES> for details.
		5537
		5538	=item real time
		5539
		5540	The physical time that is observed. It is apparently strictly monotonic :)
		5541
		5542	=item wall-clock time
		5543
		5544	The time and date as shown on clocks. Unlike real time, it can actually
		5545	be wrong and jump forwards and backwards, e.g. when you adjust your
		5546	clock.
		5547
		5548	=item watcher
		5549
		5550	A data structure that describes interest in certain events. Watchers need
		5551	to be started (attached to an event loop) before they can receive events.
		5552
		5553	=back
		5554
3673	=head1 AUTHOR	5555	=head1 AUTHOR
3674		5556
3675	Marc Lehmann <libev@schmorp.de>.	5557	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5558	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
3676		5559

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